气固下行流化床反应器Ⅱ气固两相的流动规律

COCURRENT GAS SOLID DOWNFLOW FLUIDIZED BED (DOWNER) REACTORS ⅡHYDRODYNAMICS

气固下行流化床反应器气固两相流动过程是比较复杂的，沿轴向气固两相运动可分为第一加速、第二加速和恒速３个运动段，沿径向局部气体速度、颗粒速度和颗粒浓度都具有不同程度的不均匀性。而这种不均匀性是由气固两相顺重力场湍动运动所决定的。和循环床提升管相比，下行管反应器气固两相沿径向分布的不均匀性得到有效地改善，气固可以实现超短接触操作。

Published results on hydrodynamic studies of downer reactors are summarized in this paper. The flow structure of gas solid two phase flow in downers is complex. In the axial direction, the flow is characterized by two particle acceleration sections( the first and the second acceleration sections) and a constant velocity section. In the radial direction, the distributions of local gas velocity, particle velocity and particle concentration in downers are more uniform than those in risers, with rather constant flow in the core region but somewhat increased gas velocity, particle velocity and particle concentration in the near wall region. The rather uniform gas solid two phase flow structure is due to the fact that gas and solid are flowing in the same direction as gravity. Compared with riser reactors, downer reactors have improved gas solid contact efficiency and can accommodate ultrashort contact time reactions, so that the downer reactor is a new high efficiecy gas solid short contact reactor.