Methods for thermal energy storage and thermal energy storage

Abstract

The present invention relates to a method for thermal energy storage with at least two containers, each filled with a bed of solids, wherein a heat storage medium for storing and / or releasing thermal energy is successively introduced into and / or removed from the containers, wherein temperature-stratified storage occurs via the bed of solids in the respective container, and the heat storage medium serves for heat transfer processes during storage and / or release. The present invention further relates to a corresponding thermal energy storage device.

Description

[0001] The present invention relates to a method for thermal energy storage using at least two containers, each filled with a solid bed. Furthermore, the invention relates to a thermal energy storage device.

[0002] Energy storage is advantageous for compensating for fluctuating electrical generation and consumption. Especially when using a variety of renewable energies, energy storage and provision represent an important building block for the energy transition in the face of climate change.

[0003] 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.

[0004] 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. Unlike water-based energy storage systems, saturated steam-induced internal pressure can be eliminated.

[0005] Temperature stratification can prevent, in particular, a loss of mixing or "exergy loss." Furthermore, a comparatively long extraction period at a high temperature level can be ensured if the energy storage system is appropriately charged and discharged.

[0006] To supply energy to the energy storage unit, it is charged. It is known from the prior art to introduce thermal oil from the top of the energy storage unit, allowing hot thermal oil to flow through it 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.

[0007] Since thermal oil is expensive, a cost-effective solid bed, 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 bed accounts for 60% to 70% of the volume and can provide approximately 60% to 80% of the heat capacity.

[0008] The costs for thermal oil are many times higher than those for the solid bed, for example, 10 to 20 times higher, especially for the same heat capacity. Therefore, it is desirable to further reduce the thermal oil requirement. In particular, this should continue to enable temperature stratification of the energy storage system.

[0009] Against this background, the present invention is based on the object of providing 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. Accordingly, it is provided:

[0011] 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 serves for heat transfer processes during storage and / or discharging.

[0012] A thermal energy storage device, in particular for carrying out a method according to the invention, with at least two containers, each filled with a bed of solid material, wherein the containers are connected via at least one line in such a way that a heat storage medium for storing and / or discharging thermal energy can be introduced into and discharged from the containers one after the other, wherein temperature storage takes place via the bed of solid material.

[0013] The finding underlying the present invention is to enable thermal energy storage, whereby the energy storage task can essentially be performed 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 sequentially. 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, thermal oil.

[0015] The entire thermal energy storage system is divided into at least two containers, which can be filled with the heat storage medium one after the other. This means that the respective volume of each container is small relative to the total energy storage system. 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 system. According to the invention, costs can be significantly reduced, since the costs for the heat storage medium, in particular, 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] Stratified temperature storage is understood to mean, in particular, that each container has a temperature gradient from an upper area to a lower area. In particular, the storage medium, such as the solid bed, has a higher temperature in an upper area of ​​the container than in a lower area.

[0020] Advantageous embodiments and further developments emerge from the further subclaims and from the description with reference to the figures of the drawing.

[0021] Before energy is stored, each container is at a low temperature level and, in particular, does not contain a significant amount of heat storage medium.

[0022] 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.

[0023] 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.

[0024] In a preferred embodiment, the hot heat storage medium can therefore be supplied evenly and with minimal turbulence. The supply occurs, in particular, from above into the container. This is particularly advantageous for achieving temperature stratification within the container.

[0025] This allows for temperature-controlled storage, with the tank being filled with the solid bulk material and the heat storage medium. The interior of the tank has a higher temperature, particularly in the upper area, than in the lower area.

[0026] 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.

[0027] In a preferred embodiment, the heat storage medium can therefore be transferred from the first container into a second container to initiate a storage process in the second container. The loading time for the second container corresponds to the loading process described for the first container. Thus, a plurality of containers can be filled consecutively, with the same heat storage medium being used for each container. This requires a relatively small volume of heat storage medium to store thermal energy in a large volume.

[0028] In a preferred embodiment, the heat storage medium can remain in the container last charged with thermal energy after storage. Emptying the container is therefore unnecessary, and the container can be kept in a sort of standby mode.

