Homework 5 Problem 5 Pressure Swing Distillation

# Homework 5 Problem 5 Pressure Swing Distillation - Homework...

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Unformatted text preview: Homework 5 Problem 5 Pressure Swing Distillation 60 points possible due Friday September 30, 2011 Grader: Alan Problem Statement: In the production of dimethyl carbonate from methanol, it is necessary to separate methanol from formal (also known as methylal – C3H8O2). However, an azeoptrope exists between these two components. Part 1: Using Aspen, examine the equilibrium curves (x‐y plots; methanol/formal system) between 100 kPa and 1000 kPa pressure for the (a) NRTL (b) UNIQUAC and (c) SRK thermodynamic packages. Copy and paste the graphs into MS Word to turn in the x‐y plots for 100 kPa, 500kPa, and 1000 kPa for each system with methanol mole fractions shown. Discuss the importance of using the correct thermodynamics package in the distillation design. Part 2: Assuming that UNIQUAC provides a realistic thermodynamic scenario, design a pressure swing distillation column sequence to provide for pure methanol and pure formal product streams for a process having a fresh 100 kmol/hr feed stream, F, of 30 mole % methanol: (a) show a schematic of the sequence similar to that given in Figure 8.36 on page 235 of the Seider course textbook. (The solution to this problem may not be the same as figure 8.36. You must determine the distillation products, mole fractions of each stream, and flowrates of the internal and external streams.) (b) Identify the operating pressures of the columns; justified with a thermodynamic diagram similar to Figure 8.36a and (c) determine the compositions and flowrates of the distillate and the bottoms streams for each column. DO NOT SIMULATE THE PROCESS! Method of Solution: Use ASPEN PLUSTM to generate a Pxy binary diagram, which can be used to . Solution: Part I 1) Open the ASPEN PLUSTM program. Typically, from the START menu: All Programs/AspenTech/Process Modeling V7.2/Aspen Plus/Aspen Plus User Interface 2) Select “Blank Simulation” and click OK. Page 1 of 8 3) Eventually, the Process Flowsheet Window should appear. Open the Data Browser by clicking on the icon on the toolbar. 4) First, add the system components. Open the Components section of the Data Browser. Click Find to open the Find window and type “methanol” into the component name or formula field. Then click the Find Now button. Highlight the correct component from the list of components that appears and click Add. Add formal (methylal) to the components list in the same manner. When both components have been added, close the Find Components window. 5) In the Properties section, you will need to specify the method you would like Aspen PlusTM to use to solve the system. This step is by far the most Page 2 of 8 important in obtaining accurate results. Select NRTL as the Base method. 6) Click the Next button, parameters. , to automatically enter the Binary Interactions 7) Generally, you would continue to input information and click the Next button until all required inputs were satisfied and the simulation could be run. However, in this case, we will use the components and property package that we have selected to generate equilibrium plots. From the Tools menu, select AnalysisPropertyBinary. Page 3 of 8 If the following window appears, click OK: 8) On the binary plot input window, select a Txy plot from the Analysis type drop down menu. Then select kPa for the pressure units and enter 100, 500, and 1000 for the list of values. Click the GO button. 9) The following plot should appear: Page 4 of 8 10) Right click on the plot and select Properties. Under the Label tab change the plot title to your name(s). 11) Copy and paste the plot into MS Word to turn in. Unfortunately, you cannot save an Aspen Plus™ file with an open chart. 12) Minimize the plot. There should be a Binary Analysis Results window open behind the plot showing a table of the analysis results with a Plot Wizard button at the bottom. Page 5 of 8 Click the Plot Wizard button. When the wizard opens, click the Next button. 13) Select the YX diagram and click the Next button. 14) Change the temperature to Celsius and click Finish. Page 6 of 8 15) The following plot should appear. 16) Change the plot title to your name(s). Copy and paste the plot into MS Word to turn in. Page 7 of 8 17) Close the plots and analysis windows. Change the property package from NRTL to Uniquac and repeat steps 11‐19 for the new package. Then repeat once more for the SRK fluid package. Copy and paste the x‐y plots in MS Word for 100 kPa, 500kPa, and 1000 kPa for each Property Package system with methanol mole fractions shown. Discuss the importance of using the correct thermodynamics package in the distillation design. Part 2: Assuming that UNIQUAC provides a realistic thermodynamic scenario, design a pressure swing distillation column sequence to provide for pure methanol and pure formal product streams for a process having a fresh 100 kmol/hr feed stream, F, of 30 mole % methanol: (a) show a schematic of the sequence similar to that given in Figure 8.36 on page 235 of the Seider course textbook. (The solution to this problem may not be the same as figure 8.36. You must determine the distillation products, mole fractions of each stream, and flowrates of the internal and external streams.) (b) Identify the operating pressures of the columns; justified with a thermodynamic diagram similar to Figure 8.36a and (c) determine the compositions and flowrates of the distillate and the bottoms streams for each column. DO NOT SIMULATE THE PROCESS! Page 8 of 8 ...
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