阅读说明：本技术 温跃层控制方法 (Thermocline control method ) 是由 卢卡斯·盖斯布勒 安德烈亚斯·克里斯蒂安·哈塞尔巴赫 于 2019-07-25 设计创作，主要内容包括：本发明提供了操作包括传热流体本体的热能储存装置的方法,所述传热流体本体包括高温区域、低温区域和温跃层区域,所述高温区域包括温度高于上阈值温度的传热流体,所述低温区域包括温度低于下阈值温度的传热流体,所述温跃层区域将高温区域和低温区域分开并且包括温度高于下阈值温度且低于上阈值温度的传热流体,其中在热能储存装置的储热期间,从传热流体本体的温跃层区域移出传热流体,并且当从传热流体本体的温跃层区域移出的传热流体的温度上升至高于最高温度时,使被移出的所述传热流体达到等于或低于所述最高温度的温度,其中最高温度高于下阈值温度,和/或其中在热能储存装置的减热期间,从传热流体本体的温跃层区域移出传热流体,并且当从传热流体本体的温跃层区域移出的传热流体的温度下降至低于最低温度时,使被移出的所述传热流体达到等于或高于所述最低温度的温度,其中最低温度低于上阈值温度。(The invention provides a method of operating a thermal energy storage device comprising a body of heat transfer fluid comprising a high temperature zone, a low temperature zone and a thermocline zone, the high temperature zone comprising a heat transfer fluid having a temperature above an upper threshold temperature, the low temperature zone comprising a heat transfer fluid having a temperature below a lower threshold temperature, the thermocline zone separating the high and low temperature zones and comprising a heat transfer fluid having a temperature above the lower threshold temperature and below the upper threshold temperature, wherein during thermal storage of the thermal energy storage device, the heat transfer fluid is removed from the thermocline zone of the body of heat transfer fluid, and when the temperature of the heat transfer fluid removed from the thermocline zone of the body of heat transfer fluid rises above a maximum temperature, the heat transfer fluid removed is brought to a temperature equal to or below the maximum temperature, wherein the maximum temperature is above the lower threshold temperature, and/or wherein during desuperheating of the thermal energy storage device, heat transfer fluid is removed from the thermocline region of the body of heat transfer fluid, and when the temperature of the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid falls below a minimum temperature, the heat transfer fluid removed is brought to a temperature equal to or higher than the minimum temperature, wherein the minimum temperature is below an upper threshold temperature.)

1. A method of operating a thermal energy storage device comprising a body of heat transfer fluid comprising a high temperature region comprising heat transfer fluid at a temperature above an upper threshold temperature, a low temperature region comprising heat transfer fluid at a temperature below a lower threshold temperature, and a thermocline region separating the high and low temperature regions and comprising heat transfer fluid at a temperature above the lower threshold temperature and below the upper threshold temperature,

wherein during heat storage of the thermal energy storage device, heat transfer fluid is removed from the thermocline region of the body of heat transfer fluid, and when the temperature of heat transfer fluid removed from the thermocline region of the body of heat transfer fluid rises above a maximum temperature, the heat transfer fluid removed is brought to a temperature equal to or below the maximum temperature by combining the heat transfer fluid removed and having a temperature above the maximum temperature with a heat transfer fluid having a temperature below the lower threshold temperature, wherein the heat transfer fluid having a temperature below the lower threshold temperature originates from the low temperature region of the body of heat transfer fluid, wherein the maximum temperature is above the lower threshold temperature, and/or

Wherein during desuperheating of the thermal energy storage device, heat transfer fluid is removed from the thermocline region of the body of heat transfer fluid, and when the temperature of heat transfer fluid removed from the thermocline region of the body of heat transfer fluid drops below a minimum temperature, the heat transfer fluid removed is brought to a temperature equal to or above the minimum temperature by combining the heat transfer fluid removed, preferably having a temperature below the minimum temperature, with heat transfer fluid having a temperature above the upper threshold temperature, wherein the heat transfer fluid originates from the high temperature region of the body of heat transfer fluid, wherein the minimum temperature is below the upper threshold temperature.

2. A method of operating a thermal energy storage apparatus comprising a body of heat transfer fluid according to claim 13,

wherein during heat storage of the thermal energy storage device, the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature above the maximum temperature is brought to a temperature equal to or below the maximum temperature by combining the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature below the lower threshold temperature, by adjusting the flow rate of any heat transfer fluid that is combined, and/or

Wherein during desuperheating of the thermal energy storage device, by combining a heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature below a minimum temperature with a heat transfer fluid having a temperature above the upper threshold temperature, the removed heat transfer fluid is brought to a temperature equal to or above the minimum temperature by adjusting the flow rate of any heat transfer fluid that is combined.

3. A method of operating a thermal energy storage apparatus comprising a body of heat transfer fluid according to claim 1 or 2,

wherein during heat storage of the thermal energy storage device, the flow rate of heat transfer fluid removed from the low temperature region having a temperature below the lower threshold temperature is less than the flow rate of heat transfer fluid added to the high temperature region having a temperature above an upper threshold temperature, and/or

Wherein during desuperheating of the thermal energy storage device, the flow rate of heat transfer fluid removed from the high temperature zone having a temperature above the upper threshold temperature is less than the flow rate of heat transfer fluid added to the low temperature zone having a temperature below a lower threshold temperature.

4. A method of operating a thermal energy storage apparatus comprising a body of heat transfer fluid according to any preceding claim,

wherein during thermal storage of the thermal energy storage device, a heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature above a maximum temperature is brought to a first set point temperature at or below the maximum temperature and then to a second set point temperature at or below the maximum temperature, provided that the first set point temperature and the second set point temperature are different, and/or

Wherein during desuperheating of the thermal energy storage device, a heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature below a minimum temperature is brought to a first set point temperature equal to or above the minimum temperature and then to a second set point temperature equal to or above the minimum temperature, provided that the first set point temperature and the second set point temperature are different.

5. A method of operating a thermal energy storage apparatus comprising a body of heat transfer fluid according to any preceding claim,

wherein during heat storage of the thermal energy storage device, a heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature above a maximum temperature is brought to a temperature at or below the maximum temperature and is maintained at the temperature at or below the maximum temperature, and/or

Wherein during desuperheating of the thermal energy storage device, a heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature below a minimum temperature is brought to a temperature equal to or above the minimum temperature and maintained at the temperature equal to or above the minimum temperature.

6. A method of operating a thermal energy storage apparatus comprising a body of heat transfer fluid according to any preceding claim,

wherein during heat storage of the thermal energy storage device heat transfer fluid is removed from the thermocline region of the body of heat transfer fluid, the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid is brought to a temperature equal to or below a maximum temperature when the temperature of the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid rises above the maximum temperature, wherein the maximum temperature is above the lower threshold temperature, and wherein during heat storage the process is subsequently repeated one or more times, preferably subsequently repeated one or more times until the heat transfer fluid at a temperature below the lower threshold temperature is substantially depleted, and/or

Wherein during desuperheating of the thermal energy storage device, heat transfer fluid is removed from the thermocline region of the body of heat transfer fluid, and when the temperature of heat transfer fluid removed from the thermocline region of the body of heat transfer fluid drops below a minimum temperature, the heat transfer fluid removed is brought to a temperature equal to or above the minimum temperature, wherein the minimum temperature is below the upper threshold temperature, and wherein during desuperheating the process is subsequently repeated one or more times, preferably subsequently repeated one or more times until heat transfer fluid at a temperature above the upper threshold temperature is substantially depleted.

