AU2011298700A1

AU2011298700A1 - Heat store

Info

Publication number: AU2011298700A1
Application number: AU2011298700A
Authority: AU
Inventors: Andrea Pedretti
Original assignee: Airlight Energy IP SA
Current assignee: Airlight Energy IP SA
Priority date: 2010-08-30
Filing date: 2011-08-30
Publication date: 2013-03-07
Anticipated expiration: 2031-08-30
Also published as: MX2013002034A; AU2011298700C1; CN103140732A; EP2612099A2; CH703780A2; WO2012027854A2; AU2011298700B2; MA34542B1; WO2012027854A3; ZA201300802B; US20130206356A1; CL2013000549A1

Abstract

According to the invention, the side wall (21) of a heat store (20) is supported in turn by a supporting bulk material (23) and is preferably inclined, such that the side wall (21) is subject to substantially less stress and can be produced from non-metallic material, such as concrete, for example. This type of heat store can be produced simply and cost-effectively and also permits long-term storage of large amounts of heat at high temperatures.

Description

Heat storage device The present invention relates to a heat storage device according to the preamble of claim 1 and a heat storage device according to claim 16. 5 Heat storage devices are used, inter alia, in power plants, in particular in solar power plants. Heat storage devices inserted in the ground are known for the storage of smaller quantities of heat (in contrast to storage on an industrial scale, see below), see Hahne, E: "The ITW solar heating system: an oldtimer ful 10 ly in action", SOLAR ENERGY, PERGAMON PRESS, OXFORD, GB, Vol. 69, No. 6, 1 January 2000 (200-01-01), Pages 469-493, XP004221026, ISSN: 0038 092X(00) 00115-8. The heat storage device disclosed by Hahne has a water gravel filling and is operated in a low-temperature range of 0 0 C to about 35 0 C to gether with a heat pump (see Hahne, loc. cit., Fig. 19 and Fig. 21). 15 DE 3 101 537 also discloses a heat storage device inserted in the ground in par ticular for supplying a house with heat, which is to be heated via electric current, where the operating temperature is suitable for operating the heating system of the house (Figure 3), i.e. lies far below 100C. 20 At the lower operating temperatures of this heat storage device lying below 100 0 C in conjunction with the small dimensions, the thermal expansion of the heat-storing material is insignificant. 25 Smaller or larger cylindrical steel tanks which rest on supports and have a dry filling of gravel or ceramic have become known for the storage of heat at higher temperatures, in particular above 100 0 C. Steel tanks are used to absorb the op erating forces in the storage device, which occur at operating temperatures above 100 0 C and can then have very high values. 30 A dry filling of gravel or, as mentioned, also ceramic or another suitable bulk ma terial (where reference is made hereinafter only to gravel instead of the various possible materials for the sake of simplicity) has a comparatively large heat ca 7 /26 pacity and can be perfused by a fluid, for example, a gas, since the intermediate spaces between the stones are sufficiently connected and allow a uniform perfu sion over the entire cross-section of the gravel filling. The gravel filling is heated by a hot fluid which can then for its part deliver heat subsequently to a cooler 5 fluid. Overall, heat storage devices having a heat-storing bulk material are suita ble for storing heat produced by solar energy. In particular, in the generation of heat by solar energy, however, the amount of heat actually produced depends on weather conditions (and naturally on the time 10 of day), where the fluctuations due to the weather can be very large over the day. Frequent weather fluctuations or periods of bad weather bring with it losses of heat production which can be so serious that, due to the weather, the produc tion of solar heat is not considered at sites which otherwise need not be elimi nated in advance from the solar irradiation point of view. 15 In solar thermal power plants the sun's radiation is reflected by collectors with the aid of a concentrator and is specifically focussed onto a location at which high temperatures are thereby produced. The concentrated heat can be removed and used for operating thermal machines such as turbines which in turn drive power 20 generating generators. Three basic forms of solar thermal power plants are in use today: dish Stirling systems, solar tower power plant systems and parabolic trough systems. 25 Dish Stirling systems are fitted with parabolic mirrors which concentrate the sun light onto a focal point, where a heat receiver is located. The mirrors are mount ed so that they can be rotated biaxially so that they can track the current posi tion of the sun and have a diameter from a few metres up to 10 m and more whereby powers of up to 50 kW per module can then be achieved. A Stirling en 30 gine installed at the heat receiver converts the thermal energy directly into me chanical work, through which power is generated in turn. 8 / 26 At this point reference is made to the embodiments presented in US-PS 4,543,945 and the EU Distal and Eurodish installed systems in Spain. Solar tower power plant systems have a central absorber mounted at an elevated 5 point (on the "tower) for the sunlight reflected to it by the hundreds to thou sands of individual mirrors, whereby the radiation energy of the sun is concen trated by means of the many mirrors or concentrators in the absorber and tem peratures up to 1300'C can be achieved, which is favourable for the efficiency of downstream thermal machines (usually a steam or fluid turbine power plant for 10 power generation). The "Solar two" plant in California has a power of several MW. Parabolic trough systems have a large number of collectors which have long con centrators having small transverse dimensions and therefore do not have a focal 15 point but a focal line. These linear concentrators today have a length of 20 m to 150 m. An absorber pipe for the concentrated heat (up to around 500'C) runs in the focal line, which transports this to the power plant. Thermal oil or superheat ed water vapour for example can be considered as transport medium. 20 The 9 SEGS parabolic trough power plants in Southern California together pro duce a power of about 350 MW. The "Nevada Solar One" power plant which went onto the grid in 2007 has trough collectors with 182,400 curved mirrors which are arranged over an area of 140 hectares and produces 65 MW. 25 Another example of a parabolic trough power plant is Andasol 1 in Andalusia hav ing a concentrator area of 510,000 m 2 and 50 MW power, where the temperature in the absorber pipes should reach about 400 0 C. The costs amounted to three hundred million Euro. Likewise, Andasol 2 which started test operation in mid 2009 and Andasol 3 which is to start operating in mid 2011. 