循环流化床气固提升管内的颗粒浓度及环核结构研究

Investigation on Solids Concentration and Core-annulus Flow Structure in Circulating Fluidized Bed Risers

根据100mm×15.1m循环床提升管8个截面上11个径向位置的局部颗粒浓度的系统实验数据研究了提升管中气固两相流的环核流动结构。实验结果及分析表明,局部颗粒浓度大约在无因次半径r/R=0.8处与相应截面的平均颗粒浓度 εs达到相等,操作条件和轴向位置的改变对其没有明显影响,并由此提出以εs= εs为确定核心区无因次半径的依据。近壁环形区内的颗粒浓度及其对操作条件变化的敏感性均显著大于核心区,是构成提升管截面平均颗粒浓度总体变化的主要因素。核心区和边壁区的平均颗粒浓度随 εs的增加表现出很好的线性增加关系,所得到的环、核区平均颗粒浓度关联式的预测结果与本实验数据及文献数据吻合良好。

Coreannulus flow structure in CFB risers was investigated by systematical measurements of solids concentration in a CFB riser of 15.1 m high and 0.1 m i.d. The results show that local solids concentration εs reaches the crosssectional average solids holdup s always at r/R≈0.8, obviously independent of superficial gas velocity, solids circulation rate, and axial height. By defining the r/R where εs=s as the dimensionless radius α of the core region and dividing the cross section of riser into the core and the annulus region, it can be clearly seen that the solids concentrations at the annulus region are not only much higher than at the core region, but much more sensitive to the changes of operation conditions, indicating that the total variation of average solids holdup on the whole cross section of riser are mostly due to the variation at the annulus region. It is also found that with increasing crosssectional average solids holdup, the average solids concentrations at the core and the annulus region both increase clearly in a linear manner, from which new correlations are proposed for the prediction of the solids concentration at the core or the annulus region. 