Thin-layer drying kinetics of lignite during hot air forced convection

Kinetics on the lignite thin-layer during hot air forced convective drying was investigated experimentally as a function of drying conditions (hot air temperature and speed). The experiments were conducted at hot air temperatures of 100, 110, 120, 130, 140, 150, and 160 °C and hot air speeds of 0.6, 1.4, and 2.0 m/s. The drying process of lignite presented a combination of the short warm-up period, the first falling rate period and the second falling rate period. The Midilli model gave a perfect prediction for the lignite thin layer drying. The effective moisture diffusivity of lignite thin layer was from 5.098 × 10−9 to 1.481 × 10−8 m2/s for the first falling rate period, and from 7.003 × 10−9 to 1.907 × 10−8 m2/s for the second falling rate period. The hot air temperature and speed had significant effect on the effective moisture diffusivity of the lignite sample (P < 0.05). On the hot air speeds of 0.6, 1.4, and 2.0 m/s, the apparent activation energy of lignite thin layer in the first falling rate period was determined as 17.652, 15.495, and 15.175 kJ/mol, whereas it was 16.340, 14.787, and 13.672 kJ/mol in the second falling rate period.