30 It is found that there is a very broad requirement for the storage of heat: 9 / 26 On the one hand for the most diverse amounts of heat from single small systems such as, for example, dish Stirling systems as far as heat produced on an indus trial scale by power plants such as Andasol, where heat storage devices having a capacity not achieved to date (and therefore a size not achieved) are required.. 5 On the other hand, the storage should only take place short-term (shading, maintenance works, wind etc.), then medium-term for use at night or longer term during a period of bad weather. 10 Finally, and particularly importantly, heat should be stored at the highest possi ble temperature since high temperatures are required when converting to anoth er energy form (for example, current) for a high efficiency and as mentioned above, can increasingly be provided by parabolic trough power plants, in particu lar by solar tower systems and also by small parabolic mirrors. The losses during 15 heat storage are therefore not only determined by the insulation during the stor age duration and thereby by the temperature drop but also by the temperature of the heat extracted from the storage device. As mentioned above, the heat generated in the concentrator of a parabolic trough power plant can reach above 100'C, for example, 200 0 C, 400 0 C or 500 0 C or more, with even higher tempera 20 tures being strived for by further development. The gravel filling (or dry filling, since a water filling at the said temperatures no longer makes sense as a result of the steam formation and the associated oper ating pressure) of a heat storage device for storage of heat on an industrial scale 25 now has an appreciable weight so that the container must have a corresponding ly solid steel wall in order to withstand the pressure of this gravel. For small heat storage devices the construction of a steel wall is at first glance less demanding, for large heat storage devices it is certainly no longer trivial. 30 The pressure at rest of the gravel filling (active pressure) is less problematical here since as a result of the empty spaces between the stones, an active pres sure of about 30% of a water column must be expected. Naturally the active pressure depends on the density of the bulk material and can have higher val 10/26 ues. Usually (but in no way necessarily) however, the desired perfusibility of the bulk material will have the result that a bulk material having a not very high density will be used. 5 During the operation of the heat storage device, by the very nature of the matter the gravel filling must be heated and cooled. During heating to the aforesaid temperatures of above 100'C, in a range of up to 400 0 C, 500 0 C,or even higher, the gravel filling expands, which produces an expansion pressure which the steel wall must withstand, so that a correspondingly solid structure is required. If an 10 expansion of the gravel filling is not possible due to the rigid wall, the expansion of the individual stones will be compensated by a displacement of their arrange ment with respect to one another so that the empty space between the stones is reduced by the volume consumed by the thermal expansion of the stones. The expansion pressure therefore corresponds in order of magnitude to that pressure 15 which must be applied from outside to push together a gravel filling by a vertical wall (passive pressure). The passive (naturally like the active) pressure is dependent on the type of bulk material and in the case of loosely poured gravel, is approximately three times 20 the pressure of a water column, or more. In other words, it is the case that the determining operating pressure in the conventional heat storage device corre sponds to the passive pressure which is substantially higher than the active pres sure of the gravel filling. 25 Here it should be borne in mind that steel is heated more rapidly than gravel, with the consequence that during heating of the gravel the steel wall of the grav el container is in advance of this in the temperature and therefore also in the thermal expansion. During the heating process, the volume of the container therefore increases more rapidly than that of the gravel filling, which therefore 30 collapses into itself to some extent (i.e. occupies a somewhat broader but less high volume). When the container steel wall has reached the temperature of the heating fluid (which will be somewhat above the storage device temperature), the gravel still trails behind in its temperature and begins to build up expansion 11/26 pressure due to a corresponding increase in volume, which reaches its maximum at the storage temperature. This can have the result that the yield strength of the (hot, see above, and therefore less stress-resistant) steel wall is exceeded and the container becomes deformed, and is ultimately destroyed. 5 Overall the container must really be quite armour-plated in order to be able to withstand the pressures occurring during operation, which is constructively com plex, and complicated and expensive to manufacture. 10 Accordingly, it is the object of the present invention to provide a simple heat storage device which allows the storage of small and also large amounts of heat as far as the industrial scale. This object is achieved by a heat storage device having the features of claim 1 or 15 claim 19 as well as by an operating method according to claim 27. Since the side wall is supported from outside, it is substantially only compres sively stressed without needing to withstand a circumferential expansion as a re sult of a pressure-dependent increase in diameter, which results in a considera 20 bly lower stressing of the side wall and allows a correspondingly simple construc tion. Since the support is provided by bulk material, a sufficiently robust support can surprisingly be achieved in the simplest manner since the support has an ac tive pressure in advance which lies in the order of magnitude of the operating pressure (i.e. of the active pressure) of the heat-storing bulk material. 25 The side wall used in the prior art at operating temperatures of the bulk material of above 100'C, which is configured in a constructively complex manner in order to be able to absorb forces caused by the thermal expansion of the bulk material, is omitted. 