System and method for liquefacation of natural gas

Abstract

By using the power generated by an expander by an expansion of material gas, the outlet pressure of a compressor is increased, and a requirement on the cooling capacity of a cooler is reduced. The liquefaction system ( 1 ) for natural gas comprises a first expander ( 3 ) for generating power by expanding natural gas under pressure as material gas; a first cooling unit ( 11, 12 ) for cooling the material gas depressurized by expansion in the first expander; a distillation unit ( 15 ) for reducing or eliminating a heavy component in the material gas by distilling the material gas cooled by the first cooling unit; a first compressor ( 4 ) for compressing the material gas from which the heavy component was reduced or eliminated by the distillation unit by using the power generated in the first expander; a second heat exchanger for exchanging heat between the material gas introduced into the first compressor and the material gas compressed by the first compressor; and a liquefaction unit ( 21 ) for liquefying the material gas compressed by the first compressor by exchanging heat with a refrigerant.

1 . A method for cooling a natural gas feed comprising:
 a) reducing the pressure of the natural gas feed to produce a reduced pressure material gas;   b) removing heavy components from the reduced pressure material gas to produce a top fraction and a bottom fraction;   c) cooling the top fraction to produce a cooled top fraction;   d) separating the cooled top fraction into a gas phase component and a liquid phase component;   e) increasing the pressure of the gas phase component to produce a compressed material gas; and   f) exchanging heat between the gas phase component and the compressed material gas to produce at least a cooled compressed material gas.   
     
     
         2 . The method of  claim 1  further comprising cooling the reduced pressure material gas of step (a) prior to removing heavy components in step (b). 
     
     
         3 . The method of  claim 1  further comprising at least partially liquefying the cooled compressed material gas of step (f). 
     
     
         4 . The method of  claim 1  further comprising cooling the compressed material gas of step (e) prior to step (f). 
     
     
         5 . The method of  claim 1  wherein the top fraction is cooled in step (c) by introducing the top fraction in a warm region of a spool wound heat exchanger. 
     
     
         6 . The method of  claim 5  wherein the cooled compressed material gas of step (f) is further cooled by introducing the cooled compressed material gas in an intermediate region of the spool wound heat exchanger. 
     
     
         7 . The method of  claim 1  wherein the removal of heavy components in step (b) is performed in a distillation unit. 
     
     
         8 . The method of  claim 7  further comprising recirculating the liquid phase component of step (d) to the distillation unit. 
     
     
         9 . The method of  claim 1  further comprising exchanging heat between the top fraction of step (b) and the reduced pressure material gas prior to step (c). 
     
     
         10 . The method of  claim 1  wherein step (f) comprises exchanging heat between the gas phase component of step (d), the compressed material gas of step (e), and the reduced pressure material gas of step (a). 
     
     
         11 . A method for cooling a natural gas feed comprising:
 a) reducing the pressure of the natural gas feed to produce a reduced pressure material gas;   b) removing heavy components from the reduced pressure material gas to produce a top fraction and a bottom fraction;   c) exchanging heat between the reduced pressure material gas and the top fraction to produce at least a heat exchanged top fraction;   d) cooling the heat exchanged top fraction to produce a cooled top fraction;   e) separating the cooled top fraction into a gas phase component and a liquid phase component;   f) increasing the pressure of the gas phase component to produce a compressed material gas; and   g) cooling the compressed material gas.   
     
     
         12 . The method of  claim 11  further comprising cooling the reduced pressure material gas of step (a) prior to removing heavy components in step (b). 
     
     
         13 . The method of  claim 11  wherein the compressed material gas is cooled in step (g) by introducing the compressed material gas in one or more heat exchangers. 
     
     
         14 . The method of  claim 11  wherein the removal of heavy components in step (b) is performed in a distillation unit. 
     
     
         15 . The method of  claim 14  further comprising recirculating the liquid phase component of step (e) to the distillation unit. 
     
     
         16 . A method for cooling a natural gas feed comprising:
 a) reducing the pressure of the natural gas feed to produce a reduced pressure material gas;   b) removing heavy components from the reduced pressure material gas to produce a top fraction and a bottom fraction;   c) cooling the top fraction to produce a cooled top fraction;   d) separating the cooled top fraction into a gas phase component and a liquid phase component;   e) increasing the pressure of the gas phase component to produce a compressed material gas; and   f) exchanging heat between the reduced pressure material gas and the compressed material gas of step prior to step (b) to produce at least a heat exchanged compressed material gas.   
     
     
         17 . The method of  claim 16  further comprising cooling the reduced pressure material gas of step (a) prior to exchanging heat in step (f). 
     
