Multi-temperature-zone coupled graded fused salt heat storage system and control method thereof

Abstract

The invention relates to the technical field of solar thermal power generation and energy storage, in particular to a multi-temperature-zone coupled staged fused salt heat storage system and a control method thereof.The system comprises a multi-stage heat storage module, a multi-stage heat storage module and a multi-stage heat storage module, the multi-stage heat storage module comprises a high-temperature storage tank, a medium-temperature storage tank, a low-temperature storage tank and a buffer storage tank, and the storage tanks are dynamically partitioned through adjustable partition plates; the self-adaptive heat exchange network comprises a plate heat exchanger and a double-pipe heat exchanger which are combined in series-parallel connection, the plate heat exchanger is used for a high-temperature section, the double-pipe heat exchanger is used for a medium-low-temperature section, and an electric three-way valve is arranged between the heat exchangers to automatically switch connection modes according to the temperature of a heat source; and the intelligent control module integrates a temperature gradient sensor and a fused salt flow regulating valve, and optimizes the heat storage priority and the heat release rate in real time. The heat storage density is increased by 20%-30%, and the system circulation efficiency reaches 85% or above; multi-heat-source input and multi-grade heat energy output are supported, and complex working conditions are adapted; and through the modular design, the construction cost is reduced by 30%, and the service life is prolonged to 25 years.

Description

Technical Field

[0001] The present invention relates to the technical field of solar thermal power generation and energy storage, and particularly relates to a hierarchical molten salt energy storage system with multi-temperature zone coupling and a control method thereof. Background Art

[0002] Molten salt energy storage is an energy storage technology with excellent performance, having advantages such as large capacity, long term, high stability, and low cost, and is currently widely applied in solar thermal power plants. Single-tank energy storage stratifies the cold and hot flows through an inclined temperature layer, reducing the initial investment, but there are problems such as insignificant temperature stratification and low thermal cycle efficiency, resulting in insufficient energy storage density and high heat loss; and due to multiple charging / discharging cycles, the tank body and the internal molten salt generate alternating thermal stresses due to large temperature differences, reducing the safety factor. The double-tank molten salt energy storage (cold / hot tank) technology is mature, but it has high costs and cannot achieve multi-level heat grade management. In addition, in the current molten salt energy storage system, single-temperature zone energy storage cannot adapt to multi-grade heat sources (such as solar heat collection, industrial waste heat), and the energy utilization rate is limited; and the energy storage system has a slow response speed under changing working conditions (such as irradiation fluctuations, load demand changes), and is prone to cause thermal stress damage. Based on the technical fields of solar thermal power generation and large-scale energy storage, the present invention proposes a hierarchical molten salt energy storage system based on multi-temperature zone coupling, and realizes efficient heat energy storage and on-demand release by optimizing the molten salt storage tank structure, heat management strategy, and dynamic control algorithm, providing an application reference for scenarios such as solar thermal power generation, industrial waste heat recovery, and power grid peak shaving. Summary of the Invention

[0003] The purpose of the present invention is to provide a hierarchical molten salt energy storage system with multi-temperature zone coupling, which can solve the above technical problems.

[0004] The present invention provides a hierarchical molten salt energy storage system with multi-temperature zone coupling, comprising:

[0005] A multi-level energy storage module, including a high-temperature storage tank, a medium-temperature storage tank, a low-temperature storage tank, and a buffer storage tank, and dynamic partitioning is realized between each storage tank through an adjustable partition board;

[0006] An adaptive heat exchange network, including a plate heat exchanger and a shell-and-tube heat exchanger combined in series-parallel. The plate heat exchanger is used for the high-temperature section, and the shell-and-tube heat exchanger is used for the medium-low temperature section. Electric three-way valves are configured between the heat exchangers to automatically switch the connection mode according to the heat source temperature;

[0007] An intelligent control module, integrating a temperature gradient sensor and a molten salt flow regulating valve, and optimizing the energy storage priority and heat release rate in real time.

[0008] Preferably, the temperature grading of the multi-level energy storage module is:

[0009] The temperature range of the high-temperature storage tank is 500 - 565 °C, and NaNO3 / KNO 3 (60% / 40%) binary salt;

[0010] The temperature range of the medium-temperature storage tank is 350 - 450 °C, NaNO 3 / KNO 3 (55% / 35%) binary salt and adding 10% CaCl 2 to reduce the melting point of the molten salt;

[0011] The temperature range of the low-temperature storage tank is 250 - 300 °C, using XL molten salt;

[0012] The capacity of the buffer storage tank is 10% of the total storage capacity, used for thermal shock buffering.

