Apparatus for conversion of rotary motion into heat

Abstract

A friction-based rotational-thermal converter, comprising a housing defining at least two chambers to contain working liquid, each chamber enclosing a rotor for heating the working liquid in contact with the rotor by movement of the rotor. A control apparatus varies a quantity of working liquid present in at least one of the chambers so as to modulate the interaction of the working liquid with the rotor, and the control apparatus is configured to increase the quantity of working liquid present in at least one of the chambers when a rotational speed of the rotors increases.

Description

[0001] APPARATUS FOR CONVERSION OF ROTARY MOTION INTO HEAT

[0002] Technical Field

[0003] The present invention relates to an apparatus for the conversion of rotational motion into thermal energy and, in particular, to means suitable for harvesting of thermal energy in a wind-turbine.

[0004] Background of the Invention

[0005] Wind-turbines typically function by using a “windmill” having a plurality of vanes to drive a “dynamo” via a drivetrain and thereby directly generate electricity. Typically, gearing or other control means will be included in the drivetrain of the generator. One important issue with wind is its variability. It may blow too weak or too strong for the convenience of the wind-farmer and may provide levels of energy unsuited to immediate demands for electricity. In the latter case this may be because too-little electricity can be generated given the available wind, or because excess electricity is being produced. Many solutions to the issues of storage of electricity so as to “buffer” supply against need have been explored. Another issue is reliability, as the working parts of a wind-turbine may be difficult or expensive to access.

[0006] Wind-thermal turbines convert wind directly into thermal energy, rather than generating electricity as an intermediate step. Several approaches to conversion are known. These include compression, friction, and induction-based systems. A literature review of the field of wind-thermal turbines was published in Journal of Energy Resources Technology (JERT), Transactions of the ASME, September 2021. Thermal energy may be stored in a mass of suitable material until required. This is often known as a “thermal battery” and can be as simple as an insulated pile of rocks. Small wind-thermal turbines may be suitable for space heating and hot water in a single domestic property. They may also be combined with heat-pumps to provide refrigeration. Larger turbines have the potential to supply high grade thermal energy suitable for both domestic use and the generation of electricity.The JERT review suggests that induction-based and compression-based systems can achieve temperatures of up to 600°C. These higher temperatures are preferred if the heat is to be used for the generation of electricity. The compressionbased systems use the compression of a working fluid to raise its temperature. The induction based systems use magnetic fields to heat electrical conductors moving relative to the field.

[0007] Friction-based rotational-thermal converters are also described in the JERT review. These use a shaft driven by wind vanes to mechanically rotate an impeller submerged in a working fluid. The rotation of the impeller generates heat in the working fluid, which is typically a liquid. Often this is known as a “Joule Machine” after the apparatus with which James Joule sought to demonstrate the mechanical equivalent of heat. The JERT review discloses that variants of the Joule Machine can heat a working liquid up to temperatures approaching 90°C. This low-grade heat may be suitable for district heating systems, but is not well-suited for electricity generation.

[0008] The application of Joule Machines to heating of fluids is known from the literature. In many of these applications control of heat generation may be achieved by deliberate variation of the rotational input. Only limited means are known to vary the input of a wind-turbine such as by “feathering” of vanes to change their angle of attack or turning the turbine out of the wind direction.

[0009] Our previous WO 2023 / 084223 A1 (published as EP 4430300 A1) discloses a heating system which comprises a source of rotational motion, at least one pump, a primary heat storage system, and one or more loops of piping connected to the primary heat storage system. The source of rotational motion, which may be a wind turbine, is configured to drive the at least one pump which is configured to pump liquid to repeatedly circulate around the loops of piping, resulting in frictional heating of the pumped liquid and transfer of heat to the primary heat storage system. The at least one pump may be a plurality of pumps, the source of rotatable motion may be configured to drive the plurality of pumps via a drivetrain, and the drivetrain may be configured to drive a variable number of the plurality of pumps. The primary heat storage system may, for example, store heat at a primary storage temperatureof 40°C to 90°C and may be drawn upon as a source of relatively low-grade heat for purposes such as heating rooms or providing hot water supplies.

