A device that generates electricity from flowing water

Abstract

1. An apparatus for generating electricity from a flow of water, the apparatus comprising: a converging section coupled at a downstream end to an upstream end of a mixing chamber so as to form a venturi; a diffuser section coupled to the downstream end of the mixing chamber, the diffuser configured such that, in use, a static pressure at an outlet of the diffuser is greater than the static pressure in the venturi; at least a portion of a tube disposed within the converging section so as to define an annulus between the tube and the converging section to form a first flow path, the tube defining a second flow path within the tube; and a turbine coupled to the tube, the turbine being connectable to an electric generator, the turbine being disposed within a turbine chamber coupled at a downstream end to the upstream end of the converging section.

Description

[Technical field]

[0001] The present disclosure relates to an apparatus for generating electricity from flowing water. [Background technology]

[0002] Many systems have been proposed to convert water flow into electricity. These systems require a dam, weir, or other artificial structure to intercept the flow of water across a body of water and create a hydraulic head. Once there is enough available head, the water is released to flow through a turbine, generating electricity and, in turn, converting the potential energy stored in the water into useful power. One type of device used in power generation systems is the Kaplan turbine.

[0003] Prior art systems have many drawbacks, some of which are considered below.

[0004] Indeed, prior art systems require high flow rates to enable their use for commercial energy production and operate at relatively low speeds. Operation at such high flow rates requires systems with large diameters.

[0005] Prior art systems typically require the turbine house to be dug deep into or near the upstream water source so that the unit can be fully submerged. The deeper upstream water level reduces the risk of cavitation and serves to prevent free surface vortex formation from being drawn into the turbine. To prevent cavitation, the turbine blades must rotate slowly, thus requiring a gearbox to provide a stepped increase in shaft speed for the generator.

[0006] Prior art systems typically require large screens upstream of the turbine inlet to prevent fish and other aquatic life from being drawn into the turbine. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention is an improved device for generating electricity from flowing water, and in particular aims to provide such a device which allows for lower cost and simple installation. The device is preferably self-contained. [Means for solving the problem]

[0008] In a first aspect, the present invention provides an apparatus for generating electricity from a flow of water comprising: a converging section coupled at a downstream end to an upstream end of a mixing chamber so that a venturi is formed; a diffuser section coupled to the downstream end of the mixing chamber, the diffuser configured such that, in use, a static pressure at an outlet of the diffuser is greater than the static pressure in the venturi; at least a portion of a tube disposed within the converging section such that an annulus is defined between the tube and the converging section to form a first flow path, the tube defining a second flow path within the tube; and a turbine coupled to the tube and connectable to a generator, wherein the turbine is disposed within a turbine chamber coupled at a downstream end to the upstream end of the converging section.

[0009] The coupling of the turbine with the tube, which may otherwise be referred to as the turbine tube or turbine draft tube, results in an arrangement in which the turbine is driven by pressurized fluid flow through the tube, and most preferably, the turbine is driven solely by pressurized fluid flow through the tube.

[0010] The turbine chamber is preferably connected at its upstream end to an inlet pipe. The inlet pipe preferably has a substantially constant cross-sectional area. The turbine chamber may be directly connected to the inlet pipe, or it may more preferably be connected to the inlet pipe via / through a second (or inlet) diffuser. In such a case, the second diffuser is connected to the turbine chamber at its downstream end and to the inlet tube at its upstream end. The second diffuser, if present, reduces the velocity of the water as it enters the turbine chamber.

[0011] The turbine chamber defines a closed volume. It is closed except for the inlet and the outlet. The turbine chamber is preferably pressurized in use. It is preferably completely filled with water so that there is no free surface.

[0012] The turbine chamber preferably defines a self-contained turbine module for connection to upstream and downstream components of the apparatus.

[0013] The turbine chamber preferably has a constant cross-sectional area. It may have a generally cylindrical inner surface.

[0014] The turbine chamber is preferably arranged to be openable to allow access for installation and maintenance operations, so a hatch may be provided.

[0015] The turbine chamber may be mounted so that it is out of water or so that it is fully or partially submerged.

[0016] The turbine and / or tubes are preferably slidably mounted within the turbine chamber. They may be mounted on a skid that is housed within the turbine chamber.

[0017] The inlet pipe preferably has an inlet that is fully submerged in water.

[0018] The inlet pipe is preferably equipped with a debris screen at its upstream end.

[0019] The inlet pipe may be a siphon tube, where the inlet pipe is inverted to raise it to a level above the upstream water level. The inlet pipe may in such a case be primed by a vacuum pump. If the inlet pipe takes the form of a siphon tube, the flow of water through the device may be controlled by managing the air pressure in the inlet pipe. In such a case, the flow in the device may be shut off by allowing air to enter the inlet pipe to jam the siphon.

[0020] The mixing chamber preferably has a length at least twice its internal diameter.

