Abstract:
A dispersion apparatus for dispersing a treating agent into a fluid treatment system that includes a flow duct in which a fluid stream flowing through the duct is mixed with the treating agent. The apparatus is based on a multi-pipe lance positioned in the stream flow, where each pipe supplies a minimum of feed discharge nozzles (typically one to four), and the individual pipes branch off from the same location. Use of the multi-pipe lance, in combination with a suitable baffle, results in better overall dispersion/distribution of the injected medium by surface area. By improving the surface area distribution, better utilization of the injected sorbent can be achieved. The baffle acts to generate a low pressure zone on its downstream side and creates a high-intensity turbulence plume in the fluid. The orifices of the pipe are located to inject the treating agent into the turbulence plume to better distribute and intermix the injected treating agent into the surrounding fluid.

Description:
RELATED APPLICATION 
       [0001]    This application is a continuation-in-part of U.S. patent application Ser. No. 12/152,654, filed May 15, 2008. The latter claimed priority from U.S. Provisional Patent Application No. 60/930,703 filed May 18, 2007. 
     
    
     FIELD OF INVENTION 
       [0002]    This invention relates generally to apparatus and methods for fluid treatment, and more specifically relates to apparatus for injecting a treating agent into a fluid stream while generating enhanced fluid phase turbulence to better distribute and intermix the injected treating agent into the surrounding fluid. 
       BACKGROUND OF INVENTION 
       [0003]    During the course of treating an acid or other gas, in order for example to control the atmospheric emission of polluting contaminants such as sulfur oxides, it is common as one step of the process to disperse solid particles of a treating agent such as a carbonate into the gas in order to react with or adsorb the undesired component. In order to do this a dispersion lance or other device or collection of devices may be used, the function of which is to disperse the solid particles of treating agent into the gaseous stream. Nozzles or collections of particle ejection nozzles can be used for this purpose. Since, however, simple ejection of the particles from such nozzles is not very effective in generating thorough mixing of the particles with the gas stream, it is also known to use baffles, usually positioned directly downstream of the injection point to encourage turbulence, thereby enhancing the mixing of particles with the gas stream. These prior devices and apparatus arrangements, however, have been of only limited efficacy, often because the turbulence generated has not been effective enough to break up the ejected particle streams, which to the contrary are commonly found, when examined, to advance from their injection points as rather distinct linear streams as they move into the surrounding ambient gas stream. Accordingly, a need has existed for an injection lance and baffle construction which is fully able to produce the highly turbulent conditions required for full and effective dispersion and mixing into the gas stream of the injected particles of the treating agent. 
         [0004]    Similar considerations as described above for the case of injection of solid particles into a gas flow, arise where an injection lance and baffle construction is used for injecting liquids or gaseous treating agents into a fluid flow of a gas, or injection of solid particles, liquids, or gases into a flow of a liquid phase. Such injection can, of course, be for other well-known purposes, i.e. not necessarily for eliminating or reducing contaminating sulfurous and/or other noxious components from flue gases or the like. 
         [0005]    In our aforementioned Ser. No. 12/152,654 (hereinafter referred to as &#39;654) application, apparatus is disclosed which is capable of considerably alleviating the cited difficulties of the prior art. Specifically, a dispersion lance is provided for use in combination with a fluid treatment system of the type which includes a flow duct in which a fluid stream is mixed with a treating agent. The dispersion lance includes a pipe mounted in the duct with its axis approximately transverse to the direction of the fluid stream flow, the pipe having a series of openings along its length for injecting a treating agent supplied to the pipe into the fluid stream. A baffle extends lengthwise along the pipe, the baffle having a cross-section the central portion of which is V-shaped, with the apex of the V facing upstream of the fluid stream flow, and with generally flattened wing portions extending from the legs of the V beyond the sides of the pipe in a direction where they transversely intersect the stream flow. The baffle acts to generate a low pressure zone on its downstream side, which enhances turbulence in the fluid. The orifices of the pipe are located to inject the treating agent into the low pressure zone to better distribute and intermix the injected treating agent into the surrounding fluid. 
