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In our refinery, C5/C6 isomerization process uses zeolite based catalyst and reaction loop pressure is maintained at 18 kg/cm2g. The ISOM unit uses H2 makeup from CRU and there is continuous purging of recycle gas from ISOM separator.
the design basis is 1635 kg/hr of purge gas (contains 187 kg/hr of H2) with 63 vol% H2 purity.
No HCL. 5-12 ppm of H2S.
Please advise how economical will it be to recover the H2 from purge gas using membrane separation process?
is there any refinery currently using membrane separation process for recovering H2 from purge gases at 18 kg/cm2g?
 
Answers
01/05/2018 A: Virendra Kapoor, Petroleum Refining Consultants, vkkapoor9@yahoo.com
Zeolite catalysts produce low octane isomerate relative to other latest catalysts in light naphtha is on isom plants. I understand probably one of the IOCL refineries in eastern India uses zeolite in revamped plant.
20/04/2018 A: SUDHANYA CHOUDHURI, INDIAN OIL CORPORATION LIMITED, choudhuri.sudhanya07@gmail.com
Kindly share in which refinery C5/C6 isomerization process uses zeolite based catalyst. What is the feed sulphur content maximum allowable. Do you have a benzene saturation reactor. Is there any Chlorine dosing in reactor. What are the design changes in downstream of reactor wrt convectional ISOM unit using Platinum catalyst.
09/02/2018 A: Patrick Bullen, UOP, patrick.bullen@uop.com
Isom units typically are sulfur free and do not have purge flows from the separator to maintain recycle gas hydrogen purity. High sulfur in the unit results in excessive cracking requiring the purge. Cleaning up the feed with a hydrotreater is recommended. UOP is unaware of any unit that has a membrane on the purge gas from the separator. One would think that the hydrogen flow is not sufficiently high to justify the investment of a membrane.
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07/02/2018 A: NS Murthy, GE, murthy.ns@ge.com
In early designs cascading of hydrogen supply is done from unit with low purity purge and low pressure operation (for example fixed bed reformer) to high pressure & high end point unit like first to Kero HDS and then to lube hydro finishing unit. While hydrogen is by and large better utilized, one needs to take into account of stripper section adequacy as well as energy spent in recycle gas compressor to compress the impurities as well. Membranes to recover hydrogen were studied by us in a refinery in India but did not prove to be economically viable. When we went for expanding unit capacity, we added PSA units to recover additional hydrogen and let the tail gas to low pr FG header to avoid tail gas compressor. I guess the current cost of hydrogen will be about 1800$ per ton at present crude price of 70 $/bbl and hence any saving will be worth.
06/02/2018 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
I would be very surprised if membranes could be economical. Membranes require a pressure driving force force for the hydrogen so you are going to probably need to compress the hydrogen to go across the membranes then recompress the recovered hydrogen to get it back to a useful pressure. You stand a much better chance in this case of recovering some hydrogen economically with a PSA unit.