Numerical Simulation And Experimental Study Of Self-inspirating Tank With Dual Impellers

Gas-liquid stirred tanks are widely used in many industrial processes, lots of experimental researches and numerical simulations of which are carried out. Compared with the traditional gas-liquid stirred tanks that use gas sparger to distribute gas, the self-inspirating tank is not using any gas transportation machineries, but using the pressure difference generated by mechanical agitating of the impellers to induce gas, hence it has been widely applied in many processes, such as oxidation, ammonolysis, alkylation, flue gas desulfurization, froth flotation beneficiation and waste water treatment. Therefore, through studing of the self-inspirating tank, we can deeply comprehend its internal fluid flow characteristics and gas-liquid dispersion performance, such as power demand, gas holdup and oxygen transfer performance, fully understand the advantages of self-inspirating dispersion, and provide the guidances for industrial applications of the self-inspirating tank.In this paper, the single-phase flow characteristics are qualitatively simulated based on CFD, including the influence of different blade angles of the gas dispersion channel, different types of the lower impeller, and different impeller spacing on the macro-flow field in the tank. It is found that the blade angle of the gas dispersion channel, the type of the lower impeller and the impeller spacing have significant influence on the macro-flow field in the tank. When the blade angle of the gas dispersion channel is 30°, there are non-serious flow distortion, smaller swirl, and less energy loss on the plane of the upper impeller. When the lower impeller is PDTU, it has a stronger pumping ability to effectively pump the liquid to the regions around the upper impeller. When the impeller spacing is increased, the axial circulation is strengthened, but the pumping ability may be got weakened. Numerical simulation results have laid a certain foundation to the experimental study.Based on the numerical simulation results and existing experimental conditions, the gas-liquid dispersion performance in the self-inspirating tank with dual impellers is studied and compared with the experimental data of surface aeration dispersion. The critical speed for gas induction, power demand, gas holdup and oxygen transfer performance for different types of impeller combinations and different impeller spacing are compared. Results indicate that the power demand can be effectively reduced by the self-inspirating tank. The power demand of a combination of P+PDTU is lower than a combination of DT+PDTU, the relative power demand is closed to 1, but the gas holdup and mass transfer coefficient is lower. When the impeller spacing is 0.1 m, it has lower power demand, higher relative power demand, higher gas holdup and mass transfer coefficient. Hence, as for the self-inspirating tank, when the impeller combination is DT+PDTU with the impeller spacing of 0.1 m, it is helpful to the gas-liquid dispersion and mixing, and the effectiveness of the self-inspirating gas and gas-liquid mass transfer are better.