Soot and gaseous product formation characteristics of leached high-alkali lignite pyrolysis at a high temperature

The contents of alkali and alkaline earth metals (AAEMs) in Zhundong lignite are very high, which can affect the formation of soot during coal combustion process. In this study, the effect of leaching treatment on soot and gaseous product formation characteristics from the lignite pyrolysis at 1300 ℃ is investigated. The results show that water washing only removes a small amount of water-soluble AAEMs, which has little impact on the combustion characteristics of the coal, while acid washing pretreatment largely removes Na, Mg, Ca and other ash components, causing obvious ignition delay. The acid washing obviously leads to the deterioration of oxidation characteristics and increases the yield of pyrolytic soot, and the peak diameter of soot increases from 100 nm to 200 nm. Moreover, after both water- and acid-leaching, more CO₂ is produced, while CH₄, CO, and H₂ are reduced. The yields of C₂H₄ are not changed before and after leaching. However, a certain amount of C₂H₂ is produced for acid-leached coal pyrolysis. These phenomena indicates that there may be different soot generation and evolution paths in three cases. To a certain extent, this provides a theoretical guidance for the research of effectively reducing soot emissions and improving coal utilization under high-temperature pyrolysis.