The liquid nitrogen unit developed by our unit adopts Pressure Swing Adsorption (PSA) to prepare pure nitrogen, which is then throttled by mixed-gas joule-thomson Refrigeration Cycle, MRC for short) to generate the required liquid nitrogen.Referring to the refrigerator shown in Figure 1, its working process is: low-pressure fluid refrigerant at ambient temperature T0 (corresponding to state point 1s) is compressed into high-pressure high-temperature gas (state point 2) by the compressor, and then enters the cooler, etc. Cooled down to ambient temperature (point 3), enters the regenerative heat exchanger, is further cooled by the reflux low-pressure low-temperature gas to state point 4, enters the throttle valve, adiabatic throttling to point 5, the temperature drops, and enters the evaporator to provide cold When the temperature rises to point 6, it enters the low-pressure passage of the regenerative heat exchanger, and while cooling the high-pressure incoming flow, its temperature gradually returns to point 1, and then enters the pipe connecting the heat exchanger and the compressor. There may be part of the system at this time Heat leakage, the temperature rises to the ambient temperature, returns to the state point for 1 second, and the system completes a cycle. The refrigeration system gradually lowers the temperature according to the above process, and finally provides refrigeration capacity at the set refrigeration temperature Tc. For distributed temperature load cooling, the cooling capacity is gradually provided during the reflux process, such as natural gas liquefaction, etc. The characteristics of the mixed refrigerant throttling refrigerator 1) Fast start-up and fast cooling rate. Through mixed refrigerant concentration ratio, compressor capacity adjustment and throttle valve opening control, rapid cooling requirements can be achieved; 2) The process is simple, the number of equipment is small, and the system reliability is high. The main components of the system adopt mature compressors, heat exchangers and other equipment in the refrigeration field. The system has high reliability and a wide range of equipment sources. The development cost of the mixed refrigerant liquid nitrogen unit mainly includes two parts: PSA nitrogen generator unit and MRC liquefaction unit. The PSA nitrogen generator is relatively mature and is relatively easy to buy in the domestic market.