The recovery of cold energy is manifested in two aspects. On the one hand, it is the reuse of low-temperature cold energy at different temperatures, such as the low-temperature refrigerant used in the overhead condenser, the refrigerant with a slightly higher temperature as the refrigerant at the top of the rectification tower, or the refrigerant in the intermediate condenser, etc., until all the refrigerants are vaporized and the temperature rises to near normal temperature. On the other hand, the existing refrigerants maintain a certain low-temperature refrigerant through throttling expansion or heat pump system, so as to reduce the manufacturing amount of low-temperature refrigerants and save energy. Cold box is a classic equipment with reflux cooling capacity. Using this equipment, the cold energy with lower temperature level can be generated and used as the refrigerant of demethanizer. This process can be regarded as the release of potential cold energy, which can be converted into cold energy at a lower temperature level and can be recycled.