GB1586819A

GB1586819A - Backflushing method and apparatus

Info

Publication number: GB1586819A
Application number: GB51846/77A
Authority: GB
Original assignee: Clevepak Corp
Current assignee: Madison Management Group Inc
Priority date: 1977-12-13
Filing date: 1977-12-13
Publication date: 1981-03-25

Description

(54) BACKFLUSHING METHOD AND APPARATUS (71) We, CLEVEPAK CORPORATION, a Corporation organized under the laws of the State of Delaware, United States of America, of 925 Westchester Avenue, White Plains, State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- BRIEF DESCRIPTION OF THE INVEN TION BACKGROUND AND SUMMARY OF THE INVENTION: The invention relates to a method and apparatus for efficiently mixing gas with waste water and for flushing accumulated debris from such apparatus.

Industrial waste, sewage and the like are commonly purified by pumping the liquid into a large tank, pond or basin where a bacterial population consumes the inorganic -and organic material. Because the dissolved oxygen in the waste water is usually insufficient to support the required population of bacteria, the water must be aerated. This can be done with a surface aerating machine which has beaters extending into the waste water from above the water surface to agitate the water and incorporate air. Alternatively, air can be diffused through the bottom of the basin, e.g., through a porous medium.

Surface aerators are not efficient and cause certain mechanical problems. The energy loss of diffusing air is also great and a diffused system is not suitable for installation in pre-existing pond.

Waste water can also be aerated by pumping through submerged tubes with openings through which air is drawn or pumped into the tubes to create turbulent mixing. Such devices include vortex, jet, Venturi and impingement -type devices and are much more energy efficient than diffusion or surface aerator systems.

-One-problem which can -arise with systems df this sort in which water and gas are mixed in a chamber -is that small particles in an aeration basin, tank or pond can be caught within the mixing chambers, the pump -or the conduits therebetween, to eventually clog the same. In sewage treatment, material such as hair, paper, cloth, etc. will become lodged in the chambers, eventually blocking water flow and reducing the effectiveness of the system. Since submerged systems of this type normally pump a great volume of water, even if there is only a small number of particles in the body of waste water particles will eventually become lodged within the mixing chambers. It is not normally desirable to shut down the system for maintenance, and removal of this material, even when the basin is drained, can be a difficult task.

However, we have found that submerged water/gas mixing systems can be flushed of such debris by connecting the inlets of each of the mixing chambers to which waste water is normally supplied for aeration to a backflush outlet which is at lower pressure, being closer to or above water surface. If the water pump is turned off while air continues to flow into the chambers, the difference in pressure between the mixing chambers and the backflush outlet causes flow of the air backward through the inlets to that backflush outlet, to flush the system. Surprisingly, the air pumps waste water at a substantial flow rate and pressure back through the system. A separate valved duct can be used as a backflush duct to flush the debris directly to or above the surface where it can be collected, or the waste water can be backflushed through the pump to clean the pump screen provided that the pump and its strainer are mounted above the mixing chambers.

The air can be intermittently turned on and off to create pulsations of water which act as a hammer to dislodge debris.

Embodiments of the invention will now be expalined with reference to the accompanying drawings.

Figure 1 shows a schematic side view of apparatus embodying present-invention, in use; .Figure 2 shows a plan view of the apparatus Figure 1; Figure-3 shows a sectional view of a mixing chamber; Figure 4 shows a sectional view of a helical air mixing chamber; Figure 5 shows a partial sectional view of the mixing chamber of Figure 4; Figure 6 shows a schematic view of another embodiment; and Figures 7 and 8 show a further embodiment.

Figures 1 and 2 schematically illustrate one embodiment of the present invention.

In the embodiment of Figures 1 and 2, a plurality of circumferentially disposed mixing chambers 20, each preferably identical to the other, are circularly disposed around a dome manifold 22 which includes an upper section 24 into which water is pumped and a lower section 26 connected to a source of air or oxygen at a suitable pressure. Each of the mixing chambers is of the type shown in detail in Figures 3-5 and discussed in detail below.

A plurality of conduits 30, each formed of a metal segment 32 and a plastic segment 34 connect section 24 to each mixing chamber 20 so that water is continuously pumped through each chamber 20. A similar series of conduits 40 formed of metal portion 42 and a plastic portion 44 also connect section 26 to each of the mixing chambers 20. As will be apparent below, each of the mixing chambers forms parallel streams of air and gas which interact within an extending chamber of the mixing chamber to form tiny bubbles which efficiently mix with the pumped waste water. Manifold 22 is suspended from a fibreglass floating work platform 50 by means of guide bars 52 and 54 and two bars behind them in Figure 1.

