Countercurrent modular packed bed heat storage system and heat storage and heat release control method thereof

Abstract

The invention discloses a countercurrent modular packed bed heat storage system and a heat storage and heat release control method thereof.The heat storage system comprises a plurality of heat storage units, each heat storage unit achieves heat storage and heat release, and during heat storage, the temperature of fluid at an outlet of the first heat storage unit is maintained to be low for a set time and then gradually rises; when the temperature of the fluid at the outlet rises to a set value, the fluid enters the next heat storage unit to continuously and fully release heat; the heat storage is completed by sequentially pushing forwards according to the mode; in the whole process, when a certain heat storage unit is completely filled with heat, the heat storage unit is controlled to stop heat storage; in the heat release process, when the temperature of the fluid at the outlet of the first heat storage unit is reduced to the set temperature, the fluid at the outlet of the first heat storage unit is connected into the next heat storage unit to continuously absorb heat; and in the whole process, when a certain heat storage unit completely releases heat, the heat storage unit is controlled to stop heat storage.

Description

Technical Field

[0001] This invention relates to the field of thermal storage, specifically to a countercurrent modular packed bed thermal storage system and its thermal storage and release control method. Background Technology

[0002] Packed bed sensible heat storage technology has received increasing attention in the field of solar thermal power generation due to its simple operation, low cost, and high heat exchange efficiency. Currently, various heat storage systems and methods are disclosed in existing technologies. For example, patent CN 1963371A discloses a high-temperature modular solar thermal storage system; patent CN 103292486B discloses a single-tank-double-tank composite heat storage system and method for solar thermal power generation; and patent CN119492278A discloses a large-scale solid thermal storage system and control method. However, the heat storage and release processes of existing thermal storage units have the following problems: In the later stages of heat storage, the outlet temperature of a thermal storage unit gradually increases before the heat transfer fluid has fully released heat, resulting in reduced heat utilization. Conversely, in the later stages of heat release, the outlet temperature gradually decreases, and the heat transfer fluid is not sufficiently heated, failing to meet the temperature requirements of the load side. Furthermore, existing multi-tank thermal storage systems cannot achieve interconnection between adjacent tanks to adjust the connection method when the outlet temperature changes during heat storage and release, ensuring full utilization of heat during storage and meeting temperature requirements during heat release. Moreover, the disclosed multi-tank systems are complex, with each thermal storage unit equipped with a heat exchanger and pump, resulting in high investment costs and hindering system capacity adjustment based on demand. Finally, no system-level heat storage / release sequence is proposed.

[0003] The published inventions do not address quantitative standards for thermal storage units. For example, a dimensionless standard should be proposed to measure the ratio of the internal thermal resistance of solid particles to the thermal resistance between the fluid and the solid. The heat transfer and resistance characteristics of the packed bed thermal storage unit can be obtained through quantitative calculation. Summary of the Invention

[0004] In order to solve the technical problems existing in the prior art, the present invention discloses a countercurrent modular filled bed thermal storage system and its thermal storage and release control method.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a countercurrent modular packed bed thermal storage and heat release control method, comprising multiple thermal storage units, each of which realizes thermal storage and heat release; During heat storage, the temperature of the fluid at the outlet of the first heat storage unit is initially maintained at a low temperature for a set time, and then gradually increases. When the temperature of the fluid at the outlet reaches the set value, it enters the next heat storage unit to continue to fully release heat. Heat storage is completed in this manner. During the entire process, when a heat storage unit is fully filled with heat, it is controlled to stop heat storage. During the heat release process, when the temperature of the outlet fluid of the first heat storage unit drops to the set temperature, the outlet fluid of the first heat storage unit is connected to the next heat storage unit to continue absorbing heat; the heat release is completed in this manner, and during the entire process, when a heat storage unit has completely released heat, it is controlled to stop heat storage. The standard for switching temperatures is as follows:

[0006]

[0007] That is, when the thermal storage occurs, the outlet temperature of the previous unit rises to When heat is released, the heat is connected to the inlet of the next thermal storage unit; when heat is released, the outlet temperature of the previous unit drops to... Then, connect it to the next heat release unit.

