The Application Of Pre-treatment In Producing Ash-free Coal By Low Rank Coals

The study of coal demineralization has developed for nearly half a century, a variety of de-ashing means have been presented, the preparation of ash-free coal(HPC) which proposed by Japanese scholars in recent years obtains a better effect, using the way of solvents extraction to divide coal and mineral. But the high investment in this preparation is the main factor limiting industrial development, a variety of processing methods can be applied in HPC preparation process in order to increase the yield and reduce cost. Pretreatment is a better choice to effectively improve the extraction efficiency before coal extraction.We carried out pretreatments and solvent extraction based on lignite to study the effects of different means of pretreatment on ash-free coal preparation. Pretreatment means were acid pretreatment, alkaline pretreatment and microwave pretreatment. The different consequences by acid pretreatment conditions(concentration, temperature, time), alkali pretreatment conditions(concentration, temperature, time) and microwave pretreatment conditions(temperature, time) were discussed. Through the experimental characterization and analysis of different pretreatment coals, HPC and residues, we compared the different promoting role of different means in HPC preparation process.The results show that the optimal acid pretreatment(90?, 1.0mol/L, 2h) can significantly increase the extraction rate(from 25% to 39%) while reducing the ash content(from 1.2% to 0.4%) at 300?, develop the pore structure, and improve the specific surface area of HPC. Alkali pretreatment is less than acid pretreatment It make a slight increase in the extraction rate and ash content, but a greater increase on the content of Na. The main advantage of microwave pretreatment is some sulfide removal in addition, reducing the sulfur content of HPC. According to these conclusions, we can prepare different products with different characteristics based on the different needs to broaden the application of HPC. It provides reliable theoretical support for the further industrialization of HPC.