Acetic Acid Process Plant Design | PDF - SlideShare
05 Jun.,2025
Acetic Acid Process Plant Design | PDF - SlideShare
- 1. 1
Acetic acid process plant design
By
Hisham Albaroudi
Karen Atayi
Cristian Baleca
Enoch Osae
Sinthujan Pushpakaran
Alexander Taylor
School of Chemical Engineering
Faculty of Science and Engineering
University of Hull
June
- 2. 2
Table of Contents
1.) Executive Summary 1
2.) Process Selection 2
2.1) Process Technology Selection 2
2.2) Process Flowsheet Development 5
2.3) Process Description 6
3.) Piping and Instrumentation Diagram (P&ID) 7
4.) Mechanical Design of Unit Operations 8
4.1) Reactor 8
4.1.1) Introduction 8
4.1.1.1) Propionic acid 9
4.1.1.2) Water – Gas shift 9
4.1.1.3) Methyl acetate 9
4.1.1.4) Methyl iodide 9
4.1.2) Reactor P&ID 10
4.1.3) Design Method 11
4.1.3.1) Reactants and product 11
4.1.3.2) Variations 12
4.1.3.3) Energy Balance and Heat of reaction 12
4.1.3.4) Choice of reactor 13
4.1.4) Reactor Specification 13
4.1.4.1) Choice of material 14
4.1.4.2) Vessel support 14
4.1.4.3) Piping sizing 14
4.1.4.4) Nozzles 15
4.1.4.5) Heat dissipation and vessel insulation 15
4.1.4.6) Shut down 16
- 3. 3
4.1.4.7) Process safety 16
4.1.4.8) Process control 16
4.1.5) Agitator Specification 17
4.1.6) Conclusion 19
4.1.7) Engineering Drawing of reactor 21
4.2) Flash Tank 22
4.2.1) Introduction 22
4.4.2) Flash Tank P&ID 23
4.2.3) Design Method 24
4.2.4) Flash Tank Specification 25
4.2.4.1) Process controls and safety 27
4.2.5) Conclusion 28
4.1.6) Engineering Drawing of Flash Tank 29
4.3) Drying Distillation Column 30
4.3.1) Introduction 30
4.3.2) Drying Distillation Colum P&ID 31
4.3.3) Design Method 32
4.3.4) Drying Distillation Column Specification 32
4.3.5) Conclusion 33
4.1.7) Engineering Drawing of Drying Distillation Column 34
4.4) Heavy Ends Distillation column 35
4.4.1) Introduction 35
4.4.2) Heavy Ends Distillation Colum P&ID 37
4.4.3) Acetic Acid Properties within the Column 38
4.4.4) Propionic Acid Properties within the Column 38
4.4.5) Relative Volatility 39
4.4.6) Heavy – Ends Distillation Column Specification 39
4.4.7) Summary of Design Data 41
- 4. 4
4.4.8) Conclusion 41
4.1.9) Engineering drawing of Heavy Ends Distillation Column 42
4.5) Absorption Column 43
4.5.1) Introduction 43
4.5.2) Absorption Column P&ID 44
4.5.3) Design Method 45
4.5.4) Absorption Column Specification 45
4.5.4.1) Design Considerations to Account for Drawback of Unit 45
4.5.4.2) Choice of Packing 46
4.5.4.3) Choice of Absorption Tower Equipment 46
4.5.4.4) Materials of Construction 47
4.5.4.5) External Equipment 47
4.5.4.6) Safety Control 48
4.5.4.7) Safety Considerations 48
4.5.5) Conclusion 48
4.5.6) Engineering Drawing of Absorption Column 50
4.6) Storage tank – Acetic acid 51
4.6.1) Introduction 51
4.6.2) Storage Tank – Acetic Acid P&ID 52
4.5.3) Design Method 53
4.5.4) Storage Tank Specification 53
4.5.5) Conclusion 55
4.5.6) Engineering drawing of Storage Tank – Acetic Acid 56
5.) Process Control and Instrumentation 57
5.1) Introduction to Process Control and Instrumentation 57
5.2) Objectives of Process Control 57
5.3) Implementation of Control Systems in our Design 58
- 5. 5
5.3.1) Distillation Column Control 59
5.3.2) Reactor and Flash Tank Control 61
6.) Process Economics 62
6.1) Market Analysis 62
6.2) Costing 63
6.2.1) Feedstock price estimation 64
6.2.2) Capital Cost Estimation 65
6.2.2.1) ISBL 65
6.2.2.2) Installation Factor 66
6.2.2.3) OSBL 66
6.2.2.4) Engineering costs 66
6.2.2.5) Contingency costs 66
6.2.2.6) Fixed Capital Investment 67
6.2.3) Working Capital 67
6.2.4) Total Investment 67
6.2.5) Operating Expenditure 67
6.2.6) Revenue 67
6.2.7) Gross Profit 67
6.3) Project Financing 68
6.3.1) Financing Bank Loan 68
6.3.2) Financing Investment 70
6.3.3) Net Profit 71
6.3.4) Cumulative Cash Position 72
6.3.5) Return of Investment 73
7.) Process Safety 74
7.1) Safety legislations 75
7.2) Hazard Identification 75
- 6. 6
7.2.1) Material Hazard 75
7.2.2) Material Toxicity 78
7.2.3) Flammability 79
7.3) Operating conditions hazard 80
7.3.1) Pressure relief strategy 80
7.3.2) High pressure response measures 81
7.3.3) Fire prevention strategy 81
7.3.4) Fire and gas detection 82
7.3.5) Noise 83
7.3.6) Loss of containment 83
7.4) Emergency Response plans 83
7.4.1) Fire 83
7.4.2) Explosion 85
7.4.3) Overpressure 85
7.4.4) Toxic release 85
7.4.5) Flooding 85
7.4.6) Earthquakes 86
7.4.7) Human error 86
7.4.8) Personal Protection Equipment 86
7.5) HAZOP 86
7.5.1) Scope of work 87
7.5.2) Term of Reference 87
7.5.3) Team Membership 88
7.5.4) Safety conclusions 89
7.5.5) Marked up P&ID 90
7.5.5) HAZOP findings 91
8.) Environmental Protection 95
- 7. 7
8.1) Process Selection 95
8.2) Plant Location – Environmental Considerations 95
8.3) Noise 96
8.4) Odour 96
8.5) Traffic 96
8.6) Catalyst and Water Requirement 97
8.4) Methanol Feed 97
8.5) Energy Recovery 98
8.6) Storage & Handling of Raw Materials and Product 98
8.6.1) Carbon Monoxide 98
8.6.2) Methanol 98
8.6.3) Acetic Acid 99
8.7) Undesired products: By- and Co- products 99
8.7.1) Propionic Acid 100
8.7.2) Carbon Dioxide and Hydrogen 100
8.7.3) Methyl Iodide 101
8.7.4) Aqueous and Organic Discharges 101
9.) Plant Layout and Location 102
9.1) Plant location 102
9.2) Plant layout 104
9.2.1) Site Flow Plan 107
10.) Appendices
APPENDIX [A] – Minutes 108
Meeting Week 13 – 9th
May 109
Meeting Week 12 – 3rd
May 110
Meeting Week 11 – 22nd
April 111
Meeting Week 10 – 18th
April 112
- 8. 8
Meeting Week 9 – 11th
April 113
Meeting Week 8 – 4th
April 114
Meeting Week 7 – 7th
March 115
Meeting Week 6 – 29h
February 116
Meeting Week 5 – 22nd
February 117
Meeting Week 4 – 18th
February 118
Meeting Week 3 – 8th
February 119
Meeting Week 2– 5th
December 120
Meeting Week 1 – 30th
November 121
APPENDIX [B] – Reactor Calculations 121
APPENDIX [C] – Flash Drum Calculations 140
APPENDIX [D] – Calculations for Drying Distillation Column 151
APPENDIX [E] – Calculations for Heavy – Ends Distillation Column 160
APPENDIX [F] – Calculations for Absorption Column 177
APPENDIX [G] – Calculations for Acetic Acid Storage Tank 189
- 9. 9
1. Executive Summary
The purpose of this document is to present a potential design to the client to build an acetic acid
(CH3COOH) plant in the United Kingdom. The plant will have the capacity to produce 400,000 tonnes per
annum of acetic acid base product from a feedstock of methanol and carbon monoxide. As an overview,
the methanol carbonylation process is highly efficient in that it produces acetic acid with more sought after
selectivity and purity. Although, the oxidation of ethylene is more environmentally friendly, it can only be
operated for a capacity of up to 200,000 tonnes per year, while the oxidation of hydrocarbons route for
acetic acid production is cheaper to run but it does not produce pure acetic acid and greatly affects the
environment as a result of its CO2 emissions. Even though the oxidation of ethylene and methanol
carbonylation processes do not pose much threat to the environment, the latter is still more environmentally
friendly as it produces less waste and recycles most of its reactants.
Environmental Impact Assessment has been proven successful in outlining the main environmental issues
in relation to this project. The general location considerations linked to the potential pollution produced
(odours, noise, traffic) has been analysed, justifying the measures that will be put in place to minimize
them. The handling of raw materials and the final product both on and off site has been studied in depth in
order to outline the features and add-ups that can be applied to reduce the impact on the environment:
such measures are mainly related to the close monitoring and the implementation of safety measures to be
applied whenever a containment vessel were to mechanically fail for any reason: it has been concluded
that appropriate containment chambers and process control and instrumentation are the significant routes
to apply. An eco-friendly engineering strategy has been applied to this project when dealing with significant
by-products. Although the generation of highly corrosive chemicals (such as methyl-iodide) has not been
possible to be prevent, other “waste” compounds produced in the system have been proved to be
commercially useful (propionic acid). Certainly, a comprehensive recycling system within the plant (and
especially to the reactor) is a successful strategy to ensure that non desired products are dealt with the
purpose of minimizing waste. Furthermore, even when waste streams are unable to be recycled and re-
used in the system, appropriate techniques to dispose of them have been developed in compliance with
environmental regulations and ethical considerations i.e. flares, aqueous discharge basin and pipeline.
Careful consideration of all the hazards present on the plant are outlined in the following report which
highlights efficient ways of maintaining a safe environment for the production of acetic acid.
In addition to environmental methodologies, principles of process control and instrumentation have been
applied throughout the design stage of this project with the aim of creating a process that is ultimately safe,
that complies with all the necessary safety regulations, efficient, that will not suffer unnecessary downtime to
avoidable failures and maintenance being carried out on key piece of process equipment and not suffer
performance impairments due to poor design, as well as being economically stable, linked to the plants
efficiency, an efficient plant will bring a certain amount of economic stability in addition to ensuring
unnecessary equipment or instrumentation is not put in place.
- 10. 10
Based on market research it is possible to conclude that the acetic acid market is projected to rise the
upcoming years on a global basis. Economic evaluation of this project indicates viability, the return of
investment is 53% and the net profit of £1,378,000,000 is very lucrative figure for a 20-year investment.
Both a bank loan and private equity investments would generate a greatly positive profit, although a bank
loan would represent a significantly more profitable route. The project payback time of 2 years
demonstrates that this project is highly feasible and has the potential to attract numerous investors.
2. Process Selection
2.1 Process Technology Selection
The methanol carbonylation, direct oxidation of n-butane and direct oxidation of ethylene are the three most
widely implemented methods to manufacture acetic acid.
Methanol carbonylation also known as the “Monsanto process” was initially developed by BASF in .
The process operates at 180 – 220 o
C and 30 – 40 atm via the use of a rhodium catalyst, leading to energy
costs set to a bare minimum. Although it operates at such low operating conditions, the process provides
with high selectivity of acetic acid (Yoneda et al., ). The final product holds great purity due to the
selectivities of methanol and carbon monoxide, which are 99% and 90% respectively (Yoneda et al., ).
The process outlines continuous supply of methanol and carbon monoxide into the reactor. The
combination of exhaust gas produced from the reactor and purification section are recovered as light-ends
and recycled back into the reactor. Consequently, the acetic acid produced from the reactor is separated as
a side-cut and delivered to the dehydration column (Sano et al., ). Acetic acid and water mixture are
then released at the top of the column and back to the reactor while propionic acid is taken to the
subsequent column. Further purification takes place and acetic acid is generated as a side-cut. Continuous
recycling of overhead and bottoms found in fractional column into reactor take place (Sano et al., ).
The main raw materials for this process are methanol and carbon monoxide. In the reaction process,
methyl iodide is added to the rhodium complex, which consecutively migrates to a carbonyl group and
reacts with CO to form the rhodium-acetyl complex (Kinnunen and Laasonen, ). The excess water
readily hydrolyses the acetyl iodide (CH3COI) to produce acetic acid and hydrogen iodide in order to
complete the catalytic cycle (Yoneda et al., ). However, a quantity of water (14 – 15 wt.%) is required
in order to maintain stability and activity of the catalyst, thus separation of water from acetic acid requires
excessive amount of energy, further limiting storage capacity (Wittcoff et al., ). Methanol carbonylation
produces propionic acid as the major by-product of this process (Sunley and Watson, ), present as an
impurity in methanol feed (Yoneda et al., ). In order to lower the yield of propionic acid produced, it is
suggested to decrease the amount of acetaldehyde produced by the rhodium catalyst (Yoneda et al.,
).
The direct oxidation of hydrocarbons route occurs through pumping of an ethane and oxygen mixture at
515 K and 16 bar in a multi-tubular reactor (Smejkal et al., ). The product formed is cooled to 303 K via
- 11. 11
two steps, initially through formation of high-density steam and subsequent separation of formed gas and
liquid mixture in a flash (Smejkal et al., ). The acetic acid-water mixture produced is then separated in
a rectification column and pure acetic acid is generated as the bottom product. The resulting gaseous
stream, made up of ethane, ethylene and CO2, is recycled back into the system. CO2 is separated into an
absorber, while ethylene and ethane are put back into the feedgas (Soliman et al., ). Nonetheless, the
oxidation of n-butane requires large amounts of water and generates a dilute acetic acid solution of which
concentration is highly energy intensive, as a result the yield of acetic acid produced is lower than the one
obtained in other processes (Sano et al., ). A vast amount of by-products are formed, some of which
are propionic and formic acids (Riegel, ). Furthermore, this particular process requires large quantities
of water, hence water gas shift reaction is a major drawback as extensive CO2 is produced as a result
(Wittcoff et al., ). In essence, the oxidation of hydrocarbons process is cheaper to run as a result of its
feedstock, but at the cost of being less efficient as it produces more waste and a lower grade chemical.
Flexibility in the process allows it to produce a purer acetic acid with high selectivity, however extensive
operation expenses are necessary.
The production of acetic acid through direct oxidation of ethylene was first proposed by Showa Denko K.K..
The process occurs through the mixture of ethylene and oxygen in their vapour phases at 160 – 210 o
C
over a solid catalyst (Xu et al., ), the acetic acid generated is of high selectivity. The reaction is
initiated from the cooling of gas produced in the reactor to ambient temperature, where the products of
acetic acid, water and other organic compounds are condensed and separated. The condensate transfers
to the crude acetic acid tank, while the compressor pressurizes the un-condensed gas back to the reactor.
Light-end products such as acetaldehyde, ethyl acetate and ethanol are removed through distillation,
allowing acetic acid and light-ends compounds to migrate to the purification section where pure acetic acid
is produced (Sano et al., ). This process produces large amounts of heat which is recovered as steam
and used in the purification section as a source of heat (Sano et al., ).The process meets the
requirements of being both competitive and environmentally friendly. Although it rivals methanol
carbonylation, the process is only efficient with smaller plants of about (100-250 kt/a) (Sano et al., )
and considering the fact that the feedstock price of ethylene is more expensive than raw materials used in
the other processes mentioned, thus economically it will not be as profitable as the methanol carbonylation
process given that the selectivity of both is of 90%.
Overall, the methanol carbonylation process is highly efficient in that it produces acetic acid with more
sought after selectivity and purity. The oxidation of ethylene is more environmentally friendly, however it
can only be operated for a capacity of up to 200,000 tonnes per year and the oxidation of hydrocarbons is
cheaper to run but does not produce a pure acetic acid product. The oxidation of hydrocarbons highly
affects the environment as a result of its emissions of CO2, whilst both the ethylene oxidation and methanol
carbonylation don’t pose much threat to the environment, the latter is still more environmentally friendly as
it produces less waste and recycles most of its reactants. This enables the process to be continuous and
thus economically beneficial.
- 12. 12
2.2 Process Flowsheet Development
Reactor
1
2
3
Flash tank
Light ends
distillation column
Drying
distillation column
Heavy ends
distillation column
8 12
Scrubber
9
113
14
8
1
2
3
6
9
17
16
11
15
Pressure reduction
valve
5
Figure [1]: Process Flow Diagram and Material balance of process.
Steam 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
Molar Flowrate
[kg/hr]
Methanol 0.00 .00 0.00 56.15 56.15 1.15 56.07 0.00 56.07 Trace 0.00 0.00 0.00 0.00 0.00 Trace 57.29
Carbon monoxide .36 0.00 0.00 207.44 207.44 200.88 207.55 0.00 207.55 0.00 0.00 0.00 0.00 0.00 0.00 3.02E+02 105.97
Acetic acid 0.00 0.00 0.00 .49 .49 611.25 .05 .21 .53 8.28E+04 .25 .293 .87 184.35 .63 1.60E+02 .00
Water 0.00 0.00 720.40 234.38 234.38 3.19 210.90 23.41 210.90 Trace 0.00 0.00 0.00 0.00 0.00 Trace 214.13
Ethanol 0.00 273.14 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Trace 0.00 0.00 0.00 0.00 0.00 Trace 0.00
Propionic acid 0.00 0.00 0.00 487.99 487.99 2.02 439.24 48.89 0.00 4.39E+02 0.01 439.24 0.01 439.24 0.00 Trace 2.02
Carbon dioxide 0.00 0.00 0.00 .54 .54 947.56 .36 0.00 .36 0.00 0.00 0.00 0.00 0.00 0.00 2.43E+03 .63
Hydrogen 0.00 0.00 0.00 8.69 8.69 72.79 8.69 0.00 8.69 0.00 0.00 0.00 0.00 0.00 0.00 7.99E+01 1.60
Methyl acetate 0.00 0.00 0.00 .25 .25 24.77 .89 0.00 .89 Trace 0.00 0.00 0.00 0.00 0.00 Trace .02
Hydrogen iodide 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Trace 0.00
Methyl iodide 0.00 0.00 0.00 .05 .05 60.51 .02 459.76 .02 0.00 0.00 0.00 0.00 0.00 0.00 Trace .95
Total .36 .00 720.40 .00 .00 .24 .71 .75 .53 .17 .26 .67 .16 623.51 .71 .623 .82
Temperature
[o
C]
25 25.53 26.87 160 104.45 160 104.45 104.45 79.88 117.65 141.66 117.69 117.58 131.41 117.58 18.31 69.71
Pressure
[bar]
31 31 31 30.40 1 30.40 1 1 1 1 2 1 1 1 1 1 59
- 13. 13
2.3 Process Description
Aspiring Consulting have decided to manufacture acetic acid using the Monsanto process. The first stage
of the process involves the injection of the raw materials methanol, carbon monoxide and water into the
reactor to initiate the methanol carbonylation process. The carbonylation reaction is carried out in a stirred
tank reactor on a continuous basis. Liquid is then removed from the reactor through a pressure reduction
valve. This then enters the flash tank, where light components of methyl acetate, methyl iodide, some water
and product acid are removed as vapour through the top of the vessel. The gases are fed forward to the
distillation train for further purification whilst the remaining liquid in the flash tank, containing the dissolved
catalyst, is recycled to the reactor.
Liquid from the reactor enters the lower half of a multiple-tray distillation column operating at conditions
above atmospheric conditions. Hydrogen iodide present in the feed stream is concentrated in the acetic
acid solution in the bottom of the column. This stream is recycled back to the reactor. Carbon monoxide,
water, methyl iodide and some entrained hydrogen iodide comprise the overhead stream from the column,
which passes through a condenser and phase separator where uncondensed gas is directed towards the
scrubber.
The condensate separates into two phases: a water phase consisting of some organic compounds and an
organic phase (methyl iodide) containing some water. The organic phase is recycled to the reactor whilst
part of the water phase is used as reflux in the distillation column and excess is recycled to the reactor.
Solution of acetic acid in water containing some iodide, catalyst and by-products is withdrawn from the
bottom of the column and introduced into a second multiple-tray distillation column operating at conditions
above atmospheric conditions. In this column, water and remaining inerts are withdrawn overhead and
directed towards to the scrubber. A portion of the condensate is returned as reflux to the column and
excess is recycled to the reactor. To avoid accumulation of water in the system, a portion of the water
separated in the column is discarded.
Residual hydrogen iodide in the feed stream to the column concentrates at a location near the middle of the
distillation column. By continually withdrawing the solution containing hydrogen iodide from the middle of
the distillation column, virtually all of the hydrogen iodide is removed from the column. This solution can be
recycled directly to the reactor or alternatively to the lower half of the previous distillation column, where it is
concentrated and removed with the bottoms stream of that column.
Acetic acid product is withdrawn from the drying column without further processing; acetic acid vapour is
withdrawn from the top of the column and passed through a condenser from which it is pumped to storage.
Liquid acetic acid containing residual catalyst is periodically withdrawn from the top of the column and
recycled to the reactor.
- 14. 14
3. Piping and Instrumentation Diagram (P&ID)
DC-501
P-501
P-502
V-502
V-503
V-504
V-505
FI
FIFI C
FI C
V-501
LI C
LI
2" 304SS
V506
TI
FI C
36" 304SS
V-507
TI FI C
DC-401
P-401
P-402
8" 304SS
V-402
V-403
V-404
V-405
FI
FIFI C
FI C
V-401
LI C
LI
4" 304SS
V-406
TI
FI C
V-407
TI FI C
6" 304SS
DC-301
P-301
P-302
V-302
V-303
V-304
V-305
FI
FIFI C
FI C
V-301
LI C
LI 10" 304SS
V-306
TI
FI C
TI FI C
V-307
Acetic acid
Propionic ac id
R-201
V-210
V-209
V-208
V-207
FI
FI FI C
FI C
S-601
Fl are
6" HC
V-201
LI
FI C
V-202
V-203
V-205
V-204
PIFI C
F-201
V-206
FI C
LI
V-211
FI FI C
6" HC
80" CS
V-308
FIFI C
V-212
FIFI C
CH3OHfeed
H2Ofeed
COfeed
P-101 P-102
V-102V-101
V-104V-103
FI
FIFIC
FIC
P-103 P-104
V-106V-105
V-108V-107
FI
FIFIC
FIC
1" CS
V-110V-109
V-112V-111
FI
FIFIC
FIC
3" CS
P-602
P-601
V-617
V-619
V-620
FI
FIFI C
FI C
12" 304SS
V-602 V-604
V-411
V-410
V-409
V-408
FI
FI FI C
FI C
12" HC
V-601 V-603
V-609
V-610
V-612
V-611
V-511
V-510
V-509
V-508
FI
FI FI C
FI C
V-618
V-613
V-614
V-616
V-615
LIFI C
V-605 V-607
V-606 V-608
P-503
P-504
LAH
LAL
LAH
LAL
LAH
LAL
LAH
LAL
Process
Steam
Process
Steam
Process
Steam
Process
Water
Process
Water
Process
Water
V-508
FI C FI
V-408
FI C FI
V-308
FI C FI
Figure [2]: P&ID showing all unit operation.
Tag Number R-201 Tag Number F-201 Tag Number DC-301 Tag Number DC-401 Tag Number DC-501 Tag Number S-601 Aspiring Consulting LTD. KEY
Service Reactor Service Flask Tank Service
Light Ends Distillation
Column
Service
Drying Distillation
Column
Service
Heavy Ends Distillation
Column
Service Scrubber
Process
P&ID
Client
UoH
plc
CS Carbon Steel
Design Press 33 bara Design Press 1.1 bara Design Press N/A Design Press 1.1 bara
Design
Press
1.52 bara Design Press 1.5 bara HC Hastelloy C
Design Temp 176 o
C Design Temp 115 o
C Design Temp N/A Design Temp 125 o
C
Design
Temp
150 o
C Design Temp 50 o
C Location Immingham 304SS
304 Stainless
Steel
Height 8.95 m Height 10 m Height N/A Height 23.85 m Height 21.6 m Height 10 m
- 15. 15
4. Mechanical Design of Unit Operations
4.1 Reactor
4.1.1 Introduction
The overall reaction for the production of acetic acid is given by the kinetic equation (Cheng and Kung,
):
????????3 ???????? + ???????? → ????????3 ????????????????
ΔG = -72.79 kJ/mol ΔH = -133.82 kJ/mol
The enthalpy values collected in the literature clearly indicate the exothermic nature of the process; energy
is being produced within the reactor. Typical operating conditions emphasized in literature for the Monsanto
process lay in the following ranges (Cheng and Kung, ):
Pressure Temperature
30-60 bar 150-200 oC
Table [4.1] – Ranges for operating conditions.
In order to model the simulation, different values for pressure and temperature have been selected for the
reactor; the values that appeared to give the highest selectivity yet maintaining a relatively lower generation
of by-products are 160 o
C and 30 bar respectively.
The process uses a Rhodium and Iodine complex to catalyse and promote the reaction, and this catalyst is
highly selective especially in relation to methanol conversion. Due to the high activation energy, the
reaction would not occur without the aid of a catalyst.
The catalytic reactions are listed below, and are all equilibrium limited for the purpose of the reaction
simulation. This is relatable to the fact that catalysts and promoters do not affect the stoichiometry and heat
of reaction:
CH3OH + HI ↔ CH3I + H2O
CH3I + CO ↔ CH3COI
????????3 ???????????? + ????2 ???? ↔ ????????3 ???????????????? + ????????
As far as the process simulation is concerned (Aspen PLUS), the main methanol carbonylation reaction is
kinetic, and some values in the literature have been investigated in order to model the simulation.
The following information has been used to model Aspen Plus simulation:
???????????????????????? ???????????????????????????????????????? ???????? ???????????????????????? ???????????????? = 400,000 ???????????????? ???????????? ???????????????????????????????????? ℎ???????????????? (???????? ???????????? ???????????????????????? ????????????????????????????????????????????????????)
= 50,000 ????????/ℎ????
- 16. 16
In accordance to the stoichiometry and molecular weight of the reactants, the required input methanol and
CO have been calculated for this purpose:
???????? →
186,666 ????????????????
0.9
= 207,407
????????????????
????????????????
= 25,925 ????????/ℎ????
????????????ℎ???????????????? →
213,333 ????????????????
0.99
= 215,488
????????????????
????????????????
= 26,936 ????????/ℎ????
Due to a 99% selectivity in relation to methanol, and 90% in relation to CO, not all the reactants eventually
combine to produce acetic acid. Other important side reactions occurring in the system generate acetic
acid, methyl acetate and propionic acid.
4.1.1.1 Propionic acid
????2 ????6 ???? + ???????? → ????3 ????6 ????2
Propionic acid is the major liquid by-product within the system. Ethanol impurity is present in the methanol
streams that reacts with some of the unreacted carbon monoxide. The reaction is kinetic and its value have
been researched in literature.
4.1.1.2 Water – Gas shift
????20 + ???????? → ????????2 + ????2
The reaction once again involves part of the unreacted carbon monoxide reacts with water to generate
hydrogen and carbon dioxide. This reaction is equilibrium limited.
4.1.1.3 Methyl acetate
????????3 ???????? + ????????3 ???????????????? → ????????3 ????????????????????3 + ????2 ????
A fraction of the 1% unreacted methanol combines with the product (acetic acid) to generate methyl acetate
and water. This reaction is equilibrium limited.
4.1.1.4 Methyl iodide
????????3 ???????? + ???????? → ????????3 ????????????????????3 + ????2 ????
A fraction of the 1% unreacted methanol combines with the hydrogen iodide to generate methyl iodide and
water. This reaction is equilibrium based.
An Aspen PLUS simulation has been modelled based on:
• Information researched in literature
• Appropriate calculations
- 17. 17
Methanol feed
6' SS
P-102
R101
PI
103
FI
103
FCV-102
FCV-101
101 101
FC FT
102 102
PCV-103
P-103
Methanol storage tank
P-101
FC FT
P-201
LCV-201
5.5" SS
P-202
103
FI
PCPT
203
FI
202
LIC
FTFC
PRV-201
201
PI
102 102
TI PI
103
TI
PRV-201
203
PI
FCV-205
205
205
FT
FC
H2O supply
6" SS
LAH
LAL
204 204
TI PITLH
TLL
PLH
PLL
PLH
PLH
Off to flash tank
From flash tank
Off-to scrubber
From drying column
3/8" - SS
3" - SS
80" - SS
6" – Hastelloy
6" – Hastelloy
12" – CS
CO
Supply
Figure [4.1]: P&ID of Reactor.
R-201
4.1.2 Reactor P&ID
- 18. 18
4.1.3 Design Method
4.1.3.1 Reactants and product
Since the reactants are in different phases, liquid and gas respectively, it is advantageous to insert the gas
through a sparger to facilitate even diffusion throughout the liquid. The sparger should be designed
separately.
Stream Density (kg/m3
)
Methanol 791
CO 1.14
Acetic Acid
Table [4.2] – Composition of stream and respective densities.
Table [4.3] – Material balance for reactor.
Substream:MIXED CO Methanol Water CSTR-LIQ CSTR-VAP WATER-RCY SCRUB-RCY
MassFlowkg/hr
Methanol 0.00 .00 0.00 56.15 1.15 0.00 57.29
CO .36 0.00 0.00 207.44 200.88 0.00 105.97
AceticAcid 0.00 0.00 0.00 .49 611.25 .25 .00
Water 0.00 0.00 720.40 234.38 3.19 0.00 214.13
Ethanol 0.00 5.93 0.00 0.00 0.00 0.00 0.00
PropionicAcid 0.00 0.00 0.00 487.99 2.02 0.00 2.02
CO2 0.00 0.00 0.00 .54 947.56 0.00 .63
H2 0.00 0.00 0.00 8.69 72.79 0.00 1.60
Methylacetate 0.00 0.00 0.00 .25 24.77 0.00 .02
Hydrogenchloride 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Methyliodide 0.00 0.00 0.00 16.19 0.43 0.00 13.38
TotalFlowmol/hr .00 .00 .00 .00 .76 .60 .00
TotalFlowkg/hr .36 .02 720.61 .00 .24 .50 .82
volumetricflowl/hr .00 .27 724.99 .52 .94 .02 .84
TemperatureC 25.00 25.00 25.00 160.00 160.00 220.04 69.71
Pressurebar 1.00 1.00 1.00 30.40 30.40 32.00 59.00
VaporFrac 1.00 0.00 0.00 0.00 1.00 1.00 0.00
LiquidFrac 0.00 1.00 1.00 1.00 0.00 0.00 1.00
SolidFrac 0.00 0.00 0.00 0.00 0.00 0.00 0.00
Concentration(mol/l) 25.00 25.00 1.00 14.58 0.85 1.16 17.40
Densitygm/cc 1.13 793.09 993.96 861.85 21.49 69.43 17.40
INLET OUTLET RECYCLE
- 19. 19
4.1.3.2 Variations
The material and energy balances produced refer to steady state operating conditions. There are some
situations, however, in which the system does not operate under steady state conditions, including:
• Start-up and shutdown
• Filling and emptying
• Isolation
• Preventative or corrective maintenance
• Failure or loss of process variation
• Extreme ambient conditions (temperature, severities, pressures)
4.1.3.3 Energy Balance and Heat of reaction
As acknowledged from literature, the methanol carbonylation reaction is exothermic. The heat of reaction is
therefore calculated with the aid of enthalpies of each stream (reactants and products) as seen by Figure
4.2.
Figure [4.2]: Energy balance of inlet, outlet and recycle stream.
The negative sign of heat of reaction means that the system releases energy in the form of heat. This heat
of reaction has been calculated within the simulation through the basic formula:
△ ???? ???????????????????????????????? − △ ???? ???????????????????????????????????? = ???? = ???????????????????????? ???????????????????????????????????? ????????
????????????
????????????
???????? ????????????????????????????
The specific enthalpies of each stream have been obtained by the simulation. As far as simulation is
concerned, the water inlet stream’s purpose is to enable the catalyst and promoter activity. It is not involved
in any chemical reaction and it is in fact separated later on in the process from the product stream, and
recycled back into the reactor continuously. For this reason it is possible to state that its energy contribution
is negligible and not relevant to take into account for energy balance purposes. The same principle is
applied to the recycling streams connecting the reactor to scrubber and reactor to drying column
respectively, therefore they have not been included in this energy balance.
For the purpose of design optimization and practice, heat needs to be continuously removed from the
system and applied to an appropriate heat integration system.
CO Methanol Water CSTR-LIQ CSTR-VAP
Enthalpy (cal/mol) -.54 -.93 -.29 -.00 -.50
Flowrate (mol/hr) .76
Total enthalpy (cal/hr) - -4.E+10 -2.73E+09 -2.E+11 -
Total enthalpy (cal/hr)
Enthalpy of reaction (cal/hr)
Enthalpy of reaction (kJ/hr)
- -2.E+11
-1.E+11
-5.49E+11
- 20. 20
4.1.3.4 Choice of reactor
The nature of the reaction involved in the process necessitates agitation within the system. The exothermic
nature of the main reaction emphasizes that a vessel with good temperature control is desirable.
Furthermore, the fact that a continuous operation of the vessel is required and a simple adaptation to two-
phase reaction is possible implies that a CSTR is the most suitable choice of reactor in the Monsanto
methanol carbonylation. Advantages of CSTR’s are:
• Constant operation in continuous system.
• High degree of temperature and process control.
• Simplicity of construction.
