Coal-fired unit peak shaving system and operation method

Abstract

The present application provides a coal-fired unit peak shaving system and operation method, the system comprises a coal-fired power generation system, a thermo-chemical heat storage subsystem and a supercritical carbon dioxide Brayton subsystem. A fixed bed reactor is internally provided with a heat exchange pipeline and a reaction chamber. A heat reheat steam outlet is connected to a heat exchange pipeline inlet of the fixed bed reactor, a heat exchange pipeline outlet of the fixed bed reactor is connected to the high-pressure heater; a gas discharge outlet of the fixed bed reactor is connected to the deaerator; a steam extraction pipeline of a low-pressure cylinder of a steam turbine is connected to a reaction chamber inlet of the fixed bed reactor. A cold side of a regenerator is connected between a compressor outlet and a heat exchange pipeline inlet of the fixed bed reactor, and a hot side of the regenerator is connected between an expander outlet and a cooler inlet. One technical effect of the present application is that the water vapor cycle with slow response is decoupled from the supercritical carbon dioxide cycle with rapid response, and the peak shaving depth and variable load power response rate of the coal-fired power generation unit are improved.

Description

Technical Field

[0001] This invention belongs to the field of thermal power generation and advanced energy storage technology, specifically relating to a peak-shaving system and operation method for coal-fired power units that couples thermochemical thermal storage with supercritical carbon dioxide cycle. Background Technology

[0002] As the penetration rate of renewable energy in the power grid continues to increase, coal-fired power generating units need to frequently participate in deep peak shaving to smooth power fluctuations in the grid. However, traditional coal-fired steam Rankine cycle systems are limited by the boiler's enormous thermal inertia and the temperature alternating stress of thick-walled metal components, and their load increase / decrease rate is typically only one to two percent of the rated load per minute. This slow power response capability is insufficient to meet the grid's demand for rapid frequency regulation and peak shaving on a minute or even second basis.

[0003] To improve the flexibility of generating units, thermal energy storage technology has been widely researched and applied. Calcium-based thermochemical thermal energy storage systems can store energy losslessly over long periods at room temperature, with high thermal density. However, existing thermochemical thermal energy storage systems typically return heat directly to the main steam or feedwater system of coal-fired units during heat release. Because the heat still needs to be converted through a coal-fired boiler and a large turbine unit, the problem of slow overall system response speed has not been substantially solved.

[0004] Therefore, there is an urgent need for a peak-shaving system and operation method for coal-fired power units that couples thermochemical thermal storage with supercritical carbon dioxide cycle to solve the aforementioned technical problems. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art, and to provide a new technical solution for a peak-shaving system and operation method for coal-fired power units.

[0006] According to a first aspect of the present invention, a peak-shaving system for a coal-fired power unit is provided, comprising a coal-fired power generation system, a thermochemical thermal storage subsystem, and a supercritical carbon dioxide Brayton subsystem. The coal-fired power generation system includes a reheat steam outlet, a high-pressure heater, a deaerator, and a low-pressure turbine cylinder.

[0007] The thermochemical thermal storage subsystem includes a fixed-bed reactor, which is equipped with heat exchange pipelines and a reaction chamber.

[0008] The hot reheat steam outlet is connected to the inlet of the heat exchange pipeline of the fixed bed reactor, and the outlet of the heat exchange pipeline of the fixed bed reactor is connected to the high-pressure heater; the gas outlet of the fixed bed reactor is connected to the deaerator; and the extraction steam pipeline of the low-pressure cylinder of the steam turbine is connected to the inlet of the reaction chamber of the fixed bed reactor.

[0009] The supercritical carbon dioxide Brayton subsystem includes a cooler, a compressor, a regenerator, and an expander. The cold side of the regenerator is connected between the compressor outlet and the heat exchange pipeline inlet of the fixed-bed reactor, and the hot side of the regenerator is connected between the expander outlet and the cooler inlet, forming a closed-loop circuit.

[0010] In the above embodiments, the thermochemical thermal storage reactor is used as an energy hub. The heat exchange pipeline of the fixed bed reactor receives high-temperature steam from the coal-fired power generation system to achieve heat charging during the heat storage stage, and releases heat to the supercritical carbon dioxide working medium to drive power generation during the heat release stage. This decouples the slow-responding steam cycle from the fast-responding supercritical carbon dioxide cycle, and realizes the stratified configuration of base load and rapid peak load.

