If you have the characteristic curves of an actual machine, you can put them in, and predict what the outlet temperature and pressure will be given a certain flowrate.
If you don't have them, which is the usual case for a new design, you have to specify the outlet pressure and efficiency, which will then be fixed for all flowrates.

Cheers,
Joerd

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

Hi joerd,

I did assesment of the existing centrifugal compresssor by using what you said. I put it on the vendor performance curve into hysys model such that I can predict what outlet condition that supposed to be.
How about the reiprocating compressor, could I do the same procedure? note the performance curve of reciprocating is different type with centrifugal compressor.

best regards

senno

Senno,

A recip is a fixed volume compressor, so a performance curve doesn't do much for you. I advise you to read the Section 6.2 in the HYSYS Operations Guide and http://support.aspentech.com tech solution id 112519.
When you have added the compressor on your flowsheet, on its Design tab / Parameters page select Recip compressor, then on the Settings page, you can set the other parameters.
Default values are added for all parameters with the exception of: typical design speed (rpm), volumetric efficiency (%), and speed (rpm). Volumetric efficiency will be a calculated value and should be left empty.

Typical Design speed (rpm) - Enter design speed for the compressor. This should be from compressor datasheet if available.
Speed (rpm) - Enter the current/desired compressor speed. This speed will be used in determining the current flow rate through the compressor.
The default values for all other parameters should be updated with values for the compressor that is being simulated.

Specify the compressor outlet pressure. HYSYS will calculate the flow though the compressor based on the parameters entered. Changing speed and/or loading/unloading cylinders will change the flowrate through the compressor.

Cheers,
Joerd

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

Hello,

are there any specific issues with modelling of screw compressors? They have to be modelled as the centrifugal ones?

thanks,
Joisy

A screw compressor is like a recip, it is a positive displacement compressor. It will try to displace the same volumetric flowrate independent of the head.

By the way, I recently had some correspondence with Aspentech; it appears that if you have multiple curves for a compressor (i.e. at different speeds), and only one enabled, you can still specify the outlet pressure without getting an error message. In essence the problem is overspecified in that case.

Cheers,
Joerd

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