Light gas separation process and system

Abstract

The present invention relates in one respect to a process for separating light gas components, preferably helium, from a stream containing predominantly carbon dioxide, and in another respect is directed to a process for purifying a feed stream containing predominantly carbon dioxide into a high grade carbon dioxide product stream using a warm distillation process as the primary carbon dioxide separation step.

What is claimed is: 
     
         1 . A process for separating a light gas fraction from a feed stream containing at least 85% CO2 at a pressure of at least 500 psia and having a dew point temperature below about 20° F. comprising the following steps:
 cooling and condensing at least a portion of the feed stream to a temperature (T 1 ) of not less than 25° F. below the dry gas dew point of the at least a portion of the feed stream to form a first carbon dioxide enriched stream having a purity greater than about 95% by volume carbon dioxide and a first light gas enriched stream; 
 recovering the first carbon dioxide enriched stream; 
 cooling and condensing the first light fraction stream at a temperature of less than about minus 40° F. to form a second carbon dioxide enriched stream and a second light gas enriched stream; 
 recovering the second carbon dioxide enriched stream; 
 passing the second light gas stream through a CO2 removal unit to remove residual carbon dioxide and form a third carbon dioxide rich stream having a purity greater than 95% by volume carbon dioxide and a third light gas enriched stream; and 
 recovering the third carbon dioxide enriched stream. 
 
     
     
         2 . The process of  claim 1  wherein one or more of the carbon dioxide enriched streams are recovered as a high grade carbon dioxide product stream. 
     
     
         3 . The process of  claim 1  wherein the second light gas enriched stream is passed through a catalytic oxidation unit to remove hydrogen prior to being passed to the CO2 removal unit;
 the third light gas enriched stream is passed through a cryogenic distillation unit to produce a helium rich stream and a byproduct stream; 
 the helium rich stream is then passed through a helium separation unit to produce a helium product gas stream having a purity of greater than 85% helium by volume. 
 
     
     
         4 . The process of  claim 3  wherein the helium product gas stream is at purities of greater than 99.99% helium by volume. 
     
     
         5 . The process of  claim 1  wherein a warm distillation is used for condensing at least a portion of the feed stream. 
     
     
         6 . The process of  claim 5  where the warm distillation is conducted at temperatures of not less than about 20° F. 
     
     
         7 . The process of  claim 1  wherein at least 33% by volume of the available carbon dioxide in the feed stream is separated during the cooling and condensing step. 
     
     
         8 . The process of  claim 1  wherein the first carbon dioxide rich stream is partially condensed by indirect heat exchange with a refrigerant stream. 
     
     
         9 . The process of  claim 8  wherein the refrigeration is derived from depressurizing at least a portion of the first carbon dioxide rich stream to a pressure lower than the feed pressure and a temperature T 2  higher than T 1 , and substantially vaporizing the carbon dioxide rich stream in indirect heat exchange with a cooling feed stream. 
     
     
         10 . The process of  claim 9  wherein a refrigerating stream obtained at a temperature T 3  which is lower than T 1  is subjected to indirect heat exchange with the feed stream for cooling the feed stream to a temperature T 1  from T 2 . 
     
     
         11 . The process of  claim 11  where the refrigerating stream at T 3  is a portion of the first carbon dioxide rich stream. 
     
     
         12 . The process of  claim 1  wherein the feed stream is a naturally occurring stream obtained from a well that is dried in a bulk dryer. 
     
     
         13 . The process of  claim 2  wherein the cooling and partially condensing is conducted at temperatures above about 30° F. and pressures ranging from about 500 to about 900 psia. 
     
     
         14 . The process of  claim 3  wherein the byproduct stream is compressed and returned to one or more of the carbon dioxide enriched streams. 
     
     
         15 . The process of  claim 1  wherein the first light gas enriched stream is compressed prior to deep cold separation. 
     
     
         16 . The process of  claim 1  wherein prepurification of the feed stream is conducted to remove particulates or contaminants. 
     
     
         17 . A process for recovering helium from a feed stream containing at least about 0.5% helium and predominantly carbon dioxide and having a dew point temperature below about 20° F. comprising:
 cooling and partially condensing at least a portion of the feed stream to form a first carbon dioxide enriched stream having greater than 95% by volume carbon dioxide and a first light gas enriched stream; 
 recovering the first carbon dioxide enriched stream; 
 cooling and condensing the first light gas enriched stream at a temperature of less than about minus 40° F. into a second carbon dioxide enriched stream and a second light gas enriched stream; 
 recovering the second carbon dioxide enriched stream; 
 passing the second light gas enriched stream through a catalytic oxidation unit to form a hydrogen lean stream; 
 passing the hydrogen lean stream through a CO2 removal unit to remove residual carbon dioxide and form a third carbon dioxide rich stream having greater than 95% by volume carbon dioxide and a third light gas enriched stream; 
 capturing the third carbon dioxide enriched stream; 
 passing the third light gas enriched stream through a cryogenic distillation unit to produce a helium rich stream and a byproduct stream; 
 passing the helium rich stream through a helium separation unit to form a waste light fraction stream and a helium product gas stream at purities of greater than 95% helium by volume; and 
 recovering the helium product gas stream. 
 
     
     
         18 . The process of  claim 17  wherein the helium product gas stream is at a purity of greater than 99.99% helium by volume. 
     
     
         19 . The process of  claim 18  wherein the cooling and partially condensing at least a portion of the feed stream is conducted at temperatures above about 30° F. and pressures ranging from about 500 to about 900 psia. 
     
     
         20 . The process of  claim 17  wherein the byproduct stream is compressed and returned to one or more of the carbon dioxide enriched streams.