In fact, high-intensity acoustic energy is capable of increasing heat and
mass transfer efficiency in drying of apple, red bell pepper [16], and
clipfish [17]. Power ultrasound introduces pressure variations at solid/
gas interfaces, and therefore increases the surface moisture drying rate
[18]. Therefore, external and internal resistancemay be seriously affected
during drying by acoustic energy, thus increasing drying rate [19]. In the
present study, the effects caused by sound frequency and sound pressure
level on the minimum fluidization velocity (umf) and drying rate in a
sound-assisted fluidized bed dryer were investigated. The aim of the
present study was to investigate the acoustic field which enhanced the
fluidization quality and drying rate of lignite. Based on the determination
of TG, FTIR, and BET, the structure changes of lignite were measured
which has great significance to store and utilize of lignite. The soundassisted
fluidized bed drying system has a better performance in energy
saving due to better mass and heat exchange inside the dryer.