Cryogenic liquefying / refrigerating method and
system, wherein temperature of gas-to-be-liquefied at the inlet of the compressor for compressing the gas is reduced by cooling the gas discharged from the compressor using a high-efficiency chemical refrigerating
machine and vapor compression refrigerating
machine before the gas is introduced to a multiple stage
heat exchanger thereby reducing power input to the compressor and improving liquefying / refrigerating efficiency. Gas-to-be-liquefied compressed by a compressor is cooled by aftercooler, and further cooled by an adsorption refrigerating
machine which utilizes
waste heat generated in the compressor and by an
ammonia refrigerating machine 40, then the
high pressure gas is introduced to a multiple-stage
heat exchanger where it is cooled by low pressure low temperature gas separated from a mixture of liquid and gas generated by adiabatically expanding the
high pressure gas through an expansion valve 30 and returning to the compressor, and a portion of the
high pressure gas is expanded adiabatically by expansion turbines in mid-course of flowing of the
high pressure gas through the stages of the
heat exchanger to be joined with the low pressure low temperature gas returning to the compressor.