Molten salt heat storage and coal-fired unit coupled power generation system and method

Abstract

The invention belongs to the field of power generation systems, and provides a fused salt heat storage and coal-fired unit coupled power generation system and method.The fused salt heat storage and coal-fired unit coupled power generation system comprises a coal-fired power generation unit, and the coal-fired power generation unit comprises a boiler, a steam turbine high-pressure cylinder, a reheater, a steam turbine medium-low-pressure cylinder, a condenser and a water feeding pump; the fused salt heat storage unit comprises a cold salt tank, a hot salt tank, a fused salt-feed water heat exchanger and a fused salt-steam heat exchanger; a water supply side inlet and outlet of the fused salt-water supply heat exchanger are connected to a main water supply pipeline between the water supply pump and the boiler in parallel to form a first parallel pipeline. And a steam side inlet and outlet of the fused salt-steam heat exchanger is connected to a reheating cold section pipeline between a steam exhaust port of the steam turbine high-pressure cylinder and the reheater, a second parallel pipeline is formed, and bidirectional transfer of heat energy between the coal-fired power generation unit and the fused salt heat storage unit is achieved. Efficient, bidirectional and controllable transfer of heat energy between the power generation unit and the heat storage unit can be achieved, and therefore the operation adaptability and the full-life-cycle value of the coal-fired unit are improved.

Description

Technical Field

[0001] This invention belongs to the field of power generation systems, specifically relating to a power generation system and method that couples molten salt thermal storage with a coal-fired unit. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Coal-fired power generation has long played a fundamental role in my country's power supply system, providing stable and reliable baseload power support for the power grid. With the rapid expansion of installed capacity of renewable energy sources such as wind and solar power, the grid's demand for flexible peak-shaving resources has significantly increased. Traditional coal-fired units operate at their optimal efficiency under rated conditions, but when participating in deep peak shaving and continuously operating at low loads, their thermodynamic cycle efficiency decreases significantly, fuel consumption increases, and operational economics are severely constrained. Simultaneously, frequent load fluctuations exacerbate thermal stress on equipment, adversely affecting the service life of core components such as turbines and boilers.

[0004] Molten salt thermal energy storage technology, with its advantages of high thermal density, wide operating temperature range, and mature engineering applications, has been widely applied in the field of solar thermal power generation. This technology enables the large-scale, long-term storage of thermal energy in a chemical form, providing a feasible path for energy time-lapse. Coupled with molten salt thermal energy storage systems and coal-fired power generating units is considered an important direction for improving the peak-shaving capacity of these units and optimizing energy utilization efficiency.

[0005] However, existing technical solutions have significant shortcomings: some systems only support unidirectional energy flow, such as using molten salt heat to preheat feedwater during peak load periods to increase power generation, but failing to effectively recover and store excess heat energy from the units during low load periods; other coupling methods have simple structures, resulting in inefficient heat transfer processes and difficulty in achieving dynamic energy balance between power generation and heat storage units. These deficiencies prevent the system from flexibly switching the direction of energy flow according to the real-time needs of the power grid, limiting the full release of the peak-shaving potential of coal-fired units and failing to meet the high standards of modern power grids for flexible resources. Summary of the Invention

[0006] To address the aforementioned problems, this invention proposes a power generation system and method that couples molten salt thermal energy storage with a coal-fired power unit. This invention enables efficient, bidirectional, and controllable transfer of thermal energy between the power generation unit and the thermal energy storage unit, thereby improving the operational adaptability and life-cycle value of the coal-fired power unit.

[0007] According to some embodiments, the present invention adopts the following technical solution: A power generation system coupled with molten salt thermal storage and a coal-fired unit, comprising: A coal-fired power generation unit includes a boiler, a high-pressure cylinder of a steam turbine, a reheater, a medium- and low-pressure cylinder of a steam turbine, a condenser, and a feedwater pump connected in sequence. Molten salt thermal storage unit, which includes a cold salt tank, a hot salt tank, a molten salt-feedwater heat exchanger and a molten salt-steam heat exchanger; The inlet and outlet of the molten salt-feedwater heat exchanger are connected in parallel to the main feedwater pipeline between the feedwater pump and the boiler, forming a first parallel pipeline. The steam side inlet and outlet of the molten salt-steam heat exchanger are connected to the reheat cold section pipeline between the exhaust port of the high-pressure cylinder of the steam turbine and the reheater through pipes and valves, forming a second parallel pipeline; The bidirectional transfer of thermal energy between the coal-fired power generation unit and the molten salt thermal storage unit is achieved through the first parallel pipeline, the second parallel pipeline, the molten salt-feedwater heat exchanger, and the molten salt-steam heat exchanger.

