A molten salt energy storage peak-shaving system with flue gas temperature control

Abstract

The present invention belongs to the field of molten salt energy storage technology, and particularly relates to a molten salt energy storage and peak-shaving system with flue gas temperature control. The system of the present invention includes a boiler system, a steam turbine system, and a heat storage and exchange system. The boiler system includes a boiler, and a superheater, an economizer, and an air preheater are sequentially arranged in the flue of the boiler. The steam turbine system includes a high-pressure cylinder, a medium-pressure cylinder, and a low-pressure cylinder connected to a rotating shaft in sequence. The heat storage and exchange system includes a low-temperature molten salt storage tank, a medium-temperature molten salt storage tank, a high-temperature molten salt storage tank, a reheat steam-molten salt heat exchanger, a main steam-molten salt heat exchanger, a water-molten salt heat exchanger, and an air-molten salt heat exchanger. The present invention provides a molten salt energy storage and peak-shaving system with flue gas temperature control that stores heat in a cascade and releases heat flexibly to maximize the utilization of energy of different qualities.

Description

Technical Field

[0001] The present invention belongs to the technical field of molten salt energy storage, and in particular relates to a molten salt energy storage peak-shaving system with flue gas temperature control. Background Art

[0002] To improve the economic efficiency of power plant units, most thermal power units utilize a combined heat and power (CHP) operation mode. In addition to supplying power according to grid dispatch, they also need to supply steam or hot water to heat users. To supply steam to heat users, power plants often reduce the temperature and pressure of some reheated steam to the user's desired parameters before directly supplying it. This process converts high-quality superheated steam into low-quality steam, resulting in significant energy waste. This device utilizes this lost energy to heat molten salt, releasing the stored energy through a heat exchanger.

[0003] As the proportion of renewable energy increases, the role of thermal power in the power grid is gradually shifting from being the absolute mainstay of power supply to providing baseload power. Furthermore, thermal power generation must rapidly adjust load levels according to grid instructions to accommodate the fluctuating nature of renewable energy. In other words, thermal power units shoulder the dual responsibilities of ensuring power supply and regulating peak loads. This results in increased frequency and amplitude of load adjustments, and a faster peak-shaving response. This poses new challenges to the safety, economy, and environmental performance of the units. To ensure the normal operation of the national economy, thermal power units are being pushed to load limits that are approaching or exceeding their original design ranges. This poses a significant long-term threat to unit safety and shortens their service life. Rapid load adjustments can negatively impact thermal efficiency and emissions. The economizer, denitrification unit, and air preheater located in the tail duct are particularly affected. The primary impact is abnormal exhaust gas temperatures. Under low-load operation, boiler output is insufficient, increasing the heat absorption of various heating surfaces. This results in flue gas temperatures below normal in the economizer, denitrification unit, and air preheater in the tail flue. This can cause low-temperature corrosion in the air preheater, reducing denitrification unit efficiency. Increased ammonia slip also leads to corrosion and soot accumulation in the air preheater, necessitating the use of air heaters to raise the air-side temperature of the air preheater. Most air heaters use low-pressure extraction steam as their heat source, and excessive steam extraction can reduce the boiler's overall efficiency and thermal balance. Therefore, thermal power units urgently need a system that can rapidly respond to grid commands and adjust their external load without compromising unit safety, economy, or environmental performance. This system not only utilizes molten salt to store energy for peak load regulation, but also controls flue gas temperature by adjusting the air and hot water flow rates through the molten salt heaters, altering the heat absorption of the economizer and air preheater in the tail flue, ensuring denitrification unit efficiency and exhaust gas temperature. This allows units to fulfill peak load regulation requirements without sacrificing operational efficiency and safety.

[0004] Peak shaving is a new method for thermal power plants to increase their economic returns. It uses molten salt to store excess heat generated during peak load periods, releasing it during peak demand to increase the unit's work capacity and benefit from participating in peak load regulation and generating more electricity. While steam-based energy storage is highly efficient and can be adjusted over a full range from zero to maximum load, excessive steam extraction inevitably affects the unit's thermal balance. Electricity-based energy storage offers rapid response and low unit control requirements; however, its peak shaving capacity is limited by the turbine's safe load. With the rapid development of wind and photovoltaic power in recent years, many thermal power plants have leveraged surrounding wind and solar resources and open space to deploy a certain amount of renewable energy capacity, exploring a coupled and complementary operation model between renewable energy and traditional thermal power. However, due to the intermittent nature of wind and solar power generation and safety constraints during thermal power operation, the actual results and benefits have fallen far short of expectations. Summary of the Invention

[0005] In order to solve the above problems existing in the prior art, the purpose of the present invention is to provide a molten salt energy storage peak-shaving system with flue gas temperature control that can store heat in stages and release heat flexibly to maximize the utilization of energy of different qualities.

