Macroscopic behaviors and chemical reaction mechanism for the inhibition of NH4H2PO4 powder in hybrid methane/coal dust deflagrations

In this research, the inhibition effect and microscopic mechanism of NH4H2PO4 on the macroscopic deflagration characteristics of methane (9.5 vol%) mixed with three coal samples were studied. Experimental results show that the higher the concentration of added NH4H2PO4, the more pronounced the inhibition effect on the deflagration of three coal samples mixed with methane. When the mass concentration of NH4H2PO4 reached 90%, the deflagration pressures of anthracite/methane hybrids, coking coal/methane hybrids, and long-flame coal/methane hybrids decreased by 50.80%, 45.59%, and 39.06%, respectively. The time for the flame front to reach the height of 300 mm extended by 39 ms, 30 ms, and 63 ms, respectively. In addition, the microscopic reaction mechanism of NH4H2PO4 inhibiting the methane/coal dust deflagration was revealed using a reaction kinetics model. We found that phosphorus-containing substances mainly absorbed explosive active free radicals through cyclic reactions HOPO2 = PO2 and HOPO = PO2. Through ROP analysis, we found that with an increase in inhibitor concentration, the HOPO radical, which had a better scavenging effect on oxidizer free radicals, was gradually replaced by HOPO2, resulting in a saturation effect. Sensitivity analysis showed that the inhibitory effect of NH4H2PO4 mainly depended on phosphorous substances and free radicals HOPO, HOPO2, and PO2.