Long-Term Heat Storage Device and Method for Long-Term Heat Storage of Solar Energy and Other Types of Energy with Changing Availability

The invention relates to a long-term heat storage device for long-term storage of solar energy and other types of energy, in the heat storage material of which a rock bulk material, in particular of volcanic origin, such as diabase, basalt, granite and gneiss, is used. The rock bulk material forms a polydisperse bulk material, in particular as the void volume of the rock bulk material (granulate) having a first particle size or particle size distribution takes up a granulate having a second particle size or particle size distribution. The rock bulk material can be enclosed by a bulk powder fill, in particular an ash fill, in particular with a shell of shaped rocks interposed. The rock bulk material can be enclosed, all around or predominantly, at least laterally, by a shell of shaped rocks which is in particular cylindrical, in particular by a masonry wall.

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Description
FIELD OF THE INVENTION

The invention relates to a long-term heat storage device for long-term heat storage of solar energy and other types of energy with changing availability. The long-term heat storage device comprises a heat-stage mass having an insulating layer surrounding said mass according to the preamble of claim 1. The invention further relates to a method for the long-term heat storage of solar energy and other types of energy with changing availability by means of a long-term heat storage device according to the preamble of claim 27. The aim of the invention is a new technical concept to ensure continuity when using solar energy and other types of energy with changing availability throughout the entire year. The concept essentially assumes that the solar radiation or the other type of energy with changing availability is highly concentrated with the result that high temperatures are achieved, with the result that the energy of the heat storage mass is increased and the energy efficiency of the system is raised. The energy collected from the sun or from another energy source with changing availability is stored in a long-term heat storage device with low heat losses during the winter months. The new concepts assume an efficient transfer of the solar energy or the other type of energy with changing availability to a heat transfer medium. The thermal energy is then transported into the long-term heat storage device and to the heat storage mass.

The insulation and the geometry of the heat storage device are also part of the new concept. The new type of insulation should ensure a long-term storage of the thermal energy in a particularly favourable manner where the heat losses are kept low.

TECHNOLOGICAL BACKGROUND

The major problems in the world's energy supply are becoming increasingly obvious, in particular due to the incidents which are taking place increasingly frequently in existing nuclear power plants. It is becoming increasingly clear that the safety of the world is being increasingly endangered by nuclear energy.

Already a large number of new solar, tidal and wind power plants have been built in Europe and the USA but these do not by any means meet the requirements imposed, on account of the changing availability of the respective energy source. In any case, there are only a few places on the Earth where, for example, the sun shines 365 days×8 hours a day. The present prior art does not allow power to be produced from solar energy on sunny days for 24 hours a day without needing to use energy from an additional energy source in this case, and the same applies accordingly for other types of energy with changing availability, such as water power and wind power. Recently, thermal storage devices are being used in solar thermal power plants so that these can also be operated in cloudy conditions or after sunset. In order to bridge sunless days with energy, various long-term heat storage devices are presently being developed such as: salt storage devices, concrete storage devices, compressed air storage devices, sand storage devices and pump storage devices.

Salt storage device: The excess heat is stored in a liquid salt mixture of 60% sodium nitrate (NaNO3) and 40% potassium nitrate (KMO3). Both substances are used inter alia as fertilizers and for preservation in food production. The liquid salt storage devices operate at atmospheric pressure and consist per power plant of two tanks for example having a height of 14 m and a diameter of 36 m. When pumping from the “cold” into the “hot” tank, the liquid mixture at an initial temperature of 290° C. Celsius absorbs additional heat so that it is heated to about 390° C. Celsius. A full storage device can operate a turbine for 7.5 hours. The storage capacity of this salt storage device varies around about 80-100 kWh/m3. The disadvantage is that the temperature of the salt mass must not fall below 290° C. so that additional electrical heating must be provided so that the salt mass does not solidify.

Concrete Storage Device:

The German Aerospace Centre (DLR) together with industrial partner Ed. Zublin AG has presented a new thermal storage device for solar power plants. The pilot plant is based on the storage of heat in concrete at temperatures up to 400° C. The heat transfer medium is thermal oil which is transported through steel pipes which are embedded and cast into the concrete mass. The moulds of concrete are of modular structure and specifically such that the entire storage device consists of individual modules and can be used for any powers. The production costs are relatively high relative to the specific storage capacity. In order to achieve a high specific storage capacity, the storage temperature must be substantially higher. For cost reasons these storage devices would not be suitable as long-term storage devices.

Compressed Air Storage Device:

For wind power plants heat reservoirs play only a subsidiary role. Wind plants already deliver usable power. In order that excess kilowatt hours in strong wind phases are not lost, they should drive compressed air pumps. These press compressed air into subterranean cavities such as, for example salt caverns. If the power requirement increases, the air can flow out again and set the turbine wheels of generators in rotation. However the compression and escape of compressed air is not trivial. This is because during compression the air is heated to above 600° C. Conversely it cools down when flowing out. A high efficiency of the compressed air storage device of about 70 percent can only be achieved if the compression heat is also stored and subsequently heats the outflowing air again. Major costs are involved in implementing this requirement. From this it follows that a heat storage device must be additionally provided inside a compressed air storage device in order to be able to store the thermal energy separately so that the high efficiency can be maintained. As a result, the entire process is burdened with additional costs. It is no easy task to achieve the necessary air tightness at 100 bar in underground cavities. This type of energy storage device is therefore not in a position to store energy over longer time intervals.

Sand Storage Device:

A sand storage concept has been developed at the Solar Institute Jülich of the FH Aachen, in which quartz sand is used as storage medium. This project was supported by the Federal Ministry for the Environment, Nature Conservation and Reactor Safety, by the Ministry of Economic Affairs and Energy of the State of North-Rhine Westphalia, by the German Aerospace Centre e.V, by Aachen University of Applied Sciences, by the Bavarian State Ministry of Economic Affairs, Infrastructure, Transport and Technology, by Munich power plants and by the Solar Institute Jülich. These research projects have been adequately reported in www.fz-jülich.de and in www.taz.de and in www.wdr.de. This concept promises a reduction in storage costs if an efficient transfer of air to sand can be achieved. The aim of this project is the investigation and development of a suitable air-sand heat transfer medium prototype for this purpose, which operates in the temperature range of 400-900° C. In the project a corresponding experimental structure was designed, manufactured and measured. The principle: so-called heliostats concentrate solar radiation onto a receiver at the top of a solar tower. Here the porous structure in the receiver is heated, its heat is in turn delivered to air which is sucked in from the surroundings. The air heated to max. 900° C. is supplied to the air-sand heat transfer medium for heating the sand. The heated sand is passed via a simple drop tube into a hot storage device and from there as required further into the fluidized bed cooler. The fluidized bed cooler, an aggregate which is used in a conventional fluidized bed incineration, drives a steam cycle. The generated steam is finally fed into a conventional power plant process of a steam turbine which drives the generator to produce power. The cooled sand leaves the fluidized bed cooler at a temperature of about 150° C. and is either fed back to the air-sand heat transfer medium or is stored in a cold storage device. The sand storage device has been developed by the Solar Institute Jülich with the aim of being built in the Sahara solar power plant where sand is available in abundance and is free. The assessment of the new sand storage system can be summarized as follows: the heat transfer in moving sand having a small grain diameter is high and this is the advantage. However the risk of abrasion in the sand is high. The power consumption in the sand fluidized bed is high, the specific storage capacity of the sand is high and the entire stored quantity of heat cannot be large because the quantity of sand is relatively small for process technology reasons. This heat storage device cannot be considered to be a long-term heat storage device.

