Coal-fired unit deep peak shaving system coupled with electric heating high-temperature phase change heat storage

Abstract

The invention discloses a coal-fired unit deep peak shaving system coupled with electric heating high-temperature phase change heat storage, and relates to the technical field of power generation. The matching capacity of the heat storage system and the full-working-condition operation parameters of the high-parameter coal-fired unit can be effectively enhanced, so that the deep peak regulation capacity and the variable load rate of the coal-fired unit are improved, meanwhile, the energy density, the electricity-heat conversion efficiency and the economic benefits of the heat storage device are improved, and the unit can be prevented from running in an over-low load mode so as to improve the efficiency and prolong the service life. The coal-fired unit deep peak shaving system comprises a coal-fired unit and a high-temperature phase change heat storage system. According to the invention, the peak regulation flexibility of the coal-fired unit is improved, the energy density, the electricity-heat conversion efficiency and the economic recovery period of the heat storage device are also improved, and the over-low load operation of the unit can be prevented so as to improve the efficiency and the service life.

Description

A deep peak-shaving system for coal-fired power units with coupled electrothermal high-temperature phase change thermal storage Technical Field

[0001] This invention relates to the field of power generation technology, and specifically to a deep peak-shaving system for coal-fired power units that combines electrothermal high-temperature phase change thermal storage. Background Technology

[0002] The global energy structure is rapidly transitioning towards clean energy, with the installed capacity of renewable energy sources such as photovoltaics and wind power continuing to increase. However, the intermittency and instability of these energy sources exacerbate grid load fluctuations, posing a significant challenge to the safe and stable operation of the grid. Coal-fired power units, as the "ballast" of the power system, have become a highly promising peak-shaving strategy due to their improved operational flexibility through thermal storage-assisted coal-fired power units. However, existing peak-shaving schemes using thermal storage-assisted coal-fired power units have several drawbacks: the operating temperature range of the thermal storage system is limited; molten salt poses risks of leakage and corrosion; extraction steam peak-shaving faces safety constraints; the electrothermal conversion process suffers significant losses and poor economic efficiency. These issues hinder the widespread application of this technology, necessitating targeted research to overcome these bottlenecks and adapt to the grid peak-shaving demands under a high proportion of renewable energy integration. Summary of the Invention

[0003] To address the above problems, this invention proposes a deep peak-shaving system for coal-fired power units that couples electrothermal high-temperature phase change thermal storage. This system can effectively enhance the matching capability between the thermal storage system and the full-condition operating parameters of high-parameter coal-fired power units, thereby improving the deep peak-shaving capability and load change rate of the coal-fired power units. It also improves the energy density, electrothermal conversion efficiency, and economic benefits of the thermal storage device, and can prevent the unit from operating at excessively low loads to improve efficiency and lifespan.

[0004] The technical solution of the present invention is as follows: The deep peak-shaving system of the coal-fired unit includes a coal-fired unit and a high-temperature phase change thermal energy storage system; the coal-fired unit includes a boiler 1, a steam turbine, a generator 17, and three high-pressure heaters, a feedwater pump 6, a deaerator 5, four low-pressure heaters, a condensate pump 9, and a condenser 8 connected in sequence via pipelines; the steam turbine is connected to the steam outlet side of the boiler 1, and the steam turbine includes a high-pressure cylinder 2, an intermediate-pressure cylinder 3, and a low-pressure cylinder 4 connected coaxially in sequence, and the steam turbine is coaxially connected to the generator 17, which drives the generator 17 to rotate and generate electricity; each extraction port of the steam turbine and the extraction port of the reheat cold section are respectively connected to three high-pressure heaters, one deaerator 5, one feedwater pump turbine 7, and four low-pressure heaters, and the exhaust port of the low-pressure cylinder 4 is connected to the condenser 8, which supplies hot water to the boiler 1 after passing through four low-pressure heaters, one deaerator 5, and three high-pressure heaters in sequence; the high-temperature phase change thermal energy storage system includes a circulation system. The system includes a fan 37, a heat storage device 33, and a feedwater heater 34, a steam generator 35, and a steam superheater 36 as heat exchange equipment. The heat storage device 33 comprises composite phase change heat storage bricks, a circulating air heat exchange channel, and an electric heating element. The electric heating element heats the composite phase change heat storage bricks after being energized to store heat. The outlet of the circulating fan 37 is connected to the heat storage device 33. When releasing heat, the circulating fan 37 blows the heat from the heat storage device 33 out and supplies it to the coal-fired unit through the heat exchange equipment. When assisting the coal-fired unit to increase its load for a long time, the feedwater heater 34 and three high-pressure heaters operate in parallel to reduce the amount of steam extracted from the turbine by the three high-pressure heaters. When assisting the coal-fired unit to increase its load for a short time, the steam generator 35 heats the boiler inlet feedwater into superheated steam and sends it into the high-pressure cylinder 2 for expansion to generate electricity. The steam superheater 36 heats the reheat cold section steam into superheated steam and sends it into the intermediate-pressure cylinder 3 for expansion to generate electricity, thereby increasing the unit's output load more quickly.

[0005] Furthermore, the composite phase change thermal storage brick uses MgO as the thermally conductive skeleton and Na2CO3, K2CO3 and CaCO3 as multi-element phase change core materials, and the heating element is made of chromium-nickel-iron alloy.

