Abstract:
A nozzle system for mixing contents in a tank and scouring surfaces of debris and sediment is disclosed. The system is capable of use either below or above a tank&#39;s liquid content surface as well as being adaptable to flow channels and other surfaces which may become impeded with sediment and debris. The nozzle system includes at least one nozzle receiving fluid from a pump, and a splash plate positioned to deflect a discharged stream from the nozzle in a spread and downward direction. The number and positioning of additional nozzles in the system can be determined by mapping the discharge of each splash plate equipped nozzle and arranging for the desired area of coverage.

Description:
RELATED APPLICATION 
     This application is a continuation-in-part and claims the filing priority of co-pending U.S. patent application Ser. No. 12/694,396, filed Jan. 27, 2010, titled “System Having Foam Busting Nozzle and Sub-surface Mixing Nozzle” (the &#39;396 application), the contents also of which are hereby incorporated by reference. The &#39;396 application is assigned to the assignee of the present application. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     The present device relates to a system of nozzles for use on wastewater storage tanks and the like. Particularly, the present device relates to a nozzle system for moving sediment on a tank floor. 
     BACKGROUND OF THE INVENTION 
     Storm water runoff can pose significant issues for sewage water treatment facilities. Often such facilities have a CSO (Combined Sewage Overflow) system. A CSO system is comprised of a big tank, like a huge swimming pool, that collects the storm water runoff so that the runoff does not just get dumped into the local waterways. Typically, local sewage treatment plants cannot handle the added flow from a rain storm, so they bypass the water treatment and dump thousands of gallons of untreated water into local waterways. As an alternative, the CSO system collects this rain and sewage and gradually pumps it to the treatment plant for processing. This approach keeps sewage out of the local rivers and lakes. 
     Along with pollutants and toxins, the runoff water can carry with it a great deal of debris and unsettled sediment carried from roadways, parking lots, and the like. To the extent that such sediment remains entrained in the water flow, it can be properly filtered at the treatment facility. Likewise, the pollutants and toxins can be removed with proper treatment at the facility. However, where the runoff water is held for long periods of time, the debris and sediment can settle out of the water and deposit on the CSO tank bottom where it may fill the sump and block the pump which sends the water out to the treatment plant. 
     Even if the sediment and debris does not immediately block pumping action, the buildup will continue to reduce the volume of the CSO tank. For all the reasons described above, a loss of overflow volume could lead to contamination of local waterways, such as ponds, lakes, streams and the like. 
     Another problem with prior systems has to do with nozzle pressure and clogging. Typical pumps and nozzles for such operations are sized to provide about 10 psi of head pressure at each nozzle, with a nozzle discharge velocity in the range of from about 30 to about 40 feet/second. Systems having six nozzles have been successfully used to entrain debris and wash away deposits of silt, sand and grit (i.e., small particle size sediment). However, to maintain the desired pump and system pressure and nozzle discharge velocity, nozzle openings must be a specific size. 
     For example, in one known application the nozzle openings have an diameter of no more than 2.5 inches (about 6.4 cm). When larger debris, such as shoes, balls, branches, etc., enter the CSO tank, it can quickly clog the 2.5 inch nozzles. Accordingly, nozzles having larger opening diameters must be used to prevent clogging, but using the same pump (designed for a particular optimum flow with the smaller 2.5 inch nozzles) requires the use of fewer nozzles to prevent a drop in head pressure and discharge velocity. 
     It is well-known that nozzle flow is related to discharge velocity by the equation:
 
 V= 0.408 Q/d   2  
 
where, V is velocity (ft/sec), Q is flow (U.S. gal/min) and d is nozzle opening diameter (inches). The following chart illustrates the potential drop in velocity by switching from 2.5 inch nozzles to 3.5 inch nozzles with maintained flow.
 
