Monoammonium phosphate (MAP) fertilizer drying kinetics in tray dryer

The drying behaviour of monoammonium phosphate fertilizer was examined in a static tray dryer, establishing kinetic parameters that may be used to improve the design of dryers. Drying temperatures ranged from 80 to 95°C, and surface air velocity was 0.50 m/s. The material was previously separated into two particle sizes, between 1.40 and 2.38 mm mean diameter. Drying curves were analysed qualitatively and seven empirical kinetic thin-layer models were fitted. The drying kinetic showed to be temperature-dependent: a moisture ratio reduction of 90% was achieved twice as fast at 95°C than at 80°C. On the other hand, particle size did not exert significant influence on the drying rate. The results showed a decreasing drying rate throughout the whole process. All studied models adjusted well to the experimental data: R2 values were all above 0.999. The two-term model generated the lowest RMSE and χ2 values, between 0.00621 and 0.010743 and between 0.000044 and 0.000115, respectively.