The influence of crystalliser configuration on the accuracy and precision of gibbsite crystallisation kinetics estimates

This work investigates the importance of experimental design on the accurac y and precision of estimates of the agglomeration, growth and nucleation ki netics for the gibbsite system. The work is motivated by the need to explai n the differences in crystallisation kinetics parameters reported in the li terature for this system. Experiments were conducted to estimate the kineti cs under the same process conditions (e.g. temperature, hydrodynamics and c omposition) from three different crystalliser configurations, i.e. (1) batc h; (2) semi-batch at constant composition with representative solids remova l and (3) semi-batch at constant composition with classified solids removal . The differential method of Bramley, Hounslow, and Ryall (J. Colloid Inter face Sci. 183 (1996) 155) modified For semi-batch crystallisation, was used to estimate the kinetics from each set of experimental data. Some differen ces in the kinetics estimates between the different configurations were obs erved. Dynamic simulation showed that each set of estimated kinetics was ad equate for describing the experimental CSD's. The uncertainties in the aggl omeration and growth rate estimates, obtained by Monte Carlo simulations, w ere large enough to explain the observed differences. The differences in th e nucleation source term were attributed to differences in suspension densi ty between the experiments. A sensitivity analysis found that operating con ditions have a greater impact on the uncertainties in the estimated kinetic s than the crystalliser configuration. (C) 2001 Elsevier Science Ltd. All r ights reserved.