NO20200447A1

NO20200447A1 - Thermal Energy Storage Device

Info

Publication number: NO20200447A1
Application number: NO20200447A
Authority: NO
Inventors: Jon Bøhmer; Christian Blom
Original assignee: Kyoto Group As
Priority date: 2020-04-14
Filing date: 2020-04-14
Publication date: 2021-10-15
Also published as: WO2021210986A1

Description

Thermal Energy Storage Device

The present invention concerns thermal energy storage useful in a number of energy storage applications, hereunder energy production from renewable sources like solar energy, wind energy and wave energy. More specifically the present invention concerns a thermal energy storage device as indicated by the preamble of claim 1 and an auxiliary container as claimed in claim 8, being part of a thermal energy storage device as claimed in claim 1.

Background

The increasing worldwide demand for renewable energy depends upon new and innovative solutions for energy production as such but also for technology in the sphere surrounding the production, such as short and long term energy storage. With regard to solar energy, for instance, energy is only produced during daytime and solutions for energy storage and use during night-time is therefore of vital importance.

A number of different approaches have been suggested and implemented, such as storage of electric power in batteries, of potential energy in the form of water basins arranged at a vertical elevation or gases stored under pressure and as thermal energy in the form of a heat medium stored at elevated temperature. The present invention is of the latter category.

Plants for thermal energy storage have been designed in connection to solar energy power production as a means for storing energy over a time-span of hours or a few days and are typically large scale production plants in which solar energy is focused on points or lines at which a heat medium is heated to an elevated temperature. While water may be used for storing thermal energy at temperatures below 100 °C, and pressurized water below 200 °C, more valuable utilization is obtained if thermal energy is stored at temperature in the range of e.g.500-600 °C, which is possible when using certain molten salts as heat medium. This temperature range allows the use of heat engines to turn some of the thermal energy into electricity. However, high temperatures also have a potential of high energy losses and in particular if the ratio between volume and surface area of the heat medium in the storage tanks is low, which is necessarily the case in smaller storage plants. Therefore, thermal energy storage plants have typically been designed as quite huge plants which only is meaningful if located in connection with a production plant or the like having a correspondingly high demand for power.

In areas and situations where there are smaller industry plants requiring less energy, there is a need for improvements in the technology, making thermal energy storage feasible in rather compact plants.

Objectives

An objective of the present invention is to lower the barrier for providing small and medium scaled energy power plants utilizing renewable energy sources useful in industry and other commercial systems, allowing day and night operation even if the primary energy source is not operative during the full day or night.

More particularly the objective of the present invention is to make energy power plants relying on thermal batteries more useful, simpler and more practical, in particularly small and medium sized “industry scale” energy power plants.

The present invention

The above mentioned objectives are achieved by the thermal energy storage device defined by claim 1, constituting a first aspect of the present invention.

According to a second aspect, the present invention relates to an auxiliary container for thermal energy storage as defined by claim 10.

Preferred embodiments of the present invention are disclosed by the dependent claims.

By “external devices” connected to the device of the present invention is generally understood any external device through which the liquid heat medium is arranged to flow, in particular devices in which the liquid heat medium is arranged to flow in order to release energy by temperature decrease or accumulate energy by temperature increase.

The liquid heat medium may be any medium serving the purpose of accumulating and releasing energy by temperature increase and temperature decrease respectively, such as but not limited to molten salt compositions.

The auxiliary container is a unit containing technical parts of the thermal energy storage device, such as pumps and valves, and optionally pneumatics, electronic control components and heaters. All transportation of heat medium to and from the heat medium storage containers is directed through and/ or controlled by the auxiliary container.

A computerized control unit is programmed to act in a defined manner in order to optimize the operation of the thermal energy storage device according to the present invention. A number of the programmed operations are self-evident, such as directing heat medium which has released most of its energy in a power consumption device, such as heat exchangers, turbines etc, to a power accumulation station such as a solar power plant provided with a tower surrounded by heliostats, or charging with electric heaters or evacuating conduits for heat medium during night-time, in order to prevent solidification thereof. Other programmed actions may be more sophisticated and e.g. involve controlling a sequence of operational steps when a cascaded connection of a number of heat medium storage containers are employed. Still another kind of programmed actions may relate to handling of unforeseen situations, based upon observed behaviour and abnormalities during operation. For input to the control unit a number of sensors may be connected to the control unit, in particular for the control unit to be able to monitor the temperature in any part of the system.

