Coal-fired power generation system coupled with SOEC and method for deep peak shaving operation of unit

Abstract

The application discloses a coal-fired power generation system coupled with SOEC and a deep peak regulation operation method of the unit. The depth of peak regulation of the coal-fired unit is limited by the minimum stable combustion load of the boiler, and the cylinder efficiency of the steam turbine side is obviously reduced under low load, and the operation energy consumption sharply rises. In order to solve the above problems, the application increases the working medium flow of the high-pressure cylinder and the medium-pressure cylinder and improves the cylinder efficiency of the steam turbine by adopting backheating steam extraction throttling when the coal-fired power generation unit is operated under low load; the molten salt heat storage and the solid oxide electrolysis cell SOEC are coupled, the additional electric energy generated by the backflow working medium is converted into chemical energy by the SOEC, and the oxygen-enriched air generated by electrolysis is recovered to the boiler, so that the combustion stability of the boiler under low load is improved; the product waste heat and the molten salt heat storage are used to heat the boiler feed water, the insufficient feed water temperature caused by steam extraction throttling is made up, and the SCR denitration efficiency under low load is ensured. The application realizes flexible, efficient, safe and clean collaborative improvement of the deep peak regulation process of the coal-fired power generation unit by reasonably designing the system configuration.

Description

Technical Field

[0001] This invention belongs to the field of peak-shaving operation technology of coal-fired power plants, specifically relating to a coal-fired power generation system coupled with SOEC and a deep peak-shaving operation method for the unit. Background Technology

[0002] With the vigorous development of renewable energy, the installed capacity of wind and solar power generation has increased significantly. However, renewable energy sources such as wind and solar power are intermittent and cyclical, making it difficult to guarantee a continuous and stable power supply on their own. Therefore, in order to improve the safety and reliability of power grid operation and mitigate load fluctuations caused by renewable energy, the demand for flexible peak-shaving by coal-fired power units is increasing.

[0003] The main methods for coal-fired power units to participate in peak shaving are deep peak shaving and start-up / shutdown peak shaving. During deep peak shaving operation, key parameters deviate from the rated design conditions, especially at low or extremely low loads, making it difficult to guarantee the unit's safety and efficiency. The minimum technical output for deep peak shaving in coal-fired power units is limited by the minimum stable combustion load on the boiler side. When the unit load falls below this limit, problems such as water circulation deviating from the safe range, burner instability and flameout, and uneven furnace heat load causing water-cooled wall tube rupture seriously threaten the safe and stable operation of the unit. Furthermore, while the turbine side can achieve extremely low load operation during deep peak shaving, the efficiency of the high-pressure and intermediate-pressure cylinders decreases significantly, leading to a sharp increase in unit operating energy consumption and a significant increase in peak shaving costs. Therefore, improving the load matching and operational efficiency of both the boiler and turbine sides under deep peak shaving conditions is one of the major problems that urgently needs to be solved.

[0004] Solid oxide electrolyzers (SOECs) are reverse-operating solid oxide fuel cells. In electrolysis mode, they can electrolyze water, carbon dioxide, and other substances into hydrogen and carbon monoxide, converting electrical energy into chemical energy. This achieves energy storage while simultaneously generating oxygen-enriched air, which, when properly utilized, can facilitate stable combustion under low or extremely low loads on the boiler side. However, SOEC electrolysis temperatures are relatively high. Therefore, by integrating molten salt thermal storage and rationally designing the system configuration, it is possible to synergistically achieve stable operation of coal-fired units under extremely low load peak shaving, efficient energy storage, and clean generation of industrial gas. Summary of the Invention

[0005] To overcome the challenges of mismatched load limits between the boiler and turbine sides under deep peak-shaving conditions in coal-fired power units, resulting in poor stability and safety during extremely low-load boiler operation and significantly increased energy consumption and low efficiency during low-load turbine operation, this invention increases the flow rate of the working fluid in the high- and intermediate-pressure cylinders of the turbine during low-load operation by throttling the turbine's steam extraction, thereby improving the efficiency of the high- and intermediate-pressure cylinders. Simultaneously, the additional output power of the reflux working fluid is converted into chemical energy through a solid oxide electrolyzer (SOEC), and the generated oxygen-enriched air is recovered and reintroduced into the boiler, achieving stable combustion at low loads and increasing the depth of peak shaving. Coupled with molten salt thermal storage, the invention provides the necessary reaction conditions for the SOEC and recovers the waste heat from the molten salt and reaction products to heat the boiler feedwater, improving the SCR denitrification efficiency under low loads. This comprehensive approach achieves a flexible, efficient, safe, and clean synergistic improvement in the deep peak-shaving process.

[0006] The technical solution adopted by this invention to solve its technical problem is:

[0007] A coal-fired power generation system coupled with SOEC includes a coal-fired generator thermal system, a solid oxide electrolyzer (SOEC), and a molten salt thermal storage coupled system.

