Minimum ignition temperature of carbonaceous dust clouds in air with CH₄/H₂/CO below the gas lower explosion limit

Godbert-Greenwald furnace was used to investigate the minimum ignition temperature of dust clouds (MITC) in air with the presence of flammable gas which is lower than its lower explosion limit (LEL). Three flammable gases (CH₄, H₂ and CO) and three carbonaceous dusts (anthracite coal, bituminous coal and sweet potato starch) were tested. Results showed that all flammable gases have distinct effects on the MITC of the dust samples and volatile matter content of dust plays an important role during the ignition process. Specifically, the MITC of anthracite coal dust decreased from 610 °C to 560 °C, 580 °C and 570 °C with 3% CH₄, 3% CO and 2.5% H₂, respectively. Moreover, a heterogeneous ignition mechanism model was proposed to verify the equally global ignition characteristic between hybrid anthracite coal-C_xH_y mixture and bituminous coal. All three gases had an ignorable effect on the MITC of starch dust considering the experimental error. The presence of CO and H₂ slightly promoted the ignition of bituminous coal dust, but the addition of CH₄ showed a distinct concentration effect on the MITC of bituminous coal: the MITC decreased with 1% CH₄ while increased with 2% and 3% CH₄. This negative-effect of flammable gases at such low concentrations on ignition temperature of bituminous coal dusts was found for the first time. Furthermore, the presence of the 2nd flammable gas had a smaller effect on the MITC of dust samples with a higher volatile content, resulted from the competition of heterogeneous and homogeneous ignition mechanisms.