Abstract: Based on the Frank-Kamenetskii theory and the open constant temperature heating method, characteristics of lignite spontaneous combustion were studied. 6 lignite coal samples different in particle size were put into 5, 10 and 15 cm in length cube basket, and 18 coal piles. Experiments were carried out under different constant temperature conditions to study the temperature rise process of the coal pile and to investigate the effect of particle size on the critical self-ignition temperature of the spontaneous combustion stage during coal oxidation. The experimental results show that the temperature rise process of the coal pile can be divided into four stages, an initial temperature increase stage, a slow temperature rise stage, a rapid temperature rise stage, and a spontaneous combustion (or temperature drop) stage, that under constant coal pile volume conditions, the smaller the particle size, the lower the critical self-spontaneous combustion point, and that with the increase of the coal pile size, the effect of particle size on coal critical self-ignition temperature is gradually weakened until it can be ignored.

Key words: lignite, spontaneous combustion, open constant temperature heating method, critical self-ignition temperature, coal particle size, basket volume