Method for thermal energy storage and thermal energy store

Abstract

The present invention relates to a method for thermal energy storage with at least two containers which are each filled with a solid bulk material, wherein a heat storage medium is brought into and / or out of the containers, one after the other, for introducing and / or withdrawing thermal energy, wherein a temperature-layered temperature storage is carried out via the solid bulk material in the respective container, and the heat storage medium is used for heat transfer operations during introduction and / or withdrawal. The present invention furthermore relates to a corresponding thermal energy store.

Description

[0001] Description

[0002] Processes for thermal energy storage and thermal energy storage

[0003] The present invention relates to a method for thermal energy storage using at least two containers, each filled with a solid material. Furthermore, the invention relates to a thermal energy storage device.

[0004] Energy storage is advantageous for compensating for fluctuating electrical generation and consumption. Especially when using different renewable energies, energy storage and provision represent an important building block for the energy transition in the face of climate change.

[0005] Energy can be stored in energy storage systems, for example, chemical or electrical storage systems. Thermal energy storage systems are also known, which offer advantages over chemical or electrical storage systems, particularly with regard to the cost per unit of energy and the amount of energy stored.

[0006] In the case of thermal energy storage, solid-state or liquid storage are known from the state of the art. For a temperature range of 90 °C to 400 °C, temperature-stratified energy storage systems based on thermal oil are also advantageous. In contrast to water-based energy storage systems, there is no need to take saturated steam-related internal pressure into account. Temperature stratification can, in particular, prevent a loss of mixing or "exergy loss". Furthermore, a comparatively long withdrawal at a high temperature level can be ensured if the energy storage system is charged and discharged accordingly.

[0007] To supply energy to the energy storage unit, it is charged. It is known from the prior art to introduce thermal oil into the energy storage unit from above, allowing hot thermal oil to flow from top to bottom. To remove energy from the energy storage unit, it is discharged. Cool thermal oil is introduced into the container from bottom to top.

[0008] Since thermal oil is expensive, a cost-effective solid fill, such as gravel, can be introduced into the storage tank to reduce costs. This can replace a portion of the volume of the expensive thermal oil. Storage tanks are known in particular in which the solid fill accounts for 60% to 70% of the volume and can provide approximately 60% to 80% of the heat capacity.

[0009] The costs for the thermal oil are many times higher than the costs for the solid bed, for example, 10 to 20 times higher, especially based on the same heat capacity. Therefore, it is desirable to further reduce the thermal oil requirement. In particular, temperature stratification of the energy storage device should continue to be possible. Against this background, the object of the present invention is to provide an improved method for thermal energy storage and an improved thermal energy storage device.

[0010] According to the invention, this object is achieved by a method having the features of patent claim 1 and / or by a thermal energy storage device having the features of patent claim 13.

[0011] Accordingly, it is provided that:

[0012] A method for thermal energy storage with at least two containers, each filled with a solid bed, wherein a heat storage medium for storing and / or discharging thermal energy is successively introduced into the containers and / or removed from the containers, wherein a temperature-stratified temperature storage takes place via the solid bed in the respective container, and the heat storage medium is used for heat transfer processes during storage and / or discharging.

[0013] A thermal energy store, in particular for carrying out a method according to the invention, with at least two containers, each filled with a solid bed, wherein the containers are connected via at least one line such that a heat storage medium for storing and / or discharging thermal energy can be introduced into and removed from the containers one after the other, wherein temperature storage takes place via the solid bed. The finding underlying the present invention is to enable thermal energy storage, wherein the storage task of the energy can essentially be taken over by a solid bed.

[0014] The idea underlying the present invention is to use a heat storage medium primarily for heat transport during storage and withdrawal. According to the invention, this is implemented in particular by using several small containers that can be loaded and unloaded one after the other. This allows the storage volume for the loading and unloading process to be kept small, thereby reducing the volume fraction of the required heat storage medium, such as, in particular, the thermal oil.

[0015] The entire thermal energy storage unit is divided into at least two containers, which can be filled with the heat storage medium one after the other. As a result, the volume of each container is small in relation to the total energy storage unit. Accordingly, less heat storage medium is required to charge or discharge a "small" container, a so-called sub-container, of the entire thermal energy storage unit. According to the invention, costs can be significantly reduced because, in particular, the costs for the heat storage medium are low due to the small volume proportion of the so-called "sub-volumes" of the containers.

[0016] A container can be understood as a separate volume portion in which a bed of solid material is arranged. The at least two containers can have a common dividing wall, so that sub-containers can be separated into different sub-volumes within a large container. Furthermore, the containers can be arranged side by side, separated from one another, to form an energy storage device.

