粘性颗粒聚团流态化实验与理论研究
文献类型：学位论文
| 作者 | 周涛 |
| 学位类别 | 博士 |
| 答辩日期 | 1998-12 |
| 授予单位 | 中国科学院研究生院 |
| 导师 | 李洪钟 |
| 关键词 | 粘性颗粒 流化床 固体流态化 聚团 |
| 其他题名 | Experimental and theoretical studies on Agglomerate Fluicization of Cohesive Particles |
| 学位专业 | 流态化工程 |
| 中文摘要 | 在流化床中考察了不同种类粘性颗粒的流化性能，发现不同的粘性颗粒，由于颗粒的物理性质和表面性质的差异，达到完全流化的气速不同。 在低表观气速（此气速远远大于按粘性颗粒直径计算的最小流化速度）下，粘性颗粒在流化床中易形成活塞或沟流。随表观气速增加，床内鼓泡加剧，沟流或活塞消失，但床内局部可能形成死区。 随表观气速的进一步加大，床内鼓泡剧烈，死区消失，虽然聚团大小从上到下有一个分布，但整个床内的平均聚团尺寸变小，粘性颗粒以聚团的形式平稳流化。因此增大表观气速有利于粘性颗粒流态化，但是表观气速过高， 物料扬析损失严重。 对不同床径的流态化实验可知，小床和大床之间存在放大效应。不同粒径的同种物料的流态化实验表明，颗粒粒径对流化性能有较大影响，粘性颗粒粒径越小，颗粒间粘附力越大，其流化性能越差。 粘性颗粒中添加颗粒实验表明，在粘性颗粒中添加合适的粗颗粒， 能够降低颗粒间的粘附力，改善其流化性能。利用流态化聚团准数Ae_f可计算使粘性颗粒流化的添加颗粒量，这为工业化应用提供了依据。 通过对不同颗粒的聚团密度的测量，我们得到了初步的实验结果：（1） 聚团密度基本不随聚团直径变化。（2） 如果计算时无聚团密度测量值， 可按如下方法近似： 对结合较紧密的聚团， 聚团密度取压实密度的0.85倍；对结合较松散的聚团，聚团密度取松堆密度的1.15倍。对一个聚团体和周围小聚团或颗粒的吸附与脱落的分析，提出了自然聚团准数Ae_n和流态化聚团准数Ae_f。根据自然聚团准数Ae_n和流态化聚团准数Ae_f, 可判断颗粒的流化性能，即自然聚团准数Ae_n和流态化聚团准数Ae_f越大，流化性能越差。若流态化聚团准数Ae_f≤40000, 该粘性颗粒能很好流化。通过调节流态化聚团准数Ae_f的大小，即调节颗粒间粘附力的大小或流体速度大小，可改善粘性颗粒聚团流态化的流化性能。根据流化床中聚团碰撞时聚团所受力的分析，提出了力平衡模型，并对模型中的参数进行了估算。计算中发现，参数估算是非常重要的。参数估算不准确将直接导致计算结果的不准确。据此模型计算了几种粘性颗粒在流化床中形成的聚团大小 计算结果与实测的聚团大小较接近。与其他研究者的模型比较，发现我们模型的计算结果更接近于实测值。通过对力平衡模型的分析，得到了聚团或颗粒团聚与破碎的准则，并进一步分析了聚团团聚与破碎的可能性。在粘性颗粒流化床中，不同大小的聚团相互碰撞，是分离、破碎或是团聚，取决于粘性颗粒的物性（如颗粒密度、粘性、大小等）、操作条件（如表观气速）及相互碰撞的聚团大小之比。实验与理论分析均表明，高表观气速，低颗粒粘性，以及聚团与聚团之间的碰撞对粘性颗粒聚团流态化比较有利。因此，对给定的粘性颗粒，其流态化应尽量选用高表观气速、密度较大的流体，以及通过外力场或在粘性颗粒中添加合适的颗粒以降低其粘性，使粘性颗粒能“正常”流态化。 |
| 英文摘要 | The behavior of different kinds of cohesive particles was investigated in a fluidized bed, and it was found that the superficial gas velocity required for fluidization was different for different kinds of cohesive particles, due to the diversity in the physical and surficial properties. Generally, under low superficial gas velocity (this velocity was rather greater than the minimum fluidized velocity calculated with the diameter of cohesive particles), slugs and channels were formed firstly in a fluidized bed of cohesive particles. With increasing the superficial gas velocity, slugs and channels vanished, but there existed a de-fluidized zone. When the superficial gas velocity increased to a certain value, the de-fluidized zone disappeared and cohesive particles were fluidized in the form of agglomerates. The average size of agglomerates was reduced with the increase of the superficial gas velocity, as a result, the fluidization quality was improved. But there existed a distribution of agglomerate sizes, namely, the agglomerate sizes were small in the upper zone and large in the lower zone. Therefore, increasing the superficial gas velocity was advantageous to the agglomerate fluidization of cohesive particles. However, the entrainment became severe if the superficial gas velocity was too high. It was found from the experiments with different diameter fluidized beds that there was a scale-up effect between a big and small fluidized bed. The fluidization of cohesive particles with different sizes showed that the fluidization characteristics were greatly affected by the size of particles. The smaller the size of particles, the larger the interparticle forces, and the worse the fluidization behavior. Experimental results showed that interparticle force can be reduced and fluidization behavior of cohesive particles can be improved when a right kind of particles was added in cohesive particles. Optimum amount of additive particles can be well correlated with the dimensionless fluidized agglomerate number Ae_f, which furnished theoretical basis for industrial application. With the measurements of agglomerate density of cohesive particles, it is found that (1) the agglomerate density is not changed with the agglomerate diameter, and is larger than the packed density and smaller than the tapped density; (2) the agglomerate density can be approximated in the light of our preliminary experimental results, that is, the agglomerate density is 0.85 times the tapped density for agglomerates bound tightly and 1.15 times the packed density for agglomerates bound loosely. The natural agglomerate number Ae_n and the fluidized agglomerate number Ae_f, which can be used to describe the fluidization behavior of particles, are proposed on the basis of balance of forces between the agglomerate and the outer-most cohered particles. The larger the natural agglomerate number Ae_n and the fluidized agglomerate number Ae_f, the worse the fluidization behavior of particles. The cohesive particles can be fluidized if the fluidized agglomerate number Ae_f≤40000. The fluidization behavior of cohesive particles can be improved through adjusting the value of the fluidized agglomerate number Ae_f, namely regulating the interparticle forces or superficial gas velocity. A model of force balance was developed according to analysis of forces acting on an agglomerate of cohesive particles in a fluidized bed. The parameters in the model were estimated. The size of agglomerates of cohesive particles was calculated with this model. The equilibrium agglomerate sizes calculated by this model are in reasonable agreement with the experimental values. Compared with the predicted values of other researchers' model, the calculated results with this model are closer to experimental data. Agglomerating and breaking criteria were obtained on the basis of the analysis of the solution of the force balance model. Experiments and theoretical analysis showed that higher superficial gas velocity, lower cohesion of particles, high density of fluid, and the collision between agglomerates were advantageous to the agglomerate fluidization of cohesive particles. |
| 语种 | 中文 |
| 公开日期 | 2013-09-27 |
| 页码 | 137 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/2022]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 周涛. 粘性颗粒聚团流态化实验与理论研究[D]. 中国科学院研究生院. 1998. |
入库方式： OAI收割
来源：过程工程研究所
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