[0008] Secondly, the present invention proposes a counter-current modular filled bed thermal storage system, comprising multiple thermal storage units, a heat source, and a load. One end of the heat source is connected to the load via a first main pipeline, and the other end of the heat source is connected to the load via a second main pipeline. Multiple heat storage units are connected in parallel between the first main pipeline and the second main pipeline. One end of each heat storage unit is connected to the first main pipeline via a first branch pipeline, and the other end is connected to the second main pipeline via a second branch pipeline. The first main pipeline is connected to the second main pipeline via a series pipeline, and each first branch pipeline and each second branch pipeline is connected to the series pipeline via a bypass pipeline. Valves are installed on the first main pipeline, the second main pipeline, and the bypass pipeline; at the same time, a valve is installed before and after the node where the bypass pipeline connects to the first branch pipeline, and a valve is also installed at the rear end of the node where the bypass pipeline connects to the series pipeline.

[0009] As a further technical solution, a booster pump is provided on the first main pipeline and the second main pipeline; by controlling the opening and closing of each valve, multiple thermal storage units can be connected in series or in parallel.

[0010] As a further technical solution, the Biot number of particles inside the thermal storage unit... ; where h sf Let be the heat transfer coefficient between the solid particles and the heat transfer fluid; d is the equivalent diameter of the solid particles, calculated using the formula: V is the volume; k s is the thermal conductivity of the solid particles.

[0011] As a further technical solution, when the demand for heat storage and release is small, the operation of a single heat storage unit or the operation of multiple heat storage units in series can be achieved by controlling the opening and closing of valves; when the demand for heat storage and release is large, multiple heat storage units can be operated in parallel.

[0012] As a further technical solution, when only one thermal storage unit is needed for thermal storage, it is sufficient to open the valves on the first main pipeline, the second main pipeline, and the first and second branch pipelines of the corresponding thermal storage unit, and close the other valves. As a further technical solution, when multiple thermal storage units are required for thermal storage, the valves of the first main pipeline and the second main pipeline are opened first, and the valves of the first branch pipeline and the second branch pipeline of the first thermal storage unit are opened simultaneously, while other valves are closed. When the temperature of the fluid at the outlet of the first thermal storage unit rises to a set value, the valves on the bypass pipeline at the outlet of the first thermal storage unit, the valves on the series pipeline, and the valves on the first and second branch pipelines of the second thermal storage unit are opened, thus connecting the first and second thermal storage units in series. When the temperature of the fluid at the outlet of the second thermal storage unit rises to a set value, the valves on the bypass pipeline at the outlet of the third thermal storage unit, the valves on the series pipeline, and the valves on the first and second branch pipelines of the third thermal storage unit are opened, thus connecting the first, second, and third thermal storage units in series. This process is repeated sequentially to complete the thermal storage of multiple thermal storage units. Throughout the process, when a thermal storage unit is fully filled with heat, the valves on its branch pipeline are closed.

[0013] As a further technical solution, when only one thermal storage unit needs to release heat, the valves on the first main pipeline, the second main pipeline, and the first branch pipeline at the inlet of the corresponding thermal storage unit are opened, the valves on the second branch pipeline, the bypass pipeline, and the series pipeline at the outlet of the corresponding thermal storage unit are opened, and the other valves are closed to achieve heat release.

[0014] As a further technical solution, when multiple thermal storage units need to be connected in series for heat release, the valves on the first main pipeline, the second main pipeline, and the corresponding first branch pipeline of the thermal storage unit are opened; the valves on the second branch pipeline of the thermal storage unit, the corresponding bypass pipeline of the second main pipeline, and the series pipeline are opened; other valves are closed to achieve heat release from the first thermal storage unit. When the temperature of the outlet fluid of the first thermal storage unit drops to the set temperature during heat release, some valves on the first branch pipeline, the second branch pipeline, the corresponding bypass pipeline of the second branch pipeline, and the series pipeline of the second thermal storage unit are opened to connect the outlet of the first thermal storage unit to the heat release inlet of the second thermal storage unit, and the second thermal storage unit releases heat. This process is repeated sequentially to complete the heat release of multiple thermal storage units. During the entire process, when a thermal storage unit has completely released heat, the valves on its branch pipeline are closed.

[0015] As a further technical solution, when multiple thermal storage units need to be connected in parallel for thermal storage or release, the valves on the first and second branches corresponding to each thermal storage unit, as well as the valves on the first and second main pipelines, are opened, while other valves are closed.

