A series connection molten salt high-voltage electric heating device, a control method and a thermal energy storage system

Abstract

The present application relates to molten salt energy storage and electric heating technical field, in view to the problems of high cost, large occupation of full adjustable scheme, lack of preheating function and insufficient regulation capacity of the last stage adjustable scheme of existing cascade electric heater, the present application provides a kind of cascade molten salt high-voltage electric heating equipment, control method and heat storage system, in the electric heating equipment, except the last stage heater, each stage is equipped with adjustable heating tube and fixed heating tube, and the last stage is all adjustable heating tube;Adjustable heating tube is connected to thyristor control device, and fixed heating tube is connected to high-voltage switch cabinet.Control method includes preheating mode, power regulation mode and drying mode, the whole machine is uniformly preheated by the low-power operation of adjustable heating tube, the accurate control of outlet temperature is realized by the coordinated regulation of adjustable heating tube at each stage, and the moisture removal of heating tube is realized by the mode switching of thyristor control device, the electric heating equipment considers low cost, high regulation flexibility and reliable preheating function.

Description

Technical Field

[0001] This invention relates to the field of molten salt energy storage and electric heating technology, specifically to a cascade molten salt high-voltage electric heating device, control method, and thermal energy storage system. Background Technology

[0002] With profound changes in the global energy structure and increasing environmental awareness, reducing greenhouse gas emissions and promoting a clean energy transition have become a broad international consensus. Renewable energy sources such as solar and wind power, with their inherent clean and sustainable properties, are gradually replacing traditional fossil fuels and becoming a priority and core focus of global energy development. However, the large-scale development and utilization of renewable energy faces a fundamental technological challenge: the significant intermittency and unpredictability of its power generation process. Solar power generation is affected by factors such as day-night cycles and weather changes, resulting in drastic fluctuations in output that are difficult to accurately predict. Wind power generation relies on natural conditions such as wind speed and direction, also exhibiting considerable randomness and volatility. This instability in power generation poses a severe challenge to the safe and stable operation of the power grid, urgently requiring an efficient, reliable, and large-capacity energy storage technology to smooth out power output fluctuations, achieve spatiotemporal energy transfer, and ensure that the power grid maintains frequency stability, voltage reliability, and continuous power supply even with a high proportion of renewable energy integration.

[0003] Molten salt energy storage technology, with its comprehensive advantages of large capacity, long lifespan, high safety, and good economics, has gradually become one of the core options for large-scale centralized energy storage. It is widely used in various scenarios such as energy storage in solar thermal power plants, flexible retrofitting of thermal power units, and industrial waste heat recovery. The basic principle of molten salt energy storage technology is to use molten inorganic salt as the energy storage medium. Electrical or thermal energy is converted into sensible heat and stored in high-temperature molten salt through electric heating or other heating methods. When energy needs to be released, the stored heat energy is transferred to the working medium through a heat exchanger, thereby driving a steam turbine to generate electricity or directly for industrial heating. In practical engineering, molten salt is usually stored in solid form at room temperature. Before the system is put into operation, it needs to be heated above its melting point to completely transform it into a liquid state before subsequent cyclic heat storage and release operations can be carried out. Molten salt electric heating technology is the core technology for realizing this electrical energy-heat energy conversion process. It converts electrical energy into heat energy through an electric heater, directly heating the molten salt working medium flowing through the heater, raising its temperature to the target level, and then storing it in a hot salt tank. Among them, cascade electric heaters are key core equipment for achieving high-power electrothermal conversion. Depending on the operating voltage level, cascade electric heaters can be divided into low-voltage electric heaters (rated voltage not exceeding 1kV) and high-voltage electric heaters (rated voltage of 6kV or 10kV). In high-power applications, high-voltage electric heaters have gained increasingly widespread use due to their compact size, excellent investment economy, high electrothermal conversion efficiency, and relatively simple control system configuration. Conventional cascade high-voltage electric heaters typically consist of multiple heating units connected in series. Each stage of the heater contains several heating tubes, and molten salt flows sequentially through each stage, being heated step-by-step to the final outlet temperature. Conventional design methods include equipping the heater shell with an electric heat tracing system. However, the shell heat tracing system of high-voltage electric heaters can only heat the shell portion, ensuring that the shell temperature remains above the molten salt's freezing point. Before the heater is put into operation, the molten salt space between the internal heating tubes and the shell is filled with poorly flowing air. This air layer hinders the heat transfer of the electric heat tracing system, causing the heating tube temperature to be significantly lower than the molten salt's freezing point. If put into operation directly, there is a high risk of molten salt solidification and blockage.