[0006] Furthermore, the coal-fired unit also includes a feedwater pump turbine 7; the turbine employs an eight-stage extraction system, wherein the first-stage extraction port is located on the high-pressure cylinder 2, the second-stage extraction port is located on the reheat cooling section, the third and fourth-stage extraction ports are sequentially located on the intermediate-pressure cylinder 3, and the fifth, sixth, seventh, and eighth-stage extraction ports are sequentially located on the low-pressure cylinder 4; the main steam outlet of the boiler 1 is connected to the inlet of the high-pressure cylinder 2, the reheat steam outlet of the boiler 1 is connected to the inlet of the intermediate-pressure cylinder 3, the feedwater inlet of the boiler 1 is connected to the water-side outlet of the first high-pressure heater 16, and the reheat steam outlet of the boiler 1... The inlet of the first stage steam extraction port is connected to the exhaust port of the high-pressure cylinder; the first stage steam extraction port is connected to the steam-side inlet of the first high-pressure heater 16; the second stage steam extraction port is connected to the steam-side inlet of the second high-pressure heater 15; the third stage steam extraction port is connected to the steam-side inlet of the third high-pressure heater 14; the fourth stage steam extraction port is connected to the heating steam inlet of the deaerator 5 and the inlet of the feedwater pump turbine 7; the outlet of the intermediate-pressure cylinder 3 is connected to the inlet of the low-pressure cylinder 4; the exhaust ports of the low-pressure cylinder and the feedwater pump turbine 7 are both connected to the condenser 8; the fifth stage steam extraction port is connected to the steam-side inlet of the first low-pressure heater 13; and the sixth stage steam extraction port is connected to the steam-side inlet of the second low-pressure heater 14. The steam-side inlet of the first high-pressure heater 12 is connected to the steam-side inlet of the third low-pressure heater 11, and the steam-side inlet of the eighth-stage steam heater 10 is connected to the steam-side inlet of the fourth low-pressure heater 10; the condensate outlet of the first high-pressure heater 16 is connected to the condensate inlet of the second high-pressure heater 15, the condensate outlet of the second high-pressure heater 15 is connected to the condensate inlet of the third high-pressure heater 14, and the condensate outlet of the third high-pressure heater 14 is connected to the condensate inlet of the high-pressure heater 5 of the deaerator 5; the condensate outlet of the first low-pressure heater 13 is connected to the condensate inlet of the second low-pressure heater 12, and the second low-pressure heater 14 is connected to the condensate inlet of the deaerator 5. The drain outlet of heater 12 is connected to the drain inlet of the third low-pressure heater 11, the drain outlet of the third low-pressure heater 11 is connected to the drain inlet of the fourth low-pressure heater 10, and the drain outlet of the fourth low-pressure heater 10 is connected to the drain interface of condenser 8. The outlet of condenser 8 is connected in sequence to the condensate pump 9, the fourth low-pressure heater 10, the third low-pressure heater 11, the second low-pressure heater 12, the first low-pressure heater 13, the deaerator 5, the feedwater pump 6, the third high-pressure heater 14, the second high-pressure heater 15, the first high-pressure heater 16, and the feedwater inlet of boiler 1 through pipes.

[0007] Furthermore, the high-temperature phase change thermal energy storage system also includes a first circulating air distributor 21, a second circulating air distributor 19, a first circulating air confluencer 20, a second circulating air confluencer 18, and a first valve 22, a second valve 23, a third valve 24, a fourth valve 25, a fifth valve 26, a sixth valve 27, a seventh valve 28, an eighth valve 29, a ninth valve 30, a tenth valve 31, and an eleventh valve 32; the output terminal of the generator 17 in the coal-fired unit or the power supply terminal of the power grid 38 is connected to the power input terminal of the thermal energy storage device 33; the outlet of the thermal energy storage device 33 is connected to the hot inlet of the feedwater heater 34 and the hot inlet of the steam generator 35 through the eighth valve 29 and the tenth valve 31, respectively. The hot inlet of the steam superheater 36 is connected; the hot outlets of the feedwater heater 34, steam generator 35, and steam superheater 36 are respectively connected to the inlet of the circulating fan 37 through the seventh valve 28 and the ninth valve 30; the outlet of the circulating fan 37 is connected to the inlet of the heat storage device 33; the inlet and outlet of the heat storage device 33 are provided with bypasses, and the bypasses are provided with the eleventh valve 32; the cold inlets of the feedwater heater 34, steam generator 35, and steam superheater 36 are respectively connected to the outlet of the feedwater pump 6, the feedwater inlet of the boiler 1, and the reheat cold section; the cold outlets of the feedwater heater 34, steam generator 35, and steam superheater 36 are respectively connected to the feedwater inlet of the boiler 1, the inlet of the high-pressure cylinder 2, and the inlet of the intermediate-pressure cylinder 3.

[0008] Furthermore, a first circulating air diverter 21 is provided at the outlet end of the circulating fan 37, which is suitable for diverting the air volume entering the heat storage device and the bypass air volume. A second circulating air confluencer 18 is provided at the outlet end of the heat storage device 33, which is suitable for confluencing the outlet air volume of the heat storage device 33 and the bypass air volume for controlling the output heat power and temperature. A second circulating air diverter 19 is provided at the hot inlet end of the steam generator 35 and the steam superheater 36, which is suitable for distributing the heat load entering the steam generator 35 and the steam superheater 36. A first circulating air confluencer 20 is provided at the hot outlet end of the steam generator 35 and the steam superheater 36, which is suitable for confluencing the air volume and sending it to the circulating fan for pressurization.

[0009] Furthermore, when the high-temperature phase change thermal energy storage system participates in peak shaving or heating of coal-fired units, it needs to adjust the thermal power and temperature of the output circulating air by coordinating and controlling the speed of the circulating fan and the bypass eleventh valve in real time according to the load command.

