Oxidative torrefaction of eucalyptus woodchips using a silica sand layer for bioenergy enhancement

• Silica sand replaces nitrogen, lowering oxidative torrefaction process costs. • Torrefaction improves calorific value and reduces moisture of eucalyptus chips. • Higher temperatures and times increase EF, enhancing High heating value. • Sand layer height controls oxygen diffusion and affects biomass decomposition. • Torrefaction at 300 °C, 60 min, and 3 cm shows the highest enhancement factor. Due to the increase in energy demand in recent years, renewable energy sources have gained greater prominence, with biomass considered as the fourth source of renewable energy. In Brazil, a biomass of great importance is the woodchips generated by the industrial production of eucalyptus. Eucalyptus woodchips are mainly used as fuel in several industries, however, like other biomasses, they have some disadvantages such as low calorific value and high humidity. These disadvantages can be minimized by the torrefaction process. The literature has presented several options, one of which is oxidative dry torrefaction. Within oxidative torrefaction, there is a form where the biomass is immersed in a bed of inert material, however this form of torrefaction is still under study. In this work, sand-assisted oxidative torrefaction of eucalyptus woodchips is studied, evaluating the temperature in the range of 200 – 300°C, the high of the mineral layer in 3, 6, 12 cm, and two times of torrefaction 30 and 60 min. The torrefaction temperature range was varied, in addition, variables such as time and height of the sand bed will be evaluated. The results obtained indicate that the yield of torrefied biomass is inversely proportional to temperature and time. Furthermore, the height of the sand bed has an influence on the yield and properties of the torrefied biomass. Sand-assisted oxidative torrefaction improves high heating value, reduces moisture content, and increases grindability.