Insight into suppression performance and mechanisms of ultrafine powders on wood dust deflagration under equivalent concentration.

Flame propagation characteristics of wood dust deflagration and suppression mechanism of ultrafine powders are investigated systematically. The deflagration reaction intensity of wood dust increases firstly and then decreases with the increase in dust cloud concentration. This is due to factors such as oxygen supply, positive feedback among flame characteristic parameters. Thus, there is an equivalent dust concentration for greatest deflagration intensity. Nano-sized ultrafine zirconium hydroxide (Zr(OH)4) and silicon dioxide (SiO2) powder are introduced to suppress wood dust deflagration at the equivalent concentration. It is found that Zr(OH)4 has a suppression effect of endothermic decomposition to generate zirconia (ZrO2), dilution of oxygen and absorption of free radicals; while SiO2 exerts suppression effect due to its high melting point and heat absorption. The suppression performance of Zr(OH)4 is better than that of SiO2. This is because that Zr(OH)4 and ZrO2 have a catalytic carbonization effect. It can not only improve thermal stability of wood particles by catalyzing production of high-temperature resistant residuals, but also promote the formation of catalytic sites to reduce crystallite size of carbon layer on wood particles surface, weakening heat and mass transfer between particles.