Study on Municipal Solid Waste Gasification and Ash Residue Slagging Characteristics

With China's urbanization advancing, the annual volume of municipal solid waste (MSW) collection continues to rise. MSW gasification has gained significant attention due to its large processing capacity, economic benefits, and low pollutant emissions. This study systematically investigates the effects of reaction temperature and equivalence ratio (ER) on MSW gasification using a fixed-bed reactor, focusing on syngas composition, tar formation characteristics, and slagging behavior of gasification ash. Additionally, the transformation of tar compounds and the fusion properties of gasification ash under varying conditions are explored. Experimental results show that increasing the gasification temperature enhances MSW decomposition and tar cracking, leading to higher syngas yield and calorific value. As ER increases from 0 to 0.3, tar conversion into oxygenated compounds such as aldehydes, ketones, and acids is promoted, significantly improving syngas calorific value. However, when ER exceeds 0.3, excessive oxidation of CO and H2 reduces syngas quality and calorific value. At an optimal temperature of 700 ℃ and ER of 0.3, the highest syngas calorific value of about 23.51 MJ/Nm3 is achieved, with increased gas yield and reduced tar formation. X-ray fluorescence (XRF) spectroscopy and ash fusion analysis indicate that MSW gasification ash primarily consists of SiO2, Al2O3, and CaO. As ER increases, the hemispherical temperature (THT) and flow temperature (TFT) of the ash rise, suggesting a decrease in slagging propensity. However, slagging tendency calculations indicate a significant tendency for slagging under various conditions, posing potential risks to long-term gasifier operation. This issue is attributed to the high content of alkali metal oxides (such as Fe2O3 and K2O) in the gasification ash. These oxides react with SiO2 and Al2O3 to form low-melting eutectic compounds, reducing ash viscosity and increasing adhesion, thus exacerbating slagging at high temperatures. The study further highlights that gasification ash composition is highly sensitive to operating conditions. Slagging issues can be mitigated by adjusting the MSW feedstock composition or by adding SiO2 and Al2O3 as additives to improve reactor stability. Additionally, while increasing ER promotes syngas yield by facilitating tar cracking, excessive ER leads to undesirable oxidation of valuable syngas components, resulting in a trade-off between syngas production and calorific value. In summary, reaction temperature and ER play crucial roles in determining MSW gasification efficiency and stability. Proper optimization of these parameters enhances syngas quality while reducing tar formation and slagging risks. The findings of this study provide theoretical support for the industrial application of MSW gasification technology and offer new insights into optimizing syngas composition, improving ash behavior, and advancing sustainable waste-to-energy conversion.