         [0006]    The wings of the baffle form an angle of less than 180° with respect to the legs of the central portion, and the apex of the central portion V generally subtend an angle of from about 30 to 135°, with an angle of about 90° being typical. The wings can have a generally rectangular shape, and may be provided with notches on their trailing edge. 
         [0007]    In a typical application as will be described below, the invention is applicable to the case of injection of solid particles into a gas flow. A particularly valuable such use is found in the aforementioned process of dispersing solid particles of a sorbent treating agent such as a carbonate into a flue gas in order to react with or adsorb a component of the gas to avoid its discharge into the environment, and/or to recover the component for other uses. In the following, this particular use of the invention will be emphasized. However, it will be appreciated that the invention is also applicable to the environments where an injection lance and baffle construction is to be used for injecting liquids or gaseous treating agents into a gaseous flow; or where an injection lance and baffle construction is to be used for injection of solid particles, or liquids or gases, into a flow of a liquid phase. 
       SUMMARY OF INVENTION 
       [0008]    Although the lance construction in our &#39;654 application results in much improved mixing relative to the prior art lance, the overall distribution of the surface area of the injected treating agent (such as the exemplary sorbent) was found to not be markedly uniform along the length of the lance. Through further analysis of the solids dispersion of the &#39;654 lance, the present inventors discovered that the mass and the surface area of the particles emitted from the lance were biased towards its far end (due to the momentum of the particles). This is a problem that calls for solution, in that for mass-transfer-limited reactions, the removal efficiency of an injected sorbent is a function of the distribution of surface area of the injected sorbent in the gas-carrying duct. 
         [0009]    To address this issue, we have now developed a multi-pipe lance, where each pipe supplies a minimum of feed discharge nozzles (typically one to four), and the individual pipes branch off from the same location or are otherwise fed with the sorbent or other treating agent to be dispersed. We have found that use of the multi-pipe lance in combination with a suitable baffle, results in better overall dispersion/distribution of the injected medium by surface area. By improving the surface area distribution, better utilization of the injected sorbent can be achieved 
         [0010]    The multi-pipe lance retains the bulk, in-duct mixing properties of the &#39;654 lance, and improves the distribution of surface area of the injected sorbent along the length of the lance. The improved surface area distribution is accomplished through the use of a dispersion lance mounted in the gas-carrying duct with its axis approximately transverse to the direction of the fluid stream flow, the lance having a treating agent feed section, and a plurality of parallel pipes extending from said section, each said pipe having one or more feed discharge nozzles along its length for injecting the treating agent supplied to said pipe into the fluid stream. A baffle extends lengthwise along the upstream side of the lance, the baffle preferably being formed as a partial cylindrical surface, such as the surface of a semi-cylinder. The convex side of the cylindrical surface faces upstream of the fluid stream flow, and adjoins generally flattened wing portions which extend from the lateral edges of the cylindrical surface to beyond the lateral sides of the multiple pipes, where the wings transversely intersect the stream flow. The baffle acts to generate a low pressure zone on the downstream sides of the nozzle-feed pipes, which enhances turbulence in the gas. The feed discharge nozzles of the nozzle-feed pipes are located to inject the treating agent into the low pressure zone to better distribute and intermix the injected treating agent into the surrounding gas stream. 
         [0011]    The said treating agent feed section receives feed from an inlet supply line, and includes successively in the downstream direction: a venturi section, a mixing bar section, and a feed splitter section. The venturi section redirects sorbent particles away from the walls of the main feed pipe downstream of any bends in the inlet supply line. This feature is desirable when the supply of sorbent to the lance is not uniform, which it usually will not be, and has the intended purpose of improving the performance of the mixing bar section. 