• Easy adaptation to two phase reactions (liquid-gas reaction).
• Easy maintenance / clean-up operations.
Assumptions that will be useful in the later stage of the reactor design can be made use on the CSTR of the
process:
• Steady state conditions with constant inlet (reactants) and outlet flow (products).
• Uniform stream composition inside and outside the reactor.
• Complete and uniform mixing.
4.1.4 Reactor Specification
Reactor – Design Data
Vessel volume 138.42 m3
Vessel shell diameter (internal) 4.45 m
Internal pressure 30 bara = 30.59 kg/cm2
External pressure 1 bara
Design pressure (10% of Operating pressure) 32.12 kg/cm2
= 33 bara = 3.3 N/mm2
Allowable stress (Hastelloy B) 351.63 N/mm2
Hydrostatic test pressure 39.77 kg/cm2
Density of material kg/cm3
Corrosion allowance (CA) 4 mm
A thorough calculation of reactor design can be seen in Appendix B.
- 21. 21
4.1.4.1 Choice of material
Hastelloy B-2 – (65% Ni, 28& Mo, 5% Fe) required to hold resistance against the corrosion of hydrogen
iodide and acid (Sinnott et al., , p986). Its physical and chemical properties appear to be specifically
suitable as a choice for the CSTR of this system.
???????????????????????????????????? ???????????????????? ????????????????????????????ℎ = 51 ???????????? = ????????????/????2
(Alloys and Producer, )
4.1.4.2 Vessel support
A support skirt will be required for the reactor. The design of such implementation will have to be performed
separately and in accordance to the vessel’s specifications.
4.1.4.3 Piping sizing
Pipeline Flowrate
(m3
/s)
Velocity
(m/s)
Cross -
sectional
area (m2
)
Diameter (mm) Equivalent NPS (in)
CO feed to
reactor
6. 2.000 3. .3 80
Methanol feed
to reactor
0. 2.000 0. 78.1 3
Water feed to
reactor
0. 2.000 0. 11.3 0.375
Reactor to
flash tank
0. 2.000 0. 139.1 6
Reactor to
scrubber
0. 2.000 0. 125.9 6
Drying column
to reactor
0. 2.000 0. 272.3 12
Scrubber to
reactor
0. 2.000 0. 2.5 12
Table [4.4]: Representation of pipeline diameter upon data obtained from Aspen Plus simulation and conversion
(mm to NPS) (Perry et al., ).
- 22. 22
The feed of CO to the reactor pipeline represents an offset value, which is due to the high volumetric
flowrate as a result of its gas-phase nature, leading to very low density. On the basis that a constant
velocity of 2 m/s is assumed, the CO feed pipeline will be therefore be significantly larger.
4.1.4.4 Nozzles
Divergent nozzles given a size margin of 15% and distance between nozzle entrance and flange distance
assumed to be twice of the nozzle’s diameter. Dimensions of nozzle to appropriate pipeline is given in
Table 4.5.
Table [4.5]: Representation of nozzles in relation to pipeline upon data obtained from Aspen Plus simulation and
conversion (mm to NPS) (Perry et al., ).
4.1.4.5 Heat dissipation and vessel insulation
Similarly to most systems to which the laws of thermodynamics can be applied to, there is dissipation of
energy in the form of heat to the surrounding areas. This rate of energy exchange is governed by Fourier’s
Law, which states:
???? = ℎ???????????? ???????????????????????????????? = ???? ????
dT
????????
Where:
???? = ℎ???????????? ????????????????????????????????
k = thermal conductivity of material
A = area of the vessel
???????? = temperature gradient
Pipeline Nozzle Diameter (mm) Equivalent NPS (in) Nozzle entrance to flange
(m)
CO feed to
reactor
A .23 88 4.57
Methanol feed to
reactor
B 89.78 5 0.18
Water feed to
reactor
C 12.99 0.375 0.03
Reactor to flash
tank
D 159.95 8 0.32
Reactor to
scrubber
E 144.73 6 0.29
Drying column to
reactor
F 313.15 14 0.63
Scrubber to
reactor
G 64.35 2.5 0.13
- 23. 23
???????? = thickness of material
???? = 67,301,345 kJ/hr (???????????? ???????????????????????????????????????????????? ???????? ???????????????????????????????? [????])
Normally the issue of heat dissipation from a vessel can be overcome by applying an appropriate insulation
system on the internal fitting of the vessel; in this case, however, the heat dissipated is negligible in relation
to the heat of reaction produced within the reactor:
???????????????? ???????? ???????????????????????????????? ???????????????????????????????? = 5.49 ×
kJ/hr
???? = ℎ???????????? ???????????????????????????????????????????? = 67,301,345 = 6.7 × 107
kJ/hr
Therefore by taking into account this specific system, it is fair to assume that heat dissipation is not relevant
in relation to the rate of heat of reaction produced, so the conclusion is that no insulation is required for this
vessel.
4.1.4.6 Shutdown
Shutdown procedures are required whenever an emergency shutdown or maintenance occurs. The
standard safety protocols must be followed, where the first step is to decrease production rate at constant
intervals, thus allowing the progressive reduction of pressure and temperature. When conversion reaches
0, the reactor will need to get emptied. In order to do so, the vessel is continuously purged with an inert
substance, nitrogen, to prevent formation of oxygen or other reactions for when the shell comes into
contact with the atmosphere.
4.1.4.7 Process safety
The choice of material, Hastelloy, is the first application of safety factors within the design. As a result of the
highly corrosive nature of the iodides present, hydrogen and methyl iodide, Hastelloy represents the most
suitable material choice. A high corrosion allowance (4mm) has thus been implemented. Parameters such
as temperature and pressure, other than level of fluid within the vessel are directly related to the safety
procedures, therefore appropriate process control measures have been employed to ensure a high level of
process safety in the reactor.
4.1.4.8 Process control
Methanol feedlines have been integrated with temperature and pressure indicators alongside a flow control
valve with an appropriate transmitter due to flowrate being the most relevant parameter to control in order
to allow the reaction to occur currently. A backup pump has also been employed in the methanol feed
pipelines, in case of failure of the first one. Moreover, backup flow control valves have been included in
both the CO and methanol feeds.
- 24. 24
Pressure control and a transmitter have been included in the reactor to keep a constant monitoring of the
pressure within the vessel, thus overpressure or under pressure is prevented which would affect the rate of
reaction (30 bar). A level indicator controller, with high and low alarms, have been selected to monitor the
reactor’s fluid level; they control the flow valve located in the pipeline between the liquid phase of the
reactor and the flash tank in order to maintain fluid level within vessel specification, a maximum 70% of
vessel’s volume is recommended).
Isolation valves have been fitted around the vessel to ensure a high level of control in relation to safety and
failures of the system, allowing quick shutdown of the unit operation. The pressure reduction valve located
in the pipeline which connects the liquid stream of the rector to the flash tank is fitted in order to flash the
content and reduce pressure from 30 bar to 1 bar. The other streams feeding from and to the reactor have
been fitted with appropriate flow controllers and transmitters to monitor the overall flow within the system
4.1.5 Agitator Specification
Agitators are required to increase the transfer of material within the vessel and create uniform temperature
within the reactor.
In order to evaluate which type of agitator is most suitable for the reaction, it is possible to observe a
correlation between viscosity, volume of the tank and type of agitator.
Figure [4.3]: Aspen Plus simulation data.
Stream Flowrate (kg/hr) Mass fraction
avg. viscosity (N-s/m^2)
avg.viscosity (N-s/m^2)( fraction)
CO .36 0. 1.77E-05 2.11E-06
Methanol .02 0. 0. 7.00E-05
Water 720. 3.42E-03 0. 3.12E-06
CSTR-LIQ 5.18E-01 0. 6.89E-05
CSTR-VAP .236 9.12E-03 1.83E-05 1.67E-07
WATER-RCY .5 0. 1.57E-05 2.16E-06
SCRUB-RCY .82 0. 0. 9.85E-06
Total . 1 1.56E-04
0.156 mpa.s
LIQUID VISCOSITY 0.
- 25. 25
Figure [4.4]: Aspen Plus simulation data.
The values for viscosity have been collected from the simulation on Aspen PLUS. Through implementation
of flowrates for all the streams connected to/from the reactor, a mass flowrate has been calculated, hence
leading to calculate the total liquid viscosity of the mixture, and correlating Figure 4.3, this leads to:
???????????????????????? ???????? ???????????????????????? = 138 ????3
???????????????????????? ???????????????????????????????????? = 7.9 × 10−3
????????/????2
????????????????ℎ ???????????????????????????????????????????????? = ???????????????????????????????????? ???????? ???????????????????????????? (???????????? ???????????????????????????????????????????????? ???????? ???????????????????????????????? ????)
Figure [4.5]: Impeller type for different mixture viscosities (Sinnott et al., ).
By analysing Figure 4.5, it is possible to evaluate that flat-blade turbine is the most suitable one in relation
to the liquid viscosity of 7.9 × 10-3
Ns/m2
.
Stream Flowrate (kg/hr) Mass fraction
avg. density (kg/m3)
avg.density (kg/m3)( fraction)
CO .36 0. 1. 1.35E-01
Methanol .02 0. 793. 1.03E+02
Water 720. 3.42E-03 993.957 3.39E+00
CSTR-LIQ 5.18E-01 861. 4.47E+02
CSTR-VAP .236 9.12E-03 21. 1.96E-01
WATER-RCY .5 0. 69. 9.57E+00
SCRUB-RCY .82 0. 17. 1.43E+00
Total . 1 5.64E+02
564 kg/m3
- 26. 26
Using ratios given in literature allows to specify the dimensions, location and characteristics of impellers
and blades have been identified. In order to guarantee a good level of reaction control in relation to heat
within the vessel, baffles have been integrated to the design.
Due to the fact that µ < 500 mPa.s, the type of agitator should be either a propeller or a turbine. It is
assumed that the agitation required is mild for such homogenous reaction. Therefore, assumed rotational
speed falls within the ‘low’ category, 200 rpm is the estimated rotational velocity required (Carpenter, ).
Agitator – Design Data
Diameter 1.48 m
Height above vessel bottom 1.48 m
Blade length 0.37 m
Blade width 0.45 m
Baffled width 0.45 m
Baffled height 8.9m
Liquid depth 4.45 m
Number of blades 6
Number of baffles 4
Diameter of shaft 0.053 m
Power required 194 hp
A thorough calculation of agitator design can be seen in Appendix B.
4.1.6 Conclusion
The parameters, data and information researched about the process have been defined and simulated on
appropriate software (Aspen Plus). This allowed to facilitate the collection of results in relation to mass and
energy balances in order to define the main parameters of the vessel, allowing a 20% overdesign for
potential expansion. A detailed mechanical design of the reactor including its minor components has been
completed, defining the dimensions of turbine, blades, shaft and the power required by the agitator. In
addition, a comprehensive stress analysis has outlined that the reactor’s mechanical design is suitable for
industrial application. Time taken to reach steady state conditions as well as an analysis of shutdown
operations, process control and safety has been implemented throughout the design. Furthermore, a cost
- 27. 27
estimation has been evaluated in relation to the plant location, time and local currency. The final cost for
the unit is approximately £800,000 – excluding delivery and installation costs.
- 28. 28
4.1.7 Engineering Drawing of Reactor
Figure [4.6]: Mechanical design of reactor
- 29. 29
4.2 Flash Tank
4.2.1 Introduction
The flash drum is a vapour liquid separator, its role is to split the mixture of the vapour-liquid mixture fed
from the reactor. The vapour stream is released from the top of the drum. The liquid stream leaves through
the bottom of the drum containing the Rhodium catalyst which is then recycled back to the reactor to be
reused to aid reactions within the reactor. The design approach was to specify the flash tanks operating
conditions and physical attributes (addition of demister and diameter and tank length) that directly affect the
cost of equipment and operating costs. The orientation of the vessel will be vertical as its ideal for high flow
rates, the vertical separator the process is more economical compared to the horizontal separator
(Monnery and Svreck, )
A demister pad is a device with metal mesh like structure that eliminates the possibility of liquid entrainment
within a pressure vessel. Entrainment is the entrapment of one phase within another, within the flash drum
liquid droplets can be entrained within vapour and leave liquid droplets within the vapour stream. To
prevent liquid entrainment, the velocity of vapour stream must be kept low to allow the water droplets to
disengage for the vapour stream and drop back down to the liquid pool at the base of the vessel. If the
operation requires a high vapour velocity the demister pad acts as an effective entrainment separator
(Basic et al., ).As the vapour travels through the mesh wiring pad the stream lines are deflected,
however the kinetic energy of the liquid droplet entrained within the vapour are too high to follow the
streamline, they become impinged in the wires. The liquid droplets then coalesce forming a liquid layer on
the surface of the wires. The droplets then detach from the pad. Due to the orientation of the vessel
(vertical) the liquid droplets will be captured and be drained back and form large droplets that can drop
from the upstream face of the wire mesh pad ( Al-Deffeeri et al., ).
Demister pads increase the efficiency of vapour liquid separation efficiency. Flash drums that use gravity
separation (without the demister) are dependent on a high residence time to separate the liquid from the
vapour. The more time needed for the mixture to separate, the higher the energy cost to run the flash drum
thus the plant throughput will be lower per day hence reducing revenue per day. The demister pad allows
the same degree of separation to be carried out in a smaller vessel, the reduction of volume reduces the
weight of the vessel which directly minimizes the cost of the vessel shell (Sinnott et al., )).The internal
diameter is dependant of the vessel is dependent on the terminal velocity of the particles
- 30. 30
4.2.2 Flash Tank P&ID
F-201
V-206
FIC
LI
V-211
FI FIC
R-201
V-210
V-209
V-208
V-207
FI
FI FIC
FIC
R-201
DC-301
Figure [4.7]: P&ID of Flash Tank
- 31. 31
4.2.3 Design Method
This specific sizing methodology is adopted from “two phase separators within the right limits” published in
the “Chemical engineering progress synopsis series” () the calculation initiates by the finding the
diameter of the vessel. In order to do so, vertical terminal vapour velocity, QT, is determined by obtaining
the K value using Table C1 (See Appendix C). Subsequently, QV, vapour volumetric flow rate is calculated.
The internal vessel diameter, DVD, is estimated, whilst adding 6 inches to the figure obtained to
accommodate the support for the mist eliminator. Referring to Table C2, hold up time and surge volume
relative to a “Feed to column separator” are selected. Further referring to Table C3, low liquid level height,
HLLL, is obtained, thus distance from the low liquid level, HLLL to the normal liquid level, HNLL, is estimated.
This value must be minimum of 1ft. Consecutively, the height between normal liquid level, HNLL to high liquid
level HHLL, must be 6 inches minimum. Henceforth, the height from high liquid level to the centre line of inlet
nozzle is estimated.
The disengagement height from the centre line of inlet nozzle to the bottom of demister pad is then
determined and assumption of the height of the mist eliminator pad, HME, is 6 inches and 1ft is taken from
the top of the mist eliminator to the tangent line of the flash drum.
- 32. 32
Mole Flow kmol/hr Flash in Flash vapour stream Flash liquid stream
METHANOL 1. 1. 0
CARBON MONOXIDE 7. 7. 0
ACETIC ACID .024 .921 164.
WATER 13. 11. 1.
ETHANOL 1.35E-05 1.22E-05 1.35E-06
PROPIONIC ACID 6. 5. 0.
CARBON DIOXIDE 142.194 142.194 0
HYDROGEN 4. 4. 0
METHYL ACETATE 16. 16. 0
HYDROFEN CHLORIDE 7.75E-08 7.75E-08 0
METHY-IODIDE 16. 12. 3.
Total Flow kmol/hr .262 .96 169.
Total Flow kg/hr .71 .75
Total Flow l/min 176.
Temperature C 104. 104. 104.
Pressure bar 1 1 1
Vapor Frac 0. 0. 0
Liquid Frac 0. 0. 1
Solid Frac 0 0 0
Enthalpy cal/mol - - -
Enthalpy cal/gm -.75 -.307 -.79
Enthalpy cal/sec - - -
Entropy cal/mol-K -57. -56. -67.
Entropy cal/gm-K -0. -0. -1.
Density mol/cc 0. 0. 0.
Density gm/cc 0. 0. 0.
Average MW 59. 58. 61.
Liq Vol 60F l/min .089 .876 162.
Table [4.6]: Material Balance for Flash Tank.
4.2.4 Flash Tank Specification
Flash Tank – Design Data
Design pressure 1.1 bar
Design temperature 114.89 o
C
Pressure 1 bar
Temperature 104.445 o
C
Vapour volumetric flow rate 4.4 m3
/min
Liquid volumetric flow rate 1.68 m3
/min
Vapour density 6.24 kg/m3
Liquid density 983.31 kg/m3
- 33. 33
The chosen material of construction is Hastelloy-B-3 (65% Ni, 28% Mo, 5% Fe) due to the corrosive nature
of Hydrogen Iodide and acid. The minimum allowable diameter of the vessel has to be large enough to slow
down the gas below the velocity which the particles will settle out (Sinnott et al., ).
Following calculations from (Monnery and Svreck, ):
???????????????????????????????? ???????????????????????????????? = ???? ???? = 1.32 ????/????
???????????????????????????????? ???????????????????????? ???????????????????????????????? = ???? ???? = 0.992 ????/????
???????????????????????? ???????????????????????????????????????? ???????????????????????????????? = ???? ???? = 4.4 ????3
/????
The flash drum has a mist eliminator, therefore 6 inches are added to accommodate a support ring and
rounding up to the next 6-inch increment to obtain the external diameter. Thus:
???????????????????????????????? ???????????????????????? ???????????????????????????????? = ???? ???????? = 2.53 ????
???????????????????????????????? ???????????????????????????????? = ???? = 3.66 ????
Hold up time is the time it takes for the normal liquid level to reach the lower liquid level to empty whilst
keeping a normal outlet flow rate with no feed entering the vessel. Thus:
???????????????? ???????? ???????????????? = ???? ???? = 5 ????????????????????????????
???????????????? ???????? ???????????????????????? = ???? ???? = 8.39 ????3
The surge time is the time it takes for the normal liquid level to rise from normal liquid level to maximum
when keeping normal feed flow rate and no outlet flow. Therefore:
???????????????????? ???????????????? = ???????? = 3 ????????????????????????????
The volume of liquid between the highest liquid level and the normal liquid level
???????????????????? ???????????????????????? = ???????? = 5.032 ????3
The total height of the vertical flash drum is the sum of the HLLL +HH +HS + HLIN +HD +HME + 1ft. The height of
the vessel outlet at the top of the vessel must be sufficient so the liquid droplets can disengagement from
the vapour. Henceforth, liquid heights within vessel:
???????????? ???????????????????????? ???????????????????? ℎ????????????ℎ???? = ???????????????? = 0. ????
????????????????ℎ???? ???????????????????????????? ???????????????? ???????????? ???? ???????????? = ???? ???? = 1.667 ????
????????????????ℎ???? ???????????????????????????? ???? ???????????? ???????????? ???? ???????????? = ???????? = 1 ????
????????????????ℎ???? ???????????????? ???????????????? ???????? ????ℎ???? ???????????????????????? ???????????????? ???????? ???????????????????? ???????????????????????? = ???? ???? = 3.66 ????
????????????????ℎ???? ???????????????? ???? ???????????? ???????? ???????????????????????? ???????????????? ???????? ???????????????????????? = ???????????????? = 4.062????
- 34. 34
???????????????? ???????????????????????????????????????? ℎ????????????ℎ???? = ???? ???????? = 0. ????
????????????????ℎ???? ???????????????????????????? ???????????????? ???????????????????????????????????????? ???????????? ???????????? ???????????????????????????? ???????????????? ???????? ???????????????????????? = ???? ???????? = 0.305 ????
???????????????????? ????????????????ℎ ???????????????? ℎ????????????ℎ???? = ???????????????? + ???? ???? + ???????? + ???????????????? + ???? ???? + ???? ???????? + ???? ???????? = 10 ????
When calculating the corrosion wall thickness of a vessel the corrosion allowance must be taken into
consideration. The corrosion allowance is the amount of Hastelloy material available for corrosion without
disturbing the amount of pressure the vessel can contain (Sinnott et al., ). Thus:
???????????????????????????????????? ???????????????????????????????????? = 4 ????????
Leads to:
???????????????? ????ℎ???????????????????????????? = 3.6 ???????? + 4 ????????
= 7.6 ????????
????ℎ???????????????????????????? ???????? ???????????????????????? ℎ???????????????? = 7.6 ???????? + 4 ????????
= 11.49 ????????
The internal diameters of the Hastelloy pipes leaving and entering the flash drum were calculated using
Sinnott and Towler, the method is further discussed in Appendix [C].
Pipeline Flowrate (m3
/s) Velocity (m /s) Cross
sectional area
(m2
)
Required diameter (m)
Reactor to Flash
drum
4.45 2.00 2.225 1.68
Flash drum to light
ends column
4.40 2.00 2.2 1.67
Flash drum to
reactor
0. 2.00 1.45 x 10-3 0.043
Table [4.7]: Pipeline sizing for Flash Tank
4.2.4.1 Process controls and safety
On the left hand side of the flash drum there is a level indicator which will set off an alarm when liquid level is below a
certain point, this is to avoid pump damage. When the pump is pumping air and not fluid it can lead to cavitation and
produce loud noises. The pressure indicator send sends message to the alarm system if the pressure within the
vessel is over the maximum pressure of 1.1 bar. The pressure within the flash tank is relatively low compared to the
reactor and it’s very rare that it tends to overheat because the heat exchanger reduces the temperature before all
products reach the flash drum.
Going beyond this pressure can result in boiling of the liquid within the vessel and increase of temperature. The
contents within the vessel are highly hazardous and flammable the build-up of pressure can cause an explosion and
put all site workers at risk but this is highly unlikely. If the flash tank temperature did increase it would be due to a
faulty heat exchanger feeding through high temperature streams, so to reduce the temperature the reactor must be
cooled down. So a pipeline must be installed and redirected, while the faulty heat exchanger is fixed
4.2.5 Conclusion
- 35. 35
The flash drum unit was designed with 20 % overdesign ass specified in the process specification. The
P&ID provided gives detail to the indicators and control systems essential for process safety and efficient
production. The Engineering drawing is cross sectional representation of the essential internal units and
recommended liquid levels within the flash drum. The final cost for the unit is approximately £67,000.
- 36. 36
4.2.6 Engineering Drawing of Flash Tank
Fig [4.8]: Mechanical design of Flash Tank.
- 37. 37
4.3 Drying column
4.3.1 Introduction
This section of the design project report provides a detailed design description of the drying column in the
process. The process specification requires a yield of 400,000 tonnes per year and 99% purity of acetic
acid, therefore it is mandatory that the drying column is optimized to meet the client’s specification. The
objective of this section is to calculate the operating condition and physical parameters required to optimise
the process in order to meet the client specification; for example the column diameter, height, thickness,
ends and tray sizing. The column parameters are shown in Table 4.6.
Feed rate, F kg/hr .17
Feed Composition
Acetic acid 99.6 kmol%
Water 3.56 x10-11 kmol %
Propanoic acid 0.428 kmol%
Feed Temperature, oC 118
Column operating pressure, bar 1
Column reboiler Partial Reboiler
Column condenser Partial Condenser
Distillate composition, XD 0.992
Bottoms composition, XB 0.038
Table [4.7]: Specified column parameters.
- 38. 38
4.3.2 Drying Distillation Column P&ID
Figure [4.9]: P&ID of Drying Column
DC-401
- 39. 39
4.3.3 Design Method
Kinetic and thermodynamic data were collected from literature for water and acetic acid whilst obtaining
stream properties from the simulation on Aspen Plus, thus allowing to identify XD and XB in the vapour and
liquid streams. The subsequent data allows the determination of the number of trays in the column by
utilising the McCabe – Thiele Method for binary mixtures and thus feed position and reflux conditions are
estimated. In order to propose a viable implementation of a mechanical design, dimensions of the column
need to be determined, for example diameter and height, as well as selecting a suitable materials of
construction, a preliminary mechanical design of the drying column, which comprises of column design,
plate design and general arrangements and finally estimate a proposed cost of the column, including
capital and operating cost (Sinnot et al., ).
4.3.4 Drying Distillation Column Specification
The final drying distillation column specification is based on the calculations in Appendix D. The drying
distillation column is represented diagrammatically in Figure 4.8.
The purpose of the drying column in this acetic acid synthesis process is to increase the acetic acid purity
via separating methanol, ethanol, methyl acetate and water from the product stream and recycle these
undesired compounds back in to the reactor, consequently increasing the purity of the product stream. A
sketch of the column and plate is shown in Figure 4.8.
Drying Column – Design Data
Working Pressure 1.1 bar
Inside Diameter (Di) mm
Material of construction 305 Stainless Steel
Allowable Stress 515 N/mm2
Density of material .172 kg/m3
Design pressure 1.1 bar
Height of column 23.85 m
Area of column .81 m2
Thickness of column 12 mm
End selection Torispherical
End thickness 20 mm
Number of trays 34
- 40. 40
Feed entry 16
Plate spacing 0.7 mm
Hole pitch (rectangular) diameter 5 mm
Tray thickness 3.5 mm
Packing size 75 mm
Pipe diameter Feed 216 mm
Top 178 mm
Bottom 148 mm
The design considerations were made based on the specification provided from the client, the
following should be noted in the design.
Drying Distillation Column – Design Considerations
Cost of shell and trays £364,000
Cost of reboiler £22,000.00
Cost of condenser £16,500.00
Dead-weight of shell 122 kN
Weight of plates 109.67 kN
Weight of insulation 5.6 kN
Weight of vessel 237.27 kN
Wind loading 31.94 N/mm2
Bending moment .3 N/mm2
Longitudinal stresses 84.8 N/mm2
Circumferential stresses 48.4 N/mm2
4.3.5 Conclusion
The following design specification on this unit complies with the necessary design intent specification. In
addition, the specification fulfils the plant debottleneck allowances of a 20% overdesign.
- 41. 41
4.3.6 Engineering Drawing of Drying Distillation Column
Figure [4.10]: Mechanical Design of Drying Column
- 42. 42
4.4 Heavy – Ends Distillation column
4.4.1 Introduction
This column is designed to separate the unwanted propionic acid produced as part of the process from the
desired acetic acid produced, to obtain a purity of greater than 99.9% which is required by the design brief
at a capacity of 400,000 tonnes per year.
Temperature = 125 o
C (398K)
Operating conditions Pressure = 1 atm ( Pa)
Reflux ratio = 17
For the purposes of the calculations, the average internal temperature of the column was assumed to be 125
o
C (398K) to ensure that the majority of the acetic acid, and only a minimal amount of propionic acid was in
the vapour phase in addition to operating at 1 atm ( Pa). The reflux ratio of 17 was taken from the
simulation produced as part of this project on Aspen Plus, as this gave the desired quantity and purity of
acetic acid as a top product.
The material chosen for the construction of the column is 304 stainless steel as both propionic and acetic
acid have corrosive properties and stainless steel provides a sufficient corrosion resistance to justify its choice
for the construction of the column. Grade 304 was chosen over other grades of stainless steel as the
mechanical and structural advantages provided by the other, more expensive, grades is not large enough to
justify the extra cost associated with them.
To calculate the internal diameter of the column a tray spacing has to be assumed, it is suggested that a tray
spacing of 0.5 m should be initially used to calculate the column’s diameter and if the diameter is greater than
1 m a tray spacing of between 0.3 and 0.6 m is normally appropriate (Sinnott et al., , p708-709). The
calculated column diameter was greater than 1 m, so the initial assumed tray spacing on 0.5 m was carried
forward throughout the calculations. The tray efficiency applied to the tray in this case is 70% as this is found
to be an optimal number for the preliminary design of a distillation column (Sinnott et al., , p700). It is
also suggested that 10% more tray be added in addition to tray efficiency with future expansion in mind
(Branan, , p444).
In addition to the spacing of the trays and tray efficiency, included in the cost analysis of the column is the
costing of the trays used. This required a type of plate contactor to be chosen from a selection of sieve plate,
bubble-cap plate and valve plate, each with their own advantages and disadvantages. The plate contactor
chosen in this case is the valve plate, as there are weeping issues with sieve plates at low liquid flow rates
and bubble-cap plates are approximately twice as expensive as valve plates. The valve plate is an ideal
compromise between performance and cost when compared to the other two options.
Before the tray efficiency is applied to the theoretical number of stages, there are a total of 15 rectifying
stages and 8 stripping stages giving a total of 23 theoretical stages. The location of the column inlet stream
- 43. 43
lies between the rectifying and stripping sections therefore, in this case the inlet stream is between the 15th
and 16th
stage, although this does not hold when the tray efficiency is applied as the number of stages
changes. Although the number of stages changes, the location of the feed should maintain the same ratio of
rectifying and stripping stages above and below it respectively, therefore, the initial ratio of rectifying stages
to total number of stages will be applied to the actual number of stages to find the actual inlet location of the
column.
- 44. 44
4.4.2 Heavy – Ends Distillation Column P&ID
DC-501
P-501
P-502
V-502
V-503
V-504
V-505
FI
FIFIC
FIC
V-501
LIC
LI
V506
TI
FIC
V-507
TI FIC
Acetic acid
Propionic acid
LAH
LAL
Process
Steam
Process
Water
DC-401
V-508
FIC FI
Figure [4.11]: P&ID of Heavy-Ends Distillation Column
- 45. 45
4.4.3 Acetic acid properties within the column
The vapour density of acetic acid under the conditions of the column was calculated using the ideal gas
equation (Perry, , p2-355):
ρ ???????????????????????? = ????
???? ???????????????????????????????? ????⁄
ρ ???????????????????????? = 1.84 kg/????3
The vapour pressure due to acetic acid under the conditions of the column was calculated using the Antoine
equation and the parameters specific to acetic acid (Sinnott et al., , p451):
???????????????????????????? = ???? ????−( ????
????+????⁄ )
???????????????????????????? = 136.45 ????????????
Where: A = 7. (Dean, , p539)
B = .313 (Dean, , p539)
C = 222.309 (Dean, , p539)
The mass flowrates and mass fractions for the inlet, bottom product and top product have been calculated
using values taken from the simulation produced on Aspen Plus as displayed by the PFD:
Molar flowrate
[kmol/hr]
Mass flowrate
[kg/hr]
Mass fraction
Inlet 893.86 .48 0.992
Bottom product 3.07 184.17 0.296
Top product 890.79 .34 1.0
Table [4.8]: Acetic acid mass flowrates and mass flowrate for inlet, bottom product and top product.
4.4.4 Propionic acid properties within the column
The liquid density of propionic acid was calculated by developing a relationship between known values of
propionic acid density and temperature (CAMEO Chemicals, ) and assuming the relationship remained
constant up to the operating temperature of the column.
ρ ???????????????????????????????????? = 882.39 ????????/????3
The vapour pressure due to propionic acid under the conditions of the column was taken from literature and
was given as (Clifford et al., ):
???????????????????????????????????????? = 59.86 ????????????
- 46. 46
The mass flowrates and mass fractions for the inlet, bottom product and top product have been calculated
using values taken from the simulation produced on Aspen Plus as displayed by the PFD:
Table [4.9]: Propionic acid molar flowrates and mass flowrate for inlet, bottom product and top product.
4.4.5 Relative volatility
As this is a binary mixture, the following relationship between vapour pressures can be used to calculate
relative volatility (Branan, , p450):
???? =
????????????????????????????
????????????????????????????????????????
???? = 2.
4.4.6 Heavy Ends Distillation Column Specification
The final heavy ends distillation column specification is based on the calculations in Appendix E. The heavy
ends distillation column is represented diagrammatically in Figure 4.9.
The mechanical properties of the column were calculated based upon the Smoker equations which are
applicable to systems in which the relative volatility is close to 1 as the McCabe-Thiele method would be
impractical (Sinnott et al., , p 661). Using this method and applying a 10% over design as well as a tray
efficiency of 70% give an actual number of stages required to be 37.
???????????????????????? ???????? ???????????????????????? ???????????????????????? = 37
The height of the column is calculated by multiplying the tray spacing by the number of stages as well as the
addition of height allowances for a condenser at the top of the column and a reboiler at the bottom of the
column. The height allowance for the condenser and reboiler are suggested as 4 ft (≈1.25 m) and 6 ft (≈1.85
m) respectively (Branan, , p 444). The column height, not including either end, is calculated to be 21.6
m.
???????????????????????? ℎ????????????ℎ???? = 21.6 ????
The column diameter is calculated as a function of the maximum vapour velocity through the column, which
is a function of tray spacing. The maximum vapour velocity through the column is calculated as 2.86 m/s and
the column diameter is calculated as 1.83 m.
Molar flowrate
[kmol/hr]
Mass flowrate
[kg/hr]
Mass fraction
Inlet 5.93 438.76 0.008
Bottom product 5.93 438.76 0.704
Top product 0 0 0
- 47. 47
???????????????????????????? ???????????????????????? ???????????????????????????????? = 2.86 ????/????
???????????????????????? ???????????????????????????????? = 1.83 ????
The column shell thickness chosen is a calculated minimum shell thickness required to resist the internal
pressure with the addition of a corrosion allowance of 2 mm. This equates to a column shell thickness of 12
mm.
???????????????????????? ????ℎ???????????? ????ℎ???????????????????????????? = 12 ????????
The thickness of the ends also has to be calculated as this will differ from the column shell thickness as the
stresses the ends of the column are put under vary from that of the column shell. The thickness of the end is
equal to 18 mm including a 2 mm corrosion allowance.
???????????????????????? ???????????? ????ℎ???????????????????????????? = 18 ????????
