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Ethylbenzene
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PLANT DESIGN: CPD4M2C
PRODUCTION OF ETHYL BENZENE SEPTEMBER 2012 1
UNIVERSITY OF SOUTH AFRICA
Department of Civil and Chemical Engineering
Amilcar J Beukes (3358-346-3)
Chemical Process Design IV Module B: Plant Design
CPD4M2C (Year Module)
FINAL DESIGN REPORT III:
Conceptual Design
Dr. Bilal Patel 17 September 2012
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PRODUCTION OF ETHYL BENZENE SEPTEMBER 2012 2
17 September 2012
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EXECUTIVE SUMMARY:
(i) Introduction and Background Information
The conceptual design of an ethylbenzene production facility is performed. Theindustrial production of ethylbenzene is achieved by the direct alkylation reaction
between benzene and ethylene.
In the production of ethyl benzene from the two reactants, benzene and ethylene, a
byproduct (di-ethyl benzene) may be produced. The optimization process regarding
selectivity between the two products (ethyl benzene and di-ethyl benzene) should
favour the production of ethyl benzene rather than di-ethyl benzene. The reaction is
carried out in a 74.22 m3 Alkylation catalytic packed-bed reactor.
The design includes an economic viability test, together with a HAZOP analysis anda preliminary environmental impact assessment. A concise P&ID drawing is also
included in the design which would be supported by a comprehensive control
philosophy and a start-up and shut-down procedure.
(ii) Objective
The facility is to produce 100 000 metric tons per annum of ethylbenzene with a
purity of at least 99.5 wt%. The design includes a process simulation, a HAZOP
study and a detailed design of the alkylation reactor and one of the distillation
columns. A preliminary environmental impact assessment is also included in thisfinal design document. The economic viability of the intended project was performed
and included in the design.
(iii) Process Description
Benzene and ethylene is fed to a single packed-bed reactor where most of the
reactants are converted to ethylbenzene. The product stream from the reactor is sent
downstream to different separation units, where benzene is recovered and recycled
to be re-used and to increase the overall plant conversion. A flash drum together
with two distillation columns is used to separate unwanted material from the desiredproduct (ethylbenzene).
(iv) Conclusions and Recommendations
The design confirmed the possibility and economic viability of producing the
specified amount of ethyl benzene. The PEIA additionally indicated that a facility of
this kind would not have a negative impact on the environment nor will it infringe
upon the social fabric of the inhabitants living in close approximation of the proposed
plant.
It was also found that careful optimization of the reactor operations should be done
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PRODUCTION OF ETHYL BENZENE SEPTEMBER 2012 4
to enhance the overall production of ethylbenzene and to avoid wastage of costs.
Further observations showed that a single reactor could not effectively convert the
high ratio of benzene in the feed to ethylbenzene. A series of smaller reactors are
therefore recommended.
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Table of Contents
EXECUTIVE SUMMARY: ................................................................................................................... 3
1. INTRODUCTION: ............................................................................................................................ 8
2. LITERATURE SURVEY:................................................................................................................. 9
2.1 Chemical Reactions: ................................................................................................................. 9
2.2 Process Component Properties and Description:................................................................. 9
3. DESIGN BASIS:............................................................................................................................. 11
3.1 General Design Considerations: ........................................................................................... 11
3.2 Design Philosophy................................................................................................................... 11
3.2.1 Key Assumptions:............................................................................................................. 12
3.2.2 ChemCad Operations: ..................................................................................................... 12
4. OVERALL PROCESS DESCRIPTION:...................................................................................... 12
4.1 Process Simulation:................................................................................................................. 13
5. ETHYL BENZENE PRODUCTION FACILITY, UNIT 100. ...................................................... 14
5.1 Process Notes:......................................................................................................................... 14
5.2 Process Description: ............................................................................................................... 15
5.3 Process Units: .......................................................................................................................... 17
5.3.1 The Benzene Feed Drum (V-101) ................................................................................. 17
5.3.2 The Fired-Heater (H-101)................................................................................................ 175.3.3 The Alkylation Reactor (R-101):..................................................................................... 19
5.3.4 Flash Drum (V-101): ........................................................................................................ 21
5.3.5 Benzene Tower (T-101): ................................................................................................. 22
5.3.6 Ethylbenzene Column (T-102): ...................................................................................... 23
5.3.7 Liquid Pumps (P-10i, i = 1, 2, 3): ................................................................................... 23
6. START-UP AND SHUT-DOWN PROCEDURES: .................................................................... 26
6.1 Start-Up Procedure: ................................................................................................................ 27
6.2 Shut-Down Procedure: ........................................................................................................... 27
7. EQUIPMENT LIST:........................................................................................................................ 28
8. UTILITY REQUIRMENT SCHEDULE: ....................................................................................... 28
9. PRELIMINARY ENVIRONMENTAL IMPACT ASSESSMENT: .............................................. 29
10. HAZOP STUDY: .......................................................................................................................... 30
11. DETAILED DESIGN:................................................................................................................... 35
11.1 Reactor Design .......................................................................................................................... 35
11.2 Benzene Tower Design: ............................................................................................................. 40
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THE TOWER PLATE SPECIFICATIONS: ............................................................................................ 40
12. PLANT COST ESTIMATIONS:.................................................................................................. 41
12.1 Capacity Effect on Equipment Costs:................................................................................. 41
12.2 Labour Requirements: .......................................................................................................... 43
12.3 Plant Operation Time: ........................................................................................................... 44
11.4 Economic Analysis: ............................................................................................................... 45
11.4.1 Cost Estimation: ............................................................................................................. 45
12.4.2 Manufacturing Costs:..................................................................................................... 47
12.4.3 Profitibility ........................................................................................................................ 48
13. CONCLUSIONS: ......................................................................................................................... 50
REFERENCES ................................................................................................................................... 50
APPENDIX: ......................................................................................................................................... 51
PFD with Stream Table: ................................................................................................................ 51
Centrifugal Pump (P-101 A/B) DATA SHEET: .......................................................................... 51
BENZENE TOWER DESIGN: ...................................................................................................... 52
Design Calculations of a Benzene Tower: ............................................................................. 52
CAPCOST SPREADSHEET: ....................................................................................................... 61
Reactor Design: (PolyMath Program Output Report) ............................................................... 66
Table 1: Commercial Process used to Produce Ethyl Benzene ................................................... 9
Table 2: Equipment List..................................................................................................................... 28
Table 3: PEIA ...................................................................................................................................... 30
Table 4: HAZOP Study on REACTOR............................................................................................ 33
Table 5: HAZOP Study on FLASH DRUM ..................................................................................... 34
Table 6: HAZOP Study on BENZENE TOWER ............................................................................ 34
Table 7: PolyMath Program .............................................................................................................. 38
Table 8 Spec Sheet Benzene Tower.............................................................................................. 40
Table 9: CEPCI in 2012 (Turton et al.)............................................................................................ 42Table 10: Labour Costs ..................................................................................................................... 44
Table 11: Equipment Cost ................................................................................................................ 46
Table 12: Costs Structure ................................................................................................................. 47
Table 13: Total Annual Costs ........................................................................................................... 48
Figure 1: Block Flow Process Diagram for the Production of Ethyl Benzene ........................... 13
Figure 2: PFD from ChemCad simulation ...................................................................................... 14
Figure 3: Stream Table from ChemCad.......................................................................................... 14
Figure 4: P&ID Diagram for the Production of Ethyl Benzene via the Alkylation of Benzene 16
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Figure 5: Benzene Feed Drum (V-101) .......................................................................................... 17
Figure 6: Fired-Heater (H-101)......................................................................................................... 18
Figure 7: Alkylation Reactor (R-101) ............................................................................................... 19
Figure 8: Heat Exchanger (E-101) and Flash Drum (V-101) ....................................................... 21
Figure 9: Benzene Tower (T-101) ................................................................................................... 22
Figure 10: Ethylbenzene Column (T-102) ...................................................................................... 23
Figure 11: Liquid Pumps (P-10i, i = 1, 2, 3) ................................................................................... 24
Figure 12: Flow Rate Profile along length of Reactor................................................................... 37
Figure 13: Flow Rate Profiles ........................................................................................................... 38
Figure 14: Drawing of Alkylation Reactor with Dimensions ......................................................... 39
Figure 15: Benzene Tower Dimensions.......................................................................................... 41
Figure 16: Extrapolation of Index..................................................................................................... 43
Figure 17: CEPCI (courtesy of www.EngineeringToolBox.com ) ............................................... 43
Figure 18:Utility Schedule and Costs .............................................................................................. 63
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1. INTRODUCTION:
A conceptual design of an ethylbenzene production facility is to be performed. The
industrial production of ethyl benzene is achieved by the direct alkylation reaction
between benzene and ethylene. The ethyl benzene is then used as the primary raw
material in the production of styrene. Styrene is converted into polystyrene bypolymerization. Polystyrene in turn is an important polymer in the chemical industry.