30 In a preferred embodiment, the side wall (or at least areas of the side wall) are inclined at an angle of inclination which has the result that the heat-storing bulk material is displaced upwards to some extent during the expansion which takes 12/26 place during the storage of heat, so that the volume of the bulk material filling is increased and therefore the operating pressure that really occurs is lower than the expansion pressure in the case of a vertically disposed side wall. 5 The pressure loading of the side wall is therefore reduced once again with the consequence that not only steel can be used for the side wall but according to another embodiment, this can also consist of concrete. Further preferred embodiments exhibit the features of the dependent claims. 10 The invention is described in somewhat greater detail hereinafter with reference to the figures. In the figures: 15 Figure 1 shows schematically a first embodiment of the invention with a con tainer sunk in the ground for the heat-storing bulk material Figure 2 shows schematically a preferred embodiment of the invention with an inclined side wall 20 Figure 3a to c show schematically further embodiments in which the supporting bulk ma terial is heaped up above the ground, and Figure 4 shows a concrete wall composed of concrete segments for the con tainer of heat-storing bulk material 25 Figure 5a to 5b show various configurations for a heat storage device according to the in vention and Figure 6 shows an example of a temperature distribution in the heat-storing bulk material of a heat storage device during operation according to the present in 30 vention. Figure 1 shows schematically a heat storage device 1 which is let into the ground 2 and comprises a container 3 for a dry filling of heat-storing bulk material 4. 13/26 The container 3 has a side wall 5 which encloses the heat-storing bulk material 4. A fluid line 7 leads from a power house 6 into the bottom area 8 of the heat storage device 1 where fluid can be distributed and, uniformly distributed over a sieve bottom 9, can enter into the heat-storing bulk material 4, flow through 5 this, emerge from this at the top and be returned via the fluid line 10 to the power house 6. The figure does not show the further components by which means the power house 6 is connected to a heat source such as a solar power plant. The compo 10 nents to which the stored heat extracted from the heat storage device 1 is guid ed from the power house 6 are also not shown. The figure shows a perfusion with fluid from bottom to top. The heat-storing bulk material 4 can thus be heated to above 100 0 C by hot fluid coming from the heat 15 source. As required, cold fluid can be passed subsequently through the heat storing bulk material 4, which is accordingly heated and can then be used for conversion of energy, possibly for steam generation, where the steam for its part can then drive a turbine for the production of power. 20 Preferably a gas such as air is used as fluid. Other fluids, including liquid, are al so feasible. Preferably a filling of gravel is used as heat-storing bulk material 4. Other bulk materials are also feasible. Finally, various solutions are possible for the guidance of the fluid through the heat-storing bulk material 4, for example, in such a manner that a temperature stratification is obtained in the heat-storing 25 bulk material 4 and the perfusion is accomplished in concurrent flow or in coun tercurrent flow, see the description to Figure 6 for this. The person skilled in the art can design or modify the afore-mentioned elements in order to achieve an optimal heat storage according to the circumstances on 30 site. In particular, the heat storage device 1 can be designed for the storage of the heat of a small unit or for the storage of heat on an industrial scale and can be configured accordingly. 14/26 The ground 2 shown in the figure has a different structure. On the one hand a solid structure such as, for example, rock 13 and on the other hand, a bulk material-like structure 14 such as, for example, earth or gravel. 5 During operation, the side wall 5 is loaded by the heating, heat-storing bulk ma terial by outwardly directed, in the case of a cylindrical container 3, by radial op erating pressure, where the side wall 5 for its part is supported towards the out side on the supporting bulk material 14. As a result, the side wall 5 is substan tially only compressively stressed. If the side wall 5 consists of steel, the diame 10 ter of the container 3 becomes greater due to the thermal expansion with the re sult that the supporting bulk material builds up counterpressure corresponding to its active pressure so that during the subsequent increase in the diameter of the filling of heat-storing bulk material the side wall 5 is already stably supported by the supporting bulk material and a further increase in diameter of the side walls 15 is largely or completely suppressed: according to the invention it remains basi cally as only compressive stressing of the side wall, which allows a correspond ingly easy and simple design. Here it should be added that a denser material (compared with the heat-storing material) is preferably used for the supporting bulk material 14 since this need not be perfused by a fluid. This will usually be 20 the case when using spoil from the pit in which the heat storage device 1 accord ing to the invention is laid. The passive pressure of the supporting bulk material 14 is therefore greater than that of the heat-storing bulk material 4 from the outset, with the corresponding advantage of a stable support for the side wall 5. 25 In a preferred embodiment the supporting bulk material 14 is compacted com pared with the looser filling state, which can be advantageous in particular with certain bulk materials but is hardly necessary with coarse bulk materials consist ing of hard individual parts such as coarse gravel. Here it should be noted that when selecting the supporting bulk material, the person skilled in the art will in 30 particular take into account its passive pressure but is fundamentally free in the determination of the material of the bulk material and this can be matched to the needs on site. The bulk material 14 can then be different from the material of the ground. 15/26 Figure 2 shows a preferred embodiment of a heat storage device 20 whose side wall 21 is inclined at an angle of inclination with respect to the horizontal in such a manner that the container 22 of the heat storage device 20 is expanded to 5 wards the top. In the embodiment according to Figure 2 the container 22 has the shape of an inverted truncated cone. The container 22 is completely surrounded by a supporting bulk material 23 such as gravel, for example, which fills a pit 25 indicated by the dashed lines in the figure, which has been excavated from the ground 24. It is fundamentally the case that the space between the excavated pit 10 25 and the container 22 inserted therein can be filled with the ground material again which then forms the supporting bulk material 23. Depending on the mate rial condition, the person skilled in the art can also envisage providing a different bulk material 23 for this purpose, which has the desired properties, in particular the desired active pressure. 