[0010] The deep peak-shaving system for coal-fired power units operates as follows: When a coal-fired power unit needs to reduce its load, all valves in the high-temperature phase change thermal storage system are closed, and the thermal storage device 33 starts its thermal storage mode. A portion of the electricity generated by the coal-fired power unit or additional electricity purchased from the grid is used for electric heating, reducing the net load of the coal-fired power unit on the grid. When the power consumed by the thermal storage exceeds the power generated by the unit, the unit can achieve zero-power or negative-power peak shaving. Throughout the process, the electric heating elements convert electrical energy into heat energy and heat the composite phase change thermal storage bricks until the target thermal storage temperature is reached. At 700℃, the thermal energy storage system completes the conversion of electrical energy into thermal energy. When the coal-fired unit needs to increase its load, the thermal storage device switches to the heat release mode, starts the circulating fan 37, opens the eleventh bypass valve 32, and the circulating air driven by the circulating fan 37 enters the thermal storage device 33 to carry out the heat. Then, it enters the second circulating air confluencer 18. After the temperature is regulated by the bypass air, the heat enters the coal-fired unit through the heat exchange equipment. In other stages, the coal-fired unit operates independently, the high-temperature phase change thermal storage system is shut down, and all valves in the high-temperature phase change thermal storage system are closed.

[0011] In the above scenario: if it is necessary to assist the coal-fired unit in increasing its load for an extended period, the thermal energy in the thermal storage device will be utilized at a low grade. Valve 26, 27, 28, and 29 will be opened, while valves 22, 23, 24, 25, 30, and 31 will be closed. The high-temperature circulating air from the outlet of the thermal storage device 33 will mix with the bypass air through the second circulating air confluencer 18 and enter the hot inlet of the feedwater heater 34 for heat exchange. A portion of the feedwater from the outlet of the feedwater pump 6 will be heated from 173.5℃ to 257.3℃ and then returned to the water-side outlet of the first high-pressure heater 16. The steam extraction from the turbine by the three high-pressure heaters will be reduced to increase the turbine's output power, thereby rapidly increasing the unit's output load. The 223.92℃ circulating air after heat exchange will return to the inlet of the circulating fan 37 for continuous heat release.

[0012] If a short-term auxiliary load increase for a coal-fired unit is required, the thermal energy in the heat storage device can be utilized at a high grade, providing continuous heating for the coal-fired unit for 4.74 hours. The minimum usable temperature of the heat storage device is 635.6℃ (see Figure 4). Therefore, open the first valve 22, the second valve 23, the third valve 24, the fourth valve 25, the ninth valve 30, and the tenth valve 31, and close the fifth valve 26, the sixth valve 27, the seventh valve 28, and the eighth valve 29. The high-temperature circulating air from the outlet of the heat storage device 33 mixes with the bypass air through the second circulating air confluencer 18, and then is split by the distributor. The steam enters the hot inlet of the steam generator 35 and the steam superheater 36 for heat exchange. A portion of the boiler inlet feedwater is heated from 257.3℃ to 566℃ superheated steam through the steam generator 35 and merges with the main steam at the boiler outlet before entering the high-pressure cylinder 2 to expand and generate electricity. A portion of the reheat cold section steam is heated from 309.9℃ to 566℃ superheated steam through the steam superheater 36 and merges with the reheated steam at the boiler outlet before entering the intermediate-pressure cylinder 3 to expand and generate electricity, thereby rapidly increasing the unit's output load. The 337.41℃ circulating air after heat exchange returns to the inlet of the circulating fan for continuous heat release.

[0013] This invention couples high-temperature phase change thermal energy storage with a coal-fired power unit, converting generator output or surplus grid power into thermal energy stored in the thermal storage device. When needed, this energy is carried out of the storage device via circulating air. Under bypass control, the temperature of the circulating air can be adjusted arbitrarily between ambient temperature and 700°C. The air then enters a heat exchange device to transfer the thermal energy to the coal-fired power unit for power generation or external heating. This invention not only improves the peak-shaving flexibility of the coal-fired power unit but also increases the energy density of the thermal storage device (reaching 176.82 kWh / m³). 3 The invention improves the electrothermal conversion efficiency (reaching 63.74%) and economic payback period (reaching 3.35 years), and also prevents the unit from operating under excessively low loads, thus improving efficiency and lifespan. Compared with existing technologies, the beneficial effects of this invention are: 1. It uses a high-temperature resistant composite phase change material comprising 40wt% MgO, 31.2wt% Na2CO3, 18wt% K2CO3, and 10.8wt% CaCO3. This material can achieve a thermal storage operating temperature of up to 700℃, and exhibits good chemical stability, high energy storage density, and long lifespan at high temperatures. The material has low manufacturing costs (8000 yuan / ton), good economic efficiency, and is easily mass-produced and applied. It also avoids the decomposition, corrosion, and leakage problems encountered with traditional molten salts.

[0014] Second, this invention adopts a high-temperature phase change thermal energy storage system, which directly converts the generator output or surplus power grid energy into thermal energy storage during the energy storage process. Coal-fired power generation units can achieve zero-load output, avoiding risks such as reheater overheating, turbine axial thrust imbalance, and insufficient turbine minimum cooling flow caused by peak shaving.

[0015] Third, the heat release process of the thermal storage device can control the heat release power and temperature through bypass air regulation. The temperature range is between ambient temperature and 700℃, which is flexible. When the boiler is running at low load / rapid load change, the heat release power and temperature can be quickly increased, realizing full-condition coupling with high-parameter coal-fired power generation units, and easily supporting flexible peak shaving of coal power.

[0016] Fourth, by adopting a 700℃ high-temperature thermal storage and a composite thermal storage mode of sensible heat plus latent heat, the energy storage density of the thermal storage device is improved, thereby supporting the large-capacity long-term peak-shaving capability of coal-fired units. Furthermore, the higher thermal storage temperature not only reduces the energy loss in the electrothermal conversion process, but also increases the heat exchange power without increasing the heat exchange area of ​​the heat exchange equipment, thus reducing its investment cost.

