Method and apparatus for recovering and fractionating a mixed hydrocarbon feed stream

Abstract

A condensed mixed hydrocarbon feed stream ( 10 ), recovered from an initial feed stream ( 8 ), is fractionated into one ore more fractionated streams. In this process, the condensed mixed hydrocarbon feed stream ( 10 ) is separated into at least a first part-feed stream ( 20 ) and a second part-feed stream ( 30 ). The first part-feed stream ( 20 ) is passed into a first gas/liquid separator ( 14 ), to provide at least a first fractionated stream in the form of a first gaseous overhead stream ( 40 ). A first bottom liquid stream ( 50 ) provided by the first gas/liquid separator ( 14 ) is passed into a second gas/liquid separator ( 22 ) to provide at least a second fractionated stream in the form of a second gaseous overhead stream ( 70 ), which is cooled by heat exchange ( 26 ) against the second part-feed stream ( 30 ).

1 . A method of producing a liquefied hydrocarbon stream, and recovering a mixed hydrocarbon feed stream, from an initial feed stream and fractionating the mixed hydrocarbon feed stream into one or more fractionated streams, the method comprising the step of:
 (a) providing an initial feed stream;   (b) partly condensing the initial feed stream, thereby forming a partly condensed initial feed stream;   (c) separating the partly condensed initial feed stream into an initial gaseous overhead stream and a condensed mixed hydrocarbon feed stream;   (ii) liquefying at least part of the initial gaseous overhead stream to provide a liquefied hydrocarbon stream;   (d) dividing the condensed mixed hydrocarbon feed stream into at least a first part-feed stream and a second part-feed stream;   (e) passing the first part-feed stream into a first gas/liquid separator, via a first inlet into the first gas/liquid separator, to provide at least a first fractionated stream in the form of a first gaseous overhead stream and a first bottom liquid stream;   (f) passing the first bottom liquid stream into a second gas/liquid separator to provide at least a second fractionated stream in the form of a second gaseous overhead stream and a second bottom liquid stream; and   (g) cooling the second overhead gaseous stream by heat exchange against the second part-feed stream, resulting in a warmer second part-feed stream, without integration with a refrigeration circuit associated with a liquefaction process, and wherein the second part-feed stream is reduced in pressure prior to its heat exchanging against the second overhead gaseous stream;   (h) passing the warmer second part-feed stream into the first gas/liquid separator at a level gravitationally below the first inlet.   
     
     
         2 . The method as claimed in  claim 1 , wherein at least part of the initial gaseous overhead stream is liquefied without passing the at least part of the initial gaseous overhead stream through the first gas/liquid separator. 
     
     
         3 . The method as claimed in  claim 1 , wherein the initial gaseous overhead stream is a methane-enriched stream. 
     
     
         4 . The method as claimed in  claim 1 , further comprising the steps of:
 (i) dividing the cooled second gaseous overhead stream provided by the cooling of the second gaseous overhead stream in step (g) into two or more fractions; and   (j) passing at least one of said fractions back into the second gas/liquid separator.   
     
     
         5 . (canceled) 
     
     
         6 . The method as claimed in  claim 1 , wherein the first gas/liquid separator and the second gas/liquid separator are distillation columns. 
     
     
         7 . The method as claimed in  claim 1 , wherein said passing of the warmer second part-feed stream into the first gas/liquid separator at the level gravitationally below the first inlet comprises passing the warmer second part-feed stream into the first gas/liquid separator at a height along the separator between the first inlet and the bottom of the separator. 
     
     
         8 . The method as claimed in  claim 1 , further comprising a step of drawing a reboiler stream from the first gas/liquid separator, heating the reboiler stream to produce a bottom return stream, and feeding the bottom return stream back to the first gas/liquid separator, wherein said passing of the warmer second part-feed stream into the first gas/liquid separator at the level gravitationally below the first inlet comprises passing the warmer second part-feed stream into the first gas/liquid separator between the first inlet and the bottom return stream. 
     
     
         9 . The method as claimed in  claim 1 , wherein the second overhead gaseous stream comprises >60 mol % ethane. 
     
     
         10 . The method as claimed in  claim 1 , wherein the first bottom liquid stream is a C2+ hydrocarbon stream. 
     
     
         11 . The method as claimed in  claim 1 , wherein the second bottom liquid stream is a C3+ hydrocarbon stream. 
     
