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Specifying Data for a compressor

Specifying Data for a compressor

Specifying Data for a compressor

Background : There is a existing three stage compressor module comprising of three compressors say A,B,C.
A is the ist stage, B is iind stage & C is the iird stage compressor.
The inlet conditions for A, B ,C will be different.
There is no stand by compressor.So I would like to have a stand by compressor N, which can substitute either of A,B or C.
Noting that inlet & oulet conditions are different for A,B and C are different, is it possible for a vendor to supply N
with N capable of handling different inlet and outlet conditions?

RE: Specifying Data for a compressor

With enough money you can do most anything. You could build a duplicate of your 3rd stage machine and its pressure/temperature ratings would be fine to stand in for stage 1 or stage 2, but the throughput would be a fraction of the throughput of the machines designed for those pressure ranges.

For A LOT more money you could build a duplicate of your 1st stage with cylinders and piping rated for 3rd stage conditions. This would have a throughput (and power requirement) far greater than your existing 2nd or 3rd stage machines.

You could build a proper 3 stage compressor (which could even use the after coolers from the current machines for interstage cooling), but the skid throughput would probably be less than your dedicated machines.

What you have sounds like an incompetent design (i.e., it maximizes cost by requiring a different driver for each stage), and backing it up by retaining that incompetence probably is cheapest so you might want to back it up with 3 skids.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

RE: Specifying Data for a compressor

Hello Angre,

As zdas04 noted, with no concerns for funding / design inefficiency / perpetrating incompetence, you have many options at your disposal; but since the volume/pressure conditions for any one compressor stage are incompatible with those of any of the others, I wouldn't do it.

Then again, maybe I'm being hasty...

One thing not provided in the OP was info regarding air being drawn off between stages; are there low-pressure and medium-pressure intermediate users? It's conceivable that great gouting quantities of low-pressure air are used on site, so only a proportion of the LP air is compressed to the MP stage, where maybe some more is used by MP loads, and the HP compressor provides only the HP air needed for the HP air consumers...but again, the OP didn't say; if this were the case, it would change my response considerably.

Like others have said, "More information > better answers."


"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: Specifying Data for a compressor

Hello zdas04 & crshears,
Thank you both for your views.
I would like to put in more information.
The existing compressors A,B,C are loacted on a offshore platform on an existing platform EP.There is no space for new compressor on EP.
So a new platform NP is being built to accomodate new compressor N.
I had reservations about this approach for the reason that I could not believe that N could substitute for three different compressors A,B,C.
Since I have to design this new platform, the size of the platform depends entirely on whether to have a ONLY a new N or a completely different three stage compressor module
on new platform NP.
When I raised the query to process/mechanical personnel, thay said that N could be designed to substitute any of A,B,C . They also showed me the data sheet from API 617 where in the
buyer can specify different conditions that the compressor may encounter.
The cost of putting in a new platform is tens of times the cost of compressor themselves.


RE: Specifying Data for a compressor

Since you are talking about API 617 machines (my original post assumed recip compressors since you said nothing about it being offshore), I'm going to guess that each skid is a single wheel centrifugal machine.

This sounds to me like you've been chasing lowering reservoir pressure (i.e, original machine took wellhead pressure from 600 psig to 1,000, when the required wellhead pressure went below 500 psig they added "B", when it needed to approach 200 psig they added "A"). If that is true, then there are no intermediate pressure loads, you should look at a proper 3-stage skid for platform N.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist

RE: Specifying Data for a compressor

Hello zdas04,

The compressors are used to pressurise associated gas and introduced back into the well.Thus increasing the production through "Lift Gas" .


RE: Specifying Data for a compressor


IMHO, your process and mechanical engineers are not correct.

Asusmnig this process is a single train, i.e. A feeding B feeding C with probably coolers in between, there is no way a single compressor can adequately perform the functions of all the units without severe loss of performance. The process guys are right to a certain extent in that yes the data sheet can contain a range of pressures etc for a single machine, but when the mass flow is the same between all three machines, the actual volume difference between A and C is probably of the order of four times.

Your best bet if forced into this is to make the machine equal to compressor B, but with flanges and pressure rating to match machine C.

Of course everything we say is irrelevant if not vendor can make it....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Specifying Data for a compressor

Hello zdas04,crshears,littleinch,
Thank you all.
With your inputs, I was able to push the disscussion in favor of providing a new three stage PGC.
Fortunately good sense prevailed.
I can now push ahead full steam on designing the structural topsides and jacket and firm up my offshore instllation spread with full confidence.

RE: Specifying Data for a compressor


you can have three stage compressors without one intercooler, depending on the compressor manufacturer and operating conditions. I'd advise to have a second full compressor, you can also go for aeroderivative compressors, which are relatively small in size.

Gabriel Castaneda, P.E.

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