利用CFD多相流模型优化设计沼气料液搅拌流场的方法研究

Optimizing the Stirred Flow Pattern in Biogas Fermentation Using CFD Multiphase Flow Mode

搅拌是现代沼气工程必不可少的工艺,优化料液搅拌的流场形态,可使发酵物料分布更加均匀,从而提高沼气的产量和污染物去除率。采用底部进水、高位分散式压力出口的设计方式可以显著优化流态。沼气发酵搅拌实质上是一种固液两相流过程,其初始阶段固体颗粒较大,后期将处于高浓度粘性液体(非牛顿流体)状态。文章设计了一台容积0.75 m3的厌氧消化罐,利用计算流体力学(CFD)软件,以水为介质,模拟初期的基本流态,并采用欧拉模型模拟后期的高浓度粘性流体流态,从而验证底部进水、高位分散式压力出口设计方案的优化效果。通过对几种进料速度的搅拌效果进行分析,发现在清水介质工况下,采用0.6 m·s^-1的进水流速,比1 m·s^-1流场分布更均匀,避免了分层。但在秸秆介质工况下,采用1 m·s^-1却比0.6 m·s^-1更均匀,并能避免分层。文章通过变工况模拟分析的对比演示,阐述了利用CFD多相流数值模型分析不同工况混合搅拌流场形态,优化设计搅拌参数的方法。

Stirring is an essential technology in modern biogas plant, the flow pattern of biogas fermentation can be optimized by mixing to make the fermentation material distribution more uniform, thereby the biogas production and pollutant removal rate can be increased. The design of bottom inlet and high-position dispersed outlet can significantly optimize the flow pattern. Biogas fermentation agitation is in fact a solid-liquid two-phase flow process, which has large solid particles at the initial stage, and later on will become a high concentration viscous liquid(non-Newtonian fluid). In this paper, an anaerobic digester with a volume of 0.75 m3 was designed, and the basic flow state at the initial stage was simulated by using computational fluid dynamics(CFD) software with water as medium, and the flow state of high concentration viscous fluid at the later stage was simulated by using Euler model, so as to verify the optimization effect of the design scheme of bottom inlet and high-position dispersed outlet. Through the analysis of stirring effects of several feed speeds, it was found that, under the condition of water medium, the inlet velocity of 0.6 m·s^-1 was more evenly distributed than that of 1 m·s^-1.However, under the working condition of straw medium, 1 m·s^-1 was more uniform than 0.6 m·s^-1 and could avoid stratification. This paper expounded the method of CFD multiphase flow mode to analyze the state of stirring flow field under different working conditions and optimize the design of stirring parameters.