[0017] A solid bed can fill a large portion of the volume of any container. In particular, the entire container is filled with the solid bed. Gravel, for example, can be used as the solid bed. Furthermore, various storage materials can be used, such as porous and / or void-containing materials. In particular, the solid bed is formed from spaced-apart bodies so that the heat storage medium can reach the surface of the individual elements of the solid bed.

[0018] Thermal oil, in particular, can be used as a heat storage or heat transfer medium. Other fluid media capable of storing energy are also conceivable.

[0019] Temperature-stratified storage is understood to mean, in particular, that each container has a temperature gradient from an upper region to a lower region. In particular, the storage medium, such as the solid bed, has a higher temperature in an upper region of the container than in a lower region.

[0020] Advantageous embodiments and further developments emerge from the further subclaims and from the description with reference to the figures of the drawing. Before energy is stored, each container is, in particular, at a low temperature level and, in particular, does not contain a significant amount of heat storage medium.

[0021] In a preferred embodiment, for temperature-stratified storage of thermal energy in a first container, heat storage medium can be introduced into the container from below up to a certain fill level, and then hot heat storage medium can be introduced into the container from above. When filling the container from below, cold heat storage medium, in particular cold thermal oil, is used. The use of cold heat storage medium in particular avoids mixing losses. These are to be avoided in particular if the container is not completely filled. In such a case, the lower part of the solid bed could already be heated, which would lead to unused heat input. The use of cold heat storage medium from below further prevents or reduces the occurrence of thermoelectric stresses when filling the container.

[0022] The filling with cold heat storage medium from below is continued in particular until a suitable and low-turbulence inflow with hot heat storage medium, in particular hot thermal oil, can take place from above.

[0023] In a preferred embodiment, the hot heat storage medium can therefore be supplied evenly and with little turbulence. It is supplied, in particular, from above into the container. This is particularly advantageous for achieving temperature stratification within the container. This makes it possible to achieve temperature-coated storage, with the container being filled, in particular, with the solid bed and the heat storage medium. The interior of the container has a higher temperature, particularly in the upper region, than in the lower region.

[0024] In a preferred embodiment, after thermal energy has been stored in the solid bed, the heat storage medium can be discharged downwards from the container. Since the heat storage medium is discharged from the container again after the container has been filled, it can be used to charge the next container of the energy storage system.

[0025] In a preferred embodiment, the heat storage medium can therefore be introduced from the first container into a second container to initiate a storage process in the second container. The second container is loaded at a time corresponding to the loading process described for the first container. Thus, a plurality of containers can be filled one after the other, with the same heat storage medium being used for each container. As a result, a relatively small volume of heat storage medium is required to store thermal energy in a large volume.

[0026] In a preferred embodiment, the heat storage medium can remain in the container last charged with thermal energy after storage. Emptying of the container is therefore not necessary, and the container can be kept in a standby mode, so to speak. In a preferred embodiment, for withdrawing thermal energy from a first container, heat storage medium can be introduced into the container from below until the heat storage medium reaches an outlet opening arranged at the top of the container, so that hot heat storage medium is discharged from the container from above. For withdrawing thermal energy, cold heat storage medium is in particular introduced into the container from below. This enables the withdrawal process to begin immediately.It is advantageous to maintain an appropriate temperature gradient, since a heated energy storage device is filled with a cool medium. Thus, the temperature difference between the introduced heat storage medium and the heated energy storage device should not be too great. In one possible embodiment, a certain amount of heat storage medium can be kept at the bottom of the container. Additionally or alternatively, a medium-temperature heat storage medium can be introduced from below at the beginning of the discharge process.

[0027] In a preferred embodiment, the heat storage medium can be supplied evenly and with low turbulence. This ensures, in particular, that temperature stratification is maintained within the container. After the heat storage medium has been supplied from above as a low-turbulence inflow, the heated heat storage medium is discharged upwards out of the container. This allows energy to be stored from the container.

[0028] In a preferred embodiment, after thermal energy has been extracted from the solid bed, the heat storage medium can be discharged downwards from the container. The heat storage medium can therefore be used to extract heat from another container.

[0029] In a preferred embodiment, the heat storage medium can be introduced from the first container into a second container to initiate a storage removal process in the second container. The process for removing energy from the second container can be carried out as described with respect to the first container. Thus, several containers of the energy storage device can be discharged consecutively, requiring only a small amount of heat storage medium.

