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Foam in Suction Scrubber

Foam in Suction Scrubber

Foam in Suction Scrubber

(OP)
Hi guys. Any of you ever experienced foam in a suction scrubber? Client has a tank vapor recovery system, ~0 psig suction, 190 F suction temp, 20 psig discharge, constant-speed rotary vane compressor, 150 hp, capacity control is by discharge bypass recycle. Gas is (on dry basis) ~65% CO2, ~30% C1, ~7500 ppm H2s and other sulfur compounds including mercaptans, remainder is C2 and larger, is equilibrium water-saturated at process P & T, and has other good stuff in it like trace tiny solids (mostly iron sulfide) plus the typical dirty process plant detritus and bullcrap. The foam carries over out of the scrubber, gets into the compressor and you know what happens next. Bang.

Prevailing theory for root cause of foam formation is the recycle stream, which is lube-oil-laden is somehow reacting with one or more components in the process gas or its condensate to cause the foam. No basis in fact yet. I'm thinking the first thing to try is to reroute the bypass out of the suction system and see what happens.

Just looking for any ideas or "this one's a no-sh*tter" been-there-done-that-and-here's-how-we-fixed-it stories. Thanks guys. Pete

RE: Foam in Suction Scrubber

The description seems to indicate this is an oil flooded compressor, but I've only come across oil flooded screw compressors, not for rotary vane. Some designs of recip gas compressors also result in lube oil getting into the process gas.
Given this is saturated gas, some guesses would be:
(a)is the exit line from the suction scrubber to the compressor sloping continously back to the scrubber exit nozzle ?
(b)is the capacity recycle line pipig set up free draining on either side of the recycle PCV?

RE: Foam in Suction Scrubber

Georgeverghese
The Hydrovane compressor by Compair Sydney Kellogg American are flooded vane compressors.
B.E.

You are judged not by what you know, but by what you can do.

RE: Foam in Suction Scrubber

(OP)
George thanks for the reply. The compressor is an oil-flooded rotary (sliding) vane. Unfortunately none of the lines are sloped or set up for free-draining as you suggest.

RE: Foam in Suction Scrubber

Free draining of compressor suction scrubber exit line to the compressor is a basic requirement to prevent liquid slugs from getting into the compressor for both pd and centrifugal compressors. Set up low point liquid drip / drain lines wherever you find these low point pockets and have them continously monitored at CCR for level buildup. Else see you can have these pocketed lines reconstructed.

RE: Foam in Suction Scrubber

(OP)
George - Thanks for the helpful tip. I will see if I can make this change and I will add those requirements (suction line slope back to scrubber, and add low point drain pot) to my P&ID checklist. Thank you!

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