WO2009059959A2

WO2009059959A2 - Apparatus and method for generating energy

Info

Publication number: WO2009059959A2
Application number: PCT/EP2008/064912
Authority: WO
Inventors: Theodorus István VAN BAKKUM
Original assignee: Van Bakkum Theodorus Istvan
Priority date: 2007-11-06
Filing date: 2008-11-04
Publication date: 2009-05-14
Also published as: WO2009059959A3

Abstract

An apparatus and a method for generating energy are provided. The method comprises the steps of creating a downward flow of air through a first conduit (1) having an upper end (3) and a lower end (4), an air inlet being arranged at or near the upper end, controlling the relative humidity of the air in at least the first conduit at a predetermined level, heating the air at or near the lower end of the first conduit, creating an upward flow of the heated air through a second conduit (2) having a lower end (5) and an upper end (6), an air outlet being arranged at or near the upper end, and utilizing the energy content of the heated air.

Description

Apparatus and method for generating energy

The present invention relates to an apparatus and a method for generating energy, in particular for generating energy sustainably.

In view of the increasing demand for energy, the diminishing resources of fossil fuels and the growing concern about environmental pollution, there is a desire for improved methods and apparatuses for providing and generating energy in an efficient manner and preferably in a sustainable manner. This applies for domestic energy generation, but in particular also for generation of energy on an industrial scale, i.e. for generating several tens to hundreds of kilowatts, preferably well over a megaWatt.

Several methods and/or apparatuses for providing sustainable energy are known, such as using solar energy, hydroelectricity, wind power or tidal power. Generally, in particular when on an industrial scale, such methods and apparatuses are bound to specific locations due to their specific nature, such as requiring an elevated water reservoir, a coast line with sufficient tidal height difference, vast surface areas with predictable sunshine for solar power plants etc. Other factors affecting the choice of a location for a sustainable energy plant are its impact on society, e.g. concerns about aesthetic aspects and/or noise effects of wind turbines. The energy generated by the aforementioned methods may therefore require transport over hundreds of kilometres to reach a consumer. The actual availability of some of these sources of energy may also be highly unpredictable, e.g. in the case of wind energy.

Consequently, there is a desire for an apparatus and a method for generating energy which alleviates one or more of the aforementioned problems in a reliable manner.

To that end, the apparatus according to the invention comprises a first air conduit comprising an upper end and a lower end, an air inlet being arranged at or near the upper end, a second air conduit comprising an upper end and a lower end, an air outlet being arranged at or near the upper end, the first and second air conduits being arranged such as to allow air to flow downward through the first conduit and upward through the second conduit, means for controlling the relative humidity of the air in at least the first conduit at a predetermined level, means for heating the air at or near the lower end of the first conduit, and means for utilizing the energy content of the heated air.

Correspondingly, a method for generating energy is proposed, comprising the steps of creating a downward flow of air through a first conduit having an upper end and a lower end, an air inlet being arranged at or near the upper end, controlling the relative humidity of the air in at least the first conduit at a predetermined level, heating the air at or near the lower end of the first conduit, creating an upward flow of the heated air through a second conduit having a lower end forming and an upper end, an air outlet being arranged at or near the upper end, and utilizing the energy content of the heated air.

Thus, an apparatus and a method are provided by which an air flow through the first and second conduits is controllable with respect to the amount, the temperature and/or the velocity of the air exiting the outlet of the second air conduit. Thus, at least the thermal and/or kinetic energy- content of the air exiting the apparatus is controllable, which energy content may be utilized by appropriate means for generation and/or transformation of energy, e.g. a heat exchanger and/or a turbine. Hence, a controllable energy source is provided.

The apparatus requires a small surface area compared to other means of generating energy and it may be positioned on or close to most industrial premises, significantly reducing costs for transport of and/or transport systems for the generated energy.

In case the means for heating the air comprise means for utilizing geothermal heat a sustainable energy source is provided.

The invention and its benefits will hereafter be more fully explained with reference to the drawings showing an embodiment of the invention by way of example. Fig. 1 is a schematic cross sectional view of an apparatus for generating energy according to the invention.

