Optimization of hydrogen-rich syngas from coal and sewage sludge co-gasification in supercritical water

Supercritical water gasification (SCWG) of coal and biomass waste complies with the structure of energy consumption and the targets for carbon peaking and carbon neutrality. In this work, the optimal blending ratio and thermochemical transformation characteristics of coal and sewage sludge (SS) co-gasification were explored experimentally at various temperatures (500–660 °C), residence time (0–40 min), feedstock concentrations (5–15 %), and catalyst utilization. The demethylation and dehydroxylation of intermediate products (aliphatic compounds, monocyclic aromatic hydrocarbons (MAHs)) improve the gasification performance under favorable experiment conditions (high temperature, long residence time, low feedstock concentration, and addition of catalysts). The optimal gasification results are an H₂ yield of 38.36 mol/Kg and a 118.81 % increase of CGE (cold gas efficiency) in K₂CO₃-catalyzed gasification compared to the absence of the catalyst. Subsequently, the co-gasification mechanism of coal and SS was determined by the analysis of the three-phase product. Ultimately, a regression model was first established to obtain the practical optimization mechanism and yield prediction of hydrogen-rich syngas through response surface plots and regression equations. As verified in multiple experiments under varying situations, the regression model's fitting accuracy yields an average relative error of 5.53 %.