[0008] The thermal system of the coal-fired power generation unit includes a boiler 1, a high-pressure cylinder 2 of a steam turbine, an intermediate-pressure cylinder 3 of a steam turbine, a low-pressure cylinder 4 of a steam turbine, a generator 5, a condenser 6, a condensate pump 7, a low-pressure heater 8, a deaerator 9, a feedwater pump 10, a high-pressure heater 11, a steam turbine regenerative extraction steam regulating valve 12, a first feedwater heater 13, a second feedwater heater 14, and a molten salt feedwater heater 15. The superheated steam outlet of the boiler 1 is connected to the steam inlet of the high-pressure cylinder 2 of the steam turbine via a pipeline. The extraction steam outlet of the high-pressure cylinder 2 is connected to the steam inlet of the high-pressure heater 11 via a pipeline. The connecting pipeline is equipped with a steam turbine regenerative extraction steam regulating valve 12 for regulating the extraction steam flow. The steam outlet of the high-pressure cylinder 2 is connected to the steam inlet of the intermediate-pressure cylinder 3 of the steam turbine via the boiler 1. The first-stage extraction steam outlet of the intermediate-pressure cylinder 3 is connected to the steam inlet of the high-pressure heater 11 via a pipeline, and the second-stage extraction steam outlet is connected to the steam inlet of the deaerator 9 via a pipeline. A turbine regenerative extraction steam regulating valve 12 is installed on the pipeline to regulate the extraction steam flow. The steam outlet of the intermediate-pressure cylinder 3 of the turbine is connected to the steam inlet of the low-pressure cylinder 4 of the turbine via a pipeline. The extraction steam outlet of the low-pressure cylinder 4 is connected to the steam inlet of the low-pressure heater 8 via a pipeline. The steam outlet of the low-pressure cylinder 4 is connected to the condenser 6 via a pipeline. The condensate outlet of the condenser 6 is connected to the condensate inlet of the low-pressure heater 8 via a condensate pump 7. The condensate outlet of the deaerator 8 is connected to the feedwater inlet of the deaerator 9. The feedwater outlet of the deaerator 9 is connected to the feedwater inlet of the high-pressure heater 11 via the feedwater pump 10. The feedwater inlet of the boiler 1 is connected to the feedwater outlet of the high-pressure heater 11 via the first feedwater heater 13, the second feedwater heater 14, and the molten salt feedwater heater 15. The high-pressure cylinder 2, the intermediate-pressure cylinder 3, and the low-pressure cylinder 4 of the turbine are coaxial and connected to the power grid via the generator 5.

[0009] The solid oxide electrolysis cell (SOEC) and molten salt thermal storage coupling system includes an electrolysis unit molten salt heat exchanger 23, an SOEC stack 24, a first regenerator 25, a second regenerator 26, a third regenerator 27, a fourth regenerator 29, a three-way mixing valve 30, a first fan 28, a second fan 31, an electrolysis unit water pump 33, a first hydrogen storage tank 32, a second hydrogen storage tank 38, a water storage tank 37, an electrolysis unit condenser 36, an electrolysis unit steam-water separator 34, an electrolysis unit dryer 35, an electrolysis unit feedwater regulating valve 39, a boiler combustion stabilization valve 42, an air exhaust valve 43, and connections between various devices. The pipeline system comprises the following components: molten salt heat exchanger 23, SOEC stack 24, first regenerator 25, second regenerator 26, third regenerator 27, first fan 28, fourth regenerator 29, three-way mixing valve 30, second fan 31, first hydrogen storage tank 32, electrolysis unit water pump 33, electrolysis unit steam-water separator 34, electrolysis unit dryer 35, electrolysis unit condenser 36, water storage tank 37, and second hydrogen storage tank 38, forming the SOEC electrolysis unit. The working fluid, water, originates from the outlet of the intermediate-pressure cylinder 3 of the steam turbine and is connected to the SOEC electrolysis unit via the electrolysis unit feedwater regulating valve 39. The water pump 33 and the fourth regenerator 29 are connected sequentially on the fuel side via pipelines. The reacted hydrogen gas is connected to the electrolysis working fluid water at the three-way mixing valve 30 via pipelines that connect the first hydrogen storage tank 32, the first blower 28, the fuel side of the second regenerator 26, and the fuel side of the third regenerator 27. After passing through the fuel side of the molten salt heat exchanger 23 of the electrolysis unit, it enters the fuel inlet end of the SOEC stack 24. The fuel outlet pipeline of the SOEC stack 24 sequentially passes through the exhaust gas side of the third regenerator 27, the fuel exhaust gas side of the second feedwater heater 14, the condenser 36 of the electrolysis unit, the steam-water separator 34 of the electrolysis unit, and the dryer 35 of the electrolysis unit before finally connecting to the fuel inlet end of the SOEC stack 24. The second hydrogen storage tank 38 is connected to form a closed fuel pipeline. The water separated by the steam-water separator 34 of the electrolysis unit enters the water storage tank 37 for storage. Outside air passes through the second fan 31, the first regenerator 25, the oxygen side of the molten salt heat exchanger 23 of the electrolysis unit, and enters the oxygen inlet end of the SOEC stack 24. The oxygen at the oxygen outlet end of the SOEC stack 24 passes through the tail gas side of the first regenerator 25, the tail gas side of the second regenerator 26, the tail gas side of the fourth regenerator 29, and the oxygen tail gas side of the first feedwater heater 13, and finally enters the boiler of the coal-fired unit through the boiler combustion stabilization valve 42 or is discharged to the outside environment through the air exhaust valve 43.