[0030] In a preferred embodiment, venting can occur between the containers during storage and / or withdrawal between the containers and / or with at least one intermediate storage device. In particular, when the container is filled from below with cold heat storage medium during storage, volume compensation or venting may be necessary. Likewise, during storage, when the heat storage medium is discharged downwards after thermal storage has taken place, volume compensation or venting may be necessary. During withdrawal, volume compensation or venting may be necessary if the container is filled from below with heat storage medium. Likewise, volume compensation or venting may be necessary when the heat storage medium is discharged downwards after thermal withdrawal has taken place.

[0031] For example, a protective gas can be used for ventilation or venting and / or volume equalization. Nitrogen can be used in particular to avoid oxidative effects on the heat storage medium or the other structural components. Alternatively or additionally, a gas phase can be formed by a portion of evaporated heat storage medium. This gas phase can be removed from the respective container. In one embodiment, volume equalization can take place, for example, between the containers, the containers being connected in particular by lines. In a further embodiment, alternatively or additionally, an equalization container or a storage container can be provided which can temporarily store the heat storage medium. In this way, for example, an overpressure or underpressure of a protective gas can be enabled, which exists depending on the state of the energy storage device.Thus, a closed system can be in a charged or discharged state, whereby the protective gas is either in positive pressure or negative pressure.

[0032] In a preferred embodiment, at least one container can be only partially thermally charged, with an upper part of the solid bed exhibiting a higher temperature than a lower part of the solid bed, and the container not having a heat storage medium. Convective compensation losses can be limited by such stratification. In such a state, the heat storage medium is discharged from the container, in particular downwards.

[0033] The invention further relates to a thermal energy storage device. The thermal energy storage device can be used in particular to implement the method according to the invention. Accordingly, the same features and advantages apply to the thermal energy storage device as described with regard to the method. In a preferred embodiment of the thermal energy storage device, the containers can have an inflow area which is filled with a minimum fill level of heat storage medium and / or comprise a mixing area in which a temperature transition of the heat storage medium from cold to hot is made possible. This can in particular prevent unwanted temperature stresses from forming within the container.

[0034] In a preferred embodiment, a separating device can be provided in an outflow region of at least one container, which enables a separation between a liquid phase and a gaseous phase. For example, a line can be provided in an upper region of the container, which branched off in such a way that the liquid phase can be discharged via one branch and the gaseous phase via the other branch. Appropriate valves can be used here, which are installed in the lines. For example, a subsystem for controlling the supply and discharge of protective gas can be provided, which subsystem has, for example, at least one compressor or one blower, a line system and at least one compensation tank.

[0035] The containers preferably have thermal insulation to limit heat losses.

[0036] In a preferred embodiment, the at least two containers can be connected in a respective lower region via a first line system so that cold heat storage medium can be introduced into the containers one after the other from below, and / or in a respective upper region via a second line system so that hot heat storage medium can be introduced or removed, wherein a connection to an intermediate storage device is formed in particular in the upper region. Valves can be provided in the corresponding line systems to enable or prevent an inflow or outflow to the respective container. Furthermore, at least one pump can be provided to enable the flow of the heat storage medium. Furthermore, a heat exchanger can be provided.

[0037] The above embodiments and developments can be combined with one another as desired, where appropriate. Further possible embodiments, developments, and implementations of the invention also include combinations of features of the invention not explicitly mentioned above or described below with respect to the exemplary embodiments. In particular, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention.

[0038] TABLE OF CONTENTS OF THE DRAWING

[0039] The present invention is explained in more detail below with reference to the exemplary embodiments shown in the schematic figures of the drawing. In the drawings:

[0040] Fig. 1 shows an embodiment of a container;

[0041] Fig. 2 shows a further embodiment of a container;

[0042] Fig. 3 a container with a possible temperature distribution;

[0043] Fig. 4 shows a possible heat flow when loading a container; Fig. 5 shows a possible heat flow when unloading a container;

[0044] Fig. 6 shows a possible embodiment of a thermal energy storage device.

[0045] The accompanying drawing figures are intended to provide a further understanding of embodiments of the invention. They illustrate embodiments and, in conjunction with the description, serve to explain principles and concepts of the invention. Other embodiments and many of the noted advantages will be apparent upon reference to the drawings. Elements of the drawings are not necessarily shown to scale.

[0046] In the figures of the drawing, identical, functionally identical and acting elements, features and components are provided with the same reference symbols unless otherwise stated.

