GB1596190A

GB1596190A - Aeration method and apparatus for carrying it out

Info

Publication number: GB1596190A
Application number: GB51847/77A
Authority: GB
Original assignee: Clevepak Corp
Current assignee: Madison Management Group Inc
Priority date: 1977-12-13
Filing date: 1977-12-13
Publication date: 1981-08-19

Description

(54) IMPROVED AERATION METHOD AND APPARATUS FOR CARRYING IT OUT (71) We, CLEVEPAK COR PORATION, 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: The invention relates to an improved method and apparatus for efficiently mixing aerating gas with waste water.

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 an existing pond.

The waste water can also be aerated by pumping through submerged tubes with Venturi openings through which air is drawn or pumped into the tubes to create turbulent mixing.

The present invention relates to an improved method and apparatus for mixing an aerating gas such as oxygen or air with waste water. The method includes aerating a body of waste water, by means of an aeration structure having a nozzle for liquid, a gas inlet, and an elongate chamber, wherein the interface between initially separate aerating gas and liquid streams, flowing in a generally parallel relationship with one another in the elongate chamber, is caused to become unstable and to impinge upon an interior wall surface of said elongate chamber in such manner that vortices are created whereby a gas-liquid mixture containing finely dispersed bubbles of gas is formed and caused to issue from an outlet of the elongate chamber into the body of waste water, the method including pumping waste water through the nozzle so as to initially form a liquid jet in a first portion of the elongate chamber, whilst separately introducing an aerating gas through the gas inlet into said first portion of the elongate chamber so as to initially flow in a generally parallel relationship and annularly surrounding said liquid jet, thereafter causing the interface between the separate gas and liquid streams to impinge upon the interior wall surface of the elongate chamber, thereby forming vortices resulting in intimate mixing of the liquid and gas, and causing the thus-formed gas-liquid mixture to pass through a second portion of said elongate chamber which is tapered to progressively constrict the gas-liquid mixture in the direction of flow within the elongate chamber before issuing from the outlet thereof. The apparatus for carrying out that method includes an aeration structure having a nozzle for liquid, a gas inlet and an elongate chamber, a pump for pumping waste water through said nozzle, and a pump for pumping aeration gas through said gas inlet, wherein said nozzle has an outlet into said elongate chamber with a cross-sectional area less than that of the elongate chamber at the nozzle outlet, and is adapted to form a liquid jet stream in said elongate chamber; said gas inlet is adapted to introduce a stream of aeration gas into said extending chamber, initially in a direction generally parallel to and annularly surrounding the liquid jet; and said elongate chamber has a first and a second portion, said second portion being down stream from said first portion and being tapered to progressively constrict the flow of gas and liquid therein prior to issuing from the outlet of the elongate chamber into the body of waste water, the first portion, if tapered, being tapered at a lesser angle than the second portion, and said first portion extending down stream from the outlet of said nozzle and being adapted to initially confine the separate parallel gas and liquid streams and under the influence of the constriction subsequently cause the interface therebetween to become unstable and to impinge upon an interior wall surface of the elongate chamber to thereby create vortices and intimate mixing of the gas and liquid.

In operation the mixing chamber of the apparatus is to be disposed below the surface of the waste water. A suitable gas, such as oxygen or air containing oxygen, is injected into the or each of the elongate chambers in the mixing chambers at a discontinuity in the former, to form generally parallel streams of gas and water in it. As the two streams move along the elongate chamber, the interface between the two streams becomes unstable and waves form which attach to its side walls.

This causes large frictional stresses, creating tiny bubbles which mix with the water.

Since the water and air essentially flow in the same direction the system is energy efficient.

In the apparatus the elongate chamber is tapered in the downstream direction at least at its second portion which provides its nozzle. The first portion may be parallel sided but is preferably tapered, and if it is tapered, it is tapered at a lesser angle than the second portion. The contriction afforded by at least the second portion ensures that the vortices created by the mixing do not extend out of the chamber.

This would reduce the efficiency of mixing.

Helical vanes are preferably provided in injection bores for the air to create greater wave generating conditions which extend the operating range of the device to greater air flow rates.