[0021] In a further aspect, the present invention provides an apparatus for generating electricity from a flow of water comprising: a converging section coupled to an upstream end of a mixing chamber so as to form a venturi; a diffuser section coupled to a downstream end of the mixing chamber, the diffuser configured such that, in use, a pressure at an outlet of the diffuser is greater than the pressure in the venturi; at least a portion of a tube disposed within the converging section such that an annulus is defined between the tube and the converging section to form a first flow path, the tube defining a second flow path within the tube; and a turbine coupled to the tube and connectable to a generator, wherein the mixing chamber has a length at least twice its diameter.

[0022] According to the second aspect, the turbine chamber, inlet tube and inlet diffuser may be omitted, although these elements may otherwise be included according to the first aspect.

[0023] We now briefly describe further features that may be employed in either the first or second aspect.

[0024] The turbine chamber may have a constant cross-sectional area. It may have a generally cylindrical inner surface. The inner surface may otherwise be tapered at an angle of up to 4 degrees along all or part of its length.

[0025] A tailpipe may be provided which is connected to the outlet of the diffuser and which may be used for connection to a downstream body of water, the downstream end of which is preferably fully submerged in water.

[0026] The converging section, the mixing chamber and the diffuser section together may be considered to define a pressure booster section. The tailpipe, if present, may be considered to form part of the pressure booster system. The pressure booster section reduces the pressure at the outlet of the turbine, so the available pressure across it is boosted. The diffuser section, connected to the end of the mixing chamber, is where the pressure is restored.

[0027] At its upstream end, the tube preferably comprises a screen in front of the turbine. The screen may be substantially conical. The size of the apertures in the screen is selected to allow adequate flow of water through the tube while preventing fish and other marine animals (such as otters) from entering the turbine. The screen may be made of any suitable material. It may comprise a perforated metal screen.

[0028] Since there are no turbines in the pressure amplifier section, the downstream passage of fish and other marine animals is not impeded. They can swim safely from the upstream side to the downstream side. The device can recover a large amount of energy from the water flow without causing any damage to the fish and other animals.

[0029] The inlet of the tube is preferably connected to the turbine. If a turbine chamber is provided, the inlet is preferably within the turbine chamber. The outlet is preferably located within the venturi region. The tube and the elements of the pressure amplifier section are preferably coaxial.

[0030] The tubes are preferably able to move axially forward or backward relative to the converging section and mixing chamber to maximize performance. This may be accomplished by slidably mounting the tubes. The downstream ends of the tubes may be located at the level of the venturi section, upstream of the venturi section, or downstream of the venturi section. The ends of the tubes may be selectively movable between / fixable at these positions.

[0031] The tube may be supported within a hub that is coupled to the turbine. The hub may have a smooth profile to minimize flow interference. The tube may be coupled to the turbine during installation and cantilevered within the venturi.

[0032] Any or all of the tubes, hub, and turbine may be supported by a skid, which, if present, may be attached to the bottom of the turbine chamber.

[0033] Regardless of its mounting, the outlet of the tube is preferably positioned to optimize the secondary flow rate within the tube and the pressure differential between the upstream and downstream ends of the tube.

[0034] The ratio of the cross-sectional area of ​​the mixing chamber inlet to the cross-sectional area of ​​the tube is preferably selected to optimize the secondary flow rate in the tube and the pressure difference between the upstream and downstream ends of the tube.

[0035] The diameter of the turbine may determine the diameter of the tube. The tube may have a substantially uniform diameter along its length, with the inlet and outlet having substantially the same diameter.

[0036] The diameter along the secondary tube can be varied to maintain the correct ratio between the cross-sectional area of ​​the mixing chamber inlet and the cross-sectional area of ​​the end of the secondary tube. If the turbine diameter is smaller than the optimum exit diameter of the tube, the tube profile may diverge slightly. Alternatively, it may converge slightly.

[0037] The ratio of the cross-sectional area of ​​the inlet of the converging section to the cross-sectional area of ​​the inlet of the mixing chamber is preferably selected to optimize the secondary flow rate in the tube and the pressure difference between the upstream and downstream ends of the tube.

[0038] The ratio of the cross-sectional area of ​​the inlet of the converging section to the cross-sectional area of ​​the outlet of the diffuser section is preferably selected to optimize the performance of the device.

[0039] The turbine may be coaxially connected to the generator by a drive shaft. Alternatively, the turbine may be connected to a remote generator. The connection to the generator may be by a pulley wheel, a drive belt, a chain, one or more gear wheels or drive shafts, or any mixture of the above. Pipes surrounding these components may be connected within the turbine shaft.

[0040] The outlet of the diffuser section and / or the inlet of the convergent section may have a generally rectangular, generally circular or generally elliptical cross-section.

[0041] The mixing chamber may have a generally circular cross-section along its length.

[0042] A flow control device may be provided to control the flow of fluid within the device. The flow control device may comprise, for example, a sluice gate, or a valve. The flow control device may be located upstream of the tube, downstream of the outlet pipe, or anywhere in between.

[0043] The device can be used to create a flow path through a barrier, which can be a naturally occurring structure within a body of water, a dam, or other such structure that creates a high pressure reservoir or water containment on one side.

[0044] A further aspect of the invention comprises a system for generating electricity from flowing water comprising a barrier positioned across a cross-section of a body of water and comprising at least one device as described above, wherein the device is positioned such that, in use, it provides a flow path from an upstream side of the barrier to a downstream side of the barrier.

