Coal-fired unit peak shaving system and operation method

Abstract

The application provides a coal-fired unit peak regulation system and an operation method. The system comprises a coal-fired unit system and a thermochemical heat storage subsystem. The thermochemical heat storage subsystem comprises a fixed bed reactor. The inlet of a heat exchange pipe is connected to a heat reheat steam pipe and a steam turbine high-pressure cylinder exhaust pipe through branch pipes, and the outlet of the heat exchange pipe is connected to the high-pressure heater and the heat reheat steam pipe through branch pipes. In the heat storage peak regulation stage, the steam of the heat exchange pipe is directed to the heat reheat steam pipe and the high-pressure heater. In the heat release peak stage, the steam of the heat exchange pipe is directed to the steam turbine high-pressure cylinder exhaust pipe and the heat reheat steam pipe. The exhaust outlet of the reaction chamber is connected to a deaerator. The exhaust outlet of a small steam turbine is connected to the inlet of the reaction chamber through a branch pipe. The application has the technical effect of not only realizing rapid peak regulation of the unit, but also recycling the waste latent heat of the exhaust steam of the small steam turbine and improving the grade of heat energy.

Description

Technical Field

[0001] This invention belongs to the field of peak shaving technology for coal-fired power generating units, specifically relating to a peak shaving system and operation method for coal-fired power generating units that couples small steam turbine exhaust steam with thermochemical thermal storage. Background Technology

[0002] With the continuous increase in the proportion of renewable energy installed capacity, the power grid has placed higher demands on the peak-shaving capacity of coal-fired power generating units. Coal-fired units not only need to have deep peak-shaving capabilities to cope with off-peak loads on the power grid, but also need to rapidly increase power generation output during peak hours or under rapid ramp-up commands.

[0003] Currently, coal-fired power units participate in grid peak shaving mainly by adjusting the boiler fuel input to change steam production, thereby regulating the turbine's power generation load. However, there is a significant heat transfer inertia between fuel combustion and the metal heating surfaces inside the boiler. It usually takes several minutes or even longer for the steam parameters to change significantly after adjusting the fuel input, resulting in a slow peak shaving response rate that is difficult to meet the grid's demand for rapid ramp-up.

[0004] On the other hand, the feedwater pumps of coal-fired units are usually driven by small steam turbines. The low-pressure exhaust steam discharged from the small steam turbines is generally directly discharged into the condenser and condensed by the circulating cooling water. A large amount of latent heat of vaporization carried in the exhaust steam is carried away by the circulating cooling water and is wasted, resulting in significant heat waste.

[0005] How to organically combine thermochemical thermal storage technology with coal-fired power units to recover and utilize the waste latent heat of small steam turbine exhaust steam while achieving rapid peak shaving of the units is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] 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.

[0007] In a first aspect, the present invention provides a peak-shaving system for a coal-fired power unit, comprising a coal-fired power generation system and a thermochemical thermal storage subsystem; The coal-fired power generation system includes a boiler, a high-pressure cylinder for a steam turbine, a condenser, a deaerator, a high-pressure heater, and a small steam turbine that drives the feedwater pump. The thermochemical thermal storage subsystem includes a fixed-bed reactor, which is equipped with heat exchange tubes and a reaction chamber. The heat exchanger tube inlet is connected to the hot reheat steam pipeline at the boiler outlet and the high-pressure cylinder exhaust steam pipeline of the steam turbine via pipeline branches, and the heat exchanger tube outlet is connected to the high-pressure heater and the hot reheat steam pipeline via pipeline branches; during the heat storage and peak shaving stage, the steam from the heat exchanger tube is directed to the hot reheat steam pipeline and the steam is directed to the high-pressure heater; during the heat release peak stage, the steam from the heat exchanger tube is directed to the high-pressure cylinder exhaust steam pipeline of the steam turbine and the steam is directed to the hot reheat steam pipeline; The exhaust port of the reaction chamber is connected to the deaerator; the conventional exhaust pipe of the small steam turbine is connected to the condenser, and a branch pipe from the exhaust outlet of the small steam turbine is connected to the inlet of the reaction chamber.