The size of the inlet, bottom product and top product pipes are all calculated using the density of the stream,
the velocity of the stream and the streams flowrate. The inlet pipe diameter was calculated to be 0.084 m
which corresponds to a nominal pipe size of 4 inches including an allowance for future expansion. The bottom
product pipe diameter was calculated to be 0. m which corresponds to a nominal pipe size of 3/4 inches
including an allowance for future expansion. The top product pipe diameter was calculated to be 0.78 m
which corresponds to a nominal pipe size of 36 inches including an allowance for future expansion.
???????????????????? ???????????????? ???????????????????????????????? = 4 ????????????ℎ????????
???????????????????????? ???????????????????????????? ???????????????? ???????????????????????????????? = 3/4 ????????????ℎ????????
???????????? ???????????????????????????? ???????????????? ???????????????????????????????? = 36 ????????????ℎ????????
The cost of the column shell is a function of the columns mass which is calculated to be 120,000 kg. The total
cost of the column including the cost of the shell and the trays is £145,000 (, UK basis).
????ℎ???????????? ???????????????? = .6 ????????
???????????????? ???????????? ???????? ???????????????????????? ???????????? ???????????????????? = £145,002
4.4.7 Summary of design data
To follow is a summary of the full design data of the column, calculations as to how the data has been
obtained is described fully in Appendix E.
- 48. 48
Tray selection Valve plate trays
Tray spacing 0.5 m
No. of stages 37
Feed location Stage 24
Column height 21.6 m
Column diameter 1.83 m
Shell thickness 12 mm
End thickness 18 mm
Inlet pipe diameter 4 inches
Bottom product pipe diameter 2 inches
Top product pipe diameter 36 inches
Column mass .6 kg
Installed cost of column shell and trays £145,000
4.4.8 Conclusion
The mechanical design of this unit has been completed with consideration of the 20% overdesign required
by the design brief as well as the product specification. To follow will be an engineering drawing that
describes all the data put forward, to give a clear visual representation of the design of the heavy ends
distillation column.
- 49. 49
4.4.9 Engineering Drawing of Heavy – Ends Distillation Column
Figure [4.12]: Mechanical Design of Heavy – Ends Distillation Column.
- 50. 50
4.5 Absorption column
4.5.1 Introduction
The production of waste gas components is inevitable in the case of carbonylation. The off was waste
materials (CO2, H2, CO) have to be separated from any toxic, and carcinogenic (e.g. methyl iodide)
components still present in the waste stream and then burned in the flare. It is necessary that the methyl
iodide is recycled back into the system, as it is highly toxic to the environment, and because it is required
as a reaction promoter for the carbonylation step.
The off gases are produced in the reactor phase as unwanted products are burned in the flare. While the
methyl iodide is captured in a counter-current packed absorption column using methanol and acetic acid
(i.e acetic acid is used for start-up, while methanol is sued throughout the life of the plant).
Absorption Column – Design Data
Height of transfer units 1 m
Height of packing section 8 m
Total height of column 10.5 m
Column Diameter 0.6 m
Pressure drop 0.005 bar g/m
Packing – Design Data
Type Intalox ceramic saddles
Size 25 mm (1 inch)
Packing material Ceramic
Packing arrangement Dumped
- 51. 51
4.5.2 Absorption Column P&ID
Figure [4.13]: P&ID of Absorption Column
S-601
- 52. 52
4.5.3 Design Method
Absorption is mass transfer procedure in which one or more soluble components from the gas mixture are
dissolved using a low volatility liquid. As a result the polluting material (i.e. methyl iodide) diffuses from a
gaseous sate into a liquid state, and is then recovered at the bottom of the column. The absorption rate is
driven by the driving force of the absorption, and is relatively independent of equipment used (McCabe and
Smith, ).
The absorption unit operates using a counter current design, where the methyl iodide present in the
gaseous mixture is dissolved in a liquid with a lower volatility (Sinnott et al., ). Counter current designs
have the highest theoretical removal efficiencies, and is suited for high loadings of pollutant materials while
it requires a lower solvent to gas ratios than alternative designs (e.g. crosscurrent, concurrent).
The most common choice for pollution control gas absorbers are packed towers. A packet tower is often
preferred to plate/tray towers because it can manage higher flowrates of gas, with lower pressure drops
while maintaining low liquid hold-up. It is also recommended to use a packed tower when the contacting
components have corrosive/acid proprieties, as cheaper corrosive materials are for the shell, and packing
are available. Also packed towers are preferred when there are no high temperature deviations, and the
system removes the gaseous mixture using a pressure drop. And when the diameter of the column (i.e.
based on the flowrates of material) is between 0.5-0.7 m (Sinnott et al., ).
Disadvantages of packed towers
• High clogging and fouling potential • Replacing damaged packing
• Higher waste water/solvent disposal • Removal of very small particles
4.5.4 Absorption Column Specification
The waste gas stream enters through the bottom of the column and travels vertically, counter current (i.e.
through the packing) to the falling solvent liquid. As a result, gaseous methyl iodide diffuses into a liquid
phase. The system works based on physical absorption, and achieves high efficiencies at low temperature
and pressure (Sinnott et al., ). Physical absorption is used because it relies entirely on the proprieties
of the solvent and the gas stream, and their specific characteristic (e.g. volatility, density, viscosity). In
order to achieve efficient absorption is it important that the design allows large contact area for the gas
stream and solvent to react, the capacity required for controlling high rates of waste gas, higher gas to
liquid ratios, low pressure drop and adequate distribution of solvent to gas to allow adequate pollutant
diffusion (i.e. methyl iodide)
4.5.4.1 Design considerations to account for drawback of unit
• A liquid distributor is used in order to maximize area covered by solvent in packing.
• A higher density component (e.g. acetic acid, methanol) is used as a scrubbing liquid.
- 53. 53
• The solvent used is present in the system, and is recycled into the reactor with the methyl iodide
instead
• Packing material is corrosive-resistant, meaning that damage only occurs due to physical contact;
• Packing size is chosen based on the column size, so that it maximizes particle interaction, including
very small particles.
• Dumped packing allows easier replacement in the case of damage as opposed to structured
packing.
• Packing components that are not damaged can be reused, therefore reducing costs.
• A low pressure drop will results in low energy requirements.
4.5.4.2 Choice of packing
For this unit, the packing is the most important component. This is because the absorption efficiency is
correlated to the flow capacity, and the height of the transfer units (i.e. HTU gas, HTU liquid); these factors
significantly affect the tower height of the unit, and has economic implications (e.g. installation,
maintenance, cleaning). When choosing the adequate packing, it is important that the following factors are
taken into consideration:
• The packing material has to be inert to the liquids flowing through the packing.
• The packing material needs to be corrosive resistant.
• Brittleness of component needs to withstand process conditions, without presenting excessive
weight.
• The packing must offer enough contact area, while not restricting the gas and solvent flow.
• The packing must restrict the formation of excessive liquid hold-ups.
• The packing material needs to be acquired at a reasonable cost.
The above considerations were taken into account and 25 mm Intalox ceramic saddles were chosen.
These choice poses process advantages and low cost of packing. Intalox ceramic saddles offer the best
contact area, are inexpensive, and in ideal conditions could last throughout the life of the column. It is
expected that the packing will have to be changed throughout the life of the plant. However due to the small
costs, it still supports the choice of dumped packing rather than structured packing, or plates (Sinnot et al.,
).
4.5.4.3 Choice of absorption tower equipment
The packed absorption column is comprised out of:
• Column Shell
• Mist eliminator
• Liquid distributor
• Packing restrainer
- 54. 54
• Packing support
• Packing materials
The mist eliminator is in the form of a layer of mesh; its main function is to collect any droplets that gather
at the top of the column as mist. It needs to be installed at the top of the column, so that any of the liquid
droplets collected are returned back to the column. The droplets are moved to the top of the column via a
high velocity gas stream (McCabe and Smith, ).
The liquid distributor chosen is a pressure drop spray nozzle distributer. The distributor is designed to wet
the packing, and facilitate consistent contact between the gas mixture and the solvent without constricting
the gas flow. Its main function is to spread the solvent evenly across the area of the packed bed. Some of
the disadvantages of this equipment includes plugging, formation of mist, feed rate dependent liquid
distribution. Therefore adequate maintenance is required in order to maximize the efficiency of the column
(Sinnott et al., ).
A packing support is necessary for an even distribution of the waste gas, and requires an open space
between the bottom of the absorption tower and the packing. The support plates are required to support the
total weight of the packing (i.e. while still allowing the material streams to travel freely), and are therefore a
necessity for this system (Sinnott et al., ).
A packing restrainer is required in order to prevent the high gas velocities from raising the packing into the
liquid distributors. The packing restrainer used is an unattached weighted plate placed at the top of the
packing, and which settles with the packed bed. The restrainer is required since the packing material is
ceramic, and keeping the integrity of the packed bed; therefore preventing any extra costs.
4.5.4.4 Materials of construction
The material of construction for the absorption column is Hastelloy C. Although, Hastelloy C is more
expensive when compared to a stainless steel shell lined with corrosion resistant column internals (e.g.
fibre-reinforced polymers), for this process route, Hastelloy C offers a better range for temperature and
pressure resistance. Additionally, the corrosion allowance for Hastelloy C accounts for extended use, with a
small probability of loss of containment across the column.
4.5.4.5 External equipment
The external equipment for the absorption column is comprised out of:
• Off gas movers
• Solvent pumps
• Control equipment
- 55. 55
The waste gas movers require to be cooled down to room temperature, as increased gas temperature
leads to lower absorption in the column. Methyl iodide is gaseous above 315.9 K, and is required that the
methyl iodide is cooled down to 298 K. The resulting stream after cooling down will be a mixture of gas and
liquid, helping to absorb the methyl iodide as it turns into liquid phase, as well as keeping the vessel
temperature at room temperature in order to maximize the efficiency of the absorption column.
The solvent is moved into the column using a centrifugal pump. It is recommended that the construction
material used is corrosive resistant (e.g. stainless steel) and suitable for acetic acid/methanol. The
scrubbing material will be pumped from the final pure acetic acid stream. It is recommended that a storage
tank for acetic acid is placed in the proximity of the scrubber, in order to have access to excess scrubbing
solvent if the situation requires (Sinnott et al., ).
4.5.4.6 Safety control
The absorption unit requires the following control in order to operate safely on the premises of the plant:
• Gas detectors located at the outlet vent for: Acetic acid, Methanol, Carbon Monoxide, Carbon
Dioxide, Hydrogen, Hydrogen Iodide, Methyl Acetate, and Methyl Iodide.
• Temperature indication control for the gas stream.
• Level indication control for liquid stream.
• Flow indication control at the inlet and outlet streams.
4.5.4.7 Safety considerations
Since the components entering and exiting the absorption system are hazardous, adequate maintenance
for the equipment should be done regularly (HSE Maintenance procedures, ). A safe control
methodology has to be put in place. In order to keep the safe working environment the scrubber requires:
• Pressure relief system to prevent pressure accumulation in the vessel that could lead loss of
containment.
• Adequate insulation around the column with mineral wool to prevent any unwanted temperature
deviations.
• Gas detectors located around the scrubbing unit.
4.5.5 Conclusion
It is necessary that an efficient scrubbing system is put in place in order to prevent the release of toxic
iodide into the atmosphere. It is recommended that the above dumped packing absorption tower to be
connected to a stripping column, in order to achieve an efficient pollutant removal. The methyl iodide,
alongside the hydrogen iodide are toxic materials and have to be recycled back into the stream, or
disposed of adequately. These two components are crucial for the process to operate, and an efficient
pollutant removal system is necessary. When considering the design of the absorption column, a packed
absorber operating at low temperature and low pressure will offer the required removal efficiency. The
- 56. 56
present design offers an economic alternative to other scrubbing units. The absorption unit is the safeguard
that prevents any hazardous components from polluting the environment heavily, with the adequate
safeguards and system management in place could last throughout the life of the plant.
- 57. 57
4.5.6 Engineering drawing of Absorption Column
Figure [4.14]: Mechanical Design of Absorption Column
- 58. 58
4.6 Storage tank – Acetic acid
4.6.1 Introduction
The tank is specified to be a fixed cone-roof cylindrical-type design and have a capacity of m3
. This
figure is the sum of one week production of acetic acid ( m3
) plus an extra m3
provided by the
volume of the conical head. The maximum working level for the tank is m3
, approximately 80% the
volume of the cylindrical tank and available for additional storage due to safety purposes. The storage
buffer provided will allow the plant for continuous operation for up to one week in the event of unforeseen
shutdown of the plant and/or disruption in distribution. The tank internal diameter is 24.9 m and the tank
height is 18.8 m. The internal and external pressure loads require a wall, base and roof plate thickness of
8.8 mm to meet the British design code for pressure vessels. This thickness gives a 100% safety factor
over the maximum anticipated stresses.
The product inlet line is standard nominal pipe size 4, schedule number 40s. This inlet is sized for the
maximum production flowrates. The product outlet line is of standard nominal pipe size 12, schedule
number 120. This line is sized such that a standard-size chemical ship tanker may be filled in 8 hours.
The tank must be constructed of stainless steel type 316L (‘acetic acid grade’), the specification of this
material is given in Appendix F. The design data required for this unit are specified below.
Acetic Acid Tank – Design Data
Design tank capacity m3
Design temperature 40 o
C
Design pressure 18.7 kPa
Working pressure 118 kPa absolute
Acetic acid density kg/m3
Material of construction SS316L
Design tensile strength 485 MPa
Joint efficiency 85%
The design tank capacity is estimated to be m3
. The maximum tank operating level will be
approximately m3
to give the extra tank capacity as a reserve volume. This also ensures that a
minimum of capital cost (in the form of product acid in the tank) is unused.
The design temperature represents the upper limit that acid may be fed to the tank from the process. The
working pressure represents the sum of atmospheric pressure and acid vapour pressure at the design
temperature. Details of the calculations associated with the tank design are presented in Appendix F. The
cost of this vessel is estimated (from a correlation) to be £333,000.
- 59. 59
4.6.2 Acetic Acid Storage Tank P&ID
Figure [4.15]: P&ID for Acetic acid storage tank.
T-101
- 60. 60
4.6.3 Design Method
The tank dimensions are determined according to standard tank geometries as enforced by API 650. Tank
shell thickness is sized according to the limitations imposed by the British design standard for pressure
vessels. The tank contents are flammable, toxic and corrosive, appropriate safety features are
recommended. Details of the calculations are given in Appendix G.
4.6.4 Storage Tank Specification
The final tank specification is based on the calculations in Appendix G is shown in Table 4.10. The tank is
represented diagrammatically in Figure 4.16.
The storage tank should be constructed of 316L stainless steel. To reduce corrosion of the tank bottom
exterior, application of coating is recommended between the tank and foundation. As seen by Figure 5.2,
the storage tank area is enclosed by containment facilities capable of containing the contents of the tank
and maximum expected rainfall in case of a storm event; moreover, additional safety of a small, deep diked
area is proven through lower evaporation rate and small area of fire. The enclosed area is drained through
a trap to a safe location that is protective of human health and environment and in compliance with
applicable laws and regulations. A vertical tank is implemented to provide for a more economical use of
land.
For outdoor storage of glacial acetic acid, a heating system and tank insulation is provided. The
recommended heating system consists of low-temperature electric heating pads installed between the tank
exterior and the insulation in order to maintain the temperature at a desirable level.
Acetic acid is a flammable solvent, thus to inhibit the accumulation of static charges, the storage tank,
pumps, transfer lines, and offloading vehicle are adequately grounded and fill line enters the tank through
the roof and extended downward to within 2 or 3 inches of the bottom.
The storage facility is constructed so that water cannot be introduced or generation of heat occurs. In a
confined space, considerable pressure caused by this reaction can result in an explosion that may rupture
the storage tank.
Safety features for the tank include a pressure relief-valve system on the tank roof, to be opened when
draining or adding to the tank contents. An emergency relief vent is fitted to the storage tank to allow
emergency flow due to excessive venting requirement from fire burning around the tank, thus eliminating
opportunity for a costly tank rupture, providing emergency venting from abnormal internal pressure beyond
the capability of the pressure relief vent. The operational tank venting system handles normal tank venting
due to product import/export and ambient temperature variations. In the event of fire, as vapour pressure
increases to a point where normal venting equipment capacity is exceeded, the hinged cover will lift
relieving the pressure and protecting the tank from rupture. The pressure build up will be quite slow,
therefore the cover should not open violently and cause any damage to the tank. Emitted vapours may be
ignited by the fire, but should ‘flame off’ externally until brought under control by firefighting operations.. A
manhole provides access to the tank for internal maintenance.
- 61. 61
Appropriate venting systems are issued. Vents should be angled at 45o
from vertical and cut off vertically to
prevent rain from entering. The vents are 1 inch larger in diameter than the tank fill line. A coarse-mesh
stainless steel wire screen is placed over vent openings to prevent entry of foreign objects. A blanket of
inert gas, nitrogen, is provided and equipped with a pressure/vacuum conservation vent, piped away to a
safe location that is protective of human health and the environment.
In order to counteract the strong odour generated by acetic acid, odour masking methods are utilised within
the compound. Odour control chemicals used for masking purposes are aromatic chemicals derived from
aromatic chemical manufacture. Organic odour control chemicals are numerous, some of which are vanillin,
methyl ionones, benzyl acetate, phenylethyl, eugenols and heliotropin, and thus any of the organic
compounds mentioned are viable to be implemented in this scheme. Furthermore, this method of treatment
requires no capital investment required for equipment and readily available for application.
Table [4.10]: Storage tank specification.
A standard metal staircase and railing skirts the outer edge of the tank providing access to the tank roof. A
manhole in the tank roof provides access for internal repairs. Discrete inlet and outlet lines are required to
feed into the base of the tank. A pressure relief valve is attached to the roof. This valve is opened
automatically when pumping product to, or withdrawing product from the tank. The valve is shut when
pumping stops so that vapour losses from the tank are contained. A bursting disc on the roof also provides
emergency pressure relief for an unforeseen pressure build-up within the tank.
4.6.5 Conclusion
The acetic acid storage tank required for the plant has a capacity of approximately m3
. This
represents approximately 21,000 tonnes of product acid. The tank will normally contain only about 14,000
Vertical cylindrical-type tank
Fixed conical roof
Total tank capacity m3
Normal operational capacity (maximum) m3
Tank inside diameter 24.9 m
Tank height 18.8 m
Tank wall thickness 8.8 mm
Material of construction SS316L
Inlet and outlet at tank base
Inlet line: Nominal pipe size 4, schedule number 40s
Outlet line: Nominal pipe size 10, schedule number 120
Manhole, bursting disc, pressure relief valve on roof
Mineral wool insulation 0.02 m
- 62. 62
tonnes to satisfy outside product sales. The remaining capacity is in reserve in case of plant shut-down and
issues regarding distribution. This provides a one week production buffer for the plant. The final
specification requires a tank of 24.9 m diameter, height 18.8 m, and a plate thickness of 8.8 mm.
A size delivery of m3
by means of a standard tonne chemical tanker would be desirable, as
nearly 75% of the weekly production is able to be shipped. The figure obtained for the minimum stock level
will be able to accommodate a scenario where if the plant shuts down for a few days, the remaining storage
will keep on supplying customers. Additionally, if there is a problem in distribution, the available space in
the tank will allow for continuous running of the plant until the problem is solved. Henceforth, a delivery
period of one week will provide smooth production and shipment whilst accommodating customers. The
cost of the tank has been calculated (Appendix G) from correlations to be approximately £333,000.
- 63. 63
4.6.6 Engineering drawing of Acetic Acid Storage Tank
Figure [4.16]: Mechanical design of Acetic acid storage tank.
- 64. 64
5. Process Control and Instrumentation
5.1 Introduction to Process Control and Instrumentation
The premise of process control and instrumentation consists of applying the philosophies of control to all
aspects of a process, whether that be the design of the process, the standard operation of the process or the
operation of the process under conditions that vary from the norm, for example during a start up or shut down,
as the only way to have a safe system, is to have reliable control systems in place at all times. As well as
safety, putting in place reliable and effective control systems also aids in improving plant efficiency and the
economic stability of the process while ensuring the plants compliance with the relevant environmental and
safety regulations.
As the philosophies of process control and instrumentation are incorporated into every aspect of a process,
the instrumentation that’s implemented into a process should be integrated within the earliest design instead
of being an afterthought that’s ‘bolted on’ once the design has been completed. Implementing process control
systems in this way will lead to the safety features of the process being much more effective with regards to
plant safety and the safety of those in and around the plant, in addition to being much simpler because they
have not been worked into the system, around an already complete process without the necessary control
features put in place.
5.2 Objectives of Process Control
The primary objective of the control systems and instrumentation put in place is to ensure that the process is
carried out in a safe and reliable manner while producing a product that meets the required specification
desired by the consumer. This can be achieved by (Sinnott et al., , p275):
1. Maintaining process variables within known safe operating limits around a specified set point.
2. Alerting operators to deviations from the set point and safe operating limits and provide a solution to
the deviation either via the manipulation of process equipment or shutdown systems.
3. Preventing operators from altering process variables such that operation outside the safe operating
limits is caused.
The four main process variables that have been controlled throughout the design stages of this project are:
1. Temperature.
2. Pressure.
3. Level.
4. Flow.
The variables have been controlled through the manipulation of various pieces of process equipment, such
as control valves, via information sent to them through a series of indicators, alarms and controllers. The
process equipment works to control any deviations from the desired set point, within an upper and lower limit.
The control measures also have to accommodate for planned changes in the set point, for example, during
- 65. 65
start-up and shut down in which the desired set point for each of the process variables is going to vary from
that of a steady state operation. This can be seen in the reactor, for example, during its start-up process, the
set point would be at its desired operating conditions to ensure that the reaction took and a product was
being produced. As the reaction continues and begins to reach a steady state the heat released by the
reaction will cause an increase in the temperature of the reactor and therefore, a deviation from the desired
operating conditions. In this case the set point can be decreased below the desired operating conditions while
the heat released by the reaction can be used to maintain the required temperature. Variations in the set can
be fine-tuned using the instrumentation in place to control situations like this.
In addition to process safety, operability has to be taken into consideration when implementing control
features throughout the design stages of a project, as having too many indicators and alarms, etc., can reduce
the operability of the process as having “too much data being thrown at operators reduces their ability to
understand what is happening and respond correctly” (Hurley, ). This has been taken into consideration
when implementing control features into the design of our process as it is possible to manage a combination
of process variables by manipulating just one of them. Although this could lead to undesired variations in
some of the process variables when manipulating others, therefore it is important to understand the
relationships each of the process variables share with each other and what impact their variation would have
on the process streams as well as the process equipment. An example of this can be seen in the transition
from stream 4 to stream 5 of the PFD through a pressure reduction valve. The purpose of the valve is to
reduce the streams pressure before it enters the flash tank, but as a consequence of reducing the pressure,
the temperature of the stream is also reduced. The relationship between the two process variables is clear
in this case, which would make it easier to identify the hazards a variation of pressure would cause
downstream of the valve whether that be to the flash tank or other pieces of process equipment.
5.3 Implementation of Control Systems in our Design
The types of control that have been taken advantage of throughout the design process of this project has
been feedback, feedforward and cascade, with feedback and feedforward being the simpler forms of control
and cascade being more complex. A feedback control system measures a process variable downstream of
a piece of process equipment and then send information back upstream for the process equipment to manage
the process variable directly. Similarly to feedback control, feedforward control only measures and alters one
process variable, although the process equipment is downstream of the measuring equipment instead of
being the other way round in feedback. Whereas cascade control measures a process variable then alters
another to result in a change to the original measured process variable.
Feedback control can be seen throughout the process P&ID, an example of the utilisation of feedback control
can be seen in figure 6.1. The figure shows a set of pumps in parallel with feedback controlled valves based
on the flow through the pipe. This has been implemented into the system with pump failure in mind, for
example, if P-401 was the operational pump and P-402 was being used as a backup, both V-402 and V-404
would be closed to prevent any flow through P-402 under normal operating conditions. In the event of P-401
failing, V-403 and V-405 could be closed from the control room to prevent flow through P-401 while the pump
- 66. 66
was either replaced or having maintenance carried out on it. Valves V-402 and V-404 could then be opened
from the control room and P-402 would become the operational pump in this system. The ability to switch
between pumps because of the control systems in place would lead to much less downtime required in the
event of the operational pump failing in comparison to a system without these control measures in place.
Figure [5.1]: Pumps P-401 and P-402 is parallel with flow control.
This type of control measure ensures that the operational time of the plant is not reduced due to pump failure
and therefore maintains a high plant economic efficiency.
Cascade control can be seen in the instrumentation implemented around each of the distillation columns,
more specifically around the condenser and reboiler. The temperature of the streams that are recycled from
the condenser and reboiler will impair the columns performance if they are not as they should be, therefore
it is important that the temperature is maintained in those streams. The cascade of control is used to control
the temperature of the recycle streams by controlling the flow rate of cooling water and steam into the
condenser and reboiler respectively. This system has been chosen as it is relatively easy to control the flow
of cooling water and steam via the opening and closing of a valve when compared to directly controlling
temperature.
5.3.1 Distillation column control
Cascade control can be seen in the instrumentation implemented around each of the distillation columns,
more specifically around the condenser and reboiler, as shown in Figure 5.2. The temperature of the streams
that are recycled from the condenser and reboiler will impair the columns performance if they are not as they
should be, therefore it is important that the temperature is maintained in those streams. The cascade of
control is used to control the temperature of the recycle streams by controlling the flow rate of cooling water
and steam into the condenser and reboiler respectively. This system has been chosen as it is relatively easy
to control the flow of cooling water and steam via the opening and closing of a valve when compared to
directly controlling temperature.
This system of cascade control also allows for effective pressure control when coupled with the ability to
control the flowrate of the vapour stream (Branan, , p78). Effective pressure control can be achieved
through controlling the flowrate of the vapour leaving the column, i.e. less vapour leaving the column will
- 67. 67
cause an increase in pressure throughout it. This flowrate of the vapour stream is controlled by the valves V-
308, V-408 and V-508 on the light ends, drying and heavy ends distillation columns respectively. Figure 5.2
shows V-308 on the light ends distillation column.
The temperature control element of the system, as previously described, through the control of the process
water flowrate, allows the control of the vapour stream composition and importantly, gives an operator the
ability to keep the stream composition constant (Branan, , p78).
DC-301
P-301
P-302
V-302
V-303
V-304
V-305
FI
FIFI C
FI C
V-301
LIC
LI
V-306
TI
FIC
TI FIC
V-307
FIFIC
LAH
LAL
Process
Water
V-308
FIC FI
V-308
F-201
DC-401
S-601
Figure [5.2]: P&ID of DC-301 and control systems
- 68. 68
5.3.2 Reactor and Flash tank control
Cascade control can also be seen on the system controlling the flow into, and out of, the flash tank and
reactor respectively. Figure 5.3 describes the system around the reactor, R-201, and flash tank, F-201, as
shown by the P&ID. The flowrate of the liquid leaving the reactor and therefore, entering the flash tank is
controlled by the valve, V-201 which is in turn, is being controlled by the level in the reactor through the level
instrumentation put in place. Similarly for the flask tank, the liquid flow out of the flask tank, which is being
recycled back into the reactor, is controlled by the valve, V-206 which in turn, is being controlled by the level
in the flash tank through the level instrumentation put in place.
Valve V-203 is the pressure reduction valve required by the process, as it is a key piece of process equipment
a backup valve, V-204, has been included for redundancy in the case of failure or in the event of maintenance
being required on the operational valve. As V-203 is the valve used in normal operation, V-204 would usually
be closed with V-202 and V-205 open to allow flow through V-203. Both valves V-202 and V-205 can be
closed to isolate V-203 in the event of its failure and/or requirement for maintenance.
R-201
V-210
V-209
V-208
V-207
FI
FI FI C
FI C
V-201
LI
FI C
V-202
V-203
V-205
V-204
PIFI C
F-201
V-206
FI C
LI
FIFI C
LAH
LAL
S-601
DC-301
V-211
FI FI C
R-201 Feed
Figure [5.3]: P&ID of R-201 and F-201 and control systems
- 69. 69
6. Process Economics
6.1 Market Analysis
In the current economic climate, demand for acetic acid is great and room for continuous growth is highly
probable. (Grand View Research Inc., ) predict that “Global Acetic Acid Market is expected to reach
USD 13.31 billion by ” as a result of products manufactured from acetic acid, such as Vinyl acetate
monomer (VAM) extensively growing in demand. Henceforth, the development of an acetic acid plant will
be very profitable in today’s current market.
Acetic acid is a key precursor in the production of various commercial and industrial based products.
Products range from households such as vinegar, a multifunctional household product used in cooking and
as an ingredient in renowned sauces like ketchup, mayonnaise and mustard; additionally it is also
employed in cleaning products for the unclogging of drains and removal of lime scale deposits.
Although acetic acid is a key element in the manufacture of numerous commodities, the most significant
product is Vinyl acetate monomer (VAM). The versatility of VAM allows for the production of various
polymers such as polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral and polyvinyl formal; these polymers
are employed within industry as paint, adhesives and packaging. Literature on VAM reportedly states that
the worldwide demand for the monomer back in was reported to be 4.3 million tonnes per year,
contributing to 86% of overall acetic acid production worldwide. The maximum global production was
approximately 5 million tonnes per annum, key contributors being Asia (43%), North America (34%) and
Western Europe (18%) (Chemical Week, ). An additional source (Nexant, ), highlights data that
reports global production of VAM reaching approximately 4.9 million per year in . Furthermore, recent
sources indicate further growth in VAM production (Merchant Research & Consulting Ltd, ) stating
“, the overall VAM output climbed to around 6.5 million tonnes, registering growth of nearly 4%
(259,000 tonnes)”. As previously mentioned, there is significant evidence in support of the global demand
for VAM, as a result of its thriving growth in industries such as construction, automotive, paints and coating.
Continuous global growth in infrastructure at extreme rates leads to further expansion of VAM production.
Figure 6.1, illustrates pricing for VAM, Terephthalic acid (PTA) and Polyethylene terephthalate (PET) in
/. It can be noted that the pricing history of VAM does not fluctuate. VAM price predominantly
remains constant, as further observation highlights the stable market price of just above 50 throughout
/. In comparison, the market price for other acetic acid commodities tend to be more fluctuating
as observed by PTA, in which case a price spike is highlighted in November and an estimated 10%
price increase in .
- 70. 70
Figure [6.1]: Graph showing the market pricing of the largest acetic acid products (Hicks, ).
Correspondingly, ester production also utilises acetic acid to develop acetate esters, commonly used as
solvents for inks, paints and coatings. Projected growth for cellulose acetate is encouraging as key drivers
such as growing cigarette consumption in Asia makes it a market for exploitation. According to (Strategyr,
), drivers such as surface coating are fast growing and its respective market growth increasing by up
to 4.1% CAGR. In addition, further reports project to exceed production of 951,000 tons by (Strategyr,
).
Acetic anhydride, another acetic acid based product, is correspondingly doing well in the global market. IHS
stated that “Global production of acetic anhydride has been growing at an average annual rate of 4% since
” (Ihs, ). Ihs also describes that acetic acid production in the United States, Western Europe and
Japan declined at average annual rates of 3%, 2% and 4% respectively (Ihs, ). Solvent glacial acetic
acid is also due to witness major growth, as of right now the Asia-Pacific region is the biggest market of
glacial acetic acid due to extensive growth in the automotive industry, especially China.
Each year, millions of tons of acetic acid is produced and exported globally. Numerous literatures have
portrayed a market analysis of acetic acid, thus allowing to support the economic viability of acetic acid
production. The key drivers for its demand are mentioned above, as well as projection of acetic acid market
growth where major players such as British Petroleum PLC (BP) (UK), BP PETRONAS Acetyls Sdn Bhd
(Malaysia), Celanese Corporation (USA), China Petroleum & Chemical Corporation (Sinopec Corp.)
(China), Daicel Chemical Industries Limited (Japan), Kyodo Sakusan Co. Ltd. (Japan), DuPont (USA),
Eastman Chemical Company (USA), Jilin Chemical Industrial Company Limited (China), Kuraray Co., Ltd.
(Japan), LyondellBasell Industries (The Netherlands), Millennium Chemicals Inc. (USA), Showa Denko K K
(Japan), Sterling Chemicals Inc (USA) are facing tremendous benefits, thus it is possible to deduce that
development of an acetic acid plant in this current market is viable and lucrative.
6.2 Costing
The basis for costing is to give an indication of process feasibility. Various costs are to be considered in
order to provide a full financial evaluation of this design project. The following costs will be accounted for
this study, being, feedstock costs, ISBL costs, OSBL costs, engineering costs, capital costs, working
capital, plant component costs and servicing costs. In addition, this costing section will provide an indication
of the fixed capital investment required for the project. Fixed capital investment considers the inside battery
- 71. 71
limits (ISBL) investment which portrays the cost of the plant and OSBL costs affiliated with construction,
installation, commissioning and ground preparation.
6.2.1 Feedstock price estimation
The reaction for the Monsanto process follows:
????????4 ???? + ???????? → ????2 ????4 ????2
Where, molecular weights are:
CH4O = 32 kg/mol
CO = 28 kg/mol
C2H4O2 = 60 kg/mol
The amount of methanol and carbon monoxide can then be derived through a stream analysis in Aspen.
On the assumption that conversion is ≥ 99%, a 400,000 tons of acetic acid requires:
???????? → 264,794 ???????????????? ???????????? ????????????????
???????????????? → 215,488 ???????????????? ???????????? ????????????????
???????????????????? → .55 ???????????????? ???????????? ????????????????
