In ammonium nitrate (AN) production, determining the standard particle size for the granulation process is a fundamental problem. Therefore, a system model is proposed for this final stage of the manufacturing process. In the proposed model, prilling is simulated by analyzing data from the continuity, hydrodynamics, and mass and energy transfers. The direction of the movement of AN particles, the temperature, and humidity distribution of the cooling air with variation in particle size, and the height of the prilling tower are calculated. The air temperature profile determined by the model is compared with that of an actual AN plant. The comparison shows that the results obtained by the model are consistent with the plant data. In addition, it is shown that an increase in the cooling rate of particles has the potential to enhance the properties of AN particles. Moreover, a detailed analysis of the granulation process is conducted to estimate the impact of the parameters of the proposed model such as the prilling tower height, particle size, and temperature. Thus, this model could be used to obtain more accurate results at an industrial plant.