[0011] Preferably, the reaction chamber is filled with a calcium-based thermochemical heat storage material, which is a calcium hydroxide / calcium oxide reversible reaction system; during the heat storage stage, the calcium hydroxide dehydrates to generate calcium oxide and water vapor, and during the heat release stage, the calcium oxide and water vapor undergo a hydration reaction to generate calcium hydroxide and release heat.

[0012] In the above embodiments, the calcium hydroxide / calcium oxide system has the advantages of high heat storage density, good reaction reversibility and low material cost. It can also store thermal energy in the form of chemical bond energy for a long period of time at room temperature without loss, avoiding the defects of sensible heat storage and latent heat storage that spontaneously dissipate heat over time.

[0013] Preferably, the outlet point of the hot reheat steam outlet branch pipeline is located on the main steam pipeline between the boiler reheater outlet and the turbine intermediate pressure cylinder inlet, and the branch pipeline is equipped with a heat storage control valve.

[0014] In the above embodiments, the hot reheat steam has a high temperature (usually 540~570℃), which can provide sufficient heat to drive the calcium hydroxide dehydration reaction; the outlet point is set between the reheater outlet and the intermediate pressure cylinder inlet, which can flexibly divert steam without affecting the boiler operation; the heat storage control valve can accurately control the steam flow into the reactor to match the energy storage power requirements.

[0015] Preferably, the extraction branch pipe from the low-pressure cylinder of the steam turbine to the low-pressure heater is connected to the inlet of the reaction chamber of the fixed-bed reactor via a throttling valve.

[0016] In the above embodiments, steam extracted from the low-pressure cylinder of the steam turbine is used as the steam source for the hydration reaction, avoiding the need to configure a separate steam generating device for the reactor; the throttle valve adjusts the low-pressure steam extraction to the pressure required for the reaction, ensuring that the hydration reaction is carried out under suitable operating conditions, while reducing the impact of the extraction steam volume on the normal operation of the steam turbine unit.

[0017] Preferably, the power output terminal of the expander is connected to an independent generator, or the expander is coaxially connected to the generator of the coal-fired power generation system.

[0018] In the above embodiments, the independent generator scheme allows the supercritical carbon dioxide Brayton subsystem to be started and stopped completely independently without affecting the operating logic of the coal-fired power generation system, making it suitable for rapid peak shaving scenarios; the coaxial scheme reduces equipment investment and is suitable for site-constrained renovation projects. Both schemes can be flexibly selected according to engineering conditions.

[0019] Preferably, the working fluid of the supercritical carbon dioxide Brayton subsystem is supercritical carbon dioxide, the operating pressure of the supercritical carbon dioxide Brayton subsystem is 20~30MPa, and the inlet temperature of the expander is 500~650℃.

[0020] In the above embodiments, supercritical carbon dioxide has a high density at an operating pressure of 20~30MPa, which makes the volume of the compressor and expander significantly smaller than that of a steam turbine of the same power class, facilitating compact arrangement in existing coal-fired power plants; the expander inlet temperature of 500~650℃ matches the heat release temperature of the hydration exothermic reaction, ensuring that the supercritical carbon dioxide working medium can fully absorb the heat of reaction and achieve efficient Brayton cycle work.

[0021] Preferably, in the fixed-bed reactor, the heat exchange pipeline passes through the interior of the reaction chamber, and the pipe wall of the heat exchange pipeline physically isolates the space inside the pipe from the reaction chamber, forming an indirect heat exchange interface between the fluid inside the pipe and the heat storage material inside the reaction chamber.

[0022] In the above embodiments, optimizing the structure of the fixed-bed reactor helps to improve the heat storage and heat release efficiency of the fixed-bed reactor.

[0023] According to a second aspect of the present invention, a method for operating a peak-shaving system for a coal-fired power unit is provided, wherein the system switches between a thermal storage peak-shaving mode and a heat release peak-shaving mode according to a power grid dispatching instruction.

