A quick load change control system and method for a medium speed coal mill grinding process

Abstract

The present application relates to the technical field of power plant boiler deep peak regulation, and discloses a quick load variation control system and method for the grinding process of a medium-speed coal mill. The system comprises a coal feeding unit, a grinding unit, a coal combustion unit, a hot air adjusting unit, a differential pressure control unit, a stone coal processing unit and a DCS control unit, and realizes load adjustment by coordinately controlling the coal feeding amount, the hot air volume and the differential pressure of the coal mill. The method comprises the following steps: after receiving an AGC instruction of a power grid, the coal feeding amount and the opening degree of the hot air adjusting valve are adjusted in advance by a preset time, the coal mill is used as a temporary coal bunker to dynamically control the coal powder reserve, and the load response rate is optimized in real time in combination with the differential pressure feedback. The present application shortens the response time of the coal pulverizing system to the order of seconds by predictive control without modifying the coal mill body, meets the 3%-5% Pe / min peak regulation rate requirement, improves the flexibility and economy of the deep peak regulation of the coal power unit, and ensures the operation reliability under complex coal quality conditions.

Description

Technical Field

[0001] This invention relates to the field of deep peak shaving technology for power plant boilers, specifically to a rapid load change control system and method for the grinding process of a medium-speed coal mill. Background Technology

[0002] As the global energy structure transitions towards a low-carbon model, the penetration rate of new energy power generation, especially wind and solar power, in the power grid is continuously increasing. To effectively absorb intermittent and fluctuating new energy power, the role of traditional coal-fired power generating units is undergoing a profound transformation, requiring them to evolve from a baseload operation mode to a deep peak-shaving mode. Specifically, current regional power grids are imposing more stringent requirements on the load regulation depth of coal-fired power units, generally requiring a minimum output capacity of 30%, and even as high as 20% for some power plants. This means that units need to frequently adjust within a wide load range of 30% to 100% during daily operation. Compared to the previous 50%-100% load range, the significant reduction in minimum output capacity aims to prioritize the smooth grid connection and stable operation of new energy power generation. At the same time, the power grid also has higher expectations for the load regulation rate of coal-fired units, increasing from 1%-2% Pe / min for traditional units to 3%-5% Pe / min for newly commissioned supercritical and ultra-supercritical units. This requirement for peak shaving that emphasizes both "depth" and "speed" has brought unprecedented challenges to the pulverizing systems of coal-fired power plants.

[0003] As a crucial upstream component of boiler combustion, the pulverizing system's response speed directly constrains the boiler's overall load response capability. In traditional pulverizing systems, after the power grid issues a load increase / decrease command, there is an inherent physical delay of approximately 3 minutes between the coal feeder adjusting the coal rate and the pulverized coal being ground and transported to the boiler furnace with hot air. This delay primarily stems from the time required for coal grinding and drying in the pulverizer and its transport through pipelines. This time constant makes it difficult for the boiler's load response rate to meet the power grid's desired rapid load change requirement of 3%-5% Pe / min, resulting in a significant lag between the power grid's peak-shaving commands and the boiler's actual output, severely impacting the stable operation and dispatch flexibility of the power grid. Therefore, there is an urgent need in this field to develop novel boiler load change control methods to improve the response speed of the pulverizing system.

[0004] In exploring solutions to the aforementioned challenges, existing technologies have also been attempted. For example, Chinese patent CN120571684A discloses a variable load regulating pulverizing system and method. This system aims to monitor pulverizer operating data and generate dynamic separator speed and hot air parameter adjustment commands based on operating condition analysis. This, in turn, adjusts the internal circulation rate within the pulverizer to match the pulverizing system with load changes, thereby avoiding significant fluctuations in pulverizer parameters and improving operational performance. The core of this solution lies in indirectly controlling the residence time and fineness of pulverized coal within the pulverizer through multi-parameter coupled regulation, in order to optimize the pulverizer's operating state.

[0005] However, although the CN120571684A technical solution attempts to adapt to load changes to some extent by optimizing the internal operation of the coal mill, its inherent working mechanism still has significant limitations, making it difficult to meet the stringent "second-level" rapid response requirements of the current power grid. The reasons for this are mainly as follows: First, this solution relies heavily on the mechanical transmission and heat exchange processes involving parameters such as the dynamic separator speed and hot air flow rate. These physical processes themselves have considerable inertia, and their response time remains on the order of minutes, far from meeting the "second-level" response required by the power grid for a peak-shaving rate of 3%-5% Pe / min. No matter how finely the internal circulation is adjusted, the inherent physical lag cannot be fundamentally eliminated as long as the physical grinding, drying, and conveying of pulverized coal are involved. Second, this technical solution adopts a real-time feedback regulation mode. This means that the system only begins to respond and adjust relevant parameters after the automatic generation control (AGC) command from the power grid is issued. During this time, the coal mill still needs to undergo the complete physical process of "coal feeding, grinding, separation, and conveying," resulting in a response lag of approximately 3 minutes. No pre-emptive operation mechanism has been introduced to proactively anticipate and compensate for this inherent response "time lag." At a deeper level, this scheme uses "internal circulation rate" as its core control objective. However, the internal circulation rate primarily affects the grinding efficiency and coal powder fineness within the coal mill, and its correlation with the coal powder flux, which directly determines the boiler's combustion heat release rate, is relatively low. When a rapid change in boiler output is required, adjusting the internal circulation rate cannot directly and quickly translate into a rapid change in the boiler's fuel input. Furthermore, in actual operation, this scheme does not fully consider the interference of the accumulation of coke stones in the raw coal on the differential pressure monitoring of the coal mill. Especially when the coal quality is poor, the accumulation of coke stones will significantly change the gas-solid two-phase flow characteristics inside the coal mill, leading to distortion of the differential pressure monitoring signal and a decrease in control accuracy of more than 50%. This seriously affects its reliability and accuracy under complex and variable operating conditions. Finally, to implement this scheme, a dedicated dynamic separator and its supporting feedforward submodule are required. This not only increases the complexity of the system but also brings high modification costs. The modification cost of a single coal mill is as high as 200,000 to 300,000 yuan, making it difficult for this technology to be widely adopted in terms of economics and unable to meet the comprehensive requirements of rapid response, control accuracy, and economy in current deep peak shaving scenarios.

