曝气对膜生物反应器内气-液流态影响的模拟研究

Simulation study on the influence of aeration on the gas-liquid flow regime in membrane bioreactors

采用多孔介质模型模拟具有渗透作用的分离膜,利用群平衡模型(PBM)预测膜生物反应器(MBR)内多尺寸气泡流动,对MBR内气-液流态进行模拟研究.系统分析了渗透侧抽吸作用、气泡直径、曝气速率对流态及近膜面气泡流对膜面的擦洗效果的影响.结果表明:对于远离膜面气泡流,在渗透侧抽吸负压2000 Pa下,气泡直径从0.1 mm增大到3.0 mm,含气率峰值下降16%,小气泡有利于膜反应器内气-液充分混合;曝气速率从0.5 m/s增大至1.5 m/s,气泡流含气率峰值增加12.0%.随着曝气孔靠近膜面,液相流动的循环中心也逐渐靠近膜面.对于近膜面气泡流,渗透侧抽吸压为0 Pa时,气泡直径从3.0 mm减小到1.0 mm,膜面剪切应力由1.92 Pa增大到4.87 Pa;曝气速率由0.5 m/s增大至1.5 m/s,膜面剪切速度由0.02 m/s增大到0.22 m/s,膜面剪切应力由1.97 Pa增大到3.83 Pa;曝气速率0.5 m/s下,抽吸负压3000 Pa的平均膜剪切应力为0 Pa的1.85倍;高抽吸负压下小气泡高速曝气有利于提高膜面剪切应力.研究结果将为MBR曝气工艺设计和优化提供依据.

In this study,the flow patterns of membrane bioreactor(MBR)under different aeration models were simulated.Porous media model was adopted to simulate permeable separation membrane and multi-sized bubble flow within MBR was predicted by Population Balance Model(PBM).The effects of permeate side-suction,bubble diameter and aeration velocity on the flow regime,and the impact of near-membrane bubble flow on the membrane surface scouring effect were systematically analyzed.The results show that,for bubble flows distanced from the membrane surface,smaller bubbles promote the mixing of gas and liquid phases within membrane reactor.Under the permeate side-suction pressure of-2000 Pa,the void fraction decreased by 16%with increasing bubble diameter from 0.1 to 3.0 mm,while the void fraction peak value increased by 12%with increasing aeration velocity from 0.5 to 1.5 m/s.The circulation center of liquid flow gradually moves closer to membrane surface when the aeration orifice approaches membrane surface.For bubble flows near membrane surface,the membrane shear stress increases from 1.92 to 4.87 Pa when the bubble diameter decreases from 3.0 to 1.0 mm under the suction pressure of 0 Pa.Themembrane shear velocity and stress increase from 0.02 to 0.22 m/s and 1.97 to 3.83 Pa,respectively,when the aeration velocity increasing from 0.5 to 1.5 m/s.The average membrane shear stress under the suction pressure of-3000 Pa is 1.85 times as high as that under 0 Pa under the aeration velocity of 0.5 m/s.High suction negative pressure with high-speed aeration of small bubbles is beneficial for enhanced membrane shear stress.The research results will provide guide and basis for the design and optimization of aeration processes in MBR.