方形气固流化床从鼓泡到湍动流型转变的实验研究

Experimental Study of Flow Regime Transition from Bubbling to Turbulent Fluidization in a Square Gas-solid Turbulent Fluidized Bed

在368mm×368mm方形气固床中对FCC颗粒进行流态化实验,研究了从鼓泡到湍动的流型转变行为及相关问题。实验测试了多个床层截面的压差波动,由波动标准差随表观气速变化的最大值获得了流型转变速度Uc。结果表明,方形床中的流态化平均行为在床层截面纵横两个方向一致,沿床层轴向呈现不均匀性,底部存在颗粒密相区;不同床层截面转变速度Uc不同,由床层上部向下扩展,Uc呈线性增加关系,说明流型转变至上而下进行;静床高度对Uc影响显著,静床高度增加,床层轴向各截面Uc相应增加;以上结果表明了目前仅与气固物性参数相关联的Uc预测模型有待改进。

Fluidization experiment was carried out in a 368 mm ×368 mm square fluidized bed with FCC particles to investigate the regime transition from bubbling to turbulent fluidization. The differential pressures at different axial locations were measured and the s standard deviation of pressure gradient fluctuations was used to determine the transition velocity,Uc,defined as the superficial gas velocity at which the standard deviation reaches its maximum. It was shown that,during the transition,the average behaviors of gas-solids fluidization in square fluidized bed are symmetric about the bed cross-section and non-uniformly distributed along the bed height,always with a dense particle-phase at the bed bottom. The Uc was found to be different at different axial locations. From the upper section of bed downwards to the lower,Uc increases linearly,indicating that the regime transition takes place first at the upper section of bed and then spreads downwards with increasing superficial gas velocity. Also,the static bed height has a noticeable effect on Uc and,corresponding to an increased static bed height,Uc becomes increased at all axial locations,simultaneously. The experimental results showed that the most predictive correlations reported in literatures obviously need to be improved.