Methanol required (t)
Carbon Monoxide required (t)
Rhodium iodide catalyst required (g) 5
Methanol cost per ton ($)(Chemical Market Reporter, ) USD 330.00
Carbon Monoxide price per ton ($) (Soliman et al., ) USD 50.00
Water required (tons) (Salisbury and Hallinan, ) .55
Cost of water per ton (Quandl, ) 0.39
Rhodium price (per g) 22.
TOTAL METHANOL COST ($) USD 87,382,020.00
TOTAL CARBON MONOXIDE COST ($) USD 12,268,550.00
TOTAL RHODIUM CATALYST COST USD 112.70
TOTAL COST OF WATER USD .89
TOTAL COST OF FEED USD 99,654,314.89
Cost per ton of feed ($) USD 195.34
Table [6.1]: Cost of Feedstock.
- 72. 72
6.2.2 Capital Cost Estimation
6.2.2.1 ISBL
To calculate the total ISBL costs, the Factorial method is applied, this will provide a class 4 estimated with
an accuracy of 30%. Estimation are made based on the major items required for the process and other
costs estimated as factors of the equipment cost.
Applying Lang Factors (Lang, ):
???? = ???? (∑ ????????)
Where:
C = Total plant ISBL capital cost (including engineering costs)
ΣCe = Total delivered cost of all major equipment items
F = an installation factor (Lang Factor)
Thus, the cost of the major equipment are listed (corresponding cost include location and cost index for UK
basis):
Equipment Cost of
Equipment, £
Material
Factor
Ce (incl Material Factor, £
Storage Tank 333,000.00 1.3
Reactor 756,412.00 1.55
Flash Drum 66,225.95 1.55
Light End column 542,826.88 1.55
Drying Column 363,770.96 1.3
Heavy End Column 145,002.00 1.3
Scrubber 25,000.00 1.55
2,232,237.79 3,250,000
Table [6.2]: Collated costs of equipment.
- 73. 73
6.2.2.2 Installation Factor
Installation factors then need to be accounted of, Table 6.3 contains a list of installation factors (Hand,
):
Equipment Type Installation Factor
Compressors 2.5
Distillation columns 4
Fired Heaters 2
Heat exchangers 3.5
Instruments 4
Miscellaneous Equipment 2.5
Pressure vessels 4
Pumps 4
Table [6.3]: Table of installation factors.
Thus:
???? ∑ ????????= £82,500,000
6.2.2.3 OSBL
The off-side costs (OSBL) are accountable for infrastructure, which includes laboratories for technical staff,
offices, canteens and various mandatory staffing facilities. Considerations of water treatment systems,
security warehousing and loading facilities and maintenance costs are also included within the OSBL.
OSBL costs are estimated to be approximately 40% of the ISBL costs.
Therefore:
???????????????? ???????????????????? = £33,000,000 (???????? )
6.2.2.4 Engineering costs
Engineering costs are incurred by hiring contractors, costs acquired from the design, procurement of plant
equipment, supervising construction and service installations. In addition admin charges, insurance and
contractors profit.
The cost of engineering is 20% of the sum of ISBL and OSBL costs for a large acetic acid plant.
Therefore:
???????????????????????????????????????????? ???????????????????? = £23,100,000 (???????? )
6.2.2.5 Contingency costs
The contingency cost are provisions for unexpected events that may cause financial consequences on the
project such as labour disputes, price variations, FOREX Fluctuations, unforeseen weather conditions.
The contingency cost for this acetic acid plant is estimated at 15% due to the use of well-known technology.
Therefore:
???????????????????????????????????????????? ???????????????????? = £17,300,000
- 74. 74
6.2.2.6 Fixed Capital Investment
The capital cost for this project is the sum of ISBL, OSBL, Engineering costs and contingency costs.
Therefore:
???????????????????????????? ???????????????? = £156,000,000 (???????? )
6.2.3 Working Capital
This accounts for operating expenses from the commencing of plant start-up and operations. For this
project the working capital is 20% as product inventory is fairly large.
Therefore:
???????????????????????????? ???????????????????????????? = £23,100,000
6.2.4 Total Investment
The investment is total expense. It corresponds to the sum of fixed capital investment and working capital,
Therefore:
???????????????????? ???????????????????????????????????????? = £179,000,000 (???????? )
6.2.5 Operating expenditure
OPEX for this process is assumed to be 40% of the FCI.
Therefore:
???????????????? = £62,000,000
6.2.6 Revenue
The annual revenue generated from the sale of acetic, Table: 6.4 illustrates the projected annual sales:
TOTAL COST OF FEED (£) GBP 68,800,000
Selling price of acetic acid per lb ($) USD 0.38
Selling price of acetic acid per ton ($) USD 760.00
Total sale (revenue) ($) USD 304,000,000.00
Total Sale (revenue) (£)
GBP 227,000,000 (Adapted to a temporal factor (1.06) and a location factor
(1.02 for the UK)
Table [6.4]: Table showing annual sales of acetic acid.
6.2.7 Gross Profit
The gross profit margin is given by:
???????????????????? ???????????????????????? = ???????????????????????????? − ???????????????? ???????? ???????????????? − ????????????????
= £97,000,000
Therefore:
???????????????????? ???????????????????????? = 69.81%
The margin percentage gives a good indication of how profitable the process is going to be,
correspondingly a percentage of 69.81% is very economically feasible for an acetic acid plant.
- 75. 75
6.3 Project Financing
The financing of this industrial project is based upon its financial structure, exploring debt and equity will
give an indication on the cash flow generated in order to finance the project. The project has a life span of
20 years, therefore to evaluate the annual present value of the project on a yearly basis, Net Present Value
is calculated.
The two sources of finance that are being considered is a bank loan and private investment.
The equation used for this is:
Discounting Factor =
1
(1 + ????) ????
Where:
i = financial interest rate
n = current year of project
6.3.1 Financing Bank Loan
On the assumption that the Bank of England theoretically negotiate a 7.5% interest rate– which is
reasonably near to the actual current values – the following table is produced:
Table [6.5]: Table showing the NPV of the money over a twenty-year time period on the assumption that the
discount rate is 7.5%.
Year Cash flow (£)
Discount
Factor
(1/1.075)^n
Discounted cash flow (£)
0 -£179,107,337 1 -£179,107,337.40
1 £96,606,369.54 0. £89,866,390.27
2 £96,606,369.54 0. £83,596,642.11
3 £96,606,369.54 0. £77,764,318.25
4 £96,606,369.54 0. £72,338,900.69
5 £96,606,369.54 0. £67,292,000.65
6 £96,606,369.54 0. £62,597,209.90
7 £96,606,369.54 0. £58,229,962.70
8 £96,606,369.54 0. £54,167,407.16
9 £96,606,369.54 0. £50,388,285.73
10 £96,606,369.54 0. £46,872,823.94
11 £96,606,369.54 0. £43,602,626.92
12 £96,606,369.54 0. £40,560,583.18
13 £96,606,369.54 0. £37,730,775.05
14 £96,606,369.54 0. £35,098,395.40
15 £96,606,369.54 0. £32,649,670.14
16 £96,606,369.54 0. £30,371,786.17
17 £96,606,369.54 0. £28,252,824.35
18 £96,606,369.54 0. £26,281,697.07
19 £96,606,369.54 0. £24,448,090.30
20 £96,606,369.54 0. £22,742,409.58
Total NPV £805,745,462.16
- 76. 76
The table above illustrates the credit flow in to the company over the twenty year period taking in to
consideration the 7.5% interest rate from the bank of England. The NPV of the project of £806,000,000.00
indicates that on the basis that the project financing comes from a bank loan then project will be
economically feasible. This value will now be compared to the one that could potentially be given by equity
investors, assuming this time a 25% discount rate (=i, realistic for a well-established technology).
6.3.2 Financing Investments
On the assumption that the private investment has a 25% interest rate the following table is produced:
Year Cash flow (£)
Discount Factor
(1/1.25)^n
Discounted cash flow (£)
0 -£179,107,337 1 -£179,107,337.40
1 96,606,369.54 0.8 £77,285,095.64
2 96,606,369.54 0.64 £61,828,076.51
3 96,606,369.54 0.512 £49,462,461.21
4 96,606,369.54 0. £39,569,968.97
5 96,606,369.54 0. £31,655,975.17
6 96,606,369.54 0. £25,324,780.14
7 96,606,369.54 0. £20,259,824.11
8 96,606,369.54 0. £16,207,859.29
9 96,606,369.54 0. £12,966,287.43
10 96,606,369.54 0. £10,373,029.94
11 96,606,369.54 0. £8,298,423.96
12 96,606,369.54 0. £6,638,739.16
13 96,606,369.54 0. £5,310,991.33
14 96,606,369.54 0. £4,248,793.07
15 96,606,369.54 0. £3,399,034.45
16 96,606,369.54 0. £2,719,227.56
17 96,606,369.54 0. £2,175,382.05
18 96,606,369.54 0. £1,740,305.64
19 96,606,369.54 0. £1,392,244.51
20 96,606,369.54 0. £1,113,795.61
Total NPV £202,862,958.34
Table [6.6]: Table showing the NPV of the money over a twenty-year time period on the assumption that the
discount rate is 25%.
The NPV on a private investment similarly indicates that the project is economically feasible on the basis of
a 25% interest rate. The total is £203,000,000.00 still signifies lucrativeness of the project. Comparing the
cumulative NPV of both sources, equity is very profitable assuming that the plant would reach optimal
production after 12 months. However, the net present value is exponentially lower when private equity is
required, therefore it is possible to conclude that securing a bank debt type of investment is a clearly more
suitable choice.
- 77. 77
6.3.3 Net Profit
Gross Profit of the project is calculated by subtracting cost of feed from. In order to finally formulate the net
profit, tax must be deducted from the gross value. In order to adjust the taxable value as accurately as
possible, a depreciation allowance equation is used:
Depreciation Allowance =
FCI − SV
N
Where:
FCI = fixed capital investment
SV = scrap value
N = number of years of operation
An annual scrap value of 10% of ISBL investment will be assumed; the depreciation allowance obtained is
therefore £7,400,000. This figure is used to determine the final net profit, with a corporation tax value taken
as 21%.
Year Gross Profit £) Depreciation allowance
Taxable earnings
(£)
Payable tax (£) Net profit
0 -£179,107,337 7,387,146 NA NA -£179,107,337
1 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
2 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
3 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
4 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
5 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
6 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
7 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
8 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
9 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
10 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
11 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
12 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
13 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
14 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
15 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
16 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
17 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
18 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
19 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
20 £96,606,369.54 7,387,146 £89,219,224 £18,736,036.96 £77,870,332.59
TOTAL NET
PROFIT
£1,378,299,314.36
Table [6.7]: Table showing the net profit over a twenty-year time period.
- 78. 78
The total net profit is approximately £1,381,000,000.00 over the 20 year period, this provides a clear
representation of the profitability of this project through the Monsanto process.
6.3.4 Cumulative Cash Position
An alternative way to outline the potential profit of the plant is to demonstrate the change in cash flow
throughout the years.
Assumptions for the application of the cumulative cash position of the project are:
• For the first 3 years of operation, the plant is not going to reach optimum production. The revenue
will be considered to be 25%, 50% and 75% of the maximum for years 1,2 and 3 respectively.
• Also we assume that the plant will take 2 years to build, the capital investment will be spread out
30%, 50%, 20% in the 3 years of construction and operation respectively.
• The cash flow is given by the deduction of the FCI and OPEX form the revenue.
• ADA is the annual depreciation allowance, which has a different value each year.
Year Cash Flow Cash cumulative ADA
-2 -46,799,013.96 -46,799,013.96 0.00
-1 -77,998,356.61 -124,797,370.57 0.00
0 -162,359,505.20 -287,156,875.77 0.00
1 -74,218,529.53 -361,375,405.30 147,742,918.87
2 -17,276,896.51 -378,652,301.81 73,871,459.43
3 39,664,736.52 -338,987,565.29 49,247,639.62
4 96,606,369.54 -242,381,195.75 36,935,729.72
5 96,606,369.54 -145,774,826.20 29,548,583.77
6 96,606,369.54 -49,168,456.66 24,623,819.81
7 96,606,369.54 47,437,912.89 21,106,131.27
8 96,606,369.54 144,044,282.43 18,467,864.86
9 96,606,369.54 240,650,651.98 16,415,879.87
10 96,606,369.54 337,257,021.52 22,776,653.21
11 96,606,369.54 433,863,391.06 13,431,174.44
12 96,606,369.54 530,469,760.61 12,311,909.91
13 96,606,369.54 627,076,130.15 11,364,839.91
14 96,606,369.54 723,682,499.70 10,553,065.63
15 96,606,369.54 820,288,869.24 9,849,527.92
16 96,606,369.54 916,895,238.78 9,749,794.58
17 96,606,369.54 1,013,501,608.33 8,690,759.93
- 79. 79
18 96,606,369.54 1,110,107,977.87 8,207,939.94
19 96,606,369.54 1,206,714,347.42 7,775,943.10
20 96,606,369.54 1,303,320,716.96 7,387,145.94
Table [6.8]: Table showing the net cumulative cash flow over a twenty-year time period.
Figure [6.2]: A graph showing the net cumulative cash flow over a twenty-year time period.
A graphical comparison of the Cumulative Cash is plotted against the time for the total life span of the
project.
???????????? ???????????????? ???????????????? =
???????????????????? ????????????????????????????????????????
???????????????????????????? ???????????????????????? ????????????ℎ ????????????????
= 2.75 ????????????????????
Where:
Total investment = £179,000,000
Average annual cash flow = £65,000,000
6.3.5 Return of Investment
Another important parameter to be considered when evaluating the project is the Return of Investment
(ROI).Therefore:
-£600,000,000.00
-£400,000,000.00
-£200,000,000.00
£0.00
£200,000,000.00
£400,000,000.00
£600,000,000.00
£800,000,000.00
£1,000,000,000.00
£1,200,000,000.00
£1,400,000,000.00
-5 0 5 10 15 20 25
CashFlow
Time in years
Graph of cumulative net cash flow at the end of the
project life
Cash cumulative
ADA
- 80. 80
ROI =
???????????? ???????????????????????? ????????????????????????
total investment
× 100
= 53.9%
Where:
Net annual profit = £97,000,000
Total investment = £179,000,000
7. Process Safety
Safety is a moral, and legal obligation that any chemical plant design should include. It is empirical that the
correct levels of safety are undertaken in order to protect the health and safety of employees, any
surrounding communities that might get affected by events that occur on site, the surrounding environment,
and the process itself. The risks that may arise are a combination of undesired events due to multiple
factors (e.g. human error, loss of containment personal injuries), which could consequently affect the
integrity of the process and release hazardous components.
In this case, safety risks refer to high intensity exposure (i.e. to toxic materials) over short periods of time.
While environmental risks refer to low intensity exposure over long periods of time. Finally, any health
hazards associated with the process are strongly related to any type of exposure to hazardous substances
with short, or long-lasting effects. The above mentioned risks are strongly related to loss of containment.
For the production of acetic acid loss prevention safety layers, and risk management ensure adequate
response to any damage (e.g. spillage, faulty valve) caused, while minimizing response time, and ensuring
an economical solution to any technical faults.
The production of acetic acid through the Monsanto process is a highly efficient in terms of component
selectivity. However it is highly hazardous process route due to factors such as:
• High temperatures • Toxicity of components
• High pressure • Single exposure toxicity
• Corrosiveness of components • Flammability
• Oxidising potential • Fire and Explosive hazards
• Miscibility with air/water
Table [7.1]: Process route associated risks.
Therefore, an adequate process design needs to be compiled in order to reduce any risk associated, ideally
eliminating it overall.
7.1 Safety legislations
- 81. 81
It is mandatory that any new chemical plant design complies with the Control of Major Accident Hazards
(COMAH) Regulations . The purpose of the COMAH regulations is to prevent any major accidents,
and limit the consequences to people and the surrounding environment in the event of any accidents. The
COMAH regulations are implemented in Great Britain, and implements the majority of the European
Union Seveso III Directive .
In order to determine whether the COMAH Regulations are applicable to the new acetic acid chemical
plant a basic assessment was completed (COMAH Regulations, ). This classified the chemical plant at
Tier 1 with an associated HT 1 (i.e. Hazard type). This means that Upper-tier duties apply (i.e. lower tier
duties including regulations 8-13, 16, and 18).
Regulations that have to be considered and implemented in the United Kingdom are:
• Health and Safety at Work Act ;
• Management of Health and Safety at Work Regulations ;
• Environmental Permitting Regulations (England and Wales);
• Civil Contingencies Act ;
• Environmental risk tolerability . Safety provisions;
• Preparing and planning for emergencies: the National Resilience Capabilities Programme ;
• Chemicals (Hazard Information and Packaging for Supply) Regulations ;
Regulations that belong to the European Union (EU), but have to be considered:
• Council Directive
7.2 Hazard Identification
Hazard identification refers to locating potential triggers such as the materials, the process, and plant
lineament that will lead to the occurrence of an undesirable event.
7.2.1. Material Hazard
This section will present the chemical hazards associated with the process components individually
according to Regulation (EC) No /. Which will later be quantified in terms of toxicity,
corrosiveness, and flammability in terms of individual equipment.
- 82. 82
Acetic acid (C ≥ 90%)
Skin corrosion Category 1A
Flammability Category 3
Upper explosion limit 19.9 % (by volume)
Lower explosion limit 4% (by volume
Hazard Identification by sign
Figure [7.1]: Acetic acid hazard sheet.
Carbon Monoxide (Gas under pressure)
Flammability (gas) Category 1
Acute toxicity (inhalation) Category 3
Reproductive toxicity Category 1A
Repeated exposure toxicity Category 1
Upper explosion limit 74.2 % (V)
Lower explosion limit 12.5% (V)
Figure [7.2]: Carbon Monoxide hazard sheet.
Methanol
Flammability (liquid) Category 2
Acute toxicity (oral) Category 3
Acute toxicity (inhalation)
Acute toxicity (dermal)
Category 3
Category 3
Specific target organ toxicity (single exposure) Category 1
Upper explosion limit 74% (V)
Lower explosion limit 12.5% (V)
Figure [7.3]: Methanol hazard sheet.
- 83. 83
Hydrogen
Figure [7.4]: Hydrogen hazard sheet.
Carbon Dioxide
Gases under pressure Liquefied gas
Figure [7.5]: Carbon Dioxide hazard sheet.
Propionic acid
Skin corrosion Category 1B
Flammability (liquid) Category 3
Upper explosion limit 12.1% (V)
Lower explosion limit 2.9% (V)
Hazard Identification by sign
Figure [7.6]: Propionic acid hazard sheet.
Flammability (gas) Category 1
Gases under pressure Compressed gas
Upper explosion limit 74.2 % (V)
Lower explosion limit 4% (V)
- 84. 84
Methyl Iodide
Skin irritant Category 2
Carcinogenicity Category 2
Acute toxicity (oral) Category 3
Acute toxicity (inhalation) Category 3
Acute toxicity (dermal) Category 4
Specific target organ toxicity (single exposure) Category 3
Upper explosion limit 66% (V)
Lower explosion limit 8.5% (V)
Figure [7.7]: Methyl Iodide hazard sheet.
Rhodium (powder)
Flammability (solid) Category 1
Other hazards: ingestion, or inhalation of Rhodium
particles.
Figure [7.8]: Rhodium hazard sheet.
Methyl acetate
Flammability (liquid) Category 3
Eye irritant Category 3
Hazard Identification by sign
Figure [7.9]: Methyl acetate hazard sheet.
7.2.2 Material Toxicity
The toxicity of a component is based on the frequency of exposure and the inherent toxicity. The three toxic
components of this system are: Carbon monoxide, Methanol, Methyl iodide. They have all been identified
as a safety hazard for workers. Carbon monoxide affects internal organs after prolonged or repeated
exposure. Methanol is skin and eye irritant, but over-exposure can lead to death. In case of exposure it is
- 85. 85
advised to thoroughly wash the exposed area with water for a period of minimum 15 minutes, remove any
contaminated clothing, and seek medical attention immediately. In case of severe inhalation, the person
has to be moved to a safe area as soon as possible and be administered oxygen for breathing difficulties.
In case of extreme situations, it is advised to perform mouth-to-mouth resuscitation, while keeping aware
this could cause the toxic fumes to be inhaled. For methyl iodide, the emergency answer is the same as for
methanol.
Materials with carcinogenic proprieties such as methyl iodide, and methanol are hazardous even is small
concentrations over longer exposure times. They can cause organ damage through prolonged and
repeated exposure. In order to limit the occurrence of any side effects due to being exposed to these
materials, it is advised to enforce safe exposure time, and adequate PPE in case of longer exposure is
required. This can be quantified with regards to the minimum concentration of a hazardous material that
would cause permanent health damage as a result of prolonged exposure (Table 8.2.) Also, adequate
training have to be given to all the plant staff regarding different classes of toxicity and their effects on the
human body.
Material PPM Mg/m^3
Carbon Monoxide 50 55
Methanol 200 260
Carbon Dioxide
Acetic acid 10 25
Methyl Iodide 5 28
Table [7.2]: The Permissible Exposure Limit (PEL).
7.2.3 Flammability
The process components that are flammable are: CO, Hydrogen, Methanol, Acetic acid, Propionic acid,
Methyl acetate, and Rhodium. The values regarding flammability can be seen in section 8.2.1. Material
Hazards.
It necessary to take all safety precautions regarding the handling, and management of these components in
case of loss of containment. Methanol and carbon monoxide are materials with high flammability.
Considering that these components are subjected to high temperature and high pressure in the reactor
phase in high quantities, it is advised that no source of ignition, open flames, or electrical devices (e.g.
telephones) are allowed on site in order to remove the likelihood of such scenarios. However, in the case of
a ruptured vessel it is possible for the gaseous mixture to self-ignite from the static spark created. Safety
precautions must be taken across all equipment containing any flammable liquids. These include adequate
process control systems, tripping systems, as well as heat and fire detection alarms. It is advised that in
case of open fire an alcohol-resistant foam is used. Water sprays are also recommended as a safety
- 86. 86
precaution as some of the components reacting (e.g. methanol, acetic acid) are miscible with water. An
important component for the safety system is the heat exchanger, since the capacity of the reactor does not
allow efficient cooling using a water deluge system.
7.2.4 Corrosiveness
Since material in the system have corrosive properties, it is necessary that all safety design considerations
are taken. This includes an adequate choice of construction material, adequate choice of process
equipment, as well as adequate maintenance procedures. The methyl iodide present in the system is highly
corrosive, and therefore requires special considerations for use, and handling (HSE Onshore Pipeline
Integrity Management, ).It therefore requires integrity management, and regular maintenance of
process equipment in order to assess corrosion.
7.3 Operating conditions hazard
7.3.1 Pressure relief strategy
One of the process variables that can lead to a domino effect along the whole system is the pressure. In
the scenario of a vessel, or any equipment located in its proximity failing due to overpressure. The main
pressure relief strategy is by installing a venting route that prevents any pressure accumulation. It is
recommended that any emergency pressure relief system in place be used last, after all other systems
failed, and that it is self-actuated (i.e. independent of any other components, or systems).
The pressure relief mechanism set in place will function depending on how the volume fluctuates inside the
vessel. When the volume materials going in increases, the pressure will subsequently increase. Possible
causes for an increase in volume are:
• Excess material flow;
• Gas generation from the chemical reaction;
• Thermal expansion of materials;
• Vaporization of materials inside the vessel due to high temperature input;
If any of the above variables is not between safe operating conditions, the pressure increase can lead to
cracks in the vessel, loss of containment. In extreme scenarios where the pressure increase surpasses the
maximum pressure capacity of the vessel, the vessel can be damaged beyond repair, or can lead to an
explosion. In case of under-pressure that can be caused by removal of material or heat, a vacuum stage
can develop and cause the vessel to collapse. In order to maximise the efficiency of the pressure relief
system it has to be designed according to worst case scenario reaction conditions. This includes any
potential changes in pressure, temperature, material, and composition. This will ensure that the pressure
relief system is working between adequate parameters, and that it is sized according to the maximum
output of the vessel.
Safety precautions in case of high pressure include constant monitoring of the pressure levels, a pressure
detector attached to an alarm to notify the plant control room of any unusual rise in pressure, vessel seals,
- 87. 87
and regular maintenance check. In this case, the pressure detector will have to be programmed to the
reaction conditions in order to account for regular changes. A relevant response plan has to be created in
order to efficiently manage dangerous situations, as well as to safely evacuate all staff from the plant.
7.3.2 High pressure response measures
The alarm set in place for this scenario represents one of the crucial components of the pressure vessel.
This measure will allow the control team to adequately respond to the situation, and it will also notify all
employees to evacuate the plant, or go to the nearest refuge point. It is recommended that the evacuation
plan put in place accounts for the maximum number of people present on site at a time, in order to provide:
• Sufficient safety equipment for staff and any visitors;
• Adequate number of escape routes;
• Sufficient fire exits;
• A quick and safe evacuation;
7.3.3 Fire prevention strategy
In order to effectively prevent fires on the plant it is necessary that any potential ignition sources are
accounted for, and safely secured from producing flammable medium. A standard risk assessment is
required for determining all potential sources of ignition, which will then be extended to the apparatus, as
well as all mechanical equipment ignition risk assessment (MEIRA) and electrical equipment (Etchells,
).
A prevention method required on all acetic acid plants is having machinery designed and constructed in a
manner that avoids the creation of any potential ignition sources and overheating of the equipment due to
the components used by set piece of equipment. Any electrical equipment present has to be used (e.g.
installed, maintained, repaired) only by qualified electrical personal. The areas of concern in this situation
are:
• Hot surfaces
• Any free flames, including hot work or repairs
• Friction sparks
• Electrical equipment
• Static electricity
• Lightning
• Shockwaves from exothermic reactions
It is crucial that the fire and safety strategy are completed by a competent authority.
The equipment chosen for the chemical plant needs to be in conformity with the safety policy put in place
(HSE Plant Modification, ). This refers to the manufacturer of the vessels, who has to take into account
that:
- 88. 88
• Adequate insulation that prevents the combustion of a potentially explosive medium;
• Isolate equipment for potential explosions to ensure the safety of its surroundings;
• Any electrical equipment that is installed is adequately adjusted to the plant component;
Some other precautions include the presence of supplementary equipment which will act as a safety control
equipment in the case of faulty primary equipment (Etchells, ). The employer is responsible for
conducting an adequate risk assessment for explosive atmospheres. Some of the variables that need to be
checked are:
• The possibility of explosive medium formation, and their persistence;
• The likelihood if ignition sources being created on site;
• The equipment, the materials present and their characteristics;
• The magnitude of possible hazardous scenarios;
• Explosion risk assessment;
• Classification into zones of hazardous areas;
• All equipment is operated and maintained according to safety regulations;
• The equipment is safe to use;
7.3.4 Fire and gas detection
Since all equipment will operate at constant temperature, the control room will be immediately notified in
case of any fires or explosions through fire, heat, and smoke detectors as part of the emergency response
plan (Etchells, ). The smoke detector is required in this care, since a loss of containment would
release toxic materials that could ignite from the heat source.
The heat detector will be calibrated to trigger the alarm when an unusual amount of heat is present in the
environment. All the equipment used on plant for identifying leakages should be regularly checked,
maintained, and calibrated in order to adequately assess the integrity of the vessels (Dangerous
maintenance, ). An example would be the use of a barometer for pressure measurement inside the
reactor (with a separate alarm system), as any sudden pressure drop could cause the creation of a
vacuum, and therefore a leakage of very flammable materials into the surrounding environment.
7.3.5 Noise
It is recommended to take account for the noise resulted from equipment, as well as the reactor for
employees, any surrounding communities, other industrial sites located in the proximity of the chemical
plant, and the surrounding (HSE Noise at work, ). This health and safety hazard in this situation is
being exposed to excessive noise across long periods of time, which can lead to permanent damage to
hearing. Since the noise levels are not constant across the reactor, and surrounding equipment it is
recommended that industrial sound meters be installed across the plant. In order to quantify the damage to
the ear and select appropriate protection equipment, a filter network resembling the same response as the
human can be installed adjacent to the noise meter (Controlling noise at work, ).
- 89. 89
7.3.6 Loss of containment
Loss of containment can be caused by multiple factors, and the gravity of the situation is mainly determined
by what materials are released into the atmosphere (HSE Emergency response/spill control, ). Some
of the possible originators that lead to loss of containment are:
• Poor maintenance procedures that are not adequately applied. Some of them are related to
improper purging, drainage, isolation, and seal checks that result in the release of toxic, and/or
flammable gasses. In this situation it is recommended that the area underneath the process vessels
can contain minor, as well as major spillages so that the spillage does not spread;
• Pressure relief systems;
• Unusual operating conditions that can cause a leakage in the vessel;
7.4 Emergency Response plans
7.4.1 Fire
Emergency response plans for any fire need to account for the different classes of fire hazard. It is
dependent on the type of material that caused the fire, as well as the magnitude of the fire. An appropriate
response to possible fire hazards and the appropriate response can be seen in Table 7.10.
Ignition fuel/medium Flammability category Response measure
Carbon Monoxide 1 • Dry chemical
Hydrogen Gas 1 • Dry chemical
Methanol 2
• Foam
• Carbon Dioxide
• Dry chemical
Acetic acid 3 • Foam
• Carbon Dioxide
• Dry chemical
Propionic acid 3 • Foam
• Carbon Dioxide
• Dry chemical
Rhodium catalyst 1 • Dry materials that can inhibit
the metal fire (e.g. dry sand)
Table [7.10]: Response measure to fire hazards (HSE Emergency response/spill control, )
- 90. 90
Type of fire inhibitor Effect on fire
Foam • To remove heat and oxygen from fire
Dry chemical • to remove the chemical reaction and prevent oxidation
Carbon dioxide • To remove oxygen from fire
Table [7.11]: Description of fire inhibitor actions.
It is essential that a fire source is put out as fast as possible to prevent any further complications. This
requires that employees have an adequate response this scenario. In order to improve the speed of
reaction of employees it is crucial that the plant undergoes practice drills as a response to the fire alarm.
Safety protocols dictate that when a fire alarm goes off, all the employees have to head towards the
nearest fire escape. All safety areas, and safe evacuation routes have to be identified and adequately
marked. The employer has to make sure that all the employees have undergone the fire safety drill, and
know how to adequately react. After the fire assembly point is reached, a roll will be taken to check if
everybody left the hazardous area. The sprinkler system put in place will limit the spread of the fire until the
local fire brigade arrive; it is necessary that the local fire brigade is notified of the current situation, and that
they undergo training drills prior to any accidents so that they are adequately prepared for all potential risks
present on site.
7.4.2 Explosion
In the highly unlikely case of an explosion, the system should be immediately shut down and evacuated. If
the situation allows it, all streams should be diverted to the flare in order to minimise the release of any
toxic, or flammable compounds in the atmosphere as secondary explosions are possible. Any explosions
happening on site can have catastrophic consequences for the plant, people, and the surrounding
environment (HSE Fire and explosion, ).
In the event of an explosion for this particular chemical plant, there should be set in place and emergency
plan that involves the local fire brigade, and any businesses and people living in the radius of the plant. In
such cases, local authorities have to be notified of the accident in order to minimise any exposure of
citizens to the toxic fumes released in the atmosphere; if necessary local households and businesses have
to be evacuated due to the hazardous chemicals involved. A specialized team will later analyse the
aftermath, and ensure it is safe.
7.4.3 Overpressure
- 91. 91
It is necessary that in the unlikely case of a vessel being over pressured, all employees evacuate the plant
to an assembly point located at a safe distance from the hazardous area. Local authorities will then
intervene, and ensure the safety of the plant.
7.4.4 Toxic release
Alarms will be located across the plant to detect any toxic releases in the atmosphere. The area where the
toxic material was released has to be evacuated immediately in order to avoid any unlikely scenarios, or
injuries. The immediate response put in place for this case should:
• Ensure adequate management of the toxic release and limit any further release;
• Ensure gas masks, or breathing apparatus is accessible to employees;
• Evacuate all the staff to a predetermined assembly point safe from the toxic release;
• Contact a specialised team (if available) to help in the management of toxic releases;
7.4.5 Flooding
In the unlikely case of a flooding due to heavy rain, or rise in river levels a safety strategy needs to be put in
place in order to prevent, or minimise any damage to the plant. In the event of a severe weather warning, a
trained, competent safety officer needs to be made available on-call in order to ensure that the plant is
adequately prepared. His role will be to ensure a temporary flood defence is set up around the plant in the
shortest time.
In the case of a flash flood, all equipment should be deactivated unless a safety trip is already set in place;
all the personal has to be evacuated. Competent authorities should be called to ensure safety of the plant
(HSE Emergency response/spill control, ).
7.4.6 Earthquakes
In the event of an earthquake, all employees need to be trained how to react effectively to ensure personal
safety. If employees are indoor, they are advised to not use the elevator, and stay inside the building; stand
against an interior wall, or take refuge under a table. Employees must stay as far as possible from any
heavy machinery, glass, or exterior walls (HSE Emergency response/spill control, ).
There is a high possibility of major leakages of toxic/ or flammable materials occurring after an earthquake.
In all cases, it is necessary to turn off major equipment to prevent any complications. It is required that a
skilled team check all the equipment thoroughly, and ensure any faulty equipment is fixed/removed on spot
if the circumstances allow it (HSE Maintenance procedures, ).
7.4.7 Human factor
- 92. 92
Adequate training needs to be imposed to all employees by the employer as a safety layer, to ensure there
is no human error caused by insufficient training, poor documentation, and inadequate supervision. There
is always the chance of process operators, or other employees making mistakes. However, the magnitude
of events caused by insufficient training is much bigger than events caused by simple human errors. This is
one of the most important aspects of process safety on a chemical plant, as human error can have
consequences ranging from personal injury/death (i.e. inadequate reaction to hazardous situations) to
major equipment failures (HSE Human errors, ).
