wet gas compression 3

[mlazard]

In a gas pipeline project I have several wet gas compressors (80-90% gas)
for these compressors preliminary spec. give a 85% polytropic efficiency,
which is the standard procedure to model these compressors ?
I can model as adiabatic (assuming 85% efficiency) but I would prefer a more accurate procedure.

 

[PaoloPemi]

I do not know of standards covering this specific topic,
my copy of Prode Properties includes three methods to model compressors (rigorous polytropic cycle with selectable thermodynamic packages)

a ) Huntigton, applicable to gas phase, based on (Maxell) dH=TdS+VdP, works with a simplified model for compressibility integrated from p1 to p2, quite accurate and fast (accuracy depends from correct prediction of gas volumes)

b ) Schultz (Asme PTC 10), applicable to gas phase, based on PV ^ n = C which is exact for real gases only, Schultz includes corrections for real gases, I have read reports that this method gives higher errors than Huntington but it's a reference for industry (as GPSA method)

c) Polytropic solution with phase equilibria, based on solution of phase equilibria along a polytropic path, accurate (possibly most accurate in my tests based on entropy flash), can be very slow (compared to Huntington or Schultz), I use this method when a liquid phase is present.

I think the last procedure (Polytropic solution with phase equilibria) is what you need, it's a iterative procedure, the manual has some additional information

'

http://www.prode.com/docs/pppman.pdf'

 

[zdas04]

Since you are talking about polytropic processes, I have to assume you are using dynamic compressors instead of PD machines. For PD machines, the adiabatic model yields results that match field conditions very well (if I see a recip that has any measured value more than 5% off from Ariel's "Performance" program then I start looking for a fault in the machine, not the program, and I always find one).

I have to wonder what operation uses centrifugal or axial compressors for wet gas? And when you say 80% to 90% gas what do you mean? Is the other 10-20% (by volume I'm assuming) chicken feathers, pond scum, water, or condensable hydrocarbons? 10% liquid by volume into any compressor is not going to end well. I often compress wet gas at 100% RH which ends up having 0.1% water vapor (by volume) that becomes 0.0000001% of the volume when it condenses. 10% of 1 MMSCF is 17,000 bbls of water. That is a lot of water.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

 

[poli60]

a wet compressor module is present in the last version of UNISIM

 

[pmover]

mlazard,

i recommend you contact the compressor mfg and forward your request to them. each mfg will utilize a method for modelling or determining the performance of the compressor. additionally, the mfg should be able to furnish you the performance curves of the compressor (especially if centrifugal compressor).

good luck!
-pmover

 

[mlazard]

thanks all for help

PaoloPemi,
I'll review Prode Properties and the methodology applied (not aware of that).

David,
it's a preliminary design, as you may know there are several kind of pumps/compressors allowing gas+liquid, at following stages we will define all the details

poli60,
I can model adiabatic cycle, not polytropic

pmover,
as said it's a preliminary design stage, I fully agree with you that we need to contact manufacturers to get all the details required to model the compression unit

Marie

 

[cosh]

as said by PaoloPemi depending from the amount of condensate you may need a procedure to calculate phase equilibria along a polytropic path,
for a recent project we have utilized Prode Properties,
results have been found in agreement with manufacturer's simulation,
(the problem there is the definition of the polytropic efficiency).

 

[25362]

turbolab.tamu.edu/proc/turboproc/T34/t34-12.pdf​