         [0012]    The mixing bar section serves to spread the sorbent particles uniformly across the main feed pipe cross-section in preparation for the splitter vane section. The feed splitter section allocates the uniformly distributed sorbent particles evenly into separate compartments each of which leads into one of the separate nozzle-feed pipes. The nozzle-feed pipes transfer the uniformly allocated sorbent particles to the discharge nozzles. There can be one or more discharge nozzles per feed pipe, though the number is preferably limited to the minimal required to achieve the desired spray coverage. Each discharge nozzle has an orifice opening size sufficiently small to balance the pressure drop evenly across the separate feed pipes. This serves to ensure that the pneumatic air and sorbent particles it is conveying are allocated relatively evenly between the separate feed pipes. The numbers of discharge nozzles per pipe, as well as the distance between nozzles on a single pipe, are both limited in order to minimize the bias in the mass flow rate and total surface area of solids emitted from each nozzle. The distribution of injected sorbent particles along the length of the lance can be modified to match any potential uneven distribution of gas flow along the length of the lance by adjusting the nozzle orifice opening sizes of individual nozzles and by adjusting the positions of the nozzles along the length of the lance. 
         [0013]    The baffle preferably extends below the last nozzle for a distance approximately equal to the distance between successive discharge nozzles. Due to the flue gas flow patterns in the wake of the baffle, the excess length of the baffle (past the last nozzle) serves to distribute additional sorbent beyond the last discharge nozzle. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0014]    The invention is diagrammatically illustrated, by way of example, in the drawings appended hereto, in which: 
           [0015]      FIGS. 1 and 1A  are respectively schematic transverse and plan sectional views of a typical prior art dispersion lance, which is positioned in a duct carrying a gas stream, which is being treated with a particulate injected from the lance; 
           [0016]      FIGS. 2 and 2A  are respectively schematic transverse and plan sectional views of a dispersion lance and baffle in accordance with the invention of our &#39;654 application, which are positioned in a duct carrying a gas stream which is being treated with a particulate injected from the lance; 
           [0017]      FIG. 3  is a schematic partially broken-away perspective view of a multi-pipe dispersion lance and baffle in accordance with the invention; 
           [0018]      FIG. 4  is an enlarged view of the upper portions of the  FIG. 3  apparatus; 
           [0019]      FIG. 5  is a side elevational view of the lance and baffle apparatus of  FIGS. 3 and 4 ; 
           [0020]      FIG. 6  is a front elevational view of the lance and baffle apparatus of  FIGS. 3 and 4 , looking at the apparatus from downstream of same; 
           [0021]      FIG. 7  is a top plan view, schematic and partially broken away, of the lance and baffle apparatus of  FIGS. 3 and 4 ; 
           [0022]      FIG. 8  is a schematic broken-away perspective view showing typical injected sorbent particle tracks enabled by a pair of the prior art apparatus of  FIGS. 1 and 1A ; 
           [0023]      FIG. 9  is a schematic broken-away perspective view showing typical injected sorbent particle tracks enabled by a pair of multi-pipe lance and baffle dispersion apparatus of the type shown in  FIGS. 3 through 7 ; 
           [0024]      FIG. 10  is a schematic top plan view illustrating the injected sorbent particle tracks for the prior art lance of  FIGS. 1 and 1A ; 
           [0025]      FIG. 11  is a schematic top plan view illustrating the injected sorbent particle tracks for the apparatus of the invention shown in  FIGS. 3 through 7 ; 
           [0026]      FIGS. 12A through 12F  schematically depict cross-sectional views taken 10 ft downstream of the injection plane for the prior art lance of  FIGS. 1 and 1A , and show distribution and mixing of the injected sorbent particle surface area by particle size at the said downstream position; 
           [0027]      FIGS. 13A through 13F  schematically depict cross-sectional views taken 10 ft downstream of the injection plane for the apparatus of the invention as in  FIGS. 3 through 7 , and show the distribution and mixing of the injected sorbent particle surface area by particle size at the said downstream position; 
