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, NO_x, 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 NO_x from 100 ppm to 20 ppm as expected.