[0013] Preferably, the adjustable partition is adjusted by a hydraulic drive system for the partition ratio. The pressure range of the hydraulic drive system is 20 - 35 Mpa, the response time is less than 5 s, and the partition ratio adjustment algorithm is: V_high / V_low = α·(T_sun - 400) / 100, α ∈ [0.8, 1.2].

[0014] Preferably, the storage tank material is a 316L stainless steel matrix, lined with a plasma-sprayed Al 2 O 3 -ZrO 2 composite ceramic coating, and the coating thickness is 150 ± 20 μm.

[0015] Preferably, the adaptive heat exchange network is configured as follows:

[0016] The high-temperature section uses a plate heat exchanger with a designed pressure drop of less than 50 kPa;

[0017] The medium- and low-temperature sections use a shell-and-tube heat exchanger with a flow velocity controlled at 2 - 4 m / s;

[0018] The switching logic of the electric three-way valve is: when the heat source temperature is greater than 480 °C, it is connected in parallel in the high-temperature section, and when it is 300 - 450 °C, it is connected in series in the medium-temperature section.

[0019] Preferably, the plate heat exchanger adopts an asymmetric flow channel design, the flow channel height on the high-temperature side is 4 mm, and the flow channel height on the low-temperature side is 6 mm. A spiral guide vane is arranged inside the shell-and-tube heat exchanger, and the lead angle is 30°.

[0020] Preferably, the intelligent control module includes:

[0021] Distributed thermocouples and ultrasonic flow meters. There are 3 distributed thermocouple temperature measurement points arranged per cubic meter, and the sampling frequency is 10 Hz.

[0022] Preferably, the intelligent control module uses an LSTM neural network to predict the heat load for the next 24 hours and dynamically optimize the heat storage strategy; the input dimensions of the LSTM neural network include ambient temperature, solar irradiance, and historical load data.

[0023] Preferably, the heat storage priority decision of the intelligent control module is based on electricity price signals, heat source quality, and the SOC state of the storage tank, and the heat release rate is achieved through on-line tuning of PID parameters with an adjustment period of 5 minutes.

[0024] The present invention also provides a control method for the molten salt heat storage system according to the above, comprising the following steps:

[0025] System startup phase: Initialize the baffle position, set the volume ratio of the high-temperature zone / mid-low temperature zone to 3:2, and heat the storage tank to the minimum operating temperature + 50°C through an electric heater;

[0026] Heat storage process control: Solar thermal collection is preferentially injected into the high-temperature tank, and the buffer tank is shunted when T > 550°C; industrial waste heat is stored according to its quality level, and waste heat at 200 - 300°C is stored in the low-temperature tank after being heated by a heat pump;

[0027] Heat release optimization strategy: Release the heat energy of the high-temperature tank preferentially during peak electricity periods, and achieve cascaded utilization of the heat energy of the low-temperature tank through a heat pump during valley electricity periods.

[0028] Beneficial effects:

[0029] In the multi-stage heat storage module of the present invention, each storage tank realizes dynamic partitioning through adjustable partitions, which can more effectively achieve temperature stratification. During multiple heat storage / discharge processes, this dynamic partitioning method can maintain significant temperature stratification, greatly improving the heat storage density by 20%-30%, and the system circulation efficiency reaches more than 85%. The multi-stage storage tank design shares the alternating thermal stress generated by the temperature difference change of the tank body and the internal molten salt during heat storage / discharge. Taking the high-temperature storage tank as an example, when it receives high-temperature molten salt, part of the thermal stress can be dispersed through the synergistic effect with the medium-temperature storage tank, effectively improving the safety factor of the system, reducing the risk of equipment damage caused by thermal stress, and extending the service life of the equipment. Under changing working conditions, such as irradiation fluctuations and load demand changes, the electric three-way valve can respond quickly and automatically adjust the connection mode of the heat exchanger to ensure that the system can adapt to the working condition changes in a timely manner. At the same time, the combined use of different types of heat exchangers can effectively reduce thermal stress damage, greatly improving the stability and reliability of the system. The plate heat exchanger with a series-parallel combination in the adaptive heat exchange network is used in the high-temperature section, and the shell-and-tube heat exchanger is used in the medium-low temperature section. And the connection mode can be automatically switched according to the heat source temperature through the electric three-way valve, which enables the system to efficiently adapt to multi-grade heat sources such as solar heat collection and industrial waste heat. For example, when the heat source is high-temperature solar heat collection, the plate heat exchanger can work efficiently; when the heat source is medium-low temperature industrial waste heat, the shell-and-tube heat exchanger can play a better role, thus significantly improving the energy utilization rate. Description of the Drawings

