Abstract: Local transient solids fraction and particle velocity signals were measured in a 0.418m×18m large-scale circulating fluidized bed(CFB) by a dual-optical fiber density probe and a Laser Doppler Velocimeter(LDV) system. The probability density distribution(PDD) of both transient solids fraction and particle velocity was obtained. The bimodal distribution of PDD for both solids fraction and particle velocity can be clearly seen in the riser.While in the downer, the PDD curves only exhibit single peak distribution.The results indicate that two phases, i.e., the cluster phase with solids fraction near 1-ε_mf and the void phase with solids fraction about 0.01—0.02,exists in the riser. Meanwhile, only single void phase exists in the downer. Although there exist particle clusters in the downer, they cannot form a stable cluster phase with solids fraction near 1-ε_mf.The dissimilarity of solids flow structure reveal the significant difference in gas-solids flow structure and mechanism between the along-gravity gas-solids flow in the downer and the against-gravity flow in the riser.

Key words:

瞬态流动行为, 流动结构, 提升管, 下行床

摘要： 采用双光路光纤密度探头和激光多普勒测速仪测量了内径418mm，高18m的大型循环流化床提升管和下行床中的瞬态颗粒浓度信号和颗粒速度信号.对瞬态颗粒浓度和颗粒速度的概率密度分布分析表明，下行床中存在着和提升管中不同的微观流动结构，在提升管内流动结构存在明显的两相：即颗粒团相和空穴相，两相的固含率分别为接近1-ε_mf和0.01～0.02.而在下行床中，虽然在边壁也存在着颗粒的团聚行为，但不能形成稳定的、固含接近于起始流化状态固含值的颗粒团相.这种流动结构的区别揭示了下行床中气固顺重力场运动和提升管逆重力场运动在流动机制上的差异.

关键词:

瞬态流动行为, 流动结构, 提升管, 下行床