[0016] The beneficial effects of this invention are as follows: 1. In the heat storage and release method proposed in this invention, during heat storage, the temperature of the outlet fluid of the first heat storage unit is initially maintained at a low temperature for a set time, and then gradually increases. When the temperature of the outlet fluid rises to a set value, it enters the next heat storage unit to continue fully releasing heat. This process is repeated sequentially to complete heat storage. During the entire process, when a heat storage unit is fully filled with heat, it is controlled to stop heat storage. During heat release, when the temperature of the outlet fluid of the first heat storage unit drops to a set temperature, the outlet fluid of the first heat storage unit is connected to the next heat storage unit to continue absorbing heat. This process is repeated sequentially to complete heat release. During the entire process, when a heat storage unit has completely released heat, it is controlled to stop heat storage. This invention proposes a heat storage and release sequence for each heat storage unit at the system level. Since the insulation effect of internal units is always better than that of external units in the entire system, internal units are given priority during heat storage. This minimizes heat loss to the environment after a unit has completed heat storage. Similarly, during heat release, external units should be given priority to avoid excessive heat loss from external units. This approach minimizes heat loss to improve efficiency. Furthermore, the invention provides quantitative standards for independent thermal storage units, proposes the Biot number criterion to avoid excessive temperature differences between the inside and outside of solid particles, and offers quantitative calculations of the resistance and heat transfer of the thermal storage unit to provide design references, thereby achieving the goals of reducing resistance, improving efficiency, and lowering investment costs.

[0017] 2. Each thermal storage unit in this invention can operate independently or in parallel with other units. When the demand for thermal storage and release is small, only the inlet and outlet valves of a single thermal storage unit are opened for thermal storage and release. However, since the thermal storage and release rate of a single thermal storage unit is always limited, when there is a large surplus of solar thermal resources (i.e., a large demand for thermal storage) or a large shortage of solar thermal resources (i.e., a large demand for thermal release), the inlet and outlet valves of multiple thermal storage units can be opened simultaneously to complete the thermal storage or thermal release tasks, thereby meeting the demand for high-power thermal storage and release. Therefore, the thermal storage system proposed in this invention has more flexible adjustment of thermal storage and release power and a stronger ability to adapt to the fluctuations in solar energy. 3. The thermal storage system proposed in this invention uses only one molten salt pump, installed on the main pipeline. Molten salt can be delivered to all thermal storage units by controlling the opening and closing of valves. The control valves of the corresponding units are opened only when needed for heat storage and release. Furthermore, the molten salt pump is installed at the cold end of the system, ensuring that only low-temperature molten salt flows through it, thus guaranteeing safer and more reliable operation. Additionally, the system uses only one heat exchanger installed on the main pipeline to supply heat to the heat load. Overall, the system is simple, operates stably and reliably, has low investment and operating costs, and is more conducive to system expansion. Attached Figure Description Figure 1(a) is a top view of the thermal storage process of a modular thermal storage system; Figure 1(b) is a top view of the heat release process of a modular thermal storage system. Figure 2(a) and Figure 2(b) are top views of a thermal storage system composed of multiple modules; Figure 3(a) Schematic diagram of the thermal storage process of adjacent thermal storage units; Figure 3(b) Schematic diagram of the heat release process of adjacent thermal storage units; Figure 4 This is a schematic diagram of a thermal storage system; Figure 5 This is a schematic diagram of the first unit's thermal storage device; Figure 6 Schematic diagram of the first and second thermal storage units; Figure 7 This is a schematic diagram of the second unit's thermal storage. Figure 8 This is a schematic diagram of the heat release in the first unit; Figure 9 This is a schematic diagram of the heat release in the first and second units; Figure 10 This is a schematic diagram of the heat release in the second unit; Figure 11 This is a schematic diagram of parallel thermal storage. Figure 12 This is a schematic diagram of parallel heat dissipation; Figure 13 This is a graph showing the trend of outlet temperature over time during the heat storage and release process. Figure 14A graph showing the pressure drop of fluid flowing through a packed bed region as a function of the Biot number; Figure 15 The graph shows the heat storage / release of fluid flowing through the packed bed region and the trend of heat storage / release efficiency as a function of the Biot number. In the diagram: 1. Valve; 2. Valve; 3. Valve; 4. Valve; 5. Valve; 6. Valve; 7. Valve; 8. Valve; 9. Valve; 10. Valve; 11. Valve; 12. Valve; 13. Valve; 14. Valve; 15. Valve; 16. Valve; 17. Valve; 18. Valve; 19. Valve; 20. Valve; 21. Valve; 22. Valve; 23. Valve; 24. Valve; 25. Valve; 26. Valve; 27. Valve; Detailed Implementation It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0018] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless otherwise expressly indicated by the invention, the singular form is also intended to include the plural form. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. Figure 1 shows a top view of a modular thermal storage system. One of the circular locations represents a thermal storage unit. To minimize the footprint and heat dissipation area, multiple cylindrical thermal storage units are arranged in an alternating pattern to form a hexagonal region as shown in the figure. For a thermal storage unit with a diameter of 20m and a height of 15m, its thermal storage capacity is approximately 720MWh. Under a seasonal, large-capacity, long-term thermal storage demand of 100GWh, approximately 140 single-tank thermal storage units are needed to form a large-scale thermal storage system. The specific heat storage and release methods are as follows: In Figure 1(a), the red units represent the parts that have completed heat storage, the yellow units represent the parts that are currently storing heat, and the blue units represent the parts that are yet to be stored. During heat storage, these heat storage units are heated sequentially until the heat storage process is complete. Since the internal units always have better insulation performance than the external units in the entire system, internal units are prioritized during heat storage to minimize heat loss to the environment once a unit has completed heat storage. Similarly, when releasing heat, external units should be prioritized to avoid excessive heat loss from the external units.

