A multi-stage heat storage device

Abstract

The present invention discloses a multi-stage heat storage device, including a heat storage tank and a heat exchange tube; the heat storage tank is filled with at least a first heat storage medium, a second heat storage medium, and a third heat storage medium from bottom to top, and the specific heat capacities of the third heat storage medium, the second heat storage medium, and the first heat storage medium increase in sequence; the heat exchange tube is in a snake shape in the vertical direction, and the heat exchange tube passes through the third heat storage medium, the second heat storage medium, and the first heat storage medium in sequence along the vertical direction of the heat storage tank. In the present invention, at least three heat storage media with different specific heats are filled in the heat storage tank, and the specific heats with a gradient from top to bottom can maximize the use of the temperature difference to reduce heat loss and improve the heat storage capacity. At the same time, the heat transfer medium in the heat exchange tube is gradually heated up, extending the service life of the heat exchange tube.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar thermal power generation, and in particular relates to a multi-stage heat storage device for a thermal power station. Background Art

[0002] In solar tower power stations, a heat storage system is essential to achieve continuous and stable power output, and the heat storage tank is the core equipment of the heat storage system. In addition, since the solar thermal power generation technology is already in the third generation, it requires a significant increase in power generation and heat storage temperature, which also promotes the application of new storage / heat exchange technology. In order to adapt to the development of new technologies, the design of heat storage tanks needs to carry out key innovative engineering research.

[0003] At present, heat storage tanks are mainly molten salt storage tanks, which are suitable for molten salt storage below 565°C. In the third-generation tower power station technology, the maximum temperature of the storage / heat exchange medium is at least 700°C, which forces the use of new high-temperature heat carriers. Among them, liquid metal, high-temperature carbonate, and high-temperature chloride salt are listed as key considerations. However, due to the high price of liquid metal, it is not yet suitable for heat storage medium, but it can be used as a heat exchange medium. Because it has good thermal conductivity and large specific heat capacity, it has received widespread attention and focused research in the engineering community. In order to match liquid metal as a heat exchange medium, a new heat storage system needs to be completely designed. Summary of the invention

[0004] The embodiment of the present invention provides a multi-stage heat storage device, in which at least a first heat storage medium, a second heat storage medium, and a third heat storage medium with decreasing specific heat capacities are sequentially filled in the heat storage tank from bottom to top, and the heat exchange tube passes through all the heat storage media in sequence in the vertical direction, and the second heat storage medium transfers heat to the first heat storage medium and the third heat storage medium. Since the specific heat capacities of the heat storage media are different from bottom to top, the gradient specific heat from top to bottom can maximize the use of the temperature difference to reduce heat loss and improve the heat storage capacity. At the same time, the heat exchange medium in the heat exchange tube flows through the heat storage tank to achieve gradual temperature increase, thereby extending the service life of the heat exchange tube.

[0005] The technical solution of the present invention is:

[0006] A multi-stage heat storage device comprises a heat storage tank and a heat exchange tube;

[0007] The heat storage tank is filled with at least a first heat storage medium, a second heat storage medium, and a third heat storage medium in sequence from bottom to top, and the specific heat capacities of the third heat storage medium, the second heat storage medium, and the first heat storage medium increase in sequence;

[0008] The heat exchange tube is in a snake shape in the vertical direction, and the heat exchange tube passes through the third heat storage medium, the second heat storage medium, and the first heat storage medium in sequence along the vertical direction of the heat storage tank.

[0009] The first heat storage medium is a solid heat storage medium, the second heat storage medium is a liquid heat storage medium at high temperature, and the third heat storage medium is a gas.

[0010] The multi-stage heat storage device further includes a liquid collecting box, which is arranged at the bottom of the heat storage tank, and a plurality of connecting holes connecting the liquid collecting box and the second heat storage medium are provided in the first heat storage medium. The connecting holes are provided in the first heat storage medium so that the second heat storage medium can flow into the first heat storage medium, so that the heat exchange is uniform, and the second heat storage medium after the heat exchange flows into the liquid collecting box.

