Patent Application
20170043279
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.
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.
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 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.
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.
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).
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.
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.
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.
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.
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.
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.
These and other aspects of the invention may be understood more readily from the following description and the appended 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.
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
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.
In the embodiment illustrated in
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.
As illustrated in
The dual nozzle assemblies 40 are created using the same single nozzle of
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.
Referring to
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.
As shown in
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.
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.
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).
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°.
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.
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 26 facilitates rotation of the top surface along with the lower mixing nozzles 18 to allow for the eventual coverage of the entire top surface by the de-foaming spray.
The following TABLE illustrates the effectiveness of the present system compared to the use of chemical defoamants.
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' 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.
The present application is a continuation of U.S. patent application Ser. No. 12/694,396, filed on Jan. 27, 2010, titled “System Having Foam Busting Nozzle and Sub-Surface Mixing Nozzle,” and now U.S. Pat. No. 9,486,819. The '819 patent is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12694396 | Jan 2010 | US |
| Child | 15335601 | US |