[0019] Meanwhile, the entire thermal storage system can take various forms. As seen in the pipe layout diagram, the system's pipes can be entirely located around the perimeter of the system, eliminating the need to install pipes for each storage unit within the gaps between them. Therefore, the storage units can be designed in a closely spaced configuration, as shown in Figures 2(a) and 2(b). When there is a large demand for thermal storage power and rapid thermal storage is required, multiple storage units can be connected in parallel for simultaneous thermal storage.

[0020] Figure 3 illustrates the operating mode of two adjacent thermal storage units during heat storage and release. During the heat storage process, when the temperature of the outlet fluid rises to a certain value, the fluid from the previous thermal storage unit is transferred to the next unit to continue releasing heat. Once the previous thermal storage unit is fully filled with heat, its inlet and outlet valves are closed, and the high-temperature heat transfer fluid directly enters the next thermal storage unit. This process is repeated sequentially to complete the heat storage process.

[0021] Similarly, during heat release, when the fluid temperature at the outlet of the previous unit drops to a certain temperature, it is connected to the next unit to continue absorbing heat. In this way, the heat carried in the fluid can be fully utilized during heat storage to improve heat storage efficiency, while maintaining a stable power output during heat release to meet the load side's requirements for the heat source temperature.

[0022] The standard for switching temperatures is as follows:

[0023]

[0024] The physical meanings of the symbols in the formula are as follows: The switching temperature during thermal storage; The switching temperature during heat release; The temperature of the molten salt at the inlet during thermal storage, i.e., the temperature of the high-temperature molten salt; The temperature of the inlet molten salt during heat release is the temperature of the low-temperature molten salt. The first formula above describes the switching standard during thermal storage, that is, the outlet molten salt temperature of the previous unit during thermal storage is changed from the temperature of the low-temperature molten salt (…). Gradually rising to When that happens, it is connected to the inlet of the next thermal storage unit; the second formula describes the switching standard during heat release, where the outlet molten salt temperature of the previous unit during heat release is determined by the temperature of the high-temperature molten salt ( Gradually decreased to When the heat is released, it is connected to the next heat release unit. This is mainly due to the limitations of the heat source and the temperature of the heat used, so that the outlet temperature is not too high during heat storage, which would result in the heat not being fully utilized, and the outlet temperature is not too low during heat release, which would fail to meet the heat demand.

[0025] To realize the modular thermal storage and its operation process proposed in this invention, this embodiment also designs an entire system including a heat source, thermal storage, and load, as shown in Figure 3. The piping mainly consists of four parts: red pipes are the main pipelines (the upper part is the first main pipeline, and the lower part is the second main pipeline); green pipes are branch pipes connecting each thermal storage unit to the main pipeline (the upper part is the first branch pipe, and the lower part is the second branch pipe); blue pipes are series pipes; and yellow pipes are bypass pipes branching off from the inlet and outlet of each thermal storage unit and connecting to the series pipes. Specifically, the connection method is as follows: One end of the heat source is connected to the load through a first main pipeline, and the other end of the heat source is connected to the load through a second main pipeline. Multiple heat storage units are connected in parallel between the first main pipeline and the second main pipeline. One end of each heat storage unit is connected to the first main pipeline through a first branch pipeline, and the other end is connected to the second main pipeline through a second branch pipeline. The first main pipeline is connected to the second main pipeline through a series pipeline, and each first branch pipeline and each second branch pipeline is connected to the series pipeline through a bypass pipeline. Valves are installed on the first main pipeline, the second main pipeline, and the bypass pipeline; at the same time, a valve is installed before and after the node where the bypass pipeline connects to the first branch pipeline, and a valve is also installed at the rear end of the node where the bypass pipeline connects to the series pipeline.