[0024] The heat storage and peak shaving mode is as follows: a portion of the hot reheat steam is drawn from the hot reheat steam outlet and introduced into the heat exchange pipeline of the fixed bed reactor to drive the heat storage material in the reaction chamber to undergo a dehydration and endothermic reaction for energy storage. The released steam is fed into the high-pressure heater, and the water vapor generated by the dehydration reaction is fed into the deaerator for recovery. In the heat storage and peak shaving mode, the supercritical carbon dioxide Brayton subsystem is shut down and put on standby, and the power generation of the coal-fired power generation system is reduced.

[0025] The heat release peak mode is as follows: the extraction of hot reheat steam is stopped, and low-pressure steam is drawn from the extraction steam pipeline of the low-pressure cylinder of the steam turbine and introduced into the reaction chamber of the fixed bed reactor. This drives the reaction products generated in the heat storage stage to undergo a hydration exothermic reaction, and the supercritical carbon dioxide Brayton subsystem is started simultaneously. The supercritical carbon dioxide working fluid absorbs the heat of the hydration reaction in the heat exchange pipeline of the fixed bed reactor and then enters the expander to expand and generate electricity.

[0026] Through the above operating method, the system can flexibly switch between two modes according to the grid dispatch instructions. The thermal storage peak shaving mode actively reduces the output of coal-fired power by diverting steam to cooperate with the grid during off-peak hours, while the heat release peak mode generates electricity quickly through the supercritical carbon dioxide Brayton subsystem to fill the power gap. The two modes work together to achieve deep and rapid peak shaving of coal-fired units.

[0027] Preferably, in the heat storage and peak shaving mode, the hot reheat steam releases heat to the calcium hydroxide particles in the reaction chamber through the heat exchange pipeline of the fixed bed reactor, driving the calcium hydroxide to undergo a decomposition and dehydration reaction to generate calcium oxide and water vapor. After the steam is cooled down by the heat release, the grade of the steam decreases and flows into the extraction pipeline of the high-pressure heater to transfer the residual heat to the boiler feedwater. The high-temperature water vapor that escapes from the dehydration reaction is introduced into the deaerator through the exhaust pipeline. The sensible heat and latent heat of vaporization carried by the steam are absorbed by the condensate, and the water vapor is recovered into the water circulation of the coal-fired power generation system after phase change.

[0028] In the above embodiments, the residual heat of the hot reheat steam is recovered to the feedwater heating process through a high-pressure heater, and the water vapor generated by the dehydration reaction is completely recovered by a deaerator, including its sensible heat and latent heat of vaporization, thus achieving zero-loss closed-loop recovery of the working fluid. The entire heat storage process does not discharge any waste heat or wastewater to the outside of the system, which improves the overall thermal energy utilization rate of the system and avoids the need to add independent condensers and water storage devices, simplifying the complexity of engineering implementation.

[0029] Preferably, in the heat release peak mode, the working fluid operation path of the supercritical carbon dioxide Brayton subsystem is as follows: after the carbon dioxide working fluid releases waste heat to the environment in the cooler, it enters the compressor and is pressurized to a supercritical state. The high-pressure working fluid flows through the cold side of the regenerator to absorb the waste heat from the expander exhaust for initial temperature increase. Then, it enters the heat exchange pipeline of the fixed-bed reactor to absorb the high-temperature heat released by the hydration reaction and reach the highest temperature of the cycle. The high-temperature and high-pressure supercritical carbon dioxide enters the expander to expand and do work to drive the generator to output electrical energy. The exhaust gas after doing work enters the hot side of the regenerator to release heat and finally returns to the cooler to complete the closed cycle.

[0030] In the above embodiments, the regenerator allows the waste heat from the expander exhaust to be recovered for the initial heating of the working fluid at the compressor outlet, reducing the heat required by the fixed-bed reactor and lowering the reactor's heat load; at the same time, it lowers the exhaust temperature entering the cooler, reducing the heat dissipation of the cooler, thereby improving the overall cycle thermal efficiency of the supercritical carbon dioxide Brayton subsystem.

