Parametric study of sewage sludge gasification in air and steam environments: Experimental and process simulation

Gasification of sewage sludge (SS) is a thermochemical process which converts sludge into a value-added syngas, offering a sustainable alternative treatment to conventional disposal methods such as landfilling, land application, and incineration. This study investigates the gasification of dried sewage sludge in bubbling fluidized bed conditions, primarily focusing on the effects of key operating parameters such as bed temperature, equivalence ratio (ER) and steam-to-fuel ratio (S/F) on syngas composition. A total of 36 experiments were conducted, varying the bed temperatures (650 °C, 750 °C, and 850 °C), ER (0.2, 0.3, and 0.4) and S/F (0.5, 1, and 1.5). The results indicate a direct correlation between the bed temperature and the production of hydrogen and carbon monoxide, while carbon dioxide and methane concentrations decreased with the increasing the bed temperature. The optimum ER was found to be at 0.2, yielding the highest hydrogen and carbon monoxide production. Increasing S/F favored hydrogen generation through the water gas shift reaction (H₂O_(g) + C_(s) → H₂ + CO). In addition, experimental results were further validated using Aspen Plus process simulation, which exhibited matching trends in syngas composition.