GB2491192A - A machine for aerating water and generating power - Google Patents

Abstract

A machine for the aeration of a first body of water 23 located adjacent to a physically separate second body of water 21 comprises a water path 11 linking the bodies of water, one or more injectors 61 for the injection of air into water flowing through the water path and one or more air turbines 63 and generators 65 for generating output power from air flow to the injectors. The water path comprises pipes, valves, pumps and control means. Other than for priming, no other external source of power is required. The water path may take the form of a siphon, preferably a bidirectional siphon. The siphon can include a plurality of air injectors. A priming pump 41 may be used to remove air from the siphon to allow the water flow to commence. Preferably, the generator is an electrical generator. In another aspect, a system comprising a plurality of machines is claimed. Multiple air injectors can be connected in one or more groups, wherein each group shares one air turbine and generator. A plurality of siphons may be connected in one or more groups, so that each group shares one priming pump.

Description

HYDRAULIC MACHINE

DESCRIPTION

BACKGROU ND

Bodies of water with little flow are prone to deoxygenation and/or eutrophication resulting in loss of habitat and species. This is a particular problem in impounded lagoons, for example on the landward side of coastal defences. Such water may also emit odours, making it unpleasant for local inhabitants and discouraging visitors. It is preferable to aerate such bodies of water, but to do so conventionally requires large pumps for aeration and is energy intensive.

It is desirable to minimise energy usage of machines, and to generate useful energy from renewable sources wherever possible.

Where water from the environment is passed through machines, it is desirable that the machines are designed so that wildlife (such as fish, invertebrates and small vertebrates) carried through such machines is minimally harmed.

The present invention is a water aerator using height difference between two bodies of water as a source of operating energy, which also generates additional useful power, and provides a safe passage for wildlife.

CURRENT STATE OF THE ART

Many existing systems for treatment of waste water incorporate aeration. Such systems require a significant quantity of oxygen to be present in the water in order to allow bacteria to breakdown waste components by aerobic respiration. If there is insufficient oxygen, minimal conversion may result or alternatively anaerobic reactions may occur with less desirable end products.

Two main systems of aeration are commonly used in waste water treatment. The first is to pump water through a diffuser so that it forms droplets which absorb oxygen from the air as they fall into a treatment tank. The second system injects air into water as bubbles. Such injection may proceed by actively pumping air through a body of water, for example using a pipe with many holes to allow air to escape into a tank of water and to form bubbles.

There are various machines known, using interacting flows of water and air: A hydraulic compressor is a device that uses the energy of a descending flow of water to compress air. It may operate from a source of water behind a dam. A down-pipe allows water to flow from above the dam into a specially constructed underground chamber. From there, water flows up through a riser pipe and exits below the dam. Air is introduced into the descending flow via an aerator. In the underground chamber, the air separates from the water. The water exits through a riser, whilst the air (now compressed) is extracted from a high point in the chamber. The pressure of the air may be used to drive a generator or other pneumatic equipment.

Also known are hydraulic air turbines. At a weir or dam on a river or lake, a siphon may be built to connect the upper and lower water bodies. The siphon conveys water from the upper reach to the lower. Because the top of the siphon tube is some distance above the upper water level, the pressure at the top is lower than atmospheric pressure.

Some air is admitted near the top of the downward leg, and it is carried downwards in the form of bubbles. The bubbles tend to rise relative to the water, but provided that the downward water speed is sufficient, the air is carried down and escapes at the outlet into the lower reach. The siphon works as an air pump, drawing air steadily from the atmosphere. The air flow and pressure difference are sufficient to drive an air turbine and deliver power (for example by driving an electrical generator).

Principles of a siphon A siphon is a continuous tube connecting two bodies of water, with one end below the surface of each body of water, and passing over the barrier which keeps the bodies separate. If the siphon is filled with water and the barrier is not too high, then gravity causes a flow of water through the pipe from the higher body to the lower.

In flowing through the siphon, the water falls through a net vertical distance H (called the "head"), and according to classical mechanics, a mass m of water gives up potential energy mgH where g is the acceleration due to gravity (a constant approximately equal to 9.81 ms2). If the water was able to pass through the siphon entirely without friction losses, and if none of the energy was converted to other forms, the whole of the potential energy of the water would be converted into kinetic energy at the pipe exit.

