Chemical looping gasification of sewage sludge using a two-stage bubbling fluidized bed reactor

In this study, a two-stage bubbling fluidized bed reactor system was developed to conduct experiments to obtain basic data for chemical looping gasification (CLG) of sewage sludge (SS). The two-stage bubbling fluidized bed consisted of a gasifier and a reformer. Three types of bed materials, calcium oxide, olivine, and silica sand, were investigated under various operating conditions, including gasifier and reformer temperature, steam to carbon ratio, and gas residence time in the reformer to achieve efficient recovery of fuel gas (H₂ + CO). Performance was evaluated in terms of fuel gas production and tar reforming capacity. Olivine produced the highest amount of fuel gas per kg of SS and showed the best tar reforming capacity among the three. Fuel gas production was 2.37 Nm³/kg-C in dry sludge, and fuel gas efficiency was 64.4% when the gasifier was operated at 800 °C, and the reformer at 900 °C, with Olivine as the bed material. These results suggest that the fuel gas recovery from SS by CLG is more efficient than the conventional energy recovery techniques.