The combustion of pulverised low grade lignite

Romanian lignite presents utilization problems since it is one of the lowest grade coals in the world. In order to improve the performance of pulverized lignite combustors and to reduce the environmental impact there is interest in predicting NOx emission characteristics and carbon burnout. The application of CFD modeling for this purpose has been widely used for pulverized bituminous coal flames but less attention has been directed to lignite combustion. Many of these processes are common but some aspects are significantly different, particularly the presence of the high levels of moisture and ash, and the nature of devolatilisation.The combustion of Romanian lignite in a 1-MWth pilot plant furnace has been modeled using CFD. Because of the high amount of moisture the combustion process has to be supplemented by firing natural gas and both the effect of water and the effect of firing natural gas are studied here. In order to improve the power plant efficiency it may be required to dry the moist lignite before combustion and there is an interplay between the extent of drying and the amount of natural gas used which have been investigated. The kinetics of devolatilisation of this lignite and the effect on the combustion process has also been considered.