PSA unit 2

[liberoSimulation]

Does anyone can provide me the frequent problems that occur for the PSA unit as a new PSA unit is to be built in a new plant.
From your experience, there are some major problems with the design or operation of PSA that I would like to know.

Also, from safety point of view, what are major things to be considered in the design or the installation of this unit.

Sorry for giving a generic subject, but I am after major concerns of such unit so for having proper design of our new PSA unit.

Regards to all

 

[zdas04]

This truly is a generic question. I'm always chastising people for answering questions that they have to make up the details, but here goes.

Many adsorbants will pull water vapor from the gas stream. PSA will not remove this on the depressurization cycle, it takes added heat to cook the water off. The biggest problem I've had with PSA units is that they can quickly get so saturated with water that they don't have room to attach the material you are trying to remove.

I've found this to be a slightly bigger problem than the adsorbent material migrating downstream, but that is a problem as well.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

 

[cryotechnic]

Since the PSA unit itself is relatively simple (the only moving parts are the valves) there are not much problems.
Like I said, the valves are the only moving parts, so since they will switch very frequently you can expect the most problems will be at the valves.
I know that there are PSA-unit manufacturers who took this problem into consideration and design the unit in this way that when there is a valve problem, that particular adsorber is switch off the process and the unit continous with producing on the adsorbers who are still in operation. Ofcourse this will change the adsorbtion time, which gives an increase of tailgas, but at least it's better than no production at all.

Ofcourse the control of the regenerationgas is importent, because, no good regeneration will give problems with the production and an efficiency that reduces.

Also it sometimes occurs that filters/flame arresters in the blow-off of the adsorbers are glogged by dust from the adsorbers. During the pressure relief at the end of the cycle dust is withdrawn from the adsorbers.

Cryotechnic

 

[unclesyd]

What is the process gas stream composition going to the PSA system?

 

[roker]

hello,

if the tail gas is entering a compressor be sure to put a filter (dual) at the inlet to collect adsorbent and prevent damage to the commpressor.

regards,
roker

 

[Longinthetooth]

Contaminants from upstream equipment fouling the adsorbant, particulary lube or seal oil from compressors or turboexpanders. If this is your arrangement, you should consider an upstream knockout or guard bed.

 

[tkdhwjd]

I agree with cryotechnic. As long as you change out or service the valves regularly, you should not have any operating issues with PSA. If you have any leaking or sticking valves, the cycle timing will be off, causing alarms to go off frequently, or even trip the whole system (rare). High speed trending capability is highly recommended as it is extremely useful when troubleshooting the system.

Cheers,

 

[gwbutch]

The only problems we have had regularly with our PSA system are the valves, but those problems are due to ambient wintertime conditions in Alaska.

Now for some unregular problems. Our vessels are about 20 years old. This year we have found cracks in two different vessels. The first crack we found penetrated the wall, the second did not, but almost. The cracks developed from some improper welding on the outside of the vessels. Fortunately, on PSA vessels, cracking is the typical failure mechanism and does not result in a catostrophic failure. The welding was performed by a local contractor, not the vessel fabricator, for an insulation ring near the top of the vessels. The other vessels have been thouroughly inspected and found to be in good shape.

 

[liberoSimulation]

Thanks all
roker
You brought good point but which type of compressor you mean
Is it only applicable for centrifugal type?

Regards

 

[cryotechnic]

The best is to put a filter in before EVERY type of compressor.... It doesn't matter if your using a recip or a centrifugal compressor, they both don't like any particals.

Greetings,
Cryotechnic

"Math is the ruler of your potential succes...."