7. A method of operating a thermal energy storage device comprising a body of heat transfer fluid according to any preceding claim, wherein the heat transfer fluid is a fluid in a gaseous, liquid or supercritical state.

8. A method of operating a thermal energy storage apparatus according to any preceding claim wherein the thermal energy storage is thermally connected to the following system to allow exchange of thermal energy:

the system is capable of at least partially converting thermal energy contained in a heat transfer fluid at a temperature equal to or lower than a maximum outflow temperature during heat storage and/or a heat transfer fluid at a temperature equal to or higher than a minimum outflow temperature during heat reduction into another form of energy, preferably the system is capable of converting the thermal energy into mechanical or chemical energy, and/or

The system is capable of increasing the thermal energy contained in the heat transfer fluid at a temperature equal to or lower than the highest outflow temperature during heat storage and/or reducing the thermal energy contained in the heat transfer fluid at a temperature equal to or higher than the lowest outflow temperature during heat reduction.

9. A method of operating a thermal energy storage apparatus comprising a body of heat transfer fluid according to any preceding claim,

wherein during heat storage of said thermal energy storage device, a heat transfer fluid removed from said body of heat transfer fluid at a temperature above said maximum temperature is brought to a temperature at or below said maximum temperature, and/or

Wherein during desuperheating of the thermal energy storage device, a heat transfer fluid removed from the body of heat transfer fluid at a temperature below the minimum temperature is brought to a temperature at or above the minimum temperature before being in thermal contact with a system capable of at least partially converting or reducing thermal energy contained in the heat transfer fluid at a temperature at or above the minimum temperature.

10. A thermal energy storage apparatus comprising:

a canister for containing a body of heat transfer fluid, the body of heat transfer fluid comprising a high temperature region comprising heat transfer fluid at a temperature above an upper threshold temperature, a low temperature region comprising heat transfer fluid at a temperature below a lower threshold temperature, and a thermocline region separating the high and low temperature regions and comprising heat transfer fluid at a temperature above the lower threshold temperature and below the upper threshold temperature,

the tank comprising at least one upper opening for adding heat transfer fluid having a temperature above an upper threshold temperature to a region of the tank corresponding to the high temperature region of the body of heat transfer fluid during heat storage and for removing heat transfer fluid having a temperature above an upper threshold temperature from a region of the tank corresponding to the high temperature region of the body of heat transfer fluid during desuperheating,

the tank comprising at least one lower opening for removing heat transfer fluid having a temperature below a lower threshold temperature from a region of the tank corresponding to the low temperature region of the body of heat transfer fluid during heat storage and for adding heat transfer fluid having a temperature above a lower threshold temperature to a region of the tank corresponding to the low temperature region of the body of heat transfer fluid during desuperheating,

the tank comprises at least one middle opening for removing heat transfer fluid from a region of the tank corresponding to the thermocline region of the body of heat transfer fluid during heat storage or heat reduction, the at least one middle opening being arranged between the upper opening and the lower opening, and

wherein the thermal energy storage device further comprises a plurality of valves capable of regulating flow through each of the at least one upper opening, the at least one lower opening, and the at least one middle opening during heat storage and heat reduction, and

characterized in that the at least one lower opening and the at least one middle opening are fluidly connected to each other by a conduit to allow heat transfer fluid removed from both the thermocline region and the low temperature region of the body of heat transfer fluid during heat storage to merge at an intersection of the conduit, which is positioned in particular upstream of a heat exchange device or between the at least one lower opening, the at least one middle opening and the heat exchange device,

characterized in that the at least one upper opening and the at least one middle opening are fluidly connected to each other by a conduit to allow heat transfer fluid removed from both the thermocline region and the high temperature region of the body of heat transfer fluid during desuperheating to merge at an intersection of the conduit, the intersection being positioned in particular upstream of a heat exchange device or between the at least one upper opening, the at least one middle opening and a heat exchange device, wherein the thermal energy storage device further comprises a control unit capable of controlling the plurality of valves and configured to control the plurality of valves to perform the method of operating a thermal energy storage device according to any one of claims 1 to 9.

11. A thermal energy storage apparatus comprising:

a plurality of n tanks for containing a body of heat transfer fluid, the body of heat transfer fluid comprising a high temperature zone comprising heat transfer fluid at a temperature above an upper threshold temperature, a low temperature zone comprising heat transfer fluid at a temperature below a lower threshold temperature, and a thermocline zone separating the high and low temperature zones and comprising heat transfer fluid at a temperature above the lower threshold temperature and below the upper threshold temperature,

a first tank comprising at least one upper opening for adding heat transfer fluid having a temperature above an upper threshold temperature to the high temperature region of the body of heat transfer fluid during heat storage and for removing heat transfer fluid having a temperature above an upper threshold temperature from the high temperature region of the body of heat transfer fluid during desuperheating,

a last tank comprising at least one lower opening for removing heat transfer fluid having a temperature below a lower threshold temperature from the low temperature region of the body of heat transfer fluid during heat storage and for adding heat transfer fluid having a temperature below a lower threshold temperature to the low temperature region of the body of heat transfer fluid during desuperheating,

wherein adjacent tanks are fluidly connected to each other by a plurality of n-1 pipes, each of the n-1 pipes fluidly connecting two adjacent tanks,

each of the plurality of n-1 tubes includes at least one central opening for removing heat transfer fluid from the thermocline region of the body of heat transfer fluid during heat storage or heat removal, an

Wherein the thermal energy storage device further comprises a plurality of valves capable of regulating flow through the at least one upper opening of the first tank, the at least one lower opening of the last tank, and each of the intermediate openings during heat storage and desuperheating, and

characterized in that the at least one lower opening and each of the intermediate openings of the last tank are fluidly connected to each other by a conduit to allow heat transfer fluid removed from both the thermocline region and the low temperature region of the body of heat transfer fluid during heat storage to merge at an intersection of the conduits, the intersection being located in particular upstream of a heat exchange device or between the at least one lower opening, the at least one intermediate opening and a heat exchange device,

characterized in that the at least one upper opening and each of the middle openings of the first tank are fluidly connected to each other by a conduit to allow heat transfer fluid removed from both the thermocline region and the high temperature region of the body of heat transfer fluid during desuperheating to merge at an intersection of the conduit, the intersection being positioned in particular upstream of a heat exchange device or between the at least one upper opening, the at least one middle opening and a heat exchange device, wherein the thermal energy storage device further comprises a control unit capable of controlling the plurality of valves and configured to control the plurality of valves to perform the method of operating a thermal energy storage device according to any one of claims 1 to 9.

12. The thermal energy storage device of any one of claims 10 or 11, wherein the thermal energy storage device further comprises,

a pipe capable of bypassing the tank or the plurality n of tanks during heat storage and/or heat reduction, and/or the tank comprises at least two or more than two, three or more than three, or four or more than four central openings for removing heat transfer fluid from the thermocline region of the body of heat transfer fluid during heat storage and/or heat reduction, the central openings being fluidly connected, preferably evenly spaced relative to each other in the flow direction of the heat transfer fluid during heat storage or in a vertical direction.

Technical Field

The present invention relates to a method of operating a thermal storage device comprising a body of heat transfer fluid by controlling the flow of heat transfer fluid from and into upper hot layer, lower cold layer and middle thermocline regions of the heat transfer body during heat storage (charging) and heat reduction (discharging).

