Process for cooling a gas by means of a refrigeration cycle

Abstract

In a process for cooling hydrogen by means of a refrigeration cycle, a cycle fluid ( 4 ), which is nitrogen, is cooled to a temperature lower than −100° C., at least one portion ( 8 - 1 ) of the cooled cycle fluid is expanded in a turbine (T 1 ) in order to cool the at least one portion of the cycle fluid, which produces a two-phase fluid ( 6 ) at the outlet of the turbine, the two-phase fluid is separated in a phase separator (V 1 ), and at least one portion of the gas ( 8 ) produced in the phase separator is sent to a first heat exchanger (E 1 ) in order to exchange heat indirectly with the feed gas ( 1 ) to be cooled, which produces a cooled feed gas ( 2 ) and a heated cycle gas ( 9 ), which is compressed in a compressor (C 1 ) and then cooled in a cycle.

What is claimed is: 
     
         1 . A process for cooling a hydrogen feed gas utilizing a refrigeration cycle, wherein:
 a) a nitrogen cycle fluid is cooled to a temperature lower than −100° C.,   b) at least one portion of the cooled cycle fluid is expanded in a turbine in order to cool the at least one portion of the cycle fluid, which produces a two-phase fluid at the outlet of the turbine,   and either   c) the two-phase fluid is separated in a phase separator, and   d) at least one portion of the gas produced in the phase separator is sent to a first heat exchanger in order to exchange heat indirectly with the feed gas to be cooled, which produces a cooled feed gas and a heated cycle gas, which is compressed in a compressor and then cooled in a cycle according to step a), and   e) at least one fraction of the liquid of the phase separator is vaporized in a second heat exchanger by way of indirect heat exchange with the cooled feed gas in order to further cool the feed gas or even to liquefy it,   or   f) the two-phase fluid is heated directly in a first exchanger by way of heat exchange with the feed gas to be cooled, which produces a cooled feed gas and a heated cycle gas, which is sent to a compressor as cycle fluid before being cooled according to step a).   
     
     
         2 . The process as claimed in  claim 1 , wherein the ratio between the inlet pressure and the outlet pressure in bar absolute of the turbine is equal to or greater than 11. 
     
     
         3 . The process as claimed in  claim 1 , wherein the two-phase fluid contains a proportion of liquid between 5 and 20 mol % of liquid. 
     
     
         4 . The process as claimed in  claim 3 , wherein the amount of liquid produced in the turbine is adjusted by adjusting the outlet pressure of the cycle compressor and therefore the inlet pressure of the turbine, thus modifying the expansion rate of the turbine. 
     
     
         5 . The process as claimed in  claim 1 , wherein one portion of the cooled fluid is expanded in the turbine and another portion of the cooled cycle fluid is cooled in the first exchanger until it is completely liquefied, forming a liquid, this liquid is then expanded in a valve, the expanded liquid and the two-phase fluid at the outlet of the turbine are either mixed in the phase separator or mixed before being sent directly to the first heat exchanger in order to be heated. 
     
     
         6 . The process as claimed in  claim 5 , wherein the flow of the cooled portion in the first exchanger is variable in order to adjust the level of liquid in the phase separator. 
     
     
         7 . The process as claimed in  claim 1 , wherein all of the liquid of the two-phase fluid sent to the phase separator or directly to the heat exchanger originates from the turbine. 
     
     
         8 . The process as claimed in  claim 1 , wherein the cycle fluid contains at least 90 mol % of nitrogen. 
     
     
         9 . The process as claimed in  claim 1 , wherein, during step a), the cycle fluid is cooled by an external source of cold in a third heat exchanger and is sent directly to the turbine without passing through the first heat exchanger. 
     
     
         10 . The process as claimed in  claim 1 , wherein one portion of the liquid formed in the phase separator serves as a liquid product of the process. 
     
     
         11 . The process as claimed in  claim 1 , wherein gas is added, from an external source, to the cycle downstream of the compressor, this gas having the same composition as the cycle fluid, in order to increase the inlet pressure of the compressor in order to increase the proportion of liquid produced by the turbine. 
     
     
         12 . The process as claimed in  claim 1 , wherein the cycle fluid is cooled in step a) to a temperature greater than −192° C. 
     
     
         13 . The process as claimed in  claim 1 , wherein the cooled feed gas is then liquefied. 
     
     
         14 . The process as claimed in  claim 13 , wherein the cooled feed gas is then liquefied by a refrigeration cycle in which hydrogen or helium circulates.