Fig. 2A is a schematic top and Fig. 2B a schematic cross-sectional view of a vane assembly for generating a vortex in an air flow, for use with the apparatus of Fig. 1.

Fig. 1 shows an apparatus for generating energy, comprising a first air conduit in the form of a subterranean excavated pit 1, and a second air conduit in the form of a riser pipe 2.

The pit 1 comprises an upper end 3 and a lower end 4, the upper end 3 is open to the atmosphere forming an air inlet for allowing an air flow into the pit 1, indicated with arrows A. The inlet may be closable at least partly.

The riser pipe 2 comprises an upper end 5 and a lower end 6. For providing an air flow into through the riser pipe 2, indicated with arrows B, an air outlet to the atmosphere is arranged at or near the upper end 5 and an air inlet for allowing an air flow into the riser pipe 2 is arranged at or near the lower end 6. The upper and/or lower ends 5,6 may be closable at least partly.

The apparatus further comprises means 7 for controlling the relative humidity of the air in the first conduit 1 at a predetermined level, means 8 and optional means 9 for heating the air at or near the lower end of the first conduit 1, and means 10 and 11 for utilizing the energy content of the heated air.

The air inlet at or near the upper end 3 of the first conduit 1 is preferably arranged at or near ground level, possibly provided with a surrounding wall for preventing undesired ingress of undesired matter or objects and/or as a safety measure against animals and/or people falling into the pit 1. The pit 1 is closed at the lower end 4 to prevent undesired ingress of contaminations, dirt, plant roots, burrowing animals, ground water, etc.

The apparatus operates substantially by aspiring relatively cold atmospheric air at the upper end 3 of the first conduit 1 and causing it to flow downward towards the lower end caused to rise through and exit the second conduit 2, like a chimney. The thermal and/or kinetic energy of the heated air flow is utilized for operating means for energy generation e.g. a heat exchanger or a turbine 10 with a generator 11 for generating electrical energy. The existence and maintenance of a thermal difference and/or a pressure difference between the inflowing air and the exiting air are principal driving mechanisms of the apparatus. In the embodiment shown, the pit 1 is excavated to reach into the ground, removing at least a portion of the apparatus from sight, preferably a significant portion of it. The pit 1 is advantageously dug so deep that at least the lower end 4 is significantly heated by geotherrαal heat, relative to the atmospheric temperature at the upper end 3. Thus, a temperature difference is established over the air column inside the pit 1. The means 8 for heating the air may be one or more walls of the pit 1 providing geothermal heat to the air inside the pit 1 by direct contact. The contact surface to the geothermal heat, and therewith the heating effect, may be increased by providing means 8 (additionally) in the form of a heat exchanger. Alternatively, a heat exchanger 8 may be operated with geothermal energy using an intermediate heat exchange system operated between a geothermal hot source and the heat exchanger 8 (indicated with the arrows) . As yet a further alternative, means 8 may be operated using any suitable heat source .

The riser pipe 2 is arranged partially within the pit 1, this facilitates constructing the apparatus and reduces its size. In the shown embodiment, the pipe 2 is arranged substantially free from contact with the walls of the pit 1 (except for means for mounting the pipes 1, 2 with respect to each other, not shown) . This assists thermal insulation of the pipe 2 and thus of the air inside it from (colder air in) the pit 1. Suitably, conduits 1 and 2 are arranged substantially concentric, allowing a substantially symmetric air flow in the pit 1 around the pipe 2, preventing possible stress and/or erosion due to wind shear factors within the apparatus. The upper end 5 of the pipe 2 is arranged at a higher position than the upper end 3 of the pit 1. This provides a chimney-effect and prevents admixing of the air flows flowing into and exiting from the apparatus, which may decrease the thermal difference between the ingoing and outgoing air. The means 7 comprise means for spraying a fluid such as water into the air, e.g. one or more spray nozzles. Small droplets or a fine mist are preferred. The means 7 may further comprise a sensor for sensing the level of humidity of the air incident in the pit 1 and a controller for operating the means and supplying the fluid to the air, which fluid may be substantially colder than the air temperature. The fluid evaporates in the air flow, withdrawing heat from the air. The spraying of fluid therefore causes the thus treated air to become colder and heavier than untreated air, hence causing it to flow down under gravity and assisting driving the air flow through the apparatus. The amount and/or the temperature of applied fluid may be controlled to control the air flow through the apparatus, e.g. for maintaining a substantially steady air flow. Since hotter air can hold more fluid (especially water) than colder air, additional means 7 may be provided along the length of the apparatus for further increasing the humidity of the air. Different means 7 may provide different fluids and/or fluids at different temperatures. Thus, spraying warm or hot fluid may be used for heating the air towards the lower end of the first conduit 1.

