Process and apparatus for separating a carbon dioxide-rich gas by distillation

Abstract

In a process for separating a gas rich in carbon dioxide by distillation, the gas rich in carbon dioxide is cooled in a heat exchanger and is sent to a distillation column, a gas depleted in carbon dioxide is withdrawn from the top of the column and a liquid enriched in carbon dioxide is withdrawn from the bottom of the column, a gas enriched in carbon dioxide is compressed in a compressor down to a first pressure and at least one portion of the gas enriched in carbon dioxide originating from the compressor is expanded from the first pressure to a second pressure lower than the first pressure, for example the pressure of the column, and the expanded gas is used to heat the bottom of the column.

1 . A process for separating a feed gas comprising at least 50% of carbon dioxide by distillation, comprising:
 i) Cooling the feed gas in a heat exchanger and transferring the cooled feed into a distillation column,   ii) withdrawing carbon dioxide depleted gas from the top of the column and withdrawing a carbon dioxide enriched liquid relative to the carbon dioxide-rich gas from the column sump,   iii) compressing a gas richer in carbon dioxide than the feed gas is in a compressor to a first pressure wherein the pressure of at least a part of the carbon dioxide enriched gas from the compressor is reduced from a first pressure to a second pressure lower than the first pressure, and the expanded gas is used to heat the column sump.   
     
     
         2 . The process according to  claim 1 , wherein at least part of the carbon dioxide enriched gas is produced by vaporising at least part of the carbon dioxide enriched liquid drawn off from the column. 
     
     
         3 . The process according to  claim 1 , wherein the carbon enriched dioxide gas originates at least partly from an external source. 
     
     
         4 . The process according to  claim 1 , wherein at least part of the expanded gas is transferred into the column. 
     
     
         5 . The process according to  claim 1 , wherein at least part of the expanded gas is transferred into a vaporiser in the column sump to heat part of the liquid in the column sump. 
     
     
         6 . The process according to  claim 1 , wherein a second part of the carbon dioxide enriched gas is compressed in the compressor to a third pressure higher than the first pressure. 
     
     
         7 . The process according to  claim 6 , wherein at least part of the gas at the third pressure forms an end product of the process. 
     
     
         8 . The process according to  claim 1 , wherein at least part of the gas from the compressor forms a refrigeration cycle gas for the process and is then condensed, cooled, expanded, heated and returned to the compressor. 
     
     
         9 . The process according to  claim 1 , wherein the second pressure is higher than the pressure in the column by at least 1 bar or is lower than the pressure in the column. 
     
     
         10 . An apparatus for separating a feed gas containing at least 50% of carbon dioxide by distillation comprising a heat exchanger, a distillation column, means of transferring the feed gas into the heat exchanger to be at least partially liquefied, means of transferring the at least partially liquefied fluid from the heat exchanger into the column, means of drawing off a carbon dioxide depleted gas from the top of the column, means of drawing off a carbon dioxide enriched liquid from the column sump, a compressor, means of transferring a gas richer in carbon dioxide than the feed gas to the compressor and a pressure reduction means, characterized in that it comprises the means of transferring the carbon dioxide enriched gas at a first pressure from the compressor to the pressure reduction means to reduce its pressure to a second pressure and means of transferring the carbon dioxide enriched gas from the pressure reduction means to the column or a vaporiser in order to vaporise a liquid in the column sump. 
     
     
         11 . The apparatus according to  claim 10  wherein the pressure reduction means is a turbine. 
     
     
         12 . The apparatus according to  claim 10 , comprising a means of sending the carbon dioxide enriched gas from the pressure reduction means to the column.