臭氧在柱式反应器中的强化传质过程

Research of enhancement of ozone gas mass transfer in column reactor

结合理论分析,提出了影响臭氧在水中传质效率的三大因素:表观气速μobs、初始气泡直径d、液位高H。通过实验设计,以臭氧氧化柱式反应器中气泡的行为为研究对象,以废水COD去除率及臭氧利用率为指标,考察了这三大因素对臭氧传质效率的影响,且探讨了体系中引入搅拌对强化臭氧传质的贡献。结果表明,适当地提高表观气速μobs、初始气泡直径d及液位高H都可强化气液传质、提高废水处理效果,而对于传质控制型反应效果更为显著。在低、中表观气速下,搅拌能促使气泡均匀分散,从而提高气液传质效率;而在高表观气速下,搅拌作用的强化能力是有限的。通过对搅拌作用下反应器内流体热视图分析可知,反应器内中心气泡密度、尺寸均高于近壁面位置。n=100 r·min^(-1)时,反应器内气泡直径小且分布均匀;n=200 r·min^(-1)时,反应器内气泡破碎严重,搅拌杆有气穴生成;n=500 r·min^(-1)时,反应器中心出现明显旋流与气液分层现象。

Based on theoretical analysis,the major factors that influence the efficiency of ozone mass transfer in water are superficial gas velocity μobs,bubble diameter d,and liquid height H. With bubble behavior in column reactors regarded as the research subject,the influence of the aforementioned factors on COD removal efficiency and the contribution of stirring to the enhancement of mass transfer through different experimental designs were investigated in this study. The results showed that an increase in these factors improved the mass transfer efficiency and COD removal efficiency,particularly for the mass transfer control reaction type. Furthermore,bubbles were more dispersed and the mass transfer efficiency increased after the application of stirring at low and medium superficial gas velocities,whereas the ability of stirring to improve the efficiency was limited under high values of superficial gas velocity. The analysis of fluid flow formed by stirring in hot review showed that both bubble density and size in the reactor＇s core were higher than they were near the wall. Additionally,small-sized bubbles were distributed evenly at 100 r·min^-1; the bubbles were obviously broken and a hole was generated around the stirring rod at 200 r·min^-1. Further,when the stirring speed reached 500 r·min^-1,rotational flow and stratified liquid-gas appeared in the reactor＇s core.