Effect of operating conditions on drying of Chinese lignite in a vibration fluidized bed

The drying performance of Chinese lignite particles in a laboratory scale vibration fluidized bed dryer was investigated under various operating conditions: inlet air temperature (120-200 °C), superficial air velocity (1.5 Umf (the minimum fluidization velocity)-2.2 Umf,), frequency (10-50 Hz), amplitude (1-5 mm), particle size (0.5-6 mm) and bed height (20-60 mm). The drying results showed that higher temperature, larger air velocity, higher frequency and higher amplitude (not too high), smaller particle size and lower bed height were favorable for drying. The Midilli-Kucuk model provided the best fit of these drying results and further implied that the moisture transfer of lignite was mainly controlled by internal diffusion. In comparison with the case of an ordinary fluidized bed, the gas-vibro fluidized bed dryer exhibited improvement of drying characteristics. Moreover, the drying kinetics was largely dependent on the frequency and amplitude of vibration.