Upgradation of Zhaotong Lignite through microwave drying

Upgradation of the rank of lignite is mandatory for its effective utilization as a potential energy source. Microwave drying is being explored in the present work as an effective upgradation technique. The effects of operating variables such as sample mass, particle size and sample thickness were investigated. The work also attempts to compare the quality of lignite dried using conventional hot air and microwave drying utilizing characterization techniques such as SEM, FT-IR, BET. The SEM analysis demonstrate a considerable increase in number of pores, fractures and cracks in the upgraded lignite structure after microwave drying as compared to hot air drying. The FT-IR analysis indicate an overall reduction in the number of absorbance peaks and a significant reduction in the oxygen-containing functional groups with microwave drying as compared to hot air drying. The BET analysis reveal a 30 fold increase in specific surface area with microwave drying as compared to hot air drying. The major proportion of pores in the lignite after microwave drying were either mesopores or micropores, while that dried with conventional hot air were macropores. Microwave drying as compared with hot air drying is more effective having higher fixed carbon content. The moisture re-adsorption capacity weakened after microwave drying, while it increased with increase in particle size.