气固循环床提升管内的局部颗粒浓度及流动发展

采用反射式光纤浓度探头对f100mm×15.1m循环床提升管8个轴向截面上11个径向位置的局部颗粒浓度进行了测量, 分析研究了颗粒浓度径向分布的不均匀性及其沿轴向的发展变化。结果表明:提升管内气固两相流的发展并不同步,而是一个由核心区向边壁区逐渐扩展,并最终达到总体充分发展的过程,该过程主要受边壁区发展过程所控制;相对于核心区,边壁区的发展不仅显著缓慢,而且受操作条件的影响也较显著。实验还发现:在颗粒加速段,无因次颗粒浓度的径向分布不具有相似性,不仅与径向位置有关,而且还与床层截面高度有关。

Local Solid-Particle Concentration and Flow Development in a Long CFB Riser

To investigate the non-uniformity in radial distribution of time mean solid-particle concentration and its axial development, local solid-particle concentrations at 11 radial positions on 8 axial levels of the riser in a CFB riser of 15.1m high and 0.1m i.d. were systematically measured by a reflective-type fiber-optic particle concentration probe, with superficial gas velocity ranging from 3.5 to 8.2 ms-1 and solid-particle circulation rate from 53 to 202kgm-2s-1. Results showed that the flow developments in various radial locations are not synchronized, but extended gradually from the core region to the wall, until finally a fully developed flow is achieved across the whole cross-section of the riser. The flow development at the annulus region near the wall, as a control process of the whole flow development in the riser, is not only much slower, but also more sensitive to the change of operation conditions than that at the core region. It is also found that in the acceleration section, the radial distribution of reduced solid particle concentration is related not only to the dimensionless radius but also to the axial location of corresponding section, it does not show the similarity distribution as reported in literature.