Background

The thermal storage device enables schedulable thermal energy from intermittent solar energy which can then be used as required to power a number of useful processes, such as providing electrical power through a heat engine coupled with an electrical generator or providing thermal energy for other applications such as thermochemical hydrocarbon fuel production. Therefore, the heat storage device is expected to play an important role in the future.

Recently, in particular, single tank thermal storage devices, such as those using a packed bed of low cost packing material in combination with a heat transfer fluid, have attracted considerable attention due to their lower cost than two tank systems. While such a device is attractive from a cost perspective, it has several drawbacks such as temperature degradation. Temperature degradation, also referred to as thermocline degradation, refers to the flattening of the temperature gradient in the thermal storage device during operation, i.e. due to successive heat storage-desuperheating cycles. Thermocline degradation has several negative effects. One is that the Heat Transfer Fluid (HTF) exit temperature during heat storage is increased relative to the entry temperature during desuperheating, and the heat transfer fluid exit temperature during desuperheating is decreased relative to the entry temperature during heat storage. However, it is desirable to provide a constant outflow temperature to more efficiently operate equipment that utilizes thermal energy, such as heat engines. Likewise, for efficient operation of the power-generating equipment, it is further desirable to establish steady state as quickly as possible. Another negative effect of thermocline degradation is a limited utilization factor. The greater the width of the thermocline region, the smaller the utilization factor and the greater the specific material cost stored, i.e., the material cost per utilized capacity. Thus, thermocline degradation makes the thermal storage device less efficient and more expensive.

Thus, there is a need to both increase the utilization factor and reduce the width of the thermocline region in a thermal device storage unit, while providing a constant exit temperature quickly so that the equipment utilizing thermal energy operates at maximum efficiency as early as possible.

US 8554377B 2 discloses a method for optimizing a thermocline region in a thermal energy storage fluid within a thermal storage tank. The method relies on withdrawing heat transfer fluid from the tank at a location in the thermocline region, adding thermal energy to the heat transfer fluid withdrawn from the thermocline region using a heat exchanger, and then returning the heat transfer fluid to the tank at a location above the thermocline region. By doing so, the width of the thermocline region is reduced, and the utilization factor is improved.

Disclosure of Invention

The present invention provides a new method of operating a thermal energy storage device by which the thermocline region can be controlled and the storage utilization factor can be further increased. The method also allows increasing the efficiency of a heat engine converting heat from thermal energy storage into mechanical, electrical or chemical energy by providing an effluent that is constantly at a set temperature.

It is an object of the present invention to provide a method of operating a thermal energy storage device comprising a body of heat transfer fluid comprising a high temperature zone comprising heat transfer fluid having a temperature above an upper threshold temperature, a low temperature zone comprising heat transfer fluid having a temperature below a lower threshold temperature, and a thermocline zone separating the high and low temperature zones and comprising heat transfer fluid having a temperature above the lower threshold temperature and below the upper threshold temperature, wherein during thermal storage of the thermal energy storage device heat transfer fluid is removed from the thermocline zone of the body of heat transfer fluid, and when the temperature of heat transfer fluid removed from the thermocline zone of the body of heat transfer fluid rises above a maximum temperature, said heat transfer fluid removed is brought to a temperature equal to or below said maximum temperature, wherein the maximum temperature is above the lower threshold temperature, and/or wherein during desuperheating of the thermal energy storage device, heat transfer fluid is removed from the thermocline region of the body of heat transfer fluid, and when the temperature of the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid falls below a minimum temperature, the heat transfer fluid removed is brought to a temperature equal to or above the minimum temperature, wherein the minimum temperature is below an upper threshold temperature.

In a preferred embodiment, a method of operating a thermal energy storage device comprising a body of heat transfer fluid comprising a high temperature zone comprising the heat transfer fluid at a temperature above an upper threshold temperature, a low temperature zone comprising the heat transfer fluid at a temperature below a lower threshold temperature, and a thermocline zone separating the high and low temperature zones and comprising the heat transfer fluid at a temperature above the lower threshold temperature and below the upper threshold temperature,

wherein during heat storage of the thermal energy storage device, heat transfer fluid is removed from the thermocline region of the body of heat transfer fluid, and when the temperature of the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid rises above a maximum temperature, the heat transfer fluid removed is brought to a temperature equal to or below the maximum temperature by combining the heat transfer fluid removed and having a temperature above the maximum temperature with a heat transfer fluid having a temperature below a lower threshold temperature, the heat transfer fluid having a temperature below the lower threshold temperature originating from the low temperature region of the body of heat transfer fluid, wherein the maximum temperature is above the lower threshold temperature, and/or

Wherein during desuperheating of the thermal energy storage device, heat transfer fluid is removed from the thermocline region of the body of heat transfer fluid, and when the temperature of the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid drops below a minimum temperature, the heat transfer fluid removed is brought to a temperature equal to or above the minimum temperature by combining the heat transfer fluid removed, preferably at a temperature below the minimum temperature, with the heat transfer fluid at a temperature above an upper threshold temperature, the heat transfer fluid at a temperature above the upper threshold temperature originating from a high temperature region of the body of heat transfer fluid, wherein the minimum temperature is below the upper threshold temperature.

It was found that when the above method is performed in the context of a thermal storage device, the thermal stresses experienced by a system thermally related to the thermal storage device (e.g. a thermal engine or a thermo-chemical system) can be more accurately controlled, while also reducing the width of the thermocline in the body of heat transfer fluid to ensure a higher utilization factor of the tank of the thermal storage device.

In one embodiment of the method of operating a thermal energy storage device according to one object of the invention, the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature above the maximum temperature is brought to a temperature equal to or below said maximum temperature during heat storage of the thermal energy storage device by combining the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature above the maximum temperature with the heat transfer fluid having a temperature below the maximum temperature, and/or the heat transfer fluid removed is brought to a temperature equal to or above said minimum temperature during desuperheating of the thermal energy storage device by combining the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature below the minimum temperature with the heat transfer fluid having a temperature above the minimum temperature, i.e. the two heat transfer fluids having different temperatures are mixed in the thermocline region of the body of heat transfer fluid by combining the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature below the minimum temperature Together and the resulting combined heat transfer fluid is in thermal equilibrium to bring the removed heat transfer fluid to a temperature at or above the minimum temperature. Combining the heat transfer fluids may be accomplished by, for example, combining the heat transfer fluids at the intersection between the conduits carrying the respective heat transfer fluids (i.e., at the Y-junction). The swirl generated at the intersection is in most cases sufficient to mix the combined heat transfer fluids, but it will be appreciated that mixing means, such as static mixing elements, may additionally be provided at or downstream of the intersection.

It was found that when the above method is performed in the context of a thermal storage device, the thermal stress experienced by a system thermally associated with the thermal storage device (e.g. a thermal engine or a thermo-chemical system) can be more accurately controlled, while also reducing the width of the thermocline in the body of heat transfer fluid to provide a flow of heat transfer fluid having a predetermined temperature (i.e. a temperature equal to or lower than the maximum temperature), thereby ensuring a higher utilization coefficient of the tank of the thermal storage device.

