Closed steam-water loop of fused salt energy storage system for municipal heat supply and heat and mass transfer method

Abstract

The invention relates to the field of energy technologies and municipal heat supply, in particular to a closed steam-water loop of a molten salt energy storage system for municipal heat supply and a heat and mass transfer method. The steam-water loop module realizes indirect heat exchange through closed circulation; and the control module comprises a signal acquisition unit, a controller and an execution unit and is used for monitoring and adjusting. The heat and mass transfer method comprises the steps of heat storage, circulation starting, internal preheating, main heating, heat supply output and condensation backflow. According to the system, through the closed loop and cascade heat exchange design, low-conventional mature commercial fused salt and waste heat recovery are matched, the fused salt solidification risk is effectively avoided, it is guaranteed that the system operates reliably for a long time, the system is adaptive to the municipal heat supply low-temperature working condition, and efficient consumption of off-peak electric energy and stable transfer of heat energy are achieved. The method does not need to depend on special low-freezing-point fused salt, conventional mature commercial fused salt can be adopted, and stable and efficient application of the method in urban heat supply scenes is achieved.

Description

Technical Field

[0001] This invention relates to the fields of energy technology and municipal heating, and particularly to a closed-loop steam-water circuit and heat and mass transfer method for a molten salt energy storage system for municipal heating. Background Technology

[0002] Driven by both energy transition and the demand for low-carbon heating, molten salt energy storage technology has gradually gained widespread attention in the energy storage and heating fields due to its outstanding characteristics such as high thermal density, good thermal stability, and long service life. Municipal heating, as a key area for ensuring people's livelihood, urgently needs clean and efficient energy storage heating solutions to meet the dual demands of renewable energy consumption and grid peak shaving. The off-peak electricity storage advantage of molten salt energy storage systems perfectly matches this need, making it a highly promising application technology in the municipal heating sector.

[0003] However, the application scenarios of existing molten salt energy storage systems are significantly limited. Their technical solutions are mostly designed for high-temperature conditions such as high-temperature industrial steam supply and power generation peak shaving, and have not been specifically adapted and optimized for low-temperature conditions such as municipal heating. This has led to many obstacles in their application in the field of municipal heating. The most critical issue is the contradiction between the risk of molten salt solidification and the stability of heat transfer.

[0004] Specifically, the return water temperature of municipal heating networks is significantly lower than the freezing point of commonly used molten salts. Under the existing technical architecture, if direct heat exchange or simple indirect heat exchange designs are adopted, the temperature of the molten salt can easily drop below the freezing point during the heat exchange process, leading to serious safety hazards such as pipeline blockage and equipment damage. At the same time, insufficient heat exchange matching will also result in low heat transfer efficiency, making it difficult for the system to simultaneously ensure operational safety and heating stability. This core contradiction directly limits the large-scale promotion and application of molten salt energy storage technology in the field of municipal heating.

[0005] To address these contradictions, existing technologies often attempt to mitigate the risk of molten salt solidification by employing low-freezing-point molten salts. However, this approach has significant drawbacks: low-freezing-point molten salts are not only expensive but also have poor thermal stability, and their engineering application technology is still immature, making industrialization difficult. On the other hand, while conventional commercially available molten salts offer advantages such as low cost, good thermal stability, and mature engineering applications, their freezing point is mismatched with the return water temperature of municipal heating networks, preventing direct application in municipal heating scenarios. This limitation further exacerbates the difficulty of popularizing molten salt energy storage technology in the municipal heating sector. Summary of the Invention

[0006] To overcome the above deficiencies, this invention provides a closed-loop steam-water circuit and heat and mass transfer method for a molten salt energy storage system for municipal heating. It aims to improve the existing molten salt energy storage system when applied to municipal heating, which is prone to molten salt solidification, pipeline blockage and equipment damage due to the return water temperature of the heating network being lower than the freezing point of molten salt. In addition, the heat transfer efficiency is insufficient, making it difficult to balance system operation safety and heating stability. The core improvement of this invention is that, without the need for special low-freezing-point molten salts, by optimizing the loop design and heat exchange process, it enables the stable application of conventional, mature commercial molten salts in municipal heating scenarios, reducing system costs, improving engineering applicability, and simultaneously solving the problem of heat transfer stability.

