Natural Gas Liquefaction With Feed Water Removal

Abstract

A method and apparatus for drying and liquefying a natural gas stream is described, in which: (a) the water containing natural gas feed stream is cooled; (b) the cooled natural gas feed stream is dried and further cooled; (c) the dried cooled natural gas stream is heated; (d) the dried rewarmed natural gas stream is cooled and liquefied and at least one compressed refrigerant feed stream is cooled by counter-current indirect heat exchange with an expanded cold refrigerant; and (e) the compressed cold refrigerant stream or streams are expanded, and thereby further cooled, to provide said expanded cold refrigerant; wherein the cooling of the natural gas feed stream in step (a) and heating of the dried cooled natural gas stream in step (c) is by indirect heat exchange between said two streams.

1 . A method for drying and liquefying a natural gas stream, the method comprising:
 (a) cooling a natural gas feed stream, that contains water, to produce a cooled natural gas stream;   (b) removing water from and further cooling the cooled natural gas feed stream to produce a dried cooled natural gas stream;   (c) heating the dried cooled natural gas stream to produce a dried rewarmed natural gas stream;   (d) cooling and liquefying the dried rewarmed natural gas stream and cooling at least one compressed refrigerant feed stream by counter-current indirect heat exchange with an expanded cold refrigerant, to produce a liquefied natural gas product stream, at least one compressed cold refrigerant stream, and an expanded warmed refrigerant stream; and   (e) expanding and thereby further cooling the compressed cold refrigerant stream or streams to provide said expanded cold refrigerant;
 wherein the cooling of the natural gas feed stream in step (a) and heating of the dried cooled natural gas stream in step (c) is by indirect heat exchange between said two streams. 
   
     
     
         2 . The method of  claim 1 , wherein in step (c) the dried cooled natural gas stream is heated to a temperature that is the same as or within 20° C. of the temperature of the at least one compressed refrigerant feed stream, such that there is no or less than 20° C. temperature difference between the dried rewarmed natural gas stream and the at least one compressed refrigerant feed stream at the start of step (d). 
     
     
         3 . The method of  claim 2 , wherein the temperature of the natural gas feed stream at the start of step (a) is also the same as or within 20° C. of the temperatures of the dried rewarmed natural gas stream and the at least one compressed refrigerant feed stream at the start of step (d). 
     
     
         4 . The method of  claim 1 , wherein step (d) is carried out in a wound coil cryogenic heat exchanger. 
     
     
         5 . The method of  claim 1 , wherein in step (b) the cooled natural gas feed stream is first dried, to remove water therefrom, and is then further cooled to produce the dried cooled natural gas stream. 
     
     
         6 . The method of  claim 1 , wherein the refrigerant in steps (d) and (e) is either a mixed refrigerant, the compressed cold refrigerant stream or streams in step (d) being liquid or mixed phase streams and the expanded warmed refrigerant stream in step (d) being a mixed phase or vapor stream, or is a gaseous refrigerant that remains in substantially gaseous form throughout steps (d) and (e). 
     
     
         7 . The method of  claim 1 , wherein the method further comprises:
 (f) compressing the expanded warmed refrigerant stream to provide said at least one compressed refrigerant feed stream that is cooled in step (d).   
     
     
         8 . The method of  claim 7 , wherein step (f) comprises compressing and cooling the expanded warmed refrigerant stream to provide both said at least one compressed refrigerant feed stream that is cooled in step (d) and an additional compressed refrigerant stream, the method further comprising expanding said additional compressed refrigerant stream to further cool said stream and using said further cooled additional refrigerant stream in step (b) to further cool the cooled natural gas feed stream by indirect heat exchange. 
     
     
         9 . The method of  claim 8 , wherein step (f) comprises compressing, cooling and phase separating the expanded warmed refrigerant stream to provide a vapor stream of compressed refrigerant and a liquid stream of compressed refrigerant, said vapor stream forming at least one compressed refrigerant feed stream that is cooled and at least partially liquefied in step (d), and at least a portion of said liquid stream forming the additional refrigerant stream that is expanded and then used in step (b) to further cool the cooled natural gas feed stream by indirect heat exchange. 
     
     
         10 . The method of  claim 1 , wherein in step (d) the dried rewarmed natural gas stream is cooled and liquefied to produce the liquefied natural gas product stream and an additional liquefied natural gas stream, said additional liquefied natural gas stream being used in step (b) to further cool the cooled natural gas feed stream. 
     
