Another study by Tsai at the University of British Columbia, aimed to
develop a process for coating urea with sulfur using a spouted fluidized
bed [26]. A ‘sulfur-only’ coatingwas applied and optimal process conditionswere
evaluated to attain reasonably controlled release characteristics.
Ureawas coatedwithmolten sulfur concurrentlywith fluidizing air
in a spouted bed under certain conditions of temperature and pressure.
Optimized conditions eventually comprised 80 °C, fluidizing air flow at
0.65m3/min, and pressurized atomizing air at 208 kPa. Their seven-day
trial found 30% urea dissolution. Akin to Tsai [26], in 1997Choi [27] also
studied urea coating with sulfur and derived parameters that predominantly
affected the coating performance of a spouted bed. Urea coating
with molten sulfur was carried out in batch as well as continuous operations
and then followed by the seven-day dissolution test. Nitrogen
pressurized molten sulfur was introduced with pre-heated atomizing
air at the base of the spouted bed and sprayed onto the urea fluidized
bed concurrently followed by drying andwithdrawal.He recommended
a spray angle of forty degrees and the use of multiple spouted beds as
well as an extended coating period for better results in terms of coating
uniformity, which directly affects the controlled release characteristics
of coated urea. The TVA dissolution test findings sawaminimal dissolution
of 32.8% at seven days.