The mixed refrigerant liquid nitrogen machine is based on a regenerative throttling refrigeration cycle. From ambient temperature to target refrigeration temperature, high, medium and low boiling point pure components are preferably composed of multiple mixed refrigerants, so that the effective cooling temperature areas overlap with each other. In this way, the cooling temperature zone distribution matching is perfected, and the effective cooling temperature zone matching of each boiling point component is realized, thereby realizing high-efficiency refrigeration with a large temperature span, and a relatively high throttling refrigeration effect can be obtained under a relatively small pressure difference. Therefore, a mature single-stage refrigeration compressor in the general cold field can be used to drive a closed-cycle mixed refrigerant throttling refrigerator to achieve low-temperature refrigeration. The above-mentioned mixed refrigerant throttling refrigeration technology has been applied in many applications and industrial sectors. For example, in the natural gas liquefaction industry, the mixed refrigerant refrigeration liquefaction process occupies a dominant position. For the application temperature zone and scale involved in this project, mature equipment such as compressors and heat exchangers in the general cold field can be adopted to greatly improve the reliability of the system, and the equipment sources are extensive and the cost is relatively low.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. Technical indicators and usage requirements Ambient temperature: up to 45 ℃ (summer) Altitude: 180 meters Liquid nitrogen output :3L/h to 150L/h The PSA nitrogen generator uses air as the raw material, high-quality carbon molecular sieve as the adsorbent, uses the principle of pressure swing adsorption, uses molecular sieve full of micropores to selectively adsorb air to achieve the purpose of oxygen and nitrogen separation, and produce high purity Nitrogen mainly includes equipment such as air compressors, filters, surge tanks, freeze dryers, adsorption towers, and pure nitrogen storage tanks. MRC liquefaction units mainly include pre-cooling compressor units, pre-cooling air coolers, main cooling compressor units, main cooling compressor units, main cooling air coolers, cold boxes, liquid nitrogen tanks, BOG recovery systems and control systems. The main/pre-cooling compressor unit includes the main/cold screw compressor and its matching lubricating oil separator, lubricating oil precision filter, activated carbon adsorber, lubricating oil circulating pump and mixed refrigerant storage tank, etc. The function of the MRC liquefaction unit is to use the principle of mixed working fluid regenerative throttling refrigeration to provide refrigeration for the liquefaction of nitrogen. The minimum temperature of the unit can reach -180 °C.