微型流化床内气体返混

微型流化床基础和应用在近几年受到越来越多的关注。针对微型流化床对气固反应分析的应用要求,利用脉冲示踪法研究了内径10 mm和21 mm两种尺寸微型流化床中的气体返混特性,具体考察了管内径、颗粒静床高度、床料颗粒粒径和气体表观流速对气体返混程度的影响。结果表明:随着床内径、颗粒静床高度和表观气速的减小和床料颗粒粒径的增大,气体在床内的返混程度减小。使用粒径约270 μm粗颗粒时,两种床径的浅层微型流化床中的气体返混程度都较小,对应的Peclet数在27以上,证明了床内气体流动接近平推流,从而为利用微型流化床最小化气体返混对反应测试的影响,获得近本征反应动力学参数提供了流动特性的保障。

Gas back-mixing in micro fluidized beds

More attention is being paid to the hydrodynamics and applications of micro fluidized beds in recent years.Considering the application of micro fluidized bed to gas-solids reaction analysis,the gas back-mixing characteristics in two beds of 10 mm and 21 mm inner diameter was studied by using the gas impulse tracer approach.The influences of bed diameter,static particle bed height,bed particle size and superficial gas velocity on the extent of gas back-mixing were investigated.It was shown that the extent of gas back-mixing increased with increasing inner bed diameter,static particle bed height and superficial gas velocity,but decreased with increasing bed particle size.The tested two micro fluidized beds that had a shallow layer of coarse particles in size of about 270 mm had both low extent of gas back-mixing and the estimated Peclet numbers for them were above 27,showing that the gas flow in these beds was very close to plug flow.This,as a consequence,verified that using micro fluidized bed for gas-solids reaction analysis could minimize the effect of gas back-mixing on reaction testing so as to get the near-intrinsic reaction kinetics.