Experimental study on the dehydration characteristics and evolution of the physicochemical structure of XilinGol lignite during the dehydration process

• Published in: Fuel (Guildford) 2021-05, Vol.291, p.120241, Article 120241
• Main Authors: Liu, Xiaohong, Yu, Haiyang, Wei, Lubin
• Format: Article
• Language: English
• Subjects: Aromatic compounds; Benzene; Carbon; Chemical bonds; Coal; Dehydration; Diameters; Drying; Functional group; Functional groups; Heating; Infrared analysis; Lignite; Moisture content; Oxygen distribution; Pore structure; Process parameters; Vibration; Water content; Water treatment; X ray photoelectron spectroscopy
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2021.120241

•The initial stage of lignite dehydration is determined as a constant acceleration of moisture release.•The effects of time and particle size on drying characteristics were investigated.•Dehydration time has little effect on the occurrence of structural water in lignite.•Pore structure and surface oxygen content are affected by dehydration time. The structural characteristics of dehydrated lignite are crucial for the subsequent re-adsorption thermochemical conversion, but it is challenging in enhancing their relationship for dehydration process and physicochemical structure parameters. Herein, the dehydration characteristics of coal samples at different heating rates and the influence of the particle size and initial weight on the moisture content in lignite were investigated. Subsequently, the carbon-containing chemical bonds, distribution characteristics of the pore structure and oxygen-containing functional groups (OCFGS) in dehydrated lignite were characterized, and the possible mechanism of structural change caused by water removal was proposed. As a result, the fresh lignite at different heating rates exhibited three distinguishable drying stages with increasing dehydration temperature. The initial dehydration stage of lignite is determined to be a constant acceleration of moisture release. The dehydration rate of lignite is closely related to the thickness of the lignite bed in the reactor. Additionally, the relative content of OCFGS on the surface of dehydrated lignite exhibits a gradual decreasing trend. Compared with raw coal, with the extension of the dehydration time, the specific surface area, total pore volume, and average pore diameter in dehydrated coal samples decrease, which has also been verified by XPS, SEM and FT-IR analyses. The fitting calculation of the infrared spectrum curve suggested that the dehydration time plays an important role in the change in the carbon-carbon double bond attributed to the aromatic ring or the carbon atoms in the skeleton vibration of the benzene ring.