Air gasification of dried sewage sludge in a two-stage gasifier. Part 3: Application of olivine as a bed material and nickel coated distributor for the production of a clean hydrogen-rich producer gas

Air gasification of dried sewage sludge (DSS) was performed with olivine as the bed material and coal-based activated carbon as the tar-cracking additive in a two-stage gasifier to produce a hydrogen-rich producer gas with low tar content. Additionally, to investigate the possible regeneration of coal-based activated carbon, two different activating agents (carbon dioxide and steam) were applied. Finally, to reduce ammonia and tar contents, the performance of a Ni-coated distributor was examined. In the experiments, gasification at a steam to fuel ratio (STF) of 1.11 achieved a tar removal efficiency of 98% and a maximum hydrogen content of 34 vol.%. Furthermore, the activated carbon used for the gasification was less deactivated, compared to those used in the experiments without any reforming agent. When a Ni-coated distributor was applied, the ammonia content in the producer gas was significantly reduced to 11 ppm.