Refrigeration and/or liquefaction device, and associated method

A device for refrigeration and/or liquefaction of a working gas containing helium or consisting of pure helium, the device comprising a working circuit in form of a loop for the working gas and comprising, in series:

• a working gas compression station equipped with at least one compressor;
• a cold box for cooling the working gas and comprising a plurality of heat exchangers arranged in series and at least one member for expanding the working gas;
• a system for the exchange of heat between the cooled working gas and a user;
• at least one return pipe returning to the compression station the working gas that has passed through the heat exchange system, the return pipe comprising at least one exchanger for warming the working gas, and
• the device further comprising:
• an additional system for pre-cooling the working gas at the exit from the compression station, the pre-cooling system comprising at least one volume of auxiliary cryogenic fluid such as liquid nitrogen, the volume being connected to the working circuit via at least one heat exchanger in order selectively to transfer frigories from the auxiliary fluid to the working gas, the cold box comprising a first working-gas cooling stage comprising a first exchanger arranged at the exit from the compression station and a second heat exchanger and a third heat exchanger, the first heat exchanger being of the aluminum plate and fin type, the second heat exchanger being of the welded plate or welded tube(s) type, this second heat exchanger being immersed in a bath for auxiliary cooling fluid, characterized in that the second and third heat exchangers are connected both in series and in parallel to the working circuit downstream of the first heat exchanger, which means to say that the working gas cooled in the first heat exchanger can be admitted selectively to the second and/or to the third heat exchanger, and in that the second heat exchanger is immersed in the first volume of liquefied auxiliary gas.