The heat medium storage containers may be of any suitable design, material and configuration and will naturally include one or more layer of thermal insulation in order to control the energy loss therefrom. The size of the containers may vary, but it may typically be of a standard size in order to simplify freight by conventional transport ships. When more than one heat medium storage container is employed, they will typically all be of same size.

The heat medium storage containers may be arranged side by side at a common vertical elevation, in which case a compressor or pipe tracing may be required to prime the system at start-up. In such a case, also the compressor as well as required power supply may be provided within the auxiliary container. In other embodiments, gravity priming can be employed. With gravity priming, valves may be located at the bottom of each tank.

The thermal energy storage device according to the present invention is useful when connected – via the auxiliary container- to a power plant such as a solar energy power plant in which heliostats are arranged to focus sunlight to a point or a line through which the heat medium is transported and on the other hand also connected to equipment in which the stored energy may be released through a temperature reduction of the heat medium.

The auxiliary container is typically of same size as the heat medium storage containers, for convenience both during freight as after assembly.

Details of the present invention with reference to the drawings

Figure 1 is a schematic side view of an embodiment of a thermal energy storage device according to the present invention.

Figure 2 is a schematic side view of an enlarged detail of the embodiment of Figure 1 at a stage of operation.

Figure 3 is a schematic side view of the embodiment of Figure 1 subsequent the operational step according to Figure 2.

Figure 4 is a schematic side view of the embodiment of a thermal energy storage device according to Figure 3 after some additional steps of operation.

Figure 5 is a schematic side view of an enlarged detail of the embodiment of Figures 1, 3, and 4 at a stage of operation different from the one of Figure 2.

Figure 6 is a schematic side view of the embodiment of Figure 4 subsequent the operational step according to Figure 5.

Figure 7 is a schematic side view of the embodiment of a thermal energy storage device according to Figure 6 after some additional steps of operation.

Figure 8 is a schematic side view of an embodiment of a thermal energy storage device according to the present invention which is different from the one of Figures 1-to 7.

Figure 9 is a schematic side view of still another embodiment of a thermal energy storage device according to the present invention.

An inherent property of the cascade connected container assembly shown in Figure 1, which may also be denoted a thermal battery, is that one container is always empty and able to receive liquid medium that being of a high, energy rich state or a lower, energy poor state.

Figure 1 shows a thermal battery comprising five heat medium storage containers (HMSCs) 1-5 and an auxiliary container 10. Conduits 11, 21, 31, 41, 51 lead from heat medium containers 1 - 5 respectively to the auxiliary container. The HMSCs are preferably, for convenience, of a common size and shape, but need not be exact copies of one another and do not need to be equipped with technicalities like pumps and valves. In the auxiliary container 10, the conduits 11, 21, 31, 41, 51 are split and connected to a set of outlet valves 11/51o as well as to a set of inlet valves 11/51i. The auxiliary container also contains two pumps, P1 and P2 for pumping of the liquid heat medium. Strictly, one pump would be sufficient but for the purpose of reliance and continuance of operation during maintenance, two pumps are preferred. An optional electric heater 55 is also shown in the auxiliary container, though for some purposes the electric heater may be of a size requiring a container of its own. Strictly, the heater 55 is optional, but may be useful when energy from the preferred, renewable energy sources is not available.

A compressor 60 is shown near top left of the auxiliary container 10. The compressor is useful for emptying the conduits during nighttime or shutdown, by displacing the heat medium into the HMSCs, thus preventing the heat medium to set and clog the conduits as a result of excessive temperature drop. It may also be useful for priming the system at start-up in the cases where the assembly is not arranged in manner allowing it to be primed by forces of gravity only.

To the top left of the auxiliary containers, conduits to and from an energy accumulating unit, EAU, are shown. The energy accumulating unit is typically a solar power plant, a wind based plant, a wave based power plant or the like. To the top right, conduits to and from an energy consumption unit, ECU are shown. The energy consumption unit may be any device requiring heat, in industry, transportation, municipally or other heating, etc. Return conduit from the EAU to the inlet set of valves 11/51i is denoted HTR for high temperature return of heat medium, while the return conduit from the ECU to the inlet set of valves 11/55i is denoted LTR for low temperature return of heat medium. In is worth mentioning that the low temperature return of heat medium may still have a temperature above 200 °C in many cases, while the hot return medium may be of a temperature above 500 °C, such as approximately 550 °C.

