Comparison Of Gas-liquid Cross-flow And Counter-flow Distillation Model

Different contact way between vapor and liquid in distillation column,cross flow or counter flow,has great influence on mass transfer efficiency.Effect of gas-liquid distribution,radial amplification and non-ideal flows on cross-flow and counter-flow distillation columns is also different.However,experiments cannot be conducted because of huge difference between the two columns.This study designs a multi-stage cross-flow distillation model and a multi-stage counter-flow distillation model respectively according to tray column and packed column with Aspen Plus.The impacts on the two distillation models caused by gas-liquid distribution,radial amplification and non-ideal flows are analyzed and compared.It is found that the cross-flow model has better performance than the counter-flow one because it has longer liquid flow distance and higher ratio of liquid to gas.The advantages of cross-flow distillation are stated as follows.Firstly,the comparison of cross-flow and counter-flow distillation model is carried out on ideal condition and suggests that the cross-flow model has better separation efficiency than the counter-flow one.Secondly,the cross-flow model has less product concentration loss and better operating performance than the counter-flow one with vapor-liquid maldistribution and the loss can be easily controlled by raising reflux ratio.Thirdly,the separation efficiency of cross-flow model can obviously raise with radial amplification as the liquid flow distance becomes longer and the ratio of liquid to gas gets bigger,while that of the counter-flow model tends to reduce sharply because the amplification has no benefit to gas and liquid contact in the counter-flow distillation.Finally,the effect of liquid leaking and vapor crossflow channeling on the two distillation models is also analyzed and their effect on the product concentration loss of the two models is relatively small and can be removed by raising the reflux ratio shortly.This study makes a comprehensive comparison on multi-stage cross-flow and counter-flow distillation model.The conclusions are reliable and have significant meanings to the design and determine of the distillation columns as well as the development of new internals.