Direct-fired boiler variable-load fuel system with external coupling powder bin and direct-fired boiler variable-load fuel method

Abstract

The invention discloses a direct blowing type boiler variable load fuel system with an external coupling powder bin and a method, and belongs to the technical field of thermal power generation equipment. The device comprises an external coupling powder bin, wherein the effective volume of the external coupling powder bin is configured to meet the pulverized coal consumption of 5-10 minutes under the rated load of a boiler; the combustion regulation and control unit comprises at least one independent combustor independent of a boiler main combustor. The central controller is in signal connection with the direct-blowing pulverizing unit, a material level monitoring module of the external coupling powder bin, the combustion regulation and control unit, and a regulating valve and a pulverized coal feeding device in the pulverized coal blending pipeline unit; the central controller is used for receiving boiler load signals and boiler combustion state feedback and conducting dynamic regulation and control. Through cooperative configuration of the small-capacity external coupling powder bin and the independent combustor and intelligent regulation and control of the central controller, the technical problems that load response of the direct-fired boiler is lagged and low-load stable combustion is difficult are solved, and rapid, stable and efficient operation under all working conditions is achieved.

Description

A variable load fuel system and method for a direct-fired boiler with an externally coupled pulverized coal silo Technical Field

[0001] This invention relates to the field of thermal power generation equipment technology, specifically to a variable load fuel system and method for a direct-fired boiler with an externally coupled pulverized coal silo. Background Technology

[0002] In the thermal power generation industry, boilers, as the core energy conversion equipment, directly determine the power generation efficiency and grid adaptability of generator units through their operational stability and load regulation capabilities. Direct-fired pulverized coal systems are widely used in various types of coal-fired boilers due to their advantages such as system simplicity, fewer equipment, lower investment, and smaller footprint. In particular, in large thermal power units, the application rate of direct-fired pulverized coal systems exceeds 70%.

[0003] The working principle of a direct-fired pulverized coal system is as follows: raw coal is fed from the coal bunker into the coal mill via a coal feeder, where it is ground into pulverized coal that meets combustion requirements. This pulverized coal is then carried directly into the boiler furnace by primary air for combustion. Throughout the process, the pulverized coal does not undergo intermediate storage; the pulverization system and combustion system are directly coupled. However, this structural characteristic also leads to significant technical bottlenecks in load regulation for direct-fired boilers.

[0004] When a boiler receives a load increase command, the fuel system needs to go through multiple stages, including raw coal transportation, blending, grinding, air-coal mixing, and transportation, each with a certain time delay. In existing technology, the entire process from raw coal entering the coal mill to pulverized coal being fed into the furnace for combustion typically takes 3 to 8 minutes, depending on the type, capacity, and operating conditions of the coal mill. However, the combustion process within the boiler furnace is instantaneous. Upon receiving a load command, the combustion system needs to immediately adjust the combustion rate to adapt to changes in the external load. This results in the fuel system's load response lagging behind the combustion system's control requirements, creating a situation where the control command has been issued, but the fuel supply has not kept up.

[0005] This lag leads to a series of problems: First, the boiler's slow load change speed makes it unable to quickly respond to the grid's peak-shaving needs. Especially with the increasing proportion of new energy power generation (wind power, photovoltaic), the grid's requirements for the peak-shaving flexibility of thermal power units are becoming increasingly higher. This defect of direct-fired boilers limits their peak-shaving role in the grid. Second, in order to meet the needs of load changes, operators often need to adjust the fuel system in advance. This predictive operation can easily lead to excessive or insufficient fuel supply, which in turn causes large fluctuations in furnace temperature, a decrease in combustion efficiency, and even safety hazards such as furnace fire extinguishing and deflagration. Third, long-term unsteady operation of the fuel system will increase equipment wear and energy consumption. For example, frequent start-ups and shutdowns of coal mills or drastic load changes will shorten their service life, and frequent adjustments of coal feeders will increase power consumption.

[0006] To address the issue of lag in the response of direct-fired boiler fuel systems, the industry has undertaken a series of attempts. Some studies have optimized the control strategies of the coal mill, such as using variable frequency speed control technology to improve the load regulation speed of the coal mill, or improving the structure of the coal feeder to enhance the stability of raw coal transportation. However, these methods can only shorten the delay time of individual stages to a certain extent and cannot fundamentally solve the long cycle problem of pulverization and combustion. Other studies have proposed a hybrid pulverizing system combining direct-fired and intermediate storage, adding a large pulverized coal storage silo to the existing direct-fired system. However, this approach requires large-scale renovations to the boiler plant, resulting in a large footprint, high investment costs, and safety risks such as spontaneous combustion and explosion of pulverized coal in the large storage silo, making it unsuitable for upgrading existing units. Still other studies have attempted to use new grinding equipment, such as high-speed impact mills to replace traditional ball mills or medium-speed mills, to shorten grinding time. However, the reliability and adaptability of these new equipment still require long-term verification, and the high cost of equipment replacement makes widespread adoption in the industry difficult.

[0007] Therefore, developing a direct-fired boiler fuel system that is simple in structure, easy to modify, safe and reliable, and can achieve rapid response in fuel supply has become an urgent technical problem to be solved in the current thermal power generation industry. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems in the prior art and provide a variable load fuel system for a direct-fired boiler with an externally coupled powder bin.

[0009] This invention provides a variable load fuel system for a direct-fired boiler with an externally coupled pulverized coal silo, comprising: an externally coupled pulverized coal silo with an effective volume configured to meet the pulverized coal consumption for 5 to 10 minutes under the boiler's rated load; the externally coupled pulverized coal silo is equipped with a material level monitoring module; its inlet is connected to the output end of the direct-fired pulverizing system, and its outlet is connected to a downstream pipeline via a pulverizing feeder; a combustion control unit, including at least one independent burner separate from the boiler's main burner; and a pulverized coal distribution pipeline unit, including pipelines connecting the direct-fired pulverizing system, the externally coupled pulverized coal silo, the boiler's main burner, and the independent burner, as well as regulating valves installed on the pipelines and the pulverizing feeder; the pipelines and valves are configured to enable switching of the pulverized coal transport path between the pulverizing system, the externally coupled pulverized coal silo, the main burner, and the independent burner; The central controller is connected to the direct-fired pulverizing unit, the material level monitoring module of the externally coupled pulverized coal silo, the combustion control unit, and the regulating valves and feeding equipment in the pulverized coal distribution pipeline unit. The central controller receives boiler load commands and boiler combustion status feedback, and executes the following dynamic control logic: When the load increases, it controls the feeding equipment to transport the pulverized coal in the externally coupled pulverized coal silo to the independent burner for combustion, and simultaneously increases the output of the direct-fired pulverizing system; when the load decreases, it controls the pulverized coal distribution pipeline unit to divert part of the pulverized coal from the direct-fired pulverizing system to the externally coupled pulverized coal silo for storage, and controls the independent burner to perform stable combustion operation; during steady-state operation, based on the material level status of the externally coupled pulverized coal silo and the combustion status of the boiler, it controls the pulverized coal distribution pipeline unit and the independent burner to dynamically maintain the pulverized coal silo inventory and optimize furnace combustion.

[0010] Preferably, the pulverized coal preparation pipeline unit includes: a main conveying pipeline connecting the outlet of the direct-fired pulverizing system to the main burner of the boiler; a pulverized coal feeding bypass, the first end of which is connected to the main conveying pipeline and the second end of which is connected to the feed inlet of the external coupling pulverized coal silo; and a pulverized coal taking bypass, the first end of which is connected to the discharge outlet of the external coupling pulverized coal silo through the pulverized coal feeding equipment, and the second end of which has at least two branches, respectively connected to the independent burner and the main conveying pipeline located downstream of the first end.

[0011] Preferably, a first regulating valve is provided on the branch pipe connected to the independent burner; a second regulating valve is provided on the branch pipe connected to the main delivery pipe; the central controller dynamically allocates the flow of pulverized coal from the external coupling pulverized coal silo to the independent burner and the main burner by controlling the opening ratio of the first regulating valve and the second regulating valve according to the amplitude and rate of change of the boiler load command.