7.4.8 Personal Protection equipment
It is mandatory that after a HAZOP study has been completed, adequate PPE is chosen for the chemical
plant. The PPE and equipment need to be adapted so that safe work on the chemical site is possible, as
well as emergency protection equipment. It is the duty of the employer to supply the equipment, and to
adequately train staff. However it is the employees responsibility to use it, and know how to use it for their,
and the plants’ safety.
7.5 HAZOP
The purpose of this HAZOP study is to analyse the hazardous potential of equipment on and off-site. The
HAZOP is conducted to ensure that any hazardous situations are identified, and that the right safeguards
are in place to prevent any unwanted scenarios from occurring; this step ensures that the plant is operable.
Developing a HAZOP is important for effective plant safety considerations. The current HAZOP had been
conducted on only one node, and serves as an indication of the methodology. It is a legal requirements that
a full HAZOP is conducted before a chemical plant is built in order to adequately quantify all the hazards
and risk present on site. It is recommended that HAZOP studies are carried across the lifetime of the plant,
for each individual zone. This helps take account of any process deviations, and account for them in the
current design.
Usually a HAZOP study can be conducted by itself, as it is a qualitative technique. However, it is
recommended that the below assessment techniques are used in conjunction with the HAZOP:
• H.A.Z.I.D. – Hazard identification system
• P.H.A. – Preliminary Hazard Analysis
• L.O.P.A. – Layers of protection Analysis
• S.M.S. – Safety Management System
• E.R.P. – Emergency Response Planning
It is recommended that a Fault Tree Analysis is conducted on site with the HAZOP, to maximise the
number of safety considerations taken in case of a hazardous scenario. It is important that the FTA is
conducted, as it can detect system failures before they take place. It is a reliable quantitative assessment
as it takes account of maintenance procedures such as rate of failure, failure probability, or repair rate
(HSE Plant Modification, ).
- 93. 93
7.5.1 Scope of work
In the HAZOP training, the whole team completed an assessment of the node between the reactor and the
flash tank. This sections was chosen as it has the highest potential to cause hazards to the process due to
the high temperature and pressure values. Even though the P&ID presents all the nodes, this design
project only accounted for the hazards and its effects on the node between the reactor and the flash tank.
The reason to why the HAZOP is done in this stage of the design project, is to ensure that the design is
safe, and that any hazardous situations are accounted for by adequate process control. It generates
recommendations for plant operability, operating instructions, and can offer a better insight into how certain
design alterations can minimize the costs before the construction of the plant.
7.5.2 Term of Reference
Prior to conducting the HAZOP, the design team reviewed all the completed P&IDs; the critical parameters
reviewed were characteristic to the node in question. The study includes all design parameters
characteristic to the node, including equipment, and pipework specifications.
7.5.3 Team Membership
Everybody from the design team was present during the HAZOP study, and included:
Cristian Baleca Chairman
Sinthujan Pushpakaran Scribe
Hisham Albaroudi Team member
Karen Atayi Team member
Enoch Osae Team member
Alexander Taylor Team member
Parameter Guide words
Flow No
More
Less
Reverse
Temperature More
Less
Pressure More
Less
Viscosity More
Less
Corrosion Yes
- 94. 94
Table [7.12] Parameters and guide words used in HAZOP.
The study was conducted by analysing how every parameter could be affected under the conditions
described by the guide words for the specified node. The whole team contributed to the development of the
HAZOP in order to seek solutions for the any hazards associated, and what safety barriers should be put in
place in order to achieve a safe and efficient process route.
The design team fulfilled the purpose of the operability study, and thus gained a better insight on what
actions need to be taken across the whole plant for each individual design. It needs to be noted that the
team debated any recommendations resulted from the study in order to better differentiate self-evident
information that serves as obligatory guidance, and forwarded the other outcomes to be considered for
individual designs. The HAZOP study generated relevant design considerations, and is an important part of
any safety report for any chemical plant.
7.5.4 Safety conclusions
After a careful consideration of all the hazards present on the plant, the present report shows efficient
ways of maintaining a safe environment for the production of acetic acid. The present design, even though
safe presents a hazardous potential that can only be diminished by an adequate safety management
system that has to be put in place for every process design individually. The above section presented all
the safeguards put in place for accident prevention, as well as several indications on process and plant
safety that should be implemented. Considering the nature of the hazardous components (toxic, flammable,
carcinogenic, corrosive) and the process conditions, it is recommended that all safety considerations are
applied in order to improve the overall safety of the people on site.
As any other chemical plant, it is necessary that the people working on site comprehend the nature of the
hazardous process. It is an employer’s obligation to ensure that the site is safe to work, yet in the chemical
industry it is every bodies responsibility to ensure a safe working environment. Safety is an important
aspect of a design. Many regulations are put in place in order to minimize any potential accidents, but it is a
design engineers responsibility to ensure that all safety aspects of plant safety had been considered; a safe
environment is a collective responsibility, and must always be regarded as so when dealing with hazardous
large scale industrial applications.
Vibration More
- 95. 95
7.5.5 Marked up P&ID
Figure [7.10]: Marked up P&ID to show the nodes that were analysed during the HAZOP.
- 96. 96
7.5.6 HAZOP findings
Hazard and Operability Study:-
Node No. and Title Reactor to Flash Tank node
Node Design Intent Node 1 – Line between reactor and flash tank. Transfers liquid material into the flash tank for catalysis recovery and pressure reduction.
Meeting Dates.
Team Members. Alexander Taylor, Cristian Baleca, Enoch Osae, Hisham Albaroudi, Karen Atayi, Sinthujan Pushpakaran
P&ID Nos. P&ID 1
Major Equipment Nos. R101 and FT - 301
Plant Line Nos.
Materials of Construction Hastelloy - Piping Node start/end points Reactor / Flash Tank
Normal Process Contents. Acetic acid, methanol, methyl acetate, methyl iodide, water,
propionic acid, ethanol and traces of other organic compounds
Flowrate(s) .4 kmol/hr
Normal Process Temperature 160 oC Normal Process Pressure 30 Barg
Design Temperature 189 oC Design Pressure 30 Barg
- 97. 97
Line No. Parameter Guide Word Possible causes Consequences Safeguards Action
No. Recommendations
1 FLOW
FLOW
MORE
MORE
Greater fluid density
Control faults
Damage to valves
Overflow
Flow indicator and Pressure indicator
Flow Indicator and isolation valve
1
2
Not applicable
Not applicable
1 FLOW
FLOW
FLOW
NO
NO
NO
Blockage
Pipe failure
Incorrectly fitted equipment
Damage to Flash tank, no product produced
Loss of containment
Loss of containment, lockages, equipment
failure
Isolation valve, flow indicator
Emergency shutdown
Flow indicator
3
4
5
Flow indicator in proximity
of Flash Tank
Design consideration of
piping with more
corrosion allowance
Appropriate training of
personnel
1 FLOW
FLOW
LESS
LESS
Valve failure
Loss of integrity
Increase in pressure in the upstream valve
Isolation valve
Pressure indicator and flow indicator
Pressure indicator and flow indicator
6
7
Not applicable
Not applicable
- 98. 98
Line No. Parameter Guide Word Possible causes Consequences Safeguards Action
No. Recommendations
1 PRESSURE MORE Control valve failure Loss of integrity Back-up valve within isolation
system
8 High pressure alarm
linked to pressure
indicator
1 PRESSURE LOW Loss of integrity Reduced pressure upstream of leak Emergency shutdown 9 High pressure alarm
linked to pressure
indicator
Line No. Parameter Guide Word Possible causes Consequences Safeguards Action
No. Recommendations
1 TEMPERATURE
TEMPERATURE
HIGH
HIGH
Fire situation
Pressure reduction valve
failure
Damage to equipment
Explosion
High temperature upstream
Isolation valve, emergency
shutdown
Emergency services
Isolation valve
10
11
12
Not applicable
Emergency isolation
control valve
Temperature indicator
after valve
1 TEMPERATURE LOW
LOW
Faulty valve
Ambient condition
Loss of containment
Not applicable
Isolation valve
Isolation valve
13
14
Low temperature alarm
Low temperature alarm
- 99. 99
Line No. Parameter Guide Word Possible causes Consequences Safeguards Action
No.
Recommendations
1 VISCOSITY HIGH Pressure relief valve failure Affects flow Isolation valve 15 Low temperature alarm
1 VISCOSITY LOW Pressure relief valve failure Affects flow Isolation valve 16 Low temperature alarm
Line No. Parameter Guide Word Possible causes Consequences Safeguards Action
No.
Recommendations
1 CORROSION YES Use overtime Loss of integrity Corrosion allowance 17 Check pipeline, plant
layout around node,
design consideration
1 VIBRATION HIGH High velocity Failure None 18 Check pipeline, plant
layout around node,
design consideration
Table [7.13]: HAZOP table
- 100. 100
8. Environmental Protection
Process plants are customarily subject to the release of unwanted chemicals and this project is no different.
The client demands for the design of an efficient and economically viable project whilst taking into
consideration environmental protection. As a result, focus on environmental protection in this design project
is to ensure that only the minimal amount of hazardous wastes are produced, and where possible, all
emissions and waste is neutralised before disposal. Measures to ensure acceptable and minimal disposal
of wastes and emissions whilst maintaining energy requirements have been integrated throughout the
design process.
8.1 Process Selection
A general environmental consideration to be made on the chosen methanol carbonylation process is the
lower energy requirement in comparison to its predecessor as a result of its milder operating conditions.
The cobalt based process initially developed by BASF for the production of acetic acid in the late ’s
required operating conditions of 700 atm and 250 o
C to obtain commercially viable products (Cheng and
Kung, ). The selectivity of the raw materials, methanol and carbon monoxide, respectively being 99%
and 90% also pose another positive aspect due to minimal generation of by-products and waste. An
optimised version of the Monsanto process, CativaTM
, has been developed and scaled-up accordingly
through investigation of an alternative catalyst; this route has managed to successfully reduce water
requirement in order to stabilize the catalyst in the reaction, thus effectively reducing the number of by-
products formed and purification stages. Although, this route is highly efficient, the process has been
patented and unavailable to be implemented in this project, henceforth the Monsanto route has been
chosen as it represents an optimal compromise between environmental requirements and license
availability.
8.2 Plant Location – Environmental Considerations
The chosen location for the plant is on an existing chemical complex in the United Kingdom of Great Britain
and Northern Ireland on a land owned by the company, thus remediation and ground stabilization is not
required. The selected area is designed to host chemical industries hence no impacts will be applicable to
any areas of particular environmental sensitivity (SSSI) or the skyline. In addition, other environmental
issues such as odour, noise, vibration, radiation and traffic are also negligible for the purpose of this
environmental assessment.
- 101. 101
8.3 Noise
Noise is a type of pollution that is present on the chemical plant. As a result of its location, the plant will
have minimal impact in regards to noise compared to if it was situated nearby a residential area. Sources of
noise pollution include operations of large machinery (pumps, flash tank), on-site transporting of raw
materials and final product, use of vehicles on site.
In order to tackle issues faced by noise pollution, appropriate noise reduction methods are implemented.
Noise reduction methods are more effective when implementation is executed in the design process rather
than during operational procedures. Earlier the implementation stage, higher effectiveness of the feature.
Good common practice to minimize such impacts involves integration of unit operations with noise reducing
devices or choosing unit operations with guaranteed lower noise emission, locate buildings as far as
applicably possible from the plant, designing and construction of buildings with adequate soundproofing
features, employment of solid panel fencing over traditional wire fencing in order to confine noise within the
site, implementation of a constant monitoring system to keep track of noise generated and limitation in the
transport of raw materials and other noise generating activities during the day (Erskine and Brunt, ).
8.4 Odour
Fumes and odours are natural products of chemical plants and their emissions must be monitored and
reduced as low as possible. Main sources of odours within the projected chemical plant consist of effluents
(aqueous discharge), waste gases (flare) and venting of methanol/acetic acid during feed/product dispatch
and settlement.
Likewise noise pollution, new and efficient methods to control industrial odours have been developed.
Odour masking will be the technique applied in this project. It entails the elimination of odour perception by
imposing a more pleasant fragrance to “mask” the ones generated by the process. These are often
synthetically originated and do not alter the composition or presence of odours produced in the system.
Advantages of this implementation are smooth implementation, little or no capital investment involved and
high flexibility (Bergen, ).
8.5 Traffic
The plant will be situated near the Humber River, therefore it can be stipulated that majority of
transportation of raw materials and final product will be achieved through shipment methods instead road
transport. This method of transport allows minimization of road traffic with annexed pollution and noise.
Nonetheless, traffic will occur as a result of the vehicles present on site, thus transport of raw materials will
only be occurring throughout daylight shifts in order to minimize the impacts.
- 102. 102
8.6 Catalyst and Water Requirement
The reaction necessitates a Rhodium catalyst with an iodide promoter which tend to unite into insoluble
salts such as RhI3. In order to prevent this occurrence, percentage content of water is kept relatively high
(approximately 10% w/w of combined reactants) to successfully promote the cycle. Such high usage of
water is environmentally unfavourable as an additional column is required to eliminate the water, thus
increasing demand for energy utility hence reducing overall sustainability of the process.
Nonetheless, the water intake is fully recycled from the drying column back into the reactor and able to be
reused in support of the catalyst’s action. Rhodium is continuously recycled throughout the process, thus
when considering that approximately 2 kg is required in this reaction, its environmental impact is negligible
assuming total recycling and life span of 1 year.
Figure [8.1]: The carbonylation rates for iridium and rhodium processes depending on water concentration
taken under conditions of ~ 30 % w/w methyl acetate,8.4 % w/w methyl iodide, 28 barg total pressure and
190ºC (Jones, ).
8.7 Methanol Feed
An environmental consideration regarding feedstock and main reactant, ethanol, is investigated upon.
Although normally obtained from Syngas (produced from oil), methanol can also be generated through
biomass sources such as wood, waste and sewage. This implication may eventually lead to independence
from oil, creating a more sustainable and ‘green’ process in the long term.
- 103. 103
8.8 Energy Recovery
The nature of the Rhodium-Iodide methanol carbonylation process is exothermic, meaning that the reaction
releases energy under the form of heat. In an economical and environmental perspective, it is desirable to
recover this energy either internally to use within the system or externally. An appropriate heat integration
system has therefore been implemented in order to manage energy dissipation, thus promoting
environmental awareness. Application of such heat is yet to be finalized as options on whether to use it a
source of heat for streams or to any of the industrial units found within the complex is still being debated,
thus economic implication will ultimately be the relevant factor to be considered.
8.9 Storage & Handling of Raw Materials and Product
Environmental considerations need to be taken into account in regards to storage and handling of raw
material procedures.
8.9.1 Carbon Monoxide
Carbon Monoxide (CO) is delivered to the plant from the supplier through a 1 km long pipeline. Absence of
a storage system eliminates risks associated with loss of containment and contamination of the ecosystem,
although a rupture in the pipe line would still pose a negative impact to the environment. Henceforth,
measures that can be utilised to avoid such occurrence is the combination of relief valves application and
appropriate flow control systems in conjunction with suitable preventative maintenance protocol, aimed at
sampling and leak detection, that shut down the flow of CO if necessary. As a result, in order to minimize
the risk and impact of such event, process control and instrumentation will be executed. In case of a
detected loss of containment, installation of an isolation valve would temporarily stop flow of CO until the
leakage has been fixed.
8.9.2 Methanol
Methanol feedstock is stored in proximity upon sea freight delivery from supplier in large silos located 500m
away from the plant. Due to the flammable nature of methanol, vessels will be stored off-plant and required
to be at a minimum safe distance in order to comply HSE regulations. However, the continuous reaction
requires methanol feedstock to be in proximity of the reactor so that it is delivered at a reasonably high rate.
Methanol is a corrosive substance, and any spillage and consequent release into soil and ground can
extensively damage the ecosystem and surrounding areas. For this reason, a design implementation is
integrated to the silos in order to reduce the impact of a mechanical failure, which comprises of:
• A containment chamber which collects all content of the silos
• Drainage system through a tap, leading streams to a safe location where impact on people and
environment is minimized
• Implementation aimed at preventing emissions and odours of volatile organic compounds
• Pressure relief valves
- 104. 104
In order to achieve this implication, a smaller feed tank connected to the silos is implemented. In
accordance to regulations, the volume found in this tank is far smaller and continuous feed of inert nitrogen
allows the vessel to hold an optimum pressure level. Furthermore, generation of oxygen is avoided, thus
inhibiting the flammability of methanol.
In addition, a pressure relief valve control system is integrated on the feed tank as a safety measure.
Methanol is pumped to the reactor through a pipeline system on a continuous basis. The portrayed system
represents the optimum compromise between efficiency and environmental protection precautions.
8.9.3 Acetic Acid
The final product, acetic acid, is stored in appropriate storage tanks, which is the final step before product is
collected into chemical tankers suitable for shipment and delivered to customers. As previously mentioned,
acetic acid is highly corrosive in high concentrations (99.9%) thus with the potential of damaging soil and
ecosystem in case of spillages. Preventative measures are therefore put in place to minimize risk of such
occurrence. The storage tank design has been developed in accordance:
• Integration of a containment bund which aims to contain the tank’s content in case of mechanical
failure of the vessel other than any additional expected rainfall. Other than its containment purpose,
this implementation is expected to lower potential evaporation rate.
• Enclosed area is drained through the use of a tap onto a safe location in order to comply with
regulations aiming at minimizing impacts imposed on the environment.
• These implementations are effectively aimed at preventing emissions and odours of volatile organic
compounds.
• Pressure relief emergency valves (designed in relation to fire management).
A pumping system connected to a pipeline is in place to transfer the product from the storage tank onto the
chemical tanker. This system highlights a measure taken to minimize contact with the ecosystem.
Environmental measures to be applied to pipeline and leakage monitoring will be identical to those
implemented for the delivery of methanol.
The chosen location of the plant (Immingham) will greatly affect means of transportation as the reliability of
shipments through the Humber route allows elimination of any noise, traffic, pollution from road cars.
8.10 Undesired products: By- and Co- products
Specific design implementations and features have been put in place to comply with the Environment
Protection Act () to achieve minimal waste and emissions generated throughout the plant. The
prohibition on unauthorized or harmful depositing, treatment or disposal of waste and collection, disposal or
treatment of controlled waste sections of the Environmental Protection Act () are regulations to
particularly comply with.
An analysis of the process has emphasized that application of Rhodium iodide catalyst will generate a
range of by-products who possess high and low boiling points. As a result, elimination is not an option, yet
- 105. 105
optimization of the system is instead possible to control and minimize these parameters. The catalytic cycle
operated by the Rhodium Iodide catalyst consists of 6 elementary reactions which generate some
undesired products.
8.10.1 Propionic Acid
Required purity of acetic acid is stipulated to be 99.9%, according to specification, thus it is possible to
state that 0.1% of the final product consists of co- and by- products. The scenario would be different within
the system, henceforth appropriate recycling streams and unit operations have been put in place to ensure
continuous treatment of waste generation.
The major liquid by-product of the reaction is propionic acid, originated by carbonylation of ethanol.
Propionic acid is produced out of the reactor at 1% scale of propionic to acetic acid and successfully
removed in the heavy end column. Propionic acid is not hazardous, but rather a contamination component
of the final product. Handling and contact of the acid in atmosphere is not perilous to the ecosystem,
although collection from the heavy end column and appropriate storage will take place.
Furthermore, it is an established intermediate product for the manufacture of a variety of chemicals such as
esters, pesticides and pharmaceuticals, thus turning into an asset able to be sold externally. Its commercial
use would be a bonus to the process and outweigh the CAPEX and OPEX for its removal.
8.10.2 Carbon Dioxide and Hydrogen
Carbon dioxide and Hydrogen are additional by-products generated by the water-gas shift reaction. Within
the system, vapour phase of the product, which comprises of CO, H2, CO2 and methyl iodide (the latter
requiring vessels and piping fabricated out of Hastelloy in order to tackle its corrosion levels) migrates
towards the scrubber where it undergoes an absorption reaction with a mixture of acetic acid and methanol.
Methyl iodide is allowed to be recovered and recycled back into the reactor whilst acetic acid and methanol
purge are stripped and recycled back into the system, thus eliminating losses. Meanwhile, CO2 and H2 are
disposed by directing them towards the flare. Flares are environmentally friendly systems put in place to
burn excess gases that cannot be recovered in the system that allows to prevent direct release of vapours
to the atmosphere. In accordance to the plant and systems, the method portrayed indicates a sustainable
route for the disposition of these gases.
8.10.3 Methyl Iodide
Methyl iodide is one of the most dangerous by-products originated in the process, exerting a number of
negative impacts on both human health and the environment. A potential emission of this component into
the ecosystem can potentially reach the soil and contaminate water streams, hence irreversibly affecting
the natural ecosystem. Due to its established properties as a neurotoxin, the side effects resulting from its
exposure range from nausea, diarrhoea, loss of sight, cancer (on a long-term exposure) and other neuronal
impacts, thus minimization and elimination of methyl iodide release is an essential implementation
(Erickson, ). In the system, methyl iodide is generated in the vapour stream of R-101 going into the
- 106. 106
scrubber where it is stripped with some acetic acid and methanol mixture and recycled back into the reactor
on a continuous basis. An effective monitoring and control system must be implemented on the reactor and
scrubber in order to continuously monitor and detected any leakage, this includes sensors, transmitters and
controllers.
A correct operation of the control and instrumentation system will allow constant monitoring, hence in the
scenario of a loss in containment, the protocol would be isolate unit and pipeline where leakage occurred in
order to prevent further flow, thus further loss of containment and effectuate an emergency shutdown of the
unit operation.
8.10.4 Aqueous and Organic Discharges
As of all industrial processes, unit of operations found within the plant will produce streams of aqueous
discharge throughout its operation and maintenance, thus a suitable treatment strategy will be implemented
to tackle these effluents waste. The discharges will converge to one station, thus a suitable canal system is
to be implemented to facilitate collection. To avoid contamination with acetic acid and/or methanol in the
feed, the stream will be subjected to neutralisation before it is allowed to undergo further treatment for
inertness in the eco-system. The stream should ultimately abide environmental regulations as pH levels,
toxicity and temperature of the streams are set to an allowance level before it is disposed of in the
ecosystem. At this stage, parameters of stream are continuously monitored, subsequently allowed to pass
through a pipeline into a basin, which content will be delivered to a local plant for further treatment, such as
neutralization and precipitation, and charged at the rate of Mogden formula.
- 107. 107
9. Plant Layout and Location
9.1 Plant Location
The recommended location for this plant should be in North East England (Grimsby, South Humberside).
Immingham has several chemical engineering companies situated around the Humber shore line including
the likes of Philips 66, Total Oil Refinery, Inter terminals etc. Many companies locate here in order to take
advantage of the vast supply of water used for cooling purposes and the availability of cheap land.
Figure [9.1]: Site location Grimsby North East England (Google maps, )
The feedstock needed for this operation are methanol (stored offside and transported via pipe from nearby
plant and connected by a line) and carbon monoxide. Air Products is a major gas supplier located in
Grimsby south Humberside, approximately 1 minute drive (1 km) from the chosen site location. Air
Products will provide the carbon monoxide gas needed to transport the carbon monoxide. The pipeline
should be 1 km long and carbon monoxide should directly feed the reactor. The short distance reduces fuel
costs and labour hours to transport the carbon monoxide. The shorter the distance travelled, the less likely
an accident will occur during the delivery of methanol, travelling with hazardous chemicals over great
distances is perilous as it increases the likelihood of road vehicles being involved in road accidents, hence
placing the public at risk. Methanol is contained off site in a large storage tank and a fed line allows the
pumping of small amounts to an onsite storage tank due to greater risks imposed by storage of high
quantities.
The associated British ports Immingham enables access for importing and exporting materials to and from
Europe to expand market size/consumers and in turn increase company profits. The port allows
transportation of raw materials via ship which may be more cost effective whilst holding a larger capacity in
comparison to transportation via road. A rail road running from the port to the site location allows deliveries
via ferry to the site.
- 108. 108
Figure [9.2]: Humber Estuary schematic.
The chosen location for the site is 6.3 miles away from a reliable power supply, South Humber bank power
station. It will be situated close to the Humber Estuary and middle drain for easy access to water for
cooling.
In the north east of the site, a number of universities are located around, such as the University of Hull,
Lincoln University, University of York and University of Leeds. As a result, a reliable supply of talented
potential engineers have the opportunity to be offered graduate schemes, summer placements and
apprenticeships in order to fulfil future employment necessities. The wind rose diagram shown in Figure 9.3
show that the wind direction in Immingham is predominantly towards south east throughout the year.
Although south east winds blow towards the local community as discussed in Section 8, the smell of fumes
released from the site are concealed via odour masking methods.
- 109. 109
Figure [9.3]: Wind rose diagram for Grimsby (Meteoblue, )
9.2 Plant Layout
Upon preliminary study for plant layout, the primary infrastructures to be taken consideration of are
the process units in order to allow a smooth flow of production from one location to another.
Starting from the left hand side, raw materials are delivered in via trucks and stored in a tank farm.
Moreover, carbon monoxide pipeline concludes at the top left hand corner of the plant, in proximity
of the reactor, in order to limit the time spent in the transportation of hazardous materials across
the site floor, thus reducing risks of spillages, vehicle accidents, exposure to workers, etc.
There are two security booths. One is located at the entrance of the car park found at the south
end of the site which purpose is to routinely check that all vehicles entering the site belong to site
personnel. The implementation of such security prevents threats from any external sources, some
potential hazards may be sources of ignition, bombs, etc. The second security booth is located on
the east side of the plant and its purpose is to check whether delivery trucks are transporting
hazardous raw materials, however these checks are more extensive depending on the size of the
vehicle and the contents carried.
The fire station is parallel to the process units, as a result of the high probable chance of fire
propagating from this zone. Fire services are situated nearby thus reducing time wasted on fire
- 110. 110
trucks usage, avoiding catastrophe and keep personnel safe. The faster fire services can get to
the hazard points, the less damage is inflicted on the site and increase in personnel protection.
The storage tanks containing hazardous materials such as acetic acid must be located at least 70
m away from the site boundary (Sinnott et al., ). The storage tanks are adjacent to the main
plant area, therefore a short pipeline is needed to feed acetic acid into its relative storage tank.
Prevailing wind direction determine the position of the tank farm and storage tanks. For this
reason, these are best placed on Humber estuary in order to avoid vapours from drifting back the
plant and local community. Emergency water storage units are located on the north side of the site
for easy access of the Humber estuary water. In addition, water storage is located near the
process units in order to provide quick access cooling if needed.
The shaded area around the process units indicated future room for expansion in the scenario that
the plant was to be modified and expanded. On the west side of the site, the delivery region
consisting of finishing and packaging, vehicle deliveries and rail way link to the Immingham port for
European exports is present. The finishing and packaging is opposite the acetic acid storage tank
to avoid movement of product for long distances, thus increasing risks towards personnel and
opportunity for spillages.
The control room must be located opposite the process unit area. It is located near the evacuation
zone and canteen, thus operators are not faced with travel issues regarding usage of facilities.
The utilities room will be located opposite the process unit area to ensure efficient transfer energy
in order to reduce heat dissipation.
Office, laboratories and canteen are to be situated on the South east of the site, this proves to be
a safe distance from the hazardous storage tanks and process units. It is nearby the car parks,
thus further reducing walking distances for personnel. The maintenance office is located near the
process units so that staff do not need to carry tools around the plant.
All manual valves, sample points and instruments are located at reachable heights and positions
for operators to carry out maintenance. In the process unit area, sufficient headroom for easy
access to equipment will be provided (Sinnott et al., ).
The base of all three distillation columns and vertical vessels such as the reactor and flash drum
must be elevated for sufficient NSPH to the pumps.
Methanol and carbon monoxide pipe lines are elevated on site to allow trucks to pass underneath.
The trade off is large pressure drop, however having functional pipes running throughout the site
floor is dangerous for large moving vehicles as chances of accidents occurring increases, as
potential pipe leaks can provide source of ignition .
- 111. 111
Modular construction will be used to assemble the process unit section. Only in recent years, more
sites have increasingly started to assemble sections of the plant at the manufacturing site, these
include main structural steel equipment, piping and instrumentation. These are then transported to
site by ferry or road (Sinnott et al., ). This method provides many advantages such as
reduced construction costs, improved quality control, less skilled labour on site required.
Figure 9.4 shows a layout of the plant.
- 112. 112
9.2.1 Site Flow Plan
Figure [9.4]: Plant Layout
- 113. 113
APPENDIX [A] – Minutes
Meeting Week 13 – 9th May
Time: 13:15
Venue: Chemical Engineering Room 125
Chair Person: Hisham Albaroudi
Secretary: Sinthujan Pushpakaran
Present: Alexander Taylor, Cristian Baleca, Enoch Osae, Hisham Albaroudi, Karen Atayi, Sinthujan
Pushpakaran
In Attendance: Aidan Hurley
1. No apologies.
2. Hisham – Finished environmental section and about to begin design of reactor after background
research.
Alex – Finished unit design and has made progress on process control.
Enoch – Done majority of unit design and about to begin process economics.
Cristian – Positive progress regarding unit design and about to begin process safety.
Karen – Had issues with calculations of unit design but now sorted. About to begin Plant layout
section.
3. PFD - Fix tanks and use appropriate material balance sheet.
P&ID – Fix arrangements.
Material Balance – Complete.
4. Arranged an informal deadline to have a complete report ready for draft submission by the 16th
of
May.
Send CAPEX and OPEX by Wednesday 11th
of May to Enoch.
5. Informal meeting scheduled for the 16th
of May at 11:00.
6. Nothing to be added.
Meeting closed at 13:53
- 114. 114
Meeting Week 12 – 3rd May
Time: 11:15
Venue: Chemical Engineering Room 125
Chair Person: Cristian Baleca
Secretary: Karen Atayi
Present: Alexander Taylor, Cristian Baleca, Enoch Osae, Hisham Albaroudi, Karen Atayi, Sinthujan
Pushpakaran
In Attendance: Aidan Hurley
1. Apologies accepted, Hisham absent.
2. Still working on individual unit designs, deadline extended.
3. Individual section to be completed by the end of this week
4. Individual section to be completed by the end of this week
5. Unit description should show what did you find and calculations to be set as appendices.
6. Informal meeting scheduled for Friday 6th
of May at 10:00 in Library Group Learning room
7. Informal meeting scheduled for Friday 6th
of May at 10:00 in Library Group Learning room
8. Follow layout for unit design using Dropbox document.
9. Formal meeting scheduled for 9th
of May at 13:15 in the Chemical Engineering Building.
Meeting closed at 11.53
- 115. 115
Meeting Week 11 – 22nd April
Time: 13:15
Venue: Chemical Engineering Room 125
Chair Person: Karen Atayi
Secretary: Cristian Baleca
Present: Alexander Taylor, Cristian Baleca, Enoch Osae, Hisham Albaroudi, Karen Atayi, Sinthujan
Pushpakaran
In Attendance: Aidan Hurley
1. No apologies.
2. HAZOP development was discussed.
3. Individual P&ID development still in progress
4. Delays occurring, but individual design is progressing.
5. General report layout has been chosen.
6. Aidan advised to avoid complicating the simulation.
7. Environmental effect discussed. Topics on how to improve energy efficiency, waste treatment and
how to avoid environmental impact were mentioned.
8. Formal meeting scheduled for Tuesday 3rd
May at 13:15 in the Chemical Engineering Building.
9. Informal meeting scheduled for Friday 22nd
April at 14:15 in the Chemical Engineering
Building.
Meeting closed at 14.05
- 116. 116
Meeting Week 10 – 18th April
Time: 15:15
Venue: Chemical Engineering Room 125
Chair Person: Enoch Osae
Secretary: Karen Atayi
Present: Alexander Taylor, Cristian Baleca, Enoch Osae, Hisham Albaroudi, Karen Atayi, Sinthujan
Pushpakaran
In Attendance: Aidan Hurley
10. No apologies.
11. Need to know parameters for line between reactor and flash drum for HAZOP meeting, such as
pressure, temperature, content, material of construction and volume.
12. Unit design should be approximately be about 4-6 pages for each person. It should include
introduction, what techniques have been used for the design, what each person has come up with,
how it affects the design, a mechanical design and update on cost.
13. Unit design should be approximately be about 4-6 pages for each person. It should include
introduction, what techniques have been used for the design, what each person has come up with,
how it affects the design, a mechanical design and update on cost.
14. Informal deadlines for unit design and individual sections has been set for 1st
May and 9th
May
respectively.
15. Complete P&ID to be ready on A3 for 25th
April .
16. Complete P&ID to be ready on A3 for 25th
April .
17. Formal meeting scheduled for Friday 22nd
April at 13:15 in the Chemical Engineering Building.
18. Informal meeting scheduled for Friday 22nd
April at 14:15 in the Chemical Engineering
Building.
Meeting closed at 15.44
- 117. 117
Meeting Week 9 – 11th April
Time: 15:15
Venue: Chemical Engineering Room 125
Chair Person: Alexander Taylor
Secretary: Enoch Osae
Present: Alexander Taylor, Cristian Baleca, Enoch Osae, Hisham Albaroudi, Karen Atayi, Sinthujan
Pushpakaran
In Attendance: Aidan Hurley
1. No apologies.
2. Minutes were accepted
3. Hisham advises everyone to use Aidan’s lecture notes to complete unit design.
4. Alex said Contents page has been developed.
5. P&ID is required from the Reactor to the flash drum and everybody should have made a start on
their report section.
6. Goals for next meeting:
- Complete P&ID
7. Any other business:
- Aidan mentioned HAZOP components require the hazard (MSDS) data sheet, so all potential
hazards can be listed.