           [0028]      FIGS. 14A and 14B  schematically depict cross-sectional views taken 10 ft downstream from the prior art lance of  FIGS. 1 and 1A , and from the multi-pipe lance of the invention as in  FIGS. 3 through 7 , and show for each the total distribution and mixing of injected sorbent particle surface area for all particle sizes at the said downstream position; and 
           [0029]      FIG. 15  is a graph depicting the normalized pneumatic air and sorbent surface area distribution along the length of lance for a prior art lance as in  FIGS. 1 and 1A , and for the multi-pipe lance and baffle apparatus of the invention as in  FIGS. 3 through 7 . 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
       [0030]    In  FIGS. 1 and 1A  schematic transverse and plan sectional views of a typical prior art dispersion lance  10 , which is positioned in a duct  12  carrying a gas stream flow  14  which is being treated with a particulate ejected from the lance. The position of the lance within duct  12  is not shown to scale; rather the duct  12  and its actual wall spacing from lance  10  is merely intended to be suggested by the dotted lines used here—and as well in  FIG. 2A . Also while dimensions and certain angles are shown in  FIGS. 1 ,  1 A,  2  and  2 A, these are cited for illustration only and are not in any way intended to be limiting of the invention. The lance  10  comprises a pipe  8  which is mounted in duct  12  by means not shown. Pipe  8  has two parallel lines of openings  16  along its length. As seen in  FIG. 1A  the parallel lines of openings  16  are at the downstream facing side of pipe  8 , and are oriented so that axial openings in opposed lines are at an angle of about 90° with respect to each other. The particulate treating agent to be dispersed into the flowing gas stream  14  is provided to pipe  8  and the particles are then injected into the gas stream from openings  16 . A pressurized carrier gas can be provided to pipe  8  with the particles to enable their ejection, or other means can be used to generate forces for ejection of the particles through openings  16 . 
         [0031]    In  FIGS. 2 and 2A  schematic transverse and plan sectional views appear of a dispersion lance and baffle in accordance with the &#39;654 invention, which are similarly positioned in a duct  12  carrying a gas stream which is being treated with a particulate ejected from the lance. The pipe  18  is substantially similar to pipe  8  of  FIGS. 1 and 1A , and is again provided with openings or orifices  20  arranged along two parallel lines extending along pipe  18 . However unlike the prior art device, pipe  18  is associated with a baffle  22 , which is mounted in any convenient manner in duct  12 , including by being affixed to pipe  18  by supports  24 . Pipe  18  and baffle  22  can be positioned in a vertical or horizontal orientation in duct  12 , or otherwise depending on requirements and on duct geometry. Baffle  22  extends lengthwise along pipe  18 , and has a cross-section the central portion  26  of which is V-shaped, with the apex  28  of the V facing upstream of the gas stream flow  14 , and with generally flattened wing portions  30  extending from the legs  32  of the V beyond the lateral sides of pipe  18  in a direction where they transversely intersect the gas stream flow  14 . The apex  28  of the V subtends an angle of about 90°, but more generally can be in the range of from about 30 to 135°. The V shape of the central portion  26  of baffle  22  can be modified so as to be rounded at its bottom to a concave curve (i.e. at the surface facing pipe  18 ), or even to the extent of defining a U shape as it partially encloses pipe  18 . Wing portions  30  are seen to define a second V  34  with the legs  32 . The included angle of second V  34  should be less than 180°. Wing portions  30  are typically flat rectangles as seen in  FIG. 2 , but they can also be modified, as for example by being provided with notches of various shapes on their trailing edges. 
         [0032]      FIGS. 3 through 7  depict in simplified views the improved multi-pipe dispersion lance  40  and baffle  72  of the invention.  FIGS. 3 through 7  are best considered simultaneously. Although the present invention is not in any way to be considered so limited, for purposes of concrete exemplification, the dispersion apparatus will be discussed especially in the case where it is being used for dispersing a sorbent treating agent into a flowing stream of flue gas in a duct such as has been described in connection with  FIGS. 2 and 2A . 
