Microwave induced plasma of coal particles by numerical simulation

•Different components of coal particles have significant variations in the intensity of microwave discharge due to their own dielectric properties.•The larger the particle size, the shorter the time to reach the maximum electron density, the easier the discharge.•Whether the plasma is generated between the particles depends on the particle spacing.•The electric field strengthening effect of irregular coal particles is directly related to the value of particle curvature.•The carbonaceous materials with high graphitization degree can promote more significant discharge effect. Microwave radiation can produce various thermal and non-thermal effects on coal particles. Microwave-induced plasma is one of the phenomena of microwave non-thermal effects. However, the microwave-induced plasma mechanism of coal particles is still unclear in previous studies. Moreover, the effect of mineral composition in coal and the irregularity of mineral shape on microwave-induced plasma has been ignored. The effect of mineral components, particle size, spacing, particle angle, particle shape and graphitization degree on microwave induced plasma was studied. It was found that different components of coal particles have significant variations in the intensity of microwave discharge due to their own dielectric properties. The electron density of the coal matrix combination weaker than that of the pyrite combination by 1 ∼ 2 orders of magnitude. When other particles are combined with pyrite particles, the plasma distribution is lopsided and biased to pyrite particles. As the particle size increases, the time required to reach the maximum electron density decreases, making the discharge process easier. When the particle spacing is smaller than 20 μm, plasma is generated at both ends of the particles. However, as the spacing increases, plasma is generated between the particles, resulting in a decrease in electron density. Moreover, the electric field between the particles gradually weakens with the angle increasing. The microwave discharge is weakest when the angle increases to 90°. The electric field strengthening effect of irregular coal particles is directly related to the value of particle curvature. In addition, the carbonaceous materials with high graphitization degree can promote more significant discharge effect.