Heavy Hydrocarbon Removal From A Natural Gas Stream

Abstract

A method and apparatus of removing heavy hydrocarbons from a natural gas feed stream, the method comprising using first and second hydrocarbon removal systems in series such that the first system processes the natural gas feed stream to produce a heavy hydrocarbon depleted natural gas stream and the second system processes at least a portion of the heavy hydrocarbon depleted natural gas stream from the first system to produce a natural gas stream lean in heavy hydrocarbons, wherein one of said systems is a adsorption system that comprises one or more beds of adsorbent for adsorbing and thereby removing heavy hydrocarbons from a heavy hydrocarbon containing natural gas, and the other of said systems is a gas-liquid separation system for separating a heavy hydrocarbon containing natural gas into a heavy hydrocarbon depleted natural gas vapor and a heavy hydrocarbon enriched liquid.

1 . A method of removing heavy hydrocarbons from a natural gas feed stream, the method comprising the steps of using a first heavy hydrocarbon removal system and a second heavy hydrocarbon removal system to process the natural gas feed stream to produce a natural gas stream lean in heavy hydrocarbons, wherein said first and second systems are used in series such that the first system processes the natural gas feed stream to produce a heavy hydrocarbon depleted natural gas stream and the second system processes at least a portion of the heavy hydrocarbon depleted natural gas stream from the first system to produce the natural gas stream lean in heavy hydrocarbons, and wherein one of said systems is an adsorption system that comprises one or more beds of adsorbent for adsorbing and thereby removing heavy hydrocarbons from a heavy hydrocarbon containing natural gas, and the other of said systems is a gas-liquid separation system for separating a heavy hydrocarbon containing natural gas into a heavy hydrocarbon depleted natural gas vapor and a heavy hydrocarbon enriched liquid. 
     
     
         2 . The method of  claim 1 , wherein the gas-liquid separation system comprises a stripping column or a phase separator. 
     
     
         3 . The method of  claim 1 , wherein the method is further a method of producing a liquefied natural gas stream, and further comprises liquefying at least a portion of the natural gas stream lean in heavy hydrocarbons to produce the liquefied natural gas stream. 
     
     
         4 . The method of  claim 1 , wherein the gas-liquid separation system is the first heavy hydrocarbon removal system, the method comprising the steps of:
 introducing the natural gas feed stream into the gas-liquid separation system and separating the natural gas feed stream into a heavy hydrocarbon depleted natural gas vapor stream and a heavy hydrocarbon enriched liquid stream; and   passing at least a portion of the heavy hydrocarbon depleted natural gas vapor stream through the one or more beds of the adsorption system to adsorb heavy hydrocarbons therefrom, thereby producing the natural gas stream lean in heavy hydrocarbons.   
     
     
         5 . The method of  claim 4 , wherein the method further comprises cooling the natural gas feed stream prior to said stream being introduced into gas-liquid separation system, and warming the heavy hydrocarbon depleted natural gas vapor stream prior to said stream or portion thereof being passed through the one or more beds of the adsorption system. 
     
     
         6 . The method of  claim 5 , wherein the natural gas feed stream is cooled and the heavy hydrocarbon depleted natural gas vapor stream is warmed in an economizer heat exchanger via indirect heat exchange between the natural gas feed stream and the heavy hydrocarbon depleted natural gas vapor stream. 
     
     
         7 . The method of  claim 6 , wherein the natural gas feed stream is further cooled prior to being introduced into gas-liquid separation system via expansion of the natural gas feed stream and/or via direct or indirect heat exchange with one or more other streams. 
     
     
         8 . The method of  claim 6 , wherein the method further comprises liquefying at least a portion of the natural gas stream lean in heavy hydrocarbons. 
     
     
         9 . The method of  claim 5 , wherein the method further comprises cooling at least a portion of the natural gas stream lean in heavy hydrocarbons to produce a cooled natural gas stream lean in heavy hydrocarbons, and wherein the heavy hydrocarbon depleted natural gas vapor stream is warmed and the at least a portion of the natural gas stream lean in heavy hydrocarbons is cooled in an economizer heat exchanger via indirect heat exchange between the heavy hydrocarbon depleted natural gas vapor stream and the at least a portion of the natural gas stream lean in heavy hydrocarbons. 
     
