Method for liquefying natural gas

1:

• A natural gas liquefaction method, by which a pre-treated natural gas is compressed, heat of compression is removed, the natural gas is cooled by three circuits containing mixed refrigerants, pressure of a cooled gas is reduced to produce a vapor-liquid mixture, and a liquefied gas is withdrawn, in each said circuit a mixed refrigerant is compressed, heat of compression is removed, the mixed refrigerant is sub-cooled, pressure thereof is lowered to produce in each circuit a low-pressure mixed refrigerant, and such low-pressure mixed refrigerant is used to cool down the natural gas, meanwhile in the first circuit the first mixed refrigerant is sub-cooled through evaporation of the first low-pressure mixed refrigerant, in the second circuit the second mixed refrigerant is also cooled through evaporation of the first low-pressure mixed refrigerant and sub-cooled through evaporation of the second low-pressure mixed refrigerant, in the third circuit the third mixed refrigerant is cooled through evaporation of the second low-pressure mixed refrigerant and sub-cooled through evaporation of the third low-pressure mixed refrigerant, wherein an end boiling point of the second mixed refrigerant at the pressure at which the compression thereof commences is lower than a temperature of the first mixed refrigerant after the pressure of said first mixed refrigerant has been reduced, and an end boiling point of the third mixed refrigerant at the pressure at which the compression thereof commences is lower than a temperature of the second mixed refrigerant after the pressure of said second mixed refrigerant has been reduced.