Method and Device for Separating Acid Gases from a Gas Mixture

Abstract

The invention is directed to a method for separating acid gases from a gas mixture in which the gas mixture is contacted with an absorption medium which comprises water and at least one amine and has a phase-separation temperature in the range from 0 to 130° C. In addition, the invention is directed to a device which can be used for carrying out this method.

What is claimed is: 
     
         1 . A device for separating acid gases from a gas mixture, said device comprising an absorber, a desorption column having a mass-transfer zone which comprises a liquid outlet, an evaporator and a phase-separation device for separating two liquid phases having a feed point and separate withdrawal points for the liquid phases, wherein the evaporator is arranged separately from the phase-separation device, the phase-separation device comprises withdrawal points for a water-poor liquid phase and a water-rich liquid phase, the liquid outlet of the mass-transfer zone is connected to the feed point of the phase-separation device, and the device comprises connection conduits from the withdrawal point for water-rich liquid phase to the evaporator and from the withdrawal point for water-poor liquid phase to the absorber. 
     
     
         2 . The device of  claim 1 , wherein said absorber is a scrubbing column. 
     
     
         3 . The device of  claim 2 , wherein said scrubbing column is used for a counter-current flow operation wherein a gas mixture containing acid gases are fed to a lower region of the scrubbing column and a liquid absorption medium is fed to an upper region of the scrubbing column. 
     
     
         4 . The device of  claim 2 , wherein said scrubbing column comprises internals for enlarging the phase boundary between a gas mixture and a liquid absorption medium. 
     
     
         5 . The device of  claim 4 , wherein said internals are packing elements, structured column packings, or column trays. 
     
     
         6 . The device of  claim 1 , wherein said absorber is a membrane contacter, a radial flow scrubber, a jet scrubber, a Venturi scrubber or a rotary spray scrubber. 
     
     
         7 . The device of  claim 1 , wherein the phase-separation device is arranged within the desorption column below the mass-transfer zone. 
     
     
         8 . The device of  claim 7 , wherein the desorption column has a column bottom which is separated by an overflow weir into a first zone and a second zone, the liquid outlet of the mass-transfer zone is connected to a feed point for the first zone, a withdrawal point in the first zone is connected to the evaporator via a connecting conduit, and a withdrawal point in the second zone is connected to the absorber via a connecting conduit. 
     
     
         9 . The device of  claim 1 , wherein said phase-separation device is a settler in which phases separate due to gravity. 
     
     
         10 . The device of  claim 1 , wherein said phase-separation device separates phases by centrifugal force. 
     
     
         11 . The device of  claim 1 , wherein said evaporator is a natural circulation evaporator or falling-film evaporator. 
     
     
         12 . The device of  claim 1 , wherein said evaporator is a forced-circulation evaporator or a thin film evaporator. 
     
     
         13 . The device of  claim 1 , additionally comprising a connecting conduit between the withdrawal point for water-rich liquid phase and the absorber, wherein a control valve or a controllable pump is arranged in the connecting conduit, and the phase-separation device comprises a level controller for a liquid-liquid phase boundary in the phase-separation device by which the control valve or the controllable pump is controlled. 
     
     
         14 . The device of  claim 1 , wherein a mixing device is arranged in the connecting conduit from the withdrawal point for water-poor liquid phase to the absorber, and wherein the mixing device is connected to the withdrawal point for water-rich liquid phase and mixes liquid from the withdrawal point for water-poor liquid phase with liquid from the withdrawal point for water-rich liquid phase. 
     
     
         15 . The device of  claim 14 , wherein said mixing device is a stirred tank, a tank having a liquid recirculation via an external circuit, or a static mixer. 
     
     
         16 . The device of  claim 14 , wherein one or more heat exchangers are arranged in the conduits through which water-poor liquid phase and water-rich liquid phase is fed to the mixing device. 
     
     
         17 . The device of  claim 1 , further comprising a condenser which is connected to the top of the desorption column and by which water leaving the desorption column in the vapour state together with desorbed acid gas is condensed and returned to the desorption column. 
     
     
         18 . The device of  claim 1 , wherein the mass-transfer zone of said desorption column comprises internals selected from column trays, random packings or structured packings. 
     
     
         19 . The device of  claim 1 , wherein said device is used on a gas mixture from a fermentation or from a sewage treatment plant. 
     
     
         20 . The device of  claim 1 , wherein said device is used on a gas mixture comprising one or more acid gases selected from the group consisting of CO 2 , COS, H 2 S, CH 3 SH and SO 2 .