Plant and Method for Liquefying Natural Gas

Abstract

The present invention relates to a plant ( 10 ) for liquefying natural gas ( 90 ), the plant ( 10 ) at least comprising: a pre-cooling heat exchanger train ( 1 ) comprising a final heat exchanger ( 2 a ) for cooling the natural gas stream ( 90 ); a distributor ( 4 ) located upstream of the final heat exchanger for splitting the natural gas stream ( 90 ) into at least first and second natural gas substreams; at least first and second main cryogenic systems ( 200,200′ ), each system ( 200,200′ ) comprising an outlet for liquefied natural gas ( 95,95′ ).

1 . A plant for liquefying natural gas, the plant at least comprising:
 a pre-cooling heat exchanger train comprising a final heat exchanger preceded by one or more heat exchangers, the final heat exchanger being provided with a pre-cooling refrigerant circuit for removing heat from the natural gas stream;   a distributor for splitting the natural gas stream into at least first and second natural gas substreams;   at least first and second main cryogenic systems, each system comprising a main heat exchanger having a first hot side having one inlet arranged to respectively receive the first and second natural gas substreams and an outlet for liquefied natural gas, and each system comprising a main refrigerant circuit for removing heat from the natural gas flowing through the first hot side of the corresponding main heat exchanger;   wherein the distributor is located upstream of the final heat exchanger.   
     
     
         2 . The plant according to  claim 1 , further comprising:
 at least two natural gas liquids extraction units each provided with an extraction unit inlet arranged to receive one of the natural gas substreams, and each comprising a heavy fraction outlet, and an overhead light fraction outlet;   the overhead light fraction outlets being connected to the inlets of the main cryogenic systems.   
     
     
         3 . The plant according to  claim 2 , wherein each of the natural gas liquids extraction units is provided with a reflux inlet arranged to receive a liquid reflux from a liquid reflux outlet of an overhead separator, which overhead separator is provided with an inlet in fluid communication with the overhead light fraction outlet and a vapour outlet in fluid communication with the corresponding main cryogenic heat exchanger. 
     
     
         4 . The plant of according to  claim 3 , wherein upstream of the overhead separator an overhead heat exchanger is provided for removing heat from the overhead light fraction, of which overhead heat exchanger the cold side is in fluid communication with at least one of the at least two main refrigerant circuits. 
     
     
         5 . The plant according to  claim 1 , wherein the final heat exchanger comprises two parallel heat exchangers, the plant further comprising:
 at least two natural gas liquids extraction units being present upstream of the parallel final heat exchangers.   
     
     
         6 . The plant according to  claim 1 , further comprising at least one end flash unit, connected to the outlets for liquefied natural gas of the at least two heat exchangers and comprising at least an outlet for end flash gas and an outlet for liquefied natural gas. 
     
     
         7 . The plant according to  claim 1 , wherein the distributor has at least two outlets. 
     
     
         8 . A method of liquefying a natural gas stream, the method at least comprising:
 (a) pre-cooling the natural gas stream in one or more stages including a final stage in a heat exchanger train against a pre-cooling refrigerant being cycled in a pre-cooling refrigerant circuit, wherein the heat exchanger train comprises a final heat exchanger preceded by one or more heat exchangers;   (b) splitting the natural gas stream into at least first and second natural gas substreams;   (c) further cooling the first and second natural gas substreams obtained in step (b) into full condensation against a main refrigerant in at least two main cryogenic systems, wherein in each main cryogenic system the main refrigerant is cycled in a main refrigerant circuit; and   (d) drawing a liquefied natural gas stream from the main cryogenic systems;   wherein the splitting of the natural gas stream into first and second natural substreams is effected upstream of the final pre-cooling stage.   
     
     
         9 . The method according to  claim 8 , wherein the first and second natural gas substreams obtained in step (b) are simultaneously separated in a liquid heavy fraction and a vaporous overhead light fraction, before further cooling of the vaporous overhead light fraction in step (c) into full condensation. 
     
     
         10 . The method according to  claim 9 , wherein further cooling in step (c) comprises partially condensing each of the vaporous overhead light fractions to form light condensate and light vapour, separating the light condensate from the light vapour, feeding the light condensate as a cold reflux into the step of simultaneously separating each of the first and second partially condensed natural gas substreams and further cooling the light vapour into full condensation. 
     
     
         11 . The method according to  claim 10 , wherein the partially condensing each of the vaporous overhead light fractions comprises indirect heat exchanging with the main refrigerant in at least one of the at least two main refrigerant circuits. 
     
     
         12 . The method according to  claim 8 , wherein the liquefied natural gas stream obtained in step (d) is subsequently expanded thereby obtaining a mixture comprising an even further cooled liquefied natural gas and a flash vapour, wherein the flash vapour is separated from the even further cooled liquefied natural gas, compressed, at least partly condensed and reinjected in the liquefied natural gas stream upstream of the separating the flash vapour. 
     
     
         13 . The plant according to  claim 2 , further comprising at least one end flash unit, connected to the outlets for liquefied natural gas of the at least two heat exchangers and comprising at least an outlet for end flash gas and an outlet for liquefied natural gas. 
     
     
         14 . The plant according to  claim 3 , further comprising at least one end flash unit, connected to the outlets for liquefied natural gas of the at least two heat exchangers and comprising at least an outlet for end flash gas and an outlet for liquefied natural gas. 
     
     
         15 . The plant according to  claim 4 , further comprising at least one end flash unit, connected to the outlets for liquefied natural gas of the at least two heat exchangers and comprising at least an outlet for end flash gas and an outlet for liquefied natural gas. 
     
     
         16 . The plant according to  claim 5 , further comprising at least one end flash unit, connected to the outlets for liquefied natural gas of the at least two heat exchangers and comprising at least an outlet for end flash gas and an outlet for liquefied natural gas. 
     
     
         17 . The plant according to  claim 2 , wherein the distributor has at least two outlets. 
     
     
         18 . The plant according to  claim 3 , wherein the distributor has at least two outlets. 
     
     
         19 . The plant according to  claim 4 , wherein the distributor has at least two outlets. 
     
     
         20 . The plant according to  claim 5 , wherein the distributor has at least two outlets. 
     
     
         21 . The plant according to  claim 6 , wherein the distributor has at least two outlets. 
     
     
         22 . The method according to  claim 9 , wherein the liquefied natural gas stream obtained in step (d) is subsequently expanded thereby obtaining a mixture comprising an even further cooled liquefied natural gas and a flash vapour, wherein the flash vapour is separated from the even further cooled liquefied natural gas, compressed, at least partly condensed and reinjected in the liquefied natural gas stream upstream of the separating the flash vapour. 
     
     
         23 . The method according to  claim 10 , wherein the liquefied natural gas stream obtained in step (d) is subsequently expanded thereby obtaining a mixture comprising an even further cooled liquefied natural gas and a flash vapour, wherein the flash vapour is separated from the even further cooled liquefied natural gas, compressed, at least partly condensed and reinjected in the liquefied natural gas stream upstream of the separating the flash vapour. 
     
     
         24 . The method according to  claim 11 , wherein the liquefied natural gas stream obtained in step (d) is subsequently expanded thereby obtaining a mixture comprising an even further cooled liquefied natural gas and a flash vapour, wherein the flash vapour is separated from the even further cooled liquefied natural gas, compressed, at least partly condensed and reinjected in the liquefied natural gas stream upstream of the separating the flash vapour.