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We have a crude preflash column where crude after being heated is flashed.
the column has three streams. One is the top which is light naphtha which is taken from the reflux drum via reflux pump as one stream. The other is sent as reflux on temp control The column has a fired reboiler.
A side cut is Heavy Naphtha below Hnaphtha cut is a pump around. Bottom is kerosene plus which is separated in another tower.
We wanted to reduce the EP of lt naphtha. We carried simulation on hysis and were getting the desired EP using HEPT OF 2 FT for CMR 1 as there is packed bed of 10 ft between LT and H naphtha we were getting five theoretical trays
on the plant we adjusted all perimeter as per simulation but we could not get even close to it the ep remained high. Increasing reflux severalfold could not achieve the end point.
We took delta p across the bed. It is low and pct flood predicted by Hysis is 16pct far from flood.
We reduced capacity but no avail. Could it be low flood which is responsible? We want to check all angles before we open it up. There are no gamma scan facilities available so we can't do a scan.
Can someone suggest what angle to look for?
25/04/2011 A: Rajkumar Chate, Sulzer, rajkumar.chate@sulzer.com
Low flood will not be problem for separation. As your pressure drop is not increasing and flood % is low means capacity (throughput) is not a problem. please check your distributor. If i install very good efficient packing but my distributor is not distributing the liquid properly then the goal of separation will be lost. As you have mentioned that the bed height is 10 ft with C ring packing, with in 10 ft of C ring packing it is quiet difficult to get 5 stages. The problem you are facing is not related with your operating conditioin, it is with internals. can you tell me how meny stages you have considered in simulation for LN an HN fractionation. You might have considered accurate NTS in simulation but in practical operation your packing is not giving that much stages. can you tell me the size of packing (25/50/150 ...) so that i can judge the exact NTS you can get from 10 ft of bed height.
Please check what thermo you have selected in your simulation. if there are small traces of Hydrogen in your simulation do not go with GS or BK10 go with PR or SRK and compare the result.