Influence of Particle Size and Crystalline Level on the Efficiency of Dust Explosion Inhibitors

The influence of size and crystallinity on the efficiency of dust explosion inhibition was systematically studied. We fractionated ammonium phosphate monobasic (MAP, NH4H2PO4) and dibasic (DAP, (NH4)(2)HPO4) at different size ranges, and we synthesized zirconium phosphate (alpha-ZrP, Zr(HPO4)(2)center dot H2O) at varying sizes and crystalline levels. To evaluate the inhibitor efficiency of each material, we analyzed the thermal stability of mixtures containing cornstarch and DAP/alpha-ZrP/MAP, using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). In addition, the dust explosion severity (i.e., maximum pressure (P-max) and maximum rate of pressure rise ((dP/dt)(max)) of these mixtures was obtained by performing dust explosion tests using a 36 L vessel. The experimental results show that alpha-ZrP provides the highest thermal stability but the lowest rate of heat absorption of the mixtures. DAP exhibited a lower thermal stability in comparison to alpha-ZrP and MAP, but exhibits a remarkable rate of energy absorption during its decomposition reaction. In general, the efficiency of dust inhibitors increased by decreasing particle size. Particularly, DAP and MAP presented a critical diameter (i.e., 128 mu m), where the inhibitor efficiency was enhanced. However, the performance of alpha-ZrP as an inhibitor was not considerably affected by the variation of particle size and crystalline level. Finally, a semiempirical model was developed to identify the factors dominating the reduction of cornstarch explosion severity. In agreement with aforementioned results, the simplified model presents a critical diameter below which the inhibitor efficiency is significantly improved.