15 As a result of the inclination of the side wall 21, the heat-storing bulk material 4 under expansion pressure can be displaced upwards to some extent since the re action of the wall to its individual stones has an upwardly directed component thanks to the oblique position. 20 A surface unit of the side wall 21 exerts a reaction force in accordance with the vector 25 of the reaction force, where this vector 25 has a horizontally inwardly directed component 26 as well as the afore-mentioned vertically upwardly di rected component 27, which in turn results in a movement of the individual 25 stones of the heat-storing bulk material 4 towards the top. If stones are now displaced to some extent towards the top, a pressure relief is accomplished due to the simultaneous increase in volume. This effect occurs over the entire height of the container 20. This effect certainly occurs only to a re 30 stricted extent as a result of the friction of the individual stones amongst one an other and with the side wall 21 but nevertheless to such an extent that the real operating pressure is noticeably reduced compared with the expansion pressure corresponding to the active pressure in the case of a vertical side wall. This in 16/26 turn results in pressure relief of the side wall since specifically the operating pressure acting on said wall is smaller than that in the case of a vertically aligned side wall. 5 In one embodiment of the present invention, during operation of the heat storage device the heat-storing bulk material has a passive pressure which is higher than the desired operating compressive strength (without safety margin) of the side wall of the container containing the heat-storing bulk material 4. This is possible because the angle of inclination of the side wall 21 with respect to the 10 horizontal has a value such that the operating pressure of the heat-storing bulk material 4 is smaller than the operating compressive strength of the side wall 21. The inclination of the side wall 21 not only gives the advantageous effect on the heat-storing bulk material 4 described above but at the same time the advanta 15 geous effect described by means of the force vector 40 on the supporting bulk material: a surface unit of the side wall 21 is loaded by the operating pressure and exerts a force according to the vector 40 on the corresponding region of the supporting bulk material 23 which has an outwardly directed horizontal compo nent 41 and a downwardly directed vertical component 42. 20 Due to the horizontal component 42 alone, the supporting bulk material 23 at the surface 43 could be partially pressed away upwards, as is indicated by the outline of a heap 44. As a result, the effect of the supporting bulk material would be reduced in the area of the surface 43 with the risk that this effect continues 25 downwards and the supporting bulk material 34 loosens in the area of the side wall 23 with the result that the side wall 21 must be designed for a correspond ingly higher stressing. Due to the vertically downwardly directed component 42, however, the risk of a 30 heap 44 is avoided since the pressurised supporting bulk material 23 is not only pressed away horizontally outwards but is also pressed simultaneously down wards. 17/26 In summary, on the one hand the side wall can be supported by a supporting bulk material which overall allows larger heat storage devices (i.e. heat storage devices whose filling has a large volume) since without such support, the side wall would hardly be economical to manufacture as a result of the forces to be 5 intercepted. In addition, the operating pressure can be reduced appreciably due to the described inclination of the side wall, which facilitates the construction of a conventional side wall. In combination, these two construction principles enable the stressing of the side wall to be reduced in such a manner that even for large heat storage devices, materials other than steel such as, for example, concrete 10 can be used, which in turn brings with it the further appreciable advantages ac cording to the invention, as is described in connection with Figure 4. Since the specific optimal angle of inclination of the side wall depends on which bulk materials are used, it should be added at this point that an angle of inclina 15 tion between 50 and 85 degrees enables the effect according to the invention to be achieved in almost all possible combinations of bulk materials. An angle of in clination between 60 and 80 degrees is suitable for most common bulk materials (gravel or ceramic in combination with material from the ground) whereas an angle of inclination of 70 degrees may serve as an average if uncertainties re 20 garding the angle of friction of the materials are present or non-homogeneous materials are used. For example, when selecting a heat-storing bulk material such as rounded gravel having a grain size of 28 to 32 mm, a specific weight of 15 kN/m3 and an angle 25 of friction of 40 degrees in combination with a supporting bulk material such as looser, non-cohesive "standard soil" having a specific weight of 22 kN/m3 and an angle of friction of 30 degrees with an angle of inclination of the side wall of 80 degrees with respect to the horizontal, a passive pressure of the gravel of around 269 kN/m2 is obtained whereas the passive pressure of the supporting "standard 30 soil" is 420 kN/m2. Figures 3a to 3c show various possible configurations in the structure of the sup porting bulk material. 