[0010] A known problem with wind turbines is the occasional need to apply braking, such as to avoid dangerously high rotation speeds. Wind turbine braking systems typically use mechanical brakes to control the speed of the turbine and stop it safely during, for example, grid outages or high wind conditions. Known mechanical brakes include disc brakes which operate by friction between rotating and stationary solid surfaces. If the blades are large this generates significant heat and wear in the disks / brake pads. Electrodynamic braking has also been proposed.

[0011] Further problems occur on start-up of turbines and during operation under variable wind conditions which cause variations in the torque supplied down the drivetrain to the heat-generating part of the wind-thermal converter. Problems associated with braking and torque become more significant with larger turbines, such as those typically envisaged as part of an electricity generating system.

[0012] There is a need to provide a simple and reliable means for the generation of heat by wind turbines at a temperature above that suitable for small-scale domestic uses. Control of such turbines during start-up and braking is important. We have determined that for systems which employ frictional heating of a working liquid these ends may be achieved by varying the degree of contact between the working liquid and the means to either generate heat and / or retard the turbine.

[0013] Brief Description of the Invention

[0014] According to the invention, there is provided a friction-based rotational-thermal converter as defined in the appended claim 1.

[0015] In accordance with one aspect, the friction-based rotational-thermal converter comprises a housing defining at least two chambers to contain working liquid, each said chamber enclosing a rotor, wherein the quantity of working liquid present in at least one of said chambers may be varied.Conveniently, the rotational-thermal converter is a wind-thermal converter. Other sources of rotational energy may be employed, for example energy supplied by water or even excess electrical generation.

[0016] In a preferred embodiment of the invention the quantity of working liquid present in at least one of said chambers may be varied independently of the quantity of working liquid present in at least one other of said chambers. Advantageously, the independent and selective filling or emptying of different chambers enables the engagement of working liquid with the rotors to be varied between rotors.

[0017] Typically, the working liquid is a single working liquid. Separate, or even different, working liquids can be used in different chambers, but use of a single body of working liquid reduces complexity. Typically, at least two of the rotors are not substantially identical. This enables one or more rotors to be better adapted for heating working liquid and one or more rotors to be better adapted to braking.

[0018] It also enables rotors to be used which are better adapted to particular operating conditions of speed and / or torque.

[0019] Preferably the working liquid is an oil with a boiling point above 100°C more preferably above 280°C, most preferably at least 320°C. Typically, during operation at least one working liquid reaches a temperature of at least greater than 100°C. Preferably the at least one working liquid reaches a temperature of at least 280°C, more preferably at least 320°C. Being able to achieve a temperature of 320°C is important for many industrial processes, for example in the conversion of cellulosic plant materials into ethanol.

[0020] Preferably, means are provided for heat to be extracted from the converter by a heat-transfer fluid in thermal contact with working liquid. This may be achieved by providing means to bring the heat transfer fluid into thermal contact with the housing.

[0021] In an alternative and preferred embodiment, means are provided such that working liquid can be fed from at least one chamber to at least one heat-exchanger, supplied with the heat-transfer fluid.According to a further aspect of the present invention there is provided a wind-turbine which comprises a plurality of wind-vanes, and a drivetrain connecting said vanes to a friction-based rotational-thermal converter, wherein said converter comprises a housing defining at least two chambers to contain a working liquid, each said chamber enclosing a rotor operatively connected to said drivetrain, wherein the quantity of working liquid present in at least one of said chambers may be varied so as to modulate the interaction of the working liquid with at least one rotor.

[0022] The preferred embodiments of the present invention are such that the quantity of working liquid in a chamber is varied between said chamber being substantially full or substantially empty. Partially filled chambers are less preferred as these can lead to increased wear on the rotors.