     
       
         
               
             
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Velocity drop 
               
             
          
           
               
                   
                 Flow (Q) 
                 Velocity (V) 
               
               
                   
                   
               
             
          
           
               
                   
                 2.5 inch Nozzle 
                 580 gpm 
                 38 ft/sec 
               
               
                   
                 3.5 inch Nozzle 
                 580 gpm 
                 19 ft/sec 
               
               
                   
                   
               
             
          
         
       
     
     Using six larger 3.5 inch nozzles also precipitously drops system discharge pressure, allowing the centrifugal pump to create too much flow, which leads to the creation of damaging cavitation inside the pump. As a means to maintain velocity in the 30 to 40 ft/sec range without increasing the pump power and to avoid pump damage from high-flow cavitation, fewer flow nozzles must be used—about half the number of nozzles based on the velocity drop. Unfortunately, the use of fewer nozzles in large CSO tanks presents an issue in that the resulting system will be unable to properly stir the tank contents while also simultaneously washing away settled debris at the tank center. 
     As illustrated in  FIG. 1 , a typical three nozzle tank mixing system creates high mixing velocities along the outermost zone of the tank. However, a low-velocity region exists at the tank center which allows the settling of sand, grit and debris. Over time, a large deposit of such material will exist in this low-velocity area. One way those skilled in the art may eliminate the sediment and debris is to physically enter the CSO tank and move the deposits with tools and/or large quantities of pressurized water. This can only be done, of course, when the CSO tank is substantially empty and not in use. 
     The present system, device and methods solve the numerous problems of mixing, discharging settled debris from tanks, surfaces, and the like, and preventing clogging of the nozzles. The present system, device and methods are capable of not only preventing settling of sediment and debris, but may be implemented in tanks already impinged with sediment to remove such from a tank bottom or other surfaces. The present system accomplishes these and other goals without sacrificing coverage area, head pressure, or discharge velocity. 
     SUMMARY OF THE INVENTION 
     There is disclosed herein an improved tank mixing system and mixing nozzle which avoids the disadvantages of prior devices while affording additional structural and operating advantages. The systems, devices and methods disclosed operate to prevent sediment buildup on a surface, such as a waste-water tank bottom, remove such buildup after it occurs, or both. 
     In one embodiment, a system for moving solids accumulated on a surface is disclosed. Generally, the system comprises a plurality of liquid dispensing nozzles positioned above the surface, at least one splash plate above the nozzle discharge, a liquid source, and a pump for circulating the liquid through the nozzle where it is deflected and spread when it contacts the splash plate. In this embodiment, each of the nozzles has an inlet for receiving pressurized liquid and an outlet for ejecting a liquid stream along a path. The splash plate is preferably positioned superiorly adjacent to the outlet of at least one nozzle in the path of the liquid stream and at an angle of inclination relative to the path. The splash plate deflects the liquid stream toward the accumulated solids on the surface. 
     In another embodiment, a system for removing sediment deposited on a surface comprises a supply of liquid, a liquid dispensing nozzle positioned above the surface, a splash plate, and a fluid pump coupling the nozzle and the supply of liquid. The nozzle includes an inlet for receiving pressurized liquid and an outlet for ejecting a liquid stream along a path, while the splash plate is positioned superiorly adjacent to the nozzle outlet in the path of the liquid stream at an angle of inclination relative to the path. This operates to pump material from the supply through the nozzle outlet. 
     In another embodiment, a wastewater storage tank system is specifically disclosed. The system comprises a tank, as well as a nozzle, a splash plate, and a pump, as in previous embodiments. The tank is an enclosed volume fed by an inlet for delivering wastewater into the tank and an outlet for discharging wastewater there from. The nozzle is preferably positioned within the tank and includes an inlet for receiving pressurized liquid and an outlet for ejecting a liquid stream along a path. The splash plate is again positioned superiorly adjacent to the nozzle outlet in the path of the liquid stream at an angle of inclination relative to the path. The pump includes an inlet fluidly connected to the tank and operates to pump material from the tank through the nozzle outlet. 
     In all the described system embodiments, it is an aspect of each to have an angle of inclination in the range of from about 5 degrees to about 30 degrees, preferably in the range of from about 10 degrees to about 20 degrees. The most preferred angle of inclination of the splash plate is about 15 degrees, relative to the stream of liquid. It may be an aspect of the embodiments wherein the nozzle outlet itself is also angled to direct the path of the liquid stream toward the surface, such as a tank or channel bottom. 
