Abstract:
An ammonia injection grid covered with sound adsorption material for a selective catalytic reduction (SCR) system that provides uniform distribution of ammonia to the SCR catalyst in NO X  reduction systems and provides noise suppression for heat recovery steam generation systems, packaged boilers, simple cycle catalyst systems and fired heaters for superior operational efficiency. The ammonia injection grid covered with sound adsorption material includes an injection tube having at least one nozzle for injecting ammonia into a flow of flue gas. The ammonia injection grid also includes a corrugated turbulence enhancer covered with sound adsorption material associated with the injection tube to generate turbulent wake to enhance turbulent mixing and noise suppression.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates generally to an ammonia injection grid for a selective catalytic reduction (SCR) system that provides distribution of ammonia to the SCR catalyst in NO X  reduction systems for heat recovery steam generation systems, packaged boilers, simple cycle catalyst systems and fired heaters and provides noise suppression to eliminate the need for a muffler in the exhaust stack to provide superior operational efficiency. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    NO X  refers to the cumulative emissions of nitric oxide (NO), nitrogen dioxide (NO 2 ) and trace quantities of other chemicals during combustion which are environmentally hazardous substances. Combustion of fossil fuels generates some level of NO X  due to high temperatures and availability of oxygen and nitrogen from both the fuel and air. NO X  emissions may be controlled using low NO X  combustion technology and postcombustion techniques, such as selective catalytic reduction (SCR). SCR systems catalytically reduce flue gas NO X  to nitrogen and water using ammonia (NH 3 ) in a chemical reaction. 
         [0003]    SCR systems treat the NO X  before the gas is released into the atmosphere. SCR systems rely on a catalyst to treat flue gas as the gas passes through the SCR system. Because the catalyst is an integral part of the SCR chemical reaction, SCR systems attempt to provide maximum exposure of the catalyst to the flue gas in order to ensure that all the flue gas comes sufficiently into contact with the catalyst for treatment. 
         [0004]    The catalysts used in SCR systems are carefully engineered and expensive. Thus it is beneficial to be able to control the stoichiometry of the exhaust gas/ammonia/catalyst reaction. In SCR systems, the ammonia is typically introduced into the flue gas stream using an injection grid comprised of injection tubes having a plurality of injection ports or nozzles. The injection grid is designed to provide an even distribution of ammonia throughout the flue gas. The particular injection grid configuration and size utilized within the SCR system is based upon the size of the flue conveying the flue gas stream, as well as the distance from the injection grid to the inlet of the catalyst bed of the SCR. A long distance between the injection grid and the SCR catalyst must typically be provided to assure acceptable turbulent mixing of the ammonia and flue gas. Longer distances require fewer ammonia injectors since adequate mixing can occur prior to the mixture of the flue gas and ammonia entering the SCR catalyst bed. Shortening the distance between the injection point and the catalyst is often desirable, and in new constructions a long distance is often unavailable due to a limited footprint for the ductwork. In a retrofit application, a long distance may require cost prohibitive modifications to the existing system. 
         [0005]    Commonly ammonia, as a reducing agent, is injected and distributed through the injection grid into the flow of flue gas. The nozzles on the injection grid are typically arranged so as to inject the ammonia into and parallel with the flue gas and toward the catalyst located downstream. Ammonia in commonly injected through the injection grid into the flow of flue gas by utilizing an external ammonia vaporization system wherein liquid ammonia, either in an anhydrous or aqueous state, is vaporized in a heater or vaporizer, mixed with dilution air, and then routed to the injection grid for injection into the flow of flue gas at a location upstream of the SCR system. Typically, the ammonia is diluted with water prior to being injected through the injection grid into the flow of flue gas. 
         [0006]    Ammonia injection grids with zone controls have been installed to distribute a prescribed amount of ammonia for NO X  reducing SCR systems. To increase the mixing efficiency and reduce the required mixing distance, many SCR installations are equipped with static mixers. Static mixers typically utilize elaborate designs, are difficult to fabricate, have higher construction and installation costs, and cause significantly higher pressure drop. Static mixers are typically installed between the ammonia injection grid and the SCR catalyst; however, deflectors or baffles attached to the injection nozzles or turbulence enhancers installed between the injection tubes have also been utilized. 
