Method of and system for liquefying a gas with low boiling temperature

A method of cooling and liquefying at least one relatively dry gas having a low boiling point through heat exchange with at least one part of a light main refrigerating fluid pre-cooled until its at least partial liquefaction through heat exchange with a heavy auxiliary refrigerating fluid, said refrigerating fluids being part of an incorporated cold-generating cascade of at least these two refrigerating fluids, each refrigerating fluid consisting of a mixture of several component substances with decreasing volatilities, respectively, evolving according to a closed-loop cooling cycle while successively undergoing therein:

• at least one compression in the gaseous state from a low pressure to a higher pressure, at least one preliminary cooling with possible at least partial condensation at said higher pressure through heat exchange with a cooling medium in particular of outer origin, at least one self-refrigeration with total liquefaction and then sub-cooling and thereafter expansion down to said low pressure through subsequent heat exchange (and resulting attendant vaporization) in counter-current relationship with itself before its expansion and to the other refrigerating fluid or with said gas for at least partially liquefying the latter, its low pressure vapor thus reheated being eventually recycled and recompressed, wherein the improvement consists in the steps of reducing, for a same amount of treated products, the required total input power taken by the compressions of at least the refrigerating fluids by carrying out said compression at least of said auxiliary refrigerating fluid adapted to pre-cool said main refrigerating fluid in several successive separate compressions of gradually increasing amounts and at last the total amount of said auxiliary refrigerating fluid to respectively different pressures namely at least one intermediate pressure and at least one high pressure, at least the last but one compression of which is followed by said at least partial condensation and then subjecting several distinct portions of said high pressure auxiliary refrigerating fluid to respective expansions down at least to one intermediate pressure and to said low pressure followed each one by a vaporization of at least the major part at the corresponding expanded pressure;
• that portion to be expanded to and at least partially vaporized at said low pressure as well possibly as at least one or each other portion to be expanded to and at least partially vaporized at a corresponding intermediate pressure being each one sub-cooled in the liquid state before its consecutive expansion and vaporization through heat exchange in counter-current relationship with at least one part of itself already expanded previously and then vaporized by said heat exchange, each portion thus vaporized in at least its major part being thereafter recycled for being recompressed;
• the vaporization at the last intermediate pressure being effected in particular through heat exchange with said gas initially in the moist state to cool the latter thereby resulting in its relative drying through at least partial condensation of its moisture content whereas each aforesaid portion expanded and then vaporized at another lower pressure is also in heat exchanging counter-current relationship with said main refrigerating fluid for cooling and/or at least partially condensing same.