     
         12 . An apparatus for recovering a mixed hydrocarbon feed stream from an initial feed stream and fractionating the mixed hydrocarbon feed stream into one or more fractionated streams, the apparatus comprising:
 a pre-cooling heat exchanger arranged to cool the initial feed stream to provide a partly condensed initial feed stream;   an initial gas/liquid separator arranged to separate the partly condensed initial feed stream into an initial gaseous overhead stream and a condensed mixed hydrocarbon stream;   a stream splitter to divide the condensed mixed hydrocarbon feed stream into at least a first part-feed stream and a second part-feed stream;   a first gas/liquid separator arranged to receive the first part-feed stream via a first inlet into the first gas/liquid separator, and to provide at least a first fractionated stream in the form of a first overhead gaseous stream and a first bottom liquid stream;   a second gas/liquid separator arranged to receive the first bottom liquid stream, and to provide at least a second fractionated stream in the form of a second overhead gaseous stream and a second bottom liquid stream;   a heat exchanger arranged to receive the second part-feed stream and the second overhead gaseous stream, and to provide a cooled second overhead gaseous stream and a warmer second part-feed stream; and   a second inlet into the first gas/liquid separator arranged to allow entry of the warmer second part-feed stream into the first gas/liquid separator, the second inlet being at a level gravitationally below the first inlet.   
     
     
         13 . The apparatus as claimed in  claim 12 , further comprising a main cryogenic heat exchanger arranged to receive the initial gaseous overhead stream via a path that does not pass through the first gas/liquid separator, and to provide further cooling to the initial gaseous overhead stream. 
     
     
         14 . The apparatus as claimed in  claim 12 , further comprising a pressure reduction valve between the stream splitter and the heat exchanger. 
     
     
         15 . The apparatus as claimed in  claim 12 , wherein the cooled second overhead gaseous stream is provided from the second overhead gaseous stream without integration with a refrigeration circuit associated with a liquefaction process. 
     
     
         16 . The apparatus as claimed in  claim 12 , wherein no separate refrigeration involving separate power consumption is employed for providing said cooled second overhead gaseous stream from the second overhead gaseous stream. 
     
     
         17 . The method as claimed in  claim 1 , wherein no separate refrigeration involving separate power consumption is employed for said cooling of the second overhead gaseous stream in step (g). 
     
     
         18 . The method as claimed in  claim 1 , wherein the initial feed stream is a natural gas stream. 
     
     
         19 . The method as claimed in  claim 4 , wherein said cooling of the second overhead gaseous stream in step (g) results in condensation of at least part of the second overhead gaseous stream, and wherein the at least one of said fractions in step (j) is a condensed fraction being passed back into the second gas/liquid separator as a reflux stream. 
     
     
         20 . A method of recovering a mixed hydrocarbon feed stream from an initial feed stream and fractionating the mixed hydrocarbon feed stream into one or more fractionated streams, the method comprising the step of:
 (a) providing an initial feed stream;   (b) partly condensing the initial feed stream, thereby forming a partly condensed initial feed stream;   (c) separating the partly condensed initial feed stream into an initial gaseous overhead stream and a condensed mixed hydrocarbon feed stream;   (d) dividing the condensed mixed hydrocarbon feed stream into at least a first part-feed stream and a second part-feed stream;   (e) passing the first part-feed stream into a first gas/liquid separator, via a first inlet into the first gas/liquid separator, to provide at least a first fractionated stream in the form of a first gaseous overhead stream and a first bottom liquid stream;   (f) passing the first bottom liquid stream into a second gas/liquid separator to provide at least a second fractionated stream in the form of a second gaseous overhead stream and a second bottom liquid stream; and   (g) cooling the second overhead gaseous stream by heat exchange against the second part-feed stream, resulting in a warmer second part-feed stream;   (h) passing the warmer second part-feed stream into the first gas/liquid separator at a level gravitationally below the first inlet.   
     
     
         21 . The method as claimed in  claim 20 , further comprising cooling at least part of the initial gaseous overhead stream, without passing the at least part of the initial gaseous overhead stream through the first gas/liquid separator, thereby providing provide a cooled hydrocarbon stream. 
     
     
         22 . The method as claimed in  claim 20 , further comprising liquefying at least part of the initial gaseous overhead stream, without passing the at least part of the initial gaseous overhead stream through the first gas/liquid separator, thereby providing provide a liquefied hydrocarbon stream. 
     
     
         23 . The method as claimed in  claim 20 , wherein the initial feed stream is a natural gas stream. 
     
