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At the beginning of our NHT project ( catalyst HR 506), sulfiding was done by pre-wetting condition and still now same oil in procedure has been followed that means Oil in start with DSN at 140 degC through reactor and DMDS injection start at 180 degC to maintain the H2S at 180 to 200 ppm. Finally at 280 deg C, DSN is replaced by Heavy Naphtha (HN). Mentionable that our HN is sweet so we have to inject DMDS all the time to maintain H2S limit within 180-200 ppm in the recycle gas to keep the catalyst in active phase. Now my question is that what is the demerit now to do the normal start-up by starting oil-in directly with HN at 280 degC without pre-wetting ? Is there any chance of losing Sulfur from catalyst during H2 rich gas circulation within 6 hrs to raise the temperature to 280? Is there any impact on catalyst to increase the differential Pressure (dp)of catalyst bed for pre-wetting or direct oil-in procedure? Currently dp across the reactor bed observed increasing little bit after each normal start-up by pre-wetting oil-in procedure -what could be the root cause of it?
14/03/2018 A: Emmanuel Aunde, Refining Company, lemma012@yahoo.com
I understand that pre-wetting of catalyst at a lower temperature helps because it reduces the effect of heat of absorption. If it is boycotted during sulfiding it can lead to loss of catalyst activity. To avoid that we do the sulfiding in two stages. For normal start-up, I guess the same principle is in place, to be able to control the temperature of the reactor within allowable limit, we do wetting at a lower temperature before increasing the temperature other wise the heat of absorption will push the temperature beyond our operating limit