[0017] Fifth, the electrothermal high-temperature phase change thermal energy storage system is highly flexible. It can be used as an independent energy storage system for heating, or it can be coupled with existing coal-fired power units for deep peak shaving. Two operation methods for deep peak shaving systems of coal-fired power units coupled with electrothermal high-temperature phase change thermal energy storage are proposed. Attached Figure Description

[0018] Figure 1 is a schematic diagram of the structure of the present invention.

[0019] Figure 2 is a schematic diagram of the thermal storage device in this invention.

[0020] Figure 3 shows the heat flow distribution diagrams in this invention: (a) heat flow distribution diagram of the original machine under 75% THA operation; (b) heat flow distribution diagram of the high-temperature phase change thermal energy storage system using low-grade thermal energy to assist the coal-fired unit in increasing the load under 75% THA operation; (c) heat flow distribution diagram of the high-temperature phase change thermal energy storage system using high-grade thermal energy to assist the coal-fired unit in increasing the load under 75% THA operation.

[0021] Figure 4 shows the outlet temperature at different times during the heat release process of the heat storage device in this invention.

[0022] Figure 5 shows the net present value of high-temperature phase change thermal energy storage system for peak shaving of coal-fired power units over 30 years under market electricity prices. Detailed Implementation

[0023] To clearly illustrate the technical features of this patent, the following detailed description is provided through specific embodiments and in conjunction with the accompanying drawings.

[0024] As shown in Figures 1 and 2, this embodiment provides a deep peak-shaving system for a coal-fired power unit coupled with electrothermal high-temperature phase change thermal storage, including a coal-fired power unit and a high-temperature phase change thermal storage system. In this embodiment, the coal-fired power unit includes a boiler 1, a high-pressure cylinder 2, an intermediate-pressure cylinder 3, a low-pressure cylinder 4, high-pressure heaters 14-16, a deaerator 5, low-pressure heaters 10-13, a condenser 8, a condensate pump 9, a feedwater pump 6, a feedwater pump turbine 7, and a generator 17. The main steam outlet of the boiler 1 is connected to the inlet of the high-pressure cylinder 2, the reheat steam outlet of the boiler 1 is connected to the inlet of the intermediate-pressure cylinder 3, the first-stage extraction port on the high-pressure cylinder 2 is connected to the steam-side inlet of the first high-pressure heater 16, and the second-stage extraction port on the reheat cold section is connected to the steam-side inlet of the second high-pressure heater 15. The inlet is connected to the third-stage extraction port on the intermediate-pressure cylinder 3, which is connected to the steam-side inlet of the third high-pressure heater 14. The inlet of the feedwater pump turbine 7 and the heating steam inlet of the deaerator 5 are connected to the fourth-stage extraction port on the intermediate-pressure cylinder 3. The outlet end of the intermediate-pressure cylinder 3 is connected to the inlet end of the low-pressure cylinder 4. The fifth, sixth, seventh, and eighth-stage extraction ports on the low-pressure cylinder 4 are connected to the steam-side inlets of the first low-pressure heater 13, the second low-pressure heater 12, the third low-pressure heater 11, and the fourth low-pressure heater 10, respectively. The outlet end of the low-pressure cylinder 4 and the outlet end of the feedwater pump turbine 7 are connected to the condenser 8. The condensate outlet of the first high-pressure heater 16 is connected to the condensate inlet of the second high-pressure heater 15. The drain outlet of heater 15 is connected to the drain inlet of the third high-pressure heater 14. The drain outlet of the third high-pressure heater 14 is connected to the high-pressure heater drain inlet of deaerator 5. The drain outlet of the first low-pressure heater 13 is connected to the drain inlet of the second low-pressure heater 12. The drain outlet of the second low-pressure heater 12 is connected to the drain inlet of the third low-pressure heater 11. The drain outlet of the third low-pressure heater 11 is connected to the drain inlet of the fourth low-pressure heater 10. The drain outlet of the fourth low-pressure heater 10 is connected to the drain port of condenser 8. Generator 17 is connected to the high-pressure cylinder 2, intermediate-pressure cylinder 3, and low-pressure cylinder 4 on the same shaft. The outlet of condenser 8 is connected in sequence to condensate pump 9, low-pressure heaters 10-13, deaerator 5, and feedwater pump 14 via pipelines. The water pump 6, high-pressure heaters 14-16, and the feedwater inlet of boiler 1 are connected. In this embodiment, the high-temperature phase change thermal energy storage system includes a circulating fan 37, a first circulating air distributor 21, a second circulating air distributor 19, a first circulating air confluencer 20, a second circulating air confluencer 18, a feedwater heater 34, a steam generator 35, a steam superheater 36, a thermal energy storage device 33, a first valve 22, a second valve 23, a third valve 24, a fourth valve 25, a fifth valve 26, a sixth valve 27, a seventh valve 28, an eighth valve 29, a ninth valve 30, a tenth valve 31, and an eleventh valve 32. The output terminal of the generator 17 in the coal-fired unit or the power supply terminal of the power grid 38 is connected to the power input terminal of the thermal energy storage device 33.The outlet of the heat storage device 33 is connected to the hot inlet of the feedwater heater 34, the hot inlet of the steam generator 35, and the hot inlet of the steam superheater 36 via the eighth valve 29 and the tenth valve 31, respectively. The hot outlets of the feedwater heater 34, the steam generator 35, and the steam superheater 36 are connected to the inlet of the circulating fan 37 via the seventh valve 28 and the ninth valve 30, respectively. The outlet of the circulating fan 37 is connected to the inlet of the heat storage device 33. The inlet and outlet of the heat storage device 33 are provided with bypasses, and the bypasses are equipped with the eleventh valve 32. The cold inlets of the feedwater heater 34, the steam generator 35, and the steam superheater 36 are connected to the outlet of the feedwater pump 6, the feedwater inlet of the boiler 1, and the reheat cold section, respectively. The cold outlets of the feedwater heater 34, the steam generator 35, and the steam superheater 36 are connected to the feedwater inlet of the boiler 1, the inlet of the high-pressure cylinder 2, and the inlet of the intermediate-pressure cylinder 3, respectively. In this embodiment, a first circulating air distributor is provided at the outlet end of the circulating fan 37. 21. Suitable for diverting the airflow entering the thermal storage device and the bypass airflow. A second circulating air confluencer 18 is set at the outlet end of the thermal storage device 33 to combine the outlet airflow and bypass airflow of the thermal storage device 33 for controlling the output heat power and temperature. A second circulating air diverter 19 is set at the hot inlet end of the steam generator 35 and the steam superheater 36 to distribute the heat load entering the steam generator 35 and the steam superheater 36. A first circulating air confluencer 20 is set at the hot outlet end of the steam generator 35 and the steam superheater 36 to combine the airflow and send it to the circulating fan for pressurization. This embodiment does not specifically limit the coal-fired unit. To conform to the current situation, the coal-fired unit in this embodiment is a 660MW supercritical coal-fired unit. Under 75% THA load, the main steam and reheat steam pressures are 19.1Mpa and 2.87Mpa, respectively. The main steam and reheat steam temperatures are both 566℃, and the condenser operating pressure is 4.9kPa.