[0045] A further aspect of the invention includes a method of preparing a flow path through a barrier across a body of water, the method comprising placing an apparatus as described above within the barrier.

[0046] A further aspect of the invention includes a method of generating electricity from flowing water comprising installing a system or apparatus as described above across a body of water to provide a reservoir of water such that a hydraulic head difference occurs between downstream and upstream sides of a barrier, and using the flow of water through the apparatus to rotate a turbine.

[0047] In this application, the terms "upstream" and "downstream" are used to define the relative locations of features of the device. The upstream and downstream directions are defined relative to the direction in which water flows through the device during use. The upstream end may be considered the input area and the downstream end may be considered the output area.

[0048] In the present application where two elements are specified to be connected to one another, they may be connected to one another with a fluid-tight seal. They may also be co-formed in other ways.

[0049] These and other aspects and features of the present disclosure will be more readily understood when read in conjunction with the accompanying drawings. Furthermore, it should be noted that various features of any of the above descriptions may be combined without restriction, as would be readily understood by one of ordinary skill in the art.

[0050] Non-limiting embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0051] [Figure 1] FIG. 1 is a side view of an apparatus according to one embodiment of the present invention, with a ducted inlet pipe and an upstream sluice gate, which is shown angled from the intake to the discharge. [Diagram 2] FIG. 2 is a side view of the device of FIG. 1 further comprising a siphon inlet. [Diagram 3] FIG. 1 is a diagram of a turbine arrangement with a support skid together with an underwater generator. [Figure 4] FIG. 4 is a diagram of the turbine arrangement of FIG. 3 including an upstream fish screen. [Diagram 5] FIG. 3 is an upstream view of a turbine chamber according to the arrangement of FIG. 1 or FIG. 2, showing a generator mounted on a turbine chamber skid. [Figure 6] FIG. 3 is a downstream view of the turbine chamber according to the arrangement of FIG. 1 or FIG. 2, where the cover sealing the pipes has been removed to show a view of the generator drive chain. [Figure 7] FIG. 2 is a perspective view of an upstream debris screen installed upstream of the inlet, showing a sluice gate for controlling flow through the inlet pipe. [Figure 8] FIG. 2 is an isometric view of the device of FIG. 1. [Figure 9] FIG. 9 is an isometric view corresponding to FIG. 8, but with the external generator replaced by an internal submersible generator. [Figure 10]FIG. 10 is a cross-sectional view of the arrangement of FIG. 9, with the screen (as seen in FIG. 4) omitted. [Figure 11] FIG. 9 is a cross-sectional view of a turbine assembly according to that used in FIGS. 1 and 8 with a sprocket / pulley attached to the drive shaft for coupling to an external generator, where the tubes are shown tapering in the downstream direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] Referring to the drawings, there is shown an apparatus for generating electricity from a flow of water comprising: a converging section 8 connected at its downstream end to an upstream end of a mixing chamber 9 so as to form a venturi; a diffuser section 10 connected to the downstream end of the mixing chamber 9, the diffuser section 10 configured such that, in use, the pressure at the outlet of the diffuser section 10 is greater than the pressure at the venturi; at least a portion of a tube 15 disposed within the converging section 8 such that an annulus is defined between the tube 15 and the converging section 8 to form a first flow path, the tube 15 defining a second flow path within the tube; and a turbine 14 connected to the tube 15 and connectable to a generator 25.

[0053] The turbine 14 is preferably located within a turbine chamber (or duct) 7 which is connected at its downstream end to the upstream end of the converging section 8, as is the case in the arrangement depicted in the drawings. Additionally or alternatively, the mixing chamber 9 preferably has a length at least twice its diameter.

[0054] A detailed discussion will now be given of the non-limiting arrangements depicted in the drawings.

[0055] Figures 1 and 2 show a system for converting water flow into electricity. The system converts hydraulic potential energy into mechanical energy and then into electrical energy. The system comprises a barrier 1 positioned across the width of a body of water, and an apparatus, as broadly defined above, for providing a water flow path through the barrier from an upstream side of the barrier to a downstream side of the barrier.

[0056] The device provides a flow path from a water level 2 upstream of the barrier 1 to a water level 3 downstream. The device comprises an inlet pipe 5 which draws flow from an upstream body of water. The inlet pipe is preferably encased in a diffuser 6 (second diffuser in the claims). The diffuser reduces the flow velocity before entering the turbine chamber (or duct) 7. However, the diffuser 6 may be omitted. The flow from the turbine chamber 7 enters a converging section 8 which narrows and increases the flow velocity before entering a mixing chamber 9. After the mixing chamber 9 the flow passes through a diffusing section 10 and then through a discharge tailpipe 11. The narrowing of the converging section 8 towards the mixing chamber 9 forms a venturi 13.

[0057] The device can be installed at a tilt angle θ, as seen in FIG. 1, to reduce civil work and installation time, while the inlet and tail pipes are left submerged below the water line.

