Method and apparatus for cooling a hydrocarbon stream

Abstract

A method of liquefying natural gas from a feed stream ( 10 ) comprising at least the steps of: passing the feed stream ( 10 ) against a mixed refrigerant being cycled through a heat exchanger ( 12 ), to provide an at least partly liquefied hydrocarbon stream ( 20 ) having a temperature below −100° C.; outflowing the mixed refrigerant as a liquid and vapour outflow refrigerant stream ( 80 ) and passing it through a first separator ( 18 ) to provide a vapour refrigerant stream ( 90 ) and a liquid refrigerant stream ( 110 ); recycling without substantial heat exchange the liquid refrigerant stream ( 110 ) into the heat exchanger ( 12 ); compressing and cooling the vapour refrigerant stream ( 90 ) to provide a cooled compressed stream ( 100 ) having a temperature below 0° C. and recycling it into the heat exchanger ( 12 ).

1 . A method of liquefying a hydrocarbon stream from a feed stream comprising at least the steps of:
 (a) passing the feed stream against a mixed refrigerant being cycled through a heat exchanger, to provide an at least partly liquefied hydrocarbon stream having a temperature below −100° C.;   (b) outflowing the mixed refrigerant as a liquid and vapour outflow refrigerant stream from the heat exchanger;   (c) passing the liquid and vapour outflow refrigerant stream through a first separator to provide a vapour refrigerant stream and a liquid refrigerant stream;   (d) recycling without substantial heat exchange the liquid refrigerant stream of step (c) into the heat exchanger of step (a);   (e) compressing the vapour refrigerant stream to provide a refrigerant stream;   (f) cooling the compressed refrigerant stream to provide a cooled compressed stream having a temperature below 0° C.; and   (g) recycling the cooled compressed stream into the heat exchanger of step (a).   
   
   
       2 . A method as claimed in  claim 1  wherein the heat exchanger is a tube-in-shell heat exchanger or a spool-wound heat exchanger. 
   
   
       3 . A method as claimed in  claim 1  wherein the heat exchanger wholly liquefies the feed stream. 
   
   
       4 . A method as claimed in  claim 3  wherein the feed stream is natural gas and the liquefied hydrocarbon stream is liquefied natural gas. 
   
   
       5 . A method as claimed in  claim 1  wherein the liquid refrigerant stream is recycled into the heat exchanger via a pump. 
   
   
       6 . A method as claimed in  claim 1  wherein the temperature of the liquid refrigerant stream is in the range −30° C. to −50° C. 
   
   
       7 . A method as claimed in  claim 1  wherein the temperature difference between the liquid refrigerant stream and the cooled compressed stream is <10° C. 
   
   
       8 . A method as claimed in  claim 1  wherein the cooled compressed stream is separated prior to recycle into the heat exchanger to provide a vapour inflow refrigerant stream and a liquid inflow refrigerant stream. 
   
   
       9 . A method as claimed in  claim 8  wherein the liquid inflow refrigerant stream is combined with the liquid refrigerant stream of step (c). 
   
   
       10 . A method as claimed in  claim 9  wherein the temperature difference between the liquid refrigerant stream and the liquid inflow refrigerant stream is <10° C. 
   
   
       11 . An apparatus for liquefying a hydrocarbon stream from a feed stream, the apparatus at least comprising:
 a heat exchanger for liquefying the hydrocarbon stream against a mixed refrigerant stream, the heat exchanger having a feed inlet for the feed stream, a feed outlet for its at least partly liquefied stream, one or more mixed refrigerant inlets, and a mixed refrigerant outlet for a vapour and liquid refrigerant outflow stream;   a first separator for separating the liquid and vapour outflow refrigerant stream into a vapour and a liquid, the first separator having a first outlet to provide a vapour refrigerant stream and a second outlet to provide liquid refrigerant stream;   a refrigerant inlet in the heat exchanger to inflow the liquid refrigerant stream into the heat exchanger;   
     a compressor for compressing the vapour refrigerant stream to provide a compressed refrigerant stream; 
     one or more coolers for cooling the compressed refrigerant stream to provide a cooled compressed stream having a temperature below 0° C.; and 
     a pathway for recycling the cooled compressed stream into the heat exchanger. 
   
   
       12 . The apparatus as claimed in  claim 11  wherein a pump assists flow of the liquid refrigerant stream towards the heat exchanger. 
   
   
       13 . The apparatus as claimed in  claim 11  further comprising a second separator to separate the cooled compressed stream into a vapour inflow refrigerant stream and a liquid refrigerant inflow stream. 
   
   
       14 . The apparatus as claimed in  claim 13  wherein the apparatus further comprises a combiner to combine the liquid refrigerant inflow stream and the liquid refrigerant stream prior to their recycle in the heat exchanger. 
   
   
       15 . The apparatus as claimed in  claim 13  wherein the heat exchanger includes a first refrigerant line for the vapour refrigerant stream and a second refrigerant line for the liquid inflow refrigerant stream and the liquid refrigerant stream. 
   
   
       16 . A method as claimed in  claim 1  wherein the heat exchanger is a cryogenic heat exchanger. 
   
   
       17 . A method as claimed in  claim 2  wherein the heat exchanger wholly liquefies the feed stream. 
   
   
       18 . A method as claimed in  claim 2  wherein the liquid refrigerant stream is recycled into the heat exchanger via a pump. 
   
   
       19 . A method as claimed in  claim 3  wherein the liquid refrigerant stream is recycled into the heat exchanger via a pump. 
   
   
       20 . A method as claimed in  claim 4  wherein the liquid refrigerant stream is recycled into the heat exchanger via a pump.