Separation of gases

Abstract

A process for separating a mixture of gases into a relatively condensable first component and a relatively non-condensable second component is provided. The first component comprises one or more gases selected from the group consisting of carbon dioxide, carbonyl sulphide and hydrogen sulphide and the second component one or more gases selected from the group consisting of hydrogen, methane, ethane, carbon monoxide, nitrogen, oxygen and synthesis gas. The process itself comprises the following steps: (a) compressing and cooling a mixture of said first and second components in at least one compressor and at least one heat exchanger to a temperature and elevated pressure at which the first components condense and a two-phase gas-liquid mixture is formed; (b) separating the two phase mixture so formed into separate liquid first and gaseous second component fractions in a fractionation unit; (c) extracting residual first component from the separated gaseous second component fraction by scrubbing the second component at elevated pressure with a solvent (e.g. methanol) in a scrubber. In examples, the method further includes one or more steps of warming and expanding the gaseous second component fraction using at least one heat exchanger to exchange heat with a process stream and at least one turbo-expander capable of recovering mechanical work. The process described is highly energy efficient and is especially useful in hydrogen power plants, Integrated Gasification Combined Cycles (IGCC) and for sweetening sour natural gas.

1 - 42 . (canceled) 
     
     
         43 . A process of separating a relatively condensable first component from a mixture of gases including the first component and a relatively non-condensable second component, wherein the method includes the steps of:
 (a) compressing and/or cooling the mixture of gases to a temperature and elevated pressure at which the first component condenses and a two-phase gas-liquid mixture is formed;   (b) separating the two-phase mixture so formed into separate liquid first and gaseous second component fractions; and   (c) extracting residual first component from the separated gaseous second component fraction by scrubbing the second component fraction at elevated pressure with an physical solvent and   wherein the method further includes expanding the gaseous second component fraction and recovering work and/or warming the gaseous second component fraction by exchanging heat between the gaseous second component fraction and another process stream.   
     
     
         44 . A process according to  claim 43  including the step of warming and/or expanding the scrubbed second component fraction. 
     
     
         45 . A process according to  claim 43 , further including the step of warming and/or expanding the second component fraction before the scrubbing step. 
     
     
         46 . A process according to  claim 43 , wherein the warming uses at least one heat exchanger to exchange heat with a process stream, for example the mixture of step (a). 
     
     
         47 . A process according to  claim 43 , wherein the expansion includes using at least one turbo-expander capable of recovering mechanical work. 
     
     
         48 . A process according to  claim 43 , wherein the CO2 solvent separation step is carried out at a pressure which is not more than the pressure at which the two-phase separation step occurs. 
     
     
         49 . A process according to  claim 48 , wherein the solvent separation step is carried out at a pressure of at least 60 bar, at least 80 bar, at least 100 bar or at least 120 bar. 
     
     
         50 . A process according to  claim 43 , wherein at least 50% of the first component is separated from the two-phase mixture in step b. 
     
     
         51 . A process for separating a mixture of gases into a relatively condensable first component and a relatively non-condensable second component and wherein (1) the first component comprises one or more gases selected from the group consisting of carbon dioxide, carbonyl sulphide and hydrogen sulphide and (2) the second component comprises one or more gases selected from the group consisting of hydrogen, methane, ethane, carbon monoxide, nitrogen, oxygen and synthesis gas wherein the process comprises the steps of:
 (a) compressing and cooling a mixture of said first and second components in at least one compressor and at least one heat exchanger to a temperature and elevated pressure at which the first components condense and a two-phase gas-liquid mixture is formed;   (b) separating the two phase mixture so formed into separate liquid first and gaseous second component fractions in a fractionation unit;   (c) extracting residual first component from the separated gaseous second component fraction by scrubbing the second component fraction at elevated pressure with a physical solvent in a scrubber and   (d) warming and expanding the scrubbed second component fraction using at least one heat exchanger to exchange heat with the mixture of step (a) and at least one turbo-expander capable of recovering mechanical work.   
     
     
         52 . A process as claimed in  claim 43 , wherein the mixture of gases comprises carbon dioxide, hydrogen and nitrogen. 
     