This apparatus can be quickly and easily installed in any existing aeration pond without the need for the existing system to be shut down for an extended period and without the need for the pond to be drained, a project which is difficult or impossible in most instances. It can, in fact, be installed and operating within a few minutes. In comparison with diffused air type and surface aeration devices, the energy required to incorporate a given amount of oxygen into the water is much less. Because little energy is wasted in turbulent mixing, the present method is more energy efficient than Venturi, jet or impingement type devices which depend on turbulent mixing.

Further, the bubbles which are produced are tiny, thus creating a good environment for effective use of the oxygen by the bacteria within the pond or basin. Many of the other disadvantages of surface aerators and diffusion type devices are also avoided.

Particular embodiments of the present invention will now be described with reference to the accompanying drawings.

Figure 1 shows a schematic side view of the apparatus embodying the present invention in use; Figure 2 shows a plan view of the apparatus of Figure 1; Figure 3 shows a sectional view of a mixing chamber without helical vanes; Figure 4 shows a front view of a mixing chamber with helical vanes; Figure 5 shows a partial sectional view of the mixing chamber of Figure 4; Figure 6 shows a schematic view of another embodiment; Figure 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, each formed of a metal portion 42 and a plastic portion 44, connect section 26 to each of the mixing chambers 20. Each of the mixing chambers 20 forms parallel streams of air and gas which interact within an elongate chamber in the mixing chamber to form tiny bubbles which efficiently mix with the pumped waste water as it passes between an inlet and outlet.

Manifold 22 is suspended from a fibreglass floating work platform 50 by means of guide bars 52, 54, and two bars behind bars 52 and 54. 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.

Submerged pump 66 is mounted above manifold 22 and includes a self-cleaning strainer basket 67 over the pump intake which keeps most debris from entering the pump. For many installations the basket can be omitted and the debris which collects in the pump back-flushed as described below.

Small particles do accumulate on the outside of basket 67. Conduit 68 connects pump 66 to section 24.

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 20 and pump 66. An onshore 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 clean the inevitable particles and debris which will accumulate on basket 67, within pump 66 and within mixing chambers 20, pump 66 can simply be turned off while the air pump 74 continues forcing air into mixing chambers 20.

Surprisingly, instead of moving out of the outlet on each chamber, 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 ower than the water pressure at the level of the mixing chambers 20.

Alternatively, flushing can be accomplished by operating a valve 76 in a line 78 which connects to conduit 68. The debris will now be blown 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.

FIGURES 3-5 illustrate in more detail two embodiments of the mixing chamber 20 of the present invention. Waste water flows from the inlet through passage 100 into the elongate chamber 102. At the intersection between passage 100 and chamber 102, a discontinuity 104 is provided at which a plurality of bores terminates. The bores inject gas at an angle between roughly 11 and 22-1/20. To keep the vortices within a chamber 102 at high air pressures, a chamber 110 with helical vanes 106 as shown in FIGURES 4 and 5 creates greater wave generating conditions, as the water enters a chamber (not shown) similar to the chamber shown in FIGURE 3.

Thus, two parallel streams of gas and waste water are created as shown in FIGURE 3. As the streams move along the elongate chamber 102, the friction between them causes waves to form and air thus trapped in the waves to disperse into tiny bubbles. Since the air and gas streams move in the same direction, 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 inwardly 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 favourable 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 nonaqueous liquids and gas other than air, such as pure oxygen, can be added. Accordingly, the invention is limited only by the scope of the appended claims.

Backflushing methods and apparatus illustrating a different aspect of the present embodiments are described and claimed in the complete specification of our corresponding UK Application 51846/77 (Serial No. 1586819).

WHAT WE CLAIM IS: 1. A method of aerating a body of waste water, by means of an aeration structure having a nozzle for liquid, a gas inlet, and an elongate chamber, wherein the interface between initially separate aerating gas and liquid streams, flowing in a generally parallel relationship with one another in the elongate chamber, is caused to become unstable and to impinge upon an interior wall surface of said elongate chamber in such manner that vortices are created whereby a gas-liquid mixture containing finely dispersed bubbles of gas is formed and caused to issue from an outlet of the elongate chamber into the body of waste water, the method including pumping waste water through the nozzle so as to initially form a liquid jet in a first portion of the elongate chamber, whilst separately introducing an aerating gas through the gas inlet into said first portion of the elongate chamber so as to initially flow in a generally parallel relationship and annularly surrounding said liquid jet, thereafter causing the interface between the separate gas and liquid streams to impinge upon the interior wall surface of the elongate chamber, thereby forming vortices resulting in intimate mixing of the liquid and gas, and causing the thus-formed gas-liquid mixture to pass through a second portion of said elongate chamber which is tapered to progressively constrict the gas-liquid mixture in the direction of flow within the elongate chamber before issuing from the outlet thereof.

