W火焰锅炉炉内三维流场和颗粒运动轨迹的数值模拟

Numerical Simulation of Three-dimensional Flow Field and Particle Trajectory in W-shaped Flame Boiler

W火焰锅炉具有独特的炉膛和烟气流动结构，适用于低挥发份劣质煤发电，炉膛配风和煤粉颗粒对W火焰锅炉形成良好的炉内燃烧和保证安全高效洁净燃烧影响显著．针对300MWW火焰锅炉，采用RNGk～F和DPM模型数值研究了不同工况下W火焰锅炉炉内三维流场和煤粉颗粒运动轨迹，分析了炉膛配风和煤粉粒径对流场特性的影响．研究表明：配风对流场对称性影响很大，不合理的配风可导致火焰“短路”和气流冲刷冷灰斗．炉膛折焰角结构决定了对称的配风形成非对称流场，但增加前墙配风速度可有效平衡折焰角效应．当前后墙配风比为1．05时流场对称性最佳．下炉膛冷灰斗区双旋涡流动结构可增强煤粉气流热质交换，增加煤粉停留时间，有利于煤粉燃尽．随粒径增大，煤粉深入下炉膛平均深度越大，煤粉在燃烧炉膛内停留时间先增大后减小，存在最佳煤粉粒径．研究结果对大容量W火焰锅炉设计和燃烧调整有意义．

W-shaped flame boiler is especially suitable for the electricity generation using low-volatile and poor quality coal, owing to the particular structure of the furnace and flue gas flow characteristics. The air distribution and coal particle has great effect on forming favorable combustion in the furnace of W-shaped flame boiler. The air distribution and coal particle has also great effect on ensuring boiler＇ s safe, high-efficiency and clean burning. RNG k - ω model and DPM model were used to simulate the three-dimensional flow field and the flowing trajectory of coal particle at different operating conditions of a 300MW W-shaped flame boiler. The simulations of flow field were implemented at different air distribution and different diameter of coal particle. The results indicate that the air distribu- tion has great effect on the symmetry of W-shaped flow field in furnace. The flame will be ＂short circuit＂ when the primary air is too small. The bottom ash hopper will be eroded by the flue gas flow when the secondary air is too large. Because of the nose of the furnace, symmetrical air distribution can not form symmetrical flow field. The increase of the second air velocity on the front wall can decrease the effect of the nose of the furnace. The symmetry of flow field is best when the velocity ratio of the front wall to rear wall is 1. 05. The double vortexes flow structure forming in the bottom ash hopper can enhance the heat transfer and mass transfer of coal flow.The vortexes can also increase the residence time of coal particle in the combustion chamber and be in favor of the burnout of coal The diameters of coal particle are very important to the flow and combustion in W-shaped flame boiler. The average depth of coal particle going into the furnace increases with diameters of coal particle increasing. With diameters of coal particle increasing, the average residence time of the coal particle in the furnace increases until to a maximum value, and then decreases. An optimal diameter of coal particle exists for a W-shaped flame boiler. The study results are great significant for the design of large-capacity boiler and combustion adjustments of W-flame boiler.