[0030] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0031] Figure 1 It is the process flow chart of the multi-temperature zone coupling and grading molten salt heat storage system of the present invention. Detailed Embodiments

[0032] The following will clearly and completely describe the technical solutions of the present invention in combination with the embodiments. Obviously, the described embodiments are some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0033] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0034] In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present invention, "a plurality of" means two or more unless otherwise specifically defined. In addition, the terms "mounted", "connected" and "connected to" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] Embodiment 1

[0036] A multi-temperature zone coupled hierarchical molten salt thermal energy storage system, comprising:

[0037] A multi-stage thermal energy storage module, including a high-temperature storage tank, a medium-temperature storage tank, a low-temperature storage tank and a buffer storage tank. Dynamic partitioning is achieved between each storage tank through an adjustable partition board;

[0038] An adaptive heat exchange network, including a plate heat exchanger and a shell-and-tube heat exchanger combined in series and parallel. The plate heat exchanger is used for the high-temperature section (500 - 565 °C), and the shell-and-tube heat exchanger is used for the medium- and low-temperature sections (250 - 450 °C). An electric three-way valve is configured between the heat exchangers to automatically switch the connection mode according to the heat source temperature;

[0039] An intelligent control module, integrating a temperature gradient sensor and a molten salt flow regulating valve, to optimize the heat storage priority and heat release rate in real time.

[0040] The temperature grading of the multi-stage thermal energy storage module is:

[0041] The temperature range of the high-temperature storage tank is 500 - 565 °C, and NaNO 3 / KNO 3 (60 / 40) binary salt is used;

[0042] The temperature range of the medium-temperature storage tank is 350 - 450 °C, and 5% CaCl is added 2 to lower the melting point of the molten salt;

[0043] The temperature range of the low-temperature storage tank is 250 - 300 °C, and XL molten salt is used ;

[0044] The capacity of the buffer storage tank is 10% of the total storage capacity and is used for thermal shock buffering.

[0045] The adjustable partition adjusts the partition ratio through a hydraulic drive system (such as expanding the volume of the high-temperature area during the day and compressing the low-temperature area at night). The pressure range of the hydraulic drive system is 20 - 35 Mpa, and the response time is less than 5 s. The entire tank body is a horizontal storage tank, which is divided into a high-temperature storage tank, a medium-temperature storage tank, a low-temperature storage tank, and a buffer storage tank by multiple vertical partitions. The partition is an adjustable partition that moves horizontally to change the volume of multiple storage tanks. The partition is moved by a hydraulic system or an electric system. The hydraulic system injects or extracts hydraulic oil into different piston chambers according to the instructions of the control system, thereby pushing the piston (connected to the partition) to move inside the storage tank to achieve dynamic adjustment of the partition. Alternatively, the partition is translated by an electric lead screw drive device. The lead screw is driven by a motor, and the motor is connected to the control system. The position of the partition can be remotely or automatically controlled according to production requirements. Limit switches are installed at both ends of the lead screw to prevent damage caused by excessive movement of the partition.

[0046] The partition ratio adjustment algorithm is: V_high / V_low = α·(T_sun - 400) / 100, where α ∈ [0.8, 1.2].

[0047] V_high represents the volume of the high-temperature storage tank. The high-temperature storage tank is used to store molten salt in a high-temperature state after absorbing a large amount of solar heat. After the molten salt absorbs heat and rises in temperature in the solar collector field, it is transported to the high-temperature storage tank for storage to release heat when subsequent energy demands such as power generation and heating are required. Its volume size determines the maximum amount of high-temperature molten salt that the system can store, and has an important impact on the heat storage capacity and continuous energy supply time of the system. It is a key indicator for measuring the high-temperature heat storage capacity of the system. A larger V_high means that the system can store more high-temperature molten salt when solar energy is sufficient, thereby providing a longer stable heat energy output for users during periods when solar energy is insufficient or at night.

[0048] V_low represents the volume of the low-temperature storage tank. The low-temperature storage tank is used to store the molten salt whose temperature has decreased after releasing heat. When the high-temperature molten salt flows out of the high-temperature storage tank and releases heat to the outside through a heat exchange device (such as a steam generator), its temperature decreases, and then it flows back into the low-temperature storage tank, waiting to be transported to the solar collector field again to absorb heat. The size of V_low is related to the system's capacity to hold the low-temperature molten salt, ensuring the normal circulation of the molten salt in the system. An appropriate V_low can ensure that during the molten salt circulation process, there is enough storage space for the low-temperature molten salt, avoiding affecting the normal operation of the system due to insufficient storage space.

