Apparatus for the liquefaction of gas and methods relating to same

Abstract

An apparatus, a system and a method for producing liquefied gas are provided. A liquefaction plant may be coupled to a source of, for example, unpurified natural gas, such as a natural gas pipeline at a pressure letdown station. A portion of the gas is drawn off and split into a process stream and a cooling stream. The cooling stream may pass through an expansion device. The compressed process stream is cooled, such as by a heat exchange process utilizing the expanded cooling stream, by a heat exchanger utilizing a separate, independent refrigerant, or by both. The cooled, compressed process stream is expanded to liquefy the natural gas. A gas-liquid separator separates the vapor from the liquid natural gas. A portion of the liquid gas may be used for additional cooling or substantially all of the liquid gas may be collected as product.

1 . A method of producing liquid natural gas, the method comprising: 
 providing a source of unpurified natural gas and flowing a portion of the natural gas from the source;    dividing the portion of natural gas into at least a process stream and a cooling stream;    flowing the process stream sequentially through a compressor and a first side of at least one heat exchanger,    flowing at least a portion of the process stream from the at least one heat exchanger through at least one expansion device and into a liquid-gas separator;    flowing the cooling stream sequentially through an expander and a second side of the at least one heat exchanger;    flowing a refrigerant in a heat exchange relationship with the process stream at a location of flow between the compressor and the liquid-gas separator; and maintaining the refrigerant separate from the process stream and the cooling stream.    
     
     
         2 . The method according to  claim 1 , wherein flowing at least a portion of the process stream from the at least one heat exchanger through an expansion device and into a liquid-gas separator further includes flowing the at least a portion of the process stream sequentially from the at least one heat exchanger through the first side of a second heat exchanger, through the at least one expansion device and into the liquid-gas separator.  
     
     
         3 . The method according to  claim 2 , wherein flowing a refrigerant in a heat exchange relationship with the process stream at a location of flow between the compressor and the liquid-gas separator further includes flowing the refrigerant through the second side of the second heat exchanger.  
     
     
         4 . The method according to  claim 3 , wherein flowing the at least a portion of the process stream through an expansion device includes flowing the at least a portion of the process stream through at least two expansion valves.  
     
     
         5 . The method according to  claim 4 , further comprising arranging the at least two expansion valves in a parallel flow configuration.  
     
     
         6 . The method according to  claim 5 , further comprising configuring a first expansion valve of the at least two expansion valves to exhibit a first flow capacity (Cv) and configuring a second valve of the at least two expansion valves to exhibit a second Cv, different from the first Cv.  
     
     
         7 . The method according to  claim 6 , further comprising flowing approximately 80% of the at least a portion of the process stream through the first expansion valve of the at least two expansion valves.  
     
     
         8 . The method according to  claim 7 , further comprising flowing the remainder of the at least a portion of the process stream through the second expansion valve of the at least two expansion valves.  
     
     
         9 . The method according to  claim 1 , further comprising producing a slurry of liquid natural gas and solid carbon dioxide from the at least a portion of the process stream within the liquid-gas separator.  
     
     
         10 . The method according to  claim 9 , further comprising agitating the slurry to keep the solid carbon dioxide substantially suspended within the liquid natural gas.  
     
     
         11 . The method according to  claim 10 , wherein agitating the slurry further includes bubbling a gas through the slurry.  
     
     
         12 . The method according to  claim 11 , further comprising transferring at least a portion of the slurry from the liquid-gas separator to at least one transfer tank.  
     
     
         13 . The method according to  claim 12 , wherein transferring at least a portion of the slurry from the liquid-gas separator to at least one transfer tank further comprises selectively transferring at least a portion of the slurry from the liquid-gas separator to a plurality of transfer tanks.  
     
     
         14 . The method according to  claim 13 , further comprising flowing the at least a portion of the slurry from at least one of the plurality of transfer tanks to at least one hydrocyclone.  
     
     
         15 . The method according to  claim 14 , wherein flowing the at least a portion of the slurry from at least one of the plurality of transfer tanks to at least one hydrocyclone further comprises selectively flowing the at least a portion of slurry from at least one of the plurality of transfer tanks to a plurality of hydrocyclones.  
     
     
         16 . The method according to  claim 15 , further comprising flowing a slush that is rich in solid carbon dioxide through an underflow of the at least one hydrocyclone to a sublimation tank.  
     
     
         17 . The method according to  claim 16 , further comprising subliming the solid carbon dioxide to a gas.  
     
