Membrane-based exhaust gas scrubbing method and system

Abstract

Various exemplary embodiments relate to a method and apparatus to reduce emissions of target emission gasses such as sulfur oxides, nitrogen oxides, and carbon oxides from combustion exhaust such as marine engine exhaust by gas membrane separation and liquid carrier chemical absorption. The membrane separation system consists of an absorption system containing semi-permeable hollow fiber membranes through which is circulated a liquid absorbent. Exhaust gases contact the exterior surface of the membranes and the target gasses selectively permeate the membrane wall and are absorbed by the liquid carrier(s) within the bore and thereby are removed from the exhaust stream.

1 . A method for reducing the concentration of a target emission gas (TEG) from a source of marine engine exhaust gas comprising the steps of:
 directing said engine exhaust gas from the source into an enclosed space containing at least one array of hollow fibre semi-permeable ceramic membranes, wherein said exhaust gas contacts an exterior surface of said membranes whereupon TEG within said exhaust gas permeates through said membrane thereby lowering the concentration of said TEG within said exhaust gas;   circulating a carrier liquid capable of retaining TEG compounds through bores of said hollow fibre ceramic membranes thereby elevating the concentration of said TEG compounds within said carrier liquid;   discharging said exhaust gas containing a reduced TEG concentration from the enclosed space and removing said carrier liquid containing said TEG compounds therein from said hollow fibre ceramic membrane array.   
     
     
         2 . The method of  claim 1  wherein after said carrier liquid is removed from the membrane array, said TEG compounds are separated from said carrier liquid to reduce the concentration thereof in said carrier liquid and said carrier liquid is then recycled back through said membrane array. 
     
     
         3 . The method of  claim 1  wherein said carrier liquid comprises an ionic liquid. 
     
     
         4 . The method of  claim 3  wherein the carrier liquid is a task-specific ionic liquid specific to said TEG. 
     
     
         5 . The method of  claim 4  wherein the engine exhaust gas from the source enters the enclosed space at engine pressure. 
     
     
         6 . The method of  claim 5  further comprising the step of separating said TEG compounds from said carrier liquid for storage and recycling said carrier liquid through said membrane array. 
     
     
         7 . The method of  claim 4  wherein said ionic liquid is one or more of:
 1,1,3,3-tetramethylguanidium lactate [TMG][L]; 
 Monoethanolammonium lactate [MEA][L]; 
 1-Butyl-3-methylimidazolium tetrafluoroborate [BMIm][BF4]; 
 1-Butyl-3-methylimidazolium methylsulfate [BMIm][MeSO4]; 
 1-Hexyl-3-methylimidazolium methylsulfate [HMIm][MeSO4]; 
 1-Ethyl-3-methylimidazolium methylsulfate [EMIm/][MeSO4]; 
 1-Butyl-3-methylimidazolium hexafluorophosphate [BMIm][PF6]; 
 1-Butyl-3-methylimidazolium trifluoromethanesulfonate [BMIM]OTf; or 
 1-Butyl-3-methylimidazolium hexafluoruphosphate ([C4mim][PF6]). 
 
     
     
         8 - 15 . (canceled) 
     
     
         16 . A system for lowering the concentration of at least one target emission gas (TEG) from a source of engine exhaust gas comprising:
 an enclosure for receiving a stream of engine exhaust;   a plurality of gas treatment modules configured for installation within said enclosure, each of said modules comprising a housing and an array of hollow fibre ceramic membranes supported within the housing and configured so that said exhaust contacts the membranes as the exhaust gas is circulated through the array when the module is installed within the enclosure, each of said ceramic membranes comprising a semi-permeable membrane wall which is permeable to said TEG but non-permeable to non-TEG's in said emission gas and   a hollow bore;   a liquid inlet for feeding a carrier liquid into said membrane bores in an unsaturated state;   a liquid outlet for receiving said carrier liquid from said bores after circulation therethrough in a state saturated with said TEG; and   a carrier liquid circulation subsystem to circulate said carrier liquid through said membrane bores and said liquid inlet and liquid outlet;   wherein said apparatus is configured so that exhaust gas circulates at engine pressure through said array and contacts said membranes on an exterior surface of the membranes, said liquid contacts said membranes on an opposed surface thereof and said TEG thereby permeates through said membrane from the exterior membrane surface into the bore to transfer said TEG from said TEG compounds from said exhaust gas into said carrier liquid.   
     
     
         17 . The system of  claim 16  further comprising a carrier recycling subsystem in communication with the carrier liquid outlet and liquid inlet, said recycling subsystem comprising components for removing at least one TEG from said carrier liquid wherein said carrier is circulated in an essentially closed loop through said apparatus. 
     
