The Research Of Influence Of Bubble Formation And Movement On The Flow Field In Rare Earth Electrolytic Cell

The molten salt electrolysis technology is widely adopted by rare earth industry inChina at present. Rare earth oxide is melted at high temperature in electrolytic process.Circulation flow of molten salt is the precondition of keeping electrolytic process efficientand stable. The bubble movement is the main driving force of molten salt circulation flow.However, for the limit of high temperature and strong corrosive condition of fluoridemolten salt, it is too difficult to trace the bubbles generation and movement process.Therefore, it is necessary to adopt the new research method to study bubbles behaviorchanges of electrolytic process of anode surface to improve the production efficiency.For the study of research subject, the actual high temperature molten salt replaced bywatet, natural air instead of anode gas generated by the electrochemical reaction, thehydraulic model experiment platform of the electrolytic process was established based onthe3kA neodymium electrolytic cell as the research object and similarity theory wasconsidered as the research base. The modified Froude was selected as the similaritycriterion in the experiment. High-speed cameras and PIV tester is used to record bubbleformation under different working conditions and the variation of the flow field. Air flowin the water model was calculated under different anode surface current density. Thebubble diameter, contact area, detaching time from the anode, sliding distance and otherparameters were analyzed to determine the optimal working parameters for providingreference data to electrolytic cell development.According to the nucleation theory, the bubble generation velocity had been modified.According to the equivalent modified Froude of the model and the prototype, the gas flowin the water model which corresponds to different current density is7.13ml/min,8.77ml/min,10.41ml/min,12.06ml/min,13.71ml/min by calculation. Parameter changes ofbubble formation and movement process were analyzed while the air flow was10.41ml/min. The variation of diameter, shape, ratio of transverse diameter and longitudinaldiameter, acting force of bubble separation process with time have been clear by the analysis of data above. With different air flow instead of different anode surface currentdensity, various parameter changes of bubble are analyzed. The conclusion is obtained that8.77ml/min is relatively appropriate, and the anode current density of1.6A/cm2is moreconducive to electrolysis. While the anode surface tilted downward0°,3°,5°,7°,10°andtilted upward3°,5°,7°,10°,20°respectively, various parameter changes of bubble wereanalyzed. It is concluded that the gradient anode wall is not conducive to bubbles for risingrapidly, easy to produce anode effect near the upper surface of molten salt. The efficiencyof bubble formation and separation is optimal when the anode surface tilts upward3°. Theflow field variation under different ventilation flow and insertion depth was analyzed byPIV experiment method. The results prove that the anode surface current density andelectrode insertion depth directly affect the distribution of flow field and the range ofcirculation movement. Also the bubble movement is the main driving force of molten saltcirculation flow in the cell.