- Aidan to be absent week commencing on the 25th
April .
8. Leader for HAZOP workshop – Cristian Baleca
Scribe for HAZOP workshop – Sinthujan Pushpakaran
9. Informal meeting scheduled for Thursday 14th
April
10. Formal meetings schedules for Monday 18th
April and Friday 22nd
April respectively.
Meeting closed at 15.51
- 118. 118
Meeting Week 8 – 4th April
Time: 15:15
Venue: Chemical Engineering Room 125
Chair Person: Sinthujan Pushpakaran
Secretary: Alexander Taylor
Present: Alexander Taylor, Cristian Baleca, Enoch Osae, Hisham Albaroudi, Karen Atayi, Sinthujan
Pushpakaran
In Attendance: Aidan Hurley
1. No apologies.
2. Use of Aidan’s advice to improve the simulation, don’t necessarily have to have to everything on
one simulation but values need to be consistent.
3. Apply changes in the simulation to the PFD.
4. Work on the design of each of our unit operations.
5. Work on the formal report.
6. Informal meeting scheduled for Tuesday 5th April at 14:15.
7. Formal meeting scheduled for Wednesday 11th
April at 13:15 in the Chemical Engineering
Building.
8. Goals for next meeting:
- Finalise simulation and PFD.
- Research into the design of unit operations.
- Look into the structure of the report.
9. Nothing to be added.
Meeting closed at 15.45
- 119. 119
Meeting Week 7 – 7th March
Time: 15:15
Venue: Chemical Engineering Room 125
Chair Person: Hisham Albaroudi
Secretary: Sinthujan Pushpakaran
Present: Alexander Taylor, Cristian Baleca, Enoch Osae, Hisham Albaroudi, Karen Atayi, Sinthujan
Pushpakaran
In Attendance: Aidan Hurley
1. No apologies.
2. Simulation has produced good purity. Client specified that CO, Methyl iodide and Hydrogen
iodide should be coming out. Further work in the simulation to be carried out to improve purity.
3. Client proposed an idea to fit a scrubber onto the P&ID. Carry out several P&IDs for each
component, including the majority of the details.
4. Informal meeting scheduled for Tuesday 8th
March with further informal meetings to be
scheduled after.
5. Formal meeting scheduled for Monday 4th
April in the Chemical Engineering Building.
6. P&ID agreed to be completed by Friday 11th
March.
7. Design of unis to each member has been assigned:
Hisham Albaroudi – Reactor
Cristian Baleca – Scrubber
Alexander Taylor – Column
Enoch Osae – Column
Karen Atayi – Flash tank
Sinthujan Pushpakaran – Storage tank
8. No change in action tracker.
9. Nothing to be added.
Meeting closed at 15.48
- 120. 120
Meeting Week 6 – 29h February
Time: 15:15
Venue: Chemical Engineering Room 125
Chair Person: Cristian Baleca
Secretary: Hisham Albaroudi
Present: Alexander Taylor, Cristian Baleca, Enoch Osae, Hisham Albaroudi, Karen Atayi, Sinthujan
Pushpakaran
In Attendance: Aidan Hurley
1. No apologies.
2. Everyone agreed split groups and are working towards target.
3. P&ID and simulation to be completed by 7th
March and 10th
March respectively.
4. Work on simulation needs to be faster. Cooperation between AT, CB and HA. Reactor’s results
are not as desired. Not all side reaction’s compounds are available on Aspen Plus. Only main
reactions and by-products to be used.
5. P&ID agreed to be completed by Monday 7th
March .
6. Informal meeting scheduled for Thursday 3rd
March at 12:15.
7. Formal meeting scheduled for Monday 7th
March at 15:15 in the Chemical Engineering
Building.
8. P&ID to be completed by next informal meeting. Find kinetic values for remaining reaction
9. AT, CB and HA to research on kinetics of the process.
10. Nothing to be added.
Meeting closed at 15.38
- 121. 121
Meeting Week 5 – 22nd February
Time: 15:15
Venue: Chemical Engineering Room 125
Chair Person: Karen Atayi
Secretary: Cristian Baleca
Present: Alexander Taylor, Cristian Baleca, Enoch Osae, Hisham Albaroudi, Karen Atayi, Sinthujan
Pushpakaran
In Attendance: Aidan Hurley
1. No apologies.
2. Hisham, Alex and Cristian working on simulation.
3. Enoch, Karen and Sinthujan working on MSDS (Material Datasheet).
4. Given until Week 7 to finish P&ID.
5. Informal meeting scheduled for Tuesday 23rd
February at 10:00.
6. Look into design options and how to better run the process.
7. Water is required as a separate stream, so consider recycling.
8. Get rid of Carbon Dioxide from system, spurge for P&ID or system will have losses.
9. Consider degrees of freedom for individual phases (Columns).
10. Formal meeting schedules for Monday 29th
of February .
Meeting closed at 15.38
- 122. 122
Meeting Week 4 – 18th February
Time: 12:15
Venue: Chemical Engineering Room 125
Chair Person: Enoch Osae
Secretary: Karen Atayi
Present: Alexander Taylor, Cristian Baleca, Enoch Osae, Hisham Albaroudi, Karen Atayi, Sinthujan
Pushpakaran
In Attendance: Aidan Hurley
1. No apologies.
2. Minutes from last meeting accepted.
3. Alex has made progress on flowsheet.
4. Hisham is past reactor stage on ASPEN.
5. Informal meeting scheduled for Friday 19th
February at 13:00 in the Chemical Engineering
Building to discuss simulation and mass balance.
6. To have informal meeting after Chemical Reaction Engineering lecture.
7. Formal meeting scheduled for Monday 22nd
February at 15:15
Meeting closed at 12:31
- 123. 123
Meeting Week 3 – 8th February
Time: 15:15
Venue: Chemical Engineering Room 125
Chair Person: Alexander Taylor
Secretary: Enoch Osae
Present: Alexander Taylor, Cristian Baleca, Enoch Osae, Hisham Albaroudi, Karen Atayi, Sinthujan
Pushpakaran
In Attendance: Aidan Hurley
1. No apologies.
2. Minutes from last meeting accepted.
3. Alex discussed progress on general mass balance and everybody has approved work provided.
4. Hisham provided a general flow sheet in which everyone has approved it.
5. A standard format for documents has been set e.g. Agenda and minutes.
6. Enoch developed a document to use as an action tracker and everybody approved it.
7. Goals for the next meeting:
8. Meeting amendment due to the BCCA event on Monday.
9. Informal meeting scheduled for Thursday 18th
February at 11:15 in RB 207.
10. Formal meeting scheduled for Thursday 18th
February at 12:15 in the Chemical Engineering
Building.
11. Cristian to get kinetic values for HYSYS.
Meeting closed at 15:45
- 124. 124
Meeting Week 2– 5th December
Time: 15:15
Venue: Chemical Engineering Room 125
Chair Person: Sinthujan Pushpakaran
Secretary: Alexander Taylor
Present: Alexander Taylor, Cristian Baleca, Enoch Osae, Hisham Albaroudi, Karen Atayi, Sinthujan
Pushpakaran
In Attendance: Aidan Hurley
1. Time and Date of formal meeting confirmed – Formal meetings to be held on Mondays at
15:15 in Chemical Engineering Room 125, confirmed by Aidan.
2. Rota for the position of Chair Person and Secretary agreed on by following table:
3. A dropbox group to be set up by Hisham for file sharing.
4. Goals for next meeting:
5. Continue to work on a mass balance for the process, work on Aspen HYSYS to give an
insight into the process and to make progress on a process flow sheet.
Meeting closed at 15:50
Date Chair Person Secretary
05/02/ Sinthujan Alexander
08/02/ Alexander Enoch
15/02/ Enoch Karen
22/02/ Karen Cristian
29/02/ Cristian Hisham
07/02/ Hisham Sinthujan
04/02/ Sinthujan Alexander
11/02/ Alexander Enoch
18/02/ Enoch Karen
25/02/ Karen Cristian
04/02/ Cristian Hisham
09/02/ Hisham Sinthujan
- 125. 125
Meeting Week 1 – 30th November
Time: 11:15
Venue: Chemical Engineering Room 125
Chair Person: Hisham Albaroudi
Secretary: Sinthujan Pushpakaran
Present: Alexander Taylor, Cristian Baleca, Enoch Osae, Hisham Albaroudi, Karen Atayi, Sinthujan
Pushpakaran
In Attendance: Aidan Hurley
1. Plant process decided – The Monsanto process was agreed to be the most feasible process
for the production of acetic acid. Further look into catalysts required as they are possibly
cheaper and more efficient.
2. Area of responsibility delegated:
6. Cristian Baleca (Safety)
7. Karen Atayi (Plant layout and location)
8. Alexander Taylor (Process control and instrumentation)
9. Enoch Osae (Process Economics)
10. Hisham Albaroudi (Environmental Protection)
11. Sinthujan Pushpakaran (Report and Presentation Editor)
3. Agreed regular external meetings for Thursdays at 11:15, chair of the week will book places
accordingly.
4. Future meetings with client to be decided after talking with Group 6 leader.
5. Goals for next meeting:
12. Research on mass balance by next meeting. Individual review of mass balance to be
finalized.
Meeting closed at 11:52
- 126. 126
APPENDIX [B] – Calculations for Reactor
Reactor volume and sizing
The reactor volume is a vital parameter and it is a function of the rate of reaction, inlet flowrate and
conversion as represented by the following equation:
???? =
????????0 ???? ????
−????????
The volume constraint can also be rearranged in relation to the rate coefficient (k) in the following
formula (Schneider et al., ):
???? =
???? ???? ???????????? ????
????????????????
2
(1 − ????)2
=
???? ???? ????
????????????????(1 − ????)2
Where:
Vo = volumetric flowrate of methanol = 574.105 l/min (Methanol) and l/min (CO)
= 9.56 l/s + .2 l/s
= .76 l/s (Data obtained from simulation)
X = conversion rate; XMethanol = 0.99; XCO = 0.90; XRXN = 0.95
k = 0.11 L/mol-1
s-1
(Iwase et al., )
CAo = Caverageinitial =
????
????
= 2.47 mole/l (Data obtained from simulation)
Therefore, substituting into equation, leads to:
???? = 110,740 ????????????????????????
= 110.74 ????3
Allowing a 20% overdesign as specified by the design brief:
???? = 110.74 × 1.2
= 138.42 ????3
Applying:
???? = (
????????2
4
) × ℎ
Where:
d = diameter of the reactor
h =height of the reactor
It is assumed that height of reactor is twice its diameter h = 2d (Sinnott et al., ,
p986)
- 127. 127
Therefore:
???? = (
????????2
4
) × 2????
Thus, upon rearranging:
???? = 4.45 ????
ℎ = 8.9 ????
Ellipsoidal head’s dimensions
Applying:
???????????????????????? = (
???? × ????3
24
) + (
???? × ????2
× ????. ????
4
)
Where:
D = internal diameter = mm
S.F. = straight face = assumed to be (3 × ????ℎ???????????????????????????? ???????? ????ℎ???? ℎ????????????) = 60 mm
Substituting into equation:
???????????????????????? = (
???? ×
24
) + (
???? ×
× 60
4
)
= ????????3
= 12.96 ????3
Due to the fact that ellipsoidal heads are defined as “2:1 heads”, the inside depth of the head
(excluding S.F.) is 2 times the radius of the dish, therefore:
???????????????????????? ????????????ℎ ????????????????ℎ =
????
4
=
4
= .5 ????????
= 1.13 ????
- 128. 128
Thickness of shell
Applying (Sinnott et al., , p986):
???? =
???????? ????????
2 ∗ ???????? − 1.2????????
⁄ + C
Where:
t = wall thickness, mm
Pi = internal pressure, bar = 33 bar
Di = internal diameter, mm = mm
S = maximum allowable stress, kg/cm2
= .59 kg/cm2
(Alloys and Producer, )
C = corrosion allowance = 4 mm
Substituting into equation:
???? = 33 ×
[(2 × .59 × 0.85) − 1.2 × (33)]⁄ + 4
= 28.25 ????????
Therefore, external diameter:
???? ???? = ???????? + 2????
= 4.45 + (2 × 28.25 × 10−3
)
= 4.51 ????
Thickness of vessel’s head
Ellipsoidal head is selected due to the operating pressure being less than 150 psi, thus applying
(Sinnot et al., ):
Th =
???????? ???? ???? ????
2 ∗ ???????? − 0.2????????
⁄
Where:
P = pressure, bar = 33 bar
D = diameter of outside shell, mm = mm
S = allowable stress of material = .59 kg/cm2
E = joint efficiency = 0.85
- 129. 129
Figure [B-1]: Values for Radius Factor K (Edge, ).
Therefore:
K = ????(
???? ????
2ℎ ????
) = 0.81 (Graph extrapolation)
ho = h + nt h = D/4 = 4.51/4 = 1.12 m
nt = Ts – CA = (28.25 – 4) mm = 24.25 mm = 24.25 × 10-3
ho = 1.12 + (24.25 × 10-3
) = 1.14 m
2ho = (2 × 1.14) = 2.28 m
Do = D – 2nt = [4.51 – (2 × 24.25 × 10-3
) = 4.46 m
Therefore, (
???? ????
2ℎ ????
):
= (
4.46
2.28
) = 1.95
Therefore, K:
???? = ???? (
???? ????
2ℎ ????
) = 0.88
Substituting back into thickness equation:
Th = 33 × × 0.84
[(2 × .59 × 0.88) − (0.2 × 33)]⁄
= 19.80 ????????
????ℎ = 19.80 + 4 = 23.80 ????????
- 130. 130
Applying corrosion allowance, therefore:
????ℎ = 19.80 + 4 = 23.80 ????????
Total height
Applying:
ℎ + 2????ℎ
= [8.9 + (2 × 23.80 × 10−3)]
= 8.95 ????
Calculation of stresses
Longitudinal and circumferential stresses
Applying:
σ ???? =
????????????
4????
= (
33 ×
4 × 28.25 × 10−3
)
= .56 ????????????
Applying:
σℎ =
????????????
2????
= (
33 ×
2 × 28.25 × 10−3
)
= .12 ????????????
Pressure and axial stress
Applying:
σ ???? = [
????????????
4(???????? − ????????)
]
= (
33 ×
4 × 24.25 × 10−3
)
= .9 ????????????
- 131. 131
Total weight of the shell
Density of ℎ???????????????????????????????? − ???? = kg/m3
(Alloys and Producer, )
Applying, dead-weight formula (Sinnott et al., ):
???????? = ???? ???? × ???? × ???? × ???? × (???????? + 0.8????)???? × 10−3
Where:
Cv = a factor to account for the weight of nozzles, manways, internal supports, etc.. which is taken as
1.08 for vessels with only a few internal fittings (Sinnott et al., )
ρ = density of hastelloy b-2 = kg/m3
(Alloys and Producer, )
D = mean diameter of vessel = 4.51 m
Hv = height of the vessel = 8.94 m
t = thickness of the shell = 24.25 mm
Substituting into equation:
???????? = 429,306 ????
Maximum bending moment
Applying (Sinnott et al., ):
???? = ???????? ???? ????
Where:
Fp = W = 429,306 N
Hp = 8.95 m
Therefore:
???? = 3,842,288 ????????
= 38.42 ????????????
Dead-weight stress
Applying (Sinnott et al., ):
σ ???? =
????????
????(???????? + ????)????
Where:
W = weight of the vessel = 429,306 N
Di = 4.45 m
t =thickness including corrosion allowance = 28.25 × 10-3
- 132. 132
Substituting into equation:
σ ???? = 1,271,151.57 ????/????2
= 12.71 ????????????
Bending stress
Applying (Sinnott et al., ):
σ ???? =
????
???? ????
(
????????
2
+ ????)
Where:
M = 3,842,288 Nm
lv =
????
64
(???? ????
4
− ????????
4
) = 0.42 (Sinnott et al., )
Do = 4.51 m (Sinnott et al., )
Di = 4.45 m (Sinnott et al., )
Substituting into equation:
σ ???? = 8,230,729 ????/????2
= 82.30 ????????????
Principal stresses
Applying (Sinnott et al., ):
????1=
1
2
[ σℎ + ????z + √σℎ − σ ????)2
+ 4 ]
????1=
1
2
[ σℎ + ????z - √σℎ − σ ????)2
+ 4 ]
????3 = 0.5 P
Where:
Total longitudinal stress ????z = ????L + ????W ± ????B
= negligible (Sinnott et al., )
Therefore, ????z:
(.9 + 12.71 + 82.30)
= .91 ????????????
- 133. 133
Substituting into equations:
????1 =
1
2
[.12 + .91 + √(.12 − .91)2
= .12 ????????????
????2 =
1
2
[.12 + .91 − √(.12 − .91)2
= .91 ????????????
????3 = (0.5 × 33) = 16.5 ???????????? (???????????????????????????????????????? ???????? ????ℎ???????? ????????????????????????????)
Allowable stress intensity
The allowable stress check is a technique to evaluate if the mechanical design of the vessel
(especially wall thickness) can withstand the principal stresses exerted on the unit operation; the
following three equations are used (Sinnot et al., ):
(????1 − ????2) = 990.21 ????????????
(????1 − ????3) = .62 ????????????
(????2 − ????3) = .41 ????????????
The greatest obtained value is therefore taken and compared to the maximum allowable stress of
the material (Hastelloy – B). If the value is lower than the allowable stress of the material, the
allowable stress intensity is within the range (Alloys and Producer, ).
???????????????????????????????? ???????????????????????????????????? ???????????????????????? (???????????????????????????????????? ????) = 51 ???????????? = .33 ????????????
???? > > (????1 − ????3) → ???????????????????????????????????? ???????????????????????? ???????? ???????????????? ????????????ℎ???????? ????ℎ???? ???????????????????????????????????????? ????????????????????
(Sinnott et al., )
- 134. 134
Piping sizing
Pipeline Flowrate
(m3
/s)
Velocity
(m/s)
Cross sectional
area (m2
)
Required diameter (m)
CO feed to reactor 0. 2.00 0. 0.
Methanol feed to
reactor
0. 2.00 0. 0.
Water feed to
reactor
0. 2.00 0. 0.
Reactor to flash
tank
0. 2.00 0. 0.
Reactor to
scrubber
0. 2.00 0. 0.
Drying column to
reactor
0. 2.00 0. 0.
Scrubber to
reactor
0. 2.00 0. 0.
Table [B1]: Data obtained from Aspen Plus simulation for pipe sizing.
Where:
Flowrate (m3
/s) = Obtained from stream summary table (Aspen Plus simulation) and divided by (60
× ) to convert from l/min to m3
/s.
Velocity (m/s) = A constant value of 2 m/s for determination of piping characteristics is suggested
(Perry, )
Therefore:
???????????????????? − ???????????????????????????????????? ???????????????? =
????????????????????????????????
????????????????????????????????
Thus, diameter can be calculated upon:
???????????????????????????????? = √
4 × ???????????????????? − ???????????????????????????????????? ????????????????
????
- 135. 135
Therefore diameter can be evaluated using:
???? =
???? × ????3
16
Therefore, diameter:
???? = 5.28 ???????? = 0.053 ????
Start-up
Assuming that 99% is the target conversion to reach ‘steady state’ conditions, the equation to
determine the required time to reach such condition reduces to:
???????????????? =
4.6????????
1 + ????????????
Where:
Ts =
????????
???????? ????
=
96,900
2.47
= 39,227 mol
VFluid = 96.89 m3
= 96,900 dm3
CAO = 2.47 mol/dm3
K = × 10−6
(L/mol.h) = 9.45 × 10−6
(dm3
/mol.s) (Golhosseini et al., )
Therefore:
???????????????? =
4.6 ×
1 + (9.45 × 10−6 × )
= ????
= 36.57 ℎ????????
Heat dissipation and insulation
The heat dissipation is calculated based upon Fourier’s Law by:
???? = ℎ???????????? ???????????????????????????????? = ????????
????????
????????
Where:
Q = heat transfer = W
K = thermal conductivity of material = 10 (W/m K) (Alloys and Producer, )
A = surface area of vessel = 2????????ℎ Where: r = 2.25 m h = 8.95 m
Therefore, surface area of vessel:
???????????????????????????? ???????????????? = 2 × ???? × 2.25 × 8.95
- 136. 136
= 126.74 ????2
Change in temperature calculated by:
???????? = ???????????????????????????????????? − ????????????????????????????????
Where:
TINTERNAL = temperature within the reactor = 160 o
C
TAMBIENT = ambient temperature = assumed to be 20 o
C
Therefore:
???????? = 160 − 20
= 140 °????
= 413 ????
ds is the thickness of shell, which is:
???????? = 0.028 ????
Therefore, heat transfer equals to:
???? = ℎ???????????? ???????????????????????????????? = (10 × 126.74 ×
413
0.028
)
= 18,684,150 ????
= 67,301,345 ????????/ℎ????
Start-up
Assuming that 99% is the target conversion to reach ‘steady state’ conditions, the equation to
determine the required time to reach such condition reduces to:
???????????????? =
4.6????????
1 + ????????????
Where:
Ts =
????????
???????? ????
=
96,900
2.47
= 39,227 mol
VFluid = 96.89 m3
= 96,900 dm3
CAO = 2.47 mol/dm3
K = × 10−6
(L/mol.h) = 9.45 × 10−6
(dm3
/mol.s) (Golhosseini et al., )
- 137. 137
Therefore:
???????????????? =
4.6 ×
1 + (9.45 × 10−6 × )
= ????
= 36.57 ℎ????????
Nozzle diameter = 15% Diameter for the shell’s nozzle in relation to the diameter of pipe.
Nozzle to flange distance = Value obtained as twice the nozzle diameter.
Agitator
It is acknowledged that the following calculations to determine the agitator’s sizes and
characteristic are based on calculations obtained from (Pietranski, ).
Ratios obtained from (Pietranski, ):
????1 =
???????????????????????? ????????????????????????????????
???????????????????????????????? ????????????????????????????????
= 3
Therefore:
4.45
????
= 3
???? = 1.48 ????
Thus:
????2 =
ℎ????????????ℎ???? ???????? ???????????????????????????????? ???????????????????? ????????????????????????
???????????????????????????????? ???????? ????????????????????????????????
= 1
Therefore, height:
ℎ????????????ℎ???? = 1.48 ????
Blade length is equal to:
????3 =
???????????????????? ????????????????????ℎ
???????????????????????????????? ???????? ????????????????????????????????
= 0.25
= 0.296 ????
Therefore:
???????????????????? ????????????????????ℎ
1.48
= 0.25
= 0.37 ????
- 138. 138
Blade width is equal to:
????4 =
???????????????????????????????? ???????? ????????????????????????????????
???????????????????? ????????????????ℎ
= 5
Therefore:
1.48
???????????????????? ????????????????ℎ
= 5
= 0.296 ????
Blade width is equal to:
????5 =
???????????????????????????????? ???????? ????????????????????????
???????????????????????? ????????????????ℎ
= 10
Therefore:
4.45
???????????????????????? ????????????????ℎ
= 10
= 0.45 ????
It is assumed the height of the baffle is equal to the vessel’s height excluding the thickness of
head.
Power of impeller
In order to work out the power required to operate the motor, a table of ratio constants and power
number for different types of impellers is used, therefore (Pietranski, ):
Figure [B1]: Ratio constant and power number for different types of impellers (Pietranski, ).
- 139. 139
Therefore, applying:
???????? = ????2
× ???? ×
????
????
Where:
µ = 0.79 mPa.a
d = diameter, m = 1.48 m
ρ = density, kg/m3
= 546 kg/m3
N = radial velocity = 200 rpm (as previously specified) = 3.3 rps (Carpenter,
)
Therefore, Re equals to:
???????? = 5.5 × 106
???????? > 10,000 > ???????????????????????????????????? ????????????????????????
This implies that the power of the motor required does not depend on the liquid viscosity, but on
density instead, therefore (Sinnott et al., ):
???? ???????????????????????????????????? = ???????? × ???? × ????3
× ????5
Where:
NP = power tables = 6 (From table 2) (Pietranski, )
ρ = density = 564 kg/m3
N = radial speed (rps) = 3.3 rps
D = diameter = 1.48 m
Substituting into equation:
???? ???????????????????????????????????? = 8.64 × 105
= .64 ℎ????
Further allowing losses of 25%
???? ???????????????????????? =
???? ????????????????????????????????????
1 − ????????????????????????
= .85 ℎ????
However, this value appears to be too high, thus the assumption that mild agitation is required for
the process is likely to be wrong. Another calculation can be proceeded with the estimation that 1
– 2 kW/m3
power is required to operate the agitator of a large vessel.
- 140. 140
Assuming that the volume of the tank filled with fluid is approximately 70% (Sinnott et al., ):
???????????????????????? = ???????????????????? × 0.7
Therefore:
(138.41 × 0.7)
= 96.89 ????3
Referring to Figure [], highlighting ratio between power and liquid quantity, power required for the
agitation can be calculated (Pietranski, ):
Figure [B2]: Ratio between power and liquid quantity in order to evaluate agitation required (Pietranski,
).
Therefore, power required:
???????????????????? ???????????????????????????????? = ???????????????????????? × 1.5
= 1.45 × 102
????????
= 194 ℎ????
Therefore (Pietranski, ):
???????????????????? =
ℎ????
????????????
96.89 ????3
= .82 ???????????? = 21.312 × 103
????????????
Thus, ratio required is:
???????????????????? = 9.10
Hence, intensive agitation is required for this design.
Agitator’s shaft
It is acknowledged that the following calculations are based on example work (Anon, ):
Given that:
ℎ???? = 194
???? = ???????????? = 200
- 141. 141
Therefore, torque on shaft:
???????? = (
ℎ???? × 75 × 60)
2 × ???? × ????
)
= (
194 × 75 × 60
2 × ???? × 200
)
= 694.711 ????????????
Polar modulus given by:
???? ???? =
???? ????
????????
Where:
Tm = maximum torque = 1.5Tc = .07 kgm
Shear stress = 51 ksi = .59 kg/cm2
Therefore:
???? ???? = (
1.5 × 694.711 × 100
.59
)
= 29.06 ????????3
Therefore diameter can be evaluated using:
???? =
???? × ????3
16
Therefore, diameter:
???? = 5.28 ???????? = 0.053 ????
Reactor and agitator cost
The overall cost of the unit is worked out by:
???????????????? ???????? ???????????????? = ???????????????? ???????? ???????????????????????????? + ???????????????? ???????? ????????????????????????????????
Equation used to determine cost of unit is (Sinnott et al., ):
???????? = ???? + ???????? ????
According to this equation, the estimated cost is in USD for the year (January) based on
U.S Gulf Coast location, so further currency, location and time factor are taken into account
.
- 142. 142
Reactor (jacket, agitated)
Applying:
???????? = ???? + ???????? ????
Where:
S = volume, m3
a = 14,000
b = 15,400
n = 0.7
Substituting into equation:
???????? = 14,000 + (15,400 × 138.410.7
)
????. ???? $ 499,666
Agitator
Applying:
???????? = ???? + ???????? ????
Where:
S (power kW) = 1.45 × 102
a = 4,300
b = 1,920
n = 0.8
Substituting into equation:
???????? = 4,300 + [ × (1.45 × 102
)0.8
]
= ????. ???? $107,195
Therefore, total cost of reactor:
???????????????? ???????? ???????????????????????????? = $499,666 + $107,195
= $606,861 (????. ????. ???????????????? ???????????????????? ????????????????????, )
- 143. 143
The cost of the column is based on a U.S Gulf Coast basis and has to be changed to a
UK basis using cost indexes and location factors. Although a cost index for was not
available, the cost index for will be taken as an estimate instead (Sinnott et al.,, p324):
Therefore, applying:
???????????????? ???????? ???????????????? ???? = ???????????????? ???????? ???????????????? ???? ×
???????????????? ???????????????????? ???????? ???????????????? ????
???????????????? ???????????????????? ???????? ???????????????? ????
Where:
Cost index in year A = 567.3 (Chemical Engineering, )
Cost index in year B = 499.6 (Chemical Engineering, )
Therefore, the total cost of the column is:
???????????????? ???????? ???????????????? ???? =
567.3
499.6
× $606,861
= $689,096 (????. ????. ???????????????? ????????????????????, ????????????????????)
Applying location factors (Sinnott et al., , p327):
???????????????? ???????? ???????????????????? ???????? ???????????????????????????????? ???? = ???????????????? ???????? ???????????????????? ???????? ???????????????? × ????????????
Where:
LFA (United Kingdom) = 1.02
Therefore, the total cost of the column on a United Kingdom, basis is:
???????????????? ???????? ???????????????????? ???????? ???????????????????????????????? ???? = 689,096 × 1.02
= ???????? $702,878
Currency conversion
The unit of currency also has to be changed from dollars (USD) to pounds (GBP). The exchange
rate, as of May , is 1. USD per 1 GBP (HM Revenue & Customs, ).
Therefore, total cost of the column on a UK basis is:
702,878
1.
= £488,008
- 144. 144
Material factor
The unit operation’s cost estimate is based on a carbon steel manufacturing material. The material
factor for a carbon steel is 1. Therefore, this value must be related to the material factor for
Hastelloy in order to adapt it.
???????????????????????????????? ???????????????????????? (????????????????????????????????????) = 1.55
Therefore, cost of unit in Hastelloy:
???????????????? = £488,008 × 1.55
= £756,412
≈ £ 800,000
- 145. 145
APPENDIX [C] – Calculations for Flash Tank
The mechanical design method was adopted from “Two phase separator within the right limits”
(Svrcek et al., )
Data from simulation
WV = .97 lb/hr WL = .87 lb/hr
ρV = 0. lb/ft3
ρL = 61. lb/ft3
Vapour velocity
Applying:
???? ???? = ????(
???? ???? − ???? ????
???? ????
)0.5
Where:
UT = terminal velocity, m/s
ρL = liquid density, kg/m3
ρV = vapour density, kg/m3
K =
Table [C1]: Separator K values with a mist eliminator (Svrcek et al., )
- 146. 146
Calculating K from Table C1, where P = 14.5 psig, K equals to:
???? = 0. + 0.(????) + 0.046ln(????)
= 0. + 0.(14.5) + 0.046ln(14.5)
= 0.347
Therefore, UT equals to:
???? ???? = 0.347(
61. − 0.
0.
)0.5
= 4.34 ????????/????
= 1.32 ????/????
Hence, vapour velocity calculated via:
???? ???? = 0.75 × ???? ????
Therefore:
???? ???? = 0.75(4.34)
= 3.256 ????????/????
= 0.992 ????/????
Vapour volumetric flowrate calculated via:
???? ???? =
????????
× ???? ????
=
.97
× 0.
= 155.46 ????????3
/????
= 4.4 ????3
/????
- 147. 147
Vessel diameter
Applying:
???? ???????? = (
4???? ????
???????? ????
)0.5
Where:
DVD = Vessel diameter (internal), m
D = diameter, m
= (
4(155.46)
????(3.256)
)0.5
= 7.8 ????????
The drum has a mist eliminator, therefore a range between 3-6 inches is added to accommodate a
support ring, therefore:
7.8 + 0.5
= 8.3 ????????
= 2.53 ????
A further increment of 6 inches is implemented, therefore final diameter:
???? = 3.66 ????
Liquid volumetric flowrate calculated via:
???? ???? =
????????
60 × ???? ????
Where:
QL = liquid volumetric flowrate, m3
/s
=
.97
60 × 61.
= 59.23 ????????3
/????????????
= 1.68 ????3
/????????????
- 148. 148
Hold up time
By referring to Table [], feed to column hold up time is therefore 5 mins.
Hold up volume
Applying:
???????? = ???? ???? × ???? ????
Where:
TH = hold up time
VH = hold up volume
QL = liquid volumetric flowrate, m3
/s
Therefore:
= 5 × 59.23
= 296.16 ????????3
= 8.39 ????3
Surge volume
Surge volume can be calculated via:
???????? = ???????? × ???? ????
Where:
Vs = surge volume, m3
Ts = surge time = 3
QL = liquid volumetric flowrate, m3
/s
Therefore:
= 3 × 59.23
= 177.69 ????????3
= 5.032 ????3
- 149. 149
Table [C2]: Liquid hold up and surge times (Svrcek et al., )
Low liquid level height, HLLL
Low liquid level height can be calculated by referring to Table C3[].
Knowing that Vessel diameter = 12 ft Pressure < 300 psia
Therefore:
???????????????? = 6 ????????????ℎ????????
= 0.5 ????????
= 0. ????
Table [C3]: Low liquid level height (Svrcek et al., )
Height between HLLL to HNLL
By applying:
???? ???? =
????????
(
????
4)????????????
2
- 150. 150
Where:
VH = hold up volume, m3
Dvd = vessel diameter, m
Therefore:
???? ???? =
296.16
(
????
4) × (8.3)2
= 5.47 ????????
= 1.667 ????
- 151. 151
Height from HNLL to HHLL
The position of high level column is calculated via:
???????? =
????????
(
????
4) × ???? ????????
2
Where:
HS = height between HNLL to HHLL
VS = surge volume, m3
Dvd = vessel diameter, m
=
177.69
????
4
× 8.32
= 3.28 ????????
= 1 ????
Height from high liquid level to the centre line of inlet nozzle
Applying:
???????????????? = 12 + ???? ????
Where:
dN = inlet nozzle sizing ???? ???? = (
4???? ????
????
60
√???? ????
)0.5
Where, QM is the mixture velocity and it equals to:
???? ???? = ???? ???? + ???? ????
And QL calculated via:
???? ???? =
4 × ????????????????????????????????
???? × (???????????????? ????????????????????????????????)
=
4 × 59.23
???? × 8.3
= 9.086 ????/????