[0006] The technical solution adopted in the present invention is:

[0007] A molten salt energy storage peak-shaving system with flue gas temperature control includes a boiler system, a steam turbine system and a heat storage and exchange system. The boiler system includes a boiler, and a superheater, an economizer and an air preheater are sequentially arranged in the flue of the boiler. The steam turbine system includes a high-pressure cylinder, a medium-pressure cylinder and a low-pressure cylinder connected to the rotating shaft in sequence. The heat storage and exchange system includes a low-temperature molten salt storage tank, a medium-temperature molten salt storage tank, a high-temperature molten salt storage tank, a reheat steam-molten salt heat exchanger, a main steam-molten salt heat exchanger, a water-molten salt heat exchanger, and an air-molten salt heat exchanger; the exhaust port of the high-pressure cylinder is connected to a reheat steam pipeline, and the reheat steam pipeline is divided into two paths after passing through the boiler. One path is connected to the steam inlet of the intermediate pressure cylinder, and the other path supplies steam to the outside after passing through the reheat steam-molten salt heat exchanger; it also includes a water supply pipeline, which is divided into two paths after passing through the economizer, one path enters the boiler, and the other path is connected to the steam-water separator after passing through the water-molten salt heat exchanger, and the liquid phase outlet of the steam-water separator is connected to the boiler through a pipeline; a main steam pipeline is connected between the outlet of the superheater and the steam inlet of the high-pressure cylinder, and the outlet of the superheater is also connected to the main steam heat exchange pipeline, which is connected to the steam-water separator after passing through the main steam-molten salt heat exchanger, and the gas phase outlet of the steam-water separator is connected to the inlet of the superheater through a pipeline;

[0008] It also includes an air pipeline, which is connected to the air preheater after passing through the air-molten salt heat exchanger;

[0009] A medium-temperature molten salt heat release pipeline and a low-temperature molten salt heat storage pipeline are respectively connected between the medium-temperature molten salt storage tank and the low-temperature molten salt storage tank. The medium-temperature molten salt heat release pipeline passes through a water-molten salt heat exchanger and an air-molten salt heat exchanger, and the low-temperature molten salt heat storage pipeline passes through a reheat steam-molten salt heat exchanger; a high-temperature molten salt heat release pipeline and a medium-temperature molten salt heat storage pipeline are arranged between the high-temperature molten salt storage tank and the medium-temperature molten salt storage tank. Both the high-temperature molten salt heat release pipeline and the medium-temperature molten salt heat storage pipeline pass through the main steam-molten salt heat exchanger.

[0010] The heat storage process of the present invention heats the molten salt in a staged heating process. To avoid energy losses associated with steam quality degradation caused by decompression and temperature reduction during external steam supply, the reheated steam used for external steam supply is no longer directly decompressed and temperature-reduced for external supply. Instead, it enters a reheat steam molten salt heat exchanger to heat the low-temperature molten salt pumped from the low-temperature tank. The heated molten salt is then stored in a medium-temperature molten salt tank. The reheated steam is then reduced to industrial steam that meets user requirements for external supply. When the unit is required to participate in peak load regulation, excess high-temperature superheated steam enters the main steam molten salt heat exchanger, releases heat, becomes saturated steam, enters the steam-water separator, and then enters the boiler to continue absorbing heat. The medium-temperature molten salt stored in the medium-temperature molten salt storage tank is pumped by a medium-temperature molten salt pump, heated by the main steam-molten salt heat exchanger, and then stored in a high-temperature tank. Without shutting down the boiler turbine and ensuring stable combustion and turbine safety load, the excess steam between the boiler stable combustion load and the turbine safety load can be directly stored for heat. The electricity generated by the turbine safety load is used to heat the molten salt, achieving net zero external output for the unit. The present invention realizes the storage and recovery of excess heat of the boiler and heat loss caused by the degradation of steam quality, thereby achieving the purpose of improving energy utilization efficiency and increasing the peak-shaving capacity of the boiler.

[0011] When the unit load cannot meet the demand, the molten salt system begins to release heat. The main steam-molten salt heat exchanger of the present invention uses a bidirectional reversible design to reheat the steam water. The saturated steam from the boiler steam-water separator is heated by the high-temperature molten salt to form the main steam that enters the high-pressure cylinder of the steam turbine to generate power. The high-temperature molten salt after heat release is stored in the medium-temperature tank.

[0012] The heat release process from medium-temperature molten salt to low-temperature molten salt primarily controls exhaust gas temperature. When the unit load is too low or when the load fluctuates dramatically, the unit's flue gas temperature and emissions can be significantly affected. This heat release process is accomplished by a series-connected air-molten salt heat exchanger and a water-molten salt heat exchanger. Hot air from the supply air system is reheated by the air-molten salt heat exchanger before entering the air preheater. This reduces heater energy consumption and avoids excessive use of low-pressure extraction steam, which impacts unit efficiency. It also increases the cold-end temperature of the air preheater, mitigating low-temperature corrosion and dust accumulation. Adjusting the heat absorption of the air preheater can be used to adjust the exhaust gas temperature. Hot water from the economizer is heated by the water-molten salt heat exchanger, becoming saturated water before entering the steam-water separator. This increases the boiler's external work capacity while also controlling the flue gas temperature by adjusting the heat absorption of the economizer in the flue, ensuring denitrification efficiency. After heat release, the medium-temperature molten salt is stored in the low-temperature molten salt tank. The water-molten salt heat exchanger and the air-molten salt heat exchanger are arranged in series. This arrangement can fully utilize the heat of the molten salt and improve system efficiency.

