Systems and Methods for Enhanced Recovery of NGL Hydrocarbons

Abstract

Systems and methods for the enhanced recovery of ethane and heavier hydrocarbons using an absorbing agent. Typical absorbing agents include one or more C3+ alkanes. The systems and methods separate components of a feed gas containing methane and heavier hydrocarbons, which maximizes ethane recovery, without requiring appreciable increases in capital and operating costs, and improves the safety margin with respect to the risk of CO 2 freeze-out.

1 . A method for recovering ethane and heavier hydrocarbons from a hydrocarbon feed gas, which comprises:
 cooling an absorbing agent and an inlet stream comprising the feed gas in a heat exchanger to produce a cooled absorbing agent and a chilled inlet stream;   separating the chilled inlet stream in a separator to produce a liquid hydrocarbon stream and an overhead vapor stream;   combining the cooled absorbing agent with a portion of the overhead vapor stream to form a combined stream;   cooling the combined stream into a reflux exchanger to produce a subcooled liquid stream;   expanding another portion of the overhead vapor stream in an expander to produce a demethanizer feed stream; and   introducing the liquid hydrocarbon stream, the subcooled liquid stream and the demethanizer feed stream into a demethanizer column, wherein the ethane and heavier hydrocarbons are recovered as a bottom product in the demethanizer column and methane and lighter hydrocarbons are recovered as a top product in the demethanizer column.   
     
     
         2 . The method of  claim 1 , wherein the absorbing agent comprises one or more C3+ alkanes. 
     
     
         3 . The method of  claim 1 , wherein the hydrocarbon feed gas comprises methane and heavier hydrocarbons. 
     
     
         4 . The method of  claim 1 , wherein the absorbing agent and the inlet stream are cooled in the heat exchanger by indirect heat exchange with a residue stream, a side reboiling stream and a demethanizer reboiling stream. 
     
     
         5 . The method of  claim 1 , further comprising processing the methane and lighter hydrocarbons in the reflux exchanger, the heat exchanger and a boost compressor to produce a residue gas stream. 
     
     
         6 . A method for recovering ethane and heavier hydrocarbons from a hydrocarbon feed gas, which comprises:
 combining a residue gas recycle stream and an absorbing agent to form an enriched residue gas recycle stream;   cooling the enriched residue gas recycle stream and an inlet stream comprising the feed gas in a heat exchanger to produce a chilled enriched residue gas recycle stream and a chilled inlet stream;   separating the chilled inlet stream in a separator to produce a liquid hydrocarbon stream and an overhead vapor stream;   cooling the chilled enriched residue gas recycle stream in a reflux exchanger to produce a subcooled liquid stream;   expanding the overhead vapor stream in an expander to produce a demethanizer feed stream; and   introducing the liquid hydrocarbon stream, the subcooled liquid stream and the demethanizer feed stream into a demethanizer column, wherein the ethane and heavier hydrocarbons are recovered as a bottom product in the demethanizer column and methane and lighter hydrocarbons are recovered as a top product in the demethanizer column.   
     
     
         7 . The method of  claim 6 , wherein the absorbing agent comprises one or more C3+ alkanes. 
     
     
         8 . The method of  claim 6 , wherein the hydrocarbon feed gas comprises methane and heavier hydrocarbons. 
     
     
         9 . The method of  claim 6 , wherein the enriched residue gas recycle stream and the inlet stream are cooled in the heat exchanger by indirect heat exchange with a residue stream, a side reboiling stream and a demethanizer reboiling stream. 
     
     
         10 . The method of  claim 6 , further comprising processing the methane and lighter hydrocarbons in the reflux exchanger, the heat exchanger and a boost compressor to produce a residue gas stream. 
     
     
         11 . The method of  claim 10 , wherein a portion of the residue gas stream is used to form the residue gas recycle stream. 
     
     
         12 . The method of  claim 6 , further comprising processing the ethane and heavier hydrocarbons in a demethanizer column, wherein an ethane-rich stream is recovered as another top product in the deethanizer column and another stream comprising propane and heavier components is recovered as another bottom product in the deethanizer column. 
     
