Prediction of fertilizer granulation: Effect of binder viscosity on random coalescence model

The effect of binder viscosity on the granulation of NPK fertilizers has been experimentally investigated at ambient temperature. The viscosity of the binder solutions used in these trials was higher than in any previous work on fertilizer granulation and more representative of the viscosity in industrial granulation units. In general, a higher binder viscosity resulted in a higher degree of granulation. The experimental data were correlated using a random coalescence theory, and first-stage coalescence kernels were determined for variations in binder viscosity and fractional saturation. These experimental coalescence kernels were then modeled using a normalization procedure that took the effects of binder viscosity and fractional saturation into account. The modeled data fit the experimental data well over a wide range of binder viscosities and fractional saturations. Further results were gathered from a high-temperature industrial granulation system and were used to validate the normalized coalescence model. These results indicate that high-temperature industrial granulation systems can be accurately predicted from bench-scale data if the fractional saturation of the granulate and the viscosity of the binder solution are accurately known.