[0010] The reaction temperature of the SOEC electrolysis unit is provided by the molten salt heating unit, which includes a molten salt feed water heater 15, a thermal storage medium cold tank 16, a thermal storage medium cold tank outlet regulating valve 17, a thermal storage medium cold tank outlet pump 18, a thermal storage medium flue gas heater 19, a thermal storage medium hot tank 20, a thermal storage medium hot tank outlet regulating valve 21, a thermal storage medium hot tank outlet pump 22, and an electrolysis unit molten salt heat exchanger 23. The thermal storage medium inlet of the thermal storage medium flue gas heater 19 is connected to the thermal storage medium outlet of the thermal storage medium cold tank 16 through the thermal storage medium cold tank outlet pump 18 and the thermal storage medium cold tank outlet regulating valve 17. The thermal storage medium outlet of the thermal storage medium flue gas heater 19 is connected to the thermal storage medium hot tank. The inlet of the heat storage medium of the 20 is connected by a pipeline. The outlet of the heat storage medium of the heat storage medium hot tank 20 is connected to the inlet of the medium of the molten salt heat exchanger 23 of the electrolysis unit through the outlet pump 22 and the outlet regulating valve 21 of the heat storage medium hot tank. The outlet of the medium of the molten salt heat exchanger 23 of the electrolysis unit is connected to the inlet of the heat storage medium of the cold tank 16 through the molten salt feedwater heater 15. The electrical energy of the SOEC electrolysis unit comes from the coal-fired generator set and is provided by the additional output power generated by the extraction working fluid returning to the turbine. The SOEC stack 24 is connected to the AC-to-DC inverter 41 through a cable. The AC-to-DC inverter 41 is connected to the power grid through the electrolysis unit switch 40.

[0011] The deep peak-shaving operation method for a coal-fired power generation system coupled with SOEC is as follows:

[0012] When a coal-fired power generating unit is operating under deep peak shaving conditions, the operating efficiency of the high- and intermediate-pressure cylinders of the turbine decreases significantly. Since the turbine cylinder efficiency is directly related to the flow rate of the working fluid flowing through the turbine, a throttling method of reheating and extracting steam from the high- and intermediate-pressure cylinders of the turbine is adopted under low load conditions. This involves closing the turbine reheating and extraction steam regulating valve 12, allowing the extraction working fluid to flow back from the feedwater heated in the deaerator 9 and high-pressure heater 11 to the high-pressure cylinder 2 and intermediate-pressure cylinder 3 of the turbine to perform work. This increases the flow rate of the working fluid flowing through the high- and intermediate-pressure cylinders of the turbine, thereby improving the operating efficiency of the high- and intermediate-pressure cylinders. At the same time, the electrolysis unit switch 40 is opened, and the electrical energy output by the working fluid flowing back to the turbine is converted into DC power by the AC-to-DC inverter 41 and then stored in the SOEC electrolysis unit.

[0013] When the SOEC electrolysis unit is working, the AC-to-DC inverter 41 absorbs the electrical energy from the coal-fired generator set, and the second fan 31 is turned on to flow oxygen-enriched air into the oxygen inlet of the SOEC stack 24. The oxygen-enriched air at the oxygen outlet of the SOEC stack 24 preheats the reaction gases through the first regenerator 25, the second regenerator 26, and the fourth regenerator 29, and also preheats the boiler feedwater through the first feedwater heater 13. The oxygen-enriched air after waste heat recovery is beneficial to the stable combustion of the boiler. At this time, the boiler combustion stabilization valve 42 and the air exhaust valve 43 are adjusted so that the heat-exchanged oxygen-enriched air is transported through pipelines and finally enters the furnace or is discharged to the external environment. This achieves stable combustion under low boiler load and avoids water-cooled wall vaporization or hydrodynamic safety issues. A blower 28 draws hydrogen from the first hydrogen storage tank 32 and simultaneously opens the feedwater regulating valve 39 and the water pump 33 of the electrolysis unit. By adjusting the speed of the water pump, an appropriate amount of water is drawn from the outlet of the intermediate pressure cylinder 3 of the steam turbine and introduced into the fourth regenerator 29, where it is mixed with the hydrogen three-way mixing valve 30. Finally, the mixed gas flows into the fuel side of the SOEC stack 24. The hydrogen produced by electrolysis and the hydrogen input from the front end of the SOEC stack are reheated by the third regenerator 27 for the unreacted gas, and the feedwater is preheated by the second feedwater heater 14. Finally, the hydrogen and water flow into the second hydrogen storage tank 38 and the water storage tank 37 for storage through the condenser 36, the steam-water separator 34, and the dryer 35 of the electrolysis unit, respectively.

[0014] When the SOEC electrolysis unit is working, the outlet regulating valve 21 of the thermal storage medium hot tank is opened, and the outlet pump 22 of the thermal storage medium hot tank is started. The flow rate of the thermal storage medium flowing out of the thermal storage medium hot tank 20 is regulated by the outlet pump 22. The thermal storage medium flowing out of the thermal storage medium hot tank 20 flows through the molten salt heat exchanger 23 of the electrolysis unit to exchange heat with the working fluid, creating the reaction conditions required for the electrolysis reaction. Then, the feedwater is preheated by the molten salt feedwater heater 15. The thermal storage medium after waste heat utilization enters the thermal storage medium cold tank 16. When the SOEC electrolysis unit is not working, the outlet regulating valve 17 of the thermal storage medium cold tank is opened, and the outlet pump 18 of the thermal storage medium cold tank is started. The flow rate of the thermal storage medium flowing out of the thermal storage medium cold tank 16 is regulated by the outlet pump 18. The thermal storage medium flowing out of the thermal storage medium cold tank 16 flows through the thermal storage medium flue gas heater 19 to exchange heat with the high-temperature flue gas of the boiler before flowing to the thermal storage medium hot tank 20.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] 1. When the steam turbine is running at low load, the high and medium pressure cylinders are used to reheat and extract steam to increase the flow rate of the working medium in the steam turbine. This significantly improves the efficiency of the high and medium pressure cylinders when the steam turbine is running at low load, and the operating energy consumption is significantly reduced, thus improving the efficiency of deep peak shaving operation of the coal-fired unit.

