Distillation Column
Distillation Column
(OP)
hie
thank you in advance for your help
we have a distillation column that seperates benzene as the top product and a mixture of toluene,xylene and naphthalene residues as bottoms product. the column has 60 valve trays and uses vertical thermosyphon reboiler.
we strongly suspect there is flooding in the column because of the high DP which we get. it is difficult to control the top temperature and hence to get the right spec for the top product.
could this be flooding? and can the problem be solved without opening up the column.
thank you in advance
sibongile.
thank you in advance for your help
we have a distillation column that seperates benzene as the top product and a mixture of toluene,xylene and naphthalene residues as bottoms product. the column has 60 valve trays and uses vertical thermosyphon reboiler.
we strongly suspect there is flooding in the column because of the high DP which we get. it is difficult to control the top temperature and hence to get the right spec for the top product.
could this be flooding? and can the problem be solved without opening up the column.
thank you in advance
sibongile.





RE: Distillation Column
Yes, it sounds very much like flooding. The first thing to do is to check the current operating conditions (flows, concentrations, temperatures, pressures) against the original design data.
If it is simple flooding you should find that the pressure drop suddenly increases as you increase the throughput from some initial low value.
If it is due to a mechanical problem (collapsed tray or blocked downcomer) the pressure gradient will be gentle, except in the region of the damaged tray. Of course, you will only be able to see this if you have several points where you can measure the pressure.
There are companies that can scan a column in operation using radioactive sources to see where the flooding is happening. A local tray supplier should be able to refer you to someone who does this, if they do not do it themselves.
The book by Kister (I forget its exact title) has very good tips on trouble shooting columns.
Good luck
Katmar
RE: Distillation Column
RE: Distillation Column
It sounds you have a downcomer flooding (Backup). This happens when your DP across the tray which calculates to the liquid level in the downcomer is as high or very close to your tray spacing, this due to high reflux rate (liquid loads). To rectify this look at you reflux rate historically, column dp, and the O/H cooling system performance. Also if your reboil ratio is high.
If you have a test-run data its better to find the cause of the flooding using simulation (Hysys, PRO II), high vapor/liquid traffic zones are likely the flooding place (if your trays are all the same design and column diameter don’t vary). Check if you can alter your column operation conditions using the simulation to reduce the column liquid and vapor loading and eliminate or reduce the flooding.
If your tray vendor still exist then just ask him for a tray evaluation (be careful when dealing with tray vendors they will tray to convince you to replace all your trays if your operating above the design limit)
RE: Distillation Column
The two most popular scanning companies are Synetix Services(TracerCo) and Tru-Tec. Both have a lot of experince in tower scans and flooding problems.