Pollutant Emission Characteristics During Decoupling Combustion of Municipal Solid Waste

With the rapid development of China′s socio-economic landscape, the volume of municipal solid waste (MSW) generated from daily urban life has been increasing steadily. MSW decoupling combustion technology holds significant research value due to its ability to reorganize the combustion stages of volatile components. This staged approach facilitates low-NOx combustion while offering inherent advantages such as system simplicity and robust environmental adaptability. In this study, a two-stage fixed-bed reactor was employed to investigate the combined effects of reaction temperature (T), excess air ratio (α), and gas residence time (t) on the burnout behavior of combustible gases, flue gas pollutant emissions, and particulate matter characteristics during the decoupling combustion of MSW. The pyrolysis stage primarily yielded CH4 and CO as the dominant combustible gaseous components. Results demonstrated that a higher T and a higher α significantly enhanced the burnout efficiency of combustible gases. In contrast, extending t exerted a comparatively weaker positive influence on burnout. Regarding nitrogen oxides, NO formation was found to be strongly dependent on free radical accumulation and high-temperature reaction pathways, while NO2 generation was primarily governed by the NO oxidation rate and remained largely unaffected by variations in t. PM generation displayed a complex, non-monotonic response under different decoupling combustion conditions. Crucially, the operational condition yielding the minimum PM production rate closely coincided with the condition achieving optimal burnout of combustible gasest. This strong correlation suggests a synergistic relationship between PM suppression and efficient burnout control. However, adverse effects were observed under a high α combined with a short t, where conditions favored the enrichment of highly active polycyclic aromatic hydrocarbons (PAHs), consequently elevating the potential risk of dioxin formation. Although a higher T can promote PAH cracking, effective dioxin suppression necessitates complementary measures such as rapid cooling and efficient adsorption techniques downstream. Comprehensive analysis identified the parameter set of 850 ℃, α=1.5, and t=2.5 s as offering a well-balanced performance profile at this temperature. This condition achieved satisfactory burnout of combustible gases, effective PM suppression, and significant NOx reduction, demonstrating considerable promise for practical engineering applications. While the condition of 1 000 ℃, α=1.5, and t=2.5 s delivered superior burnout and overall pollutant suppression, the substantially higher energy input required at this elevated temperature presents a significant trade-off, potentially diminishing its net energy efficiency and economic viability. This study provides essential data and insights for optimizing MSW decoupling combustion systems towards cleaner and more efficient waste-to-energy conversion.