Torrefaction of a lignin-rich biogenic waste in a directly irradiated fluidized bed reactor

Thermochemical conversion of solar power to energy carriers provides an attractive pathway to energy storage and dispatchment. Compared to sensible and latent energy storage, thermochemical energy storage provides higher densities of storage and a storage period and transport distance theoretically unlimited, though the technology is far more complex. One of the pathways for thermochemical energy storage consists in upgrading the properties of conventional and alternative solid fuels by means of solar-driven pyrolysis, gasification and torrefaction processes. The present study aims at demonstrating solar-driven thermochemical processing of a lignin-rich residue derived from a second-generation bioethanol process. Torrefaction tests were performed in both a conventional fluidized bed reactor (i.e. with electrical heating) and a directly irradiated fluidized bed reactor at different process temperatures. Chemical physical analyses were carried out on the product materials in order to investigate changes in the elemental composition and volatile matter content as a function of the reaction temperature. The heating value of the torrefied material was also characterized. The influence of operational conditions on the quality of the torrefied biomass has been assessed, with a close up on the possible role of uncontrolled particle overheating under high-flux conditions.