摘要
对循环流化床提升管及下行床两种不同气固流动方式对颗粒混合行为的影响进行了较为深入的对比分析，发现在影响循环流化床颗粒混合的众多因素（如操作条件、床层直径、颗粒性质及床层内构件等）中，气固流动方向是影响颗粒轴向混合的最主要因素．当气固流动为顺重力场时（下行床），颗粒的轴向混合很小，流型接近平推流；当气固流动为逆重力场的提升管时，轴向颗粒混合将成倍增大，颗粒流动远离平推流流动．分析表明，下行床中颗粒混合仅为单一的弥散颗粒扩散，而提升管中则存在着两种颗粒混合机制：弥散颗粒扩散及颗粒团扩散．弥散颗粒的扩散基本以平推流的形式通过循环流化床，提升管中大量的颗粒轴向返混归因于颗粒团的严重返混并由此形成了提升管中颗粒停留时间的双峰分布．
The effect of flow direction on the solids residence time distributionand the mixing mechanisms in the upflow and downflow circulating fluidized beds is discussed in details. Among the many factors such as operating condition, bed diameter, particle properties and internals,the flow direction has the largest influence on the axial solids mixingin the gas-solids suspension. When the flow is in the direction of gravity(in the downer), the solids mixing is very small and the flow pattern approaches plug flow, while when the flow is against gravity (riser), the solids mixing is significantly larger and the flow pattern is far fromplug flow.Solids mixing in the downers is found due to the dispersion of dispersed particles only. Two solids mixing mechanisms exist in the riser: the dispersions of dispersed partiales and clusters. The dispersed particles pass through the riser in the form of plug flow, while the extensive dispersion of clusters contributes to the large solids backmixing giving bimodal RTD.
出处
《化工冶金》
CSCD
北大核心
1997年第2期129-136,共8页
关键词
循环流化床
颗粒混合
流动方向
Circulating fluidized bed, Solids mixing, Flow direction