The exit velocity v of the water would be given by i(2gH).

When (more realistically) friction losses are included, the exit velocity is reduced, so that we have: In terms of energy: mgH = Friction losses + mv212 In terms of head: H = Friction loss Head + v2/2g If the downward flow of water is aerated, its mean density is reduced, and the head driving the flow is effectively reduced. So as the amount of injected air increases, the water flow rate reduces, and there comes a point where the water velocity is insufficient to prevent air bubbles rising. This point represents the maximum capacity for air injection. Any attempts to inject more air will result in breaking the continuous water path and siphonic flow will cease. Published scientific studies place the limit in the range 20% to 30% of air to water by volume.

The Invention The present invention is a water aerator using height difference between two bodies of water as a source of operating energy, which also generates additional useful power, and provides a safe passage for wildlife.

The machine comprises a main water path built from pipes (and with smaller side branches isolated by valves) linking two physically separate bodies of water.

Connected to the main water path are: * means to prime the machine by removing all air and filling it with water, means to allow ingress of air when desired, to halt the flow of water through the machine; and 1 means to allow controlled entry of air to effect aeration, These means are provided by pipes, valves and pumps Importantly the normal water path takes the form of a siphon, crossing the physical barrier which separates the two bodies of water. As described above, the pressure inside the siphon is below atmospheric pressure, and is used to cause entry of air through one or more injectors. This provides a supply of aerated water.

The air flowing into the injectors is first passed through an air turbine, and this drives a generator to create useful power which may be supplied to a means of electrical distribution and/or used local to control the machine.

Brief description of the Figure

The Figure shows a schematic side view of the invention. It is intended to make clear the structure and operation of the present invention but is not to scale and does not show the precise geometry of embodiments (which in any case vary).

Detailed description of the Invention

The present invention is a water aerator using height difference between two bodies of water as a source of operating energy, which also generates additional useful power, and provides a safe passage for wildlife.

Referring to the Figure: the machine comprises a main water path (11) built from pipes, linking a first body (21) of water with a second body (23) of water. The water path (11) passes over a physical barrier (25) separating the bodies (21 & 23) of water, and so takes the form of a siphon. The geometry of the siphon may vary in shape between embodiments as appropriate to local conditions.

The machine requires a small amount of input energy to prime the siphon (by extracting air), but thereafter runs with an energy surplus.

The pipes can be made from any convenient material including steel, plastic and/or glass reinforced plastic, as appropriate to local conditions. Other possible materials include concrete, reinforced concrete, and reinforced concrete with fillers. The pipes may be installed above ground level, or buried, as appropriate. The size and cross-section of the pipes may be any convenient size and shape, based on the water flow required (in turn based on the air flow required), and may vary within and between embodiments.

Connected to the main water path (11) is a priming pump (41) which is normally isolated from the water path by a valve (43). In order to prime the machine, the valve (43) is opened and the pump (41) operated to pump air out of the water path (11) at the top of the siphon. This causes the water path (11) to fill with water. Once this is done, the pump (41) is switched off and the valve (43) is closed, and they remain so during normal operation. Preferably the valve (43) and pump (41) are controlled by electronic and/or computational means. Manual and hydraulic means are also possible.

In normal operation the water path (11) operates as a siphon, transferring water between the two water bodies (21 & 23). The direction of flow is from the body having the higher surface level (31 or 33) to that with the lower.

Preferably the open ends of the water path (11) are protected by screens (not shown) of suitable gauge to prevent large organisms and large physical objects entering.

To stop the flow of water when desired, a valve (51) at or near the top of the siphon is opened to allow rapid ingress of air into the water path (11) and to break the continuous water path (11). The water level in each arm of the siphon drops to the level (31 or 33) of the respective body (21 or 23) of water into which that arm descends. The valve (51) is closed during normal operation. Preferably the valve (51) is controlled by electronic and/or computational means. Manual and hydraulic means are also possible.

As described above, the pressure inside a siphon is below atmospheric pressure. This is used in the present invention to cause entry of air through one or more injectors (61).

