Improving the slurrying ability of XiMeng brown coal by medium- to low-temperature thermal treatment

• Thermal modification removes the internal moisture and improves the coal rank.
• The treated brown coal samples become smooth, hard and regular.
• The surface area and pore volume of treated coal gradually decrease.
• The slurrying stability of brown coal is improved after thermal modification.
• The most suitable thermal modification temperature is between 200 °C and 250  °C.

The slurrying ability of XiMeng brown coal thermally modified at medium- to low-temperature (100 °C–350 °C) was investigated. We discussed the mechanism for improving the slurrying ability of brown coal by thermal treatment considering the coal properties, surface micro-topography, microscopic pore structure, and the moisture reabsorption characteristics. The results suggest that medium- to low-temperature thermal treatment can remove the internal moisture content of brown coal, which decreases from 19.42% (raw coal) to 1.8% after treatment at 350 °C for 0.5 h. The coal rank is increased as AC/O increases from 2.99 of raw coal to 4.88 of 350 °C. The coal surface becomes smooth and the shape becomes regular. With increasing thermal modification temperature, the surface area and BJH desorption pore volume of the coal samples first increased and then decreased, and the average pore diameter increased. All these phenomena improve the slurrying ability of brown coal. Higher thermal modification temperatures and longer time duration result in lower equilibrium moisture content of coal after moisture reabsorption. However, when the time is more than 0.5 h, its effect on the equilibrium moisture content is limited. The most suitable thermal modification temperature for improving the slurrying ability is between 200 °C and 250 °C.