Process and apparatus for sweetening and liquefying a gas stream

Abstract

A process and apparatus for liquefying a gas stream comprising hydrocarbons and sour species is provided in which the sour species are removed in liquefied form as the sweetened gas stream is progressively cooled to liquefaction temperatures. The process involves cooling the gas stream in a manner to produce a cooled gas stream comprising gaseous hydrocarbons and residual sour species. The cooled gas stream is then treated with a cold solvent to deplete the cooled gas stream of residual sour species. The resulting cooled sweetened gas stream is then further cooled to produce liquid hydrocarbons.

1 . A process for liquefying a gas stream comprising hydrocarbons and sour species, the process comprising the steps of:
 a) cooling the gas stream in a manner to produce a cooled gas stream comprising gaseous hydrocarbons and residual sour species;   b) treating the cooled gas stream with a solvent to deplete the cooled gas stream of residual sour species, thereby producing a cooled sweetened gas stream; and   c) cooling the cooled sweetened gas stream to produce liquid hydrocarbons.   
     
     
         2 . The process according to  claim 1 , wherein in step a), cooling is conducted in a manner whereby the gas stream is cooled to a first temperature to produce a mixture of solid and/or liquid sour species and a vapour containing gaseous hydrocarbons and residual sour species, and the solid and/or liquid sour species are separated from the mixture, thereby producing the cooled gas stream. 
     
     
         3 . The process according to  claim 2 , wherein cooling is conducted under a first set of temperature and pressure conditions at which the sour species solidifies and/or a liquid condensate of sour species forms. 
     
     
         4 . The process according to  claim 2 , wherein the first temperature is at or just below the temperature at which the sour species solidifies and/or condenses. 
     
     
         5 . The process according to  claim 2 , wherein the first temperature is a temperature at which freezable hydrocarbon species condense. 
     
     
         6 . The process according to  claim 2 , wherein the first temperature is a temperature at which solubility of the residual sour species in the solvent used in step b) is optimized. 
     
     
         7 . The process according to  claim 1  wherein treating the cooled gas stream with a solvent comprises contacting the cooled gas stream with a solvent in which the sour species is more soluble than the gaseous hydrocarbons. 
     
     
         8 . The process according to any  claim 2 , wherein step b) is performed under temperature conditions close to or at the first temperature. 
     
     
         9 . The process according to  claim 1  wherein in step c), cooling is conducted under a second set of temperature and pressure conditions at which hydrocarbons in the cooled gas stream condense. 
     
     
         10 . The process according to  claim 1  wherein in at least one of step a) and step c), cooling the gas stream comprises a heat exchange step selected from the group consisting of expanding the gas stream in one or more expansion steps, effecting an indirect heat exchange with one or more cooling streams, effecting a direct heat exchange with a cooling stream, one or more heat exchange and/or expansion steps. 
     
     
         11 . (canceled) 
     
     
         12 . (canceled) 
     
     
         13 . (canceled) 
     
     
         14 . The process according to  claim 2  wherein the solid and/or liquid sour species are separated from the mixture under gravity, centrifugal force, or with other suitable separation means. 
     
     
         15 . The process according to  claim 2 , wherein the process further comprises the step of removing the solid sour species, preferably by heating and melting the solid sour species, thereby forming a liquid rich in sour species. 
     
     
         16 . The process according to  claim 15 , wherein the process further comprises heating the solid sour species to a temperature at or just above the melting point of the solid sour species. 
     
     
         17 . The process according to  claim 1  wherein prior to performing step a) the gas stream is cooled in a manner arranged to produce a liquid stream of carbon dioxide, ethane and C3+ hydrocarbons and a gas stream having a reduced carbon dioxide concentration. 
     
     
         18 . The process according to  claim 1  wherein prior to performing step a), the gas stream is cooled in a manner to produce a C3+ hydrocarbon liquid and a C3+ hydrocarbon-depleted gas stream. 
     
     
         19 . A gas liquefaction apparatus for liquefying a gas stream comprising hydrocarbons and sour species, the gas liquefaction apparatus comprising:
 a first cooling zone for cooling the gas stream in a manner to produce a cooled gas stream comprising gaseous hydrocarbons and residual sour species, the first cooling zone being in fluid communication with a source of gas comprising hydrocarbons and sour species;   a separator to separate solids and/or liquids from the cooled gas stream;   a vessel arranged, in use, to treat the cooled gas stream with a solvent to deplete the cooled gas stream of residual sour species, thereby producing a cooled sweetened gas stream; and   a second cooling zone in fluid communication with the vessel, the second cooling zone being configured to receive and cool the cooled sweetened gas stream to a second temperature to produce liquid hydrocarbons.   
     
     
         20 . A process for recovering liquid carbon dioxide from a gas stream comprising hydrocarbons and carbon dioxide during liquefaction, the process comprising the steps of:
 a) cooling the gas stream to a first temperature to produce a mixture of solid and/or liquid carbon dioxide and a vapour containing gaseous hydrocarbons;   b) separating the solid and/or liquid carbon dioxide from the mixture, thereby producing a cooled gas stream comprising gaseous hydrocarbons and residual carbon dioxide;   c) heating the separated solid carbon dioxide and producing liquid carbon dioxide   d) treating the cooled gas stream with a solvent to deplete the cooled gas stream of residual carbon dioxide, thereby producing a cooled sweetened gas stream; and   e) cooling the cooled gas stream to a second temperature to produce liquefied hydrocarbons.   
     
     
         21 . A method of creating a financial instrument tradable under a greenhouse gas Emissions Trading Scheme (ETS), the method comprising the step of exploiting a process for liquefying a gas stream defined by  claim 1 . 
     
     
         22 . A method of creating a financial instrument tradable under a greenhouse gas Emissions Trading Scheme (ETS), the method comprising the step of exploiting a gas liquefaction apparatus defined by  claim 19 . 
     
     
         23 . A method of creating a financial instrument tradable under a greenhouse gas Emissions Trading Scheme (ETS), the method comprising the step of exploiting a process for recovering carbon dioxide from a gas stream comprising hydrocarbons and carbon dioxide during liquefaction defined by  claim 20 . 
     
     
         24 . A method according to  claim 1  wherein the financial instrument comprises one of either a carbon credit, carbon offset or renewable energy certificate.