Scale-up of mixer granulators for effective liquid distribution
Scale-up of mixer granulators for effective liquid distribution
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DOI：
10.1016/s0032-5910(02)00023-2
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发表时间：
2002-04
影响因子：
5.2
通讯作者：
J. Litster;K. Hapgood;J. N. Michaels;A. Sims;Micahel Roberts;S. K. Kameneni
中科院分区：
文献类型：
--
作者：
J. Litster;K. Hapgood;J. N. Michaels;A. Sims;Micahel Roberts;S. K. Kameneni
有相当多的工业轶事证据表明，不良的润湿和液体分布可导致混合制粒机中的宽粒度分布。目前的规模扩大方案导致液体分布不良和产品尺寸分布较宽。当按比例放大时，有两个问题需要考虑：喷涂区的尺寸和性质以及粉末流动模式作为喷涂比例的函数。在25 L PMA Fielder混合器中使用乳糖粉末与水和HPC溶液进行的简短的仅成核实验证明了取决于喷雾通量的不同成核机制的存在，从液滴控制成核到结块。在液滴受控状态下，在低的平均值下，每个液滴形成单个核，并且核的分布由喷雾液滴尺寸分布控制。随着喷射系数的增加，液滴在喷雾区重叠并聚结，分布迅速变宽.结果与以前的实验结果非常一致，并证实了对于液滴控制成核，Δ ε应小于0.1。造粒机流动研究表明，有两种粉末流动制度-碰撞和绳。随着叶轮转速的增加，粉末流动经历了从碰撞到成绳的过渡。绳系方式提供良好的床翻转和稳定的流态。推荐使用该制度以获得良好的液体分布和成核。采用高速摄像设备和MetaMorph图像分析软件测量了粉末表面速度随叶轮转速的变化。粉末表面速度为0.2至1 ms-1，比叶轮尖端速度低一个数量级。假设几何形状相似的制粒机，应将叶轮速度设置为在规模扩大期间保持恒定的弗劳德数，而不是恒定的尖端速度，以确保在绳状方案中操作。
There is considerable anecdotal evidence from industry that poor wetting and liquid distribution can lead to broad granule size distributions in mixer granulators. Current scale-up scenarios lead to poor liquid distribution and a wider product size distribution. There are two issues to consider when scaling up: the size and nature of the spray zone and the powder flow patterns as a function of granulator scale. Short, nucleation-only experiments in a 25L PMA Fielder mixer using lactose powder with water and HPC solutions demonstrated the existence of different nucleation regimes depending on the spray flux Ψa—from drop-controlled nucleation to caking. In the drop-controlled regime at low Ψavalues, each drop forms a single nucleus and the nuclei distribution is controlled by the spray droplet size distribution. As Ψaincreases, the distribution broadens rapidly as the droplets overlap and coalesce in the spray zone. The results are in excellent agreement with previous experiments and confirm that for drop-controlled nucleation, Ψashould be less than 0.1. Granulator flow studies showed that there are two powder flow regimes—bumping and roping. The powder flow goes through a transition from bumping to roping as impeller speed is increased. The roping regime gives good bed turn over and stable flow patterns. This regime is recommended for good liquid distribution and nucleation. Powder surface velocities as a function of impeller speed were measured using high-speed video equipment and MetaMorph image analysis software. Powder surface velocities were 0.2 to 1 ms−1—an order of magnitude lower than the impeller tip speed. Assuming geometrically similar granulators, impeller speed should be set to maintain constant Froude number during scale-up rather than constant tip speed to ensure operation in the roping regime.