[0004] To address the aforementioned issues, conventional design methods include employing either a fully adjustable control scheme or a final-stage adjustable control scheme. The fully adjustable control scheme uses a thyristor power controller for each stage of the cascade heater, achieving continuous stepless adjustment of the heating power from 0% to 100% for each stage. The second approach is a final-stage adjustable control scheme, where the last stage of the cascade heater is controlled by a thyristor to achieve stepless power adjustment. However, while the fully adjustable control scheme offers excellent adjustment performance, each stage of the heater requires a complete thyristor power control device, including the thyristor assembly, trigger circuit, protection circuit, cooling system, and corresponding measurement and control instruments. This significantly increases the equipment cost per heater and substantially expands the footprint of the control room and electrical equipment area, which is particularly disadvantageous for space-constrained engineering sites. While the investment cost of the final stage adjustable control scheme is relatively low, the output power of each heater in the preceding stage remains fixed, which severely restricts the overall power adjustment range and accuracy of the system and makes it difficult to meet the requirements for precise control of the outlet temperature under varying operating conditions.

[0005] In summary, existing cascade molten salt high-pressure electric heating equipment has varying degrees of deficiencies in terms of the economy of the control scheme, the flexibility of adjustment, and the safety of start-up preheating. There is an urgent need for a new technical solution that can balance low cost, high adjustability, and reliable preheating function to ensure the thermal stability of molten salt storage. Summary of the Invention

[0006] To address the problem that existing cascade high-voltage electric heaters cannot balance cost and stepless adjustment, this invention provides a cascade molten salt high-voltage electric heating device, a control method, and a thermal energy storage system.

[0007] To achieve the above objectives, the present invention employs the following technical solution: This invention provides a cascade molten salt high-voltage electric heating device, comprising a thyristor control device, a high-voltage switch cabinet, and several stages of heaters connected in series. The heater housings are all equipped with electric heat tracing devices; Except for the final stage heater, each stage heater contains several adjustable heating tubes and several fixed heating tubes. The heating tubes in the final stage heater are all adjustable heating tubes; The adjustable heating tubes are all connected in sequence to the thyristor control device and the high-voltage switch cabinet; the fixed heating tubes are all connected to the high-voltage switch cabinet.

[0008] Optionally, the adjustable heating tubes in each stage heater are led out by wires to the junction box of the previous stage heater of the final stage heater for unified wiring.

[0009] Optionally, the number of adjustable heating tubes accounts for 10% to 30% of the total number of heating tubes in the heater stage.

[0010] Optionally, a single-stage heater junction box is provided between the adjustable heating tube of each stage heater and the silicon controlled rectifier (SCR) control device.

[0011] Optionally, the operating modes of the thyristor control device include zero-crossing operating mode and phase operating mode.

[0012] Optionally, except for the final stage heater, the adjustable heating tubes and fixed heating tubes of each stage heater are arranged as follows: with the adjustable heating tube as the center, the fixed heating tubes are distributed around the adjustable heating tube to form a preheating unit; the fixed heating tubes are arranged in the gaps between the preheating units.

[0013] The present invention also provides a control method for a cascade molten salt high-pressure electric heater, which uses the above-mentioned cascade molten salt high-pressure electric heating equipment. The control method includes the following steps: When the heater is cold: Start the electric heat tracing device to heat the heater shell side to the target area, and at the same time start the high-voltage switch cabinet to make the fixed heating tube run; Start the thyristor control device of the final stage heater and the previous stage heater to preheat all heating tubes and internal components of the heater to the target temperature; During normal operation of the heater: After all heating tubes are put into operation, the heating power of the adjustable heating tubes is adjusted by the thyristor control device to assist in controlling the molten salt outlet temperature and complete the control. Optionally, the target temperature for preheating is greater than the freezing point temperature of the molten salt.

[0014] Optionally, the operating modes of the thyristor control device include zero-crossing operating mode and phase operating mode. When the insulation resistance of the heating tube is unqualified, the thyristor control device is set to phase operating mode to perform heating, dehumidification and heat removal treatment on the heating tube.

