Macromorphological features and formation mechanism of particulate residues from methane/air/coal dust gas–solid two-phase hybrid explosions: An approach for material evidence analysis in accident investigation

• Experimented the influence of fuel concentrations on the explosibility for methane/coal dust mixtures. • Seven types of macromorphology structures of solid residues were proposed and analyzed. • Morphological structures of the particulate residues were characterized. • Relationships between explosibility and solid particulate release were established. The present work aimed at acquiring the macromorphological features and formation mechanisms of post-explosion particulate residues from the hybrid explosion of methane/coal dust mixtures. For this purpose, a comparative study on the explosion severity of six mass concentrations of coal dust deflagration in four methane-air atmospheres was firstly experimentally performed, with the post-explosion particulate residues collected after explosion experiments. In addition, the morphological classification and formation rules of the particulate residues for methane/coal dust mixtures were preliminarily proposed based on the SEM observations, theoretical analysis, and qualitative discussions. Moreover, the fractal characteristics in particle size variation of the particulate residues were comparatively studied using the fractal theory. Furthermore, the macromorphology features and morphological structures of the post-explosion particulate residues were explored quantitatively with the aid of SEM results and image processing technique. Results demonstrated that P max , (d P /d t ) max , and K st first increased and then exhibited a decreasing tendency with the increase in coal dust concentration for various methane equivalence ratios, and they reached their maximum values as the methane equivalence ratio was 0.9. Whereas the combustion time ( t c ) showed the opposite tendency with the increasing coal dust concentration under various methane equivalence ratios. Besides, compared with pre-explosion dust samples, seven various types of particulate morphological structures occurred distinctively in the solid residues, indicating the combustion behaviors and explosion severity of the mixtures. Quantitative analysis indicated that the fractal dimension for the particle size variation of the particulate residues was smaller than that of the pre-explosion dust sample, and increased logarithmically as the methane equivalence ratio increased. Moreover, the range of the roundness distribution of the particulate residues deviated significantly from that of the pre-explosion dust sample, and expanded gradually with the increasing concentration of coal dust and then decreased negatively and logarithmically with the increasing particle size. Eventually, the coupling correlations between the particulate residues and explosion severity were established comparatively, and we ulteriorly proposed the potential utilization of qualitative-quantitative analysis on the post-explosion particulate residues in coal-dust-involved explosion accidents. This work would be conducive to disaster investigation and hazard assessment for methane/coal dust explosions.