Natural Gas Liquefaction Process

Abstract

A gas processing facility for the liquefaction of a natural gas feed stream is provided. The facility comprises a gas separation unit having at least one fractionation vessel. The gas separation unit employs adsorbent beds for adsorptive kinetic separation. The adsorbent beds release a methane-rich gas feed stream. The facility also includes a high-pressure expander cycle refrigeration system. The refrigeration system compresses the methane-rich gas feed stream to a pressure greater than about 1,000 psia. The refrigeration system also chills the methane-rich gas feed stream in one or more coolers, and then expands the chilled gas feed stream to form a liquefied product stream. Processes for liquefying a natural gas feed stream using AKS and a high-pressure expander cycle refrigeration system are also provided herein. Such processes allow for the formation of LNG using a facility having less weight than conventional facilities.

What is claimed is: 
     
         1 . A gas processing facility for the liquefaction of a natural gas feed stream, the facility comprising:
 a gas separation unit, the gas separation unit having at least one fractionation vessel comprised of:
 a gas inlet for receiving a natural gas mixture comprising methane, 
 an adsorbent material that has a kinetic selectivity for contaminants over methane greater than 5, such that the contaminants become kinetically adsorbed within the adsorbent material, and 
 a gas outlet for releasing a methane-rich gas stream; and 
 a high-pressure expander cycle refrigeration system comprised of:
 a first compression unit configured to receive a substantial portion of the methane-rich gas stream and to compress the methane-rich gas stream to greater than about 1,000 psia (6,895 kPa), thereby providing a compressed gas feed stream; 
 a first cooler configured to cool the compressed gas feed stream to form a compressed, cooled gaseous feed stream; and 
 a first expander configured to expand the cooled, compressed, gaseous feed stream to form a product stream having a liquid fraction and a remaining vapor fraction. 
 
   
     
     
         2 . The gas processing facility of  claim 1 , wherein:
 the first cooler is configured to receive a portion of the product stream from the first expander, and use the portion of the product stream to cool the compressed gas feed stream through heat exchange.   
     
     
         3 . The gas processing facility of  claim 1 , wherein:
 the first cooler is configured to use an external refrigerant stream to cool the compressed gas feed stream through heat exchange.   
     
     
         4 . The gas processing facility of  claim 1 , wherein the high-pressure expander cycle refrigeration system further comprises:
 a liquid separation vessel configured to separate the liquid fraction and the remaining vapor fraction from the first expander.   
     
     
         5 . The gas processing facility of  claim 4 , wherein:
 the first cooler receives at least a portion of the vapor fraction, and uses the vapor fraction to cool the compressed gas feed stream through heat exchange as part of a first refrigeration loop;   the first cooler releases (i) a chilled gas feed stream, and (ii) a partially-warmed product stream after heat-exchanging with the compressed gas feed stream; and   the high-pressure expander cycle refrigeration system further comprises:
 a second cooler configured to further cool the compressed gas feed stream at least partially by indirect heat exchange with a refrigerant stream and the vapor fraction; and 
 a second refrigeration loop having (i) a second compression unit configured to re-compress the refrigerant stream after the refrigerant stream passes through the second cooler, and (ii) a second expander configured to receive the re-compressed refrigerant stream, and expand the re-compressed refrigerant stream prior to returning it to the second cooler. 
   
     
     
         6 . The gas processing facility of  claim 5 , wherein the high-pressure expander cycle refrigeration system further comprises:
 a third compression unit in the first refrigeration loop for compressing the partially-warmed product stream after heat-exchanging with the compressed gas feed stream; and   a line for merging the compressed, partially-warmed product stream with the gas feed stream to complete the first refrigeration loop.   
     
     
         7 . The gas processing facility of  claim 5 , wherein the second cooler sub-cools the chilled gas feed stream after the chilled gas feed stream leaves the first cooler. 
     
     
         8 . The gas processing facility of  claim 5 , wherein the second cooler pre-cools the compressed gas feed stream before the compressed gas feed stream enters the first cooler. 
     
     
         9 . The gas processing facility of  claim 8 , wherein:
 the second cooler receives the partially-warmed product stream from the first cooler for further heat-exchanging with the compressed gas feed stream; and   releases a warmed product stream to a third compression unit to complete the first refrigeration loop.   
     