     
         53 . A process as claimed in  claim 52  wherein the mixture of gases comprises carbon dioxide, hydrogen sulphide, hydrogen and nitrogen. 
     
     
         54 . A process as claimed in  claim 43 , wherein the mixture of gases comprises natural gas containing one or more of carbon dioxide, hydrogen sulphide and carbonyl sulphide. 
     
     
         55 . A process as claimed in  claim 51 , wherein the fractionation or separation unit operates at a temperature in the range −40 to −50° C. and a pressure in the range 80 to 250 bar. 
     
     
         56 . A process as claimed in  claim 51 , wherein the physical solvent used in step (c) is an alcohol, preferably methanol. 
     
     
         57 . A process as claimed in  claim 51 , wherein the first component includes hydrogen sulphide and the method includes separating hydrogen sulphide from the mixture of gases prior to the forming of the two-phase gas-liquid mixture. 
     
     
         58 . A process as claimed in  claim 57 , wherein the hydrogen sulphide separation step includes a biological process. 
     
     
         59 . A process of separating a mixture of gases to separate a relatively condensable first component from a relatively non-condensable second component wherein the first component comprises carbon dioxide and the second component comprises one or more gases selected from the group consisting of hydrogen, methane, ethane, carbon monoxide, nitrogen, oxygen and synthesis gas wherein the mixture of gases further includes hydrogen sulphide and the method includes the steps of:
 (a) treating the gas mixture to remove hydrogen sulphide;   (b) compressing and cooling the treated gas mixture in at least one compressor and at least one heat exchanger to a temperature and elevated pressure at which the first component condenses and a two-phase gas-liquid mixture is formed;   (c) separating the two phase mixture into separate liquid first and gaseous second component fractions;   (d) extracting residual first component from the separated gaseous second component fraction by scrubbing the second component fraction at elevated pressure with a solvent in a scrubber and   wherein the method further includes the steps of warming and expanding the second component fraction using at least one heat exchanger to exchange heat with the mixture of step (b) and at least one expander capable of recovering mechanical work.   
     
     
         60 . A method according to  claim 59 , wherein the solvent comprises methanol. 
     
     
         61 . A method according to  claim 59 , wherein the separation of the sulphur-containing component is carried out using a Paques process. 
     
     
         62 . A gas separation plant for separating a mixture of gases into a relatively condensable first component and a relatively non condensable second component wherein (1) the first component comprises one or more gases selected from the group consisting of carbon dioxide, carbonyl sulphide and hydrogen sulphide and (2) the second component comprises one or more gases selected from the group consisting of hydrogen, methane, ethane, carbon monoxide, nitrogen, oxygen and synthesis gas wherein it comprises;
 (a) a compression and cooling system for compressing and cooling a mixture of said first and second components to a temperature and pressure at which the first components condense and a two-phase gas-liquid mixture is formed said compression and cooling system further comprising at least one compressor and at least one heat exchanger;   (b) a fractionation unit for separating the two phase mixture so formed in said compression and cooling system into separate liquid first and gaseous second component fractions;   (c) a scrubber for extracting residual first component from the separated gaseous second component fraction by scrubbing the second component fraction at elevated pressure with a physical solvent and   wherein the plant further includes an expansion system for warming and expanding gaseous second component fraction, preferably the expansion system comprising at least one turbo expander for recovering mechanical work and means for supplying cooling capacity to at least one of the heat exchangers in the cooling and compression system.   
     
     
         63 . A plant according to  claim 62 , further including a hydrogen sulphide removal system upstream of the fractionation unit for removing a sulphur-containing component from the gas mixture. 
     
     
         64 . A system for separating a relatively condensable first component from a mixture of gases including the first component and a relatively non-condensable second component wherein the apparatus includes:
 (a) a phase separation apparatus including
 i. at least one inlet; 
 ii. a compressor and heat exchanger for compressing and cooling a gas mixture such that the first component condenses and a two-phase gas-liquid mixture is formed; and 
 iii. a separator for separating the condensed first component and a second gaseous component from the two-phase mixture 
 iv. an outlet for the separated first component stream 
   (b) a solvent separation apparatus including
 i. at least one inlet; 
 ii. a solvent unit for separating first component and second component from the received gas mixture; 
 iii. an outlet arranged to feed separated first component from the solvent unit to the inlet of the phase separation apparatus. 
   