Pump Storage Device:

A pump storage power plant (also called pump storage plant PSW) is a particular form of a storage power plant and is used to store electrical energy by pumping water uphill in phases of energy excess. This water can subsequently be allowed to flow downhill and thereby produces electrical power again by means of turbines and generators. The electrical energy is therefore stored by converting into potential energy of water and is fed into the mains by converting this potential energy back into electrical energy. The technical development of pump storage power plants in the last few years makes it possible today to operate a hydroelectric power plant as a pump storage power plant with an overall efficiency of more than 75% for green power production. The pump storage device is today provided as a component of a solar or a wind plant. The disadvantage is that the natural conditions must be suitable for the use of a pump storage device. Enormous amounts of water are required for relatively low electrical powers and therefore such a storage system is very cost-intensive. Enormous basin areas, large height differences, pipelines having a diameter of several metres and a very expensive infrastructure are required. The storage device can only be provided at specially suitable sites. This type of storage device is in any case not suitable for storing energy over several months.

In summary the present prior art can be briefly described such that the technology level relating to ensuring continuity when using solar energy is far from satisfactory. At present it is not yet possible to produce power 365 days×24 h throughout the entire year from solar energy. As long as this aim is not achieved, solar energy or other types of energy with changing availability cannot be regarded as a reliable source of energy. This aim should be implemented according to the invention.

The complete replacement of conventional types of energy such as fossil or nuclear fuels by alternative energies is only possible through the development of appropriate energy storage systems. The sustainable energy is stored and held in readiness over fairly long periods of time. The energy buffer storage device which is capable of compensating for certain availability fluctuations in order to ensure continuity in the energy supply is required today. Of all the sustainable energies, wind energy is the most commonly encountered today, in particular in Western Europe and in the USA. Some countries have today provided a fraction of about 5% of the total energy production through wind energy. That is an appreciable amount of energy. However, the typical availability fluctuations can cause major problems in the energy supply. In this case, coal or gas power plants or nuclear power plants must be operated for a short time. This is technically very demanding and expensive. However nuclear power plants are usually only suitable for base load operation. However appreciable problems also arise when there is an excess of wind energy. The energy must be briefly removed to avoid the collapse in the energy supply.

The storage systems presently being developed therefore do not meet the requirements imposed: the salt storage device has a low storage capacity (80-100 kWh/m3) It operates in the range of relatively low temperatures (about 400° C.). In addition, the temperature of the salt mass must not fall below 290° C. therefore additional electrical heating must be provided so that the salt mass does not solidify. A concrete storage device also has a low storage capacity and is expensive to manufacture. It is operated with a thermal oil and the operating temperature is of the order of magnitude of 400° C. At this temperature a large specific storage capacity cannot be expected. A considerable quantity of steel pipes is incorporated in the concrete storage device. Steel and concrete have different expansion coefficients and there is always the risk that cracks will form in the concrete storage device which prevent heat conduction and cause an insulating effect. The sand storage device certainly operates at high temperatures and the heat transfer is high but the risk of abrasion is very high. The power consumption for transporting the sand is accordingly very high. The use of sand is possibly only appropriate in the Sahara—less so in Europe. The stored quantity of heat cannot be large because the amount of sand is relatively small for process technology reasons. This heat storage device cannot be considered to be a long-term heat storage device. For the compressed air storage device the situation appears better. Certainly a large amount of energy can be stored in the underground storage device. However other process technology grounds are present which cannot be easily overcome. During compression of air, the temperature rises. If the compressed air is stored in the underground storage device, cooling of the air is inevitable and as a result appreciable energy losses occur. On the other hand, it is technically demanding to get the underground cavern airtight. To provide an intermediate storage device after the air compression in order to store the thermal energy would incur additional costs. The use of the pump storage device requires suitable natural conditions. The complete infrastructure for a pump storage device is considerably more expensive. Enormous basin areas are required to hold the large amount of water in readiness. This solution cannot be generalized and is rarely applicable. Enormous amounts of water are required for relatively low electrical powers and therefore such a storage system is very cost-intensive. This type of storage system is in no way suitable for storing energy over several months.

Known from DE 10 2010 008 059 A1 is a long-term heat storage device which comprises a solid body having a high heat storage coefficient which is suitable for high temperatures and is thermally loaded. The type of solid body is not described; however it should be possible to use a quartz sand bulk material as is known for heat storage. In any case, its thermal loading should be accomplished by heat conduction. The heat conducting device provided for this which should have a high thermal conductivity and a high temperature resistance is also not described in detail here. A heat absorption unit for converting the solar light is located upstream of the heat conducting device and not described in detail. The entire combination of heat absorption unit, heating conducting device and heat storage device should overall be thermally insulated by an ultra-insulation. It remains unclear how this should be achieved. An energy converter unit is located in the heat storage device to decouple the energy from the heat storage device. The working temperature of the long-term heat storage device should be between 100 and 800° C. Year-round heating of apartment and office blocks should be possible.

It can be seen from this that none of the concepts put forward so far for the long-term storage of energy meet the requirements or have proven to be capable of implementation in practice.

DESCRIPTION OF THE INVENTION

It is the object of the invention to provide an inexpensive system for utilizing solar energy and other types of energy with changing availability, according to which the solar energy or other type of energy with changing availability which has been concentrated up to a maximum temperature, e.g. by means of a concentrator and transferred to a heat transfer medium as heat in an absorber, is delivered by means of the heat transfer medium to the heat storage mass which is located in the long-term heat storage device. The heat storage mass should be capable of being heated to a temperature of about 1000° C. The long-term heat storage device should be insulated in such a manner that the thermal energy can be held in readiness over a long period of time (a few months up to half a year) with low thermal losses. To solve this object a generic long-term heat storage device having the features of claim 1 and a generic method for long-term thermal storage of solar energy and other types of energy with changing availability having the features of claim 27 is proposed. Accordingly the invention proposes a generic long-term heat storage device comprising a thermally insulated solid bed of a rock bulk material serving as heat storage mass, comprising a material suitable for high operating temperatures, in particular for temperatures between 100 degrees C. and 1000 degrees C., preferably between 300 degrees C. and 900 degrees C., having a high specific heat capacity, in particular greater than 600 J/kgK, high thermal conductivity, in particular higher than W/mK and high density, in particular greater than 2 kg/dm3, preferably of volcanic origin such as diabase, basalt, granite and/or gneiss, according to claim 1 and further a generic method for the long-term heat storage of solar energy and other types of energy with changing availability according to claim 27, whereby a granular material (rock bulk material), in particular having a high specific heat capacity, high thermal conductivity and high density, in particular of volcanic origin such as basalt rock, diabase rock, granite rock and/or gneiss rock, is provided in a solid bed as heat storage mass. The granular material is insulated in a suitable manner so that the heat losses remain low over a long period of time. The heat insulating material preferably has a plurality of contact resistances and/or a low thermal conductivity and/or a spongy, fibrous and/or porous structure and particularly preferably comprises a micronized powder such as micronized ash. The thermal insulation is of independently inventive importance. The granular material of the heat storage mass is heated to a high temperature by means of a heat transfer medium interacting with the granular material, in particular the heat transfer fluid flowing through the granular material, and is insulated in a suitable manner so that the heat losses remain low over a long period of time.