     
         18 . The system of  claim 17  further comprising at least one of pH sensor system for determining a pH drop in said liquid carrier from circulating through said membrane array and a pressure sensor system for determining a pressure drop in said liquid carrier from circulating through said membrane array, said sensors being operatively linked to a signal processor for determining whether said pH drop and/or pressure drop is indicative of a reduced level of effectiveness of said membrane array at reducing concentrations of TEG. 
     
     
         19 . The system of  claim 17  further comprising a sensor for measuring TEG concentration within untreated exhaust gas from said source and a control system in operative communication with said sensor and with a pump for controlling the flow rate of said carrier liquid through said system, said control system being configured to determine the flow rate of said carrier liquid required in order to achieve a selected level of TEG concentration reduction and to control said pump to provide said flow rate. 
     
     
         20 . The system of  claim 17  further comprising a heat exchanger configured to lower the temperature of the engine exhaust gas before it enters the first of said plurality of gas treatment modules. 
     
     
         21 . The system of  claim 20  where the apparatus is configured so that the heat from said heat exchanger is used in the carrier recycling subsystem. 
     
     
         22 . A kit comprising the system of  claim 17  and at least one carrier liquid for dissolving said TEG. 
     
     
         23 . The kit of  claim 22  wherein the carrier liquid is one or more of an ionic liquid or sodium hydroxide. 
     
     
         24 . The kit of  claim 23  wherein said ionic liquid comprises one or more of:
 1,1,3,3-tetramethylguanidium lactate [TMG][L]; 
 Monoethanolammonium lactate [MEA][L]; 
 1-Butyl-3-methylimidazolium tetrafluoroborate [BMIm][BF4]; 
 1-Butyl-3-methylimidazolium methylsulfate [BMIm][MeSO4]; 
 1-Hexyl-3-methylimidazolium methylsulfate [HMIm][MeSO4]; 
 1-Ethyl-3-methylimidazolium methylsulfate [EMIm][MeSO4]; 
 1-Butyl-3-methylimidazolium hexafluorophosphate [BMIm][PF6]; 
 1-Butyl-3-methylimidazolium trifluoromethanesulfonate [BMIM]OTf; or 
 1-Butyl-3-methylimidazolium hexafluouphosphate ([C4mim][PF6]). 
 
     
     
         25 . An apparatus for lowering the concentration of sulphur oxides (SOX) from untreated marine diesel engine exhaust gas comprising:
 an enclosure for receiving a stream of untreated engine exhaust at engine pressure having a gas inlet for receiving said exhaust gas containing said SOX's and a gas outlet for discharging said exhaust gases;   at least one array of hollow fibre ceramic membranes within the enclosure for reducing the concentration of said SOX's within the exhaust gas configured whereby said exhaust gas contacts the membranes when circulated through the membrane array, each of said membranes comprising a semi-permeable membrane wall which is permeable to said SOX in said emission gas and a hollow bore;   a liquid inlet for feeding an ionic liquid into said membrane bores;   a liquid outlet for receiving said ionic liquid from said bores after circulation therethrough;   a liquid circulation subsystem to circulate said ionic liquid through said membrane bores for discharge or recycling through said membrane array;   an ionic liquid recycling subsystem in communication with the liquid outlet and inlet and comprising components for removing SOX from said ionic liquid, wherein said ionic liquid is circulated in an essentially closed loop through said apparatus; and   a sensor for measuring SOX concentration within untreated exhaust gas and a control system in operative communication with said sensor and with a pump for controlling the flow rate of said carrier liquid through said system, said control system being configured to determine the flow rate of said carrier liquid required in order to achieve a selected level of SOX concentration reduction and to control said pump to provide said flow rate.   
     
     
         26 . The system of  claim 25  further comprising a heat exchanger configured to lower the temperature of the engine exhaust gas before it enters the enclosure. 
     
     
         27 - 28 . (canceled) 
     
     
         29 . A method for reducing the concentration of a target emission gas (TEG) from a source of marine engine exhaust gas comprising the steps of:
 Directing said engine exhaust gas containing TEG from the source into an enclosed space containing at least one array of hollow fibre semi-permeable ceramic membranes, and circulating a carrier liquid capable of retaining TEG compounds through bores of said hollow fibre ceramic membranes, said bores having an inside surface, wherein said exhaust gas contacts an exterior surface of said membranes whereupon TEG within said exhaust gas permeates through said membrane and contacts said carrier liquid below the exterior surface of said ceramic membranes, thereby lowering the concentration of said TEG within said exhaust gas and elevating the concentration of said TEG compounds within said carrier liquid;   Discharging said exhaust gas containing a reduced TEG concentration from the enclosed space and removing said carrier liquid containing said TEG compounds therein from said hollow fibre ceramic membrane array.   
     
     
         30 . The method of  claim 29  where said TEG within said exhaust gas permeates through said membrane and contacts said carrier liquid at the inside surface of said bores.