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I have difficulty in drawing product from my side stripper of the atmospheric distillation tower. Whenever I raise the Stripping steam rate, this problem will occur. My initial suspect is due to the hydraulic limitation when the stripping steam is above a certain value. The technical reasoning would be when there is high vapor rate rising up the stripper tower, the vapor load creates high pressure drop across the stripping trays. Liquid flowing from the top will ultimate be restricted from flowing down the stripper tower and creates hydraulic limitation. Do you all agree on this observation?
 
Answers
24/09/2018 A: Rajkumar Chate, Sulzer, rajkumar.chate@sulzer.com
There are two types of flooding, DC flood and jet flood, flooding can be easily predicted by checking the pressure drop across the side stripper column if you have this measurement. Generally stripper columns have higher liquid load and lower vapor load, in most cases trys are limited by DC flooding and not by jet flood. For this side stripper column if we consider there is flooding in DC then vapor will not be disengaged properly in DC. When the liquid from tray DC goes to column sump then, you have enough residence time in sump to disengage vapors and this should not be the reason for pump problem.
Generally side strippers have stripping steam in the range of 0.2-2% of stripped product and i believe striping steam to side stripper in your plant is in this range. Higher stripping steam will vaporize more light component from the feed liquid and reduces the liquid coming to stripping sump but i don't expect this is the problem, if it is then adjacent side product will be off spec. Better collect the operating data, setup the simulation model and check how sensitive is the vaporization in side stripper with stripping steam.
Check that steam fed to the stripper column bottom is free from condensate. If there is small amount of steam condensate fed to coming then it will suddenly vaporize in stripper sump and creates problem for sump level and pump.
16/04/2018 A: Sudhakara Babu Marpudi, Oman Refineries and Petroleum Industries Company, m_sudhakarababu@yahoo.com
Wet stripping steam is one reason I have observed. Steam condensate from the bottom of the side stripper, will lead to pump cavitation too. Ensure the stripping steam header is free of condensate, if not dry. In Kero / Jet fuel stripper case this will lead to the bed compacting effect of the down stream Merox reactor. We were forced to bypass Merox till the bed was back flushed and loosened to improve the flow thru the Merox reactor from ZERO levels.
11/04/2018 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
The trays will have a maximum capacity (100% of flood), influenced by the combination of liquid and vapor rates. The stripping steam for a side stripper should be in the range of 0.1 lbs/gal. However, the rate can be optimized by trying different rates and performing an economics calculation by comparing any improvement in the yield distribution against the cost of the steam.