[0025] The thermal storage device includes a composite phase change thermal storage brick, a circulating air heat exchange channel, a shell, an inlet air distributor, and an electric heating element; the composite phase change thermal storage brick uses MgO as a thermally conductive skeleton and Na2CO3, K2CO3 and CaCO3 as multi-element phase change core materials, and the electric heating element is made of chromium-nickel-iron alloy.

[0026] This embodiment does not specifically limit the thermal storage device. To conform to the current situation, the composite phase change thermal storage brick in this embodiment uses 40wt% MgO, 31.2wt% Na2CO3, 18wt% K2CO3 and 10.8wt% CaCO3. The thermal storage device is rectangular, with external dimensions of 12 meters long, 13 meters wide and 13 meters high. The shell is made of steel structure and is covered with high-performance thermal insulation materials (such as ceramic fiber, rock wool / slag wool, microporous calcium silicate) to reduce heat loss. The heating element is made of chromium-nickel-iron alloy.

[0027] The high-temperature phase change thermal energy storage system also includes an operation and control unit, which comprises hardware equipment and software control logic. The operation and control unit receives a target command and, through internal models and algorithms, calculates the respective tasks to be undertaken by the high-temperature phase change thermal energy storage system and the coal-fired power unit, so as to coordinate the operation of each piece of equipment in the system. When the high-temperature phase change thermal energy storage system participates in peak shaving or heating of the coal-fired power unit, it needs to adjust the output circulating air heat power and temperature by coordinating and controlling the speed of the circulating fan and the bypass eleventh valve in real time according to the load command, so as to meet the unit's flexible peak shaving requirements.

[0028] In this embodiment, the operation control unit uses a DCS or PLC controller to coordinate the operation of the high-temperature phase change thermal storage system and the coal-fired unit, so as to realize flexible peak shaving of the coal-fired unit.

