Development, modeling and scale-up of a novel gas-liquid contactor for high viscosity pseudoplastic fluids.

摘要

This thesis presents the development, mathematical modeling and scale-up of a new reactor design for mixing and gas-liquid mass transfer in highly viscous non-Newtonian shear-thinning pseudoplastic liquids that possess a yield stress. Aqueous solutions of a biopolymer xanthan gum were used as model non-Newtonian liquids. The specific contributions of this thesis include the development of an improved stirred tank gas-liquid contacting system that has substantially better mixing gas-dispersion and mass transfer capabilities than conventional stored tank reactor designs; the development of a comprehensive and realistic multicomponent gas-liquid mass-transfer model for the new design that is scalable from laboratory to commercial size reactors; and the specification of appropriate scale-up criteria to enable scale up of the reactor design.; The new reactor design developed involves multiple up-pumping 45° pitched-blade turbines (PBT) within a draft tube in the mixing tank. The draft tube is fitted with baffles at close clearances above and below each PBT. The presence of close clearance baffling within the draft tube provides a region of high shear around each PBT where excellent dispersion of gas sparged into the bottom of the draft tube can take place. In addition, the baffling prevents any swirling within the draft tube and facilitates good axial pumping of the fluid out of the draft tube and into the annular region between the draft tube and the tank. To further facilitate bubble creation and mass transfer at the liquid surface in the reactor, a new surface aeration impeller was developed specifically for efficient operation in highly viscous shear thinning fluids.; The combination of the up-pumping PBTs in the baffled draft tube, and the surface aeration impeller provide for a very efficient mixing and gas dispersion system with uniform mixing throughout the mixing tank without any stagnant zones anywhere in the reactor.; In summary, based on extensive experimental evaluation, the design presented in this thesis has been shown to perform substantially better than current stirred tank designs, providing improved mixing and gas-liquid mass transfer in highly viscous non-Newtonian shear-thinning liquids possessing a yield stress.