     
         10 . The gas processing facility of  claim 9 , wherein the third compression unit compresses the warmed product stream to about 1,500 to 3,500 psia (10,342 to 24,132 kPa). 
     
     
         11 . The gas processing facility of  claim 1 , wherein the facility is located on (i) a floating platform, (ii) a gravity-based platform, or (iii) a ship-shaped vessel offshore. 
     
     
         12 . The gas processing facility of  claim 5 , wherein:
 the refrigerant stream comprises a gas selected from the group consisting of: nitrogen gas, nitrogen-containing gas, a side stream from the methane-rich gas stream, and the remaining vapor fraction, and combinations thereof; and   the refrigerant stream in the second refrigeration loop flows in a closed loop.   
     
     
         13 . The gas processing facility of  claim 1 , wherein the at least one fractionation vessel in the gas separation unit operates on pressure swing adsorption (PSA) or rapid cycle pressure swing adsorption (RCPSA). 
     
     
         14 . The gas processing facility of  claim 13 , wherein the at least one fractionation vessel in the gas separation unit further operates on temperature swing adsorption (TSA) or rapid cycle temperature swing adsorption (RCTSA). 
     
     
         15 . The gas processing facility of  claim 13 , wherein the at least one fractionation vessel is configured to adsorb CO 2 , H 2 S, H 2 O, heavy hydrocarbons, VOC's, mercaptans, or combinations thereof. 
     
     
         16 . The gas processing facility of  claim 13 , wherein each of the at least one fractionation vessel cooperates with other fractionation vessels to form a pressure swing adsorption system comprising:
 at least one service bed providing adsorption,   at least one bed in regeneration undergoing pressure reduction, and   at least one regenerated bed held in reserve for use in the adsorption system when the at least one service bed becomes substantially saturated.   
     
     
         17 . The gas processing facility of  claim 13 , further comprising:
 a dehydration vessel configured to receive the natural gas feed stream and remove a substantial portion of water from the natural gas feed stream, and release a dehydrated natural gas feed stream to the at least one fractionation vessel.   
     
     
         18 . The gas processing facility of  claim 17 , wherein the at least one fractionation vessel in the gas separation unit comprises a plurality of vessels in series, such that:
 a first vessel comprises an adsorption bed for the removal of water remaining in the dehydrated natural gas feed stream;   a second vessel comprises an adsorption bed designed primarily for the removal of a desiccant from the dehydrated natural gas feed stream; and   a third vessel comprises an adsorption bed designed primarily for the removal of a sour gas component from the dehydrated natural gas feed stream.   
     
     
         19 . The gas processing facility of  claim 17 , wherein the at least one fractionation vessel in the gas separation unit comprises a vessel containing a plurality of adsorbent beds in series, such that:
 a first adsorption bed is designed to primarily remove water and other liquid components from the dehydrated natural gas feed stream;   a second adsorption bed is designed to primarily remove a desiccant from the dehydrated natural gas feed stream; and   a third vessel comprises an adsorption bed primarily for the removal of a sour gas component from the dehydrated natural gas feed stream.   
     
     
         20 . A process for liquefying a natural gas feed stream, comprising:
 receiving the natural gas feed stream at a gas separation unit, the gas separation unit having at least one fractionation vessel comprised of:
 a gas inlet for receiving a natural gas mixture comprising methane, 
 an adsorbent material that has a kinetic selectivity for contaminants over methane greater than 5, such that the contaminants become kinetically adsorbed within the adsorbent material, and 
 a gas outlet configured to release a methane-rich gas stream; 
   substantially separating methane from contaminants within the natural gas feed stream;   releasing a methane-rich gas stream from the gas separation unit;   directing the methane-rich gas stream into a high-pressure expander cycle refrigeration system;   compressing the methane-rich gas stream to a pressure that is greater than 1,000 psia (6,895 kPa) in order to form a compressed gas feed stream;   cooling the compressed gas feed stream to form a compressed, cooled gaseous feed stream;   expanding the cooled, compressed, gaseous feed stream to form a product stream having a liquid fraction and a remaining vapor fraction; and   separating the vapor fraction from the liquid fraction.   
     