[0007] In a first aspect, the present invention provides the following technical solution: a closed-loop steam-water circuit for a molten salt energy storage system for municipal heating, comprising: A molten salt circuit module for storing and releasing thermal energy, which has a molten salt outlet and a molten salt inlet; The steam-water loop module has a molten salt inlet, a molten salt outlet, a heating network water inlet, and a heating network water outlet. The molten salt inlet of the steam-water loop module is connected to the molten salt outlet of the molten salt loop module, and the molten salt outlet of the steam-water loop module is connected to the molten salt inlet of the molten salt loop module. The heating network water inlet of the steam-water loop module is connected to the municipal heating return water network, and its heating network water outlet is connected to the municipal heating supply water network. It is used to transfer the heat energy of the molten salt loop module to the working medium through a closed-loop circulation system, and then transfer the heat energy to the municipal heating network return water through the working medium, thereby realizing indirect heating. The control module communicates with the molten salt circuit module and the steam-water circuit module to monitor and control their operating status.

[0008] By adopting the above technical solution: a closed-loop steam-water circuit is constructed by a molten salt circuit module, a steam-water circuit module, and a control module, and combined with a regenerator, a three-stage molten salt-steam-water heat exchanger, and low-freezing-point molten salt, indirect heat exchange between molten salt and heating network water is achieved to avoid the risk of solidification; real-time monitoring and adjustment by the storage tank, water replenishment system, and control module ensures long-term reliable operation of the system; energy utilization efficiency is optimized by storing heat during off-peak hours, releasing heat during peak hours, and recovering waste heat; and by combining electric heat tracing units and cascade heating technology, the system is adapted to low-temperature conditions in municipal heating, ultimately achieving safe, stable, and efficient heat transfer.

[0009] Preferably, the molten salt circuit module includes: Cold salt containers and hot salt containers are used to store low-temperature molten salt and high-temperature molten salt, respectively; A molten salt electric heater, connected between the cold salt tank and the hot salt tank, is used to heat the molten salt; A cold salt pump is connected between the outlet of the cold salt tank and the inlet of the molten salt electric heater; A hot salt pump is connected between the outlet of the hot salt tank and the molten salt inlet of the steam-water circuit module; The inlet of the cold salt tank constitutes the molten salt inlet of the molten salt circuit module, and the outlet of the hot salt pump constitutes the molten salt outlet of the molten salt circuit module.

[0010] Preferably, the soft drink circuit module includes: Circulating water pumps are used to drive the flow of working fluids in closed-loop circulation systems. The molten salt-steam-water heat exchanger has its working fluid side inlet connected to the downstream outlet of the circulating water pump, and its working fluid side outlet connected to the upstream inlet of the circulating water pump. Its molten salt side inlet and molten salt side outlet respectively constitute the molten salt inlet and molten salt outlet of the steam-water circuit module. A regenerator is connected between the working fluid side outlet of the molten salt-steam-water heat exchanger and the inlet of the circulating water pump, and between the outlet of the circulating water pump and the working fluid side inlet of the molten salt-steam-water heat exchanger, for heat exchange between the internal working fluids. A heating heater, connected between a regenerator and the municipal heating network, is used to release the heat energy of the working fluid into the heating network water; The molten salt-steam-water heat exchanger is connected in series with the heating heater, so that the closed-loop working fluid can first absorb the heat of the molten salt in the molten salt-steam-water heat exchanger, and then release the heat to the municipal heating network return water in the heating heater.

[0011] Preferably, the molten salt-steam-water heat exchanger is a three-stage heat exchanger, including a preheater, an evaporator, and a superheater connected in series along the flow direction of the working fluid, for transferring the heat of the molten salt to the working fluid in a stepped manner; the molten salt-side inlets of the preheater, evaporator, and superheater are connected in parallel to form the molten salt-side inlet of the molten salt-steam-water heat exchanger, and their molten salt-side outlets are connected in parallel to form the molten salt-side outlet of the molten salt-steam-water heat exchanger.

[0012] Preferably, the water-gasoline circuit module further includes a storage tank and a water replenishment system; the outlet of the storage tank is connected to the outlet pipeline of the circulating water pump; and the outlet of the water replenishment system is connected to the inlet of the storage tank.

[0013] Preferably, the water replenishment system includes a water supply pump and a pressure stabilizing tank connected in sequence, and the inlet of the water supply pump is connected to a deionized water machine.

[0014] Preferably, the control module includes: The signal acquisition unit includes temperature and pressure sensors installed in the pipelines of the molten salt circuit module and the steam-water circuit module. The controller is communicatively connected to the signal acquisition unit; The execution control unit includes an electric heat tracing unit, a molten salt flow regulating valve, and a steam-water flow regulating valve connected to the controller; the electric heat tracing unit is installed on the molten salt pipeline; the molten salt flow regulating valve is installed on the molten salt outlet pipeline of the molten salt circuit module; and the steam-water flow regulating valve is installed on the working fluid circulation pipeline of the steam-water circuit module.

[0015] Preferably, the molten salt in the molten salt circuit module has a freezing point of not less than 100°C and not more than 142°C.