[0029] In this embodiment, the operation method of the deep peak-shaving system of a coal-fired unit using coupled electrothermal high-temperature phase change thermal energy storage includes the following steps: When the coal-fired unit needs to reduce its load, the thermal energy storage device 33 starts the thermal energy storage mode. A portion of the electricity generated by the coal-fired unit or additional electricity purchased from the grid is used for electric heating, reducing the net load of the coal-fired unit on the grid. When the power consumed by the thermal energy storage is greater than the power generated by the unit, the unit can achieve zero-power or negative-power peak shaving. Throughout the process, the electrothermal element converts electrical energy into thermal energy and heats the composite phase change thermal energy storage bricks until the target thermal energy storage temperature of 700°C is reached, completing the storage of electrical energy into thermal energy. During this period, the first valve 22, the second valve 23, the third valve 24, the fourth valve 25, the fifth valve 26, the sixth valve 27, and the seventh valve... Valve 28, valve 29, valve 30, valve 31, and valve 32 are closed. When the coal-fired unit needs to increase its load, the heat storage device switches to heat release mode, starts the circulating fan 37, and opens the bypass valve 32. The circulating air driven by the circulating fan 37 enters the heat storage device 33 to carry out the heat, and then enters the second circulating air confluencer 18. After the temperature is regulated by the bypass air, the heat enters the coal-fired unit through the heat exchange equipment. At this time, if it is necessary to assist the coal-fired unit to increase its load for a long time, the heat energy in the heat storage device will be utilized at a low grade, thus releasing more heat energy, which can continuously heat the coal-fired unit for 7.17 hours. The minimum usable temperature is 358℃ (see Figure 4). Therefore, valves 26 and 32 are opened. 27, 28, and 29 are closed. First valve 22, second valve 23, third valve 24, fourth valve 25, ninth valve 30, and tenth valve 31 are closed. The high-temperature circulating air from the outlet of the heat storage device 33 mixes with the bypass air through the second circulating air confluencer 18 and enters the hot inlet of the feedwater heater 34 for heat exchange. A portion of the feedwater from the outlet of the feedwater pump 6 is heated from 173.5℃ to 257.3℃ and then returned to the water-side outlet of the first high-pressure heater 16. The high-pressure heater 14-16 reduces steam extraction from the turbine to increase turbine output power, thereby rapidly increasing the unit's output load. The 223.92℃ circulating air after heat exchange returns to the inlet of the circulating fan 37 for continuous heat release. The entire coal-fired unit's airflow is recirculated. As shown in Figure 3(b)), the thermal energy provided by the thermal storage unit is exchanged through the feedwater heater 34, and ultimately 19.48 MW of thermal energy is effectively absorbed by the boiler feedwater, replacing part of the extraction steam heat source. Compared with the original coal-fired unit (extraction steam: 98.60 MW; total turbine inlet steam: 1018.18 MW) (see Figure 3(a)), the extraction steam steam of this configuration is reduced to 74.03 MW, while the total turbine inlet steam is correspondingly increased to 1042.66 MW. However, this configuration requires an additional 6.06 MW of coal steam to be added to the boiler, ultimately increasing the net power output of the coal-fired unit by 20.61 MW. If it is necessary to assist the coal-fired unit in increasing its load for a short period of time, the thermal energy in the thermal storage device can be utilized at a high grade, providing continuous heating for the coal-fired unit.The lowest usable temperature of the thermal storage device is 635.6℃ after 74 hours (see Figure 4). Therefore, the first valve 22, the second valve 23, the third valve 24, the fourth valve 25, the ninth valve 30, and the tenth valve 31 are opened, and the fifth valve 26, the sixth valve 27, the seventh valve 28, and the eighth valve 29 are closed. The high-temperature circulating air at the outlet of the thermal storage device 33 is mixed with the bypass air through the second circulating air confluencer 18, and then split by the distributor before entering the heat inlet of the steam generator 35 and the steam superheater 36 for heat exchange. A portion of the boiler inlet feedwater is heated from 257.3℃ to 566℃ superheated steam through the steam generator 35 and merged with the main steam at the boiler outlet before entering the high-pressure cylinder 2 for expansion and power generation. A portion of the reheat cold section steam is heated from 309.9℃ to 566℃ superheated steam through the steam superheater 36 and merged with the reheat steam at the boiler outlet before entering the intermediate-pressure cylinder 3 for expansion and power generation, thereby quickly increasing the unit's output load; after heat exchange, 337℃... The 41℃ circulating air returns to the inlet of the circulating fan for continuous heat release, and the heat flow of the entire coal-fired unit is redistributed (see Figure 3(c)). The heat energy provided by the heat storage unit is exchanged through the steam generator 35 and the steam superheater 36, and finally 27.07MW (47.98-15.65-5.26) of heat is absorbed by the supplementary steam turbine inlet steam. Compared with the original coal-fired unit (extraction heat: 98.60MW; total steam turbine inlet heat: 1018.18MW) (see Figure 3), this is significantly higher. (a) This configuration increases the total turbine inlet capacity to 1020.24MW. Simultaneously, this configuration reduces the boiler's coal consumption by 6.3MW, ultimately increasing the net power output of the coal-fired unit by 20.69MW. During other stages, the coal-fired unit operates independently, the high-temperature phase change thermal energy storage system is shut down, and valves one through eleven are closed.

[0030] In this embodiment, the energy storage density of the thermal energy storage device can reach 176.82 kWh / m³ in both low-grade and high-grade thermal energy utilization modes. 3 and 116.17 kWh / m 3 During the energy storage phase, the electrothermal conversion efficiency can reach 59.85% and 63.74% under low-grade and high-grade thermal energy utilization modes, respectively. Under a given market electricity price, the investment payback period of the high-temperature phase change thermal energy storage system is 3.51 years and 3.35 years, respectively (see Figure 5), which is suitable for assisting large-capacity, long-term deep peak shaving of coal-fired units.

[0031] This invention couples a coal-fired power unit with an electrothermal high-temperature phase change thermal energy storage system. It utilizes off-peak electricity to heat phase change thermal energy storage bricks and store heat, then uses this high-temperature heat energy to heat boiler feedwater or supplementary main steam and reheat steam. Compared to traditional molten salt thermal energy storage, this method offers superior economics and a better temperature matching range, while avoiding the risks of corrosion, leakage, and stratification associated with molten salt. Furthermore, the coal-fired power unit can flexibly adjust peak loads according to grid demand, enabling flexible retrofitting of the unit. This invention addresses the problems faced by thermal energy storage-assisted coal-fired power units in peak load adjustment, including insufficient peak load depth, poor flexibility, low energy density of the energy storage device, low electrothermal conversion efficiency, long investment payback period, and safety concerns.

[0032] There are many specific ways to implement this invention. The above description is only a preferred embodiment of this invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of this invention, and these improvements should also be considered within the scope of protection of this invention.

Claims

1. A deep peak-shaving system for coal-fired power units with coupled electrothermal high-temperature phase change thermal storage, characterized in that, The deep peak-shaving system of the coal-fired unit includes a coal-fired unit and a high-temperature phase change thermal storage system; the coal-fired unit includes a boiler (1), a steam turbine, a generator (17), and three high-pressure heaters, a feed water pump (6), a deaerator (5), four low-pressure heaters, a condensate pump (9), and a condenser (8) connected in sequence by pipelines; the steam turbine is connected to the steam outlet side of the boiler (1), and the steam turbine includes a high-pressure cylinder (2), an intermediate-pressure cylinder (3), and a low-pressure cylinder (4) connected in sequence on the same shaft, and the steam turbine is connected to the generator. (17) are coaxially connected and the turbine drives the generator (17) to rotate and generate electricity; the extraction ports of the turbine and the extraction ports of the reheat cold section are respectively connected to three high-pressure heaters, one deaerator (5), one feedwater pump turbine (7) and four low-pressure heaters. The exhaust port of the low-pressure cylinder (4) is connected to the condenser (8). The condenser (8) supplies hot water to the boiler (1) in sequence through four low-pressure heaters, one deaerator (5) and three high-pressure heaters; the high-temperature phase change heat storage system includes circulating air The device includes a heat exchanger (37), a heat storage device (33), a feedwater heater (34), a steam generator (35), and a steam superheater (36). The heat storage device (33) includes a composite phase change heat storage brick, a circulating air heat exchange channel, and an electric heating element. The electric heating element heats the composite phase change heat storage brick to store heat after being energized. The outlet of the circulating fan (37) is connected to the heat storage device (33). When releasing heat, the circulating fan (37) blows the heat from the heat storage device (33) through the heat exchange device. When supplying the coal-fired unit to increase the load for a long time, the feedwater heater (34) and three high-pressure heaters are used in parallel to reduce the steam extraction from the turbine by the three high-pressure heaters; when assisting the coal-fired unit to increase the load for a short time, the boiler inlet feedwater is heated into superheated steam by the steam generator (35) and sent into the high-pressure cylinder (2) to expand and generate electricity, and the reheat cold section steam is heated into superheated steam by the steam superheater (36) and sent into the intermediate pressure cylinder (3) to expand and generate electricity, thereby increasing the unit output load faster.