         [0007]    In the exhaust gas stack there is generally a need for noise suppression. Typically, a muffler, also called a silencer, is included in the exhaust gas stack for noise suppression downstream of the ammonia injection grid and the SCR catalyst unit to provide the required noise suppression. The muffler adds length to the exhaust gas stack, increases exhaust stack system costs and increases the pressure drop in the stack. 
         [0008]    It is therefore desirable to provide an ammonia injection grid for a SCR system that provides unified distribution of ammonia to the SCR catalyst in NO X  reduction systems while providing noise suppression without a muffler. 
         [0009]    It is further desirable to provide an ammonia injection grid utilizing a novel turbulence enhancer associated with the downstream side of the injection tubes while providing noise suppression without a muffler. 
         [0010]    It is still further desirable to provide an ammonia injection grid utilizing turbulence enhancers installed on the downstream side of the injection tubes that may be retrofitted to existing ammonia injection grids while providing noise suppression without a muffler. 
         [0011]    It is yet further desirable to provide an ammonia injection grid utilizing a corrugated turbulence enhancer attached to the downstream side of the injection tubes of the ammonia injection grid to provide unified distribution of ammonia to the SCR catalyst while providing noise suppression without a muffler. 
       SUMMARY OF THE INVENTION 
       [0012]    In general, the invention relates to an ammonia injection grid including an injection tube having at least one nozzle for injecting ammonia into a flow of flue gas having sound adsorption material received on the outside of the injection tube such that the sound adsorption material allows the nozzle to inject ammonia into the flow of flue gas while providing noise suppression. The injection tube extends generally transverse to the flow of flue gas. The sound adsorption material may be a porous material or may be a combination of perforated metal material over the porous material. The invention provides the dual purpose of injecting ammonia upstream of the SCR catalyst and suppressing noise in the exhaust gas stack. 
         [0013]    Another embodiment of the invention relates to an ammonia injection grid including an injection tube having at least one nozzle for injecting ammonia into a flow of flue gas, a plurality of horizontal baffle plates upstream of the ammonia injection grid and sound adsorption material received on the outside of the baffles and the injection tube such that the sound adsorption material allows the nozzle to inject ammonia into the flow of flue gas while providing noise suppression. 
         [0014]    In yet another embodiment of the invention, the invention relates to an ammonia injection grid including an injection tube having at least one nozzle for injecting ammonia into a flow of flue gas, a corrugated turbulence enhancer associated with the injection tube to generate turbulent wake to enhance turbulent mixing and sound adsorption material received on the outside of the injection tube and the corrugated turbulence enhancer such that the sound adsorption material allows the nozzle to inject ammonia into the flow of flue gas while providing noise suppression. The injection tube may be a plurality of elongated, circular injection tubes aligned in parallel, with each injection tube having a plurality of nozzles. Further, the corrugated turbulence enhancer may be a plurality of corrugated turbulence enhancers associated with each injection tube. 
         [0015]    Each nozzle of the ammonia injection grid may form an approximate 75 degree angle relative to the upstream flow of flue gas. Further, the ammonia injection grid comprises a plurality of ammonia injection grid panels, such as at least one upper ammonia injection grid panel and at least one lower injection grid panel. The ammonia injection grid can also include an upper header and a lower header in fluid communication with the injection tube for supplying ammonia to the injection tube. The upper header and the lower header may be provided with a substantially V-shaped baffle plate to further increase the mixing efficiency of the ammonia injection grid. The substantially V-shaped baffle plate of the upper header and the lower header may form an approximate 44 degree angle relative to the flow of flue gas. The ammonia injection grid may include a nozzle in the upper header and a nozzle in the lower header, wherein the nozzle of the upper header and the nozzle of the lower header inject ammonia substantially perpendicular to the flow of flue gas. 