[0008] Furthermore, the coal-fired power generation system also includes a steam turbine intermediate-pressure cylinder, a steam turbine low-pressure cylinder, a generator, a condensate pump, a low-pressure heater, and a feedwater pump; the boiler main steam outlet is connected to the inlet of the steam turbine high-pressure cylinder; the exhaust steam from the steam turbine high-pressure cylinder is reheated by the reheater in the boiler and then sent to the steam turbine intermediate-pressure cylinder through the hot reheat steam pipeline; the exhaust steam from the steam turbine low-pressure cylinder is connected to the condenser; the condensate outlet of the condenser is pressurized by the condensate pump and then sent to the boiler feedwater system through the low-pressure heater; the small steam turbine is coaxially connected to the feedwater pump.

[0009] This invention constructs a complete steam-feedwater circulation loop by setting up components such as a steam turbine intermediate-pressure cylinder, a steam turbine low-pressure cylinder, a condensate pump, a low-pressure heater, and a feedwater pump, providing system-level support for heat exchange and water recovery between the thermochemical thermal storage subsystem and the coal-fired power generation system.

[0010] Furthermore, a heat storage control valve is provided on the branch of the hot reheat steam pipeline; a steam exhaust switching valve is provided on the branch of the small steam turbine exhaust pipeline; and a heat release control valve is provided on the branch of the steam turbine high-pressure cylinder exhaust pipeline.

[0011] This invention achieves independent and precise control of the on / off state of each steam pipeline during the heat storage peak shaving stage and the heat release peak stage by setting heat storage control valves, exhaust switching valves, and heat release control valves on the branches of the hot reheat steam pipeline, the branches of the small steam turbine exhaust pipeline, and the branches of the high-pressure cylinder exhaust pipeline of the steam turbine, respectively, so that the system can flexibly switch between the two stages.

[0012] Furthermore, a conventional exhaust valve is provided on the conventional exhaust pipeline; during the heat storage and peak shaving stage, the conventional exhaust valve is opened and the exhaust switching valve and the heat release control valve are closed, and the exhaust steam from the small steam turbine enters the condenser through the conventional exhaust pipeline; during the heat release peak stage, the conventional exhaust valve is closed and the exhaust switching valve and the heat release control valve are opened, and the exhaust steam from the small steam turbine is introduced into the reaction chamber of the fixed bed reactor through the exhaust branch pipeline.

[0013] This invention installs a conventional exhaust valve on the conventional exhaust pipeline, and combines it with the linkage opening and closing of the exhaust switching valve to realize the mutually exclusive switching of small steam turbine exhaust between the condenser and the fixed bed reactor, avoiding crossflow of exhaust pipeline between the two stages and ensuring the safety of system operation.

[0014] Furthermore, the reaction chamber of the fixed-bed reactor is filled with a reversible reaction system of calcium hydroxide and calcium oxide. During the heat storage and peak shaving stage, calcium hydroxide dehydrates to generate calcium oxide and water vapor. During the heat release peak stage, calcium oxide and water vapor undergo a hydration reaction to generate calcium hydroxide and release heat.

[0015] This invention uses a reversible reaction system of calcium hydroxide and calcium oxide as the heat storage material for a fixed-bed reactor. The reaction temperature of this system matches the temperature range of hot reheat steam and cold reheat steam in coal-fired power units. Moreover, the raw materials are widely available, inexpensive, and have high energy density, making them suitable for large-scale engineering applications.

[0016] Secondly, the present invention also provides an operation method for a peak shaving system of a coal-fired unit, which adopts the peak shaving system of the coal-fired unit described in any of the above claims, wherein the operation phase of the peak shaving system of the coal-fired unit includes a heat storage peak shaving phase and a heat release peak phase. During the heat storage and peak shaving stage, a portion of the hot reheat steam is introduced into the heat exchange tubes of the fixed-bed reactor and releases heat to the calcium hydroxide material, driving the dehydration endothermic reaction; the steam after releasing heat and cooling flows out from the heat exchange tubes and enters the high-pressure heater to heat the feedwater; the water vapor generated by the dehydration reaction is discharged from the reaction chamber into the deaerator to heat the condensate; at the same time, the exhaust steam from the small steam turbine is discharged into the condenser for condensation; During the peak heat release stage, the exhaust steam from the small steam turbine is introduced into the reaction chamber of the fixed-bed reactor to drive the calcium oxide to undergo a hydration exothermic reaction; a portion of the cold reheat steam discharged from the high-pressure cylinder of the steam turbine is passed into the heat exchange tubes of the fixed-bed reactor to absorb the heat released by the hydration reaction, and after being heated, it flows into the hot reheat steam pipeline and enters the intermediate-pressure cylinder of the steam turbine to do work.

