Hybrid cycle for the production of liquefied natural gas

Abstract

Refrigeration process for gas liquefaction which utilizes one or more vaporizing refrigerant cycles to provide refrigeration below about −40° C. and a gas expander cycle to provide refrigeration below about −100° C. Each of these two types of refrigerant systems is utilized in an optimum temperature range which maximizes the efficiency of the particular system. A significant fraction of the total refrigeration power required to liquefy the feed gas (typically more than 5% and often more than 10% of the total) can be consumed by the vaporizing refrigerant cycles. The invention can be implemented in the design of a new liquefaction plant or can be utilized as a retrofit or expansion of an existing plant by adding gas expander refrigeration circuit to the existing plant refrigeration system.Method for the liquefaction of a feed gas which comprises providing at least a portion of the total refrigeration required to cool and condense the feed gas by utilizing a first refrigeration system comprising at least one recirculating refrigeration circuit, wherein the first refrigeration system utilizes two or more refrigerant components and provides refrigeration in a first temperature range, and a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream. Compressed refrigerant in the first refrigeration system may be cooled by refrigeration provided by a third refrigeration system. Compressed refrigerant in the second refrigeration system may be cooled by refrigeration provided by a third refrigeration system. At least a portion of the pressurized gaseous refrigerant stream, prior to work expansion, may be entirely cooled separately from cooling of the feed gas.

1. A method for the liquefaction of a feed gas which comprises providing at least a portion of the total refrigeration required to cool and condense the feed gas by utilizing
 (a) a first refrigeration system comprising at least one recirculating refrigeration circuit, wherein the first refrigeration system utilizes two or more refrigerant components and provides refrigeration in a first temperature range; and  
 (b) a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream;  
 
       wherein the first recirculating  refrigeration system is operated by
 (1) compressing a first gaseous refrigerant;  
 (2) cooling and at least partially condensing the resulting compressed refrigerant;  
 (3) reducing the pressure of the resulting at least partially condensed compressed refrigerant;  
 (4) vaporizing the resulting reduced-pressure refrigerant to provide refrigeration in the first temperature range and yield a vaporized refrigerant; and  
 (5) recirculating the vaporized refrigerant to provide the first gaseous refrigerant of (1);  
 
       wherein at least a portion of the cooling in (2) is provided by indirect heat exchange with one or more additional vaporizing refrigerant streams provided by a third recirculating  refrigeration circuit  system. 
     
     
       2. The method of  claim 1  wherein the third recirculating  refrigeration circuit  system utilizes a single component refrigerant. 
     
     
       3. The method of  claim 1  wherein the third recirculating  refrigeration circuit  system utilizes a mixed refrigerant comprising two or more components. 
     
     
       4. A method for the liquefaction of a feed gas which comprises providing at least a portion of the total refrigeration required to cool and condense the feed gas by utilizing
 (a) a first refrigeration system comprising at least one recirculating refrigeration circuit, wherein the first refrigeration system utilizes two or more refrigerant components and provides refrigeration in a first temperature range; and  
 (b) a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream;  
 
       wherein the second reciculatingrefrigeration system is operated by
 (1) compressing a second gaseous refrigerant to provide the pressurized gaseous refrigerant in (b);  
 (2) cooling the pressurized gaseous refrigerant to yield a cooled gaseous refrigerant;  
 (3) working expanding the cooled gaseous refrigerant to provide the cold refrigerant in (b);  
 (4) warming the cold refrigerant to provide refrigeration in the second temperature range; and  
 (5) recirculating the resulting warmed refrigerant to provide the second gaseous refrigerant of (1);  
 
       wherein at least a portion of the cooling in (2) is provided by indirect heat exchange with one or more additional vaporizing refrigerants provided by a third recirculating  refrigeration circuit  system. 
     
     
       5. The method of  claim 4  wherein the third recirculating  refrigeration circuit  system utilizes a single component refrigerant. 
     
     
       6. The method of  claim 4  wherein the third recirculating  refrigeration circuit  system utilizes a mixed refrigerant which comprises two or more components. 
     
