Producing LNG from Methane Containing Synthetic Gas

Abstract

Described herein are methods and systems for producing liquefied natural gas (LNG) from a methane-containing synthetic gas (MCSG). An MCSG feed stream may be cooled and partially liquefied using one or more heat exchanger units. A first phase separator and a second phase separator in downstream fluid flow communication with the first phase separator may be used to separate the partially liquefied MCSG stream into a first residue gas stream and first and second feed streams, the first and second feed streams then being fed into a distillation column to produce an LNG stream and a second residue gas stream.

1 . A method for producing liquefied natural gas (LNG) from methane-containing synthetic gas (MCSG), the method comprising:
 (a) cooling and partially liquefying a MCSG feed stream to produce a partially liquefied MCSG feed stream;   (b) using a first phase separator and a second phase separator arranged in series, with the second phase separator being in downstream fluid flow communication with the first phase separator, to separate the partially liquefied MCSG feed stream into at least three streams comprising a liquid stream and two vapor streams, the liquid stream forming a first feed stream, one of the vapor streams forming a second feed stream, and the other of the vapor streams forming a first residue gas stream;   (c) introducing the first feed stream into a distillation column at a first location;   (d) introducing the second feed stream into the distillation column at a second location that is above the first location, there being at least one separation stage between the first location and second location;   (e) withdrawing an LNG stream from the distillation column formed of distillation column bottoms liquid; and   (f) withdrawing a second residue gas stream from the distillation column formed of distillation column overhead vapor.   
     
     
         2 . The method of  claim 1 , wherein step (b) comprises:
 (i) separating the partially liquefied MCSG feed stream in the first phase separator into the liquid steam that forms the first feed stream, and a vapor stream;   (ii) dividing the vapor stream from the first phase separator to form the vapor stream that forms the second feed stream, and a vapor stream that forms a third feed stream; and   (iii) cooling and partially liquefying the third feed stream and then separating the third feed stream in the second phase separator into the vapor stream that forms the first residue gas stream, and a liquid stream that forms a fourth feed stream;   wherein step (c) comprises reducing the pressure of the first feed stream and then introducing the first feed stream into a distillation column at the first location;   wherein step (d) comprises reducing the pressure of the second feed stream and then introducing the second feed stream into the distillation column at the second location; and   wherein the method further comprises reducing the pressure of the fourth feed stream and then introducing the fourth feed stream into the distillation column at a third location that is above the second location, there being at least one separation stage between the second location and third location.   
     
     
         3 . The method of  claim 2 , wherein the third location is at the top of the distillation column. 
     
     
         4 . The method of  claim 2 , wherein one or both of the first residue gas stream and the second residue gas stream are warmed via indirect heat exchange with the third feed stream in order to provide cooling duty for the cooling and partial liquefaction of the third feed stream in step (b)(iii). 
     
     
         5 . The method of  claim 1 , wherein step (b) comprises:
 (i) separating the partially liquefied MCSG stream in the first phase separator into the vapor stream that forms the first residue gas stream, and a liquid stream that forms a third feed stream; and   (ii) reducing the pressure of and partially vaporizing the third feed stream and separating said stream in the second phase separator into the liquid stream that forms the first feed stream and the vapor stream that forms the second feed stream; and   wherein step (c) comprises warming the first feed stream and then introducing the first feed stream into a distillation column at the first location.   
     
     
         6 . The method of  claim 5 , wherein there is at least one separation stage between the second location and the top of the column, and the method further comprises: compressing, cooling, expanding and thereby at least partially liquefying a portion of the second residue gas stream or distillation column overhead vapor to form a reflux stream; and introducing the reflux stream into the distillation column at a third location that is at the top of the distillation column. 
     
     
         7 . The method of  claim 5 , wherein in step (c) the first feed stream is warmed via indirect heat exchange with the MCSG feed stream in order to provide cooling duty for the cooling and partial liquefaction of the MCSG feed stream in step (a). 
     
     
         8 . The method of  claim 1 , wherein one or both of the first residue gas stream and the second residue gas stream are warmed via indirect heat exchange with the MCSG feed stream in order to provide cooling duty for the cooling and partial liquefaction of the MCSG feed stream in step (a). 
     
     
         9 . The method of  claim 1 , wherein there is at least one separation stage between the first location and the bottom of the column, and wherein the method further comprises warming and thereby at least partially vaporizing a portion of the LNG stream or distillation column bottoms liquid to form a boil-up stream, and introducing the boil-up stream into the distillation column at the bottom of the distillation column. 
     
     
         10 . The method of  claim 1 , wherein at least a portion of the second residue gas stream is compressed and combined with first residue gas stream. 
     
