SIMULATION AND EXPERIMENTAL INVESTIGATION OF POWER CONSUMPTION, GAS DISPERSION AND MASS TRANSFER COEFFICIENT IN A MULTI-PHASE STIRRED BIOREACTOR

Abstract Bio-oxidation leaching of refractory gold concentrate was carried out in a typical gas-liquid-solid three-phase stirred bioreactor. The bacteria, which adhered to solid particle surfaces and spread over the liquid phase, require sufficient oxygen and nutrient of carbon and nitrogen, and then the mass transfer rate should be considered. However, the mass transfer coefficient, which could be used to evaluate the mass transfer rate, was determined by gas holdup, bubble diameter and power consumption. Therefore, a three-phase Eulerian equation with k-ε turbulence model and additional models of two bubble diameter, a torque and a mass transfer coefficient were applied in the simulation. The simulation results were validated with experimental data and used to analyze the spatial distribution of the mass transfer coefficient. The results demonstrated that the simulation and experimental data of Sauter mean bubble diameter and power number were in good agreement and the simulation results of the mass transfer coefficient were agree with the values calculated by an empirical correlation. The Davoody model can be strongly recommended for further simulation of the bubble diameter, and the gas holdup and mass transfer coefficient were very unevenly distributed in the lower zone. Hence, the lower impeller clearance should be considered.摘要：针对难处理金精矿的生物氧化浸出（Bio-oxidation leaching）实验，于典型气液固三相搅拌生物反应器（gas-liquid-solid three-phase stirred bioreactor）中开展。附着于固体颗粒表面并扩散至液相的菌体，需充足的氧气及碳、氮营养源，同时应考量传质速率（mass transfer rate）。用于评价传质速率的传质系数（mass transfer coefficient），由气含率（gas holdup）、气泡直径（bubble diameter）与功耗（power consumption）共同决定。因此，本模拟采用结合k-ε湍流模型（k-ε turbulence model）的三相欧拉方程（three-phase Eulerian equation），并附加双气泡直径、扭矩及传质系数相关模型。模拟结果经实验数据验证后，被用于分析传质系数的空间分布规律。结果表明，索特平均气泡直径（Sauter mean bubble diameter）与功率数（power number）的模拟值与实验数据吻合良好，传质系数的模拟结果也与经验关联式（empirical correlation）的计算值保持一致。Davoody模型可被强烈推荐用于后续气泡直径的模拟研究；反应器下部区域的气含率与传质系数分布极不均匀，因此需合理优化下部桨叶间距（impeller clearance）。