Novel two-stage rectification auto-cascade natural gas liquefaction system and control method thereof

The invention discloses a novel two-stage rectification auto-cascade natural gas liquefaction system. According to the system, two-stage rectification is adopted to achieve two-stage separation of mixed refrigerant components, the proportion of low-boiling-point components in the mixed refrigerant entering an evaporator is increased, the evaporation pressure of the system is increased, the working pressure ratio of a compressor is reduced, and the system performance is improved. Meanwhile, the middle air supply technology is introduced into the novel system, high-pressure refrigerants of part of flow paths only need to be throttled to middle pressure, the throttling loss of the system is greatly reduced, and the performance of the system is further improved. 本发明公开了一种新型两级精馏自复叠天然气液化系统,该系统采用两级精馏实现混合制冷剂组分的两级分离，增大进入蒸发器的混合制冷剂中低沸点组分的比例，提高系统的蒸发压力，降低压缩机的工作压比，改善系统性能。同时，该新型系统引入中间补气技术，部分流路的高压制冷剂仅需节流至中间压力，大大降低了系统的节流损失，进一步提高系统性能。