[0015] A thermal energy storage system includes the aforementioned cascade molten salt high-pressure electric heating device.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a cascade molten salt high-voltage electric heating device. This device connects some heating tubes in each stage to a thyristor control device, while the remaining heating tubes are only connected to a high-voltage switchgear. The number of thyristor control devices is reduced from all of them in each stage to only the circuits corresponding to the adjustable heating tubes. Compared to a fully adjustable solution, the control system construction cost is reduced by more than 50%, and the footprint is reduced by more than 50%, significantly improving economy and engineering applicability while maintaining good adjustment performance. Simultaneously, because each stage heater has adjustable heating tubes, each stage heater has partial power adjustment functionality. Each adjustable heating tube can operate in low-power mode to preheat the entire heater, achieving a balanced distribution of adjustment capability among the heating stages and greatly improving the overall power adjustment flexibility of the system. All heating tubes in the final stage heater are adjustable, undertaking the critical task of accurately raising the molten salt to the final target outlet temperature. It has the highest requirement for adjustment accuracy, and the final stage heater has 100% stepless adjustment capability, enabling precise closed-loop control of the outlet temperature. Meanwhile, the preceding stages employ a mixed arrangement of adjustable and fixed heating tubes. Fixed heating tubes handle the primary fixed heating load, while adjustable heating tubes provide compensation and adjustment. This differentiated configuration strategy ensures high-precision control of the final stage outlet temperature while avoiding the high costs associated with equipping all preceding stages with thyristors, thus achieving an optimal balance between control performance and economy. It is evident that this equipment coordinates the preheating functions of the electric heat tracing device and the adjustable heating tubes, forming a dual preheating architecture combining internal and external components. The electric heat tracing device is responsible for shell insulation, preventing the molten salt from solidifying on the shell surface due to excessively low wall temperatures; the adjustable heating tubes, as the internal heat source, directly heat the heating tubes and internal components of the heater, providing uniform preheating. The two work together and complement each other, effectively solving the fundamental problem in existing technologies where shell electric heat tracing cannot adequately preheat the internal heating tubes, ensuring that the internal component temperatures meet safe operation requirements during cold start-up.

[0017] By centrally leading the wires of each adjustable heating tube to the junction box of the next-level heater for unified wiring, a highly integrated management of the adjustable heating tube control circuit is achieved. This helps reduce cable length and wiring space, lower line loss, improve the standardization and maintainability of system wiring, and facilitates centralized monitoring and unified control of each adjustable heating tube.

[0018] Within the range of 10% to 30%, the fixed heating element bears the majority of the basic heating load, while the adjustable heating element provides sufficient adjustment margin and preheating power, while keeping the number of SCR control devices to a minimum.

[0019] The single-stage heater junction box serves as an intermediate connection node between the adjustable heating tube and the thyristor control device, making the wiring of the adjustable heating tube of each stage heater relatively independent. This facilitates on-site construction and installation as well as subsequent maintenance and repair. It also benefits the layout of signal acquisition points and the installation of measuring instruments (such as current transformers and voltage transformers), providing accurate current and voltage feedback signals for the thyristor control device.

[0020] The thyristor control device operates in two modes: zero-crossing mode and phase mode. These two modes provide the thyristor control device with flexible applicability under different operating conditions. Zero-crossing mode regulates power by controlling the conduction frequency, producing a sinusoidal output voltage with extremely low harmonic content and minimal interference to the power grid. It is suitable for conventional adjustment scenarios such as preheating where electromagnetic compatibility requirements are high. Phase mode regulates power by controlling the conduction angle, resulting in a smoother and more continuous output with faster response. It is suitable for normal operating conditions requiring fine adjustment, as well as special scenarios requiring precise control of heating power, such as dehumidifying and drying heating elements. The compatibility of both modes on the same device allows the equipment to flexibly switch control strategies according to different operating needs, expanding the device's applicability.

[0021] The adjustable and fixed heating tubes of each heater are arranged with the adjustable heating tube at the center and the fixed heating tubes distributed circumferentially. This ensures that the preheating heat generated by the adjustable heating tube can be evenly transferred outward through the circumferential fixed heating tubes, avoiding localized overheating or undercooling areas during preheating and ensuring a highly uniform temperature field across the heater cross-section. Fixed heating tubes are also placed in the gaps between preheating units, further filling these gaps and making the distribution of heating tubes and heat across the entire heater cross-section even more uniform.