     
         10 . The method of  claim 9 , wherein the method further comprises liquefying the cooled natural gas stream lean in heavy hydrocarbons. 
     
     
         11 . The method of  claim 10 , wherein the natural gas feed stream is cooled and the cooled natural gas stream lean in heavy hydrocarbons is liquefied in a liquefier, the natural gas feed stream being introduced into a warm end of the liquefier and withdrawn from an intermediate location of the liquefier, and the cooled natural gas stream lean in heavy hydrocarbons being introduced into an intermediate location of the liquefier and withdrawn from a cold end of the liquefier. 
     
     
         12 . The method of  claim 4 , wherein the gas-liquid separation system is a stripping column, the method further comprising introducing a stripping gas into the stripping column at a location below the location at which the natural gas feed stream is introduced into the stripping column. 
     
     
         13 . The method of  claim 6 , wherein the gas liquid separation system is a stripping column, the method further comprising introducing a stripping gas into the stripping column at a location below the location at which the natural gas feed stream is introduced into the stripping column, and wherein the stripping gas comprises one or more gases selected from the group consisting of: natural gas taken from the natural gas feed stream prior to said stream being cooled and introduced into the stripping column; a portion of the natural gas stream depleted in heavy hydrocarbons that has been warmed in the economiser heat exchanger; a portion of the natural gas stream lean in heavy hydrocarbons; a gas obtained from re-boiling all or a portion of the heavy hydrocarbon enriched liquid stream; and a flash or boil-off gas obtained from a liquefied natural gas. 
     
     
         14 . The method of  claim 9 , wherein the gas liquid separation system is a stripping column, the method further comprising introducing a stripping gas into the stripping column at a location below the location at which the natural gas feed stream is introduced into the stripping column, and wherein the stripping gas comprises one or more gases selected from the group consisting of: natural gas taken from the natural gas feed stream prior to said stream being cooled and introduced into the stripping column; a portion of the natural gas stream lean in heavy hydrocarbons that is not cooled in the economizer heat exchanger; a portion of the natural gas stream depleted in heavy hydrocarbons that has been warmed in the economiser heat exchanger; a gas obtained from re-boiling all or a portion of the heavy hydrocarbon enriched liquid stream; and a flash or boil-off gas obtained from a liquefied natural gas. 
     
     
         15 . The method of  claim 4 , wherein the adsorption system is a temperature swing adsorption system, and the method further comprises regenerating the one or more beds of the temperature swing adsorption system by passing a gas, selected from a portion of the natural gas stream lean in heavy hydrocarbons or a flash or boil off gas obtained from a liquefied natural gas, through the one or more beds, the temperature of the one or more beds during regeneration being higher than the temperature of the one or more beds during adsorption of heavy hydrocarbons from the heavy hydrocarbon depleted natural gas vapor stream or portion thereof. 
     
     
         16 . The method of  claim 15 , wherein the method further comprises cooling and separating into liquid and vapor phases the gas obtained from the one or more beds of the temperature swing adsorption system during regeneration of said one or more beds, and recycling the vapor phase into the natural gas feed stream prior to the introduction thereof into the gas-liquid separation system. 
     
     
         17 . The method of  claim 15 , wherein the gas liquid separation system is a stripping column, and the method further comprises cooling and separating into liquid and vapor phases the gas obtained from the one or more beds of the temperature swing adsorption system during regeneration of said one or more beds, and introducing the vapor phase as a stripping gas into the stripping column at a location below the location at which the natural gas feed stream is introduced into the stripping column. 
     