         [0033]    The lance  40  comprises a main feed inlet pipe  42 , which receives the particulate treating agent such as calcium carbonate at inlet end  44  where it is carried by a pneumatic air or other gas flow. The treating agent feed section  45  receives the feed from inlet pipe  42 , and includes successively in the downstream direction: a venturi section  46 , a mixing bar section  48 , and a feed splitter section  50 . The feed thus passes successively through venturi section  46 , then through mixing bar section  48 , and to feed splitter section  50  which allocates the feed into the separate nozzle-feed pipes  52  which extend downwardly in parallel fashion. Four such feed pipes  54 ,  56 ,  58 , and  60  are shown, but different pluralities of nozzle-feed pipes may be used consistent with needs of a given system. 
         [0034]    The venturi section  46  redirects sorbent particles away from the walls of main feed pipe  42  downstream of any bends in the inlet supply line. This feature is desirable when the supply of sorbent to the lance is not uniform, which it usually will not be, and has the intended purpose of improving the performance of the mixing bar section  48 . 
         [0035]    The mixing bar section  48  includes a series of vertically spaced plates  49  each including spaced bars  51 . Section  48  serves to spread the sorbent particles uniformly across the main feed pipe cross section in preparation for the feed splitter section  50 . Section  50  includes an enlarged cylinder  62  in which is mounted splitter vanes  64  which also extend into the diametrically larger cylinder  66 . The vanes  64  divide the section  50  into four compartments  68  ( FIG. 7 ), each of which connects to one of the nozzle feed pipes  52 . The splitter section  50  allocates the uniformly distributed sorbent particles evenly into compartments  68 . The nozzle-feed pipes  52  transfer the uniformly allocated sorbent particles to the discharge nozzles  70  which are present along each of the nozzle-feed pipes. There can be one or more discharge nozzles per feed pipe, though the number is preferably limited to the minimal required to achieve the desired spray coverage. Each discharge nozzle  70  has an orifice opening size sufficiently small to balance the pressure drop evenly across the separate feed pipes. This serves to ensure that the pneumatic air and sorbent particles it is conveying are allocated relatively evenly between the separate feed pipes and nozzles. The number of discharge nozzles  70  per pipe, as well as the distance between nozzles on a single pipe, are both limited in order to minimize the bias in the mass flow rate and total surface area of solids emitted from each nozzle. 
         [0036]    It will be seen from  FIGS. 3 ,  5 , and  6  that the separate nozzle-feed pipes  52  terminate at differing distances below the compartments  68 , and that accordingly the nozzles  70  of each said pipe are at a portion of a given pipe where the nozzle discharges are not impeded by any of the remaining pipes. 
         [0037]    A baffle  72  extends lengthwise along the upstream side of lance  40 . Although the baffle can incorporate the V shape configuration of the baffle in  FIGS. 2 and 2A , or a modification in which the V is rounded to a curve at its vertex, it has been found preferable for the baffle to be formed as a partial cylindrical surface  74  ( FIG. 7 ), here as the surface of a semi-cylinder. The concave side of cylindrical surface  74  faces upstream of the fluid stream flow, and adjoins generally flattened wing portions  76  which extend from the lateral edges of the cylindrical surface to beyond the lateral sides of the multiple pipes, where the wings transversely intersect the stream flow. The baffle  72  acts to generate a low pressure zone on the downstream sides of the nozzle-feed pipes which enhances turbulence in the gas thereby enhancing mixing of the injected sorbent with the gas. The discharge nozzles  70  ( FIG. 7 ) of the nozzle-feed pipes are located to inject the discharge  71  of treating agent into the low pressure zone to better distribute and intermix the injected treating agent into the surrounding gas stream. The bottom of baffle  72  preferably extends below the last nozzle of nozzle-feed pipes  52  for a distance approximately equal to the distance between successive discharge nozzles, whereby due to the flue gas flow patterns in the wake of the baffle, the excess length of the baffle past the last nozzle serves to distribute additional particles beyond the last discharge nozzle. 
         [0038]    As will be better appreciated from the following studies, all of which were generated via Computational Fluid Dynamics modeling (CFD), the baffle  72  acts to markedly enhance gas phase turbulence to thereby better distribute and mix the injected sorbent particles into the surrounding gas flow. 
         [0039]    The CFD Modeling basis in the studies was as follows:
   Modeled a pair of vertical lances in a duct partition 9 ft-6 in tall and 12 ft-6 in wide.   Total Gas Flow in Duct Partition=396,000 acfm.   Average Gas Velocity in Duct=55.6 ft/sec   Gas Temperature=316° F.
 