     
         11 . The method of  claim 1 , wherein the method further comprises subcooling the LNG stream. 
     
     
         12 . The method of  claim 1 , wherein step (a) comprises:
 (i) dividing the MCSG feed stream into at least two portions, comprising a first portion and a second portion;   (ii) cooling and partially liquefying the first portion of the MCSG feed stream in a first heat exchanger unit or set of units via indirect heat exchange with a first refrigerant, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units;   (iii) cooling and partially liquefying the second portion of the MCSG feed stream in a second heat exchanger unit or set of units via indirect heat exchange with one or more process streams; and   (iv) combining the cooled and partially liquefied first portion of the MCSG feed stream and the cooled and partially liquefied second portion of the MCSG feed stream to form the partially liquefied MCSG feed stream.   
     
     
         13 . The method of  claim 12 , wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units. 
     
     
         14 . The method of  claim 12 , wherein in step (a)(iii) the one or more process streams comprise one or more streams selected from the first residue gas stream, the second residue gas stream, and a portion of the LNG stream or distillation column bottoms liquid. 
     
     
         15 . The method of  claim 12 , wherein the first refrigerant is a refrigerant that vaporizes as it is warmed in the first heat exchanger unit or set of units. 
     
     
         16 . The method of  claim 12 , wherein the method further comprises subcooling the LNG stream in the first heat exchanger unit or set of units via indirect heat exchange with the first refrigerant. 
     
     
         17 . The method of  claim 12 , wherein step (a)(ii) comprises cooling and partially liquefying the first portion of the MCSG feed stream in the first heat exchanger unit or set of units via indirect heat exchange with one or more streams of cooled first refrigerant, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units, and wherein the one or more streams of cooled first refrigerant are produced by also cooling the first refrigerant in the first heat exchanger unit or set of units. 
     
     
         18 . The method of  claim 1 , wherein step (a) comprises:
 (i) cooling a first refrigerant in a first heat exchanger unit or set of units to produce a cooled first refrigerant, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units;   (ii) cooling and partially liquefying the MCSG feed stream in a second heat exchanger unit or set of units, via indirect heat exchange with one or more streams of the cooled first refrigerant and one or more process streams, to form the partially liquefied MCSG feed stream.   
     
     
         19 . The method of  claim 18 , wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units. 
     
     
         20 . The method of  claim 18 , wherein in step (a)(ii) the one or more process streams comprise one or more of the first residue gas stream, the second residue gas stream, and a portion of the LNG stream or distillation column bottoms liquid. 
     
     
         21 . The method of  claim 18 , wherein in step (a)(i) the first refrigerant is cooled in the first heat exchanger unit or set of units via indirect heat exchange with a portion of the cooled first refrigerant that is produced in step (a)(i). 
     
     
         22 . The method of  claim 18 , wherein the method further comprises subcooling the LNG stream in the first heat exchanger unit or set of units. 
     
     
         23 . A method for producing liquefied natural gas (LNG) from methane containing synthetic gas (MCSG), the method comprising:
 (a) cooling and partially liquefying a MCSG feed stream to produce a partially liquefied MCSG feed stream by:
 (i) dividing the MCSG feed stream into at least two portions, comprising a first portion and a second portion; 
 (ii) cooling and partially liquefying the first portion in a first heat exchanger unit or set of units via indirect heat exchange with a first refrigerant, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units; 
 (iii) cooling and partially liquefying the second portion in a second heat exchanger unit or set of units via indirect heat exchange with one or more process streams; and 
 (iv) combining the cooled and partially liquefied first portion and the cooled and partially liquefied second portion to form the partially liquefied MCSG feed stream; 
   (b) separating the partially liquefied MCSG feed stream into a LNG stream and one or more residue gas streams.   
     
     
         24 . The method of  claim 23 , wherein in step (b) the partially liquefied MCSG feed stream is separated into the LNG stream and the one or more residue gas streams using one or more phase separators and/or one or more distillation columns. 
     
     
         25 . The method of  claim 23 , wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units. 
     
     
         26 . The method of  claim 23 , wherein in step (a)(iii) the one or more process streams comprise one or more streams selected from the one or more of the residue gas streams, a portion of the LNG stream or a portion of a distillation column bottoms liquid. 
     
     
         27 . The method of  claim 23 , wherein the first refrigerant is a refrigerant that vaporizes as it is warmed in the first heat exchanger unit or set of units. 
     
     
         28 . The method of  claim 23 , wherein the method further comprises subcooling the LNG stream in the first heat exchanger unit or set of units via indirect heat exchange with the first refrigerant. 
     
