Microwave drying performance of lignite with the assistance of biomass-derived char

ABSTRACT

Microwave lignite drying with assistance of biomass-derived char was addressed and effect of bio-char on drying rate and energy consumption was investigated in this work. Effective diffusion coefficient and activation energy for the drying process were also analyzed. The results indicated the drying process was largely dependent on the variation of sample temperature. Bio-char originated from pine wood was most favorable for lignite drying, considering its better promoting effect and advanced security. There existed an optimal bio-char addition ratio for drying process at different power. The corresponding optimal ratio was 10% at 231 W and 15% at 385 W, at which the biggest drying rate and the least energy consumption were reached. It was compared lignite drying initiated at 385 W was better for energy conservation. Effective diffusivity was improved and activation energy was simultaneously reduced, with the addition of bio-char. The minimum activation energy was 15.54 W · g⁻¹, which was gained at bio-char addition ratio of 10%. The results revealed the effect of bio-char on depressing activation energy could rival that of metal-based additives. The drying process with assistance of microwave and bio-char could present technical and economical benefits on lignite upgrading.

KEYWORDS:

• Bio-char
• drying
• lignite
• microwave

Additional information

Funding

This work was supported by Promotive Research Fund for Excellent Young and Middle-aged Scientists of Shandong Province (Project no. BS2014NJ014) and Qingdao Science and Technology Project (15-9-1-34-jch).