In one embodiment of the method of operating a thermal energy storage apparatus according to one object of the present invention, during thermal storage of the thermal energy storage device, bringing the heat transfer fluid removed and having a temperature above the maximum temperature to a temperature equal to or below the maximum temperature by combining the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature above the maximum temperature with the heat transfer fluid having a temperature below the maximum temperature, the heat transfer fluid having a temperature below the maximum temperature originates from a low temperature region of the body of heat transfer fluid, and/or during desuperheating of the thermal energy storage device, bringing the removed heat transfer fluid to a temperature equal to or higher than the minimum temperature by combining the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature below the minimum temperature with the heat transfer fluid having a temperature higher than the minimum temperature, the heat transfer fluid having a temperature above the minimum temperature is derived from a high temperature region of the body of heat transfer fluid.

It was found that when the above method is performed in the context of a thermal storage device, the thermal stress to which the thermal storage device comprising a heat transfer fluid and circulating it as a whole is subjected can be more accurately controlled, while also reducing the width of the thermocline in the body of heat transfer fluid to provide a flow of heat transfer fluid having a predetermined temperature (i.e. a temperature equal to or lower than the maximum temperature), thereby ensuring a higher utilization factor of the tank of the thermal storage device, since the flows from the same body of heat transfer fluid are combined without the need to use an external heat transfer fluid.

In one embodiment of the method of operating a thermal energy storage apparatus according to one object of the present invention, during thermal storage of the thermal energy storage device, by combining the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature above the maximum temperature with the heat transfer fluid having a temperature below the maximum temperature, the heat transfer fluid removed and having a temperature above the maximum temperature is brought to a temperature equal to or below said maximum temperature by adjusting the flow rate of any of the heat transfer fluids being combined, and/or during desuperheating of the thermal energy storage device, by combining a heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature below the minimum temperature with a heat transfer fluid having a temperature above the minimum temperature, the removed heat transfer fluid is brought to a temperature equal to or higher than the minimum temperature by adjusting the flow rate of any of the heat transfer fluids being combined.

It was found that when the above method is performed in the case of a thermal storage device, the combined flow of the heat transfer fluid removed from the thermocline and the heat transfer fluid removed from the high-temperature region or the low-temperature region can be brought to a desired temperature by merely adjusting the respective flow rates. It therefore allows both reducing the width of the thermocline during cycling of the thermal storage device and utilizing the heat transfer fluid removed from the thermocline and controlling the temperature of the combined stream to improve the overall efficiency of the thermal storage device and the heat-related system, such as a heat engine.

In one embodiment of the method of operating a thermal energy storage device according to one object of the invention, the heat storage of the thermal energy storage device, the flow of heat transfer fluid removed from low temperature regions having a temperature below the lower threshold temperature is less than the flow of heat transfer fluid added to high temperature regions having a temperature above the upper threshold temperature, and/or the desuperheating of the thermal energy storage device, the flow of heat transfer fluid removed from high temperature regions having a temperature above the upper threshold temperature is less than the flow of heat transfer fluid added to low temperature regions having a temperature below the lower threshold temperature.

It was found that when the above method is performed in the case of a thermal storage device, the width of the thermocline can be further reduced (or the steepness of the thermocline can be increased) because the portion of the thermocline below the opening through which the heat transfer fluid is removed moves slower than the portion above the opening through which the heat transfer fluid is removed.

In one embodiment of the method of operating a thermal energy storage device according to one object of the invention, the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature above the maximum temperature is brought to and maintained at a temperature equal to or below the maximum temperature during heat storage of the thermal energy storage device and/or the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature below the minimum temperature is brought to and maintained at a temperature equal to or above the minimum temperature during desuperheating of the thermal energy storage device.

It was found that when the above method is performed in the context of a thermal storage device, the mechanical strain caused by thermal expansion of the different materials can be reduced at the level of the thermal storage device, in particular at the level of downstream equipment such as pipes. Furthermore, the constant supply of heat transfer fluid with a set temperature increases the efficiency of the system thermally connected to the heat storage device.

In one embodiment of the method of operating a thermal energy storage device according to one object of the invention, the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature above the maximum temperature is brought to a first set point temperature equal to or below the maximum temperature, then to a second set point temperature equal to or below the maximum temperature, provided that the first set point temperature and the second set point temperature are different, during heat storage of the thermal energy storage device, and/or the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid and having a temperature below the minimum temperature is brought to a first set point temperature equal to or above the minimum temperature, then to a second set point temperature equal to or above the minimum temperature, provided that the first set point temperature and the second set point temperature are different, during desuperheating of the thermal energy storage device.

It was found that when the above method is performed in the case of a thermal storage device, because there is a system: it does not depend on a constant temperature but on a specific temperature profile in which, for example, the temperature varies between two set-point temperatures or even three or more set-point temperatures, so that the efficiency of the system thermally connected to the heat storage device can be further improved. It should be understood that in one embodiment, the two set point temperatures may correspond to temperature maxima and minima, respectively, of the oscillating temperature curve.

In one embodiment of the method of operating a thermal energy storage device according to one object of the present invention, the body of heat transfer fluid comprises or essentially consists of a supercritical state or a subcritical state. One example of a subcritical heat transfer fluid is a molten salt commonly used in thermal storage devices. In case the heat transfer fluid is a gas such as an inert gas, nitrogen or air, the utilization factor may be increased by a factor of seven when performing the method according to the invention when compared to performing the method without thermocline control.

In one embodiment of the method of operating a thermal energy storage device according to one object of the present invention, during heat storage of the thermal energy storage device, heat transfer fluid is removed from the thermocline region of the body of heat transfer fluid, and when the temperature of the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid rises above a maximum temperature, said heat transfer fluid removed is brought to a temperature equal to or below said maximum temperature, wherein the maximum temperature is above a lower threshold temperature, and wherein said process is subsequently repeated one or more times during heat storage, preferably subsequently repeated one or more times until the heat transfer fluid having a temperature below the lower threshold temperature is substantially exhausted, and/or during desuperheating of the thermal energy storage device, heat transfer fluid is removed from the thermocline region of the body of heat transfer fluid, and when the temperature of the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid falls below a minimum temperature, bringing the removed heat transfer fluid to a temperature equal to or above the minimum temperature, wherein the minimum temperature is below an upper threshold temperature, and wherein the process is subsequently repeated one or more times during desuperheating, preferably subsequently repeated one or more times until the heat transfer fluid having a temperature above the upper threshold temperature is substantially depleted.

It was found that when the above method is carried out in the case of a thermal storage device, the width of the thermocline can be controlled substantially continuously and thus the utilization factor can be increased even further. Although it is also necessary to increase the number of openings required in the thermal energy storage device in order to subsequently repeat the thermocline width control process as the thermocline moves up and down through the tank of the thermal energy storage device during heat storage and desuperheating, it was found that when the process is performed twice, three times or four times, i.e. subsequently repeated once, twice or three times, the cost increase of more openings is easily justified by the increase in the coefficient.

In one embodiment of the method of operating a thermal energy storage device according to one object of the present invention, the thermal energy storage device is thermally connected to the following system in order to allow the exchange of thermal energy: a system capable of at least partially utilizing and/or converting thermal energy contained in a heat transfer fluid at or below a highest outflow temperature during heat storage and/or a heat transfer fluid at or above a lowest outflow temperature during heat reduction, preferably a system capable of converting thermal energy into mechanical or chemical energy, or into a higher or lower thermal energy state. In one embodiment, the thermal energy storage may be thermally coupled to a system for thermal energy recovery, such as a system for thermal energy recovery in a steel mill or a paper mill. In steel mills, large amounts of energy can be recovered by storing the thermal energy released by the blast furnace or by the hot metal, thereby reducing energy consumption and costs. In one embodiment, the thermal energy storage device may be thermally coupled to a solar collector or solar receiver. During heat storage, the flow resulting from the combination of the heat transfer fluid removed from both the thermocline region and the low temperature region of the body of heat transfer fluid is directed to a solar collector or solar receiver, thereby being brought to a temperature above the upper threshold temperature and returned to the high temperature region of the body of heat transfer fluid in the thermal energy storage device.

