Method of and arrangement for processing through low temperature heat exchanges and in particular for treating natural gases and cracked gases

A system for refrigerating a natural gas or a cracked gas with a fluid cycle comprising multi-component refrigerant fluid at a low temperature of from -40.degree. C. to -140.degree. C., the multi-component refrigerant fluid consisting essentially of C.sub.1, C.sub.2 and C.sub.3 hydrocarbons, the system comprising:

• compression means for compressing said refrigerant fluid in the gaseous condition from an absolute pressure of about 1 bar to 3 bars at the suction side of the compression means to an absolute pressure of about 30 bars to 50 bars at the delivery side of the compression means;
• successive stage external coolers coupled to said compression means and operating with coolants selected from the group consisting of water, air, propane and propylene for providing at least full condensation of said refrigerant fluid after compression;
• at least one main heat exchanger coupled to at least one of said successive stage external cooler for receiving therefrom a first part of said condensed refrigerant fluid, and including inlet means and cold outlet means for said first part of said condensed refrigerant fluid, an expansion means at its cold end at a temperature of from about -100.degree. C. to about -140.degree. C. for expansion of said refrigerant fluid to the pressure at the suction side of the compression means, a vapor passage coupled to the expansion means for passing vaporized refrigerant fluid through the main exchanger for sub-cooling said first part of said condensed refrigerant fluid in indirect heat exchange therewith, and further inlet and further outlet means containing a warmer stream than said refrigerant vapor in indirect heat exchange relation with vapor in said exchanger;
• at least one auxiliary heat exchanger having an inlet means and a cold outlet means, the inlet means thereof being coupled to said at least one of said successive stage external coolers for receiving a second part of said condensed refrigerant fluid, and having further inlet and further outlet means containing a colder stream than said second part of said condensed refrigerant fluid for sub-cooling said second part of said condensed refrigerant fluid;
• means for coupling said vapor passage at its warm end to the suction side of said compression means;
• and
• a conduit connected to and joining the cold outlet means of said main and auxiliary heat exchangers for combining said sub-cooled first and second parts of said condensed refrigerant fluid, and connected to said expansion means.