Two stage process for producing purified gas

Abstract

The present invention provides a process for producing purified gas from a feed gas stream comprising methane and gaseous contaminants, the process comprising the steps of: 1) providing the feed gas stream; 2) cooling the feed gas stream to a temperature at which at least part of the feed gas stream is present in the liquid phase; 3) separating the cooled feed gas stream by means of cryogenic distillation into a bottom stream rich in contaminants and lean in methane, and into a top stream rich in methane and lean in gaseous contaminants, in which the bottom stream contains between 0.5 and 15% of the methane present in the feed gas stream; 4) cooling the stream rich in methane to a temperature at which solid and/or liquid phase contaminants are formed; 5) introducing the cooled stream of step 4) into a gas/liquid/solids separation vessel, and 6) removing from the gas/liquid/solids separation vessel the purified gas and a stream rich in contaminants.

1 . A process for producing purified gas from a feed gas stream comprising methane and gaseous contaminants, the process comprising the steps of:
 1) providing the feed gas stream;   2) cooling the feed gas stream to a temperature at which at least part of the feed gas stream is present in the liquid phase;   3) separating the cooled feed gas stream by means of cryogenic distillation into a bottom stream rich in contaminants and lean in methane, and into a top stream rich in methane and lean in gaseous contaminants, in which the bottom stream contains between 0.5 and 15% of the methane present in the feed gas stream;   4) cooling the stream rich in methane to a temperature at which solid and/or liquid phase contaminants are formed;   5) introducing the cooled stream of step 4) into a gas/liquid/solids separation vessel, and   6) removing from the gas/liquid/solids separation vessel the purified gas and a stream rich in contaminants.   
     
     
         2 . A process according to  claim 1 , in which the feed gas contains between 15 and 90 vol % of carbon dioxide. 
     
     
         3 . A process according to  claim 1 , in which the feed gas contains between 5 and 55 vol % of hydrogen sulphide, and between 5 and 80 vol % of methane. 
     
     
         4 . A process according to  claim 1 , in which the feed gas stream has a temperature between −10 and 70° C., and a pressure between 20 and 150 bara. 
     
     
         5 . A process according to  claim 1 , in which the cooling of the feed gas stream is done by heat exchange against a cold fluidum, comprising an external refrigerant. 
     
     
         6 . A process according to  claim 5 , in which additional cooling of the feed gas stream is done by nearly isentropic expansion or in which additional cooling of the feed gas stream is done by isenthalpic expansion. 
     
     
         7 . A process according to  claim 1 , in which the feed gas stream is cooled to a temperature between −10 and −50° C., 
     
     
         8 . A process according to  claim 1 , in which the bottom temperature of the cryogenic distillation section is between −5 and 30° C., or in which the top temperature of the cryogenic distillation section is between −60 and −30° C. 
     
     
         9 . A process according to  claim 1 , in which the top stream of the cryogenic distillation step contains between 10 and 25 wt % of the gaseous contaminants present in the feed gas stream or, in which the bottom stream of the cryogenic distillation step contains between 0.5 and 15 wt % of the methane present in the feed gas stream. 
     
     
         10 . A process according to  claim 1 , in which the cooling of the stream rich in methane in step (4) is done by isenthalpic expansion, or in which the cooling of the stream rich in methane in step (4) is done by nearly isentropic expansion. 
     
     
         11 . A process according to  claim 1 , in which the cooling of the stream rich in methane in step (4) is done by heat exchange against a cold fluidum, comprising an external refrigerant. 
     
     
         12 . A process according to  claim 1 , the process further comprises the steps of:
 (7) introducing the stream rich in contaminants into the intermediate or bottom part or both of the gas/liquid/solids separation vessel to obtain a diluted slurry of acidic contaminants;   (8) introducing the diluted slurry of acidic contaminants via an eductor into a heat exchanger in which solid acidic contaminant present in the diluted slurry of contaminants is melted into liquid acidic contaminant, wherein the heat exchanger is positioned outside the separation vessel, and eductor is arranged inside or outside the separation device or partly inside and outside the separation vessel;   (9) introducing at least a part of the liquid contaminant obtained in step 8 into a gas-liquid separator, wherein the gas-liquid separator is preferably the bottom part of the gas/liquid/solids separation vessel;   (10) introducing part or all of the liquid contaminant obtained in step 9 into the gas/liquid/solid separation vessel as described above;   (11) removing from the gas-liquid separator a stream of liquid acidic contaminant; and   (12) separating the stream of liquid contaminant obtained in step 11 into a liquid product stream and a recirculation stream which is used as a motive fluid in the eductor.   
     
     
         13 . A process according to  claim 1 , the process further comprises the steps of:
 (a) providing heat to the stream rich in contaminants to melt at least part of the solid contaminants, yielding a heated contaminant-rich stream;   (b) withdrawing the heated contaminant-rich stream from the vessel;   (c) reheating at least a part of the heated contaminant-rich stream to form a reheated recycle stream; and   (d) recycling at least a part of the reheated recycle stream to the vessel   
     
     
         14 . A process according to  claim 1 , wherein the feed gas stream is a natural gas stream and the purified gas is purified natural gas, the process further comprising the step of subjecting the purified natural gas to a second cryogenic distillation, followed by liquefying the natural gas to produce liquefied natural gas. 
     
     
         15 . (canceled)