[0058] A barrier 1 across the body of water creates a pressure head just upstream of the device. This converts some of the kinetic energy from the flow further upstream into potential energy of the elevated water level as the flow slows with the increased water depth behind the barrier. The resulting head difference H allows for the conversion of potential energy into useful mechanical energy, as shown in Figure 1. Water continues to flow from the upstream side of the barrier, through the inlet tube, through the turbine duct, into the convergent section, into the mixing section, and then out of the device through the diffuser section. A secondary flow is induced through the turbine draft tube, which drives the rotation of the turbine tube via the blade assembly, thereby generating electricity via a mechanical or electrical power offtake arrangement.

[0059] The turbine 14 is contained by and supported within the turbine chamber 7. The tubes 15 extend into the converging section 8 such that an annulus is formed between the outer surface of the tubes 15 and the inner surface of the converging section 8. The turbine 14 is preferably mounted by fastening to the support plate 17 by bolted flanges 18. Such an arrangement provides for easy removal for maintenance. However, it should be understood that many alternative mounting arrangements are possible. The turbine 14 preferably comprises guide vanes 19 and blades 20 mounted on a hub 21. As water flows through the turbine, the blade assembly drives the rotation of a turbine drive shaft 22. However, it should again be understood that the turbine 14 need not be limited to any particular configuration. Many alternative turbine configurations will be readily apparent to those skilled in the art.

[0060] A first flow path for the primary flow is defined within the annulus between the turbine draft tube 15 and the converging section 8. A second flow path for the secondary flow is defined within the turbine 14 and within the draft tube 15. It should be understood that the annulus is not limited to a circular ring-shaped space between the tube 15 and the inner wall of the converging section 8. The shape of the annulus depends on the cross-sectional shapes of the converging section 8 and the turbine draft tube 15, and therefore can take on many different profiles.

[0061] The converging section 8 accelerates the primary flow, which creates a low pressure zone in the venturi 13. The low pressure zone induces a secondary flow through the turbine 14. Both the primary and secondary flows enter a mixing duct 9 where the two flows mix. The mixed flow enters a diffuser section 10 where the velocity of the water flow slows as it passes through the diffuser section 10. As the water flows through the diffuser section 10, the flow regains its static head and loses its dynamic head before it exits the diffuser section 10. As shown, it is preferable to provide a tailpipe section 11 downstream of the diffuser section 10. If provided, this acts to keep the static head low in the venturi.

[0062] The primary flow passes through the annulus formed between the converging section 8 and the turbine draft tube 15. The secondary flow, a smaller volume of water, flows through the turbine 14, thereby driving the rotation of the turbine hub 21 and drive shaft 22 as it flows past the blades 20. As the primary flow converges towards the venturi 13, it accelerates, thereby reducing the hydrostatic head. The high velocity primary flow outside the tube 15 at the tube exit helps to entrain the slower secondary flow exiting the end of the tube 15 and entering the mixing chamber 9.

[0063] In this way, a large volume of low head flow is converted into a smaller volume of high head flow from which power can be efficiently generated by rotating turbine drive shaft 22 .

[0064] The inlet tube 5 is configured so that its upstream end is completely submerged below the upstream body of water.

[0065] A non-limiting exemplary inlet is shown in Figure 1. To control the flow through the device, flow control means 34, which may for example take the form of a sluice gate or a valve, is fitted and may for example be located in the inlet tube 5, in the mixing duct 9 or in the tail pipe 11. In this arrangement the control means comprises a sluice gate which may be in an open position, a closed position or any position in between. The sluice gate is preferably operated by an actuator 35. Control of the actuator is preferably by a control system programmed to operate the gate depending on the downstream and upstream water levels.

[0066] FIG. 2 shows an exemplary modified inlet arrangement in the form of a siphon inlet. The siphon inlet pipe 36 has its upstream end submerged below the upstream water level 2 and its downstream end connected to the inlet pipe 5. The downstream connection may be by a bolted flange as shown, or in another manner as would be apparent to one skilled in the art. The siphon pipe is inverted so that it rises above the upstream water level. To initiate flow through the device, air may be pumped out of the siphon pipe using a vacuum pump, which may be controlled by the control system. As will be readily understood, removal of air in the siphon pipe reduces the pressure and pumps up the water in the pipe. When the pressure is low enough, the siphoning action begins to draw water into the pipe. At this point, the air pump may be turned off. To stop the flow, for example, a valve may be provided which can be opened, thereby drawing air into the pipe and reducing the pressure to the point where the flow ceases.

[0067] Siphon installations are useful because they can reduce the need for large scale excavation, thus reducing costs and installation time.

[0068] A debris screen 4 is preferably mounted upstream of the inlet to block larger debris from entering the apparatus.

[0069] The turbine 14 may be mounted on a support skid 16 as shown. The turbine 14 may instead be welded or mechanically fastened within the turbine chamber 7. The turbine may be supported by any suitable support means, such as a plate or frame, whether mounted via a skid or otherwise. In the arrangement shown, a plate 17 is provided. The plate 17 is mounted to the skid and includes a bore for receiving and supporting the turbine tube 15 such that the longitudinal axis of the turbine tube 15 is substantially aligned with the longitudinal axis of the converging section 8. In an alternative arrangement, the turbine 14 may be mounted on radial supports and fastened to the inner wall of the turbine chamber 7. Regardless of the mounting arrangement, the turbine is preferably positioned such that the longitudinal axis of the turbine tube 15 is substantially aligned with the longitudinal axis of the converging section 8.