         [0016]    The corrugated turbulence enhancer of the ammonia injection grid may be associated with the downstream side of the injection tube. The corrugated turbulence enhancer may include a first trailing end and a second trailing end connected to a substantially V-shaped middle section. An apex of the substantially V-shaped middle section may form a trailing middle section, while the injection tube may be associated with a furrow of the substantially V-shaped middle section of the corrugated turbulence enhancer. Additionally, the first trailing end and the second trailing end of the corrugated turbulence enhancer may form an approximate 32 degree angle relative to the flow of flue gas. The corrugated turbulence enhancer may be substantially M-shaped in cross section. The corrugated turbulence enhancer may include a first leading end joined to the first trailing end and a second leading end joined to the second trailing end  64 . The corrugated turbulence enhancer may be in the form of three (3) contiguous, substantially V-shaped sections. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a perspective view of an ammonia injection grid utilizing circular injection tubes covered with sound adsorption material having a plurality of injection nozzles for injecting ammonia into the flow of flue gas and providing noise suppression; 
           [0018]      FIG. 2  is a perspective view of an ammonia injection grid utilizing a plurality of circular injection tubes having a plurality of injection nozzles and a plurality of horizontal baffle plates attached to the upstream side of the injection tubes for creating turbulent mixing of the ammonia and the flue gas where the tubes and baffles are covered with sound adsorption material to provide noise suppression; 
           [0019]      FIG. 3  is a perspective view of an example of an ammonia injection grid covered with noise adsorption material in accordance with an illustrative embodiment of the ammonia injection grid for selective catalytic reduction systems disclosed herein; 
           [0020]      FIG. 4  is an elevation view looking upstream of an example of an ammonia injection grid covered with sound adsorption material in accordance with an illustrative embodiment of the ammonia injection grid for selective catalytic reduction systems disclosed herein; 
           [0021]      FIG. 5  is an elevation view looking upstream of an ammonia injection grid panel covered with sound adsorption material in accordance with an illustrative embodiment of the ammonia injection grid for selective catalytic reduction systems disclosed herein; 
           [0022]      FIG. 6  is a cross section view along line  6 - 6  of the ammonia injection grid covered with sound adsorption material shown in  FIG. 4 ; 
           [0023]      FIG. 7  is a cross section view along line  7 - 7  of the ammonia injection grid panel covered with sound adsorption material shown in  FIG. 5 ; 
           [0024]      FIG. 8  is a cross section view of another example of a corrugated turbulence enhancer in accordance with an illustrative embodiment of the ammonia injection grid covered with sound adsorption material for selective catalytic reduction systems disclosed herein; and 
           [0025]      FIG. 9  illustrates an exhaust gas stack configuration with the ammonia injection grid covered with sound adsorption material for selective catalytic reduction systems disclosed herein. 
       
    
    
       [0026]    Other advantages and features will be apparent from the following description, and from the claims. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    The devices and methods discussed herein are merely illustrative of specific manners in which to make and use this invention and are not to be interpreted as limiting in scope. 
         [0028]    While the devices and methods have been described with a certain degree of particularity, it is to be noted that many modifications may be made in the details of the construction and the arrangement of the devices and components without departing from the spirit and scope of this disclosure. It is understood that the devices and methods are not limited to the embodiments set forth herein for purposes of exemplification. 
         [0029]    Referring now to  FIGS. 1 through 10 , wherein like numerals of reference designate like elements throughout the several views, and initially to referring to  FIG. 1 , a perspective view of an ammonia injection grid (AIG)  10  utilizing a plurality of circular injection tubes  12  having a plurality of injection nozzles  14 . The AIG  10  is upstream of the SCR catalyst  90  as shown in  FIG. 9 . The injection nozzles  14  along the length of the circular injection tubes  12  direct diluted ammonia into the flow of flue gas  16 . The injected diluted ammonia is mixed with the flue gas by turbulent wake created by the injection tubes. The injection tubes  12  are covered by sound adsorption material  22  to provide noise suppression so that the exhaust gas stack  92  does not require the use of a muffler as disclosed in  FIG. 9 . By eliminating the need for a muffler in the exhaust gas stack  92 , the exhaust gas stack requires less space, is less expensive and has less pressure loss for a more effective exhaust system. The sound adsorption material can be porous material  24  or a combination of porous material  24  covered by perforated metal material  26 . The porous material  24  for sound adsorption would include amorphous wool such as alcaline-earth-silicate (AES) wool or aluminium-silicate (ASW) wool, polycrystalline (PCW) wool such as alumina wool, amorphous paper, PCW paper, polyurethane, elastomeric foam, open-celled polymeric foam or a combination of amorphous wool, PCW wool, amorphous paper, PCW paper, polyurethane, elastomeric foam or open-celled polymeric foam. Some of the porous materials  24  could be used when flue gas temperatures are as high as 1000° C. (1800° F.) while others would require injection of cool air to lower flue gas temperatures to 150° C. (300° F.). Various methods may be used to situate the porous material  24  along the exterior surfaces of the tubes  12  without covering the nozzles  14  such as coating, fusing, dipping, gluing, wrapping, pinning, taping or strapping. Perforated metal material  26  for sound adsorption can be used to cover the porous material  24  to enhance sound suppression. Various methods may be used to situate the perforated materials  26  along the exterior surface of the porous material  24  such as coating, welding, soldering, brazing, fusing, dipping, gluing, wrapping, pinning or strapping. 