[0016] Secondly, the present invention provides the following technical solution: a heat and mass transfer method for a closed-loop steam-water circuit in a molten salt energy storage system for municipal heating, comprising the following steps: S1: During the heat storage stage, during off-peak electricity hours, the control module activates the molten salt circuit module to store heat, converting electrical energy into thermal energy of high-temperature molten salt. S2: During the cycle start-up phase, when heating is required, the control module starts the circulating power component in the steam-water circuit module to establish a closed working fluid cycle and starts the molten salt release component in the molten salt circuit module. S3: Internal preheating stage. Inside the steam-water circuit module, a regenerator is used to preheat the low-temperature working fluid with a high-temperature working fluid to increase its temperature. S4: In the main heating stage, the preheated working fluid absorbs heat from the high-temperature molten salt in the molten salt loop module in the molten salt-steam heat exchanger, transforming into a high-temperature working fluid and completing one transfer of heat from the molten salt to the working fluid. S5: During the heat output stage, the high-temperature working fluid transfers heat to the municipal heating network return water in the heating heater to achieve heat output. It is cooled down and completes the secondary transfer of heat from the working fluid to the heating network water. S6: Condensation and reflux stage, the cooled working fluid flows back to the inlet of the circulating power component to complete the cycle; The molten salt, after releasing heat in the molten salt-steam-water heat exchanger, is returned to the molten salt loop module.

[0017] Preferably, in step S4, the main heating stage specifically involves the working fluid sequentially flowing through the preheater, evaporator, and superheater in the molten salt-steam-water heat exchanger, undergoing liquid phase heating, phase change evaporation, and steam superheating processes, and finally transforming into high-temperature steam.

[0018] The present invention has the following beneficial effects: 1. In this invention, a closed-loop steam-water circuit is formed by a molten salt circuit module, a steam-water circuit module and a control module. Combined with a regenerator and a three-stage molten salt-steam-water heat exchanger, indirect heat exchange between molten salt and heating network water is achieved. The use of low-freezing-point molten salt effectively avoids the risk of molten salt solidification. The system completes cascade heating and waste heat recovery through heat and mass transfer methods, ensuring efficient and stable heat transfer in municipal heating scenarios.

[0019] 2. In this invention, the working fluid is replenished and the circuit pressure is maintained by the deionized water machine, water pump and pressure stabilizing tank of the liquid storage tank and water replenishment system working together. Combined with the control module to monitor the pipeline temperature and pressure in real time, the scale corrosion caused by impurities in the working fluid and the damage to the equipment caused by pressure fluctuations are avoided, which significantly improves the reliability and safety of the system in long-term operation.

[0020] 3. In this invention, molten salt is heated and stored during off-peak hours by means of a molten salt electric heater. The flow rate of the medium is dynamically adjusted by a molten salt flow regulating valve and a steam-water flow regulating valve. The efficient absorption of off-peak electricity and the release of heat energy during peak hours are achieved through heat and mass transfer methods, thereby optimizing the energy utilization structure. At the same time, the waste heat of the regenerator is recovered to improve the energy utilization rate and reduce energy loss.

[0021] 4. In this invention, the electric heat tracing unit and the controller work together to automatically start the heat tracing and adjust the flow rate of the molten salt pump when the temperature of the molten salt is close to the freezing point. Combined with the three-stage heat exchanger cascade heating process, the system can be started and operated smoothly under extreme low temperature conditions, avoiding pipeline blockage and equipment damage, and adapting to the complex environmental requirements of municipal heating in northern winters. Attached Figure Description

[0022] Figure 1 The flowchart of the closed-loop steam-water circuit of the molten salt energy storage system for municipal heating proposed in this invention is shown below. Figure 2 This is a flowchart of the heat and mass transfer method for a closed-loop steam-water circuit in a molten salt energy storage system for municipal heating proposed in this invention. Detailed Implementation

[0023] The technical solutions in 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1: In the first embodiment of the present invention, the present invention provides a closed-loop steam-water circuit for a molten salt energy storage system for municipal heating, such as... Figure 1 As shown, it includes: A molten salt circuit module for storing and releasing thermal energy, which has a molten salt outlet and a molten salt inlet; Furthermore, the molten salt circuit module includes: Cold salt containers and hot salt containers are used to store low-temperature molten salt and high-temperature molten salt, respectively; A molten salt electric heater, connected between a cold salt tank and a hot salt tank, is used to heat molten salt; A cold salt pump is connected between the outlet of the cold salt tank and the inlet of the molten salt electric heater; A hot salt pump is connected between the outlet of the hot salt tank and the molten salt inlet of the steam-water circuit module; The inlet of the cold salt tank constitutes the molten salt inlet of the molten salt circuit module, and the outlet of the hot salt pump constitutes the molten salt outlet of the molten salt circuit module. Furthermore, the molten salt in the molten salt circuit module has a freezing point of not less than 100℃ and not more than 142℃.