[0031] Preferably, the thermal energy storage peak shaving mode corresponds to the off-peak period of the power grid. By diverting some of the hot reheat steam, the steam used for power generation in the coal-fired power generation system is reduced, thereby actively reducing the system's external power generation and completing energy storage and downlink peak shaving. The heat release peak mode corresponds to the peak period of the power grid or a rapid ramp-up command. The start-up response time of the supercritical carbon dioxide Brayton subsystem is shorter than the load increase response time of the coal-fired power generation system boiler. During the process of increasing the production of the coal-fired boiler, the supercritical carbon dioxide Brayton subsystem quickly supplements the power gap, shortening the overall peak shaving response time.

[0032] In the above implementation, the thermal storage peak-shaving mode corresponds to the off-peak period of the power grid, enabling coal-fired units to actively reduce power generation by diverting steam without reducing the boiler combustion load. This avoids problems such as unstable combustion and denitrification temperature window shift caused by low boiler load operation. In the heat release peak mode, the rapid start-up characteristics of the supercritical carbon dioxide Brayton subsystem fill the response lag range of boiler load increase, shortening the overall peak-shaving response time of the system from minutes to seconds in traditional coal-fired power, effectively meeting the grid's mandatory requirements for rapid ramp-up.

[0033] One technical advantage of this invention is that: On the one hand, this application integrates an independent supercritical carbon dioxide Brayton cycle to undertake the heat release and work tasks. Utilizing its engineering characteristics of small turbine size and no need for a lengthy warm-up process, it can achieve rapid power ramp-up after receiving instructions, overcoming the technical defects of conventional coal-fired units that are limited by boiler thermal inertia and have lagging adjustment.

[0034] On the other hand, this application comprehensively considers the material balance in the thermochemical reaction process. The water vapor removed during the heat storage stage is directly introduced into the deaerator, which not only recovers the pure working water but also utilizes its latent heat of vaporization to heat the unit's feedwater, thereby improving the overall thermal energy utilization rate of the system. The system topology avoids the need for additional independent condensers and water storage devices, simplifying the complexity of engineering implementation. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of a coal-fired power unit peak-shaving system according to an embodiment of the present invention.

[0036] In the diagram: 1. Boiler; 2. High-pressure cylinder of steam turbine; 3. Intermediate-pressure cylinder of steam turbine; 4. Low-pressure cylinder of steam turbine; 5. Generator; 6. Condenser; 7. Condensate pump; 8. Low-pressure heater; 9. Deaerator; 10. Feedwater pump; 11. High-pressure heater; 12. Throttling valve; 13. Fixed-bed reactor; 14. Cooler; 15. Compressor; 16. Regenerator; 17. Expander. Detailed Implementation

[0037] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the present application.

[0038] The embodiments of this application will now be described in detail. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0039] The terms "first" and "second" in the specification and claims of this application may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise stated, "multiple" means two or more. Furthermore, "and / or" in the specification and claims indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0040] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0041] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0042] like Figure 1 As shown, the peak-shaving system of this coal-fired unit consists of three main parts: a coal-fired power generation system, a thermochemical thermal energy storage subsystem, and a supercritical carbon dioxide Brayton subsystem. Utilizing the engineering characteristics of supercritical carbon dioxide—low cyclic rotational inertia and rapid start-up and shutdown—combined with thermochemical inter-period energy storage, the peak-shaving depth and variable load power response rate of the coal-fired power generation unit are improved.

[0043] Specifically, the coal-fired power generation system includes a conventional boiler 1, a high-pressure turbine cylinder 2, a medium-pressure turbine cylinder 3, a low-pressure turbine cylinder 4, and a corresponding regenerative heating network. The thermochemical thermal storage subsystem uses a fixed-bed reactor 13 as its core component. The supercritical carbon dioxide Brayton subsystem includes a relatively independent closed-loop circuit, with components including a cooler 14, a compressor 15, a regenerator 16, and an expander 17.

[0044] For example, a branch pipe from the hot reheat steam outlet of boiler 1 in the coal-fired power generation system is connected to the heat exchange pipe inside the fixed-bed reactor 13. The branch pipe's outlet point is located on the main steam pipe between the reheater outlet of boiler 1 and the inlet of the intermediate-pressure cylinder 3 of the turbine. A heat storage control valve is installed on the branch pipe to control the flow rate of hot reheat steam entering the heat exchange pipe of the fixed-bed reactor 13. The outlet of the heat exchange pipe of the fixed-bed reactor 13 is connected to the extraction steam system of the high-pressure heater 11. The gas outlet of the fixed-bed reactor 13 is connected to the deaerator 9 of the coal-fired power generation system.