[0012] Preferably, the combustion control unit further includes a combustion state sensing module for acquiring real-time combustion state data in the furnace; the combustion state sensing module includes a furnace temperature field monitoring submodule; wherein, the furnace temperature field monitoring submodule adopts a combination of an infrared thermal imager and a wall thermocouple array, the infrared thermal imager is installed in the furnace observation hole for acquiring real-time two-dimensional temperature field imaging of the cross-sectional area inside the furnace, the wall thermocouple array is arranged at intervals along the height direction of the furnace for monitoring the temperature distribution of the furnace wall, and the furnace temperature field monitoring submodule is signal-connected to the central controller.

[0013] Preferably, the optimization of the central controller during steady-state operation is specifically configured as follows: based on the temperature field data acquired by the infrared thermal imager, identify local low-temperature or high-temperature zones within the furnace; and by adjusting the injection angle and swirl intensity of the independent burners, guide the combustion flame specifically to the low-temperature zones for reinforcement.

[0014] Preferably, the central controller executes a composite control algorithm combining fuzzy PID control and model predictive control; wherein, the model predictive control module predicts the boiler's combustion trend and pulverized coal demand over a future period based on the current combustion state and historical data, and generates feedforward control commands; the fuzzy PID control module performs feedback adjustment based on the real-time deviation between the boiler load command and the actual combustion load; the central controller integrates the feedforward control commands and feedback adjustment results to generate coordinated control signals for the pulverized coal feeding equipment, the regulating valve, and the independent burners.

[0015] Preferably, the externally coupled powder silo includes an inert gas protection system, which includes multiple oxygen content sensors arranged along the height of the silo. The central controller dynamically adjusts the flow rate of inert gas introduced into the bottom of the powder silo based on the oxygen concentration gradient monitored by each sensor, so as to maintain the uniformity of the longitudinal oxygen concentration distribution within the silo.

[0016] This invention also discloses a control method for the above-mentioned system, executed by the central controller, comprising the following steps: acquiring the target load command of the boiler and a status signal reflecting the current combustion load; determining the deviation between the target load command and the current combustion load to determine whether the boiler is in a state of increased load demand, decreased load demand, or steady-state operation demand; if it is a state of increased load demand, starting the pulverized coal feeding equipment to transport the pulverized coal stored in the externally coupled pulverized coal bin to the independent burner, and controlling the independent burner to switch to enhanced combustion mode; simultaneously, issuing an increased output command to the direct-fired pulverizing system; if it is a state of decreased load demand, adjusting the valve in the pulverized coal distribution pipeline unit to divert a portion of the pulverized coal output from the direct-fired pulverizing system to the externally coupled pulverized coal bin for storage; simultaneously, controlling the independent burner to switch to stable combustion mode; if it is a state of steady-state operation demand, monitoring the material level in the externally coupled pulverized coal bin and the combustion state in the furnace, and adjusting the operating parameters of the pulverized coal distribution pipeline unit and the independent burner accordingly to dynamically balance the pulverized coal bin inventory and optimize the combustion process.

[0017] Preferably, during steady-state operation, when the material level in the externally coupled pulverized coal silo is detected to be lower than a first preset threshold, the pulverized coal distribution pipeline unit is controlled to introduce a portion of the pulverized coal from the direct-fired pulverizing system into the externally coupled pulverized coal silo; when the material level is higher than a second preset threshold, the independent burner is controlled to increase its output to consume a portion of the pulverized coal in the externally coupled pulverized coal silo; during steady-state operation, a temperature field distribution image of the furnace cross-section is acquired in real time; the temperature field distribution image is analyzed, and if it is identified that the temperature non-uniformity exceeds the allowable range, targeted intervention is carried out in the low-temperature zone or high-temperature zone in the furnace by adjusting the pulverized coal supply, secondary air ratio, or injection angle of the independent burner.

[0018] Compared with existing technologies, the beneficial effects of this invention are as follows: By setting up a small-capacity externally coupled pulverized coal silo that only meets the pulverized coal consumption of 5-10 minutes, and flexibly connecting it to an independent burner through a pulverized coal distribution pipeline unit with switchable delivery paths, the central controller synchronously starts pulverized coal feeding from the silo and combustion from the independent burner when the load increases. Utilizing the buffering characteristics of the small-capacity silo, additional combustion fuel is instantly provided to the boiler, reducing the fuel supply response time from several minutes, which depends on the pulverization delay in traditional direct-fired systems, to the second level. This solves the problem of fuel response lag caused by the pulverization delay in traditional direct-fired systems. The problem is that during load reduction, redundant pulverized coal from the pulverizing system is immediately recycled to the pulverized coal silo for storage by switching pipelines. This avoids pulverized coal waste and frequent mill adjustments, and the independent burner switches to stable combustion mode, effectively solving the hidden danger of poor combustion stability under low load conditions. During steady-state operation, the controller dynamically adjusts the pulverized coal flow direction and optimizes the operation of the independent burner according to the pulverized coal silo level and furnace combustion status, so that the pulverized coal silo always maintains the best reserve state. At the same time, it continuously optimizes the uniformity of furnace combustion, achieving efficient, stable and flexible operation under all operating conditions, and significantly improving the boiler's peak-shaving capacity and operating economy. Attached Figure Description

[0019] Figure 1 is a schematic diagram of the variable load fuel system of the direct-fired boiler with externally coupled powder bin of the present invention.

[0020] Figure 2 is a schematic diagram of the variable load fuel system of the direct-fired boiler with externally coupled powder bin of the present invention.

[0021] In the diagram, 1. Coal mill; 2. First regulating valve; 3. First pulverized coal concentration monitor; 4. Main burner; 5. Second regulating valve; 6. Second pulverized coal concentration monitor; 7. Independent burner; 8. Main conveying pipeline; 9. Bypass conveying pipeline; 10. Furnace; 11. External coupling pulverized coal bin. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms “first,” “second,” and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as “comprising” or “including” indicate that the elements or objects preceding “comprising” or “including” encompass the elements or objects listed following “comprising” or “including” and their equivalents, and do not exclude other elements or objects. Terms such as “connected” or “linked” are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as “upper,” “lower,” “left,” and “right” are used only to indicate relative positional relationships; when the absolute position of the described objects changes, the relative positional relationship may also change accordingly.

[0024] The objectives of this invention include: shortening the load response time of the fuel system, reducing the pulverized coal supply delay during load increases from several minutes to seconds, thus meeting the boiler furnace's need for rapid adjustment of combustion rate; enabling the recovery and utilization of redundant pulverized coal during load reduction, avoiding pulverized coal waste, and reducing equipment wear caused by frequent start-ups and shutdowns of the coal mill or load fluctuations; achieving flexible access to externally coupled pulverized coal storage units through modular design without altering the main structure of the boiler or the core functions of the traditional pulverizing system, reducing the difficulty and cost of upgrading existing units; ensuring the safe operation of the externally coupled pulverized coal storage units through a comprehensive monitoring and control system, avoiding risks such as spontaneous combustion and explosion during pulverized coal storage; improving the boiler's load variation flexibility and operational stability, reducing energy consumption and pollutant emissions during peak shaving, and enhancing the adaptability of thermal power units to the power grid.

[0025] To achieve the above objectives, this invention proposes a composite fuel system architecture consisting of a traditional pulverizing system, an externally coupled pulverizing silo, precise combustion control, and intelligent collaborative control. The core design concept is as follows: retaining the basic pulverizing function of the traditional direct-fired pulverizing system to ensure steady-state operation requirements; adding a miniaturized externally coupled pulverizing silo as a pulverized coal buffer station to achieve temporary storage and rapid release of pulverized coal; introducing a combustion control unit to achieve precise combustion control of pulverized coal in the externally coupled silo through an independent burner, a multi-dimensional combustion monitoring device, and a load adaptation strategy library; and employing a fuzzy PID-model prediction composite algorithm in the central control unit to integrate data from each unit and achieve closed-loop control of the entire chain from load command to fuel supply to combustion status.

[0026] The technical solution of this invention specifically includes four core components: a direct-fired pulverizing unit, an externally coupled pulverized coal silo unit, a pulverized coal conveying and regulating unit, and a central control unit. These units work collaboratively through pipeline connections and electrical signal transmission, forming a closed-loop fuel supply and control system. The externally coupled pulverized coal silo unit is the core innovation of this invention; its volume is only 1 / 5 to 1 / 10 of that of a traditional intermediate storage silo system. Through optimized structural design and safety protection measures, it achieves miniaturization and safe operation. The pulverized coal conveying and regulating unit is the system's scheduling hub. Through a combination of multiple pipelines and valves, it achieves flexible distribution of pulverized coal among the pulverizing system, the silo unit, and the furnace. The central control unit uses control algorithms to achieve precise regulation of the operating status of each unit and timely handling of faults.

