Research On Hydrodynamic Characteristic And Axial Mixing Of A Parallel-Flow Extraction Column

A parallel-flow extraction column is divided into two equal parts by a central baffle on the basis of a traditional sieve plate extraction column,thereby greatly increasing velocity in continuous phase and extraction efficiency.In this paper,hydrodynamic characteristic and axial mixing,such as drop size,dispersed phase hold-up,flooding and continuous phase axial mixing coefficient were studied experimentally in the new column of 0.1m diameter.Besides,a Computational Fluid Dynamics(CFD)was used to expand the experimental results.The following items are meaningful conclusions and contributions of the experimental research.(1)In the kerosene-water system,the drop size is 5.7 mm;the characteristic velocity is 0.038 m/s;the operating range is 0 L/h to 29 L/h in continuous phase and is 10 L/h to 166 L/h in dispersed phase,respectively.(2)In the 30%tributyl phosphate(TBP)/kerosene-water system,the drop size is 3.6 mm;the characteristic velocity is 0.027 m/s;the operating range is 0 L/h to 34 L/h in continuous phase and is 16 L/h to 125 L/h in dispersed phase,respectively.(3)There are three regularity rules summarized from the experiment:Firstly,the hold-up in dispersed phase increases with increase in superficial velocity of dispersed phase and continuous phase,and the influence of dispersed phase velocity is larger than continuous one.Secondly,the axial mixing in continuous phase decreases with increase in superficial velocity of continuous phase while increases with increase in superficial velocity of dispersed phase.Thirdly,the flooding flux in the kerosene-water system is wider than that in the 30%TBP/kerosene-water system.(4)The correlations developed can be used for the prediction of drop size,hold-up,characteristic velocity,and axial mixing coefficient.a)d3.2=1.33(?/??g)1/2(Relative error is less than 8%)b)?=7.92(g?/uc4??)-0.311(ud/uc)0.896(?c/??)0.392(Average relative error is less than c)uo=0.283(4g???/?c2)1/4/uo=0.916(g?/??)1/4(??/?c)(Relative error is less than 5%)d)Ez=5 x 10-3uc0.44ud0.17(Relative error is less than 7%).Furthermore,the CFD was developed to study the flow process of continuous phase in four types of extraction columns including a traditional column,a new column,a new column with baffles and a new column with restriction orifices.The conclusions are as follows:(1)In the new column,the axial mixing in continuous phase is less than the traditional one.(2)The CFD result proves that the axial mixing in continuous phase decreases with increase in superficial velocity of continuous phase.(3)In the new column with baffles and the new column with restriction orifices,the axial mixing increases hugely.