Physical aspects of fire and explosion hazard of combustible dust. Part 1.Ignition

Abstract

Based on the fundamental combustible systems properties - distributed nonlinear energy sources and flow connection between the environment elements - an analysis of various combustion dust modes is presented. Depending on the ratio betweencharacteristic burning times (thermokinetic characteristics) and heat transfer (scale characteristics), limiting modes are considered as self-ignition, diffusion combustion and auto-wave combustion. Unlike gases, for dusts all the characteristics of ignition and combustion essentially depend on the internal system scales - particle sizes and distances between them. In presented part of the study, the critical ignition temperature dependences and the ignition delay time on all physicochemical dust parameters are analyzed. It is shown that these characteristics for various fuels can be described in a unified way, based on the laws of oxidation (linear and parabolic), with the systematizing parameterfbeing the ratio of the solid fuel reaction surface to the external heat exchange surface.
 Taking into account the parameter f, which is the ratio of the dust reaction surface to the external aerosuspensionheat exchange surface of the dust, the critical ignition conditions are obtained in the form of a criterion similar to the single particles ignition. It is shown that it can be used for dust with both a linear and a parabolic oxidation law. Different fuels react in the same way to a change in f, which does not contain fuel characteristics and reflects thedustheat accumulation capability. Thus, the ignition temperature is a linear function of 1/lnf, and the induction period is 1/f.
 The ignition temperature and ignition delay time are not physical or chemical, but are relativedust activity properties in relation to the their ignitionprocess. After all, they depend on the size of the reaction vessel.