Thus, QM equals to:
= 9.08 + 3.256
= 12.342 ????????3
/????
Thus, ρM is calculated via:
???? ???? = ???? ???? ???? + ???? ????(1 − ????)
- 152. 152
Where, ???? is calculated via:
???? =
???? ????
???? ???? + ???? ????
=
9.08
9.08 + 3.256
= 0.736
Therefore, ρM equals to:
???? ???? = 61.(0.736) × 0.(1 − 0.736)
= 45.28 ????????/????????3
Therefore, dN equals to:
???? ???? = 1. ????????
Thus, HLIN:
???????????????? = 12 + (1.)
= 13. ????????
= 4.062 ????
Mist eliminator height:
Disengagement height from the centreline of inlet nozzle to bottom of the demister pad equals the
external diameter, therefore:
???? ???? = 3.66 ???? = 12 ????????
An assumption of 6 inches is to be made for HME and the height between the mist eliminator and
top tangent line of vessel equals to:
???? ???????? = 1 ???????? = 0. ????
Therefore, total flash drum height:
???? ???? = ???????????????? + ???? ???? + ???????? + ???????????????? + ???? ???? + ???? ???????? + ???? ????????
= 0.5 + 5.47 + 3.28 + 13. + 12 + 0.5 + 1
= 36. ????????
≈ 36 ????????
= 10 ????
- 153. 153
Thickness of cylinder shell:
Applying:
???? =
???????? × ????????
2???? − ????????
+ ????
Where:
t = wall thickness, mm
Di = internal diameter, mm
S = allowable stress, N/mm2
C = corrosion allowance
Pi = internal pressure, bar
Therefore:
=
(1 × )
(2 × 351.39) − 1
+ 4
= 3.60 + 4
= 7.6 ????????
Thickness of Torispherical head
Applying (Sinnott et al., ):
???? =
0.885 × ???????? × ???? ????
(???? × ????) − (0.1 × ????????)
+ ????
Where:
Pi = internal pressure, bar
Rc = crown radius, mm
S = allowable stress, N/mm2
E = weld joint efficiency
Therefore:
=
0.885 × 1 ×
(351.39 × 0.85) − (0.1 × 1)
+ 4
= 11.49 ????????
- 154. 154
Shell mass
Applying:
????ℎ???????????? ???????????????? = ???? × ???????? × ???? ???? × ???? ???? × ????
Where:
Dc = vessel diameter, m
Lc = vessel length, m
tw = wall thickness, m
ρ = metal density, kg/m3
= 9,200 kg/m3
(Alloys and producer, )
Therefore:
= ???? × 3.66 × 10 × 0. × 9,200
= 8,806.718 ????????
Flash Tank cost:
Purchased equipment costs can be evaluated by the equation (Sinnott et al., ):
???????? = ???? + ???????? ????
Where:
Ce = purchased equipment cost, £,
S = characteristic size parameter
a = cost constant
b = cost constant
n = index for that type of equipment
Given data: S = .718 kg
a = - 400 (Sinnott et al., ).
b = 230 (Sinnott et al., ).
n = 0.6 (Sinnott et al., ).
Therefore:
???????? = −400 + 230(.718)0.6
= ???????? $ 53,132.34
- 155. 155
The cost of the flash tank is based on a U.S Gulf Coast Basis and has to be changed to a
UK basis using cost indexes and location factors (Sinnott et al., ). Although a cost index
for was not available, the cost index for will be taken as an estimate instead.
???????????????? ???????? ???????????????? ???? = ???????????????? ???????? ???????????????? ???? ×
???????????????? ???????????????????? ???????? ???????????????? ????
???????????????? ???????????????????? ???????? ???????????????? ????
Where:
Cost index in year A () = 567.3 (Chemical Engineering, )
Cost index in year B () = 499.6 (Chemical Engineering, )
Therefore, the total cost of the storage tank is:
???????????????? ???????? ???????????????? ???? = 53,132.34 ×
567.3
499.6
= ???????? $ 60,332.20
≈ ???????? $ 60,400
Applying location factors (Sinnott et al., ):
???????????????? ???????? ???????????????????? ???????? ???????????????????????????????? ???? = ???????????????? ???????? ???????????????????? ???????? ????. ???? ???????????????? ???????????????????? ???????????????????? × ????????????
Where:
LFA (United Kingdom) = 1.02 (Sinnott et al., )
Therefore, total cost of the storage tank is:
???????????????? ???????? ???????????????????? ???????? ???????????????????????????????? ???? = 60,400 × 1.02
= ???????? $ 61,608
The unit operation’s cost estimate is based on a carbon steel manufacturing material. The material
factor for a carbon steel is 1. Therefore, this value must be related to the material factor for Hastelloy
in order to adapt it.
???????????????????????????????? ???????????????????????? (????????????????????????????????????) = 1.55
Therefore, cost of unit in Hastelloy:
???????????????? = ???????? $ 61,608 × 1.55
= $95,492.4
Unit of currency has to be changed, from dollars (USD) to pounds (GBP). The exchange rate, as of
May , is 1. USD per 1 GBP, therefore total cost of the storage tank on a UK basis is
(HM Revenue & Customs, ):
???????????????? ???????? (£) =
???????????????? ???????? ($)
1.
= £66,300
- 156. 156
APPENDIX [D] – Calculations for Drying Distillation Column
Data from simulation
F = .17 kmol/hr XB = 0.385 mol%
ZF = 0.01 mol% D = 526.73 kmol/hr
XD = 0.99 mol% B = 978.214 kmol/hr
Reflux ratio
Applying :
???????????????????????????????????????? =
???? ????
???? + 1
Therefore :
???????????????????????????????????????? = 0.071
Figure [D1]: Vapour mole fraction against Liquid mole fraction graph.
y-x diagram for ACETI-01/WATER
Liquid molefraction, WATER
Vapormolefraction,WATER
0.000 0.025 0.050 0.075 0.100 0.125 0.150 0.175 0.200 0.225 0.250 0.275 0.300 0.325 0.350 0.375 0.400 0.425 0.450 0.475 0.500 0.525 0.550 0.575 0.600 0.625 0.650 0.675 0.700 0.725 0.750 0.775 0.800 0.825 0.850 0.875 0.900 0.925 0.950 0.975 1.000
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
1.0 bar
- 157. 157
Using the information provided, Figure [] was able to be constructed, thus allowed to determine the
following:
???? ???????????? =
???? ????
????????????????????????????????????????
− 1
=
0.99
0.75
− 1
= 0.32
Reflux ratio can be calculated via:
???? ???????????????????????? = ???? ???????????? × 1.2
Therefore:
???? ???????????????????????? = 0.32 × 1.2
= 0.384
Figure [D2]: McCabe – Thiele Representation for stages determination.
- 158. 158
Number of stages in column
Data for determination of number of stages inside column was extracted from the Figure [] and
constructed using the McCabe – Thiele Graphical Method.
Thus, number of stages:
???????????????????????? ???????? ???????????????????????? = 17 + 1 (????????????????????????????????)
Actual number of trays
Applying:
???????????????????????????? =
????????ℎ????????????????
????
Where:
ε = 0.5 (Douglas, )
Therefore, Nactual:
???????????????????????????? =
????????ℎ????????????????
????
=
17
0.5
= 34
Height of tower
Assuming a tray spacing of 0.7 m for a drying column, the following approximation was taken
(Douglas, ):
???????????????????????? = 2.3 × ????????????????????????????
Therefore:
???????????????????????? = 2.3 × 34
= 78.2 ????????
≈ 23.85 ????
- 159. 159
Vapour velocity
Due to a 20% overdesign in the design specification and applying the equation for vapour velocity
equals to:
???? ???? = ????(
???? ????− ???? ????
???? ????
)0.5
Where:
UV = vapour velocity, m/s
ρL = liquid density, kg/m3
ρV = vapour density, kg/m3
K = entrainment factor
Where, entrainment factor:
???? = 0.171????2
+ 0.27???? − 0.047
Where, T equals to:
???? = 0.701
Therefore, K equals to:
???? = 209.67
Substituting back into vapour velocity equation:
???? ???? = 209.67(
945.3 − 4.4
4.4
)0.5
Therefore:
???? ???? = .07 ????/????
Diameter of column
Applying:
???? ???????????? = (
4????
???? × ???? ???? × ???? ????
)0.5
Therefore:
???? ???????????? = 1.8 ????
- 160. 160
Taking into consideration safety from flow, diameter is increased by 5%, thus:
???? = 1.05 × 1.8
= 1.85 ????
Economic pipe diameter
To develop a pipe diameter, capital cost and flow rate were factors of consideration, due to the
impact of economic diameter on reducing annualised cost. A rule of thumb for the economic pipe
diameter is used (Genereaux, ):
????????, ???????????????????????????? = (
????
????
)0.5
Where:
G = mass flowrate, kg/s = 24.953
ρ = density, kg/m3
= 6.4
And taking into consideration, 20% overdesign, this leads to:
????????, ???????????????? ???????????????? = 216 ????????
????, ???????????????????????? ???????????????? = 178 ????????
????, ???????????????????????? ???????????????????????????? ???????????????? = 148 ????????
Design specification calculations
Thickness of shell
Applying:
???? ???? =
???????? ????????
2???? − ????????
Where:
P = Internal Design Pressure = Operating pressure + 10% allowance = 1.1 bar
D = Internal Diameter of tower = 1.85 m
S = Allowable stress of stainless steel at 125 o
C = 103.42 N/mm2
Therefore:
???? ???? = 9.89 ????????
Applying a corrosion allowance of 2 mm, thickness of shell is:
9.89 + 2
= 11.89 ????????
≈ 12 ????????
- 161. 161
Thickness of flat plate
Applying (Sinnott et al., ):
???????? = ????√
????????
????
Where:
S = maximum allowable stress = 515 N/mm2
(Shanghai STAL Precision Stainless Steel Co. Ltd ( STAL ), )
D = effective plate diameter
C = constant which depends upon edge support = 0.185
Therefore, TP:
???????? = 0.035 ????
Column End Selection
Torispherical head is selected due to the low pressure in the distillation chamber, therefore applying:
???? ???? =
0.885???????? ???? ????
???? − 0.1????????
Where:
RC = Crown radius = Di
Therefore:
???? ???? = 17.43????????
Applying a corrosion allowance of 2mm:
???? ???? = 2 + 17.43
= 19.43 ????????
= 20 ????????
Calculation of stresses
Axial stress due to pressure
???????????? =
???????? ????????
4(???? ???? − ????. ????)
= 50.875 ????/????????2
- 162. 162
Stress due to the dead-weight of vessel
Applying:
???????? = ???? ???? × ???? × ???? × ???? ???? × {????[???? ???? + (0.8???? ????)(???? ???? × 10−3)]}
Where:
Ws = dead-weight of vessel
Cw = 1.15
Dm = 1.85 m
Hv = 23.85 m
Therefore:
???????? = .81 ????
≈ 122 ????????
Weight of plates
???? ???? =
????
4
× 1.852
= 2.69 ????2
Weight of plate equals to 1.2 N, therefore:
???????? = 34 × 1.2 × 2.69
= 109.75 ????????
Weight of insulation
Knowing the following data, weight of insulation can be calculated:
Mineral wool density = 130 kg/m3
Volume of insulation = 23.6 m3
Therefore:
???????? = 23.6 × 130 × 9.81
= .1 ????
≈ 30.1 ????????
Weight of vessel
???????? = 109.75 + 122 + 30.1
= 237.3 ????????
This is an approximation based on an empty vessel, weight will vary based on other factors, such as
flooding of the column.
- 163. 163
Wind loading
The following calculations are made on the assumption that maximum wind speed is 100 mph, thus:
???????????????????????????????? ???????????????????????????????? = ???????????? = ???????? × ???? ????
= 1.85 + [2 × (12 × 10−3)]
= 1.874 ????
Therefore, loading (per linear diameter):
???? ???? = × 1.874
= .92 ????/????
Thus:
σ???? =
????????
????(???????? + ????)????
= 31.94 ????/????????2
Hence bending moment at tangent line:
???? ???? = .3 ????/????????2
Primary stresses
The longitudinal and circumferential stresses due to pressure are:
σℎ =
????????????
2????
= 84.8 ????/????????2
σ???? =
????????????
4????
= 48.4 ????/????????2
Drying Column cost
All cost estimates formulas have been sourced from (Douglas, ).
Capital cost
Applying:
???????? = (
????&????
280
) × 120???? ???? × ????0.8
× (218 + ????????)
Where:
M&S = Marshall – Shift index for UK =
Cc = Cost of shell and trays
- 164. 164
Fc = Design considerations for the column = 1.6 (approximation made based on column pressure
being 1atm) (Modla and Lang, )
DT = Diameter of column = 1.85 m
H = Height of column = 23.85 m
Therefore:
???????? = £363,770.90
Cost of Reboiler
Applying:
???????? = (
????&????
280
) × 328 × (
???????? ????
)
0.65
× ????0.65
Where:
Cr = Cost of reboiler
△Hv = Heat of vaporization of bottoms = 451.37 kJ/mol
V = Rate of Boil-Up =
???? ????
△???? ????
= 0.882 kJ/Kmol (Litpak, )
Therefore, Cr equals to:
???????? = £22,053.50
We have to assume that cooling water is available at 90 o
F and a heat transfer coefficient of 100,
the heat transfer area of the condenser heat exchanger is:
???? ???? = (
△ ???? ????
× ln (
???????? − 90
???????? − 125
) × ????
Where:
Tb = 125 o
C at 1 atm = 257 o
F
△HV = 451.37 kJ/mol
Therefore:
???? ???? = .81 ????2
- 165. 165
APPENDIX [E] – Calculations for Heavy – Ends Distillation Column
Conversions
o
F → o
C o
C = 5/9(o
F -32) (Perry, , p1-5)
lb/ft3
→ kg/m3
kg/m3
= (1/16.) lb/ft3
(Perry, , p1-6)
ft → m m = (1/0.) ft (Perry, , p1-6)
ksi → psi ksi = psi (Sinnott et al., , p982)
psi → N/mm2
psi = 0. N/mm2
(Perry, , p1-4)
Propionic acid density at 125 o
C (398K)
Temperature (oF) Density (lb/ft3) Temperature (oC) Density (kg/m3)
35 63.56 1.67 .13
40 63.37 4.44 .09
45 63.17 7.22 .89
50 62.98 10.00 .84
55 62.79 12.78 .80
60 62.6 15.56 .76
65 62.41 18.33 999.71
70 62.22 21.11 996.67
75 62.03 23.89 993.63
80 61.84 26.67 990.58
85 61.65 29.44 987.54
90 61.46 32.22 984.49
95 61.27 35.00 981.45
100 61.08 37.78 978.41
105 60.89 40.56 975.36
110 60.7 43.33 972.32
115 60.5 46.11 969.12
120 60.31 48.89 966.07
125 60.12 51.67 963.03
130 59.93 54.44 959.99
135 59.74 57.22 956.94
140 59.55 60.00 953.90
Table [E1]: Respective propionic acid densities at different temperatures (CAMEO Chemicals, ).
y = -1.x + .9
950.00
960.00
970.00
980.00
990.00
.00
.00
.00
.00
0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00
Density(kg/m3)
Temperature (C)
Density v Temperature (Propionic acid)
- 166. 166
Under the assumption that the relationship described by the graph between the density of propionic
acid and temperature stays constant, the density can be calculated at higher temperatures using the
equation of the trend line. The liquid density of propionic acid is required in later calculations.
For example at 125 o
C the density of propionic acid is equal to 882.39 kg/m3
.
882.39 = −1. × 125 + .9
Acetic acid vapour density at 125 o
C (398K)
The ideal gas law is used to calculate an estimation for the vapour density of acetic acid at 125 o
C
(398K) thus (Perry, , p2-355):
ρ = ????
???? ???????????????????????????????? ????⁄
Where:
ρ = density, kg/m3
P = pressure, Pa
Rspecific = specific gas constant, kJ/kgK
T = temperature, K
And specific gas constant given by:
???? ???????????????????????????????? = ????
????⁄
Where:
R = ideal gas constant = .39 kJ/kmolK (Perry, , p1-22)
M = molecular mass = 60.05 kg/kmol (Perry, , p2-28)
The specific gas constant for acetic acid is equal to:
.39
60.05
= 138.46 ????????/????????????
Therefore, at 125 o
C the vapour density of acetic acid is equal to:
138.46 × 398
= 1.84 ????????/????3
- 167. 167
Acetic acid vapour pressure at 125 o
C (398K)
Vapour pressure to be calculated via (Sinnott et al., , p451):
???? = ???? ????− ????
????+????⁄
Where, for acetic acid:
A = 7. (Dean, , p539)
B = .313 (Dean, , p539)
C = 222.309 (Dean, , p539)
T = 398
Therefore, at 125 o
C (398K) the vapour pressure of acetic acid is equal to:
????7.−(.313
222.309+398⁄ )
= 136.45 ????????????
Propionic acid vapour pressure at 125 o
C (398K)
The vapour pressure of propionic acid at 124.94 o
C ≈ 125 o
C is equal to 59.86 kPa (Clifford et al.,
)
Relative volatility
Relative volatility can be calculated via (Branan, , p450):
???????????????????????? ???????????????? ???????????????????????? ????????????????????????????????
???????????????????????????????????? ???????????????? ???????????????????????? ????????????????????????????????⁄ = ???? ????????????????????????/????????????????????????????????????
Therefore, the relative volatility, ???? ????????????????????????/???????????????????????????????????? is equal to:
136.45
59.86
= 2.28
Reflux ratio
The reflux ratio is taken as 17, obtained via the simulation created in Aspen Plus.
Number of column stages
The number of stages required in the column to obtain the desired distillation was calculated using
the Smoker equations (Sinnott et al., , p661-662). This was chosen as the boiling points of acetic
acid and propionic acid are relatively close and the relative volatility calculated is relatively low.
1. Rectifying section
Applying (Sinnott et al., , p662):
????
???? + 1⁄ = ????
Where:
R = Reflux ratio = 17
- 168. 168
Therefore:
???? = 17
17 + 1⁄
= 0.
Applying (Sinnott et al., , p662):
???? ????
???? + 1⁄ = ????
Where:
???? ???? = fraction of acetic acid in distillate stream = 0. ≈ 1 (From simulation)
Therefore:
???? = 1
17 + 1⁄
= 0.
Applying (Sinnott et al., , p662):
????(???? − 1)????2
+ [???? + ???? (???? − 1) − ????]???? + ???? = 0
Therefore:
0.(2. − 1)????2
+ [0. + 0.(2. − 1) − 2.]???? + 0. = 0
Using the quadratic formula to solve for k:
???? =
−???? ± √????2 − 4????????
2????
(0 < ???? < 1)
Where:
a = 0.(2. – 1) = 1.
b = [0. + 0.(2. -1) – 2.] = -1.264
c = 0.
Therefore:
???? = 0.046 (0 < ???? < 1)
Applying (Sinnott et al., , p662):
????0
∗
= ???? ???? − ????
????0
∗
= 1 − 0.046
= 0.954
Applying (Sinnott et al., , p662):
???? ????
∗
= ???????? − ????
Where:
???????? = fraction of acetic acid in column feed = 0. (From simulation)
- 169. 169
Therefore:
???? ????
∗
= 0. − 0.046
= 0.
Applying (Sinnott et al., , p662):
???? = 1 + (???? − 1)????
Therefore:
???? = 1 + (2. − 1)0.046
= 1.
Applying (Sinnott et al., , p662):
???? =
????????(???? − 1)
???? − ????????2⁄
Therefore:
???? =
0. ∗ 1.(2. − 1)
2. − 0. ∗ 1.⁄
= 1.
Thus, number of stages is calculated via (Sinnott et al., , p662):
???? =
log [
????0
∗
(1 − ???????? ????
∗
)
???? ????
∗
(1 − ????????0
∗
)⁄ ]
???????????? ( ????
????????2⁄ )
Therefore:
???? =
log [
0.954(1 − 1. ∗ 0.)
0.(1 − 1. ∗ 0.954)⁄ ]
???????????? (2.
0. ∗ 1.⁄ )
= 14.329
???? ≈ 15 ????????????????????????
- 170. 170
2. Stripping section
Applying (Sinnott et al., , p662):
???? =
???? ∗ ???????? + ???? ???? − (???? + 1)???? ????
(???? + 1)(???????? − ???? ????)⁄
Where:
???? ???? = fraction of acetic acid in bottom stream = 0. (From simulation)
Therefore:
???? = 17 ∗ 0. + 1 − (17 + 1)0.
(17 + 1)(0. − 0.)⁄
= 1.
Applying (Sinnott et al., , p662):
???? =
(???????? − ???? ????)???? ????
(???? + 1)(???????? − ???? ????)⁄
Therefore:
???? =
(0. − 1)0.
(17 + 1)(0. − 0.)
⁄
= −0.
Applying (Sinnott et al., , p662):
????(???? − 1)????2
+ [???? + ???? (???? − 1) − ????]???? + ???? = 0
Therefore:
1.(2. − 1)????2
+ [1. − 0.(2. − 1) − 2.]???? − 0. = 0
Using the quadratic formula to solve for k:
???? =
−???? ± √????2 − 4????????
2????
(0 < ???? < 1)
Where:
a = 1.(2. – 1) = 1.
b = [1. + 0.(2. – 1) – 2.] = -1.279
c = -0.
Therefore:
???? = 0. (0 < ???? < 1)
Applying (Sinnott et al., , p662):
????0
∗
= ???????? − ????
- 171. 171
Therefore:
????0
∗
= 0. − 0.
= −0.006
Applying (Sinnott et al., , p662):
???? ????
∗
= ???? ???? − ????
Therefore:
???? ????
∗
= 0. − 0.
= −0.674
Applying (Sinnott et al., , p662):
???? = 1 + (???? − 1)????
Therefore:
???? = 1 + (2. − 1)0.
= 2.
Applying (Sinnott et al., , p662):
???? =
????????(???? − 1)
???? − ????????2⁄
Therefore:
???? =
1. ∗ 2.(2. − 1)
2. − 1. ∗ 2.⁄
= −1.001
Thus, number of stages is calculated via (Sinnott et al., , p662):
???? =
log [
????0
∗
(1 − ???????? ????
∗
)
???? ????
∗
(1 − ????????0
∗
)⁄ ]
???????????? ( ????
????????2⁄ )
Therefore:
???? =
log [
−0.006(1 − (−1.001 ∗ −0.674))
−0.674(1 − (−1.001 ∗ −0.006))⁄ ]
???????????? (2.
1. ∗ 2.⁄ )
= 7.
???? ≈ 8 ????????????????????????
- 172. 172
Total number of stages = 15 + 8 = 23 stages
It is also recommended that an extra 10% be added to the total number of stages in addition to
accounting for plate efficiency (Branan, ). Therefore, the ideal number of stages for this distillation
column without the consideration of plate efficiency is:
23 + (0.1 × 23)
= 25.3
≈ 26 ????????????????????????
Plate efficiency
For preliminary designs, a plate efficiency of 70% can be assumed (Sinnott et al., , p700).
Introducing the plate efficiency to the number of ideal stages gives an actual number of:
25.3 / 0.7
= 36.1
≈ 37 ????????????????????????
Column diameter
The equations used to calculate the column diameter rely on the densities of the liquid and vapour
streams as previously calculated as well as plate spacing. An initial estimate of the plate spacing will
be taken as 0.5m (Sinnott et al., , p 709). Therefore:
???? ????̂ = (−0.171???? ????
2
+ 0.27???? ???? − 0.047) ∗ [
???????? − ???? ????
???? ????
⁄ ]
1/2
Where:
uv = maximum allowable vapour velocity, m/s
lt = plate spacing, m = 0.5 m
Therefore:
???? ????̂ = (−0.171 ∗ 0.52
+ 0.27 ∗ 0.5 − 0.047) ∗ [882.39 − 1.84
1.84⁄ ]
1
2
= 2.86 ????/????
Applying (Sinnott et al., , p 709):
???????? = √4 ????????
̂
???????? ???? ???? ????̂
⁄
Where:
Dc = column diameter, m
Vw = maximum vapour rate, kg/s =
⁄ = 13.89 kg/s
- 173. 173
Therefore, column diameter is:
???????? = √4 ∗ 13.89
???? ∗ 1.84 ∗ 2.86⁄
= 1.83 ????
Column height
For columns of diameter greater than 1m, a plate spacing of between 0.3 and 0.6m is suggested
(Sinnott et al., , p709). As the previous calculations show, the column diameter is greater than
1m therefore, the initial estimate of 0.5m plate spacing will be used.
In addition to the height due to the plate spacing, it is also suggested that an additional 4ft should be
added to the top of the tower to accommodate for the condenser, as well as 6ft being added to the
bottom of the column to accommodate for the reboiler (Branan, , p444).
Taking all of this into consideration, the height of the column is equal to:
4 ???????? = 4 ∗ 0. = 1.219 ????
6 ???????? = 6 ∗ 0. = 1.829 ????
Therefore:
(37 ∗ 0.5) + 1.219 + 1.829
= 21.55
≈ 21.6 ????
Material of construction
The material of construction will be a grade of stainless steel as opposed to carbon steel, as stainless
steel has a corrosion resistance where as carbon steel does not. This is important as the materials
flowing through the column have a corrosive nature. The grade of stainless steel chosen is 304 as the
advantages other grades of steel have over 304 are not proportional to the increase in cost associated
with them.
Column wall thickness
It is suggested that for a column of diameter of between 1 and 2m, the minimum practical wall thickness
for a vessel to withstand its own weight, including a corrosion allowance of 2mm, is 7mm. Although
the minimum wall thickness can be calculated (Sinnott et al., , p986):
???? =
???????? ????????
2 ∗ ???? − ????????
⁄
Where:
t = wall thickness, mm
Pi = internal pressure, bar
Di = internal diameter, mm
S = maximum allowable stress, N/mm2
- 174. 174
As an estimate S for 304 stainless steel at 125 o
C (398K), the maximum allowable stress at 148.89 o
C
(300 o
F) will be taken as this is known data. S for 304 stainless steel at 148.89 o
C (300 o
F) is equal to
103.42 N/mm2
(Sinnott et al., , p982).
????304−???????????????????????????????????? ???????????????????? at 300 oF (148.89 oC) = 15.0 ????????????
× 0. × 15.0
= 15.0 ????????????
= 103.42 ????/????????2
Therefore, including a corrosion allowance of 2 mm, the column thickness is equal to:
???? = 1. ∗ 1.83 ∗ 103
2 ∗ 103.42 − 1.⁄
= 9. + 2
= 11. ????????
≈ 12 ????????
Column end selection and thickness
The type of end selected for this column is torispherical shaped, as this is the most commonly used
end closure for a pressure vessel operating up to pressures of 15 bar (Sinnott et al., , p987). The
advantages of other available shaped column ends do not give a significant enough advantage to
justify the added cost.
The thickness of torispherical ends differs from the thickness of the shell, therefore this also has to be
calculated via (Sinnott et al., , p990):
???? =
0.885 × ???????? ???? ????
???? − 0.1 × ????????
⁄
Where:
Rc = crown radius = Di
Therefore, the torispherical end thickness, including a corrosion allowance of 2 mm, is equal to:
???? = 0.885 ∗ 1. × 1.83 × 103
103.42 − 0.1 × 1.⁄
= 15.912 + 2
= 17.912
- 175. 175
Feed location
To calculate the location of the feed, the original ratio of rectifying stages and stripping stages will be
applied to the final number of stages calculated as the feed will be located between the rectifying
and stripping stages.
Original ratio of rectifying stages to total original stages is:
15
(15 + 8)⁄
= 0.65
Applying this ratio to the final number of stages calculated gives a feed location of:
0.65 × 37
= 24.13
Therefore, the feed to the column will be approximately located at the 24th
stage.
Pipe sizing
To calculate the pipe diameter, the mass flowrate, density and the velocity of the fluid flowing
through the pipe has to be known. The mass flowrates will be taken from the simulation produced as
part of this project, while the densities and velocities will be calculated.
The following equation will be used to calculate the average stream density:
???? = ∑(???????? × ????????)
The stream velocity used in the following calculations will be obtained via linear interpolation of the
values for the optimum velocity in terms of fluid density (Sinnott et al., , p266).
Fluid Density [kg/m3
] Velocity [m/s]
2.4
800 3.0
160 4.9
16 9.4
0.16 18.0
0.016 34.0
Inlet pipe
The mass flow rate into the column will be calculated by multiplying the molar flowrate, taken from
the simulation, by the molecular mass of the compound. The streams conditions are as shown by
the PFD, 117.69 o
C, 1 bar.
- 176. 176
Acetic acid MOLAR flowrate = 893.86 ????????????????/ℎ????
Acetic acid MASS flowrate = 893.86 × 60 = .48 ????????/ℎ????
Propionic acid MOLAR flowrate = 5.93 ????????????????/ℎ????
Propionic acid MASS flowrate = 5.93 × 74 = 438.76 ????????/ℎ????
Acetic acid mass fraction =
.48
.48+438.76
= 0.992
Propionic acid mass fraction =
438.76
.48+438.76
= 0.008
???? ???????????????????????? = 935.646 ????????/????3
(DDBST GmbH, )
???? ???????????????????????????????????? = 890.429 ????????/????3
(Calculated from the relationship previously derived)
Therefore:
???? = (935.646 × 0.992) + (890.429 × 0.008)
= 935.279 ???????? ????3⁄
Therefore, inlet flow velocity:
???????????????????? ???????????????? ???????????????????????????????? = 3.0 + (2.4 − 3.0) ×
935.279 − 800
− 800
= 2.90 ????/????
Therefore, mass flowrate:
???????????????? ???????????????????????????????? = .48 + 438.76 = .24 =
.24
= 15.02 ????????/????
Therefore, volumetric flowrate:
???????????????????????????????????????? ???????????????????????????????? =
???????????????? ????????????????????????????????
????????????????????????????
=
15.02
935.279
= 0.016 ????3
/????
- 177. 177
Therefore, pipe cross-sectional area:
???????????????? ???????????????????? ???????????????????????????????????? ???????????????? =
???????????????????????????????????????? ????????????????????????????????
????????????????????????????????
=
0.016
2.90
= 0. ????2
Therefore, pipe diameter:
???????????????? ???????????????????????????????? = √0. × (4
????⁄ )
= 0.084 ????
A pipe diameter of 0.084 m corresponds to a nominal pipe diameter of 4 inches with an allowance
for future expansion taken into consideration.
Bottom product type
Similarly to the inlet pipe, the mass flow rate into the column will be calculated by multiplying the
molar flowrate, taken from the simulation, by the molecular mass of the compound. The streams
conditions are as shown by the PFD, 131.41 o
C, 1 bar.
Acetic acid MOLAR flowrate = 3.07 ????????????????/ℎ????
Acetic acid MASS flowrate = 3.07 × 60 = 184.17 ????????/ℎ????
Propionic acid MOLAR flowrate = 5.93 ????????????????/ℎ????
Propionic acid MASS flowrate = 5.93 × 74 = 438.76 ????????/ℎ????
Acetic acid mass fraction =
184.17
184.17+438.76
= 0.296
Propionic acid mass fraction =
438.76
438.76+184.17
= 0.704
???? ???????????????????????? = 917.954 ????????/????3
(DDBST GmbH, )
???? ???????????????????????????????????? = 875.334 ????????/????3
(Calculated from the relationship previously derived)
Therefore:
???? = (917.945 × 0.296) + (875.334 × 0.704)
= 887.934 ????????/????3
- 178. 178
Therefore, outlet flow velocity:
???????????????????????? ???????????????? ???????????????????????????????? = 3.0 + (2.4 − 3.0) ×
887.934 − 800
− 800
= 2.93 ????/????
Therefore, mass flowrate:
???????????????? ???????????????????????????????? = 184.17 + 438.76 = 622.92 =
622.92
= 0.17 ????????/????
Therefore, volumetric flowrate:
???????????????????????????????????????? ???????????????????????????????? =
???????????????? ????????????????????????????????
????????????????????????????
=
0.17
887.934
= 0. ????3
/????
Therefore, pipe cross-sectional area:
???????????????? ???????????????????? ???????????????????????????????????? ???????????????? =
???????????????????????????????????????? ????????????????????????????????
????????????????????????????????
=
0.
2.93
= 0. ????2
Therefore, pipe diameter:
???????????????? ???????????????????????????????? = √0. × (4
????⁄ )
A pipe diameter of 0. m corresponds to a nominal pipe diameter of 3/4 inches with an allowance
for future expansion taken into consideration.
- 179. 179
Top product type
As this stream is virtually 100% acetic acid, the flowrate and the density will consist of the values
true to acetic acid under the stream conditions. The streams conditions are as shown by the PFD,
117.58 o
C, 1 bar. As the vapour density of acetic acid has already been calculated, it will be
assumed that this is the density of acetic acid in the stream, therefore:
???? ???????????????????????? = 1.84 ???????? ????3⁄
Acetic acid MOLAR flowrate = 890.789 ????????????????/ℎ????
Acetic acid MASS flowrate = 890.789 × 60 = .34 ????????/ℎ????
Top product flow velocity:
???????????? ???????????????????????????? ???????????????? ???????????????????????????????? = 18.0 + (9.4 − 18.0) ×
1.84 − 0.16
16 − 0.16
= 17.09 ????/????
Therefore, mass flowrate:
???????????????? ???????????????????????????????? = .34 =
.34
= 14.85 ???????? ????⁄
Therefore, volumetric flowrate:
???????????????????????????????????????? ???????????????????????????????? =
???????????????? ????????????????????????????????
????????????????????????????
=
14.85
1.84
= 8.07 ????3
/????
Therefore, pipe cross-sectional area:
???????????????? ???????????????????? − ???????????????????????????????????? ???????????????? =
???????????????????????????????????????? ????????????????????????????????