Industrial air piping conduit 60 is attached to guide bar 54 for supplying air to section 26.

Cable 62 connects the manifold 22 to a frame 64 on platform 50 for lifting manifold 22 and holding manifold 22 in position for maintenance.

A conventional submersible pump 66 is mounted above manifold 22 and includes an optional strainer basket 67 which keeps most debris from entering the pump and being lodged therein. For many installations the basket can be omitted and the debris which collects in the pump, backflushed as described below. Conduit 68 connects pump 66 to section 24.

Floating work platform 50 is provided with suitable railings 70 of a height so that the unit can be lifted to a level for convenient work on the mixing chambers and pump. An on-shore air pump 74 is schematically shown as connected to line 60 for pumping air, oxygen or other gas to section 26 for mixing with the pumped waste water.

When it is desired to clear the particles and debris which inevitably will accumulate within the pump 66 and the mixing chamber 20, pump 66 can simply be turned off while the air pump 74 continues forcing air into the mixing chambers. However, surprisingly, instead of moving out of the outlet, the air will pump waste water back through the inlet, opposite to the direction of flow during aeration, through conduits 34 and 32 into section 22, through conduit 68 and through pump 66, blowing off the debris which has accumulated on the outside of strainer basket 67. This occurs because the water pressure at the level of the strainer basket is lower than the water pressure at the level of the mixing chambers 20. The water inlet thus becomes the backflush outlet and for this reason should be as close to the waterline as possible. Alternatively, flushing can be accomplished by operating a valve 76 in a separate backflush line 78 which connects to conduit 68. With many pumps, particularly those mounted out of the water, flushing through a separate line is preferable to flushing through the pump. The debris will now be blown through the backflush outlet formed by the end of the pipeline 78 into the air and since the pressure differential is greater, the force produced, by the air which works as an air hammer, will blow the debris through the system and back-flush all of the material in a few minutes. Turning the air on and off repeatedly creates pulsations which will dislodge almost all debris and backflush it from the system.

Figures 3-5 illustrate in more detail the mixing chamber 20. Waste water flows from the inlet through passage 100 into the extending chamber 102. At the intersecion between passage 100 and section 102, a discontinuity 104 is provided at which a plurality of bores terminates. To keep the vortices within chamber 102 at high air pressure, the bores inject the gas at an angle between roughly 11 and 22 1/2". A chamber with helical vanes in the bores as shown in Figures 4 and 5 creates greater wave generating conditions.

Thus, two parallel streams of gas and waste water are created as shown in Figure 3. As streams move along the chamber 102, the friction between them causes waves to form and the air thus trapped in waves to disperse into tiny bubbles. Since the air and gas streams move in the same diretion, effective mixing is achieved at minimum energy consumption. It is desirable that under most conditions the mixing take place within chamber 102 and for that reason the chamber is slightly tapered inwardly within the portion 110 with the cross-section decreasing in the direction from inlet to outlet and more radically tapered within portion 112. These tapers extend the maximum air flow rate with which the system will operate by several times without substantial loss of efficiency.

The helical guide vanes 106 provide a twisting motion to the air and thus create more waves which also help the interface break up more quickly by creating instability.

The mixing chambers can be made of any suitable materials such as stainless steel, aluminium or plastics.

Figure 6 shows another embodiment in which the submersible pump is replaced with a conventional waste water pump 200 mounted beside tank 202 and connected to manifold 204 by line 206. Pump 200 has an inlet 207. A plurality of mixing chambers 208 are mounted about manifold 204 and can be any suitable mixing device such as a jet, vortex, Venturi or impingement type device. Air pump 210 is also mounted beside tank 202 and is connected to manifold 204 by line 212. Valve 214 can be opened to back-flush waste water as described above while pump 200 is turned off and pump 210 continues- to force gas into the mixing chambers of device 208. The gas then pumps the waste water back through manifold 204 and line 206 where it leaves via valve 214.

The waste water returns to the tank and the debris is caught in strainer 216 if desired.

