Deep peak regulation method for coal-fired unit

Abstract

The invention provides a deep peak regulation method for a coal-fired unit, relates to the technical field of thermal power generation, and can solve the problem of low-load flame shift, stabilize the combustion core and inhibit the fluctuation of NOx emission concentration by dynamically regulating and controlling a combustion field in a boiler. The energy storage system and the boiler are configured for cooperative operation, the energy storage system is used for rapidly transferring / releasing heat energy, the limitation of the heat storage rate of the boiler is broken through, the two-way peak regulation capacity and the regulation speed of the coal-fired unit in the load reducing stage and the load increasing stage can be remarkably improved, and therefore the boiler efficiency is improved under the low load, and the station service power consumption rate is reduced. By constructing an intelligent control system in communication connection with the DCS, automatic control can be realized.

Description

Technical Field

[0001] This invention relates to the field of thermal power generation technology, and in particular to a deep peak shaving method for coal-fired power units. Background Technology

[0002] In thermal power plants, coal-fired units include boilers and steam turbines. The boiler's air inlet is connected to an air preheater for preheating the air. 30MW-class coal-fired units, as the main force for peak shaving in regional power grids, need to frequently operate at 20% to 50% of rated load (low load), which presents three major drawbacks: 1. Poor combustion stability: Under low load, the ignition delay of pulverized coal is high (>80ms), the flame center offset is large (>15°), and NO... x Emissions fluctuate significantly (±80ppm); 2. Slow response speed: The boiler's heat storage release speed is slow (<2MW / min), resulting in a slow response speed to load change rate; 3. Economic deterioration: When operating at 50% of rated load, boiler efficiency drops to 82% (92% under rated conditions), and plant power consumption rate rises to 8.5%.

[0003] Existing solutions such as oxygen-enriched combustion (increasing costs by 12%) and plasma ignition (equipment investment > 5 million yuan) present a contradiction between economic efficiency and technological adaptability. Therefore, there is an urgent need to develop new dynamic control technologies. Summary of the Invention

[0004] In view of the above, the present invention provides a deep peak shaving method for coal-fired power units, which aims to solve at least one of the defects pointed out in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for deep peak shaving of coal-fired power units, comprising: Step S1: Configure a combustion field control system to dynamically control the combustion field inside the boiler, ensuring that the flame center positioning error is ≤0.5m, stabilizing the pulverized coal ignition distance in the range of 1.2-1.5m, and controlling the flame center height in the range of 1.2-1.6m. Step S2: Configure an energy storage system to enable the coal-fired power unit to have bidirectional peak-shaving capability during both load reduction and load increase phases; During the load reduction and peak shaving phase of coal-fired power units: the tail flue gas of the boiler is introduced into the energy storage system to absorb the waste heat of the flue gas; during the load increase and peak shaving phase of coal-fired power units: the waste heat of the flue gas absorbed by the energy storage system is released to the upstream of the air preheater to increase the air supply temperature of the air preheater; the air preheater is used to preheat the air entering the boiler. Step S3: Construct an intelligent control system that communicates with the DCS system. The intelligent control system predicts the combustion state through digital twins and controls NO. xEmission concentration fluctuations are controlled within ±15ppm.

[0006] In some embodiments of the present invention, step S1 includes: Step S11: Distribute 12 sets of φ300mm swirl secondary air nozzles evenly in the tangential burner area at the four corners of the boiler; The opening and outlet angle of the swirl secondary air nozzles are adjusted by the actuator, the wind speed is continuously adjustable from 0-80m / s, and the angle deflection is ±30°; Deploy flame center position monitoring instruments and laser particle imaging velocimeters inside the boiler. Step S12: Optimize the wind speed-angle combination through CFD simulation; Step S13: When the load of the coal-fired unit drops below 30% of the rated value, it automatically switches to a 45m / s wind speed and +15° upward tilt mode to forcibly raise the flame center height by 0.3m; when the coal-fired unit is in the 30%-50% load range, it automatically switches to a 60m / s wind speed and 0° horizontal mode.