     
     
         65 . A system according to  claim 64 , wherein the first component comprises carbon dioxide. 
     
     
         66 . A system according to  claim 64 , wherein the solvent unit includes an alcohol, preferably methanol. 
     
     
         67 . A system according to  claim 64 , wherein the phase separation apparatus generates a gas product stream comprising gas of the two-phase gas-liquid mixture, the solvent separation apparatus being arranged downstream of the phase separation apparatus such that gas of the gas product stream is fed to the inlet of the solvent separation apparatus. 
     
     
         68 . A system according to  claim 64 , wherein the system is arranged to feed a liquid stream including the condensed first component from the separator of the phase separation apparatus to a heat exchanger for exchanging heat within the system. 
     
     
         69 . A system according to  claim 68 , wherein the system is adapted such that the condensed first component at least partly evaporates at or upstream of the heat exchanger. 
     
     
         70 . A system according to  claim 64 , including an expander system arranged for receiving separated second component, the expander system including at least one heat exchanger for exchanging heat within the system and at least one expander capable of recovering mechanical work. 
     
     
         71 . A system according to  claim 70  wherein the expander system is arranged to receive separated second component from the solvent separation system. 
     
     
         72 . A system according to  claim 70  wherein the expander system is arranged to receive separated second component from the phase separation apparatus. 
     
     
         73 . A system according to  claim 64 , wherein the system has a single outlet point for separated first component. 
     
     
         74 . A system according to  claim 64 , further including a sulphur removal apparatus upstream of the phase separation apparatus. 
     
     
         75 . A process of separating a relatively condensable first component from a mixture of gases including the first component and a relatively non-condensable second component wherein the method includes the steps of:
 i. compressing and cooling a gas mixture such that the first component condenses and a two-phase gas-liquid mixture is formed;   ii. separating the condensed first component stream and a second gaseous component stream from the two-phase mixture   iii. feeding the second gaseous component stream to a solvent separation apparatus, the solvent separation apparatus including a solvent and being adapted for separating a first component stream from the received gas mixture; and   iv. feeding the first component stream from the solvent separation apparatus to the phase separation apparatus.   
     
     
         76 . A process according to  claim 75 , wherein substantially all of the first component separated by the solvent separation apparatus is fed to the phase separation apparatus. 
     
     
         77 . A process according to  claim 75  wherein the two-phase mixture fed to the separator is at a pressure of above 60 bar, preferably at least 80 bar, preferably at least 120 bar. 
     
     
         78 . A process according to  claim 75  wherein the pressure of the solvent separation apparatus is at least 50 bar, preferably greater than 60 bar, preferably at least 80 bar. 
     
     
         79 . A process according to  claim 75  wherein the pressures of operation of the separator of the phase separation apparatus and of the solvent separation apparatus are substantially the same. 
     
     
         80 . A process according to  claim 75 , wherein at least 50% of the first component is separated from the two-phase mixture in step ii. 
     
     
         81 . A process according to  claim 75 , wherein at least a part of a liquid stream including the condensed first component is fed from the separator of the phase separation apparatus to a heat exchanger for exchanging heat within the system. 
     
     
         82 . A process according to  claim 81 , including at least partly evaporating the condensed first component at or upstream of the heat exchanger. 
     
     
         83 . A process according to  claim 75 , further including warming and expanding a separated second component fraction using at least one heat exchanger to exchange heat and at least one turbo-expander capable of recovering mechanical work. 
     
     
         84 . A process of separating carbon dioxide from a mixed gas using a system including a plurality of carbon dioxide separation units, wherein the carbon dioxide stream separated by a first carbon dioxide separation unit is fed to a second carbon dioxide unit, such that a separated carbon dioxide stream is withdrawn from the system from a single region of the system.