[0027] The direct-fired pulverizing unit in this embodiment is existing technology, used to receive, store, blend, grind, and transport primary pulverized coal, ensuring the boiler's fuel requirements during steady-state operation and slow load changes. This unit utilizes the mature structure of existing direct-fired systems, including a raw coal bunker, a coal feeder, a pulverizer, and primary air-coal ducts. The specific design is as follows: The raw coal bunker adopts a cylindrical structure, with a volume designed based on the boiler's raw coal consumption over 8-12 hours under rated load. Anti-clogging inclined plates and vibration devices are installed on the inner wall to prevent raw coal from accumulating and clogging within the bunker. Multiple discharge ports are located at the bottom of the raw coal bunker, each corresponding to a coal feeder. Different coal types are blended by adjusting the opening of different discharge ports to meet the boiler's combustion requirements for coal quality. The coal feeder is a belt-driven feeder equipped with a variable frequency speed-regulating motor with a speed range of 0-100% of rated speed. It can precisely adjust the coal feed rate according to the instructions of the central control unit, with an adjustment accuracy of ±1%. The coal feeder is equipped with weighing and speed sensors to monitor the coal feed rate in real time and feed it back to the central control unit, forming a closed-loop control of the coal feed rate.

[0028] The coal mill adopts a medium-speed bowl mill, whose grinding pressure can be adjusted via a hydraulic device to adapt to the characteristics of raw coal with different hardness. The mill's interior contains grinding bowls, grinding rollers, and a separator. After being ground into coal powder between the grinding bowls and rollers, the raw coal is carried into the separator by primary air. The separator separates the unqualified coarse coal powder and sends it back to the grinding area for regrinding, while the qualified fine coal powder enters the primary air-coal duct. The mill is equipped with inlet and outlet temperature and pressure sensors to monitor its operating status in real time and prevent abnormal conditions such as over-temperature and over-pressure. The primary air-coal duct is welded from wear-resistant steel plates, and the inner wall of the duct is coated with a wear-resistant ceramic coating to extend its service life. Flow measurement devices and pressure monitoring points are installed on the duct to monitor the flow rate and pressure of the air-coal mixture, ensuring the stability of coal powder transportation.

[0029] An externally coupled pulverized coal silo, connected in parallel with the direct-fired pulverizing unit, is used for temporary storage, safety monitoring, and on-demand output of pulverized coal. The externally coupled silo unit includes a silo body, a level monitoring module, a temperature monitoring module, a pressure monitoring module, and an inert gas protection module. The silo body adopts a double-cone structure design, with a pulverized coal inlet and pressure relief valve at the top, a ring-shaped temperature sensor array in the middle, and a conical discharge port at the bottom. A wear-resistant liner and an anti-clogging stirring device are installed at the discharge port. The effective volume of the silo body is the amount of pulverized coal consumed in 5-10 minutes under the boiler's rated load, and the inner wall is coated with an anti-stick coating made of a composite coating of polytetrafluoroethylene and ceramic particles. The externally coupled pulverized coal silo is the core innovation of this invention, its function being to achieve temporary storage, safety monitoring, and on-demand output of pulverized coal, providing emergency pulverized coal reserves for rapid boiler load changes. This unit adopts a modular design and can be directly installed in an empty area of ​​the boiler plant without requiring large-scale modifications to the existing plant structure. The specific design is as follows:

[0030] The pulverized coal silo adopts a double-cone structure, with a conical feeding section at the top, a cylindrical storage section in the middle, and a conical discharge section at the bottom. This structural design effectively prevents pulverized coal from accumulating inside the silo, ensuring smooth discharge. The effective volume of the silo is determined based on the pulverized coal consumption over 5-10 minutes under the boiler's rated load, meeting the replenishment needs during load increases while avoiding increased investment and safety risks due to excessive volume. The silo is made of Q345R low-alloy high-strength steel, with an inner wall coated with a composite anti-stick coating of polytetrafluoroethylene and ceramic particles. The coating thickness is 0.5-1 mm, and the surface roughness is ≤Ra0.8 μm, effectively reducing pulverized coal adhesion to the silo wall.

[0031] The material level monitoring module adopts a dual monitoring structure of ultrasonic level gauge and weighted level gauge. The ultrasonic level gauge is installed at the top center of the powder silo body to monitor the continuous material level of coal powder in the silo in real time. The weighted level gauge is installed at the top edge of the powder silo body to periodically calibrate the measurement data of the ultrasonic level gauge. The measurement data of both are processed by a data fusion algorithm and then output to the central control unit, improving the measurement accuracy to ±3mm.

[0032] The data fusion algorithm utilizes a weighted fusion algorithm, combining signals from ultrasonic level gauges and plumb bob level gauges. Core formula: In the formula, : Ultrasonic value after temperature / pressure compensation; : Signal value of the weighted level gauge; The confidence weight of the ultrasound (0~1) is closer to the calibration time of the weighted hammer. The closer to 1; the further away, Linear decrease; : Confidence weight of the hammer ( =1− Only at the moment of weight measurement =1, and the rest of the time decays over time.

[0033] The material level monitoring module employs a dual monitoring scheme of ultrasonic level gauges and a plumb bob level gauge to ensure the accuracy and reliability of material level measurement. The ultrasonic level gauge is installed at the center of the top of the powder silo. It calculates the pulverized coal level height by emitting high-frequency ultrasonic waves and receiving reflected waves. The measurement range is 0-5 m, with a measurement accuracy of ±10 mm and a response time ≤0.5 s, suitable for real-time continuous monitoring. The plumb bob level gauge is installed at the top edge of the powder silo. It measures the material level height by the raising and lowering of a plumb bob. The measurement range is 0-5 m, with a measurement accuracy of ±5 mm. It is mainly used for periodic calibration of the ultrasonic level gauge's measurement data to avoid measurement errors caused by pulverized coal dust. The measurement data from both gauges is transmitted to the central control unit, processed by a data fusion algorithm, and finally outputs accurate material level information.

[0034] The temperature monitoring module employs a ring-shaped temperature sensor array. Four to six platinum resistance temperature sensors are evenly arranged circumferentially along the cylindrical storage section in the middle of the pulverized coal silo. The sensors are inserted 100 to 150 mm into the silo, with a measurement range of 0 to 200 °C and an accuracy of ±0.5 °C. Additionally, one temperature sensor is installed in the gas space at the top of the silo and at the discharge port at the bottom to comprehensively monitor temperature changes in different areas within the silo and promptly detect early signs of spontaneous combustion of pulverized coal.

[0035] The pressure monitoring module includes a pressure transmitter and a pressure relief valve. The pressure transmitter is installed on the top of the powder silo body to monitor the gas pressure inside the silo. The measurement range is -5 kPa to 10 kPa, and the measurement accuracy is ±0.1 kPa. The pressure relief valve is installed at the exhaust port on the top of the powder silo. When the pressure inside the silo exceeds 15 kPa, it automatically opens to release pressure and ensure the structural safety of the powder silo body.

[0036] The inert gas protection module includes a nitrogen storage tank, a pressure reducing valve, a flow controller, a gas distributor, and an oxygen concentration gradient monitoring device. The gas distributor is installed at the bottom of the pulverized coal silo using a ring-shaped pipe network structure. Several gas injection holes are evenly arranged around the circumference of the ring-shaped pipe network, with the injection holes facing the inner wall of the silo and the area in contact with the pulverized coal. The oxygen concentration gradient monitoring device has 3-4 sets of oxygen content sensors installed at intervals along the height of the silo to monitor the oxygen concentration distribution at different heights in real time. The central control unit controls the supply pressure and flow rate of the inert gas based on the real-time data from the temperature monitoring module and the pressure monitoring module, so that the oxygen content in the silo is maintained below 8%, the temperature is maintained below 50°C, and the oxygen concentration difference between the upper and lower regions does not exceed 2%.