     
         18 . A method for cooling a natural gas feed comprising:
 a) reducing the pressure of the natural gas feed to produce a reduced pressure material gas;   b) removing heavy components from the reduced pressure material gas in a distillation unit to produce a top fraction and a bottom fraction;   c) cooling and partially liquefying the top fraction to produce a cooled top fraction;   d) separating the cooled top fraction to produce a gas phase component and a liquid phase component;   e) recirculating the liquid phase component to the distillation unit;   f) exchanging heat between the reduced pressure material gas and the gas phase component to produce at least a heat exchanged gas phase component; and   g) increasing the pressure of the heat exchanged gas phase component to produce a compressed material gas.   
     
     
         19 . The method of  claim 18  further comprising cooling the reduced pressure material gas of step (a) prior to exchanging heat in step (f). 
     
     
         20 . A method for cooling a natural gas feed comprising:
 a) reducing the pressure of the natural gas feed to produce a reduced pressure material gas;   b) removing heavy components from the reduced pressure material gas to produce a top fraction and a bottom fraction;   c) increasing the pressure of the top fraction to produce a compressed material gas; and   d) exchanging heat between the top fraction and the compressed material gas to produce at least a cooled compressed material gas.   
     
     
         21 . The method of  claim 20  further comprising cooling the reduced pressure material gas of step (a) prior to step (b). 
     
     
         22 . The method of  claim 20  further comprising cooling the compressed material gas of step (c) prior to exchanging heat in step (d). 
     
     
         23 . A system for liquefaction of a natural gas feed comprising:
 a first expander to reduce the pressure of the natural gas feed to produce a reduced pressure material gas;   a distillation unit for removing heavy components from the reduced pressure material gas to produce a top fraction and a bottom fraction;   a first heat exchanger for cooling the top fraction to produce a cooled top fraction;   a first gas-liquid separation vessel to separate the cooled top fraction into a gas phase component and a liquid phase component;   a first compressor for compressing the gas phase component to produce a compressed material gas; and   a second heat exchanger for exchanging heat between the gas phase component and the compressed material gas.   
     
     
         24 . The system of  claim 23  further comprising a first cooling unit for cooling the reduced pressure material gas prior to introduction in the distillation unit. 
     
     
         25 . The system of  claim 23  further comprising a second cooling unit for cooling the compressed material gas prior to introduction in the second heat exchanger. 
     
     
         26 . The system of  claim 23  wherein the first heat exchanger is a warm region of a spool wound heat exchanger. 
     
     
         27 . The system of  claim 26  further comprising a third heat exchanger for cooling the compressed material gas after the compressed material gas passes through the second heat exchanger; wherein the third heat exchanger is an intermediate region of the spool wound heat exchanger. 
     
     
         28 . The system of  claim 23  further comprising piping to recirculate the liquid phase component from the first gas-liquid separation vessel as reflux to the distillation unit. 
     
     
         29 . The system of  claim 23  further comprising a fourth heat exchanger for exchanging heat between the top fraction from the distillation unit and the reduced pressure material gas. 
     
     
         30 . The system of  claim 23  wherein the second heat exchanger exchanges heat between the gas phase component, the compressed material gas, and the reduced pressure material gas. 
     
     
         31 . The system of  claim 23  wherein the first expander generates power, and the first compressor uses the power generated by the first expander. 
     
     
         32 . A system for liquefaction of a natural gas feed comprising:
 a first expander to reduce the pressure of the natural gas feed to produce a reduced pressure material gas;   a distillation unit for removing heavy components from the reduced pressure material gas to produce a top fraction and a bottom fraction;   a first heat exchanger for exchanging heat between the top fraction and the reduced pressure material gas to produce at least a heat exchanged top fraction;   a second heat exchanger for cooling the heat exchanged top fraction to produce a cooled top fraction;   a first gas-liquid separation vessel to separate the cooled top fraction into a gas phase component and a liquid phase component; and   a first compressor for compressing the gas phase component to produce a compressed material gas.   
     
     
         33 . The system of  claim 32  further comprising a first cooling unit for cooling the reduced pressure material gas prior to introduction in the distillation unit. 
     
     
         34 . A system for liquefaction of a natural gas feed comprising:
 a first expander to reduce the pressure of the natural gas feed to produce a reduced pressure material gas;   a first cooling unit for cooling the reduced pressure material gas to produce a cooled reduced pressure material gas;   a distillation unit for removing heavy components from the cooled reduced pressure material gas to produce a top fraction and a bottom fraction;   a warm region of a spool wound heat exchanger for cooling the top fraction to produce a cooled top fraction;   a first gas-liquid separation vessel to separate the cooled top fraction into a gas phase component and a liquid phase component;   a piping system for recirculating the liquid phase component to the distillation unit;   a first compressor for compressing the gas phase component to produce a compressed material gas;   a second cooling unit for cooling the compressed material gas to produce a cooled compressed material gas;   a third heat exchanger for exchanging heat between the cooled compressed material gas and the gas phase component to produce a further cooled compressed material gas; and   an intermediate region of the spool wound heat exchanger for at least partially liquefying the further cooled compressed material gas.