[0011] The solid heat storage medium is a mixture of solid iron-based materials, and the second heat storage medium is molten salt.

[0012] The solid heat storage medium is cast steel, the second heat storage medium is molten salt, and the third heat storage medium is inert gas. An inert gas filling hole is provided at the top of the heat storage tank, and the filling holes are respectively connected to a vacuum pump and an inert gas filling device. The redundant part above the molten salt is filled with inert gas, and the inert gas obtains high temperature through heat transfer through the molten salt. On the one hand, the high temperature is used to keep the molten salt warm, and on the other hand, the heat insulation effect of the inert gas also plays a role in heat preservation. The inert gas uses the temperature difference to maximize the preservation of the heat lost by the molten salt, and ultimately improves the heat storage capacity.

[0013] The heat storage tank is provided with a second heat storage medium inlet.

[0014] In the horizontal direction, from the inlet of the second heat storage medium, from far to near, the cross-sectional area of ​​the fluid in the plurality of connecting holes decreases successively. That is, in the horizontal direction, from the inlet of the second heat storage medium, from far to near, the diameter of the connecting holes decreases successively; or in the horizontal direction, from the inlet of the second heat storage medium, from far to near, the number of the connecting holes opened in the first heat storage medium decreases. Both implementations are conducive to more second heat storage medium far from the inlet of the second heat storage medium entering the first heat storage medium, and the second heat storage medium near the inlet of the second heat storage medium has a longer retention time in the first heat storage medium, which can increase the contact time between the second heat storage medium and the surface of the first heat storage medium, and perform sufficient heat exchange; and it is conducive to the temperature balance of the fluid, so that the first heat storage medium is evenly heated, and the heat exchange medium in the heat exchange tube directly absorbs heat from the first heat storage medium, which can improve the heat absorption efficiency.

[0015] The heat exchange tube includes a first connector and a second connector. The heat exchange tube in the third heat storage medium is connected to the heat exchange tube in the second heat storage medium by the first connector, and the heat exchange tube in the second heat storage medium is connected to the heat exchange tube in the first heat storage medium by the second connector, and the first connector and the second connector are arranged outside the heat storage tank. The connector design is easy to disassemble, and convenient for the inspection and replacement of the heat exchange tube; secondly, the connector design is easy to process and design the heat storage tank, and the layout of the heat exchange tube is relatively simple.

[0016] The bottom of the liquid collecting tank is an inclined plane, and the bottom plane of the liquid collecting tank adopts an inclined design to facilitate the second heat storage medium to flow out of the liquid collecting tank, avoid the second heat storage medium from accumulating at the bottom of the liquid collecting tank, and ensure the operation safety of the liquid collecting tank.

[0017] A base with an inclined plane matching the shape of the liquid collecting tank is arranged below the liquid collecting tank to ensure the stability of the liquid collecting tank and the heat storage tank.

[0018] The embodiment of the present invention adopts the above technical solution, so it has the following advantages and positive effects compared with the prior art:

[0019] In the heat storage device of the embodiment of the present invention, the second heat storage medium is both a heat absorbing medium and a heat storage medium. The heat storage tank is filled with at least the first heat storage medium, the second heat storage medium, and the third heat storage medium from bottom to top, and the specific heats of the first heat storage medium, the second heat storage medium, and the third heat storage medium are successively reduced. The second heat storage medium contacts the first heat storage medium and transfers heat to the first heat storage medium. Since the first heat storage medium has a large specific heat capacity, the heat storage capacity of the same volume state is stronger, which is beneficial to a smaller heat storage space; the second heat storage medium transfers heat to the third heat storage medium at the same time; since the specific heat capacities of the third heat storage medium, the second heat storage medium, and the first heat storage medium increase successively, during the heat release process, due to the inevitable heat loss, the three A temperature difference gradually appears, and the specific heat that is gradient from top to bottom can maximize the use of the temperature difference to reduce heat loss and improve the heat storage capacity. Specifically: the first heat storage medium has the largest specific heat capacity, and its temperature is the highest after a certain period of heat release. The third heat storage medium is the opposite. On the one hand, the second heat storage medium is in a high temperature state and has a heat preservation effect on the first heat storage medium. On the other hand, its specific heat is smaller than that of the first heat storage medium, and it uses the temperature difference to absorb heat to maximize the preservation of the heat dissipated by the first heat storage medium. The third heat storage medium also obtains a high temperature after being heated in the early stage. On the one hand, it uses the high temperature to keep the second heat storage medium warm. On the other hand, the third heat storage medium uses the temperature difference to maximize the preservation of the heat dissipated by the molten salt, and finally improves the heat storage capacity.

[0020] In the heat storage process, as the specific heat of the third heat storage medium, the second heat storage medium and the first heat storage medium gradually increases, before reaching temperature equilibrium, the temperatures of the three are reduced at once, and the high-temperature medium transfers heat to the low-temperature medium, which improves the heat storage efficiency to a certain extent.

[0021] The third heat storage medium heats the heat exchange tube for the first time, the second heat storage medium heats the heat exchange tube for the second time, and the third heat storage medium heats the heat exchange tube for the third time. Since the specific heat of the three heat storage media increases from top to bottom, during the heat release process, the heat transfer medium in the heat exchange tube will gradually and steadily increase in temperature when flowing through the heat storage tank, which will not cause a large cold and hot shock to the heat exchange tubes of each part, thereby extending the service life of the pipeline.

[0022] In another embodiment of the present invention, a three-stage heating method is directly adopted. The heat storage medium filled from bottom to top includes cast steel, molten salt, and inert gas. There is a redundant design above the molten salt liquid level of the heat storage tank. The redundant part of the tank body has not been specially treated, and there is impurity gas. The impurity gas mixes with the molten salt and enters the system pipeline, which will cause a certain degree of pipeline corrosion, or cause cavitation between the pipe and the fluid, resulting in a decrease in heat exchange efficiency. In addition, in the molten salt storage tank, the redundant part of the gas will be heated, but the heat obtained is not fully utilized, resulting in a waste of heat energy. The present invention fills inert gas above the molten salt liquid level, so that the amount of impurity gas in the working fluid of the heat absorption and storage pipeline is reduced, thereby reducing the corrosion effect of impurity gas on the system pipeline; the inert gas obtains high temperature through heat transfer of the molten salt. On the one hand, the high temperature is used to keep the molten salt warm, and on the other hand, the heat insulation effect of the inert gas also plays a role in heat preservation. The inert gas uses the temperature difference to maximize the preservation of the heat lost by the molten salt, and ultimately improves the heat storage capacity;

[0023] In addition, the thermal conductivity of cast steel is much greater than that of molten salt, which can quickly heat the heat transfer medium in the heat exchange tube and improve the heat exchange efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the structure of a multi-stage heat storage device in an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram of the connection of the multi-stage heat storage device of the present invention in a solar thermal power station system;

[0026] Figure 3 It is a front view of the liquid collecting tank in the embodiment of the present invention;

[0027] Figure 4 1 is a top view of a liquid collecting tank in an embodiment of the present invention.

[0028] Explanation of the accompanying drawings: 1-heat exchange medium pipeline, 2-multi-stage heat storage device, 3-heat absorption medium pipeline; 4-heat exchange tube; 5-inert gas; 6-first connecting piece; 7-cast steel; 8-steel pipe; 9-heat storage tank; 10-liquid collecting tank; 11-second connecting piece; 12-molten salt inlet; 13-molten salt; 14-filling hole valve; 15-filling device valve; 16-vacuum pump valve; 17-vacuum pump; 18-filling device; 19-gas cylinder; 20-molten salt outlet; 21-base. DETAILED DESCRIPTION

[0029] The following is a further detailed description of a multi-stage heat storage device proposed by the present invention in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description and claims.

