降膜对喷淋塔吸收特性的影响

Analysis of the falling film effects on the absorption characteristics in the spray tower

吸收液在喷淋塔内以液滴和降膜两种形式存在,为了深入考察降膜对喷淋塔吸收特性的影响,以多孔分布板代替传统的压力式喷嘴,实现了降膜和液滴流量的可控调节,结合喷淋塔流体力学特性和双膜理论,建立了液滴及降膜的传质模型,并进行了试验验证,通过定量计算,分别考察了喷淋量及空塔气速对降膜吸收速率分率的影响。结果表明:所建模型可以较好地模拟喷淋塔脱氨过程,相对误差小于4%;降膜吸收速率分率几乎不随空塔气速而变化,但随喷淋量增大而减小;当大量吸收液在塔内壁形成降膜时,要达到相同吸收率所需喷淋液量将更大。

This paper is aimed at presenting the analysis of the falling film effects on the absorption characteristics in the spray tower.It is known that spray towers have been widely used as a kind of chemical reactor for gas purification,particularly,in recent years.However,little is known on the study of the falling film absorption features of the absorber.So far as we know,two forms of the absorption liquid can be used in the tower to reduce and decrease the film features for the time being.In order to make a profound study of the effects of the falling film on the absorption characteristics in the tower,the general rule is to replace the conventional pressure-swirl nozzle by a perforated plate in hoping to achieve the controllable flow rate of the falling film and droplets.To achieve the purpose,we have to build up a mathematical model to imitate the mass transfer of droplets and liquid film in a spray actual tower on the basis of the dual-film theory and aerodynamic principles,which has already been proved by the corresponding experimental data.And,then,we have analyzed the influences of the spray flux and the superficial gas velocity on the dropping film absorption fraction quantificationally.The results of our analysis show that the present model we have introduced in the paper can be well used to simulate the ammonia removal process in a spray tower,by which we have found that the deviation gap of the absorption efficiency between the model prediction and the actuality of the simulation results should be below 4%.What is more,a higher ammonia absorption efficiency can be achieved by decreasing the superficial gas velocity or increasing the spray flux.However,little has been found of the falling film absorption fraction changes with the superficial gas velocity,though it tends to decrease with the increase of the spray flux.Thus,it can be concluded thal,when the falling film resulted by the massive absorbent on the inner wall of the tower,more spray flux should be required to achieve specified absorption efficiency.In accordance with the calculation results of this model,we would like to propose an optimized design version for the spray tower in the ammonia removal system.A further step we would like to improve on the model of ours and find more possibilities to bring the aforementioned model of ours to other gas purification systems equipped with the spray tower more conveniendy and efficiendy.