[0008] As an alternative implementation, the steam-side inlet and outlet of the molten salt-steam heat exchanger are also connected to the main steam pipeline between the superheated steam outlet of the boiler and the main steam inlet of the high-pressure cylinder of the steam turbine via pipes and valves, forming a third parallel pipeline.

[0009] As an alternative implementation, the molten salt thermal storage unit further includes an electric heater, which is disposed on the molten salt pipeline between the cold salt tank and the molten salt-steam heat exchanger.

[0010] As an alternative implementation, the molten salt outlet of the molten salt-feed water heat exchanger is connected to the cold salt tank, and the molten salt inlet is connected to the hot salt tank.

[0011] As an alternative implementation, the molten salt inlet of the hot salt tank is connected to the molten salt outlet of the molten salt-steam heat exchanger, and the molten salt inlet of the molten salt-steam heat exchanger is connected to an electric heater.

[0012] As an alternative implementation, both the molten salt-feedwater heat exchanger and the molten salt-steam heat exchanger are indirect heat exchangers, with their molten salt side completely isolated from the steam side or feedwater side.

[0013] An operating method for the above-mentioned power generation system includes: a thermal storage mode and a thermal release mode; In thermal storage mode, perform the following steps: A portion of medium-pressure steam is drawn from the exhaust port of the high-pressure cylinder of the steam turbine and transported to the molten salt-steam heat exchanger; Low-temperature molten salt from the cold salt tank exchanges heat with medium-pressure steam in the molten salt-steam heat exchanger. The medium-pressure steam is cooled into condensate and returned to the reheat cold section pipeline, while the low-temperature molten salt is heated into high-temperature molten salt and stored in the hot salt tank. In heat release mode, perform the following steps: The high-temperature molten salt from the hot salt tank flows through the molten salt-feed water heat exchanger; A portion of the main feedwater from the feedwater pump is diverted into the molten salt-feedwater heat exchanger, where it exchanges heat with the high-temperature molten salt. After being heated, it returns to the main feedwater pipeline and then enters the boiler.

[0014] As an alternative implementation, the thermal storage mode further includes: A portion of the high-pressure main steam is drawn from the superheated steam outlet of the boiler and transported to the molten salt-steam heat exchanger; The low-temperature molten salt from the cold salt tank exchanges heat with the high-pressure main steam in the molten salt-steam heat exchanger. The high-pressure main steam is cooled into condensate and returned to the main steam pipeline, while the low-temperature molten salt is heated into high-temperature molten salt and stored in the hot salt tank.

[0015] As an alternative implementation, in the heat storage mode, an electric heater is also activated to use external electrical energy to assist or directly heat the molten salt flowing through the molten salt-steam heat exchanger.

[0016] As an alternative implementation, the method selects a mode based on the real-time load command and / or electricity price signal from the power grid: The thermal storage mode is activated when the grid load demand is low or the electricity price is lower than the first threshold. The heat release mode is activated when the grid load demand is high or the electricity price is higher than the second threshold.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention achieves efficient bidirectional heat transfer between the two units through a deep coupling design of molten salt thermal storage units and coal-fired power generation units. The parallel piping design of the molten salt-feedwater heat exchanger and the molten salt-steam heat exchanger works in tandem to recover excess heat energy during low-load operation in thermal storage mode, avoiding the heat energy waste caused by low-load operation of traditional coal-fired units; in heat release mode, the stored heat energy is released to enhance power generation capacity during peak hours, thereby optimizing the overall operating efficiency of the unit. This bidirectional transfer mechanism solves the problem of unidirectional heat energy flow or low utilization efficiency in existing technologies, providing a more flexible technical path for coal-fired units to participate in grid peak shaving.

[0018] This invention forms a parallel pipeline structure on the main feedwater pipeline and the reheat cold section pipeline by using a molten salt-feedwater heat exchanger and a molten salt-steam heat exchanger, thereby realizing the dynamic bidirectional transfer of heat energy between the power generation unit and the heat storage unit, and improving the peak-shaving capacity and operational flexibility of the coal-fired unit.

[0019] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0021] Figure 1 This is a schematic diagram of a power generation system structure according to one embodiment. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0023] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0024] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0025] Where there is no conflict, the embodiments and features described in this application may be combined with each other.