[0017] Furthermore, during the heat storage and peak shaving stage, the heat storage control valve is opened, and part of the hot reheat steam is diverted through a branch of the hot reheat steam pipeline and enters the heat exchange tube of the fixed bed reactor to release heat to the calcium hydroxide material. The released steam flows out of the heat exchange tube and enters the high-pressure heater to heat the feedwater. The water vapor generated by the dehydration reaction is discharged from the reaction chamber into the deaerator and merges with the condensate.

[0018] In the heat storage and peak shaving stage, this invention diverts a portion of the hot reheat steam to the heat exchange tubes of the fixed-bed reactor by opening the heat storage control valve to drive the dehydration endothermic reaction. Hot reheat steam with the ability to perform work is extracted to serve as the heat source for heat storage, reducing the amount of steam entering the intermediate-pressure cylinder and low-pressure cylinder of the turbine, thus achieving an active reduction in the overall power generation output of the system. The water vapor produced by the dehydration reaction is discharged into the deaerator to heat the condensate, maintaining the mass balance of the working fluid within the system.

[0019] Furthermore, during the peak heat release stage, the low-pressure steam discharged from the small steam turbine is introduced into the reaction chamber of the fixed-bed reactor through the exhaust branch pipeline and the exhaust switching valve. The low-pressure steam, as a reactant, undergoes a hydration exothermic reaction with the calcium oxide material in the reaction chamber.

[0020] In the peak heat release stage, this invention introduces the low-pressure exhaust steam discharged from the small steam turbine into the reaction chamber of the fixed-bed reactor as a reactant for the hydration reaction. This converts the latent heat of vaporization of the exhaust steam, which is discarded by the circulating cooling water in conventional units, into high-grade chemical reaction heat for utilization, thereby improving the overall energy utilization efficiency of the system.

[0021] Furthermore, during the peak heat release stage, a portion of the cold reheat steam discharged from the high-pressure cylinder of the turbine is introduced into the heat exchange tube of the fixed-bed reactor through the heat release control valve on a branch of the turbine high-pressure cylinder exhaust pipe. It exchanges heat with the heat released by the hydration exothermic reaction in the reaction chamber. The heated steam flows out from the heat exchange tube and merges into the hot reheat steam pipeline before entering the intermediate-pressure cylinder of the turbine.

[0022] In the peak heat release stage, this invention utilizes the chemical energy stored in the fixed-bed reactor to directly heat the cold reheat steam discharged from the high-pressure cylinder of the steam turbine through heat exchange tubes. The heated steam then flows into the hot reheat steam pipeline and enters the intermediate-pressure cylinder of the steam turbine to perform work. This avoids the heat transfer delay process of fuel combustion and metal heating surfaces inside the boiler, and significantly improves the response rate of coal-fired units to increase power generation load.

[0023] Furthermore, the heat storage peak shaving stage is executed during the off-peak load period of the power grid, and the steam intake of the intermediate-pressure cylinder and the low-pressure cylinder of the turbine is adjusted by controlling the diversion ratio of hot reheat steam through the heat storage control valve; the heat release peak stage is executed during the peak load period of the power grid or when a rapid ramp-up command is received, and the flow rate of cold reheat steam entering the heat exchange tube of the fixed-bed reactor is controlled by the heat release control valve.

[0024] This invention schedules the heat storage peak shaving phase to be executed during the off-peak load period of the power grid, and the heat release peak phase to be executed during the peak load period of the power grid or when a rapid ramp-up command is issued. By adjusting the hot reheat steam diversion ratio and the cold reheat steam inflow rate through the heat storage control valve and the heat release control valve respectively, the unit output can be rapidly increased and flexibly adjusted without increasing boiler fuel consumption.

[0025] One technical advantage of this invention is that: This invention constructs a thermochemical thermal storage subsystem that integrates heat storage and heat release by adding a fixed-bed reactor to a coal-fired power generation system. The hot reheat steam pipeline, the high-pressure cylinder exhaust pipeline of the steam turbine, and the exhaust pipeline of the small steam turbine are coupled and connected to the heat exchange tubes and reaction chamber of the fixed-bed reactor, respectively. This enables the coal-fired unit to flexibly adjust the power generation load without changing the boiler operating conditions. Attached Figure Description

[0026] 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.

