WO2005061886A1 - Hydrodynamic turbine for sea currents - Google Patents

Abstract

The invention relates to a hydrodynamic turbine comprising a rotor which uses the energy of the sea currents and which also acts as a suction pump since it is equipped with hollow turbine blades having pointed tips which, by means of the venturi and centrifugal effect, draw in an inner current at a greater velocity. The aforementioned current can be used to actuate a turbine having a much smaller diameter and more revolutions than the rotor and to which the electrical generator can be solidly connected without a mechanical multiplier, such as to produce a hydrodynamic multiplier . The fluid flow with greater energy density can be conveyed to other points of the fluid medium through tubular support structures for applications such as desalting water or producing H2 by means of electrolysis. The invention also relates to different configurations for the anchoring and self-orientation of the turbines, as well as underwater coupling systems for maintenance operations (minimal). In this way, the invention offers technology to compete with other energy sources, which also constitutes a predictable generation-type renewable energy.

Description

HYDRODYNAMIC TURBINE FOR MARINE CURRENTS DESCRIPTION OF THE INVENTION

This invention deals with a new design of the Hydrodynamic Turbine and its applications to take advantage of the enormous energy potential of marine currents, in order to reduce manufacturing, installation and maintenance costs in the always difficult marine environment and to minimize the environmental impact, helping to make this technology competitive with other renewable energy sources.

STATE OF THE ART

Boosting the use of renewable energy for growth. Sustainable and a reduction in the effects on climate change, wind energy in particular has undergone a great technological development recently. Based on this wind experience, similar technologies are being developed to take advantage of the great energy potential of marine currents.

In addition to large ocean currents, tidal currents (tidal) are considered as priority in locations near the coast and reach speeds greater than 2.5 m / s (5 knots), with higher energy density than ocean currents. in general, although the latter have immense flows.

If we compare with wind energy, the diameter of the marine rotor is of the order of 3 times smaller for the same power, since the ratio of sea / air densities is of the order of 820. The prediction in the generation of power by currents marine (following the time of rise and fall of the tides), as well as the high capacity factor that can be greater than 45%, are other comparative advantages. Although the experience and wind technology, including offshore, is usable for the development of this new technology, it is necessary to continue deepening in various aspects of equipment, installation and maintenance in the marine environment, phenomena of cavitation in the blades, etc. Prototypes of vertical axis turbines (Darrieus type) are being tested for installation on the seabed or suspended on bridges, but, like wind, the greatest development is focused on horizontal axis turbines. A 300 Kw horizontal axis prototype with a 2-blade rotor, multiplier and asynchronous generator has been installed on the Devon coast (UK). Current designs consider anchoring to the sea floor (at a maximum depth of 30 m) using a "monopile" pile that can support up to 2 twin turbines whose plane is perpendicular to the currents in both directions. This pile emerges from the surface to support the maintenance platform, through special hoisting systems for the turbines, etc. EXPLANATION OF THE INVENTION

The innovative Hydrodynamic Turbine for marine currents has a horizontal axis (rotor axis aligned with currents) and comprises all the elements to transform the energy of the currents into "useful energy". Referring to Figure-1, the different elements that make it up can be seen, the most prominent being the rotor, which normally consists of the blades (1), the hub (3) that supports the blades and the bearing ( 5) which rests on the support structures and allows the rotor to rotate freely.

In this invention, the hub and hollow blades are designed and shovel-tip nozzles (2) are incorporated such that there is an internal fluid vein between the center of the rotor and the pointed nozzles. In addition, the hub has an open area in which a crown of fixed blades (4) is inserted, integral with the hub, and which serves as a connection between the hub and the bearing.

