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In the our HDS unit it treat light distillate cut (Ibp 40 C Ebp 230 C) come to unit from CDU unit and after treated go again to CDU unit to separate the light distillate to products LSR , NAPHTHA and KEROSENE .
In the last 3 weeks till now we had tested Naphtha in the lab. for sulphur content and the result is > 1 ppm the normal result is < 0.5 ppm which is suitable for SR reforming unit as feed ...we do many changes in the operations setting in the stripper column but that change nothing. The stripper column bottom temperature maintained by circulating to furnace and we noted that the level in reflux drum increased abnormally in the last month so we increased the reflux flow rate to the overhead. Are there any recommendations for this situation?
 
Answers
28/04/2019 A: Muhammad Faisal, Oman Oil Refineries & Petroleum Industry (Orpic)-Oman, engr.faisalfraz@gmail.com
probable cause/action are:
(1). check olefin in feed SRN. (2). Reactor inlet /outlet temp. during sulfur correction, only increase in steps RIT. but if ROT > 335c, recombining R'x (result RSH) could increase TS in sptripper bottom. (3). purge recycle gas, increase purity, check recycle H2 purity. (4). Reduce the load and observe if reduction trend of TS. (5). reduce the SRN-EP from CDU (High MW-contains high TS component). (6). After checking all above action, if still TS is higher side (1wtppm OR higher, then check any feed-effluent exchanger leak, check by sampling inlet/out of each exchanger in NHT).
17/04/2019 A: Prakash Pimparkar, Environmental Consulting Services , prakash.pimparkar@yahoo.in
From the information provided, I think the problem could be in the recycle hydrogen composition.Try to jack up Hydrogen pp in the HDS reactor. Secondly is the catalyst overused? and so loaded with carbon ?.
It is difficult to reason out in absence of historical operating data but most probably it is due to above two reasons assuming you have not changed any operating conditions and the crude source and hence the composition particularly sulfur concentration and species.
16/04/2019 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
The most common cause for high naphtha sulfur in systems like this is mercaptan recombination. As the reactor temperature increases to meet desulfurization targets for diesel, at some point in the run you start to get a little hydrocracking going on. The olefin formed can react with an H2S to form a mercaptan. Some catalytic reformers have a sulfur sorber on the feed to remove these trace mercaptans in the feed.
16/04/2019 A: keith bowers, B and B Consulting, kebowers47@gmail.com
First --measure and identify the sulfur species---H2S, mercaptan, sulfide.etc. What is sulfur level in HDS reactor effluent B4 any heat exchange. Leaking heat exchangers are often the cause of off-spec very low sulfur levels.
When you have measured and analyzed sulfur in ALL the streams, that will identify where the sulfur is coming from.
16/04/2019 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Where are you located?