2. Apparatus for carrying out the method of aerating a body of waste water as claimed in claim 1 which apparatus includes an aeration structure having a nozzle for liquid, a gas inlet and an elongate chamber, a pump for pumping waste water through said nozzle, and a pump for pumping aeration gas through said gas inlet, wherein said nozzle has an outlet into said elongate chamber with a cross-sectional area less than that of the elongate chamber at the nozzle outlet, and is adapted to form a liquid jet stream in said elongate chamber; said gas inlet is adapted to introduce a stream of aeration gas into said elongate chamber, initially in a direction generally parallel to and annularly surrounding the liquid jet; and said elongate chamber has a first and a second portion, said second portion being down stream from said first portion and being tapered to progressively constrict the flow of gas and liquid therein prior to issuing from the outlet of the elongate chamber into the body of waste water, the first portion, if tapered, being tapered at a lesser angle than the second portion, and said first portion extending down stream from the outlet of said nozzle and being adapted to initially confine the separate parallel gas and liquid streams and under the influence of the constriction subsequently cause the interface therebetween.to become unstable and to impinge upon an interior wall surface of the elongate chamber to thereby create vortices and intimate mixing of the gas and liquid.

3. Apparatus according to claim 2 wherein the first portion of said extending chamber is tapered inwardly to progressively constrict the gas and liquid flow in said extending chamber, the angle of taper of said first portion relative to the direction of flow being less than such angle of taper of said second portion.

4. Apparatus according to claim 2 or claim 3 wherein the gas inlet is a plurality of bores surrounding the said outlet of the nozzle.

5. Apparatus according to claim 4 wherein there is a helical vane disposed in at least one of the bores.

6. Apparatus according to any one of claims 2 to 5 having a plurality of said aeration structures extending outwardly from a straight pipe, which pipe is adapted to conduct waste water from the waste water pump to said nozzles, and having a second pipe extending parallel to the first pipe and being adapted to conduct aerating gas from the gas pump to the gas inlet of each aeration structure.

7. Apparatus according to any of claims 2 to 5 having a plurality of aeration structures extending radially from a manifold through which the waste water and aerating gas are respectively supplied to each aerating structure.

8. Apparatus according to claim 7 wherein the manifold is adapted to be suspended within a body of waste water, and there are provided means for mounting the waste water pump in the body of waste water, above the manifold.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. 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 nonaqueous liquids and gas other than air, such as pure oxygen, can be added. Accordingly, the invention is limited only by the scope of the appended claims. Backflushing methods and apparatus illustrating a different aspect of the present embodiments are described and claimed in the complete specification of our corresponding UK Application 51846/77 (Serial No. 1586819). WHAT WE CLAIM IS:

1. A method of aerating a body of waste water, by means of an aeration structure having a nozzle for liquid, a gas inlet, and an elongate chamber, wherein the interface between initially separate aerating gas and liquid streams, flowing in a generally parallel relationship with one another in the elongate chamber, is caused to become unstable and to impinge upon an interior wall surface of said elongate chamber in such manner that vortices are created whereby a gas-liquid mixture containing finely dispersed bubbles of gas is formed and caused to issue from an outlet of the elongate chamber into the body of waste water, the method including pumping waste water through the nozzle so as to initially form a liquid jet in a first portion of the elongate chamber, whilst separately introducing an aerating gas through the gas inlet into said first portion of the elongate chamber so as to initially flow in a generally parallel relationship and annularly surrounding said liquid jet, thereafter causing the interface between the separate gas and liquid streams to impinge upon the interior wall surface of the elongate chamber, thereby forming vortices resulting in intimate mixing of the liquid and gas, and causing the thus-formed gas-liquid mixture to pass through a second portion of said elongate chamber which is tapered to progressively constrict the gas-liquid mixture in the direction of flow within the elongate chamber before issuing from the outlet thereof.

9. Apparatus according to claim 7 or

claim 8, further including a buoyant platform and means for suspending the manifold and pump from the platform.

10. Apparatus according to any one of claims 2 to 8, including a strainer basket covering an inlet to the waste water pump.