Process for liquefying carbon dioxide resulting from a natural gas stream

Abstract

A process for producing liquefied natural gas and liquid carbon dioxide comprising: Step a): separating a natural gas feed gas into a CO 2 -enriched gas stream and a CO 2 -depleted natural gas stream; Step b): liquefying the CO 2 -depleted natural gas stream in a liquefaction unit comprising at least a main heat exchanger and a system for producing frigories, said liquefaction unit comprising at least one refrigeration cycle fed by a refrigerant stream; Step c): simultaneous liquefying of the CO 2 -enriched gas stream resulting from step a) in a CO 2 liquefaction unit; wherein the refrigeration necessary for the liquefaction of the CO 2 -enriched gas stream and for the liquefaction of the natural gas is supplied by said frigorie-producing system of the liquefaction unit and in that the refrigeration necessary for the liquefaction of the CO 2 -enriched gas stream originates from a portion of said refrigerant stream supplying the refrigeration cycle of said liquefaction unit.

What is claimed is: 
     
         1 . A process for producing liquefied natural gas and liquid carbon dioxide comprising at least the following steps:
 Step a): separating a natural gas feed gas, containing hydrocarbons and carbon dioxide in a treatment unit, into a CO 2 -enriched gas stream and a CO 2 -depleted natural gas stream;   Step b): liquefying the CO 2 -depleted natural gas stream resulting from step a) in a natural gas liquefaction unit comprising at least a main heat exchanger and a system for producing frigories, said natural gas liquefaction unit comprising at least one refrigeration cycle fed by a refrigerant stream;   Step c): simultaneous liquefying of the CO 2 -enriched gas stream resulting from step a) in a CO 2  liquefaction unit;   
       wherein the refrigeration necessary for the liquefaction of the CO 2 -enriched gas stream and for the liquefaction of the natural gas is supplied by said frigorie-producing system of the natural gas liquefaction unit and in that the refrigeration necessary for the liquefaction of the CO 2 -enriched gas stream originates from a portion of said refrigerant stream supplying the refrigeration cycle of said natural gas liquefaction unit; and wherein the feed gas comprises from 0.1 mol % to 5 mol % of CO 2 . 
     
     
         2 . The process according to  claim 1 , wherein in that the CO 2 -enriched gas stream resulting from step a) comprises at least 95 mol % of CO 2 . 
     
     
         3 . The process according to  claim 1 , wherein prior to step b), the natural gas stream resulting from step a) is pretreated in a pretreatment unit. 
     
     
         4 . The process according to  claim 1 , wherein said treatment unit used in step a) is an amine scrubbing unit. 
     
     
         5 . The process according to  claim 1 , wherein the CO 2 -enriched gas stream resulting from step a) is purified prior to step c), the refrigeration necessary for this purification being provided by said frigorie-producing system of the natural gas liquefaction unit. 
     
     
         6 . The process according to  claim 1 , wherein the CO 2 -enriched stream thus purified comprises at least 99.5 mol % of CO 2 . 
     
     
         7 . The process according to  claim 1 , wherein said system for producing frigories comprises at least one compressor. 
     
     
         8 . The process according to  claim 1 , wherein refrigerant stream supplying said at least one refrigeration cycle of said natural gas liquefaction unit contains at least one of the constituents selected from the group consisting of nitrogen, methane, ethylene, ethane, propane, ammonia, butane and pentane.