It is another object of the present invention to provide a thermal energy storage apparatus comprising a tank for containing a body of heat transfer fluid, the body of heat transfer fluid comprising: a high temperature region containing a heat transfer fluid having a temperature above an upper threshold temperature, a low temperature region containing a heat transfer fluid having a temperature below a lower threshold temperature, and a thermocline region separating the high temperature region from the low temperature region and containing a heat transfer fluid having a temperature above the lower threshold temperature and below the upper threshold temperature, the tank comprising at least one upper opening for adding a heat transfer fluid having a temperature above the upper threshold temperature to a region of the tank corresponding to the high temperature region of the body of heat transfer fluid during heat storage and for removing a heat transfer fluid having a temperature above the upper threshold temperature from a region of the tank corresponding to the high temperature region of the body of heat transfer fluid during desuperheating, the tank comprising at least one lower opening for removing a heat transfer fluid having a temperature below the lower threshold temperature from a region of the tank corresponding to the low temperature region of the body of heat transfer fluid during heat storage and for removing a heat transfer fluid having a temperature above the lower threshold temperature during desuperheating The heat transfer fluid is added to a region of the tank corresponding to a low temperature region of the body of heat transfer fluid, the tank comprising at least one central opening for removing heat transfer fluid from a region of the tank corresponding to a thermocline region of the body of heat transfer fluid during heat storage or heat reduction, the at least one central opening being arranged between the upper and lower openings, and wherein the thermal energy storage device further comprises a plurality of valves capable of regulating flow through each of the at least one upper opening, the at least one lower opening and the at least one central opening during heat storage and reduction, and characterised in that the at least one lower and at least one central openings are fluidly connected to each other by a conduit so as to allow heat transfer fluid removed from both the thermocline region and the low temperature region of the body of heat transfer fluid during heat storage to merge at the intersection of the conduits, the intersection is in particular located upstream of the heat exchange device or between the at least one upper opening, the at least one middle opening and the heat exchange device.

It is another object of the present invention to provide a thermal energy storage apparatus comprising a plurality n of tanks, i.e. 2 or more tanks, for containing a body of heat transfer fluid comprising: a high temperature region containing a heat transfer fluid at a temperature above the upper threshold temperature, a low temperature region containing a heat transfer fluid at a temperature below the lower threshold temperature, and a thermocline region separating the high temperature region from the low temperature region and containing a heat transfer fluid at a temperature above the lower threshold temperature and below the upper threshold temperature, the first tank comprising at least one upper opening for adding heat transfer fluid at a temperature above the upper threshold temperature to the high temperature region of the body of heat transfer fluid during heat storage and for removing heat transfer fluid at a temperature above the upper threshold temperature from the high temperature region of the body of heat transfer fluid during desuperheating, the last tank comprising at least one lower opening for removing heat transfer fluid at a temperature below the lower threshold temperature from the low temperature region of the body of heat transfer fluid during heat storage and for adding heat transfer fluid at a temperature above the lower threshold temperature to the low temperature region of the body of heat transfer fluid during desuperheating Wherein adjacent tanks are fluidly connected to each other by a plurality of n-1 pipes, each of the n-1 pipes fluidly connecting two adjacent tanks, each pipe of the plurality of n-1 pipes comprising at least one middle opening for removing heat transfer fluid from the thermocline region of the body of heat transfer fluid during heat storage or desuperheating, and wherein the thermal energy storage device further comprises a plurality of valves capable of regulating the flow through the at least one upper opening of the first tank, the at least one lower opening of the last tank and each middle opening during heat storage and desuperheating, and characterized in that the at least one lower opening and each middle opening of the last tank are fluidly connected to each other by a pipe so as to allow heat transfer fluid removed from both the thermocline region and the low temperature region of the body of heat transfer fluid during heat storage to merge at the intersection of the pipes, the intersection is in particular located upstream of the heat exchange device or between the at least one upper opening, the at least one middle opening and the heat exchange device, characterized in that the at least one upper opening and each middle opening of the first tank are fluidly connected to each other by a conduit so as to allow heat transfer fluid removed from both the thermocline region and the high temperature region of the body of heat transfer fluid during desuperheating to merge at the intersection of said conduit, the intersection being in particular located upstream of the heat exchange device or between the at least one upper opening, the at least one middle opening and the heat exchange device.

Thus, a thermal energy storage device according to an object of the invention can be used to achieve an outflow of heat transfer fluid during heat storage and heat reduction, which outflow will have a constant temperature due to the controlled flow at each opening. In particular, where the thermal energy storage device comprises a plurality of n tanks (n being the number of tanks and comprising n-1 intermediate valve-controlled openings fluidly connected to conduits between adjacent tanks), it is believed that the heat transfer fluid can be removed without causing a substantial amount of turbulence in the body of the heat transfer fluid, since the removal of the heat transfer fluid from the conduits, which are significantly restricted in diameter relative to the tanks as a result and through which the heat transfer fluid is collected, results in less turbulence. Furthermore, in terms of the design of the tank, the use of a central opening at the pipe is easier to achieve than a central opening at the tank.

In one embodiment of the thermal energy storage apparatus according to one object of the invention, the thermal energy storage apparatus further comprises a control unit capable of controlling a plurality of valves capable of regulating the flow through each of the at least one upper opening, the at least one lower opening and the at least one middle opening, and configured to control the valves so as to perform a method of operating the thermal energy storage apparatus according to any one of the methods of operating the thermal energy storage apparatus described above.

Thus, by using a control unit configured to control the flow rate towards each intersection accordingly, any of the above described methods of operating a thermal energy storage device may be implemented using a thermal energy storage device according to the above embodiments. It will be appreciated that in order to achieve temperature control of the heat transfer fluid exiting the intersection by controlling the flow rate through the openings, the temperature downstream of the intersection or at each opening or both is determined and received by the control unit so that the flow rate can be controlled in dependence on the temperature determined by the sensor.

In one embodiment of the thermal energy storage device according to one object of the invention, the thermal energy storage device further comprises a conduit capable of bypassing the thermal energy storage device during heat storage and/or heat removal.

Thus, even after the thermal energy storage device is filled with a heat transfer fluid having a temperature above the upper threshold temperature or with a heat transfer fluid having a temperature below the lower threshold temperature, the thermal energy storage device according to the above embodiments may be used by bypassing the thermal energy storage device and redirecting additional heat transfer fluid having a temperature above the upper threshold temperature or heat transfer fluid having a temperature below the lower threshold temperature directly towards a system thermally connected to the thermal energy storage device.

In one embodiment of the thermal energy storage device according to one object of the invention, the tank comprises at least two or more, three or more, or four or more central openings for removing the heat transfer fluid from the region of the tank corresponding to the thermocline region of the body of heat transfer fluid during heat storage and/or desuperheating, the central openings preferably being evenly spaced relative to each other in the flow direction of the heat transfer fluid during heat storage or in the vertical direction.

