出口结构对矩形循环流化床稀相区颗粒速度分布影响的实验研究

Effect of exit structure on the particle velocity distribution in the dilute region of a rectangular circulating fluidized bed riser

为了研究不同工况下出口偏置结构、挂屏的布置对稀相区颗粒速度分布的影响,在一矩形截面流化床冷态试验台上,采用高速摄影分别对稀相区左墙和前墙进行拍摄,结合粒子图像测速技术分析,获得速度分布图像。实验结果表明,分离器的偏置布置对稀相区流场的分布影响较大,受出口效应影响,左墙颗粒已不再呈现环核流动分布,中心区向后墙出口区域颗粒几乎完全为横向运动,出口下方磨损较严重。受到挂屏的阻挡和壁面摩擦,颗粒的运动方向改变,挂屏与壁面之间的区域出现了颗粒的再分布,颗粒轴向速度呈现出跟整个床截面相似的抛物线分布。挂屏的布置削弱了出口效应的影响,右墙侧颗粒的分布主要受气流和壁面摩擦的约束。

In order to study the effect of exit deflecting arrangement and hanging screen arrangement on the particle velocity distribution under different operation parameters, the left wall and front wall in the dilute region were tested by using a high-speed video camera, in a plexiglas rectangular CFB cold model. The particle velocity profile were analyzed through combining with particle image velocimetry （PIV） technology. The results showed that the distribution of flow field was dramatically affected by exit deflecting arrangement. Under the action of exit gravity, a core-annulus distribution of flow zone near the left wall side was no longer presented, with the complete lateral velocity hardly, and severe erosion below the exit. Because of the blocking of the hanging screen and wall friction, the direction of the particle mo- tion was changed, and a particle re-distribution appeared in the flow zone between the hanging screen and wall, showing the parabola profile of the particle axis velocity similar to the whole cross-section of the furnace. As the furnace outlet effects were weakened by hanging screen arrangement, the particle distribution near the right wall were mainly restrained by the flow and wall friction.