The air flow may further be started, increased, maintained and/or generally controlled by forced flowing such as by reducing the air pressure at or near at least the upper end 5 of the second conduit 2 and/or increasing the air pressure at or near the upper end 3 of the first conduit 1, compared to the atmospheric pressure at the inlet of the first air conduit 1 and/or the outlet of the second air conduit 2. E.g., the turbine 10 may be driven, e.g. by an external power supply, for generating an initial air flow through the apparatus, after which the apparatus will exhibit its operation and drive the turbine in return for generating energy.

A convective vortex may be generated in at least the second air conduit for reducing the pressure therein, thus increasing the pressure difference across the air flow path through the apparatus. A convective vortex system also increases turbulence in the air and may therewith increase energy exchange within the flowing air, homogenising the temperature of the swirling air column of the vortex. Thus, steady operation and predictability of the operation of the apparatus be increased.

A vortex in an air flow within a conduit may be generated or maintained by a substantially open three- dimensional vane assembly 12 of which the vanes 13 are tangentially oriented, as indicated in Figs. 2A and 2B, arranged in or on the conduit through which the air flows, here riser pipe 2. The central portion 14 of the vane assembly in between the vane tips 13A is substantially empty.

The vanes may be interconnected towards the central portion 14, e.g. with a ring or a hub.

Preferably the conduit is vertically arranged, the air, which may be heated, flowing out upwards. The air is forced to rotate or swirl in one direction by the vane assembly, or an existing rotation may be amplified by it. Such a vortex reduces the air pressure in the centre at the lowest position of the vortex with respect to the surrounding air pressure and the pressure of the air escaping from the vortex at or near its top.

The vanes of the vane assembly may be fixed in position or be controilably variable in shape and/or position. A variable assembly may vary the force of the vortex, and therewith vary the pressure reduction at the lower end of the vortex. Thus, a low pressure or a pressure difference may be controilably maintained at a desired value substantially independently of external (atmospheric) factors such as air pressure, air velocity, air humidity and/or air temperature. Advantageously, means, such as a sensor and a controller, may be provided for controlling the shape and/or position of one or more vanes.

Various aspects of the vane assembly affect the details of its operation, such as the number, sizes, shapes, directions and surface quality of the vanes. The tips of the vanes leave the central portion 14 in the centre of the riser-pipe (s) open. Suitable sizes for the diameter of the opening 14 are be between about 1/6 - 1/3 of the diameter of the riser-pipe (s) 2, and individual vanes have a length of between about 1/4 - 1/2 of the diameter of the riser-pipe (s) 2.

The distance d of the tips of the vanes 13A from the upper end 5 of the riser-pipes (s) 2 on the inside thereof (see Fig. 2B) is preferably between about 1/10 - 1/5 of the diameter of the riser-pipe 2 to overcome possible wind shear effects disturbing the natural created vortex.

The surfaces of the curved vanes 13 may be polished to improve their smoothness for maximising the efficiency of the Coanda effect.

The three-dimensional shape of the vanes is arranged such that an air flow passing the vanes can usefully benefit from the Coanda effect, forcing the ascending air to rotate. A vortex rotation may extend for large distances above the source of the vorticity, here being the vane assembly.

A vortex may also be created at an exhaust of a turbine such as turbine 10, for increasing the pressure difference and thus the operational efficiency of the turbine and an associated generator. The amount of energy which may be derived from the apparatus depends on the sizes of the apparatus and the temperature difference.