[0023] A wind turbine according to the present invention preferably comprises an auxiliary pump and control means capable of selectively filling at least two of said chambers. More preferably when all said chambers are filled with said working liquid said drivetrain, and hence said wind turbine, is decelerated to a halt. It is particularly preferred that the wind-turbine can be brought to a halt within two or less rotations.

[0024] A benefit of the present invention is a potential simplification of the drivetrain. Rotors having a common drive-shaft may, for example, be brought into and taken out of engagement with working liquid independently. By reducing the quantity of working liquid within a chamber the torque required to turn the rotor in that chamber is reduced. This is advantageous at start-up. By emptying all of the chambers the start-up torque may be minimised.

[0025] Conventional vanes may be employed. Vanes are preferably aerofoils.

[0026] Typically, means are provided to feather the vanes for over-speed protection. In typical existing systems for utility use of 1 MW or above vane feathering will, for example, start at wind-speeds of 12ms’1and reach a limit at wind-speeds of ~25ms’1at which time the protection of feathering is exhausted and the system would be shut down. In many cases this is due to the limitations of a directly coupled electrical generator, limited to a maximum rpm. In preferred embodiments of the present invention the system may continue to operate at higher wind speeds, for example upto 18ms’1, before feathering begins to be required. Higher tolerance for stronger wind enables more effective energy harvesting.

[0027] Typically, the drivetrain comprises a gearbox. The ratio and / or capacity of the gearbox will be selected for the operating conditions. For electrical generation known gearboxes have a ratio of around 1 :120 between the vanes and the generator. In preferred embodiments of the present invention the gearbox ratio is above 1:130. This enables the vanes to rotate at lower speed reducing noise. Such a higher ratio gearbox may take advantage of the benefit that start-up torque is reduced by emptying some or all of the chambers.

[0028] Optionally, the housing comprises baffles. These are configured to promote turbulent flow in working liquid. Different chambers may have different configurations of baffles.

[0029] The housing is preferably provided with two or more ports to enable transfer of working liquid into and out of each chamber. The apparatus may also comprise a vessel for the storage of working liquid communicating with the housing.

[0030] Conveniently, at least two rotors, and preferably each of them, may be mounted on the drive-shaft. More complex ways of connecting the rotors to the driveshaft are possible, for example the drive shaft a plurality of parallel drive-shafts may be employed. However, a common drive-shaft allows for a simple modular construction.

[0031] Preferably, the housing comprises one or more bearing carriers. It is preferred that bearings are distanced from working liquid so as to reduce heating of bearings. Suitable oils for use as the working liquid include mineral oils, synthetic oils and mixtures thereof.

[0032] Preferably at least one rotor is configured to generate heat in working liquid by means of peripheral drag-inducing elements. The said rotor may be a disk having slots extending to the outer edge or grooves / teeth on the outer edge. The operatingconsideration being to generate heat without stalling the rotor. A particularly preferred shape for such a rotor is that of a ratchet gear.

[0033] Preferably at least one rotor is configured to retard the rotor by means of nonperipheral drag-inducing elements. The said rotor may be a disk having apertures in its faces which do not extend to the outer edge. The operating consideration being to stall the rotor in a controlled manner. A particularly preferred shape for such a rotor is a disk with a plurality of through-holes.

[0034] Preferably a heat-transfer fluid is used to extract heat from working liquid. This may comprise a service circuit in contact with the housing. Preferably, heat is extracted from working liquid by means of one or more separate heat-exchangers whereby working liquid comes into thermal contact with a heat-transfer fluid. This heat-transfer fluid may be a liquid or a gas.

[0035] Preferably control apparatus is provided to manage the movement of working liquid into and out of at least one chamber. Preferably, said control apparatus comprises an auxiliary pump which augments any pumping action of a rotor. Further control elements, for example valves, may be provided. A particular benefit of embodiments of the present invention is that the conversion of wind-driven rotation to energy in the form of heat may be performed more efficiently, including over a broader range of wind-speeds, than would be the case if the rotation were being converted directly to electricity.

