A multi-temperature zone coupled hierarchical molten salt heat storage system and its control method

Abstract

The present invention relates to the field of solar thermal power generation and energy storage technology, and in particular to a multi-temperature zone coupled hierarchical molten salt heat storage system and its control method. The system comprises: a multi-stage heat storage module, including a high-temperature storage tank, a medium-temperature storage tank, a low-temperature storage tank, and a buffer tank, each of which is dynamically partitioned by an adjustable partition; an adaptive heat exchange network, including a series-parallel combination of plate heat exchangers and tube-in-tube heat exchangers, the plate heat exchanger being used for the high-temperature section and the tube-in-tube heat exchanger being used for the medium- and low-temperature sections, with electric three-way valves configured between the heat exchangers to automatically switch the connection mode according to the heat source temperature; and an intelligent control module, integrating a temperature gradient sensor and a molten salt flow control valve, to optimize the heat storage priority and heat release rate in real time. The present invention increases the heat storage density by 20%-30% and the system cycle efficiency by over 85%; supports multiple heat source inputs and multi-grade heat outputs, adapting to complex working conditions; reduces construction costs by 30% through modular design, and extends the life cycle to 25 years.

Description

Technical Field

[0001] The present invention relates to the field of solar thermal power generation and energy storage technology, and in particular to a multi-temperature zone coupled hierarchical molten salt heat storage system and a control method thereof. Background Art

[0002] Molten salt heat storage is a high-performance energy storage technology with advantages such as large capacity, long-term operation, high stability, and low cost. It is currently widely used in solar thermal power plants. Single-tank heat storage stratifies hot and cold flows through a temperature gradient, reducing initial investment. However, it suffers from issues such as insignificant temperature stratification and low thermal cycle efficiency, resulting in insufficient heat storage density and high heat loss. Furthermore, due to the multiple storage and release cycles, the tank and the molten salt within it experience alternating thermal stresses due to large temperature differences, reducing the safety factor. Dual-tank molten salt heat storage (cold / hot tank) technology is mature, but it is expensive and cannot achieve multi-level thermal grade management. Furthermore, in current molten salt heat storage systems, single-temperature zone heat storage cannot accommodate multiple heat sources (such as solar thermal collectors and industrial waste heat), limiting energy utilization. Furthermore, the heat storage system responds slowly to changing operating conditions (such as irradiation fluctuations and changes in load demand), which can easily 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 heat storage system based on multi-temperature zone coupling. By optimizing the molten salt storage tank structure, thermal management strategy and dynamic control algorithm, efficient thermal energy storage and on-demand release are achieved, providing application references for scenarios such as solar thermal power generation, industrial waste heat recovery and grid peak regulation. Summary of the Invention

[0003] The object of the present invention is to provide a multi-temperature zone coupled hierarchical molten salt heat storage system that can solve the above technical problems.

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

[0005] 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;

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

[0007] The intelligent control module integrates a temperature gradient sensor and a molten salt flow control valve to optimize heat storage priority and heat release rate in real time.

[0008] Preferably, the temperature classification of the multi-stage heat storage module is:

[0009] The high temperature storage tank temperature range is 500-565℃, using NaNO3 / KNO3 (60% / 40%) binary salt;

[0010] The medium temperature storage tank temperature range is 350-450℃, NaNO3 / KNO3 (55% / 35%) binary salt and 10% CaCl2 is added to reduce the melting point of the molten salt;

[0011] The temperature range of low temperature storage tank is 250-300℃. XL molten salt;

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

[0013] Preferably, the adjustable partition adjusts the partition ratio through a hydraulic drive system, the pressure range of the hydraulic drive system is 20-35Mpa, the response time is less than 5s, 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 is made of a 316L stainless steel substrate and lined with a plasma-sprayed Al2O3-ZrO2 composite ceramic coating with a coating thickness of 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 design pressure drop of less than 50kPa;

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

[0018] 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.

[0019] Preferably, 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. The shell and tube heat exchanger is provided with a spiral guide vane with a lead angle of 30°.

[0020] Preferably, the intelligent control module includes:

[0021] Distributed thermocouples and ultrasonic flowmeters are used, with three distributed thermocouple temperature measurement points arranged per cubic meter, and a sampling frequency of 10 Hz.

[0022] Preferably, 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.

[0023] Preferably, 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, and the heat release rate is achieved through online tuning of PID parameters with an adjustment cycle of 5 minutes.

