Propane Screw Compressor control

[abbmct]

I am working on a scheme to install screw compressor in a closed loop propane referigeration circuit. Can someone enlighten me the different kinds of controls for this applications. I have seen valve unloader using suction pressure to control. How does the discharge pressure controlled?

Thanks in advance

 

[zdas04]

Discharge is typically controlled by flow resistance within the system. The compressor discharge pressure will increase until the gas will flow or the compressor runs out of hp.

David

 

[25362]

In refrigeration systems it is usually the condenser, located nearby, that fixes the discharge pressure which corresponds to the vapor pressure of the refrigerant (propane), line friction drops are usually small in comparison.

Can you tell us the reason for selecting a screw compressor for propane ?

 

[zdas04]

25362,
You misunderstood my post if you thought that "flow resistance within the system" meant line friction. I meant all flow resistance, including the condenser, TXV, throttled valves, friction, or whatever else takes a pressure drop. Without knowing the system it really is impossible to say which component will control within a given system.

BTW Propane is a very common refrigerent in Oil & Gas facilities, it seems to work just fine.

David

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 harder I work, the luckier I seem

 

[dcasto]

Go to the sullaire web sight, they have the latest and greatest ih control packages. SCSI is a packager and they also have the control down. Typically you'll have speed control, varible capacity control with a slide valve and variable VI (or variable ratio control too).

A screw compressor will have a fixed ratio, doesn't matter what the system resistance is it'll do that ratio. You can change the raio automatically with newer units. The control is complex, because you have 3 controllers and each one will change the performance and most of all the efficency.

 

[25362]

Visit thread404-181559 and the links therein.