8 replies to this topic

[USR]

Hi...this is my first query in professional forum...am a fresh graduate..i am undergoing my training in a UOP licensed PENEX plant..we are using recycle cum make up hydrogen gas reciprocating compressors for hydrotreating naphtha..my query is regarding the capacity control..the compressor has stepped cap control and can run at 100%,78%,44%,0%..from what i have observed in the field is that there are two suction valves each at head end and crank end and a valve at clearance end these i could make out are solenoid operated valves(as instrument air supply line is present).the discharge valves are however spring loaded check valves(no instrument air line)..are my observations right..problem is that panel operators do not have details..they just load and unload the valves from DCS..there is a loading sequence for various capacity..ofcourse with valves we are changing the volumetris efficieny of the compressor but if someone has any material regarding this,,it could be of great help..
and there is a refrigeration section in my plant..it has a screw compressor..this anyway has a stepless control and could be run at any capacity(stepless capacity control)..i would like to have details regarding this too..thanks..

[Art Montemayor]

USR:

Please do not post duplicate threads of the same topic. There is no need to do this and it only causes confusion and annoyance in that our members don’t know which thread to respond to. I have deleted your other duplicate post in this Forum.

What you are inquiring about is a favorite subject of mine, since I spent a lot of my young graduate years laboring with, repairing, operating, modifying, and designing reciprocating compressors. I have written a lot of threads on our Forums on this subject – specifically the control and operation of reciprocating compressors at various capacity controls and how they operate. If you use our SEARCH machine, you should be able to resource all this prior information.

Basically, I can tell immediately that you have little or no experience with reciprocating compressors because what you state is some information that is not correct. That’s OK; that is way that we all start our learning career in engineering.

It is very difficult to understand your writing. You write in phrases when you should use complete, comprehensive sentences. Proper and correct communications are critical if you are to succeed in requesting information and obtaining what you need. Additionally, it would aid everyone if you could submit a detailed sketch of what you have and how it is connected. For example, is it a multiple-stage compressor (as I suspect)? Does it have intercoolers, surge drums, and suction separators?

You should supply a complete and detailed description of your compressor – a Data sheet would be the perfect description.

Await your response.

[USR]

 Book1.xlsx   8.86KB   110 downloads

Dear Art

I must tell you that i have been reading your posts since my college days. You have inspired me a lot.

Now, coming to the query. I might not be able to give you a detailed sketch right now, but I am attaching a workbook which gives the loading sequence of the compressor. Maybe this could give some information you are asking for. Rest assured it is a single stage (two cylinders) reciprocating compressor. It has recycle gas and make-up gas knock out drums, recycle & make up gas suction snubbers, recycle & make up gas discharge snubbers. Again the operating personnel didn't clarify my doubt regarding snubbers, this however I searched and found that they are pulsation bottles. I could give you a detailed sketch within a few days; right now this is what i have.

Thanks a lot.

[USR]

Anyone having any details or material regarding capacity control,kindly share.It would be a great help.

[csp_process]

Dear USR,

I'm also working with Penex plant. There are may things which are confusing in your question?

• A makeup cum-recycle gas compressor? that too reciprocating.
• Another Screw compressor_why do u need a refrigeration section in Penex unit. What I presume is your Penex unit is in same area with CCR(reforming), anyways that is different subjec

Ask your question more clearly? Check with Technical service guyz they must be having manual for that compressor. If you need general citation on compresor then there are so many books. e.g GPSA and others.

[USR]

Dear csp,
I don't know the details of your penex plant but i do have a clear understanding of my plant.I would like to clarify things for you:
1.It is a reciprocating compressor having two cylinders driven by a single synchronous motor.The recycle cylinder receives the hydrogen rich recycle gas from the separator.The hydrogen consumed is replenished by the make up hydrogen from the PSA plant.The make up hydrogen is routed to the make up cylinder of my compressor.I hope you had a look at the attached worksheet.If you did it shouldn't have created doubt about the type of compressor.
2.The screw compressor is installed in my refrigeration section to recover LPG to prevent it from leaving alongwith the lighter offgas.The refrigerant(propylene) vapour from the accumulator is routed to the screw compressor and condensed and sent back to my refrigerant receiver.
Working in a similar kind of plant i think we can discuss a lot of things.Await your reply.

[Art Montemayor]

USR:

As you probably know, there are basically only four practical and recommended methods to vary the capacity delivered by a reciprocating compressor:

• Recycling discharge gas back to suction;
• Suction Valve Finger Unloaders;
• Clearance Pockets and Plug Valves;
• Varying the compressor rpms.

Of the above, only clearance pockets and speed variations are the practical and dependable methods to apply to serious, economical, and critical service reciprocating compressors.

Recycle control is energy inefficient; suction valve finger unloaders are the type of unloading that cannot be used as good practice (and obviously the method you refer to).

If your installation is a modern one and it was well-designed and engineered, then it should have at least a good Plug valve method or clearance pocket type of unloading system for the reciprocating compressors. If it doesn’t, then I strongly advise you to install one – or change the type of cylinders presently installed.

You should discuss this aspect of your installation in detail with your compressor manufacturer.

I am attaching a series of compressed files for your reading and studying. I highly recommend this material as it represents the state-of-the-art in reciprocating compressor valves and capacity control. For you application I highly recommend the use of Poppet-type valves made of PEEK material with either clearance pockets or Plug type of suction valves. Some times it is practically impossible to add or retro-fit clearance pockets to an existing reciprocating compressor. If that is the case, there is still the possibility of designing and installing Plug type of suction valves. In the extreme case, I would change the cylinders with new ones incorporating clearance pockets. I would try to avoid the suction valve finger unloaders at all costs.

I am assuming that you are well-versed and trained in reciprocating compressors and that I am not using terminology and information that is over your head or out of reach. I can continue to send you a lot of specific information, but it would be more efficient and profitable for you to state the specific topics that you may need information or recommendations on.

I hope all this helps you out in your Hydrogen 2-stage compression application.

Attached Files

•  Manley Compressor Valves2.zip   1.36MB   193 downloads

[Art Montemayor]

USR:

I finally finished the sketch I generated for your application in which I illustrate what is happening with your unloading capacity using suction valve finger unloaders.

I hope this helps.

Attached Files

•  Hydrogen Compressor Capacity Control.xls   194.5KB   153 downloads

[USR]

Dear Art,

I am going through the materials you have furnished.

Thanks for the efforts you have taken to help me out through this. I will ask specific doubts after I finish my part of the work.