煤粉射流燃烧及火焰传播的大涡仿真

Large Eddy Simulation of Pulverized Coal Jet Combustion and Flame Propagation

研究煤粉射流燃烧优化控制问题,针对射流速度及挥发份含量对煤粉射流燃烧特性的影响,以小型炉膛模型为研究对象,采用大涡仿真方法(LES)和雷诺平均方法(RANS)对煤粉射流燃烧进行数值仿真,结果能够更精细地反映浓度及温度分布,且能更准确地预测火焰中心位置和炉内回流情况。然后,采用不同射流速度和挥发份含量下炉内流场分布模型特点进行仿真。仿真结果表明,射流速度过大会使火焰中心靠后,火焰直射对墙,造成较大的碰撞损失,分析发现5m/s为最优射流速度。通过不同挥发份含量煤粉对比,发现高挥发份煤的着火距离明显短于低挥发分煤,且在炉膛上部存在强烈的回流,将炉膛中心的高温气流卷吸到喷口附近,从而加快煤粉气流的升温及着火速度。仿真结果可为煤粉射流燃烧的稳定性和系统优化设计提供理论依据。

To explore the influence of jet velocity and volatile content on the characteristics of pulverized coal jet combustion, the paper took a test-furnace as the study subject. Firstly, based on the open-source computational flu- id dynamic （ CFD ） code OpenFOAM, large eddy simulation （ LES ） and Reynolds - averaged Navier - Stokes （RANS） were used respectively to simulate the combustion process. The comparing results suggest that the ability of LES to capture the high and low values of temperature and species concentrations is better, and it can capture the flame centre and predict the recirculation flows more accurately than RANS. Then, coal combustions with different jet velocities and volatile contents were simulated with LES. The results indicate that when the jet velocity is too high, the flame center is too close to the opposite wall, and coal jets directly to the opposite wall, which causes large colli- sion loss. Through tests of different jet velocities, an optimal velocity 5 m/s was found. The simulation results of dif- ferent volatile content indicate that the ignited distance is shorter for high volatile coal, and the strong backflows which sweep high temperature gas towards the nozzle can accelerate the ignited speed. The analysis results can pro- vide a good theoretical foundation for the optimal design of coal combustion.