Permanent gas refrigeration method

Abstract

In cooling a permanent gas stream (e.g. of nitrogen) at elevated pressure to below its critical temperature (e.g. in a process for the liquefaction of the permanent gas), the stream is heat exchanged with a main stream of working fluid (typically also nitrogen) that has been work-expanded in expansion turbine. The refrigeration provided by this stream is supplemented by that provided by at least two supplementary streams of work expanded working fluid. The temperatures at which the supplementary streams are introduced into heat exchange relationship with the permanent gas stream are in a defined range extending from 5.degree. K. above the point at which the rate of change of the heat capacity (at constant pressure) of the gas per standard cubic meter increases by about 1% per Kelvin as the gas is cooled to 5.degree. K. below the point at which the rate of change with temperature of the heat capacity (at constant pressure) of the gas per standard cubic meter is at a maximum.