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

Abstract

The device (600) for liquefying a natural gas comprises: —a first centrifugal compressor (605), —a fractionating means (110), —a second centrifugal compressor (610), —a first heat exchange body (115), —a second heat exchange body (120) and —a return conduit (125) leading to the first compressor, —upstream of an inlet (116) in the first exchange body, a third heat exchange body (420), —a third centrifugal compressor (620), the first and third centrifugal compressors being actuated by a single common turbine (630), —a casing (635) common to the first compressor and the third compressor, —a cooling means (430) and —a transfer conduit (435) leading to the third exchange body.

1 . A device for liquefying a natural gas, comprising:
 a first centrifugal 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 compressed light fraction of the first mixture and the natural gas cooled in the first exchange body in order to liquefy the natural gas, and   a conduit for returning the first coolant mixture vaporized in the heat exchange bodies to the first compressor,   
       characterized in that it comprises:
 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 third centrifugal compressor of the second vaporized compound, the first and third centrifugal compressor being actuated by a single common turbine, 
 a casing common to the first compressor and the third compressor, 
 a means for cooling the second compressed compound, 
 a conduit for transferring the second cooled compound towards the third exchange body, 
 between the second compressor and the second exchange body, a fourth centrifugal compressor of the light fraction of the first mixture, the second and fourth centrifugal compressor being actuated by a single common turbine, and 
 a casing common to the second compressor and the fourth compressor. 
 
     
     
         2 . A device according to  claim 1 , wherein the turbine actuating the first and third compressors are coupled mechanically. 
     
     
         3 . A device according to  claim 2 , wherein the turbines are combined. 
     
     
         4 . A device according to  claim 1 , which comprises:
 a separator of a gas fraction and a liquid fraction of the compressed light phase, the fourth compressor compressing the separated gas fraction,   a regulator for the liquid fraction of the light phase heated in the second exchange body,   the turbine of the fourth compressor being actuated by the expansion energy.   
     
     
         5 . A device according to  claim 1 , wherein the second chemical compound comprises a pure substance comprising nitrogen, propane and/or ammonia. 
     
     
         6 . 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.   
     
     
         7 . A device according to  claim 1 , which comprises:
 a regulator for the liquefied natural gas,   a collector for the evaporation gas produced during the expansion of the gas in the regulator, and   a conduit for injecting the evaporation gas at the inlet of the second exchange body.   
     
     
         8 . A device according to  claim 1 , wherein the means for cooling the second compound comprises an outlet for the second compound, the device comprising, between said outlet 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. 
     
     
         9 . A device according to  claim 1 , wherein the first exchange body and/or the second exchange body is a coil exchanger. 
     
     
         10 . 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. 
     
     
         11 . A method for liquefying a natural gas, comprising:
 a first step of centrifugal compression of a first vaporized coolant chemical mixture,   a step of fractionating the compressed mixture into a heavy fraction and a light fraction,   a second step of centrifugal compression of the 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 cooled natural gas in the first exchange body in order to liquefy the natural gas, and   a step of returning the first coolant mixture vaporized during the heat exchange steps to the first compression step,   
       characterized in that it comprises:
 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 third step of centrifugal compression of the second vaporized compound, the first and third centrifugal compression step being actuated by a single common turbine, 
 the first and third compression step being carried out in a common casing, 
 a step of cooling the second compound compressed during the third exchange step, 
 a step of transferring the second cooled compound towards the third exchange step, 
 between the second compression step and the second exchange step, a fourth step of centrifugal compression of the light fraction of the first mixture, the second and fourth centrifugal compression step being actuated by a single common turbine, and 
 the first and third compression step being carried out in a common casing.