[0025] Specifically, the cold salt tank in the molten salt circuit module stores low-temperature molten salt at around 200°C, while the hot salt tank stores high-temperature molten salt at 375°C. The separate design avoids heat loss caused by direct mixing of cold and hot molten salt, ensuring the system's heat storage capacity remains stably maintained at 4MWh. The molten salt electric heater has a rated power of 500kW and operates continuously at full load for 8 hours during off-peak electricity hours, heating the low-temperature molten salt transported from the cold salt tank to 375°C, achieving efficient conversion and maximum utilization of off-peak electricity into heat energy. The cold salt pump provides power for the circulation of molten salt from the cold salt tank to the molten salt electric heater. By precisely adjusting the output flow rate to match the heating power, it avoids localized overheating or insufficient heating of the molten salt, ensuring the safety and temperature uniformity of the heating process. The hot salt pump is responsible for stably transporting the high-temperature molten salt from the hot salt tank to the steam-water circuit module, providing continuous power. The output ensures that the heating power is maintained at 500kW to meet the municipal heating load of a specific area. The molten salt used is a representative conventional commercial ternary nitrate molten salt, composed of 53% potassium nitrate, 40% sodium nitrite and 7% sodium nitrate, with a freezing point of 142℃ and an operating temperature range of 200℃ to 375℃. The core advantage of this solution is that it abandons the high cost and immature application of low freezing point molten salt in existing technologies. Through the closed-loop steam-water circuit design, this conventional commercial molten salt with a relatively high freezing point, mature technology and low cost can be safely applied to low-temperature municipal heating scenarios. With its excellent thermal stability and heat capacity characteristics, it effectively avoids the risk of pipeline blockage caused by low-temperature freezing and significantly improves the system energy storage density, truly realizing the large-scale application of conventional mature commercial molten salt in the field of municipal heating.

[0026] The steam-water loop module has a molten salt inlet, a molten salt outlet, a heating network water inlet, and a heating network water outlet. The molten salt inlet of the steam-water loop module is connected to the molten salt outlet of the molten salt loop module, and the molten salt outlet of the steam-water loop module is connected to the molten salt inlet of the molten salt loop module. The heating network water inlet of the steam-water loop module is connected to the municipal heating return water network, and its heating network water outlet is connected to the municipal heating supply water network. It is used to transfer the heat energy of the molten salt loop module to the working medium through a closed-loop circulation working medium, and then transfer the heat energy to the municipal heating network return water through the working medium, thereby realizing indirect heating. Furthermore, the soft drink circuit module includes: Circulating water pumps are used to drive the flow of working fluids in closed-loop circulation systems. The molten salt-steam-water heat exchanger has its working fluid side inlet connected to the downstream outlet of the circulating water pump, and its working fluid side outlet connected to the upstream inlet of the circulating water pump. Its molten salt side inlet and molten salt side outlet respectively constitute the molten salt inlet and molten salt outlet of the steam-water circuit module. A regenerator is connected between the working fluid side outlet of the molten salt-steam-water heat exchanger and the inlet of the circulating water pump, and between the outlet of the circulating water pump and the working fluid side inlet of the molten salt-steam-water heat exchanger, for heat exchange between the internal working fluids. A heating heater, connected between a regenerator and the municipal heating network, is used to release the heat energy of the working fluid into the heating network water; The molten salt-steam-water heat exchanger is connected in series with the heating heater, so that the closed-loop working fluid can first absorb the heat of the molten salt in the molten salt-steam-water heat exchanger, and then release the heat to the municipal heating network return water in the heating heater. Furthermore, the molten salt-steam-water heat exchanger is a three-stage heat exchanger, including a preheater, an evaporator, and a superheater connected in series along the flow direction of the working fluid, which are used to transfer the heat of the molten salt to the working fluid in stages; the molten salt side inlets of the preheater, evaporator, and superheater are connected in parallel to form the molten salt side inlet of the molten salt-steam-water heat exchanger, and their molten salt side outlets are connected in parallel to form the molten salt side outlet of the molten salt-steam-water heat exchanger. Furthermore, the water-gasoline circuit module also includes a storage tank and a water replenishment system; the outlet of the storage tank is connected to the outlet pipeline of the circulating water pump; the outlet of the water replenishment system is connected to the inlet of the storage tank. Furthermore, the water replenishment system includes a water supply pump and a pressure stabilizing tank connected in sequence, and a deionized water machine is connected to the inlet of the water supply pump.

