[b]I. Overview of Boiler Combustion Equipment[/b] The No. 3 boiler of Meixian Power Plant is an SG-420/13.7-M419 type ultra-high pressure intermediate reheat natural circulation drum boiler designed and manufactured by Shanghai Boiler Factory for burning local anthracite coal. The combustion equipment adopts a four-corner tangential combustion method. The burner adopts the "WR" type burner introduced and improved by the American "CE" company. A wave-shaped diffuser cone is installed at the coal powder nozzle outlet. A concentric positive and negative tangential circle combustion system is adopted. The fuel air (primary air, oil gun air, tertiary air) jet enters the furnace tangentially with a tangential circle diameter of ф600/ф540 and rotates counterclockwise in the furnace. The secondary air jet that starts to rotate, which is close to the lower and middle primary air, enters the furnace in the opposite direction (deflected by 25°) to the fuel air, thus forming clockwise tangential combustion. A de-swirl secondary air is arranged above the tertiary air, which is opposite to the direction of the starting secondary air. The burner consists of, from top to bottom, a series of secondary air streams: swirl-free secondary air, tertiary air (with perimeter secondary air), upper oil gun secondary air, upper primary air (with perimeter secondary air), upper start-up secondary air, middle primary air (with perimeter secondary air), lower primary air (with perimeter secondary air), lower start-up secondary air, and lower oil gun air. To improve the ignition stability and complete combustion of anthracite, a 150m² protective combustion zone is arranged within the burner area. The designed coal type is: Mar=8.8%; Aar=26.4%; Vdaf=6.83%; Car=59.6%; Qnet=19.88MJ/kg; the actual coal type used is: Mar=7.33%; Aar=27.4%; Vdaf=3.73%; Car=61.72%; Qnet=20.75MJ/kg; the designed stable combustion load without oil injection is 70% of the rated load, and the design efficiency is 86%. [b]II. Basic Status After Commissioning[/b] The boiler was put into operation in October 1997. Due to the discrepancy between the actual coal consumption and the designed coal consumption, the boiler could only operate stably with complete oil removal at 80% load, and the thermal efficiency did not reach the design value. The combustible content of fly ash was generally above 10%. Our plant organized several efforts to address these problems, adjusting the burner angle and adding guide baffles. In order to improve the temperature of the burner area, we also significantly increased the area of ​​the combustion zone (from the designed 150㎡ to 320㎡), which improved the stability and economy of operation. The thermal efficiency reached the design level, the combustible content of fly ash decreased to about 8%, and the boiler could operate stably with complete oil removal at 75% load. However, due to the large area of ​​the combustion zone and the significant changes in coal quality, coking is severe during operation, causing the combustion zone to easily detach, leading to a decrease in boiler operation stability and economy, and several forced shutdowns due to large coke shedding. Therefore, it is necessary to find a practical technology to modify the burner that can both appropriately reduce the combustion zone area and further improve boiler operation stability and economy. [b]III. Working Principle of Louvered Burner:[/b] The structure of the louvered burner is shown in Figure 3-1. Five louvered blades (concentration grids) are installed in the primary air duct before entering the primary air nozzle, so that the primary air-coal airflow forms two coal powder airflows with large concentration differences: one concentrated on the left (fire side) and one diluted on the right (back fire side). After flowing through the louvered nozzle, the coal powder is injected into the furnace in the tangential direction of the imaginary tangential circle at the center of the furnace, forming a stable reflux zone at the nozzle outlet. This allows the high-temperature flue gas to continuously flow back to the root of the coal powder flare, thereby increasing the contact surface between the primary air-coal powder-air mixture and the reflux high-temperature flue gas, forming a "three-high" (high temperature, high humidity, high temperature, high temperature) reflux zone. This area (high pulverized coal concentration, high velocity gradient, and high temperature) allows the pulverized coal to ignite stably and burn rapidly, thereby reducing the combustible content of fly ash. Furthermore, due to the low pulverized coal concentration on the lean side, an oxidizing atmosphere is formed in the water-cooled wall area. Under this oxidizing atmosphere, the ash melting point increases, making it less prone to coking on the water-cooled wall tubes near the nozzle. Additionally, while peripheral air is difficult to introduce in conventional burners, it can be appropriately introduced in louvered burners. Its introduction not only reduces coking around the burner but also supplements the insufficient air during combustion, promoting complete combustion. 