Drawdown mechanism of light particles in baffled stirred tank for the KR desulphurization process

To improve the efficiency of the desulfurization process, the drawdown mechanism of light particles in stirred tank is studied in this paper. For both up and down pumping modes, the just drawdown speeds (N_jd) of floating particles in transformative Kanbara Reactor (KR) are measured in one and four baffled stirred tanks experimentally. Then numerical simulations with standard k-ε model coupled with volume of fluid model (VOF) and discrete phase model (DPM) are conducted to analyze the flow field at the just drawdown speed N_jd. The torques on the impeller obtained from experiments and simulations agree well with each other, which indicates the validity of our numerical simulations. Based on the simulations, three main drawdown mechanisms for floating particles, the axial circulation, turbulent fluctuation and largescale eddies, are analyzed. It's found that the axial circulation dominates the drawdown process at small submergence (S=1/4T and 1/3T) and the large-scale eddies play a major role at large submergence (S=2/3T and 3/4T). Besides, the turbulent fluctuation affects the drawdown process significantly for up pumping mode at small submergence (S=1/4T and 1/3T) and for down pumping mode at large submergence (S=2/3T and 3/4T). This paper helps to provide a more comprehensive understanding of the KR desulphurizer drawdown process in the baffled stirred tank.