     
       7. A method for the liquefaction of a feed gas which comprises providing at least a portion of the total refrigeration required to cool and condense the feed gas by utilizing
 (a) a first refrigeration system comprising at least one recirculating refrigeration circuit, wherein the first refrigeration system utilizes two or more refrigerant components and provides refrigeration in a first temperature range; and  
 (b) a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream;  
 
       wherein the first refrigerant system is operated by
 (1) compressing a first gaseous refrigerant;  
 (2) cooling and partially condensing the resulting compressed refrigerant to yield a vapor refrigerant fraction and a liquid refrigerant fraction;  
 (3) further cooling and reducing the pressure of the liquid refrigerant fraction, and vaporizing the resulting liquid refrigerant fraction to provide refrigeration in the first temperature range and yield a first vaporized refrigerant;  
 (4) cooling and condensing the vapor refrigerant fraction, reducing the pressure of at least a portion of the resulting liquid, and vaporizing the resulting liquid refrigerant fraction to provide additional refrigeration in the first temperature range and yield a second vaporized refrigerant; and  
 (5) combining the first and second vaporized refrigerants to provide the first gaseous refrigerant of (1);  
 
       wherein vaporization of the resulting liquid in (4) is effected at a pressure lower than the vaporization of the resulting liquid refrigerant fraction in (3), and wherein the second vaporized refrigerant is compressed before combining with the first vaporized refrigerant. 
     
     
       8. A method for the liquefaction of a feed gas which comprises providing at least a portion of the total refrigeration required to cool and condense the feed gas by utilizing
 (a) a first refrigeration system comprising at least one recirculating refrigeration circuit, wherein the first refrigeration system utilizes two or more refrigerant components and provides refrigeration in a first temperature range; and  
 (b) a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream;  
 
       wherein the second refrigeration system is operated by
 (1) compressing a second gaseous refrigerant to provide the pressurized gaseous refrigerant in (b);  
 (2) cooling the pressurized gaseous refrigerant to yield a cooled gaseous refrigerant;  
 (3) work expanding the cooled gaseous refrigerant to provide the cold refrigerant in (b);  
 (4) warming the cold refrigerant to provide refrigeration in the second temperature range; and  
 (5) recirculating the resulting warmed refrigerant to provide the second gaseous refrigerant of (1);  
 
       wherein the feed gas is natural gas, the resulting liquefied natural gas stream is flashed to lower pressure to yield a light flash vapor and a final liquid product, and the light flash vapor is used to provide the second gaseous refrigerant in the second refrigerant circuit  refrigeration system. 
     
     
       9. A method for the liquefaction of a feed gas which comprises providing at least a portion of the total refrigeration required to cool and condense the feed gas by utilizing
 ( a )  a first refrigeration system comprising at least one recirculating refrigeration circuit, wherein the first refrigeration system utilizes two or more refrigerant components and provides refrigeration in a first temperature range; and      ( b )  a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream;      
       
         wherein the second refrigeration system is operated by  
         (   1   )  compressing a second gaseous refrigerant to provide the pressurized gaseous refrigerant in  ( b );  
         (   2   )  cooling the pressurized gaseous refrigerant to yield a cooled gaseous refrigerant;    
         (   3   )  work expanding the cooled gaseous refrigerant to provide the cold refrigerant in  ( b );  
         (   4   )  warming the cold refrigerant to provide refrigeration in the second temperature range; and    
         (   5   )  recirculating the resulting warmed refrigerant to provide the second gaseous refrigerant of  (   1   );  
       
         wherein at least a portion of the pressurized gaseous refrigerant in  (   2   )  is entirely cooled separately from the cooling of the feed gas.   
     
     
       10. The method of  claim 9  wherein all of the pressurized gaseous refrigerant is cooled separately from cooling of the feed gas. 
     
     
       11. The method of  claim 9  wherein a portion of the pressurized gaseous refrigerant is cooled by indirect heat exchange with the at least one recirculating refrigeration circuit of ( a ). 
     
     
       12. The method of  claim 9  wherein the first refrigeration system comprises a mixed component, pure component, and/or a cascaded vapor recompression refrigeration system. 
     
