Structure of expander in air separation unit: turbine expansion unit is one of the units matched with gas separation device. Its principle is to use air expansion to generate cooling capacity, so as to meet the cooling capacity loss of gas separation unit and compensation device. The turbine expansion unit consists of turbine expansion, oil station, base, cold box, part of oil and water, gas pipeline, etc. The gas entering the turbo expander needs to be clean gas free of mechanical impurities.