     
         18 . The method of  claim 1 , wherein the adsorption system is the first heavy hydrocarbon removal system, the method comprising the steps of:
 passing the natural gas feed stream through the one or more beds of the adsorption system to adsorb heavy hydrocarbons therefrom, thereby producing a heavy hydrocarbon depleted natural gas stream; and   introducing at least a portion of the heavy hydrocarbon depleted natural gas stream into the gas-liquid separation system and separating said stream or portion thereof into a natural gas vapor stream that is further depleted in heavy hydrocarbons, thereby providing the natural gas stream lean in heavy hydrocarbons, and a heavy hydrocarbon enriched liquid stream.   
     
     
         19 . The method of  claim 18 , wherein the method further comprises cooling the heavy hydrocarbon depleted natural gas stream or portion thereof introduced into gas-liquid separation system prior to said stream or portion thereof being introduced into gas-liquid separation system. 
     
     
         20 . The method of  claim 19 , wherein the method further comprises liquefying the natural gas stream lean in heavy hydrocarbons. 
     
     
         21 . The method of  claim 20 , wherein the heavy hydrocarbon depleted natural gas stream or portion thereof is cooled and the natural gas stream lean in heavy hydrocarbons is liquefied in a liquefier, the heavy hydrocarbon depleted natural gas stream or portion thereof being introduced into a warm end of the liquefier and withdrawn from an intermediate location of the liquefier, and the natural gas stream lean in heavy hydrocarbons being introduced into an intermediate location of the liquefier and withdrawn from a cold end of the liquefier. 
     
     
         22 . The method of  claim 18 , wherein the gas liquid separation system is a stripping column, the method further comprising introducing a stripping gas into the stripping column at a location below the location at which the heavy hydrocarbon depleted natural gas stream or portion thereof is introduced into the stripping column. 
     
     
         23 . The method of  claim 22 , wherein the stripping gas comprises one or more gases selected from the group consisting of: natural gas taken from the natural gas feed stream prior to said stream being passed through the one or more beds of the adsorption system; a portion of the heavy hydrocarbon depleted natural gas stream; a gas obtained from re-boiling all or a portion of the heavy hydrocarbon enriched liquid stream; and a flash or boil-off gas obtained from a liquefied natural gas. 
     
     
         24 . The method of  claim 18 , wherein the adsorption system is a temperature swing adsorption system, and the method further comprises regenerating the one or more beds of the temperature swing adsorption system by passing a gas, selected from a portion of the heavy hydrocarbon depleted natural gas stream or a flash or boil off gas obtained from a liquefied natural gas, through the one or more beds, the temperature of the one or more beds during regeneration being higher than the temperature of the one or more beds during adsorption of heavy hydrocarbons from the natural gas feed stream. 
     
     
         25 . The method of  claim 24 , wherein the method further comprises cooling and separating into liquid and vapor phases the gas obtained from the one or more beds of the temperature swing adsorption system during regeneration of said one or more beds, and recycling the vapor phase into the natural gas feed stream prior to said stream being passed through the one or more beds of the temperature swing adsorption system. 
     
     
         26 . The method of  claim 24 , wherein the gas liquid separation system is a stripping column, and the method further comprises introducing a stripping gas into the stripping column at a location below the location at which the heavy hydrocarbon depleted natural gas stream or portion thereof is introduced into the stripping column, wherein said stripping gas comprises: the gas obtained from the one or more beds of the temperature swing adsorption system during regeneration of said one or more beds; or the vapor phase obtained from cooling and separating into liquid and vapor phases the gas obtained from the one or more beds of the temperature swing adsorption system during regeneration of said one or more beds. 
     
     
         27 . The method of  claim 1 , wherein the natural gas feed stream is lean in aliphatic hydrocarbons having from 3 to 5 carbon atoms in total. 
     