[0017] 2. By coupling molten salt thermal storage and solid oxide electrolysis (SOEC), the system configuration is rationally designed. The molten salt thermal storage provides the reaction temperature required by SOEC. The SOEC converts the additional electrical energy generated by the extraction working fluid returned to the turbine into chemical energy, thereby achieving efficient storage of electrical energy and clean generation of industrial gas.

[0018] 3. When the boiler is running at low load, the oxygen-enriched air generated by SOEC electrolysis is recovered and sent to the boiler flue gas inlet, which effectively improves the operating stability and hydrodynamic safety of the boiler under low load, increases the peak shaving depth of the unit, reduces the minimum technical output of the unit, and enhances the operational flexibility of the deep peak shaving unit; the waste heat of the reaction products and the heat storage of molten salt are used to heat the boiler feedwater, which makes up for the insufficient feedwater temperature caused by the steam extraction return, and realizes the comprehensive utilization of waste heat while improving the SCR denitrification efficiency under low load. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a coal-fired power generation system coupled with SOEC proposed in this invention. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0021] like Figure 1 As shown, the present invention proposes a coal-fired power generation system coupled with SOEC, comprising a coal-fired generator thermal system, a solid oxide electrolyzer (SOEC), and a molten salt thermal storage coupling system.

[0022] The thermal system of the coal-fired power generation unit includes a boiler 1, a high-pressure cylinder 2 of a steam turbine, an intermediate-pressure cylinder 3 of a steam turbine, a low-pressure cylinder 4 of a steam turbine, a generator 5, a condenser 6, a condensate pump 7, a low-pressure heater 8, a deaerator 9, a feedwater pump 10, a high-pressure heater 11, a steam turbine regenerative extraction steam regulating valve 12, a first feedwater heater 13, a second feedwater heater 14, and a molten salt feedwater heater 15. The superheated steam outlet of the boiler 1 is connected to the steam inlet of the high-pressure cylinder 2 of the steam turbine via a pipeline. The extraction steam outlet of the high-pressure cylinder 2 is connected to the steam inlet of the high-pressure heater 11 via a pipeline. The connecting pipeline is equipped with a steam turbine regenerative extraction steam regulating valve 12 for regulating the extraction steam flow. The steam outlet of the high-pressure cylinder 2 is connected to the steam inlet of the intermediate-pressure cylinder 3 of the steam turbine via the boiler 1. The first-stage extraction steam outlet of the intermediate-pressure cylinder 3 is connected to the steam inlet of the high-pressure heater 11 via a pipeline, and the second-stage extraction steam outlet is connected to the steam inlet of the deaerator 9 via a pipeline. A turbine regenerative extraction steam regulating valve 12 is installed on the pipeline to regulate the extraction steam flow. The steam outlet of the intermediate-pressure cylinder 3 of the turbine is connected to the steam inlet of the low-pressure cylinder 4 of the turbine via a pipeline. The extraction steam outlet of the low-pressure cylinder 4 is connected to the steam inlet of the low-pressure heater 8 via a pipeline. The steam outlet of the low-pressure cylinder 4 is connected to the condenser 6 via a pipeline. The condensate outlet of the condenser 6 is connected to the condensate inlet of the low-pressure heater 8 via a condensate pump 7. The condensate outlet of the deaerator 8 is connected to the feedwater inlet of the deaerator 9. The feedwater outlet of the deaerator 9 is connected to the feedwater inlet of the high-pressure heater 11 via the feedwater pump 10. The feedwater inlet of the boiler 1 is connected to the feedwater outlet of the high-pressure heater 11 via the first feedwater heater 13, the second feedwater heater 14, and the molten salt feedwater heater 15. The high-pressure cylinder 2, the intermediate-pressure cylinder 3, and the low-pressure cylinder 4 of the turbine are coaxial and connected to the power grid via the generator 5.

