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Unformatted text preview: Homework 6 Problem 2 HYSYS™ Distillation Column Processing and
Design Using the Short Cut Column Method
20 points possible due Monday October 10, 2011 Grader: Alan Problem Statement: A bubble cap distillation column with an 18 inch tray spacing is to be used to separate a biphenyl/fluorene mixture. The multicomponent feed enters the column at a temperature of 536oF and pressure of 31.17 psia with the composition shown below: m , lb/hr
m , lb/hr
Component Toluene 44.965 m‐Cresol 13.085 Naphthalene 204.95 Fluorene 171.04 Biphenyl 2,596.1 Phenanthrene 137.06 o‐Cresol 22.493 m‐Terphenyl 441.96 p‐Cresol 36.010 It is desired to obtain 98% biphenyl recovery in the distillate with a column pressure drop of 23.435 psia. Determine the distillate and bottoms concentrations and flow rates, number of trays, optimum feed location, and the reflux ratio. Method of Solution: Use the Shortcut Distillation Column in HYSYSTM to simulate the design generated by hand calculations to separate the feed mixture. Solution: 1) Open HYSYSTM and start a New Case. 2) The Simulation Basis Manager window will open. Click the Fluid Pkgs tab, and click Add. 3) Select the appropriate property package. Since the process streams are hydrocarbon and phenol mixtures, select the PRSV equation of state. Page 1 of 7 4) Click View next to the Component List Selection box. 5) Add the process components. When the Selected Components List is complete, close the Component List View and Fluid Package windows. 6) Click Enter Simulation Environment. 7) Click on the Shortcut Distillation icon on the Object Palette, and click again in the PFD workspace to place the column in the PFD. [The shortcut distillation column operation in HYSYSTM performs Fenske‐Underwood short cut calculations for simple columns. It is a good first estimate for the Page 2 of 7 vapour and liquid flow rates in the enriching and stripping sections, the duties of the condenser and reboiler, the number of theoretical trays, and the optimal feed location. More information on the uses of the shortcut distillation model can be found in the HYSYSTM Help menus.] 8) Double‐click on the column you just placed on the PFD to open the column window. The Design‐Connections page allows you to rename your column and specify the connecting material and energy streams. For this problem, specify a feed stream, distillate product stream, bottoms product stream, condenser duty stream, and reboiler duty stream. We’ll assume that the column utilizes a total condenser and the Top Product Phase is liquid. 9) Click on the Parameters option on the left‐side of the window to specify the key components. From material balances, we know the mole fraction of light key in the bottoms and heavy key in the distillate. The problem statement specified a pressure drop of 23.435 psia, which means that the Page 3 of 7 condenser and reboiler pressures are 7.735 psia. For now the External Reflux Ratio can be left blank. 10) We still need to input our feed stream conditions. Close the column input window and open the feed stream. Enter a temperature of 536oF and a pressure of 31.17 psia. Page 4 of 7 11) Click on the Composition option. Click the Basis… button and change the compositions basis to Mass Flow. Input the given mass flow rate of Toluene and press ENTER. Enter the flow rate of each component; be sure that each is input with the correct units. When all component flow rates have been entered, click OK. 12) Close the feed stream window and open the short‐cut column input window. The Minimum Reflux Ratio should now be calculated by HYSYS and displayed. We will also assume that R = 1.5*Rmin and input an External Reflux Ratio of 0.956. Page 5 of 7 13) Notice that the status bar has turned green and displays “OK”, indicating that the column has converged. Click on the Performance tab to view the results. Results/Considerations: For comparison, a summary of the HYSYSTM results and the hand calculations are displayed in Table 1 below. Page 6 of 7 Nmin N ND NB Rmin R HYSYS Results 7.918 17 8 9 0.637 0.956 Hand Calc Solution 7.011 14 6 8 0.668 1.001 Notice that the HYSYSTM estimates for the number of theoretical trays required for the separation are slightly higher than the hand calculations. It may be beneficial to use the Shortcut Column results to then simulate the process using the more detailed Distillation Column unit. Page 7 of 7 ...
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