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

[0025] System startup phase: Initialize the partition position, set the high temperature zone / medium and low temperature zone volume ratio to 3:2, and use the electric heater to heat the storage tank to the minimum operating temperature of +50℃;

[0026] 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 waste heat at 200-300℃ is heated by the heat pump and stored in the low-temperature tank;

[0027] Heat release optimization strategy: During peak power periods, the heat energy of high-temperature tanks is released first, and during off-peak power periods, the heat energy of low-temperature tanks is utilized in a cascade manner through heat pumps.

[0028] Beneficial effects:

[0029] Each storage tank in the multi-stage heat storage module of the present invention is dynamically partitioned by an adjustable partition, which can more effectively achieve temperature stratification. During multiple heat storage / release processes, this dynamic partitioning method can maintain significant temperature stratification, greatly improving the heat storage density, which is increased by 20%-30%, and the system circulation efficiency is over 85%; the multi-stage storage tank design shares the alternating thermal stress generated by the tank body and the internal molten salt during heat storage / release due to temperature differences. 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 synergy 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 radiation fluctuations and changes in load demand, the electric three-way valve can respond quickly and automatically adjust The heat exchanger connection method ensures that the system can adapt to changes in working conditions in a timely manner. At the same time, the combined use of different types of heat exchangers can effectively reduce thermal stress damage and greatly improve the stability and reliability of the system. The series-parallel combination of plate heat exchangers in the adaptive heat exchange network is used for the high-temperature section, and the shell and tube heat exchanger is used for the medium and low-temperature section. The electric three-way valve can automatically switch the connection method according to the heat source temperature, which enables the system to efficiently adapt to multiple heat sources such as solar thermal collection and industrial waste heat. For example, when the heat source is high-temperature solar thermal collection, the plate heat exchanger can work efficiently; when the heat source is medium and low-temperature industrial waste heat, the shell and tube heat exchanger can play a better role, thereby significantly improving energy utilization. BRIEF 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 briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0031] Figure 1 This is a process flow chart of the multi-temperature zone coupled graded molten salt heat storage system of the present invention. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0033] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are 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 understood as limiting the present invention.

[0034] In addition, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be a communication between the 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] Example 1

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

[0037] 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;

[0038] Adaptive heat exchange network, including a series-parallel combination of plate heat exchangers and shell-and-tube heat exchangers. The plate heat exchanger is used in the high-temperature range (500-565°C), and the shell-and-tube heat exchanger is used in the medium- and low-temperature range (250-450°C). Electric three-way valves are configured between the heat exchangers to automatically switch the connection mode according to the heat source temperature.

[0039] The intelligent control module integrates a temperature gradient sensor and a molten salt flow control valve to optimize heat storage priority and heat release rate in real time.

[0040] The temperature classification of the multi-stage heat storage module is:

[0041] The high temperature storage tank temperature range is 500-565℃, using NaNO3 / KNO3 (60 / 40) binary salt;

[0042] The temperature range of the medium temperature storage tank is 350-450℃, and 5% CaCl2 is added to lower the melting point of the molten salt;

[0043] The temperature range of low temperature storage tank is 250-300℃. XL molten salt;

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

[0045] The adjustable partitions adjust the partition ratio through a hydraulic drive system (such as expanding the high-temperature zone volume during the day and compressing the low-temperature zone at night). The pressure range of the hydraulic drive system is 20-35Mpa, and the response time is less than 5s. The entire tank body is a horizontal storage tank, which is divided into high-temperature storage tanks, medium-temperature storage tanks, low-temperature storage tanks and buffer storage tanks by multiple vertical partitions. The partitions are adjustable partitions that move horizontally to change the volume of multiple storage tanks. A hydraulic system or an electric system is used to move the partitions. The hydraulic system injects or extracts hydraulic oil into or out of different piston chambers according to the instructions of the control system, thereby pushing the piston (connected to the partition) to move in the tank to achieve dynamic adjustment of the partition. Alternatively, the partition is translated by an electric screw drive device. The 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 needs. Limit switches are installed at both ends of the 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, 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 that has absorbed a large amount of solar heat and is at a high temperature. After absorbing heat and heating in the solar collector field, the molten salt is transported to the high-temperature storage tank for storage, ready for release when energy is needed for power generation, heating, and other purposes. Its volume determines the maximum amount of high-temperature molten salt that the system can store, significantly impacting the system's heat storage capacity and continuous energy supply duration. It is a key indicator of the system's high-temperature heat storage capacity. A larger V_high means the system can store more high-temperature molten salt when solar energy is sufficient, thereby providing users with longer-term stable heat output during periods of insufficient solar energy or at night.