[0036] Preferably an auxiliary pump and control means are capable of selectively filling at least two of said chambers. In a preferred embodiment the auxiliary pump supplies oil to a manifold and valve means enable oil to flow from the manifold into selected chambers. The same said pump preferably ensures effective flow of working liquid through any separate heat-exchanger.

[0037] Ancillary means may be provided for the pre-heating of the working fluid should this be required after a period of shutdown under sufficiently cold conditions. It is particularly preferred that, in operation, individual chambers are either substantially empty or substantially full of working liquid. However the or eachchamber wherein a rotor is configured to stall the thermal converter may be operated only partially full. It is envisaged that the rotor in the or each said chamber, which is intended for occasional braking, would not be in continuous engagement with working liquid.

[0038] A particular benefit of a preferred embodiment of the invention is that the occasional braking enabled by the or each rotor configured to stall the thermal converter recovers energy as useful heat in working liquid. This improves the overall efficiency of the thermal converter as compared with, for example, a directly driven electrical generator where braking heat is lost. It is particularly preferred that when all said chambers are filled with working liquid said drivetrain is decelerated close to a halt.

[0039] Preferably, means are provided to lock the rotors and prevent rotation relative of the housing. Conveniently, an auxiliary brake is provided which may use contact between solid surfaces, for example a friction disk or drum brake. Such an auxiliary brake enables a rapid stoppage of vane rotation and / or locking in place of the vanes and / or drivetrain when the turbine is “parked”.

[0040] The auxiliary brake is typically non-regenerative and would only be used in exceptional circumstances such as an “emergency stop” being required for example, due to loss of working liquid or, in the alternative, to secure vanes during maintenance. Under normal operation it is envisaged that the retarding action of the rotors would be sufficient to slow the converter to the extent needed.

[0041] Ancillary equipment in combination with the thermal converter of the present invention may comprise a thermal battery and / or means for the generation of electricity. Suitable thermal batteries include those which store sensible heat, latent heat or thermochemical energy. By a suitable configuration of ancillary equipment the output of the thermal converter may be used to generate electricity during periods of sufficiently high wind. Under favourable operating conditions the working liquid is heated sufficiently that this heat may be used to boil water and create steam. It is preferred that the thermal battery stores sufficient sensible heat that this can be used to create steam and operate an electrical generator.At times when the wind-speed is too low for the generation of electricity, or when the demand for electricity is itself low, the output of the thermal converter may be used to charge the thermal battery. Heat extraction from the thermal battery may be used to generate electricity should demand for electricity rise, and / or used for other purposes, such as heating. This can provide a useful buffer for energy management given variations in the demand for energy and availability of wind.

[0042] A particularly preferred apparatus according to the present invention is a rotational thermal converter which comprises, in combination:

[0043] a) a gearbox for connection to the vanes of a wind-turbine,

[0044] b) a friction-based rotational-thermal converter driven by said gearbox and comprising a housing defining at least two chambers to contain working liquid, each said chamber enclosing a rotor, operatively coupled to the output of said gearbox, such that movement of at least one such rotor heats the working liquid in contact with said rotor,

[0045] c) means by which the quantity of working liquid present in at least one of said chambers may be varied selectively, the arrangement being such that as the wind speed increases the engagement of working liquid with rotors may be increased so as to selectively retard said vanes.

[0046] Such an apparatus may be employed in new-build wind turbines, but may also be used to replace the electrical generator in existing wind turbines. At low wind speeds the working liquid provides low-grade heat useful for district heating and / or to charge a thermal battery. At higher wind-speeds the working liquid provides highgrade heat sufficient to raise steam for electrical generation and other industrial applications. Under suitable operating conditions this high-grade heat may be used to “charge” a thermal battery to temperatures in excess of 300°C. In the event that the wind-speed becomes excessive the working liquid may be used to retard the wind-turbine while still recovering useful heat.