     
         13 . The method of  claim 12 , wherein a portion of the another stream is recycled to form the absorbing agent. 
     
     
         14 . A method for recovering ethane and heavier hydrocarbons from a hydrocarbon feed gas, which comprises:
 combining a portion of an inlet stream comprising the feed gas and an absorbing agent to form an enriched split feed stream;   cooling another portion of the inlet stream comprising the feed gas and the enriched split feed stream in a heat exchanger to produce a chilled enriched split feed stream and a chilled inlet stream or cooling the another portion of the inlet stream comprising the feed gas and an enriched inlet stream in the heat exchanger to produce the chilled enriched split feed stream and the chilled inlet stream;   separating the chilled inlet stream in a separator to produce a liquid hydrocarbon stream and an overhead vapor stream;   cooling the chilled enriched split feed stream in a reflux exchanger to produce a subcooled liquid stream or cooling an overhead vapor separator stream in the reflux exchanger to produce the subcooled liquid stream;   expanding the overhead vapor stream in an expander to produce a demethanizer feed stream; and   introducing the liquid hydrocarbon stream, the subcooled liquid stream and the demethanizer feed stream into a demethanizer column, wherein the ethane and heavier hydrocarbons are recovered as a bottom product in the demethanizer column and methane and lighter hydrocarbons are recovered as a top product in the demethanizer column.   
     
     
         15 . The method of  claim 14 , wherein the absorbing agent comprises one or more C3+ alkanes. 
     
     
         16 . The method of  claim 14 , wherein the hydrocarbon feed gas comprises methane and heavier hydrocarbons. 
     
     
         17 . The method of  claim 14 , wherein the another portion of the inlet stream and the enriched split feed stream or the enriched inlet stream are cooled in the heat exchanger by indirect heat exchange with a residue stream, a side reboiling stream and a demethanizer reboiling stream. 
     
     
         18 . The method of  claim 14 , further comprising processing the methane and lighter hydrocarbons in the reflux exchanger, the heat exchanger and a boost compressor to produce a residue gas stream. 
     
     
         19 . The method of  claim 14 , further comprising compressing and cooling the enriched split feed stream to produce the enriched inlet stream. 
     
     
         20 . The method of  claim 14 , further comprising:
 separating the chilled enriched split feed stream in another separator to produce the overhead vapor separator stream and a bottom liquid separator stream; and   combining the bottom liquid separator stream and the liquid hydrocarbon stream.   
     
     
         21 . A method for recovering ethane and heavier hydrocarbons from a hydrocarbon feed gas, which comprises:
 cooling an absorbing agent and an inlet stream comprising the feed gas in a heat exchanger to produce a cooled absorbing agent and a chilled inlet stream;   contracting the chilled inlet stream with the cooled absorbing agent in an absorber to produce a liquid hydrocarbon stream and an enriched overhead vapor stream;   cooling a portion of the enriched overhead vapor stream in a reflux exchanger to produce a subcooled liquid stream;   expanding another portion of the enriched overhead vapor stream in an expander to produce a demethanizer feed stream; and   introducing the liquid hydrocarbon stream, the subcooled liquid stream and the demethanizer feed stream into a demethanizer column, wherein the ethane and heavier hydrocarbons are recovered as a bottom product in the demethanizer column and methane and lighter hydrocarbons are recovered as a top product in the demethanizer column.   
     
     
         22 . The method of  claim 21 , wherein the absorbing agent comprises one or more C3+ alkanes. 
     
     
         23 . The method of  claim 21 , wherein the hydrocarbon feed gas comprises methane and heavier hydrocarbons. 
     
     
         24 . The method of  claim 21 , wherein the absorbing agent and the inlet stream are cooled in the heat exchanger by indirect heat exchange with a residue stream, a side reboiling stream and a demethanizer reboiling stream. 
     
     
         25 . The method of  claim 21 , further comprising processing the methane and lighter hydrocarbons in the reflux exchanger, the heat exchanger and a boost compressor to produce a residue gas stream.