[0027] Specifically, the circulating water pump in the steam-water loop module provides continuous flow power for the working fluid in the closed loop. By adjusting the speed, it adapts to different heating load changes, ensuring the stability of the working fluid circulation and the efficiency of heat transfer. The working fluid is water, and the circulating water pump drives the water to circulate stably in the closed loop, providing power support for the process of heat transfer from the three-stage heat exchanger to the high-temperature water and heat transfer from the heating heater to the low-temperature return water. The molten salt-steam-water heat exchanger is the core heat transfer equipment with a rated heat exchange power of 550kW. Its three-stage preheater, evaporator and superheater, connected in series, respectively undertake the functions of liquid phase heating, phase change evaporation and steam superheating of the working fluid, thereby fully realizing the stepwise transfer of heat from high-temperature molten salt to high-temperature working fluid. The parallel design on the molten salt side ensures that the high-temperature molten salt flows evenly through each heat exchange unit, avoiding local heat load concentration, improving heat exchange efficiency, and reducing thermal stress damage to the equipment. The regenerator adopts a structure in which cold water flows through the tube side and hot steam flows through the shell side. The high-temperature working fluid releases heat in the shell side, while the low-temperature working fluid absorbs heat in the tube side and is preheated to above 142°C. This avoids the risk of solidification caused by direct contact between molten salt and low-temperature working fluid from the source, and lays the foundation for efficient heat exchange between high-temperature molten salt and working fluid in the future, further ensuring the safe operation of conventional commercial molten salt. The heating heater is a phase change heat exchanger. High-temperature steam from the regenerator flows through the shell side, while low-temperature return water from the municipal heating return water network flows through the tube side. A large amount of latent heat is released through steam condensation, heating the heating network water from 30°C to 50°C, realizing the final transfer of heat from the high-temperature working fluid water to the low-temperature heating network water. The heated low-temperature return water enters the municipal heating network through the heating network water outlet of the steam-water loop module.

[0028] The storage tank in the steam-water loop module stores the backup working fluid for the closed loop. The backup working fluid is deionized water, which buffers the volume expansion and contraction of the working fluid due to temperature changes, maintains stable loop pressure, and avoids damage to the heat exchange equipment caused by pressure fluctuations. The water replenishment system consists of a deionized water machine, a feed water pump, and a pressure stabilizing tank connected in sequence. The deionized water machine treats tap water into high-purity deionized water, avoiding pipe scaling and equipment corrosion caused by impurities in the working fluid. The feed water pump provides stable power for water replenishment, and the pressure stabilizing tank adjusts the water replenishment pressure in real time to match the loop pressure. The three work together to achieve precise replenishment of the working fluid and dynamic balance of loop pressure, ensuring long-term stable operation of the system and thus ensuring the continuous, safe, and efficient application of conventional commercial molten salt in municipal heating scenarios.

[0029] The control module communicates with the molten salt circuit module and the steam-water circuit module to monitor and control their operating status.

[0030] Furthermore, the control module includes: The signal acquisition unit includes temperature and pressure sensors installed in the pipelines of the molten salt circuit module and the steam-water circuit module. The controller is communicatively connected to the signal acquisition unit; The control unit includes an electric heat tracing unit, a molten salt flow regulating valve, and a steam-water flow regulating valve connected to the controller. The electric heat tracing unit is installed on the molten salt pipeline. The molten salt flow regulating valve is installed on the molten salt outlet pipeline of the molten salt circuit module. The steam-water flow regulating valve is installed on the working fluid circulation pipeline of the steam-water circuit module.

[0031] Specifically, the signal acquisition unit in the control module has temperature sensors arranged in the molten salt pipeline, steam-water loop pipeline, and heating network water pipeline to monitor the molten salt temperature, working fluid temperature, and heating network water supply and return temperatures in real time. Pressure sensors are arranged in the inlet and outlet pipelines of the molten salt-steam-water heat exchanger, regenerator, and heating heater to monitor the pressure parameters at each key node, providing reliable decision-making basis for the controller through accurate acquisition of operating data. The controller receives real-time data from the signal acquisition unit, combines it with peak and off-peak electricity price information, and generates control commands through built-in logic operations to adjust the heating power of the molten salt electric heater, the flow rate of the cold salt pump and hot salt pump, and the speed of the circulating water pump. The electric heat tracing unit of the execution control unit is wrapped around the outside of the molten salt pipeline. When the molten salt temperature is detected, the controller will detect the temperature of the molten salt pipeline. The system automatically activates when the salt temperature drops below 142℃, supplementing heat to prevent molten salt from solidifying and ensuring that conventional commercial molten salt remains within its safe operating temperature range. A molten salt flow regulating valve is located between the hot salt pump and the molten salt-steam-water heat exchanger. By adjusting the flow rate to match the heating load, it ensures stable efficiency of the three-stage molten salt-steam-water heat exchanger in transferring heat from the high-temperature molten salt to the high-temperature water. A steam-water flow regulating valve is located between the circulating water pump and the regenerator, controlling the working fluid circulation speed to ensure stable heat transfer from the high-temperature water to the low-temperature heating network water. This ensures that the heated network water smoothly enters the municipal heating network, ultimately guaranteeing system safety and preventing condensation, achieving economical operation under peak-valley electricity price differences, and maximizing the application advantages of conventional commercial molten salt.