Suitable sizes for a substantially concentric, cylindrical arrangement are a diameter of the pit 1 between about 5 and 10 m, and a depth between about 250 and 1250 m. The diameter of the second conduit 2 may be between about 5 and 7.5 m. An apparatus with such dimensions may exhibit an air flow between about 500 and 1000 m³/sec and may generate between about 0.75 and 1.5 MW of energy in a sustainable fashion. Heat coming from external sources such as process waste heat and/or from geothermal sources may be delivered by a secondary heat transfer system, e.g. a hot water circulating system, with temperatures between about 50⁰C and 90°C to the heat exchanger 8 which results in an air inlet temperature at the lower end 6 of the riser-pipe (s) 2 of between about 45°C and 85°C. At the outlet of the riser-pipe (s) 2 the air temperature will have cooled down to between about 30⁰C and 50⁰C.

Suitable construction materials for the apparatus are mainly commercially available materials such as metals, e.g. aluminium, and/or rigid reinforced plastic materials for the riser pipe 2, while the first drilled conduit 1 alternatively can be build from concrete. The first and/or second conduit 1, 2 may be provided with thermal insulation material along one or more portions of their length, for insulating that portion from a colder environment. In case the one or more second conduit (s) 2 are thermally insulated substantially along its entire length, cooling down of the upward flowing air is reduced, improving the yield of the apparatus. Moreover, the chimney effect may be maintained better than in an un-insulated apparatus, thus improving the total air flow through the apparatus.

In other words, the invention relates to a deep subterranean excavated pit 1, in which one or more riser-pipes 2 are arranged and in which a natural free vertical air displacement is generated due to differences in air density between air present above and below ground (the chimney-effect) . The difference in air density between the air above and below ground is controlled inter alia by bringing aspirated outside air both directly and indirectly in contact with heat, e.g. geothermal heat (of ground and ground water) which has elevated temperatures in deep ground layers.

A preferred embodiment comprises a pit construction 1 arranged vertically into the ground which raises the temperature and reduces the density of aspirated outside air with an initial high density, under the influence of heat present deeper in the ground, by which a pressure difference develops and a natural free vertical displacement of air is generated in one or more riser pipes 2 which may be arranged substantially centrally in the pit 1.

The difference in the air density of the relatively heavy outside air and the heated relatively light air which has descended provides a substantially static pressure difference causing a natural vertical air flow. The relatively heavy air to be aspirated by the apparatus is kept or brought at a desired relative humidity in a controlled manner, preferably at the maximum possible relative humidity, by measuring, preferably constantly, the relative humidity of the air at ground level and by spraying or misting additional water in the aspirated air by a humidifying apparatus 7 when necessary.

The end(s) 5 of the riser pipe(s) 2 above ground level may be higher than the inlet aperture (s) of the pit 1, to prevent contamination between incoming outside air and heated air flowing out, such that in the pit 1 a continuous descending cold air flow causes a hydrostatic pressure profile acting in a pumping manner, wherein inter alia by virtue of the rotation of the earth the lighter air column will rise vertically accelerated in the one or more riser pipes 2 as well as possibly forming a somewhat rotating air spiral.

The pit 1 is fed with the outside air which is always locally present and which is relatively heavy and dense, and which will exert a descending or hydrostatic effect on the air descending in the pit 1, and at the same time the upward air flow velocity is increased by the aspirating effect at the lower end 6 of the riser pipe 2. Thus, during the passage of air through the increasingly lower deposited ground layers an increasingly higher temperature will be supplied to or exchanged with the passing mass of supplied outside air.

In the pit 1, one or more riser pipes 2 are arranged, such that the outside air passing downward in the pit 1 along the outside of the pipe(s) 2 will increase in temperature and due to the physical properties of air the heated air will "look for an escape" towards the lower end 4 of the pit 1 and at the lower open end of the riser pipe 2, thus the heated air will move increasingly accelerated over a large distance through the pipe(s) 2 towards the earths surface.

The difference between the density of the heated relatively light air which flows into the lower end 6 of the riser pipe 2 and the outside air at the outlet of the pipe 2 results in a further increase of the static pressure and the natural vertical air flow.

