Method and apparatus for cooling and liquefying a hydrocarbon stream

Abstract

Method of driving two or more refrigerant compressors in a hydrocarbon cooling process. In such a hydrocarbon cooling process a hydrocarbon feed stream ( 10 ) may be passed against partly evaporating refrigerant streams. The at least partly evaporated refrigerant streams ( 35 a, 37 a ) are compressed through refrigerant compressors ( 34, 36 ). One or more gas turbines ( 54 ) are driven to provide electrical power ( 56 ) and hot gas. The hot gas ( 57 ) is passed through one or more steam heat exchangers ( 58 ) to provide steam power, which is used to drive one or more steam turbines ( 82 ) to drive at least one of the refrigerant compressors ( 34 ). The electrical power is used to drive ( 76 ) at least another one of the refrigerant compressors ( 36 ).

1 . A method of cooling and liquefying a hydrocarbon stream on one of the croup consisting of a floating vessel and an off-shore platform, the method comprising at least the steps of:
 (a) passing a hydrocarbon feed stream against at least two refrigerant streams to provide a cooled liquefied hydrocarbon stream and at least two at least partly evaporated refrigerant streams;   (b) compressing at least one of the at least two at least partly evaporated refrigerant streams through at least one first refrigerant compressor;   (c) compressing at least the one other of the at least two at least partly evaporated refrigerant streams through at least one second refrigerant compressor;   (d) driving at least one gas turbine to provide:   (i) electrical power; and   (ii) hot gas;   (e) passing the hot gas of step (d)(ii) through at least one steam heat exchanger to provide steam power;   (f) using the electrical power to drive at least one second refrigerant compressor; and   (g) using the steam power to drive at least one steam turbine to drive at least one first refrigerant compressor;   
       the method being carried out on one of the group consisting of a floating vessel and an off-shore platform comprising at least one storage tank for liquefied hydrocarbons and/or components for the refrigerants, whereby the at least one gas turbine is driven in a turbine-assembly area being located on or within the floating vessel or off-shore platform and remotely from the first and second refrigerant compressors and from the at least one storage tank. 
     
     
         2 . The method as claimed in  claim 1 , wherein at least one of the at least one second refrigerant compressor is a cryogenic refrigerant compressor. 
     
     
         3 . The method as claimed in  claim 1 , wherein at least one of the at least one first refrigerant compressor is a pre-cooling refrigerant compressor. 
     
     
         4 . The method as claimed in  claim 1 , wherein the method further comprises at least one further treatment step of at least one of the group consisting of the hydrocarbon feed stream prior to step (a) and the cooled hydrocarbon stream of step (a), such further treatment step(s) involving at least one further compressor, and wherein at least one of the electrical power and the steam power drive at least one of the further compressor(s). 
     
     
         5 . The method as claimed in  claim 4 , wherein the at least one of the further compressor(s) is for compressing at least one stream other than the at least partly evaporated refrigerant stream(s) of step (b) and step (c). 
     
     
         6 . The method as claimed in  claim 1 , further comprising at least one further providers of steam power or electrical power. 
     
     
         7 . The method as claimed in  claim 1 , wherein remotely means at least 50 meters distant. 
     
     
         8 . The method as claimed in  claim 1 , wherein the liquefied hydrocarbon stream has nominal capacity in the range 1 to 10 MTPA. 
     
     
         9 . The method as claimed in  claim 1 , involving at least a first cooling stage and a second cooling stage, and wherein the refrigerant streams for the first and second cooling stages are mixed refrigerants. 
     
     
         10 . The method as claimed in  claim 1 , wherein at least one of the at least one steam turbine of step (g) is a condensing steam turbine. 
     
     
         11 . The method as claimed in  claim 1 , wherein the one of the group consisting of the floating vessel and off-shore platform is less than 600 m long and less than 100 m wide. 
     
     
         12 . The method as claimed in  claim 1 , wherein step (a) comprises a first cooling stage wherein the hydrocarbon feed stream is pre-cooled against at least one first refrigerant stream to provide a cooled hydrocarbon stream and at least one at least partly evaporated first refrigerant stream that is compressed in step (b) and a second cooling stage separate from the first cooling stage, wherein the temperature of the cooled hydrocarbon stream is reduced by at least one second refrigerant stream, to provide a liquefied hydrocarbon stream and at least one at least partly evaporated second refrigerant stream that is compressed in step (c). 
     
     
         13 . The method as claimed in  claim 1 , wherein the hydrocarbon stream comprises, or essentially consists of, natural gas. 
     
     
         14 . A floating vessel comprising an apparatus for cooling and liquefying a hydrocarbon stream on or within the floating vessel, the apparatus comprising:
 at least two cooling stages through which a hydrocarbon feed stream passes against at least two refrigerant streams to provide a cooled and liquefied hydrocarbon stream and at least two at least partly evaporated refrigerant streams;   at least one first refrigerant compressor to compress at least one of the at least two at least partly evaporated refrigerant streams;   at least one second refrigerant compressor to compress at least one other of the at least two at least partly evaporated refrigerant streams;   at least one gas turbine to provide:   
       (i) electrical power to drive at least one of the second refrigerant compressor(s); and 
       (ii) hot gas;
 at least one steam heat exchanger to provide steam power from the hot gas; 
 at least one steam turbine driven by the steam power to drive at least one of the first refrigerant compressor(s); 
 at least one storage tank for liquefied hydrocarbons and/or components for the refrigerants, 
 
       whereby the at least one gas turbine is located in a turbine-assembly area which is located remotely from the first and second refrigerant compressors and from the at least one storage tank. 
     
     
         15 . The floating vessel as claimed in  claim 14 , wherein remotely means at least 50 meters distant. 
     
     
         16 . The floating vessel as claimed  claim 14 , further comprising at least one further treatment step of the hydrocarbon stream involving at least one further compressor compressing at least one stream other than the at least partly evaporated refrigerant stream(s), wherein the at least one further compressor is driven using at least one of the electrical power and the steam power. 
     
     
         17 . An off-shore platform comprising an apparatus for cooling and liquefying a hydrocarbon stream on or within the off-shore platform, the apparatus comprising:
 at least two cooling stages through which a hydrocarbon feed stream passes against at least two refrigerant streams to provide a cooled and liquefied hydrocarbon stream and at least two at least partly evaporated refrigerant streams;   at least one first refrigerant compressor to compress at least one of the at least two partly evaporated refrigerant streams;   at least one second refrigerant compressor to compress at least one other of the at least two partly evaporated refrigerant streams;   at least one gas turbine to provide:   
       (i) electrical power to drive at least one of the second refrigerant compressor(s); and 
       (ii) hot gas;
 at least one steam heat exchanger to provide steam power from the hot gas; 
 at least one steam turbine driven by the steam power to drive at least one of the first refrigerant compressor(s); 
 at least one storage tank for liquefied hydrocarbons and/or components for the refrigerants, 
 
       whereby the at least one gas turbine is located in a turbine-assembly area which is located remotely from the first and second refrigerant compressors and from the at least one storage tank. 
     
     
         18 . The off-shore platform as claimed in  claim 17 , wherein remotely means at least 50 meters distant. 
     
     
         19 . The off-shore platform as claimed  claim 17 , further comprising at least one further treatment step of the hydrocarbon stream involving at least one further compressor compressing at least one stream other than the at least partly evaporated refrigerant stream(s), wherein the at least one further compressor is driven using at least one of the electrical power and the steam power. 
     
     
         20 . Method as claimed in  claim 1 , wherein the liquefied hydrocarbon stream has nominal capacity in the range 3.5 to 7 MTPA.