[0006] In summary, existing technical solutions for addressing the rapid response issue in deep peak shaving of coal-fired power units suffer from inherent physical lag, limitations of feedback control, insufficient correlation between control objectives and actual needs, lack of anti-interference capabilities, and high retrofit costs. These inherent contradictions make them insufficient to meet the increasingly stringent requirements of modern power grids for rapid, precise, and economical load variation control of coal-fired power units. Therefore, overcoming the inherent physical inertia of the pulverizing system and achieving rapid load variation control of the grinding process in medium-speed coal mills through an innovative method and system that balances rapid response, high precision, high reliability, and low retrofit costs has become a key challenge and an urgent technical problem for those skilled in the art. Summary of the Invention

[0007] This invention provides a rapid load change control system and method for the grinding process of a medium-speed coal mill, aiming to solve the problems of insufficient load response rate caused by the inherent physical lag of the pulverizing system of coal-fired power generation units in the prior art, and the difficulty of traditional feedback control strategies in meeting the stringent requirements of the power grid for "second-level" rapid load change response during deep peak shaving.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] On one hand, the present invention provides a rapid load change control system for the grinding process of a medium-speed coal mill, comprising:

[0010] The coal feeding unit includes a coal feeder and a coal chute connected together. The coal feeder is used to transport raw coal and regulate the coal feed rate. The grinding unit is a coal mill connected to the coal chute. The coal mill is used to grind raw coal into pulverized coal. The coal combustion unit includes a pulverized coal pipe and a boiler connected together. The output end of the coal mill is connected to the boiler through the pulverized coal pipe. The hot air regulating unit includes a hot air header, a hot air pipe connected to the hot air header, and a regulating valve installed on the hot air pipe. The hot air pipe is connected to the coal mill. The regulating valve is used to control the flow rate of hot air entering the coal mill to regulate the pulverized coal concentration and differential pressure inside the coal mill. The differential pressure control unit includes an electrically connected differential pressure measuring point and an analog-to-digital converter. The differential pressure measuring point is located on the upper part of the coal mill and is used to monitor the inlet and outlet differential pressure signals of the coal mill. The stone coal processing unit includes a stone coal output pipe and a stone coal collection device connected together. The lower part of the coal mill is connected to the stone coal collection device through the stone coal output pipe.

[0011] The control unit, a DCS system, is electrically connected to the coal feeder, regulating valve, and analog-to-digital converter. It receives automatic power generation control commands from the power grid and controls the coal feed rate and the opening of the regulating valve based on the differential pressure value monitored by the differential pressure measuring point and the coal powder output adjustment rate. The DCS system is configured to: before receiving the automatic power generation control command from the power grid, coordinate the coal feed rate of the coal feeder and the opening of the regulating valve according to the load change direction indicated by the command, thereby pre-adjusting the coal powder reserve inside the coal mill. This adjustment process is guided by monitoring the differential pressure value at the differential pressure measuring point. Upon receiving the automatic power generation control command, it rapidly adjusts the opening of the regulating valve according to the expected coal powder output adjustment rate to release or reduce coal powder output, achieving rapid load changes.

[0012] On the other hand, the present invention also provides a rapid load change control method for the grinding process of a medium-speed coal mill, comprising the following steps:

[0013] S1: Receive automatic generation control commands from the grid side through the DCS system to obtain the expected load change demand and corresponding peak shaving rate; the automatic generation control commands include the load change direction;

[0014] S2: When the automatic power generation control command indicates a rapid increase in load, the DCS system controls the coal feeder to increase the raw coal feed rate at a preset time before the automatic power generation control command is issued, and simultaneously controls the regulating valve to reduce the hot air flow rate entering the coal mill, so as to realize the coal mill as a temporary pulverizer, causing the differential pressure value monitored by the differential pressure measuring point inside the coal mill to rise, thereby increasing the coal powder reserve inside the coal mill; when the automatic power generation control command indicates a rapid decrease in load, the DCS system controls the coal feeder to reduce the raw coal feed rate at a preset time before the automatic power generation control command is issued, and simultaneously controls the regulating valve to increase the hot air flow rate entering the coal mill, causing the differential pressure value monitored by the differential pressure measuring point inside the coal mill to fall, thereby reducing the coal powder reserve inside the coal mill.