     Also disclosed is a method for removing sediment deposited onto a surface using tank mixing nozzles. An embodiment of the disclosed method comprises the steps of aiming a liquid dispensing nozzle at an area of a surface having deposited sediment, pumping liquid at a sufficient pressure from a liquid source to an outlet of the nozzle, discharging the liquid from the nozzle in a concentrated stream along a path directed substantially at the deposited sediment, and deflecting the liquid stream downward to spread the stream outward in a direction substantially perpendicular to the concentrated stream. Preferably, the step of deflecting the liquid stream comprises the step of securing a splash plate in the path of the concentrated stream. The splash plate is preferably secured at an angle relative to the path of concentrated stream. 
     In another embodiment of a method, steps for preventing the deposit of sediment onto a surface using tank mixing nozzles is disclosed. The preventative method comprises the steps of aiming a liquid dispensing nozzle at an area of a surface prone to deposition of sediment, pumping liquid at a sufficient pressure from a liquid source to an outlet of the nozzle, discharging the liquid from the nozzle in a concentrated stream along a path directed toward the area of the surface subject to deposition of sediment, and deflecting the liquid stream downward to spread the stream outward in a direction substantially perpendicular to the concentrated stream. 
     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 
       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. 
         FIG. 1  is a computational fluid dynamic (CFD) image of a prior art tank system; 
         FIG. 2  is a CFD image of an embodiment of the present tank mixing system; 
         FIG. 3  is a perspective view of one embodiment of a liquid dispensing nozzle in accordance with the present invention; 
         FIG. 4  is a side view of an embodiment of the present system; 
         FIG. 5  is a top view of an embodiment of the present system; 
         FIG. 6  is a top view of an embodiment of the present system illustrating representative spray patterns; 
         FIG. 7  is a partial perspective view of an embodiment of the nozzle system employed in a influent channel; 
         FIG. 8  is a side cross section of the channel opening of  FIG. 7 ; 
         FIG. 9  is a top view of a mixing system employing an embodiment of the present nozzle system; and 
         FIG. 10  is a side view of the mixing system shown in  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     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. 
     Referring to  FIGS. 2-10 , there are illustrated various aspects of a tank mixing and surface scouring system, including methods, generally designated by the numeral  10 . While the disclosed embodiments are shown primarily in conjunction with a storage tank, alterations may be made to adapt the system  10  to, for example, mixing tanks of any kind and for most any purpose where solid deposits may cause a problem. 
     Generally speaking, a preferred system  10  has a cylindrical tank  20  having a floor sloped toward a sump  22 , a plurality of liquid dispensing nozzles  12 , a splash plate  14  attached to at least some of the nozzles, and a pump  16  for circulating a supply of liquid, preferably the liquid or liquid slurry which exists within the tank  20 . In a preferred method, the liquid is pumped from the tank  20  and through the plurality of nozzles  12 , where the resulting stream is deflected by the splash plates  14  to spread outward in a direction perpendicular to the initial stream. The stream is also deflected downward toward the tank floor. The resulting mixing action is exemplified in the CFD image of  FIG. 2 . In contrast to the prior art system of  FIG. 1 , the lack of a low-velocity zone in the tank center of  FIG. 2  helps prevents entrained sediment from settling out and collecting on the tank bottom. 
     In one configuration, the disclosed system  10  is intended for use in what is known as a “Combined Sewer Overflow” (CSO) system which collects rain and sewer water during storms for holding until such material can be pumped into the sewage treatment plant. Typically, when about ten feet or so of liquid is left in the tank, the nozzle system  10  is activated and mixing begins. This process allows entrainment of any settled and accumulated solids at the tank bottom so such sediment may be pumped out of the tank. 
     A CSO tank system is illustrated in  FIGS. 1 and 2 , as well as in  FIGS. 4-6 . In the demonstrated systems, three single nozzles (Rotamix® system by Vaughan Company of Montasano, Wash.) are positioned within a cylindrical tank at 120 degree intervals about the tank circumference and a distance inward of the tank wall. The three nozzles (A, B, and C) in each tank are floor-mounted via a feed pipe  24  which typically rises approximately one foot above the tank floor. In the system of  FIG. 1  (the prior art), each nozzle is aimed to discharge a stream horizontally at anywhere from about 25 to about 45 degrees to the right of a radius intersecting the nozzle base. When submerged, a mostly tangential mixing flow is created from the three nozzles (see labeled dark flow lines of  FIG. 1 ), leaving a low-velocity hole at the center of the tank (see labeled light zone of  FIG. 1 ) which allows settling of solids to the tank bottom. 