????????????????????????????????
=
8.07
17.09
= 0.472 ????2
Therefore, pipe diameter:
???????????????? ???????????????????????????????? = √0.472 × (4
????⁄ )
= 0.78 ????
A pipe diameter of 0.78 m corresponds to a nominal pipe diameter of 36 inches with an allowance
for future expansion taken into consideration.
- 180. 180
Column mass and cost
Shell mass calculated via (Sinnott et al., , p322):
????ℎ???????????? ???????????????? = ???? × ???????? × ???? ???? × ???? × ????
Where:
lc= column length, m
ρ304 = kg/m3
(Sinnott et al., , p322)
Therefore:
????ℎ???????????? ???????????????? = ???? × 1.83 × 21.6 ∗ 12 × 10−3
×
= .6 ????????
Column cost
1.0 Shell cost
Applying (Sinnott et al., , p319):
???? + ???????? ????
Where:
a304 = - (Sinnott et al., , p319)
b304 = 600 (Sinnott et al., , p320)
n304 = 0.6 (Sinnott et al., , p320)
S = shell mass, kg (90 < shell mass < ) (Sinnott et al., , p320)
Therefore:
???????????????? ???????????? ???????? ????ℎ???????????? = − + 600 × (.60.6)
= $157,416
2.0 Trays cost
Applying (Sinnott et al., , p319):
???? + ???????? ????
Where:
avalve = 130 (Sinnott et al., , p319)
bvalve = 146 (Sinnott et al., , p320)
nvalve = 2.0 (Sinnott et al., , p320)
S = diameter, m (0.5 < diameter < 5.0) (Sinnott et al., , p320)
- 181. 181
Therefore:
???????????????? ???????????? ???????? ???? ???????????????????????? ???????????????? = 130 + 146 × (0.52.0)
= $619
???????????????? ???????????? ???????? 37 ???????????????????? = 619 × 37
= $22,901
Therefore, the total capital cost due to the column according to an U.S Gulf Coast, basis is:
$22,901 + $157,416
= $180,317
The cost of the column is based on a U.S. Gulf Coast basis and has to be changed to a
UK basis using cost indexes and location factors. Although a cost index for was not available,
the cost index for will be taken as an estimate instead, therefore (Sinnott et al., , p324):
???????????????? ???????? ???????????????? ???? = ???????????????? ???????? ???????????????? ???? ×
???????????????? ???????????????????? ???????? ???????????????? ????
???????????????? ???????????????????? ???????? ???????????????? ????
Where:
Cost index in year A = 567.3 (Chemical Engineering, )
Cost index in year B = 499.6 (Chemical Engineering, )
Therefore, total cost of the column on an U.S Gulf Coast, basis is:
???????????????? ???????? ???????????????? ???? = ×
567.3
499.6
= $204,752
Applying location factor (Sinnott et al., , p327):
???????????????? ???????? ???????????????????? ???????? ???????????????????????????????? ???? = ???????????????? ???????? ???????????????????? ???????? ???????????????? × ????????????
Where:
LFA (United Kingdom) = 1.02
Therefore, total cost of the column on an U.S Gulf Coast, basis is:
???????????????? ???????? ???????????????????? ???????? ???????????????????????????????? ???? = × 1.02
= $208,847
Currency conversion
The unit of currency also has to be changed, from dollars (USD) to pounds (GBP). The exchange
rate, as of May , is 1. USD per 1 GBP (HM Revenue & Customs, ).
Therefore, total cost of the column on a UK basis is:
1.⁄
= £145,002
- 182. 182
APPENDIX [F] – Calculations for Absorption Column
Vessel thickness
Applying:
???? =
???????? × ????????
2???????? − ????????
+ ????
Where:
Pi = internal pressure
Di = internal diameter
S = maximum allowable stress on vessel
E = welding efficiency
c =corrosion allowance (4 mm)
Therefore substituting in equation:
???? = 0.45 + 4
= 4.45 ????????
≈ 5 ????????
Literature suggest that an absorption column should have a minimum thickness of 5 mm with a 2
mm corrosion allowance. This means that the design vessel should have a thickness of 7 mm with
a 4 mm corrosion allowance.
Hemispherical head thickness
Applying:
???? ???????????????? =
???????? × ????????
4 × ???? × ???? − 0.4 × ????????
+ ????
Where:
Pi = internal pressure
Di = internal diameter
S = maximum allowable stress on vessel
E = welding efficiency
c =corrosion allowance (4 mm)
Therefore substituting in equation:
0.25 + 4
= 4.25 ????????
≈ 5 ????????
- 183. 183
Hemispherical head was chosen for this unit since it has a tougher shape and capable of resisting
twice the pressure of a tori-spherical head while having the same thickness. Although, they are more
expensive, they resist better under higher pressure.
Diameter of column
Applying:
????
????
√
???? ????
???? ????
Where:
L = liquid mass flowrate = 0.5 kg/s
G = gas mass flowrate = 0.45 kg/s
qG = density of gas = 1.1 kg/m3
qL = density of solvent = kg/m3
Equalling to:
= 0.035 ????
Therefore percentage of flooding by referring to Figure 11.44, the table gave a value for the
abscissa of (Sinnott et al., ):
????4.1 = 1.7
And at flooding (Sinnott et al., ):
????4.2 = 5
Therefore applying:
???????????????????????????????????????? ???????? ???????????????????????????????? = √????4.1/????4.2 × 100
Substituting in equation:
???????????????????????????????????????? ???????? ???????????????????????????????? = 58%
The value agrees within the range of 50 – 90% thus plausible (Sinnott et al., )
Therefore applying gas flowrate per unit cross-sectional area:
???? ???? = √
????4 × ???? ???? × (???? ???? − ???? ????)
13.1 × ???? ???? × (
???? ????
???? ????
)0.1
- 184. 184
Where:
k4 = constant
qG = density of gas = 1.1 kg/m3
qL = density of solvent = kg/m3
FP = packing factor = 300 m-1
µL = viscosity of solvent = 1.12 cp
Therefore substituting into equation:
???? ???? = 1.6 ????????/????2
????
Therefore column area:
???? = ????/???? ????
= 0.3 ????2
Therefore diameter is calculated via:
???????????????????????????????? = √
4 × ????
????
= 0.6 ????
Flat-end
Applying:
???? = ???????? × √
???? × ????????
???? × ????
Where:
C = design constant
D = nominal plate diameter
S = maximum stress allowed
E = joint efficiency
Therefore substituting into equation:
???? = 9.5 ????????
- 185. 185
Height of tower:
Applying:
2..0
2
21.075.0
45.1exp1
a
L
g
aL
a
L
a
a
LL
w
L
w
L
w
l
cw
Where:
a = surface area per unit packing = 253 m2
/m3
σG = critical surface tension for particular packing material = 61 × 10-3
N/m
σL = liquid surface tension = 27.1 × 10-3
N/m
µL = viscosity of solvent = 1.12 cp
ρL = density of solvent = kg/m3
Substituting into equation:
???? ???? = 80.34 ????2
/????3
Therefore, applying liquid film mass transfer coefficient equation:
4.0
2
1
3
2
3
1
.0 p
LL
L
Lw
w
L
L ad
Da
L
g
K L
Where:
dp = packing size = 25 × 10-3
m
DL = 1.6 × 10-9
m2
/s
µL = viscosity of solvent = 1.12 cp
g = gravitational acceleration = 9.81 m.s-2
ρL = density of solvent = kg/m3
a = surface area per unit packing = 253 m2
/m3
Substituting into equation:
???????? = 1.3 × 10−4
????/????
- 186. 186
Therefore applying gas film mass transfer coefficient equation:
2
3
1
7.0
5
p
gg
g
g
w
g
gG
ad
Da
V
K
aD
RTK
Where:
DG = 1.8 × 10-5
m2
/s
k5 = 5.23
µG = viscosity of gas mixture = 0.10 cp
ρG = density of gas = 1.1 kg/m3
a = surface area per unit packing = 253 m2
/m3
dp = packing size = 25 × 10-3
m
Tg = temperature of inlet gas = 323 K
Therefore substituting into equation:
???? ???? = 6.82 × 10−4
????????????????/????2
????
Hence gas film transfer unit height gas:
???? ???? =
???? ????
???? ???? ???? ???? ????
Where:
Gm = G / MG G = gas mass flowrate = 0.45 kg/s MG = molecular weight of gaseous mixture
KG = gas film transfer coefficient
P = pressure
aw = height of transfer units = 80.34 m2
/m3
Substituting into equation:
???? ???? = 1 ????
Applying liquid film transfer unit height equation:
???????? =
???? ????
???????? ???? ???? ????????
- 187. 187
Where:
Ct = qL/ ML ρL = density of solvent = kg/m3
ML = molecular weight of solvent = 60.05 kg/mol
KL = liquid film mass transfer coefficient
aw = height of transfer units = 80.34 m2
/m3
Therefore HL:
???????? = 0.045 ????
Applying, (Sinnott et al., ):
L
m
m
GoG H
L
mG
HH
Where:
y1 = 0.017 Aspen Plus data
y2 = 0. Aspen Plus data
m = 0.78 Aspen Plus data
Gm/Lm = 0.89 Aspen Plus data
Therefore HOG :
???? ???????? = 1.03 ????
Applying :
???? = ???? ???????? × ???? ????????
Where:
NOG = number of transfer units = 8 m
HOG = height of transfer units = 1.03 m
Therefore assuming 1m allowance for liquid and gas distribution:
???????????????????? ℎ????????????ℎ???? ???????? ???????????????????? = 10 ????
- 188. 188
Total dead weight:
Dead weight of vessel
Applying:
???????? = ???? ???? × ???? × ???? ???? × ???? ???? × ???? × (???? ???? + 0.8 × ???? ????) × ???? × 10−3
Where:
CW = factor accounting for weight of nozzles and other internal support of the vessel
qm = density of vessel material
Dm = mean diameter of vessel
t = thickness
Substituting into equation:
???????? =
Dead weight of packing
???????????????????????????? ???????????????????????? = 2.4 ????3
???????????????? ???????????????????????????? ???????????? 1 ????????????ℎ ???????????????????????????? = 673 ????????/????3
???????????????? ????????????????ℎ???? ???????? ???????????????????????????? = 24 × 673 × 9.81 = ????
Weight of insulation
???????????????????????????? ???????????????? ???????????????????????????? = 130 ????????/????3
???????????????????????? ???????? ???????????????????????????????????????? = ???? × ???? × ???? × ???????????????????????????????????????????? × 10−3
= 0.98 ????3
????????????????ℎ???? ???????? ???????????????????????????????????????? = 0.98 × 130 × 9.81 = ????
Therefore total dead-weight:
???????? = + +
= ????
- 189. 189
Primary stresses:
Longitudinal stress
Applying:
???????? =
???? × ????????
4????
= 3 ????/????????2
Where:
P = pressure
Di = internal diameter
t = thickness
Hoop stress
Applying:
????ℎ =
???? × ????????
2????
= 6 ????/????????2
Direct stress due to weight of vessel
Applying:
???? ???? =
????????
???? × (???????? + ????) × ????
Where:
WV = total dead-weight
Di = inside diameter
t = thickness
Therefore substituting into equation:
???? ???? = 2.17 ????/????????2
- 190. 190
Wetting rate
Applying:
???????????????????????????? ???????????????? =
???????????????????????? ???????????????????????????????????????? ???????????????????????????????? ???????????? ???????????????? ???????????????????? − ???????????????????????????????????? ????????????????
????
Therefore:
???????????????????????????? ???????????????? = 6.14 × 10−6
????3
/????2
????
Pressure drop
Applying:
???????????????????????????????????????? = 0.115 ????????
0.7
Where:
???????????????????????????????????????? = 6.23 ???????? ????2 ????/ft of packing
Therefore:
???????????????????????????????????????? = 0.05 ???????????? = 0.05 ????????????
Dynamic Wind Pressure for smooth cylindrical column
Applying:
PW = 0.05uw
2
= 281 ????/????2
Where:
PW = wind pressure per unit area, N/m2
uw
2
= wind speed, km/hr
It can be assumed due to the values obtained, that the stresses are negligible.
Piping sizing
Optimum cross sectional area for the piping is calculated using the below formula:
???????????????????? − ???????????????????????????????????? ???????????????? =
????????????????????????????????
????????????????????????????????
And then the diameter is calculated using:
???????????????????????????????? = √
4 × ???????????????????? − ???????????????????????????????????? ????????????????
????
- 191. 191
Thus, the following flowrates were collected from Aspen Plus simulation:
Pipeline Flowrate
(m3
/s)
Velocity
(m/s)
Cross sectional
area (m2
)
Required diameter (m)
Combined inlet Gas
Stream
0.78 2.00 0.39 0.7 m
Off-gas 0.61 2.00 0. 0.625 m
Solvent feed 0. 2.00 0.31 0.05 m
Scrubber to reactor 0. 2.00 0. 0.060
- 192. 192
Cost of packing:
1 inch Intalox ceramic saddles have an average cost of 20$/ft3
of packing. Since packing volume is
2.4 m3
, then:
???????????????? ???????? ???????????????????????????? ???????????????????????????????? = $
≈ $
Mass of shell
????ℎ???????????? ???????????????? = ???? × ???? ???? × ???? ???? × ???? ???? × ????
= .1 ????????
Capital cost
Applying (Sinnott et al., , p319):
???? + ???????? ????
Where:
a = - (Sinnott et al., , p319)
b = 600 (Sinnott et al., , p320)
n = 0.6 (Sinnott et al., , p320)
S = shell mass, kg (90 < shell mass < ) (Sinnott et al., , p320)
Therefore:
???????????????? ???????????? ???????? ????ℎ???????????? = − + 600 × (.50.6)
= $31,940.4
???????????????? ???????? ℎ????????????????????ℎ???????????????????????? ℎ???????????? = $
The cost of the column is based on a U.S. Gulf Coast basis and has to be changed to a
UK basis using cost indexes and location factors. Although a cost index for was not available,
the cost index for will be taken as an estimate instead, therefore (Sinnott et al., , p324):
???????????????? ???????? ???????????????? ???? = ???????????????? ???????? ???????????????? ???? ×
???????????????? ???????????????????? ???????? ???????????????? ????
???????????????? ???????????????????? ???????? ???????????????? ????
Where:
Cost index in year A = 567.3 (Chemical Engineering, )
Cost index in year B = 499.6 (Chemical Engineering, )
Therefore, total cost of the column on an U.S Gulf Coast, basis is:
???????????????? ???????? ???????????????? ???? = 33,140.4 ×
567.3
499.6
= $37,631
- 193. 193
Applying location factor (Sinnott et al., , p327):
???????????????? ???????? ???????????????????? ???????? ???????????????????????????????? ???? = ???????????????? ???????? ???????????????????? ???????? ???????????????? × ????????????
Where:
LFA (United Kingdom) = 1.02
Therefore, total cost of the column on an U.S Gulf Coast, basis is:
???????????????? ???????? ???????????????????? ???????? ???????????????????????????????? ???? = × 1.02
= $38,384
Currency conversion
The unit of currency also has to be changed, from dollars (USD) to pounds (GBP). The exchange
rate, as of May , is 1. USD per 1 GBP (HM Revenue & Customs, ).
Therefore, total cost of the column on a UK basis is:
1.⁄
= £26,650
- 194. 194
APPENDIX [G] – Calculations for Acetic Acid Storage Tank
Volume of storage tank
Annual acetic acid production = 400,000 tonnes
= 400,000,000 kg
Weekly production acetic acid =
400,000,000
52
= .692 kg
= 7.7 × 106
kg
Therefore, volume of acetic acid can be calculated, using the density of acetic acid of kg/m3
(Sciencelab, ):
???????????????????????? =
????????????????
????????????????????????????
=
7.7 × 106
= .324 ????3
≈ ????3
Therefore, minimum capacity of storage tank = m3
Closest dimensions for m3
tank ( m3
): Diameter = 24.9 m
Height = 18.8 m
Aspect ratio (
????
????
) = 0.76
To confirm whether dimensions are correct, liquid volume formula is used (Perry, ):
???? = ????????2
(
????
57.30
− ????????????????????????????????)
Where:
???????????? ???? = 1 −
????
????
= 1 −
2????
????
???????????? ???? = 1 − 2(
18.8
24.9
)
???????????? ???? = −
127
249
???? = 120.7 ????
???????????? ???? = 0.86
- 195. 195
Substituting into main equation:
???? = [(18.8 × 12.452)][(
120.7
57.30
) − (0.86 × −
127
249
)]
= .5 ????3
Using partially filled heads equation for volume of head (Perry, ):
???? = 0.215????2
(3???? − ????)
= 0.215 × 18.82
× [(3 × 12.45) − 18.8]
= ????3
Therefore, total volume of storage tank:
???????????????????? ???????????????????????????? ???????????????? ???????????????????????? = +
= ????3
≈ ????3
Wall thickness
Using minimum wall thickness equation to resist hydrostatic pressure (Sinnott et al., ):
???????? =
???? ???? × ???????? × ???? × ????????
2 × ???????? × ???? × 103
Where:
es = tank thickness at depth HL, mm
HL = liquid depth, m
ρL = liquid density, kg/m3
J = Joint factor / efficiency
g = gravitational acceleration, 9.81 ms-2
ft = design stress for tank material, N/mm2
Dt = tank diameter, m
Known data: Joint factor = 0.85 (Rosenfeld, )
ρL of acetic acid = kg/m3
(Sciencelab, )
ft of stainless steel 316L = 485 N/mm2
(Azom, )
- 196. 196
Substituting in equation:
???????? =
× 18.8 × 9.81 × 24.9
2 × 485 × 0.85 ×
= 5.8 ????????
A corrosion allowance of 3mm is added, thus a final recommendation of 8.8mm for the tank shell is
proposed based on circumferential stress.
Design pressure
Using Clausius – Clapeyron equation to find vapour pressure of acetic at 40 o
C (Senese, ):
ln (
????1
????2
) = (
∆???? ????????????
????
)(
1
????2
−
1
????1
)
Where:
T1 = 40 o
C = 313 K
P2 = Pa
T2 = 118 o
C = 391 K (Sciencelab, )
∆Hvap = 23.4 kJ/mol (National Institute and Standards of Technology, )
R = 8.314 J/mol K
Therefore, substituting in equation:
ln (
????
) = (
8.314
)(
1
391
−
1
313
)
ln (
????
) = −1.79
????
= ????−1.79
???? = .7 ????????
= ????????
≈ 17 ????????????
Therefore:
Vapour pressure acetic acid at 40o
C = 17 kPa
Operating pressure storage tank = 17 kPa
Design pressure should be 10% more than operating pressure, therefore:
???????????????????????? ???????????????????????????????? = 1.1 × 17
= 18.7 ????????????
Design temperature = 40o
C
- 197. 197
Calculation of stresses:
Dead-weight stress
The material for construction is Stainless steel 316L with density = 8 tonnes/m3
(Azom, )
The insulating material is mineral wool with density = 130 kg/m3
(Engineeringtoolbox, )
Dead-weight stress for metal Volume of metal = Tank shell + Tank roof
Therefore:
{????[24.9 + (2 × 0.) × 0. × 18.8]} + 1.3 [(
????
4
) × 24.92
× 0.]
= 12.951 + 5.571
= 18.5 ????3
Therefore:
???????????????? ???????? ???????????????? = ???????????????????????? × ????????????????????????????
= 18.5 × 8
= 148.2 ????????????????????????
Therefore:
????????????????ℎ???? ???????????????????????? =
????????
(???????? ???? ????)
=
(148.2 × 9.81)
{???? × [24.9 + (2 × 0.)] × 0.}
= ????????????
= 2.1 ????????????
Dead-weight stress for insulation Volume of insulation = π × h × Di × ti
Therefore:
???? × 18.8 × 24.9 × 0.02
= 29.4 ????3
Therefore:
???????????????? ???????? ???????????????????????????????????????? = ???????????????????????? × ????????????????????????????
= 29.4 × 130
= ????????
= 3.8 ????????????????????????
- 198. 198
Weight of insulation is doubled to account for extra fittings, therefore:
???????????????? ???????? ???????????????????????????????????????? = 3.8 × 2
= 7.6 ????????????????????????
Therefore:
????????????????ℎ???? ???????????????????????? = ????????/???? ????
Where:
???? ???? = ???????????????????? − ???????????????????????????????????? ????????????????
=
7.6 × 9.81
???? × (24.9)2
4
= 0.153 ????/????2
= 0. ????????????
≈ 1.5 × 10−4
????????????
Therefore:
???????????????????? ???????????????? ????????????????ℎ???? = ????????????????????????????????ℎ???? ???????? ???????????????? + ????????????????????????????????ℎ???? ???????? ????????????????????????????????????????
= (148.2 × 9.81 × ) + (7.6 × 9.81 × )
= ????
???????????????????? ???????????????????????? ???????????? ???????? ????????????????????????????????ℎ???????? = + (1.5 × 10−4
)
= . ????????????
≈ ????????????
= 2.1 ????????????
Axial stress
Axial stress calculated using (Stevenson, ):
???????? ????
4???????? ????
Where:
P = Design pressure
Do = Outside diameter
J = Joint factor / efficiency
ts = Minimum thickness
- 199. 199
Therefore:
0.{24.9 + (2 × 0.)}
(4 × 0.85 × 0.)
= 15.6 ????????????
Hoop stress
Hoop stress to be found using (Stevenson, ):
2 × ???????????????????? ????????????????????????
= 2 × 15.6
= 31.2 ????????????
Wind stresses
Wind stresses are disregarded because of the high ratio of tank diameter to tank height.
Analysis of stresses
???????? ???????????????? = ???????????????????? ???????????????????????? − ????????????????????????????????ℎ???? ????????????????????????
= 15.6 − 2.1
= 13.5 ????????????
???????????????? ???????????????? = ???????????????? ???????????????????????? − ????????????????????????????????ℎ???? ????????????????????????
= 31.2 − 2.1
= 29.1 ????????????
???????????????????????? ???????????????????????? = 0.5 × ???????????????????????? ????????????????????????????????
= 9.35 ????????????
Therefore:
???????????????????????????? ???????????????????????? = 33????????????
The maximum stress is approximately 93% below the design stress of 485 MPa, and therefore the
shell thickness used in this design is considered acceptable.
- 200. 200
Storage tank emissions:
Total emissions are equal to the sum of the working loss and standing loss, and can be calculated via
(South Coast Air Quality Management District, ):
???? ???? = ???? ???? + ???? ????
Where:
Lr = total loss, lbs/yr
Lw = working loss, lbs/yr
Ls = standing loss, lbs/yr
Using equation to work out working loss (South Coast Air Quality Management District, ):
???? ???? = 0.024 × ???? ???? × ???????????? × ???? × ???? ???? × ???? ????
Where:
Lw = working loss, lbs/yr
MV = average vapour molecular weight, lb/lbmole
PVA = true vapour pressure of stored liquid at average liquid surface temperature, psia
Q = annual throughput, Mgallon/yr
KN = turn over factor, dependent on Q and C If Q/C ≤ 36 KN = 1.0
If Q/C > 36 KN = [
(180 ×????)+????
6????
]
KP = working loss product factor KP = 0.75 for crude oil and 1.0 for other materials
Therefore:
Converting tonne/yr to Mgallon/yr Q = 400,000 tonne/yr = 37 Mgallon/yr
Converting m3
to Mgallons C = m3
= 1.9 Mgallons
Thus:
????
????
=
37
1.9
= 19.5
Q/C is smaller than 36, thus KN = 1.0
Substituting values in working loss equation:
???? ???? = 0.024 × 60.05 × 0.21 × 37 × 1 × 1
= 11.2 ????????????/????????
= 49.8 ????/????????
- 201. 201
Using equation to work out standing loss (South Coast Air Quality Management District, ):
???? ???? = ???? × ???????? × ???????? × ???? ???? × ????????
Where:
Ls = standing loss, lbs/yr
U = number of days of the year that the tank is used to store liquid material
VV = vapour space volume, calculated:
???????? = (66.84 × ????) + ????????
C = tank capacity, Mgallon
VF = vapour space function, depending on tank diameter
WV = vapour density, lbs/ft3
KE = vapour space expansion factor
KS = vented vapour saturation factor, calculated via:
???????? =
1
1 + (???????? × ????) + (???? ???? × ????)
SA, SB = vapour saturation factors
D = tank diameter, ft
H = tank height, ft
Therefore, vapour space volume is calculated using:
???????? = (66.84 × ????) + ????????
= (66.84 × 1.9) +
=
And vented vapour saturation factor, KS worked out through:
???????? =
1
1 + (???????? × ????) + (???? ???? × ????)
Converting m to ft: Height = 18.8 m = 61.7 ft
Diameter = 24.9 m = 81.7 ft
Therefore:
???????? =
1
1 + (0. × 61.7) + (0. × 81.7)
= 1.38
- 202. 202
Thus, standing storage loss:
???? ???? = 365 × × 0. × 0.039 × 1.38
= .4 ????????????/????????
= .9 ????/????????
≈ 5.1 ????????/????????
Therefore, total emissions:
???? ???? = ???? ???? + ???? ????
= 49.8 +
= .8 ????/????????
= 5.1 ????????/????????
Tank Blanketing:
Inert gas, N2, is utilised to blanket the fixed-roof tank for safety. It is lost in two ways, either from
breathing losses from day/night temperature differential and working losses to displace changes in
active level.
Using vapour volume formula, breathing losses can be calculated (Branan, ):
???????? =
???? × ????2
4 × (????????????. ????????????????????????)
Where:
Vo = Vapour volume, scf
D = Tank diameter, ft
VV = avg.outage = average vapour space, ft
Therefore:
???????? =
???? × 81.72
4 ×
= 0.189 ????????????
= 5.4 × 10−3
????3
Therefore, daily breathing losses are worked out via (Branan, ):
???????????? = ????????{
460 + ???????? +
????????????
2
460 + ???????? + ∆ −
????????????
2
− 1.0}
- 203. 203
Where:
TS = storage temperature, o
F
Tdc = daily temperature, o
F
DBL = daily breathing loss, scf
∆ = Adjustment for the differential between blanketing and pressure-relief settings (normally 2-4 o
F)
Also using displacement equivalents of inert gas to tank liquid (Branan, ):
1 ???????????? × 5.615 = 1 ???????????? ???????????????????? ????????????
Therefore, substituting into daily breathing losses equation:
???????????? = 0.189{
460 + 104 +
37.4
2
460 + 95 + 3 −
37.4
2
− 1.0}
= 0.015 ????????????/????
= 0.45 ????????????/????????????????ℎ
And monthly working loss:
????????????????ℎ???????? ???????????????????????????? ???????????????? =
12(5.165)
= 309 ????????????/????????????????ℎ
Thus, total inert gas usage:
???????????????????? ???????????????????? ???????????? ???????????????????? = 309 + 0.45
= 309.45 ????????????/????????????????ℎ
= 8.8 ????3
/????????????????ℎ
Inlet/Outline diameters:
The inlet and outlet diameters are sized for a recommended liquid flowrate of 2 m/s (Perry, ).
Inlet pipe
Given data from simulation Mass flowrate = .1 kg/hr
Inlet line sizing is determined by allowing 20% above the normal product flowrate of kg/hr.
Therefore:
× 1.2 = ????????/ℎ????
Therefore, mass flowrate in seconds:
???????????????? ???????????????? =
= 17.4 ????????/????
- 204. 204
Density of acetic acid is known, therefore volumetric flowrate:
???????????????????????????????????????? ???????????????? =
17.4
= 0.017 ????3
/????
Therefore, area of pipe:
???????????????? ???????? ???????????????? =
???????????????????????????????????????? ????????????????
????????????????????????????????
=
0.017
2
= 8.5 × 10−3
????2
Thus, diameter of pipe:
???????????????????????????????? ???????? ???????????????? = √(8.5 × 10−3
×
4
????
)
= 0.104 ????
= 104 ????????
The nearest commercial pipe size is a nominal pipe size of 4, schedule number 40s (with inside
diameter of 102 mm and a wall thickness of 6mm) (Perry,).
Outlet pipe
Outlet line sizing is determined by the outlet flowrate calculated based upon the need to fill a standard
tonne chemical tanker in 8 hours. This corresponds to a volumetric flowrate of 0.099 m3
/s.
Converting tonne to kg 5,000,000 kg
Converting hours to seconds s
Therefore, mass flowrate:
???????????????? ???????????????????????????????? =
5,000,000
= 173.6 ????????/????
Acetic acid density of kg/m3
enables the working out of volumetric flowrate:
???????????????????????????????????????? ???????????????????????????????? =
173.6
= 0.166 ????3
/????
Since outlet diameter is sized for a recommended liquid flowrate of 2 m/s, area of pipe can be
calculated:
???????????????? ???????? ???????????????? =
???????????????????????????????????????? ????????????????????????????????
????????????????????????????????
= 0.166/2
= 0.083 ????2
≈ 0.08 ????2
- 205. 205
Therefore, diameter of pipe:
???????????????????????????????? ???????? ???????????????? = [ ???????????????? ×
4
????
]0.5
= [0.08 ×
4
????
]0.5
= 0.319 ????
= 319 ????????
The nearest commercial pipe size is a nominal pipe size of 12, schedule number 120 (with an inside
diameter of 273mm and a wall thickness of 25mm) (Perry, ).
Size of delivery
Volume of storage tank = m3
Weekly production of acetic acid = m3
Thus, empty volume space of storage tank:
= −
= ????3
Based on the empty volume space of the storage tank, an estimation of the optimum size delivery can
be achieved, thus:
???????????????????????? ???????????????????????????????????????? ???????????????????????? ???????????????? − ???????????????????? ???????????????????????? ???????????????????? ???????? ???????????????????????????? ???????????????? = ???????????????????????? ???????? ???????? ????????????????????????????????????
= −
= ????3
≈ ????3
A further 500 m3
is deducted from the figure obtained in order to set a minimum stock level in the tank,
thus optimum size delivery:
− 500 = ????3
Therefore, minimum stock level in the tank:
−
= ????3
- 206. 206
Therefore, diameter of pipe:
???????????????????????????????? ???????? ???????????????? = [ ???????????????? ×
4
????
]0.5
= [0.05 ×
4
????
]0.5
= 0.252 ????
= 252 ????????
The nearest commercial pipe size is a nominal pipe size of 10, schedule number 120 (with an inside
diameter of 230mm and a wall thickness of 21mm)
Size of delivery
Volume of storage tank = m3
Weekly production of acetic acid = m3
Thus, empty volume space of storage tank:
= −
= ????3
Based on the empty volume space of the storage tank, an estimation of the optimum size delivery can
be achieved, thus:
???????????????????????? ???????????????????????????????????????? ???????????????????????? ???????????????? − ???????????????????? ???????????????????????? ???????????????????? ???????? ???????????????????????????? ???????????????? = ???????????????????????? ???????? ???????? ????????????????????????????????????
= −
= ????3
≈ ????3
A further 500 m3
is deducted from the figure obtained in order to set a minimum stock level in the tank,
thus optimum size delivery:
− 500 = ????3
Therefore, minimum stock level in the tank:
−
= ????3
A size delivery of m3
would be desirable, as nearly 75% of the weekly production is able to be
shipped. The figure obtained for the minimum stock level will be able to accommodate a scenario
where if the plant shuts down for a few days, the remaining storage will keep on supplying customers.
Additionally, if there is a problem in distribution, the available space in the tank will allow for
continuous running of the plant until the problem is solved. Henceforth, a delivery period of one week
will provide smooth production and shipment whilst accommodating customers.
Tank cost:
Purchased equipment costs can be evaluated by the equation (Sinnott et al., ):
???????? = ???? + ???????? ????
Where:
Ce = purchased equipment cost, £,
S = characteristic size parameter
a = cost constant
b = cost constant
n = index for that type of equipment
Given data: S = m3
a = (Sinnott et al., ).
b = 700 (Sinnott et al., ).
n = 0.7 (Sinnott et al., ).
Therefore:
???????? = + 700()0.7
= ???????? $ 409,565
≈ ???????? $ 410,000
The cost of the storage tank is based on a U.S Gulf Coast Basis and has to be changed to a
UK basis using cost indexes and location factors (Sinnott et al., ). Although a cost index for
was not available, the cost index for will be taken as an estimate instead.
???????????????? ???????? ???????????????? ???? = ???????????????? ???????? ???????????????? ???? ×
???????????????? ???????????????????? ???????? ???????????????? ????
???????????????? ???????????????????? ???????? ???????????????? ????
Where:
Cost index in year A () = 567.3 (Chemical Engineering, )
Cost index in year B () = 499.6 (Chemical Engineering, )
Therefore, the total cost of the storage tank is:
???????????????? ???????? ???????????????? ???? = 410,000 ×
567.3
499.6
= ???????? $ 465,558
≈ ???????? $ 470,000
- 207. 207
Applying location factors (Sinnott et al., ):
???????????????? ???????? ???????????????????? ???????? ???????????????????????????????? ???? = ???????????????? ???????? ???????????????????? ???????? ????. ???? ???????????????? ???????????????????? ???????????????????? × ????????????
Where:
LFA (United Kingdom) = 1.02 (Sinnott et al., )
Therefore, total cost of the storage tank is:
???????????????? ???????? ???????????????????? ???????? ???????????????????????????????? ???? = 470,000 × 1.02
= ???????? $ 479,400
Unit of currency has to be changed, from dollars (USD) to pounds (GBP). The exchange rate, as of
May , is 1. USD per 1 GBP, therefore total cost of the storage tank on a UK basis is
(HM Revenue & Customs, ):
???????????????? ???????? (£) =
???????????????? ???????? ($)
1.
= £ 332,847
≈ £ 333,000
- 208. 208
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