Dynamic Modeling of Encrust Formation and Mitigation Strategy in a Continuous Plug Flow Crystallizer

Encrustation, also known as fouling or scale formation, on the wall of plug flow crystallizers (PFC) can cause major operational and economic problems in pharmaceutical industries. These include increased energy requirements due to increment of thermal resistance and pressure drop, and clogging of the crystals due to reduction of flow area. In this work, a mathematical model for predicting the dynamic behavior of a PFC undergoing encrustation is presented. This model describes the formation of encrust layer by considering various mechanisms such as rate of solute transport from bulk to the wall, integration and removal due to shear stress induced by fluid turbulence. A population balance model for describing the crystallization process in the PFC is also coupled with the encrustation model in order to obtain the appropriate concentration profile in the PFC as well as product crystal size distribution (CSD). Based on this model, a mitigation strategy is proposed that relies on injection of pure solvent to dissolve the encrust layer.