Laboratory studies on sulphur‐coating urea by the spouted bed process

Abstract

AbstractA spouted bed facility, which includes a 0.154 m ID x 0.91 m high bed with a 60° conical bottom, was used for the batch‐wise production of sulphur coated urea. Molten sulphur was sprayed into the cone and the droplets froze upon impact with the cooler urea particles thereby forming coats which increased with time.The quality of the coated urea was studied as a function of bed temperature (48–86 C), sulphur flow rate (34–260 g/min), atomizing air flow rate (0.402–0.785 m3/hr) and bed depth (0.28–0.47 m). No attempt was made to seal the product with wax or other materials. Bed temperature had the greatest effect on product quality, with quality improving up to approximately 80 C and then decreasing again. The quality also increased with the sulphur flow rate and decreased with the atomizing air flow rate. These measurements are explained in terms of the phase transition from monoclinic to orthorhombic sulphur and the sulphur droplet size which influences the spreading of liquid sulphur on impact with the urea particles. Electronmicrographs are presented in support of these explanations and the implications of the results for commercial sulphur coating facilities are discussed.