A review of biomass thermochemical gasification: Toward solar hybridized processes for continuous and controllable fuel production

Gasification of carbonaceous feedstocks into value-added syngas is a mature chemical process, developed at industrial scale for the production of chemicals and liquid fuels. Biomass gasification could open the path toward renewable fuel production, waste valorization, and carbon capture, but a fraction of the initial feedstock is burnt for process heat. Hence, allothermal solar heating is an attractive option for a clean and efficient production of syngas, enabling solar energy storage under a chemical form. Solar gasification potentially converts the whole feedstock mass while the produced syngas is not contaminated by combustion by-products and the high temperatures help to ensure high syngas yields with minimized char and tars production. Such results were however obtained under favorable solar power input conditions. In practice, the solar power fluctuations and intermittency must be managed carefully, with a control of the reactor inputs round the clock for stable syngas production. This review aims to provide a state-of-the-art on the variety of scientific topics involved in developing a stable and controllable solar gasification process, and it further addresses the challenges of hybridized solar-autothermal processes. Conventional gasification is first tackled, unraveling the historical background and current applications of the process. Associated chemical mechanisms are described, with some modeling considerations. Concentrated solar power technologies are then described, with a focus on thermochemical applications and existing solar gasification technologies. Finally, the methods to smoothen the effects of fluctuating solar power availability on solar syngas production are assessed, including thermal heat storage and solar-autothermal hybridization for continuous day-night operation. The implementation of dynamic control methods is addressed, to assess the practical application of control strategies, paving the way toward continuous solar fuels production.