[0022] This invention also provides a control method for a cascade molten salt high-voltage electric heater. Using the aforementioned cascade molten salt high-voltage electric heating equipment, this method, during normal operation, after all heating tubes are put into operation, utilizes the adjustable heating tubes at each stage for precise power adjustment via a thyristor control device. The adjustable heating tubes compensate for the deviation between the output power of the fixed heating tube and the target power. Since each stage is equipped with an adjustable heating tube, the outlet temperature of each stage can be independently controlled through the power adjustment of the adjustable heating tube at that stage, achieving precise closed-loop regulation of the outlet temperature of each stage heater. A preheating step is performed in the cold state. Liquid molten salt is injected only after the temperature of each key component inside the heater reaches the target temperature. After the molten salt injection is completed, all heating tubes are put into operation, and the system enters the normal operation phase, ensuring that the heater starts under safe temperature conditions, avoiding equipment damage and molten salt solidification due to low-temperature operation, and achieving safe, stable, and precise control throughout the entire process from cold start to normal operation.

[0023] Setting the preheating target temperature to be higher than the molten salt freezing point ensures that the heating tube temperature can be maintained above the molten salt freezing point when the liquid molten salt is injected into the heater and comes into contact with the surface of the heating tube. This essentially eliminates the possibility of molten salt solidifying and clumping on the surface of the heating tube, ensuring smooth molten salt injection and initial flow.

[0024] The present invention also provides a thermal energy storage system, including the above-mentioned cascade molten salt high-voltage electric heating equipment. The system has the characteristics of low investment cost, small footprint, adjustable power at each stage, whole machine preheating function, and good moisture-proof and dehumidification capabilities, laying a good foundation for flexible peak shaving of thermal power and industrial waste heat recovery. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the connection structure of a cascade molten salt high-voltage electric heating device according to the present invention.

[0026] Figure 2 This is a structural diagram of the distribution of a single-stage heating tube in a cascade molten salt high-voltage electric heating device according to the present invention.

[0027] Among them, 1-adjustable heating tube, 2-fixed heating tube, 3-single-stage heater junction box, 4-thyristor control device, 5-high voltage switch cabinet, 6-wire, 7-electric heat tracing device, 8-preheating unit. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0030] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0031] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0032] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0033] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0034] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0035] Example 1 See Figure 1 The present invention provides a cascade molten salt high-voltage electric heating device, including a thyristor control device 4, a high-voltage switch cabinet 5, and several stages of heaters connected in series. Each heater is equipped with an electric heat tracing device 7 on its housing; Except for the final stage heater, each stage heater is equipped with several adjustable heating tubes 1 and several fixed heating tubes 2; the adjustable heating tubes 1 in each stage heater are led out through wires 6 to the junction box of the previous stage heater for unified wiring. The heating tubes in the final stage heater are all adjustable heating tubes 1; The adjustable heating tubes 1 are all connected in sequence to the thyristor control device 4 and the high-voltage switch cabinet 5; the fixed heating tubes 2 are all connected to the high-voltage switch cabinet 5; a single-stage heater junction box 3 is provided between the adjustable heating tube 1 of each stage heater and the thyristor control device 4.

[0036] The number of adjustable heating tubes 1 accounts for 10% to 30% of the total number of heating tubes in this stage of heater.

[0037] The operating modes of the thyristor control device 4 include zero-crossing operating mode and phase operating mode.

[0038] Example 2 See Figure 1 and Figure 2 The present invention provides a cascade molten salt high-voltage electric heating device, including a thyristor control device 4, a high-voltage switch cabinet 5, and several stages of heaters connected in series. Each heater is equipped with an electric heat tracing device 7 on its housing; Except for the final stage heater, each stage heater is equipped with several adjustable heating tubes 1 and several fixed heating tubes 2; the adjustable heating tubes 1 in each stage heater are led out through wires 6 to the junction box of the previous stage heater for unified wiring. The heating tubes in the final stage heater are all adjustable heating tubes 1; The adjustable heating tubes 1 are all connected in sequence to the thyristor control device 4 and the high-voltage switch cabinet 5; the fixed heating tubes 2 are all connected to the high-voltage switch cabinet 5; a single-stage heater junction box 3 is provided between the adjustable heating tube 1 of each stage heater and the thyristor control device 4.