This design, however, focuses on the production of ethyl benzene only.
In the production of ethyl benzene from the two reactants, benzene and ethylene, a
byproduct (diethyl benzene) may be produced. The optimization process regarding
selectivity between the two products (ethyl benzene and di-ethyl benzene) should
favour the production of ethyl benzene rather than di-ethyl benzene. The reaction is
normally performed in the presence of an acidic catalyst.
The design further includes an economic viability test, together with a HAZOPanalysis and a preliminary environmental impact assessment. A concise P&ID
drawing is included in the design which would be supported by a comprehensive
control philosophy and a start-up and shut-down procedure.
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2. LITERATURE SURVEY:
Commercially, ethyl benzene is produced by vapour or liquid phase alkylation of
benzene with ethylene (P. K. Sahoo et al.,2011). The reaction type can be classified
according to the catalyst used. Two type of catalysts are commonly used, namely a
zeolite-based or a Lewis acid catalyst. The catalyst type will also dictate the bi-products produced.
Table 1 shows the different processes available to produce ethyl benzene on
industrial scale.
Table 1: Commercial Processes used to Produce Ethyl Benzene (SRI Consulting, 1999)
2.1 Chemical Reactions:The direct alkylation reaction between benzene and ethylene produces the
ethylbenzene in the presence of an acidic catalyst. The reaction is shown below:
C6H6 + C2H4 C6H5C2H5 (reaction 1)
Benzene ethylene ethyl benzene
The reaction between benzene and ethylene may also produce a further reaction
between ethylene and ethyl benzene to produce the undesired product, di-ethyl
benzene, according to the following reaction:
C6H5C2H5 + C2H4 C6H4 (C2H5)2 (reaction 2)
Ethyl benzene ethylene di-ethyl benzene
Other side reactions are not included in this design.
2.2 Process Component Properties and Description:
2.2.1 Benzene:
Benzene chemically defined by the formula C6H6 and classed in the hydrocarbon
family because it contains only carbon and hydrogen atoms. It can be naturally found
Liquid-phase, aluminum chloride catalyst
Liquid-phase, aluminum chloride catalyst
Liquid-phase, aluminum chloride catalyst
Liquid-phase, boron trifluoride catalyst
Separation from C8 aromatics:
Distillation (superfractionation) Badger
Eurotecnica
UOP
Developer
Alkylation of benzene with ethylene
Vapour-phase, zeolite-catalyst (Appl to this Design)
Liquid-phase, zeolite catalyst
Extraction and purification
Liquid-phase adsorption
Monsato
Union Carbide/Badger
Petroflex
UOP
Mobil/Badger
Lummus Crest/Unocal/UOP
Process Type/Technology
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in volcanoes and Forest fires. Industrially it is used as a solvent in the manufacture
of paints and products such as dyes, detergents, nylon, plastics, drugs and
pesticides. Benzene is also a byproduct of the coking process during steel
production. Being a natural ingredient of crude oil, it is known as the most basic
petrochemical.
It is characterized as aromatic because of its sweet smell. It is a colourless highly
flammable gas which evaporates into the air very quickly and dissolves slightly in
water. Benzene boils at 80.1C (176.2F) and freezes at 5.45.5C (41.7 41.9F).
2.2.2 Eth ylen e:
Ethylene is chemically defined by the formula C2H4 is one of the simplest
unsaturated hydrocarbons. Being a natural plant hormone it is widely used in the
agricultural industry to force fruit to ripen. The other use of ethylene is in the
manufacture of plastics, such as packing films, wire coatings, and squeeze bottles.
Ethylene melts at -169 degrees Celsius and boils at -104 degrees Celsius. It is
characterized as a colourless , flammable , sweet and musky smelling gas. Ethylene
is also known as Ethene and can be produced in two ways:
1. Through fractional distillation it can be extracted from natural gas.
2. Through fractional distillation it can be extracted from crude oil.
Ethylene is the raw material used in the manufacture of polymers such as
polyethylene (PE), polyethylene terephthalate (PET), polyvinyl chloride (PVC) and
polystyrene (PS) as well as fibers and other organic chemicals.
2.2.3 Ethy l b enzene:
Ethyl benzene is an organic compound with the formula C6H5C2H5 => C8H10. This
aromatic hydrocarbon is important in the petrochemical industry as an intermediate
in the production of styrene, which in turn is used for making polystyrene, a common
plastic material.
It melts at -95 C and boils at 136 C. Ethyl benzene is a clear colourless aromatic
liquid which evaporates easily and is highly flammable. Ethyl benzene is used as asolvent in the coatings industry for paints, lacquers, and varnishes. It can be
detected in air, water and soil.
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3. DESIGN BASIS:
The objective of this design document is to demonstrate a design of an ethyl
benzene production facility that will produce 100 000 metric tons of ethyl benzene
per annum. The ethyl benzene product should have a purity of at least 99.5 weight
%. Being the first unit erected at the plant, the plant would therefore be located atunit 100 of the facility.
The raw materials used in the production process will be limited to a pure benzene
stream available at 1 bar and 25 C as well as an ethylene stream available at 1 bar
and 25 C containing 5 mol % ethane. Periodic shut-downs and maintenance would
mean that annual plant operations would be reduced to 330 days per year.
3.1 General Design Considerations:
The ethyl benzene production plant will have to meet the following design
requirements:
Location UNIT 100
Available Utilities
LP Steam @ 618 kPa saturated
MP Steam @ 1135 kPa saturated
HP Steam @ 4237 kPa saturated
Fuel Gas external supply and internal production
Electricity external supply and internal production
Boiler Feed Water
Cooling Water @ 516 kPa and 30 C
Plant Control Designed to use Closed and Open-loop
control
Unattended control operations to dominate
Plant Design Life Expectancy 30 years
Process/Plant Safety NOSA and periodic Hazop Analysis
Considerations
Process Water Municipal Potable Water Supply
3.2 Design Philosophy
The design is limited to a preliminary study and analysis of the production of ethylbenzene used in the chemical industry. The design approach was to use thecomputer package ChemCad, PolyMath and Microsoft Excel to perform the energyand material balances over the unit processes and to determine most of the keyparameters that influences the processes. The operating parameters included thefollowing:
the operating temperatures the feed composition, amounts and conditions to the plant
available utilities
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Most of the data was obtained from literature as well as the prescribeddocumentations made available on MyUnisa. The assumptions made are clearlystated and justified where needed. A preliminary process flow diagram (PFD) isincluded to give a visual indication of the process.
The production capacity of the production facility is provided in the user specificationdata supplied.
3.2.1 Key Assumptions:
The following key assumptions were made with regards to the ChemCad simulation:
It was assumed that the reactor achieved a 98 % conversion of benzene,according to the reaction 1 above
The alkylation reactor was assumed to be adiabatic Flow rates were assumed to be constant with negligible fluctuations in stream
compositions
Impurity levels in all streams were assumed to be negligible or non-existent,except were stated otherwise
3.2.2 ChemCad Operations:
ChemCad was used to perform the material balances over the entire process.
4. OVERALL PROCESS DESCRIPTION:
Benzene and ethylene feed streams are fed to a reactor to produce ethyl benzene. A
conversion of 98 % for benzene is achieved in the reactor. The reactions take place
in an adiabatic reactor. Non-condensable gases in the reactor effluent are separated
from the mixed liquids in a phase separator. The ethyl benzene product and theunreacted benzene are then separated by distillation in the distillation column
downstream from the separator. The overhead from the distillation column contains
mostly benzene which is recycled back as reactor feed. Figure 1 shows a block flow
diagram of the process.
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Figure 1: Block Flow Process Diagram for the Production of Ethyl Benzene
4.1 Process Simulation:
A ChemCad simulation was performed on this design problem. The design basis
was used to perform typical optimization simulations of the design parameters.