[0049] T_sun refers to the temperature of the molten salt at the outlet of the solar collector, usually in degrees Celsius (°C). The solar collector is a key device that converts solar energy into heat energy and heats the molten salt. T_sun reflects the effect of the collector absorbing solar energy and transferring it to the molten salt, embodying the strength of the solar energy resources at that time and the efficiency of the heat collection process. As the core input variable of the adjustment algorithm, the change of T_sun determines the proportional relationship between the volumes of the high-temperature storage tank and the low-temperature storage tank. The system dynamically adjusts the volume allocation of the two storage tanks according to the real-time monitoring of T_sun to adapt to different solar energy resource conditions and system operation requirements.

[0050] α is a proportionality coefficient, and its value range is between [0.8, 1.2]. This coefficient is used to correct and adjust the adjustment algorithm to adapt to the characteristics and actual operation requirements of different molten salt thermal energy storage systems. Due to differences in factors such as geographical location, meteorological conditions, and equipment performance in different systems, the response to solar temperature changes and the requirements for storage tank volume allocation also vary. α can make the algorithm have better versatility and adaptability.

[0051] When the value of α is close to 0.8, it indicates that the system's response to the change of T_sun is relatively conservative, and the adjustment range of V_high / V_low is small; when the value of α is close to 1.2, the system is more sensitive to the change of T_sun, and the adjustment range of V_high / V_low will be larger.

[0052] This formula describes the quantitative relationship between the volume ratio of the high-temperature storage tank and the low-temperature storage tank and the molten salt temperature at the outlet of the solar collector. As T_sun increases, the value of V_high / V_low increases, meaning that the volume of the high-temperature storage tank needs to be relatively increased to store more high-temperature molten salt and make full use of the abundant solar energy resources; as T_sun decreases, the volume of the low-temperature storage tank needs to be relatively increased to provide enough space for the storage of the cooled molten salt. In this way, the system can dynamically adjust the volume allocation of the high-temperature and low-temperature storage tanks according to the actual situation of solar energy, realizing the efficient operation of the molten salt heat storage system and the reasonable storage and utilization of energy. The medium-temperature storage tank plays a transitional and regulating role in the whole process, helping the system better adapt to the molten salt temperature changes and energy storage requirements under different working conditions.

[0053] The storage tank is made of 316L stainless steel matrix, lined with plasma-sprayed Al 2 O 3 -ZrO 2 composite ceramic coating, and the coating thickness is 150±20μm.

[0054] The adaptive heat exchange network is configured as follows:

[0055] The high-temperature section uses a plate heat exchanger with a designed pressure drop of less than 50 kPa;

[0056] The medium-low temperature section uses a shell-and-tube heat exchanger with a flow velocity controlled at 2-4 m / s;

[0057] The switching logic of the electric three-way valve is: when the heat source temperature is greater than 480 °C, it is connected in parallel in the high-temperature section, and when it is 300-450 °C, it is connected in series in the medium-temperature section.

[0058] The plate heat exchanger adopts an asymmetric flow channel design, with a flow channel height of 4 mm on the high-temperature side and 6 mm on the low-temperature side. A spiral guide vane is set inside the shell-and-tube heat exchanger, and the lead angle is 30°.

[0059] The intelligent control module includes:

[0060] Distributed thermocouples and ultrasonic flow meters. There are 3 distributed thermocouple temperature measurement points arranged per cubic meter, and the sampling frequency is 10 Hz.

[0061] The intelligent control module uses an LSTM neural network to predict the heat load in the next 24 hours and dynamically optimize the heat storage strategy; the input dimension of the LSTM neural network includes ambient temperature, solar irradiance, and historical load data.

[0062] The heat storage priority decision of the intelligent control module is based on the electricity price signal, heat source grade, and the SOC state of the storage tank. The heat release rate is realized by online tuning of the PID parameters, and the adjustment period is 5 minutes.

[0063] The present invention also provides a control method according to the above molten salt heat storage system, comprising the following steps:

[0064] System startup phase: Initialize the baffle position, set the volume ratio of the high-temperature zone / mid-low temperature zone to 3:2, and heat the storage tank to the minimum operating temperature +50°C through an electric heater;

[0065] Heat storage process control: Solar heat collection preferentially injects into the high-temperature tank, and the buffer tank shunt is opened when T > 550°C; Industrial waste heat is stored according to grade classification. The waste heat of 200 - 300°C is stored in the low-temperature tank after being heated by a heat pump;

[0066] Heat release optimization strategy: Preferentially release the heat energy of the high-temperature tank during peak electricity periods, and realize the cascade utilization of the heat energy of the low-temperature tank through a heat pump during valley electricity periods.