     
         28 . An apparatus for removing heavy hydrocarbons from a natural gas feed stream, the apparatus comprising a first heavy hydrocarbon removal system and a second heavy hydrocarbon removal system for processing the natural gas feed stream to produce a natural gas stream lean in heavy hydrocarbons, wherein said first and second systems are connected in fluid flow communication with each other and are arranged in series such that in use the first system processes the natural gas feed stream to produce a heavy hydrocarbon depleted natural gas stream and the second system processes at least a portion of the heavy hydrocarbon depleted natural gas stream from the first system to produce the natural gas stream lean in heavy hydrocarbons, and wherein one of said systems is an adsorption system comprising one or more beds of adsorbent for adsorbing and thereby removing heavy hydrocarbons from a heavy hydrocarbon containing natural gas, and the other of said systems is a gas-liquid separation system for separating a heavy hydrocarbon containing natural gas into a heavy hydrocarbon depleted natural gas vapor and a heavy hydrocarbon enriched liquid. 
     
     
         29 . An apparatus according to  claim 28 , wherein the gas-liquid separation system comprises a stripping column or a phase separator. 
     
     
         30 . An apparatus according to  claim 28 , wherein the apparatus is further for producing a liquefied natural gas stream, and further comprises a liquefier connected in fluid flow communication with the second heavy hydrocarbon removal system for receiving and liquefying at least a portion of the natural gas stream lean in heavy hydrocarbons to produce the liquefied natural gas stream. 
     
     
         31 . An apparatus according to  claim 28 , wherein the gas-liquid separation system is the first heavy hydrocarbon removal system, the apparatus comprising:
 a gas-liquid separation system for receiving and separating the natural gas feed stream into a heavy hydrocarbon depleted natural gas vapor stream and a heavy hydrocarbon enriched liquid stream;   an adsorption system, in fluid flow communication with the gas-liquid separation system, for receiving at least a portion of the heavy hydrocarbon depleted natural gas vapor stream, and comprising one or more beds of adsorbent for adsorbing heavy hydrocarbons from said at least a portion of the heavy hydrocarbon depleted natural gas vapor stream, to thereby produce the natural gas stream lean in heavy hydrocarbons; and   an economizer heat exchanger for cooling the natural gas feed stream, prior to said stream being introduced into gas-liquid separation system, and warming the heavy hydrocarbon depleted natural gas vapor stream, prior to said stream or portion thereof being passed through the one or more beds of the adsorption system, via indirect heat exchange between the natural gas feed stream and the heavy hydrocarbon depleted natural gas vapor stream.   
     
     
         32 . An apparatus according to  claim 28 , wherein the gas-liquid separation system is the first heavy hydrocarbon removal system, the apparatus comprising:
 a gas-liquid separation system for receiving and separating the natural gas feed stream into a heavy hydrocarbon depleted natural gas vapor stream and a heavy hydrocarbon enriched liquid stream;   an adsorption system, in fluid flow communication with the gas-liquid separation system, for receiving at least a portion of the heavy hydrocarbon depleted natural gas vapor stream, and comprising one or more beds of adsorbent for adsorbing heavy hydrocarbons from said at least a portion of the heavy hydrocarbon depleted natural gas vapor stream, to thereby produce the natural gas stream lean in heavy hydrocarbons; and   an economizer heat exchanger for warming the heavy hydrocarbon depleted natural gas vapor stream, prior to said stream or portion thereof being passed through the one or more beds of the adsorption system, and cooling at least a portion of the natural gas stream lean in heavy hydrocarbons via indirect heat exchange between the heavy hydrocarbon depleted natural gas vapor stream and the at least a portion of the natural gas stream lean in heavy hydrocarbons.   
     
     
         33 . An apparatus according to  claim 28 , wherein the adsorption system is the first heavy hydrocarbon removal system, the apparatus comprising:
 an adsorption system for receiving the natural gas feed stream, and comprising one or more beds of adsorbent for adsorbing heavy hydrocarbons from the natural gas feed stream, to thereby produce a heavy hydrocarbon depleted natural gas stream; and   a gas-liquid separation system, in fluid flow communication with the adsorption system, for receiving at least a portion of the heavy hydrocarbon depleted natural gas stream and separating said stream or portion thereof into a heavy hydrocarbon enriched liquid stream and a natural gas vapor stream that is further depleted in heavy hydrocarbons, the latter providing the natural gas stream lean in heavy hydrocarbons.