In the simulation, a stoichiometric reactor was used with a 98% conversion of
benzene. Only the main benzene-ethylene reaction was included, since it was
assumed that there were no other reactions taking place and that the process
conditions was favourable to assume same.
A Flash Drum was chosen for the phase separation and a distillation column was
chosen for the benzene tower. All of the above is subject to changes in the
consequent phases of this design problem. Optimization of the above will also be
done.
ReactorPhase
Separator
Benzene Tower
Conversion
98% Benzene
Benzene
Ethylene
Mixed liquids
Mixed gases
Ethylbenzene
Recycled Benzene
Primary Reaction: C6H6C + C2H4 C6H5C2H5 Di-Ethylbenzene
EthylBenzeneColumn
Secondary Reaction: C6H5C2H5 + C2H4 C6H4(C2H5)2
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Figure 2: PFD from ChemCad simulation
Figure 3: Stream Table from ChemCad
5. ETHYL BENZENE PRODUCTION FACILITY, UNIT 100.
5.1 Process Notes:
Ethyl benzene is commonly used in the production of styrene, a precursor in the
production to polystyrene and many other copolymers of industrial importance.
Industrially, ethyl benzene is produced by the direct alkylation reaction of benzene
with ethylene in the presence of an aluminum chloride catalyst or a zeolite catalyst.
The vast majority of ethyl benzene alkylation units are performed in an adiabatic
reactor. Most commonly two-or-more reactors are used in series with inter-stage
cooling accompanied by the relevant heat exchangers. Additionally, to avoid
undesired side reaction or undesired products, a benzene-ethylene feed ratio of at
FLOW SUMMARIES:
Stream No. 1 2 3 4 5 6 7 8 9 10
Stream Name benzene recycle
Temp C 25 25 15.874 400 696.7777 70 70 70 134.3185 44.439
Pres bar 1.1 1.1 1.1 0.9 2 1.1 1.1 1.1 1.1 1.1
Enth MJ/h 3.14E+05 2.91E+05 6.60E+05 1.47E+06 1.47E+06 3.35E+04 -2.07E+04 5.43E+04 7.93E+04 5.52E+04
Vapor mass frac. 0 1 0 1 1 0 1 0 0 0
Total kmol/h 6400.9 6393.2 14248.6 14248.3 8174.7 8174.7 400.4 7774.3 6319.9 1454.4
Total kg/h 500000.0 180000.0 802943.1 802921.0 802915.0 802915.0 16864.8 786050.0 663107.0 122943.1
Total std L m3/h 565.356 513.793 1218.744 1218.719 935.086 935.086 35.229 899.857 760.261 139.595
Total std V m3/h 143467.54 143295.5 319362.38 319355.7 183224.95 183224.96 8974.48 174250.49 141651.15 32599.33
Flowrates in kg/h
Benzene 500000.029 0 587611 587585 113154.499 113154.513 3674.039 109480.507 21870.008 87610.438
Ethylene 0 170387.792 170387.792 170387.792 0 0 0 0 0 0
Ethylbenzene 0 0 35329.806 35332.812 680145 680145 3578.555 676566.302 641237 35329.799
Ethane 0 9612.215 9615.033 9615.032 9615.032 9615.032 9612.214 2.818 0 2.818
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least 8:1 should be considered. The most prominent undesired product is di-ethyl
benzene.
5.2 Process Description:
The P&ID Diagram of the ethyl benzene process is shown in Figure 4. A pure stream
of benzene is mixed with an ethylene and benzene-rich recycled stream. The mixedstream is sent through a fired heater (H-101) where it is brought to the reaction
temperature of 400 C. The mixed stream then enters as the feed to an adiabatic
packed-bed reactor (R-101). The elevated temperatures mean that the reaction
inside the reactor takes place in the gas phase. The reaction is exothermic.
The effluent from the reactor is passed through the heat exchanger (E-101), where it
is cooled to 80 C prior to a flash drum (V-101). The inert ethane, unreacted benzene
and ethylene, together with the ethyl benzene product are separated in the flash
drum. The overhead from the flash drum is received as fuel gas while the condensed
liquid is sent to a distillation column, the benzene tower (T-101). This means that all
the bottoms from the flash drum are sent to the benzene tower where the unreacted
benzene is sent back to the feed stream as recycled feed to the reactor.
The ethyl benzene is captured in the bottoms of the tower.
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Figure 4: P&ID Diagram for the Production of Ethyl Benzene via the Alkylation of Benzene
H-101FiredHeater
R-101Reactor
E-101ReactorEffluentCooler
V-102FlashDrum
T-101BenzeneTower
E-104Condenser
E-103TowerKettleReboiler
UNISA
D
C
B
A
D
C
B
A
6 5 4 3 2 1
TITLE: PFD of EthylbenzeneManufacturing Process
Department: CHEMICAL ENGINEERING
SCALE: A4
UNIT: 100
DATE: September 2012CPD4M2CAmilcar J BeukesPlant Design
87
1
2
9
Benzene
Ethylene
Fuel Gas
Di-ethylbenzene
R-101
V-102
T-101
3
6
4
Air
Natural Gas
E-101
E-104
E-103
H-101LIC V-101
5
V-101BenzeneFeedDrum
TC
LC
PC
FC
LCLC
AC
FC
AC
TC
AC
PC
P-102 A/B
P-101 A/B
ACO2
1
2
3
1
T-102
E-106
E-105
Ethylbenzene
TC
LC
PC
FC
LC
AC
FC
3
1P-103 A/B
E-102
V-103V-104
2
1
4
5
1 13
C-101Compressor
E-102TowerFeedHeater
V-103RefluxDrum
P-101 A/BTowerBottomsPump
T-101EthylBenzeneColumn
E-106Condenser
E-105ColumnKettleReboiler
E-102ColumnFeedHeater
V-104RefluxDrum
v1
v2
v3
v4
v5
v6
v7
v8
v9v10
v11 v12
v13
v14v15
v16 v17
v18
1 1
1
12
1113
14
15
10
CODE DESCRIPTION
1
2
3
4
5
Chemical sewer drainage
Sampling Port
Vent to Flare
Cooling Water
Heating Water
5
PC
3
FFC
AC
FC
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5.3 Process Units:
5.3.1 The Benzene Feed Drum (V-101)
The inclusion of inventories in chemical plants is very important. In cases where
major temporary disruption of flows occur, operations may resume unperturbed.
These periodic cases may include late delivery of feed material to a plant, individualunit shut-downs for mandatory maintenance. The disadvantage is that large
inventories may become costly, especially if the expected fluctuations in feed
material are for a long period.
The main purpose for the Benzene Feed Drum is to allow adequate mixing of the
pure benzene feed and the recycled benzene that is routed back from the Benzene
Tower.
Figure 5: Benzene Feed Drum (V-101)
CONTROL PHILOSOPHY:
The level in the Benzene Feed Drum is to be controlled by adjusting the benzene
feed flow into the vessel. An averaging level control strategy is applied so that the
level remains within specified limits. This control strategy dictates that the
manipulated flow should however not experience rapid variations that have a
significant magnitude, which may cause irreparable damage to the equipment. The
reason for this control strategy is the fact that slight variations in the level are notgoing to cause downstream problems. Tight level control is therefore not necessary
for the feed drum, to satisfy the control objectives.
5.3.2 The Fired-Heater (H-101)
The primary purpose of the fired heater is topre-heat the feedstream to the reactor.
Combustion reactions are taking place inside the heater. Air and fuel gasses are
used to supply the heat to the burner. The air-to-gas ratio is important for the
effective combustion of the gases. Air is normally supplied in excess, to allow for all
the fuel gasses to be used, and hence the term complete combustion. Typical
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combustion gasses include the following, amongst others:
CO2
H2O
CO
SO2
These gases may cause environmental problems and should be closely monitored.
The reason for using natural gases to burn in air is the corresponding vast amount of
heat energy that it produces.
Figure 6: Fired-Heater (H-101)
CONTROL PHILOSOPHY:
The inlet temperature to the downstream reactor is of critical importance for the
effective conversion of the specified reactants to produce high quality ethylbenzene.The control strategy for the fired heater would be to tightly control the outlet
temperature (this temperature would also be the inlet temperature to the reactor).
This control strategy is coupled in a cascade control loop downstream and would
therefore be discussed further below under the reactor section.
