NUMERICAL MODEL OF THREE STAGE SPRAY DRYING FOR ZEOLITE 4A-WATER SUSPENSIONS COUPLED WITH A CFD FLOW FIELD

摘要

In the present work, a detailed description of a three-stage spray drying model capable of accurate simulation of drying of zeolite suspensions coupled with a CFD flow solver is presented. The models resolve the temperature field in the interior of the droplet, which consists of zeolite particles with adsorbed water and liquid water in the porous channels between the particles. The diffusion process in the interior of the particle is described by the Stefan diffusion model in the dried outer region, and the temperature field is accounted for by the unsteady state heat conduction model with a phase transition at the interface of the wet core. A new approach to the specification of the effective porosity of the dried crust is proposed, where a linear variation of the effective porosity with respect to radial position is applied. The correctness of the model is tested on the drying conditions, determined by the CFD computation, of droplets of different size in a pilot scale spray dryer. The computational results show, that the developed model presents an important upgrade to the single stage spray drying model, as used in the majority of multiphase CFD codes.