A solar-driven biomass gasifier with bimodal radiative heating: Heat transfer characteristics and operational parameter optimization

Concentrated solar thermal energy can drive endothermic biomass gasification, improving biomass conversion efficiency and reducing carbon emissions. However, the optimal heating strategy — direct or indirect — remains a subject of debate. This study introduces a novel solar gasifier where perforated panels create an adjustable hybrid heating mode, combining the high solar absorption efficiency of direct heating with the stability of indirect heating. This configuration has the potential to establish a controllable temperature gradient between the radiation panel and biomass reaction zone, enabling cascaded solar energy utilization, flexible control of the syngas H₂/CO molar ratio, and potential in-situ tar cracking. In this work, the heat transfer characteristics of the gasifier were investigated by coupling an energy-partitioning Monte Carlo radiative model with a chemical equilibrium model of biomass gasification reactions. Multi-objective optimization was employed to identify the optimal conditions for energy conversion efficiency, H₂/CO molar ratio, and the energy upgrade factor. The results revealed that the peak performance is achieved at high panel perforation ratios, with biomass reaction temperatures maintained between 950 K and 1100 K. Under these conditions, the energy upgrade factor approaches 1.25, the carbon conversion ratio approaches unity, and the H₂/CO molar ratio can be precisely tuned to the ideal 2:1 ratio required for Fischer–Tropsch synthesis and methanol production. This work provides the initial thermodynamic evaluation for a flexible solar gasification technology, paving the way for its industrial-scale application in converting waste biomass into high-value fuels.