Use of dense fluid expanders in cryogenic natural gas liquids recovery

Abstract

A system and a process for processing a natural gas liquid feed is provided. In the system, a dense fluid expander is positioned downstream from a subcooler heat exchanger. The subcooler heat exchanger cools one or more reflux streams against an overhead vapor stream and a distillation column positioned downstream from the dense fluid expander. An increase in recovery of natural gas liquids is provided through the use of this system having at least one dense fluid expander.

1 . A system for producing natural gas liquid products comprising
 a. a dense fluid expander positioned downstream from a subcooler heat exchanger, wherein said subcooler heat exchanger cools one or more reflux streams against an overhead vapor stream   b. and a distillation column positioned downstream from said dense fluid expander.   
     
     
         2 . The system of  claim 1  wherein a backpressure valve is located between said dense fluid expander and said distillation column. 
     
     
         3 . The system of  claim 1  further comprising a Joules-Thomson valve positioned on a line parallel to said dense fluid expander. 
     
     
         4 . The system of  claim 1  wherein said dense fluid expander is positioned to accept the liquid feed from said dense fluid expander into an upper portion of said distillation column. 
     
     
         5 . The system of  claim 1  wherein said distillation column has an upper exit for a residue gas stream and a lower exit for a liquid stream. 
     
     
         6 . The system of  claim 1  further comprising a recycle line positioned to return a portion of the residual gas stream to said distillation column. 
     
     
         7 . The system of  claim 6  further comprising a dense fluid expander on said recycle line. 
     
     
         8 . A process for separating a hydrocarbon mixture into a liquid stream and a vapor stream, said process comprising the steps of:
 a. cooling a hydrocarbon feed to produce a two-phase mixture;   b. separating said two-phase mixture into a vapor stream and a liquid stream;   c. sending at least a portion of said vapor stream through a subcooler heat exchanger to produce a liquefied stream;   d. sending the liquefied stream through a dense fluid expander to produce an expanded liquefied stream; and   e. sending said expanded liquefied stream to a distillation column to produce a liquids stream and a residual gas stream.   
     
     
         9 . The process of  claim 8  further comprising sending said expanded liquefied stream through a backpressure valve to maintain a liquid state and then to said distillation column. 
     
     
         10 . The process of  claim 8  wherein a portion of said residual gas stream is returned to said distillation column. 
     
     
         11 . The process of  claim 8  wherein said hydrocarbon feed comprises a natural gas stream. 
     
     
         12 . The process of  claim 8  wherein said liquids stream comprises a natural gas liquids stream. 
     
     
         13 . The process of  claim 8  wherein said liquids stream comprises a mixture of propane and butane. 
     
     
         14 . The process of  claim 8  wherein said dense fluid expander increases a percentage of liquids in said expanded liquid stream. 
     
     
         15 . The process of  claim 8  wherein power produced by said dense fluid expander is recovered in a generator or is allowed to dissipate. 
     
     
         16 . The process of  claim 8  wherein said power is dissipated by being sent to an oil brake.