Q & A > Question Details
Please advice about the operation practice of the reciprocating compressor in order to increase life time of discharge valves in the compressor cylinders.
We're operating a Naphtha Hydrotreater - Platformer complex, where reciprocating machines are used as recycle gas compressors in NHT ( 2 Units ) and as Net Gas Compressors ( 2 Units ) in recontact loop of Platformer. A Net Gas Compressor comprises of 2 stages, where first stage is handling gas with 80% purity and the second stage is handling 90% H2 purity. The RG Compressor in NHT handling gas from second stage discharge of Net Gas Compressor.
All compressors are equipped with double block-bleed on the suction and discharge piping. These double block-bleed are left open even for stand by machines in order to enable quick start up action.
The problem always happens to first stage of stand by Net Gas Compressor. Just 15~30 days after starting, the discharge valves in the cylinder always gets leak and failure. Upon dismantling, we used to find some debris and gum particle in between valve plate and valve stop. Even after suction surge drum cleaning, the problem occurs over and over again.
Please advise whether the stand by machine must be isolated and can only be onlined just before starting or can be left online as long as the suction surge drum is free of liquid ?
The gum particle is 100% olefins which is suspected due to di-olefin condensation. And the rust is 100% Carbon which is suspected from coke breakthrough from reactor. But why this olefin and coke never cause any problem to the second stage, or even to the first stage of "non stand by" one, as well as no problem so far to the NHT Recycle Gas Compressor ?
FYI, the stand by compressor suction line is 20 m distance from non stand by one. How to solve these all these problems?
 
Answers
02/03/2012 A: Bruce Carr, Suncor Inc, matukaze1@hotmail.com
The gum is probably PolyNuclearAromatics (PNA's).... is it more prevelant at end of run? They will plug up fine mesh filters and will not drain down when checking for moisture in suction bottles. Plate valves will not work properly if it gets between the plate and stop. Have you considered changing over to "Magnum" valves. instead of plates they use dozens of small poppet valves. Up to 30% of these poppets can fail before the valve is considered non functional. The valves are available in all sizes and are normally a straight swap out with no retrofitting needed.
28/02/2012 A: Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
The issues you may be seeing could well be due to liquid condensation products, and / or solids in the hydrogen recycle gas (pipescale , rust, & sometimes ammonium salts). Many refiners report similar issues with recycle gas compressor valves on their reciprocating machines.
High efficiency Seprasol LG Coalescers can remove virtually all free liquids - including aerosol sized droplets as small as 0.1um plus virtually all particulate matter including 'black powder' , corrosion products and ammonium salts. We would also recommend that after the coalescer vessel to heat trace and / or insulate the pipework to prevent any further condensation after the coalescer vessel. It is generally prudunt to have the LG coalescer as close as possible to the compressor to minimise piping length as well.
Many refiners have reduced suction & discharge valve failures on recip compressors such as HDT, HDS, HCU or reformer recycle gas compressors which are very sensitive to contaminants in the process gas. Our experience is that suction drums, mesh strainers, or KO pots / mesh pads are not fully effective in removing all the contaminants present because of the fine size of the contaminants. ( suction drums may remove +300um sized droplets but not aerosol sized contaminants created by condensation either in the separator drum or in the piping between the separator and the recycle gas compressor.
The type and quantity of liquids present can be measured with a pilot test rig which is often very useful information for later sizing a commercial LG coaleser unit. Such analysis & consulting servies are available from Pall in most countries around the world.
27/02/2012 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
My guess is that you have bottom suction compressors with a common suction drum for each pair of compressors. It is better to have top suction compressors with a suction drum for each compressor located no more than 10 feet from the compressor inlet nozzle. Then, with all valves open for “flying switches”, the suction line will always be free of liquid and polymerization products. If I were you, I would run both compressors and shut down one of them only for maintenance.