Study on moisture re-absorption characteristics and equilibrium prediction model of coal dust with different rank

Moisture re-absorption is an effective method to measure wettability of coal dust, but for different types of coal dust, there are difference in their hydrophilicity. In order to explore the moisture re-absorption characteristics of coal dust with different degrees of coalification, the variation of moisture re-absorption rate of coal dust under different ambient temperature and relative humidity was compared and analyzed by a self-designing moisture re-absorption experimental system. The effect of coal dust properties on moisture re-absorption characteristics was clarified, and a prediction model for the moisture re-absorption equilibrium of coal dust with different degrees of coalification was established. The results showed that, with the increase of ambient temperature, the moisture re-absorption rate of coal sample firstly increased and then decreased, and the time to reach the re-absorption equilibrium was gradually shortened. In the same temperature condition, the moisture re-absorption rate of coal dust increased with increasing relative humidity, and the time to reach moisture re-absorption equilibrium was proportional to relative humidity. The higher the degree of coalification led to the stronger moisture re-absorption capacity. As the contact angle of coal dust increased, the moisture re-absorption rate was linearly inversely related to the contact angle, and the wettability of coal dust was positively linearly related to the moisture re-absorption capacity. The moisture re-absorption rate overall increased linearly with the increasing proportion of oxygen-containing functional groups. The increase of specific surface area of coal dust will inhibit the moisture re-absorption process, while the increase of pore size will promote the storage of adsorbed water, and the increase of total pore volume will provide more space for moisture re-absorption. The moisture re-absorption rate and wettability with different coalification can be effectively predicted based on the characteristic parameters of coal dust. By comparing and analyzing the fitted results of each prediction model, it was found that the Henderson model had the highest fitting degree among all the prediction models and was the most suitable for accurate prediction of moisture re-absorption equilibrium of coal dust at different coalification. The results will help to qualitatively analyze the hygroscopicity of different coal dust and provide a reference for coal dust wetting and reduction techniques.