Abstract：Urea is produced in a tower with falling liquid droplets to enhance the evaporation and drying of the urea particles. The physical process has a liquid column feeding an atomizer. This study analyzes the effect of the nozzle diameter, liquid velocity and air flow velocity on the urea maximum drop diameter. A model is developed to predict the critical heights of the liquid column and the maximum drop diameter. The model predictions agree well with the experimental data, indicating its ability to predict the maximum drop diameter. The atomizer nozzle diameter and the tangential velocity at the orifice strongly influence the drop size, while the liquid velocity at the orifice has little impact on the maximum drop diameter. The air flow velocity in the tower also affects the maximum drop diameter when the air flow velocity is greater than 1.5 m·s-1, but the effect is very small for the air flow velocity less than 1.5 m·s-1. Thus, the maximum drop diameter can be increased by increasing the atomizer nozzle diameter and the tangential velocity at the orifice. Secondary breakup will occur with large drops falling in the tower during cooling and solidification. The critical Weber number gives the maximum drop diameter of urea in the tower for granulation processing about 4 mm.
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