18/26 Figure 3a shows a container 30 of a heat storage device partially sunk on the ground, where the appurtenant fluid lines and further components are omitted to unburden the figure. A bulk material 31 surrounds the side wall 32 over its entire 5 height, on the one hand fills the pit 33 and on the other hand forms a mound 34. The flank of the mound 34 is flatter than the angle of friction of the supporting bulk material 31 with the result that the mound remains stable and can absorb the appreciable forces of the operating pressure. The stability of the flank of the mound 34 is supported by the inclination of the side wall 32 which additionally 10 compacts the mound 34 in a stabilising manner under operating pressure by means of the downwardly directed force component (see Figure 2, downwardly directed force component 42). Figure 3b shows a container 35 partially sunk in the ground, where the ground 15 produces sufficient active pressure to support the side wall 36. The mound 37 of supporting bulk material is for its part supported on the outside by an outer end wall 38. This results in a reduction in the diameter of the arrangement since the flank of the supporting bulk material shown in Figure 3a is omitted. As a result of the internal friction in the supporting bulk material 37, the outer end wall is 20 comparatively little stressed by the operating pressure acting on the side wall 36 and can easily be executed in a conventional manner by the person skilled in the art. Preferably the spoil for the pit in which the container 35 is located is used for the mound 37. 25 Figure 3c shows a container 40 standing on the ground (or even above the ground, for example, on a frame) where the supporting bulk material 42 is heaped around the side wall 41 so that its side wall 41 is protected by a mound 42 of supporting bulk material, where an outer end wall 43 surrounds and delim its the mound 42. 30 The arrangements in Figures 3a to 3c or mixed forms thereof, can preferably be selected by the person skilled in the art according to the conditions prevailing on site. 19/26 Figure 4 shows a side wall 51 of a heat storage device according to the invention consisting of concrete elements 50 (see Figure 2). All the concrete elements 50 have the same shape, can therefore be produced in series. The concrete ele 5 ments 50 are slightly conically configured over the length so that the angle of in clination of the side wall 51 determined by the person skilled in the art in the specific case is formed when the concrete elements 50 are joined together to form this. Here it should be added that the side wall can also be made of a dif ferent non-metal material. The term "non-metal" or "concrete" does not however 10 exclude the fact that the person skilled in the art can provide metal reinforce ments as a result of the envisaged stressing of the side wall or the elements forming the side wall. Admittedly, according to the invention the side wall is fun damentally only compressively stressed. As a result of the constructive circum stances in the real heat storage device executed according to the invention, a 15 certain further stressing cannot be excluded, which can definitely be desired by the person skilled in the art in addition to using the advantages according to the invention. The longitudinal edges 52, 53 of the concrete elements 50 have a step 54 so that 20 a broader surface 55 and a narrower surface 56 is formed. The concrete ele ments 50 are now positioned adjacent to one another, with the broader surface 55 and then the narrower surface 56 directed outward, with the result that the stepped longitudinal edges 52, 53 are supported on one another so that the side wall 51 is closed. 25 The person skilled in the art can also provide a different geometry of the edges 52, 53 so that the concrete elements 50 suitably intermesh. As a result of this in termeshing, a mutually defined position of the respectively adjoining concrete el ements is obtained. At the same time, due to the step shape, a slight relative 30 movement of the adjoining elements 50 in the built-in state is possible as before, whereby the flanks of the steps slide on one another to some extent so that re maining extremely small displacements of the elements are possible as a result of the operation of the heat storage device. 20/26 In detail, a concrete element 50 is formed as an elongate, flat panel whose two straight longitudinal edges 52, 53 are formed as a step 54 which can be brought into engagement with the step 54 of an adjacent concrete element 50. The width 5 of a concrete element 50 at the lower edge 62 is smaller than the width at the upper end 63. In addition, the lower width 62, the upper width 63 and the ratio of the widths 62, 63 are formed in such a manner that a number of concrete el ements 50 with engaged longitudinal edges can be joined together to form a closed jacket of a truncated cone, as shown in the figure. 10 The body of a concrete element 50 can preferably be curved in the direction of its width (this is however over its entire length), where the radius of curvature becomes smaller from the broader end towards the narrower end and is config ured in such a manner that it substantially corresponds to the radius of curvature 15 of the truncated cone. The supports 57 shown by the dashed lines are further provided in the figure, which allow the concrete elements 50 to be arranged and aligned with respect to one another in the prepared pit during construction of the heat storage device so 20 that the pit can then be filled with the supporting bulk material. During operation of the heat storage device according to the invention, however, the supporting effect of these supports 57 is of subordinate importance. A base 65 of the container 51 can also be seen. 25 The thermal conductivity of concrete is massively lower than that of steel which allows the longer storage of high-temperature heat without greater additional expenditure on insulation. In order to prevent any cooling convection of air, ac cording to the embodiment of Figure 4, a side wall is preferably surrounded by a 30 sealing film on the outside, which for its part then rests on the supporting bulk material. Between the side wall 51 and the supporting bulk material, there is a special insulating layer according to the invention, which however must be capa 21/26 ble of pressure loading since it lies between the side wall 51 and the supporting bulk material (this is not indicated to unburden the figure). Such containers can, for example, have a diameter of 5 m to 25 m and a height 5 of 4 m to 9.5 m. Figure 5a shows another configuration according to the invention for a heat stor age device according to the invention. The side wall 70 as a whole is divided into different segments 71, 72. In this case, only the segment 71 is inclined with re 10 spect to the horizontal and the segment 72 is arranged vertically, which however is sufficient to reduce the operating pressure of the heat-storing bulk material provided therein (and omitted to unburden the figure) in such a manner that the side wall can be formed of non-metal materials such as the concrete elements 50 described above. The person skilled in the art will, for example, select such a 15 configuration when the available space on the one side of the pit provided for the heat storage device is small. At this point it should be noted that, for example, at the location of the vertical segment 72 rocky ground could be present so that the person skilled in the art need only support the inclined segment 72 by a support ing bulk material whilst the vertical segment 71 would be directly supported by 20 the rock. Such mixed forms are certainly within the range of the present inven tion but are rare and are usually motivated by special soil information. Usually the entire side wall 70 is configured to be round as a truncated cone and sur rounded by supporting bulk material. 