一次风速度对煤颗粒群着火特性影响的实验研究

Experimental Study on Effects of Primary Flow Velocity on Ignition of Coal Particles

利用Hencken型平面携带流反应器,研究了一次风速度对两种高挥发分褐煤和一种贫煤射流着火特性的影响.实验结果表明,低雷诺数(Re=878)条件下,贫煤煤粉气流先后发生外层单颗粒着火燃烧和内层颗粒群着火燃烧,煤粉颗粒着火和燃烧轨迹十分规则.但在高雷诺数(Re=4,392)条件下,贫煤煤粉气流更难形成群燃火焰,呈现出暗红色火焰.随着一次风速度的增加,尽管煤粉颗粒的停留时间减小,但湍流强度的增加使颗粒加热速率以及挥发分析出的强化作用占主导,使得煤粉气流的着火距离减小.此外,群燃火焰在挥发分聚集到一定程度后产生,是颗粒群燃烧的特有现象,而煤种挥发分含量的增加和有效聚集有利于群燃火焰的出现.

Effects of primary flow velocity on ignition of coal particle jets were investigated on an optical entrained flow reactor system using a Hencken burner. The results show that for low Reynolds number（Re=878）coal jets,particles around the outer layer are preferentially heated,devolatilized and ignited,and that major coal streams ignite at a certain height and yellow flames are formed. While for high Reynolds number（Re=4,392）coal jets,darkred flames are observed due to high heating rate and strong blowing off effects of the turbulence. The ignition distance decreases with the primary flow velocity though residual time of coal particles decreases,indicating that the increase of turbulent intensity largely enhances the mixing process of the coal streams and hot surroundings. Group flame is an important feature of the group combustion of coal particles differing from the combustion of a single particle,and volatile contents in coal particles are very important to the formation of group flame.