[0047] Fig. 1 shows an embodiment of a container 1. The container 1 is part of a thermal energy storage device 7, as described for example in Figure 6. The container 1 is accordingly designed as a partial storage device of the energy storage device 7 and filled with a solid bed 2. Preferably, the container 1 is essentially completely filled with the solid bed 2. In the lower region of the container 1, a line 8 is shown, through which the container 1 can be filled. In the upper region of the container 1, an outlet opening 5 is provided so that an outflow region 10 can be formed. This can also be connected to a line 8. By way of example, a fill level 4 is shown in the middle region of the container 1, which shows the fill level of a heat storage medium 3.The container 1 can be filled with or emptied of heat storage medium 3 via the openings in the upper and lower regions. This allows thermal energy to be stored in or released from the container 1.

[0048] Fig. 2 shows a further embodiment of a container 1. In the upper region of the container 1, a line 8 can be seen which splits into two partial lines. This makes it possible to form a separating device 11 so that a liquid phase 12 and a gaseous phase 13 can be discharged from the container 1 via different partial lines. This can be used in particular for ventilation or venting and volume equalization if, for example, a protective gas is used. During storage or withdrawal, venting or ventilation in or out of the container 1 can be made possible. An inflow area 9 is provided in the lower region of the container 1. The illustration shows a minimum fill level 4 in the container 1, the heat storage medium 3 only being present in the lower region of the container 1. This can represent a state as it exists before storage or withdrawal.may be present before saving.

[0049] Fig. 3 shows a container 1 with a possible temperature distribution T. The temperature distribution T is shown from a lower region L to an upper region H of the container 1 in the schematic diagram shown. In the lower region of the container 1 there is a lower temperature than in an upper region of the container 1. The entire container 1 can be filled with the solid fill 2. By means of targeted loading, for example, a mixing region can be created, shown with the dashed line inside the container 1, in which mixing region a gradual temperature transition of the heat storage medium 3 from cold to hot temperatures is made possible. Consequently, even when the heat storage medium 3 is discharged from the container 1, the solid fill 2 can have the temperature gradient shown. Consequently, temperature-stratified storage and withdrawal can be implemented using the heat storage medium 3.

[0050] Fig. 4 shows a possible heat flow when loading a container 1. The fill level 4 of the heat storage medium 3 is first raised to the upper region of the container 1. Then warm heat storage medium or hot heat storage medium is filled into the container from above. This can generate a heat flow Q, with the container initially heating up more strongly from an upper region H. Then the fill level 4 can be reached, as in the right-hand area of ​​the illustration, by lowering the level. The heat storage medium 3 can in particular be released downwards from the container 1.

[0051] Fig. 5 shows a possible heat flow when discharging a container 1. The container 1 is first filled from below with heat storage medium 3 until the heat storage medium 3 reaches an upper region H of the container 1, and heated heat storage medium 3 can be removed from an upper region of the container 1. When the heated heat storage medium 3 is removed from the upper region H of the container 1, a heat flow Q is generated in the direction of the upper region H, as shown by the direction of the arrow. The interior of the container 1 is cooled in the process. After the discharging process is complete, the heat storage medium is removed downwards, whereby the fill level 4 can be reached as on the right-hand side of the illustration.

[0052] Fig. 6 shows a possible embodiment of a thermal energy storage device 7. In this embodiment, the thermal energy storage device 7 has four containers 1a to 1d. The containers 1a to 1d are connected in the lower region via a first line system 8a. In the upper region, the containers are connected via a second line system 8b. This makes it possible to create a so-called cold branch which essentially connects the containers 1 to one another at the bottom, and a hot branch which essentially connects the containers 1 to one another at the top. Various valves can be provided in the lines 8 in order to enable the heat storage medium 3 to flow into and out of the containers 1. Furthermore, the valves can enable the supply and discharge of protective gas in order to implement ventilation or venting.

[0053] In the upper region 15 of Fig. 6, the line system 8b is exposed to a high temperature. The lines 8b lead to an intermediate storage tank 6b, which can be provided as a compensation tank for protective gas handling. For example, at least one compressor or one fan can be provided in the upper region.

[0054] In the lower area 14 of Fig. 6, the pipe system 8a is subjected to a low temperature. In the lower area, a type of sub-system for filling or emptying with heat storage medium can be implemented. For this purpose, a pump 16 can be provided, with which the heat storage medium 3 can be conveyed. In this way, the heat storage medium 3 can be conveyed from a first container 1a to a second container 1b and then to a third container 1c and a fourth container 1d. In the left-hand area of ​​the illustration in Fig. 6, a further intermediate storage device 6a is shown, which in one embodiment can be implemented in the form of a volume compensation system for the heat storage medium 3. This intermediate storage device 6a can also be connected to the pipe system 8a via a pump.

