Using Reciprocating Compressor and Centrifugal Compressor in paralell

[Orangel]

Dear Sirs:

At this time I have a Reciprocating Compressor delivering Natural Gas to a 12" pipeline. Can I install a Centrifugal Compressor in parallel with this unit delivering Natural Gas to the same pipeline?. Outlet conditions (Pressure, Temperature, Flow, etc) of both equipments are equal. Will there any trouble with Antisurge System of the Centrifugal Compressor related to nearly discharge of the Reciprocating one?. Do somebody know about this kind of installation in the past?

Regards.

Eng. Orangel Roca
Inelectra S.A.C.A
Caracas, Venezuela.

 

[georgeverghese]

Though I dont know of such installations, running a recip compressor in parallel with a centrifugal should be possible, provided capacity - pressure controls for both these machines is configured correctly. Obviously, compression eff for the recip will be better than for the centrifugal. Overall eff for each train will also depend on the driver and if variable speed is enabled.

 

[zdas04]

While I can't give you a good root cause for the performance I've seen, I have seen this tried 3 different times and none of the three sites had acceptable performance. Maintenance costs were very high at all 3 sites and none ever quite got the throughput that they should have. On the surface I cannot give you a logical hypothesis, but in all 3 cases they ended up turning off one or the other technology within a year of installation. The maintenance issues were different in all 3 sites.

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

 

[LittleInch]

Can you sketch your system? If the outlet of the compressors tess into a bigger line as separate connections it will work better than if the two are connected and then if low together down a length of pipeline into another pipeline.

You are essentially mixing tow different systems. whilst in theory the outputs are the same, the issue is whether the discharge pressure actually stays constant or not. Even a 5 or 10% variation will cause big changes in the flow in either machine. Naturally when flowing two machines, there will be a different discharge pressure than if only one machine is running so I'm not sure how you cope with that scenario.

The anti surge should be within the centrifugal system limits.



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[rotw]

The centrifugal compressor has its specific response to a change in flow capacity, inlet conditions etc. I deem different than a reciprocating one. So in this case the compressor controls will not be very common or typical, to say the least.

Since you indicate that the centrifugal compressor and reciprocating one are operating with same flow, I conclude that your centrifugal compressor is operating at a quite low efficiency (considering the area where reciprocating and centrifugal compressors normally overlap). So it would mean that temperatures at discharge of both machines should be necessarily different, unless you have some sort of a very light gas with low compression ratio. And at the end, if you intended to say that both machines have identical "mass flow", because of the different temperatures at discharge the volume flow at the discharge will necessarily be different and you end up mixing different volume flows and temperatures at the common discharge manifold.

Another issue is the pulsations due to the reciprocating one. The pulsations may affect to a certain extent the surge line and operating map of centrifugal compressor.