Experiments were conducted with shallow beds, in the presence of atomizing air injected into the base, under the following conditions: Particles — urea, sulphur coated urea, polyethylene, polyformaldehyde and polystyrene; particle diameters (dp) – 2.1 to 2.8 mm; cone angle – 60°; cylindrical bed diameter (D) – 0.24 and 0.45 m; bed height (H) – 0.24 to 0.40 m; orifice diameter (di) – 21 to 35 mm; main spouting air (Qs) ≤ 37 L(actual)/s; atomizing air (Qa) ≤ 0.87 L(actual)/s. The minimum spouting velocity is well represented by: Ums = 13.5 (2gH)0.5 (dp/D')1.17 (D'i/D')0.372 (H/D')−0.148 [(τp ‐ τ)/τ]0.289 where D' and D'i denote the modified column and orifice diameter, respectively. Qa, which affects D'i, significantly influenced the air velocity in the spout, but not the pressure profiles in the annulus. Morgan and Littman's (1980) correlation could be adapted to predict the experimental pressure profiles in the annulus.

Sulfur coated urea (SCU) is an effective and economical slow-release nitrogen fertilizer, and its production in a spouted bed was investigated. SCU was produced by batch and continuous operations. Higher quality products were typically produced by the batch process, but at significantly lower production rates than the continuous process. In order to understand such operations, mathematical models describing the coating process were developed and verified through experiments. The production of SCU was studied in shallow spouted beds fitted with a pneumatic molten sulfur spray nozzle located at the cone inlet. Bed hydrodynamics, coating mechanism, particle coating distribution and product quality were examined under the following conditions: Bed diameter of cylindrical section-0.24 and 0.45 m; bed height-0.11 to 0.63 m; included cone angle-60'; particle diameter-2.1 to 2.8 mm; particle density 930 to 1490 kg/m3; main spouting air 37 L(actual)/s; atomizing air S 0.87 L(actual)/s; urea feed rate-7.6 to 20 g/s; sulfur injection rate-2.1 to 6.1 g/s; orifice diameter-21 to 35 mm; bed temperature-18 to 70 °C; sulfur content < 60 %. The temperatures of atomizing air and molten sulfur were fixed for all runs at approximately 160 and 150 °C, respectively. The coating process was successfully modeled using mass and momentum balance equations, inertial sulfur droplet deposition as the dominant coating mechanism, and Monte Carlo simulations. The hydrodynamic model was based on the one-dimensional mass and momentum balances suggested by Lefroy and Davidson (1969) for gas and particle motion in the spout, the axial pressure correlation given by Morgan and Littman (1980), and the vector form of the Ergun (1952) equation for gas motion in the annulus. The effect of atomizing air entering through the spray nozzle was successfully incorporated into the model by considering the total momentum flux into the bed. Conical beds were found to behave similar to

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