【作者】 訾灿； 黄正梁； 廖祖维； 蒋斌波； 王靖岱； 阳永荣；

【Author】 ZI Can;HUANG Zhengliang;LIAO Zuwei;JIANG Binbo;WANG Jingdai;YANG Yongrong;College of Chemical and Biological Engineering,State Key Laboratory of Chemical Engineering,Zhejiang University;

【机构】 化学工程联合国家重点实验室浙江大学化学工程与生物工程学院；

【摘要】 颗粒振荡循环现象是循环流化床中一种典型的不稳定循环状态,研究其发生机制对循环流化床的稳定运行具有重要意义。本文基于压力平衡和质量守恒分析,建立了颗粒振荡循环过程的动态模型,通过对比床层各部分压降的计算值和实验值随时间的变化曲线,证实了模型的准确性。进一步利用模型分析了颗粒循环量、气体流量等参数随时间的变化规律,揭示了颗粒振荡循环的机理。研究发现颗粒转移过程受提升段、下降段中的颗粒流型、气体流量和颗粒质量的协同控制。当下降段为移动床时,颗粒在重力推动下从下降段向提升段转移;当下降段、提升段均为流化床时,颗粒转移的方向和速率由提升段、下降段底部的颗粒浓度差决定,下降段气体流量先增加后减小,直至下降段中颗粒流型再次转变为移动床,从而引起颗粒振荡循环。研究结果为循环流化床中颗粒振荡循环过程的调控奠定了基础。更多还原

【Abstract】 Solids oscillation circulation behavior, an unstable solids circulation, in circulating fluidized bed features with serious fluctuation of the pressure drop within riser and downer and significant entrainment. Therefore, it is very important to explore this process in order to eliminate its bad effect. A dynamic model, with pressure balance and material balance, is established to investigate the solids transfer process and the oscillation circulation mechanism. According to the simulated results, solids transfer is related to the flow pattern, gas flow rate and bed inventory in riser and downer. When the solids in downer act as moving bed, the solids transfer from downer to riser features with a decreasing transfer rate, because the driving force decreases with the decreasing bed level and the resistance owing to the gas drag force increases with the increasing gas flow rate in downer. When the solids in riser and downer act as fluidized bed, the solids transfer is controlled by the differential solids concentration between the riser bottom and the downer bottom. The downer structure, wide at the top and narrow at the bottom, contributes to the oscillation mechanism. When the solids in downer changes from moving bed into fluidized bed, the solids distribution and solids transfer has the opposite effects on the downer pressure drop. Therefore, the gas flow in downer increases first and then decreases, which results in the flow pattern transition from fluidized bed to moving bed in downer.更多还原