Effect of the optimal combination of bituminous coal with high biomass content on particulate matter (PM) emissions during co-firing

Abstract

The co-firing of bituminous coal with woody biomass provided an available approach for cutting carbon emissions. In this work, a study on the application of high blending ratios of biomass with coal in co-firing was experimentally conducted in a lab-scale drop tube furnace (DTF) to reduce CO2 emissions and control deposition and corrosion due to the particulate material (PM) yield on the heating surface. Two kinds of woody biomass were blended with two kinds of bituminous coals at dosages of 5 wt%, 15 wt% and 30 wt% to investigate the PM emissions of different combinations during co-firing. With the addition of biomass, the experimental results show that the PM emission during co-firing may greatly increase or remain approximately stable compared with that during the single combustion of coal, which is dominantly determined by the combination of coal and biomass. To quantitively understand this effect, a mathematical method for the prediction and verification of PM yield during co-firing was developed by using a FactSage calculation based on the computer‐controlled scanning electron microscopy (CCSEM) analysis of raw fuel and fly ash. The predicted proportions of sticky particles with a liquid amount of >70 wt% demonstrate a significant difference with the variation in fuel type and biomass dosage during co-firing. According to predictions, 45.3% more sticky particles can be produced due to the diversity of added biomass when co-fired with the same kind of coal, conversely resulting in a 54.8% suppression of particles with an aerodynamic diameter of 2.5 μm or less (PM2.5) emissions. The morphological and elemental distribution of PM further validates that the liquid substance formed can be the decisive factor in generating sticky particles to control the formation of precursors by adsorption of alkali vapor or agglomeration of fine grains, thus inhibiting the PM yield with the addition of woody biomass during co-firing. The optimal combination for the co-firing of coal with high concentrations of biomass can be ascertained to simultaneously realize the reduction of carbon and PM emissions, which could provide a novel approach for the survival and development of coal-fired plants.