     
         21 . The process of  claim 20 , wherein the high-pressure expander cycle refrigeration system comprises:
 a first compression unit configured to receive a substantial portion of the methane-rich gas stream and to generate the compressed gas feed stream;   a first cooler configured to cool the compressed gas feed stream to form the compressed, cooled gaseous feed stream; and   a first expander configured to expand the cooled, compressed, gaseous feed stream to form the product stream.   
     
     
         22 . The process of  claim 21 , wherein cooling the compressed gas feed stream comprises:
 delivering at least a portion of the vapor fraction from the product stream to the first cooler as part of a first refrigeration loop; and   heat-exchanging the vapor fraction of the product stream with the compressed gas feed stream to cool the compressed gas feed stream.   
     
     
         23 . The process of  claim 22 , wherein:
 the high-pressure expander cycle refrigeration system further comprises a liquid separation vessel; and   separating the vapor fraction from the liquid fraction is done using the liquid separation vessel.   
     
     
         24 . The process of  claim 23 , further comprising:
 releasing from the first cooler (i) a chilled gas feed stream as the product stream, and (ii) a partially-warmed product stream as a working fluid;   directing the partially-warmed product stream to a third compression unit; and   merging the compressed, partially-warmed product stream from the third compression unit with the methane-rich gas stream to complete the first refrigeration loop.   
     
     
         25 . The process of  claim 24 , wherein the high-pressure expander cycle refrigeration system further comprises:
 a second cooler configured to further cool the compressed gas feed stream at least partially by indirect heat exchange between a refrigerant stream and the vapor fraction; and   a second refrigeration loop having (i) a second compression unit configured to re-compress the refrigerant stream after the refrigerant stream passes through the second cooler, and (ii) a second expander configured to receive the compressed refrigerant stream, and expand the compressed refrigerant stream prior to returning it to the second cooler.   
     
     
         26 . The process of  claim 25 , wherein the second cooler sub-cools the chilled gas feed stream after the chilled gas feed stream leaves the first cooler. 
     
     
         27 . The process of  claim 25 , wherein the second cooler pre-cools the compressed gas feed stream before the compressed gas feed stream enters the first cooler. 
     
     
         28 . The process of  claim 23 , wherein the facility is located on (i) a floating platform, (ii) a gravity-based platform, or (iii) a ship-shaped vessel offshore. 
     
     
         29 . The process of  claim 23 , wherein the at least one fractionation vessel in the gas separation unit operates on pressure swing adsorption (PSA) or rapid cycle pressure swing adsorption (RCPSA). 
     
     
         30 . The process of  claim 23 , wherein the at least one fractionation vessel in the gas separation unit further operates on temperature swing adsorption (TSA) or rapid cycle temperature swing adsorption (RCTSA). 
     
     
         31 . The process of  claim 30 , wherein the at least one fractionation vessel is configured to adsorb CO 2 , H 2 S, H 2 O, heavy hydrocarbons, VOC's, mercaptans, or combinations thereof. 
     
     
         32 . The process of  claim 31 , further comprising:
 passing the natural gas feed stream through a dehydration vessel in order to remove a substantial portion of water from the natural gas feed stream; and   release a dehydrated natural gas feed stream to the at least one fractionation vessel for contaminant removal.   
     
     
         33 . The process of  claim 32 , wherein the at least one fractionation vessel in the gas separation unit comprises a plurality of vessels in series, such that:
 a first vessel comprises an adsorption bed for the removal of water remaining in the dehydrated natural gas feed stream;   a second vessel comprises an adsorption bed designed primarily for the removal of a desiccant from the dehydrated natural gas feed stream; and   a third vessel comprises an adsorption bed designed primarily for the removal of a sour gas component from the dehydrated natural gas feed stream.   
     
     
         34 . The process of  claim 32 , wherein the at least one fractionation vessel in the gas separation unit comprises a vessel containing a plurality of adsorbent beds in series, such that:
 a first adsorption bed is designed to primarily remove water and other liquid components from the dehydrated natural gas feed stream;   a second adsorption bed is designed to primarily remove a desiccant from the dehydrated natural gas feed stream; and   a third vessel comprises an adsorption bed designed primarily for the removal of a sour gas component from the dehydrated natural gas feed stream.   
     
