Method and apparatus for cooling a stream, in particular a hydrocarbon stream such as natural gas

Method of cooling a stream, wherein the stream is cooled in a heat exchanger against a refrigerant fluid being cycled in a refrigerant circuit, the cycling of the refrigerant fluid comprising:

• (a) feeding a first refrigerant fluid into an axial compressor;
• (b) compressing the first refrigerant fluid in the axial compressor, thereby obtaining a compressed first refrigerant fluid;
• (c) feeding the compressed first refrigerant fluid at a first pressure level into a centrifugal compressor at a first inlet;
• (d) feeding a second refrigerant fluid at a second pressure level into the centrifugal compressor at a second inlet, the second pressure level being lower than the first pressure level;
• (e) compressing the compressed first refrigerant fluid fed in step (c) and the second refrigerant fluid fed in step (d) in the centrifugal compressor, thereby obtaining a compressed refrigerant fluid mixture;
• (f) cooling the compressed refrigerant fluid mixture obtained in step (e) in a heat exchanger against a cooler stream, thereby obtaining a cooled compressed refrigerant fluid mixture;
• (g) separating the cooled compressed refrigerant fluid mixture obtained in step (f) into at least two streams;
• (h) evaporating the at least two streams obtained in step (g) at different pressure levels of a heat exchanger in heat exchanging contact with the stream to be cooled thereby cooling the stream;
• and
• (i) retrieving the first and second refrigerant fluids from the at least two streams evaporated in step (h).