[0013] As a preferred embodiment of the present invention, the medium-temperature molten salt heat storage pipeline is connected to a molten salt electric heater group. Considering the minimum safe operating load limit of the steam turbine, the erratic fluctuations in steam user demand, and the fact that many thermal power plants, or those with nearby wind and solar power generation equipment, have a certain capacity, but the electricity generated is difficult to effectively utilize for various reasons, a molten salt electric heater group is provided. This molten salt electric heater group can flexibly heat low-temperature molten salt into medium- or high-temperature molten salt, or medium-temperature molten salt into high-temperature molten salt, according to system needs, to achieve energy storage. The presence of the molten salt electric heater effectively increases the heat storage capacity, significantly improving the peak-shaving capability of the unit and enabling zero unit output during deep regulation. Electrically heated molten salt can absorb curtailed solar and wind power and can also be used to purchase off-grid electricity from the grid during off-peak periods to increase the unit's peak-shaving capability and enhance economic benefits. Furthermore, another key function of the present invention is to control the flue gas temperature by adjusting the heat absorption of the heating surfaces in the tail flue through the heat release of the medium-temperature molten salt. To achieve this function, medium-temperature molten salt is continuously consumed. Given a fixed external steam supply, this can lead to insufficient medium-temperature molten salt for flue gas temperature control. Alternatively, during the heat storage phase, medium-temperature molten salt may not be sufficient to meet the heat release requirements of the high-temperature main steam. The molten salt electric heater effectively overcomes this shortcoming, flexibly selecting a power source to heat the low-temperature molten salt and ensuring the medium-temperature molten salt supply meets usage requirements.

[0014] As a preferred embodiment of the present invention, the low-temperature molten salt storage tank is connected to the molten salt electric heater group via a pipeline, and the low-temperature molten salt can directly enter the molten salt electric heater group for heating.

[0015] As a preferred embodiment of the present invention, a first bypass is connected in parallel to the water-molten salt heat exchanger, to which a first molten salt control valve group is connected. The first bypass adjusts the heat absorption of the economizer, thereby precisely controlling the flue gas inlet and exhaust temperatures of the denitrification device.

[0016] As a preferred embodiment of the present invention, a second bypass is connected in parallel to the air-molten salt heat exchanger, to which a second molten salt control valve group is connected. This second bypass adjusts the heat absorption of the air preheater, thereby precisely controlling the flue gas inlet temperature and exhaust temperature of the air preheater.

[0017] As a preferred solution of the present invention, a high-temperature feed water mixing tank is connected to the pipeline between the economizer and the water-molten salt heat exchanger, and a branch of the feed water pipeline is connected to a steam-water separator.

[0018] As a preferred solution of the present invention, a first high-temperature feed water control valve group is connected to the pipeline between the economizer and the high-temperature feed water mixing tank, and a second high-temperature feed water control valve group is connected to the section of the feed water pipeline connected to the high-temperature feed water mixing tank.

[0019] As a preferred embodiment of the present invention, the water supply pipeline is connected in sequence with a water supply pump, a condenser and a deaerator, the exhaust port of the low-pressure cylinder is connected to the condenser through a pipeline, and the exhaust port of the medium-pressure cylinder is connected to the deaerator and the steam inlet of the low-pressure cylinder through pipelines respectively.

[0020] As a preferred solution of the present invention, a pressure reducing valve is connected to the pipeline between the main steam-molten salt heat exchanger and the steam-water separator.

[0021] As a preferred solution of the present invention, the air pipeline is connected to an air supply system and an air control valve group.

[0022] The beneficial effects of the present invention are:

[0023] 1. The present invention utilizes high-temperature, medium-temperature, and low-temperature molten salt storage tanks for tiered heat storage, maximizing the utilization of energy of varying qualities and providing a more flexible heat release method. Low-temperature molten salt heating replaces medium-temperature molten salt, allowing for the recovery of energy lost to degraded steam quality due to external steam supply.

[0024] 2. This invention utilizes a molten salt electric heating unit in parallel with a steam-molten salt heat exchanger, enabling the unit to be adjusted from full load to zero load, enhancing its deep peak-shaving capabilities. The molten salt electric heater can flexibly adjust its power, directly heating low-temperature molten salt to high-temperature molten salt, or first heating it to medium-temperature molten salt and then further heating it to high-temperature molten salt. This invention utilizes the molten salt electric heater unit to achieve three key functions: consuming "green electricity," converting valley electricity, and performing peak-shaving operations.

[0025] 3. During heat release, the main steam-molten salt heat exchanger uses the heat from the high-temperature molten salt to heat the saturated steam in the steam-water separator to form main steam. During heat storage, the main steam-molten salt heat exchanger reverses the flow of the main steam, releasing heat to form saturated steam and heating the medium-temperature molten salt to high-temperature molten salt, simplifying the structural layout. During heat release, the medium-temperature molten salt transfers heat through the water-molten salt heat exchanger and the air-molten salt heat exchanger, heating the high-temperature hot water at the economizer outlet to saturated water for the steam-water separator and heating the hot air from the air supply system to the air preheater. By adjusting the heat absorption of the economizer and air preheater in the tail flue, the flue gas temperature can be accurately controlled, the denitrification efficiency of the denitrification unit can be improved, the ammonium bisulfate blockage and low-temperature corrosion of the rotary preheater can be alleviated, the fan power consumption can be reduced, and the unit's operational safety can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the present invention.

[0027] In the figure: 1- boiler; 2- superheater; 3- economizer; 4- air preheater; 5- high pressure cylinder; 6- medium pressure cylinder; 7- low pressure cylinder; 8- feed water pump; 9- condenser; 10- deaerator; 11- low temperature molten salt storage tank; 12- low temperature molten salt pump; 13- medium temperature molten salt storage tank; 14- first medium temperature molten salt pump; 15- second medium temperature molten salt pump; 16- molten salt electric heater group; 17- high temperature molten salt storage tank; 18- high temperature molten salt pump; 1 9-Main steam-molten salt heat exchanger; 20-Water-molten salt heat exchanger; 21-Air-molten salt heat exchanger; 22-First molten salt control valve group; 23-Second molten salt control valve group; 24-Reheat steam-molten salt heat exchanger; 25-Air control valve group; 26-First high-temperature feed water control valve group; 27-Air supply system; 28-Steam-water separator; 29-Second high-temperature feed water control valve group; 30-High-temperature feed water mixing header; 31-Pressure reducing valve. DETAILED DESCRIPTION

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0029] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. It should be noted that the embodiments of the present invention and the features therein may be combined with each other unless there is a conflict.