     
         35 . A method for liquefying a natural gas feed stream, comprising:
 receiving the natural gas feed stream at a gas processing facility;   passing the natural gas feed stream through a dehydration vessel in order to remove a substantial portion of water from the natural gas feed stream;   releasing a dehydrated natural gas feed stream to a gas separation unit as a dehydrated natural gas feed stream;   in the gas separation unit, passing the dehydrated natural gas feed stream through a series of adsorbent beds in order to separate methane gas from contaminants in the dehydrated natural gas feed stream using adsorptive kinetic separation;   releasing a methane-rich gas stream from the gas separation unit;   directing the methane-rich gas stream into a high-pressure expander cycle refrigeration system;   compressing the methane-rich gas stream to a pressure that is greater than 1,000 psia (6,895 kPa) in order to form a compressed gas feed stream;   cooling the compressed gas feed stream to form a compressed, cooled gaseous feed stream;   expanding the cooled, compressed, gaseous feed stream to form a product stream having a liquid fraction and a remaining vapor fraction.   
     
     
         36 . The method of  claim 35 , wherein the series of adsorbent beds comprises:
 a first adsorption bed for the removal of water remaining in the dehydrated natural gas feed stream;   a second adsorption bed designed primarily for the removal of a desiccant from the dehydrated natural gas feed stream; and   a third adsorption bed designed primarily for the removal of a sour gas component from the dehydrated natural gas feed stream.   
     
     
         37 . The method of  claim 36 , wherein the first, second, and third adsorption beds are aligned in series with flow of the dehydrated natural gas feed stream in a single pressure vessel. 
     
     
         38 . The method of  claim 36 , wherein the first, second, and third adsorption beds reside in separate pressure vessels that are aligned in series with the flow of the dehydrated natural gas feed stream. 
     
     
         39 . The method of  claim 36 , wherein each of the adsorbent beds comprises a solid adsorbent bed fabricated from a zeolite material. 
     
     
         40 . The method of  claim 37 , wherein each of the adsorbent beds has associated with it two additional adsorbent beds to form three adsorbent beds, with:
 a first of the three adsorbent beds being in service for adsorbing a selected contaminant;   a second of the three adsorbent beds undergoing regeneration; and   a third of the adsorbent beds being held in reserve to replace the first of the three adsorbent beds; and wherein   the regeneration is part of a pressure-swing adsorption process.   
     
     
         41 . The method of  claim 36 , wherein cooling the compressed gas feed stream comprises:
 passing the compressed gas feed stream through a first heat exchanger in order to provide heat exchange with a cooled refrigerant stream, thereby forming a sub-cooled gas feed stream; and   passing the sub-cooled gas feed stream through a second heat exchanger in order to provide heat exchange with a cooling gas stream, thereby forming the compressed, cooled gaseous feed stream.   
     
     
         42 . The method of  claim 41 , further comprising:
 withdrawing a portion of the remaining vapor fraction from the product stream;   reducing the pressure of the withdrawn portion of the remaining vapor fraction down to a pressure of about 30 to 200 psia (207 to 1,379 kPa) to produce a reduced pressure gas stream;   passing the reduced pressure gas stream through the second heat exchanger as the cooling gas stream; and   releasing the reduced pressure gas stream from the second heat exchanger as a partially-warmed gas stream.   
     
     
         43 . The method of  claim 42 , further comprising:
 passing the partially-warmed gas stream through the first heat exchanger as a cooling gas stream; and   returning the partially-warmed gas stream to the dehydrated natural gas feed stream for compressing with the methane-rich gas stream.   
     
     
         44 . The method of  claim 36 , wherein:
 compressing the methane-rich gas stream comprises compressing the methane-rich gas stream to a pressure that is between about 1,200 psia (8,274 kPa) to 4,500 psia (31,026 kPa); and   
       expanding the cooled, compressed, gaseous feed stream comprises reducing the pressure of the cooled, compressed, gaseous feed stream to a pressure between about 50 psia (345 kPa) and 450 psia (3,103 kPa).