[0055] The right-hand section of Fig. 6 shows a possibility for storing or withdrawing thermal energy from or into the system or the thermal energy storage device 7. In the illustrated embodiment, a pump 16 and a heat exchanger are provided. The hot heat storage medium 3 can be fed to the heat exchanger via lines 8a and 8b and discharged from or introduced into the system.

[0056] Although the present invention has been fully described above using preferred embodiments, it is not limited thereto, but can be modified in a variety of ways. In particular, the number of containers 1 of a thermal energy storage device 7 can differ from the embodiment shown in Fig. 7. For example, only two containers or more than four containers, in particular four to 10 containers, can be provided.

Claims

Patent claims 1. A method for thermal energy storage with at least two containers (1), each filled with a solid bed (2), wherein a heat storage medium (3) for storing and / or discharging thermal energy is introduced into the containers (1) one after the other and / or removed from the containers (1), wherein a temperature-stratified temperature storage takes place via the solid bed (2) in the respective container (1), and the heat storage medium (3) is used for heat transfer processes during storage and / or discharging.

2. Method according to claim 1, characterized in that for a temperature-stratified storage of thermal energy in a first container (la), heat storage medium (3) is introduced into the container (la) from below up to a certain fill level (4), and then hot heat storage medium (3) is introduced into the container (la) from above.

3. Method according to claim 2, characterized in that the supply of the hot heat storage medium (3) is carried out evenly and with little turbulence.

4. Method according to one of the preceding claims, characterized in that after thermal energy has been stored in the solid bed (2), the heat storage medium (3) is discharged downwards from the container (1a).

5. Method according to one of the preceding claims, characterized in that the heat storage medium (3) is introduced from the first container (1a) into a second container (1b) in order to start a process for storage in the second container (1b).

6. Method according to one of the preceding claims, characterized in that the heat storage medium (3) remains after storage in the container (1) last loaded with thermal energy.

7. Method according to one of the preceding claims, characterized in that for the storage of thermal energy from a first container (la), heat storage medium (3) is introduced into the container (la) from below until the heat storage medium (3) reaches an outlet opening (5) arranged at the top of the container (la), so that hot heat storage medium (3) is discharged from the top of the container (la).

8. Method according to claim 7, characterized in that the supply of the heat storage medium (3) is uniform and low-turbulence.

9. Method according to one of the preceding claims, characterized in that after thermal energy has been stored out of the solid bed (2), the heat storage medium (3) is discharged downwards from the container (1a).

10. Method according to one of the preceding claims, characterized in that the heat storage medium (3) is introduced from the first container (1a) into a second container (1b) in order to start a process for discharging it into the second container (1b).

11. Method according to one of the preceding claims, characterized in that during the storage and / or the withdrawal, venting takes place between the containers (1a, 1b) among themselves and / or with at least one intermediate storage device (6).

12. Method according to one of the preceding claims, characterized in that at least one container (1a, 1b) is only partially thermally charged, an upper part of the solid bed (2) having a higher temperature than a lower part of the solid bed (2), and the container (1a, 1b) has no heat storage medium (3).

13. Thermal energy storage device (7), in particular for carrying out a method according to one of the preceding claims, with at least two containers (1a, 1b), each filled with a solid bed (2), wherein the containers (1a, 1b) are connected via at least one line (8) in such a way that a heat storage medium (3) for storing and / or discharging thermal energy can be introduced into and discharged from the containers (la, 1b) one after the other, whereby temperature storage takes place via the solid bed (2).

14. Thermal energy storage device (7) according to claim 13, characterized in that the containers (1a, 1b) have an inflow area (9) which is filled with a minimum filling level of heat storage medium (3) and / or comprise a mixing area in which a temperature transition of the heat storage medium from cold to hot is made possible.

15. Thermal energy storage device (7) according to claim 13 or 14, characterized in that a separating device (11) is provided in an outflow region (10) of at least one container (1a, 1b), which enables a separation between a liquid phase (12) and a gaseous phase (13).

16. Thermal energy store (7) according to one of claims 13 to 15, characterized in that the at least two containers (1a, 1b) are connected in a respective lower region via a first line system (8a) so that cold heat storage medium (3) can be introduced into the containers (1a, 1b) one after the other from below, and / or are connected in a respective upper region via a second line system (8b) so that hot heat storage medium (3) can be introduced or removed, wherein in particular in the upper region a connection to an intermediate storage (6) is formed.

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