Thus, the thermal energy storage device according to the above embodiments may be used more efficiently, as more central openings for removing the heat transfer fluid from the region of the tank corresponding to the thermocline region means that during heat storage/desuperheating the thermocline region of the body of heat transfer fluid may decrease in width at multiple heights of the tank as the heat transfer fluid moves through the tank (which fluid may then merge with heat transfer fluid from the region of the tank corresponding to the lower region during heat storage and with heat transfer fluid from the region of the tank corresponding to the upper region during desuperheating).

In one embodiment of the thermal energy storage apparatus according to an object of the present invention, the tank comprises a packed bed of solids, such as gravel or spheres of inorganic material. Alternatively, a packed bed of encapsulated phase change material may also be used.

Further embodiments of the invention are given in the dependent claims.

Drawings

Preferred embodiments of the present invention are described below with reference to the accompanying drawings, which are for the purpose of illustrating the presently preferred embodiments of the invention and are not for the purpose of limiting the invention.

In the drawings, there is shown in the drawings,

fig. 1 shows a schematic view of the operation of a thermal storage device in which the thermoclines are controlled by taking out the thermoclines individually using one opening located at half height between the upper and lower openings. The black solid line indicates a thermocline obtained by taking out the thermocline for control, and the dotted line corresponds to a thermocline obtained by not taking out control at the same instant. (a) Showing the heat storage of the thermal storage device just before the removal of the thermocline through the central opening is opened, (b) showing the heat storage of the thermal storage device immediately after the removal of the heat transfer fluid through the lower opening is opened. (c) Showing the heat reduction of the heat storage device just before the removal of the thermocline through the central opening is activated, and (d) showing the heat reduction of the heat storage device immediately after the removal of the heat transfer fluid through the upper opening is activated.

Fig. 2 shows a schematic view of the operation of a thermal storage device in which the thermocline is controlled by injecting heat transfer fluid from a high temperature zone into the thermocline alone using one opening located at half height between the upper and lower openings. The black solid line indicates a thermocline resulting from control by injection of the thermocline, and the dotted line corresponds to a thermocline resulting from no control at the same instant. (a) Showing the heat storage of the thermal storage device just before the injection into the thermocline through the central opening is started, (b) showing the heat storage of the thermal storage device immediately after the injection into the thermocline through the central opening is started. (c) Showing the desuperheating of the heat storage device just before the injection into the thermocline through the central opening is started, and (d) showing the desuperheating of the heat storage device immediately after the injection into the thermocline through the central opening is started.

FIG. 3 shows a schematic of the operation of a thermal storage device in which the thermocline is controlled by mixing the heat transfer fluid from the low temperature zone with the heat transfer fluid from the thermocline zone by removing the heat transfer fluid from the thermocline zone using one opening located at half the height between the upper and lower openings and combining it with the heat transfer fluid removed from the low temperature zone. The black solid line indicates the thermocline resulting from control by mixing, while the dotted line corresponds to the thermocline resulting from no control at the same instant. (a) Showing heat storage of the thermal storage device just prior to initiating removal of the heat transfer fluid from the thermocline through the central opening, (b) showing heat storage of the thermal storage device just after initiating removal of the heat transfer fluid from the thermocline through the central opening and merging it with the heat transfer fluid removed from the low temperature zone at the intersection, (c) showing desuperheating of the thermal storage device just prior to initiating removal of the heat transfer fluid from the thermocline through the central opening, (d) showing desuperheating of the thermal storage device just after initiating removal of the heat transfer fluid from the thermocline through the central opening and merging it with the heat transfer fluid removed from the high temperature zone.

Fig. 4 shows a schematic diagram of the operation of the thermal storage device, wherein the thermocline is not controlled. The dashed lines correspond to thermoclines during heat storage (a) and heat reduction (b).

Fig. 5 shows the time evolution of the flow (dashed line) and the temperature (solid black line) at the upper, middle and lower openings of the heat storage device, wherein the thermocline is controlled by: mixed heat transfer fluid, operating during heat storage (left side) with the thermal storage device having one middle opening at half height between the upper and lower openings. As the descending thermocline passes through the central opening, the temperature of the heat transfer fluid removed through the central opening increases and the flow rate decreases. At the same time, the flow rate of the heat transfer fluid removed through the lower opening is increased to provide a combined effluent with a constant temperature, and operated during desuperheating (right side) with the thermal storage device having one middle opening located at half height between the upper and lower openings. As the rising thermocline passes through the central opening, the temperature of the heat transfer fluid removed through the central opening decreases and the flow rate decreases. At the same time, the flow rate of the heat transfer fluid removed through the upper opening is increased to provide a combined effluent having a constant temperature.

Fig. 6 shows the time evolution of the flow (dashed line) and the temperature (solid black line) at the upper, middle and lower openings of the heat storage device, wherein the thermocline is controlled by: mixed heat transfer fluid, operating during heat storage (left) and heat reduction (right) with the thermal storage device having three intermediate openings between the upper and lower openings.

FIG. 7 illustrates the evolution of the thermocline at the end of the continuous heat storage and desuperheating cycle, wherein the thermocline is controlled by withdrawing, injecting and mixing a heat transfer fluid using three central openings spaced apart in the vertical direction; and as a comparison the evolution of the thermocline at the end of the continuous heat storage and desuperheating cycle in which the thermocline was not controlled (no TCC). It can be seen that in the case of control of the thermocline by mixing the heat transfer fluid, not only is the steady state reached quickly, but the thermocline remains steeper than in the control of the thermocline by withdrawal or injection. Therefore, in the case of controlling the thermocline control by mixing the heat transfer fluid, the utilization factor is maximized.

Fig. 8 shows the time evolution of the effluent temperature during heat storage at quasi-steady state for various thermocline control variants in the case of a thermal storage device with three middle openings between the upper and lower openings (solid line). It can be seen that in the case of controlling the thermocline control by mixing the heat transfer fluid, the temperature change is suppressed and the set temperature can be maintained.

Fig. 9 shows the time evolution of the effluent temperature during desuperheating at quasi-steady state for various thermocline control variants in the case of a heat storage device with three middle openings between the upper and lower openings (solid line). It can be seen that in the case where the thermocline is controlled by mixing the heat transfer fluid, the temperature change is suppressed and the set temperature can be maintained.

