Effect of temperature, oxygen concentration, and CaO addition on SO₂ and NO_x emissions during oxygen-fuel combustion of municipal sludge

Oxygen-fuel combustion is an effective and promising method of steadily minimizing municipal sludge volume at the same time exploiting available heat and falling emissions. The effects of temperature, oxygen concentration, and CaO addition on SO₂ and NO_x emissions from municipal sludge combustion in CO₂/O₂ atmosphere were systematically explored via a lab-scale electrically heated tubular furnace in this work. The results show that the minimum average emissions of both SO₂ and NO_x were observed at 800 °C. Compared with air, all oxygen-fuel atmospheres reduced SO₂ emission, and a salient effect was observed with 30% of oxygen concentration. In contrast, the inhibition of NO_x emission was inconspicuous and exacerbated in some cases. With a lower oxygen concentration (21%), CaO evidently reduced SO₂ emission and 8 wt% addition performed the best. The removal efficiency of NO by CaO addition was poor and only exhibited slight inhibition with 5 wt% addition.