Method and apparatus for separating one or more c2+ hydrocarbons from a mixed phase hydrocarbon stream

Abstract

A method for separating one or more C 2 + hydrocarbons from a mixed phase hydrocarbon stream such as partly vapourised liquefied natural gas, the method at least comprising the steps of: (a) supplying a mixed phase hydrocarbon feed stream ( 10 ) to a first gas/liquid separator ( 12 ); (b) separating the hydrocarbon feed stream ( 10 ) in the first gas/liquid separator ( 12 ) into a first gaseous stream ( 20 ) from a first outlet ( 23 ) and at least one C 2 + liquid stream ( 30 ); (c) passing the first gaseous stream ( 20 ) through a compressor ( 14 ) to provide a compressed stream ( 60 ); and (d) cooling the compressed stream ( 60 ) in one or more heat exchangers ( 16 ) to provide an at least partly condensed hydrocarbon product stream ( 70 ); wherein a second gaseous stream ( 40 ) is added to a stream ( 20, 60, 70 ) downstream of the first outlet ( 23 ).

1 . A method for separating one or more C 2 + hydrocarbons from a mixed phase hydrocarbon stream, the method at least comprising the steps of:
 (a) supplying a mixed phase hydrocarbon feed stream in the form of a partly vapourised hydrocarbon feed stream, to a first gas/liquid separator;   (b) separating the hydrocarbon feed stream in the first gas/liquid separator into a first gaseous stream from a first outlet, and at least one C 2 + liquid stream;   (c) passing the first gaseous stream through a compressor to provide a compressed stream; and   (d) cooling the compressed stream in one or more heat exchangers to provide an at least partly condensed hydrocarbon product stream;   (e) adding a second gaseous stream to a stream downstream of the first outlet, wherein the second gaseous stream comprises boil-off gas drawn from one or more liquid hydrocarbon storage tanks.   
   
   
       2 . A method as claimed in  claim 1 , wherein the second gaseous stream comprises compressed boil-off gas. 
   
   
       3 . A method as claimed in  claim 1 , wherein the second gaseous stream has a temperature of −25° C. or below, and comprises at least 70 mol % methane. 
   
   
       4 . A method as claimed in  claim 1 , wherein the mixed phase hydrocarbon feed stream is provided from one or more liquid hydrocarbon storage tanks. 
   
   
       5 . A method as claimed in  claim 1 , wherein the second gaseous stream is drawn from the one or more liquid hydrocarbon storage tanks in gaseous form. 
   
   
       6 . A method as claimed in  claim 1 , wherein both the second gaseous stream and the mixed phase hydrocarbon feed stream are provided from the same liquid hydrocarbon storage tank(s). 
   
   
       7 . A method as claimed in  claim 1 , wherein the second gaseous stream is added to one or more of the group comprising: the first gaseous stream, the compressed stream, and the at least partly condensed hydrocarbon product stream downstream of the first outlet. 
   
   
       8 . A method as claimed in  claim 1 , wherein the second gaseous stream is combined with the first gaseous stream prior to step (c). 
   
   
       9 . A method as claimed in  claim 1 , wherein the first gaseous stream is passed into a second gas/liquid separator to provide a separated gaseous stream prior to step (c). 
   
   
       10 . A method as claimed in  claim 9 , wherein the second gaseous stream is also passed into the second gas/liquid separator. 
   
   
       11 . A method as claimed in  claim 1 , wherein at least one of the one or more liquid hydrocarbon storage tanks is located in a sea-going transporter. 
   
   
       12 . A method as claimed in  claim 1 , wherein the compressed stream is cooled in step (d) against a liquid hydrocarbon source stream to provide the mixed phase hydrocarbon feed stream and the at least partly condensed hydrocarbon product stream. 
   
   
       13 . A method as claimed in  claim 1 , wherein the at least partly condensed hydrocarbon product stream is subsequently vapourised in a vaporiser. 
   
   
       14 . A method as claimed in  claim 1 , further comprising the step of:
 (F) dividing the at least partly condensed hydrocarbon product stream into a first at least partly liquid stream and a second at least partly liquid stream.   
   
   
       15 . A method as claimed in  claim 14 , wherein the first at least partly liquid stream is subsequently vaporised in a vaporiser. 
   
   
       16 . Apparatus for separating one or more C 2 + hydrocarbons from a mixed phase hydrocarbon stream, the apparatus at least comprising:
 a first gas/liquid separator having an inlet for a mixed phase hydrocarbon feed stream in the form of a partly vapourised hydrocarbon stream, a first outlet for a first gaseous stream and a second outlet for at least one C 2 + hydrocarbon liquid stream;   a compressor to compress the first gaseous stream to provide a compressed stream;   one or more heat exchangers to cool the compressed stream to provide an at least partly condensed hydrocarbon product stream;   a line connected to one or more hydrocarbon storage tanks to provide a second gaseous stream comprising boil-off gas drawn from the one or more hydrocarbon storage tanks;   a combiner to combine the second gaseous stream with a stream downstream of the first outlet of the gas/liquid separator.   
   
   
       17 . Apparatus as claimed in  claim 16 , wherein the combiner combines the second gaseous stream with one or more of the group comprising: the first gaseous stream, the compressed stream, and the at least partly condensed hydrocarbon product stream; downstream of the outlet of the gas/liquid separator. 
   
   
       18 . Apparatus as claimed in  claim 16 , wherein the combiner comprises a second gas/liquid separator to receive the first gaseous stream and the second gaseous stream prior to the compressor. 
   
   
       19 . Apparatus as claimed in  claim 16 , wherein the line bypasses the first gas/liquid separator. 
   
   
       20 . Apparatus as claimed in  claim 16 , wherein the inlet of the first gas/liquid separator is in fluid communication with one or more liquid hydrocarbon storage tanks to provide the mixed phase hydrocarbon feed stream.