The invention discloses a process for precooling, expanding and liquefying
natural gas. The process includes (a), compressing
nitrogen at two stages, then cooling the compressed
nitrogen by the aid of coolers, and precooling the cooled compressed
nitrogen in multi-
stream heat exchangers; (b), expanding the nitrogen by the aid of turbo expanders and filling
backflow to heat exchangers; (c), secondarily expanding the nitrogen by the aid of the turbo expanders and sequentially filling
backflow to the heat exchangers; (d), compressing and pressurizing
propane by the aid of
propane compressors; (e), enabling the pressurized
propane to flow through water coolers; (f), performing cooling and depressurization to generate a
gas phase and a
liquid phase, filling the
gas phase and the
liquid phase into the multi-
stream heat exchangers and precooling the
natural gas and high-pressure refrigerants by the aid of the multi-
stream heat exchangers; (g), cooling the
natural gas by the heat exchangers at first; (h), depressurizing and cooling the cooled natural gas by the aid of
throttle valves to generate a
gas phase, and storing the remaining
liquid phase in
liquefied natural gas storage tanks; (i), filling the gas phase as
backflow gas into the heat exchangers to provide
cooling capacity for the heat exchangers, reheating the backflow gas and using the reheated backflow gas as regenerated gas for purifiers for pre-treating the natural gas. The process has the advantages that the natural gas can be quickly liquefied, and
power consumption and the cost are low.