Investigation and optimization of syngas generation during chemical looping gasification of municipal sludge using Fe/Al oxygen carrier

To contribute to the reduction of carbon emissions, municipal sludge has to be utilized as a resource instead of being disposed of, especially since current sludge disposal methods encounter problems such as high dehydration energy consumption and secondary pollution. In this study, Fe/Al composite oxygen carriers (FOCs) were prepared using Al2O3 particles as carriers and Fe(NO3)3·9H2O as a precursor. Chemical looping gasification (CLG) of wet municipal sludge was conducted in a FOC-loaded fixed bed reactor, and the effect of reaction parameters and conditions on FOCs and syngas generation characteristics were analyzed by various methods. The results showed that the participation of water vapor in the gasification reaction significantly improved the hydrogen production rate of sludge gasification and avoided the over-reduction of the FOC. The vapor released from sludge significantly improved the thermal conversion efficiency of the sludge. Higher temperatures were conducive to the gasification reaction in the first stage, but when the reaction temperature reached 900 °C, the FOC slightly sintered, the reaction atmosphere was affected, and the hydrogen ratio in syngas started decreasing. Controlling the mixing ratio of FOC to sludge (O/H) was an important influencing factor for preparing high-quality syngas. When O/H was higher than 0.25, the quality of syngas decreased significantly. The conclusions obtained in this study can guide the selection of reaction conditions for the CLG of wet sludge using FOCs to prepare hydrogen-rich syngas. •Steam facilitates the acceleration of the sludge pyrolysis reaction, thereby promoting the CLG reaction.•Sludge self-moisture can enhance the reforming reaction of volatile matter, thereby improving the syngas quality.•As O/H ratio increases, the redox reaction between OC and sludge intensifies, diminishing the syngas quality.