8 replies to this topic

[gunjan]

Hello Friends/Vetarans,

Well I was going through API 618 for Reciprocating Compressor. There I have found that it has been mentioned that the discharge temperature of recip compressor shall not exceed 150 C (300 F). So can anybody throw some light on this. Why this requirement is necessary ? Is it because it will reach an autoignition temperature for lubricating type of recip compressor or is it because if you go for higher temperature then Capex of compressor will increase.

Thank you in anticipation.

Cheers,

Gunjan

[Art Montemayor]

gunjan:

I don't know what you mean by "Capex"; however, I've had a lot of experience with reciprocating compressors, their temperature limitations, and API 618.

The 300 ^oF value for the maximum discharge temperature allowed in each stage of compression first came about because of the danger involving the auto-combustion of lubricating cylinder oil in the prescence of hot, compressed air. It later became a further issue brought out by a lot of us old, weathered veterens who were tired of seeing exhorbitant compression ratios and their related high discharge pressures when operating oil-lubricated natural gas reciprocating compressors. Oil-lubricated cylinders (& their valves) will suffer from having their lubrication oil converted to sludge and sometimes solid coke due to high discharge temperatures. Once a discharge valve starts to leak, it will hardly ever re-seat itself again. In fact, the moment it starts to leak, the discharge temperature starts to escalate higher and higher due to the natural re-compression of increasingly higher temperature gas. This effect can really get out hand very fast. That's why API 618 finally fixed the recommended discharge temperature at 300 ^oF. That is also why the API has TWO standards for reciprocating compressors - one for so-called "slow speed" recips and another for so-called "high speed" recips. I don't agree with the API's definition of "slow" or "high" speed. In fact, I think that you will find the API totally avoids discussing the subject. But at least we got them to recognize that a lot of business-oriented and profit-oriented compressor manufacturers cater to what I call "high speed" machines that are, in my opinion, self-destructive because of the exhorbitant piston speeds (higher than 750 ft/min) and very high compression ratios (higher than 4:1). High speed recips are, in my opinion, designed to consume themselves in a specific amount of time. They are not designed to endure for the long haul; in other words, they are designed for one specific, short-duration project and that is all their life is supposed to be dedicated to. After that, they are scrapped and recycled as scrap iron.

I always design the discharge temperatures of reciprocating compressors to be 250 ^oF +/- 10 degrees. The result has always been a machine that has endured, has resulted in excellent valve life, has yielded minimal maintenance and has performed consistantly. Of course, by fixing the discharge temperatures I also am fixing the number of stages required for the machine.

I hope this helps explain why the allowable discharge temperatures are fixed at 300 ^oF.

[gunjan]

Hello Mr. Montemayor...

Thank you very much for your quick and clear response. I really appreciate that. By the way by Capex I meant Capital Expenditure.

Regards,

Gunjan

[ARC]

Dears

I have newly joined this forum. ihave some queries regarding make up H2 reciprocating compressor.
Can some body tell me about the relation between clearance voume and compression ratio. Is clearance voume is costant for given compression ratio? Is cleararance volume is needs to be taken from manufacturer? Is adaibatic power decrease with decrease with decrease with compression ratio.

[Art Montemayor]

ARC:

Welcome to the Forums.

You have injected different and divergent questions that "take over" Gunjan's original thread and try to convert it for your purposes. This is analogous to skyjacking a thread and is not allowed for the obvious reasons:

1. Respect for the original poster (Gunjan) and his/her work effort in seeking help;

2. You can easily do what other posters do - start your own, original thread with your query(ies).

I recognize that you have interesting and perhaps valuable engineering questions for the Forum, but I also know that your queries can best be handled in a specific and direct manner if they are presented in their own thread. Therefore, please copy your questions into a new, and independent thread so that we can immediately put our attention on it and answer your questions directly. Once you have done that, I will erase this posting so that attention and responses can be generated onto your new thread.

Thanks

[Fr3dd]

Hello everybody!

I'm dealing with a reciprocating compressor right now and i've found problems with this specific issue. If the post owner allows me, i will ask a little question that you guys surely know.

API 618 and other international standards mentions this discharge temperature limit on this type of compressors, however it always refers to interstage streams; is this temperature limit also applicable for compressor discharge stream (outlet of the last stage)?

Sorry for "invading" your post gunjan, but the background of my question was already clear and it was so easy to ask

Thanks in advance guys!,

[Art Montemayor]

If you read my post carefully, you will come across the statement: “The 300 oF value for the maximum discharge temperature allowed in each stage of compression first came about because of the danger involving the auto-combustion of lubricating cylinder oil in the presence of hot, compressed air.” I have not said “interstage discharge temperatures” – and neither has API 618, I believe. All discharge temperatures affect the compressor in the same way – whether they are interstage or final.

[Fr3dd]

Good Afternoon,

First of all, i'm sorry if my question bothered you, my intention never was to contradict your explanations; actually i'm a big fan of your vast experience and knowledge in engineering. I say this because i'm detecting like an "on the denfensive" attitude, sincerely, i never meant to contradict your statements.

About my question, i know it's a dummy one, but it was a doubt that come to me reading the GPSA standards (not API as i said, my bad):

"Limits to compression ratio per stage — The maximum ratio of compression permissible in one stage is usually limited by the discharge temperature or by rod loading, particularly in the first stage."

The words "particulary on the first stage" shot the alarms in my head and, after some research, none of the standards i reviewed clarified this doubt.

Sorry again, i swear it was a misunderstanding.

Best Regards,

[Art Montemayor]

Fr3dd:

First of all, Forum questions don’t “bother” me. Proof that I can offer for this statement are the 2,257 posts I have made to date on our Forums. If I was bothered, I certainly must love the pain – which I don’t (at my age). You are free to form your own perceptions of course; but on this one you are wrong. This previous statement of mine doesn’t mean I have an “attitude”. It simply means you are wrong in your perception.

I am a professional engineer and when I detect something I know is wrong or not correct, I take the steps or actions to express what I know to be correct. If I turn out to be wrong, that is good news for me because I wind up learning something new or correcting my engineering knowledge. That is the way I have accumulated 49 years of engineering in my career. There is nothing “personal” about engineering knowledge; it belongs to everyone. That’s why I continue to share mine on these Forums and others as well.

No engineering question is a “dummy” question if it clears up any doubts, reinforces your basic knowledge, or reveals something new. Questions are the real basis of what our Forums are based on. Without them, we wouldn’t need Forums – or old, antiquated engineers such as I.

You obviously confused API 618 with the GPSA Engineering Databook. That’s OK. One is a standard (API 618) and the other is an advanced and specific “text book” on engineering techniques and methods as practiced in the Oil & Gas Industry.

I hope the basis and the method of calculating, specifying, and process designing a reciprocating compressor are clear to you now and if you have any further questions or inquietudes, always feel free to bring them forth in our Forums – in English or Spanish.