Co-production of syngas and zinc via combined solar-driven biomass gasification and ZnO carbo-thermal reduction in a continuously-operated solar reactor

The solar thermochemical gasification of biomass with in-situ ZnO carbo-thermal reduction was carried out in a lab-scale (1.5 kW) continuously-fed solar reactor. The objective of this study was to demonstrate the feasibility of the combined process involving wood biomass gasification with ZnO as an oxidizing agent under continuous process operation for co-production of syngas and metallic Zn. A controlled mixture of biomass and ZnO particles was injected in a cavity-type receiver directly irradiated by concentrated solar radiation. The influence of temperature (1050-1250°C) on syngas production was experimentally investigated and compared to the case of a pyrolysis process (without any oxidizing agent). H₂ production increased drastically, CO production tended also to increase, while CH₄ and CO₂ concentrations decreased when increasing the temperature. The global syngas production of the combined gasification and ZnO carbo-thermal reduction was higher in comparison with pyrolysis. Collected products at the reactor outlet indicated high Zn content, with low recombination to ZnO in the solid products. The energy content of the feedstock was upgraded by the solar power input in the form of both syngas and Zn, thus outperforming pyrolysis in addition to delivering higher syngas output per unit of feedstock.