3 replies to this topic

[Alfreedo]

Can anyone tell me how I would enter the attached curves into HSYS to model a pair of coupled expander/compressors in a cryogenic application I'm working on?  I've attached the Curves.  TE-301 (First Stage expansion) drives AK-301 (2nd stage compression) and TE-302 (2nd Stg Expansion) drives AK-302 (1st Stage compression).  The gas leaves enters TE-301, then through TE-302 and goes through a series of exchangers and then comes back to AK-302, on to AK-301 and out.  I need to size a PSV on the discharge of 301 for blocked flow and am setting up a dynamic simulation to do so.  I just haven't worked enough with HSYS compressors/expanders to know much about how to enter curves there.  I also have some derived polytropic head curves for the compressors at least - can those be entered directly into HYSYS?  Any help would be appreciated.  Please see dimensionless curves attached from original supplier.

Attached Files

•  Expander_Compressor Performance Curves_Sanitized.pdf   446.6KB   7 downloads

[Dacs]

You can place the volume flow vs head vs efficiency table if under the Expander module (Rating -> Add Curve).

 

Your curves are dimensionless. So you need to figure out how to convert it to the data Hysys will accept.

[Alfreedo]

Thanks Dacs.  Yes that is precisely what I'm asking is if anyone has some experience in doing that conversion that could share some tidbits.  I believe that the dimensionless curve provided for the compressors can be entered directly as is when you select the option to enter dimensionless numbers into hysys curves you can plug psi and phi in directly.  Not sure if the n on that chart represents efficiency directly.  I've input those numbers but haven't tried to run it yet as I need to plug in the curves for the expanders first.  It just seems a little daunting to convert that one.   Haven't been able to find an easy to follow reference on that one.

[Dacs]

Hysys accepts actual volume flow vs differential head. So you need to convert the curve into something Hysys can use.

 

From your documentation provided:

 

Φ = Dimensionless volumetric flow, most probably actual flow

Ψ = Dimensionless something, most probably either head or discharge pressure

η = Looks like efficiency

w dot (w for short) = mass flow (lb/s)

 

P4 seems to be like discharge pressure, P3 suction (maybe?). Both in psiA. MW is also given.

 

If you have site data, then get the suction pressure Ps,s, discharge pressure Pd,s and a way to get the actual volumetric flow Qs

 

I'll calculate the equivalent actual volumetric flow (Qc) using P3, T3 and MW and w. 

 

Then I'll get the Φ = Qs / Qc. 

 

Then I'll calculate the corresponding Ψ from the curve and compare with the ratio of Pd,s / P4 and (Pd,s - Ps,s) / (P4 - P3). 

 

I'm leaning towards Ψ = (Pd,s - Ps,s) / (P4 - P3).

 

Let me know how it goes.

 

EDIT: If you just want to do it blindly, then you can calculate the differential pressure Pdelta = Ψ * (P4 - P3), then calculate the corresponding head from Pdelta. Then use it to directly in Hysys.

Edited by Dacs, 22 April 2025 - 10:18 PM.