[0007] In some embodiments of the present invention, the energy storage system includes: a cold tank, a hot tank, a first heat exchanger, a second heat exchanger, and a molten salt pump; In some embodiments of the present invention, molten salt is stored in the cold tank and the hot tank; the molten salt in the cold tank can flow through the cold side of the first heat exchanger, and the tail flue gas of the boiler can flow through the hot side of the first heat exchanger; the molten salt in the hot tank can flow through the hot side of the second heat exchanger, and the air flows through the cold side of the second heat exchanger before entering the air preheater, and the molten salt in the hot tank and the air exchange heat in the second heat exchanger.

[0008] In some embodiments of the present invention, the components of the molten salt include, by weight, 60% NaNO3 and 40% KNO3.

[0009] In some embodiments of the invention, the cold tank is equipped with a heater.

[0010] In some embodiments of the present invention, the hot tank volume is 60 m³. 3 80 m³ of cold storage tank 3 .

[0011] In some embodiments of the present invention, step S2 includes: Step S21: Configure the energy storage system; Step S22: During the load reduction and peak shaving phase of the coal-fired unit: the 350-400℃ tail flue gas of the boiler is introduced into the first heat exchanger, and molten salt is pumped through the first heat exchanger at a flow rate of 120t / h by a molten salt pump to absorb the waste heat of the flue gas. During the peak load adjustment phase of coal-fired power units: 560℃ molten salt is transported to the upstream of the air preheater, and the air supply temperature is increased from 235℃ to 320℃ through the second heat exchanger; Step S23: After the molten salt is cooled to 300°C by heat exchange, it enters the cold tank; when the temperature inside the cold tank is less than 240°C, the heater is started to maintain the operating temperature of the cold tank ≥240°C.

[0012] In some embodiments of the present invention, step S3 includes: Step S31: The intelligent control system collects multi-dimensional parameters from the DCS system in real time through the OPC UA protocol, and inputs them into the LSTM time series prediction model after normalization processing.

[0013] Step S32: Predict the flame center location and NO using the LSTM time series prediction model. x Key indicators such as concentration were used to obtain prediction results; Step S33: Drive the model predictive controller to solve the multi-objective optimization problem online through the prediction results to obtain the dynamic control parameters; the dynamic control parameters include the wind speed-angle combination of the swirl secondary air nozzle and the rotation speed of the molten salt pump.

[0014] Step S34: Based on dynamic control parameters, dynamically control the operating status of the combustion field and energy storage system in the boiler.

[0015] In some embodiments of the present invention, the training method of the LSTM time series prediction model is as follows: The training was conducted using historical data, with a sampling period of 6 months and a data volume of 2TB, which was divided into: 80% training set, 15% validation set, and 5% test set; the LSTM time series prediction model was optimized using the Adam optimizer during training.

[0016] In some embodiments of the present invention, step S34 includes: The model predictive controller aims to achieve NOx ≤ 35mg / Nm³ and combustion efficiency ≥ 98%. Under the constraints of a primary air rate of 20-35%, molten salt temperature at the hot tank inlet of 300-560℃, and flame center height of 1.2m-1.6m, it dynamically calculates the optimal combination of wind speed and angle of the swirling secondary air nozzle and the molten salt pump speed command.

[0017] The embodiments of the present invention have at least the following advantages or beneficial effects: By dynamically controlling the combustion field inside the boiler, the problem of flame deviation under low load can be solved, the combustion core can be stabilized, and NO can be suppressed. x Fluctuations in emission concentrations. By configuring an energy storage system to operate in conjunction with the boiler, and utilizing the energy storage system to rapidly transfer / release heat energy, the limitations of boiler heat storage rate can be overcome. This significantly improves the bidirectional peak-shaving capability and regulation speed of coal-fired units during load reduction and load increase phases, thereby increasing boiler efficiency and reducing plant power consumption under low load conditions. Automated control can be achieved by constructing an intelligent control system that communicates with the DCS system.