[0026] like Figure 1 As shown in the figure, an embodiment of the present invention proposes a power generation system coupled with molten salt thermal storage and a coal-fired unit, comprising: A coal-fired power generation unit includes a boiler, a high-pressure cylinder of a steam turbine, a reheater, a medium- and low-pressure cylinder of a steam turbine, a condenser, and a feedwater pump connected in sequence. Molten salt thermal storage unit, which includes a cold salt tank, a hot salt tank, a molten salt-feedwater heat exchanger and a molten salt-steam heat exchanger; Among them, the inlet and outlet of the molten salt-feedwater heat exchanger are connected in parallel on the main feedwater pipeline between the feedwater pump and the boiler, forming the first parallel pipeline; The steam side inlet and outlet of the molten salt-steam heat exchanger are connected to the reheat cold section pipeline between the exhaust port of the high-pressure cylinder of the steam turbine and the reheater through pipes and valves, forming a second parallel pipeline; The system is configured to enable bidirectional transfer of thermal energy between the coal-fired power generation unit and the molten salt thermal storage unit via molten salt-feedwater heat exchangers and molten salt-steam heat exchangers.

[0027] Among them, the coal-fired power generation unit can be understood as a traditional thermal power generation system based on the Rankine cycle, whose core function is to convert the chemical energy of fuel into electrical energy.

[0028] Furthermore, the boiler in this unit is used to generate high-temperature, high-pressure steam. The high-pressure cylinder, reheater, and intermediate- and low-pressure cylinders of the turbine sequentially complete the steam expansion and work process, while the condenser is used to condense the exhaust steam. The feedwater pump is responsible for returning the condensate to the boiler to maintain circulation. In practical applications, the boiler can be a pulverized coal boiler or a circulating fluidized bed boiler, and the turbine can be selected according to different power levels based on specific requirements.

[0029] The molten salt thermal energy storage unit is designed to achieve the storage and release of thermal energy. The cold salt tank and the hot salt tank are used to store low-temperature molten salt and high-temperature molten salt, respectively, while the molten salt-feed water heat exchanger and the molten salt-steam heat exchanger serve as the core components for heat energy exchange.

[0030] Specifically, the feedwater inlet and outlet of the molten salt-feedwater heat exchanger are connected to the main feedwater pipeline via a first parallel pipeline, allowing the main feedwater to be diverted to the heat exchanger for preheating in exothermic mode. In this embodiment, the first parallel pipeline can achieve precise flow control through a regulating valve, thereby optimizing heat exchange efficiency. The steam-side inlet and outlet of the molten salt-steam heat exchanger are connected to the reheat cold section pipeline via a second parallel pipeline, allowing the heat energy in the exhaust steam from the high-pressure cylinder of the steam turbine to be transferred to the molten salt in thermal storage mode. For example, the second parallel pipeline can achieve flexible adjustment of steam flow through a combination of multiple valves.

[0031] The innovation of this invention lies in the deep coupling design of the molten salt thermal storage unit and the coal-fired power generation unit, which enables efficient bidirectional transfer of heat energy between the two units. Specifically, the parallel piping design of the molten salt-feedwater heat exchanger and the molten salt-steam heat exchanger works in tandem to recover excess heat energy during low-load operation in thermal storage mode, avoiding the heat energy waste caused by low-load operation of traditional coal-fired units; in heat release mode, the stored heat energy is released to enhance power generation capacity during peak hours, thereby optimizing the overall operating efficiency of the unit. This bidirectional transfer mechanism solves the problem of unidirectional heat energy flow or low utilization efficiency in existing technologies, providing a more flexible technical path for coal-fired units to participate in grid peak shaving.

[0032] The working principle of this invention is as follows: Through the coordinated design of a coal-fired power generation unit and a molten salt thermal energy storage unit, the system achieves efficient bidirectional transfer of thermal energy between power generation and thermal energy storage. The coal-fired power generation unit includes a boiler, a high-pressure turbine cylinder, a reheater, a medium- and low-pressure turbine cylinder, a condenser, and a feedwater pump. These devices are sequentially connected to form a complete steam circulation loop, providing the system with basic power generation capacity. The molten salt thermal energy storage unit consists of a cold salt tank, a hot salt tank, a molten salt-feedwater heat exchanger, and a molten salt-steam heat exchanger, used for storing and releasing thermal energy.

