Effect of acoustic field on minimum fluidization velocity and drying characteristics of lignite in a fluidized bed

• We present the fluidization characteristics of lignite in a sound-assisted fluidized bed
• The addition of acoustic field can improve the fluidization quality of lignite.
• Drying characteristics and structure changes of lignite in a fluidized bed are discussed.

The fluidization and drying characteristics of Shengli lignite in a sound-assisted fluidized bed are investigated. The effects caused by sound frequency and sound pressure level on the minimum fluidization velocity and drying rate are studied. Experiments indicated that acoustic field can improve the fluidization quality and drying rate of Shengli lignite. The minimum fluidization velocity decreased with an increase in sound pressure level and has a minimum value at a sound frequency of 1.5 kHz. The drying rate of Shengli lignite was especially increased during the initial period of the drying process, while the effect was minor toward the end of process. Based on the determination of TG, FTIR, and BET, the structure changes of Shengli lignite were measured to assess the changes in the quality of dried lignite with the assistance of acoustic field. The weight loss rate of dried lignite decreased with the introduction of acoustic waves. Total pore volume, average pore diameter, and specific surface area were significantly reduced with introducing acoustic waves. Carbonyl decreased progressively with the assistance of acoustic field while carboxyl and hydroxyl increased and decreased thereafter. In addition, the energy consumption of fluidized bed drying system after inducing acoustic field is investigated.

The effects caused by sound frequency and sound pressure level on the drying rate in a sound-assisted fluidized bed dryer are studied. The constant rate period becomes shorter and drying takes place mostly at falling rate period. Moisture removal at f = 1.5 kHz and SPL = 150 dB was higher and faster than the other investigated sound wave parameters.Figure optionsDownload as PowerPoint slide