4 replies to this topic

[SawsanAli311]

Dear All, 

 

I have been working mainly with centrifugal compressors and recently we considered installing reciprocating compressors in one of our projects. For multi-stage reciprocating compressor with interstage cooling and liquid scrubbing, what are the specific unique seal system requirements for such compressors, I am aware nitrogen purging is  required for the inner board compartment as well as the packing of the suction valve unloader stem.....

[Art Montemayor]

The specific seal system requirements for reciprocating compressors are set by the machine's manufacturer and are set forth in their customary operations and maintenance manual.  They are not necessarily "unique".  They should be what the manufacturer has developed to be not only dependable, but also the correct one for the application.  Unless you specify a seal system to be used - which may, or may not be recommended by the manufacturer - you will receive a seal system in accordance with their recommended design.   If a recommend a seal purge gas, then there must be a good reason for such.

 

However, you have not given us any idea of the simplest basic data regarding any compressor: the fluid gas being compressed and the stages, pressures, and unloading systems involved.  That leaves me with only guess work to apply to your query.  Why you are stating that nitrogen gas is required is any body's guess.  I specified, installed, operated and maintained a lot of recips in my career and I never used nitrogen on any seals - even on gases such as oxygen, CO₂, nitrous oxide, ethane, natural gas, hydrogen, nitrogen, ammonia, etc., etc.  Perhaps you have a "unique" application.  Why don't you share some of your basic data and perhaps our Forum members can contribute positive responses?

[SawsanAli311]

Thank you Mr.Art for your reply, 

 

We are actually doing a concept study where we are still in the phase of designing and selecting reciprocating compressors for processing rich sour gas with a MW between 30-35 for injection applications. 

As I am doing utility consumption estimations, I wanted to know any specific requirement for recip machines when it comes to sealing the packing rods and other auxiliaries. 

We contacted vendors and they recommended spill back capacity control with constant clearance pocket control. 

I also wanted to understand another aspect: due to the uncertainty in the composition of the reservoir and hence the resultant injection gas, the required wellhead injection pressure is foreseen to be increased in future beyond the original design point. Accordingly, since reciprocating machines work under backpressure, we are thinking about increasing the discharge design pressure i.e. PSV set point at the last 4th stage and the pipeline design pressure. However, I am wondering what would be the impact on the preceding three stages and will they will be able to cope with such a scenario. Please correct me if I am wrong: the motor power of the recip. machine is more dependent on the suction conditions and what load the cylinder rod is experiencing?

[Bobby Strain]

You need to give your compressor vendors all the information you have. They will tell you then what the power requirement is. They will design cylinders and rods for whatever conditions dictate. But you should not waste their time. If you want to explore on your own, Ariel has free software for you.

 

Bobby

[Art Montemayor]

Sawsan:

 

Thank you for the informative reply.  Now the picture is clearer and your scope of work is defined.  This is the type of details and specific data that helps our Forum members to give you useful and experienced advice.  Read carefully what Bobby Strain writes.  His advice is important and worth a lot of time and effort that can be saved.  Fill in an API 618 reciprocating compressor Data Sheet as the one I’m attaching.

 

Work through a recognized and experienced reciprocating compressor manufacturer and do exactly as Bobby advises: do not fail to tell ALL the truth and facts about your project and cooperate with them in reviewing their recommendations as to what type, size, and design of recip is recommended.  Once you have that basic preliminary information, you can study, review and accept - or comment on - their recommendations.  Sour gas to me means hydrogen sulfide, H₂S, - a deadly and stealthy killer of a gas.  If that is what you propose to compress, point this out to your selected potential manufacturer and detail it out in the Data Sheet.  I don’t believe you will insist on inventing and specifying your own type of seal.  You will have to buy-in to the type that the manufacturer recommends and you should insist on details, history, past performance and experience on that type of application.  That, I am sure, is what Bobby is stating about not wasting their time and I am 100% in agreement with him.

 

You probably have process requirements such as in-between stage condensation and related liquid separators, positive seal design, interstage coolers-condensers, capacity controls, driver specifications, and many other items, so be sure to fill in all the API 618 Data Sheets.

 

 API 618 1995 Compressor Data Sheets Rev1.xlsx   1.65MB   33 downloads