Suppression mechanism of Al dust explosion by melamine polyphosphate and melamine cyanurate

The suppression mechanism of melamine polyphosphate (MPP) and melamine cyanurate (MCA) for Al dust explosions is investigated experimentally and computationally. Results show that depending on the concentration of suppressants, the addition of MCA and MPP promotes or suppresses Al dust explosion. For high additive concentration, large agglomerated residues are generated, and condensed phase residues may contain Al particles, MCA or MPP. The chemical composition of condensed phase residues of Al/MCA mixture explosion is mainly Al₂O₃ and the high boiling products of MEL decomposition (mainly C‒ and N‒containing species). The explosion residues of Al/MPP mixture are composed of Al₂O₃, high boiling products of MEL decomposition and condensed phosphates. To understand the reasons for pressure enhancement and explosion suppression, a kinetic model considering both gas and surface chemistry of Al particles combustion is developed. The simulations indicate that the high pressure rise is caused by the extra heat released from the exothermic reactions of suppressants and the increase of gas phase products. MPP and MCA can suppress surface reaction by decreasing Al(L) site fraction. Additionally, the vaporization rate of Al particles and the diffusion rate of oxidizers close to the droplet surface are reduced by MPP and MCA addition.