[0030] The multi-stage heat storage medium in this embodiment is used in a solar thermal power station. Figure 1 The device comprises a heat storage tank 9, a heat exchange tube 4 and a liquid collecting tank 10, and the liquid collecting tank 10 is arranged at the bottom of the heat storage tank 9;

[0031] The heat storage tank in this embodiment is filled with cast steel 7, molten salt 13, and inert gas 5 from bottom to top. Since it is difficult to process a connecting hole connecting the molten salt 13 and the liquid collecting tank 10 in the cast steel 7, a steel pipe connecting the molten salt 13 and the liquid collecting tank 10 is provided in the cast steel 7, and the steel pipe 8 is cast integrally with the cast steel 7 to avoid the difference in expansion coefficient caused by the inconsistency of the materials of the two, and ensure the stability of the structure. The steel pipe 8 is arranged vertically, which is convenient for the molten salt 13 to go down and transfer heat to the cast steel 7. The molten salt 13 enters the liquid collecting tank 10 through the steel pipe 8, and transfers heat to the cast steel 7 while flowing into the steel pipe 8;

[0032] A molten salt inlet 12 is provided on the heat storage tank 9, and the high-temperature molten salt 13 enters the heat storage tank 9 to transfer heat to the heat transfer medium in the heat exchange tube 4. The liquid collecting tank 10 is provided with a molten salt outlet 20. After the molten salt 13 transfers heat to the heat transfer medium, the low-temperature molten salt 13 flows into the liquid collecting tank 10, and the molten salt in the liquid collecting tank 10 continues to absorb the heat of the solar energy; an inert gas 5 filling hole is provided at the top of the heat storage tank 9, and the rear end of the filling hole is connected to the vacuum pump 17 and the inert gas filling device 18 through a three-way valve, respectively. The filling of the inert gas 5 is carried out through the filling structure on the upper part of the heat storage tank 9, and the rear end of the filling hole is connected to the vacuum pump 17 and the inert gas filling device 18 through a three-way valve, respectively. Specifically, the filling hole is connected to the vacuum pump 17, the filling hole valve 14 and the vacuum pump valve 16 are opened, and the heat storage device is evacuated. After completion, the filling hole valve 14 and the vacuum pump valve 16 are closed; then, the filling hole valve 14 and the inert gas filling device valve 15 are opened, and through the pressure difference between the inert gas cylinder 19 and the heat storage tank 9, the inert gas 5 passes through the filling device 18 and automatically fills the redundant part of the upper part of the heat storage tank 9, completing the filling of the inert gas 5. After the filling of the inert gas 5 is completed, the filling hole valve 14 and the inert gas filling device valve 15 are closed;

[0033] The heat exchange tube 4 is serpentine in the vertical direction. The heat exchange tube 4 passes through the inert gas 5, molten salt 13, and cast steel 7 in sequence along the vertical direction of the heat storage tank, and then is connected to the heat exchanger of the subsequent generator set.

[0034] It should be noted that in the process of solar thermal power generation, molten salt is both a heat absorbing medium and a heat storage medium. It heats the heat transfer medium in the heat exchange tube and directly transfers the heat stored in the molten salt to the heat transfer medium in the heat exchange tube. Therefore, Figure 2 As shown, the heat exchange pipe 4 of the multi-stage heat storage device is connected to the heat exchange medium pipeline 1, and the molten salt inlet 12 is connected to the heat absorption medium pipeline 3. The working medium in the heat exchange medium pipeline 1 is liquid metal, and the working medium in the heat absorption medium pipeline 3 is molten salt. The molten salt absorbs solar energy from the heat absorber; after absorbing heat, the molten salt enters the heat storage device, exchanges heat with the inert gas and cast steel, and stores heat. At the same time, the molten salt itself also stores heat; after the liquid metal heat exchange is completed, it enters the heat exchanger of the subsequent generator set for heat exchange.

