Studies On The Fluid Dynamics And Flowsheet Simulation Of Biorefining Processes Of Lignocellulosic Feedstocks

Lignocellulose biorefining has great potentials of feedstock supply and product market in the major agricultural countries. However, severe technical barriers of the present biorefining processes exist and the cost for cellulosic ethanol production is still greater than the acceptable market range. Cutting the processing cost of cellulosic ethanol to a profitable level is crucially important to survive the lignocellulose biorefinery industry from the current dilemma. In this dissertation for the application of the doctor degree of philosophy in biochemical engineering, the fluid dynamics and flowsheet simulation properties on the biorefining processes of lignocellulosic feedstocks for production of biofuels and biochemcials were studied targeting the industrial scale plants. The major results were summarized as follows:(1) The helical mixing was introduced into the pretreatment reactor and the process was able to operate under the very high solids loading till the complete dry lignocellulose feedstocks. The mock-up method and the computational fluid dynamics (CFD) method were applied into the fluid dynamics of the dry pretreatment system under the fluid assumption for the solid state corn stover feedstocks. The power-law model for non-Newtonian fluid was used to indicate the apparent rheological properties of the assumed corn stover "pseudo-fluid". The consistency index of power law fluid Kp1and the power law index number n were determined for the system and applied into the modeling of the scale-up process from50L,50L, and400L mock-up and the CFD model. Various parameters such as the impeller geometry (d/D) were investigated using the established CFD modeling for the large scale reactors and will be used as the important tools for the design and scale-up of the industrial pretreatment reactor.(2) The flowsheet simulation model for the industrial scale biorefining process of cellulosic ethanol production using lignocellulosic feedstocks was established. The physical property database was established based on the materials analysis and parameter estimation methods for the biomass components involved in the lignocellulose processing. The biorefining plant with the processing capacity of300,000tons corn stover annual for production of50,000tons fuel ethanol annual was simulated using the established Aspen plus model. The water and energy consumptions of the processes were analyzed. The overall mass and enthalpy balance were calculated. The model can be used in the future industrial plants for the process design, operation optimization and economic evaluation.(3) A lactic acid bacterium with high tolerance of temperature and lignocellulose derived inhibitor was isolated and characterized as Pediococcus acidilactici DQ2. The strain used in the simultaneous saccharification and fermentation (SSF) for high titer lactic acid production at the high solids loading of corn stover. Corn stover was pretreated using the dry sulphuric acid pretreatment, followed by a biological detoxification to remove the inhibitors produced in the pretreatment. The bioreactor with a novel helical impeller was used to the SSF operation of the pretreated and biodetoxified corn stover. The results show that a typical SSF operation at48℃, pH5.5, and near30%(w/w) solids loading in both5L and50L bioreactors was demonstrated. The lactic acid titer, yield, and productivity reached101.9g/L,77.2%, and1.06g/L/h, respectively. The result provided a practical process option for cellulosic lactic acid production using virgin agriculture lignocellulose residues.