| Pretreatment is the key step of biorefinery processes from lignocellulose to biofuels and biochemicals. Dry dilute sulfuric acid pretreatment at high solids loading leads to the reduction of waste water and energy consumption, thus is considered with potential of industrial applications. Conventional pretreatment reactors generally are lack of efficient heat and mass transfer mechanism and the pretreatment intensity is not uniformly distributed. The situation leads to the increased inhibitors generation and then affects the subsequent enzymatic hydrolysis and microbial fermentation. In this thesis, firstly, a new pretreatment reactor (20L) equipped with the helical ribbon impeller was applied into the pretreatment of corn stover. The pretreatment efficiency was evaluated, and the results indicate that helically agitated mixing improved the pretreatment efficiengy. Secondly, the rheological model to characterize the high solids conaining lignocellulose system was developed. The rheological properties of corn stover system with different water content and pretreatment time showed the shear-thinning non-Newtonian fluid, and the increase of water content and pretreatment time enhanced its shear-thinning properties. Thirdly, based on the rheological model, the computational fluid dynamics (CFD) model was established with using Solidworks, Ansys CFD and CFX. The fluid dynamics experiments of corn stover-water mixing at high solids loading were carried out in three reactors with different scales. The calculated power consumption and mixing efficiency by CFD modeling were in good agreements with the experimental results. Finally, the CFD model was applied to the design and structure optimization of the bottom and helical ribbon impeller in the2.5m3pretreatment reactor. This study provided a practical method for rheology characterization at high solids loading and developed the CFD model, which could be applied to the design and scale-up of dry pretreatment reator. |
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