Abstract:
A surface foam diffuser system having a first nozzle disposed above a top surface of the at least partially liquid contents, a splash plate positioned adjacent to the first nozzle outlet, and a second nozzle disposed below the top surface of the at least partially liquid contents is disclosed for suppressing foaming in large processing tanks. The system nozzles each have an inlet for receiving pressurized liquid and an outlet for ejecting a liquid stream into the tank, the depth of the second nozzle and the direction of the liquid stream there from being such that rotation of the top surface is facilitated. The spray of the first nozzle, as dispersed by the splash plate, reduces foam on at least a portion of the top surface, with the rotation of the top surface allowing each portion of the top surface to eventually fall within the reducing spray.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present system relates to a foam busting and sub-surface mixing configuration for use in processing tanks such as, for example, waste-water digesters. Particularly, the present system relates to a unique nozzle arrangement which provides greater foam suppression in sludge-type compositions. 
       BACKGROUND OF THE INVENTION 
       [0002]    Surface foaming and sediment deposition can both create problems in storage and treatment tanks where large volumes of liquid/slurry are stored and stirred, mixed, or agitated. In many cases the two problems are inversely related. That is, solving one of the problems may directly worsen the other. This relationship can make it very difficult for those skilled in the art to design and implement a system which addresses and solves both problems. 
         [0003]    For example, in activated sludge secondary treatment plants, slurries in large tanks are typically stirred, mixed, or agitated in order to suspend solids in the liquid prior to emptying the tank. Without such mixing, the solids would settle to the bottom of the tank. The settling of solids over even a short period of time can develop into a huge problem, as the build-up of sediment on the tank bottom reduces the volume of the tank. Other benefits of the auxiliary mixing of digester tank contents are: reduction of thermal stratification; dispersing substrate for better contact with active biomass; reduction in scum buildup; dilution of inhibitory substances or adverse pH and temperature feed characteristics; increased effective volume of the reactor; and, separation of reaction product gases is improved. However, stirring, agitation and mixing can also result in increased surface foam due to the abundance of surfactants which can be found in such liquids. 
         [0004]    Similarly, surface foaming can be a problem in anaerobic digesters, where gases are the natural product of the digestion process. The gases create foam in the form of bubbles and/or scum on the surface of the liquid/slurry in the tank. If the foaming problem is not addressed, the foam uses up volume in the tank, or the tank can overflow. Further, agitation of the tank contents to assist the digestion process may exacerbate the foaming as noted above. 
         [0005]    In both cases, anti-foaming agents may be added to the tanks to suppress foaming. However, these agents are expensive and, in some instances, are either too limited in their ability to suppress foaming or may have negating effects on other favored processes (e.g., digestion). 
         [0006]    Another common problem for many activated sludge plant digesters is the creation of a thick (viscous) upper surface. This happens because thickened sludges from the aerobic digestion side of the plant get fed back into the anaerobic digesters to further break down the sludge. This makes the anaerobic digester sludge much more viscous and harder to mix, sometimes resulting in lower level tank mixing but not in upper surface mixing. Floor-mounted mixing nozzles do not necessarily assure upper surface rotation. 
         [0007]    Mechanical anti-foaming devices, such as the nozzle system disclosed in U.S. Pat. No. 7,628,183 to Dorsch et al. and assigned to the Assignee of the present technology, are very effective at suppressing foaming. The complete disclosure of U.S. Pat. No. 7,628,183 is hereby incorporated by reference. However, without surface rotation, and due to the extensive size of digester tanks, expensive plumbing for a plurality of anti-foaming nozzles would be required to adequately suppress foaming. 
         [0008]    The present invention overcomes these and many other disadvantages of previous devices and processes. Disclosed is a system which is effective at suppressing foaming, even during mixing, stirring and agitation, without the use of expensive anti-foaming agents and the system is easy and relatively inexpensive to manufacture and install. 
       SUMMARY OF THE INVENTION 
       [0009]    There is disclosed herein an improved nozzle configuration for suppressing foaming in a treatment tank filled to a level with at least partially liquid contents which avoids the disadvantages of prior devices while affording additional structural and operating advantages. 