It is now possible to implement the invention in various ways. It has been shown inter alia that the geometry of the long-term heat storage device has a substantial influence on the heat losses. The geometry of the heat-stage device should be optimized in this sense. Furthermore an optimal insulation and an optimal thickness of the insulating layer have been found. It has further been shown that the relative heat losses of the heat storage device decrease with increasing storage capacity. It has further been shown that a rock bulk material of volcanic origin is suitable for high operating temperatures and at the same time has good physical properties such as high specific heat capacity, high thermal conductivity and high density. Preferably types of rock of volcanic origin come into consideration here such as basalt rock, diabase rock, granite rock and gneiss rock. In order to be able to achieve an efficient insulation of the heat storage mass over long periods of time, a heat insulating material with good insulating properties is used. This heat insulating material should inter alia be inexpensive in order to keep the economic viability of the plant sustainable. The heat insulating material should have a plurality of contact resistances. Furthermore, convective flow inside the insulating layer should be prevented. As a result of the large number of contact resistances, the heat transfer resistance due to radiation is increased. The more particles lie adjacent to one another, the greater is the number of heat conduction resistances. As a result of the large number of contact resistances, the heat conduction resistance due to convection and due to radiation is comparatively high. The heat conduction between two particles takes place at a point through contact. If the distance between two particles at the contact point is shorter than the free molecular path length, the thermal conductivity of the air decreases by a factor of 10 and acts as insulation. The smaller are the particles and accordingly the larger the number of contacts, the higher is the heat transfer resistance. It was found that these properties could be found in micronized powder. A micronized powder in the sense of the invention is understood as a powder in which the particle diameter is less than 100μ (micron). The powder can be obtained, for example, by fine grinding or from the electric filter in power plants. Micronized ash from electric filters in coal power plants can be considered to be particularly suitable. Among the various types of micronized powders, in particular types of ash, those having a low bulk density (in particular of 500 kg/m3 to 1000 kg/m3) were found to be particularly suitable. A thermal conductivity of the micronized power layer of about λ=0.09 W/mK to about λ=0.01 W/mK, in particular of about 0.03 W/mK can be seen as the criterion for a good insulating property. Accordingly, the thermal conductivity of the insulating material should be low, which is why the insulating material should preferably have a spongy or porous structure. It was further found that not only the insulating material is important for good insulation but also the geometry of the heat storage mass and the heat storage device with the insulation acquires a particular importance. An optimized insulating layer thickness is also important. It is also important that heat bridges are maximally avoided.

A long-term heat storage device according to the invention preferably satisfies the following conditions inter alia: the heat storage mass is resistant to high temperatures of several hundred to thousand degrees Celsius; the heat storage mass is present in the form of granular material in order to have sufficient heat exchange area for heat transfer; the granular material is resistant to temperature change; the grain size of the granular material lies in a certain order of magnitude in order to keep the pressure losses of flowing air or another heat transfer fluid through the bulk material within the framework; the heat insulation of the heat storage mass has a relatively low thermal conductivity and is inexpensive and available in large quantities; the insulation thickness and the geometry of the heat storage device are matched to one another so that the heat losses of the bulk material are reduced to a technical or economically meaningful minimum; the capacity, the size and the geometry of the long-term heat storage device are matched with the storage time so that the heat losses for these relationships are minimal.

The grain size of the rock bulk material of the heat storage mass can be designed according to another aspect of the invention as a polydisperse system so that the desired bulk material density is achieved and therefore the specific heat storage capacity can be brought to a desired value. A polydisperse system in the sense of the invention is understood as a multigrain bulk material. The multigrain bulk material can be composed so that the porosity or the intermediate grain volume of the bulk material acquires a certain value. A single-grain bulk material (that is, for example a ball bulk material consisting of balls of the same diameter) is designated as a monodisperse system on the other hand. The bulk material density of a multigrain bulk material and therefore also the specific heat storage capacity of the bulk material can be substantially enlarged by skilful mixing ratios of the grain size spectrum. This is preferably accomplished whereby the void volume of the granular material having a first grain size or grain size distribution is filled by a granular material having a second grain size or grain size distribution. Here, bearing in mind the band widths of the fine and coarse bulk material, as is particularly preferred it is possible to talk of a quasi bidisperse bulk material. Both granular matters can be of the same or different species/type.

Preferably a rock bulk material of volcanic origin is used as the heat storage mass. Types of rock which are particularly preferably used as heat storage mass are:

True Specific Thermal Elastic density heat conductivity modulus Elongation Rock kg/dm3 J/kgK W/mK N/mm2 1/K Basalt 2.85-3.05 800 1-1.6 9-10 × 104 1-7 × 10−8 Diabase 2.75-2.95 810-900 2-4  9-10 × 104 2-5 × 10−8 Granite 2.6-2.8 790 2.8  4-8 × 104 3-8 × 10−8 Gneiss 2.65-2.85 1000  2.9 4-10 × 104 2-7 × 10−8

The heat storage mass should be capable of being heated to at least 800° C. Assuming a mean void volume of the rock bulk material of 40% (ε=0.4), this gives a mean bulk density of about 1740 kg/m3. In this case, the true density of the diabase rock ρw=2900 kg/m3 is taken as the basis. If the rock bulk material is configured as a polydisperse system such as, for example, as a bidisperse system, as mentioned above, the bulk material density and therefore also the specific heat storage capacity of the rock bulk material can be substantially enlarged by skilled mixing ratios of the grain size spectrum, as illustrated in the exemplary embodiments.

It has been found that the usable storage capacity depends substantially on the method or on the type of use of the stored energy. For example, when the storage device is used for the purpose of heating buildings, the temperature in the storage device can be run down from, e.g. 800° C. to 100° C. Here Δt=700° C. In power production the cooling of the heat storage device is run down from e.g. 800° C. to 400° C. and in this case Δt=400° C. When using the heat for heating, the storage capacity is then therefore greater. The use of stored solar energy for heating or cooling buildings has the advantage that for heating the heat storage mass can be cooled down to 100° C. If on the other hand power is produced by means of an air machine which operates according to the Carnot cycle, it is possible to work with a high efficiency of 70% (at a temperature of the working medium of 700° C.) down to a diminishing efficiency of 21% (at a temperature of the working medium of 100° C.). It is difficult to envisage that a steam turbine can operate in the variable pressure range of, for example, 200 bar at 500° C. to 10 bar at 180° C. If on the other hand an air machine is heated externally by means of the energy stored according to the invention and depending on how the temperature of the heat source decreases, the air pressure in the machine is reduced accordingly, e.g. automatically, the maximum possible Carnot efficiency for the respective temperatures of the heat source is thereby extracted; this is naturally taking into account heat and friction losses.

The working medium in the air machine moves in a closed cycle whereby good conditions are created for achieve a high efficiency during the energy decoupling from the heat storage device.

In a practical embodiment of the invention, it is a question of suitably taking into account the computational, theoretical and process-technology relationships in order to achieve an optimum for the long-term heat storage with the lowest heat losses. As already mentioned, the geometry of the heat storage device also plays an important role. It can be demonstrated that the heat storage losses in a long-term heat storage device having a spherical geometry are the lowest, after this comes a cylinder geometry in which the height is equal to the diameter, cubes and parallelepipeds in which the heat losses are highest.

One embodiment according to the invention provides that the heat storage mass preferably has a cylinder shape (diameter=height of the cylinder). In order to achieve this, the rock bulk material is inserted into a cylindrical brick (annular) masonry wall. A circular plate, preferably of steel, can be placed on a foundation, preferably of concrete. An annular masonry wall, preferably made of solid brick and by means of mortar which is suitable for high temperatures (800° C.) is erected on the plate in a circular shape. A micronized powder, such as micronized ash which accumulates, for example, in an electric filter, can be used as ground insulation for the heat storage mass. The layer thickness of the micronized powder is determined so that the heat losses are minimal.