[0018] Other features and advantages of the present invention will be set forth in the following description. Detailed Implementation

[0019] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention.

[0020] The embodiments of the present invention will be described in detail below.

[0021] This embodiment provides a deep peak-shaving method for coal-fired power units, including the following steps: Step S1: Configure a combustion field control system to dynamically control the combustion field inside the boiler, ensuring that the flame center positioning error is ≤0.5m, stabilizing the pulverized coal ignition distance in the range of 1.2-1.5m, and controlling the flame center height in the range of 1.2-1.6m, thereby solving the problem of flame deviation under low load and stabilizing the combustion core.

[0022] Pulverized coal ignition distance: The axial distance measured downstream (in the upward direction of the flame) along the centerline of the furnace from the end face of the primary air nozzle. Flame center height: The axial height upward with the end face of the primary air nozzle as the zero point (a positive value indicates that it is higher than the end face of the nozzle). The primary air nozzle is used to eject pulverized coal.

[0023] Step S2: Configure an energy storage system to enable the coal-fired power unit to have bidirectional peak-shaving capability during both load reduction and load increase phases; When the power grid requires a rapid decrease in load, that is, during the load reduction and peak shaving phase of coal-fired units: the tail flue gas of the boiler is introduced into the energy storage system to absorb the waste heat of the flue gas. When the power grid requires a rapid load recovery, that is, during the peak load shaving phase of coal-fired units: the waste heat from the flue gas absorbed by the energy storage system is released upstream of the air preheater to increase the air supply temperature of the air preheater. The air preheater is used to preheat the air entering the boiler.

[0024] Step S3: Construct an intelligent control system that communicates with the DCS system. The intelligent control system predicts the combustion state through digital twins and controls NO. x Emission concentration fluctuations are controlled within ±15ppm to dynamically balance environmental protection and economic efficiency.

[0025] By dynamically controlling the combustion field inside the boiler, the problem of flame deviation under low load can be solved, the combustion core can be stabilized, and NO can be suppressed. xFluctuations in emission concentrations. By configuring an energy storage system to operate in conjunction with the boiler, and utilizing the energy storage system to rapidly transfer / release heat energy, the limitations of boiler heat storage rate can be overcome. This significantly improves the bidirectional peak-shaving capability and regulation speed of coal-fired units during load reduction and load increase phases, thereby increasing boiler efficiency and reducing plant power consumption under low load conditions. Automated control can be achieved by constructing an intelligent control system that communicates with the DCS system.

[0026] The combustion field control system includes a secondary air nozzle, a flame center position monitoring instrument (visible light monitoring), a laser particle imaging velocimeter (PIV), and an actuator; the opening of the swirling secondary air nozzle supports stepless adjustment from 0 to 100%; the opening and air outlet angle (pitch angle) of the swirling secondary air nozzle are adjusted by the actuator.

[0027] Step S1 includes: Step S11: Distribute 12 sets of φ300mm swirl secondary air nozzles evenly in the tangential burner area at the four corners of the boiler; the opening and pitch angle (outlet angle) of the swirl secondary air nozzles are adjusted by actuators, with the air velocity continuously adjustable from 0-80m / s and the angle deflection ±30°. Deploy flame center position monitoring instruments and laser particle imaging velocimeters inside the boiler to trigger the corresponding actuators to adjust the opening and outlet angle of the swirl secondary air nozzles with real-time feedback data (response delay ≤2s).

[0028] Step S12: Optimize the wind speed-angle combination through CFD simulation; for example: 45m / s wind speed, +15°; 60m / s wind speed, 0°.