         [0010]    Generally speaking, the surface foam diffuser system comprises a first nozzle disposed above a top surface of the at least partially liquid contents, a splash plate positioned adjacent to the first nozzle outlet, and a second nozzle disposed below the top surface of the at least partially liquid contents. The system nozzles each have an inlet for receiving pressurized liquid and an outlet for ejecting a liquid stream into the tank, the depth of the second nozzle and the direction of the liquid stream there from being such that rotation of the top surface is facilitated. 
         [0011]    In a particular embodiment, the system further comprises a plurality of mixing nozzles positioned proximate a bottom surface of the tank to keep solids entrained within the liquid medium by creating a liquid flow pattern in the tank. The liquid stream from the second nozzle is preferably supportive of the established flow pattern. 
         [0012]    These and other aspects of the invention may be understood more readily from the following description and the appended drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    For the purpose of facilitating an understanding of the subject matter sought to be protected, there are illustrated in the accompanying drawings embodiments thereof, from an inspection of which, when considered in connection with the following description, the subject matter sought to be protected, its construction and operation, and many of its advantages should be readily understood and appreciated. 
           [0014]      FIG. 1  is a plan view of one embodiment of the present system; 
           [0015]      FIG. 2  is a side view of the system illustrated in  FIG. 1 ; 
           [0016]      FIG. 3  is a close up view of an embodiment of a sub-surface nozzle and surface defoaming spray nozzle combination; 
           [0017]      FIGS. 4-6  are various views of one embodiment of a mixing nozzle used in embodiments of the present system; 
           [0018]      FIGS. 7-9  are various views of one embodiment of another mixing nozzle used in embodiments of the present system; and 
           [0019]      FIGS. 10 and 11  are views of one embodiment of an anti-foaming nozzle used in embodiments of the present system. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0020]    While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail a preferred embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to embodiments illustrated. 
         [0021]    Referring to  FIGS. 1-11 , there is illustrated an anti-foaming tank and nozzle system, generally designated by the numeral  10 . The described system  10  is discussed with respect to mixing tank contents, which is typically a combination of liquids and solids. More specifically, however, the system  10  is described for use on very large tanks, where mixing at the surface is somewhat diminished, and for use in digesters and the like, wherein a viscous top surface, due to the formation of scum and foam, reduces surface mixing. These particular foaming and scum problems may be found anywhere large processing tanks are used, such as, but not limited to, bio-waste plants, chemical plants, water treatment plants, waste-water treatment plants and where the tank contents include a 1-6% total solids concentration. 
         [0022]    Accordingly, the system  10  is described herein with reference to three distinct zones: tank bottom (A), content upper surface (B), and above the content surface (C). The drawings illustrate a specific embodiment of the system as used in a specific tank construction, but principles of the invention can be used for virtually any storage tank in which surface foam (including scum) may cause a problem. 
         [0023]    In the embodiment illustrated in  FIGS. 1 and 2 , a tank  11  is shown to include a lid  12 , a sidewall  13  and a conical base  14 . The representative embodiment is used for a cylindrical digester tank having a radius of 108 feet (about 32.9 meters), a bottom cone of 4.25 feet (129.5 cm) depth, an overall depth from the bottom sidewall of 30 to 50 feet, and a mixing system including a chopper pump  16  and nozzle assemblies  18  such as those available from Vaughan Co., Inc., of Montesano, Wash., and sold under the trademark ROTAMIXT™. 
         [0024]    The present system  10  can be installed to achieve its defoaming effect wherever it is needed. Appropriate valves are provided at the pump  16  for directing liquid from the tank  11  to the pipe  22  and then to supply pipes  28  for the mixing system nozzle assemblies  18 , and pipes  30  for the diffuser  24  and sub-surface mixing nozzle  26 . By “sub-surface” it is meant that the nozzles are positioned within the tank contents below the surface within the top 30% of the content depth (e.g., not more than 3 feet deep in 10 feet of tank contents), preferably within the top 20% of the content depth, and most preferably within the top 10% of the content depth. Liquid from the tank  11  is supplied to the pump  16  by inlet piping, which can withdraw liquid from the lower center portion of the tank  11  (via a sump), and extends to the pump  16 . 
