Comparative study of explosion processes controlled by homogeneous and heterogeneous combustion mechanisms

Ignition temperature and mechanism of carbonaceous dust clouds: The roles of volatile matter, CH4 addition, O2 mole fraction and diluent gas

Minimum ignition temperature of dust clouds (MITC) was studied experimentally and theoretically in different atmospheres. Three carbonaceous dusts were tested in both air and O₂/CO₂ atmospheres with CH₄ mole fraction from 0% to 2%. Results showed that the ignition risk of the three dusts significantly increases (decrease of MITC by ~100 ℃) with increasing X_O2 from 21% to 50%, but significantly decreases replacing N₂ in air with CO₂. The inhibition effect of CO₂ on MITCs could be diminished by increasing X_O2 or adding CH₄. The addition of small amount of CH₄ has different effects on the MITCs of different dust samples, following the opposite order of volatile matter content: anthracite>bituminous coal>starch. Two modified steady-state ignition models, considering the density of mixture gas and dust cloud, X_O2 and its diffusivity, were developed to interpret the experimental observations. The analysis revealed that the global heterogeneous ignition model suits well for the hybrid mixtures of anthracite or bituminous coal dusts. In contrast, the proposed global homogeneous ignition model was found to be only valid for the pure starch dust, and the extra CH₄ addition could strongly affect the ignition process of starch, particularly in O₂/CO₂ atmospheres with higher X_O2.

Explosion parameters and combustion kinetics of biomass dust

In this study, a 20-L spherical explosion vessel, hot plate apparatus, Godbert-Greenwald furnace apparatus, and TG-FTIR were used to investigate the explosion and combustion characteristics of three biomass dusts: dalbergia cochinchinensis (DC), pine sawdust (PS), and cupressus funebris (CF). DC with lower minimum explosible concentration (70-80 g/m³), larger maximum explosion pressure (0.742 MPa) and larger maximum explosion pressure rise rate (80.14 MPa/s) had the greatest explosion hazard in three biomass dusts. The apparent activation energy of DC and CF were lower than that of PS, and the main gas products of three samples included CO₂, CO, CH₃COOH, and H₂O. The volatile matter content of DC characterized by the weight loss and the number of gas products of combustion process was higher than those of PS and CF, showing that the volatile matter content of biomass dust was one of the main factors affecting combustion and explosion hazard.