[0030] like Figure 1 As shown, the molten salt energy storage and peak-shaving system with flue gas temperature control of this embodiment includes a boiler 1 system, a steam turbine system and a storage and heat exchange system. The boiler 1 system includes a boiler 1, and a superheater 2, an economizer 3 and an air preheater 4 are sequentially arranged in the flue of the boiler 1. The steam turbine system includes a high-pressure cylinder 5, a medium-pressure cylinder 6 and a low-pressure cylinder 7 connected to the rotating shaft in sequence. The heat storage and exchange system includes a low-temperature molten salt storage tank 11, a medium-temperature molten salt storage tank 13, a high-temperature molten salt storage tank 17, a reheat steam-molten salt heat exchanger 24, a main steam-molten salt heat exchanger 19, a water-molten salt heat exchanger 20, and an air-molten salt heat exchanger 21; the exhaust port of the high-pressure cylinder 5 is connected to a reheat steam pipeline, and the reheat steam pipeline is divided into two routes after passing through the boiler 1, one route is connected to the steam inlet of the medium-pressure cylinder 6, and the other route is supplied to the outside after passing through the reheat steam-molten salt heat exchanger 24. Steam; It also includes a water supply pipeline, on which a water supply pump 8, a condenser 9 and a deaerator 10 are connected in sequence. The exhaust port of the low-pressure cylinder 7 is connected to the condenser 9 through a pipeline, and the exhaust port of the intermediate-pressure cylinder 6 is connected to the deaerator 10 and the steam inlet of the low-pressure cylinder 7 through pipelines respectively; the water supply pipeline is divided into two paths after passing through the economizer 3, one path enters the boiler 1, and the other path is connected to the steam-water separator 28 after passing through the water-molten salt heat exchanger 20, and the liquid phase outlet of the steam-water separator 28 is connected to the boiler 1 through a pipeline; A main steam pipeline is connected between the outlet of the superheater 2 and the steam inlet of the high-pressure cylinder 5, and the outlet of the superheater 2 is also connected to a main steam heat exchange pipeline, which is connected to the steam-water separator 28 after passing through the main steam-molten salt heat exchanger 19, and the gas phase outlet of the steam-water separator 28 is connected to the inlet of the superheater 2 through a pipeline;

[0031] It also includes an air pipeline, which is connected to the air preheater 4 after passing through the air-molten salt heat exchanger 21;

[0032] A medium-temperature molten salt heat release pipeline and a low-temperature molten salt heat storage pipeline are respectively connected between the medium-temperature molten salt storage tank 13 and the low-temperature molten salt storage tank 11. The medium-temperature molten salt heat release pipeline passes through the water-molten salt heat exchanger 20 and the air-molten salt heat exchanger 21, and the low-temperature molten salt heat storage pipeline passes through the reheat steam-molten salt heat exchanger 24; a high-temperature molten salt heat release pipeline and a medium-temperature molten salt heat storage pipeline are arranged between the high-temperature molten salt storage tank 17 and the medium-temperature molten salt storage tank 13, and the high-temperature molten salt heat release pipeline and the medium-temperature molten salt heat storage pipeline both pass through the main steam-molten salt heat exchanger 19.

[0033] The low-temperature molten salt storage tank 11 is connected to the molten salt electric heater group 16 through a pipeline. A high-temperature feed water mixing tank 30 is connected to the pipeline between the economizer 3 and the water-molten salt heat exchanger 20, and a branch of the feed water pipeline is connected to the steam-water separator 28. A first high-temperature feed water control valve group 26 is connected to the pipeline between the economizer 3 and the high-temperature feed water mixing tank 30, and a second high-temperature feed water control valve group 29 is connected to the section of the feed water pipeline connected to the high-temperature feed water mixing tank 30. A pressure reducing valve 31 is connected to the pipeline between the main steam-molten salt heat exchanger 19 and the steam-water separator 28. The air pipeline is connected to an air supply system 27 and an air control valve group 25.

[0034] The heat storage process of the present invention adopts a staged temperature increase method to heat the molten salt. In order to avoid the energy loss caused by the reduction of temperature and pressure when supplying steam to the outside, the reheated steam used for external steam supply is no longer directly reduced in temperature and pressure before being supplied to the outside, but enters the reheated steam molten salt heat exchanger to heat the low-temperature molten salt sent by the low-temperature molten salt pump 12 in the low-temperature tank. The heated molten salt enters the medium-temperature molten salt tank for storage, and the reheated steam is reduced to industrial steam that meets user needs and is supplied to the outside. When the unit is required to participate in peak regulation, the excess high-temperature superheated steam enters the main steam molten salt heat exchanger to reheat the steam water, releases heat, becomes saturated steam, enters the steam-water separator 28, and then enters the boiler 1 to continue absorbing heat. The medium-temperature molten salt stored in the medium-temperature molten salt storage tank 13 is transported by the medium-temperature molten salt pump, heated by the reheated steam water in the main steam-molten salt heat exchanger 19, and enters the high-temperature tank for storage. Without shutting down the steam turbine in Boiler 1 and ensuring stable combustion and a safe load, the excess steam between the stable combustion load and the safe load can be directly stored as heat. The electricity generated by the safe load is then used to heat the molten salt, achieving net zero external output for the unit. This invention allows for the storage and recovery of excess heat from Boiler 1, as well as heat lost due to degraded steam quality, thereby improving energy efficiency and increasing the peak-shaving capacity of Boiler 1.