[0026] High-temperature fluids from heat sources such as solar absorbers, after meeting the heat requirements for power generation, will release excess heat if any remains. Some of this high-temperature fluid will flow from the top of the packed bed thermal storage unit, transferring heat to the solid particles within and storing it as it flows downwards. The cooled fluid, after releasing heat, will flow out from the bottom of the storage unit and return to the absorber for reheating. If the temperature at the outlet of the first thermal storage unit rises, the heat transfer medium flowing from the bottom of the first unit will be sent through another pipeline to the top inlet of the next thermal storage unit to continue releasing heat from the low-temperature solid particles.

[0027] When solar thermal energy cannot meet the power generation needs of the load side, the heat stored in the thermal storage unit can serve as a supplementary heat source. At this time, the low-temperature heat transfer fluid enters from the bottom of the thermal storage unit, absorbs heat from the solid particles during the upward flow, and flows out from the top of the thermal storage unit after the temperature rises. Together with the high-temperature fluid from the solar heat absorption field, it provides the required heat for the load.

[0028] As the heat release process proceeds, the temperature of the heat transfer medium flowing out from the top will decrease. At this time, the fluid flowing out from the top outlet of the heat storage unit is led through a bypass pipe to the bottom inlet of the next heat storage unit to continue absorbing heat. The high-temperature fluid flowing out from the top outlet of the next unit is sent to the load to release heat. In this way, the heat storage system can maintain a relatively stable output power.

[0029] One of the thermal storage units is a cylindrical thermal storage unit. This thermal storage device consists of the thermal storage unit, solid thermal storage particles, and fluid inlet and outlet pipes. To ensure more uniform and stable fluid flow within the thermal storage unit, flow equalizers are installed at the top and bottom of the unit. Additionally, a metal support frame is installed at the bottom of the unit to support the solid thermal storage particles. The spherical thermal storage particles accumulate within the cylindrical thermal storage unit to form a packed bed, with the gaps created by their mutual support serving as channels for fluid flow and heat exchange.

[0030] For a single thermal storage unit, the thermal storage process is as follows: at temperature T ch,in The high-temperature heat transfer medium flows in from the upper channel, passes through the flow equalizer, and enters the packed bed region. Within the packed bed region, the high-temperature fluid heats the solid particles, transferring heat energy to the storage spheres for storage as sensible heat. The cooled, low-temperature fluid flows out from the lower channel. When the heat storage process is completely finished, the heat storage device is filled with a temperature of T. ch,in The heat transfer fluid and solid particles. The heat release process occurs at temperature T. dis,in The cryogenic fluid enters from the lower channel, absorbs heat from the solid particles, rises in temperature, and flows out from the top channel of the thermal storage unit. When the heat release process of the thermal storage unit is completely finished, it is filled with fluid at a temperature of T. dis,in The heat transfer fluid and solid heat storage particles.

[0031] The following describes the heat storage and release process: The thermal storage process is as follows: When the first thermal storage unit stores heat: (e.g.) Figure 4 As shown, valves 1, 2, 5, 6, 7, 8, 26, and 27 are open, while the remaining valves are closed; the specific valves that are opened are... Figure 5 The valves on the solid line; the flow direction of the high-temperature fluid is as follows: the high-temperature fluid coming out of the heat source first flows through valve 1 and valve 26 to heat the load. After heating the load, the low-temperature fluid passes through valve 27 and valve 2 and then re-enters the heat source for heating. When the high-temperature fluid meets the heat requirements of the load, the heat of the high-temperature fluid will be stored in the heat storage unit. At this time, part of the high-temperature fluid flows through valve 1, valve 5, and valve 6 to enter the first heat storage unit. Then, after coming out of the first heat storage unit, it passes through valve 7, valve 8, pump, and valve 2 and re-enters the heat source for heating and circulation. When the temperature of the fluid at the outlet of the first thermal storage unit rises to a certain value, its outlet is connected to the inlet of the second thermal storage unit: For example... Figure 6As shown, in this state: Valves 1, 2, 4, 5, 6, 7, 10, 14, 15, 16, 17, 18, 19, 26, and 27 are open, and the remaining valves are closed; specifically, the open valves are... Figure 5 Valves on solid lines; Once the first thermal storage unit is fully filled with heat, the high-temperature fluid is directly connected to the second thermal storage unit: For example... Figure 6 As shown, in this state: valves 1, 2, 13, 14, 15, 16, 26, and 27 are closed; the remaining valves are open. Specifically, the open valves are: Figure 6 Valves on solid lines; When the outlet temperature of the second thermal storage unit rises to a certain value, its outlet is connected to the third thermal storage unit, and so on.