By rotating the rotor by the action of marine currents on the blades, an internal current or "secondary current" is created at a higher speed, which flows from the center of the rotor through the interior of the blades to the outlet through the nozzles. This current originates from the centrifugal effect inside the blades and from the venturi effect in the nozzles, so that the rotor, in addition to capturing energy, also performs the function of a suction pump. The secondary current, with higher energy density, can drive a turbine impeller (6) with a diameter much smaller than the rotor, which can be housed inside the hub as a bulb-type turbine aligned with the axis of the rotor. Since the turning speed of this turbine is much higher than that of the rotor, the electric generator (7) can be jointly connected to it. It can be said that with this contraption a hydraulic jump is created within the sea, as a difference between the hydrostatic pressure of the medium (at the hub depth) and the depression created in the inner fluid vein (center of the rotor). An important advantage of this invention is that there are no torques on the rotor axis, since it is at the periphery of the rotor that the energy is captured and, in turn, transmitted to the secondary current. Another very important advantage is to dispense with the mechanical multiplier (with all its problems of periodic maintenance, environmental impact due to the use of lubricants, etc.), since the rotor converts the captured energy into another of higher density, as a "hydrodynamic multiplier" . Another advantage, as we will see later, is that the rotor is self-regulating to operate or variable speed, thus avoiding the active control systems of the blades, which can be fixed. The greatest tendency to cavitation resides in the extrados of the blade end (which is one of the limitations of this technology), depending on the relative speed of the fluid at the tip of the blade and the hydrostatic pressure depending on the depth of the rotor. . If we properly practice grooves in these areas under greater depression, the internal fluid (water) will come out suctioned avoiding cavitation on the one hand and creating the secondary current on the other. However, as a large exit area is required, pointed nozzles oriented in the relative speed direction are considered. For performance reasons, it is convenient that the absolute speed and the direction of exit of the secondary current coincide with the marine current, with which there are relative exit speeds of the order of the speed of the blade tip, but in the opposite direction. Therefore, the Lambda specific speed coefficient (ratio of shovel tip speed to sea current speed) is similar to the speed ratio: Secondary current / sea current. As the secondary current has a speed of the order of Lambda times greater, we can drive a turbine on the rotor shaft with a Lambda diameter ^{3 2} times less than that of the rotor, provided they are similar. In order to appreciate the order of magnitude of these parameters, and considering a design speed of the marine current of 2.5 m / s and a rotor diameter of the order of 20 m (power of 1 Mw) at Lambda 6, we have the rotor rotating at 15 rpm, while the 1.2 m diameter turbine rotates at about 300 rpm. The design parameters are highly dependent on the hub depth (rotor axis) in the marine currents at each site. The design strategies for different situations are outlined below. In order to reduce the speed of the rotor by limiting cavitation, 4 blades are considered (greater solidity than with the 3 blades in wind power), which also facilitates a greater circulation area for the secondary current. For variable currents caused by the tides (sinusoidal speed) and with the generator connected to the network (fixed frequency, 50 Hz) and integral with the turbine, it is designed at constant speed with deflectors (8) of passive regulation at the input to optimize the performance in a certain range of flow velocities requested by the rotor, which operates at variable speed to also improve its performance in capturing energy and to dampen fluctuations of currents, although its own extreme deviations or conditions do not occur here of wind power.

The variable speed of the rotor is self-regulating at "constant Lambda", since the speed of the marine current (which generates the rotor power) and the secondary current (which absorbs this power and transfers it to the turbine) must be kept at a constant ratio, with the ratio of rotor and turbine powers also constant proportional to Lambda. When the nominal power speed is exceeded, the turbine's power limiting valve (9) is activated, since the differential pressure (outside and inside the hub) would overcome the resistance of the valve's "tared" spring that would allow an input of flow in by-pass, increasing the speed of the rotor (although limited by the viscous medium) to dissipate excess energy. All this leads us to a generator (synchronous) with 10 pairs of poles, with which the dimensions, weight and cost are drastically reduced (in a ratio of 1: 20) compared to a generator directly coupled to the τotor, which due to the other side would have to be of variable speed based on frequency converters of 100% of the generated power.

The synchronous generator can be permanent magnets, for simplicity and to avoid thermal dissipation (rotor coils). However, at variable speed currents, and therefore at variable power, the generator power factor could not be controlled with permanent magnets (constant magnetic flux). For this, a grid-connected transformer with load regulation is used. The number of pole pairs could even be reduced to 6, depending on the conditions of the location and arrangement of the turbine, modified bulb type, which in this case would operate at 500 rpm.

Therefore, under variable current conditions, it is considered a Kaplan turbine (steerable impeller blades) or, at least, semi-Kaplan which would be easier because only the flow deflector blades (8) could be steerable. For constant (oceanic) currents, a propeller turbine is considered, which is the simplest because it has the deflector blades and the fixed impeller blades.

The consequence of the simplicity of the. systems, together with the use of resistant materials, is a "maintenance-free" Hydrodynamic Turbine. Therefore, this design does not contemplate a surface platform, minimizing the environmental impact: no landscaping, sufficient free depth for navigation, rotor slower than fish (in principle), etc.