The in particular micronized powder layer can preferably be surfaced in two layers, with stone, in particular of brick. A small-grained fine bulk material of the same origin as the heat storage mass is, for example, scattered and levelled on the stone layer or layers. A fine bulk material in the sense of the invention is understood as a bulk material which, unlike the filling and coarse bulk material of the heat storage mass, has a smaller mean grain diameter. For example, as is preferred in this respect, the bulk material fill can have a grain size between 30 and 60 mm and the fine bulk material can have a grain size between 10 and 20 mm. On and/or between the fine-grained bulk material (fine bulk material), for example, made of chamotte brick, supply channels for a heat transfer fluid, in particular air, are formed so that air can flow through these as heat transfer medium and be uniformly distributed over the ground of rock bulk material. The aim is to distribute the heat transfer fluid uniformly over the rock bulk material. In order to achieve this, the supply channels are distributed uniformly over the contact surface. The height of the rock bulk material is ideally equal to its diameter. The annular masonry wall encloses the rock bulk material over the entire height and at the tip of the rock bulk material, discharge channels for the heat transfer fluid are formed in the same way as the supply, in particular made of chamotte brick. Likewise the intermediate spaces between the supply and/or discharge channels are filled with rock bulk material. The air flowing through the rock bulk material is removed outwards through the discharge channels and if desired is held in circulating motion. The rock bulk material ends at channel height. Furthermore, preferably the fine-grained bulk material, preferably of the same origin as the correspondingly coarser rock bulk material is applied on which the air channels of chamotte bricks are laid. The fine-grained bulk material can improve the laying of the bricks. As result of the relatively larger flow resistance, a better and more uniform air distribution can be achieved due to the fine bulk material. The fine-grained bulk material can again be surfaced, in particular in two layers, with conventional stone, in particular of brick. The heat storage mass is thereby enclosed on all sides. At a certain distance from the brick masonry wall, a cylinder, preferably made of steel, can be located, which encloses the entire area. The intermediate space between one such jacket and the annular masonry wall can be filled with micronized powder such as micronized ash which serves as insulation for the heat storage mass. Preferably a uniform insulation thickness is provided around the brick masonry wall in order to keep the heat losses to a minimum. Here the finding is very important that each energy content of the heat storage mass can be assigned an optimal layer thickness of thermal insulation in which the heat losses are minimal. With increasing layer thickness of the insulating layer, the diameter of the heat storage device increases accordingly and therefore the outer heat transfer area. Here also the economic viability of the whole is an important factor so that sometimes higher heat losses can be accepted and specifically as a compromise between the heat losses and the investment costs. Naturally the costs of the stored energy play an important role. On the other hand: in the case of greater heat losses the concentrator possibly used must accordingly be designed to be larger to cover these losses. It was found that the optimal solution should be sought by optimizing the heat losses.

The relationships can best be illustrated by means of an example: We assume that a house having a living area of 150 m2 and a room height H=2.6 m is to be heated. 390 m3 is to be heated for which an average heating power during the 6 months (from November to April of the next year) of about 12 kW is required, or the total amount of energy during 6 months is 30600 kWh.

A storage device can be designed with the diameter of the heat storage mass Dsm=4.5 m and with the height of the heat storage mass Hsm=4.5 m. Diabase rock of volcanic origin having a bulk density of 2100 kg/m3 is assumed for the heat storage mass.

The grain diameter of the rock bulk material lies between 30-60 mm and the bulk material consists of the 15-30 mm fraction in order to achieve a bulk density of 2100 kd/m3. The granular material is inserted in a cylindrical (annular) masonry wall of 250 mm wall thickness. The brick masonry wall is filled with a 1.4 m ash layer and over this in two layers, 120 mm of brick as surfacing and above the brick, a fine-grained bulk material 100 mm thick is uniformly distributed. A cladding of sheet metal 3 mm thick is provided around the brick masonry wall. Between the brick masonry wall and cladding, the ash layer 1.4 m thick is provided as insulating layer. Above the rock bulk material the ash layer 1.4 m thick is also provided for insulation. The external dimensions of the heat storage device are therefore: diameter about 8 m and height about 8 m.

With these dimensions and the insulation concept shown, the heat losses for the period from April to November during the storage of solar energy can be calculated as 7624 kWh which is about 21% in relation to the storage capacity of 36700 kWh.

It is shown that for greater storage capacity relative losses become increasingly smaller. If we make a design for 10000 m2 living area (200 dwellings), it will be shown that the relative losses are in the order of magnitude of 4% and for a living area of 100000 m2 (2000 dwellings) relative losses are in the order of magnitude of about 1.6%.

From this it can be concluded that the concept of the long-term heat storage device according to the invention offers an exceptional scope for storing solar energy in the summer months and providing full heating during the winter months.

The aforesaid components and those claimed and described in the exemplary embodiments to be used according to the invention are not subject to any particular framework conditions in their size, shape, material selection and technical conception so that the selection criteria known in the field of application can be used unrestrictedly.

Further details, features and advantages of the subject matter of the invention are obtained from the subclaims and from the following description and the relevant drawings in which, as an example, an exemplary embodiment of a long-term heat storage device is shown. Individual features of the claims or the embodiments can also be combined with other features of other claims and embodiments.

BRIEF DESCRIPTION OF THE FIGURES

In the drawings:

FIG. 1 shows in vertical section a schematic diagram of the long-term heat storage device filled with rock granular material of volcanic origin which is inserted in a closed cylindrical brick masonry wall. Air distribution channels are located at the bottom of the rock granular material and air collecting channels are provided at its top; an insulating ash layer is provided around the enclosing brick masonry wall in order to keep the heat losses to the outside low or prevent them;

FIG. 1A shows a cross-section along the line A-A according to FIG. 1 through the long-term heat storage device. The air distribution channels for heating air can be seen at the bottom of the rock bulk material;

FIG. 1B shows in plan view the air distribution channels according to FIG. 1 and FIG. 1A made of chamotte brick;

FIG. 1C shows a detail FIG. 1 for the arrangement of the chamotte bricks to form air channels;

FIG. 1D shows in detail a cross-section through the main distribution channel;

FIG. 1E shows an alternative possible embodiment to FIG. 1 whereby the entire brick masonry wall lies on the insulating ash layer. As a result of this type of design, the heat losses of the heat storage device are small but this embodiment is more difficult from the production technology viewpoint;

FIG. 1F shows a detail “A” from FIG. 1, namely: the rock bulk material, the insulating ash layer, the brick masonry wall, the air distribution channels, the surfacing of the ash layer by means of the bricks and the fine-grained bulk material;

FIG. 2 shows the long-term heat storage device according to FIG. 1 with external cladding;

FIG. 2A shows across-section through the long-term heat storage device with external cladding along the line A-A according to FIG. 2;

FIG. 3 shows a possible embodiment of the external cladding of the long-term heat, storage device made of sheet metal shells which are mounted in segments;

FIG. 4 shows a plan view of the cladding according to FIG. 3;

FIG. 5 shows an improved embodiment of the long-term heat storage device with an additional insulation which is applied over the external cladding and a protective sheet for the insulation;

FIG. 5A shows a cross-section through the heat storage device according to FIG. 5;

FIG. 6 shows a possible embodiment for the long-term heat storage device which is disposed in the ground;

FIG. 6A shows a cross-section of the long-term heat storage device according to FIG. 6;

FIG. 7A shows a diagram of the heat losses of a heat storage device (cylindrical shape with D=H) as a function of the insulation thickness of the ash which stores the solar energy from April to November; the storage capacity corresponds to a living area of 150 m2 (3 apartments or one house);

FIG. 7B shows the heat losses and (as an example) the efficiency of a heat storage device (cylindrical shape with D=H) as a function of the insulation thickness of the ash which stores the solar energy from April to November; the storage capacity corresponds to a living area of 10,000 m2 (200 apartments);

FIG. 7C shows the heat losses of a heat storage device (cylindrical shape with D=H) as a function of the insulation thickness of the ash which stores the solar energy from April to November; the storage capacity corresponds to a living area of 100,000 m2 (2000 apartments);

 DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

According to FIG. 1, a rock bulk material 1 of volcanic origin is inserted in a cylindrically walled (masonry wall 2) cavity. The masonry wall 2 cylindrically surrounding the cavity lies on a plate 3, e.g. made of steel which in turn lies on a foundation 4 made of concrete. The plate 3 serves, inter alia, to prevent possible diffusion of moisture from the foundation 4 into the ash layer (bulk powder fill 5) located thereover. The bulk powder fill 5 (hereinafter also designated as ash fill 5) is used for base insulation of the rock bulk material 1. The ash fill 5 is surfaced at its top in two layers by means of rock 6 preferably consisting of brick (hereinafter also designated as bricks 6) in order, inter alia to prevent ash dust from entering into the stream of the heat transfer agent preferably consisting of air. A fine-grained bulk material 7 is placed on the bricks 6 on which air supply channels, in particular in the form of an air supply channel 8 (hereinafter also designated as main air supply channel 8) and air supply distribution channels 8a branching therefrom are laid. The fine-grained bulk material 7 is preferably provided from the same material as the rock bulk material 1 but with a smaller mean grain diameter. The grain size in the rock bulk material 1 preferably varies in the order of magnitude between 30 and 80 mm and the fine-grained bulk material between 15 mm and 30 mm. The air supply channels 8 and 8a are laid on the fine-grained bulk material 7 so that the heating air is supplied through an inlet pipe 9 to the main air supply channel 8 and from there is distributed to the laterally laid air distribution channels 8a. The air supply channels 8 and 8a are preferably manufactured from chamotte brick 10 or from another stone, in particular brick which is suitable for high temperature. The type of structure of the air channels 8 and 8a is illustrated in FIG. 1B, FIG. 10 and FIG. 1D. FIG. 1F shows detail “A” to illustrate FIG. 1.

Heated air leaves the base channels 8a through openings 11 (FIG. 1B) and is distributed uniformly over the base of the rock bulk material 1. The hot air flow passes the rock bulk material 1 and releases its heat to said material. Exhaust air channels 12, 12a located above the rock bulk material 1 have the same structural form as the air supply channels 8 and 8a. The exhaust air channels 12, 12a are positioned at or on the upper end of the rock bulk material 1. The intermediate spaces between the exhaust air channels 12, 12a are, as shown and in this respect preferred, filled with rock bulk material 1. Another fine-grained bulk material 7a of the same material as the rock bulk material 1 is applied over the rock bulk material 1 and the exhaust air channels 12, 12a. The fine-grained bulk material 7a is surfaced in two layers by means of stones 17 such as bricks. Thus, the rock bulk material 1—as explained additionally further below—is surrounded spatially by shaped stones.

The exhaust air channels are designated as air collecting channels. The cooled air stream leaves the heat storage device through an air discharge pipe 13 connected to the air collecting channels (FIG. 1). The air discharge pipe 13 is thermally insulated and the insulation 14 is clad by means of a steel pipe 15 which is embedded together with the masonry wall 2 in an ash fill 16 (FIG. 1). The air inlet pipe 9 is preferably thermally insulated in the same way. The ash fill 16 supplements the ash fill 5 laid in the base region below the two lower layers of stones 6.

The masonry wall 2 (FIG. 1) laterally surrounds the rock bulk material 1 which serves as the heat storage mass. The two layers of stones 6 such as bricks and stones 17 such as bricks which can form layers in a similar manner to the stones 6 enclose the heat storage mass at the bottom or top. The heat storage mass together with the air supply and exhaust air channels is therefore surrounded on all sides by rock, in particular in the form of a masonry wall and/or shaped stones. The aforementioned encasement of the ash fills 5 and 16 is located around this masonry wall 2, 6 and 17 (FIG. 1). These are provided in a thickness AA where the long-term heat storage device 100, as shown in (FIG. 1) and in this respect preferred, has a cylindrical shape with the ratio D=H (diameter=height). The only heat bridge towards the outside is the cylindrical part of the supporting brick masonry wall 2a where a certain increased heat loss is possible. In the exemplary embodiment this heat loss is about 3%. The solution according to FIG. 1E however shows that the brick masonry wall 2 can be provide without a connection in the form of the supporting brick masonry wall 2a to the foundation. Therefore this heat bridge towards the outside is avoidable. The entire brick masonry wall 2, 6 and 17 then lies on the ash fill 5 (FIG. 1E). The rock bulk material 1 is therefore preferably together with the air supply and air removal enclosed on all sides, in particular with an interposed shell of shaped stones, by a powder fill, in particular by an ash fill 5, 16.

An outer cladding (18) can (according to FIG. 2) be arranged around the insulating ash layer (16) so that the insulating layer is held and the ingress of water and moist air is largely prevented. The outer cladding 18 of the long-term heat storage device 100 can be designed in various ways, according to FIG. 2 the outer cladding 18 consists of a plurality of cylindrical segments 19 which are firmly connected to one another by means of flange connections 20. The first base segment 21 is, if desired, welded to the base plate (steel plate 3), e.g. in order to prevent the ingress of moisture into the ash layer. The outer cladding 18 can be connected in an airtight manner and/or terminated by means of a cover 22 by flange connections. The cover 22 can be provided with a plurality of openings 22a and 22b which can be used to fill the heat storage device with insulating ash (powder fill 16). The steel pipes 15 which are used to protect the air lines 9 and 13 can be embedded in the ash layer 16 and be welded to the outer jacket and the segments 19 which are used for cladding. An insulation of ceramic wool 14 can be provided between the air pipelines 9 and 13 and protective pipes 15. An undisturbed expansion of the air pipelines 9 and 13 during a change in temperature can therefore be made possible. One of the advantages with this design is that there is no possibility for ingress of moisture into the ash fill which is important for the problem-free long-term function of the long-term heat storage device. FIG. 2a shows a horizontal section through the long-term heat storage device according to FIG. 2 for illustration.

According to FIGS. 3 and 4 another embodiment for the cladding 23 of the heat storage device is reproduced, i.e. the outer cladding 23 consists of sheet metal shells 24 which are fastened to one another around in a circle and over the height by means of screw connections. The sheet metal shells 24 form a regular polygon. According to FIG. 4 the plan view of the outer cladding 23 of the heat storage device is shown for illustration. Shown here is: a cover 26 with webs 27 and with openings 28 which serve for filling the heat storage device with insulating ash.

According to FIG. 5 an improved embodiment of the long-term heat storage device with an additional insulation is shown. This can consist of mineral wool which is applied over the outer cladding 23. The insulating layer 29 can also be clad by means of metal sheets, in particular by means of so-called trapezoidal sheets 30, in order to protect the insulation layer 29 from moisture. FIG. 5A shows a horizontal section through the heat storage device in order to illustrate the insulation.

According to FIG. 6 an embodiment is reproduced in which the long-term heat storage device 100 is disposed in the ground 31, as in the soil. This has the difference from FIG. 1 that the outer cladding is executed as a completely closed cylinder 32. The cylinder 32 is preferably made of steel sheet and is terminated in a water- and airtight manner. The heated air is supplied from below through pipeline 33 to the long-term heat storage device and the cooled air is extracted from it through pipeline 34. FIG. 6A shows a horizontal cross-section through the long-term heat storage device according to FIG. 6. The remaining structure of the long-term heat storage device 100 (rock bulk material, air supply and exhaust air guidance, encasement with shaped stones—also in the form of concreted walls—and encasement with fine-grained bulk material and possibly sheet metal encasement) can be executed as in the preceding exemplary embodiments.

Storage capacity: Each storage capacity and each geometrical shape has an optimal layer thickness of the insulation layer (powder fill 16, 5) for which the heat losses during the storage time are minimal (FIGS. 7A to 7C). The curves show the dependence of the heat losses/insulation thickness for a circular cylinder geometry (H=D) of the heat storage device. Assuming 180 days storage time, a minimum is obtained for a certain minimum insulating layer thickness (16, 5). The optimal economic insulating layer thickness (16, 5) lies in the range of 0.5 m to 2 m and can be taken into account for all storage capacities.