[0070] The turbine draft tube 15 provides a flow path between the high hydrostatic head in the turbine chamber 7 and the low hydrostatic head in the venturi 13. Secondary flow passes through the turbine 14 and the turbine draft tube 15 and is induced by the amplified head between the upstream end of the turbine tube 15 and the venturi.

[0071] The turbine draft tube 15 can have a substantially constant inner diameter along its length. Alternatively, it may taper towards its downstream end, for example as shown in FIG. 11. As shown, the diameter of the turbine tube converges along its length, such that the inlet of the turbine draft tube has a larger diameter than the outlet of the turbine draft tube. Providing a tapered turbine tube can help generate greater efficiency of the device due to improved venturi performance.

[0072] The turbine tube 15 may be of sufficient length to be positioned just before or within the mixing duct such that it spans from the high pressure in the turbine chamber 7 to the low pressure at the venturi 13. For example, as shown in FIG. 10, the downstream end of the turbine draft tube 15 may be positioned within the mixing chamber (or tube) 9 such that it extends into the mixing tube by a distance X. Distance X may be selected to optimize performance of the device and may be zero, positive or negative. When distance X is positive, the turbine tube extends into the mixing tube. When distance X is negative, the outlet of the turbine tube terminates upstream of the inlet of the mixing tube. When distance X is zero, the outlet of the turbine tube is approximately coincident with the inlet of the mixing tube.

[0073] The power off take arrangement for the device can take a variety of different forms, as will be readily understood by those skilled in the art. Two non-limiting exemplary power take off options for the device are described below. The power take off arrangement may be mechanical or electrical, one example of each of which is described in detail below.

[0074] An exemplary mechanical offtake arrangement is shown in Figure 11. Rotation of the turbine shaft 22 drives a chain or belt 23 connected to the shaft of a generator 25. The generator is mounted outside the turbine chamber 7. Numerous structures are readily apparent to effect such an arrangement, but for illustrative purposes only, a specific, non-limiting arrangement is described in detail below.

[0075] A chain or belt 23 runs up through the turbine chamber 7. A sealing cover 26 is preferably placed over the chain / belt to prevent water ingress. The sealing cover 26 may take the form of a pipe or tube, for example. The sealing cover is preferably sealed at the base and at the tube duct. Any suitable sealing arrangement may be implemented. For example, O-rings or flanged connections may be used.

[0076] The turbine drive shaft 22 passes within a sleeve 27 which houses all bearings 28, 29, seals 30 and the power offtake spigot / pulley 24. The drive shaft assembly is preferably sealed to help minimize frictional resistance in the drive chain and reduce the risk of corrosion. The downstream face of the drive shaft sleeve may be connected to the turbine hub via a seal flange. Upstream, the drive shaft sleeve may be closed. Fixation means for a screen may be provided, such as a blind tapped hole. A contoured nose may be provided to reduce hydraulic losses.

[0077] The drive shaft is preferably supported by a pair of bearings. The bearings may be, for example, water lubricated bushings or roller bearings. The downstream bearing 28 may be a roller bearing or a water lubricated polymeric bushing supported radially or otherwise within the drive shaft sleeve 27. The bearings, bushings or otherwise may be fixed by conventional means, for example, by mechanical fasteners, by interference fit or the like. The upstream bearing may, for example, preferably comprise a thrust bearing 29 configured to prevent the turbine tube from moving axially downstream as the turbine rotates. The thrust bearing may be supported radially and longitudinally by any conventional means. It may be supported radially within the drive shaft sleeve 27 and longitudinally by an internal flange or otherwise. Thrust forces from the turbine may be transferred through the drive shaft sleeve to the turbine support skid 16 or to other mounting means.

[0078] A chain spigot or belt pulley 24 is preferably disposed on the drive shaft 22 and may be secured by any conventional means, for example by mechanical fasteners or by an interference fit. A chain or belt 23 is connected to and extends to a location external to the turbine chamber 7. As will be readily understood by one skilled in the art, the chain / belt may extend to any location around the circumference of the turbine duct as required for the installation.

[0079] The sealing cover 26, which is preferably placed over the chain / belt 23, may be contoured or fitted with an additional fairing to reduce hydraulic losses in the flow so as to minimize flow disturbance in the duct.

[0080] The generator 25 is located outside the turbine chamber 7. Its location is not limited. However, it is preferred that the generator 25 is mounted out of the water, i.e. on a dry location. The generator may be supported, for example, by the external turbine chamber support structure 12. Such structure may comprise a skid, as shown, but need not be limited to such. The generator shaft is preferably mounted on a spigot / pulley that is connected to a chain / belt 23. The spigot / pulley ratio may be modified to provide a step-up in speed from the turbine to the generator. Additionally or alternatively, a gearbox may be provided between the turbine and the generator.

[0081] The generator may be controlled by a variable speed controller that controls the speed of the turbine by varying the electrical load on the generator to maximize the power output from the system.