[0032] The heat release process is as follows: When the first thermal storage unit releases heat, valves 1, 2, 3, 4, 5, 6, 7, 26, and 27 are opened, and the remaining valves are closed. Specifically, the valves that are opened are: Figure 8 The valves on the solid line; after the low-temperature fluid flows out from the load valve 27, part of it enters the heat source for heating through the pump body and valve 2; the other part enters the first heat storage unit for heating through valves 3, 4 and 7 in sequence. The heated fluid enters the load through valves 6, 5 and 26 to heat the load. When the temperature of the outlet fluid in the first thermal storage unit drops to a certain temperature during the heat release process, its outlet is connected to the heat release inlet of the second unit, such as... Figure 9 As shown; valves 1, 2, 3, 4, 6, 7, 11, 12, 13, 14, 15, 18, 19, 26, and 27 are open, and the remaining valves are closed; the specific valves that are open are... Figure 8 The valves are shown on the solid line. The specific process is as follows: the heated fluid from the first thermal storage unit exits from the top of the unit and sequentially passes through valves 6, 11, 19, 18, 12, 15, 14, 13, and 26 before entering the load to heat it. Once the first unit has completely released its heat, the cryogenic fluid directly enters the second unit to absorb heat. For example... Figure 10 As shown, valves 1, 2, 3, 10, 12, 13, 14, 15, 26, and 27 are open, while the remaining valves are closed; the specific valves that are opened are... Figure 10The valves on the solid line; the specific process is as follows: after the low-temperature fluid flows out from the load valve 27, part of it enters the heat source for heating through the pump body and valve 2; the other part enters the second heat storage unit for heating in sequence through valves 3, 10, 12, and 15. The heated fluid enters the load through valves 14, 13, and 26 to heat the load. When the outlet temperature of the second heat storage unit drops to a certain value, its outlet is connected to the third heat storage unit, and so on.

[0033] Furthermore, the thermal storage system provided in this embodiment can also utilize multiple tanks connected in parallel for thermal storage and release, such as... Figure 11 This is a schematic diagram of parallel thermal storage. Figure 12 This is a schematic diagram of parallel heat dissipation; such as Figure 11 As shown, when the first and second thermal storage units are connected in parallel, valves 1, 2, 5, 6, 7, 8, 13, 14, 15, 16, 26, and 27 are closed; the remaining valves are closed. Specifically, the open valves are: Figure 10 The valves on the solid line; the specific process is as follows: the high-temperature fluid coming out of the heat source first flows through valve 1 and valve 26 to heat the load. After heating the load, the low-temperature fluid passes through valve 27 and valve 2 and then re-enters the heat source for heating. When the high-temperature fluid meets the heat requirements of the load, the heat of the high-temperature fluid will be stored in the heat storage unit. At this time, part of the high-temperature fluid flows through valve 1, valve 5, and valve 6 to enter the first heat storage unit. After exiting the first heat storage unit, it passes through valve 7, valve 8, pump, and valve 2 and re-enters the heat source for heating and circulation. At the same time, part of the high-temperature fluid flows through valve 1, valve 13, and valve 14 to enter the second heat storage unit. After exiting the bottom of the second heat storage unit, it passes through valve 15, valve 16, pump, and valve 2 and re-enters the heat source for heating and circulation. like Figure 12 As shown, when the first and second thermal storage units are connected in parallel to release heat, valves 1, 2, 3, 4, 5, 6, 7, 10, 12, 13, 14, 15, 26, and 27 are closed; the remaining valves are closed. Specifically, the open valves are: Figure 11The valves on the solid line; the specific process is as follows: After the cryogenic fluid flows out from valve 27 of the load, a portion of it enters the heat source for heating through the pump body and valve 2; simultaneously, another portion enters the first heat storage unit for heating through valves 3, 4, and 7 in sequence, and the heated fluid enters the load through valves 6, 5, and 26 to heat the load; at the same time, another portion enters the second heat storage unit for heating through valves 3, 10, 12, and 15 in sequence, and the heated fluid enters the load through valves 14, 13, and 26 to heat the load; Furthermore, in packed bed thermal storage tanks, the heat carried by the heat transfer fluid is first transferred to the surface of the solid particles, and then transferred to the center of the particles through thermal conduction. In order to transfer heat from the outer surface to the center with a small temperature gradient and avoid excessive temperature difference between the inside and outside of the particles, which would reduce the heat storage and release efficiency, a dimensionless criterion for estimating the relative importance of the internal thermal resistance of the particles, namely the Biot number, is proposed, which is defined as follows:

[0034] Among them, h sf Let d be the heat transfer coefficient between the solid particles and the heat transfer fluid, d be the diameter of the solid particles, and k be the heat transfer coefficient. s is the thermal conductivity of the solid particles.

[0035] To meet the above requirements, when the heat transfer fluid is molten salt and the solid particulate material is steel slag, the ratio of the solid particle thermal resistance described by the Biot number to the convective heat transfer thermal resistance should be 0.339.

[0036] Furthermore, the experimental process for the resistance and heat transfer characteristics of each thermal storage unit is as follows, with the resistance characteristics analyzed as follows: The pressure drop of fluid flowing through the packed bed region varies with the Biot number as follows: Figure 14 As shown in the figure, the characteristics of the pressure drop across the packed bed region with respect to the Biot number are as follows: when the Biot number in the packed bed is 0.238, 0.339, 0.42, and 0.491, the corresponding pressure drops are 15.08, 4.07, 1.95, and 1.16 Pa, respectively. Therefore, it can be seen that when the Biot number increases from 0.238 to 0.491, the pressure drop begins to decrease rapidly, and then the rate of decrease becomes smaller with further increases in the Biot number.

[0037] The analysis process for the heat transfer characteristics is as follows: As the Biot number increases, the stored and released heat gradually decreases. When the Biot number is 0.238, the stored heat is 484.9 MW and the released heat is 428.4 MW. When the Biot number is 0.491, the stored heat is 438.5 MW and the released heat is 294.4 MW. Figure 15As shown in the storage / release efficiency curves, both storage and release efficiencies decrease approximately linearly with increasing Biot number, with the release efficiency decreasing more rapidly. At a Biot number of 0.238, the storage and release efficiencies are 0.94 and 0.83, respectively; at a Biot number of 0.491, the storage and release efficiencies are 0.85 and 0.57, respectively.

[0038] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlling heat storage and release in a counter-current modular packed bed, comprising multiple heat storage units, each of which performs both heat storage and heat release, characterized in that: During heat storage, the temperature of the fluid at the outlet of the first heat storage unit is initially maintained at a low temperature for a set time, and then gradually increases. When the temperature of the fluid at the outlet reaches the set value, it enters the next heat storage unit to continue to fully release heat. Heat storage is completed in this manner. During the entire process, when a heat storage unit is fully filled with heat, it is controlled to stop heat storage. During the heat release process, when the temperature of the outlet fluid of the first heat storage unit drops to the set temperature, the outlet fluid of the first heat storage unit is connected to the next heat storage unit to continue absorbing heat; the heat release is completed in this manner, and during the entire process, when a heat storage unit has completely released heat, it is controlled to stop heat storage. The standard for switching temperatures is as follows: That is, when the thermal storage occurs, the outlet temperature of the previous unit rises to When heat is released, the heat is connected to the inlet of the next thermal storage unit; when heat is released, the outlet temperature of the previous unit drops to... Then, connect it to the next heat release unit.

2. A countercurrent modular packed bed thermal storage and heat release system for implementing the thermal storage and heat release control method of claim 1, characterized in that: Includes multiple thermal storage units, heat sources, and loads; One end of the heat source is connected to the load via a first main pipeline, and the other end of the heat source is connected to the load via a second main pipeline. Multiple heat storage units are connected in parallel between the first and second main pipelines. One end of each heat storage unit is connected to the first main pipeline via a first branch pipeline, and the other end is connected to the second main pipeline via a second branch pipeline. The first main pipeline is connected to the second main pipeline via a series pipeline, and each first branch pipeline and second branch pipeline is connected to the series pipeline via a bypass pipeline. Valves are installed on the first main pipeline, the second main pipeline, and the bypass pipeline. A valve is installed before and after the node where the bypass pipeline connects to the first branch pipeline, and a valve is also installed at the rear end of the node where the bypass pipeline connects to the series pipeline.

