Current status of the research work on cleaning, ash reduction and upgrading of lignite

High-ash and high-moisture lignite can find limited utilization due to its low calorific value and conversion efficiency, and work needs to be made for its upgrading.The paper presents an overview of the lignite cleaning processes and equipment currently applied in China, as well as the progress of the research work made both within and abroad on ash reduction of lignite using flotation process, and particularly the exploratory study of the oil-bubble flotation process.The study made in the paper may serve as a reference for the upgrading of other low-rank coal and oxidized coal and minerals.