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CHE655 Plant Design Project #2 Summer 2014

DESIGN OF A CUMENE PRODUCTION PROCESS

(Courtesy of the Department of Chemical Engineering at West Virginia University)

Introduction

Cumene (isopropyl benzene) is produced by reacting propylene and benzene over an acid

catalyst. Cumene may be used to increase the octane in gasoline, but its primary use is as a

feedstock for manufacturing phenol and acetone.

The plant where you are employed has been buying cumene to produce phenol. Management

is considering manufacturing cumene rather than purchasing it to increase profits. Someone

has made a preliminary sketch for such a process and has submitted to the engineering

department for consideration. Your group is assigned the problem of evaluating the sketch and

recommending improvements in the preliminary design. Note that optimization is NOT

required in this design project.

Process Description

Figure 1 is a preliminary process flow diagram (PFD) for the cumene production process. The

raw materials are benzene and propylene. The propylene feed contains 5 wt% propane as an

impurity. It is a saturated liquid at 25C. The benzene feed, which may be considered pure, is

liquid at 1 atm and 25C. Both feeds are pumped to about 3000 kPa by pumps P-201 and P-

202, are then vaporized and superheated to 350C in a fired heater (H-201). The fired heater

outlet stream is sent to a packed bed reactor (R-201) in which cumene is formed as a desired

product and p-diisopropyl benzene (PDIB) as an undesired product. The reactor effluent is sent

to a flash unit (V-201) in which light gases (mostly propane and propylene, some benzene,

cumene and PDIB) are separated as vapor in Stream 9. Stream 10, containing mostly cumene

and benzene, is sent to a distillation column (T-201) to separate benzene for recycle from

cumene product. The desired cumene production rate is 100,000 metric tons/yr.

Process Details

Feed Streams

Stream 1: benzene, pure liquid, 25C and 1 atm

Stream 2: propylene with 5 wt% propane impurity, saturated liquid at 25C

Effluent Streams

Stream 9: fuel gas stream, credit may be taken for LHV of fuel

Stream 12: cumene product; must be > 99 wt% purity

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Equipment

Pump (P-201):

The pump increases pressure of the benzene feed from 1 atm to about 3000 kPa.

Pump (P-202):

The pump increases the pressure of the propylene feed to about 3000 kPa.

Fired Heater (H-201):

The fired heater desubcools, vaporizes, and superheats the mixed feed up to 350C. Air

and natural gas must be fed to the fired heater. Natural gas is priced at its lower heating

value. The fired heater is 75% efficient.

Reactor (R-201):

The reactor feed must be between 300C - 400C and between 2800 kPa - 3200 kPa.

Benzene must be present in at least 50% excess. Conversion of the limiting reactant is

92%. The reactor may be assumed isothermal, and the exothermic heat of reaction is

removed by vaporizing boiler feed water to make high-pressure steam. Credit may be

taken for the high-pressure steam.

Main reaction:

cumenebenzenepropylene

1296663 HCHCHC

Side reaction:

benzene ldiisopropy-pcumenepropylene

181212963 HCHCHC

Flash Vessel (V-201):

This is actually a combination of a heat exchanger and a flash drum. The temperature

and pressure are lowered in order to separate the propane and propylene from the

cumene and benzene. Cooling water is used to lower the temperature.

Distillation Column (T-201):

Here all cumene and PDIB impurity in Stream 10 goes into Stream 12, and is in the

liquid phase. All benzene, propylene and propane go to Stream 11, and is also in the

liquid phase. A distillation column requires both heat addition and heat removal. Heat

removal is accomplished in a condenser (not shown), which requires an amount of

cooling water necessary to condense the contents of Stream 11. Heat addition is

accomplished in a reboiler (not shown), which requires an amount of high-pressure

steam necessary to vaporize the cumene in Stream 12.

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Design of Heat Exchanger in V-201

A detailed design of the heat exchanger in V-201 is required for base-case conditions. It should

be assumed that cooling water is available at the conditions specified in the Appendix of this

problem statement. For this heat exchanger design, the following information should be

provided:

Diameter of shell

Number of tube and shell passes

Number of tubes per pass

Tube pitch and arrangement (triangular/square/..)

Number of shell-side baffles, if any, and their arrangement (spacing, pitch, type)

Diameter, tube-wall thickness, shell-wall thickness, and length of tubes

Calculation of both shell- and tube-side film heat transfer coefficients

Calculation of overall heat transfer coefficient (you may assume that there is no fouling on either side of the exchanger)

Heat transfer area of the exchanger

Shell-side and tube-side pressure drops (calculated, not estimated)

Materials of construction

Approximate cost of the exchanger

A detailed sketch of the exchanger should be included along with a set of comprehensive

calculations in an appendix for the design of the heat exchanger. You should use ASPEN

Exchanger Design & Rating (EDR) in the ASPEN Plus simulator to carry out the detailed

design.

Cumene Production Reaction For final design of this process, the kinetics for the reactions given below should be used. For

the desired reaction:

cumenebenzenepropylene

HCHCHCk

12966631

r k c c

kRT

p b1 1

1435 10

24 90

mole / g cat sec

. exp.

For the undesired reaction:

C H C H C H

propylene cumene p diisopropyl benzene

k3 6 9 12 12 18

2

5

r k c c

kRT

p c2 2

262 9 10

35 08

mole / g cat sec

. exp.

where the units of the activation energy are kcal/mol, the units of concentration are mol/L, and

the temperature is in Kelvin.