[0082] Water is preferably removed from within the drive shaft sleeve 27 to help minimize frictional resistance in the drive chain 23 and further help reduce the risk of corrosion.

[0083] The drive shaft sleeve may be connected to the venturi 23 via an air hose 33, which may be formed, for example, from nylon, so that water can be passively pumped out during operation by the low pressure in the venturi. If there is no water in the drive shaft sleeve, air is pulled through the hose to the point where the pressure in the drive shaft sleeve equals the venturi and no fluid passes.

[0084] A power offtake arrangement will now be described, in which power and signal cables run from the turbine within the turbine chamber to a generator located outside the turbine chamber 7. Again, numerous configurations are readily apparent to effect such an arrangement, but a specific, non-limiting arrangement is described in detail below for illustrative purposes only.

[0085] A permanent magnet, synchronous or asynchronous generator, or other, may be directly coupled to the turbine runner and may be structurally supported via flanges or other on the turbine guide vanes. The generator is preferably sealed. For example, it may be sealed with static O-rings and mechanical seals to prevent water ingress. All bearings are located within the generator housing. Power and signal cables may run from the generator through a gland or the like and through sealed conduits outside the turbine chamber.

[0086] The generator may be connected to the venturi via an air hose to passively pump out any water ingress due to low pressure in the venturi that may break the seal. If there is no water in the generator, air is drawn through the hose to a point where the pressure is equal and no fluid passes. One or more check valves may be installed to prevent water ingress back into the air hose. The air hose may also be taken out along with the signal cable and folded back down through a conduit so that the high point of the hose is above the maximum water level.

[0087] Returning to the turbine chamber 7 as provided according to any embodiment, it is preferably in the form of a circular duct having an inlet at one end for receiving flow from upstream of the barrier and an outlet for releasing the flow into the convergence 8. While there are a number of mounting options for mounting the turbine chamber in situ, the turbine chamber 7 is preferably mounted on a structural skid 12 as shown. The skid may be mounted on a concrete pad, for example, to reduce installation time, cost and complexity on site.

[0088] During operation the turbine chamber 7 is pressurized by the upstream water level 2 and is kept full during operation. By operating the turbine duct as a pressurized chamber with no free surface, the formation of free surface vortices is not possible, which is highly beneficial.

[0089] The turbine duct 7 is preferably provided with a maintenance hatch 39 which is sealed to maintain operating pressure during operation. The maintenance hatch is preferably profiled to match the hatch. In the arrangement depicted in the drawings it is profiled to maintain the inner circular form of the turbine duct to reduce hydraulic losses.

[0090] For example, the turbine assembly, including the turbine 14, the turbine draft tube 15, the generator and the screen 38 (if present, as described below), may be mounted together to form a single assembly. The turbine assembly may further include power offtake components 27, 24, 22. The turbine assembly may be mounted, for example, on a fixed skid 12 to form a single assembly. Such an arrangement is beneficial to reduce installation time and costs and to aid in the location of the equipment. Assembly and functional testing of the turbine assembly may be performed off-site. During assembly on-site, the turbine assembly may be lifted through a maintenance hatch 39 and placed in the turbine chamber 7. The turbine assembly, including the skid or another, may be mounted on a profiled plate that confirms the profile of the turbine chamber, such as maintaining the inner circular form of the turbine chamber, to reduce hydraulic losses.

[0091] Maintenance of the turbine and other machinery can be carried out by removing the entire turbine assembly from within the turbine duct 7 and transporting it to a workshop. This provides a further advantage of minimising downtime, where a spare turbine assembly may be replaced after removal for maintenance.

[0092] In the siphon arrangement, the invert of the mixing duct 9 is located above the downstream water level 3. By preventing flow from entering upstream (via a sluice, siphon breaking, drop off, gate valve, or otherwise), the system is made self-draining. After pumping out any remaining standing water, safe, dry access can be provided via a maintenance hatch 39.

[0093] If necessary, a fish screen 38 may be bolted to the front of the turbine 14 to prevent fish and other aquatic life from entering the turbine. The screen 38 may be cone-shaped. The screen 38 may comprise bars that run longitudinally parallel to the flow. Such an arrangement is beneficial for reducing hydraulic losses. The spacing of the bars may increase toward the turbine. The maximum spacing of the bars may be selected based on the type of fish and other aquatic life present in the water stream.

[0094] Considering a conical screen 38, the secondary flow Qs passes through the screen and the remaining flow Qp passes over and around the screen. As the remaining flow passes over the screen, it passively cleans the screen, thereby ensuring that it remains debris-free during operation. The angle of the screen may be selected so that the flow velocity perpendicular to the screen is low enough to prevent impingement on the fish and other aquatic life. A nose cone may be provided in front of the screen to further reduce hydraulic losses and to guide the fish safely away from the screen. The fish can safely pass through the venturi. This device provides the fish with a safe alternative route to migrate downstream.

[0095] The preferred unitary construction of the components forming the turbine tube and support boss helps reduce installation time and cost and also aids in site location of the equipment.

