Project 6: Design of a New, 100,000-Metric-Tons-per-Year Cumene Production Facility

C.6.1 Background

In the opinion of our marketing research department, the demand for phenol-derived plasticizers is on the rise. Therefore, we are investigating the possibility of a new, grassroots phenol plant to handle the anticipated increase. Because phenol is made from cumene, a grassroots cumene plant would also be necessary. Given your experience in troubleshooting our existing cumene process, we would like you to study the economics of a new cumene plant. Specifically, we would like a complete preliminary design of a grassroots, 100,000 tonne/y cumene process using benzene and propylene.

There is a new, proprietary catalyst, and the kinetics are included in Table C.18. The economics of continuing to use propylene with 5% propane impurity at $0.095/lb should be investigated versus purer propylene feed. In preparing this preliminary design, it should be assumed that all steam made can be used elsewhere in the plant with the appropriate economic credit, that condensed steam can be returned as boiler feed water for the appropriate credit, and that fuel gas can be burned for credit at its LHV (lower heating value). Additional information is given in Table C.19.

Table C.18 Reaction Kinetics for Cumene Reactions (Unit 800)

The kinetics for the reactions are as follows:

C3H6propylene + C6H6benzene →k1 C9H12cumene r1=k1cpcb mole/g cat seck1=3.5 × 104 exp(−24.90RT)C3H6propylene + C9H12cumene →k2 C12H18           p-diisopropyl benzene r2=k2cpcc mole/g cat seck2=2.9 × 106 exp(−35.08RT)

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 ρcat = 1600 kg/m3

Void fraction ε = 0.50

Heat transfer coefficient from packed bed to tube wall h = 60 W/m2°C

Use standard tube sheet layouts as for a heat exchanger

If the tube diameter is larger than in tube sheet layouts, assume that the total tube cross-sectional area is 1/3 of the shell cross-sectional area

Table C.19 Additional Information (Unit 800)

Cost of Manufacture

In order to estimate the cost of manufacture (not including depreciation), COMd, the following Equation (8.2) should be used:

COMd=0.180 FCI + 2.73 COL + 1.23 (CUT + CWT + CRM)(8.2)

The current MACRS method for depreciation should be used in the calculations (see Chapter 9).

Hints for Process Simulator

The CHEMCAD process simulator was used to generate the flow table given in Project 5. The hints given here are specifically directed to CHEMCAD users but should also be applicable for other process simulators.

The SRK (Soave-Redlich-Kwong) thermodynamics package for VLE and enthalpy calculations should be used for all the equipment in the process.

For heat exchangers with multiple zones, it is recommended that each zone be simulated with a separate heat exchanger. Actual equipment may include several zones, so costing should be based on the actual equipment specifications.

For the reactor, an isothermal reactor may be assumed to estimate the volume of catalyst and heat-exchange area. For more accurate results, the temperature profile in the reactor should be modeled by completing a differential heat and material balance on the reactor.

For the distillation columns, the Shortcut method (SHOR) should be used to get estimates for the rigorous distillation simulation (TOWR or SCDS). The Shortcut method may be used until an optimum case is near. It is then expected that the final design will be completed using rigorous simulation of the columns.

When simulating a process using “fake” streams and equipment, it is absolutely necessary that the process flow diagram presented not include any “fake” streams and equipment. It must represent the actual process.

C.6.2 Assignment

The assignment is to provide the following:

  1. An optimized preliminary design of a plant to make cumene from benzene and propylene using the new catalyst

  2. An economic evaluation of the optimized process, using the following information:

    • After-tax internal hurdle rate = 9% p.a.

    • Depreciation = MACRS (6-year schedule; see Chapter 9)

    • Marginal taxation rate = 35%

    • Construction period = 2 years

    • Project plant life = 10 years after start-up

Specifically, the following is to be prepared by ... (four weeks from now):

  1. A written report detailing the design and profitability evaluation of the new process

  2. A clear, complete, labeled process flow diagram of the optimized process including all equipment and the location of all major control loops

  3. A clear stream flow table including T, P, total flowrate in kg/h and kmol/h, component flowrate in kmol/h, and phase for each process stream

  4. A list of new equipment to be purchased, including size, cost, and materials of construction

  5. An evaluation of the annual operating cost for the plant

  6. An analysis of the after-tax NPV (10 years, 9%), and the discounted cash flow rate of return on investment (DCFROR) for the recommended process

  7. A legible, organized set of calculations justifying the recommendations, including any assumptions made

C.6.3 Report Format

This report should be in the standard design report format, consistent with the guidelines given in Chapter 29. It should include an abstract, results, discussion, conclusions, recommendations, and an appendix with calculations.

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