[0037] The inert gas protection module is crucial for ensuring the safe operation of the coal silo. The nitrogen storage tank is designed with a volume 1.2 times that of the silo body to ensure sufficient inert gas supply. The pressure reducing valve lowers the nitrogen pressure from the storage tank pressure to 0.2~0.3 MPa. The flow controller adjusts the nitrogen flow rate according to the instructions of the central control unit, with an adjustment range of 0~50 m³ / h. The gas distributor adopts a ring-shaped pipe network structure installed at the bottom of the silo body. The ring-shaped pipe network is evenly arranged with 20~30 gas injection holes with a diameter of 5~8 mm, facing the inner wall of the silo and the area in contact with the coal powder, so that the nitrogen can be evenly distributed in the silo and effectively inhibit the oxidation of the coal powder. The oxygen content sensor is installed at the exhaust port at the top of the silo to monitor the oxygen content in the silo in real time. The measurement range is 0~21%, and the measurement accuracy is ±0.1%. When the oxygen content exceeds 8%, the central control unit automatically starts the inert gas supply system until the oxygen content drops below 8%.

[0038] In addition, an anti-clogging agitator is installed at the conical discharge port at the bottom of the powder silo. This device is driven by a variable frequency motor to rotate the agitator blade, which has a spiral structure and a rotation speed range of 0~30 r / min, effectively preventing bridging and blockage of pulverized coal at the discharge port. The agitator is linked to the material level monitoring module, automatically reducing the rotation speed when the material level is lower than the preset value, thus reducing energy consumption.

[0039] The combustion control unit is connected to the externally coupled pulverized coal bin unit, the pulverized coal conveying regulation unit, and the boiler furnace, respectively, and is used to realize precise combustion control of pulverized coal in the externally coupled pulverized coal bin and dynamic optimization of the combustion state in the furnace. The combustion control unit includes an independent burner, a combustion state sensing module, and a combustion optimization subsystem. The independent burner in the combustion control unit adopts a staged combustion structure, including a primary air-coal nozzle, a secondary air regulating mechanism, and a central stable combustion ignition device, and is installed in the lower part or side wall area of ​​the boiler furnace, forming a complementary layout with the original main burner. The independent burner adopts a staged combustion structure and is installed in the lower part or side wall of the furnace, forming a complementary layout with the main burner. The primary air nozzle is a zoom type, with an adjustable spray speed range of 15~30m / s and an adjustable diffusion angle range of 15°~45° to adapt to different load requirements; the secondary air regulating mechanism adopts adjustable swirl blades, with stepless adjustment of swirl intensity from 0.3 to 1.2, to achieve precise control of oxygen content in the combustion zone; the central stable ignition device integrates plasma ignition (power 50~100kW) and a small oil gun (oil consumption 0.5~1kg / h), which automatically starts under low load to ensure stable ignition of pulverized coal.

[0040] The combustion state sensing module includes a furnace temperature field monitoring submodule, a flue gas composition analysis submodule, and a combustion stability assessment submodule. The furnace temperature field monitoring submodule uses a combination of an infrared thermal imager and a wall thermocouple array. The infrared thermal imager is installed in the furnace observation port to achieve real-time imaging of the furnace cross-section temperature field with a measurement accuracy of ±5℃. The wall thermocouple array is arranged at intervals along the furnace height to monitor the furnace wall temperature distribution. The flue gas composition analysis submodule uses a laser gas analyzer installed at key locations at the furnace outlet and flue to monitor O2, CO, and NO in real time. x With equal component concentrations and a response time ≤ 1s, the combustion stability assessment submodule constructs a combustion stability index based on the temperature fluctuation coefficient and the CO concentration change rate. When the index falls below a preset threshold, a combustion optimization command is triggered. When constructing the combustion stability index, the combustion stability index S is determined according to the following formula:

[0041] If the combustion stability index S is less than the stability threshold , will fuel ratio Adjust to ,in, This represents the proportionality coefficient; if, after adjusting the fuel ratio, the combustion stability index is less than the stability threshold... If the duration exceeds a preset time threshold, the fuel supply will be cut off.

[0042] The combustion optimization subsystem has a built-in load-adaptive combustion strategy library, including a load-increasing enhanced combustion strategy, a load-reducing stable combustion strategy, and a steady-state precise combustion strategy. When the load increases, the independent burners and the main burner supply pulverized coal in coordination. The independent burners adopt a large swirl and high-velocity injection method to quickly increase the local combustion intensity. When the load decreases, the main burner reduces the pulverized coal supply, and the independent burners switch to a low-velocity, strong stable combustion mode. The local high-temperature zone is maintained by the central stable combustion ignition device. At the same time, the combustion optimization subsystem adjusts the secondary air ratio according to the flue gas composition data to control the oxygen concentration at the furnace outlet at 3%~5%. During steady-state operation, based on the temperature field uniformity target, the injection angle and pulverized coal supply of the independent burners are adjusted to suppress the formation of local high-temperature and low-temperature zones.

[0043] The combustion state sensing module enables comprehensive monitoring of the combustion process: Furnace temperature field monitoring utilizes a combination of an infrared thermal imager and a wall thermocouple array. The infrared thermal imager generates a furnace cross-sectional temperature field image every 2 seconds, and the thermocouple array is arranged every 3 meters along the furnace height to monitor the furnace wall temperature. Flue gas composition analysis employs a laser gas analyzer, installed at the furnace outlet and flue, to monitor O2 (0~21%), CO (0~5000ppm), and NO in real time. x(0~1000ppm) concentration, response time ≤1s; the combustion stability assessment submodule constructs a combustion stability index of 0~100 based on the temperature fluctuation coefficient (≤5% is stable) and the CO concentration change rate (≤10% / min is stable). An index ≥80 is excellent, and <60 triggers an optimization command.

[0044] The combustion optimization subsystem has a built-in load-adaptive combustion strategy library: When the load increases, the independent burners adopt a large swirling (0.8~1.2) and high wind speed (25~30m / s) injection to quickly improve the local combustion intensity; when the load decreases (<30% of the rated load), it switches to a low wind speed (15~20m / s) and weak swirling (0.3~0.6) mode, the central combustion stabilization device is activated, and the secondary air ratio is adjusted to primary air: secondary air = 1:3~4 to maintain the local high temperature zone; during steady-state operation, based on the temperature field uniformity target, the injection angle and coal supply of the independent burners are adjusted to ensure that the temperature difference between the highest and lowest cross-sections of the furnace is ≤200℃.

[0045] The pulverized coal conveying and regulating unit is connected to the direct-fired pulverizing unit, the externally coupled pulverized coal silo unit, and the burner in the boiler furnace, respectively. It is used to switch the pulverized coal conveying path, regulate the flow rate, and control the conveying stability. The pulverized coal conveying and regulating unit includes a main conveying pipeline 8, a bypass conveying pipeline 9, a first regulating valve 2, a second regulating valve 5, a first pulverized coal concentration monitor 3, and a second pulverized coal concentration monitor 6.

[0046] In the pulverized coal conveying and regulating unit, one end of the main conveying pipeline 8 is connected to the outlet of the coal mill 1, and the other end is directly connected to the main burner 4 of the boiler furnace 10. The first regulating valve 2 and the first pulverized coal concentration monitor 3 are installed sequentially on the main conveying pipeline 8. One bypass conveying pipeline 9 is connected to the coal mill 1, and the other end is connected to the independent burner 7. The second regulating valve 5 and the second pulverized coal concentration monitor 6 are installed sequentially. The regulating valve adopts a servo control valve with an adjustment accuracy of ±0.5%, so as to realize the precise control of the pulverized coal supply to the independent burner.

[0047] The pulverized coal conveying and regulating unit is used to achieve flexible distribution and precise conveying of pulverized coal among various units. The optimized design is as follows: The main conveying pipeline has a diameter of DN300~DN500 and is equipped with an electric eccentric rotary valve (first regulating valve) and a microwave-based pulverized coal concentration monitor (first pulverized coal concentration monitor, range 0~10kg / m³, accuracy ±0.2kg / m³). A new pulverized coal intake branch and an independent burner inlet pipeline are added to the bypass conveying pipeline, supplying pulverized coal to the independent burner through the independent burner inlet pipeline.

[0048] The inlet pipeline of the independent burner is equipped with a servo-controlled valve with an adjustment accuracy of ±0.5%; the combustion fan adopts a variable frequency centrifugal fan with an air volume adjustment range of 0~5000m³ / h to ensure stable coal powder transportation. All pipelines are arranged with an inclination angle of ≥5°, and compressed air purging ports are installed at bends, which automatically purge once per hour to prevent coal powder accumulation.