For providing to the aspirated outside air before its entry into the riser pipe 2 a particular desired heat content, a heat exchanger assembly 8 is provided at or near the lower end of the pit 1 which is fed by an external source, e.g. a fluid such as water pumped up from ground layers deeper down the earth, for increasing the rising velocity of the air in a controlled fashion.

An optional second pre-heating heat exchanger assembly 9 may be fed by excess heat or recuperated heat, e.g. by heat recuperated from the heat escaping from the pipe 2 at ground level (indicated with the arrows) .

The total power of the apparatus may vary with the seasons and/or with the time of day with and local varying environmental conditions such as air humidity, wind velocity, air temperature, atmospheric pressure, temperature of the ground at different depths, geothermal heat flux at different depths, properties of ground water such as its presence, temperature and flow velocity and other varying structural conditions of the earths crust. The closed pit 1 comprises a vertically arranged pit or shaft construction, of which the lowest end is closed to prevent uncontrolled ingress of contaminations.

The outer side of the wall of the pit 1 is in direct contact with the earth, so that the geothermal heat transfers heat directly to the downward descending mass of outside air via conduction, convection and radiation. At the same time, the riser pipe(s) 2 opposite the pit walls are also heated by conduction, convection and radiation, heating the air mass descending along the outer walls of the riser pipe(s) 2, which is thus also (pre-) heated indirectly by geothermal heat.

The riser pipe(s) 2 may be isolated on the inner and/or outer side for maintaining a relatively high pressure differences between the pit 1 and the riser pipe(s) 2, preferably maximising the pressure difference. This pressure difference is a determining factor for the amount of power to be reached from the static and kinetic energy generated in the apparatus.

The naturally created air flow and the generated static pressure may be transformed into electricity in a turbine 10 combined with a generator 11.

The air rising velocity obtained in the riser pipe(s) 2 by the natural draft is fed to one or more turbines 10 arranged in the one or more riser pipe(s) 2. The turbine (s) 10 will rotate under the influence of the hot air passing at a high velocity, which rotation may be transferred to one or more apparatus to be connected with the turbine axle, e.g. a generator 11 with which electric energy is generated from the kinetic energy of the air. By choosing different shapes and/or sizes of the pit 1, diameters of the riser pipe(s) 2, length, width and depth, more or less volume can be created in the pit 1, by which the velocity of the incident cooler outside air can increase or decrease, thus the duration of the exchange of heat and the velocity of the heated air in the riser pipe(s) 2 can increase or decrease. Thus, the generated kinetic power of the air mass flowing from the apparatus is affected.

To promote the air flow velocity in the riser pipe(s) 2, the relative humidity of the outside air is determined at the entrance of the pit 1 and the passing air mass is brought to a variably controllable desired relative humidity by a sensor- operable humidifying apparatus 7. By this, a maximum downward flow power for the descending air may be achieved.

The heat of the heated air which exits the riser pipe(s) 2 can be utilized by a hot air heat exchanger which may be arranged over the riser pipe(s) 2 and which may return at least a portion of the heat of the emitted hot air to a fluid circulation system inside the heat exchanger (e.g. a water circulation system) . This fluid may transport the heat via insulated piping to a heat exchanger 9 arranged at or near the lower end 4 of the pit 1 for pre-heating the outside air which is fed towards the lower end 4 of the pit 1 prior to the passing of the pre-heated air through a hot geothermal heat exchanger 8. Alternatively, after passing the exit heat exchanger the exiting air may be discharged to a nearby heat circulation system (e.g. a hot water circulation system), which may be coupled with external, non-geothermic operated heat sources such as city block heating systems, or it may be used in systems such as an organic Rankine system for the generation of electricity. As an example, an apparatus according to the above- described principles may be used for direct delivery of electricity around the clock to end-consumers of fully sustainably generated energy in substantially any desired location on earth. As a further example, the apparatus may be used for generating electricity autonomously and sustainably for local production (electrolysis) and condensation of liquid cryogenic gasses which are separable from air and/or water and which are obtainable by cooling (which may comprise electrically operated compression and expansion) . Such gases, e.g. air, hydrogen, oxygen and nitrogen, may be utilized for local delivery to gas- driven means of transportation and/or for storage of electricity for local charging of electrically driven means of transportation.