[0032] Example 2: This example is applied to a municipal heating scenario in northern China during winter. This scenario presents three core technical challenges: First, the extreme low temperatures in winter cause a significant decrease in the efficiency of traditional heating equipment, resulting in high carbon emissions and operating costs for gas-fired boilers, and a marked decline in the heating performance of air-source heat pumps. Second, the large temperature difference between the freezing point of conventional commercial molten salt and the return water temperature of the municipal heating network makes direct heat exchange prone to molten salt solidification and pipe blockage. Third, under low-pressure conditions, molten salt-steam-water heat exchangers are prone to hydrodynamic instability, affecting heat exchange efficiency and equipment lifespan. To solve these problems, the heat and mass transfer method for a closed-loop steam-water circuit in a molten salt energy storage system for municipal heating, as provided in this invention, is adopted. Its structure is as follows: Figure 2 As shown. Includes the following steps:

[0033] S1: During the heat storage stage, during off-peak electricity hours, the control module activates the molten salt circuit module to store heat, converting electrical energy into thermal energy of high-temperature molten salt. S2: During the cycle start-up phase, when heating is required, the control module starts the circulating power component in the steam-water circuit module to establish a closed working fluid cycle and starts the molten salt release component in the molten salt circuit module. S3: Internal preheating stage. Inside the steam-water circuit module, a regenerator is used to preheat the low-temperature working fluid with a high-temperature working fluid to increase its temperature. S4: In the main heating stage, the preheated working fluid absorbs heat from the high-temperature molten salt in the molten salt loop module in the molten salt-steam heat exchanger, transforming into a high-temperature working fluid and completing one transfer of heat from the molten salt to the working fluid. S5: During the heat output stage, the high-temperature working fluid transfers heat to the municipal heating network return water in the heating heater to achieve heat output. It is cooled down and completes the secondary transfer of heat from the working fluid to the heating network water. S6: Condensation and reflux stage, the cooled working fluid flows back to the inlet of the circulating power component to complete the cycle; The molten salt, after releasing heat in the molten salt-steam-water heat exchanger, is returned to the molten salt loop module.

[0034] Furthermore, in step S4, the main heating stage specifically involves the working fluid sequentially flowing through the preheater, evaporator, and superheater in the molten salt-steam-water heat exchanger, undergoing liquid phase heating, phase change evaporation, and steam superheating processes, and finally transforming into high-temperature steam.

[0035] Specifically, during off-peak electricity hours, the control module receives the electricity price signal and starts the molten salt circuit module. The cold salt pump draws conventional commercial ternary nitrate molten salt at 200°C from the cold salt tank and delivers it to a molten salt electric heater with a rated power of 500kW at an appropriate flow rate. The heater operates at full load for 8 hours to heat the molten salt to 375°C. The high-temperature molten salt is then transported through pipelines to a hot salt tank for storage, realizing the conversion and storage of off-peak electricity into thermal energy. The thermal storage capacity reaches 4MWh. This process fully utilizes the advantages of conventional commercial molten salt, such as low cost and good thermal stability, while eliminating the disadvantages of low-freezing-point molten salt, thus achieving efficient thermal storage of conventional commercial molten salt.

[0036] When the heating demand of the municipal heating network is detected, the control module starts the circulating water pump of the steam-water circuit module and the hot salt pump of the molten salt circuit module. The circulating water pump drives the working fluid in the closed circuit to flow at a set speed to establish a stable circulation, where the working fluid is water. The hot salt pump slowly increases the output flow rate to smoothly transport the high-temperature molten salt in the hot salt tank to the molten salt-steam-water heat exchanger, avoiding system shocks caused by sudden flow changes and ensuring the stable cascade transfer of heat from the high-temperature molten salt to the high-temperature water.

