Preconditioning of Dust and Fluid in a 20 L Chamber During Ignition by a Chemical Ignitor

Abstract

Dust explosion prevention and mitigation of the consequences thereof require measurement of dust explosion parameters. Testing methods are defined by European and American standards, producing results in explosion chambers of a 1 m3 standard volume and, alternatively, 20 L. However, the results are influenced by some processes that are neglected by the standards, perhaps because it is believed that their effect is small in a 1 m3 chamber. But their effect becomes significant in a smaller 20 L chamber. Preconditioning of the system caused by dust dispersion itself, as well as the ignitor flame, is one such problem. The aim of this work is to further investigate the physical and chemical processes caused by dust preheating after an ignitor's action. Analytical methods, such as STA, GC/MS and FTIR, were used to analyse the composition of the atmosphere after exposure of lycopodium dust, a natural material, to certain temperatures up to 550 degrees C in air and nitrogen. In the second step, gas samples were taken from the 20 L chamber after dispersion of lycopodium and ignition by two 5 kJ pyrotechnical ignitors. Depending on the temperature and atmosphere, various concentrations of CO, CO2, H2O, NOx and organic compounds were measured. It was observed that the dispersed dust decomposed into mostly CO and CO2 in the area near the ignitors, even in an atmosphere in which the oxygen concentration was lower than 2% by volume. The concentrations of other organic compounds were very low and included mostly methane, ethylene and acetaldehyde. However, when incorporating CO, the overall concentration of flammables was high enough to generate a hybrid mixture.