     
         24 . The method as claimed in  claim 20 , wherein the initial gaseous overhead stream is a methane-enriched stream. 
     
     
         25 . The method as claimed in  claim 20 , further comprising the steps of:
 (i) dividing the cooled second gaseous overhead stream provided by the cooling of the second gaseous overhead stream in step (g) into two or more fractions; and   (j) passing at least one of said fractions back into the second gas/liquid separator.   
     
     
         26 . The method as claimed in  claim 25 , wherein said cooling of the second overhead gaseous stream in step (g) results in condensation of at least part of the second overhead gaseous stream, and wherein the at least one of said fractions in step (j) is a condensed fraction being passed back into the second gas/liquid separator as a reflux stream. 
     
     
         27 . The method as claimed in  claim 20 , wherein the second part-feed stream is reduced in pressure prior to its heat exchanging against the second overhead gaseous stream in step (g). 
     
     
         28 . The method as claimed in  claim 20 , wherein the first gas/liquid separator and the second gas/liquid separator are distillation columns. 
     
     
         29 . The method as claimed in  claim 20 , wherein said passing of the warmer second part-feed stream into the first gas/liquid separator at the level gravitationally below the first inlet comprises passing the warmer second part-feed stream into the first gas/liquid separator at a height along the separator between the first inlet and the bottom of the separator. 
     
     
         30 . The method as claimed in  claim 20 , further comprising a step of drawing a reboiler stream from the first gas/liquid separator, heating the reboiler stream to produce a bottom return stream, and feeding the bottom return stream back to the first gas/liquid separator, wherein said passing of the warmer second part-feed stream into the first gas/liquid separator at the level gravitationally below the first inlet comprises passing the warmer second part-feed stream into the first gas/liquid separator between the first inlet and the bottom return stream. 
     
     
         31 . The method as claimed in  claim 20 , wherein the second overhead gaseous stream comprises >60 mol % ethane. 
     
     
         32 . The method as claimed in  claim 20 , wherein the first bottom liquid stream is a C2+ hydrocarbon stream. 
     
     
         33 . The method as claimed in  claim 20 , wherein the second bottom liquid stream is a C3+ hydrocarbon stream. 
     
     
         34 . The method as claimed in  claim 20 , wherein the second overhead gaseous stream is cooled in step (g) without integration with a refrigeration circuit associated with a liquefaction process. 
     
     
         35 . The method as claimed in  claim 20 , wherein no separate refrigeration involving separate power consumption is employed for said cooling of the second overhead gaseous stream in step (g). 
     
     
         36 . A method of producing a liquefied hydrocarbon stream, and recovering a mixed hydrocarbon feed stream, from an initial feed stream, and fractionating the mixed hydrocarbon feed stream into one or more fractionated streams, the method at least comprising the step of:
 (a) providing an initial feed stream;   (b) partly condensing the initial feed stream, thereby forming a partly condensed initial feed stream;   (c) separating the partly condensed initial feed stream into an initial gaseous overhead stream and a condensed mixed hydrocarbon feed stream;   (ii) liquefying at least part of the initial gaseous overhead stream to provide a liquefied hydrocarbon stream;   (d) dividing the condensed mixed hydrocarbon feed stream into at least a first part-feed stream and a second part-feed stream;   (e) passing the first part-feed stream into a first gas/liquid separator, via a first inlet into the first gas/liquid separator, to provide at least a first fractionated stream in the form of a first gaseous overhead stream and a first bottom liquid stream;   (f) passing the first bottom liquid stream into a second gas/liquid separator to provide at least a second fractionated stream in the form of a second gaseous overhead stream and a second bottom liquid stream; and   (g) cooling the second overhead gaseous stream by heat exchange against the second part-feed stream, resulting in a warmer second part-feed stream.   
     
     
         37 . The method as claimed in  claim 36 , wherein at least part of the initial gaseous overhead stream is liquefied without passing the at least part of the initial gaseous overhead stream through the first gas/liquid separator. 
     
     
         38 . The method as claimed in  claim 36 , wherein the second part-feed stream is reduced in pressure prior to its heat exchanging against the second overhead gaseous stream in step (g). 
     
     
         39 . The method as claimed in  claim 36 , wherein the second overhead gaseous stream is cooled in step (g) without integration with a refrigeration circuit associated with a liquefaction process. 
     
     
         40 . The method as claimed in  claim 36 , wherein no separate refrigeration involving separate power consumption is employed for said cooling of the second overhead gaseous stream in step (g).