Fig. 10 shows a thermal energy storage device during heat storage and heat reduction according to an embodiment of the invention, comprising one tank (1) for containing a body of heat transfer fluid, having one upper opening (2) for adding heat transfer fluid to the body of heat transfer fluid during heat storage and for removing heat transfer fluid from the body of heat transfer fluid during heat reduction, having one lower opening (3) for removing heat transfer fluid from the low temperature region of the body of heat transfer fluid during heat storage and for adding heat transfer fluid to the body of heat transfer fluid during heat reduction, having three middle openings (4, 4', 4 ") for removing heat transfer fluid from the body of heat transfer fluid during heat storage or heat reduction and arranged between the upper opening (2) and the lower opening (3), and three valves (5, 4") capable of regulating the flow through the three middle openings during heat storage and reduction, 5 ', 5 ") and two valves (6, 6 ') allowing to selectively fluidly connect the middle opening with the upper or lower opening via a conduit or to bypass the tank, and two valves (7, 7 ') capable of regulating the flow through the upper opening (2) and the lower opening (3). During heat storage, the valve (7) is open, the valve (6) is closed and the valve (6 ') is open, and the valves (5, 5', 5 ") are individually and sequentially opened as the thermocline region moves down to remove heat transfer fluid from the thermocline region and combine it with heat transfer fluid removed from the low temperature region via the lower opening (3). By controlling the flow through the valves (5, 5 ' and 7 '), it is possible to control the temperature of the heat transfer fluid downstream of the intersection (8 ') resulting from the merging of the heat transfer fluid from the thermocline region and the low temperature region of the heat transfer fluid body. During desuperheating, the valve (7 ') is open, the valve (6 ') is closed and the valve (6) is open, and the valves (5, 5 ', 5 "') are individually and sequentially opened as the thermocline region moves up and through the central opening (4, 4 ', 4") to remove heat transfer fluid from the thermocline region and combine it with heat transfer fluid removed from the high temperature region via the upper opening (2). By controlling the flow through the valves (5, 5' and 7), the temperature of the heat transfer fluid downstream of the intersection (8) resulting from the merging of the heat transfer fluid from the thermocline region and the high temperature region of the heat transfer fluid body can be controlled. In each case, the arrows indicate the flow direction of the heat transfer fluid.

Fig. 11 shows a thermal energy storage device during heat storage and desuperheating according to one embodiment of the invention, comprising three tanks (1) for containing a body of heat transfer fluid, having one upper opening (2) for adding heat transfer fluid to the body of heat transfer fluid during heat storage and for removing heat transfer fluid from the body of heat transfer fluid during desuperheating, having one lower opening (3) for removing heat transfer fluid from the low temperature region of the body of heat transfer fluid during heat storage and adding heat transfer fluid to the body of heat transfer fluid during desuperheating, having three middle openings (4, 4 ', 4 ") for removing heat transfer fluid from the body of heat transfer fluid during heat storage or desuperheating and each arranged between adjacent tanks, and three valves (5, 4', 4") capable of regulating the flow through the three middle openings during heat storage and desuperheating, 5 ', 5 ") and two valves (6, 6 ') allowing to selectively fluidly connect the middle opening with the upper or lower opening via a conduit or to bypass the tank, and two valves (7, 7 ') capable of regulating the flow through the upper opening (2) and the lower opening (3). During heat storage, the valve (7) is open, the valve (6) is closed and the valve (6 ') is open, and the valves (5, 5 ', 5 ") are individually and sequentially opened as the thermocline region moves down and through the central opening (4, 4 ', 4") to remove heat transfer fluid from the thermocline region and merge it with heat transfer fluid removed from the low temperature region via the lower opening (3). By controlling the flow through the valves (5, 5 ') and (7 '), it is possible to control the temperature of the heat transfer fluid downstream of the intersection (8 ') resulting from the merging of the heat transfer fluid from the thermocline region and the low temperature region of the heat transfer fluid body. During desuperheating, the valve (7 ') is open, the valve (6 ') is closed and the valve (6) is open, and the valves (5, 5 ', 5 "') are individually and sequentially opened as the thermocline region moves up and through the central opening (4, 4 ', 4") to remove heat transfer fluid from the thermocline region and combine it with heat transfer fluid removed from the high temperature region via the upper opening (2). By controlling the flow through the valves (5, 5') and the valve (7), the temperature of the heat transfer fluid downstream of the intersection (8) resulting from the merging of the heat transfer fluid from the thermocline region and the high temperature region of the heat transfer fluid body can be controlled. In each case, the arrows indicate the flow direction of the heat transfer fluid.

Detailed Description

In the context of the present invention, the term "heat storage" of the thermal energy storage device means that a heat transfer fluid with a temperature above an upper threshold temperature is added to the body of heat transfer fluid, whereas the term "heat reduction" of the thermal energy storage device means that a heat transfer fluid with a temperature below a lower threshold temperature is added to the body of heat transfer fluid.

It is an object of the present invention to provide a method of operating a thermal energy storage apparatus comprising a body of heat transfer fluid comprising: a high temperature region containing a heat transfer fluid at a temperature above an upper threshold temperature, a low temperature region containing a heat transfer fluid at a temperature below a lower threshold temperature, and a thermocline region separating the high temperature region from the low temperature region and containing a heat transfer fluid at a temperature above the lower threshold temperature and below the upper threshold temperature, wherein during thermal storage of the thermal energy storage device, the heat transfer fluid is removed from the thermocline region of the body of heat transfer fluid, and when the temperature of the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid rises above a maximum temperature, the removed heat transfer fluid is brought to a temperature equal to or below the maximum temperature, wherein the maximum temperature is above the lower threshold temperature, and/or wherein during desuperheating of the thermal energy storage device, the heat transfer fluid is removed from the thermocline region of the body of heat transfer fluid, and when the temperature of the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid falls below the minimum temperature, bringing the removed heat transfer fluid to a temperature at or above the minimum temperature, wherein the minimum temperature is below an upper threshold temperature. In most cases, a high temperature region containing a heat transfer fluid at a temperature above the upper threshold temperature and a low temperature region containing a heat transfer fluid at a temperature below the lower threshold temperature are separated in the vertical direction by a thermocline region, i.e., the high temperature region is above the thermocline region and the low temperature region is below the thermocline region. During heat storage of the thermal energy storage device, the fluid is brought to a temperature equal to or lower than the maximum temperature, for example by conducting a heat transfer fluid removed from the thermocline region into a heat exchanger, for example, i.e. without combining or mixing the fluid into a fluid having a lower temperature, and once the temperature equal to or lower than the maximum temperature is reached, the fluid is then brought into thermal contact with a system capable of converting thermal energy into another type of energy, such as a heat engine.

It will be appreciated that in general the opening in the thermal energy storage device may be in any form and preferably in the form of a port, and more preferably a port which may be controlled with respect to flow. The ports may be controlled with respect to flow by equipping the ports directly with valves or placing valves downstream of the ports.

It is also understood that in general the thermal energy storage device may be equipped with one or more temperature sensors placed individually in the vertical direction of the tanks of the thermal energy storage or integrated into the openings of the thermal energy storage device.

It is also understood that, in general, the opening and the temperature sensor, with respect to which the flow can be controlled, are connected and can be controlled by a control unit of the thermal energy storage device, said control unit being able to carry out the method according to the invention.

Further, it should be understood that, in general, heat transfer fluid removed from the thermocline region of the body of heat transfer fluid during heat storage and/or heat removal may or may not return to the body of heat transfer fluid, and may return directly or indirectly. In some embodiments, the heat transfer fluid removed from the thermocline region during heat storage may be returned to a high temperature region of the body of heat transfer fluid, while the heat transfer fluid removed from the thermocline region during desuperheating may be returned to a low temperature region of the body of heat transfer fluid. Typically, in the case of heat storage, the heat transfer fluid removed from the thermocline region may be directed to a device, such as a solar collector or solar receiver, capable of using or increasing the thermal energy contained in the heat transfer fluid removed from the thermocline region before it is returned to the body of heat transfer fluid.