[0033] Furthermore, the inlet and outlet of the molten salt-feedwater heat exchanger are connected in parallel to the main feedwater pipeline between the feedwater pump and the boiler, forming the first parallel pipeline. In exothermic mode, the main feedwater is diverted into the molten salt-feedwater heat exchanger to exchange heat with the high-temperature molten salt from the hot brine tank, thereby increasing the feedwater temperature. As a result, the feedwater temperature entering the boiler increases, reducing the amount of fuel required for boiler heating. With the same amount of coal, this increases the unit's power generation capacity, meeting peak-hour electricity demand.

[0034] Meanwhile, the steam-side inlet and outlet of the molten salt-steam heat exchanger are connected via pipes and valves to the reheat cold section pipe between the turbine's high-pressure cylinder exhaust port and the reheater, forming a second parallel pipeline. In thermal storage mode, a portion of the medium-pressure steam is drawn from the turbine's high-pressure cylinder exhaust port and transported to the molten salt-steam heat exchanger. During this process, low-temperature molten salt is pumped from the cold salt tank into the heat exchanger to exchange heat with the medium-pressure steam, transferring the heat energy from the steam to the molten salt. The steam is cooled into condensate and returned to the reheat cold section pipe, while the low-temperature molten salt is heated to high-temperature molten salt and stored in the hot salt tank. This design effectively recovers heat energy that might be wasted during low-load operation, avoiding energy loss.

[0035] Specifically, the system achieves bidirectional heat transfer through the design of the two parallel pipelines mentioned above. In heat storage mode, the second parallel pipeline transfers excess heat from the coal-fired power generation unit to the molten salt heat storage unit; in heat release mode, the first parallel pipeline releases the stored heat to the coal-fired power generation unit for preheating feedwater to improve power generation efficiency. Thus, the system can store heat when grid load is low or electricity prices are low, and release heat when grid load is high or electricity prices are high, thereby optimizing the unit's overall operating efficiency and solving the problem of decreased efficiency and increased coal consumption in coal-fired units due to low-load operation. Simultaneously, it achieves flexible and efficient heat transfer between the power generation and heat storage units.

[0036] In this embodiment, the steam side inlet and outlet of the molten salt-steam heat exchanger are also connected to the main steam pipeline between the superheated steam outlet of the boiler and the main steam inlet of the high-pressure cylinder of the steam turbine through pipes and valves, forming a third parallel pipeline.

[0037] Specifically, the third parallel pipeline refers to an independent steam flow channel added to the existing system. It can be implemented using pipes of appropriate diameter and pressure rating, coupled with electric or pneumatic valves. The molten salt-steam heat exchanger is the core equipment enabling efficient heat exchange between steam and molten salt; its efficiency can be improved by optimizing the heat exchange area and flow channel design. In practical applications, valves are key components used to control the steam flow direction; precise control can be achieved using shut-off valves or regulating valves with rapid opening and closing functions.

[0038] In detail, in thermal storage mode, when rapid, high-power thermal storage is required, the system controller issues a command to open two valves on the third parallel pipeline, introducing high-pressure main steam generated by the boiler into the molten salt-steam heat exchanger. Since the temperature and pressure of the main steam are much higher than those of the reheat cold-section steam, this design allows the system to directly utilize the high-grade thermal energy generated by the boiler. During the heat exchange process, low-temperature molten salt from the cold salt tank is pumped to the molten salt-steam heat exchanger, where it exchanges heat with the high-pressure main steam and is heated to the target temperature before being stored in the hot salt tank. This design retains the original thermal storage function of the reheat cold-section steam while adding a main steam thermal storage path. Valve control allows for flexible switching or simultaneous operation of the two steam sources, ensuring dynamic matching between the thermal storage process and the unit's operating status. Based on this, the system not only solves the problem of limited thermal storage efficiency in the basic scheme but also significantly improves peak-shaving flexibility and thermal storage capacity, providing more reliable technical support for coal-fired units to participate in deep peak shaving.

[0039] In this embodiment, the molten salt thermal storage unit also includes an electric heater, which is installed on the molten salt pipeline between the cold salt tank and the molten salt-steam heat exchanger.

