Surface Modification of Powder by Dehydration Reaction at High Temperature and Its Application to Fluidized Bed Granulation

为了开发一种高贵造粒工艺，不使用任何粘结剂，而是通过改变高温流化床中原料粉的表面性质来生产具有中等抗压强度的各种粒度的颗粒。通过对不同粒度的氧化铝颗粒在喷动床中于700K以下形成的筛分分析和扫描电子显微镜观察，研究了颗粒的粒度分布、形状及其回收率等形态特征与实验条件的关系。对于粒径大于2微米的饲料粉，没有观察到颗粒的形成。2)颗粒的平均直径在70~110微米之间，并且随着温度的升高而增大。颗粒回收率随温度…的升高而增大在对数正态概率图中用两条直线表示，除个别例外情况外，颗粒的累积细度服从双峰分布。由单模分布确定的颗粒大小的几何标准差与气速、温度等操作条件之间的关系没有发现任何规律性的趋势。4)得到的颗粒强度适中，在筛分过程中不易解体。5)对于较高的温度(600K以上)，气速对颗粒平均直径和回收率的影响不如温度显著。在常温下，颗粒的平均直径和回收率均随气速的增加而减小。6)操作时间方面，造粒在最初几分钟内基本完成，然后颗粒平均直径随时间逐渐增大。颗粒回收率在造粒初期随着时间的推移而增大，然后随着时间的延长而减小，最大值伴随着相对较小颗粒的夹带。较少

To develop a noble granulation process in which the granules of various size having a moderate compressing strength are produced not by using any binding material but by modifying the surface properties of feed powder in high temperature fluidized bed, the morphological properties of granules such as their size distribution and shape and their recovery fraction were related with the experimental conditions by sieving analysis and SEM observation of the granules composed of various size fraction of alumina particles, which were formed in a spouting type fluidized bed at the temperature up to 700 K.The following results were obtained.1) Spherical shaped granules were obtained for feed powders having the mean size under 1mum. For feed powders with the size over 2mum, the formation of granules was not observed.2) The value of average diameter of granules was ranged from 70mum to 110mum, and increased with temperature rise. The value of recovery fraction of granules also increased with temp … More erature.3) The cumulative undersize fraction of granules was obeyed by a bimodal distribution which is expressed by two straight lines in log-normal probability diagram with a few exception. Any regular trend was not found in the relation between the geometric standard deviation of granules size, which was determined by assuming a single mode distribution, and the operational conditions such as gas velocity and temperature.4) The granules obtained had the moderate strength such that they were not easily disintegrated during the course of sieving.5) For relatively high temperature (above 600 K) , the effects of gas velocity on the average diameter and the recovery fraction of granules were not so remarkable as those of temperature. For room temperature, the value of both the average diameter and the recovery fraction of granules decreased with increasing gas velocity.6) As for the operating time, the granulation was almost completed in a first few minute, and then the average value of granule diameter increased gradually with time. The value of recovery fraction of granules increased with time elapsed in the initial period of granulation, and then decreased with time via its maximum accompanied by the entrainment of relatively small granules. Less