On the right hand side of Figure 1, a control unit 70 is visualized, being able to control the action of the valves 11o/51o 11i/51i, the pumps P1, P2, the heater 55, and the compressor 70. The control unit 70 may have the form of a personal computer located externally of the thermal energy storage device or of a unit programmable by a personal computer located internally in or externally of the auxiliary container 10. The controlling action caused by the control unit may have the form of purely electric signals and/ or actions conducted by pneumatic devices.

With reference to Figures 1 and 2, at a given point in time, for instance at the end of a sunny day, all the non-empty heat medium storage containers (HMSCs) 1-4 may be filled with high temperature (HT) heat medium of e.g.550 °C while HMSC No.5 is empty (E). When the sun has set and the energy accumulated during daytime is needed for consumption, liquid heat medium from e.g. HMSC No 4 is pumped by pump P1 from HMSC 4 via conduit 41, through valve 41o to an energy consumption unit ECU. The valve 41o is one valve among the set of valves 11/51o within the auxiliary container. When energy has been consumed by the ECU and the temperature of the heat medium having been reduced correspondingly, the heat medium of reduced temperature is returned to the previously empty HMSC 5 through conduit CR, valve 51i in the auxiliary container and conduit 51. The previously empty HMSC 5 is this way gradually filled with heat medium of reduced temperature while HMSC 4 is gradually emptied. Figure 3 shows the situation after this process step has been completely conducted. The process at the ECU is adjusted to ensure that the heat medium is not reduced to an extent in which the heat medium may set. It is contemplated, though not shown in Figure 3 and the following drawings, that a control unit (70) is connected to the system one way or the other, whether as a component in the auxiliary container or not.

If more energy than that of one HMSC is required before the heat medium can be reheated, the process described above is repeated using hot heat medium from HMSC 3, which is returned to HMSC 4 with a reduced temperature. At the end of an extensive energy requiring period, the situation may be as shown by Figure 4, in which HMSC 1 is empty and all the other HMSCs are holding heat medium of reduced temperature. Hence, no more energy is available from this source before recharging this thermal battery.

Figures 5 and 6 illustrate the first step of recharging the thermal battery. Here, low temp heat medium is pumped by pump P1 from HMSC 5, through pipe 51, the pump P1 and further on to an energy accumulating unit EAU in which the temperature of the heat medium is raised to desired temperature before being returned to the empty HMSC of the thermal battery which in this case happens to be HMSC 1. After completion of this step, HMSC 5 is empty, HMSC 1 holds high temperature heat medium and HMSCs 2-4 still hold low temperature heat medium as shown by Figure 6. As mentioned, the EAU is typically a power plant based on renewable energy.

It should be emphasized, though not apparent from the drawings, that the energy accumulating unit EAU of Figure 5 as well as the energy consumption unit ECU of Figure 2 may physically be much larger than the thermal battery.

The energy accumulating or recharging step illustrated by Figures 5 and 6 may, and typically will, be repeated until all HMSCs except the empty one, hold high temperature heat medium ready for use as shown by Figure 7.

Using a plurality of cascade connected heat medium storage containers allows the benefit of a higher degree of utilization of the equipment compared to operating only two containers in which case half the accessible volume is empty at all times. This is a benefit of a general character for cascade connected containers, not a specific one with the present invention.

The present invention, however, is still useful in a thermal battery having fewer or more than five HMSCs. Even though not recommended, the thermal battery may comprise only two HMSCs as shown in Figure 8 in which case one of the HMSCs is always empty when the other one is full, that being whether the full one is full of low temperature heat medium or high temperature heat medium. This design is not as efficient as a plurality of cascaded HMSCs, but may still be useful in small scale.

An even simpler design is shown in Figure 9, where there is just one HMSC having an internal barrier 80 that separates high temperature heat medium on one side thereof from low temperature heat medium of the other side thereof. The barrier 80 must be dynamic, i.e. having the ability to move up and down in accordance with the relative amounts of high temp and low temp heat medium.

