Optimizing co-combustion of sewage sludge and bamboo scraps: Analysis of NO emissions and ash slagging behavior

This paper investigates the co-combustion of sewage sludge (SS) and bamboo scraps (BS) in a tubular furnace at 700 °C, 800 °C, and 900 °C, focusing on NO emission characteristics and ash slagging behavior. NO emissions from SS combustion occur in two distinct stages, corresponding to the release and reaction of volatile-N and char-N, respectively. Increasing the BS content decreases total NO emissions but raises NO formation from char-N. BS promotes NO production from volatile-N while delaying and reducing NO from char-N, resulting in an overall increase in total NO under most conditions. Flue gas analysis shows that higher temperatures accelerate combustion but reduce the conversion rate of nitrogen to NO. Ash characterization by XRF, XRD, and SEM reveals that ash fusibility increases with temperature. SS ash, rich in SiO₂ and Al₂O₃, forms refractory mineral phases like mullite (3Al₂O₃·2SiO₂), which cause partial sintering and adhesion, increasing slagging risk during cooling. Conversely, BS ash contains higher alkali metal oxides, lowering the ash melting temperature and enhancing fluidity, which reduces slagging risk at high temperatures but may promote slag deposition in cooler zones. Co-combustion fosters the formation of alkali-metal silicates, influencing ash melting behavior. Optimizing the SS/BS blend ratio can balance NO emissions and slagging tendencies, offering guidance for sustainable biomass waste utilization.