Hello All,
I am currently working on a fixed speed multistage gas centrifugal compressor package (including motor, transformer, lube oil system, DGS, etc.) I have a couple of understandings that I would like to get feedback on from the chemical engineers with experience in such compressors:
For a fixed speed multistage compressor, with fixed inlet temperature, pressure and compression ratio:
1. If the Molecular weight of the gas increased, the gas becomes easier to compressor since it has a higher density, which means that the polytropic head required to achieve the compression ratio becomes lower. Since the mass flow rate is higher (because the of the higher density), the BHP required by the compressor increases. On a separate note, the compressor required speed (i.e. RPM) is lower since the gas requires a lower polytropic head to achieve the required compression ratio.
2. If the Molecular weight of the gas decreased, the gas becomes harder to compressor since it has a lower density, which means that the polytropic head required to achieve the compression ratio becomes higher. Since the mass flow rate is lower (because the of the lower density), the BHP required by the compressor decreases. On a separate note, the compressor required speed (i.e. RPM) is higher since the gas requires a higher polytropic head to achieve the required compression ratio.
Is my basic understanding correct? (I know that there are other factors like impeller tip speed and gas relative velocity that can play a part but I just want feedback on my basic understanding)
Also, does anyone have a spreadsheet that simulates the outlet parameters of a centrifugal based on the polytropic process?
Many thanks.