[0040] An electric heater is a device that converts electrical energy into heat energy, which can be achieved through resistance heating, electromagnetic induction heating, or electric arc heating. In practical applications, the introduction of electric heaters aims to solve the problem of ineffective use of external electrical energy for molten salt heating in coal-fired power units during low-load operation or shutdown, thereby improving the system's flexibility and economy. The molten salt pipeline between the cold salt tank and the molten salt-steam heat exchanger refers to the piping system connecting the cold salt tank and the molten salt-steam heat exchanger, and its function is to transport low-temperature molten salt to the heat exchanger for heat exchange. The purpose of installing an electric heater at this location is to ensure that the low-temperature molten salt is preheated before entering the molten salt-steam heat exchanger, thereby optimizing heat transfer efficiency and ensuring stable system operation under various operating conditions.

[0041] Specifically, this scheme integrates an electric heater into the molten salt pipeline between the cold salt tank and the molten salt-steam heat exchanger, enabling the system to directly heat the molten salt using external electrical energy when the coal-fired unit is under low load or shut down. When the grid load is low or the electricity price is low, the electric heater can start and convert electrical energy into heat energy stored in the molten salt, avoiding the shortcomings of traditional schemes where insufficient steam extraction prevents sufficient heat storage. Furthermore, since the initial temperature of the molten salt in the cold salt tank is low, direct flow into the molten salt-steam heat exchanger would reduce heat exchange efficiency or increase steam demand. Therefore, installing an electric heater here can pre-raise the molten salt temperature, making it easier to achieve efficient heat exchange with subsequent steam, or independently complete the molten salt heating process when the steam supply is interrupted. This design not only optimizes the continuity and stability of heat transfer but also significantly enhances the system's adaptability under unsteady conditions, thus ensuring that the system maintains reliable heat storage capacity under various operating conditions.

[0042] Through the above technical solution, the system achieves an independent conversion path from electrical energy to thermal energy, and can fully utilize external energy sources during peak demand periods or low-price electricity periods, significantly improving overall flexibility and economy. Simultaneously, this solution forms an organic whole with the coal-fired power generation unit and molten salt thermal storage unit, solving the problem of limited thermal storage capacity under low-load conditions and providing the system with additional energy input options, further enhancing its adaptability and competitiveness in complex power grid environments.

[0043] In this embodiment, both the molten salt-feedwater heat exchanger and the molten salt-steam heat exchanger are indirect heat exchangers, with the molten salt side completely isolated from the steam side or the feedwater side.

[0044] Specifically, a shell-and-tube heat exchanger is a device that enables heat transfer between two fluids through a solid wall. In practical applications, this type of heat exchanger can be implemented using shell-and-tube, plate, or spiral plate structures. The purpose is to ensure that the molten salt and feedwater or steam remain physically isolated during the heat exchange process, avoiding direct contact between the two.

[0045] In detail, the core design of molten salt-feedwater heat exchangers and molten salt-steam heat exchangers lies in using solid walls as a separating medium, ensuring that the molten salt side and the feedwater or steam side remain completely separate during heat exchange. This design not only inherits the original system's bidirectional heat transfer function but also fundamentally avoids equipment corrosion and system failures caused by molten salt leakage. For example, when heating the main feedwater, the molten salt-feedwater heat exchanger relies on wall conduction rather than fluid mixing, ensuring that the low-temperature feedwater remains separated from the molten salt throughout the heating process, maintaining both feedwater purity and boiler feedwater quality. Similarly, when using medium- or high-pressure steam to heat the molten salt, the isolation design between the steam and molten salt sides of the molten salt-steam heat exchanger prevents molten salt intrusion during steam condensation, eliminating the risk of impurities carried by condensate returning to the pipeline. Based on these technical solutions, the water-steam circulation system of a coal-fired power generation unit can maintain high reliability and safety during long-term operation, providing a crucial guarantee for the deep integration of molten salt thermal energy storage technology with coal-fired units.

[0046] Furthermore, this solution, working in conjunction with other components in the aforementioned system, significantly enhances the overall system's stability and economy. For example, when the system is in heat storage or heat release mode, the isolation characteristics of the indirect heat exchanger ensure that bidirectional heat transfer can proceed efficiently and safely under both low and high load conditions, thereby enhancing the unit's operational flexibility and life-cycle economics.

[0047] Example 2 An operating method based on the system provided in Embodiment 1 includes: a heat storage mode and a heat release mode; In thermal storage mode, perform the following steps: A portion of medium-pressure steam is drawn from the exhaust port of the high-pressure cylinder of the steam turbine and transported to the molten salt-steam heat exchanger. The low-temperature molten salt from the cold salt tank exchanges heat with the medium-pressure steam in the molten salt-steam heat exchanger. The medium-pressure steam is cooled into condensate and returned to the reheat cold section pipeline, while the low-temperature molten salt is heated into high-temperature molten salt and stored in the hot salt tank. In heat release mode, perform the following steps: The high-temperature molten salt from the hot salt tank flows through the molten salt-feedwater heat exchanger; a portion of the main feedwater from the feedwater pump is diverted into the molten salt-feedwater heat exchanger to exchange heat with the high-temperature molten salt, and after being heated, it returns to the main feedwater pipeline and then enters the boiler.

