Column operation

[raingal79]

Hi,

For purification column operation, if the feed rate to the column is increased in order to increase top side draw of high purity product, what should be the change to reflux rate, reboiler steam input etc to ensure that there's no flooding in the column? WHat do I expect to see in the temperature profile along the column?

Thanks.

 

[phex]

Reboiler steam input will rise linearly. Look into your design specifications for the column, there you should find an indication of the operating range. If the ratio of increase in feed throughput is inside this operating range, flooding should be no problem. If the feed tray is located in the optimum position and the change in feed rate is not abrupt, you should not notice substantial change in the temperature profile. This will also give you the chance to adjust reflux rate according to the product analysis to maintain the product specifications.

If the change in feed rate is very strong and abrupt, I guess the temperature profile all over the column will drop. If you do not change the steam (heat) input to the reboilers accordingly, there is quite a good chance to disturb column operation in a magnitude that material flow will interupt completely, as rising vapors will be condensed by the feed stream.

To ensure there is no flooding, change gradually and keep constant watch on the overhead product flowrates and overhead temperatures. If you notice a substantial drop in either one of those, you are flooding the column. Keep in mind to increase reboiler steam flowrate (heat input) proportionally to feed increase. And wait for some more experienced guy from this forum to verify my suggestions

hth,
chris

 

[25362]

For starting tutorials the Google sites:

http://eweb.chemeng.ed.ac.uk/courses/control/restricted/course/fourth/course/module3-1.html

http://www.svce.ac.in/~sundar/Distillation Column.htm

may be of help.

Otherwise, get hold of Distillation Control For Productivity and Energy Conservation by F.G. Shinskey (McGraw-Hill) to better understand the parameters and constraints that affect the operation of the column, including flooding conditions.