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

Abstract

The device (400) for liquefying a natural gas comprises: a compressor (105) of a first vaporized coolant chemical mixture, a means (110) for fractionating the compressed mixture into a heavy fraction and a light fraction, —a first body (115) for exchanging heat between the heavy fraction of the first mixture and the natural gas to cool at least the natural gas, a second body (120) for exchanging heat between the light fraction of the first mixture and the natural gas cooled in the first exchange body to liquefy the natural gas, —a conduit (125) for returning the first vaporized coolant mixture in the heat exchange bodies to the compressor, —a regulator (405) for the liquefied natural gas, a collector (410) for the evaporation gas produced during the expansion of the gas in the regulator, —a conduit (415) for injecting the evaporation gas at the inlet of the second exchange body, upstream of an inlet (116) for the natural gas in the first exchange body (115), a third body (420) for exchanging heat between the natural gas and a second chemical coolant compound, —a means (425) for compressing the second vaporized compound, a means (430) for cooling the second compressed compound and a conduit (435) for transferring the second cooled compound towards the third exchange body.

1 . A device for liquefying a natural gas, comprising:
 a compressor of a first vaporized coolant chemical mixture,   a means for fractionating the compressed mixture into a heavy fraction and a light fraction,   a first body for 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 body for exchanging heat between the light fraction of the first mixture and the natural gas cooled in the first exchange body to liquefy the natural gas, and   a conduit for returning the first coolant mixture vaporized in the heat exchange bodies to the compressor,   
       characterized in that it comprises:
 a regulator for the liquefied natural gas, 
 a collector for the evaporation gas produced during the expansion of the gas in the regulator, 
 a conduit for injecting the evaporation gas at the inlet of the second exchange body, 
 upstream of an inlet for the natural gas in the first exchange body, a third body for exchanging heat between the natural gas and a second coolant chemical compound, 
 a means for compressing the second vaporized compound, 
 a means for cooling the second compressed compound, and 
 a conduit for transferring the second cooled compound towards the third exchange body. 
 
     
     
         2 . A device according to  claim 1 , which comprises, between an outlet for the second compound of the means for cooling the second compound and the third exchange body, a circuit for cooling the second compound with the heavy fraction of the first mixture inside the first exchange body. 
     
     
         3 . A device according to  claim 1 , wherein the second compound is a pure substance which comprises propane and/or ammonia. 
     
     
         4 . A device according to  claim 1 , wherein the means for cooling the second compound is an exchanger of heat between the second compound and water. 
     
     
         5 . A device according to  claim 1 , wherein the first cooling mixture comprises nitrogen and methane and at least one compound amongst:
 ethylene;   ethane;   propane; and/or   butane.   
     
     
         6 . A device according to  claim 1 , wherein the first exchange body and/or the second exchange body is a coil exchanger. 
     
     
         7 . A ship, characterized in that it comprises a device for liquefying a natural gas according to  claim 1 . 
     
     
         8 . A method for liquefying a natural gas, comprising:
 a step of compressing a first vaporized coolant chemical mixture,   a step of fractionating the compressed mixture into a heavy fraction and a light fraction,   a first step 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 of exchanging heat between the light fraction of the first mixture and the natural gas cooled during the first exchange step to liquefy the natural gas, and   a step of returning the first coolant mixture vaporized in the heat exchange bodies to the compressor step,   
       characterized in that it comprises:
 a step of expanding the liquefied natural gas; 
 a step of collecting evaporation gas produced during the expansion step; and 
 a step of injecting the evaporation gas at the inlet of the second exchange body. 
 upstream of a step of inputting the natural gas into the first exchange step, a third step of exchanging heat between the natural gas and a second coolant chemical compound; 
 a step of compressing the second vaporized compound. 
 a step of cooling the second compressed compound; and 
 a step of transferring the second cooled compound towards the third exchange body.