[0048] The core innovation of this embodiment lies in combining the molten salt-feedwater heat exchanger and the molten salt-steam heat exchanger through a first parallel pipeline and a second parallel pipeline, thereby achieving efficient bidirectional transfer of heat energy between the coal-fired power generation unit and the molten salt thermal storage unit. This design not only solves the problems of decreased efficiency and increased coal consumption of coal-fired units during low-load operation, but also significantly improves the unit's peak-shaving flexibility and overall operating economy. Specifically, in thermal storage mode, the system can recover low-grade heat energy and avoid energy waste; in heat release mode, the stored heat energy is used to preheat feedwater, reducing boiler fuel consumption and thus increasing power generation capacity during peak hours.

[0049] Through the above technical solutions, the system can store thermal energy when the grid load is low or the electricity price is low, and release thermal energy when the grid load is high or the electricity price is high, thereby optimizing the unit's overall operating efficiency. This flexible energy time-shifting mechanism provides a more efficient technical path for coal-fired units to participate in grid peak shaving, while enhancing the overall operating economy and environmental friendliness of the unit.

[0050] In an optional embodiment, under the heat storage mode, the method further includes: drawing a portion of high-pressure main steam from the superheated steam outlet of the boiler and conveying it to a molten salt-steam heat exchanger; allowing the low-temperature molten salt from the cold salt tank to exchange heat with the high-pressure main steam in the molten salt-steam heat exchanger, wherein the high-pressure main steam is cooled into condensate and returned to the main steam pipeline, while the low-temperature molten salt is heated into high-temperature molten salt and stored in a hot salt tank.

[0051] Specifically, high-pressure main steam refers to steam with high temperature and high pressure characteristics drawn from the superheated steam outlet of the boiler. In practical applications, the introduction of high-pressure main steam aims to provide higher-grade thermal energy to compensate for the insufficient thermal storage efficiency of medium-pressure steam, thereby significantly improving the system's thermal storage capacity and response speed.

[0052] The molten salt-steam heat exchanger can be understood as a device that enables efficient heat exchange between high-pressure main steam and low-temperature molten salt. Specifically, it can be implemented through a partitioned heat exchange structure, ensuring complete isolation between the two working fluids while simultaneously transferring heat. The purpose of this design is to fully utilize the high enthalpy of the high-pressure main steam to rapidly heat the low-temperature molten salt to the target temperature, meeting the system's demand for high-power thermal energy storage.

[0053] In detail, by drawing high-pressure main steam from the boiler's superheated steam outlet and delivering it to the molten salt-steam heat exchanger, seamless integration with existing heat exchange equipment is achieved. During this process, the large temperature difference between the high-pressure main steam and the low-temperature molten salt accelerates the heat transfer rate, enabling the low-temperature molten salt to quickly absorb sufficient energy to heat up. Simultaneously, the high-pressure main steam is cooled into condensate and returned to the main steam pipeline, maintaining the integrity of the boiler's steam-water circulation, avoiding working fluid loss, and ensuring the system's economic efficiency and safety. Finally, the low-temperature molten salt is heated to high-temperature molten salt and stored in a hot salt tank, providing a high-quality heat source reserve for subsequent exothermic processes.

[0054] Furthermore, the aforementioned solution effectively addresses the bottleneck issue of insufficient medium-pressure steam thermal energy storage capacity by introducing a high-pressure main steam thermal energy storage path. Based on the high enthalpy characteristics of the high-pressure main steam, the system can complete large-scale thermal energy storage in a short time, thereby significantly enhancing the thermal energy recovery efficiency and overall operational flexibility of coal-fired units during low-load periods. This improvement not only enhances thermal energy storage efficiency but also provides more flexible and reliable technical support for coal-fired units to participate in deep peak shaving.

[0055] In an alternative implementation, in the heat storage mode, an electric heater is also activated to use external electrical energy to assist or directly heat the molten salt flowing through the molten salt-steam heat exchanger.

