Air gasification of dried sewage sludge in a two-stage gasifier: Part 1. The effects and reusability of additives on the removal of tar and hydrogen production

Air gasification of dried sewage sludge was conducted in a two-stage gasifier. In the experiments, natural occurring materials, such as natural zeolite, olivine and dolomite, as well as biomass-based and coal-based activated carbons, were applied to the upper reactor of a two-stage gasifier, while sand and calcined dolomite were used as the fluidized bed material in the lower reactor. The reusability of the spent coal-based activated carbon and spent calcined dolomite was also investigated. The combination of calcined dolomite as the bed material and coal-based activated carbon in the upper reactor produced the highest H2 (28 vol.%) and CO (21 vol.%) contents. Furthermore, total amount of tar generated with the combination was 91% less than that generated with no additive in the upper reactor and sand in the lower reactor. The H2 content and tar removal efficiencies in the experiments with the spent activated carbons and spent calcined dolomites were shown to be better than those without additives in the upper reactor.