Effects of drying method on self-heating behavior of lignite during low-temperature oxidation

• Published in: Fuel processing technology 2016-10, Vol.151, p.11-18
• Main Authors: Zhao, Huan, Geng, Xiuzhen, Yu, Jianglong, Xin, Binbin, Yin, Fengkui, Tahmasebi, Arash
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Carbon monoxide; Drying; Gas flow; Lignite; Low-temperature oxidation; Moisture content; Oxidation; Particle size; Pore structure; Pre-drying
• ISSN: 0378-3820; 1873-7188
• DOI: 10.1016/j.fuproc.2016.05.031

Pore structure changes during pre-drying of lignite affect its low-temperature oxidation and increase the susceptibility to spontaneous combustion. In this study, the effects of drying methods (i.e., vacuum drying and N2 drying) on self-heating of Indonesian lignite during oxidation were investigated using a dual fixed-bed quartz reactor. The variation of coal temperatures was recorded and the release of CO2 and CO was measured by a gas chromatography. The pore volume and surface area of dried samples were measured using Brunauer-Emmett-Teller (BET) method. Mesopores in lignite initially increased and collapsed with further increasing drying intensity during drying in N2, resulting in a rapid self-heating rate of lignite within a critical moisture content range of 6–13%. However, vacuum drying caused a gradual increase in mesopores, which lead to a monotonic increase in self-heating rate with decreasing residue moisture content in lignite. The experimental results indicated that the production rates of both CO2 and CO during oxidation of raw lignite increased with reducing particle size and increasing gas flow rate, but decreased at lower moisture contents. Typically, the variation of production rates of both CO2 and CO as a function of particle size and gas flow rate followed a similar trend to that of raw lignite when the lignite was completely dried by the vacuum drying method. The impacts of lignite particle size and gas flow rate on the yields of CO2 and CO was limited due to less diffusion of O2 into small pores, suggesting that the oxidation reaction between lignite and oxygen has been shifted from diffusion controlled to kinetic controlled reactions. •Drying method affected self-heating during low temperature oxidation of lignite.•The increase in mesopore volume accelerates the self-heating of lignite.•CO2 and CO formation during oxidation was limited by O2 transport in small pores.•Increased drying intensity leads to a decrease in the oxidation reactivity.