Upstream pressure control for centrifugal compressors

[MortenA]

For a fixed speed centrigugal compressor:

For upstream pressure control would throttling on the inlet or outlet of the compressor be the best with regards to operation and overall economy? Pressure range is 30-40 barg at suction and 110-120 at discharge (this is in the early engineering phase so no need to request additional info re. compressor type etc im just asking for a general guideline)

Best regards

Morten

 

[zdas04]

Either one wastes hp to some extent. For upstream control, a suction pressure controller will be markedly more effective than a discharge pressure controller.

I find varying rpm to be the best means of capacity control for any technology, for centrifugals the next best is a suction controller.

A discharge controller has got your applied hp between the point you're controlling and the control device. Shutting it down will tend to raise both suction pressure and discharge pressure (until you run out of power). Most times that I see a discharge controller, people are trying to do something like minimizing the dP across a VI plate in a flooded screw to try to minimize oil loss (by the way it is better to change the VI plate than to do this).

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The Plural of "anecdote" is not "data"

 

[jay165]

A suction side control valve will waste only half the energy that a discharge side valve will if you can't vary the speed. In addition, you will need an automated spillback line to control surge.

 

[25362]

Lieberman & Lieberman on their A Working Guide to Process Equipment (McGraw-Hill) Chapter 28: "Centrifugal Compressors and Surge", deal somewhat humorously with the precise subject of this thread.