The heat supplied or generated inside the heater will greatly depend on the air-to-
gas ratio that is fed to the heater. It is for this reason that the heater outlet gas
composition is controlled by a single feedback loop which would allow for the
adjustment of the air inlet valve. This would ensure the most effective combustion to
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take place, while avoiding excess and unnecessary natural gas usage.
5.3.3 The Alkylation Reactor (R-101):
The alkylation reactor used in the design is a vapour-phase adiabatic reactor, with a
reaction temperature of approximately 400 C. The following exothermic reaction
takes place inside the reactor:
C6H6 + C2H4 C6H5C2H5
benzene ethylene ethyl benzene
A major side reaction also takes place, but could be avoided by adjusting relevant
process conditions. The undesired di-ethyl benzene is produced according to the
following reaction:
C6H5C2H5 + C2H4 C6H4 (C2H5)2
Ethyl benzene ethylene di-ethyl benzene
The reactor effluent is cooled in a heat exchanger that uses process cooling water. A
conversion of 98% for benzene is assumed to take place inside the reactor.
Figure 7: Alkylation Reactor (R-101)
2
Ethylene
R-101
6
4
Air
Natural Gas
H-101
5
AC
TC
AC
O2
2
1
v2
v3v4
v5
PC
3
FFC
AC
11.5 Sch 45 SS
PC
PT
PAHPAL
101
101101
FC
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CONTROL PHILOSOPHY:
The design criteria would be directed by a small range variation in the inlet
temperature to the reactor. Tight control of the reactor inlet temperature would
therefore be required. In addition to the inlet temperature requirements would be the
percentage conversion inside the reactor. The reactor effluent composition shouldtherefore also be controlled.
A cascade control strategy is used to control the reactor outlet composition, the
reactor temperature and the fuel flow to the burner. A change in the fuel flow to the
fired heater influences the feed temperature to the reactor which influences the
reactor temperature (and the conversion inside the reactor) which further indirectly
influences the reactor outlet composition. A three-level cascade control over the
reactor would attenuate such a disturbance on the fuel flow to the fired heater. This
would allow the outlet composition, the temperature inside the reactor and the fuel
flow to the fired heater to be controlled.
The reactor temperature and the fuel flow to the fired heater would act as the
secondary controlled variables, while the effluent composition would act as the
primary controlled variable. In cascade control, an additional secondary measuredprocess variable is used which has the characteristic of indicating the occurrence of
the key disturbance (s). This means that should the outlet composition deviate from
the set point, the fuel flow to the fired heater would be adjusted, which would mean
that an adjustment to the reactor temperature would be initiated, which would bring
the outlet composition back to its set point.
The cascade controller would be effective in attenuating any variations in feed
temperatures to the reactor as well as controlling the primary composition controller.
The dynamics for the composition control will thus be greatly enhanced in
comparison with a single feedback loop control strategy. A cascade control strategy
is only employed if a feedback loop strategy would be too slow and if one or more
secondary measured variables are available.
A sudden increase in the pressure inside the reactor could pose a safety risk as well
as potential damage to process equipment. It is therefore necessary to control the
pressure in the reactor as well. The pressure is released through a pressure releasevalve that is vented to a flare that may incinerate the toxic gases released. The
pressure release valve is controlled by a pressure controller, by means of a simple
feedback loop.
The reactor is also equipped with high and low pressure alarms. Should the pressure
in the reactor drop below 1.2 bar, the low-pressure alarm would go off. Should the
pressure inside the reactor increase above 3.5 bar the high-pressure alarm would be
triggered. The alarms will give a digital indication as well as a manual (high pitched
sound) indication. This will allow operators in the control room as well as operators at
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the plant itself to be aware of the situation.
It is further important for the feed ratio to be adequate to produce enough of the
desired product and to avoid excess production of unwanted by-products (such as
di-ethylbenzene). For this reason, a cascade ratio control loop is included in the
control strategy. A composition controller is used to control the feed ratio of benzeneversus ethylene to the reactor, while a ratio flow controller is used to control the
amount of ethylene directed to the reactor feed stream.
5.3.4 Flash Drum (V-101):
The flash drum is used as a phase separator. The condensable gases from the
reactor (benzene and ethyl benzene) are separated from the non-condensable
gases. The bottom condensed liquids are then sent to the benzene tower. The
overhead gases are captured as fuel gases that are used in other process units
upstream and downstream.
The flash process includes both the phase separator (V-102) and the heat
exchanger (E-101).
Figure 8: Heat Exchanger (E-101) and Flash Drum (V-101)
CONTROL PHILOSOPHY:
The control objectives of the Flash Drum, is to control the bottoms composition, the
level and the pressure in the drum. Three single loop controllers are used to control
the three parameters of concern. Due to the sensitive nature of the phase separation
process and the high dependence on the feed temperature to the Flash Drum, the
bottoms composition is controlled by adjusting the cooling water inlet flow valve to
the Reactor Effluent Cooler (E-101).
The level in the drum is controlled by a single level controller that adjusts the valve
that allows the bottoms to flow to the Benzene Tower. The pressure inside the drum
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is controlled by a single loop pressure controller that adjusts the top outlet valve.
5.3.5 Benzene Tower (T-101):
All the benzene and lighter components are separated from the heavier ethyl
benzene. The lighter gases are recycled to the feed of the reactor, while the ethyl
benzene together with the other by-products is captured as bottoms liquid.
Figure 9: Benzene Tower (T-101)
CONTROL PHILOSOPHY:
The dynamics of the Benzene Tower is such that long dead times and long analyser
delays may be expected. A myriad of controllers may be required to adequately
control the relevant parameters to satisfy the design objectives of such a tower. It is
for this reason that two cascade control loops are employed and three single loop
controls.
The level inside the bottom part of the tower is controlled by adjusting the bottomsoutlet valve. The bottoms composition is controlled as the primary controlled variable
in cascade control loop where the feed to the Tower Reboiler (E-103) act as the
secondary controlled variable. This allows for a consistently high quality separation
process inside the tower.
The temperature inside the tower is controlled via a cascade control system that
uses the reflux flow to the tower as secondary variable, while adjusting the reflux
valve to the tower. A level controller is also used to control the level in the reflux
drum, which is situated after the condenser. The pressure in the overhead is then
controlled by adjusting the valve after the condenser.
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This control strategy allows for safe, effective and efficient operations of the Benzene
Tower.
5.3.6 Ethylbenzene Column (T-102):
The bottoms product from benzene tower (T-101) is sent to ethylbenzene column (T-
102). In the ethylbenzene column, the ethylbenzene is recovered as a top productand the di-ethylbenzene is collected in the bottoms liquid stream.
Figure 10: Ethylbenzene Column (T-102)
CONTROL PHILOSOPHY:
The control strategy for the Ethylbenzene Column is similar to that of the Benzene
Tower. Please see above.
5.3.7 Liquid Pumps (P-10i, i = 1, 2, 3):
The best choice of pump for transporting liquid, such as benzene, ethylene and
ethylbenzene is the centrifugal pump. It is a simple concept of converting electrical
energy into kinetic energy and thereby creating pressure used to transport a fluidwhere it is needed. The kinetic energy conversion is actualized through the rotational
acceleration of the impeller. The rotating action creates a suction that moves the
water in continuous pockets, creating a low pressure is at the inlet of the pump and
an area of high pressure at the exit.
The kinetic energy that is created and used to transport the fluid is proportional to the
velocity with which the fluid exits the pump i.e. the greater the energy the fluid exit.
This was formulated by the Dutch-Swiss mathematician, Daniel Bernoulliin his well-
known formula, the Bernoulli Equation.
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Figure 11: Liquid Pumps (P-10i, i = 1, 2, 3)
The start-up procedure can be given in point form:
Make sure the immediate upstream process unit(s) has adequate feed fluid to
avoid cavitations
Ensure upstream valves are sufficiently open before pump start-up
Before starting the pump, allow the fluid to wet the inside of the pump casings
While wetting the pump, open the airing bolt to allow trapped air bubbles to
escape
Start-up the pump
Monitor the pump for a few minutes after extended periods of shut-down
Downstream valves should be opened slowly to avoid pressure bursts that may
damage the pump and/or other process units, equipment and instrumentation
Shut-dow n proc edure:
The procedure starts with slowly closing the furthest discharge valve and
consecutively moving backwards up to the closest valve to the pump. Switch the pump motor off
Close the upstream suction valves
Maintenance:
Centrifugal pump operations may encounter three general problems:
Inadequate design
Negligent operations
Poor maintenance
The general pump maintenance procedure for operators can be summarized into
four basic steps, namely:
1. Switch pump of and remove pump from system, by disconnecting all piping and
electrical connections
2. Disassemble the pump. Clean all parts and components.
3. Drain all fluid from the bearing housing and inspect each component. Make sure
damaged components are replaced
4. Reassemble all components
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Operat ion:
Cavitation is the main concern when operating a centrifugal pump. Cavitation occurs
when the pressure of a liquid is rapidly decreased below its vapour pressure as a
result of a flow phenomenon. The operational procedure to prevent cavitation is as
follows.
