Auto-ignition Parameters of Bituminous Coal Dusts

摘要

Self-heating of coal piles may lead to spontaneous fires and explosions. It is essential for plant operators to know the conditions (temperature, duration and quantity) at which storage will be safe and therefore to know the factors that influence spontaneous ignition. The hot storage self-ignition temperatures are reported for three different coal dust samples (South African coal, Indonesian Sebuku coal, Pittsburgh No.8 coal) using five different volumes of cylindrical baskets (25ml, 50ml, 100ml, 400ml and 1600ml) placed in an isothermal oven. The induction time is recorded as well. The experimental data are analyzed to predict self-ignition temperature and induction time based upon the theoretical models of Pseudo-Arrhenius, Semenov and Frank-Kamenetskii (F-K) and a scaling correlation is derived according to the European standard [EN 15188]. The heat release method and the crossing-point temperature method are applied to determine the activation energy. It can be concluded that the sensitivity to self-ignition increases significantly with increasing coal samples volume. In spite of the fact that the safe storage time of Indonesian Sebuku coal is shorter than Pittsburgh No.8 coal and South African coal, it is less prone to undergo spontaneous ignition at the same volume. This is due mainly to its higher content of volatile material and lower content of fixed carbon which yield markedly higher ignition temperatures. As for determining the activation energy, the F-K method is more dependable. However, it is time-consuming as it requires the determination of the critical temperature for several sample volumes. The results of this study provide important data for future hot storage tests of coal dust accumulations in oxygen enriched atmospheres, which is an important safety aspect of the oxy-coal combustion.