The refrigeration process in air separation plants mainly follows the classical refrigeration cycle, where air is cooled through the steps of compression, condensation, expansion and evaporation.
The air is first compressed by a multi-stage compressor, gradually increasing the pressure, the air temperature rises, but the pressure also increases accordingly. The compressed air enters the cooling system, where the temperature is reduced by heat exchangers, expanders and other equipment. At the same time, impurities in the air (e.g. moisture, carbon dioxide, acetylene, etc.) are removed. Reducing the air temperature increases the efficiency of the subsequent separation process; purifying the air and protecting the equipment from impurities. The air temperature is significantly reduced and the impurity content is reduced. The cooled and purified air enters the expander for expansion, increasing volume and reducing pressure. The gas is utilised to do work on the outside during the expansion process, releasing internal energy and thus lowering the temperature. The temperature of the air is further reduced, and at low temperatures, the oxygen, nitrogen and other components of the air begin to liquefy. Through the distillation tower and other separation equipment, using the boiling point difference of different components for separation, to get liquid oxygen, liquid nitrogen and other products.
The refrigeration effect of the air separation equipment directly affects the output and quality of the products. By optimising the refrigeration process, energy consumption can be reduced, separation efficiency can be improved and equipment life can be extended.
