固态发酵反应器流场数值分析及搅拌参数优选

为研究厨余垃圾固态发酵反应器中机械搅拌装置的搅拌流场特性及优选机械搅拌设计参数,采用计算流体力学技术(CFD)方法模拟5种机械搅拌桨型的混合流场,并对搅拌桨的桨径比、转速等参数通过搅拌功率、混合时间、混合能和死区百分比等指标进行定量分析.模拟结果表明:二折叶搅拌桨、六折叶涡轮搅拌桨死区百分比大,对物料扰动范围小,不能有效进行混合;双螺带搅拌桨死区百分比最小,对物料扰动范围最大,搅拌功率也最大.对于双螺带搅拌桨桨径,物料死区随桨径比的增加而减小,当桨径比增大至0.75后不再减小,而搅拌功率随桨径比增大而一直增大.对于双螺带搅拌桨,随着转速增加,搅拌功率呈直线式增加,混合时间以抛物线式降低,混合能逐渐增加.综合考虑混合效果和搅拌功耗,转速为20 r/min、桨径比为0.75的双螺带搅拌桨是本研究反应器中的最佳搅拌设计.

Numerical analysis of flow field and optimization of agitation parameters in solid state fermentation reactor

To investigate the characteristics of the flow field of high solids in solid state fermentation reactor with mechanical agitators and optimize the design parameters of mechanical agitators, computational fluid dynamics (CFD) method was used to simulate the flow field of five types of mechanical agitators, and parameters such as ratio of impeller diameter and stirring speed were analyzed quantitatively through the indexes of stirring power, mixing time, mixing energy, and the percentage of dead zone. Simulation results show that the high solids had a small range of disturbance and a large percentage of dead zone, indicating that it cannot be effectively mixed through double blade and turbine agitator. The high solids had the largest range of disturbance, the smallest percentage of dead zone, and the biggest stirring power through double helical agitator. For the impeller diameter of the double helical agitator, the dead zone decreased with the increase of the ratio of impeller diameter, and when the ratio of impeller diameter increased to 0.75, it no longer decreased, while the stirring power increased with the increase of the ratio of impeller diameter all along. With regard to the stirring speed of the double helical agitator, the stirring power increased linearly with the increase of the stirring speed, the mixing time decreased along a parabolic curve, and the mixing energy gradually increased. Considering a balance of mixing performance and mixing power, the double helical agitator with a stirring speed of 20 r/min and the ratio of impeller diameter of 0.75 was the best agitator design in this reactor.