[0049] The central control unit is electrically connected to the direct-fired pulverizing unit, the externally coupled pulverized coal silo unit, and the pulverized coal conveying and regulating unit, respectively. It is used to receive boiler load commands and dynamically regulate the operating parameters of each unit based on a preset algorithm. The central control unit includes a PLC controller, a human-machine interface, and a data storage module.

[0050] The preset algorithm of the central control unit is a fuzzy PID-model prediction composite control algorithm, which includes a fuzzy control module, a PID control module, and a model prediction module. The fuzzy control module outputs the correction value of the PID control parameters based on the deviation and the rate of change of the deviation between the boiler load command and the actual combustion rate. The model prediction module constructs a combustion process prediction model based on furnace temperature field data, flue gas composition data, and combustion stability index, predicts the combustion state change trend in the next 30-60 seconds, and outputs an advance control command. Based on the corrected parameters and the advance control command, the PID control module performs closed-loop control on the coal feed rate of the coal feeder, the grinding load of the coal mill, the opening degree of each regulating valve, the speed of the variable frequency pulverizer, and the operating parameters of the independent burners.

[0051] The central control unit receives boiler load commands, integrates monitoring data from various units, and dynamically adjusts the operating parameters of each unit through control algorithms to achieve automated and intelligent operation of the entire fuel system. This unit includes a PLC controller, a human-machine interface, a data storage module, a fault diagnosis module, and an alarm module, as detailed below:

[0052] The PLC controller employs a programmable logic controller, equipped with a high-speed processing module and a multi-channel input / output module, capable of simultaneously processing analog and digital signals from various monitoring modules. The PLC controller incorporates a fuzzy PID composite control algorithm, which is the core of the control strategy of this invention. This algorithm enables precise regulation of the pulverized coal supply based on the dynamic characteristics of boiler load changes. The working principle of the fuzzy PID composite control algorithm is as follows: First, the fuzzy control module takes the deviation (e) and the rate of change of deviation (ec) between the boiler load command and the actual combustion rate in the furnace as input quantities. Through preset fuzzy rules (based on a large amount of operational data and expert experience), it outputs corrected values ​​for the PID control parameters (proportional coefficient Kp, integral coefficient Ki, and derivative coefficient Kd). Then, based on the corrected Kp, Ki, and Kd parameters, the PID control module performs closed-loop control of the coal feeder's coal rate, the pulverizer's grinding pressure, the opening degree of each regulating valve, and the variable frequency pulverizer's speed, enabling the pulverized coal supply to quickly and stably track the boiler load demand. Compared with traditional PID control, the fuzzy PID composite control algorithm has stronger adaptability and robustness, and can effectively cope with the nonlinearity and large time lag characteristics of fuel systems.

[0053] The human-machine interface uses a touchscreen and has display, operation, and setting functions. The interface can display key parameters in real time, such as boiler load commands, actual load, coal mill operating status, pulverized coal silo level, pulverized coal concentration, temperature, and pressure in each pipeline, using intuitive display formats such as bar charts and line graphs to facilitate operator monitoring of system operation. Simultaneously, the interface supports manual operation, allowing operators to manually adjust the operating parameters of various devices under special circumstances, such as manually opening / closing regulating valves and adjusting the variable frequency feeder speed. Furthermore, the interface also supports setting and modifying control parameters, such as setting upper and lower limits for pulverized coal silo level and the control range for inert gas.

[0054] The data storage module uses industrial-grade solid-state drives with a storage capacity of 1TB, capable of storing system operating data in real time, including various monitoring parameters, equipment operating status, control commands, etc., with a storage period of up to one year. The stored data can be used for traceability analysis of system operating status, optimization and upgrading of control algorithms, and fault diagnosis, while also meeting the power industry's requirements for archiving operating data.

[0055] The fault diagnosis module, based on a neural network algorithm, constructs a fault identification model by collecting real-time and historical operating data from various monitoring modules. The module can identify fault types including: abnormal silo level (too high or too low), abnormal silo temperature (overheating indicating a risk of spontaneous combustion), abnormal silo pressure (overpressure or negative pressure), stuck regulating valves, abnormal feeder operation (mismatch between speed and feed rate), abnormal pulverized coal concentration (too high or too low), and abnormal mill operation (excessive vibration, excessive temperature). When a fault is identified, the fault diagnosis module immediately triggers the alarm module and outputs the fault type, fault location, and suggested handling measures.

[0056] The alarm module includes both audible and visual alarms and SMS alarms. The audible and visual alarm is installed on the cabinet of the central control unit. In the event of a general fault, it emits a yellow light and intermittent alarm sound; in the event of a serious fault (such as overheating or overpressure in the powder silo), it emits a red light and continuous alarm sound. The SMS alarm is linked to the operator's mobile phone via a GSM module. In the event of a serious fault, it automatically sends an alarm SMS to a preset mobile phone number, ensuring that the operator is promptly informed and can handle the fault.

[0057] In addition, the central control unit also has the function of communicating with the boiler distributed control system (DCS). It can interact with the DCS system through the Ethernet interface, receive boiler load commands issued by the DCS system, and feed back the fuel system operating status to the DCS system to realize the coordinated control of the entire boiler unit.

[0058] As another preferred embodiment, this embodiment also includes a pulverized coal quality pretreatment and adaptation module. This module is installed between the coal mill and the pulverized coal conveying and regulating unit, and includes a pulverized coal screening device, a magnetic separation device, and a pulverized coal humidity regulating device. The pulverized coal screening device adopts a rotating screen structure, and the screen aperture can be adjusted according to the boiler combustion requirements to screen out pulverized coal particles with excessive particle size. The magnetic separation device has a built-in strong magnetic rod array to remove metallic impurities from the pulverized coal. The pulverized coal humidity regulating device sprays a quantitative amount of demineralized water onto the pulverized coal through an ultrasonic atomizing nozzle, controlling the pulverized coal humidity within the optimal combustion range of 2%~4%, with a humidity control accuracy of ±0.2%. The fault diagnosis module, based on real-time data and historical operating data from each monitoring module, identifies faults such as pulverized coal silo blockage, valve jamming, pulverized coal feeder malfunction, and unstable combustion through a combination of neural network algorithms and fault tree analysis. It outputs specific optimized control schemes for combustion-related faults, such as adjusting the independent burner's stable combustion parameters and optimizing the secondary air ratio to achieve fault self-repair.

[0059] System Installation and Debugging Installation Process The installation of this system can be divided into five stages, as follows: Stage 1: Foundation Construction. Based on the equipment dimensions and weight of the external coupling pulverized coal silo unit and the pulverized coal conveying and regulating unit, a concrete foundation is poured in the available area of ​​the boiler room. The bearing capacity of the foundation must be at least 1.5 times the weight of the equipment, and anchor bolt holes are reserved. After the foundation construction is completed, curing is carried out for no less than 28 days.

[0060] Phase Two: Equipment Installation. First, hoist the pulverized coal silo onto the concrete foundation and secure it with anchor bolts, ensuring the silo's verticality deviation is ≤1‰. Second, install the traditional pulverizing units such as the coal mill and feeder, ensuring the installation accuracy meets relevant standards. Next, install the main and bypass conveying pipelines of the pulverized coal conveying and regulating unit. The pipeline welding uses an argon arc welding root pass followed by manual electric arc welding for the cover pass. After welding, a hydrostatic test is conducted at 1.5 times the working pressure to ensure no leaks. Finally, install the central control unit cabinet. The cabinet should be installed in a location easily accessible for operators, while being away from high-temperature and humid areas.

[0061] Phase 3: Installation of Monitoring and Control Modules. Install the sensors for the material level monitoring module, temperature monitoring module, pressure monitoring module, and inert gas protection module in the preset positions, ensuring that the sensors are securely installed and the measurements are accurate; connect the control lines of various regulating valves, variable frequency powder feeders, powder conveying fans, and other equipment to the PLC controller of the central control unit. The wiring should be protected by conduit to avoid interference.

[0062] Phase 4: Pipeline Connection and Sealing. Complete the pipeline connection between the traditional pulverizing unit, the externally coupled pulverizing silo unit, and the pulverized coal conveying and regulating unit. All flange connections use temperature-resistant and wear-resistant gaskets to ensure a tight seal. Conduct an airtightness test on the pulverizing silo body at a pressure of 0.1 MPa for 30 minutes. The pressure drop should be ≤0.005 MPa to ensure no leakage from the silo.