Increase the pressure at the at the suction head of the pump
The temperature liquid that is being pump must be reduced
The flow rate as well as the head losses in the pump suction piping can be
reduced
Reduce the speed of the impeller
Cavitation may cause the following damages to a pumping system:
Damage to the pump impeller as well as degraded performance of the pump
Vibration of the pump that results in flow and pressure disturbances
CONTROL PHILOSOPHY
Control strategies are important in pumping systems e specially when operating
centrifugal pumps. Although these types of pumps are reliable, they often stop
working. For this reason engineers design plants with back-up pumps as a standard.
These pumps must have some form of automated control that will allow pumping
systems to switch from a used pump that stops working to a back-up pump. Usually
in pumping applications with adjustable speed drives and variable flow rates efficient
control strategies is of utmost importance to throttling or bypass methods.The centrifugal pumps are all supplied with programme drive controllers to avoid
operating pumps at speeds that may cause equipment damage or system
resonances.
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6. START-UP AND SHUT-DOWN PROCEDURES:
When starting-up a catalytic reactor it is important to monitor the temperature and
concentration profiles of the reactants and products as they approach steady-state.
Rapid overshoots and/or undershoots in the temperature may cause reactant and/or
product degradation. Over/Under-shoot may also be a safety hazard and cause theactivity of the catalyst to be affected. A practical stability limit may be exceeded
when start-up overshoots are excessive. This stability limit may include upper and
lower boundary temperatures, reactant concentrations, product concentrations
and/or the pressure drop across the catalytic bed.
Before any upstream process units are started, the cooling fluid must be allowed to
flow through the condensers. In the case of brand new columns, flushing of the
whole system should be initiated to remove any unwanted material and early
identification of blockages. Process control devices and instrumentation should be
installed and tested as per the dictates of the P&ID provided. An operations manualof all equipment and instrumentation should be supplied by the manufacturer or
drawn up by the design team in consultation with the HAZOP team (referred to later
in this document). Process control software should be supplied by a general dealer
and all control devices should be compatible with the latest software systems in the
market today.
The column and tower condensers are in series with a lot of other process units. It is
imperative that the column and tower should not be switched off before process units
upstream is not totally turned off and no liquid-vapour is fed to the column. All valves
and equipment should be switched off in the tested order prescribed in theoperations manual provided. The column and tower must never be open to air for
long periods as it may cause rusting of the interior.
Annual shutdowns of the Ethylbenzene Plant should include internal inspections of
heat exchangers and other process units. During these periodic inspections the
following items should be considered:
Scaling and corrosion of equipment
Internal lining conditions
Tube and piping surfaces Metal thickness tests should regularly be performed
Expansion of equipment joints
Welding joint conditions
General condition of the heat exchangers and the fired heater
If tube and/or piping leakages are suspected, extensive tests must be performed to
replace or repair such tubes and/or pipes. Record sheets should be kept to ensure
tubes and pipes dont exceed their repair life.
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6.1 Start-Up Procedure:
1. Close all drain and flare valves
2. Switch the benzene feed valve (v1) to manual mode
3. Open valve manually to allow liquid to partially fill the feed drum (V-101)
4. Slightly open drum outlet valve (v2)5. Allow liquid to flow through the pump and fired heater (H-101)
6. Keep air and natural gas valves closed (va and v3)
7. Open reactor feed and outlet valves (v4 and v5) to allow fluid to wet the catalyst
and the interior of the reactor
8. Keep the heat exchanger (E-101) valve (v6) closed
9. Fluid will now flow into the flash drum and through the bottoms pump (P-102 A/B)
10. Open valve (v8) and allow fluid to flow through tower feed heater (E-102), while
filling the benzene tower (T-101)
11. The same procedure would follow for the ethylbenzene column
12. Do not open the two product valves (v15 and v17)13. Switch the pumps on when the fluid reaches the two product valves (v15 and
v17)
14. Immediately open the two valves (v15 and v17) and
15. Open the air and gas valves (va and v3) and start the fired heater up
16. Make sure all other valves are open
17. Monitor the system closely until steady-state is reached
18. Open all heat exchanger valves to allow process cooling and heating
19. Switch all automated control systems on
6.2 Shut-Down Procedure:
1. Switch all pumps off and close air and gas valves (va and v3) to fired heater (H-
101)
2. Open drain and flare valves to allow the process units to fully drain
3. Switch automated control systems off
4. Allow system to cool off by closing heat exchanger valves
5. Close valves starting from the furthest part of the plant downstream moving back
up until the benzene feed valve (v1) is closed
6. Allow fluids to drain into the chemical sewer
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7. EQUIPMENT LIST:
Table 2: Equipment List
Identification MOC Orientation Type
V-101 CS Horizontal
P-101 A/B CS Centrifugal
C-101 CS Horizontal Centrifugal
H-101 316SS/CS Vertical Fired
R-101 SS/Refractory Vertical Adiabatic
E-101 316SS/CS Shell&Tube
V-102 SS Vertical
P-102 A/B CS
E-102 CS/SS Shell&Tube
T-101 SS Vertical DistillationE-103 316SS Kettle
E-104 SS Shell&Tube
V-103 CS Horizontal
P-103 A/B CS Centrifugal
E-105 CS Shell&Tube
T-102 SS Vertical Distillation
E-106 CS Kettle
E-107 SS Shell&Tube
V-104 SS Horizontal
Tower Feed Heater
Benzene Tower
EQUIPMENT
Benzene Feed Drum
Heater Feed Pump
Ethylene Compressor
Fired Heater
Column Reboiler
Column Condenser
Column Reflux Drum
Tower Reboiler
Tower Condenser
Tower Reflux Drum
Tower Bottoms Pump
Ethylbenzene Column Feed Heater
Ethylbenzene Column
Alkylation Reactor
Reactor Effluent Cooler
Flash Drum
Flash Bottoms Pump
8. UTILITY REQUIRMENT SCHEDULE:Name Total Module Cost Grass Roots Cost Utility Used Efficiency Actual Usage Annual Utility Cost
C-101 9,100,000$ 13,000,000$ NA
E-101 42,094$ 55,000$ Cooling Water 18500 MJ/h 52,000$
E-102 33,600$ 43,900$ Low-Pressure Steam 1500 MJ/h 157,800$
E-103 197,500$ 257,000$ Low-Pressure Steam 1300 MJ/h 136,700$
E-104 359,000$ 444,000$ Cooling Water 4300 MJ/h 12,100$
E-105 42,000$ 55,000$ Low-Pressure Steam 1500 MJ/h 157,800$
E-106 197,500$ 257,000$ Low-Pressure Steam 1300 MJ/h 136,700$
E-107 143,000$ 204,000$ Cooling Water 5000 MJ/h 14,000$
H-101 2,340,000$ 3,340,000$ Natural Gas 0.9 12000 MJ/h 1,054,900$
R-101 24,400$ 31,300$ N/A
T-101 103,000$ 132,000$ NA
T-102 204,000$ 250,000$ NA
V-101 534,000$ 710,000$ NA
V-102 208,000$ 245,000$ NA
V-103 38,100$ 45,900$ NA
V-104 24,600$ 32,200$ NA
Totals 13,600,000$ 19,100,000$ 1,722,000$
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9. PRELIMINARY ENVIRONMENTAL IMPACT ASSESSMENT:
Due to the sensitivity of setting up a chemical manufacturing plant that may be
harmful to the environment as a whole, has led proposals for designing such plants
to actively include detailed Environmental Impact Assessment (EIA) procedures
which shall involve public participants. In this design document, a PreliminaryEnvironmental Impact Assessment (PEIA) will be performed.