As another example, the apparatus may be used for continuous and sustainable generation of electricity for continuous direct delivery to an available power transport- or distribution network, such as a centralised, decentralised or micro-network.

A further benefit is that by the continuous and sustainable generation of energy, at the same time continuously is contributed to eliminating emission of green house gasses and fine dust particles which would otherwise be emitted by fossil fuel power plants.

The invention is not restricted to the above described embodiments which can be varied in a number of ways within the scope of the claims. For instance, the shape and/or relative positions of the conduits 1 and 2 may be varied and additional heat exchangers and/or heat sources may be provided. Several apparatus may be combined for providing a high-power power plant .

Means for controlling the relative humidity of the air may also be provided in the second conduit. A plurality of vane assemblies may be provided. A vane assembly may be rotatable.

A vane assembly for generating a vortex may be power- operable as a fan for initiating or accelerating an air flow through the apparatus . A vane assembly may be provided for creating a vortex in the first conduit.

Claims

1. Apparatus for generating energy, comprising a first air conduit (1) comprising an upper end (3) and a lower end (4), an air inlet being arranged at or near the upper end, a second air conduit (2) comprising an upper end (5) and a lower end (6), an air outlet being arranged at or near the upper end, the first and second air conduits being arranged such as to allow air to flow downward through the first conduit and upward through the second conduit, means (7) for controlling the relative humidity of the air in at least the first conduit at a predetermined level, means (8, 9) for heating the air at or near the lower end of the first conduit, and means (10, 11) for utilizing the energy content of the heated air.

2. Apparatus according to claim 1, wherein the means for heating the air (8, 9) comprise means (8) for utilizing geothermal heat.

3. Apparatus according to claim 1 or 2, wherein the first air conduit (1) comprises a subterranean excavated pit and the second air conduit (2) is arranged within the first air conduit.

4. Apparatus according to any one of the claims 1-3, wherein the upper end (5) of the second conduit (2) is arranged at a higher position than the upper end (3) of the first conduit (1).

5. Apparatus according to claim 4, wherein the upper end (3) of the first conduit (1) is arranged at or near ground level .

6. Apparatus according to any one of the claims 1-5, wherein the means (7) for controlling the relative humidity of the air are configured for spraying water into the air.

7. Apparatus according to any one of the claims 1-6, wherein the means (10, 11) for utilizing the energy content of the heated air comprise a heat exchanger, a turbine (10), an Organic Rankine system and/or any other type of Binary system.

8. Apparatus according to any one of the claims 1-7, comprising means for generating and/or maintaining a reduced pressure at or near at least the outlet of the second conduit

(2) and/or an increased air pressure at or near the upper end

(3) of the first conduit (1) compared to the atmospheric pressure.

9. Apparatus according to any one of the claims 1-8, comprising means (12) for generating and/or maintaining a vortex in the air flow through at least the second air conduit (2) .

10. Method for generating energy, comprising the steps of creating a downward flow of air through a first conduit (1) having an upper end (3) and a lower end (4), an air inlet being arranged at or near the upper end, controlling the relative humidity of the air in at least the first conduit at a predetermined level, heating the air at or near the lower end of the first conduit, creating an upward flow of the heated air through a second conduit (2) having a lower end (5) and an upper end (6), an air outlet being arranged at or near the upper end, and utilizing the energy content of the heated air.

11. Method according to claim 10, comprising heating the air by means of geothermal heat.

12. Method according to claim 10 or 11, comprising recuperating heat from the heated air at or near the upper end (5) of the second conduit (2) and utilizing the recuperated heat for heating air at or near the lower end (4) of the first conduit (1) .

13. Method according to any one of the claims 10-12, the relative humidity of the air is increased by spraying water into the air.

14. Method according to any one of the claims 10-13, comprising reducing the air pressure at or near at least the upper end (5) of the second conduit (2) and/or increasing the air pressure at or near the upper end (3) of the first conduit (1) compared to the atmospheric pressure.

15. Method according to any one of the claims 10-14, comprising generating and/or maintaining a vortex in the air flow through at least the second conduit (2) .