3. The countercurrent modular packed bed thermal storage and release system as described in claim 2, characterized in that: A booster pump is installed on the first main pipeline and the second main pipeline; by controlling the opening and closing of each valve, multiple thermal storage units can be connected in series or in parallel.

4. The countercurrent modular packed bed thermal storage and release system as described in any one of claims 2-3, characterized in that: Biwo number of particles inside the thermal storage unit ; where h sf Let be the heat transfer coefficient between the solid particles and the heat transfer fluid; d is the equivalent diameter of the solid particles, calculated using the formula: V is the volume; k s is the thermal conductivity of the solid particles.

5. A control method for a counter-current modular packed bed thermal storage and release system as described in any one of claims 2-4, characterized in that: When the demand for heat storage and release is small, the operation of a single heat storage unit or multiple heat storage units can be achieved by controlling the opening and closing of valves; when the demand for heat storage and release is large, multiple heat storage units can be operated in parallel.

6. A control method for a countercurrent modular packed bed thermal storage and release system as described in any one of claims 2-4, characterized in that: When only one thermal storage unit is needed for thermal storage, simply open the valves on the first main pipeline, the second main pipeline, and the first and second branch pipelines of the corresponding thermal storage unit, and close the other valves.

7. A control method for a countercurrent modular packed bed thermal storage and release system as described in any one of claims 2-4, characterized in that: When multiple thermal storage units are required for thermal storage, first open the valves of the first and second main pipelines, and simultaneously open the valves of the first and second branch pipelines of the first thermal storage unit, while closing the other valves. When the temperature of the fluid at the outlet of the first thermal storage unit rises to the set value, open the valves on the bypass pipeline at the outlet of the first thermal storage unit, as well as the valves on the series pipelines, and the valves on the first and second branch pipelines of the second thermal storage unit, thus connecting the first and second thermal storage units in series. When the temperature of the fluid at the outlet of the second thermal storage unit rises to the set value, open the valves on the bypass pipeline at the outlet of the third thermal storage unit, as well as the valves on the series pipelines, and the valves on the first and second branch pipelines of the third thermal storage unit, thus connecting the first, second, and third thermal storage units in series. This process is repeated sequentially to complete the thermal storage of multiple thermal storage units. Throughout the process, when a thermal storage unit is fully filled with heat, the valves on its branch pipelines are closed.

8. A control method for a countercurrent modular packed bed thermal storage and release system as described in any one of claims 2-4, characterized in that: When only one thermal storage unit needs to release heat, open the valves on the first main pipeline, the second main pipeline, and the first branch pipeline at the inlet of the corresponding thermal storage unit; open the valves on the second branch pipeline, the bypass pipeline, and the series pipeline at the outlet of the corresponding thermal storage unit; and close the other valves to release heat.

9. A control method for a countercurrent modular packed bed thermal storage and release system as described in any one of claims 2-4, characterized in that: When multiple thermal storage units need to be connected in series for heat release, open the valves on the first main pipeline, the second main pipeline, and the first branch pipeline of the corresponding thermal storage unit; open the valves on the second branch pipeline of the thermal storage unit, the bypass pipeline corresponding to the second branch pipeline, and the series pipeline; close the other valves to release heat from the first thermal storage unit. When the temperature of the outlet fluid of the first thermal storage unit drops to the set temperature during heat release, open the valves on the first branch pipeline, the second branch pipeline, the bypass pipeline corresponding to the second branch pipeline, and some valves on the series pipeline of the second thermal storage unit to connect the outlet of the first thermal storage unit to the heat release inlet of the second thermal storage unit, and the second thermal storage unit releases heat. Proceed in this manner to complete the heat release of multiple thermal storage units. During the entire process, once a thermal storage unit has completely released heat, close the valves on its branch pipeline.

10. A control method for a countercurrent modular packed bed thermal storage and release system as described in any one of claims 2-4, characterized in that: When multiple thermal storage units need to be connected in parallel for thermal storage or release, open the valves on the first and second branches corresponding to each thermal storage unit, as well as the valves on the first and second main pipelines, and close the other valves.

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