Method for liquefying natural gas with improved injection of a mixed refrigerant stream

The invention relates to a method for liquefying a stream of hydrocarbons such as natural gas from a feed stream (110), said method comprising the following steps: a) injecting the feed stream (110) into a first heat exchanger (E1); b) injecting a first refrigerant stream (30) into the heat exchanger (E1); c) extracting from the heat exchanger (E1) a plurality of partial refrigerant streams (301, 302, 303) originating from the first refrigerant stream (30) through separate outlets (11, 12, 13); d) injecting each partial refrigerant stream (301, 302, 303) originating from step c) into an expansion member (V1, V2, V3) and expanding each partial refrigerant stream (301, 302, 303) so as to produce a plurality of two-phase refrigerant streams at different pressures; e) injecting each two-phase refrigerant stream originating from step d) into a phase separating member (24, 25, 26) so as to produce a gaseous refrigerant stream (31, 32, 33) which is diverted from the first exchanger (E1) and a liquid refrigerant stream (34, 35, 36) which is injected into the first exchanger (E1) via respective inlets (4, 5, 6); f) vaporising each liquid refrigerant stream (31, 32, 33) by heat exchange with at least the feed stream (110) and the first refrigerant stream (30) so as to extract a cooled hydrocarbon stream (102) at the outlet of the first heat exchanger (E1) and to extract a plurality of vaporised refrigerant streams from respective outlets (14, 15, 16) of the first heat exchanger (E1). According to the invention, the method further comprises, for each of the vaporised refrigerant streams originating from step f), the following steps: g) measuring the temperature of the vaporised refrigerant stream at its respective outlet (14, 15, 16); h) determining the dew temperature of the vaporised refrigerant stream; i) determining a first temperature deviation corresponding to the difference between the temperature measured in step g) and the dew temperature determined in step h); j) adjusting a flow rate setpoint applied to the expansion member (V1, V2, V3) as a function of the first temperature deviation determined in step i), so as to reduce the flow rate of partial refrigerant stream expanded in step d) when the first temperature deviation is less than a first predetermined value and to increase the flow rate of partial refrigerant stream expanded in step d) when the first temperature deviation is greater than said first predetermined value.