Discharge temperature and interstage cooling

The dischai e temperature of a compressor can be calculated by Eq, (4) or Eq. (9), it is a fimetion of inl gas temperature, compression ratio, isentioplc exponent, and compressor efficiency. Compressor discharge temperature is sensitive to the value of isentroptc or polytropic exponent. This is true for all types of compressors. 

Compressor horsepower is directly proportional to gas inlet temperature. Therefore, it makes sense to cool gas at compressor inlet or between stages. Another reason to cool gas between stages is due to the temperature limitation for the compressor. For centrifugal compressor, this temperature limitation is about 350 F. [I] For certain service, such as compression of oxygen, chlorine, and acetylene, the discharge temperature is limited to 200 F- For horizontal split compressor, thermal stress of bolt joint may limit the discharge temperature. [5] 

Most interstage cooling is achieved using external cooler. Sometimes, cooling inside casing or cooling by liquid injection is used. 

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