[0063] Phase 5: System Integration. Establish communication connections between the central control unit and the boiler DCS system, and configure the data exchange protocol; organize and label the wiring of the entire system to ensure clear wiring and ease of maintenance.

[0064] 1.2 Debugging Process After the system installation is completed, a comprehensive debugging is required to ensure that each unit operates normally and works well in coordination. The debugging process is as follows: First Stage: Single Machine Debugging. The equipment of the traditional coal pulverizing unit, external coupling coal bin unit, coal powder conveying and regulating unit, and central control unit is debugged separately. For the coal feeder, test its variable frequency speed regulation function and the accuracy of the coal feeding amount; for the coal mill, test its grinding pressure regulation function and the stability of the inlet and outlet temperature and pressure; for the coal bin unit, test the measurement accuracy of the level, temperature, and pressure monitoring modules, as well as the start-stop and regulation functions of the inert gas protection module; for the regulating valve and variable frequency coal feeder, test their response speed and regulation accuracy; for the central control unit, test its data acquisition, display, and storage functions.

[0065] Second Stage: Local Linkage Debugging. After the single machine debugging is qualified, local equipment coordination tests are carried out according to the functional module division, focusing on verifying the accuracy of the logical cooperation of the equipment within the module.

[0066] Linkage between Coal Pulverizing and Coal Storage: Test the load matching of the coal feeder and the coal mill. When the fineness of the coal powder at the outlet of the coal mill meets the standard, the feed valve of the coal bin is automatically linked and opened, and the coal feeding is automatically shut down when the level reaches the preset upper limit, verifying the reliability of the interlock control logic.

[0067] Linkage between Coal Storage and Coal Feeding: Test the linkage regulation of the coal bin level signal and the variable frequency coal feeder. When the level is lower than the lower limit value, the coal feeding amount is automatically reduced to avoid idling; the inert gas protection module is linked with the coal feeding fan, and inert gas is automatically introduced before the fan starts, and the coal feeding can only be started after the oxygen content drops below the safe value.

[0068] Linkage of Control Modules: Test the closed-loop control of the temperature and pressure monitoring data and the regulating valve. When the pipeline temperature or pressure exceeds the set range, the valve can automatically adjust the opening degree to ensure that the parameters are stable within the allowable range.

[0069] Third Stage: Full System No-Load Joint Debugging. Simulate the actual operation process and conduct full system linkage tests without coal powder load to verify the collaborative working ability of each unit.

[0070] Verification of Startup Process: Start the system according to the preset program, and test the startup sequence of the coal feeder, coal mill, coal feeding fan, and control unit in turn to ensure that there is no logical conflict or startup failure.

[0071] Monitoring of Operating Status: Operate continuously for 2 hours, record the operating parameters (current, voltage, temperature, pressure) of each device, and verify the real-time data interaction between the central control unit and the boiler DCS system without data loss or delay.

[0072] Fault simulation test: Simulate scenarios such as sensor failure, valve jamming, and power fluctuation to verify the effectiveness of the system's alarm function and emergency shutdown procedure, ensuring that related equipment can be quickly shut down in the event of a fault to avoid cascading damage.

[0073] Phase 4: Load-bearing commissioning. The system is then tested under actual operating conditions using real pulverized coal as the medium, gradually increasing the load to the design rating to verify actual operational performance.

[0074] Graded load test: Starting from 30% of the rated load, gradually increase to 50%, 80%, and 100%, and run stably for 1 hour at each load level to test the stability of coal powder conveying and the uniformity of powder feeding, and ensure that there is no powder accumulation or blockage in each pipeline.

[0075] Hot performance verification: The system was continuously operated under rated load for 4 hours to monitor the grinding efficiency of the coal mill, the insulation effect of the powder silo, and the heat loss of the pipeline. The system parameters under hot conditions were verified to be stable and the Nusselt number and resistance coefficient met the design requirements.

[0076] Re-inspection of sealing performance: During operation under load, the main body of the powder silo, the flange connection of the pipeline and the sealing surface of the valve were checked and no coal powder leakage was found; the air tightness of the powder silo was checked again and the pressure drop was still ≤0.005 MPa.

[0077] Phase 5: Debugging, Finalization, and Acceptance. After load testing is completed, a comprehensive review and optimization process is conducted, along with document archiving, to ensure the system meets delivery requirements.

[0078] Function optimization: Based on load debugging data, fine-tune PLC control parameters to optimize equipment response speed and operational stability, and resolve minor deviations found during debugging.

[0079] Comprehensive performance testing: Acceptance is carried out item by item according to the design specifications, including coal feeding accuracy, pulverized coal conveying efficiency, temperature and pressure control accuracy, fault response time, etc., to ensure that all indicators meet the relevant standards.

[0080] Documentation: Record debugging data, troubleshooting solutions, and parameter settings at each stage to form a complete debugging report; organize equipment manuals, wiring diagrams, and control program backups to provide a basis for subsequent operation and maintenance.

[0081] This embodiment also provides a method for regulating a direct-fired boiler variable load fuel system with an externally coupled pulverized coal silo as follows: S1: System initialization. The central control unit directly reads the current boiler load and pulverizer operating status from the boiler controller, i.e., obtains the pulverizer motor switch signal, pulverized coal silo level, furnace temperature field, and various monitoring parameters. The inert gas concentration in the pulverized coal silo is adjusted to a preset range, and each regulating valve is at its initial opening of 20%~30%. The independent burners enter standby mode. S2: The central control unit receives the boiler load signal and, combined with the real-time data from the combustion status sensing module, determines whether the load change type is load increase, load decrease, or steady-state operation. It then calculates the target combustion parameters, including the target coal feed rate, target total air volume, target air-coal ratio, and target oxygen content. When the change is deemed to be in compliance, the preset deviation between the actual load and the set load is less than ±3%~±5%. If the deviation between the actual load and the set value is within the allowable range, it is determined to be a stable load. If the load set value increases or the actual load continues to increase, it is determined to be a load increase. If the load set value decreases or the actual load continues to decrease, it is determined to be a load decrease.

[0082] S3: If it is a load increase command, calculate the pulverized coal demand corresponding to the load increase, and compare the current maximum pulverized coal supply capacity of the coal mill with the remaining pulverized coal in the pulverized coal silo: When calculating the pulverized coal demand corresponding to the load increase, first calculate the increased heat power ΔQ. ; Target load thermal power (kW / MW); Current load thermal power (kW / MW); ΔQ: Required additional heat output; Calculate the corresponding increase in pulverized coal ΔB. ΔB: The amount of pulverized coal required (kg / s or t / h), ΔQ: The thermal power (kW) corresponding to the load increment. The net calorific value of pulverized coal (kJ / kg) is calculated based on the received weight. Boiler efficiency (0.88~0.92).

[0083] S31: If the remaining pulverized coal in the pulverized coal bin meets the load increment demand, the central control unit controls the opening of the first regulating valve, starts the variable frequency pulverizer, and simultaneously controls the opening ratio of the first and second regulating valves based on the target opening degree of the first regulating valve, the target opening degree of the second regulating valve, and the optimal ratio command of the two output by the model prediction module. Pulverized coal is rapidly replenished through the coordinated method of independent burner and main conveying pipeline bypass replenishment; at the same time, the coal mill load is gradually increased to a new steady-state pulverized coal supply level, that is, after the coal mill load is increased, the coal output is stable, continuous, and stable. S32: After the coal mill's coal supply stabilizes, the variable frequency feeder speed is gradually reduced using a fuzzy PID algorithm to prioritize consuming the coal powder in the pulverizer; S4: If the remaining coal powder in the pulverizer is insufficient, the central control unit controls the variable frequency feeder to operate at its maximum safe speed, the independent burner supplies coal at full load, and simultaneously increases the coal mill load and coal feeder rate. The coal powder quality pretreatment and adaptation modules simultaneously improve screening accuracy and humidity control accuracy, shortening the coal mill's coal supply response time until the boiler load reaches the command value; S5: If it is a load reduction command, the load reduction is calculated to affect the... To address the corresponding coal powder redundancy, the central control unit reduces the opening of the first regulating valve while simultaneously opening the second regulating valve and the coal powder supply fan. This allows the surplus coal powder ground by the pulverizer to be sent to the coal powder storage silo via the coal powder supply branch. The main burner's coal powder supply is reduced to 80%–90% of the new load demand. The independent burners are then activated and switched to stable combustion mode. The combustion optimization subsystem adjusts the coal powder supply and secondary air ratio of the independent burners to maintain the combustion stability index within the acceptable range. This process continues until the pulverizer's coal powder supply matches the new load demand. Finally, the coal powder supply branch is closed, ensuring a smooth transition between the main burner and the independent burner. The burner's coordinated stable combustion mode: when the load is reduced, the main burner is reduced to only 80% to 90% of the new load demand, avoiding drastic fluctuations in furnace heat load caused by a sudden drop in pulverized coal supply; at the same time, the independent burner is put into operation and switched to stable combustion mode. Through the combustion optimization subsystem, the pulverized coal supply and secondary air ratio of the independent burner are precisely adjusted, which can quickly stabilize the furnace flame, maintain a reasonable air-coal ratio, and ensure that the combustion stability index is within the qualified range. This significantly improves the stability, safety and load regulation response speed of the boiler during the load reduction process, and enhances the boiler's deep peak shaving and adaptability to changing operating conditions.