[0047] Brief Introduction to the DrawingsEmbodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which:

[0048] Fig. 1 shows a thermal converter in accordance with an embodiment of the invention;

[0049] Fig. 2 shows ports, valves and piping enabling controlled flow of working liquid into and out of chambers of the thermal converter of Fig. 1 ; and

[0050] Fig. 3 shows wind vanes for driving a drive shaft of the thermal converter of Fig. 1.

[0051] Detailed Description of the Invention

[0052] Fig. 1 shows a schematic representation of a thermal converter according to the present invention. Housing 1 defines annular chambers 2a, 2b, 2c, 2d and 2e to potentially contain a working liquid. A single drive shaft 3 extends through each of the chambers. Disk-like rotors 4a, 4b, 4c, 4d and 4e are fixedly attached to the driveshaft 3. Baffles such as 5a, 5b, 5c, are attached to the housing. Ports, valves and piping enable controlled flow of working liquid into and out of chambers, as shown in Fig. 2. An auxiliary pump 10 assists in flow, circulating the working liquid. A vessel 20 provides for storage of the working liquid. A heat-exchanger 30 provides for thermal contact of the working liquid with a heat-transfer fluid.

[0053] In use drive-shaft 3 is supplied with rotary energy by a drivetrain 15 connected to wind-vanes 28 (see Fig. 3). This causes rotation of rotors 4a-4e within chambers 2a-2e. Interaction of the rotors with working liquid and the working liquid with baffles in any filled or partially filled chambers generates heat, raising the temperature of working liquid by the extraction of energy from the drivetrain. In empty (air filled) chambers the rotors experience little drag.

[0054] In the embodiment shown rotors 4a-4c are configured to extract energy and generate heat without stalling the converter. Chambers 2a-2c can act as heating chambers for the working liquid when said chambers are filled with working liquid. Rotors 4a-4c comprise disks with a toothed periphery. Bearing carriers 8 spaced away from the working liquid support the drive shaft 3.In actual bench experiments with a single heating chamber and a rotor having a toothed periphery it was found possible to heat oil circulated through the chamber to a temperature of 320°C.

[0055] Rotors 4d- 4e are retardation rotors. The chambers 2d-2e are configured such that they function as retardation chambers and, when filled with working liquid, can stall the converter significantly, slowing the drivetrain. Rotors 4d-4e have apertures passing through them, and are configured to interact aggressively with the working liquid such that they extract energy from the drivetrain significantly more rapidly than it is being supplied, and cause the rotors to decelerate.

[0056] Filling of chambers is selected such that the extraction of energy in the form of heating of the working liquid balances that supplied by the drivetrain along shaft 3 as rotational motion. At start-up all of the chambers may be empty, so as to minimise the torque from the wind-vanes needed to start rotation of the drivetrain and the converter.

[0057] Sensors are used to sense the rotational speed of the drive-shaft and the temperature of the working liquid, and an electronic controller 40 controls the auxiliary pump(s) and valve(s) to change the quantities of working liquid in the chambers based on the sensor measurements. The valves may comprise input and output solenoids 15 and 16 for each chamber to control the working liquid in the chamber.

[0058] In the event that the availability of rotational energy increases, further working liquid may be introduced into empty heating chambers. Similarly, if less rotational energy is being supplied working liquid may be withdrawn from heating chambers. In the event that the supply of rotary energy becomes excessive, one or both of the retardation chambers may be filled with working liquid causing a rapid slowing of the drivetrain, heating the working liquid and effecting braking. It is preferable that the braking effect is such that when all the chambers are filled with the working liquid the drivetrain is brought close to a halt.The controller 40 controls the auxiliary (circulation) pump 10 and the solenoids 15, 16 based on the detected temperature(s) T, the speed of the driveshaft 3 and / or the flow rate detected by the flow meter. The excess working liquid, for example when not all the chambers are filled with working liquid, is stored in the expansion vessel 20. When the speed of the drivetrain increases and / or the temperature of the working liquid increases, the controller 40 opens more of the input and outputs solenoids 15, 16 to fill more of the chambers 2a -2e with working liquid.