[0027] 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. Small steam turbine; 12. High-pressure heater; 13. Fixed-bed reactor. Detailed Implementation

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] Example 1 like Figure 1 As shown, this embodiment provides a peak-shaving system for a coal-fired unit, which couples the exhaust steam from a small steam turbine with thermochemical heat storage, and uses the low-grade exhaust steam discharged from the small steam turbine as a trigger for thermochemical reactions to convert waste heat into high-grade heat energy to directly heat the main unit's power steam.

[0034] It should be noted that, in Figure 1 In the diagram, the long dashed line represents the fluid path during the heat storage peak shaving stage, and the short dashed line represents the fluid path during the heat release peak stage.

[0035] Specifically, the peak-shaving system of the coal-fired unit includes a coal-fired power generation system and a thermochemical thermal storage subsystem.

[0036] The coal-fired power generation system includes a boiler 1, a high-pressure cylinder of a steam turbine 2, a medium-pressure cylinder of a steam turbine 3, a low-pressure cylinder of a steam turbine 4, a generator 5, a condenser 6, a condensate pump 7, a low-pressure heater 8, a deaerator 9, a feedwater pump 10, a small steam turbine 11, and a high-pressure heater 12.

[0037] The main steam outlet of boiler 1 is connected to the inlet of the high-pressure cylinder 2 of the steam turbine. The exhaust steam from the high-pressure cylinder 2 is reheated in the reheater inside boiler 1 and then sent to the intermediate-pressure cylinder 3 of the steam turbine through the hot reheat steam pipeline. The exhaust steam from the intermediate-pressure cylinder 3 enters the low-pressure cylinder 4 of the steam turbine to continue doing work, and the exhaust steam from the low-pressure cylinder 4 enters the condenser 6. The high-pressure cylinder 2, intermediate-pressure cylinder 3, and low-pressure cylinder 4 of the steam turbine are all coaxially connected to the generator 5 to drive it to generate electricity.

[0038] The condensate from the condenser 6 is pressurized by the condensate pump 7 and then flows sequentially through the low-pressure heater 8 and deaerator 9 into the boiler feedwater system. The feedwater pump 10 drives the water in the deaerator 9 into the boiler feedwater system. The feedwater pump 10 is driven by a small steam turbine 11, and the two are coaxially connected. The conventional exhaust pipe of the small steam turbine 11 is connected to the condenser 6. This constitutes a complete steam-feedwater circulation loop, providing system-level support for heat exchange and fluid recovery between the thermochemical thermal storage subsystem and the coal-fired power generation system.

[0039] The thermochemical thermal energy storage subsystem includes a fixed-bed reactor 13. The fixed-bed reactor 13 contains heat exchange tubes and a reaction chamber filled with a reversible reaction system of calcium hydroxide and calcium oxide. During the thermal energy storage and peak shaving phase, calcium hydroxide undergoes a dehydration reaction upon heating to generate calcium oxide and water vapor, absorbing heat to complete the storage of chemical energy. During the peak heat release phase, calcium oxide and water vapor undergo a hydration reaction to generate calcium hydroxide, releasing heat to complete the release of chemical energy. The reaction temperature of this system matches the temperature range of hot and cold reheat steam in coal-fired power units, and the raw materials are widely available, inexpensive, and have high energy density, making it suitable for large-scale engineering applications.

[0040] The inlet of the heat exchange tubes of the fixed-bed reactor 13 is connected via pipeline branches to the hot reheat steam pipeline at the outlet of boiler 1 and the exhaust steam pipeline of the high-pressure cylinder 2 of the steam turbine, respectively. The outlet of the heat exchange tubes is connected via pipeline branches to the high-pressure heater 12 and the hot reheat steam pipeline, respectively. During the heat storage and peak shaving stage, the steam from the heat exchange tubes is directed to the hot reheat steam pipeline and to the high-pressure heater 12; during the peak heat release stage, the steam from the heat exchange tubes is directed to the exhaust steam pipeline of the high-pressure cylinder 2 of the steam turbine and to the hot reheat steam pipeline.