     
       13. An apparatus for the liquefaction of a feed gas comprising
 ( a )  a first refrigeration system comprising at least one recirculating refrigeration circuit, wherein the first refrigeration system utilizes two or more refrigerant components and provides refrigeration in a first temperature range, wherein at least a portion of the first temperature range is between − 40 ° C. and − 100 ° C.; and      ( b )  a second refrigeration system which provides refrigeration in a second temperature range by work expanding a pressurized gaseous refrigerant stream, wherein at least a portion of the second temperature range is below − 100 ° C.;      
       
         wherein the first refrigeration system comprises:  
         (   1   )  compression means for comprising a first gaseous refrigerant;    
         (   2   )  heat exchange means for cooling and at least partially condensing the resulting compressed refrigerant;    
         (   3   )  means for reducing the pressure of the resulting at least partially condensed compressed refrigerant;    
         (   4   )  heat exchange means for vaporizing the resulting reduced - pressure refrigerant to provide refrigeration in the first temperature range and yield a vaporized refrigerant; and    
         (   5   )  means for recirculating the vaporized refrigerant to provide the first gaseous refrigerant of  (   1   );  
       
         and wherein the apparatus comprises additional heat exchange means to provide at least a portion of the cooling of  (   2   )  by indirect heat exchange with one or more additional vaporizing refrigerant streams and a third refrigeration system to provide the one or more additional vaporizing refrigerant streams.   
     
     
       14. The apparatus of  claim 13 , wherein the second refrigeration system comprises
 (   6   )  compression means for compressing a second gaseous refrigerant to provide the pressurized gaseous refrigerant;      (   7   )  heat exchange means for cooling the pressurized gaseous refrigerant to yield a cooled gaseous refrigerant;      (   8   )  expansion means for work expanding the cooled gaseous refrigerant to provide the cold refrigerant;      (   9   )  heat exchange means for warming the cold refrigerant to provide refrigeration in the second temperature range; and      (   10   )  means for recirculating the resulting warmed refrigerant to provide the second gaseous refrigerant of  (   6   ).   
     
     
       15. The apparatus of  claim 14 , wherein at least one of the heat exchange means in the first and second refrigeration systems comprises a wound coil heat exchanger. 
     
     
       16. An apparatus for the liquefaction of a feed gas comprising
 ( a )  a first refrigeration system comprising at least one recirculating refrigeration circuit utilizing two or more refrigerant components and providing refrigeration in a first temperature range; and      ( b )  a second refrigeration system which provides refrigeration in a second temperature range having a lowest temperature less than the lowest temperature in the first temperature range;      
       
         wherein the second refrigeration system comprises  
         (   1   )  compression means for compressing the second gaseous refrigerant to provide the pressurized gaseous refrigerant;    
         (   2   )  heat exchange means for entirely cooling at least a portion of the pressurized gaseous refrigerant separately from cooling of the feed gas to yield at least a portion of the cooled gaseous refrigerant;    
         (   3   )  expansion means for work expanding the cooled gaseous refrigerant to provide the cold refrigerant;    
         (   4   )  heat exchange means for warming the cold refrigerant to provide refrigeration in the second temperature range; and    
         (   5   )  means for recirculating the resulting warmed refrigerant to provide the second gaseous refrigerant of  (   1   ). 
       
     
     
       17. The apparatus of  claim 16  wherein the heat exchange means of (   2   )  cools all of the pressurized gaseous refrigerant separately from cooling of the feed gas.   
     
     
       18. The apparatus of  claim 16  wherein the first refrigeration system comprises
 ( A )  compression means for compressing the first gaseous refrigerant;      ( B )  heat exchange means for cooling and at least partially condensing the resulting compressed refrigerant;      ( C )  pressure reducing means for reducing the pressure of the resulting at least partially condensed compressed refrigerant;      ( D )  heat exchange means for vaporizing the resulting reduced - pressure refrigerant to provide refrigeration in the first temperature range and yield the vaporized refrigerant; and      ( E )  means for recirculating the vaporized refrigerant to provide the first gaseous refrigerant of  ( A ).   
     
     
       19. The apparatus of  claim 16  wherein at least a portion of the cooling in the heat exchanger of (   2   )  is provided by indirect heat exchange by warming the cold refrigerant in  (   4   ). 
     
     
       20. The apparatus of  claim 18  wherein at least one of the heat exchange means of the first and second refrigeration systems comprises a wound coil heat exchanger.