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We have Refinery off gas PSA processing CLPS off gases from hydrocracker and CCR off gas at 23 kg/cm2g. Tail gas from this PSA is at 0.5 kg/cm2g which is compressed to 4 kg/cm2g using oil flooded screw compressor and routed to fuel gas header.
During upset or flow variation in PSA frequent LO filter choking is observed for the screw compressor. Sometimes the filter choking is so fast that compressor trips on high differential pressure between LO and gas. What could be the reason for such high filter choking during particular time of PSA variation. We then clean the oil using continuous filtration and it takes 2-3 days to again normalize the things. Once the lube oil DP gets normalized it continues to run longer without any LO filter change out. Blackish deposits are observed on filter cartridges. Is anyone facing similar issue in tail gas screw compressor? What remedial actions are available to resolve the issue?
 
Answers
10/09/2015 A: keith bowers, B and B Consulting, kebowers47@gmail.com
Analysis of the filtered fines will likely show they are bits of the adsorbent material---a normal effect if the adsorbent (or absorbent) material is agitated by excessive fluid velocities in the bed. Decrepitation of the material can be severe. Installing two multi-cartridge oil filters in parallel (with isolation valves) will reduce frequency of filter plugging anf enable cartridge replacement on-line. I suggest using 'wound cotton' elements wit a 5 micron rating and PLENTY of filter area to avoid frequent plugging, and keeping at least a months worth of filter cartridges in stock. I do not recommend installing any 'automatic back wash; filter cleaning system unless the plugging frequency approaches twice weekly or more. It may be possible to install a centrifugal separator in the screw inlet gas line to remove the particulates before they enter the rotary compressor if rotor wear becomes an issue..
02/09/2015 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
Have you analyzed the deposits? Is it possible that some of the PSA sorbent material is getting carried out of the vessels during upsets?