[0056] Specifically, an electric heater is a device that converts electrical energy into heat energy, which can be achieved using technologies such as resistance heating and electromagnetic induction heating. In practical applications, the purpose of introducing an electric heater is to provide additional heat source support to ensure that molten salt can be fully heated to the target temperature under various operating conditions.

[0057] In detail, the electric heater is activated in thermal storage mode. This feature ensures that when the steam extracted from the turbine is insufficient, the system can promptly activate an additional heat source, thus maintaining the continuity of the thermal storage process. The design of using external electrical energy to heat the molten salt allows the system to respond to low-cost electricity signals from the grid, converting inexpensive electricity into thermal energy for storage. Especially during periods of wind or solar power curtailment, using external electrical energy as a supplementary heat source not only makes up for the steam extraction heat gap but also achieves efficient conversion of electrical energy into thermal energy. For the molten salt flowing through the molten salt-steam heat exchanger, auxiliary heating or direct heating is performed. In auxiliary heating mode, the electric heater provides precise supplementary heating when the steam extraction heat is insufficient, ensuring that the molten salt temperature rises steadily to the design value. In direct heating mode, the electric heater operates independently, allowing the system to continue thermal storage operations even when the coal-fired unit is shut down, expanding the system's application capabilities during off-peak hours. Simultaneously, the path design of the molten salt flowing through the heat exchanger ensures isolation from the main system's steam-water circulation, maintaining system safety and reliability.

[0058] Through the above technical solutions, the system significantly improves the thermal storage capacity under low-load operation or coal-fired unit shutdown conditions, enhances peak-shaving flexibility and economy, especially when the grid provides cheap electricity, it can make full use of external electricity for thermal storage, thereby achieving more efficient energy management.

[0059] The operating method in this embodiment selects the mode based on the real-time load command and / or electricity price signal from the power grid: When the grid load demand is low or the electricity price is below the first threshold, the thermal storage mode is activated. The heat release mode is activated when the grid load demand is high or the electricity price is higher than the second threshold.

[0060] Specifically, the real-time load command of the power grid refers to a dynamic data signal generated by monitoring the actual current electricity demand of the power grid. This can be achieved using load forecasting algorithms combined with real-time collected power grid data. The purpose of introducing this feature is to ensure that the system can flexibly adjust its operating mode according to the actual demand of the power grid, thereby improving the overall peak-shaving capacity. The electricity price signal can be understood as real-time electricity price information provided by the power grid operator, which can be obtained through smart meters or dedicated communication interfaces. It aims to optimize the system's revenue performance by using economic incentives to drive mode switching. The design of the first and second thresholds is to clarify the boundary conditions for mode switching. These can be set based on historical operating data, economic analysis, and power grid characteristics to ensure the stability and efficiency of the system under different operating conditions.

[0061] In detail, the above-mentioned technical solution replaces traditional manual judgment or fixed schedule methods by using real-time grid signals as the core decision-making basis for mode switching. Specifically, when grid load demand is low or electricity prices are below a first threshold, the system automatically enters thermal storage mode, using excess heat energy generated by coal-fired power generation units or low-priced electricity to heat molten salt and store it in a hot salt tank. This process not only avoids the waste of heat energy during low-load periods but also lays the foundation for energy release during subsequent peak periods. When grid load demand is high or electricity prices are above a second threshold, the system switches to heat release mode, transferring the stored heat energy to the main feedwater through a molten salt-feedwater heat exchanger, increasing the temperature of the boiler inlet feedwater, thereby reducing coal consumption and increasing power generation output. This dynamic response mechanism based on real-time signals effectively solves the problems of missed energy storage opportunities or untimely heat release caused by response lag in traditional methods.

[0062] Furthermore, the aforementioned technical solution forms a close functional relationship with the key components of the system. For example, the molten salt-steam heat exchanger and the molten salt-feedwater heat exchanger undertake the core heat exchange tasks in heat storage and heat release modes, respectively, and their efficient heat transfer performance directly determines the effectiveness of mode switching. Meanwhile, the cold salt tank and the hot salt tank, as important nodes in the molten salt circulation, ensure the smooth flow of molten salt and heat storage in different modes. Through this design, the system can not only accurately match the dynamic demands of the power grid but also achieve a balance between economy and peak-shaving flexibility, thereby significantly improving overall operating efficiency and profitability.