[0023] The solid oxide electrolysis cell (SOEC) and molten salt thermal storage coupling system includes an electrolysis unit molten salt heat exchanger 23, an SOEC stack 24, a first regenerator 25, a second regenerator 26, a third regenerator 27, a fourth regenerator 29, a three-way mixing valve 30, a first fan 28, a second fan 31, an electrolysis unit water pump 33, a first hydrogen storage tank 32, a second hydrogen storage tank 38, a water storage tank 37, an electrolysis unit condenser 36, an electrolysis unit steam-water separator 34, an electrolysis unit dryer 35, an electrolysis unit feedwater regulating valve 39, a boiler combustion stabilization valve 42, an air exhaust valve 43, and connections between various devices. The pipeline system comprises the following components: molten salt heat exchanger 23, SOEC stack 24, first regenerator 25, second regenerator 26, third regenerator 27, first fan 28, fourth regenerator 29, three-way mixing valve 30, second fan 31, first hydrogen storage tank 32, electrolysis unit water pump 33, electrolysis unit steam-water separator 34, electrolysis unit dryer 35, electrolysis unit condenser 36, water storage tank 37, and second hydrogen storage tank 38, forming the SOEC electrolysis unit. The working fluid, water, originates from the outlet of the intermediate-pressure cylinder 3 of the steam turbine and is connected to the SOEC electrolysis unit via the electrolysis unit feedwater regulating valve 39. The water pump 33 and the fourth regenerator 29 are connected sequentially on the fuel side via pipelines. The reacted hydrogen gas is connected to the electrolysis working fluid water at the three-way mixing valve 30 via pipelines that connect the first hydrogen storage tank 32, the first blower 28, the fuel side of the second regenerator 26, and the fuel side of the third regenerator 27. After passing through the fuel side of the molten salt heat exchanger 23 of the electrolysis unit, it enters the fuel inlet end of the SOEC stack 24. The fuel outlet pipeline of the SOEC stack 24 sequentially passes through the exhaust gas side of the third regenerator 27, the fuel exhaust gas side of the second feedwater heater 14, the condenser 36 of the electrolysis unit, the steam-water separator 34 of the electrolysis unit, and the dryer 35 of the electrolysis unit before finally connecting to the fuel inlet end of the SOEC stack 24. The second hydrogen storage tank 38 is connected to form a closed fuel pipeline. The water separated by the steam-water separator 34 of the electrolysis unit enters the water storage tank 37 for storage. Outside air passes through the second fan 31, the first regenerator 25, the oxygen side of the molten salt heat exchanger 23 of the electrolysis unit, and enters the oxygen inlet end of the SOEC stack 24. The oxygen at the oxygen outlet end of the SOEC stack 24 passes through the tail gas side of the first regenerator 25, the tail gas side of the second regenerator 26, the tail gas side of the fourth regenerator 29, and the oxygen tail gas side of the first feedwater heater 13, and finally enters the boiler of the coal-fired unit through the boiler combustion stabilization valve 42 or is discharged to the outside environment through the air exhaust valve 43.

[0024] The reaction temperature of the SOEC electrolysis unit is provided by a molten salt heating unit, which includes a molten salt feed water heater 15, a thermal storage medium cold tank 16, a thermal storage medium cold tank outlet regulating valve 17, a thermal storage medium cold tank outlet pump 18, a thermal storage medium flue gas heater 19, a thermal storage medium hot tank 20, a thermal storage medium hot tank outlet regulating valve 21, a thermal storage medium hot tank outlet pump 22, and an electrolysis unit molten salt heat exchanger 23. The thermal storage medium inlet of the thermal storage medium flue gas heater 19 is connected to the thermal storage medium outlet of the thermal storage medium cold tank 16 through the thermal storage medium cold tank outlet pump 18 and the thermal storage medium cold tank outlet regulating valve 17. The thermal storage medium outlet of the thermal storage medium flue gas heater 19 is connected to the thermal storage medium... The inlet of the heat storage medium in the hot tank 20 is connected to the heat storage medium inlet via a pipeline. The outlet of the heat storage medium in the hot tank 20 is connected to the inlet of the molten salt heat exchanger 23 of the electrolysis unit via the outlet pump 22 and the outlet regulating valve 21 of the heat storage medium in the hot tank. The outlet of the molten salt heat exchanger 23 of the electrolysis unit is connected to the inlet of the heat storage medium in the cold tank 16 via the molten salt feedwater heater 15. The electrical energy of the SOEC electrolysis unit comes from the coal-fired generator set and is provided by the additional output power generated by the extraction working fluid flowing back to the turbine. The SOEC stack 24 is connected to the AC-to-DC inverter 41 via a cable. The AC-to-DC inverter 41 is connected to the power grid via the electrolysis unit switch 40.

[0025] When coal-fired power generating units operate under deep peak-shaving conditions, the efficiency of the high- and intermediate-pressure turbine cylinders decreases significantly. Taking the actual operating data of a 660MW single-reheat coal-fired power generating unit as an example: when the unit operates at 100% rated load, the high-pressure cylinder efficiency is 87.7%. However, when the unit operates at 50%, 40%, and 30% of rated load, the high-pressure cylinder efficiency drops to 79.4%, 78.7%, and 76.0%, respectively, causing an increase in coal consumption for power generation of 3.3%, 6.0%, and 9.1%, respectively. With the rapid development of renewable energy, deep peak-shaving operation will gradually become the normal operating condition for coal-fired power generating units, and the problem of a sharp increase in coal consumption for power generation due to the decline in turbine cylinder efficiency will become increasingly prominent. The efficiency of a steam turbine cylinder is directly related to the flow rate of the working fluid flowing through the turbine. Therefore, under low load conditions of a coal-fired power generation unit, a throttling method of reheating and extracting steam from the high and intermediate pressure cylinders of the steam turbine is adopted. This involves closing the reheating and extraction steam regulating valve 12, allowing the extraction working fluid to flow back from the feedwater heated in the deaerator 9 and high-pressure heater 11 to the high-pressure cylinder 2 and intermediate pressure cylinder 3 of the steam turbine to perform work. This increases the flow rate of the working fluid flowing through the high and intermediate pressure cylinders and improves the operating efficiency of the high and intermediate pressure cylinders. At the same time, the electrolysis unit switch 40 is opened, and the electrical energy output by the working fluid flowing back to the steam turbine is converted into DC power by the AC-to-DC inverter 41 and then stored in the SOEC electrolysis unit.

