Theoretical Approach to Dust Explosion

Abstract

A number of experimental researches on dust explosion have been published with measured data of the explosive characteristics such as the ignition temperature, the flame propagation velocity, the upper and lower limit explosible concentrations and the rate of pressure rise.In this study the above-mentioned explosive characteristics are dealt with systematically based on a simple model of uniformly dispersed dust cloud consisting of particles of the same size, from the viewpoint of heat transfer process.Comparing the computed results with the empirical law and the experimental data, it is assured that the explosive characteristics can be predicted theoretically. In addition, the analysis of the area for the pressure relief venting is conducted to minimize the damage, leading to a new dimensionless vent ratio. Prediction of ignition temperaturethe heat emitting from the solid surface into the atmosphere by convection q 2 are taken on the ordinate. When q 1 is less than q 2 , the reaction is always kept at the level of oxidation. On the other hand, when q 1 is more than q 2 , the reaction of combustion makes continuous progress. A steady state can be kept only on the conditions ofq1 =q2 anddq1/dTs =dq2/dT 8 •The reading of the horizontal axis T (surrounding temperature) on this condition is experimentally defined as the ignition temperature. 1 Definition of ignition temperature')The ignition temperature is defined as the gas temperature at which a mass of particles begin to burn, when they are heated in an oven with a certain shape and size. It has been measured with a great number of materials. In Fig. 1, the surface temperature of solid T 8 is displayed on the abscissa and the heat of reaction q 1 and The reaction rate of oxidation of a single spherical particle with a diameter of Dp is given by Hottel eta!. s) as follows:where m is mass of the particle, t time, ks rate constant of reaction, E activation energy and Cg concentration of oxygen. The number of the particles n in the dust cloud with a diameter land the dust concentration Cd isfor the particle of a density Ps· The generated heat G in the lump of the particles and the emitted heat U from them are calculated in the KONA No.1 (1983)

Two‐dimensional analysis of a dust explosion

“…One series of theoretical studies on the deflagration of dust clouds was presented by Mitsui and Tanaka (1973) and Tanaka (1983). In these works, it is assumed that the principal mechanism for energy propagation in the gas phase is conduction through the gas between the combusting dust particles.…”