Syngas Production from Sewage Sludge By Solar-Driven CO2 Gasification

Conventional CO₂ gasification of sewage sludge requires a certain portion of feedstock to be combusted to supply necessary reaction heat, which releases a large amount of gaseous byproducts to the environment. The high-temperature energy, harvested from high-flux concentrated solar radiation, has been proved to supply the gasification process heat. In this work, the solar thermochemical gasification of CO₂-based sewage sludge was investigated theoretically by coupling concentrated solar energy as the heat source of high-temperature process heat. A dynamic model using CO₂ as a gasifying agent was developed to couple radiative transfer with fluid flow, heat and mass transfer, and thermochemical reaction kinetics. A fluidized gasifier with electric furnace was applied to simulate the thermal atmosphere of solar gasifier and to validate the theoretical model. Sensitivity of parameters on solar gasifier performance was assessed in terms of operating conditions, material properties, solar shape, and geometric structure. Thermodynamic-based analysis revealed that solar driven CO₂ gasification could potentially improve the quality of product syngas. Simulations indicate that the solar-to-syngas energy conversion increases with increasing flux density of solar irradiation. Furthermore, theoretical upgraded ratio of syngas using solar gasification has been investigated as well under various solar irradiances.

Keywords: CO₂ gasification; fluidized gasifier; sewage sludge; syngas; concentrated solar energy.