CFD modelling of continuous precipitation of barium sulphate in a stirred tank

By a combination of computational fluid dynamics (CFD), population balance and kinetic modelling, model solutions have been obtained for the precipitation of BaSO4 in a dual-feed pipe, 0.3 in diameter continuous reactor agitated by a Rushton turbine. The conditions simulated include four agitator speeds from 200 to 950 rpm, two mean residence times (100 and 1180 s) and two shape factors (k(v) = 58 and pi/6). The flow field was solved using the multiple reference frame technique to give residuals < 10(-4) and this solution was then transferred to a stationary reference frame and the iterations for other differential equations were carried Out Until the residuals were < 10(-7). The results showed that >95% BaSO4 precipitated in the reactor, which intuitively seems correct but this finding is in contrast to much lower values in earlier work, probably because of the more stringent convergence requirements used here. Agitation speed had little effect on the results, as has been recently shown in the literature, justifying the decision not to include a microinixing model in the analysis. However, mean residence time and shape factor did have a very substantial effect on the precipitate crystal size. (C) 2002 Elsevier Science B.V. All rights reserved.