The present invention relates to a technology for liquefying
natural gas, which is subsequently transported by rivers and oceans and ultimately regasified. Pretreated
natural gas is compressed by a compressor 1, the heat of compression is removed in an air or
water cooler 2, and multi-stage pre-cooling is subsequently performed by evaporating a heavy
refrigerant in an
evaporator 3. The light
refrigerant vapor and its pre-
evaporation cold are recovered in a shell-and-tube
heat exchanger 7, where the pressure of the gas to be liquefied is reduced by a pressure
reducer 10, unliquefied gas is separated, and
liquefied natural gas is discharged. The heavy
refrigerant obtained by
evaporation is compressed by a compressor 4, condensed in an air or
water cooler 5, and reused in the multi-stage pre-cooling of
natural gas. A light refrigerant is compressed by at least two compressors 11, the heat of compression is removed in an air or
water cooler 12, and then passes through continuous cooling by a low-pressure light refrigerant in a double-flow
superheater 12 and an evaporating heavy refrigerant in an
evaporator 3. The high-pressure light refrigerant is then split into two streams. The first
stream is expanded through an isentropic process in an expander 14. The second
stream passes through continuous cooling in a shell-and-tube
heat exchanger 7, then expanded through an isenthalpic process in a
throttle valve 15, and evaporated by
subcooling natural gas in an
evaporator 8. The streams are then mixed at equal pressure and used as a single
stream of low-pressure light refrigerant to cool the second stream of light refrigerant before expansion and
evaporation in the isenthalpic process with natural gas in the shell-and-tube
heat exchanger 7, and to cool a single stream of high-pressure light refrigerant in a double-flow
superheater 13. The present invention provides stronger cooling of the natural gas, reduces the amount of boil-off gas and the work required for its recompression and recycling, and provides a simpler hardware design for the heat exchanger.