Experimental study on influence of water immersion and air-drying process on coal spontaneous combustion characteristics

Abstract

In order to find out the influence of water immersion and air drying process on the macroscopic characteristics and microstructure changes of coal spontaneous combustion, the low-temperature oxidation characteristics of non-caking raw coal and long-term soaked and air-dried coal were experimentally studied, and the effects of soaking time and particle size on the gas generation and activation energy of coal during the oxidation heating process were analyzed. As an explanation in support of the influence of water immersion on the spontaneous combustion and oxidation characteristics of coal, the variation of relative content of oxygen-containing functional groups and the mechanism of gas generation were analyzed. The results indicated that CO and CO2 are the main components of the gas generated by coal oxidation reaction. Compared with raw coal, the gas production of coal samples after 90 days and 180 days soaking and air-drying is higher in the process of oxidation heating. In the accelerated oxidation stage, the activation energy decreased by 2.72 kJ/mol and 35.74 kJ/mol, respectively, which indicates that the coal sample after long-term soaking has a higher spontaneous combustion tendency than that after short-term soaking. Water plays a promoting role in the formation of oxygen-containing complexes, resulting in the relative content of oxygen-containing functional groups in soaked coal being higher than that of raw coal. Meanwhile, -COOH and C=O are the main sources of CO2 and CO respectively, which could explain the phenomenon of higher concentration of CO2 and CO produced by soaked coal than that by raw coal.

Keywords

• soaked and air-dried coal
• spontaneous combustion characteristics
• apparent activation energy
• oxygen-containing functional group
• reaction mechanism