[0096] The converging section 8 is funnel-shaped with a first opening at one end as an inlet for receiving water from behind the barrier 1 and a narrower opening at the opposite end as an outlet for discharging water into the mixing chamber 9. The converging section 8 tapers from the upstream end towards the inlet of the mixing chamber 9. A venturi 13 is defined at the boundary of the converging section and the mixing tube. The parameters of the converging section such as the angle of convergence, the length of the section and the size such as the diameter of the inlet and outlet of the converging section can be selected to optimize the performance of the device as will be apparent to one skilled in the art.

[0097] As shown, the mixing chamber, which may take the form of a mixing pipe / tube, provides a section of the apparatus where the secondary flow Qs and the primary flow Qp can mix to form a substantially uniform flow. The flows are approximately uniform before exiting the mixing chamber 9 and entering the diffuser section 10, and have a velocity profile such that sufficient pressure recovery of the flow through the diffuser section can maintain a pressure differential between the low pressure in the venturi and the higher pressure at the exit of the diffuser section.

[0098] The mixing tube is configured to maximize the power output of the turbine tube through which the secondary flow (Qs) passes. This is accomplished, at least in part, by a mixing section configured to optimize the flow regime in the region immediately downstream of where the secondary flow through the turbine begins to mix with the primary flow induced by the low pressure of the venturi. The mixing tube is configured to optimize the energy transfer from the primary flow to the secondary flow within the mixing tube.

[0099] The mixing chamber has an opening, an outlet, and a non-zero length, providing a sufficient length of space between the opening and the outlet where the flows can mix. The length L of the tube defining the mixing tube is selected to provide a properly conditioned flow before the flows enter the diffuser section. Selecting a length appropriate for the flow and pressure conditions ensures that there is an optimal energy transfer between the fast flowing primary flow and the slower secondary flow, and that there is an acceptable velocity profile across the two flows before the merging flows enter the diffuser section. Through extensive research, the inventors have independently determined that it is particularly beneficial if the mixing chamber has a length at least twice its diameter.

[0100] In one embodiment of the invention, the mixing chamber may taper in the downstream direction by a half-cone angle of R>, beta, such that the outlet of the mixing chamber is narrower than its inlet. The half-cone angle of the mixing chamber may be positive or negative. In an alternative embodiment, the mixing chamber may taper in the upstream direction, such that the outlet of the mixing chamber is wider than the inlet of the mixing chamber, i.e., the mixing chamber diverges along its length towards the diffuser section.

[0101] Having a tapered mixing chamber can facilitate energy transfer between the higher velocity primary flow through the annulus and the slower secondary flow exiting the turbine tube.

[0102] The downstream end of the mixing chamber 9 is connected to a diffuser section 10. The diffuser section is funnel-shaped with a first opening as an inlet to receive water from the mixing tubes 9 and a wider opening at the opposite end as an outlet to discharge the water. As explained, the water is preferably discharged into a tailpipe 11 before returning to the free stream downstream of the barrier 1. The diffuser section 10 diverges outwardly from the outlet of the mixing tubes 9, slowing the flow and regaining static pressure before it leaves the diffuser section 10, minimizing energy losses due to turbulence. The angle of divergence can be selected to optimize the performance of the diffuser.

[0103] The parameters of the diffuser section, such as the length of the section, the angle of divergence, and the ratio of the cross-sectional areas of the first and second openings, are selected to reduce turbulence and energy losses caused by flow separation as the flow slows back to free stream velocity. Excessive turbulence, vortices, and flow separation can impair pressure recovery as the flow approaches the diffuser section exit. The parameters are selected to maximize pressure recovery, as would be readily apparent to one skilled in the art, such that the pressure at the diffuser exit, set by the downstream water depth, is as high as possible compared to the pressure at the venturi.

[0104] The convergent section 8, mixing tube 9, diffuser section 10, and tailpipe 11 may be manufactured as a single continuous tube. Alternatively, the convergent section, mixing tube diffuser, and tailpipe may be manufactured as one or more separate sections that are fastened together by bolts or by other conventional joining means or techniques. As shown in Figures 8 and 9, the convergent section, mixing tube, diffuser, and tailpipe may be manufactured as separate components, with two adjacent sections held together by bolted flanges 40.

[0105] Between any two adjacent sections, a rounded transition may be formed to minimize energy loss due to induced turbulence, which can occur when there is a sharp edge transition between the sections. This helps to increase the energy conversion efficiency of the system.

[0106] A typical hydroelectric dam, where a barrier across the water source directs all water flow to the turbine, typically requires a head differential of 3.5 m or more to make the generator work efficiently, but because of the pressure amplification of the induced secondary flow, the present invention allows such turbines to cost-effectively operate with a head differential of about 1.0 m.