[0067] Finally, it should be noted that: The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: They can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; And these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A multi-temperature zone coupled hierarchical molten salt heat storage system, characterized in that: include: Multi-stage heat storage module, including high-temperature storage tank, medium-temperature storage tank, low-temperature storage tank and buffer storage tank, each tank is dynamically partitioned by adjustable partitions; Adaptive heat exchange network, including plate heat exchangers and shell-and-tube heat exchangers in series-parallel combination, the plate heat exchanger is used for the high temperature section, the shell-and-tube heat exchanger is used for the medium and low temperature section, and an electric three-way valve is configured between the heat exchangers to automatically switch the connection mode according to the temperature of the heat source; Intelligent control module, integrated temperature gradient sensor and molten salt flow control valve, optimizes heat storage priority and heat release rate in real time.

2. The molten salt heat storage system according to claim 1, characterized in that: The temperature classification of the multi-stage heat storage module is: The temperature range of high temperature storage tank is 500-565℃, using NaNO3 / KNO3 (60 / 40) binary salt; The temperature range of the medium temperature storage tank is 350-450℃, and 5% CaCl2 is added to reduce the melting point of the molten salt; The temperature range of the low temperature storage tank is 250-300℃. Molten salt; The buffer tank capacity is 10% of the total reserve and is used for thermal shock buffering.

3. The molten salt heat storage system according to claim 1, characterized in that: The adjustable partition adjusts the partition ratio through a hydraulic drive system, the pressure range of the hydraulic drive system is 20-35 MPa, and the partition ratio adjustment algorithm is: V_high / V_low=α·(T_sun-400) / 100, α∈[0.8,1.2].

4. The molten salt heat storage system according to claim 1, characterized in that: The tank is made of 316L stainless steel substrate and lined with plasma-sprayed Al2O3-ZrO2 composite ceramic coating with a coating thickness of 150±20μm.

5. The molten salt heat storage system according to claim 1, characterized in that: The adaptive heat exchange network configuration is as follows: The high temperature section uses a plate heat exchanger with a designed pressure drop of less than 50kPa; The medium and low temperature sections use a shell-and-tube heat exchanger with a flow rate controlled at 2-4m / s; The switching logic of the electric three-way valve is: when the heat source temperature is greater than 480℃, the high temperature section is connected in parallel, and when it is 300-450℃, the medium temperature section is connected in series.

6. The molten salt heat storage system according to claim 1, characterized in that: The plate heat exchanger adopts an asymmetric flow channel design, the high-temperature side flow channel height is 4 mm, and the low-temperature side flow channel height is 6 mm. A spiral guide vane is arranged in the shell-and-tube heat exchanger, and the lead angle is 30°.

7. The molten salt heat storage system according to claim 1, characterized in that: The intelligent control module comprises: Distributed thermocouples and ultrasonic flowmeters, with 3 distributed thermocouple temperature measurement points arranged per cubic meter, and a sampling frequency of 10Hz.

8. The molten salt heat storage system according to claim 1, characterized in that: The intelligent control module uses an LSTM neural network to predict the heat load in the next 24 hours and dynamically optimize the heat storage strategy; the input dimensions of the LSTM neural network include ambient temperature, solar irradiance and historical load data.

9. The molten salt heat storage system according to claim 1, characterized in that: The heat storage priority decision of the intelligent control module is based on the electricity price signal, the heat source grade and the SOC status of the storage tank. The heat release rate is achieved through online adjustment of PID parameters with an adjustment cycle of 5 minutes.

10. A control method of the system according to any one of claims 1 to 9, characterized in that The following steps are involved: System startup phase: Initialize the baffle position, set the volume ratio of high temperature zone / medium and low temperature zone to 3:2, and use the electric heater to heat the storage tank to the minimum working temperature of +50℃; Heat storage process control: solar heat is first injected into the high-temperature tank, and when T>550℃, the buffer tank is opened for diversion; industrial waste heat is stored according to grade, and 200-300℃ waste heat is heated by the heat pump and stored in the low-temperature tank; Heat release optimization strategy: During peak power periods, the heat energy of high-temperature tanks is released first, and during valley power periods, the heat energy of low-temperature tanks is utilized in a cascade manner through heat pumps.

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