Flame inhibition of aluminum dust explosion by NaHCO3 and NH4H2PO4

Abstract

To evaluate the inhibition capacity of NaHCO3 and NH4H2PO4 on the flame in aluminum dust explosions, the inhibition of 5 μm and 30 μm aluminum dust explosions by NaHCO3 and NH4H2PO4 has been studied experimentally, using a high-speed camera for measurement of flame propagation behaviors and a thermocouple for measurement of flame temperatures. The mechanism of flame inhibition is further investigated computationally. It is found that the concentration of NH4H2PO4 required to inhibit the aluminum dust explosion is lower in comparison with NaHCO3. The acceleration and the maximum flame speed significantly decrease and the flame morphology becomes irregular and discrete, as the inhibitor concentration increases. The NH4H2PO4 addition exerts a stronger effect on aluminum flame temperature compared to NaHCO3 addition. The chemical kinetic model indicates that the addition of the inhibitor decreases the concentrations of AlO and O in the reaction zone. This reduction becomes larger with increasing the inerting ratio. Na- and P-containing species promote highly reactive O atoms to recombine and form a stable combustion product O2, which leads to less heat release and a lower flame temperature. For Na-containing compounds, NaO ⇔ Na inhibition cycle is effective to reduce O atoms. NH3 that decomposed by NH4H2PO4 could consume O2 and reduce the flame temperature of aluminum in air. In addition, the gas‒phase chemical effect of inhibitors is significant for aluminum particles in the diffusion-controlled regime.