1 - Rich side outlet; 2 - Lean side outlet; 3 - Concentrator (louvers); 4 - Primary air duct; 5 - Louvered nozzle. The louvered burner nozzle outlet creates a localized "three-high" zone (high pulverized coal concentration, high velocity gradient, and high temperature), which has many positive effects on the stable combustion of the pulverized coal flare. These effects can be summarized as follows: 1. It reduces the ignition heat of the primary air pulverized coal flow. The increased local pulverized coal concentration relatively reduces the primary air volume in that area, lowering the ignition heat and accelerating the ignition of the pulverized coal flow. 2. The rapid temperature rise and large agitation of the pulverized coal flow accelerate the oxidation reaction rate of the pulverized coal, greatly enhancing the combustion of fixed carbon, reducing the combustible content of fly ash, and improving thermal efficiency. 3. The increased pulverized coal concentration lowers the ignition temperature of the primary air pulverized coal flow. The experiment shows that the relationship between pulverized coal concentration and ignition temperature of pulverized coal gas flow is shown in Table 3. Coal Type: Anthracite, Bituminous Coal; Initial Pulverized Coal Concentration in Pulverized Coal Gas Flow (kg/kg): 0.51, 5.0, 10.0, 0.43, 3.0, 5.0; Ignition Temperature of Pulverized Coal Gas Flow (°C): 1200, 800, 700, 540, 370, 325.　4. Increased pulverized coal concentration increases the emissivity of the flame and the heat absorption of radiation inside the furnace; it promotes ignition and increases the flame propagation speed. [b]IV. Burner Modification and Operation Adjustment Plan:[/b] 1. Replace the middle and lower primary air nozzles with new louvered burners; 2. Restore the upper and lower perimeter air (connected to the secondary air box hot air) of the middle and lower primary air nozzles, which were originally blocked to increase the local coal powder concentration at the burner outlet, and install actuator-controlled dampers. Operators can easily operate from the central control room according to load changes, effectively adjusting the incoming cooling air volume. This not only forms a large recirculation zone at the nozzle, thus effectively ensuring stable combustion under low load and preventing nozzle burnout due to premature ignition, but also timely replenishes the oxygen required for combustion after premature coal powder ignition; 3. Reduce the area of ​​the combustion zone from 320 m2 to 252 m2; in addition, increase the distance between the combustion zone and the nozzle from 30mm to 80mm to reduce coking around the nozzle; 4. Strictly implement the operating procedures, ensuring that the air velocity and coal powder feed rate of the primary air ducts at the four corners remain basically consistent; 5. Regularly reduce the pulverized coal level in the pulverized coal silo and maintain an appropriate pulverized coal level to prevent uneven pulverized coal feeding due to silo blockage or coal pulverized coal flow. 6. Before boiler ignition, appropriately open the cooling air of the louvered burner. After oil cut-off or when the load changes, adjust the opening of the cooling air damper in a timely manner to maintain a suitable ignition distance, ensure stable combustion, and prevent nozzle burnout. 7. Regardless of the load conditions, under the premise of ensuring no pipe blockage, the pulverized coal feed rate of the intermediate and lower primary air should be increased as much as possible to fully utilize the dominant role of the louvered burner in stabilizing and enhancing combustion and improving combustion efficiency. **V. Effects of the Modification:** 1. Stable boiler combustion: During normal operation, the temperature in the burner area remains relatively stable at around 1350℃, with minimal fluctuations in furnace negative pressure. Even when the load drops to 50%, normal combustion is maintained. 2. Significantly improved boiler efficiency: Test results show that the boiler efficiency was 87.3% before the overhaul and increased to 91.2% afterward. Actual operation statistics also indicate that the average combustible content in fly ash was 7.8% several months before the overhaul and decreased to 4.1% several months afterward, a reduction of 3.7%. 3. Significantly improved boiler coking: No large coke deposits were observed during operation. After more than two months of operation, the combustion belt remained intact upon inspection, and no large coke lumps were found inside the furnace. This demonstrates that the modification significantly improved the stability and economy of boiler operation, achieving the goal of reducing the combustion belt area while further improving boiler stability and economy. The modification yielded satisfactory results and has further promotional value. Therefore, the plant plans to apply this modification to the other three boilers. **References** 1. *Power Plant Boiler Principles*, Rong Luan'en, Yuan Zhenfu, Liu Zhimin, et al. [M]. Beijing: China Electric Power Press, 1997. 2. Shanxi Electric Power Industry Bureau. *Boiler Equipment Operation* [M]. China Electric Power Press, 1996. 3. Research and Application of Louvered Burners, Zhou Shaoji, Liu Hongliang, et al., *Huazhong Electric Power*, 1998.6. Author Biography: Xiao Shaoyun (1971-), male, from Dapu, Guangdong, boiler operation technician, engaged in centralized control operation management, contact number: 13823837109.