[0029] In a preferred embodiment, for the storage of 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, such that hot heat storage medium is discharged from the top of the container. For the storage of thermal energy, in particular cold heat storage medium is introduced into the container from below. This enables the storage process to begin immediately. It is advantageous if an appropriate temperature gradient is maintained, since a heated energy storage device is filled with cool medium. The temperature difference between the introduced heat storage medium and the heated energy storage device should therefore not be selected to 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, medium temperature heat storage medium can be introduced from below at the beginning of the discharge process.

[0030] 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 is 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.

[0031] In a preferred embodiment, after thermal energy has been stored from the solid bed, the heat storage medium can be discharged downwards out of the container.

[0032] The heat storage medium can therefore be used to store another container.

[0033] In a preferred embodiment, the heat storage medium can be transferred from the first container to a second container to initiate a storage removal process in the second container. The process for removing heat from the second container can be carried out as described for the first container. Thus, multiple containers of the energy storage device can be discharged consecutively, requiring only a small amount of heat storage medium.

[0034] 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 equalization or venting may be necessary. Likewise, during storage, when the heat storage medium is discharged downwards after thermal storage has taken place. During withdrawal, volume equalization or venting may be necessary if the container is filled from below with heat storage medium. Likewise, volume equalization or venting may be necessary when the heat storage medium is discharged downwards after thermal withdrawal has taken place.

[0035] For example, a protective gas can be used for ventilation or venting and / or volume equalization. Nitrogen can be used in particular to prevent 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 discharged from the respective container. In one embodiment, volume equalization can take place, for example, between the containers, wherein the containers are 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 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.For example, a closed system can be in a charged or discharged state, meaning that the protective gas is either under positive pressure or under negative pressure.

[0036] 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, particularly downwards.

[0037] 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.

[0038] In a preferred embodiment of the thermal energy storage device, the containers can have an inflow area filled with a minimum amount of heat storage medium and / or a mixing area in which a temperature transition of the heat storage medium from cold to hot is enabled. This can, in particular, prevent unwanted thermal stresses from developing within the container.

[0039] 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 branches out 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.

[0040] The containers preferably have thermal insulation to limit heat loss.

[0041] 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 connected 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 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.

[0042] The above embodiments and further developments can be combined with one another as desired, where appropriate. Further possible embodiments, further developments, and implementations of the invention also include combinations of features of the invention not explicitly mentioned above or described below with regard to the exemplary embodiments. In particular, those skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the present invention. TABLE OF CONTENTS OF THE DRAWING

[0043] The present invention will be explained in more detail below with reference to the exemplary embodiments shown in the schematic figures of the drawing. In the drawings: Fig. 1 an embodiment of a container; Fig. 2 shows a further embodiment of a container; Fig. 3 a container with a possible temperature distribution; Fig. 4 a possible heat flow when loading a container; Fig. 5 a possible heat flow when unloading a container; Fig. 6 a possible embodiment of a thermal energy storage device.

[0044] 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 become apparent upon review of the drawings. Elements of the drawings are not necessarily shown to scale relative to one another.

[0045] 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.

[0046] Fig. 1 shows an embodiment of a container 1. The container 1 is part of a thermal energy storage device 7, such as in Fig. 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 can therefore be filled with the heat storage medium 3 or emptied of heat storage medium 3 via the openings in the upper and lower regions of the container 1. This allows thermal energy to be stored in or released from the container 1.

[0047] In 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 sub-lines. This can create a separating device 11 so that a liquid phase 12 and a gaseous phase 13 can be discharged from the container 1 via different sub-lines. This can be used in particular for ventilation or venting and volume equalization, for example when a protective gas is used. During storage or withdrawal, venting or ventilation can be enabled in or out of the container 1. 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, with the heat storage medium 3 only being present in the lower region of the container 1. This can represent a state that may exist before storage or withdrawal.

[0048] 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, the temperature is lower than in an upper region of the container 1. The entire container 1 can be filled with the solid bed 2. Through targeted loading, for example, a mixing zone can be created, shown by the dashed line inside the container 1, in which a gradual temperature transition of the heat storage medium 3 from cold to hot temperatures is enabled. Consequently, even when the heat storage medium 3 is discharged from the container 1, the solid bed 2 can have the temperature gradient shown. Consequently, temperature-stratified storage and withdrawal can be implemented using the heat storage medium 3.