[0029] Step S13: When the load of the coal-fired unit drops below 30% of the rated value, automatically switch to a 45m / s wind speed, +15° upward tilt mode (outlet air angle 15° upward) to forcibly raise the flame center height by 0.3m (confirmed by PIV flow field test: for every 5° increase in the secondary air deflection angle, the flame center moves upward by 0.3m (R)). 2 =0.96)); When the coal-fired unit is in the 30%-50% load range, it will automatically switch to a wind speed of 60m / s and a 0° horizontal mode (horizontal air outlet) to ensure that the flame center positioning error is ≤0.5m, stabilize the pulverized coal ignition distance in the range of 1.2-1.5m, and control the flame center height in the range of 1.2-1.6m; the wind speed is adjusted by adjusting the opening of the swirl secondary air nozzle.

[0030] The energy storage system includes a molten salt energy storage unit (energy storage density ≥120kWh / m³, charge / discharge efficiency ≥90%), enabling the coal-fired unit to adjust its capacity from 30MW to 15MW within 15 minutes, or from 15MW to 30MW within 15 minutes. The molten salt energy storage unit includes a cold tank (80m³, operating temperature ≥220℃), a hot tank (60m³, operating temperature ≥560℃), a first heat exchanger, a second heat exchanger, and a molten salt pump. 3 80 m cold tank 3 The total heat storage is approximately 200 MWh (multiple hot and cold tanks are possible). The cold tank stores molten salt at 240°C, which flows through the cold side (tube side) of the first heat exchanger, while the boiler's tail gas flows through the hot side (shell side). Heat exchange occurs between the molten salt in the cold tank and the tail gas in the first heat exchanger. The cold tank is equipped with a heater to maintain an operating temperature ≥240°C to prevent the molten salt from solidifying. The hot tank stores molten salt at 560°C, which flows through the hot side of the second heat exchanger. Air flows through the cold side of the second heat exchanger before entering the air preheater, where heat exchange occurs between the molten salt in the hot tank and the air, raising the supply air temperature from 235°C to 320°C, achieving an instantaneous release of 15MW of thermal energy. The molten salt uses a binary nitrate formula (by weight): 60% NaNO3 + 40% KNO3 (eutectic salt, melting point approximately 220°C). Molten salt pumps are used to connect cold and hot tanks to form a circulation path, allowing molten salt (working fluid) to circulate between the two tanks. Molten salt pump parameters: power 75kW (frequency converter control, speed 1450-2900rpm), rated head 320 m, efficiency 78%.

[0031] Step S2 includes: Step S21: Configure the above-mentioned molten salt energy storage device (energy storage system); Step S22: During the load reduction and peak shaving phase of the coal-fired unit: the 350-400℃ tail flue gas of the boiler is introduced into the first heat exchanger, and molten salt is pumped through the first heat exchanger at a flow rate of 120t / h by a molten salt pump to absorb the waste heat of the flue gas (energy storage rate 10MW / h). During the peak load shaving phase of coal-fired power units: molten salt at 560℃ is transported to the upstream of the air preheater, and the supply air temperature is increased from 235℃ to 320℃ through the second heat exchanger (shell-side heat transfer coefficient ≥80W / m²K, tube-side design pressure 12 MPa), achieving instantaneous release of 15MW-level thermal energy. Step S23: After the molten salt is cooled to 300°C by heat exchange, it enters the cold tank; when the temperature inside the cold tank is less than 240°C, the heater is started to maintain the operating temperature of the cold tank at ≥240°C to prevent solidification.

[0032] Step S3 includes: Step S31: The intelligent control system acquires multi-dimensional parameters (20+ dimensions, including coal calorific value, secondary air volume ratio, NO) in real time via the OPC UA protocol (sampling frequency 1Hz) from the DCS system. x Emission concentrations, etc., are normalized and then input into the LSTM (Long Short-Term Memory) time series prediction model.

