Patent Publication Number: US-2018028964-A1

Title: Activated Carbon Bed For Use With A Wet Scrubber System

Description:
TECHNICAL FIELD 
     The present application and the resultant patent relate generally to combustion plant emissions control systems and more particularly relate to a activated carbon bed system for removal of dioxins in flue gases flowing through a wet scrubber system. 
     BACKGROUND OF THE INVENTION 
     Waste-to-energy combustion plants and the like often include a wet scrubber system for the removal of gaseous pollutants and recovery of condensation heat so as to improve overall plant efficiency. Specifically, a portion of the heat of the hot flue gases produced in the combustion process may be recovered and applied for useful work. A common means of removing pollutions and recovering such heat is through a packed bed scrubber and the like. Generally described, the hot flue gases may enter the scrubber at the bottom thereof and rise through a packed bed while a fluid flows downward therethrough so as to remove gaseous pollutants and to exchange heat with the flue gases. The packed bed is often a random filling or a structured bed made out of a thermoplastic such as polypropylene. The now warmed fluid then may be applied for any useful purpose. 
     One of the drawbacks with the use of a packed bed wet scrubber is that the polypropylene or other type of thermoplastic or other type of packing material may have a tendency to accumulate dioxins (chlorinated dibenzo(p)-dioxin and furan compounds) formed in the combustion process. Specifically, dioxins are heavy aromatic molecules that have a great affinity to organic surfaces such as polypropylene and thus may be absorbed therein. The accumulated dioxins, however, may be released back into the flue gas steam if the operating temperatures or other types of operating conditions change. The increase in the dioxin content of the flue gas stream is known as the “memory effect.” 
     The memory effect may be prevented or at least reduced if the dioxins can be bound to the thermoplastic. One binding method is to add activated carbon to the thermoplastic matrix of the packed bed. Although effective, this method generally requires the complete replacement of all of the packing at a regular interval depending upon the dioxin load. The addition of the activated carbon also adds to the overall material costs. 
     SUMMARY OF THE INVENTION 
     The present application and the resultant patent thus provide a wet scrubber system for treating a flow of flue gases with dioxins therein with a flow of a fluid. The wet scrubber system may include a column member, a packed bed positioned within the column member, and an activated carbon filter bed system in communication with the column member such that at least a portion of the flow of the fluid passes through the activated carbon filter bed system to remove the dioxins therein before being recirculated back to the column member. 
     The present application and the resultant patent further provide a method of removing dioxins from a flow of flue gases in a wet scrubber system. The method may include the steps of flowing the flue gases through a packed bed of the wet scrubber system, flowing a fluid through the packed bed of the wet scrubber system, dissolving dioxins in the flue gases in the fluid, flowing the fluid through an activated carbon filter bed to remove the dioxins therein, and recirculating the fluid back to the packed bed. 
     The present application and the resultant patent further provide a packed bed condensing system for cooling a flow of flue gases with dioxins therein with a flow of a cooling fluid. The packed bed condensing system may include a column member, a polypropylene packed bed positioned within the column member with the flow of flue gases and the flow of the cooling fluid passing through the packed bed, and an activated carbon filter bed system in communication with the column member such that at least a portion of the flow of the cooling fluid passes through the activated carbon filter bed system to remove the dioxins therein before being recirculated back to the packed bed of the column member. 
     These and other features and improvements of the present application and resultant patent will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an example of a wet scrubber system. 
         FIG. 2  is a schematic diagram of a wet scrubber system as may be described herein. 
         FIG. 3  is a schematic diagram of an alternative embodiment of a wet scrubber system as may be described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings, in which like numerals refer to like elements throughout the several views,  FIG. 1  shows an example of a known wet scrubber system  10 . The wet scrubber system  10  may remove gaseous pollutants and exchange heat between a flow of flue gases  12  and a flow of a fluid  14 . The fluid  14  may be water or any type of conventional fluid flow. 
     Generally described, the wet scrubber system  10  may include an elongated column member  15 . The column member  15  may be generally cylindrical in shape but could be rectangular, square, and the like. The column member  15  may have a lower end  20 , an upper end  25 , and a central cavity  30  therebetween. One or more packed beds  31  may be positioned within the central cavity  30  forming an upper condensing bed  32 . Specifically, an upper scrubber packed bed  32  may be positioned within the central cavity  30 . The upper condensing packed bed  32  may be made out of any suitable type of packing materials  34  such as polypropylene and other types of thermoplastics, arranged as a random filling or a structured bed. Combinations of different types of packing materials also may be used herein. 
     An upper liquid distributor  36  may be positioned at the upper end  25  of the column member  15  above the upper condensing packed bed  32 . The upper liquid distributor  36  may be any type of conventional spray or mist delivery devices used to deliver the cooling fluid  14  to the upper condensing packed bed  32 . An upper liquid collector  38  may be positioned beneath the upper condensing packed bed  32 . An upper recirculation line  40  may extend from the upper liquid collector  38  back to the upper liquid distributor  36  for at least a portion of the cooling fluid flow  14 . One or more pumps  42  or other types of fluid moving devices may be positioned on the recirculation line  40 . A heat exchanger  44  may be positioned on the recirculation line  40  so as to recover a portion of the heat in the flow of flue gases  12 . The recovered heat may be applied to any useful purpose. 
