"Ullmann's Encyclopedia of Industrial Chemistry" is the benchmark reference in chemistry and chemical and life science engineering, covering inorganic and organic chemicals, advanced materials, pharmaceuticals, polymers and plastics, metals and alloys, biotechnology and biotechnological products, food chemistry, process engineering and unit operations, analytical methods, environmental protection, and much more.
The present article is part of the topic collection "Environmental Protection and Industrial Safety". It covers plant and process safety, focusing on hazardous materials and process conditions.
The self-ignition of coal dust deposits and its subsequent smoldering combustion pose a high fire hazard to oxy-fuel power systems which burn fuels using pure oxygen for the sake of carbon capture and storage. The increasing risk of explosion in the gas-phase and self-ignition in the solid-phase for an oxygen enhanced combustion environment has not been well studied yet. In this work, the heterogeneous reactions of a bituminous coal dust are investigated by using a novel hot-basket apparatus with an emphasis on the roles of O2 and diluent gas in chemisorption and smoldering. Experiments show that increasing O2 mole fraction accelerates both self-ignition and the following smoldering combustion. On the other hand, the presence of CO2 increases the ignition temperature and reduces the maximum smoldering temperature. However, the promotion in the fire and explosion risk by elevating O2 mole fraction is substantially stronger than the retardation effected by presence of CO2. The emission-gas measurements show that the CO to CO2 ratio increases significantly after self-ignition, and CH4 counts for 1–8% of the total carbon emission. This research may help improve the understanding of heterogeneous coal combustion and the fire safety in oxy-fuel power systems.
Smouldering fires and explosions arising from self-ignition of coal dust deposits represent a serious hazard for human being, environment and industry. It is essential for plant operators to know the conditions (temperature, duration and quantity) at which storage will be safe. In this work, self-ignition behaviour of three bituminous coal dusts in large scales are theoretically studied, based on the experimental data via a standardized hot-basket apparatus. A comprehensive 2-D transient model is developed, using a 2nd-order reaction kinetics considering both coal and oxygen consumptions, to investigate self-ignition parameters of coal dust accumulations. The numerical model shows a less conservative prediction compared with the steady-state methods. The computational self-ignition temperature and ignition delay time show a satisfaction agreement with lab-scale experimental results. In addition, the influences of ambient temperature and moisture content are analysed. The result shows that the moisture content delays the ignition and a small variation of the ambient temperature nearby the critical condition will lead to a large difference of the ignition delay time.