纤维素酶水解反应器的开发与放大

以木质纤维素生产燃料乙醇为背景,在考察玉米秸秆同步糖化与发酵反应特征基础上,给出了合适的反应器构型:螺带型搅拌槽;直径0.2～0.8m,高径比1～2,转速20～120r/min,着重从冷模实验对搅拌槽性能进行了考察,为反应器放大提供必要的基础。实验结果发现,层流流动条件下,随流体剪切稀化性质增强,搅拌功率(Np)显著降低,而无因次混合时间(Ntm)则变化不大;给出适用于强剪切稀化流体的Metzner常数Ks关联式,且Ks与搅拌槽直径无关;对于几何相似的螺带桨,随着搅拌槽直径增大,若保持相同的单位体积功率,Ntm是相同的,这为我们提供了一个螺带型搅拌槽的放大准则;搅拌槽功耗及Ntm随着搅拌槽高径比的增大而增大;最后采用数值计算方法对搅拌槽内分散混合效率进行了考察,发现,根据混合效率的不同,可将螺带型搅拌槽分成几个不同的区域,搅拌槽内体积平均分散混合效率接近于0.5(简单剪切流)。纤维素酶水解反应器的放大,小试给出关键参数(单位体积生产能力),冷模实验提供混合性能、几何结构设计基础,经验判据与CFD相结合,关注基本流型的尺寸效应,兼顾单位体积功率及最大剪切速率。

Development and scale up of the enzymatic cellulose hydrolysis reactor

The helical ribbon stirred tank was put forward for the simultaneous saccharification and fermentation at high solids loadings based on the reaction characteristics in the context of production of ethanol from lignocellulosic biomass.Attention was paid on the investigation of mixing performance of the helical ribbon stirred tank by cold-flow model experiments in the range of 0.2~0.8 m diameter,1~2 aspect ratio and 20~120 r/min rotation speed,providing the basis for the reactor scale up.The experimental results showed that power consumption decreased significantly with the fluid pseudoplastic,while the dimensionless mixing(Ntm) did not change obviously;for geometry similar impellers,Ntm was nearly the same as the tank diameter increased if kept the specific power equal,which offering a rule of thumb for the reactor scale up;the power consumption and Ntm increased with the aspect ratio;Finally,the dispersive mixing efficiency was studied in the tank employing numerical methods.It was found that the helical ribbon stirred tank can be divided into different sections based on the magnitude of the dispersive mixing efficiency.The volumetric average dispersive mixing efficiency in the helical ribbon stirred tank was 0.5(simple shear flow).As to the scale up of the reactor,bench scale experiments give key parameter(volumetric productivity) and cold-flow model provides the basis of mixing performance and geometry design.Combine the experimental results with computational fluid dynamics,concerning the size effect of flow field and consider the specific power and the maximum shear strain rate.