[0037] Low-temperature water pumped by the circulating water pump enters the tube side of the regenerator, while high-temperature water output from the molten salt-steam-water heat exchanger flows into the shell side of the regenerator. The low-temperature water is preheated to above 142°C through shell-and-tube heat exchange, which avoids the risk of solidification from direct contact between molten salt and low-temperature water, ensuring the safe operation of conventional commercial molten salt, and recovers the waste heat of the high-temperature water, thereby improving the system's energy utilization rate.

[0038] The preheated working fluid enters the molten salt-steam-water heat exchanger, flowing sequentially through a preheater, evaporator, and superheater connected in series. In the preheater, it absorbs heat from the high-temperature molten salt, raising its temperature to near the saturation temperature at the current pressure. Upon entering the evaporator, it undergoes phase change evaporation under the influence of the medium-temperature molten salt, transforming into saturated steam. Finally, it is heated by the superheater to form high-temperature steam at 200°C to 375°C. Thus, the first heat transfer from the high-temperature molten salt to the high-temperature steam is completed through the three-stage molten salt-steam-water heat exchanger. The parallel design of the molten salt side of the heat exchangers ensures uniform heat exchange and avoids localized heat load concentration.

[0039] The high-temperature steam is divided into two streams. One stream flows back to the regenerator as a preheating heat source, and the other stream is sent to the shell side of the phase change heat exchanger type heating heater, where it exchanges heat with the municipal heating network return water flowing into the tube side. The steam condenses and releases latent heat, heating the heating network water to 50°C before being sent to the municipal heating water supply network. This completes the second heat transfer from the high-temperature steam to the low-temperature heating network water, achieving heat output. The steam itself is cooled to become subcooled water.

[0040] The subcooled water from the outlet of the heating heater flows back to the inlet of the circulating water pump through the pipeline, and is then pumped back to the regenerator to complete the closed working fluid cycle. The molten salt, after releasing heat in the molten salt-steam-water heat exchanger, drops to about 200°C and returns to the cold salt tank through the pipeline, waiting for the next heat storage cycle.

[0041] Throughout the process, the control module receives real-time operating data from temperature and pressure sensors and dynamically adjusts the system based on peak and off-peak electricity pricing: during off-peak electricity storage, the flow rate of the cold salt pump is optimized to match the heater power; during peak electricity supply, the flow rate of the medium is adjusted through the molten salt flow regulating valve and the steam-water flow regulating valve to maintain a heating power of 500kW; when the temperature of the molten salt pipeline is detected to be below 142℃, the electric heat tracing unit is automatically started and the flow rate of the molten salt pump is increased to ensure safe anti-condensation and economical operation of the system.

[0042] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A closed-loop steam-water circuit for a molten salt energy storage system for municipal heating, characterized in that, include: A molten salt circuit module for storing and releasing thermal energy, which has a molten salt outlet and a molten salt inlet; The steam-water loop module has a molten salt inlet, a molten salt outlet, a heating network water inlet, and a heating network water outlet. The molten salt inlet of the steam-water loop module is connected to the molten salt outlet of the molten salt loop module, and the molten salt outlet of the steam-water loop module is connected to the molten salt inlet of the molten salt loop module. The heating network water inlet of the steam-water loop module is connected to the municipal heating return water network, and its heating network water outlet is connected to the municipal heating supply water network. It is used to transfer the heat energy of the molten salt loop module to the working medium through a closed-loop circulation system, and then transfer the heat energy to the municipal heating network return water through the working medium, thereby realizing indirect heating. The control module is connected in communication with the molten salt circuit module and the steam-water circuit module to monitor and control their operating status.

2. The closed-loop steam-water circuit of the molten salt energy storage system for municipal heating according to claim 1, characterized in that, The molten salt circuit module includes: Cold salt containers and hot salt containers are used to store low-temperature molten salt and high-temperature molten salt, respectively; A molten salt electric heater, connected between the cold salt tank and the hot salt tank, is used to heat the molten salt; A cold salt pump is connected between the outlet of the cold salt tank and the inlet of the molten salt electric heater; A hot salt pump is connected between the outlet of the hot salt tank and the molten salt inlet of the steam-water circuit module; The inlet of the cold salt tank constitutes the molten salt inlet of the molten salt circuit module, and the outlet of the hot salt pump constitutes the molten salt outlet of the molten salt circuit module.

