Air gasification of dried sewage sludge in a two-stage gasifier. Part 4: Application of additives including Ni-impregnated activated carbon for the production of a tar-free and H₂-rich producer gas with a low NH₃ content

The gasification of dried sewage sludge was performed using various additives (activated carbon, Ni-impregnated activated carbon, dolomite, and CaO) in a two-stage gasifier to produce a tar-free gas with a low NH₃ content. This research also examined the effect of feed rate on the tar removal efficiency and the stability of the two-stage gasification system conducting a ∼3.7 h gasification. In all experiments, natural olivine was used as a fluidized bed material, and air as a gasifying agent. The equivalence ratio was kept almost constant at ∼0.36. When Ni (8.9 wt%)/activated carbon was applied, a tar-free gas with 31.3 vol% H₂ and 114 ppm NH₃ was obtained, with a tar removal efficiency of 97%. A higher feed rate turned out to have a negative effect on the tar removal. The gasification performed using multiple additives for ∼3.7 h produced a tar-free gas with 146 ppm NH₃.