[0063] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art without creative effort within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A power generation system coupled with molten salt thermal storage and a coal-fired unit, characterized in that, include: A coal-fired power generation unit includes a boiler, a high-pressure cylinder of a steam turbine, a reheater, a medium- and low-pressure cylinder of a steam turbine, a condenser, and a feedwater pump connected in sequence. Molten salt thermal storage unit, which includes a cold salt tank, a hot salt tank, a molten salt-feedwater heat exchanger and a molten salt-steam heat exchanger; The inlet and outlet of the molten salt-feedwater heat exchanger are connected in parallel to the main feedwater pipeline between the feedwater pump and the boiler, forming a first parallel pipeline. The steam side inlet and outlet of the molten salt-steam heat exchanger are connected to the reheat cold section pipeline between the exhaust port of the high-pressure cylinder of the steam turbine and the reheater through pipes and valves, forming a second parallel pipeline; The bidirectional transfer of thermal energy between the coal-fired power generation unit and the molten salt thermal storage unit is achieved through the first parallel pipeline, the second parallel pipeline, the molten salt-feedwater heat exchanger, and the molten salt-steam heat exchanger.

2. The power generation system coupled with molten salt thermal storage and a coal-fired unit as described in claim 1, characterized in that, The steam-side inlet and outlet of the molten salt-steam heat exchanger are also connected to the main steam pipeline between the superheated steam outlet of the boiler and the main steam inlet of the high-pressure cylinder of the steam turbine via pipes and valves, forming a third parallel pipeline.

3. The power generation system coupled with molten salt thermal storage and a coal-fired unit as described in claim 1, characterized in that, The molten salt thermal storage unit also includes an electric heater, which is installed on the molten salt pipeline between the cold salt tank and the molten salt-steam heat exchanger.

4. A power generation system coupled with molten salt thermal storage and a coal-fired unit as described in claim 1, characterized in that, The molten salt outlet of the molten salt-feed water heat exchanger is connected to the cold salt tank, and the molten salt inlet is connected to the hot salt tank.

5. A power generation system coupled with molten salt thermal storage and a coal-fired unit as described in claim 1, characterized in that, The molten salt inlet of the hot salt tank is connected to the molten salt outlet of the molten salt-steam heat exchanger, and the molten salt inlet of the molten salt-steam heat exchanger is connected to the electric heater.

6. A power generation system coupled with molten salt thermal storage and a coal-fired unit as described in claim 1, characterized in that, Both the molten salt-feedwater heat exchanger and the molten salt-steam heat exchanger are indirect heat exchangers, with their molten salt side completely isolated from the steam side or feedwater side.

7. A method for operating a power generation system as described in any one of claims 1-6, characterized in that, include: Heat storage mode and heat release mode; In thermal storage mode, perform the following steps: A portion of medium-pressure steam is drawn from the exhaust port of the high-pressure cylinder of the steam turbine and transported to the molten salt-steam heat exchanger; Low-temperature molten salt from the cold salt tank exchanges heat with medium-pressure steam in the molten salt-steam heat exchanger. The medium-pressure steam is cooled into condensate and returned to the reheat cold section pipeline, while the low-temperature molten salt is heated into high-temperature molten salt and stored in the hot salt tank. In heat release mode, perform the following steps: The high-temperature molten salt from the hot salt tank flows through the molten salt-feed water heat exchanger; A portion of the main feedwater from the feedwater pump is diverted into the molten salt-feedwater heat exchanger, where it exchanges heat with the high-temperature molten salt. After being heated, it returns to the main feedwater pipeline and then enters the boiler.

8. The operating method as described in claim 7, characterized in that, in The heat storage mode also includes: A portion of the high-pressure main steam is drawn from the superheated steam outlet of the boiler and transported to the molten salt-steam heat exchanger; The low-temperature molten salt from the cold salt tank exchanges heat with the high-pressure main steam in the molten salt-steam heat exchanger. The high-pressure main steam is cooled into condensate and returned to the main steam pipeline, while the low-temperature molten salt is heated into high-temperature molten salt and stored in the hot salt tank.

9. The operating method as described in claim 7, characterized in that, in In the heat storage mode, an electric heater is also activated to use external electrical energy to assist or directly heat the molten salt flowing through the molten salt-steam heat exchanger.

10. The operating method as described in claim 7, characterized in that, Mode selection is performed based on real-time load instructions and / or electricity price signals from the power grid: The thermal storage mode is activated when the grid load demand is low or the electricity price is lower than the first threshold. The heat release mode is activated when the grid load demand is high or the electricity price is higher than the second threshold.

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