[0033] Step S32: Predict the flame center location and NO using the LSTM time series prediction model. x Key indicators such as concentration were used to obtain prediction results; Training methods for LSTM time series prediction models: The training was conducted using historical data, with a sampling period of 6 months and a data volume of 2TB, divided into: 80% training set, 15% validation set, and 5% test set; the LSTM time series prediction model was optimized using the Adam optimizer (learning rate 0.001) during training.

[0034] Step S33: The prediction results drive the Model Predictive Controller (MPC) to solve the multi-objective optimization problem online, obtaining dynamic control parameters. These parameters include the velocity-angle combination of the swirl secondary air nozzle (the opening and pitch angle of the swirl secondary air nozzle) and the molten salt pump speed. The MPC settings are: 20 steps (200 s) in the prediction time domain, 5 steps (50 s) in the control time domain, with a step size of 10 s. The 20-step prediction time domain with a step size of 10 s matches the DCS system sampling frequency (1Hz) while avoiding frequent actuator wear, covering the complete delay time (approximately 180 seconds) from fuel change to NOx generation in the boiler.

[0035] Step S34: Based on dynamic control parameters, dynamically control the operating status of the combustion field and energy storage system in the boiler, including: the model predictive controller aims to meet NOx≤35mg / Nm³ and combustion efficiency≥98%, and dynamically calculates the optimal combination of wind speed and angle of the swirl secondary air nozzle and the molten salt pump speed command under the constraints of primary air rate of 20-35% (referring to the volume percentage of primary air (air carrying pulverized coal) entering the burner between 20% and 35% of the total combustion air volume), molten salt temperature at the hot tank inlet of 300-560℃, and flame center height of 1.2m-1.6m, and refreshes the dynamic control parameters every 10 seconds.

[0036] After implementing the above method: Investment payback period: 4.2 years (excluding carbon trading revenue); The energy storage system can release 120MWh of thermal energy within 15 minutes, raising the air supply temperature of the air preheater by 85°C; LSTM time series prediction model for NO xThe concentration prediction error is ≤4.7%, and the driven model predictive controller (MPC) reduces the deviation of combustion parameters by 62%.

[0037] Finally, it should be noted that the above are merely preferred embodiments of this application and are not intended to limit this application. For those skilled in the art, this application can have various modifications and variations. Without conflict, the embodiments and features described in the embodiments of this application can be arbitrarily combined with each other. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for deep peak shaving of coal-fired power units, characterized in that, include: Step S1: Configure a combustion field control system to dynamically control the combustion field inside the boiler, ensuring that the flame center positioning error is ≤0.5m, stabilizing the pulverized coal ignition distance in the range of 1.2-1.5m, and controlling the flame center height in the range of 1.2-1.6m. Step S2: Configure an energy storage system to enable the coal-fired power unit to have bidirectional peak-shaving capability during both load reduction and load increase phases; During the load reduction and peak shaving phase of coal-fired power units: the tail flue gas of the boiler is introduced into the energy storage system to absorb the waste heat of the flue gas; during the load increase and peak shaving phase of coal-fired power units: the waste heat of the flue gas absorbed by the energy storage system is released to the upstream of the air preheater to increase the air supply temperature of the air preheater; the air preheater is used to preheat the air entering the boiler. Step S3: Construct an intelligent control system that communicates with the DCS system. The intelligent control system predicts the combustion state through digital twins and controls NO. x Emission concentration fluctuations are controlled within ±15ppm.

2. The deep peak-shaving method for coal-fired power units according to claim 1, characterized in that, Step S1 includes: Step S11: Distribute 12 sets of φ300mm swirl secondary air nozzles evenly in the tangential burner area at the four corners of the boiler; The opening and outlet angle of the swirl secondary air nozzles are adjusted by the actuator, the wind speed is continuously adjustable from 0-80m / s, and the angle deflection is ±30°; Deploy flame center position monitoring instruments and laser particle imaging velocimeters inside the boiler. Step S12: Optimize the wind speed-angle combination through CFD simulation; Step S13: When the load of the coal-fired unit drops below 30% of the rated value, it automatically switches to a 45m / s wind speed and +15° upward tilt mode to forcibly raise the flame center height by 0.3m; when the coal-fired unit is in the 30%-50% load range, it automatically switches to a 60m / s wind speed and 0° horizontal mode.