25 Figure 5b shows an additional configuration according to the invention for a heat storage device according to the invention. The side wall 80 is divided as a whole into different segments 81 to 84. One of the segments 81 is vertically aligned, the other segments 82 to 84 are aligned with respect to the horizontal according to the invention, which is sufficient to reduce the operating pressure of the heat 30 storing bulk material present therein (and omitted to unburden the figure) in such a manner that the side wall can be formed of non-metal materials such as the concrete elements 50 described above. In addition, the segment 84 is con figured to be flat. 22/26 The person skilled in the art will determine such geometrically mixed forms ac cording to the conditions on site, but will provide the inclination and the surface fraction of the inclined segments in such a manner that the effect of the inclined 5 side wall according to the invention is effective. Figure 6 shows an example of a temperature distribution in the heat-storing bulk material of a heat storage device during operation according to the present in vention. 10 A diagram is shown where curve 90 gives the temperature distribution in 0 C in a heat-storing bulk material of a heat storage device according to Figure 1 in ac cordance with a model calculation. The assumptions made here are: height of bulk material 3 m, where in the diagram the height on its upper side is given by 15 0 m and at the bottom of the heat storage device by 3 m. The perfusion with heat-supplying gas is accomplished from top to bottom at 0.1 kg/s and an inlet temperature of 550 0 C. The diagram shows the temperature distribution in the bulk material after 20 h. 20 A temperature stratification is found with an uppermost layer or zone A of the bulk material having the highest temperature (section 91 of curve 90) and a low ermost layer C having the lowest temperature (section 92 of curve 90). In this case, the highest temperature reaches and exceeds 500 0 C whilst the lowest tem perature lies below 100 0 C. 25 A middle zone or zone B of the bulk material (section 93 of curve 90) shows an approximately uniform temperature drop over its height. In cases of longer-lasting or shorter-lasting supply of heat to the storage device, 30 the curve 90 is shifted to the right or to the left, where the flank thereof, i.e. the section 93 thereof, remains substantially unchanged. The height of the layer or zone B therefore remains substantially the same. 23/26 Accordingly, zone A can extend over a height of a few cm at the beginning of the heat storage as far as about 2 m, where the temperature of the bulk material at the bottom in the layer C which is still present as before but now only just 0.5 m thick, remains at around 50 0 C. 5 This means that the supporting of the side wall according to the invention prefer ably extends over the entire height of the heat storage device even when the temperature of the bulk material in layer C is kept below 100 0 C. This applies likewise for the synergetic slope of the side wall for supporting according to the 10 invention. In an operating method according to the present invention only so much heat is supplied to the heat storage device that a lower layer C having a temperature below 100'C is always present (which is not compulsory) so that the outlet tem 15 perature of the fluid supplying the heat to the storage device is also 100 0 C (the temperature of the fluid is always somewhat higher than the bulk material heat ed by it) or is preferably lower at around 50 0 C. In this operating mode the fluid then delivers a maximum amount of heat to the storage device, which is advan tageous for the efficiency of the heat storage in the power plant. 20 The advantages according to the invention are achieved as soon as the inlet temperature of the fluid exceeds 100 0 C, i.e. the heat storage takes place by means of a dry filling at temperatures relevant for thermal expansion thereof. Depending on the design of the power plant on site or the installations provided, 25 in which a heat storage device according to the invention is integrated, the inlet temperature can be or exceed 200 0 C, 300 0 C, 400 0 C or 500 0 C. Accordingly, an operating method for a heat storage device according to the in vention having a heat-storing dry filling of bulk material, which is surrounded by 30 a side wall (5) enclosing said material, is characterised in that - the bulk material (4) has a temperature exceeding 100 0 C during the heat storage and the side wall (5, 21, 32, 36, 41, 51, 70, 80) is for its part supported against the outside on a supporting bulk material (14, 23, 33, 24/26 37, 42) to absorb the operating pressure of the heat-storing bulk material (4), - wherein the bulk material (4) for storage of heat is perfused by a hot fluid from top to bottom, whose inlet temperature lies below 100'C, in such a 5 manner - that the bulk material (4) in an upper zone of the heat storage device is heated to substantially the inlet temperature, in a middle zone lies be tween substantially the inlet temperature and 100 0 C and in a lower zone lies below 100'C and that the further supply of heat is determined in such 10 a manner that the temperature in the lower zone during the storage dura tion is always below 100 0 C. Overall, the present invention provides a heat storage device which is suitable for 15 small systems and for the storage of large amounts of heat such as are produced in large solar power plants. For large amounts of heat a single large, or several suitably connected smaller, heat storage devices are provided since the heat storage device according to the invention, in particular in a design having a side wall made of concrete elements, can be produced in series cost-effectively and 20 on site. As a result of the insulating effect of the supporting bulk material and a side wall consisting of concrete (naturally the person skilled in the art can also provide the base and the cover of the container made of a material such as con crete), a long-term storage time is possible even for heat having a high tempera ture which is 500 degrees C or higher, e.g. 650 degrees C. 25 25 /26

