What is the purpose of liquid injection in compound compression systems?

Liquid injection in compound compression systems serves the specific purpose of desuperheating the discharge gas of the first stage. This process involves introducing liquid refrigerant directly into the compressor, where it evaporates and absorbs heat from the discharge gas that has been compressed to high pressure and temperature.

By desuperheating the gas, the liquid injection helps to lower the temperature of the gas before it proceeds to the next stage of compression. This is crucial because high-temperature gas can lead to inefficiencies or damage in subsequent stages due to elevated stress on the components. The cooling effect of the injected liquid allows for more efficient and stable operation of the compressor, as it reduces the temperature and ensures that the refrigerant reaches its saturation point without overheating.

Thus, liquid injection helps improve the thermodynamic process within multi-stage compression systems. This process ultimately contributes to better system performance and reliability while preventing compressor wear or potential failure due to excessive heat.