Method and installation for the production of a liquefied cryogenic fluid

Abstract

A method for producing a liquefied cryogenic fluid such as liquefied natural gas from a gaseous stream of gas that is to be cooled containing at least methane and heavy hydrocarbons containing 6 or more carbon atoms, including the steps of mixing the gaseous stream of gas that is to be cooled with part of the liquefied cryogenic fluid withdrawn from downstream of a liquefier, to form a two-phase stream. In a tank such as a phase separator, separating the two-phase stream into a gaseous first fraction and a liquid second fraction containing the majority of the heavy hydrocarbons, containing 6 or more carbon atoms, of the gaseous stream of gas that is to be cooled. Introducing the gaseous first fraction into the liquefier to produce the liquefied cryogenic fluid.

What is claimed is: 
     
         1 . A method for producing a liquefied cryogenic fluid such as liquefied natural gas from a gaseous stream of gas that is to be cooled containing at least methane and heavy hydrocarbons containing 6 or more carbon atoms, in an installation for producing a liquefied cryogenic fluid, the method comprising the steps of:
 mixing the gaseous stream of gas that is to be cooled with part) of the liquefied cryogenic fluid withdrawn from downstream of a liquefier, to form a two-phase stream;   in a tank such as a phase separator, separating the two-phase stream into a gaseous first fraction and a liquid second fraction, the liquid second fraction containing the majority of the heavy hydrocarbons, containing 6 or more carbon atoms, of the gaseous stream of gas that is to be cooled;   introducing the gaseous first fraction into the liquefier to produce the liquefied cryogenic fluid;   increasing the pressure of the part of the liquefied cryogenic fluid before mixing with the gaseous stream of gas that is to be cooled, by means of a hydrostatic head.   
     
     
         2 . The method according to  claim 1 , wherein the step of mixing the gaseous stream of gas that is to be cooled with the part of the liquefied cryogenic fluid is performed upstream of the tank before the two-phase stream is introduced into the tank. 
     
     
         3 . The method according to  claim 1 , wherein the step of mixing the gaseous stream of gas that is to be cooled with the part of the liquefied cryogenic fluid is performed by injecting the part of the liquefied cryogenic fluid into the tank. 
     
     
         4 . The method according to  claim 1 , further comprising a step of pre-cooling the stream of gas that is to be cooled before mixing with the part of the liquefied cryogenic fluid. 
     
     
         5 . The method according to  claim 1 , further comprising a step of expanding the gaseous stream of gas that is to be cooled. 
     
     
         6 . An installation for producing a liquefied cryogenic fluid from a gaseous stream of gas that is to be cooled containing at least methane and heavy hydrocarbons containing 6 or more carbon atoms, comprising:
 a circuit for gas that is to be cooled and having an upstream end configured to be connected to the gaseous stream of gas that is to be cooled and a downstream end for delivering the liquefied cryogenic fluid;   a tank, in the circuit for gas that is to be cooled, the installation being configured so that the tank receives the gaseous stream of gas that is to be cooled and part of the liquefied cryogenic fluid so as to form a two-phase stream and/or the installation being configured so that the tank receives a two-phase stream derived from the mixing-together of the gaseous stream of gas that is to be cooled and the part of the liquefied cryogenic fluid, the tank being configured to allow the two-phase stream to be separated into a gaseous first fraction and a liquid second fraction containing the majority of the heavy hydrocarbons, containing 6 or more carbon atoms, of the gaseous stream of gas that is to be cooled;   a liquefier configured to cool the gaseous first fraction and produce the liquefied cryogenic fluid, the installation being configured to create a hydrostatic head between a withdrawal point at which the part of the liquefied cryogenic fluid is withdrawn and a mixing point at which the withdrawn part of the liquefied cryogenic fluid is mixed with the gaseous stream of gas that is to be cooled.   
     
     
         7 . The installation according to  claim 6 , further comprising a compression member, the compression member being positioned in a loop of the circuit for gas that is to be cooled, and configured to be able to raise the pressure of the part of the liquefied cryogenic fluid before mixing with the gaseous stream of gas that is to be cooled. 
     
     
         8 . The installation according to  claim 6 , further comprising an expansion member comprising at least a valve and/or an ejector, the expansion member being configured to expand the gaseous stream of gas that is to be cooled and being positioned upstream of the tank.