[0045] For example, the exhaust steam from the low-pressure cylinder 4 of the steam turbine is connected to the deaerator 9 via the condenser 6, condensate pump 7, and low-pressure heater 8 in sequence. The outlet of the deaerator 9 is connected to the boiler 1 via the feed water pump 10 and high-pressure heater 11.

[0046] The extraction steam pipeline from the low-pressure cylinder 4 of the steam turbine to the low-pressure heater 8 is connected to the inlet of the reaction chamber of the fixed-bed reactor 13 via a throttle valve 12.

[0047] In the supercritical carbon dioxide Brayton subsystem, the carbon dioxide working fluid pipeline connects in series with cooler 14, compressor 15, the cold side of regenerator 16, the heat exchange pipeline of fixed-bed reactor 13, and expander 17. The outlet of expander 17 returns to cooler 14 via the hot side of regenerator 16, forming a closed-loop circuit. The cold side of regenerator 16 is connected between the outlet of compressor 15 and the inlet of heat exchange pipeline of fixed-bed reactor 13, and the hot side of regenerator 16 is connected between the outlet of expander 17 and the inlet of cooler 14. The power output terminal of expander 17 can be connected to an independent generator or coaxially connected to generator 5 of a coal-fired power generation system.

[0048] The reaction chamber of the fixed-bed reactor 13 is filled with calcium-based thermochemical heat storage material, specifically a calcium hydroxide / calcium oxide reversible reaction system.

[0049] In this embodiment of the application, when the peak-shaving system of the coal-fired unit implements the thermal storage peak-shaving operation, the fluid operation path follows... Figure 1 The long dashed line in the middle indicates this.

[0050] Upon receiving a deep load reduction command from the power grid, the coal-fired unit's peak-shaving system activates the thermal storage control valve. The exhaust steam from the high-pressure cylinder 2 of the turbine, after being reheated by boiler 1, is partially drawn off before entering the intermediate-pressure cylinder 3 of the turbine. This partially reheated steam is introduced into the heat exchange pipelines inside the fixed-bed reactor 13. The calcium hydroxide material pre-placed inside the fixed-bed reactor 13 absorbs the heat conducted through the pipelines, undergoing a decomposition and dehydration reaction to generate calcium oxide and water vapor, storing the thermal energy in the form of chemical bond energy.

[0051] After the hot reheat steam releases heat in the heat exchanger, its temperature decreases, and it then flows into the extraction steam line of the high-pressure heater 11, transferring residual heat to the boiler feedwater. Simultaneously, a dehydration reaction generates a large amount of water vapor in the reaction chamber. This water vapor is directly introduced into the deaerator 9 through the exhaust pipe. Its sensible and latent heat is absorbed by the condensate in the deaerator, and after a phase change, the water vapor mixes with the feedwater of the coal-fired unit, achieving zero-loss recovery of the working fluid. For example, a large amount of water vapor generated in the reaction chamber enters the deaerator 9 through the auxiliary heating steam inlet.

[0052] Under the thermal storage and peak shaving conditions, due to the diversion of some high-temperature steam used for power generation and the shutdown and standby status of the supercritical carbon dioxide Brayton subsystem, the external power generation of the entire system is significantly reduced, thus achieving the purpose of energy storage and downlink peak shaving.

[0053] When the peak heat release condition is implemented in the peak heat release mode of the coal-fired unit's peak shaving system, the fluid flow path follows Figure 1 The short dashed line in the middle indicates this.

[0054] Upon receiving a rapid load increase command from the power grid, the system closes the thermal storage control valve and stops extracting reheat steam. Throttling valve 12 is opened, allowing a small amount of steam to be drawn from the extraction pipe connecting the turbine's low-pressure cylinder 4 to the low-pressure heater 8. This portion of low-pressure steam is adjusted to the pressure required for the reaction via throttling valve 12 and then introduced into the reaction chamber of the fixed-bed reactor 13. The steam comes into contact with the calcium oxide material generated during the thermal storage stage, undergoing a hydration reaction to produce calcium hydroxide and release a large amount of heat, causing the temperature of the reaction bed in the fixed-bed reactor 13 to rise accordingly.

