Relationship between the power of a centrifugal compressor and the gas being compressed
Thread Content
Here’s the situation: I have two gases that need to be compressed, hydrogen and carbon monoxide. According to the formulas for centrifugal compressors, the shaft power is related to the inlet pressure, flow rate, and adiabatic index. I checked the relevant data; the adiabatic indices of hydrogen and carbon monoxide differ by very little, at around 1.41. If I keep the same compression ratio (i.e., the same ratio of exhaust pressure to intake pressure), and the intake pressure and flow rate remain identical, can it be assumed that the required shaft power is the same? However, among the two rotary compressors, the compression ratio can be considered similar; the inlet pressure and flow rate differ (higher pressure and flow rate for hydrogen at the compressor inlet). Why then is the power requirement of the carbon monoxide compressor much higher than that of the hydrogen compressor? What is the root cause? Could someone help me explain this, preferably by analyzing it through formulas? Thank you!
I’m not familiar with the equipment nor do I understand the formulas used by the original poster, but since the molecular weights of hydrogen and carbon monoxide differ so much, with the same pressure, flow rate, and compression ratio, the amount of work done by the equipment must be different! Please ask the experts for guidance
The greater the molecular weight, the easier it is to compress; under the same conditions, more power is naturally required
What you might be meaning is that hydrogen is easy to compress, right? It has a low molecular weight, so it is easy to compress. However, the issue of molecular weight is not taken into account in the power calculation; the formula is N=1.634×PV×m/(m-1)×e^(m-1)/m, where m is merely a function of the adiabatic index and the polytropic efficiency, and e represents the pressure ratio, that is, the ratio of inlet to outlet pressure. The adiabatic index of hydrogen is not very different from that of carbon monoxide. The polytropic efficiency can be determined from charts; it is related to flow rate and the adiabatic index. Intuitively, hydrogen molecules have a low molecular weight and are therefore easy to compress, but how can this be explained here? It’s of course understandable that their critical temperatures and critical pressures are different; by looking at the compressibility factor charts, it can be seen that their compressibility factors are also different. What I mean is, if that’s the case, how can I relate them to each other? It can’t be done through intuitive reasoning, right? I searched online a lot, but all the answers were off-topic.
OP, do you have an answer yet? I agree; based on the power specifications, it seems that the compressor power has nothing to do with the molecular weight.