According to FIG. 7A, the heat losses of a heat storage device according to the invention are plotted as a function of the layer thicknesses of a rock bulk material of ash. The heat storage device should be able to absorb sufficient solar energy in order to fully heat an object having a 150 m2 living area from, e.g. November to the following April. The storage time then lasts from April to the end of October and the heat losses during the storage time are plotted in the diagram of FIG. 7A. From this diagram it can be seen that for a certain layer thickness, in this case it is about 1.8 m thick, the heat losses during the storage time are minimal. From this diagram it can be seen that with increasing layer thickness of the ash layer, the heat losses increase again. For the absolute layer thickness of the ash in the exemplary embodiment, absolute (total) heat losses of about 7,300 kWh are obtained. These losses account for about 48% of the stored energy. Here it should also be mentioned that the geometry of the heat storage device is a cylinder for which D=H. If the heat storage device on the other hand has the shape of a cube, the minimum for the heat losses (under, otherwise the same conditions) is about 58% of the stored energy, i.e. higher than for a cylinder shape with the characteristic D=H. In a heat storage device which has the shape of a sphere, the heat losses on the other hand were only around 30%. From this it can be concluded that the geometry of the long-term heat storage device plays an important role in the heat losses.

According to FIG. 7B, a long-term heat storage device has been taken into account as a cylinder (D=H) which can store sufficient thermal energy during the 6 summer months in order to be able to heat 10,000 m2 (200 apartments) from November to April. It can be seen from the diagram in FIG. 7B that the minimum for the ash layer has shifted towards a larger layer thickness. It can further be seen that there is no major difference in regard to the heat losses for a layer thickness between 1.8 m and 4 m. This finding is very important for the economic viability of the long-term heat storage device. The heat losses during the storage time for a layer thickness of 1.8 m are around 38,000 kWh and in relative terms, relative to the stored energy, are about 3.9%. From this it can be concluded that with the increasing storage capacity the relative heat losses decrease enormously. In a comparably designed long-term heat storage device but with a cubic shape, the relative heat losses are about 4.9%.

In a long-term heat storage device taken as the basis in FIG. 7C for a living area of 100,000 m2 (2000 apartments) and in cylindrical shape (D=H), it can be seen that the minimum for the heat losses is further shifted towards greater layer thicknesses of the ash. The difference in the heat losses for 1.8 m layer thickness and 4 m layer thickness is comparatively small. The heat losses during the storage time are about 160,000 kWh as absolute value (1.8 m layer thickness of the ash) and the relative heat losses are about 1.6%. For a cube shape the heat losses were 180,000 kWh (1.8 m layer thickness of the ash) and the relative heat losses are about 1.8% whereas for a spherical shape the heat losses are 93000 kWh (1.8 m layer thickness of the ash) or the relative heat losses are 0.9%.

It has accordingly been shown that the advantage is clearly in favour of spherical long-term heat storage devices. After this comes the heat storage device having a cylindrical shape (D=H). The heat storage device having the cubic shape has the highest heat losses. From the production technology point of view, the spherical heat storage device would be cost-intensive and complicated to implement in practice. A cylindrical heat storage device with D=H can be seen as an optimum compromise solution having an insulating ash layer thickness which lies in the order of magnitude of 1.4 m to 1.8 m.

Further Exemplary Embodiments

1) The long-term heat storage device according to this invention can achieve a breakthrough in the area of utilization of alternative energy because an appreciable fraction of the energy problems can be solved by the long-term storage of solar energy. For example, the whole of Europe as far as Southern England can use the new heat storage system according to this invention to solve the energy problems. There is no longer any need to attempt to achieve the “DESERTEC” project (Sahara project) in order to secure power production for Europe. In every Southern European country (Spain, Italy, Greece, Turkey) it will be possible to build economic solar power plants with continuous power production throughout the entire year (day and night) by using the long-term heat storage according to this invention. In addition to obtaining power from solar energy, it is also possible to build solar heating power plants where the complete heating requirement can be met by means of solar energy.

2) When using solar energy for heating buildings, the storage capacity of the long-term heat storage device is greater than the storage capacity for power production because the temperature difference for the heating is (800° C.-100° C.) 700° C. In power production the temperature difference in the long-term heat storage device during the decoupling of heat is at best 500° C. During the decoupling of heat from the long-term heat storage device for heating (in heating power plants), the temperature difference is 700° C. (max. 800° C.−min. 100° C.). This gives a storage capacity of, for example, 450 kWh/m3 whilst in power production with a temperature difference of 500° C. the specific storage capacity is about 324 kWh/m3.

3) If the long-term heat storage device is designed to heat, for example, a city having 50,000 dwellings each having 50 m2 living area per dwelling during the winter, and assuming that about 11000 kWh is required to heat a dwelling having a living area of 50 m2 from November to April of the next year, the dimension of the storage medium can be determined as: D=113 m and H=113 m. With an insulating ash layer the outside diameter of the long-term heat storage device is; D=116 m Ha=116 m.

4) Assuming that the sun also shines in winter, according to statistics e.g. for Balkan countries, the energy production can be determined during the winter months. The hours of sunshine in the winter months are as follows: in November there are 118 h, in December 54 h, in January 78 h, in February 90 h, in March 150 h and in April 208 h. If a good concentrator for concentrating the solar energy in a long-term heat storage device is considered which uses the solar energy in winter, it would be appropriate to design the heat storage device for 90 days storage time, and according to this the dimensions: D=90 m, H=90 m would be obtained for the storage mass. With the insulating ash layer in addition the outside diameter of the heat storage device becomes: D=93 m, H=93 m. In this case the heat losses during storage of the solar energy (180 days) are 0.6% relative to the total stored energy. It can be seen from this that the size of the long-term heat storage device should agree with the size and with the number of concentrators in order to be able to achieve the optimum ratios during usage of the solar energy. It is quite clear that the new heat storage system forms the breakthrough in the use of alternative energy.

5) Apart from solar energy it is also possible to store other types of energy. For example, heat from biomass, e.g. in the manner that in summer various waste is burnt and the stored energy is used in winter for heating. Wind energy can also be stored and during windless days power can be generated from the stored energy. In this way continuity would be secured with wind energy. In this case the power need not necessarily be generated by means of water vapour (the efficiency is too low) but by means of an air machine which operates with hot air. Thus a high efficiency (of the order of magnitude of 40% to 50%) can be achieved accordingly. This air machine must operate according to the Carnot process. The use of a Stirling motor can also be appropriate.

6) Numerically the storage capacity can be determined as follows by means of an example: a bulk density of ρs=2100 kg/m3 is desired, this bulk density corresponds to a void volume of =0.276. From this it follows that the rock bulk material should preferably be designed as a polydisperse bulk material in order to obtain the required bulk density. The grain size composition is determined in the laboratory. Assuming that the maximum temperature of the bulk material should be 800° C. and if the mean specific thermal capacity of the rock bulk material between 20° C. and 800° C. is 1200 J/kgK, a specific heat storage capacity of the rock bulk material in the temperature range between 100° C. and 800° C. of 488 kWh/m3 is obtained. The storage capacity depends on the temperature level to which the temperature of the bulk material should be able to be decreased due to the heat decoupling. If the focus is on power production in which water vapour and 20 bar pressure is used (213° C. saturated vapour temperature), it is expedient to cool the heat storage mass down to 300° C. For this temperature of the heat storage mass a storage capacity of 348 kWh/m3 is obtained.

