Final Design -Assignment III

7/14/2019 Final Design -Assignment III

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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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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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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, 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$






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


32/67



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.pdf


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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

Final Design -Assignment III

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