In a preferred embodiment, the thermal storage device suitable for use in the method of operating a thermal energy storage device comprises a tank for containing a body of heat transfer fluid, said tank being equipped with at least one upper opening for allowing the addition of heat transfer fluid having a temperature above an upper threshold temperature to a high temperature region of the body of heat transfer fluid comprising heat transfer fluid having a temperature above the upper threshold temperature, for example during heat storage of the thermal storage device. Thus, during desuperheating of the thermal storage device, the at least one upper opening is used to allow removal of heat transfer fluid having a temperature above the upper threshold temperature from a high temperature region of the body of heat transfer fluid containing heat transfer fluid having a temperature above the upper threshold temperature. The tank may further comprise a plurality of upper openings, which may preferably be arranged at the same height in the vertical direction or in the flow direction of the heat transfer fluid being added or removed.

In a preferred embodiment, the thermal storage device suitable for use in the method of operating a thermal energy storage device comprises a tank for containing a body of heat transfer fluid, said tank being equipped with at least one lower opening for allowing heat transfer fluid having a temperature below a lower threshold temperature to be removed from a low temperature region of the body of heat transfer fluid containing heat transfer fluid having a temperature below the lower threshold temperature, for example during heat storage of the thermal storage device. Thus, during desuperheating of the thermal storage device, the at least one lower opening is used to allow the addition of heat transfer fluid having a temperature below the lower threshold temperature into the low temperature region of the body of heat transfer fluid containing heat transfer fluid having a temperature below the lower threshold temperature. The tank may further comprise a plurality of lower openings, which may preferably be arranged at the same height in the vertical direction or in the flow direction of the heat transfer fluid being added or removed.

In a preferred embodiment, the thermal storage device suitable for use in the method of operating a thermal energy storage device comprises a tank for containing a body of heat transfer fluid, said tank being provided with at least one central opening for allowing heat transfer fluid having a temperature below an upper threshold temperature and above a lower threshold to be removed from a thermocline region of the body of heat transfer fluid. The tank may further comprise a plurality of intermediate openings, preferably one, two, three or four intermediate openings, between the upper and lower openings, preferably arranged in a vertical direction or in the flow direction of the heat transfer fluid being added or removed, and more preferably evenly spaced apart. When the tank comprises a plurality of central openings, it becomes possible to remove the heat transfer fluid at different levels in the vertical direction when the thermocline travels from one side of the tank to the other during heat storage and desuperheating, thereby increasing the efficiency with which the width of the thermocline can be controlled.

The present invention is not limited to a method of operating a thermal energy storage device comprising a single tank containing a body of heat transfer fluid. In a thermal energy storage device comprising a plurality of tanks, each tank is fluidly connected to each other via a pipe, and the central opening is preferably located at the pipe fluidly connecting adjacent tanks. In one embodiment of the thermal energy storage device, the central opening in the conduit fluidly connecting adjacent tanks is a T-joint and/or an intersection.

The present invention is not limited to methods of operating a particular kind of thermal energy storage device. For example, both the tank and the heat transfer fluid may vary depending on the particular needs of the system that is thermally associated with the thermal energy storage device. Exemplary heat transfer fluids may be water, aqueous solutions, molten salts, and gases such as nitrogen, carbon dioxide, or air. The heat transfer fluid may be in any state as long as it can flow, i.e., the heat transfer fluid may be a liquid, a gas, or even a fluid in a supercritical state such as supercritical carbon dioxide. Exemplary tanks may be formed of metal, ceramic, or stone, or may be cavities in a rock formation. The tank may or may not be provided with an outer insulating layer. The upper and lower threshold temperatures are not particularly limited and may be freely selected within the thermal limits of the thermal storage device and the heat transfer fluid as needed for the particular system thermally coupled to the thermal storage device.

For example, in case the system is a system capable of converting thermal energy into chemical energy, such as a thermochemical fuel synthesis system based on a redox system, and preferably on a redox system of metal oxides such as cerium (IV) oxide-cerium (III) oxide cycle or iron oxide cycle or zinc-zinc oxide cycle, the heat transfer fluid is preferably a gas, such as inert gas, carbon dioxide, steam, nitrogen or air, or a supercritical fluid. The use of gases or supercritical fluids in thermochemical fuel synthesis systems that can easily flow without significant back pressure allows higher fuel yields to be achieved because metal oxides are often in the form of porous structures, such as high surface packed beds or solid foams or metal oxides are encapsulated in, for example, tubes. Typical reduction temperatures are 1100 ℃ to 1500 ℃ and typical oxidation temperatures are 800 ℃ to 1100 ℃.

Accordingly, in one preferred method of operating a thermal energy storage device comprising a body of heat transfer fluid, the body of heat transfer fluid comprises: a high temperature region containing a heat transfer fluid having a temperature above an upper threshold temperature, a low temperature region containing a heat transfer fluid having a temperature below a lower threshold temperature, and a thermocline region separating the high temperature region from the low temperature region and containing a heat transfer fluid having a temperature above the lower threshold temperature and below the upper threshold temperature, the heat transfer fluid being a gas such as an inert gas or air in a subcritical, critical or supercritical state, wherein during heat storage of the thermal energy storage device the heat transfer fluid is removed from the thermocline region of the body of heat transfer fluid, and said removed heat transfer fluid is brought to a temperature equal to or below a maximum temperature when the temperature of the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid rises above said maximum temperature, wherein the maximum temperature is above the lower threshold temperature, and wherein the temperature equal to or below said maximum temperature corresponds to effecting oxidation of a metal oxide involved in a thermochemical cycle (e.g. to decompose water) Or carbon dioxide), and/or wherein during desuperheating of the thermal energy storage device, heat transfer fluid is removed from a thermocline region of a body of heat transfer fluid, and when the temperature of the heat transfer fluid removed from the thermocline region of the body of heat transfer fluid falls below a minimum temperature, the removed heat transfer fluid is brought to a temperature equal to or higher than the minimum temperature, wherein the minimum temperature is below an upper threshold temperature, and wherein the temperature equal to or higher than the minimum temperature corresponds to a temperature at which reduction of metal oxides participating in the thermochemical cycle is achieved (e.g., to release oxygen and reduce metal oxides to a non-stoichiometric state). As an exemplary embodiment, in case the thermochemical cycle is based on a cerium (IV) oxide-cerium (III) oxide cycle, the typical reduction temperature is 1100 ℃ to 1500 ℃, and the typical oxidation temperature is 800 ℃ to 1100 ℃. In particular, in the case of thermochemical cycles that use as substrate a porous structure, such as a foam of metal oxide, which is monolithic as opposed to a packed bed substrate, it is advantageous to reduce the temperature fluctuations in order to reduce the mechanical strains caused by thermal expansion. When using the method of the invention, mechanical strain can be minimized, since the temperature of the removed heat transfer fluid can be controlled while increasing the utilization coefficient of the thermal energy storage device. It should be noted that a heat transfer fluid having a temperature at which oxidation of the metal oxide and/or reduction of the metal oxide can be achieved can be brought into direct contact with the porous structure comprising the metal oxide capable of thermochemical fuel synthesis, provided that it comprises water or carbon dioxide or both, which are then decomposed using the porous structure comprising the metal oxide capable of thermochemical fuel synthesis. Alternatively, the thermal energy may be transferred through a metal housing, such as a tube that surrounds and prevents direct contact of the single unitary body of porous metal oxide structure with the heat transfer fluid. To perform thermochemical fuel synthesis, a fluid stream containing water or carbon dioxide or both is directed through the lumen when the temperature corresponds to the oxidation temperature of the metal oxide used to decompose the water or carbon dioxide.

List of reference numerals

1-pot 5-valve

2 upper opening 6 valve

3 lower opening 7 valve

4 intersection of central opening 8