Separation of a gas mixture

Abstract

A method is described for use in the separation of carbon dioxide from a gas mixture comprising carbon dioxide. The method includes the steps of: (i) compressing and cooling the gas mixture using a compressor to form a two-phase mixture including liquid carbon dioxide (ii) separating a liquid carbon dioxide stream from the two-phase mixture; and (iii) recirculating at least a part of the liquid carbon dioxide stream and introducing the recirculated liquid stream into a process stream by recirculating separated liquid CO 2 into an upstream process stream, cooling of the process stream can be obtained. By using the liquid stream, additional cooling is possible as cooling is affected by the evaporation of the liquid CO 2 . Thus the recirculated liquid can be used to reduce the temperature of the process stream.

1 . A method for use in the separation of carbon dioxide from a gas mixture comprising carbon dioxide, the method comprising the steps of:
 (i) compressing and cooling the gas mixture using a compressor to form a two-phase mixture including liquid carbon dioxide   (ii) separating a liquid carbon dioxide stream from the two-phase mixture; and   (iii) recirculating at least a part of the liquid carbon dioxide stream and introducing the recirculated liquid stream into a process stream.   
     
     
         2 . A method according to  claim 1 , wherein the recirculated CO 2  liquid stream is introduced upstream of the compressor. 
     
     
         3 . A method according to  claim 1 , wherein a gaseous stream is fed to the compressor and at least a part of the recirculated liquid carbon dioxide stream is introduced into the gaseous stream, such that the liquid carbon dioxide evaporates before entering the compressor. 
     
     
         4 . A method according to  claim 1  wherein the gas mixture further includes hydrogen, the two phase mixture comprising liquid carbon dioxide and a hydrogen rich gas, wherein the hydrogen rich gas is separated from the two-phase mixture and at least a part of the separated hydrogen rich gas stream is recirculated to the compressor. 
     
     
         5 . A method according to  claim 2 , wherein the gaseous stream that is fed to the compressor, is a hydrogen rich gas stream. 
     
     
         6 . A method according to  claim 2 , wherein the recirculated liquid carbon dioxide is sprayed into the stream. 
     
     
         7 . A method according to any  claim 2 , wherein the particle size of the liquid carbon dioxide entering into the gaseous stream is less than 200 μm. 
     
     
         8 . A method according to  claim 1 , including the further steps of:
 determining information relating to a parameter of the system, and   controlling the recirculation of carbon dioxide on the basis of the determined information.   
     
     
         9 . A method according to  claim 8 , wherein the parameter relates to flow rate of a stream and/or to the compressor surge of one or more compressors. 
     
     
         10 . A method according to  claim 1 , comprising the following steps:
 (i) determining a gas flow rate of the process;   (ii) controlling the amount of carbon dioxide that is recirculated on the basis of the determined gas flow rate.   
     
     
         11 . A method according to  claim 1  wherein the recirculated carbon dioxide stream split into a plurality of sub streams, each substream being introduced in one or a plurality of introduction points in the process. 
     
     
         12 . A method according to  claim 1 , wherein at least a part of the carbon dioxide stream is removed from the system. 
     
     
         13 . A method according to  claim 1  wherein the gas mixture includes hydrogen and a hydrogen rich stream is separated from the gas mixture, wherein at least a part of the hydrogen rich gas stream is fed to an expansion system wherein it is subjected to isentroic expansion in an expander, such that a hydrogen rich gas stream is withdrawn from the expander at reduced temperature and reduced pressures and wherein isentropic expansion of the hydrogen rich gas in the expander generates motive power. 
     
     
         14 . A method for use in a system for the separation of carbon dioxide from a feed stream comprising carbon oxide(s) in an apparatus including a compressor, the method comprising the following steps:
 (i) compressing and cooling the feed stream to form a two-phase mixture including carbon dioxide; and   (ii) separating a carbon dioxide stream from the two-phase mixture; and   (iii) recirculating at least a part of the carbon dioxide stream to upstream of the compressor, wherein the method further includes:   determining information relating to a parameter of the system, and   controlling the recirculation of carbon dioxide on the basis of the determined information.   
     
     
         15 . An apparatus for carrying out a method according to  claim 1 . 
     
     
         16 . An apparatus for use in the separation of carbon dioxide from a gas mixture comprising carbon dioxide, the apparatus including:
 (i) a compressor and heat exchanger for compressing and cooling the gas mixture to form a two-phase mixture including liquid carbon dioxide   (ii) a separator for separating a liquid carbon dioxide stream from the two-phase mixture; and   (iii) a recirculation path, for recirculating at least a part of the liquid carbon dioxide stream from the separator and arranged for introducing the recirculated liquid stream into a process stream.   
     
     
         17 . An apparatus according to  claim 16 , wherein the recirculation path is arranged for introducing the recirculated liquid stream into a process stream upstream of the compressor. 
     
     
         18 . An apparatus according to  claim 16 , further including a spray device for spraying recirculated liquid carbon dioxide into a process stream. 
     
     
         19 . An apparatus according to  claim 16 , further including a sensor for determining information relating to a parameter of the system, and a control device for controlling the recirculation of carbon dioxide on the basis of the determined information. 
     
     
         20 . An apparatus according to  claim 19  wherein the sensor comprises a flow rate sensor for determining information relating to the flow rate of a process stream.