Liquefaction of Production Gas

Abstract

A method and apparatus for liquefying a feed gas stream comprising natural gas and carbon dioxide. A method includes compressing an input fluid stream to generate a first intermediary fluid stream; cooling the first intermediary fluid stream with a first heat exchanger to generate a second intermediary fluid stream, wherein a temperature of the second intermediary fluid stream is higher than a carbon dioxide-freezing temperature for the second intermediary fluid stream; expanding the second intermediary fluid stream to generate a third intermediary fluid stream, wherein the third intermediary fluid stream comprises solid carbon dioxide; separating the third intermediary fluid stream into a fourth intermediary fluid stream and an output fluid stream, wherein the output fluid stream comprises a liquefied natural gas (LNG) liquid; and utilizing the fourth intermediary fluid stream as a cooling fluid stream for the first heat exchanger.

What is claimed is: 
     
         1 . A method, comprising:
 compressing an input fluid stream to generate a first intermediary fluid stream;   cooling the first intermediary fluid stream with a first heat exchanger to generate a second intermediary fluid stream, wherein a temperature of the second intermediary fluid stream is higher than a carbon-dioxide-freezing temperature for the second intermediary fluid stream;   expanding the second intermediary fluid stream to generate a third intermediary fluid stream, wherein the third intermediary fluid stream comprises solid carbon dioxide;   separating the third intermediary fluid stream into a fourth intermediary fluid stream and an output fluid stream, wherein the output fluid stream comprises a liquefied natural gas (LNG) liquid; and   utilizing the fourth intermediary fluid stream as a first cooling fluid stream for the first heat exchanger.   
     
     
         2 . The method of  claim 1 , further comprising, after utilizing the fourth intermediary fluid stream as the cooling fluid stream, burning the fourth intermediary fluid stream. 
     
     
         3 . The method of  claim 2 , wherein the burning comprises flaring, consuming as fuel, or a combination thereof. 
     
     
         4 . The method of  claim 3 , wherein about 5 mass % to 10 mass % of the input fluid stream is burned. 
     
     
         5 . The method of  claim 4 , wherein less than about 1 mass % of the input fluid stream is burned by flaring. 
     
     
         6 . The method of  claim 1 , further comprising, before expanding the second intermediary fluid stream, further cooling the second intermediary fluid stream with a second heat exchanger. 
     
     
         7 . The method of  claim 6 , further comprising, before utilizing the fourth intermediary fluid stream as a cooling fluid stream for the first heat exchanger, utilizing the fourth intermediary fluid stream as a cooling fluid stream for the second heat exchanger. 
     
     
         8 . The method of  claim 1 , further comprising:
 expanding the output fluid stream to generate a fifth intermediary fluid stream; and   separating the fifth intermediary fluid stream into a sixth intermediary fluid stream and a second output fluid stream, wherein the second output fluid stream comprises a LNG liquid.   
     
     
         9 . The method of  claim 8 , further comprising burning the sixth intermediary fluid stream, wherein the burning comprises flaring, consuming as fuel, or a combination thereof. 
     
     
         10 . The method of  claim 1 , further comprising utilizing a mixed refrigerant loop to provide a second cooling fluid stream for the first heat exchanger. 
     
     
         11 . The method of  claim 1 , further comprising utilizing an open refrigerant loop to provide a second cooling fluid stream for the first heat exchanger. 
     
     
         12 . The method of  claim 11 , wherein:
 the open refrigerant loop further provides a third cooling fluid stream for the first heat exchanger, and   a consumable cooling fluid of the third cooling fluid stream comprises gaseous nitrogen.   
     
     
         13 . The method of  claim 11 , further comprising expanding the second cooling fluid stream with a turboexpander to produce a third cooling fluid stream. 
     
     
         14 . The method of  claim 13 , further comprising:
 generating power with the turboexpander; and   driving a compressor with the generated power.   
     
     
         15 . The method of  claim 1 , further comprising, after utilizing the fourth intermediary fluid stream as the cooling fluid stream for the first heat exchanger:
 compressing the fourth intermediary fluid stream to generate a seventh intermediary fluid stream;   cooling the seventh intermediary fluid stream with a third heat exchanger to generate an eighth intermediary fluid stream, wherein a temperature of the eighth intermediary fluid stream is higher than a carbon dioxide freezing temperature for the eighth intermediary fluid stream;   expanding the eighth intermediary fluid stream to generate a ninth intermediary fluid stream, wherein the ninth intermediary fluid stream comprises solid carbon dioxide; and   separating a third output fluid stream from the ninth intermediary fluid stream, wherein the third output fluid stream comprises a LNG liquid, wherein about 80 mass % to 95 mass % of the input fluid stream is extracted in a combination of the output fluid stream and the third output stream.   
     
     
         16 . A method comprising:
 producing associated gas at a liquid hydrocarbon-producing well site;   generating a liquefied natural gas (LNG) slurry at the well site from the associated gas, wherein generating the LNG slurry comprises:
 compressing an input fluid stream of the associated gas to generate a first intermediary fluid stream; 
 cooling the first intermediary fluid stream with a first heat exchanger to generate a second intermediary fluid stream, wherein a temperature of the second intermediary fluid stream is higher than a carbon-dioxide-freezing temperature for the second intermediary fluid stream; 
 expanding the second intermediary fluid stream to generate a third intermediary fluid stream, wherein the third intermediary fluid stream comprises solid carbon dioxide; and 
 separating the LNG slurry from the third intermediary fluid stream; and 
   transporting the LNG slurry away from the well site.   
     
     
         17 . The method of  claim 16 , wherein generating the LNG slurry further comprises:
 separating a fourth intermediary fluid stream from the third intermediary fluid stream; and   utilizing the fourth intermediary fluid stream as a cooling fluid stream for the first heat exchanger.   
     
     
         18 . The method of  claim 16 , wherein:
 generating the LNG slurry further comprises utilizing an open refrigerant loop to provide a second cooling fluid stream for the first heat exchanger, and   a consumable cooling fluid of the open refrigerant is generated away from the well site.   
     
     
         19 . The method of  claim 16 , wherein generating the LNG slurry further comprises:
 measuring a composition of the input fluid stream; and   adjusting the temperature of the second intermediary fluid stream based on the measured composition.   
     
     
         20 . The method of  claim 19 , wherein adjusting the temperature comprises at least one action selected from a group of actions consisting of:
 adjusting a throttle pressure in a refrigerant stream for the first heat exchanger; and   adjusting a flow rate in the refrigerant stream for the first heat exchanger.