[0015] S3. When a rapid load increase command is issued, the DCS system controls the regulating valve to increase the hot air volume, carrying the coal powder stored in the coal mill to the boiler to match the rapid load increase demand; when a rapid load decrease command is issued, the DCS system controls the regulating valve to decrease the hot air volume, reducing the coal powder output of the coal mill to match the rapid load decrease demand.

[0016] S4: Based on the peak shaving rate of the automatic power generation control command, the DCS system sets the target value of the differential pressure at the inlet and outlet of the coal mill in stages, and uses this target value as the differential pressure control guide in step S2.

[0017] Preferably, the preset time is set to 15 minutes.

[0018] Preferably, the process also includes periodically performing a stone and coal venting operation, which includes: S5: controlling the hot air regulating valve through the DCS system to reduce the amount of hot air entering the coal mill until the minimum ventilation volume is reached, wherein the minimum ventilation volume is 30% to 40% of the rated ventilation volume of the coal mill; S6: monitoring the material level sensor signal of the stone and coal collection device or observing for a preset time to confirm that the stone and coal have been vented; S7: controlling the hot air regulating valve through the DCS system to increase the amount of hot air entering the coal mill until the normal ventilation volume is restored, wherein the normal ventilation volume is 60% to 80% of the rated ventilation volume of the coal mill.

[0019] Preferably, the stone and coal collection device uses an automatic conveying and discharging method or a manual discharging method for clearing and transporting stone and coal.

[0020] Preferably, in step S2, when the load change demand is a rapid increase in load, the differential pressure value monitored by the differential pressure measuring point increases to 2-3 kPa based on the original differential pressure, thereby increasing the coal powder concentration in the coal mill.

[0021] Preferably, in step S2, when the load change requires rapid load reduction, the differential pressure value monitored by the differential pressure measuring point decreases to 2-3 kPa based on the original differential pressure, thereby reducing the coal powder concentration in the coal mill.

[0022] Preferably, the DCS system controls the differential pressure value monitored by the differential pressure measuring point of the coal mill according to the peak shaving rate of the automatic power generation control command; if the peak shaving rate is ≥3%Pe / min, the differential pressure value is controlled at 3kPa; if the peak shaving rate is <3%Pe / min, the differential pressure value is controlled at 2kPa.

[0023] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0024] This invention innovatively uses a coal mill as a "temporary pulverized coal silo," employing a predictive control strategy to adjust the coal feed rate and hot air volume in advance before the power grid's AGC command is issued. It also precisely controls the pulverized coal reserve through the differential pressure value of the coal mill, effectively overcoming the inherent physical lag of traditional pulverizing systems. This technical solution requires no large-scale hardware modifications to the coal mill itself; it can be achieved solely through optimization of the DCS system algorithm and adjustment of the control logic, significantly reducing implementation costs and safety risks. The system and method can shorten the response time of the pulverizing system from several minutes to several seconds, enabling the load regulation rate of coal-fired units to meet the stringent requirements of the power grid for peak-shaving rates of 3%-5% Pe / min or even higher, greatly improving the flexibility and economy of coal-fired power units participating in deep peak shaving of the power grid. Simultaneously, by integrating a stone coal processing function, the accuracy of differential pressure measurement and the reliability of the system under complex coal quality conditions are ensured. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the rapid load change control system for the grinding process of a medium-speed coal mill according to the present invention.

[0026] Figure 2 This is a flowchart of the rapid load change control method for the grinding process of a medium-speed coal mill according to the present invention.

[0027] The attached figures are labeled as follows:

[0028] 1. Raw coal; 2. Coal feeder; 3. Coal chute; 4. Coal mill; 5. Hot air duct; 6. Hot air main duct; 7. Pulverized coal duct; 8. Boiler; 9. Differential pressure measuring point; 10. Analog-to-digital converter; 11. DCS system; 12. Stone and coal output pipeline; 13. Stone and coal collection device; 14. Regulating valve. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] Please refer to Figure 1 This invention provides a rapid load change control system for the grinding process of a medium-speed coal mill 4, comprising a coal feeding unit, a grinding unit, a coal combustion unit, a hot air regulating unit, a differential pressure control unit, a stone coal processing unit, and a control unit that work in sequence and in coordination.

[0031] Specifically, the coal feeding unit includes a coal feeder 2 and a coal chute 3. The coal feeder 2 is a belt-mounted feeder 2, equipped with a high-precision weighing sensor and a variable frequency speed-regulating motor, used to transport raw coal 1 to the inlet end of the coal chute 3 at a preset or dynamically adjusted rate according to received control commands. The coal chute 3 is a gravity conveying pipe, its inlet end mechanically connected to the outlet end of the coal feeder 2, and its outlet end mechanically connected to the feed inlet of the grinding unit, used to safely and stably guide raw coal 1 into the grinding unit. The variable frequency speed-regulating motor inside the coal feeder 2 precisely controls the linear speed of the belt, thereby precisely adjusting the conveying flow rate of raw coal 1, with a control accuracy within ±0.5% of the rated flow rate.