2. The deep peak-shaving system for coal-fired power units with coupled electrothermal high-temperature phase change thermal storage according to claim 1, characterized in that, The composite phase change thermal storage brick uses MgO as the thermally conductive skeleton and Na2CO3, K2CO3 and CaCO3 as multi-element phase change core materials. The heating element is made of chromium-nickel-iron alloy.

3. The deep peak-shaving system for coal-fired power units with coupled electrothermal high-temperature phase change thermal storage according to claim 1, characterized in that, The coal-fired unit also includes a feedwater pump turbine (7); the turbine adopts an eight-stage extraction system, wherein the first stage extraction port is located on the high-pressure cylinder (2), the second stage extraction port is located on the reheat cold section, the third and fourth stage extraction ports are sequentially located on the intermediate-pressure cylinder (3), and the fifth, sixth, seventh, and eighth stage extraction ports are sequentially located on the low-pressure cylinder (4); the main steam outlet of the boiler (1) is connected to the inlet of the high-pressure cylinder (2), the reheat steam outlet of the boiler (1) is connected to the inlet of the intermediate-pressure cylinder (3), the feedwater inlet of the boiler (1) is connected to the water-side outlet of the first high-pressure heater (16), and the reheat steam inlet of the boiler (1) is connected to the high-pressure cylinder... The exhaust ports are connected; the first-stage extraction port is connected to the steam-side inlet of the first high-pressure heater (16), the second-stage extraction port is connected to the steam-side inlet of the second high-pressure heater (15), the third-stage extraction port is connected to the steam-side inlet of the third high-pressure heater (14), the fourth-stage extraction port is connected to the heating steam inlet of the deaerator (5) and the inlet of the feedwater pump turbine (7), the outlet of the intermediate-pressure cylinder (3) is connected to the inlet of the low-pressure cylinder (4), the exhaust ports of the low-pressure cylinder and the exhaust ports of the feedwater pump turbine (7) are both connected to the condenser (8), the fifth-stage extraction port is connected to the steam-side inlet of the first low-pressure heater (13), and the sixth-stage extraction port is connected to the steam-side inlet of the second low-pressure heater (12). The side inlet is connected, the seventh stage steam extraction port is connected to the steam side inlet of the third low-pressure heater (11), and the eighth stage steam extraction port is connected to the steam side inlet of the fourth low-pressure heater (10); the condensate outlet of the first high-pressure heater (16) is connected to the condensate inlet of the second high-pressure heater (15), the condensate outlet of the second high-pressure heater (15) is connected to the condensate inlet of the third high-pressure heater (14), and the condensate outlet of the third high-pressure heater (14) is connected to the high-pressure heater condensate inlet of the deaerator (5); the condensate outlet of the first low-pressure heater (13) is connected to the condensate inlet of the second low-pressure heater (12), and the condensate outlet of the second low-pressure heater (12) is connected to the condensate inlet of the second low-pressure heater (12). The condensate outlet of the third low-pressure heater (11) is connected to the condensate inlet of the fourth low-pressure heater (10), and the condensate outlet of the fourth low-pressure heater (10) is connected to the condensate outlet of the condenser (8). The outlet of the condenser (8) is connected in sequence to the condensate pump (9), the fourth low-pressure heater (10), the third low-pressure heater (11), the second low-pressure heater (12), the first low-pressure heater (13), the deaerator (5), the feed water pump (6), the third high-pressure heater (14), the second high-pressure heater (15), the first high-pressure heater (16), and the feed water inlet of the boiler (1) via pipelines.

4. The deep peak-shaving system for coal-fired power units with coupled electrothermal high-temperature phase change thermal storage according to claim 1, characterized in that, The high-temperature phase change thermal energy storage system also includes a first circulating air splitter (21), a second circulating air splitter (19), a first circulating air confluencer (20), a second circulating air confluencer (18), and a first valve (22), a second valve (23), a third valve (24), a fourth valve (25), a fifth valve (26), a sixth valve (27), a seventh valve (28), an eighth valve (29), a ninth valve (30), a tenth valve (31), and an eleventh valve (32); the output end of the generator (17) in the coal-fired unit or the power supply end of the power grid (38) is connected to the power input end of the thermal energy storage device (33); the outlet of the thermal energy storage device (33) is connected to the hot inlet of the feedwater heater (34), the hot inlet of the steam generator (35), and the steam generator (35) through the eighth valve (29) and the tenth valve (31), respectively. The hot inlet of the steam superheater (36) is connected; the hot outlets of the feedwater heater (34), steam generator (35), and steam superheater (36) are connected to the inlet of the circulating fan (37) through the seventh valve (28) and the ninth valve (30), respectively; the outlet of the circulating fan (37) is connected to the inlet of the heat storage device (33); the inlet and outlet of the heat storage device (33) are provided with bypasses, and the bypasses are provided with the eleventh valve (32); the cold inlets of the feedwater heater (34), steam generator (35), and steam superheater (36) are connected to the outlet of the feedwater pump (6), the feedwater inlet of the boiler (1), and the reheat cold section, respectively; the cold outlets of the feedwater heater (34), steam generator (35), and steam superheater (36) are connected to the feedwater inlet of the boiler (1), the inlet of the high-pressure cylinder (2), and the inlet of the medium-pressure cylinder (3), respectively.