Different configurations and applications, or embodiments, are described below with reference to the figures:

Figure-2. For currents due to tides, to depths not much greater than 30 m, it is possible to place two twin rotors (10) at both ends of a horizontal tubular structure (11), supported in a "T" shape on another anchored vertical structure to the bottom or pile (12), on which the turbine-generator group (13) is coupled by gravity. The secondary current sucked by both rotors, through the tubular structures, drives the turbine jointly connected to the generator. The guided submarine coupling system of the group is made up of two or more guide cables (14) that can slide through holes (15) in the support base of the group on the pile. The lower end of the cables is attached to a counterweight (16) that descends by gravity to the stops (17). The upper end is provided with a float (18), whose upward thrust is less than the counterweight but maintains the hitch (19) at the preset height, making it possible to catch it from the surface barge. Once the hitch has been taken, it is raised to the surface, the counterweight abuts the horizontal structure, so that the cables subjected to tension can lead the guide points (20) of the group during lifting and lowering operations. The lifting tool is also connected to the hooking point (21) of the group through the guide wires. The group is coupled by gravity at its base, with fittings between the two pieces that prevent it from turning. Figure-3. To align the rotor axis perfectly with the currents, in both directions, the rotor is allowed to rotate on the horizontal axis (22) of s and support structure. A counterweight (23) is placed diametrically opposite the rotor, with respect to this axis, to locate the center of gravity of the assembly close to said axis. The center of the axial thrust force (24) of the rotor is displaced from said axis, which contains the bearing (26), so that it keeps the rotor aft always aligned with the current.

Rotation of the horizontal structure on the vertical axis (25) can also be allowed, so that the plane of both rotors is auto-oriented perpendicular to the sea current, due to the axial thrust forces of both rotors, with the point of application behind the axis of rotation on the vertical structure. In this case, the guided submarine coupling system is implemented for the set of the two rotors. Figure-4. The previously described configurations can be used to desalinate water by the reverse osmosis method, replacing the electric generator with a pressure pump (27), which drives the pressurized seawater through the osmosis membranes (28). The fresh water is collected in the tank (29) and the brine is returned to the sea, its disposal not being a problem.

Another more direct way is to dispense with the turbine-pump, sucking the secondary stream through the tubular structure from the surface, through throttling nozzles (30), where a depression would be reached below the saturation pressure of the water. The generated steam would ascend to a condensation chamber (31), cooled by a recirculation of water from the seabed, obtaining the desalinated water. Figure-5. Finally, in locations at greater depth (especially for ocean currents, where the rotor diameter would be greater), the Floating Hydrodynamic Turbine design is presented, which solves the difficulty (or impossibility) of piloting in a simpler and more economical way . Launching is possible from the ballast barge (32), turbine and float (33), with the corresponding mooring cables that position the turbine constantly self-aligned with the currents, semi-floating and in stable equilibrium, with a high damping capacity of efforts. In addition, the very configuration of the mooring to the ballast and the float, together with the points of application of the weight (34) and the axial thrust (35) allows that, in the face of an increase in the speed of the currents above design, it can move the turbine down away from the maximum current lines and the plane of the rotor is tilted projecting a smaller sweep area in the direction of the currents, so that some self-control of power occurs. In the case of ocean currents, or sites with a distance to land such that the laying of the submarine electrical cable is unfeasible (36), the energy produced by large parks of floating turbines can be used for the massive generation of hydrogen in Marine Platforms. DESCRIPTION OF THE DRAWINGS

Figure-1: Represents a section of the rotor of the Hydrodynamic Turbine, which consists of the blades (1) with pointed nozzles (2), the hub (3) that supports the blades and the fixed blades (4) to the hub that connect it to the bearing (5). The generator housing (7) supports said bearing, as well as that of the impeller of the turbine (6), which is equipped with flow baffles (8) and a power limiting valve (9).

It serves as a clarification to Claim 1.

Figure-2: Represents an embodiment of the turbine with two twin rotors (10), whose secondary current drives the turbine-generator group (13), located vertically on the pile (12) anchored to the seabed.

The group's guided underwater docking system is also presented. It is an appropriate design for shallow water locations. It serves as a clarification to Claim 2.

Figure-3: idem to the previous one, where the self-orientation of each rotor with respect to the horizontal axis (22) or the set of rotors with respect to the vertical axis (25) can be seen. It serves as a clarification to Claims 3 and 4.

Figure-4: Represents an application to desalinate water, either by reverse osmosis using a pressure pump turbine (27), osmosis membranes (28) and a fresh water collection tank (29), or by an evaporation method in throttle nozzles (30) and subsequent steam condensation in the condensation chamber (31). It serves as a clarification to Claim 5.

Figure-5: Represents another embodiment of the turbine, Floating Hydrodynamic Turbine, which remains self-oriented with the currents and in stable equilibrium, due to the configuration of the mooring to the ballast (32) and the float (33).

It is an appropriate design for deep water locations. It serves as a clarification to Claim 6.

