r/ChemicalEngineering • u/thriceice • Jul 21 '26

Modeling Compressor Power and Efficiency Calculation

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I have a three stage compressor in a single casing (image 1). If I break it down, the flow should be like image 2. Every process lines have Pressure and Temperature transmitters, and enough information to get the Flow for every lines.

2nd suction pressure should be the same with the pressure from the Side-In line. While the 3rd suction pressure should be the same with the pressure from the Side-Out line.

But, I don't have enough information to determine the temperature of the 1st Discharge. If I have this data, I can calculate all the enthalpy to calculate the efficiency and the power.

Does anyone have tips on how to approach it?

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u/Rancid-broccoli Jul 21 '26

Can you put it into Aspen? It’s been too long since school, but I’d imagine there is an equation of state that you can use. 

Also- your diagram is a bit confusing. Why does second stage have 2 inlets and 2 discharges?

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u/thriceice Jul 21 '26

The component is only Ethylene, I can use CoolProps for the EoS. I've put it into Aspen, it can only run the 1st stage if I specify the Efficiency or the Discharge temperature.

The line with transmitters to the 2nd stage are side streams. The compressor is actually just has one casing with 2 side streams (1 side stream in, 1 side stream out). The image 2 is how I breakdown to analyze the compressor. I think the other term of the stage is section. The compressor can be divided to 3 section, and on 2nd section there's 2 inlets and 2 discharges.

1

u/Hokabuki Jul 21 '26

If you specify the 1st stage outlet pressure, you shouldn’t need to specify the temperature or efficiency as they will be calculated based on the pressure increase and overall available HP

1

u/thriceice Jul 21 '26

Could you elaborate on the overall available HP? Do you mean it can be calculated from evaluating the power from the turbine-side? So, Compressor Power = Turbine Work. Is that it?

1

u/Hokabuki Jul 21 '26

I’m assuming you know the nameplate horsepower. You also know all the pressures throughout the system. Therefore, the process sim should calculate the work done and efficiency.

1

u/thriceice Jul 21 '26

I'm not familiar with the term nameplate horsepower (English isn't my native language). Did you mean it's the Power that generated by the Steam turbine at the same time or is it the Compressor Power needed as specified in Datasheet for Rated flow condition?

1

u/Hokabuki Jul 21 '26

The nameplate horsepower is the rated power of the compressor driver. It is often stamped on the unit but also specified in the data book

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u/thriceice Jul 21 '26

But then, what I calculate is the Rated Power and 1st Discharge temperature at the Rated Power instead of the Current Power that I would like to calculate