Systems and Methods for Recovering Desired Light Hydrocarbons from Refinery Waste Gas Using a Back-End Turboexpander

Abstract

Systems and methods for recovering light hydrocarbons from refinery waste gas using a back-end turboexpander to generate a higher recovery of the light hydrocarbons for use as petrochemical feedstock and to remove the liquid light hydrocarbons before entering the turboexpander.

1 . A system for recovery of light hydrocarbons, which comprises:
 a gas chiller/dryer;   a distillation column connected to the gas chiller/dryer for recovering the light hydrocarbons;   a first liquid/gas separator connected to the distillation column for separating the light hydrocarbons in a liquid state from the light hydrocarbons in a gas state;   a turboexpander connected to the first liquid/gas separator for cooling the light hydrocarbons in a gas state to produce a condensed liquid and a remaining vapor;   a second liquid/gas separator connected to the turboexpander for separating the condensed liquid from the remaining vapor;   a remaining vapor line connected to the second liquid/gas separator for transporting the remaining vapor;   a first condenser connected to the remaining vapor line for cooling the distillation column using the remaining vapor;   a condensed liquid line connected to the second liquid/gas separator for transporting the condensed liquid to the distillation column for further processing; and   a product line in communication with the distillation column for removal of the light hydrocarbons.   
     
     
         2 . (canceled) 
     
     
         3 . (canceled) 
     
     
         4 . The system of  claim 1 , wherein the distillation column is a deethanizer. 
     
     
         5 . The system of  claim 1 , further comprising:
 a second condenser in the distillation column for cooling the distillation column using a cooled refrigerant.   
     
     
         6 . The system of  claim 1 , wherein the distillation column is a demethanizer. 
     
     
         7 . The system of  claim 5 , further comprising:
 a heat exchanger in communication with the light hydrocarbons in the distillation column.   
     
     
         8 . The system of  claim 1 , wherein the light hydrocarbons comprise ethylene and the light hydrocarbons having a molecular weight greater than ethylene. 
     
     
         9 . A method for recovering light hydrocarbons from a gas stream, which comprises:
 treating the gas stream by compressing, amine-treating, drying and chilling to produce a residue lighter gas;   separating the residue lighter gas in a distillation column between an overhead product and a raw column bottom liquid product containing the light hydrocarbons;   removing a liquid from the overhead product prior to processing in a turboexpander;   processing the overhead product through the turboexpander to obtain a condensed liquid and a remaining vapor;   separating the condensed liquid and the remaining vapor before returning the condensed liquid to the distillation column;   returning the condensed liquid to the distillation column; and   flowing the remaining vapor through a first condenser in the distillation column.   
     
     
         10 . (canceled) 
     
     
         11 . The method of  claim 9 , further comprising:
 heating a portion of the raw column bottom liquid product in a first heat exchanger to obtain a heated portion of the raw column bottom liquid product; and   injecting the heated portion of the raw column bottom liquid product into the distillation column.   
     
     
         12 . The method of  claim 9 , wherein the distillation column is a deethanizer. 
     
     
         13 . The method of  claim 11 , further comprising:
 providing a cooled refrigerant to a second condenser in the distillation column.   
     
     
         14 . The method of  claim 9 , wherein the distillation column is a demethanizer. 
     
     
         15 . The method of  claim 14 , further comprising:
 heating a portion of the raw column bottom liquid product in a first heat exchanger to obtain a heated portion of the raw column bottom liquid product; and   injecting the heated portion of the raw column bottom liquid product into the distillation column.   
     
     
         16 . The method of  claim 15 , further comprising:
 heating a portion of the raw column bottom liquid product in a second heat exchanger to obtain a second heated portion of the raw column bottom liquid product; and   injecting the second heated portion of the raw column bottom liquid product into the distillation column.