Claims

1) Hydrodynamic turbine for marine currents, among other applications, whose rotor is of horizontal axis and is normally composed of two to four blades (1) that capture the energy of said currents, the hub (3) that supports said blades and the bearing (5) which allows it to rotate on its axis, characterized in that the blades are hollow and communicate with the bushing, which is also hollow, enabling an internal fluid vein from the entrance through the center of the open bushing to the streams, to the exit by nozzles (2) (or grooves in areas of blade with greater depression due to high relative velocity of the fluid medium), placed at the tip of the blades. By rotating the rotor by the action of marine currents on the outside of the blades, the internal fluid vein is suctioned by centrifugal effect inside the blades and by venturi effect on the nozzles, performing the rotor in turn the function of pump suction This results in a "secondary current" at a higher speed than the marina, which circulates radially, entering the center of the rotor and exiting through the nozzles, in a direction almost opposite to their movement. Said secondary current with higher energy density (speed similar to the blade tip), can be driven by support tubular structures, to other points of the fluid medium for various applications, among them is to drive a turbine impeller (6) of very diameter lower and at higher revolutions than the rotor. In the axis of said turbine impeller, an electric generator (7), pressure pump, etc., can be coupled in solidarity, regardless of the intermediate mechanical multiplier. This rotor, therefore, converts the captured marine energy into another of higher density, as a "hydrodynamic multiplier". 2) Hydrodynamic turbine according to claim 1, characterized in that the turbine-generator group (13) is positioned vertically on the pile (12) or support structure of one or more rotors (10), placed at the ends of tubular structures (11) horizontal that are supported by its central part in the pile, in the form of "T", through which the secondary current sucked by the rotors can circulate, to drive said turbine (or other device) in the most convenient place. For the installation or hoisting of the group (maintenance operations), the guided underwater coupling system is used, consisting of two or more guide wires (14) that can be drilled by holes (15) in the support base of the group on the pile. The lower end of the cables joins a counterweight (16) that descends by gravity to stops (17). The upper end is provided with a float (18), whose upward thrust is lower than the counterweight but keeps the hitch (19) at the preset height, - its capture being possible - from surface barge. Once the hitch is taken, it is raised to the surface, stopping the counterweight (16) with the horizontal structure (11), so that the cables under tension can drive the guide points (20) of the group during lifting and lowering operations of the same. The lifting tool is also connected to the coupling point (21) of the group through the guide wires. The group is coupled by gravity at its base, with fittings between both pieces that prevent its rotation. 3) Hydrodynamic turbine according to claims 1 and 2, characterized in that it contains a plurality of rotors capable of self-orientation with sea currents. Each rotor can be oriented by rotating on a bearing (26) connecting with the support structure, in an axis (22) perpendicular to that of the rotor itself. The center of the axial thrust force (24) of the rotor is behind said axis according to the direction of the currents, so that it keeps the rotor aft always aligned with the sea current, even if it changes direction. Diametrically opposed to the rotor with respect to said axis, a counterweight (23) of compensation of the gravitational moments of the rotor is placed. The counterweight and tubular structures that drive the secondary currents are hydrodynamic in the horizontal direction. 4) Hydrodynamic turbine according to claims 1 and 2, characterized in that it consists of two (or more) rotors at both ends of a horizontal tubular structure that can rotate at its central point of support on the pile, with respect to the vertical axis (25), so that the plane of both rotors is oriented perpendicularly to the sea current, due to the axial thrust forces of the rotors whose application point is behind (aft) the axis of rotation on the pile. The guided underwater coupling system is implemented for the rotor assembly, in this case. 5) Hydrodynamic turbine according to claims 1, 2, 3 and 4, characterized in that the electric generator is replaced by a pressure pump (27) capable of desalinating water by the reverse osmosis method, or the turbine-generator group is eliminated so that the secondary current directly descends from the surface through the tubular structure, being sucked by the rotors. The water would desalinate by evaporation, upon reaching a depression below the saturation pressure of the water at that temperature. To the depression caused by the suction of the secondary current, it is necessary to add the one generated by the acceleration of the water (Bernouilli effect) to its passage through specific throttling nozzles (30). The steam generated there rises to a condensation chamber (31), cooled by a recirculation of colder water from the seabed. ) Hydrodynamic turbine according to claim 1, characterized in that the turbine-generator group and the rotor are on the same horizontal axis, the turbine impeller (bulb type) being housed within the rotor hub. The generator housing supports the coaxial bearings of the turbine and rotor, as well as the ties (cables) of the ballast (32) and the float (33), which position the self-oriented system in the field of currents, counteracting the drag forces (35) and gravity (34), in stable equilibrium. The mooring configuration itself, together with the drag and gravity forces, allows the turbine to move downwards away from the maximum current lines and, when the speed increases in the currents above the design. plane of the rotor projecting a smaller sweep area in the direction of the currents, so that there is a certain power self-control and a damping of forces.