Continuous Distillation Hints updated 3/1/2005

1. You need to make sure that you are at steady-state conditions. Use a component mass balance to do this rather than merely the compositions. This means monitoring the recovery in the top and the bottom.
2. The refractometer is sensitive to temperature. Try to take all of your measurements at the same temperature in the refractometer.
3. E_mv = E_ov in the Oldershaw column.
4. Remember that E_mv is the efficiency averaged across the tray.
5. There is a step-by-step procedure to get the E_mv from the E_ov for the new column. This procedure is on the web page.
6. You may consider a different E_mv for trays above the feed than for trays below the feed.
7. Don’t push separation efficiency too much; there are not enough stages.
8. We want to operate in a condition where the revovery of methanol in the top is roughly the same as the revovery of ehtanol in the bottom.
9. Remember to measure the feed composition each day. It may not be exactly 50-50.
10. The overall mass balance closes quickly. Find the bottoms stream flow rate by subtraction. It is too hard to keep the level constant in the boilup collection vessel.
11. When you want to make a measurement of the bottoms product, pump out the collection vessel to nearly empty, then stop the pump and let it fill up for a moment. Then pump it out again and measure the composition. This should always be more representative of the true bottoms composition.
12. An acurate value for the heat losses is important for correlating the HYSYS model with the actual data. An energy balance around the column brings you into the ball park, but the column is very sensitive to even small (5-10 W) changes in the reboiler heat duty. If the assumed losses are 5-10 W off, considerable differences occur between the predicted and measured compositions.