Co-Combustion of Coal and Biomass: Heating Surface Slagging and Flue Gases

An experimental study was carried out on the ignition and combustion processes of particles (100–200 µm in size) of coals of different degrees of metamorphism and biomass, as well as mixtures based on them, under conditions of conductive and convective heating, which correspond to the conditions of fuel ignition in boiler furnaces at grates and flaring combustion. The biomass contents in the composition of the coal-based fuel mixtures were 10, 20, and 30 wt.%. Under the conductive (at 700–1000 °C) and convective (at 500–800 °C) heating of fuel particles, ignition delay times were determined using a hardware–software complex for the high-speed video registration of fast processes. The ignition delay times were found to vary from 1 to 12.2 s for conductive heating and from 0.01 to 0.19 s for convective heating. The addition of 10–30 wt.% biomass to coals reduced the ignition delay times of fuel mixtures by up to 70%. An analysis of the flue gas composition during the combustion of solid fuels allowed us to establish the concentrations of the main anthropogenic emissions. The use of biomass as an additive (from 10 to 230 wt.%) to coal reduced NOx and SOx emissions by 19–42% and 24–39%, respectively. The propensity of fuels to cause slagging depending on their component composition was established. The use of up to 30 wt.% of biomass in the mixture composition did not affect the increase in the tendency to cause slagging on heating surfaces in the boiler furnace and did not pose a threat to the layer agglomeration during the layer combustion of the mixtures.