For a shell and tube packed bed, the recommended configuration, the following data may be

assumed:

catalyst particle diameter dp = 3 mm

catalyst particle density cat = 1600 kg/m3

void fraction = 0.50

heat transfer coefficient from packed bed to tube wall h = 60 W/m2C

use standard tube sheet layouts as for a heat exchanger

if tube diameter is larger than in tube sheet layouts, assume that tube area is 1/3 of shell area

Economic Analysis

When evaluating alternative cases, you should carry out an economic evaluation and

profitability analysis based on a number of economic criteria such as payback period, internal

rate of return, and cash flow analysis. In addition, the following objective function should be

used. It is the equivalent annual operating cost (EAOC), and is defined as

EAOC = -(product value - feed cost - other operating costs - capital cost annuity)

A negative EAOC means there is a profit. It is desirable to minimize the EAOC; i.e., a large

negative EAOC is very desirable, although you are not being asked to carry out optimization.

The costs for cumene (the product) and benzene (the feed) should be obtained from the

Chemical Marketing Reporter, which is in the Evansdale Library. The impure propylene feed is $0.095/lb.

The capital cost annuity is an annual cost (like a car payment) associated with the one-time,

fixed cost of plant construction. The capital cost annuity is defined as follows:

1)1(

)1(

n

n

i

iiFCIannuitycostcapital

where FCI is the installed cost of all equipment; i is the interest rate, i = 0.15; and n is the plant

life for accounting purposes, n = 10.

For detailed sizing, costing, and economic evaluation including profitability analysis, you may

use the Aspen Process Economic Analyzer (formerly Aspen Icarus Process Evaluator) in Aspen

Plus. However, it is also a good idea to independently verify the final numbers based on other

sources such as cost data given below.

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Other Information

You should assume that a year equals 8000 hours. This is about 330 days, which allows for

periodic shut-down and maintenance.

Final Comments

As with any open-ended problem; i.e., a problem with no single correct answer, the problem

statement above is deliberately vague. You may need to fill in some missing data by doing a

literature search, Internets search, or making assumptions. The possibility exists that as you

work on this problem, your questions will require revisions and/or clarifications of the problem

statement. You should be aware that these revisions/clarifications may be forthcoming.

Moreover, in some areas (e.g. sizing/costing) you are given more data and information than

what is needed. You must exercise engineering judgment and decide what data to use. Also you

should also seek additional data from the literature or Internet to verify some of the data, e.g.

the prices of products and raw materials.

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Cost Data

Raw Materials

Benzene (> 99.9 wt% purity) see Chemical Marketing Reporter

Propylene ( 5 wt% propane impurity) $0.095/lb

Product

Cumene (> 99 wt% purity) see Chemical Marketing Reporter

Utility Costs Low Pressure Steam (446 kPa saturated) $3.00/1000 kg

Medium Pressure Steam (1135 kPa saturated) $6.50/1000 kg

High Pressure Steam (4237 kPa saturated) $8.00/1000 kg

Natural Gas (446 kPa, 25C) $3.00/106 kJ

Fuel Gas (446 kPa, 25C) $2.75/106 kJ

Electricity $0.08/kWh

Boiler Feed Water (at 549 kPa, 90C) $300.00/1000 m3

Cooling Water $20.00/1000 m3

available at 516 kPa and 30C

return pressure 308 kPa

return temperature is no more than 15C above the inlet temperature

Refrigerated Water $200.00/1000 m3

available at 516 kPa and 10C return pressure 308 kPa return temperature is no higher than 20C

Waste Treatment $1/kg organic waste

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Equipment Costs (Purchased)

Pumps $630 (power, kW)0.4

Heat Exchangers $1030 (area, m2)0.6

Compressors $770 (power, kW)0.96 + 400 (power, kW)0.6

Turbine $2.18105 (power output, MW)0.6 assume 65% efficiency

Fired Heater $635 (duty, kW)0.8

assume 80% thermal efficiency

assume can be designed to use any organic compound as a fuel

Vessels $[1.67(0.959 + 0.041P - 8.310-6P2)]10z z = (3.17 + 0.2D + 0.5 log10L + 0.21 log10L

2)

D = diameter, m 0.3 m < D < 4.0 m

L = height, m L/D < 20

P = absolute pressure, bar

Catalyst $2.25/kg

Reactor Cost as vessel with appropriate additional volume for cooling coil

(fluidized bed) or tubes (shell and tube packed bed)

Packed Tower Cost as vessel plus cost of packing

Packing $(-110 + 675D + 338D2)H0.97

D = vessel diameter, m; H = vessel height, m

Tray Tower Cost as vessel plus cost of trays

Trays $(187 + 20D + 61.5D2)

D = vessel diameter, m

Storage Tank $1000V0.6

V = volume, m3

It may be assumed that pipes and valves are included in the equipment cost factors.

Location of key valves should be specified on the PFD.

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Equipment Cost Factors

Pressure < 10 atm, 0.0 does not apply to turbines, compressors, vessels,

(absolute) 10 - 20 atm, 0.6 packing, trays, or catalyst, since their cost equations

20 - 40 atm, 3.0 include pressure effects

40 - 50 atm, 5.0

50 - 100 atm, 10

Carbon Steel 0.0 Stainless Steel 4.0

Total Installed Cost = Purchased Cost (4 + material factor + pressure factor)

Heat Exchangers

For heat exchangers, use the following approximations for heat transfer coefficients to allow

you to determine the heat transfer area:

situation h (W/m2C)

condensing steam

6000

condensing organic 1000

boiling water

7500

boiling organic 1000

flowing liquid

600

flowing gas

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References

1. Felder, R.M. and R.W. Rousseau, Elementary Principles of Chemical Processes (2nd ed.),

Wiley, New York, 1986.

2. Perry, R.H. and D. Green, eds., Perrys Chemical Engineering Handbook (6th ed.), McGraw-Hill, New York, 1984, p. 9-74.