     
         18 . The method according to  claim 14 , further comprising flowing liquid natural gas through an overflow of the hydrocyclone to a storage tank.  
     
     
         19 . The method according to  claim 18 , further comprising flowing the liquid natural gas through at least one filter prior to flowing the liquid natural gas to the storage tank.  
     
     
         20 . The method according to  claim 19 , further comprising flowing at least a portion of the cooling stream back into the source of unpurified natural gas.  
     
     
         21 . The method according to  claim 20 , further comprising compressing the at least a portion of the cooling stream prior to flowing it into the source of unpurified natural gas.  
     
     
         22 . The method according to  claim 20 , further comprising recirculating at least a portion of the cooling stream back into at least one of the cooling stream and the process stream.  
     
     
         23 . The method according to  claim 22 , further comprising compressing the at least a portion of the cooling stream prior to recirculating it into at least one the cooling stream and the process stream.  
     
     
         24 . The method according to  claim 1 , further comprising compressing the portion of the natural gas flowed from the source prior to dividing the portion of natural gas into at least a process stream and a cooling stream.  
     
     
         25 . The method according to  claim 1 , wherein flowing at least a portion of the process stream sequentially from the at least one heat exchanger through the first side of a second heat exchanger, through an expansion device and into a liquid-gas separator includes flowing substantially all of the process stream sequentially from the at least one heat exchanger through the first side of a second heat exchanger, through the at least one expansion device and into the liquid-gas separator.  
     
     
         26 . The method according to  claim 25 , further comprising producing a slurry of liquid natural gas and solid carbon dioxide from the at least a portion of the process stream within the liquid-gas separator.  
     
     
         27 . The method according to  claim 26 , further comprising separating a vapor component from the slurry.  
     
     
         28 . The method according to  claim 27 , further comprising substantially separating the liquid natural gas from the solid carbon dioxide.  
     
     
         29 . The method according to  claim 28 , further comprising collecting and storing substantially all of the separated, liquid natural gas.  
     
     
         30 . A liquefaction plant comprising: 
 a compressor;    a first expansion device;    a first heat exchanger;    at least a second expansion device;    a gas-liquid separator;    a first flow path defined and configured for sequential delivery of a first stream of gas through the compressor and a first side of the first heat exchanger;    a second flow path defined and configured for sequential delivery of a second stream of gas through the first expansion device and a second side of the first heat exchanger;    at least one additional flow path defined and configured for delivery of at least a portion of the first stream of gas from the first heat exchanger through the at least a second expansion device and into the gas-liquid separator; and    a refrigerant loop configured to flow a refrigerant stream in a heat exchange relationship with the first stream, wherein the refrigerant stream remains separate from the first stream and the second stream.    
     
     
         31 . The liquefaction plant of  claim 30 , further comprising at least a second heat exchanger, and wherein the at least one additional flow path is defined and configured for sequential delivery of the at least a portion of the first stream of gas from the first heat exchanger through the first side of the second heat exchanger, through the at least a second expansion device and into the gas-liquid separator.  
     
     
         32 . The liquefaction plant of  claim 31 , wherein the refrigerant loop is configured to flow the refrigerant stream through a second side of the second heat exchanger.  
     
     
         33 . The liquefaction plant of  claim 32 , further comprising at least one transfer tank located and configured to receive a solid-liquid slurry from the gas-liquid separator.  
     
     
         34 . The liquefaction plant of  claim 33 , wherein the at least one transfer tank includes at least two transfer tanks which are in selective communication with the gas-liquid separator.  
     
     
         35 . The liquefaction plant of  claim 33 , further comprising at least one hydrocyclone in selective communication with the at least one transfer tank.  
     
     
         36 . The liquefaction plant of  claim 35 , further comprising a storage tank in communication with an overflow of the at least one hydrocyclone.  
     
     
         37 . The liquefaction plant of  claim 36 , wherein the at least one hydrocyclone includes at least two hydrocyclones and wherein the storage tank is in selective communication with each of the at least two hydrocyclones.  
     
     
         38 . The liquefaction pant of  claim 36 , further comprising at least one filter disposed in a flow path between the at least one hydrocyclone and the storage tank.  
     
     
         39 . The liquefaction plant of  claim 38 , further comprising a sublimation tank in communication with an underflow of the at least one hydrocyclone.  
     
     
         40 . The liquefaction plant of  claim 32 , further comprising a recompression compressor configured to receive a flow of gas from the second side of the first heat exchanger.  
     
     
         41 . The liquefaction plant of  claim 40 , further comprising a further flow path extending from the recompression compressor to an exit of the plant.