Effects of alkali-oxygen oxidation temperature on the structures and combustion properties of Shengli lignite

Abstract

Spontaneous combustion has become a critical limiting factor for the safe and efficient utilization of low rank coals. In this work, the alkali-oxygen oxidation (AOO) of Chinese Shengli lignite was conducted to inhibit the spontaneous combustion tendency, and the influences of AOO on the structures and combustion properties were investigated. The structures of AOO treated lignite under different conditions were characterized by XRD, Raman, XPS and FTIR. The combustion characteristics of the samples were investigated by thermogravimetric analysis and fixed bed combustion. The results revealed that the temperature of AOO treatment had significant influence on the crystallite structures and combustion characteristics of Shengli lignite. After the AOO pretreatment, the benzene ring skeleton structures in lignite had no obvious changes, but the amounts of aliphatic side chains on the aromatic nucleus decreased. Compared with raw lignite, the degree of order and ignition temperature increased after AOO treatment, especially when the AOO temperature was 150–200 °C. The ignition temperatures moved from 310 °C for raw lignite to 740–760 °C for the samples treated by AOO at 150–200 °C. On further increasing the AOO temperatures to 250–300 °C, the ignition temperature of the samples decreased to 410–440 °C. In conclusion, AOO pretreatment under suitable conditions is an efficient way to inhibit the spontaneous combustion tendency of low rank lignite, and it is believed that the results in this work are meaningful for the safe transportation and efficient utilization process of lignite in industry.