5 replies to this topic

[chemdoc]

for process simulation of compressors / expanders I adopt the method = PSPF() exported in Excel as macro from Prode Properties dll library, 

for natural gas mixtures I select GERG 2008 / AGA 2017 models,

the method works in most cases with options 1 or 2 but in some cases at high pressures (> 300 Bar) it can return 0, 

since options 1 and 2 are for gas phase only I suspect that at high pressures, in dense phase, Prode can identify the state as liquid (not gas) thus generating an error for option 1...

I could select options 3 or 4 (the polytropic solution with phase equilibria available for expanders, pumps etc.) but I am not sure about the accuracy at high pressure,

what do you think ? 

Edited by chemdoc, 06 April 2018 - 08:45 AM.

[PaoloPemi]

the polytropic solution with phase equilibria (options 3 and 4 in Prode Properties) adopts a procedure not too different from integration of the Z function (options 1 and 2) but adopts a numerical method while for options 1 and 2 there is a analytic solution,

both procedures integrate (analytical or numerical solution) Maxwell equation

 

dH = T*dS + V*dP

 

working with a gas phase, the polytropic solution with phase equilibria (options 3 and 4) is a bit less accurate than integration of the Z function (options 1 and 2) and slower (due to VLE calc's),

anyway, you can adopt the polytropic solution with phase equilibria (options 3 and 4) in all cases where the procedure based on integration of the Z function (options 1 and 2) fails (possibly due to detection of liquid phase)

[chemdoc]

thanks Paolo,

do you know if there is a possibility to force a vapor or a liquid state in dense phase region working with Prode Properties ?

[PaoloPemi]

before to answer I did some tests at high pressures with the compostion C1 0.5 CO2 0.5 model GERG 2008 , with data given in paper "Limitations of ASME PTC 10 in Accurately Evaluating Centrifugal Compressor Thermodynamic Performance"  (Sandberg, Colby) which compares different methods,

there is a comparison table with several cases (I include two here)

 

P1 1500 psia T1 90 F P2 5364.3 psia T2 291.3 F , Poly.Eff. 0.82  Prode calculates 0.82062

....

P1 1700 psia T1 70 F P2 9266.9 psia T2 311.5 F , Poly.Eff. 0.82  Prode calculates 0.82086

 

in all the the cases which I tested,  Prode Properties calculated the correct values with (very) limited errors (compared to ASME PTC 10 method),

 

anyway, you can force vapor state by increasing the minimum allowed value for liquid density,

 

 ProdePropertiesdensephasesettings.jpg   132.28KB   1 downloads

 

if you increase the value to 500 Kg/M3 or above the software in most cases will detect a vapor / gas phase...

[chemdoc]

thanks, that solves the problem...

[Andresblgr]

Hello 

 

I found this android App where you can check the performance of compressor and turboexpanders

 

https://play.google.com/store/apps/details?id=appinventor.ai_methane_solutions.GasEngineering