         [0030]      FIG. 2  is a perspective view of another embodiment of the ammonia injection grid  10  utilizing a plurality of horizontal baffle plates  20  attached to the upstream side of the injection tubes  12  for creating turbulent mixing of the ammonia and the flue gas. The AIG  10  of  FIG. 2  is comprised of a plurality of injection tubes  12  each having a plurality of nozzles  14 . The nozzles  14  are arranged so as to inject the diluted ammonia into the flow of the flue gas  16  prior to entering the SCR catalyst  90  (not shown) located downstream. The ammonia supplied to the injection tubes  12  may be via headers  46 . 48  (not shown). The plurality of horizontal baffle plates  20  are attached to the upstream side of the injection tubes  12  for creating a wake to increase the turbulent mixing between the ammonia and the flue gas. The horizontal baffle plates  20  have sound adsorption material situated along the external surface of said baffle plates to enhance the noise suppression capabilities of the AIG  10 . The sound adsorption material can be porous material  24  or a combination of porous material  24  covered by perforated metal material  26 . 
         [0031]      FIG. 3  is a perspective view and  FIG. 4  is an elevation view looking upstream of an ammonia injection grid  10  having at least one injection tube  12  with at least one nozzle  14  for injecting ammonia into the flow of flue gas  16 . Each injection tube  12  extends generally transverse to the flow of flue gas, depicted by arrow,  16  and includes at least one corrugated turbulence enhancer  36  associated therewith to generate a turbulent wake downstream of the injection to enhance mixing of the injected ammonia and flue gas. Both the injection tube  12  and the corrugated turbulence enhancer  36  have sound adsorption material  22  being situated along their external surfaces for enhanced noise suppression such that a muffler is not required in the exhaust gas stack  92 . The sound adsorption material  22  can be porous material  24  or a combination of porous material  24  covered by perforated metal material  26 . The AIG  10  may include a plurality of injection tubes  12 , with each injection tube  12  having a plurality of nozzles  14 . The nozzles  14  may form an upstream angle  38  relative to the flow of flue gas  16 , such as an approximate seventy-five (75) degree angle opposite to the flow of flue gas  16 . Each of the injection tubes  12  may have a plurality of corrugated turbulence enhancers  36  associated therewith. The injection tubes  12  may be vertical and in parallel alignment. However, those skilled in the art will appreciate that other alignments and arrangements may be used with the AIG  10 , such as horizontal or diagonal. As shown, the injection tubes  12  are aligned along the same plane, but may also be in a staggered arrangement. 
         [0032]    As shown in  FIG. 4 , the AIG  10  may include a plurality of ammonia injection panels  40 , such as at least one upper ammonia injection panel  42  and at least one lower ammonia injection panel  44  adjacent each other. Each ammonia injection panel  40  may include an upper header  46  and a lower header  48 , with a plurality of elongated, circular injection tubes  12  disposed there between. The upper header  46  and the lower header  48  have sound adsorption material  22  being situated along their external surfaces for enhanced noise suppression. The sound adsorption material  22  can be porous material  24  or a combination of porous material  24  covered by perforated metal material  26 . 
