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Unformatted text preview: f the Blocks folder. Under the Specifications tab, click the Reflux Ratio radio button and input a reflux ratio of 1.5. Input condenser and reboiler pressures of 15 psi. We are assuming that there is no pressure drop throughout the column. The Key component recoveries section allows you to input values for the recovery (the amount of the component in the distillate divided by the amount of the component in the feed) for the light and heavy keys. For the Light Key, choose ACETONE in the Comp field and type 0.99 in the Recov field. For the Heavy Key, choose METHY‐01 in the Comp field and type 0.01 in the Recov field. 7. Click on the Calculation Options tab. Check the box next to the option for the reflux ratio vs. total number of calculated theoretical trays. 8. Reinitialize your simulation, and save under a new filename. 9. Run your simulation. 10. Select the Results option under the DSTWU option in the Blocks folder of the Data Browser. Click on the Reflux Ratio Profile tab to view the reflux ratio profile of the column. (Note: The reflux ratio profile is extremely valuable when doing a cost‐benefit analysis. Each additional tray increases the equipment costs of the column, but increasing the reflux ratio increases the operating costs.) 11. Looking over the simulation results, notice that the acetone product was only achieved at 88% purity, below our 90% specification of acetone. Let’s add a design specification to try to reach the target value. Select the Flowsheeting Options tab of the Data Browser. Add a New design spec. Set up the design specification so the mass fraction of acetone in the acetone product stream has a target value of 0.9. Click the Vary tab and input the appropriate information so that the molar reflux ratio (Block‐Var) is varied between 0.5 and 5.0. Let’s use a tolerance of 0.5%. 12. Reinitialize and Run your simulation. 13. Looking over the Control Panel window, notice that the system did not converge. Under closer inspection you should find that note, ‘SPEC FUNCTION NOT CHANGING…’ Because of the simplifications used in this type of distillation column, the purity level of the Acetone product is not affected by the reflux rate. This can be confirmed by looking at the Convergence tab in the Data Browser window. Page 8 of 10 14. This step was completed to provide a warning to you in your future simulation efforts. While some of the shortcut methods appear to provide a quick way to obtain results, they do not always work or provide the accuracy that is desired. 15. For this reason you will complete the same calculations with the RadFrac column to see it the results are any different. B. RadFrac 1. Open the simulation that you saved before adding the DSTWU column. 16. Select a RadFrac column from the Columns tab in the Equipment Model Library, and add it to the Process Flowsheet. Connect the combined acetone/MIBK stream from the new mixer to the column Feed, and two new liquid product streams fr...
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- Spring '08