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

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 (SO2 and NO). 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 SO2 and NO are evolved in two stages during co-combustion as described by the shrinking core model and 3D-diffusion model. NO is reduced by char and CO and the reduction is catalyzed by the alkaline species(especially CaO) in ash. SO2 emission behavior is significantly varied by the competitive reactions of calcium oxide with silica/alumina species. Overall, NO is decreased by about 10 % relatively at 900–1100 °C while SO2 is notably enhanced at 1000 °C by 23 %. The mechanism of formation and reaction of SO2 and NO 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.