[0041] The exhaust port of the reaction chamber of the fixed-bed reactor 13 is connected to the deaerator 9. A branch pipe is led out from the exhaust outlet of the small steam turbine 11 and connected to the inlet of the reaction chamber.

[0042] A heat storage control valve is installed on the branch of the hot reheat steam pipeline, an exhaust switching valve is installed on the exhaust branch of the small steam turbine 11, and a heat release control valve is installed on the branch of the exhaust pipeline of the high-pressure cylinder 2 of the steam turbine. The conventional exhaust pipeline and the exhaust branch pipeline are connected in parallel, and a conventional exhaust valve is installed on the conventional exhaust pipeline. Through the aforementioned heat storage control valve, exhaust switching valve, and heat release control valve, independent and precise control of the on / off state of each steam pipeline during the heat storage peak shaving stage and the heat release peak stage is achieved, enabling the system to flexibly switch between the two stages. The coordinated opening and closing of the conventional exhaust valve in conjunction with the exhaust switching valve achieves mutually exclusive switching of the exhaust steam from the small steam turbine 11 between the condenser 6 and the fixed-bed reactor 13, avoiding cross-flow of exhaust steam between the two stages and ensuring the safety of system operation.

[0043] Example 2 This embodiment provides an operation method for the peak shaving system of a coal-fired unit as described in Embodiment 1. The operation method includes a heat storage peak shaving stage and a heat release peak stage.

[0044] (I) Thermal storage and peak shaving stage The thermal energy storage peak-shaving phase is executed during the off-peak load period of the power grid. At this time, the thermal energy storage control valve and the conventional vent valve are opened, while the vent switching valve and the heat release control valve are closed.

[0045] Part of the hot reheat steam, after being branched off from the hot reheat steam pipeline, enters the heat exchange tubes of the fixed-bed reactor 13. Inside the heat exchange tubes, the hot reheat steam indirectly exchanges heat with the calcium hydroxide material in the reaction chamber, releasing heat to the calcium hydroxide and driving its endothermic dehydration reaction. Ca(OH)2→ CaO + H2O(g); After releasing heat and cooling, the steam flows out from the heat exchange tubes and enters the high-pressure heater 12 to heat the feedwater, making full use of the remaining heat. The water vapor produced by the dehydration reaction is discharged from the exhaust port of the reaction chamber and enters the deaerator 9 to merge with the condensate and heat it. Because the water vapor is recovered to the deaerator 9 instead of being directly discharged, the mass balance of the water medium within the system is maintained.

[0046] Meanwhile, the exhaust steam from the small steam turbine 11 is discharged into the condenser 6 for condensation through the conventional exhaust steam pipeline and conventional exhaust steam valve, maintaining normal operating conditions.

[0047] Because some of the hot reheat steam is diverted to the fixed-bed reactor 13 as a heat storage source, the steam flow into the intermediate-pressure cylinder 3 and the low-pressure cylinder 4 of the turbine is reduced accordingly, resulting in a decrease in the overall power generation output of the system and achieving the peak-shaving target of actively reducing load. By adjusting the diversion ratio of the hot reheat steam through the heat storage control valve, the steam intake of the intermediate-pressure cylinder 3 and the low-pressure cylinder 4 of the turbine can be controlled, thereby adjusting the depth of downward peak shaving.

[0048] (ii) Peak heat release stage The peak heat release phase is executed during peak grid load periods or when a rapid ramp-up command is received. At this time, the regular exhaust valve is closed, and the exhaust switching valve and heat release control valve are opened.

[0049] The low-pressure steam discharged from the small steam turbine 11 is introduced into the reaction chamber of the fixed-bed reactor 13 via the exhaust branch pipe and exhaust switching valve. This low-pressure steam, as a reactant, contacts the calcium oxide material within the reaction chamber, undergoing a hydration exothermic reaction. CaO + H2O(g) → Ca(OH)2+ Q (heat released in the reaction); Through the above reaction, the latent heat of vaporization of the exhaust steam, which is discarded by the circulating cooling water in conventional units, is converted into high-grade chemical reaction heat for utilization, thereby improving the overall energy utilization efficiency of the system.

