Lng liquefaction system and process

Abstract

The present invention comprises systems and methods for natural gas liquefaction. In embodiments, the systems comprise a methane-based refrigeration system that also uses a slip stream of LNG for additional cooling.

1 . A method for natural gas liquefaction, comprising:
 providing a clean gas stream  1  and a recirculation gas stream  28  at a first pressure;   mixing the clean gas stream  1  and the recirculation gas stream  28  to form a mixed gas stream  1 A;   splitting the mixed gas stream  1 A into at least a first stream  2  and a second stream  3 ;   passing the first stream  2  through a heat exchanger  100 ;
 wherein the heat exchanger  100  cools the first stream  2  to form a first liquefied stream  4  by cross exchanging with one or more refrigeration streams, wherein the one or more refrigeration streams comprise:
 an expander refrigeration stream  11 ; 
 a secondary refrigeration stream  15 ; and 
 a tertiary refrigeration stream  34 ; and 
 
   cooling the second stream  3  by passing it through the heat exchanger  100  to form a cooled gas stream  5 ;   passing the cooled gas stream  5  through a turbo-expander  300  to form the expander refrigeration stream  11 ;   passing the expander refrigeration stream  11  through the heat exchanger  100  to form a first refrigeration return gas stream  12 ;   generating a first slipstream  14  from the first liquefied stream  4  and reducing pressure of the first slipstream  14  to form secondary refrigeration stream  15 ;   passing the secondary refrigeration stream  15  through the heat exchanger  100  to form a second refrigeration return gas stream  16 ;   combining the first refrigeration return gas stream  12  and the second return gas stream  16  to form a first combined stream  20 ;   generating a second slipstream  32  from the first liquefied stream  4  and reducing pressure of the second slipstream  32  to form reduced-pressure slip stream  33 ;   combining the reduced-pressure slipstream  33  with a boil off gas stream  31  from liquid natural gas storage  1500  to form the tertiary refrigeration stream  34 ;   passing the tertiary refrigeration stream  34  through the heat exchanger  100  to form a tertiary refrigeration return gas stream  35 ;   compressing the tertiary refrigeration return gas stream  35  using a first compressor  700  to form a compressed tertiary refrigeration return gas stream  36 ;   combining the compressed tertiary refrigeration return gas stream  36  with the first combined stream  20  to form a second combined stream  21 ;   compressing and optionally cooling the second combined stream  21  using one or more additional compressor(s) (e.g.,  900 ,  1000 ,  1200 , and/or  1900 ) and optionally one or more cooler(s) ( 1100  and/or  1150 ) to form the recirculation gas stream  28  at pressure P recycle ;   reducing pressure of the first liquefied stream  4  to form a two-phase product stream  8 ; and   recycling the one or more refrigeration streams through the system until a desired cryogenic liquid storage temperature is reached.   
     
     
         2 . The method of  claim 1 , wherein the clean gas stream  1  is free of or reduced in impurities that tend to freeze at cryogenic temperatures. 
     
     
         3 . The method of  claim 1 , wherein the first stream  2  is cooled by the heat exchanger  100  to a cryogenic temperature. 
     
     
         4 . The method of  claim 1 , wherein one or more of the compressing steps is performed using part of or all work extracted at the turbo-expander  300 . 
     
     
         5 . The method of  claim 1 , further comprising monitoring one or more of flow rate, flow volume, gas temperature, gas composition, or gas pressure. 
     
     
         6 . The method of  claim 1 , further comprising adjusting one or more of flow rate, flow volume, and/or flow ratio of one or more of the clean gas stream  1 , the first stream  2 , the second stream  3 , the expander refrigeration stream  11 , the secondary refrigeration stream  15 , and/or the tertiary refrigeration stream  34  based on the monitoring. 
     
     
         7 . The method of  claim 1 , further comprising expanding, decreasing the pressure of, and/or cooling one or more stream by way of one or more pressure-reducing valves. 
     
     
         8 . The method of  claim 1 , further comprising delivering the two-phase product stream  8  to a storage container once the desired cryogenic liquid storage temperature is reached. 
     
     
         9 . The method of  claim 1 , wherein the turbo-expander  300 , and one or more compressor are part of a single system coupled via a bull gear and pinions. 
     
     
         10 . The method of  claim 1 , further comprising serially compressing the second combined stream  21  by compression with: i) a first compressor or compression stage  900 , then ii) a second compressor or compression stage  1000 , and then iii) a third compressor or compression stage  1200  or  1900  to form the recirculation gas stream  28 . 
     
     
         11 . The method of  claim 1 , wherein the compressing of the second combined stream  21  is performed using a compander. 
     
     
         12 . The method of  claim 1 , wherein the compressing of the second combined stream  21  is performed using a recycle compressor package and the compression side of an expander package. 
     
     
         13 . The method of  claim 12 , wherein the expander package comprises a compressor and expander, wherein the expander package is separate and independent from the recycle compressor package. 
     
     
         14 . The method of  claim 12 , wherein the recycle compressor package comprises a multi-stage compressor, such as two or more stages, with a single prime mover and a single shaft. 
     