[0048] V_low represents the volume of the cryogenic storage tank. This tank is used to store molten salt that has cooled after releasing heat. When the high-temperature molten salt flows out of the high-temperature storage tank, it passes through heat exchange equipment (such as a steam generator) and releases heat to the outside world, where its temperature drops. It then flows back into the cryogenic storage tank, awaiting transport to the solar collector field to absorb heat again. The size of V_low is related to the system's capacity for low-temperature molten salt, ensuring the proper circulation of the molten salt within the system. An appropriate V_low ensures sufficient storage space for the low-temperature molten salt during its circulation, preventing system operation from being impacted by insufficient storage space.

[0049] T_sun refers to the temperature of the molten salt at the outlet of the solar collector, usually measured in degrees Celsius (°C). Solar collectors are key devices that convert solar energy into thermal energy and heat the molten salt. T_sun reflects how effectively the collector absorbs solar energy and transfers it to the molten salt, reflecting the strength of the solar energy resource at the time and the efficiency of the heat collection process. As the core input variable of the regulation algorithm, changes in T_sun determine the proportional relationship between the high-temperature and low-temperature storage tank volumes. The system monitors T_sun in real time and dynamically adjusts the volume distribution of the two tanks based on this temperature value to adapt to different solar energy resource conditions and system operation requirements.

[0050] α is a proportionality factor, ranging from 0.8 to 1.2. This factor is used to modify and adjust the control algorithm to suit the characteristics and actual operating requirements of different molten salt thermal energy storage systems. Different systems respond differently to solar temperature changes and require different storage tank volume allocations due to factors such as geographic location, meteorological conditions, and equipment performance. α can enhance the algorithm's versatility and adaptability.

[0051] When the value of α is close to 0.8, it indicates that the system responds relatively conservatively to changes in T_sun, 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 changes in 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 and low-temperature storage tanks and the temperature of the molten salt at the outlet of the solar collector. As T_sun increases, the value of V_high / V_low increases, which means 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 sufficient space for the storage of the molten salt after cooling. In this way, the system can dynamically adjust the volume distribution 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 thermal storage system and the rational storage and utilization of energy. The medium-temperature storage tank plays a transition and regulatory role in the entire process, helping the system better adapt to the changes in molten salt temperature and energy storage requirements under different working conditions.

[0053] 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.

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

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

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

[0057] 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.

[0058] The plate heat exchanger adopts an asymmetric flow channel design. The high-temperature side flow channel height is 4mm, and the low-temperature side flow channel height is 6mm. Spiral guide vanes are installed in the shell-and-tube heat exchanger with a lead angle of 30°.

[0059] The intelligent control module includes:

[0060] Distributed thermocouples and ultrasonic flowmeters are used, with three distributed thermocouple temperature measurement points arranged per cubic meter, and a sampling frequency of 10 Hz.

[0061] 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.

[0062] The heat storage priority decision of the intelligent control module is based on the electricity price signal, heat source grade and tank SOC status. The heat release rate is achieved through online tuning of PID parameters with an adjustment cycle of 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 partition position, set the high temperature zone / medium and low temperature zone volume ratio to 3:2, and use the electric heater to heat the storage tank to the minimum operating temperature of +50℃;

[0065] 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 waste heat at 200-300℃ is heated by the heat pump and stored in the low-temperature tank;

[0066] Heat release optimization strategy: During peak power periods, the heat energy of high-temperature tanks is released first, and during off-peak power periods, the heat energy of low-temperature tanks is utilized in a cascade manner through heat pumps.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to 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 a series-parallel combination of plate heat exchangers and shell-and-tube heat exchangers. The plate heat exchanger is used for the high-temperature section, and the shell-and-tube heat exchanger is used for the medium and low-temperature sections. Electric three-way valves are configured between the heat exchangers to automatically switch the connection mode according to the heat source temperature. The intelligent control module integrates a temperature gradient sensor and a molten salt flow control valve to optimize 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 high temperature storage tank temperature range 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 lower the melting point of the molten salt; The temperature range of low temperature storage tank is 250-300℃. molten salt; The buffer storage 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. 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 design 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, with the high-temperature side flow channel height being 4 mm and the low-temperature side flow channel height being 6 mm. A spiral guide vane is provided in the shell-and-tube heat exchanger with a lead angle of 30°.

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

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, heat source grade and tank SOC status. The heat release rate is achieved through online tuning of PID parameters with an adjustment cycle of 5 minutes.

10. A control method for a system according to any one of claims 1 to 9, characterized in that The following steps are involved: System startup phase: Initialize the partition position, set the high temperature zone / medium and low temperature zone volume ratio to 3:2, and use the electric heater to heat the storage tank to the minimum operating 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 waste heat at 200-300℃ 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 off-peak power periods, the heat energy of low-temperature tanks is utilized in a cascade manner through heat pumps.

Images