Calculation of the ignition sensitivity of dust clouds of varying size distributions

For a cloud of flammable dust in air to ignite, the temperature of the air must be a specific value that depends upon properties of the dust material and of the dust cloud.First, a theoretical treatment is used to explain variations in experimental ignition temperatures in terms of particle size. The theory modifies Cassel and Liebman's method to take account of residence time of dust in experimental furnaces or in hot air. It is shown that it is possible for the ignition temperature of mono-sized coal particles (about 50 μm diameter) to be minimal under a limited residence time.The theory is extended to deal with dust clouds with a distribution in particle size. It is shown that there exists a range of size distributions for which the possibility of ignition is at a maximum. The calculated results are presented in the form of Rosin—Rammler charts indicating the distribution most sensitive to ignition.