7) In order to increase the specific storage capacity of the long-term heat storage device, a polydisperse bulk material-for example a granular material comprising at least two grain sizes and/or grain size distributions/band widths is used: it will be shown how the specific heat storage capacity of a heat storage device can be influenced by the design of the grain spectrum of the bulk material:

Let the true density of the diabase rock be ρw:=2900 kg/m3 and the porosity of the granular bulk material ε:=0.4. The bulk density can then be calculated as: ρs:=ρw(1−ε)=1.74×103 kg/m3. Assuming that the rock bulk material is heated to a maximum temperature tsmax:=800° C. and is cooled to a minimum temperature tmin:=100° C., Δ:=tsmax−tmin=700° C. is obtained. With a specific heat capacity of the rock of C:=1050 J/kgK, the storage capacity of the rock bulk material per unit volume can be calculated as follows:

Δ Q ? ( ρ s · C · Δ t ) 3612000 = 354.07 kWh / m 3 . ? indicates text missing or illegible when filed

The specific storage capacity of the bulk material for ε1:=0.35 and ρs1:=ρw(1−ε1)=1.885×103 kg/m3 is Δ“Q1” “=[” ((ρs1−C·Δt))/3612000]=383.576 kWh/m3 and for ε2:=0.3 and ρs2:=ρw(1−ε2)=2.03×103 kg/m3: Δ“Q2” “=[” ((ρs2−C·Δt))/3612000]=413.081 kWh/m3 and for ε3:=0.2 and ρs3:=ρw(1−ε3)=2.32×103 kg/m3: Δ“Q3” “=[” ((ρs3−·C·Δt))/3612000]=472.093 kWh/m3. It can be seen from this that the specific storage capacity of the bulk material increases as a result of the increase in the bulk density. At the same time, the increase in the bulk density can be achieved by the skilful mixing of various grain fractions as is shown by means of a numerical example:

We assume that the initial bulk material is composed of the following grain fraction: v1:=0.3 m3/m3 volume fraction, d1:=0.03 m grain diameter and ε1:=0.4 void volume, v2:=0.3 m3/m3 volume fraction, d2:=0.05 m grain diameter and LE2:=0.4 void volume, v3:=0.4 m3/m3 volume fraction d3:=0.08 m grain diameter and ε3:=0.4 void volume. This should be the initial bulk material I and the mean grain diameter and the mean specific surface are can be calculated as dpm:=48 mm and fspm:=75.6 m2/m3, εm:=0.4 is the mean void volume and ρs:=ρw(1−ε)=1.74×103 kg/m3 is the bulk density of the initial bulk material I.

If a fraction of smaller diameter is added to the initial bulk material, it is found that the bulk density can be increased. Properties of the fine-grained bulk material mixed with the initial bulk material are:

v4:=0.3 m3/m3 volume fraction (30%), d4:=0.005 m grain diameter and ε4:=0.4 void volume, v3:=0.4 m3/m3 volume fraction (40%), d5:=0.01 m grain diameter and ε5:=0.4 void volume, v6:=0.3 m3/m3 volume fraction (30%), d6:=0.02 m grain diameter and ε6:=0.4 void volume (in each case with single-grain bulk material).

For this fine-grained mixture the mean grain diameter, mean specific surface area, void volume and bulk density can be calculated: dpml:=8.696 mm, fspmis:=414 m2/m3 emis:=0.4 kg/m3, ρsmis:=ρw(1−εmis)=1.74×103.

Taking as the basis the heat storage mass having the dimensions: diameter (Dsp) of the heat storage mass Dsp:=4.46 m, H:=4.46 m, the height of the heat storage mass, volume (Vspm) of the storage mass Vspm:=69.678 m3, the void volume (VL) in the storage device is then: VL:=εm. Vspm=27.871 m3. If it is further assumed that 50% of the void volume is filled with a fine-grained mixture, after mixing the two coarse and fine-grained bulk materials, this gives: a mean void volume of the bulk material εtot:=0.28, a mean bulk density of the bulk material ρstot:=ρw(1−εtot)=2.088×103, a mean specific surface area of the bulk material of fsptot:=165.6 m2/m3 and a mean grain diameter of the bulk material of dmtot:=26 m. If the new parameters are included in the calculation, the specific capacity can be calculated as follows: Δ“Qtot” “=[” ((ρstot−C·Δt)/361200]=424.804 kWh/m3. It can be seen from this that by adding fine-grained bulk material the increase in the specific storage capacity is thus: ΔQtot−ΔQ=70.814 kWh/m3, which means a 20% increase.

For a grain size spectrum of the mixed bulk material in the sense of this invention, the minimal intermediate spacing can be determined for the grains of minimal diameter and the intermediate spacing of the grains for the maximum diameter, e.g. for a square and for a rhombic packing. Herein the rhombic packing is taken into account with ⅔ and the square packing with ⅓ volume fraction. This can be determined by calculation, where the following grain distribution of the fine-grained granules is obtained: ⅓ grain spectrum from 12 to 30 mm and ⅔ grain spectrum from 4 mm to 12 mm.

TABLE 1 8) Λeff k = (Λeff/ Λp (W/mK) (W/mK) Δ) W/m2K Thermal t ° C. Effective thermal Heat transfer Dp (mm) conductivity Temperature conductivity Δ(m) coefficient Particle of the of the bulk of the Bulk density through the No. diameter particles material insulating layer of the insulation insulating layer 1 0.0011(μ) 0.1 100 0.033 2 0.0165 2 0.0110(μ) 0.1 100 0.058 2 0.029 3 0.1100(μ) 0.1 100 0.064 2 0.032 4 1 0.1 100 0.067 2 0.0335 5 5 0.1 100 0.079 2 0.0395 6 10 0.1 100 0.089 2 0.0445 7 20 0.1 100 0.105 2 0.0525 8 50 0.1 100 0.138 2 0.069

Table 1 gives the dependence of the effective thermal conductivity (Λeff(W/mK)) and corresponding to this the heat transfer coefficient K=(Λeff/Δ) of the insulating bulk material (in this case this is the micronized ash) as a function of the grain diameter where the temperature in the bulk material and the thermal conductivity of the grain remain as constant quantities.

TABLE 2 Λeff k = (Λeff/ Λp (W/mK) (W/mK) Δ) W/m2K Thermal t ° C. Effective thermal Heat transfer Dp (mm) conductivity Temperature conductivity Δ(m) coefficient Particle of the of the bulk of the Bulk density through the No. diameter particles material insulating layer of the insulation insulating layer 1 0.0011(μ) 1.5 100 0.045 2 0.0225 2 0.0110(μ) 1.5 100 0.148 2 0.074 3 0.1100(μ) 1.5 100 0.22 2 0.11 4 1 1.5 100 0.241 2 0.1205 5 5 1.5 100 0.272 2 0.136 6 10 1.5 100 0.307 2 0.1535 7 20 1.5 100 0.375 2 0.1875 8 50 1.5 100 0.549 2 0.2745

In Table 2 all the quantities apart from the thermal conductivity of the particles Λp (W/mK) have remained the same. It can be seen from Table 2 that the thermal conductivity of the particles plays a major role in the heat conduction through the bulk material. The value for Λp=1.5 W/mK is deliberately taken into account to check whether the sand in the desert can be used as insulating layer because usually no ash is present in the desert. It can be seen from Table 2 that the thermal conductivity of the insulating bulk material increases sharply. From this it can be concluded that as an alternative to micronized ash for the insulating layer, a mineral substance having a spongy structure can be used. By grinding, the spongy material can be brought into micronized form and used as insulating material. The micronized ash is already present in sponge form because the carbon has reacted with the oxygen from the lattice structure as a result of the combustion reaction.

In summary it can therefore be said that apart from micronized ash, a mineral substance which has a spongy structure can be used as insulating material for the heat storage device. Possibly insulating ceramic or waste from brick can be used which has previously been brought into micronized form. It further follows from Table 2 that desert sand can possibly be used as insulating material if the grain is comminuted to less than 10μ. Here the question of the economic viability arises.

In this sense a new possibility is afforded, namely to develop a new technology which produces extra micronized ash (100%) from ash-rich coal. In this case, the thermal energy can be used for power production as usual. This would be a meaningful possibility.