[0032] The grinding unit is a coal mill 4, specifically a medium-speed roller mill 4, such as an HP-type medium-speed coal mill 4. The feed end of the coal mill 4 is mechanically connected to the outlet end of the coal chute 3, and is used to receive the raw coal 1 conveyed by the coal chute 3. The coal mill 4 is equipped with grinding rollers, a grinding disc, and a dynamic-static separator. The raw coal 1 is pulverized by the grinding rollers rolling and crushing on the grinding disc. The coal mill 4 also has the function of drying the raw coal 1 and using hot air to carry out the coal powder. The design volume of the coal mill 4 allows it to temporarily store a certain amount of coal powder inside, serving as the core physical carrier of the "temporary powder silo" described in this invention.

[0033] The coal-fired unit includes a pulverized coal pipe 7 and a boiler 8. The pulverized coal outlet of the coal mill 4 is mechanically connected to the burner area of ​​the boiler 8 via the pulverized coal pipe 7. The pulverized coal pipe 7 is used to transport the pulverized coal produced by the coal mill 4 and the hot air carrying the pulverized coal. The boiler 8 is a coal-fired boiler used to receive and burn the pulverized coal to generate steam to drive a steam turbine generator set for power generation.

[0034] The hot air regulating unit includes a hot air header 6, a hot air duct 5, and a regulating valve 14 installed on the hot air duct 5. The hot air header 6 is part of the boiler 8's air supply system, providing high-temperature, high-pressure hot air. The hot air header 6 is connected to the hot air inlet of the coal mill 4 through the hot air duct 5. The regulating valve 14 installed on the hot air duct 5 is specifically a multi-blade or butterfly damper, precisely positioned by an electric or pneumatic actuator. The regulating valve 14 is used to precisely control the flow rate of hot air entering the coal mill 4 according to the instructions of the control unit, thereby regulating the coal powder concentration, drying efficiency, and powder carrying capacity inside the coal mill 4, and affecting the pressure difference between the inlet and outlet of the coal mill 4. The positioning accuracy of the regulating valve 14 can reach within ±0.2% of its full opening, and the response time is within 3 seconds.

[0035] The differential pressure control unit includes an electrically connected differential pressure measuring point 9 and an analog-to-digital converter 10. The differential pressure measuring point 9 is located at the pressure tap on the upper part of the coal mill 4, specifically in the gas-solid two-phase flow region between the hot air inlet and the pulverized coal outlet of the coal mill 4. The differential pressure measuring point 9 uses a high-precision differential pressure transmitter with a range of 0 to 10 kPa and an accuracy class of 0.1% FS, used for real-time and continuous monitoring of the differential pressure signal between the inlet and outlet of the coal mill 4. The signal output terminal of the differential pressure measuring point 9 is electrically connected to the analog-to-digital converter 10 via a signal cable. The analog-to-digital converter 10 uses a 16-bit high-resolution industrial-grade module with high-speed sampling capability and a sampling rate of 100 ms, used to accurately convert the analog current signal (e.g., 4-20mA) output by the differential pressure measuring point 9 into a digital signal, and transmits the digital signal to the control unit via an industrial Ethernet protocol (e.g., Modbus TCP or Ethernet / IP).

[0036] The stone and coal processing unit includes a stone and coal output pipe 12 and a stone and coal collection device 13. The lower part of the coal mill 4, namely the bottom conical hopper area of ​​the coal mill 4, is mechanically connected to the stone and coal collection device 13 through the stone and coal output pipe 12. The stone and coal output pipe 12 is a gravity chute made of wear-resistant material. The stone and coal collection device 13 is specifically a closed hopper structure, with an electric gate valve and a screw conveyor at its bottom. The stone and coal collection device 13 is equipped with a non-contact level sensor (such as an ultrasonic level gauge or a capacitive level gauge) for real-time monitoring of the accumulated amount of stone and coal. The stone and coal collection device 13 is used to periodically or irregularly collect and discharge the stone and coal separated from the raw coal 1 during the grinding process, so as to avoid excessive accumulation of stone and coal inside the coal mill 4, which would affect the normal operation of the coal mill 4 and the measurement accuracy of the differential pressure measuring point 9.

[0037] The control unit is a distributed control system (DCS system). The DCS system 11 is electrically connected to the coal feeder 2, the regulating valve 14, and the analog-to-digital converter 10 via an industrial communication network. The DCS system 11 is the core executor of the entire control strategy, possessing a built-in communication interface module for receiving automatic generation control (AGC) commands from the grid side, and the ability to program and execute advanced control algorithms. Based on the differential pressure value monitored in real-time by the differential pressure measuring point 9 and the expected coal powder output adjustment rate, the DCS system 11 precisely controls the coal feed rate of the coal feeder 2 and the opening degree of the regulating valve 14 using a built-in proportional-integral-derivative (PID) control algorithm. Based on the load change direction and peak-shaving rate of the AGC commands, the DCS system 11 predictively adjusts the coal powder reserve inside the coal mill 4, realizing the function of the coal mill 4 as a "temporary pulverized coal silo."

[0038] Please see Figure 2 This invention further provides a rapid variable load control method for the grinding process of a medium-speed coal mill 4. This method utilizes the control system to achieve refined and predictive control of the pulverizing process. The method includes the following steps:

[0039] During the implementation of the method, the control unit receives and parses AGC commands from the grid side in real time through its communication interface. The AGC commands include the expected direction of unit load change (increase or decrease) and the corresponding peak-shaving rate (e.g., percentage per minute). Based on the received AGC commands, the control unit initiates the corresponding control logic.

