Influence of hydrodynamics on precipitation: A computational study

A method is proposed to describe the influence of hydrodynamic conditions on precipitation processes. It is based on spatially distributed moment equations, on relations for the kinetics of nucleation and growth of the precipitating compound and on the solution of the flow field as calculated by the commercially available software package 'Fluent'. Local quantities are calculated, such as liquid velocities, local supersaturation and local moments of the particle size distribution. The method was applied to simulate a double jet continuous reactor for the precipitation of calcium phosphate. The influence of the location of feed points on the conversion, product average size and coefficient of variation of the product size distribution was shown. The conversion varied within the range of 0.57 to 0.83, the average size changed by a factor 1.9 and the coefficient of variation by a factor 1.5. It was shown that only a small fraction of the reactor volume is effectively used for nucleation and growth. The results were correlated to the fundamental processes governing the reactor behavior.