Recovering Natural Gas Liquids

Abstract

Systems and methods for recovering natural gas liquids include a distillation column; a thermosyphon reboiler fluidly connected to the distillation column; a Joule-Thomson valve fluidly connected to the distillation column and operable to control a flow of fluid into the distillation column; and a lift gas control valve operable to control a flow of lift gas into the distillation column through a return line of the thermosyphon reboiler. An interlock system operatively couples the Joule-Thomson valve and the lift gas control valve to operate the lift gas control valve in response to operation of the Joule-Thomson valve.

What is claimed is: 
     
         1 . A system for recovering natural gas liquids, the system comprising:
 a distillation column;   a thermosyphon reboiler fluidly connected to the distillation column;   a Joule-Thomson valve fluidly connected to the distillation column and operable to control a flow of fluid into the distillation column;   a lift gas control valve operable to control a flow of lift gas into the distillation column through a return line of the thermosyphon reboiler; and   an interlock system that operatively couples the Joule-Thomson valve and the lift gas control valve to operate the lift gas control valve in response to operation of the Joule-Thomson valve.   
     
     
         2 . The system of  claim 1 , wherein the interlock system comprises a controller communicatively coupled to the Joule-Thomson valve and the lift gas control valve, the controller configured to perform operations comprising:
 receiving a signal to start the flow of fluid into the distillation column;   operating the Joule-Thomson valve to control the flow of fluid; and   operating the lift gas control valve in coordination with operating the Joule-Thomson valve to control the flow of lift gas to reduce thermal stress on the thermosyphon reboiler.   
     
     
         3 . The system of  claim 2 , further comprising a differential pressure sensor to measure a pressure difference across the thermosyphon reboiler. 
     
     
         4 . The system of  claim 3 , wherein the operations further comprise measuring the pressure difference across the thermosyphon reboiler using the differential pressure sensor. 
     
     
         5 . The system of  claim 4 , wherein operating the lift gas control valve is based on the measured pressure difference. 
     
     
         6 . The system of  claim 2 , further comprising a temperature sensor to measure a temperature of the thermosyphon reboiler. 
     
     
         7 . The system of  claim 6 , wherein the operations further comprise:
 measuring the temperature of the thermosyphon reboiler; and   determining a rate of temperature change based on the measured temperature.   
     
     
         8 . The system of  claim 7 , wherein operating the lift gas control valve is based on the determined rate of temperature change. 
     
     
         9 . The system of  claim 7 , wherein the operations further comprise in response to determining that the rate of temperature change exceeds a threshold rate of temperature change, operating the lift gas control valve to increase the flow of lift gas. 
     
     
         10 . The system of  claim 9 , wherein the operations further comprise in response to determining that the rate of temperature change is below the threshold rate of temperature change, operating the lift gas control valve to decrease the flow of lift gas. 
     
     
         11 . The system of  claim 2 , further comprising a turbo-expander fluidly connected to the distillation column in parallel with the Joule-Thomson valve. 
     
     
         12 . The system of  claim 11 , wherein receiving the signal to start the flow of fluid into the distillation column occurs in response to a trip of the turbo-expander. 
     
     
         13 . A method for recovering natural gas liquids, the method comprising:
 receiving a signal to start a flow of fluid into a distillation column;   operating a Joule-Thomson valve to control the flow of fluid into the distillation column; and   operating a lift gas control valve in coordination with operating the Joule-Thomson valve to control a flow of lift gas to the distillation column through a return line of a thermosyphon reboiler to reduce thermal stress on the thermosyphon reboiler.   
     
     
         14 . The method of  claim 13 , wherein operating the lift gas control valve occurs in response to operating the Joule-Thomson valve. 
     
     
         15 . The method of  claim 13 , further comprising measuring a pressure difference across the thermosyphon reboiler using a differential pressure sensor. 
     
     
         16 . The method of  claim 15 , wherein operating the lift gas control valve is based on the measured pressure difference. 
     
     
         17 . The method of  claim 13 , further comprising:
 measuring a temperature of the thermosyphon reboiler; and   determining a rate of temperature change based on the measured temperature.   
     
     
         18 . The method of  claim 17 , wherein operating the lift gas control valve is based on the determined rate of temperature change. 
     
     
         19 . The method of  claim 17 , further comprising:
 in response to determining that the rate of temperature change exceeds a threshold rate of temperature change, operating the lift gas control valve to increase the flow of lift gas; and   in response to determining that the rate of temperature change is below the threshold rate of temperature change, operating the lift gas control valve to decrease the flow of lift gas.   
     
     
         20 . The method of  claim 13 , wherein receiving the signal to start the flow of fluid into the distillation column occurs in response to a trip of a turbo-expander fluidly coupled to the distillation column in parallel with the Joule-Thomson valve.