WO2007112460A1

WO2007112460A1 - Aeration system for tank

Info

Publication number: WO2007112460A1
Application number: PCT/ZA2006/000151
Authority: WO
Inventors: Mathew Benedict Carlisle
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-03-28
Filing date: 2006-12-21
Publication date: 2007-10-04
Anticipated expiration: 2008-09-28
Also published as: AP2008004688A0; ZA200805931B; AP2604A

Abstract

An aeration system for liquid tanks, includes an outlet (14) from the tank through which liquid is drawn by a circulating pump (18) to which is connected a down-pipe (28) located in the tank via an inlet pipe (20) which includes an in-line venturi (22) which entrains air in the liquid. The down-pipe (28) is of greater diameter than the inlet pipe (20) and has an outlet (30) at a low-level in the tank which is adapted to release liquid and entrained air in a horizontal plane to ensure efficient dispersion of air throughout the liquid in the tank.

Description

AERATION SYSTEM FOR TANK

TECHNICAL FIELD OF THE INVENTION

This invention relates to an aeration system for liquid tanks and in particular sewage tanks.

BACKGROUND ART

The treatment of sewage requires that it be effectively aerated.

In tanks, it is usually attempted to achieve aeration by pumping pressurised air into the bottom, the air typically entering the tank via a pipe having a large number of small holes at the outlet, or a grating such that a myriad of air bubbles enters the tank and bubble up toward the surface, in so doing aerating the liquid.

This method does not result in satisfactory dissolution of air into the liquid and in addition, problem with the clogging of the outlet are commonly experienced.

It is therefore an object of this invention to provide an aeration system which is more effective than prior art systems.

The aeration system is not restricted to use in sewage systems and may find a wide range of applications in other tank systems.

DISCLOSURE OF THE INVENTION

According to the invention an aeration system for a liquid tank includes an outlet from the tank in communication with a circulating pump, connected to a down-pipe located in the tank via an inlet pipe including an in-line venturi, the down-pipe being vertically orientated and of substantially greater diameter than the inlet pipe and including an outlet located at a low level within the tank, the outlet being adapted to release liquid and entrained air in a substantially horizontal plane, for efficient dispersion throughout the liquid in the tank.

In the preferred form of the invention, the down-pipe outlet includes a bend towards a horizontal plane which ensures that the liquid and entrained air is forced into a wide area near the base of the tank.

Also in the preferred form the down-pipe outlet includes an elongated substantially horizontal pipe section which is closed along the upper portion thereof, but which includes one or more apertures in the lower portion thereof. In the preferred form the horizontal pipe section is cut diagonally from a point near the terminal point of the bend, to a point at or near the end of the horizontal pipe section to form a single, tapered opening in the lower portion thereof.

The tapered pipe section has several advantages. These include the absence of small apertures which tend to become clogged, but more importantly, it has the effect of forcing the air entrained liquid to be forced horizontally across the diameter of the tank to be dispersed across a much greater area than would be the case if a vertical outlet was used, or even a simple horizontal outlet pipe.

In operation, the system operates by drawing liquid into the pump from the tank and pumping it a sufficient velocity to create a low pressure at the venturi and suck in air. Air is entrained in the liquid and passes along the pipe through a bend and into the enlarged vertical down-pipe. The air liquid mixture passes down the down-pipe at a velocity which allows some of the entrained bubbles to coalesce and rise up the down- pipe and form an air bubble at the top of the down-pipe. Thus in the down-pipe, four activities take place, namely, transport of entrained air bubbles into the main body of liquid and secondly, coalescing of entrained bubbles which rise up the down-pipe against the flow of liquid. An air bubble forms at the top of the down-pipe which is under pressure and the exit flow of the air and gas bubbles is directed into the main body of liquid.

These activities all assist in ensuring enhanced aeration and mixing. The efficiency of the system in dissolving air in the liquid is dependent upon the following factors:

1. The velocity of the liquid through the venturi

2. The size of the pipe and venturi in relation to the pump

3. The depth of the vertical enlarged section, and therefore the back pressure in the enlarged section

4. The velocity of the liquid/gas mixture in the vertical enlarged section. This is related to the pump and the diameter of the enlarged section.

The system of the invention has several advantages over prior art systems which use air pumps to force pressurised air into liquid tanks. Firstly, liquid pumps are efficient, attain relatively high pressures and are easily obtainable in comparison to air pumps. Secondly, the system utilizes pressure, counter current flows and vigorous mixing to attain rapid and thorough dissolution of air/gas in the liquid. Excellent mixing is obtained because of large flows through the pump. There are no small apertures below the surface in the system, this avoids the problems of clogging of pipes and apertures associated with aeration in biological systems or systems containing sludges etc. The system can be accessed without draining the tanks being aerated.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention is described below with reference to the accompanying drawing which is a sectional view through a tank having its contents aerated using the system of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In the drawings, a tank 10 is filled with liquid sewage 12 and has an outlet 14 at a high level. Liquid is drawn from the outlet 14 via pipe 16 and using a circulating pump 18. Liquid is pumped through pipe 20 which includes an in-line venturi 22 through which air is drawn into the pipe via air intake 24. The liquid and entrained air enters down-pipe 28 via bend 26. The down-pipe 28 has a substantially larger diameter than the pipe 20. The down-pipe has an outlet 30 near the base of the tank. The outlet includes a bend 32 to the horizontal and an elongated horizontal portion 34 having a tapered opening 36 in the lower portion thereof.

Air bubbles coalesce in the down-pipe and rise up it to form a bubble at the top 38 through which the incoming liquid must travel. This enhances dissolution. The air entrained liquid is then dispersed across a wide area at the base of the tank to further increase the efficiency of aeration as the air rises up through the liquid.

Claims

CLAIMS:

1. An aeration system for a liquid tank characterised in that the system includes an outlet from the tank in communication with a circulating pump, connected to a down-pipe located in the tank via an inlet pipe including an in-line venturi, the down-pipe being vertically orientated and of substantially greater diameter than the inlet pipe and including an outlet located at a low level within the tank, the outlet being adapted to release liquid and entrained air in a substantially horizontal plane, for efficient dispersion throughout the liquid in the tank.

2. An aeration system according to claim 1 characterised in that the down-pipe outlet includes a bend towards a horizontal plane which ensures that the liquid and entrained air is forced into a wide area near the base of the tank.

3. An aeration system according to claim 1 or claim 2 characterised in that the down-pipe outlet includes an elongated substantially horizontal pipe section which is closed along the upper portion thereof, but which includes one or more apertures in the lower portion thereof.

4. An aeration system according to claim 3 characterised in that the horizontal pipe section is cut diagonally from a point near the terminal point of the bend, to a point at or near the end of the horizontal pipe section to form a single, tapered opening in the lower portion thereof.

5. An aeration system according to any of the above claims substantially as described with reference to the accompanying drawings.