         [0025]    As illustrated in  FIG. 1 , the mixing nozzle assemblies  18  can include an inner ring of nozzles and an outer ring of nozzles positioned at the tank bottom (A), with each nozzle oriented in the same general rotational direction to induce rotation of the contents of the tank about a vertical axis  20 . The outer ring preferably comprises four dual nozzle assemblies  40 , while the inner ring comprises at least two single nozzle assemblies  50 . The pump outlet is connected to a supply pipe  22  feeding pipes  28  to the mixing nozzle assemblies  18 . The purpose of the lower mixing nozzle assemblies  18  is to create a rotational, stirring flow pattern in the tank contents. A suitable system is described in U.S. Pat. No. 7,025,492 to Dorsch et al., and assigned to Vaughan Co., Inc. or Montesano, Wash. The &#39;492 patent is hereby incorporated by reference 
         [0026]      FIGS. 4-6  illustrate the preferred single nozzle  52  as a glass-lined ductile iron nozzle having an 8-inch inlet reduced to 6-inch at the bend before reaching a tapered outlet. Although the nozzle outlet  44  is of substantially lesser diameter than the pipes  22  and  28 , nevertheless, the diameter at the outlet  44  still is much larger than conventional spray nozzles or apertures so that the nozzle will not become clogged with rags, hair, fiber, or other thick, tough, stringy, or solid material from the tank. 
         [0027]    The dual nozzle assemblies  40  are created using the same single nozzle of  FIG. 5  coupled to the intermediate nozzle  27  of  FIG. 9 . Similarly, the sub-surface nozzle  26  also utilizes the configuration illustrated in the drawings of  FIGS. 7-9 . The configuration of the intermediate nozzle  27  (as nozzle  26  or nozzle  52 ) is well-known in the field, allowing a second nozzle (e.g., diffuser nozzle  24 ) to be connected adjacent using the same feed pipe. The nozzles  27  and  52  should be 360° fully adjustable to allow directional positioning to create the desired stirring flow pattern within the tank  11 , be it for lower tank mixing or sub-surface mixing. 
         [0028]    As shown and described in U.S. Pat. No. 7,628,183, a diffuser can be conveniently mounted in a manhole of the type commonly used in tanks of this type. However, for the presently illustrated embodiment, the supply pipe  22  which feeds pipe  30  to the surface foam diffuser  24  and sub-surface mixing nozzle  26  is preferably located within the tank  11 , running from the bottom center of the tank  11  toward the sidewall  13 . The location of the diffuser  24  along the sidewall  13 , of course, varies depending on the tank. 
         [0029]    Referring to  FIG. 2 , supply pipe  22  (8-inch diameter in a representative embodiment) connects to the upright diffuser inlet pipe  30 . Pipe  30  extends upward to an 8-inch to 6-inch reducer  32  to allow attachment of the 6-inch flange  34  and piping  36  of mixing nozzle  26  ( FIG. 3 ). A diffuser nozzle  24  is then attached approximately one foot or more above the mixing nozzle  26 . The mixing nozzle  26  and the diffuser nozzle  24  are identical to the nozzles described above, with the added features described below. 
         [0030]    The outlet of the diffuser nozzle  24  is sized for a desired concentration of the liquid ejected from the nozzle, and can be 1½ inches (3.8 cm) to 2¾ inches (7.0 cm) in diameter for a representative installation. The horizontally directed stream of liquid impinges on a splash plate or deflector  38  to break the liquid stream into a reasonably uniform dispersion of droplets over a substantial area of the surface of the liquid in the tank  11  without a great upward arc which would contact the lid  12  of the tank or require that liquid be maintained at a lower level, thereby wasting room in the tank  11 . For most installations, an additional four feet (1.2 meters) of “head room” is required above the diffuser nozzle  24  to allow the stream to be dispersed without contacting the tank lid  12 . 
         [0031]    As shown in  FIGS. 10 and 11 , the diffuser nozzle  24  includes a standard coupling  41  to attach to the pipe  36  leading from mixing nozzle  26  ( FIG. 3 ). The splash plate or deflector  38 , described in detail below is carried by a support arm  46  pivoted to the underside of the nozzle coupling  48  by a pivot pin or bolt  51 . Upright clamps  52  are attached to the support arm  46  and secure the deflector  38  to the nozzle at the desired angle. 