In the drawing only one injector (61) is shown for clarity. This provides aerated water.

The design of aerating injectors (61) is well known in the literature. Typically such a component consists of a pipe or box with many small holes in its surface, through which air passes, forming air bubbles which diffuse into the passing liquid. In embodiments of the present invention, the aerating means are constructed with rounded external shape and either protected with coverings of soft material (such as expanded plastics) or composed of such materials. Consequently they present no sharp-edges.

The aerating injectors (61) preferably extend around the perimeter of the pipework, and optionally extend across the cross-section, in order to inject air into many parts of the water flow.

The air flowing into the injector (61) is first passed through an air turbine (63) which can be used to drive local equipment, but preferably is coupled to a generator (65, preferably an electrical generator) to create useful power. The amount of power available at any time depends on the air flow, which depends on the water flow, which in turn depends on the difference in height at that time between the surfaces (31 & 33) of the two bodies (21 & 23) of water.

Care must be taken that the influx of air via the injector (61) is not too great (so as to avoid breaking the continuous water path). Preferably this is accomplished passively by design of the air pathway from intake, through the air turbine (63) and injector (61).

Modelling tools for fluid dynamics are well known and are readily available to assess a range of geometries. Active control techniques may also be used, by means of flow gauging (eg hot-wire anemometry) and active throttling of the air flow, as is also well known.

In one embodiment the surface (33) of the body of water (23) being aerated is at all times at a lower elevation than the surface (31) of the other body (21) of water (23). In this configuration the machine runs continuously in one direction until halted.

For example, the machine may be used to aerate a coastal lagoon, using the height difference between the lagoon (here 23) and the sea (here 21). If the height of the surface (33) of the lagoon (23) lies at all times below the low-tide level (31 minimum) of the sea (21), then the machine runs continuously in one direction aerating the lagoon (23) until halted.

In another embodiment the machine is equipped with air injecting means (61) in both arms of the siphon (not shown in the drawing for clarity). If the height of the surface (33) of the lagoon (23) lies between the minimum and maximum levels of the tide (31 minimum and maximum) in the sea (21), then this embodiment may run in two modes.

During the period around high tide, it will aerate the lagoon (23) while simultaneously generating power. Because this embodiment is equipped with means of aeration (61) in the tidal side of the siphon (which are also connected to the air turbine (63)), then in the period around low tide (when the water flows towards the sea (21)), the machine can also generate useful power (although clearly it will not be aerating the lagoon (23) during this part of the tide cycle).

The machine cannot be used to aerate a coastal lagoon (23) if the elevation of the surface (33) of the lagoon (23) lies above the high tide level (31 maximum) of the sea (21), because water never flows towards the lagoon (23).

The machine may be constructed with a plurality of siphonic water paths (11) operating in parallel, and each delivering aerated water.

In embodiments with a plurality of water paths (11), the priming valves (43) are preferably similarly connected together in groups, each group sharing one priming pump (41).

In embodiments with a plurality of air injectors (61), either within a single water path (11) and/or in a plurality of water paths (11) the air injectors (61) are preferably connected together in groups, each group sharing one turbine (63) and generator (65), allowing easy scaling of installations.

The optimum size for such groups is preferably based on considerations of construction and maintenance cost versus single-point-of-failure analysis, as is well known.

Importantly, there are no pumps (41) or valves (51 & 43) in the water path (11). Also the air injectors (61) are sympathetically constructed (as described above). Consequently there are no moving parts or sharp-edged structures in the water path (11). These important aspects of the machine ensure that fish and other wildlife (such as invertebrates and small vertebrates) can pass through the machine with the flow of water while incurring minimal risk of physical harm. This is of particular benefit when the machine is installed in an environmentally sensitive location.

It is possible to construct embodiments of the machine so that the pipework is buried underground, and the other associated equipment may be installed in an underground chamber, so that there is minimal visual environmental intrusion.

It is possible to construct other embodiments entirely or partly above ground.

While the invention has been described in terms of several embodiments, those skilled in the art will recognize that the invention is not limited to the embodiments described, but can be practised with modification and alteration within the spirit and scope of the appended claims. The Description is thus to be regarded as illustrative instead of limiting.