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You are an engineer assigned the task of designing a distillation ...

By Ernest Foster,2015-02-14 21:34
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Step 5: Using ASPEN Plus flow-sheet simulator validate your design. Use Grayson- Street thermo option. a. Use short-cut methods. Rigorous methods ...

ECH 4265 PROJECT Spring 00

    You are an engineer assigned the task of designing a separation process to separate streams that contain hydrogen (raw material), methane (by-product), benzene (main product) and toluene (Raw material). The feed1 which is saturated liquid and is at 1 atmosphere has 30 (mole) % benzene, 5 % Hydrogen, 5 % Methane and rest toluene while feed2 which is saturated vapor and is 1 atmosphere has 60 (mole) % benzene, 5 % Hydrogen, 5 % Methane and rest toluene. Both streams have a rate of 100 lbmoles/hr. The streams were mixed at constant pressure and flashed at 1 atmosphere prior to distillation column giving a single feed stream. The toluene and benzene in the vapor phase of the product stream of flash column is 0.5 %. The benzene product stream has to be 99 % pure while toluene stream can be 95 % pure.

    Step 0: Describe the process and draw the block diagram identifying tasks to be completed.

    Step 1: Perform the flash calculations using Raoult's law and data from Ref.1. Assume ?H = 0. mixing

    Step2: Design the base case using McCabe-Thiele method using total condenser and partial reboiler. For the base case:

     R= 1.3 R. minColumn pressure is 1 atmosphere with no pressure drop.

    Use sieve trays.

    Use Raoult's law and Ref.1 for phase behavior data.

    Assume no methane and hydrogen in the feed to distillation column. 2oTake U(Btu/ft-hr-F) = 150 for condenser, 300 for reboiler.

    Step 3: Repeat distillation calculations using Fenske-Underwood-Gilliland method.

    Step 4: Cost the exchangers and distillation column using the cost information below.

    Step 5: Using ASPEN Plus flow-sheet simulator validate your design. Use Grayson-Street thermo option.

    a. Use short-cut methods

    b. Rigorous methods

    Step 6. Minimize the annualized total cost function where the reflux ratio is your decision variable.

Step 7: What happens if

    a. The pressure is 5 atmosphere (Use Aspen short-cut).

    b. The pressure is 0.5 atmosphere (Use Aspen short-cut).

    c. If the feeds are not mixed prior to entering the column (Use McCabe

    Thiele Method).

    d If your boss wants a 60 % toluene stream at a 50 lbmole/hr rate along with

    two other product streams (Use McCabe Thiele Method).

    e. The feed rate is increased 25 % Use Aspen rigorous).

Cost and Sizing Data:

    Distillation Column Cost:

    M&S??1.55Installed Cost,$?4.7DH??280??

where D = Diameter,ft

     H = Column height, ft

     M&S = 1200

     Heat Exchangers:

    M&S??0.65Installed Cost,$?300A??280??

     2where A = Heat exchange area,ft

     M&S = 1200

     Utilities:

Cost of steam (saturated at 600psia) = $5/1000lb oCost of cooling water (available at 70F) = $0.05/1000gal

     Total annualized cost (TAC):

TAC = (Total Equipment Cost)0.2 + Total Annual Utility Cost

    One year has 8400 operating hours

Reference:

     th The Properties of Gases and Liquids”, Reid, Prausnitz, Pooling, McGraw-Hill 4Edition,

    1987.

    Reporting Requirements

     Write a separate memo for each step. In the memo, include summary of results as

    shown in the table below.

     Due Date Reporting Requirements Step 1 March 23 Flowsheet

    Stream Summary

    Step 2 March 30 Revised Flowsheet

    Stream Summary

    Number of Stages

    McCabe Diagram

    Stage Composition Profiles

    L', V', L, V, D, B rates

    Q, A, Q, Areboilerreboilercondensercondenser

    W, Wsteamcooling water

    Column Height

    Column Diameter

    Step 3 April 6 Revised Flowsheet

    Stream Summary

    Number of Stages

    McCabe Diagram

    Stage Composition Profiles

    L', V', L, V, D, B rates

    Q, A, Q, Areboilerreboilercondensercondenser

    W, Wsteamcooling water

    Column Height

    Column Diameter

    Step 4 April 6 Column Cost

    Condenser Cost

    Reboiler Cost

    Cooling Water Cost

    Steam Cost

    Total Annualized Cost Step 5 April 13 a. Revised Flowsheet

    b. Revised Flowsheet Step 6 April 13 Discussion on Annualized Cost versus Reflux Ratio

    Step 7 April 20 a. Discussion, Attach Aspen Run

    b. Discussion, Attach Aspen Run

    c. Discussion, Revised McCabe Thiele Diagram

    d. Revised Flowsheet Stream Summary

    e. Discussion, Attach Aspen Run

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