     Conversely, in the system of  FIG. 2  (an embodiment of the present invention), a splash plate  14  is attached above each nozzle opening. As shown in  FIG. 3 , as a concentrated liquid stream  30  is discharged from the nozzle  12 , the initial stream  30  is deflected downward by the splash plate  14  and dispersed outward in a direction perpendicular to the initial nozzle discharge. The “B” and “C” nozzles of the system  10  in  FIGS. 2 ,  5  and  6  are aimed to discharge a stream slightly downward, preferably in a range of from about 5 to about 20 degrees below horizontal, most preferably about 11.5 degrees below horizontal, and off-center from about 25 to about 45 degrees to the right of a radius intersecting the nozzle base, preferably about 30 degrees to the right of the intersecting radius. In the illustrated embodiment, the “A” nozzle of the tank is similarly aimed downward, but instead of being off-center it is directed at the center point of the tank  20 . As noted above, this configuration provides a good mixing velocity for the tank contents, while avoiding the creation of a large low-velocity zone in the tank center. 
     As the contents are drained from the tank  20 , another advantage of the system  10  can be recognized. Even in the best of systems some debris and sediment will settle to the tank bottom. The present system  10  will effectively remove such debris and sediment to prepare the CSO tank  20  for the next time it is needed. That is, the downwardly directed spray from the splash plate covered nozzles  12  will wash any residual solids on the tank bottom into a sump  22  located at the low end of the sloped floor. 
     In other embodiments, it is understood that even a single nozzle  12  equipped with a splash plate  14 , as shown in  FIG. 3 , could be employed to scour a surface to remove settled debris. For example, the influent channels  40  illustrated in  FIGS. 7 and 8  feed liquid to a larger grit chamber  45  and may use nozzles  12  with attached splash plates  14  to create a spread stream which will move solid material into the grit chamber  45 . These channels  40  are not typically used to hold water for any period of time like a CSO tank  20  ( FIG. 2 ), but they can channel large volumes of fluid having entrained solids. The channel opening  42 , an area just before the grit chamber  45  shown best in  FIG. 8 , is occasionally subject to development of a low-velocity pool where debris may collect and sediment may settle out. If the buildup is large enough, flow from the channel may become impeded. 
     Placement of even a single splash plate-fitted nozzle  12  at this low-velocity area, or two such nozzles  12  as shown in  FIG. 7 , would serve to scour the channel bottom surface to help maintain fluid flow. 
     The present system  10  is not limited to use in channels and circular mixing or holding tanks. Further, the splash plate  14  equipped nozzle  12  of  FIG. 3  is also not limited to tank bottom positioning, as it may also be used at or even above the liquid surface of a mixing tank. The downward directed spread of liquid has demonstrated effectiveness at driving floating debris into the mixing pattern of a system. 
     For example, tanks are employed in some plants for creating energy from a ground corn (i.e., corn stover) and animal manure slurry for downstream hydrolysis and digester tanks (not shown). One known system, illustrated in  FIGS. 9 and 10 , is comprised of a rectangular tank (approx. 33 ft.×16 ft.×13 ft.) having four Rotamix® nozzles  12 A-D at two different levels. Two of the nozzles,  12 A and  12 B, are positioned at floor level and the other two nozzles,  12 C and  12 D, are positioned at the top of the tank  20 . The floor-mounted nozzles,  12 A and  12 B, are preferably positioned on opposite sides at a longitudinal centerline and are aimed approximately +22.5 degrees off-center. Conversely, the two top-mounted nozzles,  12 C and  12 D, are located in corners opposite each other and opposite the aimed direction of the closest floor-mounted nozzle—i.e., to the negative angle side. The top-mounted nozzles  12 C,  12 D are preferably aimed downward at about 22.5 degrees and 45 degrees off the adjacent tank walls. Of course, the noted angle measures of the nozzles are approximate and specific to the illustrated embodiment, as is the number and positioning of the nozzles. Alterations will likely be necessary to customize a nozzle system for each system. Such alterations would certainly be possible by those skilled in the art after an explanation of the present system. 
     Still referring to  FIGS. 9 and 10 , each nozzle  12 C and  12 D includes a splash plate  14  so as to further direct a discharge downward in a spray at the tank contents. The mixing pattern for rectangular tanks is generally rotational—though not circular—about the tank&#39;s vertical axis with vertical (up/down) mixing as well due to the four corners. Any floating corn debris is driven downward into the mixing slurry by the spray from the upper nozzles  12 C,  12 D. The use of a splash plate  14  mounted above the opening on each of the top-mounted nozzles  12 C,  12 D allows a greater area of the tank content surface to be covered by the spray. 
     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.