[0035] This solution also features a molten salt electric heater group 16, connected in parallel with the reheat steam water from the reheat steam molten salt heat exchanger and the reheat steam water from the main steam-molten salt heat exchanger 19. Considering the turbine's minimum safe operating load, the erratic fluctuations in steam user demand, and the fact that many thermal power plants have or have nearby wind and solar power generation capacity, but the electricity generated is difficult to effectively utilize for various reasons, a molten salt electric heater group 16 is installed in parallel with the steam molten salt heat exchanger reheat steam water group. The molten salt electric heater group 16 can flexibly heat low-temperature molten salt to medium- or high-temperature molten salt, or medium-temperature molten salt to high-temperature molten salt, according to system needs, thereby storing energy. The presence of the molten salt electric heater effectively increases heat storage, significantly improving the unit's peak-shaving capacity and enabling zero unit output during deep regulation. Electrically heated molten salt can absorb curtailed solar and wind power and can also be used to purchase off-grid electricity from the grid during low-demand periods, thereby increasing the unit's peak-shaving capacity and boosting economic returns. At the same time, another main function of the present invention is to adjust the heat absorption of the heating surface in the tail flue by the heat release of the medium-temperature molten salt to control the flue gas temperature. In order to achieve this function, the medium-temperature molten salt will be continuously consumed. When the external steam supply is constant, it may lead to insufficient medium-temperature molten salt for regulating the flue gas temperature; or in the heat storage stage, the medium-temperature molten salt is not enough to meet the heat release demand of the main steam in the high-temperature section. The setting of the molten salt electric heater effectively compensates for this shortcoming. The flexible selection of power supply to heat the low-temperature molten salt can ensure that the amount of medium-temperature molten salt meets the use requirements.

[0036] When the unit load cannot meet the demand, the molten salt system begins to release heat. The main steam-molten salt heat exchanger 19 of the present invention uses a bidirectional reversible design to reheat the steam water. Saturated steam from the steam-water separator 28 of the boiler 1 is heated by the high-temperature molten salt to form the main steam that enters the high-pressure cylinder 5 of the steam turbine to generate power. After the heat is released, the high-temperature molten salt is stored in the medium-temperature tank.

[0037] The heat release process from medium-temperature molten salt to low-temperature molten salt has the main function of controlling the exhaust gas temperature. When the unit load is too low or the load changes drastically, the unit flue gas temperature and emission indicators will be greatly affected. The heat release process from medium-temperature molten salt to low-temperature molten salt is completed by the air molten salt heat exchanger reheating steam water and the water molten salt heat exchanger reheating steam water arranged in series. The hot air from the air supply system 27 is heated again through the air-molten salt heat exchanger 21 and enters the air preheater 4. On the one hand, it reduces the energy consumption of the heater and avoids the excessive use of low-pressure extraction steam to affect the unit efficiency; on the other hand, it increases the temperature of the cold end of the air preheater 4 and reduces the low-temperature corrosion and dust accumulation of the air preheater 4. The purpose of adjusting the exhaust gas temperature can be achieved by adjusting the heat absorption of the air preheater 4. After being heated by the water molten salt heat exchanger reheating steam water, the hot water from the economizer 3 becomes saturated water and enters the steam-water separator 28. Similarly, on the one hand, the external work capacity of the boiler 1 is increased, and on the other hand, the flue gas temperature can be controlled by adjusting the heat absorption of the economizer 3 in the flue to ensure the denitrification efficiency. After the medium-temperature molten salt releases heat, it enters the low-temperature molten salt tank for storage. The water-molten salt heat exchanger 20 and the air-molten salt heat exchanger 21 reheat steam water are arranged in series. The series arrangement can make full use of the heat of the molten salt and improve the efficiency of the system. A first bypass is connected in parallel to the water-molten salt heat exchanger 20, and a first molten salt control valve group 22 is connected to the first bypass; a second bypass is connected in parallel to the air-molten salt heat exchanger 21, and a second molten salt control valve group 23 is connected to the second bypass. The setting of the first bypass and the second bypass realizes the separate adjustment of the heat absorption of the economizer 3 and the air preheater 4, thereby accurately controlling the flue gas inlet temperature of the denitrification device, the flue gas inlet temperature of the air preheater 4 and the exhaust gas temperature.

[0038] The present invention utilizes a high-temperature molten salt storage tank 17, a medium-temperature molten salt storage tank 13, and a low-temperature molten salt storage tank 11 for tiered heat storage, maximizing the utilization of energy of varying qualities and providing a more flexible heat release method. Furthermore, the medium-temperature tank temperature can be controlled below 400°C, reducing material costs and process complexity. The low-temperature molten salt heating uses medium-temperature molten salt, which can recover energy lost to external steam supply due to reduced steam quality.

[0039] The present invention utilizes a molten salt electric heating group in parallel with a steam-molten salt heat exchanger, enabling the unit to be adjusted from full load to zero load, enhancing its deep peak-shaving capability. The molten salt electric heater can flexibly adjust power, directly heating low-temperature molten salt to high-temperature molten salt, or first heating it to medium-temperature molten salt and then further heating it to high-temperature molten salt. The present invention utilizes the molten salt electric heater group 16 to achieve three key functions: consuming "green electricity," converting valley electricity, and performing peak-shaving operations.

