Device and method for liquefying a natural gas and ship comprising such a device

Abstract

The device ( 100 ) for liquefying a natural gas comprises: a compressor ( 105 ) for a first vaporized coolant chemical mixture, a means ( 110 ) for fractionating the compressed mixture into a heavy fraction and a light fraction, a first heat exchange body ( 115 ) for heat exchange between the heavy fraction of the first mixture and the natural gas in order to cool at least the natural gas, a second heat exchange body ( 120 ) for heat exchange between the light fraction of the first mixture and the cooled natural gas in the first exchange body in order to liquefy the natural gas, and a return pipe ( 125 ) for return of the first vaporized coolant mixture in the heat exchange body to the compressor ( 105 ), upstream from an inlet ( 116 ) for the natural gas in the first exchange body ( 115 ) or downstream from an outlet ( 121 ) of liquefied natural gas from the second exchange body ( 120 ), a third heat exchange body ( 130, 135 ) for heat exchange between the natural gas and a second coolant chemical compound, and a means ( 140, 145 ) for compressing the second vaporized compound.

1 . Device ( 100 ) for liquefying a natural gas, comprising:
 a compressor ( 105 ) for a first vaporized coolant chemical mixture,   a means ( 110 ) for fractionating the compressed mixture into a heavy fraction and a light fraction,   a first heat exchange body ( 115 ) for heat exchange between the heavy fraction of the first mixture and the natural gas in order to cool at least the natural gas,   a second heat exchange body ( 120 ) for heat exchange between the light fraction of the first mixture and the cooled natural gas in the first exchange body in order to liquefy the natural gas, and   a return conduit ( 125 ) for return of the first vaporized coolant mixture in the heat exchange body to the compressor ( 105 ),   
       characterized in that it comprises:
 upstream from an inlet ( 116 ) for the natural gas in the first exchange body ( 115 ) or downstream from an outlet ( 121 ) of liquefied natural gas from the second exchange body ( 120 ), a third heat exchange body ( 130 ,  135 ) for heat exchange between the natural gas and a second coolant chemical compound, and 
 a means ( 140 ,  145 ) for compressing the second vaporized compound. 
 
     
     
         2 . Device ( 100 ) according to  claim 1 , wherein the third exchange body ( 130 ) is positioned upstream from the inlet ( 116 ) for the natural gas in the first exchange body ( 115 ), the device ( 100 ) comprising:
 a means ( 150 ) for cooling the second compressed compound; and   a conduit ( 155 ) for transferring the second cooled compound to the third exchange body ( 130 ).   
     
     
         3 . Device ( 100 ) according to  claim 2 , wherein the second compound is a pure substance composed of nitrogen, propane and/or ammonia or a mixture of nitrogen and propane. 
     
     
         4 . Device ( 100 ) according to one of  claims 1  to  3 , wherein the first cooling mixture comprises nitrogen and methane and at least one compound amongst:
 ethylene; 
 ethane; 
 propane; and/or 
 butane. 
 
     
     
         5 . Device ( 100 ) according to one of  claims 1  to  4 , wherein the third exchange body ( 130 ) is positioned upstream from the inlet ( 116 ) for the natural gas in the first exchange body ( 115 ), the device ( 100 ) comprising, downstream from the outlet ( 121 ) for liquefied natural gas from the second exchange body ( 120 ):
 a fourth body ( 135 ) for exchanging heat between the liquefied natural gas and the nitrogen; 
 a means ( 145 ) for compressing the vaporized nitrogen; 
 a means ( 160 ) for cooling the compressed nitrogen; and 
 a conduit ( 165 ) for transporting the cooled nitrogen to the fourth exchange body. 
 
     
     
         6 . Device ( 100 ) according to  claim 5 , wherein the means ( 150 ) for cooling the second compound is an exchanger of heat between the second compound and water. 
     
     
         7 . Device ( 100 ) according to one of  claims 1  to  6 , which comprises, between an outlet ( 131 ) for the second compound of the means ( 150 ) for cooling the second compound and the third exchange body ( 130 ), a circuit ( 170 ) for cooling the second compound with the heavy fraction of the first mixture inside the first exchange body ( 115 ). 
     
     
         8 . Device ( 100 ) according to  claim 7 , wherein one portion of the cooling circuit ( 170 ) is configured to cool the second compound by exchanging heat with the light fraction of the first mixture in the second exchange body ( 120 ). 
     
     
         9 . Device ( 100 ) according to one of  claims 1  to  8 , wherein the first exchange body ( 115 ) and/or the second exchange body ( 120 ) is a coil exchanger. 
     
     
         10 . Ship ( 200 ), characterized in that it comprises a device ( 100 ) for liquefying a natural gas according to one of  claims 1  to  9 . 
     
     
         11 . Method ( 300 ) for liquefying a natural gas, comprising:
 a step ( 305 ) of compressing a first vaporized coolant chemical mixture,   a step ( 310 ) of fractionating the compressed mixture into a heavy fraction and a light fraction,   a first step ( 315 ) of exchanging heat between the heavy fraction of the first mixture and the natural gas in order to cool at least the natural gas,   a second step ( 320 ) of exchanging heat between the light fraction of the first mixture and the natural gas cooled during the first exchange step in order to liquefy the natural gas, and   a step ( 325 ) of returning the first coolant mixture vaporized in the heat exchange bodies to the compressor step,   
       characterized in that it comprises:
 before an input of the natural gas of the first exchange step or after an output of liquefied natural gas from the second exchange step, a third step ( 330 ) of exchanging heat between the natural gas and a second coolant chemical compound, and 
 a step ( 335 ) of compressing the second vaporized compound.