Numerical study on heat and mass transfer characteristics of particle coating in a spray fluidized bed with draft plates

Spray fluidized bed wet granulation, combining dynamic fluidization with atomized spraying, is widely used for functional particle manufacturing in pharmaceuticals, food, and chemicals. However, the coating growth process involves complex gas-liquid-solid coupling, making precise control challenging. Therefore, based on the discrete element model, and coupling droplet motion and evaporation models, droplet-particle collision models, and liquid bridge force models, a pseudo-three-phase mathematical model of “gas-droplet-particle” suitable for describing the particle coating process in a spray fluidized bed was developed. On this modeling basis, the effects of different draft plate configurations on particle flow, heat and mass transfer characteristics, and particle growth mechanisms were investigated. Under the investigated operating conditions, it was found that optimizing draft plate spacing, increasing plate length, and reducing plate height promote faster particle entry into the fountain zone and extend their residence time therein. These adjustments improve the overall fluidization state of the bed, enhance particle circulation trajectories, and effectively increase both the coating ratio and growth uniformity of particles, while mitigating excessive coating in the spouted zone.