Lignocellulose Bioconversion:Helical Ribbon Stirred Reactor Engineering Research

This research aims at the development and scale up of the simultaneous saccharification and fermentation reactor at high lignocellulose solids loading. Considering the demands of the reaction on the transfer behavior of the reactor, the type and internals of the reactor were determined on the basis of the investigation of engineering characteristics of enzymatic hydrolysis. The reactor equipped with combined helical ribbon/double helical ribbon-pitched blade impeller was designed for the lignocellulose bioconversion. The research was carried out both in the reactor and cold flow set up in the combination of experiments and computational fluid dynamics (CFD). The dynamic characteristics of the reaction material were investigated systematically. The flow and mixing of the Theologically complex fluids were investigated in the helical ribbon stirred tank, including the mixing of high viscosity fluids, liquids with different viscosities, multiphase and non-newtonian fluids.This research consisted of three parts which were shown as follows:(1) Practices in the enzymatic hydrolysis/ethanol fermentation reactor at laboratory scaleThe dynamic characteristics of the reaction material and the reactor were investigated systematically in the simultaneous saccharification and fermentation of corn stover at high solids loading. The state of the com stover is wet solids, paste, slurry and suspension with the evolution of the reaction. The decrease of the viscosity is the major characteristic of the material rheology, the power consumption decreased also. Synergism effect existed between reaction and rheology. The carbon dioxide was released in the fermentation stage and the reaction material becomes gas-liquid-solid three phase system.The effect of the impeller rotational speed on the reactor performance was investigated. The product concentration (glucose) was sensitive to the rotational speed at the presaccharification stage and insensitive at the SSF stage (ethanol concentration); if the impeller rotational speed was too low, the corn stover particle will descend to the bottom of the tank. Based on the above results, the operating strategy of simultaneous saccharification and fermentation reactor at solids loading was put forward. The key parameters for the design and scale up of the reactor were obtained. They are:the volumetric power consumption and specific productivity.(2) The engineering characteristics research of the reactorThe effect of fluid rheology and reactor size on the power consumption and mixing time were studied in the helical ribbon/double helical ribbon stirred tank in the range of<Φ200-800. The power consumption of the impeller decreased with the pseudoplastic of fluid. The Metzner constant correlation was given for the highly shear-thinning fluid, applicative for both single liquid and solid-liquid two phase fluid.Ntm=234in the helical ribbon stirred tank, irrespective of the fluid flow behavior and tank diameter. The liquid phase mixing time increases with the aspect ratio. The mixing time of the slurry system is less than that of single phase liquid. The mixing of the liquids with different viscosities and densities was investigated in helical ribbon stirred tank and it was found that the mixing time increased2-5times compared to that of the mixing of liquids with similar properties, the influence of the volume ration and density difference is significant.The flow field and shear strain rate were investigated by computational fluid dynamics in the helical ribbon stirred tank. The clear picture of the flow structure in the tank was got. The profile of velocity and its influencing factor were given, the pitch and diameter of the helical ribbon is the most sensitive geometric parameters. The flow behavior of the high viscosity fluid, shear thinning fluid and highly shear thinning fluid are different from each other. The shear strain rate increases with the fluid pseudoplastic.The bubbling mixing were investigated for the low and high viscosity fluid in the context of the generation of the carbon dioxide in the fermentation, different fluid dynamics were observed under gas stirred conditions.(3) Suggestion on the scale up strategy for the helical ribbon bioconversion reactorMaking use of the results of the reactor engineering characteristics and reaction feature of the simultaneous saccharification and fermentation of lignocellulose, the reactor was developped. The reactor type was properly chosen and the key operating parameters can be adjusted. The scale up effect was analyzed for the bioconversion process, the scale up strategy was put forward and the method for the evaluation of key reactor dimensions’was suggested.