布风板孔径对流化特性影响的数值模拟及试验

Numerical simulation and experiment of the effect of distributor′s hole diameter on fluidization characteristics

采用双欧拉流体模型与颗粒流动理论相结合的方法,对3种不同孔径布风板下颗粒流化效果进行数值模拟,获得颗粒的流态化特性。同时通过流化床反应器冷态实验,验证了孔径对流态化特性曲线的影响。结果显示,在1、2、3 mm孔径的布风板中,孔径越小,最终压力降越大,同时临界流化气速越低;1 mm孔径下床层的膨胀较为显著,流化床中气泡所含固体体积分数较低,且漏料最少,同时减小孔径有利于颗粒做规律性的循环运动,从而促进物料混合;流化稳定后,在静床层高度以上的位置上,颗粒体积分数随着高度的增加而迅速下降,且1 mm孔径的下降趋势最平缓,颗粒分布较均匀;颗粒在流化床内的径向分布为典型的环-核结构,且孔径越小,核区的颗粒速度越低,而环区速度越高。

An Eulerian-Eulerian model incorporating the kinetic theory of the granular flow is applied to numerically test the fluidization characteristics of particles in gas distributors. Three different hole diameters are considered in the simulation. Meanwhile, a fluidized-bed reactor equipment and the appropriate distributors are designed. The fluidization is tested in the cold state based on the equipment. The effect of the hole diameter on the fluidization characteristics is verified. It is shown that the ultimate pressure drop increases with the decrease of the hole diameter （1 mm, 2 mm and 3 mm）. On the other hand, the critical fluidizing gas velocity increases with the hole diameter. The expansion of the bed is more significant in the case of fluidizing with 1 mm hole diameter. Also, the larger the hole diameter, the more leakage of the material, as is consistent with the observation. The particles circulate in the fluidized-bed more regularly when using the gas distributor of a smaller hole diameter. It is very important since the regular movement of the particles might improve the mixing of the material. In the steady fluidization, the solid concentration is plummeted with the increase of the height of the bed. And this trend is gentler in the case of lmm hole diameter, which indicates that a smaller hole diameterieads t5 a more uniform distribution. The result also shows that the radial distribution of the solid is in a typical core- annulus structure. The velocity of the particles at the core and annulus areas decreases and increases with the increase of the hole diameter, respectively.