Effect of Co-firing Rate on Dewatered Sludge and Municipal Solid Waste Incineration: Pollutants Emissions, Operational Performance and Byproducts
Co-firing municipal sludge with municipal solid waste (MSW) provides a viable solution for sludge disposal. This study evaluated the effect of sludge co-firing rate (0%, 5%, and 10%) on flue gas pollutant emissions, operational performance, and incineration byproduct characteristics in a waste-to-energy plant. The results showed that under all co-firing rates, the concentrations of SO2, NOx, CO, HCl, particulate matter, and dioxins complied with the limits specified in the Standard for Pollution Control on Municipal Solid Waste Incineration (GB 18485—2014). As the co-firing rate increased from 5% to 10%, concentrations of all flue gas pollutants except NOx and HCl exhibited an upward trend. The optimal operational performance under the test conditions was achieved at a 5% co-firing rate, when the flue gas volume, fan volume, and ammonia and lime consumption were minimized. Compared to the 5% rate, increasing the co-firing rate to 10% resulted in elevated flue gas volume, fan volume, and reagent consumption. Steam production decreased from 2.778 t/t (0% co-firing rate) to 2.358 t/t (5% co-firing rate) and 2.117 t/t (10% co-firing rate), indicating a reduction in power generation efficiency with increasing sludge co-firing rates. Leaching toxicity analysis of fly ash revealed significant reductions in the leached concentrations of Zn and Pb, while those of Hg, As, Ba, and Se showed slight increases, all remaining well below regulatory limits. This study confirms the technical feasibility of directly co-firing mechanically dewatered sludge (with a moisture content of 50% to 60%) without thermal drying. A 5% co-firing rate is identified as the optimal balance between operational economy and system efficiency.