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

本发明提供一种不使用任何粘合剂，而是通过在高温流化床中改变进料粉末的表面性质，通过筛分分析和扫描电镜观察，研究了颗粒的粒度分布、形状和回收率等形态特征与实验条件的关系由不同粒度分数的氧化铝颗粒组成，这些颗粒在高达700 K的温度下在喷动型流化床中形成。得到以下结果。1）对于平均粒度小于1 μ m的进料粉末，获得球形颗粒。2）颗粒的平均粒径在70 ~ 110 μ m之间，且随温度的升高而增大。颗粒回收率随温度升高而增大 关于我们 3）筛下颗粒的累积分数服从双峰分布，在对数正态概率图中由两条直线表示，只有少数例外。采用单模分布确定的颗粒尺寸几何标准偏差与操作条件（如气速和温度）之间的关系没有发现任何规律性趋势; 4）所得颗粒具有中等强度，不易在筛分过程中破碎; 5）对于较高的温度（600 K以上），气速对颗粒平均粒径和回收率的影响不如温度的影响显著。在室温下，随着气速的增加，颗粒的平均粒径和回收率均减小。6）在操作时间上，造粒在开始的几分钟内基本完成，之后颗粒的平均粒径随着时间的延长而逐渐增大。颗粒的回收率的值随着时间的推移，在造粒的初始阶段，然后随着时间的推移，通过其最大值伴随着相对较小的颗粒夹带减少。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