Amine sweetening in flash gas

Abstract

Certain implementations of amine sweetening of flash gas are described. Flash gas including acid gas is flowed from a flash drum through a column section connected to the flash drum. A lean amine stream is flowed through the column section. The lean amine stream is configured to treat the acid gas flowed from the flash drum through the column section. A quantity of the lean amine stream flowed through the column section is controlled based, in part, on a rate at which the flash gas including the acid gas is flowed from the flash drum through the column section and a concentration of the acid gas in the flash gas.

1 . A system for treating natural gas comprising:
 a column section configured to receive flash gas comprising residual acid gas from a flash drum coupled to the column section;   a pump fluidically coupled to the column section, the pump configured to flow a lean amine stream at a flow rate to the column section, the lean amine stream configured to treat the residual acid gas; and   a controller connected to the pump, the controller configured to operate the pump to periodically vary the flow rate of the lean amine stream based, in part, on a rate at which the flash gas flowed from the flash drum through the column section and a concentration of the residual acid gas in the flash gas.   
     
     
         2 . The system of  claim 1 , further comprising a flash gas flow meter configured to measure the rate at which the flash gas is flowed from the flash drum through the column section, the flash gas flow meter coupled to the controller and configured to transmit the measured rate at which the flash gas is flowed from the flash drum through the column section to the controller. 
     
     
         3 . The system of  claim 2 , further comprising a flash gas analyzer configured to measure the concentration of the residual acid in the flash gas, the flash gas analyzer coupled to the controller and configured to transmit the measured concentration of the residual acid in the flash gas to the controller. 
     
     
         4 . The system of  claim 1 , further comprising a filtering column configured to receive treated flash gas exiting the column section, the filtering column configured to filter benzene, toluene and xylenes (BTX) and particulates in the treated flash gas. 
     
     
         5 . The system of  claim 4 , wherein the filtering column comprises:
 an activated charcoal bed to filter the BTX; and   a mechanical filter to filter the particulates.   
     
     
         6 . The system of  claim 1 , wherein the controller is configured to operate the pump to periodically vary the flow rate of the lean amine stream according to the following equation: 
       
         
           
             
               
                 
                   Set 
                   ⁢ 
                       
                   point 
                   ⁢ 
                       
                   of 
                   ⁢ 
                       
                   lean 
                   ⁢ 
                       
                   amine 
                 
                 = 
                 
                   
                     
                       
                         
                           
                             
                               
                                 Flash 
                                 ⁢ 
                                     
                                 gas 
                                 ⁢ 
                                     
                                 
                                   rate 
                                   ⨯ 
                                 
                               
                             
                           
                           
                             
                               
                                 Acid 
                                 ⁢ 
                                     
                                 gas 
                                 ⁢ 
                                     
                                 
                                   concentration 
                                   ⨯ 
                                 
                               
                             
                           
                         
                       
                     
                     
                       
                         
                           Amine 
                           ⁢ 
                               
                           mole 
                           ⁢ 
                               
                           factor 
                         
                       
                     
                   
                   
                     
                       
                         
                           Lean 
                           ⁢ 
                               
                           amine 
                           ⁢ 
                               
                           acid 
                           ⁢ 
                               
                           
                             loading 
                             ⨯ 
                           
                         
                       
                     
                     
                       
                         
                           Lean 
                           ⁢ 
                               
                           amine 
                           ⁢ 
                               
                           concentration 
                         
                       
                     
                   
                 
               
               , 
             
           
         
       
       wherein Set point of lean amine is the flow rate of the lean amine stream, Flash gas rate is the rate at which the flash gas comprising the acid gas are flowed, Amine mole factor is a constant selected based on a type of the lean amine stream, Lean amine acid loading is an amount of acid gas separated by the lean amine stream, and Lean amine concentration is an amount of amine in the lean amine stream.