底隙十字挡板对四边形流化床流体力学性能优化数值模拟

通过置入内构件实现流化床底隙区多相流矢量由混沌到归一的转化可获得床体内流体流化性能的改善.基于此,以底隙区置入十字挡板的四边形流化床为研究对象,使用Fluent软件进行三维可视化模拟,利用Eulerian-Eulerian双流体模型模拟其在厌氧、水解及好氧条件下优化反应器流体力学性能的能力,考察置入挡板前后流化床内流场、液相运动速率、气体相含率及湍流耗散率的反馈变化,分析其对流体运动的影响,并提出工程优化设计的方向.结果表明:底隙区置入十字挡板后,四边形流化床内液体循环速度最大提升15.7%,在上升区截面上的分布更加均匀,液速峰值下降,有利于维持活性污泥的团聚作用,对提高流化床污泥负荷有利;整体气含率下降3.5%~6.9%,应用时可加入漏斗型内构件予以改进;在水解与好氧生物的模拟过程中,底隙区十字挡板的置入更能优化水力条件,湍流动能耗散率最大降低31.9%,对降低系统能耗提供了有利证据.研究证明,反应器内构件的设置通过流体力学性能的数值模拟可以成为一种优化开发的捷径技术.

Numerical optimization on hydrodynamic characteristics of rectangular fluidized bed with a cross-shaped baffle on the bottom

To improve the fluid performance of the reactor, the inner component was implanted to lead the multiphase flow vectors from chaos to normalization at the bottom of biological fluidized bed. Eulerian-Eulerian multi-phase model in Fluent was used to visually simulate the three-dimensional hydrodynamics characteristics of the rectangular fluidized bed before and after implantation of a cross-shaped baffle on the bottom of the reactor under anaerobic, hydrolysis and aerobic conditions. To analyze the impact on fluid motion and to optimize the engineering design of the reactor, the variations of flow field, the liquid circulation velocity, the gas holdup and the turbulent dissipation rate were investigated. Results demonstrated that the liquid circulation velocity had a maximum increase at 15.7% with more even distribution at the rising area section, while the peak value of liquid circulation velocity decreased. These characteristics contributed to the union of activated sludge and increased the sludge loading of the reactor. Moreover, the placement of a funnel-shaped inner component was suggested to overcome the slight decrease of overall gas holdup which ranged from 3.5% to 6.9%. The behavior of the cross-shaped baffle optimized the hydraulic condition better under hydrolysis and aerobic condition, and the turbulent dissipation rate had a maximum decrease at 31.9%. This proved the energy saving performance of this structure. The study results implied that numerical simulation of hydrodynamics characteristics is a shortcut way to optimize the inner component development of the bioreactor.