[0059] The thermal converter may form part of a wind turbine, and Fig. 3 shows wind vanes 28 of the wind turbine that are used to drive the rotation of the drive shaft 3. A drivetrain or gearbox 15 increases the speed of the drive shaft 3 relative to the wind vanes 28.

Claims

CLAIMS1. A friction-based rotational-thermal converter comprising:a housing defining at least two chambers to contain working liquid, each chamber enclosing a rotor for heating the working liquid in contact with the rotor by movement of the rotor;a control apparatus for varying a quantity of working liquid present in at least one of the chambers so as to modulate the interaction of the working liquid with the rotor,wherein the control apparatus is configured to increase the quantity of working liquid present in at least one of the chambers when a rotational speed of the rotors increases.

2. A converter according to claim 1 , wherein the converter is a wind-thermal converter.

3. A converter according to any preceding claim, wherein the quantity of working liquid present in at least one of the chambers is variable independently of the quantity of working liquid present in at least one other of the chambers.

4. A converter according to any preceding claim wherein at least two of the rotors are not substantially identical.

5. A converter according to any preceding claim wherein the working liquid is an oil with a boiling point above 100°C.

6. A converter according to any preceding claim further comprising an auxiliary brake to lock the rotors and prevent rotation relative to the housing.

7. A converter according to any preceding claim, wherein the control apparatus is configured to fill at least one of the chambers with the working liquid and not to leave the chamber in a partially filled state in which only partial contact occurs between to the rotor and the working fluid.

8. A converter according to any preceding claim, further comprising a heat transfer fluid in thermal contact with the working liquid, and a thermal battery for storage of heat delivered by the heat transfer fluid from the working liquid.

9. A converter according to any preceding claim wherein the control apparatus comprises an auxiliary pump for varying the quantity of working liquid present in at least one of the chambers.

10. A converter according to claim 9 when appended to claim 8, wherein the auxiliary pump is configured to pump the working fluid into a heat exchanger for transfer of heat to the heat transfer fluid.

11. A converter according to claim 9 or 10, wherein the control apparatus comprises an electronic controller for controlling the auxiliary pump.

12. A converter according to any preceding claim, wherein the rotors are connected to a drive shaft.

13. A converter according to claim 12 when appended to claim 11 , wherein the control apparatus comprises a sensor for detecting a rotational speed of the drive shaft and the electronic controller is configured to control the auxiliary pump based on the detected rotational speed.

14. A converter according to claim 11 or any claim dependent thereon, wherein the control apparatus comprises a temperature sensor for detecting a temperature of the working fluid and wherein the electronic controller is configured to control the auxiliary pump to increase the quantity of working fluid in at least one of the chambers in response to an increased temperature measurement.

15. A converter according to claim 12 or any claim dependent thereon, wherein the housing comprises a plurality of bearing carriers that support the drive shaft, wherein the bearing carriers are spaced away from the working fluid.

16. A converter according to any preceding claim, wherein at least one of the rotors is a disk having grooves or teeth on an outer circumferential edge of the disk.

17. A wind turbine comprising a plurality of wind-vanes, the friction-based rotational-thermal converter of any preceding claim, and a drivetrain connecting the wind-vanes to the rotors of the converter.

18. A wind turbine according to claim 17 further wherein the control apparatus of the converter is capable of selectively filling at least two of the chambers.

19. A wind turbine according to claim 17 or 18 wherein the working liquid is an oil and wherein when all of the chambers are filled with the working liquid the drivetrain is decelerated to a halt.

20. A wind turbine according to claim 17, 18 or 19, wherein the drivetrain comprises a gearbox and wherein the rotors are connected to an output of the gearbox.

21. A wind turbine according to any one of claims 17 to 20, wherein one or more of the rotors are adapted for heating working liquid and one or more other ones of the rotors are adapted for slowing the wind-vanes to a halt.

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