| The extraction process with heterogeneous liquid-liquid two-phase and mass transfer is a basic chemical unit operation,in which the mixer-settler is widely used as a basic multistage extraction equipment.The traditional horizontal square mixer-settler has the problem of poor airtightness,which will lead to organic gas leakage,environmental pollution,fire,explosion and other safety accidents in the chemical workshop.Compared with square mixer-settler,tubular mixer-settler has many advantages,such as good airtightness,flexible length adjustment,convenient use of corrosion-resistant inner wall(enamel),etc.It has a broad application prospect in chemical industry.However,there is a lack of systematic research on the multiphase flow behavior in the tubular mixer settler.In this thesis,the standard k-ε turbulent model and Eulerian-Eulerian multiphase flow model were used to simulate the multiphase flow in tubular and square mixer settler.The multi reference framework method was used to deal with the contact region between the rotating blade and the liquid surface.The numerical simulations of the tubular and square mixer-settler were carried out.In the water-kerosene system,the effects of droplet size(d32=100 μm～500 μm),O/A ratio(O:A=1:1～1:5),inlet baffle and inlet position on the mixing and settling performance were systematically investigated,and the simulation results of tubular mixer-settler were compared with traditional square mixer-settler.The conclusions are as follows:(1)Under the condition of low power,the power and the pressure head of the impeller in the tubular mixer at different speeds were investigated by experiments.The experimental results were compared with the simulation results.It was found that the selected multiphase flow model,turbulence model and the grid were reasonable and accurate.(2)The liquid-liquid two-phase flow behavior in tubular mixer and square mixer under different operating conditions was systematically studied.The results show that the flow field distribution in the tubular mixer is more efficient and it is not easy to form a flow dead zone.In the tubular mixer,a lower pressure region is formed above and below the impeller,so the average turbulent kinetic energy of the fluid is larger and the stirring performance is better.The volume fraction variance of dispersed phase in circular mixer is larger than that in square mixing chamber.(3)The influence of different operation conditions on the performance of tubular mixer-settler was systematically studied.In the tubular mixer,the lower the dispersed phase d32 and the greater the feed O/A ratio,the moer excellent mixing performance can be observed.In the settler,the higher the dispersed phase d32 and the O/A ratio and slower the inlet flow rate,the more excellent settling performance.Adding baffles at the inlet of the settler can effectively change the flow field distribution,increase the residence time of two-phase flow and then improve the settling performance;the inlet of two-phase flow from the middle of the baffles is better than that from the top and bottom.(4)The flow and mass transfer performance of tubular and square mixer-settler under different operating conditions(residence time of mixing chamber between 90 s～150 s,agitation speed 270 rpm～390 rpm,O/A ratio 1:1～3:1)were investigated by the extraction and separation experiment of CeS2O8.It was found that tubular and square mixer-settler had similar extraction efficiency.With the increase of residence time of mixer,agitation speed and O/A ratio,the extraction efficiency of mixer-settler increased.Both extraction efficiency of tubular and square mixer-settler can reach 100%by manipulating the operational conditions. |
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