Canadian Journal of Chemical Engineering, Vol.96, No.6, 1382-1395, 2018
CFD-PBE-PBE SIMULATION OF AN AIRLIFT LOOP CRYSTALLIZER
A complete solver (CFD-PBE-PBE) for crystallization processes in an airlift loop crystallizer is developed in OpenFOAM (open-source field operation and manipulation) in this work. It combines computational fluid dynamics (CFD) with population balance equations (PBE) for both gas bubbles and crystals. Models for gas-liquid mass transfer and chemical reaction are included as well in the solver. PBE describing bubble coalescence and breakage is solved by the cell average method. Primary nucleation, secondary nucleation, and particle growth are considered in the PBE describing the crystallization process. The solver is validated with the formation of calcium carbonate via the reaction of CO2 with Ca(OH)(2) solution in an airlift reactor. Effects of the chemical enhancement factor and crystallization kinetics on predictions are systematically investigated. Variation of predicted pH value, concentration of Ca2+, mean particle size, and crystal size distribution (CSD) with time is in qualitative and semi-quantitative agreement with the published experimental data, when the appropriate crystallization kinetics are used. Effects of operation parameters such as initial concentration and superficial gas velocity are further numerically examined. The increase in superficial gas velocity results in the increasing consumption rates of OH-and Ca2+, while the particle diameter seems unchanged in the present simulation. A higher initial concentration of reactants will lead to a smaller particle diameter and a narrower CSD. The predicted results indicate that the developed solver is feasible, and can be used for the design and scale-up of airlift loop crystallizers.