[0040] When the control unit detects an impending load change command, the method performs the following pre-adjustment steps:

[0041] The DCS system 11 establishes a lead time communication interface with the power grid dispatching system, or based on historical dispatching data and load prediction algorithms, to predict AGC commands 15 minutes in advance. When the AGC command indicates a rapid increase in load, the control unit will, 15 minutes before the actual issuance of the AGC command, gradually increase the speed of the variable frequency speed control motor of the coal feeder 2 through a built-in control algorithm, thereby increasing the coal feed rate of raw coal 1. Simultaneously, the control unit will gradually reduce the hot air volume entering the coal mill 4 by sending commands to the actuator of the regulating valve 14, thereby reducing the coal powder carry-out efficiency. This combined operation aims to increase the coal powder reserve inside the coal mill 4, causing the differential pressure value at the inlet and outlet of the coal mill 4 monitored by the differential pressure measuring point 9 to slowly rise by 2-3 kPa from the original stable differential pressure, thereby increasing the concentration of coal powder in the gas-solid two-phase flow inside the coal mill 4. The preset time of "first 15 minutes" is the optimal pre-response time window determined by system modeling and analysis of a large amount of operating data, based on the physical inertia of coal powder grinding, drying and accumulation inside the coal mill 4, the average coal quality characteristics, and the typical peak-shaving command response cycle of the power grid. This ensures that sufficient coal powder reserves have been formed inside the coal mill 4 when the AGC command arrives.

[0042] When the AGC command instructs a rapid reduction in load, the control unit, 15 minutes before the actual issuance of the AGC command, will gradually reduce the speed of the variable frequency speed-regulating motor of the coal feeder 2 through a built-in control algorithm, thereby reducing the amount of raw coal 1 fed. Simultaneously, the control unit will gradually increase the volume of hot air entering the coal mill 4 by sending commands to the actuator of the regulating valve 14, thereby improving the coal powder carry-out efficiency. This combined operation aims to reduce the amount of coal powder stored inside the coal mill 4, causing the differential pressure value at the inlet and outlet of the coal mill 4 monitored by the differential pressure measuring point 9 to slowly decrease by 2-3 kPa from its original stable differential pressure, thereby reducing the concentration of coal powder in the gas-solid two-phase flow inside the coal mill 4.

[0043] Subsequently, when the AGC command for rapidly increasing the load is officially issued at the preset time, the control unit will immediately control the actuator of the regulating valve 14 to rapidly increase the hot air volume. This operation will quickly carry the high-concentration pulverized coal stored inside the coal mill 4 to the boiler 8, achieving an immediate response to the demand for rapid load increase. This rapid increase in hot air volume can raise the pulverized coal output flow rate to the target value within seconds, effectively avoiding the approximately 3-minute response delay traditionally caused by the lag in the grinding process.

[0044] Similarly, when the AGC command for rapid load reduction is issued at the preset time, the control unit will immediately control the actuator of the regulating valve 14 to rapidly reduce the hot air volume. This operation will quickly reduce the amount of pulverized coal carried out from the coal mill 4, achieving an immediate response to the demand for rapid load reduction. This rapid reduction of hot air volume can reduce the pulverized coal output flow rate to the target value within seconds.

[0045] In a preferred embodiment of the present invention, the control unit dynamically sets the target value of the differential pressure at the inlet and outlet of the coal mill 4 according to the peak shaving rate included in the AGC command, and uses this target value as a guide for differential pressure control in the pre-adjustment step. Specifically, if the peak shaving rate is ≥3%Pe / min, the control unit controls the differential pressure value to be near the target value of 3kPa. If the peak shaving rate is <3%Pe / min, the control unit controls the differential pressure value to be near the target value of 2kPa. The dynamic setting of the differential pressure target value enables more refined management of the coal powder reserve inside the coal mill 4, allowing it to more flexibly adapt to load adjustment needs at different rates.

[0046] The method of the present invention also includes periodically performed stone and coal venting operations to ensure the accuracy of differential pressure measurement and the stable operation of the coal mill 4. The stone and coal venting operation includes the following specific steps:

[0047] The control unit sends commands to the actuator of the regulating valve 14 to gradually reduce the amount of hot air entering the coal mill 4 until the hot air volume reaches the minimum ventilation volume, which is between 30% and 40% of the rated ventilation volume of the coal mill 4. At this minimum ventilation volume, the hot air's powder-carrying capacity decreases significantly, and under the action of gravity, the coarse coal and coarse coal particles will accelerate to settle to the bottom of the coal mill 4.

[0048] After maintaining this minimum ventilation rate for a period of time (typically 5 to 10 minutes, depending on the coal quality and the amount of accumulated gravel), the control unit continuously monitors the level sensor signal inside the gravel collection device 13. When the level sensor indicates that the accumulated gravel has reached a preset threshold, or when observed and confirmed for a preset 15-minute period without the assistance of a level sensor signal, it indicates that the gravel has been largely emptied. The "preset 15-minute period" is determined empirically based on typical gravel settling velocity and airflow characteristics inside the coal mill 4.

