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I am working in Crude distillation unit. Heavy Naptha yield is coming very low. Around 4-5 M3/Hr against 26 M3/Hr. It is observed, whenever HN stripping steam reducing stripper level is increasing. Stripping steam reduced from 400 Kg/Hr to 200 Kg/Hr. Even then we are able to get 4 M3/Hr. Could any one advise to overcome this problem?
 
Answers
07/04/2017 A: Rajkumar Chate, Sulzer, rajkumar.chate@sulzer.com
Check the Heavy Naphtha in crude assay, if you estimate ~26 m3/h HN then check where this HN is going, with LN or with kero. Without checking the crude assay you can even easily check the quality of LN and Kero, and you will see some change in quality. If it is going with LN (90% and 95% becomes higher) then increase the top reflux and reduce draw rate of LN, incase if it is going with Kero (in this case kero flash point will be less and 5%, 10% will be lower) then reduce the PA duty below HN draw. If HN is going with Kero and even after reducing the duty of PA, problem continues then there is possibility of some leakage in draw chimney tray (if you have level control then check it). Couple of hundred kg stripping steam does not add much vapour rate back to the main column and it will not have big impact on overall column vapor/liquid loadings.
I believe you have HN PA, if there is leakage through chimney tray then you may notice it in pump operation as well.
01/04/2017 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
It could be any number of things. Most likely is a crude change to one that has much lower naphtha yields. There could also be operational changes to maximize light naphtha and/or kerosine & diesel yields. It is also possible that something like damaged trays in the crude column could be changing the distillation performance. Stripping steam normally has minimal impact on product yield, unless the rate is so high that it causes flooding. Then the liquid can't make it down the stripping column and gets held up internally in the stripper temporarily.
01/04/2017 A: Peter Marsh, XBP Refining Consultants Ltd, peter.marsh@xbprefining.co.uk
If you are expecting 26 m3/hr of HN based on crude assay and target cut points but are only achieving 4 - 5 m3/hr at normal operating conditions, then either there is a problem with your crude assay, a problem with temperature or flow instrumentation or a problem with the atmos crude column internals. If this is a recent problem after startup from turnaround, perhaps an isolation blind has been left in the HN stripper overhead line? Have you done a pressure survey or radioactive tracer study over this section of the column to look at liquid traffic in the column to determine if tray damage or missing tray manway is a possibility?
01/04/2017 A: Ganesh Maturu, Self, maturu.ganesh@gmail.com
Did you check your crude distillation and amount of HN in it? If you have enough heavy naphtha in crude, you can recover HN by maintaining sufficient vapor-liq traffic in crude column. Reduce pump around duties if required to get enough vapour liq traffic in HN draw tray.
01/04/2017 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Is the crude composition changing? Compare the gaps and overlaps with previous data and correlate with the yield differences. If you have an assay, run your simulator to see how much heavy naphtha should be there. Is the light naphtha increasing? The kero cut?
31/03/2017 A: NS Murthy, Suez, murthy.ns.ext@suez.com
Look at both naphtha quality and kerosene (jet fraction) distillation and assess the likely loss of HN. It looks there is practically no internal reflux in HN withdrawal tray.