Dust Explosion Characteristics of South African Coal in Oxy-Fuel Atmospheres

Safety is of major importance to facilities and companies working with combustible materials like dust. To reduce the risk associated with dust, we need to assess the risk of explosion. This assessment can be based on the determination of the explosion characteristics of the dust. A fuel such as coal was allowed to combust in oxy-fuel atmospheres (mixtures of oxygen and carbon dioxide). The explosion risk was found to increase especially in oxygen enriched atmospheres with an O-2-concentration greater than 21 %. To determine the explosion characteristics of the bituminous South African coal, experiments were performed with different mixture concentrations of coal, CO2 and O-2. Measuring the minimum ignition energy (MIE) which is an important ignition sensitivity parameter showed that the MIE decreased significantly when the oxygen concentration in the mixture was increased. The violence of the explosion, which is a parameter for the explosion severity, is expressed by the maximum rate of pressure rise (dP/dt) (max) or K-st-value. This K-st was measured with a standard test apparatus with a content of 20 L using pyrotechnical igniters. This paper also explores the maximum burning velocity which was derived from the pressure histories. In order to achieve the burning velocities, experimental data were analyzed based upon the theoretical model of Dahoe and Van den Bulck. These models were induced by using a two-zone model for the adiabatic combustion in closed vessels. The results revealed that there is a strong relationship between the severity characteristic, the burning velocity and the oxygen concentration. However it was also observed that these coal characteristics were strongly dependent on the dust concentration. Furthermore the burning velocity reached its maximum value when the rate of pressure rise reached its maximum.