Interactions of co-firing coal gangue and high sodium coal: Combustion characteristics and emission behaviors of polluting gases.

[Display omitted] • Interactions during co-firing high sodium coal and coal gangue examined. • AAEM are responsible for synergistic combustion of the blended fuel. • N O is reduced while S O 2 is enhanced during co-firing at 1000 °C. • CaO particpates competitive reactions with both minerals and desulfurization. • Formation and emission mechanism of NO and S O 2 is proposed. To promote the utilization of coal gangue (CG) as alternative fuels for heat or power generation, this work investigated the interactions between a CG (denoted as XJG) and a high sodium coal (HSQ) during co-combustion as well as the evolution behaviors of gaseous pollutants (S O 2 and N O). Results show that co-firing HSQ with less than 30 % XJG does not deteriorate its combustion performance. Synergistic conversion is observed due to the complementarity of the fuels in volatile matter, fixed carbon, ash content and reactivity. Moreover, alkali and alkaline-earth metals promote co-firing and lower activation energy of combustion from 100 to 70 kJ/mol. Both S O 2 and N O are evolved in two stages during co-combustion as described by the shrinking core model and 3D-diffusion model. N O is reduced by char and C O and the reduction is catalyzed by the alkaline species(especially CaO) in ash. S O 2 emission behavior is significantly varied by the competitive reactions of calcium oxide with silica/alumina species. Overall, N O is decreased by about 10 % relatively at 900–1100 °C while S O 2 is notably enhanced at 1000 °C by 23 %. The mechanism of formation and reaction of S O 2 and N O are proposed. These results provide useful reference for clean utilization of CG and controlling of polluting gas emission, thus boosting sustainable development of energy, ecology and environment. [ABSTRACT FROM AUTHOR]