     
         29 . The method of  claim 23 , wherein step (a)(ii) comprises cooling and partially liquefying the first portion of the MCSG feed stream in the first heat exchanger unit or set of units via indirect heat exchange with one or more streams of cooled first refrigerant, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units, and wherein the one or more streams of cooled first refrigerant are produced by also cooling the first refrigerant in the first heat exchanger unit or set of units. 
     
     
         30 . A method for producing liquefied natural gas (LNG) from methane containing synthetic gas (MCSG), the method comprising:
 (a) cooling and partially liquefying a MCSG feed stream to produce a partially liquefied MCSG feed stream by:
 (i) cooling a first refrigerant in a first heat exchanger unit or set of units to produce a cooled first refrigerant, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units; 
 (ii) cooling and partially liquefying the MCSG feed stream in a second heat exchanger unit or set of units, via indirect heat exchange with one or more streams of the cooled first refrigerant and one or more process streams, to form the partially liquefied MCSG feed stream; 
   (b) separating the partially liquefied MCSG feed stream into a LNG stream and one or more residue gas streams.   
     
     
         31 . The method of  claim 30 , wherein in step (b) the partially liquefied MCSG feed stream is separated into the LNG stream and the one or more residue gas streams using one or more phase separators and/or one or more distillation columns. 
     
     
         32 . The method of  claim 30 , wherein the second heat exchanger unit or set of units is a plate fin heat exchanger unit or set of units. 
     
     
         33 . The method of  claim 30 , wherein in step (a)(ii) the one or more process streams comprise one or more of the first residue gas stream, the second residue gas stream, and a portion of the LNG stream or distillation column bottoms liquid. 
     
     
         34 . The method of  claim 30 , wherein in step (a)(i) the first refrigerant is cooled in the first heat exchanger unit or set of units via indirect heat exchange with a portion of the cooled first refrigerant that is produced in step (a)(i). 
     
     
         35 . The method of  claim 30 , wherein the method further comprises subcooling the LNG stream in the first heat exchanger unit or set of units. 
     
     
         36 . A system for producing liquefied natural gas (LNG) from methane containing synthetic gas (MCSG), the system comprising:
 one or more heat exchanger units for receiving, cooling and partially liquefying a MCSG feed stream to produce a partially liquefied MCSG feed stream;   a first phase separator and a second phase separator in fluid flow communication with the one or more heat exchanger units and arranged in series, with the second phase separator being in downstream fluid flow communication with the first phase separator, for separating the partially liquefied MCSG feed stream into at least three streams comprising a liquid stream and two vapor streams, the liquid stream forming a first feed stream, one of the vapor streams forming a second feed stream, and the other of the vapor streams forming a first residue gas stream; and   a distillation column having: a first inlet at a first location for receiving the first feed stream; a second inlet at second location for receiving the second feed stream, the second location being above the first location; at least one separation stage between the first location and second location; an outlet at the bottom of the distillation column for withdrawal of an LNG stream formed of distillation column bottoms liquid; and an outlet at the top of the distillation column for withdrawal of a second residue gas stream formed of distillation column overhead vapor.   
     
     
         37 . A system for producing liquefied natural gas (LNG) from methane containing synthetic gas (MCSG), the system comprising:
 a set of conduits for dividing a MCSG feed stream into at least two portions, comprising a first portion and a second portion;   a first heat exchanger unit or set of units via for receiving the first portion and cooling and partially liquefying the first portion via indirect heat exchange with a first refrigerant, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units;   a second heat exchanger unit or set of units for receiving the second portion and cooling and partially liquefying the second portion via indirect heat exchange with one or more process streams;   a set of conduits for receiving and combining the cooled and partially liquefied first portion and the cooled and partially liquefied second portion to form a partially liquefied MCSG feed stream; and   one or more phase separators and/or one or more distillation columns for receiving and separating the partially liquefied MCSG feed stream into a LNG stream and one or more residue gas streams.   
     
     
         38 . A system for producing liquefied natural gas (LNG) from methane containing synthetic gas (MCSG), the system comprising:
 a first heat exchanger unit or set of units for cooling a first refrigerant to produce a cooled first refrigerant, wherein the first heat exchanger unit or set of units is a coil-wound heat exchanger unit or set of units;   a second heat exchanger unit or set of units for receiving one or more streams of the cooled first refrigerant from the first heat exchanger unit, for receiving one or more process streams, and for receiving an MCSG feed stream and cooling and partially liquefying the MCSG feed stream to form a partially liquefied MCSG feed stream via indirect heat exchange with the one or more streams of the cooled first refrigerant and the one or more process streams; and   one or more phase separators and/or one or more distillation columns for receiving and separating the partially liquefied MCSG feed stream into a LNG stream and one or more residue gas streams.