[0084] S5: In steady-state operation, the central control unit maintains stable operation of the coal mill and monitors the coal pulverizer level and furnace combustion status in real time. When the coal pulverizer level is lower than the preset lower limit, the coal pulverizer supply in the main conveying pipeline is appropriately reduced, and some coal pulverizer is sent to the coal pulverizer for replenishment. When the coal pulverizer level is higher than the preset upper limit, the coal pulverizer supply to the coal pulverizer is stopped, and the coal pulverizer in the coal pulverizer is consumed by the independent burner. At the same time, based on temperature field data and flue gas composition data, the coal pulverizer supply, injection angle, and secondary air parameters of the independent burner are dynamically optimized through the model prediction module, so that the uniformity of the furnace temperature field is improved by more than 20%, and the CO emission is reduced by more than 15%. The model prediction module is based on the furnace combustion heat balance, flow and reaction dynamics. According to the current temperature field, flue gas composition, and burner parameters, iteratively predicts the furnace temperature distribution and flue gas composition changes in the short term in the future. With the goal of the most uniform temperature field and the lowest CO emission, the optimal control quantity of the independent burner is solved iteratively.

[0085] S6: Throughout the operation, the central control unit collects data in real time through various monitoring modules. If abnormal parameters or fault signals are detected, corresponding control measures or fault handling procedures are immediately executed. Abnormal parameters refer to key monitoring values ​​such as temperature, pressure, flow rate, material level, current, and oxygen content exceeding the normal operating range or changing at an excessively rapid rate, but before triggering a protective shutdown. Fault signals refer to fault status signals emitted by the equipment itself, actuators, sensors, or safety circuits, indicating that the equipment has failed, lost power, lost synchronization, tripped, or poses a safety hazard. For abnormal oxygen levels at the furnace outlet, adjust the pulverized coal feed rate / total air volume and correct the air-coal ratio; for abnormal negative pressure in the furnace, adjust the induced draft fan opening and strengthen furnace suction; for abnormal mill temperature, adjust the cold air opening, increase the hot air ratio, and improve drying output; for low primary air pressure / flow, increase the primary air fan frequency to prevent pulverized coal blockage and interruption; for excessively low pulverized coal silo levels, trigger a feeding reminder, limit high-load increases, and avoid coal shortages; for large fluctuations in pulverized coal flow, optimize the pulverizer speed, stabilize the primary air pressure, and smooth pulverized coal supply; for combustion stability index below the threshold, activate the stable combustion emergency plan, increase the output of independent burners, and slow down the pulverized coal supply rhythm of the main burner.

[0086] When the burner shuts off / flame detection malfunctions, immediately cut off the pulverized coal supply, start purging, and prohibit forced pulverization; when the pulverizer main motor trips / malfunctions, interlock and close the corresponding pulverized coal valve, start the standby pulverizer, and reduce the load; when the pulverizer lubricating oil pressure is low, prohibit starting, or if already running, trigger the trip protection; when the coal feeder stops coal supply, stalls, or malfunctions, stop feeding, start the unblocking logic, and alarm to remind maintenance; when the primary / secondary air fan malfunctions and shuts down, quickly reduce the load, interlock protection, and prevent combustion deterioration; when the damper / regulating valve is stuck or feedback is lost, switch to manual control, alarm, and prohibit automatic large-scale adjustment; when the temperature / pressure / level sensor is disconnected / failed, switch to redundant signals, automatically limit load changes, and alarm for maintenance; when the pulverized coal silo temperature is high, start cooling, inerting, and fire alarm, and prohibit continued pulverization.

[0087] When the combustion stability index falls below the threshold, the emergency plan of the combustion optimization subsystem is automatically activated to restore combustion stability by enhancing the combustion stability of the independent burners and adjusting the coal supply rhythm of the main burner.

[0088] Under low-load conditions (load less than 30% of rated load), the central control unit monitors the ignition point position and temperature of the independent burner in real time through the combustion status sensing module. When the ignition point deviates by more than 100mm or the temperature is lower than 800℃, the power of the central stable ignition device and the intensity of the secondary air swirl are automatically adjusted to ensure stable ignition. At the same time, the coal powder quality pretreatment and adaptation module adjusts the coal powder humidity to 3%~4% to improve the ignition performance of the coal powder.

[0089] This invention, through a composite architecture of a traditional pulverizing system, an externally coupled pulverizing silo, and intelligent control, has significant technical advantages and practical value compared to existing direct-fired boiler fuel systems. The specific beneficial effects are as follows: 1. Dual improvement in load response speed and combustion stability: Through the synergy of the externally coupled pulverizing silo and the independent burner, the fuel response delay is shortened from several minutes to seconds; under low load conditions, the stable combustion design of the independent burner improves the combustion stability index and solves the potential for fire extinguishing under low load conditions.

[0090] 2. Achieving redundant pulverized coal recovery and utilization to reduce energy consumption and equipment wear: In existing direct-fired pulverized coal systems, redundant pulverized coal from the pulverizer is often wasted due to the lack of a storage path when the load is reduced. Furthermore, the pulverizer requires frequent start-ups and shutdowns or drastic load adjustments, exacerbating equipment wear and energy consumption. While traditional mixed pulverizing systems can store pulverized coal, they lack a targeted recovery mechanism. This invention, through the bypass pipeline design of the pulverized coal conveying and regulating unit, can efficiently deliver redundant pulverized coal from the pulverizer to an externally coupled pulverized coal silo for storage during load reduction, avoiding pulverized coal waste. Simultaneously, it reduces the frequency of pulverizer start-ups and shutdowns and the amplitude of load fluctuations, extending the service life of core equipment such as the pulverizer and feeder, reducing equipment maintenance costs, and minimizing the additional power consumption caused by frequent feeder adjustments, achieving the dual benefits of energy saving and consumption reduction.

[0091] 3. Optimized Combustion Efficiency and Environmental Performance: Multi-dimensional combustion monitoring and composite control algorithms effectively improve furnace temperature field uniformity and combustion efficiency, reducing CO and NO emissions. x Emissions meet environmental protection requirements.

[0092] 4. Constructing a comprehensive safety protection system to mitigate coal powder storage risks: Existing large-scale storage systems suffer from safety hazards such as spontaneous combustion and explosion of coal powder due to their large volume and insufficient ventilation and monitoring; some simplified coal powder storage improvement schemes lack comprehensive safety control measures. This invention's externally coupled coal powder silo unit is equipped with a triple monitoring module for material level, temperature, and pressure, combined with a ring-shaped temperature sensor array and real-time oxygen content monitoring, achieving comprehensive perception of the coal powder storage status; through an inert gas protection module, it precisely controls the oxygen content inside the silo to ≤8% and the temperature to ≤50 ℃, suppressing spontaneous combustion of coal powder oxidation from the source; in conjunction with a pressure relief valve and an anti-clogging stirring device, it completely avoids safety risks such as silo blockage, overpressure, and explosion, with safety far exceeding that of traditional storage silos and simplified coal powder storage schemes.

[0093] 5. Improve combustion stability and control precision, and reduce pollutant emissions. Existing systems often require operators to predictively adjust fuel supply due to lag in response, which can easily lead to excessive or insufficient pulverized coal, causing furnace temperature fluctuations, decreased combustion efficiency, and even the risk of flameout or deflagration. This invention integrates data from various monitoring modules through a fuzzy PID composite algorithm in the central control unit, dynamically adjusting the coal feed rate, valve opening, and feeder speed to precisely match the pulverized coal supply with the furnace combustion demand. Simultaneously, an optional pulverized coal quality pretreatment module removes coarse particles and metallic impurities, optimizes pulverized coal combustion performance, and reduces pollutant emissions caused by incomplete combustion, thus improving boiler operational stability and meeting environmental protection requirements.

