Abstract:

In this paper, the process of biodegradation of phenol wastewater in the internal loop airlift reactor (ILALR) was studied using computational mass transfer method. The Euler approach is carried out with RNG k-ε method to predict the hydrodynamics of the reactor. The population balance model is adopted to describe the bubble size distribution. The recently developed computational mass transfer \overline{c^{\mathrm{2}}}-ε_c model is used to close the turbulent mass transfer differential equations, so the turbulent mass diffusivity can be determined without using empirical methods. The simulated results of dissolved phenol concentration and cell concentration are compared to the experimental data in the literature, and good agreement is observed. The simulated results reveal that the distribution of the calculated turbulent Schmidt number is not a constant in the ILALR, so the traditional method of assuming a constant turbulent Schmidt number by experience is not reasonable. Moreover, the simulated shear stress in the ILALR is increased with the increase of the superficial gas velocity, and the highest shear stress is found in the top region of the draft tube.

Key words: internal loop airlift reactor, mass transfer, computational fluid dynamics, turbulent mass diffusivity, degradation

摘要：

利用计算传质学方法对内循环气升式环流反应器（ILALR）内生物降解苯酚废水过程进行了研究。采用欧拉多相流模型结合RNG k-ε湍流模型对ILALR中气-液两相流动过程进行模拟，采用气泡群平衡模型（PBM）对反应器内气泡的尺寸分布进行预测。利用近年来提出的计算传质学\overline{c^{\mathrm{2}}}-ε_c模型对湍流扩散系数进行计算，从而摆脱了传统需要预估湍流Schmidt数的经验方法。模拟得到的液相苯酚和菌体浓度与实验测量值吻合良好，从而证明了所建立模型的有效性。研究结果表明ILALR内湍流传质过程中湍流扩散系数及湍流Schmidt数并非常数，因此基于传递相似性假设得到的湍流Schmidt数经验模型不适用于ILALR内湍流传质过程的模拟。模拟得到的ILALR中液相剪应力随表观气速的增大而增大，局部最大值出现在导流筒的上部。

关键词: 内循环气升式环流反应器, 传质, 计算流体力学, 湍流扩散系数, 降解