[0035] The three-stage heat storage method of this embodiment is not limited to the three-stage heat storage method. For example, a heat storage medium can be added between the molten salt and the inert gas, etc. In this embodiment, the inert gas 5 is located in the redundant part required by the original heat storage tank 9 design. Its filling can remove the impurity gas of the original system, thereby reducing the corrosion effect of the impurity gas on the system pipeline (for example, a high oxygen content will accelerate the oxidation reaction between the molten salt 13 and the pipeline steel, and chemically corrode the steel). At the same time, the inert gas 5 has a heat preservation effect on the molten salt 13 part, and also heats it. The inert gas uses the temperature difference to maximize the preservation of the heat lost by the molten salt, and ultimately improves the heat storage capacity;

[0036] The steel pipe 8 design of the cast steel 7 can prolong the retention time of the high-temperature molten salt 13 in the secondary heating zone and improve the heat storage capacity; the specific heat capacities of the cast steel 7, molten salt 13, and inert gas 5 decrease in sequence. During the heat release process, due to the inevitable heat loss, a temperature difference gradually appears among the three. The gradient specific heat from top to bottom can maximize the use of the temperature difference to reduce heat loss and improve the heat storage capacity. In addition, since the specific heat capacity of the cast steel 7 is twice that of the molten salt 13, the volume of the cast steel 7 is much smaller than that of the molten salt 13 under the same heat storage capacity, and the volume of the heat storage tank 9 can be reduced;

[0037] The inert gas 5 heats the liquid metal entering the heat storage tank 9 for the first time, the molten salt 13 heats the liquid metal for the second time, and the cast steel 7 heats the liquid metal for the third time. Since the specific heats of the inert gas 5, the molten salt 13, and the cast steel 7 increase successively, during the heat release process, the liquid metal in the heat exchange tube 4 will gradually and steadily heat up when flowing through the heat storage tank 9, and the thermal conductivity of the cast steel 7 is much greater than that of the molten salt 13, so the liquid metal in the heat exchange tube 4 can be quickly heated to improve the heat exchange efficiency.

[0038] like Figure 3 and Figure 4As shown, in the horizontal direction, from the molten salt inlet 12, from far to near, the cross-sectional area of ​​the molten salt 13 in a single steel pipe 8 decreases successively; or, in the horizontal direction, from the molten salt inlet 12, from far to near, the total cross-sectional area of ​​the molten salt 13 in the steel pipe 8 decreases successively. That is, in the horizontal direction, from the molten salt inlet 12, from far to near, the number of steel pipes 8 in the cast steel 7 gradually decreases; or on the horizontal plane, from the molten salt inlet 12, from far to near, the diameters of several steel pipes 8 decrease successively. Far away from the molten salt inlet 12, the number of steel pipes 8 arranged is large or the diameter of the steel pipe 8 is increased, which is conducive to more molten salt 13 far away from the molten salt inlet 12 entering the collecting tank 10; and the high-temperature molten salt 13 near the molten salt inlet 12 has a longer retention time in the cast steel 7, which can increase the contact time between the high-temperature molten salt 13 and the surface of the cast steel 7, and perform sufficient heat exchange, so that the cast steel 7 can store more heat, thereby reducing the heat storage capacity of the molten salt 13, and the volume of the tank can be reduced; furthermore, the temperature of the molten salt 13 far away from the molten salt inlet 12 is often lower than the temperature near the molten salt inlet 12. This encrypted layout form can increase the flow rate of the molten salt 13 far away from the molten salt inlet 12 entering the collecting tank 10, accelerate the replacement of the molten salt 13, ensure that the temperature of the molten salt 13 in the secondary heat storage part is always in a high state, and the temperature of the molten salt 13 in the secondary heat storage part remains relatively balanced, which is conducive to the temperature consistency of the fluid, so that the cast steel 7 is evenly heated.