Specific advantages of the present invention

The present invention allows a very simple design of the HMSCs since these containers do not have to include any technical equipment like valves or pumps, which again allows these containers to be provided from any external supplier provided they satisfy basic requirements of quality, size, shape and conduit interfaces.

By locating the devices for adding (charging) or removing (discharging) heat separately from the storage containers, the system can output constant temperature until fully discharged. If these devices were located in each container, the result would be declining temperature with discharge. Offering constant temperature to processes allows external devices such as turbines and steam generators perform evenly during the discharge and the control system can be simplified.

Another advantage is that all the movable parts are contained in one container which can be tested as such at factory (Factory Acceptance Testing) before the auxiliary container is shipped to a site of operation. This reduces technical risk and can simplify financing of said storage system.

The position of the valves and pumps away from the HMSCs and rather in a separate container allows their operation to take place in a controlled environment rather than being exposed to weather and surroundings. It also increases safety of operation and allows strict access control to the technical components of the storage array.

Furthermore, the number of pumps may be reduced when the device of the present invention is configured in a cascade counting a plurality of heat medium storage containers. A device counting e.g. five HMSCs may in principle be served by a single fluid pump, though it is sensible for operational requirements that at least one additional pump is included for redundancy.

At the site of use, the individual containers may be connected by persons without engineering background, as the required operation only involves simple mechanical attachment operations, connecting conduits of standard types, which any plumber can do, and making electric connections of a kind any electrician can do. It may be convenient, also to put solar cells on top of all the containers and connecting them to a battery which again could be located in the auxiliary container, to have a backup power source for the power required to control the pumps, valves etc. to make the system running if grid power is not available.

Claims

1. Thermal energy storage device comprising at least one thermally insulated heat medium storage container (1, 2, 3, 4, 5) for a liquid heat medium, conduits (11, 21, 31, 41, 51) to transfer liquid heat medium to and from the at least one heat medium storage container (1, 2, 3, 4, 5) and a control unit (70) arranged to control the charge and discharge of liquid heat medium to and from the heat medium storage container via valves (11o/51o, 11i/51i) and pumps (P1, P2) controlled by the control unit (70), characterized in further comprising an auxiliary container (10) containing at least conduits and a pump (P1) through which liquid heat medium is circulated to energy accumulating units (EAU) and/ or energy consuming units (ECU).

2. Thermal energy storage device as claimed in claim 1, further comprising said valves (11o/51o, 11i/51i) controlled by the control unit (70).

3. Thermal energy storage device as claimed in claim 1 or 2, wherein said auxiliary container (10) is physically attached to the at least one heat medium storage container (1, 2, 3, 4, 5).

4. Thermal energy storage device as claimed any one of the preceding claims, wherein the auxiliary container (10) furthermore comprises at least one of an electric heater (55), pneumatics, and the control unit (70).

5. Thermal energy storage device as claimed in any one of the preceding claims, wherein the auxiliary container (10) furthermore comprises a compressor (60) arranged to prime the thermal energy storage device at start-up.

6. Thermal energy storage device as claimed in any one of the preceding claims, wherein said at least one thermally insulated heat medium storage container (1, 2, 3, 4, 5) is one having an outer shell selected from the group consisting of stainless steel, composite material and/ or concrete.

7. Thermal energy storage device as claimed in any one of the preceding claims, wherein said auxiliary container (10) has the same size and shape as the at least one thermally insulated heat medium storage container (1, 2, 3, 4, 5).

8. Thermal energy storage device as claimed in any one of the preceding claims, comprising three or more heat medium storage containers (1, 2, 3, 4, 5) connected in cascade to valves (11o/51o, 11i/51i) within the auxiliary container (10).

9. Thermal energy storage device as claimed in any one of claims 1-4 or 6-8, wherein the at least one thermally insulated heat medium storage container (1, 2, 3, 4, 5) is arranged at a vertical elevation allowing priming of the device to take place by the force of gravity.

10. Auxiliary container for thermal energy storage device, characterized in comprising all required pumps (P1, P2), valves (11o/51o, 11i/51i), and conduits to function as an interface between at least one heat medium storage container (1, 2, 3, 4, 5) and external energy accumulating units (EAU) and/ or energy consuming units (ECU).