Agglomeration Effect on Combustion and Explosion Properties of Nanoparticles

Nanoparticles have been demonstrated to possess significantly high ignition sensitivities compared with micro-particles, e.g., much lower minimum ignition energy (MIE) and feasible spontaneous ignition phenomena, and have been predicted to have high deflagration index of dust explosion (K_st) and low minimum explosive concentration (MEC). However, some experimental results are inconsistent with what as expected or even scattered, which were attributed to the agglomerations of nanoparticles. Multi-scale agglomerations, including soft and hard agglomerations, have been observed in nanofiber systems, which may serve as proper platforms to validate this assumption. In this work, theoretical analyses were performed for three different kinds of carbonaceous particles—single nanoparticle, nanoparticles in agglomerated size of 20 μm, and single micro-sized particles in size of 20 μm—to investigate the combustion and explosion behavior. Influences of parameters such as specific surface area, bulk density, and kinetic terms on K_st and MEC were evaluated by utilizing either one-film or two-film carbon combustion models as well as heat transfer models. To verify the results, experiments with three kinds of carbon materials—de-agglomerated carbon nanofibers, agglomerated carbon nanofibers, and carbon particles with identical diameter as agglomerated ones—were conducted correspondingly in a 36-L explosion vessel.