Claims

1. Heat storage device comprising a container for heat-storing material, which comprises a side wall (5) enclosing said material, characterised 5 in that the heat-storing material consists of a dry filling of bulk mate rial, having a temperature exceeding 100 0 C during the heat storage and that the side wall (5, 21, 32, 36, 41, 51, 70, 80) for receiving the operating pressure of the heat-storing bulk material (4) is for its part supported towards the outside on a supporting bulk material (14, 23, 10 33, 37,42).

2. The heat storage device according to claim 1, wherein the supporting bulk material (14, 23, 33, 37, 42) is compacted compared with the looser filling state. 15

3. The heat storage device according to claim 1, wherein at least seg ments of the side wall (21, 32, 36, 41, 51, 70, 80) are inclined at an angle of inclination with respect to the horizontal in such a manner that the container (22, 30, 35, 40) expands towards the top. 20

4. The heat storage device according to claim 3, wherein the angle of inclination is between 50 and 85 degrees, preferably between 60 and 80 degrees, particularly preferably 70 degrees. 25

5. The heat storage device according to claim 3, wherein the heat storing bulk material (4) has a passive pressure during operation which is higher than the operating compressive strength of the side wall (21, 32, 36, 41, 51, 70, 80) and wherein its angle of inclination with respect to the horizontal has a value in such a manner that the 30 operating pressure of the heat-storing bulk material (4) is lower than the operating compressive strength of the side wall (21, 32, 36, 41, 51, 70, 80). 1 / 26

6. The heat storage device according to any one of claims 1 to 5, where in this is sunk in the ground (24) and the material of the ground (23) at least partially forms the supporting bulk material (4) or that a bulk 5 material is used that is different from the material of the ground.

7. The heat storage device according to any one of claims 1 to 5, where in this is partially sunk in the ground and the ground itself at least partially forms the supporting bulk material (33) for the sunken area 10 of the side wall (32) and wherein the region of the side wall project ing above the ground is supported by a heaped supporting bulk mate rial (31).

8. The heat storage device according to any one of claims 1 to 5, where 15 in this is disposed on or above the ground and the supporting bulk material (42) is heaped around the side wall (43).

9. The heat storage device according to any one of claims 1 to 8, where in the supporting bulk material (42) is surrounded by an outer end 20 wall (43).