3. The deep peak-shaving method for coal-fired power units according to claim 1, characterized in that, The energy storage system includes: a cold tank, a hot tank, a first heat exchanger, a second heat exchanger, and a molten salt pump; Molten salt is stored in both the cold and hot tanks. The molten salt in the cold tank can flow through the cold side of the first heat exchanger, and the flue gas from the tail end of the boiler can flow through the hot side of the first heat exchanger. The molten salt in the hot tank can flow through the hot side of the second heat exchanger. Before entering the air preheater, the air first flows through the cold side of the second heat exchanger, and the molten salt in the hot tank and the air exchange heat in the second heat exchanger.

4. The deep peak-shaving method for coal-fired power units according to claim 3, characterized in that, The molten salt components, by weight, include: 60% NaNO3 and 40% KNO3.

5. The deep peak-shaving method for coal-fired power units according to claim 4, characterized in that, The cold tank is equipped with a heater.

6. The deep peak-shaving method for coal-fired power units according to claim 3, characterized in that, Hot tank volume 60 m³ 3 80 m³ cold storage tank 3 .

7. The deep peak-shaving method for coal-fired power units according to claim 3, characterized in that, Step S2 includes: Step S21: Configure the energy storage system; Step S22: During the load reduction and peak shaving phase of the coal-fired unit: the 350-400℃ tail flue gas of the boiler is introduced into the first heat exchanger, and molten salt is pumped through the first heat exchanger at a flow rate of 120t / h by a molten salt pump to absorb the waste heat of the flue gas. During the peak load adjustment phase of coal-fired power units: 560℃ molten salt is transported to the upstream of the air preheater, and the air supply temperature is increased from 235℃ to 320℃ through the second heat exchanger; Step S23: After the molten salt is cooled to 300°C by heat exchange, it enters the cold tank; when the temperature inside the cold tank is less than 240°C, the heater is started to maintain the operating temperature of the cold tank ≥240°C.

8. The deep peak-shaving method for coal-fired power units according to claim 2, characterized in that, Step S3 includes: Step S31: The intelligent control system collects multi-dimensional parameters from the DCS system in real time through the OPC UA protocol, and inputs them into the LSTM time series prediction model after normalization. Step S32: Predict the flame center location and NO using the LSTM time series prediction model. x Key indicators such as concentration were used to obtain prediction results; Step S33: Drive the model predictive controller to solve the multi-objective optimization problem online through the prediction results to obtain the dynamic control parameters; the dynamic control parameters include the wind speed-angle combination of the swirl secondary air nozzle and the rotation speed of the molten salt pump; Step S34: Based on dynamic control parameters, dynamically control the operating status of the combustion field and energy storage system in the boiler.

9. The deep peak-shaving method for coal-fired power units according to claim 8, characterized in that, Training methods for LSTM time series prediction models: The training was conducted using historical data, with a sampling period of 6 months and a data volume of 2TB, which was divided into: 80% training set, 15% validation set, and 5% test set; the LSTM time series prediction model was optimized using the Adam optimizer during training.

10. The deep peak-shaving method for coal-fired power units according to claim 8, characterized in that, Step S34 includes: The model predictive controller aims to achieve NOx ≤ 35mg / Nm³ and combustion efficiency ≥ 98%. Under the constraints of a primary air rate of 20-35%, molten salt temperature at the hot tank inlet of 300-560℃, and flame center height of 1.2m-1.6m, it dynamically calculates the optimal combination of wind speed and angle of the swirling secondary air nozzle and the molten salt pump speed command.