Modeling of the crystallization of gypsum produced in the digestion tank of an industrial phosphoric acid manufacturing process

Abstract

The present paper deals with the development of a model of gypsum crystallization during the production of phosphoric acid. The objective is to predict the kinetics of formation of products and consumption of reagents, as well as the time-varying crystal size distribution. The population balance model involving primary and secondary nucleation and crystal growth rates is thus investigated using the method of moments, along with the Pitzer thermodynamic model. Both models involve unknown parameters to be identified from experimental data. Two databases are therefore used, (i) the first one which consists of equilibrium measurements is used to identify the unknown parameters of the Pitzer model, (ii) and the second one which contains temporal profiles of supersaturation ratio, is used to determine the nucleation and growth unknown parameters. The identified parameters are then used to compare the predictions of the developed models with the experimental measurements. The results are very promising, and the models can be used in the design and optimization of gypsum crystallization processes.