WASTE DERIVED FUELS TORREFACTION IN A SOLAR DRIVEN FLUIDIZED BED REACTOR: INFLUENCE OF FUEL MIXING/SEGREGATION CONDITIONS

The use of biogenic waste derived fuels for energy production is currently a hot research topic. This path allows indeed a virtual decrease in CO2 emission (waste derived fuels can be considered the same way as biomass), and a simultaneous lightening of the landfill load. Nevertheless, it is often hindered by the relatively poor thermal and chemical properties of waste derived fuels. Torrefaction processes can be applied to upgrade the properties of such residues through an increase of the heating value, a destruction of the organic pathogens and a stabilization/homogenization of their biochemical matrix. In a previous work, the use of solar energy via Concentrated Solar Power (CSP) systems to perform solar-assisted torrefaction of a lignin-rich residue was successfully demonstrated in a lab-scale directly irradiated Fluidized Bed (FB) reactor. This work proceeds along the laid path, and provides an in depth study of this process integration by exploring the use of different fluidization conditions to expose or hide the reactive materials to the high concentrated radiation impinging on the FB surface. To this aim, torrefaction tests on two waste biomass materials, a lignin-rich residue and a sewage sludge, were performed in a lab-scale directly irradiated FB reactor under different fluidization conditions. Chemical physical analyses were carried out on the product materials to investigate changes in the elemental composition and volatile matter content as a function of the reaction temperature and process conditions. A thermal infrared camera was used to map the FB surface during selected torrefaction tests to assess the possible interaction between reactive materials and concentrated radiations.