Method and apparatus for treating a hydrocarbon stream and method of cooling a hydrocarbon stream

Abstract

Method and apparatus for treating a mixed hydrocarbon feed stream ( 10 ), such as a natural gas stream. The mixed hydrocarbon feed stream ( 10 ) is expanded into a mixed-phase hydrocarbon stream ( 20 ), which is separated the to provide at least a light overhead stream ( 30 ) and a heavy bottom stream ( 50 ). The light overhead stream ( 30 ) is compressed in one or more first compressors ( 16 ) to provide one or more first compressed light streams ( 40 ) and further compressed in one or more second compressors ( 22 ) to provide one or more further compressed light streams ( 60 ). One or more first compressor recycle lines ( 42 ) extend around the or each first compressor ( 16 ), and one or more second compressor recycle lines ( 32 ) having one or more in-line coolers ( 34 ) extend around the or each second compressor ( 22 ). The method and apparatus may be used in a method of cooling an initial hydrocarbon stream ( 100 ).

1 . Apparatus for treating a mixed hydrocarbon feed stream, the apparatus at least comprising an NGL recovery system comprising:
 (a) an expander to expand the mixed hydrocarbon feed stream into a mixed-phase hydrocarbon stream;   (b) a first gas/liquid separator to separate the mixed-phase hydrocarbon stream to provide at least a light overhead stream and a heavy bottom stream;   (c) a first compressor having a first inlet and a first outlet, to compress the light overhead stream and to provide a first compressed light stream;   (d) a second compressor having a second inlet and a second outlet, to compress the first compressed light stream to provide a further compressed light stream;   (e) a first compressor recycle line around the first compressor between the first outlet and the first inlet; and   (f) a second compressor recycle line provided with one or more in-line coolers around the second compressor between the second outlet and the second inlet.   
     
     
         2 . The apparatus as claimed in  claim 1 , wherein the expander is one of two or more expanders arranged in parallel, and the first compressor is one of two or more first compressors arranged in parallel, whereby the second compressor is arranged to receive the combined first compressed light streams from the two or more first compressors. 
     
     
         3 . The apparatus as claimed in  claim 1 , wherein the expander and the first compressor are mechanically linked by a common drive shaft. 
     
     
         4 . The apparatus as claimed in  claim 1 , wherein the gas/liquid separator is a distillation column. 
     
     
         5 . The apparatus as claimed in  claim 1 , further comprising one or more cooling stages upstream and/or downstream of the NGL recovery system. 
     
     
         6 . The apparatus as claimed in  claim 5 , wherein the one or more cooling stages comprise a first cooling stage able to cool an initial hydrocarbon stream to provide a cooled and partly condensed initial hydrocarbon stream; and further comprising a separator able to separate the cooled and partly condensed initial hydrocarbon stream to provide the mixed hydrocarbon feed stream and a stabilized condensate stream. 
     
     
         7 . The apparatus as claimed in  claim 5 , wherein the one or more cooling stages comprise a second cooling stage downstream of the second compressor arranged to receive and further cool at least a fraction of the further compressed light stream to provide a cooled hydrocarbon stream. 
     
     
         8 . The apparatus as claimed in  claim 1 , further comprising a throttle control valve between the first compressor and the second compressor, to throttle the pressure between the first compressor and the second compressor. 
     
     
         9 . The apparatus as claimed in  claim 1 , further comprising a first bypass line around the expander and a second bypass line around the first compressor. 
     
     
         10 . The apparatus as claimed in  claim 1 , wherein the first compressor recycle line is an uncooled recycle line. 
     
     
         11 . The apparatus as claimed in  claim 1 , wherein no cooler is present between the first outlet and the second inlet. 
     
     
         12 . A method of treating a mixed hydrocarbon feed stream, the method at least comprising the steps of:
 (a) providing a mixed hydrocarbon feed stream;   (b) expanding the mixed hydrocarbon feed stream through an expander to provide a mixed-phase hydrocarbon stream;   (c) passing the mixed-phase hydrocarbon stream into a first gas/liquid separator to provide at least a light overhead stream and a heavy bottom stream;   (d) passing the light overhead stream through a first compressor having a first inlet and a first outlet, to provide a first compressed light stream;   (e) passing the first compressed light stream through a second compressor having a second inlet and a second outlet, to provide a further compressed light stream; and   (f) selectively recycling at least a fraction of the first compressed light stream through a first compressor recycle line, around the first compressor between the first outlet and the first inlet; and   (g) selectively cooling and recycling at least a fraction of the further compressed light stream through a second compressor recycle around the second compressor between the second outlet and the second inlet, the second compressor recycle line provided with one or more in-line coolers.   
     
     
         13 . The method as claimed in  claim 12 , wherein the mixed hydrocarbon feed is derived from a natural gas stream. 
     
     
         14 . The method as claimed in  claim 12 , wherein at least a fraction of the further compressed light stream is subsequently cooled to provide a cooled hydrocarbon stream. 
     
     
         15 . The method as claimed in  claim 14 , wherein the subsequent cooling comprises liquefying, to provide the cooled hydrocarbon stream in the form of a liquefied hydrocarbon stream. 
     
     
         16 . The method as claimed in  claim 12 , further comprising cooling an initial hydrocarbon stream to provide a cooled and partly condensed initial hydrocarbon stream; and
 separating the cooled and partly condensed initial hydrocarbon stream to provide the mixed hydrocarbon feed stream and a stabilized condensate stream.   
     
     
         17 . The method as claimed in  claim 12 , wherein the selective recycling in step (f) is uncooled. 
     
     
         18 . The method as claimed in  claim 12 , wherein the first compressed light stream is passed to the second compressor without cooling. 
     
     
         19 . A method of cooling an initial hydrocarbon stream, comprising at least the steps of:
 (i) passing the initial hydrocarbon stream through a separator to provide a stabilized condensate stream and a mixed hydrocarbon feed stream;   (ii) treating the mixed hydrocarbon feed stream to provide one or more further compressed light streams; and   (iii) cooling at least a fraction of the one or more further compressed light streams to provide a cooled hydrocarbon stream,   
       wherein said treating in step (ii) at least comprises the steps of:
 (b) expanding the mixed hydrocarbon feed stream through an expander to provide a mixed-phase hydrocarbon stream; 
 (c) passing the mixed-phase hydrocarbon stream into a first gas/liquid separator to provide at least a light overhead stream and a heavy bottom stream; 
 (d) passing the light overhead stream through a first compressor having a first inlet and a first outlet, to provide a first compressed light stream; 
 (e) passing the first compressed light stream through a second compressor having a second inlet and a second outlet, to provide the further compressed light stream; and 
 (f) selectively recycling at least a fraction of the first compressed light stream through a first compressor recycle line, around the first compressor between the first outlet and the first inlet; and 
 (g) selectively cooling and recycling at least a fraction of the further compressed light stream through a second compressor recycle around the second compressor between the second outlet and the second inlet, the second compressor recycle line provided with one or more in-line coolers. 
 
     
     
         20 . The according to  claim 19 , wherein the cooling comprises liquefying to provided the cooled hydrocarbon stream in the form of a liquefied hydrocarbon stream.