According to the actual production situation and technological requirements of an iron and steel enterprise,recycle the waste heat of compressed air in the oxygen production unit of 40 000m3/h for preheating the dirty nitrogen used in the heating process of molecular sieve purification,reducing the power consumption of electric heater,and reducing the temperature of compressed air can reduce the power consumption of chiller in the air precooling system,achieving the purpose of saving energy,reducing consumption,reducing emission and increasing efficiency.