[0049] After confirming that the coal and stone have been emptied, the control unit sends a command to the actuator of the regulating valve 14 to gradually increase the hot air volume entering the coal mill 4 until the hot air volume is restored to the normal ventilation volume between 60% and 80% of the rated ventilation volume of the coal mill 4. The normal ventilation volume ensures the stable powder carrying and drying efficiency of the coal mill 4 when it returns to normal operation mode.

[0050] As a specific implementation of the stone and coal processing unit, the stone and coal collection device 13 can adopt an automatic conveying and discharging method for the removal of stone and coal. For example, the control unit automatically controls the opening and closing of the electric gate valve and starts the screw conveyor to continuously or intermittently transport the stone and coal to the external stone and coal silo or dry slag system. This automation method improves operating efficiency and reduces the need for manual intervention. Manual discharging can also be used, for example, by on-site operators manually or electrically operating the gate valve to periodically open the discharge port for removal. Regardless of the removal method adopted, it is necessary to ensure that air backflow into the coal mill 4 is avoided during the stone and coal discharge process, which would affect the stability of the negative pressure inside the coal mill 4 and the accuracy of measurement. Therefore, the sealing design between the electric gate valve and the screw conveyor is crucial.

[0051] To further illustrate the implementation effects and technical advantages of the rapid load change control system and method described in this invention, the invention will be further explained below with reference to a case of a tangential combustion boiler.

[0052] A certain 660MW boiler is a high-efficiency ultra-supercritical variable pressure once-through boiler, model HG-2109 / 29.3-YM8, designed and manufactured by Harbin Boiler Factory Co., Ltd. The boiler type is a single-furnace, single-intermediate reheat, four-corner tangential combustion, tail-end double flue structure, balanced ventilation, solid ash discharge, all-steel frame, fully suspended structure, and tightly enclosed Π-shaped boiler.

[0053] Boiler 8 has a furnace dimension of 19082.3mm × 19082.3mm and a top elevation of 95780mm for the large plate girder. Boiler 8 is designed under maximum continuous load (B-MCR) conditions, with a maximum continuous evaporation capacity of 2109t / h, a superheater outlet steam temperature of 605℃, a reheater outlet steam temperature of 623℃, and a feedwater temperature of 309℃. The design lower heating value of the coal is 17105kJ / kg. The furnace combustion method is a tangential combustion, with oscillating burners, and low-NOx technology combining horizontal rich-lean burners and separate burnout air (SOFA). Each corner of the burner has six sets of burners, with the bottom two layers being plasma burners and the remaining five layers being pulverized coal burners. Each layer is paired with one coal mill 4. Approximately 6133mm above the upper pulverized coal nozzles, there are two sets of six-layer separate SOFA air nozzles (corner arrangement). Their function is to supplement the air needed for later-stage fuel combustion, lower the furnace temperature, and suppress NOx formation. They also have a reverse tangential function, which can eliminate residual rotation in the furnace and reduce outlet flue gas temperature deviation. Boiler 8 is equipped with six HP1103 medium-speed coal mills, with five operating and one standby, meaning that five coal mills 4 (hereinafter referred to as mills A, B, C, D, and E) can operate at full load.

[0054] Affected by wind and solar power generation, the coal-fired power unit operates normally during the day with a load of 264MW (40% load). One evening at 6 pm, the evening peak began, and the power grid required the unit to increase the load at a rate of 3%Pe / min, from 264MW to 660MW. The unit was operated by ABC coal mills.

[0055] Before applying this invention: the operators operated as follows: when the load increase command was issued at 18:00, the coal feed rate of the coal feeder 2 corresponding to the ABC mill increased from 35 tons / hour to 45 tons / hour. During the three minutes from 18:00 to 18:03, the load could only increase at a rate of 1%Pe / min (not reaching a rate of 3%Pe / min). After 18:03, the increased coal feeder 2 was successfully fed into the boiler 8, and the load increase rate increased from 1%Pe / min to 3%Pe / min. Subsequently, the operation was carried out according to the operators' habits, that is: when the load increased to 330MW, the D mill (the fourth coal mill) was started; when the load increased to 550MW, the E mill (the fifth coal mill) was started; when the load increased to 660MW, the coal feed rate of the coal feeder 2 corresponding to each mill was 65 tons / hour.

[0056] After applying this invention: Since the unit adopts the AGC operation mode, the operators know the load curve for the whole day in advance. Starting at 17:45, the coal feed rate of ABC mills increased from 35 tons / hour to 45 tons / hour. At the same time, the opening of the hot air pipe regulating valve 14 decreased by 5%, and the differential pressure between the inlet and outlet of ABC mills slowly increased from 3 kPa to 6 kPa. When the load increase command was issued at 18:00, ABC mills had stored more than ten tons of pulverized coal. The opening of the hot air regulating valve 14 of ABC mills increased by 5%, while maintaining the coal feed rate of ABC mills at 45 tons / hour. In the three minutes from 18:00 to 18:03, the load could be increased at a rate of 3% Pe / min. After 18:03, the increased coal feed from coal feeder 2 was successfully delivered to boiler 8. Subsequent operations could be carried out according to the operators' habits, that is: when the load increased to 330MW, start D mill; when the load increased to 550MW, start E mill; when the load increased to 660MW, the coal feed rate of each coal mill 4 corresponding to coal feeder 2 was 65 tons / hour. Through this invention, the coal powder output begins to adjust within 5-10 seconds after the AGC command is issued, and load matching is completed within 3 minutes. It is clarified that "seconds" refers to the response start time rather than the complete matching time.

