Gasification of dried sewage sludge using an innovative three-stage gasifier: Clean and H₂-rich gas production using condensers as the only secondary tar removal apparatus

Air gasification of dried sewage sludge was performed in a new-type three-stage gasifier consisting of an auger, a fluidized bed, and a tar-cracking reactors. The study aimed to evaluate the possibility of gasification using only condensers for the secondary tar removal method. The effects of Ni- and Fe-impregnated active carbons on the quality of producer gas were also investigated. Finally, to investigate the deactivation behavior of active carbon, a spent active carbon obtained after about 4.3 h of gasification, was used again for approximately 3.7 h of gasification. The active carbons used effectively reduced the contents of condensed and gaseous tars. Ni-impregnated active carbon produced a gas with a high H₂ content (26 vol%) and a low NH₃ content (198 ppmv), while Fe-impregnated active carbon produced a gas with a low H₂S content (96 ppmv). The compositions of the producer gases obtained solely using condensers were similar to those obtained using electrostatic precipitator. During the total ∼8 h of gasification, active carbon could efficiently remove tar; however, its surface area and total pore volume slowly decreased with time.