Experimental investigation of the influence of inert solids on ignition sensitivity of organic powders

This work presents the results of the experimental characterization of the ignition sensitivity of solid inertant/combustible powders mixtures. Three inert solids (alumina, Kieselguhr, aerosil) and eleven organic powders have been considered and the following parameters have been determined: (1) the minimum ignition energy, (2) the minimum ignition temperature in cloud and (3) the minimum ignition temperature in 5 mm layer. The effects of the addition of inert solids are described and a simple model is proposed to represent the experimental results. Generally, increasing inert solid content in a powder leads to a higher minimum ignition energy as well as a higher minimum ignition temperatures in cloud and in layer. In some cases, the flammability is influenced above a threshold concentration value, which can be quite high (up to 85 wt.%). Indeed, the proposed model shows a zone below the minimum ignition concentration (MIC), which does not enable an efficient or safe inerting: either the admixed inert solid does not provide a sufficient effect, or it can even facilitate the ignition of the dust by notably improving its dispersability. The influence of key parameters such as the thermal conductivity or optical properties on the efficiency of the inerting by admixed solid need to be further assessed in a future work in view to better understand the mechanisms involved and to extend the scope to other types of oxidizable materials. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.