[0057] At 22:00, the evening peak ended, and the units reduced their load to 264MW according to the grid requirements at a rate of 3%Pe / min. Before applying this invention, the operators operated as follows: starting at 22:00, the coal feeder 2 corresponding to ABCDE coal mill 4 began to reduce coal from 65 tons / hour to 50 tons / hour. From 22:00 to 22:03, the load could only be reduced at a rate of 1%Pe / min (not reaching the 3%Pe / min load reduction rate). After 22:03, the operators operated according to their usual practice, that is: when the load dropped to 550MW, mill E was shut down; when the load dropped to 330MW, mill D was shut down, reducing the load to 264MW. Finally, the coal feeder 2 corresponding to each coal mill 4 was 35 tons / hour.

[0058] After applying this invention: Because the unit adopts AGC operation mode, the operators know the load curve for the whole day in advance. Starting at 21:45, the coal feeder 2 corresponding to mills ABCDE begins to reduce coal supply from 65 tons / hour to 60 tons / hour. The opening of regulating valve 14 in the hot air pipe increases by 5%, and the differential pressure between the inlet and outlet of mill 4 slowly decreases from 6 kPa to 3 kPa. When the load reduction command is issued at 22:00, from 22:00 to 22:03, the opening of hot air regulating valve 14 in mills ABCDE decreases by 5%-10% (depending on the adjustment characteristics of the hot air damper of each mill). The load decreases at a rate of 3% Pe / min. After 22:03, according to the operators' usual operation, mill E is shut down when the load drops to 550MW, mill D is shut down when the load drops to 330MW, and the load is reduced to 264MW. Finally, the coal feed rate of each mill corresponding to feeder 2 is 35 tons / hour.

[0059] To prevent excessive stones in the coal from interfering with the differential pressure, at 21:00, with the 660MW load stable and each mill feeding 65 tons / hour, the airflow in the hot air duct 5 of the regulating valve 14 of mills ABCDE was reduced sequentially until the minimum ventilation volume (100 tons / hour, adjusted individually for each mill). The minimum ventilation volume was calculated as 30%-40% of the rated ventilation volume of mill 4. At this time, the amount of stone coal in each mill increased. After confirming that the stone coal had been emptied by the material level sensor signal of the stone coal collection device 13 or by observing every 15 minutes, the airflow in the hot air duct 5 was increased again through the regulating valve 14 until the normal ventilation volume was reached (calculated as 60%-80% of the rated ventilation volume of mill 4, for example, 200-250 tons / hour). This operation depends on the coal quality on site. This operation is only considered when there are many stones in the coal. If the coal quality is relatively stable and there are not many stones, this adjustment can be omitted.

[0060] In summary, the rapid load change control system and method for the grinding process of a medium-speed coal mill described in this invention innovatively uses the coal mill as a "temporary pulverizer silo." Utilizing a predictive control strategy, it adjusts the coal feed rate and hot air volume in advance before the power grid's AGC command is issued, and precisely controls the coal powder reserve through the differential pressure value of the coal mill, thereby effectively overcoming the inherent physical lag of traditional pulverizing systems. This technical solution requires no large-scale hardware modification of the coal mill itself; it can be achieved solely through optimization of the DCS system algorithm and adjustment of the control logic, significantly reducing implementation costs and safety risks. The system and method can shorten the response time of the pulverizing system from several minutes to several seconds, enabling the load regulation rate of coal-fired units to meet the stringent requirements of the power grid for peak-shaving rates of 3%-5% Pe / min or even higher, greatly improving the flexibility and economy of coal-fired power units participating in deep peak shaving of the power grid. Simultaneously, by integrating the stone coal processing function, it ensures the accuracy of differential pressure measurement and the operational reliability of the system under complex coal quality conditions, providing a solid technical guarantee for the stable operation and deep peak-shaving capability of coal-fired units in the new power system.

