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

开发一种高档造粒工艺，不使用任何粘结材料，而是通过在高温流化床中改变饲料粉末的表面特性，生产出各种大小、抗压强度适中的颗粒。通过筛分分析和扫描电镜观察，在喷淋式流化床温度高达700 K的条件下，对不同粒度氧化铝颗粒组成的颗粒进行筛分分析，得出颗粒的粒度分布、形状和回收率等形貌特征与实验条件的关系。得到了以下结果：1)饲料粉平均粒径在1ma以下，可获得球形颗粒。对于粒径大于2mum的饲料粉，未观察到颗粒的形成。2)颗粒平均直径在70mum ~ 110mum之间，随温度的升高而增大。颗粒的回收率随温度和温度的增加而增加。3)颗粒的累积小于粒径分数服从双峰分布，在对数正态概率图中以两条直线表示，少数例外。采用单模态分布确定的颗粒粒径几何标准差与气速、温度等操作条件之间的关系没有规律性的变化趋势。4)所得颗粒强度适中，在筛分过程中不易崩解。5)在较高温度（600 K以上）条件下，气速对颗粒平均粒径和回收率的影响不如温度对颗粒平均粒径和回收率的影响显著。在室温条件下，随着气速的增大，颗粒的平均直径和回收率均减小。6)在操作时间上，最初几分钟造粒基本完成，随后粒径平均值随时间逐渐增大。颗粒的回收分数在造粒初期随时间的增加而增加，然后随着时间的增加而降低，达到最大值并伴有较小颗粒的夹带。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