The PEIA is compiled as a forerunner for the EIA for the proposed Ethylbenzene
Production Unit. The Processing plants that involve industrial scale operations would
opt to be as close as possible to the source for the raw materials used to reduce
astronomical costs related to the transportation and infrastructure. Also, when a lot of
energy is required in an industrial operation, the plant should be close to an energy
source and infrastructure. Chemical Production Plants are normally situated far from
densely populated areas and for that reason the impact that such processes have on
the environment is often overlooked. An increasing environmental awareness ofglobal warming and the future/present dangers posed by pollution has shed
increasing light on the role and impact chemical processes have in the global crisis.
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Table 3: PEIA
ITEM DESCRIPTION Risk Grade EFFECT ACTION REQUIRED
E xc es sive heat releas ed to the environment highThe highly exothermic nature of theprocesses involved generate a lot of
thermal energy that may escape
Continuous monitoring of equipment isnecessary to ensure no excess ive heat losses
Risk of fugitive emissions of toxic noxiousgases, eg. the c ombustion gases from the FiredHeater (H-101)
high
air quality deterioration canadversely affect the ecosy stem, thesurrounding fauna and flora as well
as humans
Emergency alert devices will be installed forquick detection of toxic gas emmissions,scrubbing units will be installed if needed
Other toxic c ontaining gas emmissions aboveregulatory standards
high
The sulphur containing gasemmissions pose the danger ofproducing acid rain and serious
health threats to humans
The plantt is designed to eliminate this theat tothe environment
Changes in water quality high
increases in the salinity, odour,temperature, nutrients, turbudity, pHor contaminants/pollutants(eg. oils,
toxins etc.
Introduction of an additional water and waste-water treatment plant on-site might be
proposed
Ground water consumption high Depletion of ground water aquifersConsultations with local hydrology
departments to keep ground water usagesbelow regulatory limits
Landscape and visual disturbances low
The Ethylbenzene plant will be builtin the vicinity of the existing Styrene
plant boundaries which will haveminimal visual and landscape
impact
Proposed plant should not be extended outsidethe existing S tyrene Plant boundaries
Affecting the exist ing demographic s of thesurrounding communities
moderate
The increasing influx of people fromother regions displacing the existing
community members foremployment competition
Employing local community members at theconstruction and operations of the proposed
plant
Dis rupt ions to the li vel ihood of communit y lowThe deprevation of access to the
environment, facilities, etc.
Keeping a continuous favourable relationshipwith the local communities and involving them
in decision making
Health, safety, privacy and general welfare ofcommunity members
moderate
Factors such as odour problems,noise, radiation, vibrations etc mayhinder the health, safety, privacyand general welfare of community
members
Educate and inform the relevant stakeholdersof the risks posed to them personally and sendout alerts well in advance when the problems
may arise
Changes in community resource low
Local businesses may bethreatened by employment
competition created by additionalemployment opportunities at theproposed plant with substantial
losses in labour power
Involving the community in employmentstrategies.
Tourism lowTourism may suffer due to
uninformed scares of proposedplants health risks
Informing and involving tourism bureas of thehealth and safety issues related to the plant aswell as the environmental impact the proposed
plant may or may not have.
General and Endangered species moderateThreats to the habitat and resources
of endangered species due to theconstruction the proposed plant
Relevant documentations regarding the floraand fauna in the vicinity should be well
researched to assess any impact the proposedplant may have on the different species and
how to avoid it.
In the workplace high
Health and Safety iss ues inunfavourable working conditions,
such as extreme heat environmentand toxic gas environments
Draw up well researched and structured healthand safety manuals for staff, as well as
adequate training of all relevant staff members.
Infrastructure changes and demand lowInfrastructural changes in nearby
residential areas may affect propertydemand
Make provisions for additional infrastructuralconstruction rather then buying existing
property to avoid overflooding the propertymarket
Traffic changes lowSudden increases in traffic may
cause time delays and frustrationsin the existing communities.
Address future traffic prblems with localmunicipal authorities to achieve alternative
means of transport or alternative trafficarrangements to avoid traffic congestion.
Housing demand highHousing market may be flooded due
to additional employmentBuild new houses for new employees.
6. Health and safety
7. Infrastructure, housing and traffic
PRELIMINARY ENVIRONMENTAL IMPACT ASSESSMENT
1. Air Quality
2. Water Quality
3. Lanscaping issues
4. Socio-economic environment
5. Fauna and Flora
10. HAZOP STUDY:
HAZOP is the industrialized method of identifying and preventing problems
associated with hazardous conditions at a commercial plant, normally a chemical
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plant. The hazard identification procedure forms an integral part of design and
operation of a new plant. The procedure is constantly repeated and revised during
the design process to ensure safety and operability. If the design is preceded by a
pilot study, such a study would be used to identify potential hazards and the
significance of those potential hazards can then be assessed by means of a well-structured experiments.
The HAZOP study is specifically employed to identify potential hazards. The design
may be altered to eliminate some of these hazards. The main objectives of a HAZOP
are therefore to:
i. Identify potential hazards and/or mal-operations
ii. Assess the most likely consequences
iii. Recommend the most appropriate corrective actions to be taken
For each plant a distinct HAZOP Team will be assembled to deal with hazardousconditions and problems associated with safety at the plant. The HAZOP Team Afor
the Ethylbenzene Production Facility comprise of the following individuals:
Project Engineer or Project Manager:
This is the person who will manage the overall design of the new plant. All
deliverables and important decisions vest in this person. He/she will also be
responsible for the budget and cost estimations. It is therefore important that he/she
be part of the HAZOP team. The identified hazardous conditions at the plant can
then be reassessed and mitigated or eliminated by decisions taken by the Project
Engineer together with his/her design team.
Process, Chemical or Metal lurg ical Engin eer:
The Process Engineer is the main person responsible for the detailed design and
draw up of the process flow diagram and equipment selection. The in-depth
knowledge of this individual will be critical in identifying hazardous conditions at
specific processing units as well as knowledge of possible mitigating alternatives to
attenuate such conditions. He/she may also estimate the likelihood of hazardous
conditions causing damage or safety concerns.
Comm iss ion ing Engineer:
The initial start-up of the new plant is done under the auspices of this engineer.
He/she may be the same person as the person in bullet number 2, above. At each
start-up and shut-down of a chemical processing plant, non-steady state conditions
prevail which may be a major safety and hazardous concern for the people and the
plant equipment. The Commissioning Engineer will predict the likelihood of such
dangers and with his theoretical knowledge and relevant experiences he/she will
make informed decisions regarding those dangers.
Instrumentat ion Design Engineer:
This person will be in control of the process control systems installation. He/she will
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advise on the most appropriate control instrumentation and devices to use for the
specific control strategies.
Chemist :
Chemical sampling will be important in the HAZOP study and the Chemist will be in
control of the sampling to ensure accurate judgment regarding Hazardous material.
Electr ical Engineer:
The electrical engineer will be in control of all electrical equipment.
HAZOP Expert:
This person is normally an Environmental Scientist or a Health and Safety Officer,
with vast experience in the operations of HAZOP studies. He/she will guide and
manage the team accordingly. Even though this person may be lower ranked (Salary
and Status) at the plant, he will be leading the team. It is expected that he/she lead
the team without want or favour and with an iron fist to ensure a successful HAZOPstudy, since lives depend on this study.
A HAZOP study was performed on the following process units:
The Adiabatic Alkylation Reactor (R-101)
The Flash Drum (V-102)
The Benzene Tower (T-101)
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Table 4: HAZOP Study on REACTOR
Page: 1 of 1
100 Rev no.: Date:
Meeting date:
Material: Activity:
Source: Destination:
1 More of
Sudden
increase in
Temperature
Sudden increase in flow
of air and fuel gas to
Fired Heater, control
dynamics too slow
Fire in reactor,
explosions, piping
corrosion, damage
caused to catalyst
Reactor inlet
temperature
controlled
2 Less of
Sudden
decrease in
Temperature
Insufficient fuel and air
flow to Fired Heater,
Decrease in reactant
inlet flow
Low reactor conversion
Reactor inlet
temperature
controlled
3 More of
Concentration
of Benzene in
Effluent
To much
benzene in
reactor effluent
stream
Low conversion due to:
(i) low feed temperature
or (ii) too little ethylene
in reactor feed or (iii)
deactivation of c atalyst
ethyl benzene product
not sufficiently
produced
Reactor outlet
composition
controlled. Reactor
temperature
controller installed.
