Drying characteristic and kinetics of Huolinhe lignite in nitrogen and methane atmospheres

• Drying characteristics, kinetics of lignite in methane were investigated.
• Drying process of HLH lignite follows random nucleation mechanism.
• Moisture re-adsorption properties were studied by static desiccator method.
• Moisture desorption and re-adsorption isotherms are irreversible.

Lignite drying in methane atmosphere is a potential approach to utilize moisture in lignite as a feedstock for H2 production via steam reforming of methane. In this paper, experiments on drying and moisture re-adsorption properties of Huolinhe lignite in nitrogen and methane were carried out in a fixed-bed apparatus and thermogravimetric analyzer to investigate the effect of drying temperature, particle size, moisture content, drying medium and sample weight on drying rates and drying dynamics. The drying kinetics and mechanism were studied by thermal analysis and thin layer models. The moisture of lignite decreases with increasing drying temperature, decreasing particle size and sample weight. The drying process follows random nucleation mechanism and Logarithmic model is the optimal thin layer model for drying process of Huolinhe lignite. The activation energy in methane is lower than that in nitrogen. Static adsorption method was used to analyze the equilibrium moisture contents (Me) of dried coal sample. The results show that Me decreases with the increase of drying temperature and Me of dried coal is lower than that of raw coal. The moisture desorption and re-adsorption isotherms are irreversible.