Suppression mechanism of ultrafine water mist containing phosphorus compounds in methane/coal dust explosions

Abstract The effect of ultrafine water mist with phosphorus-containing compounds (PCCs) on the flame in CH4/coal dust explosion is experimentally and numerically investigated. In this research, dimethyl methylphosphonate (DMMP) and phytic acid (PA) are selected as additives. The thermal stability of the mixture of coal and additives, and the products of mixture pyrolysis in the gas phase are analyzed by STA-FTIR and STA-GC-TCD. The results show that water mist can act as a thermal barrier and effectively lower flame temperature. DMMP water mist can significantly slow down the flame speed and cut off the flame. PCC additives can boost the heat absorption ability of water mist. Compared to PA, DMMP can efficiently lower the concentration of toxic (CO) and combustible (CH4 and H2) gases in CH4/coal dust hybrid explosions. The chemical suppression mechanism of DMMP water mist is further investigated. The kinetic model indicates that the main suppression reactions of lean CH4/coal flame are HOPO2 + H = PO2 + H2O and PO2 + H + M = HOPO. Gas-phase species with P in higher oxidation states (+5, +3) produced by the decomposition of DMMP play an essential role in suppressing a lean flame.