[0026] When the SOEC electrolysis unit is operating, the AC-to-DC inverter 41 absorbs the electrical energy from the coal-fired generator set, and the second blower 31 opens to draw oxygen-enriched air into the oxygen inlet of the SOEC stack 24. The oxygen-enriched air at the oxygen outlet of the SOEC stack 24 preheats the reaction gases through the first regenerator 25, the second regenerator 26, and the fourth regenerator 29, and also preheats the boiler feedwater through the first feedwater heater 13. The first blower 28 draws hydrogen from the first hydrogen storage tank 32, and simultaneously the electrolysis unit feedwater regulating valve 39 and the electrolysis unit water pump 33 are opened. The electrolysis unit water pump is adjusted... The turbine's intermediate pressure cylinder 3 outlet takes an appropriate amount of water and introduces it into the fourth regenerator 29, where it mixes with the hydrogen three-way mixing valve 30. The final mixed gas flows into the fuel side of the SOEC stack 24. The hydrogen produced by electrolysis and the hydrogen input from the front end of the SOEC stack are reheated by the third regenerator 27 to reheat the unreacted gas, and the feedwater is preheated by the second feedwater heater 14. Finally, the hydrogen and water flow into the second hydrogen storage tank 38 and the water storage tank 37 for storage through the electrolysis unit condenser 36, the electrolysis unit steam-water separator 34, and the electrolysis unit dryer 35, respectively. The minimum technical output of deep peak shaving for coal-fired power units is limited by the minimum stable combustion load on the boiler side. When the unit load is lower than this limit, problems such as water circulation deviating from the safe range, burner instability and flameout, and uneven furnace heat load causing water-cooled wall tube rupture seriously threaten the safe and stable operation of the unit. Therefore, the oxygen-enriched air after waste heat recovery is reused. The boiler stable combustion valve 42 and air exhaust valve 43 are adjusted so that the oxygen-enriched air after heat exchange is transported through pipelines and finally enters the furnace or is discharged to the external environment. This not only achieves stable combustion under low boiler load, but also avoids water-cooled wall vaporization or hydrodynamic safety problems caused by excessive heat absorption by the water-cooled wall.

[0027] SOEC electrolysis has a high temperature, which allows for the coupling of the coal-fired power unit's thermal system with the SOEC system using a heat storage medium, creating the reaction conditions required for the electrolysis reaction. When the SOEC electrolysis unit is operating, the outlet regulating valve 21 of the heat storage medium tank is opened, and the outlet pump 22 of the heat storage medium tank is started. The flow rate of the heat storage medium flowing out of the heat storage medium tank 20 is regulated by the outlet pump 22. The heat storage medium flowing out of the heat storage medium tank 20 flows through the molten salt heat exchanger 23 of the electrolysis unit to exchange heat with the reaction working fluid, and then... The feedwater is preheated by the molten salt feedwater heater 15, and the heat storage medium after waste heat utilization enters the heat storage medium cold tank 16. When the SOEC electrolysis unit is not working, the outlet regulating valve 17 of the heat storage medium cold tank is opened and the outlet pump 18 of the heat storage medium cold tank is started. The flow rate of the heat storage medium flowing out of the heat storage medium cold tank 16 is regulated by the outlet pump 18. The heat storage medium flowing out of the heat storage medium cold tank 16 flows through the heat storage medium flue gas heater 19 to exchange heat with the high temperature flue gas of the boiler before flowing to the heat storage medium hot tank 20.

[0028] This invention improves turbine cylinder efficiency by employing regenerative steam extraction throttling to increase the working fluid flow rate in the high and medium pressure cylinders during low-load operation of coal-fired power generating units. It also couples molten salt thermal storage and a solid oxide electrolysis (SOEC) cell, using SOEC to convert the additional electrical energy generated by the reflux working fluid into chemical energy and recovering the oxygen-enriched air produced by electrolysis to the boiler, thus improving the boiler's combustion stability under low load. Furthermore, it utilizes waste heat from the products and molten salt thermal storage to heat the boiler feedwater, compensating for insufficient feedwater temperature caused by steam extraction throttling and ensuring SCR denitrification efficiency under low load. Through a rationally designed system configuration, this invention reduces the minimum technical output of the unit, achieving a flexible, efficient, safe, and clean synergistic improvement in the deep peak-shaving process of coal-fired power generating units.