5. A deep peak-shaving system for coal-fired power units with coupled electrothermal high-temperature phase change thermal storage as described in claim 4, characterized in that, The outlet end of the circulating fan (37) is provided with a first circulating air diverter (21) to divert the air volume entering the heat storage device and the bypass air volume. The outlet end of the heat storage device (33) is provided with a second circulating air confluencer (18) to combine the outlet air volume of the heat storage device (33) and the bypass air volume for controlling the output heat power and temperature. The hot inlet end of the steam generator (35) and the steam superheater (36) is provided with a second circulating air diverter (19) to distribute the heat load entering the steam generator (35) and the steam superheater (36). The hot outlet end of the steam generator (35) and the steam superheater (36) is provided with a first circulating air confluencer (20) to combine the air volume and send it to the circulating fan for pressurization.

6. A deep peak-shaving system for coal-fired power units with coupled electrothermal high-temperature phase change thermal storage as described in claim 5, characterized in that, When the high-temperature phase change thermal energy storage system participates in peak shaving or heating of coal-fired units, it needs to adjust the thermal power and temperature of the output circulating air by coordinating and controlling the speed of the circulating fan and the bypass eleventh valve in real time according to the load command.

7. An operation method for a deep peak-shaving system for a coal-fired power unit with coupled electrothermal high-temperature phase change thermal storage as described in claim 1, characterized in that, The following method shall be followed: When the coal-fired unit needs to reduce its load, all valves in the high-temperature phase change thermal storage system shall be closed, and the thermal storage device (33) shall start the thermal storage mode. Part of the electricity generated by the coal-fired unit or additional electricity purchased from the grid shall be used for electric heating, and the net load of the coal-fired unit on the grid shall be reduced. When the power consumed by the thermal storage is greater than the power generated by the unit, the unit can achieve zero power or negative power peak shaving. In the whole process, the electric heating element converts electrical energy into heat energy and heats the composite phase change thermal storage brick to raise its temperature until the thermal storage target temperature of 700℃ is reached, thus completing the electric heating process. The thermal energy can be stored; when the coal-fired unit needs to increase the load, the thermal storage device switches to the heat release mode, starts the circulating fan (37), opens the eleventh bypass valve (32), and the circulating air driven by the circulating fan (37) enters the thermal storage device (33) to carry out the heat, and then enters the second circulating air confluencer (18). After the temperature is regulated by the bypass air, the heat enters the coal-fired unit through the heat exchange equipment; in other stages, the coal-fired unit operates independently, the high-temperature phase change thermal storage system is shut down, and all valves in the high-temperature phase change thermal storage system are closed.

8. The operation method of a deep peak-shaving system for a coal-fired power unit with coupled electrothermal high-temperature phase change thermal storage according to claim 7, characterized in that, If it is necessary to assist the coal-fired unit to increase the load for a long time, the heat energy in the heat storage device will be used at a low grade. Open the fifth valve (26), the sixth valve (27), the seventh valve (28), and the eighth valve (29), and close the first valve (22), the second valve (23), the third valve (24), the fourth valve (25), the ninth valve (30), and the tenth valve (31). The high-temperature circulating air at the outlet of the heat storage device (33) is mixed with the bypass air through the second circulating air confluencer (18) and enters the heat inlet of the feedwater heater (34) for heat exchange. A portion of the feedwater at the outlet of the feedwater pump (6) is heated from 173.5℃ to 257.3℃ and then returned to the water side outlet of the first high-pressure heater (16). The high-pressure heater is reduced from drawing steam from the turbine to increase the output power of the turbine, thereby rapidly increasing the unit's output load. The circulating air at 223.92℃ after heat exchange returns to the inlet of the circulating fan (37) for continuous heat release.

9. The operation method of a deep peak-shaving system for a coal-fired power unit with coupled electrothermal high-temperature phase change thermal storage according to claim 7, characterized in that, If a short-term auxiliary coal-fired unit needs to increase its load, the thermal energy in the heat storage device can be utilized at a high grade, providing continuous heating for the coal-fired unit for 4.74 hours. The minimum usable temperature of the heat storage device is 635.6℃ (see Figure 4). Therefore, open the first valve (22), the second valve (23), the third valve (24), the fourth valve (25), the ninth valve (30), and the tenth valve (31), and close the fifth valve (26), the sixth valve (27), the seventh valve (28), and the eighth valve (29). The high-temperature circulating air at the outlet of the heat storage device (33) is mixed with the bypass air through the second circulating air confluencer (18), and then through the distribution... After being diverted by the flow generator, the steam enters the heat inlet of the steam generator (35) and the steam superheater (36) for heat exchange. A portion of the boiler inlet feedwater is heated from 257.3°C to 566°C superheated steam through the steam generator (35) and merges with the main steam at the boiler outlet before entering the high-pressure cylinder (2) to expand and generate electricity. A portion of the reheat cold section steam is heated from 309.9°C to 566°C superheated steam through the steam superheater (36) and merges with the reheated steam at the boiler outlet before entering the medium-pressure cylinder (3) to expand and generate electricity, thereby rapidly increasing the unit's output load. The 337.41°C circulating air after heat exchange returns to the inlet of the circulating fan for continuous heat release.

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