         [0032]    The deflector  38  is a key component of the surface foam diffuser system  10 . As noted above, it is desired that the nozzle outlet be of substantial diameter to prevent clogging. It also is desired that the exit velocity of the stream be quite high in order to reach a sizeable area. The purpose of the deflector is to break up the stream from the nozzle into droplets and disburse the droplets over a long and wide area, while minimizing the height of the spray to minimize the headroom required inside the tank  11 . Many different shapes and contours have been tested, with the illustrated device constituting the current preferred embodiment. 
         [0033]    The deflector plate  38  is angled upward from below the nozzle outlet at a small acute angle so that the horizontally directed stream of liquid from the nozzle is deflected upward without excessive loss of energy or a resulting high arc. A 10° to 20° angle of inclination, preferably about 15°, has been found to achieve the desired deflection. 
         [0034]    The outer peripheral edge of the deflector  38  is a circular arc centered at about the nozzle outlet, and of at least 90° angular extent, preferably at least about 120°. If the shape is too narrow, the spray and droplets fall off the sides of the plate in an uncontrolled manner. In this embodiment, the radius of the arc is about 14 inches (35.6 cm), resulting in the maximum width of the “fan” being just over 21 inches (over 53.3 cm). 
         [0035]    The outer arcuate edge is preferably formed with “saw tooth” fingers  62  bent up relative to the inner portion of the plate, preferably at an angle of about 45°. The fingers or teeth are of a sharp “V” shape having a tip radius no greater than 0.06 inch (1.5 mm), and a base radius between teeth no greater than 0.06 inch (1.5 mm). The teeth are small and closely spaced which has been found to break up the stream and spread apart the spray of droplets. A simple deflector with no teeth tends to concentrate the spray pattern at a constant radius, whereas large teeth at mixed angles and sizes break up the spray pattern, but not much water falls within a 10-foot radius of the nozzle and the pattern is not evenly distributed. The small, sharp teeth achieve a more uniform pattern. In this embodiment, the teeth are about 0.625 inch (1.59 cm) long with a pitch (tip-to-tip) of about 0.575 inch (1.46 cm), resulting in an included angle between adjustment tooth edges of about 50°. 
         [0036]    The plate portion of the deflector  38  is not planar, but rather is curved about its center line at a radius of approximately 36 inches so that the outer corners droop downward about 2 inches (5.1 cm) with respect to the center of the deflector  38 . The convex upper surface has been found to assist in disbursing the spray more evenly from side to side. 
         [0037]    The resulting spray from the diffuser  24  may cover as much as about 50% of the top surface area of the tank contents. The sub-surface mixing nozzle_facilitates rotation of the top surface along with the lower mixing nozzles_to allow for the eventual coverage of the entire top surface by the de-foaming spray. 
         [0038]    The following TABLE illustrates the effectiveness of the present system compared to the use of chemical defoamants. 
         [0000]    
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 
               
             
             
               
                   
               
               
                 Spray vs. Chemical 
               
             
          
           
               
                   
                 Increasing 
                 High Level 
                 Diffuser 
               
               
                   
                 Concentration 
                 Concentration 
                 Nozzle with 
               
               
                   
                 of Chemical 
                 of Chemical 
                 Sub-Surface 
               
               
                 Foam Height 
                 Defoamant 
                 Defoamant 
                 Mixing Nozzle 
               
               
                   
               
               
                 Maximum Foam 
                 17 to 19+ feet 
                 11 to 12 feet 
                 4+ feet 
               
               
                   
                 above liquid level 
               
               
                 Minimum Foam 
                 5.5 to 6.5 feet 
                 8 to 9 feet 
                 2 feet 
               
               
                   
                 above liquid level 
               
               
                 Approx. Avg. 
                 12 to 13 feet 
                 10 feet 
                 3 feet 
               
               
                 Foam 
                 above liquid level 
               
               
                   
               
             
          
         
       
     
         [0039]    The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. While particular embodiments have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made without departing from the broader aspects of applicants&#39; contribution. The actual scope of the protection sought is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.