CHEMICAL ENGINEERING TRANSACTIONS edition:43 location:Milan date:19-22
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 is allowed to combust in oxy-fuel atmospheres (mixtures of oxygen and carbon dioxide) and the explosion risk increases especially in oxygen enriched atmospheres with an O2-concentration greater than 21 %. To determine the explosion characteristics of the bituminous South African coal, experiments are performed with different mixture concentrations of coal, CO2 and O2. Measuring the minimum ignition energy (MIE) which is an important ignition sensitivity parameter shows that the MIE decreases significantly when the oxygen concentration in the mixture is 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 Kst-value. This Kst is measured with a standard test apparatus with a content of 20 L using pyrotechnical igniters. This paper also explores the maximum burning velocity which is derived from the pressure histories. In order to achieve the burning velocities, experimental data are 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 considerable dependence among the severity characteristic and the burning velocity and the oxygen concentration. However it is also observed that these coal characteristics are strongly dependent on the dust concentration. Furthermore the burning velocity reaches its maximum value when the rate of pressure rise reaches its maximum.