     
         11 . The method of  claim 10 , wherein in step (b) the cooled natural gas feed stream is further cooled by countercurrent direct heat exchange with said additional liquefied natural gas stream. 
     
     
         12 . An apparatus for drying and liquefying a natural gas stream, the apparatus comprising:
 an economizer heat exchanger for receiving a water-containing natural gas feed stream and a dried cooled natural gas stream and for cooling the water-containing natural gas feed stream and warming the dried cooled natural gas stream by indirect heat exchange with each other, so as to produce a cooled water-containing natural gas feed stream and a dried rewarmed natural gas stream;   natural gas feed water removal and natural gas feed cooling systems, in fluid flow communication with the economizer heat exchanger and each other, for receiving the cooled water-containing natural gas feed stream from the economizer heat exchanger, drying and further cooling said stream, and returning the resulting dried cooled natural gas stream to the economizer heat exchanger;   a main cryogenic heat exchanger for cooling and liquefying the dried rewarmed natural gas stream and for cooling at least one compressed refrigerant feed stream by counter-current indirect heat exchange with an expanded cold refrigerant, so as to produce a liquefied natural gas product stream, at least one compressed cold refrigerant stream, and an expanded warmed refrigerant stream;   a conduit arrangement for transferring the dried rewarmed natural gas stream from the economizer heat exchanger to the warm end of the main cryogenic heat exchanger, and for withdrawing the liquefied natural gas product stream from the cold end of the main cryogenic heat exchanger; and   a refrigerant expansion system, in fluid flow communication with the main cryogenic heat exchanger, for receiving at least one compressed cold refrigerant stream from the cold end of the cryogenic heat exchanger, expanding and thereby further cooling said cold refrigerant, and returning expanded cold refrigerant to the cold end of the cryogenic heat exchanger.   
     
     
         13 . An apparatus according to  claim 12 , wherein the main cryogenic heat exchanger is a wound coil heat exchanger. 
     
     
         14 . An apparatus according to  claim 12 , wherein the natural gas feed water removal system is upstream of the natural gas feed cooling system, such that cooled water-containing natural gas from the economizer heat exchanger is first dried in said water removal system, and dried natural gas from said water removal system is then further cooled in said cooling system to produce dried cooled natural gas that is then returned to the economizer heat exchanger. 
     
     
         15 . An apparatus according to  claim 12 , wherein the apparatus further comprises:
 a refrigerant compression system, in fluid flow communication with the main cryogenic heat exchanger, for receiving the expanded warmed refrigerant stream from the warm end of the cryogenic heat exchanger, compressing said refrigerant, and returning at least one compressed refrigerant feed stream to the warm end of the cryogenic heat exchanger.   
     
     
         16 . An apparatus according to  claim 15 , wherein the main cryogenic heat exchanger, refrigerant expansion system, and refrigerant compression system form or form part of a closed loop refrigerant system, the refrigerant contained and circulating within said closed loop system comprising said compressed and expanded refrigerant streams, said refrigerant being a mixed refrigerant or pure nitrogen or argon. 
     
     
         17 . An apparatus according to  claim 15 , wherein the refrigerant compression system compresses and cools the expanded warmed refrigerant, and the natural gas feed cooling system is an indirect heat exchanger, and wherein the apparatus further comprises an additional expansion system, in fluid flow communication with the refrigerant compression system and the natural gas feed cooling system, for receiving a stream of compressed and cooled refrigerant from the refrigerant compression system and expanding said stream to further cool said stream, the natural gas feed cooling system using said further cooled stream to further cool the cooled natural gas feed stream by indirect heat exchange. 
     
     
         18 . An apparatus according to  claim 17 , wherein the refrigerant compression system further comprises at least one phase separator, for separating the compressed and cooled refrigerant into liquid and vapor phases, said phase separator or separators being in fluid flow communication with the main cryogenic heat exchanger and the additional expansion system such that a vapor stream of compressed refrigerant is fed to the warm end of the cryogenic heat exchanger and a liquid stream of compressed refrigerant is fed to the additional expansion system. 
     
     
         19 . An apparatus according to  claim 12 , wherein the apparatus further comprises a conduit arrangement for transferring an additional liquefied natural gas stream from the main cryogenic heat exchanger to the natural gas feed cooling system, the feed cooling system using said additional liquefied natural gas stream to further cool the cooled natural gas feed stream. 
     
     
         20 . An apparatus according to  claim 19 , wherein the natural gas feed cooling system is a scrub column, in which the cooled natural gas feed stream is further cooled by countercurrent direct heat exchange with said additional liquefied natural gas stream.