         [0033]    The AIG  10  may include headers, such as at least one upper header  46  and at least one lower header  48 , in fluid communication with the injection tubes  12  to supply ammonia from an ammonia vaporizer or heater (not shown) to each of the injection tubes  12 . Further, the AIG  10  may be integrated into an SCR system (not shown). Each of the headers  46  and  48  may include at least one nozzle  50 . Each of the nozzles  50  may inject ammonia substantially perpendicular to the flow of the flue gas  16 . The headers  46  and  48  may also include at least one baffle plate  52  to further increase the mixing efficiency of the injected ammonia and flue gas. The baffle plate  52  associated with each of the headers may be a substantially V-shaped baffle plate  52 . As shown in  FIG. 6 , the substantially V-shaped baffle plate may be associated with the downstream side of the header  46  or  48 . The substantially V-shaped baffle plate  52  may be secured to the header  46  or  48  at an angle  54 , and may also form an angle  56 , for example approximate forty-four (44) degrees, with the nozzle  50  of the header  46  or  48 , as shown in  FIG. 6 . The opposing ends  58  and  60  of the substantially V-shaped baffle plate  52  of the header  46  or  48  may form an angle  62 , for example approximately one-hundred and sixteen (116) degrees. The substantially V-shaped baffle plate  52  associated with the header  46  or  48  acts in conjunction with the corrugated turbulence enhancer  36  for uniform distribution of ammonia and flue gas prior to flowing to the downstream SCR catalyst  92 . The substantially V-shaped baffle plates  52  have sound adsorption material  22  being situated along their external surfaces for enhance noise suppression. The sound adsorption material  22  can be porous material  24  or a combination of porous material  24  covered by perforated metal material  26 . 
         [0034]    The corrugated turbulence enhancer  36  associated with each of the injection tubes  12  of the AIG  10  may be associated with the downstream side of each injection tube  12 . Turning now to  FIG. 7 , the corrugated turbulence enhancer  36  may be substantially M-shaped, with a first trailing end  64  and a second trialing end  66  connected to a substantially V-shaped middle section  68 . An apex  70  of the substantially V-shaped middle section  68  of the corrugated turbulence enhancer  36  can form a trailing middle section. A furrow  72  of the substantially V-shaped middle section  68  of the corrugated turbulence enhancer  36  may be associated with the injection tube  12 . The first and second trailing ends  64  and  66  of the corrugated turbulence enhancer  36  are at an angle  74  relative to the flow of flue gas  16 , such as an approximate thirty-two (32) degree angle. 
         [0035]      FIG. 8  illustrates another example of the corrugated turbulence enhancer  36  of the ammonia injection grid  10 . As shown in  FIG. 8 , the corrugated turbulence enhancer  36  may be associated with the downstream side of each injection tube  12 . The corrugated turbulence enhancer  36  may include a first leading end  80  joined to the first trailing end  66  and a second leading end  82  joined to the second trailing end  64 . As shown, the corrugated turbulence enhancer  36  may be in the form of three (3) contiguous, substantially V-shapes. The two (2) outer V-shapes of the corrugated turbulence enhancer may form an angle  78 , which may be approximately one-hundred (100) degrees. Further, an angle  76  between the apex  70  of the substantially V-shaped middle section  68  of the corrugated turbulence enhancer  36  and the apex of each of the substantially V-shaped outer sections may be approximately one-hundred and sixteen (116) degrees. The addition of the first leading end  80  and the second leading end  82  to the corrugated turbulence enhancer  36  further enhances the turbulent wake downstream of the injection tubes  12 , resulting in an increased mixing efficiency between the injected ammonia and the flow of flue gas  16 . As shown in  FIG. 6 , the V-shaped baffle plates  52  have sound adsorption material  22  being situated along their external surfaces for enhance noise suppression. The sound adsorption material  22  can be porous material  24  or a combination of porous material  24  covered by perforated metal material  26  to further enhance the noise suppression of the AIG  10  for superior operational efficiency. 
         [0036]    The corrugated turbulence enhancer  36  covered by sound adsorption material  22  of the AIG  10  dramatically increases mixing efficiency, reduces the mixing distance and reduces the exhaust gas stack length by elimination of the muffler as shown in  FIG. 9 . This reduction and increased efficiency allows for a compact SCR system and provides a significant capital cost reduction. The corrugated turbulence enhancer  36  covered by sound adsorption material  22  disclosed herein allows for a low downstream pressure drop to further increase the overall efficiency of the SCR system. In addition, the corrugated turbulence enhancer  36  disclosed herein may be retrofitted to existing ammonia injection grids to achieve the benefits discussed above. The corrugated turbulence enhancer  36  may be secured to existing ammonia injection grids on the downstream side of the injection tubes  12 . 
         [0037]    The entire ammonia injection grid may be constructed to be mounted on a skid to be easily transported to a desired location. 
         [0038]    Whereas, the devices and methods have been described in relation to the drawings and claims, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the spirit and scope of this invention.