[0107] Thus, the disclosed apparatus is well adapted to obtain the objects and advantages described, as well as those inherent therein. The particular embodiments disclosed above are illustrative only, and thus the teachings of the disclosure may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Moreover, it is not intended to be limited to the details of construction or design shown herein, except as described in the following claims. Thus, it is apparent that the particular exemplary embodiments disclosed above may be altered, combined or modified, and all such variations are contemplated as being within the scope of the present disclosure. The systems and methods illustratively disclosed herein may suitably be practiced in the absence of any element not specifically disclosed herein and / or any optional element disclosed herein. Although compositions and methods are described in terms "comprising," "containing," or "including" various components or steps, the compositions and methods may also "consist essentially of" or "consist of" the various components and steps. All of the numbers and ranges disclosed above may be varied by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any numerical value within that range and any included range is specifically disclosed. In particular, all ranges of values ​​disclosed herein (in the form of "about a to about b", or equivalently, "from about a to b", or equivalently, "from about a to b") should be understood to describe all numerical values ​​and ranges encompassed within the broader range of values. Moreover, the terms in the claims have their plain and ordinary meanings unless expressly and unambiguously defined otherwise by the patent owner. Moreover, the indefinite article "a" or "an" as used in the claims is defined herein to mean one or more than one of the element it represents. In the event of any inconsistency in the use of a phrase or term in this specification and one or more patent documents or other documents that may be incorporated herein by reference, the definition consistent with this specification should be adopted.

[0108] As used herein, the phrase "at least one of" preceding a list of items, including the term "and" or "or" separating any items, modifies the list as a whole and not each member (i.e., each item) of the list. The phrase "at least one of" allows for a meaning including at least one of any one of the items, and / or at least one of any combination of the items, and / or at least one of each of the items. By way of example, the phrase "at least one of A, B, and C" or "at least one of A, B, or C" refers to only A, only B, or only C, any combination of A, B, and C, and / or at least one of each of A, B, and C.

[0109] While various exemplary embodiments have been disclosed, those of ordinary skill in the art will recognize that certain modifications are possible within the scope of the present disclosure. For this reason, the following claims should be considered to determine the scope and content of the present disclosure.

Claims

1. A device for generating electricity from flowing water, a converging section coupled at a downstream end to the upstream end of the mixing chamber such that a venturi is formed; a diffuser section coupled to the downstream end of the mixing chamber, the diffuser configured such that, in use, the static pressure at an outlet of the diffuser is greater than the static pressure at the venturi; at least a portion of the tube disposed within the converging section such that an annulus is defined between the tube and the converging section to form a first flow path, the tube defining a second flow path within the tube; and a turbine coupled to the tube and connectable to a generator; Equipped with The apparatus wherein the turbine is disposed within a turbine chamber coupled at a downstream end to an upstream end of the converging section.

2. The apparatus of claim 1 , wherein the turbine chamber is connected at its upstream end to an inlet pipe.

3. The apparatus of claim 1 , wherein the turbine chamber is connected to an inlet pipe through a second diffuser.

4. 4. The apparatus of claim 2 or 3, wherein the inlet pipe comprises a siphon.

5. 10. The apparatus of claim 1, wherein the turbine chamber is pressurized in use.

6. The apparatus of claim 1 , wherein the turbine chamber has a substantially constant cross-sectional area.

7. The apparatus of claim 1 , wherein the turbine chamber comprises a generally cylindrical interior surface.

8. The apparatus of claim 1 , wherein the turbine chamber includes a hatch in a wall thereof to provide access to an interior of the turbine chamber.

9. The apparatus of claim 1 , wherein the turbine and the tubes are mounted to a turbine support structure that is removably mounted within the turbine chamber.

10. The apparatus of claim 9 , wherein the turbine support structure comprises a skid.

11. The apparatus of claim 1 , wherein the turbine and / or the tube are slidably mounted within the turbine chamber.

12. The apparatus of claim 1 , further comprising a tailpipe coupled to an outlet of the diffuser.

13. The apparatus of claim 1 , wherein the turbine chamber comprises a self-contained unit separable from the remainder of the apparatus.

14. 10. The device of claim 1, wherein the mixing chamber has a length at least twice its diameter.

15. A device for generating electricity from flowing water, a converging section coupled to the upstream end of the mixing chamber such that a venturi is formed; a diffuser section coupled to the downstream end of the mixing chamber, the diffuser configured such that, in use, the static pressure at an outlet of the diffuser is greater than the static pressure at the venturi; at least a portion of the tube disposed within the converging section such that an annulus is defined between the tube and the converging section to form a first flow path, the tube defining a second flow path within the tube; and a turbine coupled to the tube and connectable to a generator; Equipped with The apparatus wherein the mixing chamber has a length at least twice its diameter.

16. The apparatus of claim 15, wherein the mixing chamber is approximately cylindrical.

17. 16. The device of claim 15, wherein the mixing chamber tapers at an angle of up to 4 degrees.

18. 10. A system for generating electricity from flowing water, comprising: a barrier positioned across a cross-section of a body of water; and the device of claim 1; 10. A system wherein the device of claim 1 is positioned to provide a flow path from an upstream side of the barrier to a downstream side of the barrier.

19. 20. A method of generating electricity from flowing water, comprising: installing the system of claim 18 across a body of water providing a reservoir of water such that a hydraulic head difference exists between downstream and upstream sides of the barrier; and using the flow of water through the device to rotate the turbine.

20. 10. A method of preparing a flow path through a barrier across a body of water, the method comprising placing the device of claim 1 within the barrier.

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