[0039] The operating modes of the thyristor control device 4 include zero-crossing operating mode and phase operating mode.

[0040] See Figure 2 Except for the final stage heater, the adjustable heating tubes 1 and fixed heating tubes 2 of each stage heater are arranged as follows: with the adjustable heating tube 1 as the center, the fixed heating tubes 2 are distributed around the adjustable heating tube 1 to form a preheating unit 8; the fixed heating tubes 2 are arranged in the gaps between the preheating units 8.

[0041] The control objectives of the aforementioned cascade molten salt high-voltage electric heating equipment are: During the initial startup phase, uniform preheating of the heater body can be achieved, ensuring that the heater meets the temperature requirements before operation. This function helps ensure the safe and stable startup and operation of the heater, extends the service life of the equipment, and prevents potential hazards such as molten salt blockage caused by excessive temperature difference between the molten salt and the electric heater during initial commissioning, as well as molten salt leakage at metal welds, flanges, and other connections inside the heater.

[0042] During operation, each stage of the electric heater can have a portion of its heating power adjustable. This function helps to achieve precise control of the molten salt temperature at the outlet of each stage of the heater and improves the overall power regulation capability of the heater.

[0043] If, after maintenance or before restarting the equipment, the heating elements become damp, or their insulation deteriorates and fails to meet insulation requirements, the adjustable group of heating elements can be operated at low power to uniformly heat and dry all the heating elements, thus achieving the dehumidification function. This function helps enhance the heater's adaptability to the operating environment.

[0044] There are three modes available for use: Preheating Mode: When the heater is cold, the electric heat tracing device 7 is first activated to heat the heater shell side. Based on feedback from the shell-side temperature sensing element, the electric heat tracing temperature is stabilized within a reasonable range. Simultaneously, the (n-1)th and nth stage (n stages in total for the heater) thyristor control devices 4 are activated to preheat all heating elements and internal heater components. By adjusting the output of the thyristor control devices using zero-crossing or phase-based operating modes, the heating power of the adjustable group of heating elements is adjusted, enabling flexible control of parameters such as preheating power, preheating temperature, preheating time, and preheating temperature rise curve. This ensures the heater completes the preheating process safely, stably, and smoothly. What is the goal of preheating? That is, to what extent should it be preheated? Adjustable power mode: During normal operation of the heater, after the conventional fixed group is put into operation, the outlet molten salt temperature of each stage of the heater is usually controlled by adjusting the molten salt flow rate at the heater inlet. Under this control method, about 15% of the heating tubes in the original fixed group heater are set as adjustable groups. The heating power of this part can be finely adjusted by the thyristor control device 4, thereby making the control of the molten salt outlet temperature more precise, the temperature curve smoother, and the fluctuations significantly reduced.

[0045] Drying Mode: When the insulation resistance measurement of the heating element fails, the adjustable section of the heater is activated, and the SCR control device 4 is set to phase operation mode. By adjusting parameters such as the output voltage, output power, and running time of the SCR control device 4, the heating element is slowly and evenly dehumidified at low power to ensure safe operation of the equipment. Furthermore, in high-humidity areas such as coastal regions, the heater is more likely to become damp after shutdown. After shutdown, the operating mode of the SCR device can be adjusted to apply low voltage and low power heating to the heating element for insulation, thus preventing moisture buildup.

[0046] Example 3 The present invention also provides a control method for a cascade molten salt high-pressure electric heater, which uses the above-mentioned cascade molten salt high-pressure electric heating equipment. The control method includes the following steps: When the heater is cold: Start the electric heat tracing device 7 to heat the heater shell side to the target area, and at the same time start the high voltage switch cabinet 5 to make the fixed heating tube 2 run; Start the thyristor control device 4 of the final stage heater and the previous stage heater of the final stage heater to preheat all heating tubes and internal components of the heater to the target temperature; preferably, the target temperature of preheating is greater than the solidification point temperature of molten salt, and more preferably the target temperature of preheating is 10-50°C greater than the solidification point temperature of molten salt.