Claims

1. A coal-fired power generation system coupled with SOEC, characterized in that: This includes the thermal system of coal-fired power generating units, solid oxide electrolyzers (SOEC), and molten salt thermal storage coupling systems; The thermal system of the coal-fired power generation unit includes a boiler (1), a high-pressure cylinder (2) of a steam turbine, an intermediate-pressure cylinder (3) of a steam turbine, a low-pressure cylinder (4) of a steam turbine, a generator (5), a condenser (6), a condensate pump (7), a low-pressure heater (8), a deaerator (9), a feedwater pump (10), a high-pressure heater (11), a steam turbine regenerative extraction regulating valve (12), a first feedwater heater (13), a second feedwater heater (14), and a molten salt feedwater heater (15); the superheated steam outlet of the boiler (1) and the steam outlet of the high-pressure cylinder (2) of the steam turbine... The inlets are connected by pipes. The extraction steam outlet of the high-pressure cylinder (2) of the steam turbine is connected to the steam inlet of the high-pressure heater (11) by pipes. A steam turbine regenerative extraction steam regulating valve (12) is installed on the connecting pipes to regulate the extraction steam flow. The steam outlet of the high-pressure cylinder (2) of the steam turbine is connected to the steam inlet of the intermediate-pressure cylinder (3) of the steam turbine through the boiler (1). The first-stage extraction steam outlet of the intermediate-pressure cylinder (3) of the steam turbine is connected to the steam inlet of the high-pressure heater (11) by pipes. The second-stage extraction steam outlet is connected to the steam inlet of the deaerator (9) by pipes. A turbine regenerative extraction steam regulating valve (12) is installed on the connecting pipeline to regulate the extraction steam flow. The steam outlet of the intermediate pressure cylinder (3) of the turbine is connected to the steam inlet of the low pressure cylinder (4) of the turbine through a pipeline. The extraction steam outlet of the low pressure cylinder (4) of the turbine is connected to the steam inlet of the low pressure heater (8) through a pipeline. The steam outlet of the low pressure cylinder (4) of the turbine is connected to the condenser (6) through a pipeline. The condensate working fluid outlet of the condenser (6) is connected to the condensate working fluid inlet of the low pressure heater (8) through a condensate pump (7). The low pressure heater (8) The condensate outlet of the boiler (1) is connected to the feedwater inlet of the deaerator (9). The feedwater outlet of the deaerator (9) is connected to the feedwater inlet of the high-pressure heater (11) via the feedwater pump (10). The feedwater inlet of the boiler (1) is connected to the feedwater outlet of the high-pressure heater (11) via the first feedwater heater (13), the second feedwater heater (14), and the molten salt feedwater heater (15). The high-pressure cylinder (2), the intermediate-pressure cylinder (3), and the low-pressure cylinder (4) of the turbine are coaxial and connected to the power grid via the generator (5). The solid oxide electrolytic cell (SOEC) and molten salt thermal storage coupling system includes an electrolysis unit molten salt heat exchanger (23), an SOEC stack (24), a first regenerator (25), a second regenerator (26), a third regenerator (27), a fourth regenerator (29), a three-way mixing valve (30), a first fan (28), a second fan (31), an electrolysis unit water pump (33), a first hydrogen storage tank (32), a second hydrogen storage tank (38), a water storage tank (37), an electrolysis unit condenser (36), an electrolysis unit steam-water separator (34), an electrolysis unit dryer (35), an electrolysis unit feedwater regulating valve (39), a boiler combustion stabilizing valve (42), an air exhaust valve (43), and various connecting components. The piping between the equipment includes the following components: molten salt heat exchanger (23), SOEC stack (24), first regenerator (25), second regenerator (26), third regenerator (27), first fan (28), fourth regenerator (29), three-way mixing valve (30), second fan (31), first hydrogen storage tank (32), electrolysis unit water pump (33), electrolysis unit steam-water separator (34), electrolysis unit dryer (35), electrolysis unit condenser (36), water storage tank (37), and second hydrogen storage tank (38), forming the SOEC electrolysis unit. The working fluid water for electrolysis comes from the outlet of the intermediate pressure cylinder (3) of the steam turbine and is connected to the SOEC electrolysis unit by the electrolysis unit feedwater regulating valve (39). The reaction hydrogen is connected to the working fluid water at the three-way mixing valve (30) via pipelines through the fuel side of the electrolysis unit water pump (33) and the fourth regenerator (29). The reaction hydrogen is connected to the first hydrogen storage tank (32), the first blower (28), the fuel side of the second regenerator (26), and the fuel side of the third regenerator (27). After passing through the fuel side of the molten salt heat exchanger (23) of the electrolysis unit, it enters the fuel inlet end of the SOEC stack (24). The fuel outlet pipeline of the SOEC stack (24) passes through the tail gas side of the third regenerator (27), the fuel tail gas side of the second feedwater heater (14), the condenser (36) of the electrolysis unit, the steam-water separator (34) of the electrolysis unit, and the dryer (35) of the electrolysis unit in sequence. Finally, it is connected to the second hydrogen storage tank (38) to form a closed fuel pipeline. The water separated by the steam-water separator (34) of the electrolysis unit enters the water storage tank (37) for storage. The outside air passes through the second fan (31), the first regenerator (25), the oxygen side of the molten salt heat exchanger (23) of the electrolysis unit, and enters the oxygen inlet end of the SOEC stack (24). The oxygen at the oxygen outlet end of the SOEC stack (24) passes through the tail gas side of the first regenerator (25), the tail gas side of the second regenerator (26), the tail gas side of the fourth regenerator (29), and the oxygen tail gas side of the first feedwater heater (13), and finally enters the coal-fired unit boiler through the boiler combustion stabilization valve (42) or is discharged to the outside environment through the air exhaust valve (43).