[0050] Simultaneously, a portion of the cold reheat steam discharged from the high-pressure cylinder 2 of the steam turbine is introduced into the heat exchange tubes of the fixed-bed reactor 13 via a branch of the exhaust pipe of the high-pressure cylinder 2 and a heat release control valve. The cold reheat steam indirectly exchanges heat with the heat released by the hydration reaction in the reaction chamber within the heat exchange tubes, absorbing the heat of the chemical reaction and thus increasing its temperature. The heated steam flows out of the heat exchange tubes, merges into the hot reheat steam pipeline, and enters the intermediate-pressure cylinder 3 of the steam turbine to perform work.

[0051] By controlling the flow rate of cold reheat steam into the heat exchange tubes of the fixed-bed reactor 13 through the heat release control valve, the heat release rate and the steam temperature rise can be adjusted.

[0052] As the steam entering the intermediate-pressure cylinder 3 of the turbine absorbs the heat of the chemical reaction and its temperature rises, its ability to perform work is enhanced, and the power output of the unit is correspondingly increased. This process utilizes the chemical energy stored in the fixed-bed reactor 13 to directly heat the cold reheat steam. After the steam is heated, it directly enters the intermediate-pressure cylinder 3 of the turbine to perform work, avoiding the heat transfer delay process of fuel combustion and metal heating surfaces inside the boiler 1. This significantly improves the response rate of the coal-fired unit to increase the power generation load, and can achieve a rapid increase in unit output without increasing boiler fuel consumption.

[0053] In the embodiments of this application, the present invention has the following technical effects: First, the exhaust steam from the small steam turbine that drives the feedwater pump is introduced into the reaction chamber. The latent heat of the waste steam is used to drive the hydration of calcium oxide, converting low-grade waste heat into high-grade reaction heat, thus reducing the heat loss from the condenser's cold source.

[0054] Second, the heat release stage utilizes the high-temperature heat generated by the chemical reaction to directly heat the cold reheat steam, enabling the intermediate-pressure cylinder of the turbine to obtain high-parameter steam before the boiler's thermal load is fully established. This avoids the heat transfer delay of the boiler's heating surface and improves the unit's response rate to load changes.

[0055] Third, the water vapor generated during the dehydration process in the heat storage stage is directly discharged into the deaerator, eliminating the need for a separately arranged condensate storage device and simplifying the scope of engineering modifications.

[0056] 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, characterized in that, This includes coal-fired power generation systems and thermochemical thermal storage subsystems; The coal-fired power generation system includes a boiler, a high-pressure cylinder for a steam turbine, a condenser, a deaerator, a high-pressure heater, and a small steam turbine that drives the feedwater pump. The thermochemical thermal storage subsystem includes a fixed-bed reactor, which is equipped with heat exchange tubes and a reaction chamber. The heat exchanger tube inlet is connected to the hot reheat steam pipeline at the boiler outlet and the high-pressure cylinder exhaust steam pipeline of the steam turbine via pipeline branches, and the heat exchanger tube outlet is connected to the high-pressure heater and the hot reheat steam pipeline via pipeline branches; during the heat storage and peak shaving stage, the steam from the heat exchanger tube is directed to the hot reheat steam pipeline and the steam is directed to the high-pressure heater; during the heat release peak stage, the steam from the heat exchanger tube is directed to the high-pressure cylinder exhaust steam pipeline of the steam turbine and the steam is directed to the hot reheat steam pipeline; The exhaust port of the reaction chamber is connected to the deaerator; the conventional exhaust pipe of the small steam turbine is connected to the condenser, and a branch pipe from the exhaust outlet of the small steam turbine is connected to the inlet of the reaction chamber.

2. The peak-shaving system for coal-fired power units according to claim 1, characterized in that, The coal-fired power generation system also includes a steam turbine intermediate-pressure cylinder, a steam turbine low-pressure cylinder, a generator, a condensate pump, a low-pressure heater, and a feedwater pump. The main steam outlet of the boiler is connected to the inlet of the steam turbine high-pressure cylinder. The exhaust steam from the steam turbine high-pressure cylinder is reheated by the reheater in the boiler and then sent to the steam turbine intermediate-pressure cylinder through the hot reheat steam pipeline. The exhaust steam from the steam turbine low-pressure cylinder is connected to the condenser. The condensate outlet of the condenser is pressurized by the condensate pump and then sent to the boiler feedwater system through the low-pressure heater. The small steam turbine is coaxially connected to the water supply pump.

