多场耦合下电弧熔融法制备高纯MgO的机理研究

Using arc-fusion method for high-purity MgO production is a trend for the fused magnesia industry. The problem of purification mechanisms of heat and mass transfer in the fused magnesia furnace is the primary bottleneck for the improvement of this method. According to measured data of the furnace, this project will establish three dimensional numerical simulation model for the multi-field coupling analysis of the furnace to calculate the electromagnetic, thermal and flow fields. The model will illuminate the effect of Lorentz force on the flow patterns of the melt, clarify the condition for the transition between the forced convection and natural convection, calculate the changes of the bath's shape and position during different melting stages through solid-liquid interface tracking technology, and reveal the control mechanisms of phase current and voltage on the MgO crystal growth environment. Based on measurement of the chemical compositions of the fused magnesia obtained in the furnace and multi-physics field analysis, distributions of various impurities in molten bath will be calculated in a solute transport model, and influences of the melt convection, temperature gradient and the shape of solid-liquid interface on the segregation behaviors will be studied to reveal the corresponding removal mechanisms for each impurity. The results of these investigations will offer new ideas and control theory for the purification and crystal growth of the refractory by arc-fusion method.

利用电弧熔融法制备高纯MgO产品是电熔镁行业的发展趋势。电熔镁炉内传质与传热过程的提纯机制尚不明确是制约工艺水平大幅提升的理论瓶颈。本项目基于实际生产监控数据建立电熔镁炉的多场耦合分析数值模拟模型，通过炉内电磁-热-流场的耦合计算，分析洛伦兹力对熔体流动方式的影响，确定熔体内强制对流与自然对流相互转换的条件；利用固液界面追踪技术研究不同冶炼阶段炉内熔池形态和位置的变化，掌握相电流及相电压等控制参数对MgO晶体生长环境的影响规律。基于各种杂质在熔体中分布的测量和多物理场耦合数值模拟结果，建立溶质传输模型计算各种杂质的浓度场，分析熔体对流、温度梯度和固液界面形态对杂质偏析的影响，揭示杂质去除及MgO晶体生长的控制机制。研究结果将为弧熔法制备高纯MgO及其它难熔物晶体提供新思路和理论依据。

为了揭示电熔镁炉的多场耦合对熔炼过程的影响，本项目从三个方面开展了工作：.电熔镁炉熔池的多场耦合计算方面：建立了三相交流电熔镁炉和双电极直流电熔镁炉的多场耦合模型，通过计算无量纲参数来表征熔体对流。结果表明：直流和交流电熔镁炉熔池的对流皆能发展成非常充分的紊流状态，而且流场和温度场都受到电流大小的显著影响；在几种典型的冶炼状态下，熔池内的自然和强制对流都不可忽略不计。熔池等效三相电路的线电阻的定量分析表明，其值更容易受熔池半径的影响而不是熔池高度。对交流电熔镁炉的电磁场分析揭示了各种影响因素与涡流损耗的关系，如果炉盖的设计采用混合材质，则会显著降低涡流损耗。.电弧等离子体MHD计算方面：模型还预测出洛伦兹力力所引起的电弧偏转的角度，电流越大，电极间距越小，则电弧偏转越明显。在模型基础上，还进一步计算并讨论了电弧对熔池的四种不同的传热机制（对流，辐射，凝聚和电子传输的能量）的分布情况。.电熔镁炉的监控系统设计方面：通过虚拟仪器技术，采集了容量为5000kVA的电熔镁喷炉故障发生前后的声信号，对比了不同状态下电弧声信号的时频图，发现了喷炉前期电弧声信号的变化规律，开发了基于声信号的喷炉抑制系统。