[0040] During heat release, the main steam-molten salt heat exchanger 19 uses the heat from the high-temperature molten salt to heat the saturated steam in the steam-water separator 28 into main steam. During heat storage, the main steam-molten salt heat exchanger 19 reverses the flow of the main steam, releasing heat to saturated steam and heating the medium-temperature molten salt into high-temperature molten salt, simplifying the structural layout. During heat release, the medium-temperature molten salt transfers heat through the water-molten salt heat exchanger 20 and the air-molten salt heat exchanger 21, heating the high-temperature hot water at the outlet of the economizer 3 into saturated water, which is then fed into the steam-water separator 28. It also heats the hot air from the air supply system 27 and feeds it to the air preheater 4. By adjusting the amount of heat absorbed by the economizer 3 and the air preheater 4 in the tail flue, the flue gas temperature can be accurately controlled, the denitrification efficiency of the denitrification unit can be improved, the ammonium bisulfate blockage and low-temperature corrosion of the rotary preheater can be alleviated, the fan power consumption can be reduced, and the unit's operational safety can be improved.

[0041] The typical working mode of this system is as follows:

[0042] The heat storage phase primarily utilizes the main steam-molten salt heat exchanger 19, supplemented by the molten salt electric heater group 16. When the boiler 1 load exceeds the turbine load, excess main steam at the outlet of superheater 2 enters the main steam-molten salt heat exchanger 19, releasing high-temperature sensible heat to heat the medium-temperature molten salt to a specified temperature. The high-temperature molten salt then flows from the outlet of the main steam-molten salt heat exchanger 19 to the molten salt electric heater group 16 for further heating. After heating, the high-temperature molten salt is transferred from the molten salt electric heater group 16 to the high-temperature molten salt storage tank 17 for storage. After releasing heat and cooling, the main steam passes through the pressure reducing valve 31, where it is reduced in temperature and pressure to become saturated steam. This steam is then fed into the vapor phase of the steam-water separator 28, where it mixes with the remaining saturated steam and enters the superheater 2 screen group for further heat absorption. The amount of main steam matching the turbine load enters the turbine's high-pressure cylinder 5 for normal work. The main steam that has completed work enters the boiler 1 for reheating according to the process. The reheated steam required for external steam supply enters the reheated steam-molten salt heat exchanger 24 to heat the low-temperature molten salt into medium-temperature molten salt and then enters the medium-temperature molten salt storage tank 13 for standby use; the other part of the reheated steam directly enters the medium-pressure cylinder 6 to perform work.

[0043] Considering the operational safety of boiler 1 and the power limitations of the heat exchanger, when the load difference between boiler 1 and the turbine is too large, the main steam exceeding the heat load of the main steam-molten salt heat exchanger 19 continues to work according to the normal power generation process, and the generated power is used to start the molten salt electric heater group 16. The molten salt electric heater group 16 first heats the low-temperature molten salt to medium-temperature molten salt, thereby replenishing the medium-temperature molten salt that is limited by the external steam supply.

[0044] When the unit is in deep regulation, the excess heat between boiler 1's minimum stable combustion load and the turbine's safe load is stored in the high-temperature molten salt storage tank 17 via the main steam-molten salt heat exchanger 19. The electricity generated at the turbine's safe load can be stored in the high-temperature molten salt storage tank 17 or the medium-temperature molten salt storage tank 13 via the molten salt electric heater group 16 for future use.

[0045] During the heat release phase, the main steam-molten salt heat exchanger 19 primarily produces superheated steam. The water-molten salt heat exchanger 20 and the air-molten salt heat exchanger 21 heat the high-temperature feed water and hot air, primarily regulating the performance of boiler 1. During peak power generation, the high-temperature molten salt in the high-temperature molten salt storage tank 17 releases heat through the main steam-molten salt heat exchanger 19, heating the saturated steam from the vapor phase of the steam-water separator 28 into superheated steam. This steam then merges with the superheated steam from the outlet of superheater 2 and enters the high-pressure, intermediate-pressure, and low-pressure cylinders 5, 6, and 7, respectively, to generate power. After releasing heat, the high-temperature molten salt becomes intermediate-temperature molten salt and enters the intermediate-temperature molten salt storage tank 13 for storage until further use.

[0046] The medium-temperature molten salt heats the high-temperature feed water and hot air through the water-molten salt heat exchanger 20 and the air-molten salt heat exchanger 21. During peak power generation, the first high-temperature feed water control valve group 26 and the second high-temperature feed water control valve group 29 regulate the heat absorption of the economizer 3 to ensure that the flue gas temperature remains within a reasonable range. The high-temperature feed water in the high-temperature feed water mixing tank 30 is heated by the water-molten salt heat exchanger 20, becoming saturated water before entering the liquid phase of the steam-water separator 28. This input of external heat improves the unit's power generation capacity. The medium-temperature molten salt heats the hot air from the air supply system 27 through the air-molten salt heat exchanger 21. This hot air can replace the circulating air used to raise the temperature of the air preheater 4, reducing the possibility of ash blockage in the air preheater 4. Alternatively, it can be mixed with the hot air from the zone heater, reducing the heater load and increasing the cold-end temperature of the air preheater 4. The increased inlet air temperature increases the incoming heat, improving the efficiency of the boiler 1.

