Assignment 3, additional problem: Fifty mol% methanol in water at 101 kPa is con
ID: 701823 • Letter: A
Question
Assignment 3, additional problem: Fifty mol% methanol in water at 101 kPa is continuously distilled in a seven-plate, perforated-tray column, with a total condenser and a partial reboiler heated by steam. Normally 100 kmol/h of feed is introduced on the third plate from the bottom. The overhead product contains 90 mol% methanol, and the bottoms 5 mol%. One mole of reflux is returned for each mole of overhead product. Recently it has been impossible to maintain the product purity in spite of an increase in the reflu: atio. The following test data were obtained: Stream Feed Waste Product Reflux Kmol/h 11% alcohol 51 100 62 53 94 12 80 Ohat is the most probable cause of this poor performance? What further tests would you conduct to establish the reason for the trouble? VLE data at 1 atm for methanol-water is: 0.0321.10.0523-10.075-10.154 0.225 | 0.349 | 0.813 | 0.918 0.1900 0.2940 0.3520.516 0.593 0.703 0.918 0.963Explanation / Answer
There are two possible reasons for Methanol composition Profile to change in the column despite of maintaining temperature profile in the column
1) Back pressure at the column top: Check the vapor pressure coming out of Column. If this has changed and deviated from earlier profile, then need to check if there's some choking in the downstream of column
2) Channeling inside the column: Check the Pressure drop between each stage of the column. Compare it with earlier or theoretical values. If this has deviated, then that deviated stages need to be replaced.