[0047] During normal operation of the heater: After all heating tubes are put into operation, the heating power of the adjustable heating tube 1 is adjusted by the thyristor control device 4 to assist in controlling the molten salt outlet temperature and complete the control.

[0048] Preferably, the operating modes of the thyristor control device 4 include a zero-crossing operating mode and a phase operating mode. When the insulation resistance of the heating tube is unqualified, the thyristor control device 4 is set to the phase operating mode to perform heating, dehumidification and heat removal treatment on the heating tube.

[0049] The present invention also provides a thermal energy storage system, including the above-mentioned cascade molten salt high-voltage electric heating equipment. The system has the characteristics of low investment cost, small footprint, adjustable power at each stage, whole machine preheating function, and good moisture-proof and dehumidification capabilities, laying a good foundation for flexible peak shaving of thermal power and industrial waste heat recovery.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the technical solution of the present invention in any way. Those skilled in the art should understand that, without departing from the spirit and principles of the present invention, the technical solution can be modified and replaced in several simple ways, and these modifications and replacements are all within the scope of protection covered by the claims.

Claims

1. A cascade molten salt high-voltage electric heating device, characterized in that, It includes a thyristor control device (4), a high-voltage switchgear (5), and several stages of heaters connected in series. Each heater is equipped with an electric heat tracing device (7) on its shell. Except for the final stage heater, each stage heater is equipped with several adjustable heating tubes (1) and several fixed heating tubes (2). The heating tubes in the final stage heater are all adjustable heating tubes (1). The adjustable heating tubes (1) are all connected in sequence to the thyristor control device (4) and the high-voltage switchgear (5); the fixed heating tubes (2) are all connected to the high-voltage switchgear (5).

2. The cascade molten salt high-voltage electric heating device according to claim 1, characterized in that, The adjustable heating tube (1) in each stage heater is led out through the wire (6) to the junction box of the previous stage heater of the final stage heater for unified wiring.

3. The cascade molten salt high-voltage electric heating device according to claim 1, characterized in that, The number of adjustable heating tubes (1) accounts for 10% to 30% of the total number of heating tubes in this stage of heater.

4. The cascade molten salt high-voltage electric heating device according to claim 1, characterized in that, A single-stage heater junction box (3) is provided between the adjustable heating tube (1) of each stage heater and the thyristor control device (4).

5. The cascade molten salt high-voltage electric heating device according to claim 1, characterized in that, The operating modes of the thyristor control device (4) include zero-crossing operating mode and phase operating mode.

6. The cascade molten salt high-voltage electric heating device according to claim 1, characterized in that, Except for the final stage heater, the arrangement of the adjustable heating tubes (1) and fixed heating tubes (2) of each stage heater is as follows: with the adjustable heating tube (1) as the center, the fixed heating tubes (2) are distributed around the adjustable heating tube (1) to form a preheating unit (8); the fixed heating tubes (2) are arranged in the gaps between the preheating units (8).

7. A control method for a cascade molten salt high-voltage electric heater, characterized in that, The control method for using the cascade molten salt high-voltage electric heating equipment according to any one of claims 1-6 includes the following steps; When the heater is cold: Start the electric heat tracing device (7) to heat the heater shell side to the target range, and at the same time start the high voltage switch cabinet (5) to make the fixed heating tube (2) run; Start the thyristor control device (4) of the final stage heater and the previous stage heater of the final stage heater to preheat all heating tubes and internal components of the heater to the target temperature; During normal operation of the heater: After all heating tubes are put into operation, the heating power of the adjustable heating tube (1) is adjusted by the thyristor control device (4) to assist in controlling the molten salt outlet temperature and complete the control.

8. The control method for the cascade molten salt high-voltage electric heater according to claim 7, characterized in that, The target temperature for preheating is higher than the freezing point of the molten salt.

9. The control method for the cascade molten salt high-voltage electric heater according to claim 7, characterized in that, The operating modes of the thyristor control device (4) include zero-crossing operating mode and phase operating mode. When the insulation resistance of the heating tube is not qualified, the thyristor control device (4) is set to phase operating mode to heat the heating tube for dehumidification.

10. A thermal energy storage system, characterized in that, Includes the cascade molten salt high-pressure electric heating device as described in any one of claims 1-6.

Images