[0049] Fig. Figure 4 shows a possible heat flow when filling a container 1. The fill level 4 of the heat storage medium 3 is initially raised to the upper region of the container 1. Warm heat storage medium or hot heat storage medium is then poured into the container from above. This generates a heat flow Q, with the container initially heating up more strongly from an upper region H. Fill level 4 can then be reached, as shown in the right-hand area of ​​the diagram, by lowering the level. The heat storage medium 3 can be released downwards from the container 1, in particular.

[0050] In Fig. 5 shows a possible heat flow during the unloading of 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 a removal of heated heat storage medium 3 from an upper region of the container 1 can take place. 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 discharge process is completed, the heat storage medium is removed downwards, whereby the fill level 4 can be reached as on the right-hand side of the illustration.

[0051] 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 that essentially connects the containers 1 to one another at the bottom, and a hot branch that essentially connects the containers 1 to one another at the top. Various valves can be provided in the lines 8 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 to implement ventilation or venting.

[0052] In the upper area 15 of the Fig. 6, the line system 8b is subjected to a high temperature. The lines 8b lead to an intermediate storage tank 6b, which can be provided as an equalizing tank for protective gas handling. In the upper area, for example, at least one compressor or fan can be provided.

[0053] In the lower area 14 of the Fig. 6, the pipe system 8a is subjected to a low temperature. In the lower area, a type of subsystem 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. This allows the heat storage medium 3 to be conveyed from a first container 1a to a second container 1b and subsequently to a third container 1c and a fourth container 1d. In the left area of ​​the illustration of the Fig. 6 shows a further intermediate storage unit 6a, which in one embodiment can be implemented as a volume equalization system for the heat storage medium 3. This intermediate storage unit 6a can also be connected to the pipe system 8a via a pump.

[0054] In the right area of ​​the Fig. Figure 6 shows a possibility for storing or discharging 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.

[0055] Although the present invention has been fully described above with reference to preferred embodiments, it is not limited thereto, but can be modified in many ways. In particular, the number of containers 1 of a thermal energy storage device 7 can be varied from the illustrated embodiment in Fig. 6. For example, only two containers or more than four containers, in particular four to 10 containers, may be provided.

Claims

[1] 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 successively introduced into the containers (1) 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 by that for a temperature-stratified storage of thermal energy in a first container (1a), heat storage medium (3) is introduced into the container (1a) from below up to a certain fill level (4), and then hot heat storage medium (3) is introduced into the container (1a) from above. [3] Method according to claim 2, characterized bythat the supply of the hot heat storage medium (3) is uniform and low in turbulence. [4] Method according to one of the preceding claims, characterized by that after thermal energy has been stored in the solid bed (2), the heat storage medium (3) is discharged downwards out of the container (1a). [5] Method according to one of the preceding claims, characterized by 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 by 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 byin that, for the purpose of discharging thermal energy from a first container (1a), heat storage medium (3) is introduced into the container (1a) from below until the heat storage medium (3) reaches an outlet opening (5) arranged at the top of the container (1a), so that hot heat storage medium (3) is discharged from the top of the container (1a). [8] Method according to claim 7, characterized by that the supply of the heat storage medium (3) is uniform and low-turbulence. [9] Method according to one of the preceding claims, characterized by that after thermal energy has been stored out of the solid bed (2), the heat storage medium (3) is discharged downwards out of the container (1a). [10] Method according to one of the preceding claims, characterized by 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 by that during the storage and / or 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 by that at least one container (1a, 1b) is only partially thermally charged, wherein an upper part of the solid bed (2) has 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 bulk material (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 removed from the containers (1a, 1b) one after the other, wherein temperature storage takes place via the solid bed (2). [14] Thermal energy storage device (7) according to claim 13, characterized by 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 by 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 storage device (7) according to one of claims 13 to 15, characterized by 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 device (6) is formed.

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