     
         15 . The method of  claim 1 , wherein the compressing of the second combined stream  21  is performed using a multi-stage compressor system with:
 i) a compression system with at least three compression stages; or 
 ii) a compression system with at least three stand-alone compressors; or 
 iii) at least two compressors each sharing a shaft with a compressor or expander; or 
 iv) a first compressor comprising first  900  and second  1000  compression stages sharing a first shaft and a second compressor  1200  comprising a third compression stage; or 
 v) a first compressor comprising first  900  and second  1000  compression stages sharing a first shaft and a second compressor  1200  sharing a second shaft with an expander, such as a turbo-expander  300 , and comprising a third compression stage; or 
 vi) a first stand-alone compressor  900 , a second stand-alone compressor  1000 , and a third compressor  1900  sharing a shaft with a compressor or expander, such as a turbo-expander  300 ; 
 or vii) a first compression stage  1900  of a compressor sharing a shaft with a compressor or expander, such as a turbo-expander  300 , a second stand-alone compressor  900 , and a third stand-alone compressor  1000 ; or 
 viii) a first compressor comprising first  900  and second  1000  compression stages sharing a first shaft and a second compressor  1900  comprising a third compression stage, and optionally wherein compression stage  1900  is a stand-alone compressor or compression stage  1900  is a compressor sharing a shaft with a compressor or expander, such as a turbo-expander  300 ; or 
 ix) a first compressor comprising a first compression stage sharing a first shaft with an expander, such as a turbo-expander  300 , a second stand-alone compressor  900 , and a third stand-alone compressor  1000 . 
 
     
     
         16 . The method of  claim 9 , wherein a single motor provides all external power required to perform the method. 
     
     
         17 . The method of  claim 15 , wherein part of or all work extracted at expander  300  is used in compressing the second combined stream  21 . 
     
     
         18 . The method of  claim 1 , wherein the tertiary refrigeration return gas stream  35  is boosted in pressure by way of a low-pressure compressor. 
     
     
         19 . A method for natural gas liquefaction, comprising:
 providing a gas stream  1  and a recirculation gas stream  28 ;   mixing the gas stream  1  and the recirculation gas stream  28  to form a mixed gas stream  1 A;   splitting the mixed gas stream  1 A into at least a first stream  2  and a second stream  3 ;   passing the first stream  2  and the second stream  3  through a heat exchanger  100  comprising:
 an expander refrigeration stream  11 ; 
 optionally, a secondary refrigeration stream  15 ; and 
 optionally, a tertiary refrigeration stream  34 ; 
 wherein the heat exchanger  100  cools the first stream  2  to form a first liquefied stream  4 , which is split to form a two-phase stream of natural gas  8 , and i) optionally a first slipstream  14 , and ii) optionally a second slipstream  32 , and iii) optionally the first slipstream  14  is reduced in pressure to provide the secondary refrigeration stream  15 , and optionally the second slipstream  32  is reduced in pressure to provide reduced-pressure slipstream  33  which is optionally combined with boil-off gas stream  31  to form the tertiary refrigeration stream  34 ; 
 wherein the heat exchanger  100  cools the second stream  3  by passing it through the heat exchanger  100  to form a cooled gas stream  5 : 
 wherein the cooled gas stream  5  is passed through a turbo-expander  300  to provide the expander refrigeration stream  11 ; 
   wherein one or more of the expander refrigeration stream  11 , the secondary refrigeration stream  15 , and/or the tertiary refrigeration stream  34  are optionally passed through a heat exchanger  100  and are compressed one or more times, individually or together, to provide a portion or all of the recirculation gas stream  28 .   
     
     
         20 . A system for natural gas liquefaction, comprising:
 one or more heat exchanger  100  comprising:
 an expander refrigeration stream  11 ; 
 a secondary refrigeration stream  15 ; and 
 a tertiary refrigeration stream  34 ; 
   wherein one or more of the heat exchangers  100  comprise one or more inputs to receive one or more mixed gas streams  1 A from a natural gas stream and a recirculation gas stream;   wherein one or more of the heat exchangers is configured to cool the mixed gas streams and provide a first liquefied stream  4  and a cooled gas stream  5  therefrom;   at least one turbo-expander  300  configured to receive the cooled gas stream  5  and to provide the expander refrigeration stream  11  for input into one or more of the heat exchangers  100 ;   storage  1500  configured to receive all or a portion of a two-phase product stream  8  which has been reduced in pressure from the first liquefied stream  4 , wherein optionally the first liquefied stream  4  is split and reduced in pressure to provide for the secondary refrigeration stream  15  and/or the tertiary refrigeration stream  34 ;   wherein one or more of the heat exchangers  100  comprises one or more inputs to receive one or more or all of the expander refrigeration stream  11 , the secondary refrigeration stream  15  and/or the tertiary refrigeration stream  34 ;   one or more compressors with one or more inputs for receiving one or more or all of the expander refrigeration stream  11 , the secondary refrigeration stream  15  and/or the tertiary refrigeration stream  34 , which compressor(s) provide the recirculation gas stream  28  as an output.