Figures 7 and 8 illustrate yet another embodiment of the invention which utilizes mixing chambers as described above. In the arrangement of Figures 7 and 8, water in a suitable tank 300 is pumped through a straight line pipe 302 by a pump 304. A plurality of mixing chambers 306 extend outwardly from pipe 302 at separated locations as shown in Figure 7. Air is supplied to a second pipe 308 which extends above and parallel to pipe 302. Alternatively, one pipe can be within the other. Pipe 308 is connected to the individual mixing chambers for injecting air into those chambers. Pipes 302 and 308 preferably extend along the center of the basin 300 parallel to the edges so as to cause a favorable pattern of water flow from one side to the other using a minimum amount of energy to create maximum flow and aeration. The system is flushed by opening valve 310 while pump 304 is turned off and air continued to be supplied to chambers 306.

Many changes and modifications in the above described embodiments of the invention can of course, be carried out without departing from the scope of the invention.

The system can be used with non-aqueous liquids and gas other than air such as pure oxygen can be added. Accordingly, the invention is limited only by the scope of the

Claims

appended claims.

The mixing apparatus described here is also one embodiment of the invention described and claimed in the complete specification of our co-pending UK Application No.

51847/77.

WHAT WE CLAIM IS: 1. A method of backflushing apparatus used for mixing gas with waste water, the mixing including pumping wste water through a passage into a mixing chamber having an outlet and feeding gas to the mixing chamber to interact with the waste water and become intimately mixed with before leaving the outlet of the mixing chamber, the backflushing including ceasing pumping the waste water and continuing to feed gas to the mixing chamber, the gas thereby causing backflow of waste water from the outlet of the mixing chamber through the passage to flush debris to a backflush outlet which communicates with the passage and is at a pressure lower than that of the mixing chamber outlet.
2. A method according to claim 1 wherein the continuation of the flow of gas is intermittent whereby to produce pulsations in the backflow.
3. A method according to claim 1 or claim 2 wherein the backflushing includes opening a valve in a backflush duct between the passage and the backflush outlet thereby permitting the said backflow of waste water through said duct and out of the backflush outlet.
4. A method according to claim 3 which includes having the backflush outlet above the surface of the waste water.
5. A method according to any one of claims 1 to 3 wherein the mixing includes pumping waste water through a pump and the backflush outlet is the pump inlet, said backflow occuring through the pump.
6. A method according to claim 5 which includes catching the debris by having a strainer basket at the pump inlet.
7. A method according to any one of the preceding claims in which the gas contains oxygen.
8. A method as in any one of the preceding claims, wherein said fluid is circulated through a first pipe extending in a straight line and having said chambers extending outwardly therefrom at separated locations and said causing including supplying the gas through a second pipe extending parallel to said first pipe and connected to said chambers.
9. A method as in claim 8 wherein said pipes are positioned in the middle of a tank of waste water.
10. Methods of backflushing substantially as herein described with reference to the accompanying drawings.
11. Apparatus for mixing gas with waste water, and further allowing backflushing to remove debris, having a pump connected to supply waste water to a passage of a mixing chamber which has an outlet and means for supplying gas to the mixing chamber to become intimately mixed with waste water before leaving the outlet of the mixing chamber, the facility for backflushing being provided by a backflush outlet in communication with said passage which outlet is to be at a pressure lower than that at the outlet of the mixing chamber, such that when the supply of waste water to the chamber is ceased whilst the supply of gas continues there is a backflow of waste water through the apparatus to the backflush outlet.
12. Apparatus according to claim 11 wherein the gas supply means includes a pump to be out of the waste water.
13. Apparatus according to claim 11, including means for mounting a submersible said pump above said manifold.
14. Apparatus according to claim 11 claim 12 or claim 13 wherein means the mixing chambers are connected at separated locations to a straight pipe, and gas supply means includes a second pipe connected to said chambers.
15. Apparatus according to claim 11, claim 12 or claim 13 including a manifold with a plurality of mixing chambers, the manifold being separated into a first section connected to the waste water pump and to said passages and a second section connected to said mixing chambers and to gas supply means, the mixing chambers extending radially outward from said first section.
16. Apparatus according to any one of claims 11 to 15, including a strainer basket over the inlet of said waste water pump.
17. Apparatus according to any one of claims 11 to 16 wherein a backflush duct is provided which is at least partly separated from the connection of the pump to the passage or passages the backflush duct being valved between the passage(s) and the backflush outlet.
18. Apparatus according to any one of claims 11 to 17 wherein the mixing chamber(s) include(s) a discontinuity at which the gas supply means terminate, to produce parallel streams of gas and fluid in said passage(s).
19. Apparatus for mixing gas with a fluid in a body of fluid and allowing backflushing, substantially as herein described with reference to Figures 1 to 5 or 6 to 7 and 8 of the accompanying drawings.