Method and apparatus for liquefying a hydrocarbon stream

Abstract

Method of liquefying a hydrocarbon stream such as natural gas from a feed stream ( 10 ), the method at least comprising the steps of: (a) circulating a first refrigerant stream ( 70 ) in a first refrigerant circuit ( 110 ); (b) cooling the first refrigerant stream ( 70 ) in one or more heat exchangers ( 14 ) of a first cooling stage ( 100 ) to provide a cooled first refrigerant stream ( 20 ); (c) passing at least part of the cooled first refrigerant stream ( 20 ) through one or more expanders to provide one or more expanded cooled first refrigerant streams ( 30 ); (d) passing the or at least one of the expanded cooled first refrigerant streams ( 30 ) and the feed stream ( 10 ) through the first one or more heat exchangers ( 14 ) to provide a cooled hydrocarbon stream ( 40 ); (e) passing the cooled hydrocarbon stream ( 40 ) through a second cooling stage ( 200 ) against a second refrigerant stream ( 50 ) to provide a liquefied hydrocarbon stream ( 60 ); wherein at least one expander is an expansion turbine ( 12 ) whose work energy created in step (c) is used in the first refrigerant circuit ( 110 ).

1 .- 15 . (canceled) 
     
     
         16 . A method of liquefying a hydrocarbon stream from a feed stream, the method at least comprising the steps of:
 (a) circulating a first refrigerant stream in a first refrigerant circuit;   (b) cooling the first refrigerant stream in one or more heat exchangers of a first cooling stage to provide a cooled first refrigerant stream;   (c) passing at least part of the cooled first refrigerant stream through one or more expanders to provide one or more expanded cooled first refrigerant streams;   (d) passing the or at least one of the expanded cooled first refrigerant streams and the feed stream through the first one or more heat exchangers to provide a cooled hydrocarbon stream;   (e) passing the cooled hydrocarbon stream through a second cooling stage against a second refrigerant stream to provide a liquefied hydrocarbon stream;   
       wherein at least one expander is an expansion turbine whose work energy created in step (c) is used in the first refrigerant circuit, wherein the created work energy is used to drive one or more pumps circulating the first refrigerant stream to increase the pressure of the first refrigerant stream thereby providing a pumped stream, the method further comprising reducing the temperature of the pumped stream in one or more ambient coolers prior to the first heat exchanger. 
     
     
         17 . The method according to  claim 16  wherein the temperature of the cooled hydrocarbon stream after the first cooling stage is in the range −20° C. to −70° C., and wherein the second cooling stage is separate from the first cooling stage. 
     
     
         18 . The method according to  claim 16  wherein the first refrigerant stream is a re-condensed stream obtained by compressing vapourized refrigerant collected and outflowed from the one or more heat exchangers of the first cooling stage and subsequent cooling by a water and/or air cooler. 
     
     
         19 . The method according to  claim 16  wherein the second cooling stage is separate from the first cooling stage whereby the second cooling stage comprises one or more separate heat exchangers using a second refrigerant circulating in a second refrigerant circuit. 
     
     
         20 . The method according to  claim 19  wherein the refrigerant of the second refrigerant stream also passes through at least one heat exchanger of the first cooling stage. 
     
     
         21 . The method according to  claim 16  wherein each expander in step (c) is an expansion turbine. 
     
     
         22 . The method according to  claim 16  wherein the first cooling stage comprises two or three heat exchangers. 
     
     
         23 . The method according to  claim 22  wherein each heat exchanger has an associated expansion turbine through which at least a part of the first cooled refrigerant stream passes to provide an expanded cooled first refrigerant stream to its respective heat exchanger. 
     
     
         24 . The method according to  claim 22  wherein each heat exchanger of the first cooling stage involves a different first refrigerant pressure for step (c). 
     
     
         25 . The method according to  claim 16  wherein the refrigerant of the first refrigerant stream is a mixed refrigerant comprising a mixture of gases, said gases selected from the group comprising nitrogen, methane, ethane, ethylene, propane, propylene, butane and pentane. 
     
     
         26 . The method according to  claim 16  wherein the refrigerant of the second refrigerant stream passes through all the heat exchangers of the first cooling stage. 
     
     
         27 . An apparatus for liquefying a hydrocarbon stream from a feed stream, the apparatus at least comprising:
 a first refrigerant circuit circulating a first refrigerant stream;   a first cooling stage having one or more heat exchangers to receive the first refrigerant stream and to provide a cooled first refrigerant stream;   one or more expanders to expand at least a part of the cooled first refrigerant stream to provide one or more expanded first refrigerant streams, at least one expander being an expansion turbine whose work energy created by the expansion is used in the first refrigerant circuit;   one or more pumps to circulate the first refrigerant stream, wherein the work energy created by the expansion is used to drive one or more of the pumps;   one or more ambient coolers downstream of the one or more pumps and prior to the first one or more heat exchangers;   the or each heat exchanger having a first inlet to pass the feed stream thereinto, and a second inlet to pass the or at least one of the expanded first refrigerant streams thereinto to cool the feed stream and so provide a cooled hydrocarbon stream; and   a second cooling stage comprising one or more heat exchangers arranged to receive the cooled hydrocarbon stream from the first cooling stage and to provide a liquefied hydrocarbon stream.   
     
     
         28 . The apparatus according to  claim 27  wherein the first cooling stage comprises two or more heat exchangers, each having an associated expansion turbine. 
     
     
         29 . The apparatus according to  claim 27  further comprising a compressor and a water and/or air cooler upstream of the one or more pumps. 
     
     
         30 . The apparatus according to  claim 27  wherein the first cooling stage provides a cooled first refrigerant stream having a temperature in the range −20° C. to −70° C., and wherein the second cooling stage is separate from the first cooling stage. 
     
     
         31 . The apparatus according to  claim 27  wherein the second cooling stage is separate from the first cooling stage whereby the second cooling stage comprises one or more separate heat exchangers using a second refrigerant circulating in a second refrigerant circuit. 
     
     
         32 . The apparatus according to  claim 31  wherein the refrigerant of the second refrigerant stream also passes through at least one heat exchanger of the first cooling stage. 
     
     
         33 . The method according to  claim 17  wherein the first refrigerant stream is a re-condensed stream obtained by compressing vapourized refrigerant collected and outflowed from the one or more heat exchangers of the first cooling stage and subsequent cooling by a water and/or air cooler. 
     
     
         34 . The method according to  claim 17  wherein the second cooling stage is separate from the first cooling stage whereby the second cooling stage comprises one or more separate heat exchangers using a second refrigerant circulating in a second refrigerant circuit. 
     
     
         35 . The method according to  claim 18  wherein the second cooling stage is separate from the first cooling stage whereby the second cooling stage comprises one or more separate heat exchangers using a second refrigerant circulating in a second refrigerant circuit.