[0039] like Figure 1 As shown, the heat exchange tube includes a first connector 6 and a second connector 11, the heat exchange tube 4 in the inert gas 5 and the heat exchange tube 4 in the molten salt 13 are connected by the first connector 6, the heat exchange tube 4 in the molten salt 13 and the heat pipe in the cast steel 7 are connected by the second connector 11, and the first connector 6 and the second connector 11 are both arranged outside the heat storage tank 9. The heat exchange tubes in each heat storage medium are connected by connectors, which is convenient for disassembly, and convenient for the inspection and replacement of the heat exchange tube 4; secondly, the connector design is convenient for the processing design of the heat storage tank 9, and the layout of the heat exchange tube 4 is relatively simple.

[0040] See also Figure 1 The bottom of the liquid collecting tank 10 is an inclined plane, and the bottom plane of the liquid collecting tank 10 is inclined, which is convenient for the molten salt 13 to flow out of the liquid collecting tank 10, and does not cause the molten salt 13 to accumulate at the bottom of the liquid collecting tank 10, thereby ensuring the operation safety of the liquid collecting tank 10. A base 21 with an inclined plane matching the shape of the liquid collecting tank 10 is provided below the liquid collecting tank 10 to ensure the stability of the liquid collecting tank 10 and the heat storage tank 9.

[0041] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, if these changes fall within the scope of the claims of the present invention and their equivalents, they still fall within the protection scope of the present invention.

Claims

1. A multi-stage heat storage device, characterized in that: Including heat storage tank and heat exchange tube; At least a first heat storage medium, a second heat storage medium, and a third heat storage medium are sequentially arranged in the heat storage tank from bottom to top, and the specific heat capacities of the third heat storage medium, the second heat storage medium, and the first heat storage medium increase in sequence; The heat exchange tube is in a snake shape in the vertical direction, and the heat exchange tube passes through the third heat storage medium, the second heat storage medium, and the first heat storage medium in sequence along the vertical direction of the heat storage tank; The first heat storage medium is a solid heat storage medium, the second heat storage medium is a liquid heat storage medium at high temperature, and the third heat storage medium is a gas; The multi-stage heat storage device further comprises a liquid collecting box, the bottom of which is an inclined plane, the liquid collecting box is arranged at the bottom of the heat storage tank, and the first heat storage medium is provided with a connecting hole connecting the liquid collecting box and the second heat storage medium; The heat storage tank is provided with a second heat storage medium inlet. In the horizontal direction, from the second heat storage medium inlet, the cross-sectional areas of the fluids in the plurality of communication holes decrease successively from far to near.

2. The multi-stage heat storage device according to claim 1, characterized in that: The solid heat storage medium is a mixture of solid iron-based materials.

3. The multi-stage heat storage device according to claim 1 or 2, characterized in that: The solid heat storage medium is cast steel, the second heat storage medium is molten salt, and the third heat storage medium is inert gas.

4. The multi-stage heat storage device according to claim 1, characterized in that: The heat exchange tube includes a first connector and a second connector. The heat exchange tube located in the third heat storage medium is connected to the heat exchange tube located in the second heat storage medium by using the first connector, and the heat exchange tube located in the second heat storage medium is connected to the heat exchange tube located in the first heat storage medium by using the second connector. The first connector and the second connector are arranged outside the heat storage tank.

5. The multi-stage heat storage device according to claim 1, characterized in that: During the heat release process, the second heat storage medium utilizes the temperature difference to absorb heat to preserve the heat dissipated by the first heat storage medium, and the third heat storage medium utilizes the temperature difference to preserve the heat dissipated by the second heat storage medium.

6. The multi-stage heat storage device according to claim 1, characterized in that: A base with an inclined plane matching the shape of the liquid collecting box is arranged below the liquid collecting box.

Images