2. A coal-fired power generation system coupled with SOEC according to claim 1, characterized in that: The reaction temperature of the SOEC electrolysis unit is provided by the molten salt heating unit, which includes a molten salt feed water heater (15), a thermal storage medium cold tank (16), a thermal storage medium cold tank outlet regulating valve (17), a thermal storage medium cold tank outlet pump (18), a thermal storage medium flue gas heater (19), a thermal storage medium hot tank (20), a thermal storage medium hot tank outlet regulating valve (21), a thermal storage medium hot tank outlet pump (22), and an electrolysis unit molten salt heat exchanger (23). The thermal storage medium inlet of the thermal storage medium flue gas heater (19) is connected to the thermal storage medium outlet of the thermal storage medium cold tank (16) through the thermal storage medium cold tank outlet pump (18) and the thermal storage medium cold tank outlet regulating valve (17). The thermal storage medium outlet of the thermal storage medium flue gas heater (19) is connected to the thermal storage medium outlet of the thermal storage medium cold tank (16). The inlet of the heat storage medium of the heat storage medium tank (20) is connected to the heat storage medium outlet of the heat storage medium tank (20) and the inlet of the molten salt heat exchanger (23) of the electrolysis unit through the heat storage medium tank outlet pump (22) and the heat storage medium tank outlet regulating valve (21). The outlet of the molten salt heat exchanger (23) of the electrolysis unit and the inlet of the heat storage medium of the cold tank (16) of the heat storage medium are connected to the molten salt feed water heater (15). The electrical energy of the SOEC electrolysis unit comes from the coal-fired generator set and is provided by the additional output power generated by the extraction working fluid flowing back to the turbine. The SOEC stack (24) is connected to the AC-to-DC inverter (41) through a cable. The AC-to-DC inverter (41) is connected to the power grid through the electrolysis unit switch (40).

3. The deep peak-shaving operation method for a coal-fired power generation system coupled with SOEC as described in claim 2, characterized in that: When a coal-fired power generation unit is operating under deep peak shaving conditions, the operating efficiency of the high and intermediate pressure cylinders of the turbine decreases significantly. Since the turbine cylinder efficiency is directly related to the flow rate of the working fluid flowing through the turbine, a throttling method of reheating and extracting steam from the high and intermediate pressure cylinders of the turbine is adopted under low load conditions. That is, the turbine reheating and extraction steam regulating valve (12) is closed, so that the extraction working fluid, which is heated in the deaerator (9) and the high pressure heater (11), flows back to the high pressure cylinder (2) and the intermediate pressure cylinder (3) of the turbine to do work, thereby increasing the flow rate of the working fluid flowing through the high and intermediate pressure cylinders of the turbine and improving the operating efficiency of the high and intermediate pressure cylinders of the turbine. At the same time, the electrolysis unit switch (40) is opened, and the electrical energy output by the working fluid flowing back to the turbine is converted into DC power by the AC to DC inverter (41) and then enters the SOEC electrolysis unit for storage. When the SOEC electrolysis unit is working, the AC-to-DC inverter (41) absorbs the electrical energy of the coal-fired generator set, and the second blower (31) is turned on to flow oxygen-enriched air into the oxygen inlet of the SOEC stack (24); the oxygen-enriched air at the oxygen outlet of the SOEC stack (24) is preheated by the reaction gas through the first regenerator (25), the second regenerator (26) and the fourth regenerator (29), and preheated by the boiler feedwater through the first feedwater heater (13). The oxygen-enriched air after waste heat recovery is conducive to the stable combustion of the boiler. At this time, the boiler combustion stabilization valve (42) and the air exhaust valve (43) are adjusted so that the oxygen-enriched air after heat exchange is transported through the pipeline and finally enters the furnace or is discharged to the outside environment. This achieves stable combustion of the boiler under low load and avoids water-cooled wall vaporization or hydrodynamic safety problems; the first blower (21) is turned on to flow oxygen-enriched air into the furnace or discharge to the outside environment through the pipeline. This achieves stable combustion of the boiler under low load and avoids water-cooled wall vaporization or hydrodynamic safety problems; the first blower (21) is turned on to flow oxygen-enriched air into the furnace. 8) Hydrogen is drawn from the first hydrogen storage tank (32), and the feedwater regulating valve (39) and the water pump (33) of the electrolysis unit are opened at the same time. By adjusting the speed of the water pump of the electrolysis unit, an appropriate amount of water is taken from the outlet of the intermediate pressure cylinder (3) of the steam turbine and introduced into the fourth regenerator (29) and mixed with the hydrogen three-way mixing valve (30). Finally, the mixed gas flows into the fuel side of the SOEC stack (24). The hydrogen generated by electrolysis and the hydrogen input at the front end of the SOEC stack are reheated by the third regenerator (27) for the unreacted gas, and the feedwater is preheated by the second feedwater heater (14). Finally, the hydrogen and water flow into the second hydrogen storage tank (38) and the water storage tank (37) respectively through the condenser (36) of the electrolysis unit, the steam-water separator (34) of the electrolysis unit, and the dryer (35) of the electrolysis unit for storage. When the SOEC electrolysis unit is working, the outlet regulating valve (21) of the thermal storage medium tank is opened, and the outlet pump (22) of the thermal storage medium tank is started. The flow rate of the thermal storage medium flowing out of the thermal storage medium tank (20) is regulated by the outlet pump (22). The thermal storage medium flowing out of the thermal storage medium tank (20) flows through the molten salt heat exchanger (23) of the electrolysis unit to exchange heat with the working medium, creating the reaction conditions required for the electrolysis reaction. Then, the feed water is preheated by the molten salt feed water heater (15), and the waste heat is used to preheat the feed water. After use, the heat storage medium enters the heat storage medium cold tank (16). When the SOEC electrolysis unit is not working, the outlet regulating valve (17) of the heat storage medium cold tank is opened and the outlet pump (18) of the heat storage medium cold tank is started. The flow rate of the heat storage medium flowing out of the heat storage medium cold tank (16) is regulated by the outlet pump (18). The heat storage medium flowing out of the heat storage medium cold tank (16) flows through the heat storage medium flue gas heater (19) and exchanges heat with the high temperature flue gas of the boiler before flowing to the heat storage medium hot tank (20).

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