[0047] However, the primary purpose of the heat release process in the medium-temperature section is to control the flue gas temperature in the tail flue, ensure the efficiency of the denitrification system, and reduce the malfunction rate of the air preheater 4. Therefore, both the water-molten salt heat exchanger 20 and the air-molten salt heat exchanger 21 are equipped with parallel bypasses to independently control the heat absorption of the economizer 3 and the air preheater 4. When performing peak load regulation, the furnace heat load decreases, resulting in lower furnace flue gas temperatures. However, the SCR denitrification efficiency decreases with decreasing operating temperature. SCR catalyst efficiency generally reaches its peak at 350°C. When the unit operates at low load, the flue gas temperature decreases. When the flue gas temperature drops to the ammonium bisulfate precipitation temperature, ammonium bisulfate precipitates, covering the active sites and micropores of the catalyst, rendering it ineffective. This significantly reduces catalyst activity and the system's denitrification efficiency. Furthermore, ammonium bisulfate is moderately acidic and highly viscous, easily adhering to the catalyst, reducing catalytic performance. It also adheres to heat exchange components in downstream equipment, exacerbating equipment corrosion and ash blockage. At the same time, the turbine-side steam inlet valve opening decreases, increasing throttling losses and lowering the steam pressure and temperature entering the turbine. This necessitates increasing air volume control during combustion to maintain the reheat steam temperature. During low-load operation, the coal feed decreases, reducing the uniformity of the pulverized coal particles and increasing ignition difficulty. This deteriorates Boiler 1's combustion stability and necessitates an appropriate increase in the secondary air ratio. This increases the flue gas flow rate and exhaust heat losses.

[0048] Under low load, the thermal load of boiler 1 is low, and the flue gas temperature is also relatively low. The water-molten salt heat exchanger 20 heats the mixed high-temperature water from the inlet and outlet of economizer 3. The first high-temperature feedwater control valve group 26 and the second high-temperature feedwater control valve group 29 control the flow rate into the high-temperature feedwater mixing tank 30 at the outlet and inlet of economizer 3, respectively. The high-temperature feedwater at the outlet and inlet of economizer 3 is mixed as required and then enters the water-molten salt heat exchanger 20, where it is heated to become saturated water and enters the water side of the steam-water separator 28, bringing external heat into the unit. When the flue gas temperature is relatively low, increasing the opening of the second high-temperature feedwater control valve group 29 reduces the amount of high-temperature feedwater flowing through economizer 3. The heat absorbed by economizer 3 in the tail flue is reduced, and the flue gas temperature after passing through economizer 3 is increased, keeping the efficiency of the denitrification system within a reasonable range. This avoids increasing the amount of ammonia injection due to insufficient efficiency, which would increase the amount of ammonium bisulfate produced.

[0049] The low temperature at the cold end of the air preheater 4 will lead to increased ash blockage and corrosion of the air preheater 4, a decrease in the uniformity of coal powder particles under low load, and poor combustion stability of the boiler 1, requiring an increase in the air-coal ratio and an increase in the air temperature. The medium-temperature molten salt further heats the hot air from the air supply system 27 through the air-molten salt heat exchanger 21, which can reduce the load of the heater and the amount of low-pressure steam extraction. The hot air heated by the air-molten salt heat exchanger 21 and then entering the air preheater 4 can increase the temperature of the cold end of the air preheater 4, reducing low-temperature corrosion and the degree of ash blockage of the air preheater 4. It also effectively increases the primary and secondary air temperatures at the outlet of the air preheater 4, which is beneficial to the ignition of the boiler 1 and the stability of the combustion of the boiler 1 under low load.

[0050] The amount of medium-temperature molten salt is limited by the amount of steam supplied to the outside, but in the peak-shaving stage, the medium-temperature molten salt is used to absorb the excess heat of the unit and release heat to control the flue gas temperature, resulting in a serious shortage of medium-temperature molten salt. Therefore, a molten salt electric heater group 16 is provided in parallel with the steam molten salt heat exchange system to heat the molten salt to the specified parameters on demand. In the peak-shaving stage, the main steam flow for heating the molten salt can be reduced, and the excess electricity generated by the unit can be used to start part of the molten salt electric heater group 16 to heat the low-temperature molten salt to medium-temperature molten salt, so as to meet the requirements of ensuring the performance of the unit and peak-shaving, and even to achieve a net zero output of the unit to the outside. Secondly, when the unit load is high and the heat storage is insufficient, the "wind and light" green electricity or parity valley electricity near the thermal power plant can be selectively used as the energy source, and the energy can be stored in the high-temperature and medium-temperature molten salt storage tanks 13 as needed for standby use.

[0051] In particular, the unit can adjust its steam supply and power generation based on actual conditions, cooperating and complementing the molten salt energy storage system to meet user electricity, steam, and heating needs. The steam generation system's heat exchanger group can be adjusted based on the system's actual operating parameters, including the type and number of heat exchangers, such as a double-row arrangement, kettle-type evaporators, or integrated heat exchangers. To directly generate superheated steam, this system uses a special molten salt with a higher temperature limit.

[0052] The present invention is not limited to the above-mentioned optional implementation modes. Anyone can derive other forms of products under the inspiration of the present invention. However, no matter what changes are made in the shape or structure, any technical solution that falls within the scope defined by the claims of the present invention falls within the scope of protection of the present invention.