[0055] The supercritical carbon dioxide Brayton subsystem is started synchronously. After releasing waste heat to the environment in cooler 14, the carbon dioxide working fluid enters compressor 15 and is pressurized to a supercritical state. The high-pressure working fluid flows through the cold side of regenerator 16 to absorb the waste heat from the expander exhaust for initial heating, and then enters the heat exchange pipeline of fixed-bed reactor 13. In the heat exchange pipeline, the carbon dioxide working fluid absorbs the high-temperature heat released by the hydration reaction, reaching the maximum temperature of the cycle. The high-temperature and high-pressure supercritical carbon dioxide then enters expander 17 to expand and do work, driving the connected generator to output electrical energy. The low-pressure, high-temperature exhaust gas after doing work enters the hot side of regenerator 16 to release heat, and finally returns to cooler 14 to complete the closed cycle.

[0056] Because of the rapid cycle response of supercritical carbon dioxide, this peak heat release condition can effectively supplement the power gap during the production increase process of coal-fired boilers and shorten the peak shaving response time. The start-up response time of the supercritical carbon dioxide Brayton subsystem is shorter than the load increase response time of coal-fired power generation system boilers. During the production increase process of coal-fired boilers, the supercritical carbon dioxide Brayton subsystem can quickly supplement the power gap and shorten the overall peak shaving response time.

[0057] This invention breaks through the limitations of the traditional approach of "achieving frequency regulation and peak shaving by changing the steam flow rate into the turbine," and adopts a new model of "thermochemical thermal storage - supercritical carbon dioxide performing work in the expander - rapid peak shaving." Utilizing a fixed-bed reactor as the energy hub, the thermal storage stage absorbs excess heat from the coal-fired power generation system and stores it in the form of chemical energy. In the heat release stage, a separate supercritical carbon dioxide Brayton subsystem rapidly generates electricity, effectively decoupling the slow-responding steam cycle from the fast-responding supercritical carbon dioxide cycle, thus achieving a tiered configuration of base load and rapid peak-shaving load for coal-fired units.

[0058] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A peak-shaving system for a coal-fired power unit, comprising a coal-fired power generation system, said coal-fired power generation system including a reheat steam outlet, a high-pressure heater, a deaerator, and a low-pressure turbine cylinder, characterized in that, It also includes thermochemical thermal storage subsystems and supercritical carbon dioxide Brayton subsystems; The thermochemical thermal storage subsystem includes a fixed-bed reactor, which is equipped with heat exchange pipelines and a reaction chamber. The hot reheat steam outlet is connected to the inlet of the heat exchange pipeline of the fixed bed reactor, and the outlet of the heat exchange pipeline of the fixed bed reactor is connected to the high-pressure heater; the gas outlet of the fixed bed reactor is connected to the deaerator; the extraction steam pipeline of the low-pressure cylinder of the steam turbine is connected to the inlet of the reaction chamber of the fixed bed reactor. The supercritical carbon dioxide Brayton subsystem includes a cooler, a compressor, a regenerator, and an expander. The cold side of the regenerator is connected between the compressor outlet and the heat exchange pipeline inlet of the fixed-bed reactor, and the hot side of the regenerator is connected between the expander outlet and the cooler inlet, forming a closed-loop circuit.

2. The peak-shaving system for coal-fired power units according to claim 1, characterized in that, The reaction chamber is filled with a calcium-based thermochemical heat storage material, which is a reversible reaction system of calcium hydroxide / calcium oxide. During the heat storage stage, the calcium hydroxide dehydrates to generate calcium oxide and water vapor. During the heat release stage, the calcium oxide and water vapor undergo a hydration reaction to generate calcium hydroxide and release heat.

3. The peak-shaving system for coal-fired power units according to claim 1, characterized in that, The outlet point of the hot reheat steam outlet branch pipeline is located on the main steam pipeline between the boiler reheater outlet and the turbine intermediate pressure cylinder inlet, and the branch pipeline is equipped with a heat storage control valve.

4. The peak-shaving system for coal-fired power units according to claim 1, characterized in that, The extraction branch pipe from the low-pressure cylinder of the steam turbine to the low-pressure heater is connected to the inlet of the reaction chamber of the fixed-bed reactor via a throttling valve.

