Sol_HW9_KS_9nov05_v4 - Chemical Engineering 150B- Fall 2005...

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Chemical Engineering 150B- Fall 2005 Problem Set #9 Solutions Problem 1. (20 Points) Determine by the Kremser method the separation that can be achieved for the absorption operation indicated below for the following combinations of conditions: (a) Six equilibrium stages and 75 psia operating pressure, (b) Three equilibrium stages and 150 psia operating pressure, (c) Six equilibrium stages and 150 psia operating pressure, At 90 o F, the K values are as follows for the two different pressures: 75 psia 150 psia Notice that nC10 is being stripped since it enters at the top of the column, while the other components are being absorbed since they enter at the bottom of the column. Note to graders: There is one typo: the K value for C1 at 75 psia, 90 F is 29 (not 2.9 as shown above). This value is consistent with Figure 2.8 in the book. Do not penalize if C1 answers for part(a) are incorrect.
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Using Excel with the equations mentioned above : N 6 29 1660 0.0086207 0.9913793 1645.7 14.3 6.5 168 0.0384615 0.9615385 161.5 6.5 1.95 96 0.1282051 0.8717954 83.7 12.3 0.61 52 0.4098358 0.5913125 30.7 21.3 0.19 24 1.3157888 0.0541833 1.3 22.7 0.0011 0.0011 500 0.0044 0.9956 2.2 497.8 total 1925.2 574.8 2000.0011 500 10 pt for Kremser method setup 7 pt for tables 3 pt for recognizing K values change between parts a, b, & c
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Problem 2. (35 Points) A fractionation column operating at 101 kPa is to separate 30 kg/h of a solution of benzene and toluene containing 0.6 mass fraction toluene into an overhead product containing 0.97 mass fraction benzene and a bottoms product containing 0.98 mass fraction toluene. A reflux ratio of 3.5 is to be used. The feed is liquid at its boiling point, feed is to the optimal tray, and the reflux is at saturation temperature. (a) Determine the quantity of top and bottom products. (b) Determine the number of stages required using a McCabe-Thiele Diagram. (c) Generate a plot of number of stages versus reflux ratio using ASPEN. For ASPEN, use the NRTL property model and the DSTW column model. You will have to specify the reflux ratio, operating pressure, the condenser type, and the distillate compositions. Use the values from your hand calculations. You can generate a table of reflux ratio versus number of theoretical stages under the “Calculation Options” in the input for the DSTW column. Include a printout of your ASPEN flowsheet and stream table for the case when reflux ratio is 3.5. Equilibrium Data Mole Fraction Benzene, 101 kPa: y 0.21 0.37 0.51 0.64 0.72 0.79 0.86 0.91 0.96 0.98 x 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.95
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5 pt
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For part c, use the DSTW type of distillation column. Specify the reflux ratio (3.5), operating pressure (101000 Pa), the condenser type (total), and the % distillate recoveries (0.974 benzene, 0.02 toluene). 3 pt for q line 5 pt for rectifying O.L. 5 pt for stripping O.L. 7 pt for staging correctly
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Look up results for the DSTW column and find the tab where ASPEN generated n versus reflux ratio. Theoretical stages Reflux ratio 9 9.821432 10 5.561028 11 3.387937 12 2.828747 13 2.519747 14 2.279941 15 2.047204 16 1.833878 B1 F D B HW9 problem2 Stream ID B D F Temperature K 382.8 353.8 366.9 Pressure atm 1.00 1.00 1.00 Vapor Frac 0.000 0.000 0.000 Mole Flow kmol/hr 0.194 0.155 0.349 Mass Flow kg/hr 17.844 12.156 30.000 Volume Flow l/min 0.380 0.249 0.627 Enthalpy MMBtu/hr 0.005 0.008 0.013 Mole Flow kmol/hr BENZENE 0.004 0.150 0.154 TOLUENE 0.190 0.005 0.195 5 pt for print out and stream table
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0 2 4 6 8 10 12 14 16 18 05 1 0 1 5 Reflux ratio
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This homework help was uploaded on 04/02/2008 for the course CHEM 150b taught by Professor Bell during the Spring '08 term at University of California, Berkeley.

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Sol_HW9_KS_9nov05_v4 - Chemical Engineering 150B- Fall 2005...

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