曝气池曝气管布置方式对流速分布影响的数值模拟研究

Numerical simulation of velocity distributions in aeration tanks influenced by different aeration tube arrangements

曝气池是活性污泥法污水处理工艺的核心设备,探明曝气池内的流场结构旨在提高其氧转移效率和污水处理效率。采用欧拉-欧拉多相流模型和标准k-ε紊流模型(FLUENT 6.3)对一典型的推流式曝气池进行了数值模拟研究,通过分析曝气管分别布置在曝气池一侧和曝气池中间时池内的流速分布规律,比较各特征断面的流速不均匀系数和气液两相之间的速度差,发现当曝气管布置在一侧时池内流速更加均匀,气液两相之间的速度差值更小,有利于曝气池内气液两相的稳定混掺;通过分析比较不同时刻曝气管中心纵向断面的气相体积分数分布图,得出当曝气管布置在一侧时气相体积分数分布均匀。流场结构与气相体积分数分布规律皆有利于气液两相之间发生氧传质,从而提高氧气利用率,并减少能耗。研究成果可为污水处理工程设计优化提供一定参考。

Aeration tank is a core device in treatment of activated sludge waste water, and understanding its flow structure is crucial to improvement of its oxygen transfer and sewage treatment. An Euler-Euler multiphase flow model combined with a standard k-e turbulence model （FLUENT 6.3） has been used in this study to simulate a typical plug-flow aeration tank. We analyzed the velocity distributions for two cases of different aeration tube installation, located at the tank centerplane and near a tank wall, and compared their velocity uniformity coefficients and velocity differences between the gas and liquid phases at characteristic cross sections. Our findings are that in the near-wall case the flow is more uniform and the velocity difference of two phases smaller, which is a favorable condition for flow mixing in the tank. In this case, the distribution of gas-phase volume fraction over the central longitudinal section at different time is more uniform. Thus, aeration tube installed near a tank wall is a case where both the flow structure and gas content are beneficial to oxygen and mass transfer between the two phases, leading to a higher rate of oxygen utilization and lower energy consumption. The results are useful for optimization of waste water treatment designs.