Process and appartus for removing gaseous contaminants from gas stream comprising gaseous contaminants

Abstract

An apparatus and process for removing gaseous contaminants from a feed gas comprising methane and gaseous contaminants, in which the feed gas is cooled to obtain a slurry comprising solid contaminant, liquid contaminant and a methane enriched gaseous phase. The slurry is introduced into a separation device from which the methane enriched gaseous phase is removed. The slurry is diluted with liquid contaminant and passed through a heat exchanger wherein solid contaminant is melted into liquid contaminant. A stream comprising liquid contaminant is removed from the separation device at a position below the slurry level in the separation device by means of a pump and at least part of the removed liquid contaminant is recovered as a stream product and at least part is recycled and introduced into the separation device to dilute the slurry inside the separation device.

1 . A for removing gaseous contaminants from a feed gas stream which comprises methane and gaseous contaminants, the process comprising:
 1) providing the feed gas stream;   2) cooling the feed gas stream to a temperature at which a slurry is formed which comprises solid contaminant, liquid phase contaminant and a methane enriched gaseous phase;   3) introducing the slurry as obtained in step 2) into the top part or intermediate part of a cryogenic separation device;   4) removing from the top part of the separation device a stream which comprises the methane enriched gaseous phase;   5) introducing a stream comprising liquid phase contaminant into the intermediate part or the bottom part of the separation device or both to dilute the slurry which has been introduced into the separation device in step 3);   6) passing the diluted slurry as obtained in step 5) through a heat exchanger which is arranged inside the separation device, whereby at least part of the solid contaminant present in the diluted slurry is melted into liquid phase contaminant;   7) removing from the separation device by means of a pump, preferably an eductor, a stream comprising liquid phase contaminant, which pump is situated below the heat exchanger and arranged outside or inside the separation device or partly inside or outside the separation device;   8) removing a stream comprising liquid phase contaminant from the separation device at a position below the slurry level in the separation device;   9) separating the stream of liquid phase contaminant obtained in step 8) into a liquid product stream and a recirculation stream which is used as a motive fluid in the eductor in the case that an eductor is used; and   10) introducing into the separation device as described above in step 5) at least part of the stream as removed in step 7) and at least part of the recirculation stream as obtained in step 9).   
     
     
         2 . A process according to  claim 1 , in which the pump, is arranged outside the separation device and communicates with the separation device. 
     
     
         3 . A process according to  claim 1  in which the feed gas stream is a natural gas stream in which the gaseous contaminants are carbon dioxide and/or hydrogen sulphide and/or C 2+  hydrocarbons. 
     
     
         4 . A process according to  claim 3 , in which the natural gas stream comprises between 5 and 50 vol % of hydrogen sulphide. 
     
     
         5 . A process according to  claim 3  or  4 , in which the natural gas stream comprises between 5 and 90 vol % of carbon dioxide. 
     
     
         6 . A process according to  claim 1  in which the feed gas contains between 0 and 25 vol % of C 2+  hydrocarbons. 
     
     
         7 . A process according to  claim 1  in which the feed gas stream comprises between 75 and 100 vol % of methane. 
     
     
         8 . A process according to  claim 1  in which the feed gas stream in step 1) has a temperature between −20 and 150° C., preferably between −10 and 70° C., and a pressure between 10 and 250 bara, preferably between 80 and 120 bara. 
     
     
         9 . A process according to  claim 1  in which the cooling in step 2) is done by isenthalpic expansion. 
     
     
         10 . A process according to  claim 1  in which the feed gas stream is cooled in step 2) to a temperature between −40 and −100° C. 
     
     
         11 . A process according to  claim 1  in which substantially all the solid contaminant present in the slurry of contaminants is melted in step 6). 
     
     
         12 . A process according to  claim 1  in which in step 5) the stream comprising liquid phase contaminant or the slurry contaminants stream is introduced into the separation device at a level which is lower than the level at which the methane enriched gaseous phase is removed from the separation device in step 4). 
     
     
         13 . A cryogenic separation device for carrying out the process according to  claim 1 , which separation device comprises a top part, an intermediate part and a bottom part; means to introduce a slurry which comprises solid contaminant, liquid phase contaminant and a methane enriched gaseous phase into the top or intermediate part of the separation device; means to remove a methane enriched gaseous phase from the top part of the separation device; means for introducing a stream comprising liquid phase contaminant into the top or intermediate part of the separation device to dilute the slurry inside the separation device; a heat exchanger arranged inside the separation device; a pump, which is arranged at a level which is below the level at which the heat exchanger is arranged for removing a stream comprising liquid phase contaminant from the separation device; means to remove a stream comprising liquid phase contaminant from the intermediate or bottom part of the separation device; and means to separate liquid phase contaminant removed from the intermediate or bottom part into a liquid product stream and a recirculation stream for use as a motive fluid in the eductor in the case an eductor is used, in which the pump is arranged outside the separation device and communicates with the separation device. 
     
     
         14 . A Purified gas stream obtained by a process according to  claim 1 . 
     
     
         15 . A process for liquefying a feed gas stream comprising purifying the feed gas stream according to  claim 1 , followed by liquefying the feed gas stream by methods known in the art.