REFERENCE LIST

  • 1 Rock bulk material
  • 2 Masonry wall
  • 2a Supporting masonry wall
  • 3 Plate
  • 4 Foundation
  • 5 Powder fill
  • 6 Stones
  • 7 Fine-grained bulk material
  • 7a Fine-grained bulk material
  • 8 Air supply channel
  • 8a Air supply distribution channels
  • 9 Inlet pipe for hot air
  • 10 Chamotte brick
  • 11 Outlet openings for hot air
  • 12 Exhaust air channel
  • 13 Air discharge pipe
  • 14 Insulation of air lines
  • 15 Steel pipe
  • 16 Powder fill
  • 17 Stones
  • 18 Outer cladding
  • 19 Cladding segment
  • 20 Flange connection
  • 21 Base segment of outer cladding
  • 22 Cover for the outer cladding
  • 22a Small opening
  • 22b Large opening
  • 23 Outer cladding
  • 24 Sheet metal shell
  • 25 Polygon of sheet metal shells (24)
  • 26 Cover
  • 27 Web
  • 28 Openings
  • 29 Insulation
  • 30 Trapezoidal sheet metal
  • 31 Ground
  • 32 Cylinder
  • 33 Air pipeline hot air inlet
  • 34 Air pipeline air outlet
  • 100 Long-term heat storage device
  • Delta A Thickness
  • D Diameter
  • H Height

Claims

1. Long-term heat storage device for the long-term storage of solar energy and other types of energy comprising a heat storage mass, characterized by a thermally insulated solid bed of a rock bulk material serving as heat storage mass, comprising a material suitable for high operating temperatures, in particular for temperatures between 100° C. and 1000° C., and having a high specific heat capacity greater than 600 J/kgK, a high thermal conductivity higher than 1 W/mK and a high density greater than 2 kg/dm3, the rock bul material being of volcanic origin such as diabase, basalt, granite and/or gneiss.

2. The long-term heat storage device according to claim 1, characterized by a thermally insulated solid bed of a rock bulk material serving as heat storage mass, the rock bulk material forms a polydisperse bulk material whereby the void volume of the rock bulk material (granular material) having a first grain size or grain size distribution takes up a granular material having a second grain size or grain size distribution.

3. The long-term heat storage device according to claim 1, characterized by a thermally insulated solid bed of a rock bulk material serving as heat storage mass, the rock bulk material together with an air supply and air removal is partially or fully surrounded with an interposed shell of shaped stones, by a bulk powder fill such as an ash fill.

4. The long-term heat storage device according to claim 1, characterized by a thermally insulated solid bed of a rock bulk material serving as heat storage mass, the rock bulk material together with an air supply and air removal is partially or fully surrounded by an in particular cylindrical shell of shaped stones such as by a masonry wall.

5. The long-term heat storage device according to claim 1, characterized in that the rock bulk material lays directly or indirectly on a bulk material comprising in particular micronized powder of a solid having a porous or fibrous structure, in particular of a group comprising micronized ash, powder having a large interior porous structure, sand having a porous structure, ground clay, ground brick, ground reacted solids such as activated charcoal or ground rock having a porous (spongy) structure as well as various organic substances having a fibrous structure.

6. The long-term heat storage device according to claim 1, characterized in that one or more layers of stone such as bricks, is/are disposed on the bulk material.

7. The long-term heat storage device according to claim 1, characterized in that a fine-grained bulk material is disposed underneath the rock bulk material and which has the same origin as the rock bulk material.

8. The long-term heat storage device according to claim 1, characterized in that the rock bulk material such as a masonry wall surrounding the rock bulk material is surrounded by a bulk powder fill such as micronized ash.

9. The long-term heat storage device according to claim 1, characterized in that incoming air distribution channels are disposed below the rock bulk material such as on a fine-grained bulk material.

10. The long-term heat storage device according to claim 9, characterized in that a main air channel and air distribution channels are shaped so that outlet openings for hot air are provided at the air distribution channels so that the air is distributed uniformly over the entire base of the rock bulk material.

11. The long-term heat storage device according to claim 1, characterized in that at the upper end of the rock bulk material exhaust air channels are laid so that the outflowing air is collected over the entire cross-section of the rock bulk material in the channels and is removed outwards.

12. The long-term heat storage device according to claim 10, characterized in that the intermediate spaces of the air supply channels and/or the air collecting channels are filled with rock bulk material.

13. The long-term heat storage device according to claim 11, characterized in that the space above the air collecting channels is filled with fine-grained bulk material.

14. The long-term heat storage device according to claim 13, characterized in that the fine-grained bulk material is constructed in two layers by means of the brick.

15. The long-term heat storage device according to claim 14, characterized in that a bulk powder fill is provided as insulation over the rock bulk material such as over the stones.

16. The long-term heat storage device according to claim 15, characterized in that the bulk material has the same thickness as the bulk material which is disposed laterally around the brick masonry wall.

17. The long-term heat storage device according to claim 9, characterized in that an insulated air supply pipeline inserted in a protective pipe is provided for the air inlet into the air supply distribution channels and/or for the air outlet from the exhaust air distribution channels which pipeline is provided with a cladding.

18. The long-term heat storage device according to claim 1, characterized in that a cladding made of sheet metal shells is provided around the insulating ash layer surrounding the rock bulk material.

19. The long-term heat storage device according to claim 18, characterized in that a covering of the rock bulk material of the masonry wall, the stones and the insulating ash layer is provided by means of the cover in such a manner that the cover is connected to the outer cladding in a watertight manner.

20. The long-term heat storage device according to claim 19, characterized in that filling openings are provided on the cover, in order to fill the space between the outer cladding and the masonry wall with bulk powder fill.

21. The long-term heat storage device according to claim 20, characterized in that the entire masonry wall and the rock bulk material lies on a bulk powder fill.

22. The long-term heat storage device according to claim 11, characterized in that the thickness of the bulk powder fill is selected according to the storage capacity and according to the geometry.

23. The long-term heat storage device according to claim 1, characterized in that the long-term heat storage device has the shape of a cylinder in which the diameter and the height of the heat storage mass are equal (D=H) and after insulation of the heat storage mass with bulk powder fill the diameter and the height of the cylinder are approximately the same (D=H).

24. The long-term heat storage device according to claim 1, characterized in that the heat storage device lies on a plate to prevent ingress of moisture into the insulation or into the heat storage mass.

25. The long-term heat storage device according to claim 1, characterized in that the heat storage device is laid underground so that the heat storage device is enclosed in a sleeve which is watertight in order to prevent the penetration of moisture into the insulation or into the heat storage mass.

26. The long-term heat storage device according to claim 1, characterized in that the rock bulk material has a bulk density of at least 1600 kg/m3.

27. Method for the long-term heat storage of solar energy and other types of energy with changing availability by means of a long-term heat storage device in which the solar energy or the other type of energy with changing availability is initially transferred to a heat transfer medium and then the thermal energy is transported into the long-term heat storage device and to the heat storage mass, characterized in that a granular material (rock bulk material) has a high specific heat capacity, high thermal conductivity and/or high density, and has a volcanic origin such as basalt rock, diabase rock, granite rock and/or gneiss rock, and is provided in a solid bed as heat storage mass, that the granular material is insulated in a suitable manner so that the heat losses remain low during a long period of time, wherein the heat insulating material has a plurality of contact resistances and/or its thermal conductivity is low and/or its structure is spongy, fibrous or porous and comprises a micronized powder such as micronized ash and that the granular material is heated to a high temperature by means of a heat transfer medium interacting with the granular material by means of air.

Patent History
Publication number: 20150159959
Type: Application
Filed: May 11, 2012
Publication Date: Jun 11, 2015
Inventor: Vladan Petrovic (Kragujevac)
Application Number: 14/400,150
Classifications
International Classification: F28D 20/00 (20060101); F24J 2/34 (20060101);