Hydrogen production of solar-driven steam gasification of sewage sludge in an indirectly irradiated fluidized-bed reactor

Abstract A fluidized-bed based solar steam gasification of sewage sludge for production of high-quality syngas with a high content of hydrogen is numerically modeled and validated by experimental data generated from a lab-scale fluidized bed. The solar gasifier is mainly composed of a fluidized bed and a concentrically tubular cavity. A transient model coupling a two-phase fluidization model (in terms of reaction kinetics and hydrodynamics) and a solar cavity receiver model is established to conduct the parametric investigation of the proposed solar gasifier, including the effects of the direct normal irradiance, gasifying agent composition, and spatial flux distribution at the freeboard wall on the performance criteria of solar gasification i.e. solar upgraded ratio and solar-to-fuel efficiency. The transient simulation of the solar gasifier with ~2.2 MW solar power input is performed. A H2 yield range of 61.2–67.6 g/kg(sludge) can be achieved through solar steam gasification of sewage sludge, which can be adjusted by modifying the steam content of the gasifying agent and the direct normal irradiance. Under the condition of the direct normal irradiation of 1000 W/m2, the mean concentration ratio of 1000 suns at the dense bed, and 100 vol% N2 content, a maximum solar upgraded ratio of 1.0 and solar-to-fuel efficiency of 0.26 can be achieved.