5. The peak-shaving system for coal-fired power units according to claim 1, characterized in that, The power output terminal of the expander is connected to an independent generator, or the expander is coaxially connected to the generator of the coal-fired power generation system.

6. The peak-shaving system for coal-fired power units according to claim 1, characterized in that, In the fixed-bed reactor, the heat exchange pipeline passes through the interior of the reaction chamber. The pipe wall of the heat exchange pipeline physically isolates the space inside the pipe from the reaction chamber, forming an indirect heat exchange interface between the fluid inside the pipe and the heat storage material inside the reaction chamber.

7. An operation method for a peak-shaving system of a coal-fired power unit as described in claim 1, characterized in that, The system switches between thermal storage peak shaving mode and thermal release peak shaving mode according to the power grid dispatch instructions. The thermal storage peak shaving mode is as follows: a portion of the hot reheat steam is drawn from the hot reheat steam outlet and introduced into the heat exchange pipeline of the fixed bed reactor to drive the thermal storage material in the reaction chamber to undergo a dehydration endothermic reaction for energy storage. The released steam is fed into the high-pressure heater, and the water vapor generated by the dehydration reaction is fed into the deaerator for recovery. In the thermal storage peak shaving mode, the supercritical carbon dioxide Brayton subsystem is shut down and put into standby mode, and the power generation of the coal-fired power generation system is reduced. The heat release peak mode is as follows: the extraction of hot reheat steam is stopped, and low-pressure steam is drawn from the extraction steam pipeline of the low-pressure cylinder of the steam turbine and introduced into the reaction chamber of the fixed bed reactor. This drives the reaction products generated in the heat storage stage to undergo a hydration exothermic reaction, and the supercritical carbon dioxide Brayton subsystem is started simultaneously. The supercritical carbon dioxide working fluid absorbs the heat of the hydration reaction in the heat exchange pipeline of the fixed bed reactor and then enters the expander to expand and generate electricity.

8. The operating method according to claim 7, characterized in that, In the heat storage and peak shaving mode, hot reheat steam releases heat to the calcium hydroxide particles in the reaction chamber through the heat exchange pipeline of the fixed bed reactor, driving the calcium hydroxide to undergo a decomposition and dehydration reaction to generate calcium oxide and water vapor. After the steam cools down, the grade of the steam decreases and flows into the extraction pipeline of the high-pressure heater to transfer the residual heat to the boiler feedwater. The high-temperature water vapor that escapes from the dehydration reaction is introduced into the deaerator through the exhaust pipeline. The sensible heat and latent heat of vaporization carried by it are absorbed by the condensate, and the water vapor is recovered into the water circulation of the coal-fired power generation system after phase change.

9. The operating method according to claim 7, characterized in that, In the heat release peak mode, the working fluid operation path of the supercritical carbon dioxide Brayton subsystem is as follows: after the carbon dioxide working fluid releases waste heat to the environment in the cooler, it enters the compressor and is pressurized to a supercritical state. The high-pressure working fluid flows through the cold side of the regenerator to absorb the waste heat from the expander exhaust for initial temperature increase. Then, it enters the heat exchange pipeline of the fixed-bed reactor to absorb the high-temperature heat released by the hydration reaction and reach the highest temperature of the cycle. The high-temperature and high-pressure supercritical carbon dioxide enters the expander to expand and do work to drive the generator to output electrical energy. The exhaust gas after doing work enters the hot side of the regenerator to release heat and finally returns to the cooler to complete the closed cycle.

10. The operating method according to claim 7, characterized in that, The thermal energy storage peak shaving mode corresponds to the off-peak period of the power grid. By diverting some of the reheat steam, the steam used for power generation in the coal-fired power generation system is reduced, thereby actively reducing the system's external power generation and completing energy storage and downlink peak shaving. The heat release peak mode corresponds to the peak period of the power grid or a rapid ramp-up command. The start-up response time of the supercritical carbon dioxide Brayton subsystem is shorter than the load increase response time of the coal-fired power generation system boiler. During the process of increasing the production of the coal-fired boiler, the supercritical carbon dioxide Brayton subsystem quickly fills the power gap, shortening the overall peak shaving response time.

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