10. The heat storage device according to claim 1, wherein the side wall (51) consists of a non-metallic material and preferably has metal re inforcing elements. 25

11. The heat storage device according to claim 10, wherein the side wall (51) consists of preferably pre-fabricated segments (50), which in termesh at the edge. 30

12. The heat storage device according to claim 10 or 11, wherein the side wall (51) consists of concrete. 2 / 26

13. The heat storage device according to claim 12, wherein the side wall (51) consists of compacted light concrete or aerocrete.

14. Concrete segment for the side wall of a heat storage device according 5 to claim 1, characterised in that it is formed as an elongate flat panel (50), whose two straight longitudinal edges (53, 54) are configured as a step, which can be brought into engagement with the step of a neighbouring concrete segment (50), wherein the width of the con crete segment at the lower end (62) is smaller than that at the upper 10 end (63) and the lower width (62), the upper width (63) and the ratio of the widths (62, 63) is pre-determined in such a manner that a number of concrete segments (50) with engaged longitudinal edges (53, 54) can be joined together to form a closed jacket of a truncated cone. 15

15. The concrete segment according to claim 14, wherein its body is curved over its length in the direction of the width, wherein the radius of curvature becomes smaller from the broader end (63) towards the narrower end (62) and is configured in such a manner that it sub 20 stantially corresponds to the radius of curvature of the truncated cone.

16. The concrete segment according to claim 14 or 15, wherein the angle of inclination of the jacket of the truncated cone with respect to the 25 horizontal is between 50 to 85 degrees, preferably between 60 to 80 degrees, particularly preferably 70 degrees.

17. The concrete segment according to claim 14, wherein the side wall (51) consists of concrete, preferably light concrete or aerocrete. 30

18. The concrete segment according to claim 17, wherein the concrete is compacted. 3 /26

19. A heat storage device having a container for heat-storing material which comprises a side wall (5) enclosing said material, characterised in that the heat-storing material consists of a dry filling of bulk mate 5 rial, having a temperature exceeding 100 0 C during the heat storage and that at least segments of the side wall (21, 32, 36, 41, 51, 70, 80) are inclined at an angle of inclination with respect to the horizon tal in such a manner that the container (22, 30, 35, 40) expands to wards the top. 10

20. The heat storage device according to claim 1, wherein the angle of inclination is between 50 to 85 degrees, preferably between 60 to 80 degrees, particularly preferably 70 degrees. 15

21. The heat storage device according to claim 19, wherein the heat storing bulk material (4) has a passive pressure during operation which is higher than the operating compressive strength of the side wall (21, 32, 36, 41, 51, 70, 80) and wherein its angle of inclination with respect to the horizontal has a value in such a manner that the 20 operating pressure of the heat-storing bulk material (4) is lower than the operating compressive strength of the side wall (21, 32, 36, 41, 51, 70, 80).

22. The heat storage device according to claim 19, wherein the side wall 25 (51) consists of a non-metal material and preferably has metal rein forcing elements.

23. The heat storage device according to claim 8, wherein the side wall (51) consists of preferably pre-fabricated segments (50), which in 30 termesh at the edges, wherein the segments (50) particularly prefer able consist of concrete. 4 / 26

24. The heat storage device according to claim 1 or 22, wherein a tem perature of the heat-storing bulk material (4) reaches or exceeds at least 100'C, preferably at least 200 0 C, particularly preferably at least 400 0 C, even more preferably 500'C. 5

25. The heat storage device according to claim 1 or 22, wherein the tem perature distribution in the heat-storing bulk material (4) is stratified during the storage of heat, wherein an uppermost layer of the bulk material (4) has the highest temperature and a lowermost layer of 10 the bulk material (4) has the lowest temperature.

26. The heat storage device according to claim 25, wherein the highest temperature reaches or exceeds 500 0 C and the lowest temperature lies below 100C. 15

27. A method for operating a heat storage device according to any one of the preceding claims having a heat-storing dry filling of bulk material, which is surrounded by a side wall (5) enclosing said material, char acterised in that the bulk material (4) has a temperature exceeding 20 100 0 C during the heat storage and the side wall (5, 21, 32, 36, 41, 51, 70, 80) is for its part supported against the outside on a support ing bulk material (14, 23, 33, 37, 42) to absorb the operating pres sure of the heat-storing bulk material (4), wherein the bulk material (4) for storage of heat is perfused by a hot fluid from top to bottom, 25 whose inlet temperature lies below 100 0 C, in such a manner that the bulk material (4) in an upper zone of the heat storage device is heat ed to substantially the inlet temperature, in a middle zone lies be tween substantially the inlet temperature and 100 0 C and in a lower zone lies below 100 0 C and that the further supply of heat is deter 30 mined in such a manner that the temperature in the lower zone dur ing the storage duration is always below 100 0 C. 5 / 26

28. The method according to claim 27, wherein the temperature in the upper zone reaches or exceeds at least 200 0 C, particularly preferably at least 400 0 C, even more preferably 500 0 C. 5 6 / 26