Combustion Characteristics of Ultrafine Coal Particles-Light Diesel Oil Mixtures in a Cylindrical Horizontal Furnace

This work presents an experimental study that aims at investigating the effect of the loading ratio of coal in a coal-diesel fuel mixture on the combustion characteristics and exhaust emissions. Sub-bituminous coal from the El-Maghara coal mine is utilized. It is washed, dried, and grounded to particle sizing of ≤ 30 μm. The experiments are conducted inside a horizontal, segmented water-cooled cylindrical furnace fitted with a coaxial burner having a central air-assisted atomizer for oil-coal mixture admittance. All experiments are executed at constant input heat of 350 kW and air-to-fuel ratio of 15:1 while varying the percentage (mass basis: 5% and 10%) of coal in the fuel mixture. The measurements within the flame zone include mean gas temperatures, dry volumetric analyses of species (CO2, NOx, and O2) concentrations, and the accumulative heat transfer to the cooling jacket along the combustor. All measurements are compared regarding the pure oil flame. The results indicate that increasing the coal-loading ratio up to 5 wt% leads to a progressive increase in the accumulated heat transferred and the combustor overall efficiency from 40% to 58% within a percentage increase around 45%. In addition, there is a slight reduction in mean gas temperature within the flame zone when compared with the pure oil flame. The reduced flame temperature due to increasing the coal-loading ratio caused a decline in the volumetric concentrations of NOx from 100 ppm to 20 ppm as expected.