Claims

1. A molten salt energy storage peak-shaving system with flue gas temperature control, characterized by: The invention comprises a boiler (1) system, a steam turbine system and a heat storage and exchange system, wherein the boiler (1) system comprises a boiler (1), a superheater (2), an economizer (3) and an air preheater (4) are sequentially arranged in the flue of the boiler (1), the steam turbine system comprises a high-pressure cylinder (5), a medium-pressure cylinder (6) and a low-pressure cylinder (7) connected to the rotating shaft in sequence, and the heat storage and exchange system comprises a low-temperature molten salt storage tank (11), a medium-temperature molten salt storage tank (13), a high-temperature molten salt storage tank (17), a reheat steam-molten salt heat exchanger (24), a main steam-molten salt heat exchanger (19), a water-molten salt heat exchanger (20), and an air-molten salt heat exchanger (21); the exhaust port of the high-pressure cylinder (5) is connected to a reheat steam pipeline, and the reheat steam pipeline is divided into two paths after passing through the boiler (1), one path is connected to the main steam-molten salt heat exchanger (19), the main steam-molten salt heat exchanger (19), the water-molten salt heat exchanger (20), and the air-molten salt heat exchanger (21); the exhaust port of the high-pressure cylinder (5) is connected to a reheat steam pipeline, and the reheat steam pipeline is divided into two paths after passing through the boiler (1), and one path is connected to the main steam-molten salt heat exchanger (19). The steam inlet of the medium-pressure cylinder (6) is connected to the steam inlet of the medium-pressure cylinder (6), and the other part passes through the reheat steam-molten salt heat exchanger (24) to supply steam to the outside; it also includes a water supply pipeline, which is divided into two parts after passing through the economizer (3), one part enters the boiler (1), and the other part passes through the water-molten salt heat exchanger (20) and is connected to the steam-water separator (28), and the liquid phase outlet of the steam-water separator (28) is connected to the boiler (1) through a pipeline; a main steam pipeline is connected between the outlet of the superheater (2) and the steam inlet of the high-pressure cylinder (5), and the outlet of the superheater (2) is also connected to the main steam heat exchange pipeline, and the main steam heat exchange pipeline passes through the main steam-molten salt heat exchanger (19) and is connected to the steam-water separator (28), and the gas phase outlet of the steam-water separator (28) is connected to the inlet of the superheater (2) through a pipeline; It also includes an air pipeline, which is connected to the air preheater (4) after passing through the air-molten salt heat exchanger (21); A medium-temperature molten salt heat release pipeline and a low-temperature molten salt heat storage pipeline are respectively connected between the medium-temperature molten salt storage tank (13) and the low-temperature molten salt storage tank (11), the medium-temperature molten salt heat release pipeline passes through a water-molten salt heat exchanger (20) and an air-molten salt heat exchanger (21), and the low-temperature molten salt heat storage pipeline passes through a reheat steam-molten salt heat exchanger (24); a high-temperature molten salt heat release pipeline and a medium-temperature molten salt heat storage pipeline are provided between the high-temperature molten salt storage tank (17) and the medium-temperature molten salt storage tank (13), and both the high-temperature molten salt heat release pipeline and the medium-temperature molten salt heat storage pipeline pass through a main steam-molten salt heat exchanger (19).

2. The molten salt energy storage peak-shaving system with flue gas temperature control according to claim 1, characterized in that: The medium-temperature molten salt heat storage pipeline is connected to a molten salt electric heater group (16).

3. The molten salt energy storage peak-shaving system with flue gas temperature control according to claim 2, characterized in that: The low-temperature molten salt storage tank (11) and the molten salt electric heater group (16) are connected via a pipeline.

4. The molten salt energy storage peak-shaving system with flue gas temperature control according to claim 1, characterized in that: A first bypass is connected in parallel to the water-molten salt heat exchanger (20), and a first molten salt control valve group (22) is connected to the first bypass.

5. The molten salt energy storage peak-shaving system with flue gas temperature control according to claim 1, characterized in that: A second bypass is connected in parallel to the air-molten salt heat exchanger (21), and a second molten salt control valve group (23) is connected to the second bypass.

6. The molten salt energy storage peak-shaving system with flue gas temperature control according to claim 1, characterized in that: A high-temperature water supply mixing tank (30) is connected to the pipeline between the economizer (3) and the water-molten salt heat exchanger (20), and a branch of the water supply pipeline is connected to a steam-water separator (28).

7. The molten salt energy storage peak-shaving system with flue gas temperature control according to claim 6, characterized in that: A first high-temperature feed water control valve group (26) is connected to the pipeline between the economizer (3) and the high-temperature feed water mixing header (30), and a second high-temperature feed water control valve group (29) is connected to the section of the feed water pipeline connected to the high-temperature feed water mixing header (30).

8. The molten salt energy storage peak-shaving system with flue gas temperature control according to claim 1, characterized in that: The water supply pipeline is connected to a water supply pump (8), a condenser (9) and a deaerator (10) in sequence. The exhaust port of the low-pressure cylinder (7) is connected to the condenser (9) through a pipeline, and the exhaust port of the medium-pressure cylinder (6) is connected to the deaerator (10) and the steam inlet of the low-pressure cylinder (7) through pipelines.

9. The molten salt energy storage peak-shaving system with flue gas temperature control according to claim 1, characterized in that: A pressure reducing valve (31) is connected to the pipeline between the main steam-molten salt heat exchanger (19) and the steam-water separator (28).

10. The molten salt energy storage peak-shaving system with flue gas temperature control according to any one of claims 1 to 9, characterized in that: The air pipeline is connected to an air supply system (27) and an air control valve group (25).

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