Enhanced production of hydrogen-rich gas from municipal sewage sludge gasification using a CaO-RM composite catalyst

Abstract

Hydrogen-rich gas, characterized by high yield and purity, can be effectively generated through the steam gasification of sewage sludge (SS), offering substantial benefits for organic solid waste treatment and resource conservation. This study evaluated the gasification performance in a horizontal moving-bed reactor employing a wet-mixed CaO-red mud (CaO-RM) composite catalyst. The effects of CaO loading rate (CaO/RM), catalyst-to-SS ratio (CaO-RM/SS), and reaction temperature on the syngas yield, lower heating value (LHV), carbon conversion ratio, H2 to CO (H2/CO) ratio, and H2 yield were investigated. Results indicated that red mud loaded with a calcium-based catalyst significantly enhanced syngas production, particularly for hydrogen generation, during SS gasification. A maximum hydrogen molar fraction of 50.84% and a yield of 7.07 mol/kg were achieved with a CaO/RM of 40% and a CaO-RM/SS of 30% at 750 °C. With the reaction temperature increase from 700 to 900 °C, the catalytic performance for secondary tar cracking and steam reforming was further enhanced. The total syngas yield, H2 yield, hydrogen molar fraction, LHV of syngas, and carbon conversion rate peaked at 0.79 m³/kg, 19.30 mol/kg, 54.41%, 10,249.48 kJ/kg, and 65.67%, respectively, at 900 °C.