Ethylene feed
controller installed
4 More of
Substantial
pressure
increase over
catalyst bed
Catalyst fouling and/or
deactivation
Ineffective conversion of
reactants
Reactor Pressure
controlled
5 Less of
Pressure drop
over catalyst
bed
Leakages
gas escapes,
insufficient products,
low conversion
Reactor Pressure
controlled
6 No Feed FlowNo reactants in
inlet pipe
Valve malfunction,
blockages and/or
leakages
Empty reactor, no
reactions taking place,
no products
Reactor inlet flow
controlled
7 More of
Cooling fluid
flow increase
above required
value
Control valve fails open
or controller fails and
opens valve
Reactor cools, reactant
concentration buildup,
runaway of reactor
Temperature Alarm
to indicate
unwanted drop in
reactor temperature,
install high-flow
alarm
8 Less of
Cooling fluidflow decrease
below required
value
Plugged cooling line(partially), water source
failure, control valve fail
to respond
Low cooling and
reactor temperature
increases. Possiblereactor runaway,
reaction rate increases
releasing additional
heat, pressure
increase, reactor
explodes
Install low-flow
alarm, low-flow
controller
9 No
Cooling fluid
does not flow
into reactor
Control valve fails
closed, cooling water
service failure, controller
fails and closes valve
No cooling and reactor
temperature increase.
Reactor runaway. High
buil-up of pressure may
cause explosion.
Equipment damage
Install low-flow
alarm, low-flow
controller and water
source failure alarm.
Include a standby
water source
10 Reverse
Cooling fluid
flows
backwards
Backflow of cooling
water due to high back
pressure,control valve
fails closed, cooling
water service failure.
No cooling and reactor
temperature increase.
Reactor runaway. High
buil-up of pressure may
cause explosion.
Equipment damage
Install no-flow
alarm, no-flow
controller. Include a
standby water
source. Install a
water source
switch. Install a no-return valve
Actions
Adjust fuel and air inflow to Fired
Heater
Increase reactant feed ratio, and
control feed temperature by
adjusting fuel and air to Fired
Heater
Possible
Consequence Safeguards Comments
Regenerate or replace catalyst
Adjust fuel and air inflow to Fired
Heater
Frequent leakage inspections
No flow indicator
Stop plant and check water
source. Check and correct water
source failure. Switch cooling
system to standby water source.
Part Considered:
R-101
1-Aug-12
TITLE:
UNIT
HAZOP Team:
Ethylbenzene Production Plant
A
Adiabatic Reactor
1-Aug-12
Design intent:Process
Parameter
Carbon Steel
Feed Tanks
React Benzene with Ethylene
Flash Drum (V-102)
No.Deviation
(Guide Word) Devia tion Possible causeElement
(Study Node)
Reactor
Temperature
Reactor
Pressure
Stop plant or fix valve and/or
controller, adjust manual valve
Cooling Coil
Flow
Stop plant and flush cooling pipe
line with appropriate reagent.
Replace and/or fix control valve
Stop plant and check water
source. Check and correct water
source failure. Switch cooling
system to standby water source.
Replace and/or fix control valve
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Table 5: HAZOP Study on FLASH DRUM
100 Rev no.: Date:Meeting date:
Material: Activity:Source: Destination:
1 more of Pressure
too muchvapour flow,
suddentemperature
rise
malfunction of ReactorEffluent Cooler (E-101)
Corossion, equipment
damage, pipingruptures
Level Controller,
Vapour OutletPressure Controller
2 Less of No feed to flash
drum
Piping ruptures,upstream process
malfunction
Corossion, equipmentdamage
Level Controller
3 More of Pressure
increase andlevel increase
Upstream malfunctions,Reactor Effluent Cooler
ineffective
Corossion, equipmentdamage, piping
ruptures
Analys er and LevelController
HAZOP team: APart c onsidered:
Design intent: Stainless SteelAdiabati c React or (R-101)
UNIT V-102
No. Guide Word Element Deviation Possible cause Safeguards CommentsConsequence
Benzene Tower (T-101)
Acti ons
1-Aug-121-Aug-12
Flash Drum
Phase Separation
Flow
Adjust bottoms outlet valve to
allow more liquid drainage
Open Flash Drum Vapour valve(v7) to release pressure
Close bot toms valve (v9)
Table 6: HAZOP Study on BENZENE TOWER
100 Rev no.: Date:
Meeting date:
Material: Activity:
Source: Destination:
Adjust Vapour valve (v13), Decrease
Reflux Flow to the Tower
Adjust Vapour valve (v13), Decrease
Reflux Flow to the Tower
Malfunction of Tower Feed Heater (E-102),
Leakages in Column, Temperature decrease in
Tower
Ineffective Production Rate,
Bottoms Product
Contaminated, Equipment
Damage
Temperature increase in TowerTower Feed Heater Malfunction
Malfunction of Tower Feed Heater,Adjust bottoms outlet valve (v9) to allow
level in Tower to drop
Part c onsidered: Benzene Tower
Design intent:Stainless Steel Phase Seperation
Flash Drum Ethylbenzene Column
UNIT T-101 Aug-12
HAZOP team: A Aug-12
Safeguards Comments Actions
1 Less of
Overhead
Pressure
Sudden
decrease in
Vapour Flow
Temperature
Controller, Pressure
Controller in Vapour
Product Stream
No.Guide
WordElement Deviation Possible cause Consequence
2 More of
Sudden
increase in
Vapour FlowVapour Stream
Pressure Controller
3 More of Bottoms
Flow
High Tower
Level
Equipment Damage, Ineffective
separation of feed componentsLevel Controller
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11. DETAILED DESIGN:
11.1 Reactor Design
The production of ethyl benzene (EB) by the alkylation reaction of benzene (B) and
ethylene (E) involves the following reactions:
C6H6 + C2H4 C6H5C2H5 reaction 1
benzene ethylene ethyl benzene
A major side reaction also takes place, but could be avoided by adjusting relevant
process conditions. The undesired di-ethyl benzene (DEB) is produced according to
the following reaction:
C6H5C2H5 + C2H4 C6H4 (C2H5)2
Ethyl benzene ethylene di-ethyl benzene reaction 2
The two reactions can be written in the form below:
Reaction 1: B + E EB
Reaction 2: EB + E DEB
1. Mole Balances:
Ethylene:
Benzene:
Ethyl benzene:
Di-ethylbenzene:
2. Rate Laws:
Reaction 1:
Reaction 2: R = 1.987 kcal/kmol.K
k0,1 = 1.00 x 106
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k0,2 = 6.00 x 105
E = 22 500 kcal/kmol
Net Rates:
3. Stoichiometry:
The volumetric flow rate is
We assume there is no pressure drop for the purpose of simplification and
that the reaction is carried out isothermally. Therefore, P = P0 and T = T0, we
also assume there is no change in the total number of moles. This means
that:
4. Parameter Evaluation:
The plant is assumed to be running at 330 days/annum, to allow for periodic
shut-down as well as maintenance, with a production rate of 100 000 metric
tons per annum. This is equivalent to a 12 626 kg/hr ethyl benzene production
rate. The benzene (B) and ethylene (E) is fed to the reactor at a ratio of 8:1,
to avoid production of the unwanted di-ethylbenzene byproduct. The feed tothe reactor is therefore:
and
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These equations are solved simultaneously using the PolyMath program. The flow
rate profiles along the length of the reactor are shown in Figure 10 below.
Figure 12: Flow Rate Profile along length of Reactor
This profile indicates that a very small amount of di-ethylbenzene is produced in
comparison to the ethyl benzene. This is mainly due to the high benzene ethylene
feed ratio, a condition that favours the production of ethyl benzene.
If we alter the feed ratio in such a manner that there is more ethylene than benzene
in the feed we will observe a significant production of di-ethylbenzene. At a certain
point in the reactor, ethyl benzene reacts (or is consumed) to such an extent that it
starts to decrease along the remainder of the reactor. The graph below
demonstrates this.
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0 2 4 6 8 10 12
Flow
rate(kmol/s)
reactor length (m)
FE
FEB
FDEB
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Figure 13: Flow Rate Profiles
The graph shows the significance of keeping the ratio of benzene and ethylene in the
feed as high as possible to ensure a high production of ethyl benzene and a low
production of the undesired di-ethylbenzene by-product. The conversion of benzene
will however not be sufficiently high. To remedy this, a few reactors in series would
increase the overall conversion of the plant together with a recycled stream of
benzene that would ensure the maximum utilization of the reactants. Table 6 shows
the PolyMath program used to perform the calculations for the reactor.
