Effect of functional groups on spontaneous combustion characteristics of high water-rich coal after long-term soaking and drying

Spontaneous combustion of waterlogged coal accounts for many coal mine fire accidents. The soaking process affects the chemical properties of the coal, causing it to be highly susceptible to spontaneous combustion. Changes in functional groups of highly water-rich coals after flooding and drying are discussed, and the structural parameters were characterized by infrared spectroscopy (FTIR). The results show that the highest aliphatic hydrocarbons, oxygenated functional groups, and aromatic hydrocarbons are reached when air-dried after soaking for 30 days. The substitution of the dumb ring is changed with growing immersion time. C-O rose from 13% to 26% at 30 days and remained constant. Methyl and self-conjugated hydroxyl groups are increasing. Analysis of the structural parameters revealed that aromaticity decreases and increases with soaking time, while the degree of fatty chaining increases and decreases. Prolonged water immersion and air-drying change the coal's aromatization and aliphatic chain structure, resulting in the continuous loss of the branched chains, thus making the skeleton of coal more sparse and the low-temperature oxidation reactions easier to carry out. It is sufficient to show that the theoretical basis for prevention and control of highly water-rich coal combustion after long-term immersion and drying is provided.