Claims

1. A rapid load change control system for the grinding process of a medium-speed coal mill, characterized in that, include: The coal feeding unit includes a coal feeder (2) and a coal drop pipe (3) connected together. The coal feeder (2) is used to transport raw coal (1) and regulate the coal feeding rate. The grinding unit is a coal mill (4) connected to the coal drop pipe (3). The coal mill (4) is used to grind the raw coal (1) into coal powder and can also be used as a temporary powder silo to realize the dynamic adjustment of the internal coal powder reserve. The coal-fired unit includes a coal powder pipe (7) and a boiler (8) connected together. The output end of the coal mill (4) is connected to the boiler (8) through the coal powder pipe (7). The hot air regulating unit includes a hot air header (6), a hot air pipe (5) connected to the hot air header (6), and a regulating valve (14) installed on the hot air pipe (5). The hot air pipe (5) is connected to the coal mill (4). The regulating valve (14) is used to control the flow rate of hot air entering the coal mill (4) in order to regulate the coal powder concentration and differential pressure in the coal mill (4). The differential pressure control unit includes an electrically connected differential pressure measuring point (9) and an analog-to-digital converter (10). The differential pressure measuring point (9) is located on the upper part of the coal mill (4) and is used to monitor the inlet and outlet differential pressure signals of the coal mill (4). The stone coal processing unit includes a stone coal output pipe (12) and a stone coal collection device (13) connected together. The lower part of the coal mill (4) is connected to the stone coal collection device (13) through the stone coal output pipe (12). The control unit, a DCS system (11), is electrically connected to the coal feeder (2), regulating valve (14), and analog-to-digital converter (10). It is used to receive automatic power generation control commands from the grid side, obtain the load change direction and peak shaving rate contained in the commands, and, within a preset time before the automatic power generation control command is issued, coordinate the coal feed rate of the coal feeder and the opening degree of the regulating valve (14) according to the differential pressure value monitored by the differential pressure measuring point (9) to pre-adjust the coal powder reserve inside the coal mill. It is also used to adjust the hot air flow rate according to the coal powder output rate when the automatic power generation control command is issued, and control the opening degree of the regulating valve (14) to match the load change requirements of the boiler.

2. A rapid variable load control method for the grinding process of a medium-speed coal mill, characterized in that, The control system for the rapid load change of the medium-speed coal mill grinding process as described in claim 1 includes the following steps: S1: Receive automatic generation control commands from the grid side through the DCS system (11) to obtain the expected load change demand and corresponding peak shaving rate; the automatic generation control commands include the load change direction; S2: When the automatic power generation control command indicates a rapid increase in load, before the automatic power generation control command is issued, the DCS system (11) controls the coal feeder (2) to increase the amount of raw coal (1) fed, and at the same time controls the opening of the regulating valve (14) to reduce the amount of hot air entering the coal mill (4), so that the differential pressure value monitored by the differential pressure measuring point (9) in the coal mill (4) increases, and the coal powder reserve inside the coal mill (4) increases. When the automatic power generation control command indicates a rapid reduction in load, the DCS system (11) controls the coal feeder (2) to reduce the amount of raw coal (1) fed before the automatic power generation control command is issued, and at the same time controls the opening of the regulating valve (14) to increase the amount of hot air entering the coal mill (4), so that the differential pressure value monitored by the differential pressure measuring point (9) in the coal mill (4) decreases, thereby reducing the coal powder reserves inside the coal mill (4). S3. When a rapid load increase command is issued, the DCS system (11) controls the opening of the regulating valve (14) to increase the hot air volume, carrying out the coal powder stored in the coal mill (4) to the boiler (8) to match the rapid load increase demand; when a rapid load decrease command is issued, the DCS system (11) controls the opening of the regulating valve (14) to decrease the hot air volume, reducing the coal powder output of the coal mill (4) to match the rapid load decrease demand. S4: According to the peak shaving rate of the automatic power generation control command, the DCS system (11) sets the target value of the differential pressure at the inlet and outlet of the coal mill (4) in stages, and uses this target value as the differential pressure control guide in step S2.

3. The rapid load change control method for the grinding process of a medium-speed coal mill according to claim 2, characterized in that: The preset time is set to 15 minutes.

4. The rapid load change control method for the grinding process of a medium-speed coal mill according to claim 2, characterized in that: This also includes periodically performing stone and coal venting operations, which include: S5: The opening of the hot air regulating valve (14) is controlled by the DCS system (11) to reduce the amount of hot air entering the coal mill (4) until the minimum ventilation volume is reached, which is 30% to 40% of the rated ventilation volume of the coal mill (4); S6: Monitor the level sensor signal of the stone and coal collection device (13) or observe it through a preset time to confirm that the stone and coal have been discharged; S7: The opening of the hot air regulating valve (14) is controlled by the DCS system (11) to increase the hot air volume entering the coal mill (4) until it is restored to the normal ventilation volume, which is 60% to 80% of the rated ventilation volume of the coal mill (4).

5. The rapid load change control method for the grinding process of a medium-speed coal mill according to claim 4, characterized in that: The stone and coal collection device (13) uses an automatic conveying and discharging method or a manual discharging method for the removal of stone and coal.

6. The rapid load change control method for the grinding process of a medium-speed coal mill according to claim 2, characterized in that: In step S2, when the load change demand is a rapid increase in load, the differential pressure value monitored by the differential pressure measuring point (9) rises to 2-3 kPa on the basis of the original differential pressure, increasing the coal powder concentration in the coal mill (4).

7. The rapid load change control method for the grinding process of a medium-speed coal mill according to claim 2, characterized in that: In step S2, when the load change demand is to reduce the load rapidly, the differential pressure value monitored by the differential pressure measuring point (9) drops to 2-3 kPa based on the original differential pressure, thereby reducing the coal powder concentration in the coal mill (4).

8. The rapid load change control method for the grinding process of a medium-speed coal mill according to claim 6 or 7, characterized in that: The DCS system (11) controls the differential pressure value monitored by the differential pressure measuring point (9) of the coal mill (4) according to the peak shaving rate of the automatic power generation control command; If the peak shaving rate is ≥3%Pe / min, then the differential pressure value is controlled at 3kPa; If the peak shaving rate is less than 3%Pe / min, then the differential pressure value is controlled at 2kPa.

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