Hydrogen -rich syngas production via sorption -enhanced steam gasification of sewage sludge

Thermal conversion is an effective non-traditional method for sewage sludge disposal. Herein, the application of sorption-enhanced steam gasification to sewage sludge treatment is experimentally investigated to generate hydrogen-rich syngas in a fixed bed setup. The main aim was to determine the optimal conditions and suitable sorbents for this process. CaO was selected as the sorbent, and different CaO sorbents were prepared via the sol-gel method. Al2O3, La2O3, and ZrO2 were used as support materials for CaO to enhance the sorbent activity and stability. The CO2 capture capacities and stabilities of the sorbents over multiple cycles were examined. Additionally, different metal additives including CoO, MgO, and CeO2 were combined with the sorbent to increase the hydrogen mole fraction and gas yield. The integration of the support material increased the stability of the sorbents over multiple cycles. High temperature increased the syngas yield and cold gas efficiency but decreased the hydrogen mole fraction. In comparison to CaOLa and CaOZr, CaOAl afforded a higher hydrogen mole fraction and yield. Moreover, as Al2O3 is cheaper than La2O3 and ZrO2, it was selected as the most suitable support material for CaO, considering both its performance and cost. Transition metal Co was also investigated as a catalyst for gasification. A high Co loading ratio improved the hydrogen yield and cold gas efficiency but decreased the hydrogen mole fraction. These findings suggest that the CaO sorption-enhanced gasification to produce hydrogen-rich syngas is an appropriate method for sewage sludge disposal.