Method and apparatus for separating nitrogen from a mixed stream comprising nitrogen and methane

Abstract

A method and apparatus for separating nitrogen from a mixed stream comprising nitrogen and methane employes a monolith sorption contactor formed of a unitary construction of active carbon, the contactor housing one or more separation flow channels, the one or more channels having at least one inlet to, and at least one outlet from, said contactor, the one or more channels defining one or more first internal surfaces of the monolith sorption contactor, the contactor further comprising one or more first external surfaces provided with a barrier layer, the first external surfaces being different from the first internal surfaces. The mixed stream is passed through at least one of the separation flow channels, where methane is sorbed. The contactor can be regenerated by contacting the contactor with a heat exchange fluid via the barrier layer at one or more of the external surfaces.

1 . A method of separating nitrogen from a mixed stream comprising nitrogen and methane, the method comprising at least the steps of:
 (a) providing a monolith sorption contactor formed of a unitary construction of active carbon, said contactor housing one or more separation flow channels intersecting the monolith sorption contactor, said one or more separation flow channels having at least one inlet to, and at least one outlet from, said contactor, said one or more separation flow channels defining one or more first internal surfaces of the monolith sorption contactor, said contactor further comprising one or more first external surfaces provided with a barrier layer, said first external surfaces being different from said first internal surfaces;   (b) passing the mixed stream into at least one of the one or more separation flow channels via the at least one inlet;   (c) sorbing the methane in the sorption contactor via the one or more first internal surfaces in the at least one of the one or more separation flow channels at a temperature lower than or equal to −60° C. to provide a nitrogen-enriched stream at the at least one outlet;   (d) interrupting the passage of the mixed stream through the contactor;   (e) regenerating the contactor by contacting the contactor with a heat exchange fluid stream at the one or more first external surfaces provided with the barrier layer, to heat the contactor to a temperature above −60° C. to desorb methane and provide a cool heat exchange fluid stream; and   (f) withdrawing the desorbed methane as a methane-enriched stream from the at least one outlet from the contactor;   wherein the barrier layer serves to provide a fluid barrier against passage of the heat exchange fluid into the monolith sorption contactor.   
     
     
         2 . The method according to  claim 1 , wherein the sorbing step (c) is carried out at a temperature in the range of from −160 to −60° C. 
     
     
         3 . The method according to  claim 1  wherein the regenerating in step (e) is carried out by raising the temperature of the contactor, to a temperature in the range of from −40 to −30° C. 
     
     
         4 . The method according to  claim 1 , further comprising cooling the contactor by passing the nitrogen-enriched stream through one or more of the one or more separation flow channels. 
     
     
         5 . The method according to  claim 1 , further comprising, optionally prior to step (c), a step of:
 cooling the contactor by contacting at least one of the one or more first external surfaces having the barrier layer with the cool heat exchange fluid stream to provide the warm heat exchange fluid stream.   
     
     
         6 . The method according to  claim 4  wherein cooling the contactor reduces the temperature of the contactor to less than or equal to −60° C. 
     
     
         7 . The method according to  claim 1  wherein the barrier layer comprises an epoxy resin. 
     
     
         8 . The method according to  claim 1  wherein the mixed stream is derived from a liquefaction unit and the heat exchange fluid is a refrigerant from said liquefaction unit. 
     
     
         9 . The method according to  claim 1  wherein step (e) further comprises passing a flushing fluid stream through the one or more separation channels. 
     
     
         10 . The method according to  claim 1 , further comprising the steps of passing a purging fluid stream through the one or more separation channels between steps (d) and (e). 
     
     
         11 . The method according to  claim 1  wherein the mixed stream is obtained from a gas/liquid separator providing a gaseous hydrocarbon-containing stream, and a liquid hydrocarbon-containing stream. 
     
     
         12 . The method according to  claim 10 , wherein at least a part of the gaseous hydrocarbon-containing stream is contacted with the activated carbon as the mixed stream. 
     
     
         13 . The method according to  claim 1  wherein the mixed stream is at a temperature below 0° C. 
     
     
         14 . The method according to  claim 1  wherein the mixed stream is at a pressure of less than or equal to 10 bar. 
     
     
         15 . The method according to  claim 11  wherein at least a part of the mixed stream has been liquefied upstream of the gas/liquid separator. 
     
     
         16 . An apparatus for separating nitrogen from a mixed stream comprising nitrogen and methane, the apparatus comprising at least:
 a source of a mixed stream comprising methane and nitrogen at a temperature of less than or equal to −60° C. in a mixed stream line;   a source of a warm heat exchange fluid stream in a warm heat exchange fluid stream line;   a source of a cool heat exchange fluid stream in a cool heat exchange fluid stream line;   a monolith sorption contactor formed of a unitary construction of active carbon, said contactor housing one or more separation flow channels intersecting the monolith sorption contactor, said one or more separation flow channels having at least one inlet in fluid communication with the mixed stream line, and at least one outlet in fluid communication with a nitrogen-enriched stream line, said one or more separation flow channels defining one or more first internal surfaces of the monolith sorption contactor, said contactor further comprising one or more first external surfaces, said first external surfaces being different from said first internal surfaces and being in heat exchange communication with said warm heat exchange fluid stream line and said cool heat exchange fluid stream line; and   a barrier layer provided on the one or more first external surfaces to provide a fluid barrier against passage of the warm and cool heat exchange fluids into the monolith sorption contactor.