[0094] 6. High level of intelligence, reducing operation and maintenance costs and operational complexity. Existing systems mostly rely on manual monitoring and control, resulting in high operational complexity and lagging fault identification; some improvement solutions have low levels of intelligence and lack integrated management capabilities. The central control unit of this invention achieves full-process automation of data acquisition, status monitoring, precise control, and fault diagnosis. It intuitively displays operating parameters through a human-machine interface and supports manual / automatic mode switching; the fault diagnosis module is based on neural network algorithms, which can identify faults such as powder silo blockage and valve jamming in advance and trigger audible, visual, and SMS alarms. With detailed fault handling suggestions, it reduces the skill requirements of operators, reduces manual intervention costs, and improves operation and maintenance efficiency and system reliability.

[0095] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A variable load fuel system for a direct-fired boiler with an externally coupled pulverized coal silo, characterized in that, include: The externally coupled pulverized coal silo is configured with an effective volume to meet the pulverized coal consumption for 5 to 10 minutes under the boiler's rated load; the externally coupled pulverized coal silo is equipped with a material level monitoring module; Its inlet is connected to the output end of the direct-fired pulverizing system, and its outlet is connected to the downstream pipeline through a pulverizing feeder; the combustion control unit includes at least one independent burner set independently of the boiler main burner; the pulverized coal distribution pipeline unit includes pipelines connecting the direct-fired pulverizing system, the externally coupled pulverizing silo, the boiler main burner, and the independent burner, as well as regulating valves installed on the pipelines and the pulverizing feeder; the pipelines and valves are configured to enable switching of the pulverized coal conveying path between the pulverizing system, the externally coupled pulverizing silo, the main burner, and the independent burner; the central controller is connected to the direct-fired pulverizing unit, the material level monitoring module of the externally coupled pulverizing silo, the combustion control unit, and the pulverized coal distribution pipeline. The regulating valves and pulverized coal feeding equipment in the pipeline unit are connected by signals. The central controller is used to receive boiler load signals and boiler combustion status feedback, and execute the following dynamic control logic: When the load increases, the pulverized coal feeding equipment is controlled to transport the pulverized coal in the external coupling pulverized coal bin to the independent burner for combustion, and the output of the direct-fired pulverizing system is increased simultaneously. When the load decreases, the pulverized coal distribution pipeline unit is controlled to divert part of the pulverized coal from the direct-fired pulverizing system to the external coupling pulverized coal bin for storage, and the independent burner is controlled to perform stable combustion operation. During steady-state operation, based on the material level status of the external coupling pulverized coal bin and the combustion status of the boiler, the pulverized coal distribution pipeline unit and the independent burner are controlled to dynamically maintain the pulverized coal bin inventory and optimize furnace combustion.

2. The variable load fuel system for a direct-fired boiler with an externally coupled pulverized coal silo as described in claim 1, characterized in that, The pulverized coal preparation pipeline unit includes: a main conveying pipeline connecting the outlet of the direct-fired pulverizing system to the main burner of the boiler; a pulverized coal feeding bypass, the first end of which is connected to the main conveying pipeline and the second end of which is connected to the feed inlet of the external coupling pulverized coal silo; and a pulverized coal taking bypass, the first end of which is connected to the discharge outlet of the external coupling pulverized coal silo through the pulverized coal feeding equipment, and the second end of which has at least two branches, respectively connected to the independent burner and the main conveying pipeline located downstream of the first end.

3. The variable load fuel system for a direct-fired boiler with an externally coupled pulverized coal silo as described in claim 2, characterized in that, A first regulating valve is installed on the branch pipe connected to the independent burner; a second regulating valve is installed on the branch pipe connected to the main delivery pipeline; the central controller dynamically allocates the flow of pulverized coal from the external coupling pulverized coal silo to the independent burner and the main burner by controlling the opening ratio of the first regulating valve and the second regulating valve according to the amplitude and rate of change of the boiler load command.

4. The variable load fuel system for a direct-fired boiler with an externally coupled pulverized coal silo as described in claim 1, characterized in that, The combustion control unit further includes a combustion state sensing module for acquiring real-time combustion status data in the furnace; the combustion state sensing module includes a furnace temperature field monitoring submodule; wherein, the furnace temperature field monitoring submodule adopts a combination of an infrared thermal imager and a wall thermocouple array, the infrared thermal imager is installed in the furnace observation hole for acquiring real-time two-dimensional temperature field imaging of the cross-sectional area inside the furnace, the wall thermocouple array is arranged at intervals along the height of the furnace for monitoring the temperature distribution of the furnace wall, and the furnace temperature field monitoring submodule is signal-connected to the central controller.

5. The variable load fuel system for a direct-fired boiler with an externally coupled pulverized coal silo as described in claim 4, characterized in that, In the optimization of steady-state operation, the central controller is specifically configured to: identify local low-temperature or high-temperature zones in the furnace based on the temperature field data acquired by the infrared thermal imager; and guide the combustion flame to the low-temperature zone for reinforcement by adjusting the injection angle and swirl intensity of the independent burner.

6. The variable load fuel system for a direct-fired boiler with an externally coupled pulverized coal silo as described in claim 1, characterized in that, The central controller executes a composite control algorithm combining fuzzy PID control and model predictive control. The model predictive control module predicts the boiler's combustion trend and pulverized coal demand over a future period based on the current combustion state and historical data, and generates feedforward control commands. The fuzzy PID control module performs feedback adjustment based on the real-time deviation between the boiler load command and the actual combustion load. The central controller integrates the feedforward control commands and feedback adjustment results to generate coordinated control signals for the pulverized coal feeding equipment, the regulating valves, and the independent burners.

7. The variable load fuel system for a direct-fired boiler with an externally coupled pulverized coal silo as described in claim 1, characterized in that, The externally coupled powder silo includes an inert gas protection system, which includes multiple oxygen content sensors arranged along the height of the silo. The central controller dynamically adjusts the flow rate of inert gas introduced into the bottom of the powder silo based on the oxygen concentration gradient monitored by each sensor, so as to maintain the uniformity of the longitudinal oxygen concentration distribution within the silo.

8. A control method for a variable load fuel system of a direct-fired boiler with an externally coupled pulverized coal silo as described in any one of claims 1-7, characterized in that, The process, executed by the central controller, includes the following steps: acquiring the target load command of the boiler and a status signal reflecting the current combustion load; determining the deviation between the target load command and the current combustion load to ascertain whether the boiler is in a state of increased load demand, decreased load demand, or steady-state operation demand; if it is a state of increased load demand, starting the pulverized coal feeding equipment to transport the pulverized coal stored in the externally coupled pulverized coal silo to the independent burner, and controlling the independent burner to switch to enhanced combustion mode; simultaneously, issuing an increased output command to the direct-fired pulverizing system; if it is a state of decreased load demand, adjusting the valves in the pulverized coal distribution pipeline unit to divert a portion of the pulverized coal output from the direct-fired pulverizing system to the externally coupled pulverized coal silo for storage; simultaneously, controlling the independent burner to switch to stable combustion mode; if it is a state of steady-state operation demand, monitoring the material level in the externally coupled pulverized coal silo and the combustion state in the furnace, and adjusting the operating parameters of the pulverized coal distribution pipeline unit and the independent burner accordingly to dynamically balance the pulverized coal silo inventory and optimize the combustion process.

9. The method according to claim 8, characterized in that, During steady-state operation, when the material level in the externally coupled powder silo is detected to be lower than the first preset threshold, the coal powder distribution pipeline unit is controlled to introduce a portion of the coal powder from the direct-fired pulverizing system into the externally coupled powder silo. When the material level is higher than the second preset threshold, the independent burner is controlled to increase its output to consume some of the pulverized coal in the externally coupled pulverized coal bin. During steady-state operation, the temperature field distribution image of the furnace cross section is acquired in real time. If the temperature field distribution image is analyzed and it is found that the temperature non-uniformity exceeds the allowable range, the low-temperature zone or high-temperature zone in the furnace is targeted by adjusting the pulverized coal supply, secondary air ratio or injection angle of the independent burner.

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