Improvement of the Fluidizability of Cohesive Powders through Mixing with Small Proportions of Group A Particles
Improvement of the Fluidizability of Cohesive Powders through Mixing with Small Proportions of Group A Particles
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DOI：
10.1002/cjce.5450830602
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发表时间：
2008-05
影响因子：
2.1
通讯作者：
A. Ajbar;K. Alhumazi;M. Asif
中科院分区：
文献类型：
--
作者：
A. Ajbar;K. Alhumazi;M. Asif
被分类为Geldart C组的细粘性粉末的气体流化行为已知以导致床中严重非均匀性的裂纹和通道为特征。另一方面，已知Geldart A组颗粒显示出更均匀和规则的流化行为。本文研究了添加少量A组粉对C组粉流化行为的影响。在两种情况下，记录了采样频率为200 Hz的压差波动数据。在第一种情况下，床仅包含C组粉末，而在第二种情况下，将少量的A组颗粒添加到现有的C组粉末中。结合时间序列分析的视觉/图像观察表明，即使在低表观气速下，添加小比例的A组颗粒也显著改善了床的流化行为，从而导致更均匀的流化。平均值和标准偏差的评估显示了混合两种粉末的优势，因为它允许更大的压力波动和更小的标准偏差。另一方面，功率谱表明，与波动幅度小且结构宽带的C组不同，混合物显示出更强的周期性行为，这是由于裂缝和通道中气体流动引起的小而快的波动衰减的结果。先进的方法，如嵌入式轨迹的主成分分析允许两个系统的流化行为之间的定量比较。
The gas fluidization behaviour of fine cohesive powders, classified as Geldart group C, is known to be characterized by cracks and channels leading to severe non-homogeneities in the bed. Geldart group A particles, on the other hand, are known to show more homogeneous and regular fluidization behaviour. This paper studies the effects of the addition of small proportions of group A on the fluidization behaviour of a group C powder. Differential pressure fluctuations data at a sampling frequency of 200 Hz were recorded for two cases. In the first case, the bed contained only group C powder while in the second case small amounts of group A particles were added to the existing group C powder. Visual/image observations coupled with time series analysis showed that the addition of small proportions of group A particles substantially improved the fluidization behaviour of the bed even at low superficial gas velocities, leading to a more uniform fluidization. Evaluation of mean and standard deviations has shown the advantage of mixing the two powders as it allowed larger pressure fluctuations and smaller standard deviations. Power spectra, on the other hand, showed that unlike group C, for which fluctuations were small in magnitude and broadband in structure, the mixture showed stronger periodic behaviour as result of the attenuation of the small and rapid fluctuations caused by the flow of gas in the cracks and channels. Advanced methods such as the principal component analysis of the embedded trajectories allowed a quantitative comparison between the fluidization behaviour of the two systems.