Solids Particle Size Distribution for treating agent
   Sauter Mean Diameter=8.5 micron   Volume Mean Diameter=23.3 micron   Divided into 6 discrete sizes:   
 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                  1 micron 
                 5% by volume 
               
               
                   
                  3 micron 
                 5% 
               
               
                   
                 11 micron 
                 40%  
               
               
                   
                 30 micron 
                 40%  
               
               
                   
                 46 micron 
                 5% 
               
               
                   
                 87 micron 
                 5% 
               
               
                   
                   
               
             
          
         
       
       
         Pneumatic Carrier Air Flow per Lance=15 scfm 
         Solids Injection Rate per Lance=25.5 lb/hr 
       
     
         [0049]    Thus in  FIG. 8  a schematic broken-away perspective view shows typical particle tracks enabled by the prior art apparatus of  FIGS. 1 and 1A , where two lances  10  of the prior art type are present in the duct. This is to be compared with the  FIG. 9  schematic broken-away perspective view, which shows typical particle tracks enabled by the apparatus of the invention based on two multi-pipe lances  40  of the type depicted in  FIGS. 3 through 7  placed side by side in a flue gas duct partition. It will be evident that the prior art arrangement results in the ejected particles moving downstream in narrow distinct, confined and separated bands or columns. Increasing the amount of energy used to eject the particles pushes particles further out from the lance, but still results in columns of particles in the gas path. In contrast, the multi-pipe lances  40  of the present invention by generating increased gas turbulence and recirculation downstream of the lance, rapidly produce a highly intermixed and dispersed cloud of particles, and indeed one that becomes more spread out and dispersed in the surrounding gas as the particles proceed in the downstream direction. As mentioned above, and due to the flue gas flow patterns in the wake of the baffle, the excess length of the baffle  72  (past the last nozzle as seen at  74 ) serves to distribute additional sorbent beyond the last discharge nozzle. The baffle  72  typically extends below the last nozzle for a distance approximately equal to the distance between successive discharge nozzles. 
         [0050]      FIGS. 10 and 11 , which are each schematic top plan views of the lance particle tracks, again show the much greater dispersion achieved by use of the invention lance  40  ( FIG. 11 ) as compared with the use in  FIG. 10  of the prior art lance  10  of  FIGS. 1 and 1A . 
         [0051]    The Figures illustrate how the present invention generates a low pressure zone in the area directly behind (downstream) of the lance baffle. The feed discharge nozzles  70  in the present invention are placed within this low pressure zone generated by baffle  72 . Positioning the orifices within the low pressure zone provides the added benefit of reducing air pressure requirements if the injected particles are pneumatically conveyed. In addition to the low pressure zone, the lance baffle generates a high-intensity turbulence plume in the gas phase immediately downstream of the lance. It is this turbulence plume that results in the marked improvement in dispersion of the particulate in comparison to the prior art. 
         [0052]      FIGS. 12A through 12F  schematically depict cross-sectional views taken 10 ft downstream from the prior art lance  10  of  FIGS. 1 and 1A , and show distribution of the total surface area of the ejected particles by particle size at the said downstream position. This is to be compared with  FIGS. 13A through 13F  which schematically depict cross-sectional views taken 10 ft downstream from the multi-pipe lance  40  of the invention as in  FIGS. 3 through 7 , and which similarly shows distribution of the total surface area of the ejected particles by particle size at the downstream position. 
         [0053]      FIG. 14A  schematically depicts a cross-sectional view taken 10 ft downstream from the prior art lance  10  of  FIGS. 1 and 1A , and shows the distribution of the total surface area of the ejected particles of all particle sizes at the said downstream position. This is to be compared with  FIG. 14B  showing the same cross-sectional view taken 10 ft downstream from the multi-pipe lance  40  of the invention as in  FIGS. 3 through 7 , and again showing the distribution of the total surface area of the ejected particles of all particle sizes at the said downstream position. The much wider and taller dispersion of particles in the gas stream achieved by the invention will be evident. 
         [0054]    The graphical showing of  FIG. 15  depicts the normalized pneumatic carrier air and sorbent surface area distribution along the length of a prior art lance  10  as in  FIGS. 1 and 1A , and of a multi-pipe lance  40  of the invention. As already mentioned each discharge nozzle has an orifice opening size sufficiently small enough to balance the pressure drop evenly across the exemplified four separate feed pipes. This serves to ensure that the pneumatic air and sorbent particles it is conveying are allocated relatively evenly between the separate feed pipes. The multi-pipe lance  40  (denoted by a black solid line for surface area distribution and a black solid line with squares for airflow distribution) is seen to perform better than the simple pipe lance  10  because the maximum deviation from 1.0 (where the value 1.0 equates to a completely even distribution) is less than the simple pipe lance for both sorbent surface area and air flow distributions. 
         [0055]    While the present invention has been set forth in terms of specific embodiments thereof, it will be appreciated that in view of the present disclosure, numerous variations upon the invention are now enabled to those skilled on the art, which variations yet reside within the present teachings. Accordingly the invention is to be broadly construed, and limited only by the scope and spirit of the disclosure and of the claims now appended hereto.