Method of cooling a natural gas feed stream and recovering a natural gas liquid stream from the natural gas feed stream

Abstract

The invention relates to a method and system for cooling a natural gas feed stream and recovering a natural gas liquid stream from the natural gas feed stream using an expansion-based cooling unit and a natural gas liquid removal unit which are integrated. The integration is done by using (part of) a cooling stream from the expansion-based cooling unit to provide cooling duty to the natural gas liquid removal unit.

1 . A method of cooling a natural gas feed stream and recovering a natural gas liquid stream from the natural gas feed stream, the method comprising:
 a) operating an expansion based cooling unit, comprising obtaining a cooling stream being derived from the natural gas feed stream,   b) operating a natural gas liquid removal unit, comprising passing a feed stream being derived from the natural gas feed stream to a separation unit and obtaining a C 5   +  depleted top stream from the separation unit,
 wherein the method comprises cooling the C 5   +  depleted top stream in an overhead condenser against at least part of the cooling stream. 
   
     
     
         2 . The method according to  claim 1  comprising:
 a) operating an expansion based cooling unit, comprising
 a1) obtaining a compressed process stream and a cooling stream from a pressure unit, both the compressed process stream and the cooling stream being derived from the natural gas feed stream, 
 a2) passing the compressed process stream and at least part of the cooling stream to an indirect heat exchanger to cool the compressed process stream against the at least part of the cooling stream to obtain a cooled compressed process stream and a warmed cooling stream, 
 a3) recycling the warmed cooling stream to the pressure unit to be comprised in the compressed process stream and/or the cooling stream, 
 
 b) operating a natural gas liquid removal unit, comprising
 b1) passing a feed stream being derived from the natural gas feed stream to a separation unit and obtaining the natural gas liquid stream from a lower part of the separation unit and a C 5   +  depleted top stream from the separation unit, 
 b2) cooling the C 5   +  depleted top stream thereby obtaining a cooled C 5   +  depleted top stream, 
 b3) passing the cooled C 5   +  depleted top stream to a separation vessel, thereby obtaining a further gaseous top stream and a liquid bottom stream, 
 b4) feeding back the liquid bottom stream to an upper part of the separation unit as a reflux stream, 
 b5) passing the further gaseous top stream to the expansion based cooling unit, 
 wherein the method comprises cooling the C 5   +  depleted top stream in an overhead condenser against at least part of the cooling stream. 
 
 
     
     
         3 . The method according to  claim 1 , further comprising:
 expanding the natural gas feed stream in an inlet expander to obtain an expanded natural gas feed stream and   passing the expanded natural gas feed stream to the separation unit thereby providing the feed stream to the separation unit.   
     
     
         4 . The method according to  claim 3 , wherein cooling the C 5   +  depleted top stream in the overhead condenser is done against the entire cooling stream or part of the cooling stream, thereby obtaining a warmed cooling stream, the method further comprising the steps of:
 passing the further gaseous top stream to the expansion based cooling unit comprises combining the further gaseous top stream with the warmed cooling stream to obtain a combined stream and passing the at least part of the cooling stream to the indirect heat exchanger in a2) is done by passing the combined stream to the indirect heat exchanger. 
 
     
     
         5 . The method according to  claim 1 , wherein:
 a1) further comprises passing the warmed further gaseous top stream to the pressure unit to be part of the compressed process stream and/or the cooling stream;   a2) further comprises splitting the cooling stream in a first cooling stream portion and a second cooling stream portion, wherein the at least part of the cooling stream passed to the indirect heat exchanger is formed by the first cooling stream portion; and   wherein cooling the C 5   +  depleted top stream in the indirect heat exchanger is done against the second cooling stream portion, thereby obtaining a warmed second cooling stream portion.   
     
     
         6 . The method according to  claim 1 , further comprising the steps of:
 cooling the natural gas feed stream in an inlet heat exchanger against the further gaseous top stream obtained from the separation vessel to obtain a cooled natural gas feed stream and a warmed further gaseous top stream,   passing the cooled natural gas stream to the separation unit thereby providing the feed stream.   
     
     
         7 . The method according to  claim 1 , wherein the warmed cooling stream and the warmed second cooling stream portion are passed to a recompression unit. 
     
     
         8 . The method according to  claim 1 , wherein cooling the C 5   +  depleted top stream is done in the overhead condenser against the cooling stream, thereby obtaining a warmed cooling stream, and wherein:
 a1) further comprises feeding the natural gas feed stream and a recycle stream to the pressure unit, 
 and wherein the method comprises the steps of: 
 passing the warmed cooling stream to the separation unit thereby providing the feed stream to the separation unit; 
 passing the further gaseous top stream obtained in b3) to the indirect heat exchanger thereby providing the at least part of the cooling stream which is passed to the indirect heat exchanger in a2); and 
 passing the warmed cooling stream which is obtained in a2) to a recompression unit to obtain the recycle stream. 
 
     
     
         9 . A system for cooling a natural gas feed stream and recovering a natural gas liquid stream from the natural gas feed stream, the system comprising an expansion based cooling unit arranged to generate a cooling stream and a natural gas liquid removal unit comprising a separation unit arranged to discharge a C 5   +  depleted top stream,
 wherein the system further comprises an overhead condenser fluidly connected to the separation unit to receive the C 5   +  depleted top stream and fluidly connected to the expansion based cooling unit to receive at least part of the cooling stream to cool the C 5   +  depleted top stream against the at least part of the cooling stream. 
 
     
     
         10 . The system according to  claim 9 , comprising an expansion based cooling unit, wherein the expansion based cooling unit comprises:
 a pressure unit which is arranged to receive at least a recycle stream and generate and discharge a compressed process stream and a cooling stream,   an indirect heat exchanger fluidly connected to the pressure unit to receive the compressed process stream and the cooling stream to cool the compressed process stream against the at least part of the cooling stream thereby obtaining a cooled compressed process stream and a warmed cooling stream,   the system further comprising a recompression unit being fluidly connected to the expansion based cooling unit to receive and compress at least the warmed cooling stream, the recompression unit being arranged to discharge the recycle stream, which is at least partially derived from the warmed cooling stream, the recompression unit being in fluid communication with the pressure unit,   
       wherein the system further comprises a natural gas liquid removal unit, the natural gas liquid removal unit comprising
 a separation unit arranged to receive a feed stream and separate the feed stream to obtain and discharge a natural gas liquid stream and a C 5   +  depleted top stream, 
 an overhead condenser fluidly connected to the separation unit to receive the C 5   +  depleted top stream and fluidly connected to the expansion based cooling unit to receive at least part of the cooling stream to cool the C 5   +  depleted top stream against the at least part of the cooling stream thereby obtaining a cooled C 5   +  depleted top stream, and 
 a separation vessel fluidly connected to the overhead condenser to receive the cooled C 5   +  depleted top stream and separate the cooled C 5   +  depleted top stream to obtain and discharge a further gaseous top stream and a liquid bottom stream, wherein the separation vessel is fluidly connected to an upper part of the separation unit to feed back the liquid bottom stream to the upper part of to the separation unit as a reflux stream, wherein the separation vessel is fluidly connected to the expansion based cooling unit.