3. The peak-shaving system for coal-fired power units according to claim 2, characterized in that, A heat storage control valve is installed on a branch of the hot reheat steam pipeline; a steam exhaust switching valve is installed on a branch of the exhaust steam pipeline of the small steam turbine; and a heat release control valve is installed on a branch of the exhaust steam pipeline of the high-pressure cylinder of the steam turbine.

4. The peak-shaving system for coal-fired power units according to claim 3, characterized in that, A conventional exhaust valve is installed on the conventional exhaust pipeline; During the heat storage and peak shaving phase, the conventional exhaust valve is opened and the exhaust switching valve and the heat release control valve are closed, and the exhaust steam from the small steam turbine enters the condenser through the conventional exhaust pipeline; During the peak heat release stage, the conventional exhaust valve is closed and the exhaust switching valve and the heat release control valve are opened. The exhaust steam from the small steam turbine is introduced into the reaction chamber of the fixed-bed reactor through the exhaust branch pipeline.

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

6. A method for operating a peak-shaving system for a coal-fired power unit, characterized in that, The peak shaving system of a coal-fired power unit as described in any one of claims 1 to 5 is used, wherein the operation phase of the peak shaving system of the coal-fired power unit includes a heat storage peak shaving phase and a heat release peak phase; During the heat storage and peak shaving stage, a portion of the hot reheat steam is introduced into the heat exchange tubes of the fixed-bed reactor and released heat to the calcium hydroxide material to drive the dehydration endothermic reaction. After releasing heat and cooling, the steam flows out of the heat exchange tube and enters the high-pressure heater to heat the feedwater; the steam generated by the dehydration reaction is discharged from the reaction chamber into the deaerator to heat the condensate; at the same time, the exhaust steam from the small steam turbine is discharged into the condenser for condensation. During the peak heat release stage, the exhaust steam from the small steam turbine is introduced into the reaction chamber of the fixed-bed reactor to drive the calcium oxide to undergo a hydration exothermic reaction; a portion of the cold reheat steam discharged from the high-pressure cylinder of the steam turbine is passed into the heat exchange tubes of the fixed-bed reactor to absorb the heat released by the hydration reaction, and after being heated, it flows into the hot reheat steam pipeline and enters the intermediate-pressure cylinder of the steam turbine to do work.

7. The operating method according to claim 6, characterized in that, During the heat storage and peak shaving stage, the heat storage control valve is opened, and part of the hot reheat steam is diverted through a branch of the hot reheat steam pipeline and enters the heat exchange tube of the fixed bed reactor to release heat to the calcium hydroxide material. The released steam flows out of the heat exchange tube and enters the high-pressure heater to heat the feed water. The water vapor generated by the dehydration reaction is discharged from the reaction chamber into the deaerator and merges with the condensate.

8. The operating method according to claim 6, characterized in that, During the peak heat release stage, the low-pressure steam discharged from the small steam turbine is introduced into the reaction chamber of the fixed-bed reactor through the exhaust branch pipeline and the exhaust switching valve. The low-pressure steam, as a reactant, undergoes a hydration exothermic reaction with the calcium oxide material in the reaction chamber.

9. The operating method according to claim 6, characterized in that, During the peak heat release stage, a portion of the cold reheat steam discharged from the high-pressure cylinder of the steam turbine is introduced into the heat exchange tube of the fixed-bed reactor through the heat release control valve on a branch of the exhaust pipe of the high-pressure cylinder of the steam turbine. It exchanges heat with the heat released by the hydration exothermic reaction in the reaction chamber. The heated steam flows out from the heat exchange tube and merges into the hot reheat steam pipeline before entering the intermediate-pressure cylinder of the steam turbine.

10. The operating method according to claim 6, characterized in that, The heat storage peak shaving phase is executed during the off-peak load period of the power grid. The steam intake of the intermediate-pressure cylinder and the low-pressure cylinder of the turbine is adjusted by controlling the diversion ratio of hot reheat steam through the heat storage control valve. The heat release peak phase is executed during the peak load period of the power grid or when a rapid ramp-up command is received. The flow rate of cold reheat steam into the heat exchange tube of the fixed-bed reactor is controlled by the heat release control valve.

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