Table 7: PolyMath Program
__________________________________________________________________
ODE Report (STIFF)
Differential equations as entered by the user[1] d(FE)/d(L) = (-rate1-rate2)*A[2] d(FB)/d(L) = (-rate1)*A[3] d(FEB)/d(L) = (rate1-rate2)*A[4] d(FDEB)/d(L) = rate2*A
Explicit equations as entered by the user
[1] v0 = 0.261[2] CB = FB/v0[3] T = 673[4] k1 = 1.00*10^6*exp(-22500/(1.987*T))[5] CEB = FEB/v0[6] FT0 = (2000/(8.314*673))*v0[7] k2 = 6.00*10^5*exp(-22500/(1.987*T))[8] CE = FE/v0[9] rate1 = k1*CE*CB[10] rate2 = k2*CE*CEB[11] A = 7.07[12] X = (0.0810-FB)/0.0810
___________________________________________________________________
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0 2 4 6 8 10 12
flow
rate(km
ol/s)
reactor length (m)
FE
FB
FEB
FDEB
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Figure 14: Drawing of Alkylation Reactor with Dimensions
The packed bed reactor has the following specifications obtained from the
calculations done in PolyMath:
Volume = 74.22 m3
Diameter = 3 m
Length = 10.5 m
Material of Construction = Carbon Steel
Catalyst = Zeolite (ZSM -6)
Maximum Pressure = 3.2 bar
Maximum allowable temperature = 480 C Maximum allowable temperature for catalyst = 550 C
Vertical orientation
Catalyst Packed Tubes
3 m
10.5 m
Inlet
Outlet
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11.2 Benzene Tower Design:Table 8 Spec Sheet Benzene Tower
THE TOWER PLATE SPECIFICATIONS:
Layout Sketches:
SPECIFICATION SHEET OF DISTILLATION COLUMN:
PLATE THICKNESS:
IDENTIFICATION:NO. REQUIRED:
TRAY TYPE:
FUNCTION:
PLATE I.D:
190 mm liquid
ACTIVE HOLES:
PLATE PRESSURE DROP:
Benzene Tower (T-101)1
Sieve Tray
Benzene separation
0.340 m
Continuous
70 % maximum rate
OPERATIONS:
TURNDOWN RATIO:
PLATE MATERIAL:
HOLE SIZE:
PLATE SPACING:
Stainless Steel
5 mm
0.5 m
5 mm1100
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Figure 15: Benzene Tower Dimensions
12. PLANT COST ESTIMATIONS:
CAPCOST was used to obtain cost estimates for all standard/generic equipment
such as the reactor, heat exchangers, pumps, fired heater, distillation columns and
process vessels. Specialized equipment costs, such as the catalyst used in the
reactor was obtained from industrial manufacturers advertisements online.
The design and performances of the different processing units were determinedusing vendor supply information and from previous study material. Costing
estimations were performed using commercially available software such as
CAPCOST and vendor supply information. All the cost estimates use a 2nd quarter
2012 basis. The operating costs were determined from the process material and
energy balances together with manufacturers standard costs.
12.1 Capacity Effect on Equipment Costs:
The current equipment purchase costs can be obtained from the relation between an
attribute of the equipment that is related to the capacity of the unit and is given in the
equation below (Turton et al, 2009):
()
With A = the equipment cost attribute
C = the purchased cost
n = cost exponent
The subscripts a and b are related to the required attribute and the base attribute,
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respectively. In short, these types of correlations are used to determine cost
estimates for equipment through the use of past purchasing costs data, by updating
the present equipment unit with respect to its capacity attribute. The correlation
below is also taken from the Turton textbook and include the decreasing effect that
inflation has on equipment purchasing costs. This correlation is heavily dependenton time, since inflation is the erosion in the purchasing or buying power of money.
The cost estimate is therefore calculated taking into consideration the changing
conditions in the economy.
()With C = the purchased costs
I = the cost index
The subscripts 1 and 2 are related to the base time when the costs are known and
the time when costs are desired, respectively. There are numerous cost indexes
available in industry that includes the economic effect of inflation. For this design the
Chemical Engineering Plant Cost Index (CEPCI) will be used since it was used in the
CAPCOST excel spreadsheet as well.
Table 9: CEPCI in 2012 (Turton et al.)
Determination Year CEPCI
2004 4442005 468
2006 500
2007 527
2008 555
2009 583
2010 611
2011 639
2012 667
Historic
al
Extrapolated
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Figure 16: Extrapolation of Index
An estimation can be made to obtain the CEPCI cost indexin August 2012 as can
be seen above in the Table and Figure above. The extrapolation is done by using the
most recent data (2004-2006 in Turton et al, 2007) that showed a linear yearly
increase in the index. This is only a rough estimate.
The latest values for the CEPCI is given by
(www.nt.ntnu.no/users//magnehi/cepci_2011_py.pdf)
Figure 17: CEPCI (courtesy ofwww.EngineeringToolBox.com)
12.2 Labour Requirements:
Operating labour costs was determined from the number of major processing unit
operations. The number of operators and supervisory staff was taken from the
Suncors LO-CAT unit as an example. Standard industry salary was used tocalculate the labour costs. The total operating labour costs was therefore calculated
by multiplying each worker with the estimated standard salary as per the dictates of
444
468
500
527555
583
611
639
667
y = 28x - 55669
R = 0.9932
400
450
500
550
600
650
700
2002 2004 2006 2008 2010 2012
index
year
historical
extrapolated to
2012 for EB Plant
Linear (historical)
http://www.nt.ntnu.no/users/magnehi/cepci_2011_py.pdfhttp://www.nt.ntnu.no/users/magnehi/cepci_2011_py.pdfhttp://www.nt.ntnu.no/users/magnehi/cepci_2011_py.pdfhttp://www.nt.ntnu.no/users/magnehi/cepci_2011_py.pdfhttp://www.nt.ntnu.no/users/magnehi/cepci_2011_py.pdfhttp://www.nt.ntnu.no/users/magnehi/cepci_2011_py.pdfhttp://www.nt.ntnu.no/users/magnehi/cepci_2011_py.pdfhttp://www.engineeringtoolbox.com/http://www.engineeringtoolbox.com/http://www.engineeringtoolbox.com/http://www.engineeringtoolbox.com/http://www.engineeringtoolbox.com/http://www.nt.ntnu.no/users/magnehi/cepci_2011_py.pdf7/14/2019 Final Design -Assignment III
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South African petrochemical employees salaries as an example and standard.
The number of operators that will be operating the plant was determined from the
standard three shift/day rate of labour and with the four operators/shift required to
operate the plant. The salaries were taken at a standard monthly salary that included
bonus incentives and miscellaneous income after income tax deductions, to avoidtedious calculations. The same principles were performed on the supervisory units of
the plant, which included the management, foremen, clerks, professionals, and the
peremptory security personnel. The operating labour cost calculations are displayed
in the table below.
Table 10: Labour Costs
12.3 Plant Operation Time:
Industrial facilities use procedures to sustain the plant while the plant is still in
operation. These procedures may include inspection, repairs, alterations,
replacements as well as minor maintenance to existing process units. However, all
industrial plants require a scheduled period to perform major maintenance that will
be costly to the process but necessary. This is commonly called plant shutdowns.
Delaying or ignoring scheduled plant shutdowns may be disastrous and may cause
the entire facility to stop operations indefinitely. In performing economic analysis the
total annual operating hours is important to determine since it is used in most cost
estimate calculations. It is also used in the CAPCOST Excel Spreadsheet. The plant
capacity factor refers to the amount of annual operating hours, presented as a
percentage of the total possible operating hours per year available. There are 365days in a year that is available for a plant to operate, but sulphur recovery units
normally only operate at a plant capacity factor of 90.4%. The equation follows:
() This puts the annual operating hours of this design at 7920 operating hours per
year. This amounts to 35 days of shutdown, which is almost 1.3 months. Due tothe high cost normally incurred by shutdowns in industrial plants, the possibility is
Number Salary Salary Cost
EMPLOYEE No. per month per month
Managers 2 19,200.00R 38,400