气升式微藻培养反应器曝气结构与性能优化数值模拟研究

Numerical simulation study on aeration structure and performance optimization of air-lift microalgae culture reactor

利用计算流体动力学(Computational Fluid Dynamics,CFD)软件并采用欧拉模型模拟不同曝气结构的光生物反应器流场,湍流模型为标准k-ε模型。(1)通过在4种结构(球形、球冠、下半球、平板)中对5种参数(气含率、平均气速、平均液速、湍流动能、传质系数)进行分析,结果显示球形结构具有更好的曝气效果。其中,球形结构平均液速相较于平板结构提高了约52%,湍流动能相较于下半球结构高约78%。(2)研究反应器高度对曝气效果的影响,结果显示生物反应器的最优高度为30~40 cm。生物反应器高度为30 cm时,湍流动能最大,为0.182 m^(2)/s~2,比高度为20 cm时增大了约30%。(3)将双曝气头与单个曝气头的曝气性能进行比较,结果发现双曝气头具有更好的曝气效果。26孔双曝气头的湍流动能最高,为0.213 m^(2)/s~2;36孔双曝气头的湍流动能低于26孔双曝气头的湍流动能,为0.189 m^(2)/s~2,比球形结构的湍流动能提高约25%;36个孔的双曝气头传质系数为1.089 s^(-1),相较于球形装置的传质系数提高约56.9%。

As an important way to culture microalgae,photobioreactors are optimized to improve the efficiency of microalgae culture and to maximize the economic benefits of microalgae production.In this paper,the flow field of photobioreactors with different aeration structures is simulated by CFD software.The Eulerian model is used and the turbulence model was the standard k-ε model.Firstly,the gas phase distribution clouds are obtained by analyzing five parameters(gas content,average gas velocity,average liquid velocity,turbulent kinetic energy,and mass transfer coefficient),and the optimal aeration structure is determined to be the spherical structure.Among them,the average liquid velocity value of the spherical structure is increased by about 52% compared with that of the flat plate structure,and the turbulent kinetic energy of the spherical structure is about 78% higher compared with that of the lower hemisphere structure.The effects of different reactor heights(20 cm,30 cm,40 cm,50 cm) on the reactor flow field conditions and the mass transfer effect between the gas-liquid phases are investigated,and 30-40 cm is determined as the optimal height of the reactor.With the increase of reactor height,the turbulent kinetic energy shows a trend of increasing and then decreasing,and the maximum turbulent kinetic energy is 0.182 m^(2)/s~2 at a height of 30 cm,and the minimum turbulent kinetic energy is 0.141 m^(2)/s~2 at a height of 20 cm,which is increased by about 30%.By further optimization of the aeration device,it is determined that the double aeration head has a better aeration effect than the single aeration head.The turbulence kinetic energy of the 26-well double aerator is the highest,which is 0.213 m^(2)/s~2.The turbulence kinetic energy of the 36-well double aerator is lower than that of the 26-well double aerator,which is 0.189 m^(2)/s~2,about 25% higher than that of the spherical structure.The mass transfer coefficient of the double aerator with 36 holes is 1.089 s^(-1),about 56.9% higher than that of the spherical device.