     A lower scrubber packed bed  46  may be positioned within the central cavity  30  beneath the upper condensing packed bed  32 . The primary purpose of the lower scrubber packed bed  46  is to remove gaseous pollutants, i.e., HCl, NH 3 , and the like. Some cooling also may take place until the flue gases  12  become fully saturated. The lower scrubber packed bed  46  may be considered a “polishing scrubber” to reduce the remaining pollutants. The lower scrubber packed bed  46  may be made out of any suitable type of packing materials  34  such as polypropylene and other types of thermoplastics arranged as a random filling or a structured bed. Combinations of different types of packing materials also may be used herein. A lower liquid distributor  48  may be positioned above the lower scrubber packed bed  46 . The lower liquid distributor  48  may be any type of conventional spray or mist delivery devices used to deliver a fluid flow  16  to the lower scrubber packed bed  46 . A lower liquid collector  50  may be positioned beneath the lower scrubber packed bed  46 . A lower recirculation line  52  may extend from the lower liquid collector  50  back to the lower liquid distributor  48  for at least a portion of the fluid flow  16 . One or more pumps  42  or other types of fluid moving devices may be positioned on the recirculation line  52 . Other components and other configurations may be used herein. 
     The wet scrubber system  10  also may include a number of valves, flow meters, and other types of flow regulating components as may be conventionally used. The wet scrubber system  10  described herein is for the purpose of example only. Many other and different types of wet scrubber systems  10  and components thereof may be used in any suitable size, shape, or configuration. 
       FIG. 2  shows an example of a wet scrubber system  100  as may be described herein. The wet scrubber system  100  largely may include components of the wet scrubber system  10  described above in whole or in part. Other components and other configurations may be used herein. 
     The wet scrubber system  100  also may include an activated carbon filter bed system  110 . The activated carbon filter bed system  110  may include an activated carbon filter bed  120 . The activated carbon filter bed  120  may have any suitable size, shape, or configuration. The activated carbon filter bed  120  may have a volume of an activated carbon material  130  therein. The activated carbon  130  may be of conventional type and/or grade. Any suitable volume of the activated carbon  130  may be used herein. The activated carbon  130  may be replaceable. Other components and other configurations may be used herein. 
     The activated carbon filter bed  120  may be in communication with the upper condensing packed bed  32  of the column member  15  via a slipstream line  140 . The slipstream line  140  may extend from the upper recirculation line  40  or elsewhere to the activated carbon filter bed  120 . The activated carbon filter bed system  110  also may include a return line  150 . The return line  150  may extend from the activated carbon filter bed  120  to the upper recirculation line  40  and/or elsewhere in communication with the column member  15  and the upper condensing packed bed  32 . The activated carbon filter bed system  110  also may include any number of the valves, the flow meters, and other types of flow control devices. Other components and other configurations also may be used herein. 
     In use, the cooling fluid  14  from the upper liquid distributor  40  flows downward into the upper condensing packed bed  32  within the central cavity  30  of the column member  15  as the hot flue gases  12  rise therein through the lower scrubber packed bed  46  and into the upper condensing packed bed  32 . The cooling fluid  14  exchanges heat with the hot flue gases  12 . Dioxins in either and/or both the flue gases  12  and/or the polypropylene of the upper condensing packed bed  32  may be dissolved in the cooling fluid  14  as the fluid drops into the upper liquid collector  38  and is forwarded to the upper recirculation line  40 . Dissolving the dioxins into the cooling fluid flow  14  may eliminate or at least reduce the return of the dioxins from the polypropylene of the upper condensing packed bed  32  to the flue gases  12  in the memory effect. 
     Specifically, a slipstream from the main recirculation flow of the cooling fluid  14  may be diverted to the slipstream line  140  and the activated carbon filter bed  120 . Any dioxins in the recirculated cooling fluid  14  may be trapped within the activated carbon  130  before being returned to the upper condensing packed bed  32  of the column member  15  via the return line  150 . The volume of the diverted slipstream of the cooling fluid  14  should be sufficient to effectively prevent or at least reduce the memory effect in the upper condensing packed bed  32 . 
       FIG. 3  shows a further embodiment of an activated carbon filter bed system  160  as may be described herein. In this example, the activated carbon filter bed system  160  may include an upper activated carbon bed  170  and a lower activated carbon bed  180 . The upper activated carbon bed  170  may function as described above. The lower activated carbon bed  180  may be in communication with the lower scrubber packed bed  46  via the lower recirculation line  52 . The activated carbon beds thus may in communication with the upper condensing packed bed  32 , the lower scrubber packed bed  46 , and/or both. Other components and other configurations may be used herein. 
     The activated carbon filter bed system  110  thus may be less expensive as compared to binding the activated carbon into the packing material  34 . Moreover, replacement of the activated carbon in the activated carbon filter bed  120  also may be simplified as compared to replacing all of the packing material itself. Significantly, the activated carbon filter bed system  110  need only be employed when the overall dioxin levels exceed a predetermined level as opposed to continuous operation. The activated carbon filter bed system  110  may be original equipment or part of a retrofit. 
     It should be apparent that the foregoing relates only to certain embodiments of the present application and resultant patent. Numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and the equivalents thereof.