在具有锥形料腿的循环流化床中流化CaCO3超细颗粒

根据粘附性颗粒在流化过程中形成的聚团具有较宽粒径分布并因此导致大聚团在流化床中沉积和死床的问题，提出了循环流化床的锥形回料系统设计. 该回料系统包括两部分：锥形料腿和带辅助进气的V型阀. 实验证明，锥形料腿通过提供变化的表观流化气速，克服了流化聚团沉积死床等现象；而V型阀的辅助进气，对于保证V型阀顺利输送粘附性颗粒具有关键性作用. 借助这种回料系统，实现了高粘附性超细CaCO3颗粒在循环流化床的稳定快速流化. 从提升管内部拍摄的照片显示，尽管提升管采用较高的流化气体速度，但超细CaCO3颗粒仍然是以聚团的形式被流化. 对在提升管不同高度采集的聚团分析表明，处于快速流化状态的CaCO3聚团的直径远小于传统流化床中聚团的直径，并且在提升管高度方向聚团直径没有较大的变化. 同时实验还显示，提升管轴向空隙率呈S型分布，而径向则体现环-核结构，具有典型的快速床特征.

Fluidization of Ultrafine CaCO3 Powder in a CFB with Conical Dipleg

Based on the fluidizing characteristics of cohesive powders, such as the formation of agglomerates with wide size distribution during fluidization, and partial defluidization due to disposition of large agglomerates, a novel design of CFB dipleg, the conical dipleg, was put forward for fluidizing ultrafine and cohesive powders. The conical dipleg consists of a conical dipleg and a V-valve with aeration of gas. Experiments on the conical dipleg showed that it can prevent the fluidized dipleg from disposition and defluidization of large agglomerates at the bottom of the bed and elutriation of smaller agglomerates at the top of the bed by providing variational superficial fluidizing gas velocity. The experiments also showed that the aeration gas is essential for V-valve to feed highly cohesive powders into riser smoothly. With the aid of the conical dipleg, stable circulation of highly cohesive ultrafine CaCO3 powder was achieved. Pictures taken from the inside of riser show that the ultrafine CaCO3 powders in the fluidized riser are in agglomerate form in spite of the high fluidizing gas velocity. The size of agglomerates is much smaller than that in conventional fluidized beds, and it has no significant variation along the riser height. Experiments also showed that the axial solids concentration in the riser is of S-shape distribution; and the lateral solids concentration displays a core-annulus structure. These phenomena are typical features of fast fluidization.