3. The closed-loop steam-water circuit of the molten salt energy storage system for municipal heating according to claim 1, characterized in that, The soda circuit module includes: Circulating water pumps are used to drive the flow of working fluids in closed-loop circulation systems. The molten salt-steam-water heat exchanger has its working fluid side inlet connected to the downstream outlet of the circulating water pump, and its working fluid side outlet connected to the upstream inlet of the circulating water pump. Its molten salt side inlet and molten salt side outlet respectively constitute the molten salt inlet and molten salt outlet of the steam-water circuit module. A regenerator is connected between the working fluid side outlet of the molten salt-steam-water heat exchanger and the inlet of the circulating water pump, and between the outlet of the circulating water pump and the working fluid side inlet of the molten salt-steam-water heat exchanger, for heat exchange between the internal working fluids. A heating heater, connected between a regenerator and the municipal heating network, is used to release the heat energy of the working fluid into the heating network water; The molten salt-steam-water heat exchanger is connected in series with the heating heater, so that the closed-loop working fluid can first absorb the heat of the molten salt in the molten salt-steam-water heat exchanger, and then release the heat to the municipal heating network return water in the heating heater.

4. The closed-loop steam-water circuit of the molten salt energy storage system for municipal heating according to claim 3, characterized in that, The molten salt-steam-water heat exchanger is a three-stage heat exchanger, including a preheater, an evaporator, and a superheater connected in series along the flow direction of the working fluid, which are used to transfer the heat of the molten salt to the working fluid in a stepwise manner; the molten salt side inlets of the preheater, evaporator, and superheater are connected in parallel to form the molten salt side inlet of the molten salt-steam-water heat exchanger, and their molten salt side outlets are connected in parallel to form the molten salt side outlet of the molten salt-steam-water heat exchanger.

5. The closed-loop steam-water circuit of the molten salt energy storage system for municipal heating according to claim 3, characterized in that, The steam-water circuit module also includes a storage tank and a water replenishment system; the outlet of the storage tank is connected to the outlet pipeline of the circulating water pump; the outlet of the water replenishment system is connected to the inlet of the storage tank.

6. The closed-loop steam-water circuit of the molten salt energy storage system for municipal heating according to claim 5, characterized in that, The water replenishment system includes a water supply pump and a pressure stabilizing tank connected in sequence, and a deionized water machine is connected to the inlet of the water supply pump.

7. The closed-loop steam-water circuit of the molten salt energy storage system for municipal heating according to claim 1, characterized in that, The control module includes: The signal acquisition unit includes temperature and pressure sensors installed in the pipelines of the molten salt circuit module and the steam-water circuit module. The controller is communicatively connected to the signal acquisition unit; The execution control unit includes an electric heat tracing unit, a molten salt flow regulating valve, and a steam-water flow regulating valve connected to the controller; the electric heat tracing unit is installed on the molten salt pipeline; the molten salt flow regulating valve is installed on the molten salt outlet pipeline of the molten salt circuit module; and the steam-water flow regulating valve is installed on the working fluid circulation pipeline of the steam-water circuit module.

8. The closed-loop steam-water circuit of the molten salt energy storage system for municipal heating according to claim 2, characterized in that, The molten salt in the molten salt circuit module has a freezing point of not less than 100°C and not more than 142°C.

9. A heat and mass transfer method for a closed-loop steam-water circuit in a molten salt energy storage system for municipal heating, characterized in that, The closed-loop steam-water circuit of the molten salt energy storage system for municipal heating as described in any one of claims 1-8 comprises the following steps: S1: During the heat storage stage, during off-peak electricity hours, the control module activates the molten salt circuit module to store heat, converting electrical energy into thermal energy of high-temperature molten salt. S2: During the cycle start-up phase, when heating is required, the control module starts the circulating power component in the steam-water circuit module to establish a closed working fluid cycle and starts the molten salt release component in the molten salt circuit module. S3: Internal preheating stage. Inside the steam-water circuit module, a regenerator is used to preheat the low-temperature working fluid with a high-temperature working fluid to increase its temperature. S4: In the main heating stage, the preheated working fluid absorbs heat from the high-temperature molten salt in the molten salt loop module in the molten salt-steam heat exchanger, transforming into a high-temperature working fluid and completing one transfer of heat from the molten salt to the working fluid. S5: During the heat output stage, the high-temperature working fluid transfers heat to the municipal heating network return water in the heating heater to achieve heat output. It is cooled down and completes the secondary transfer of heat from the working fluid to the heating network water. S6: Condensation and reflux stage, the cooled working fluid flows back to the inlet of the circulating power component to complete the cycle; The molten salt, after releasing heat in the molten salt-steam-water heat exchanger, is returned to the molten salt loop module.

10. The heat and mass transfer method for a closed-loop steam-water circuit in a molten salt energy storage system for municipal heating according to claim 9, characterized in that, In step S4, the main heating stage specifically involves the working fluid sequentially flowing through the preheater, evaporator, and superheater in the molten salt-steam-water heat exchanger, undergoing liquid phase heating, phase change evaporation, and steam superheating processes, and finally transforming into high-temperature steam.

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