半炭化固体バイオ燃料の正味エネルギー量評価

抄録

The torrefied solid biofuels have come to attract attention as promising alternative fuels to coal in coal-fired power plants and industrial boilers. The torrefaction is a thermal treatment performed at mild pyrolysis temperatures to reform biomass and includes two distinct technologies, dry torrefaction (DT) and wet torrefaction (WT). The DT is the conventional thermal treatment conducted in the absence of oxygen under atmospheric pressure in a temperature range of 200-300 ℃, while the WT is a thermal treatment in hydrothermal media or hot compressed water in a temperature range of 180-260 ℃. Both torrefaction treatments can produce energy dense solid biofuels with better chemical, physical properties than original biomass feedstock, but the external energy input is required for the torrefaction treatment. Especially, when producing the torrefied solid biofuels from biomass feedstock with high moisture content, the energy consumption for drying process may have a negative impact on the sustainability of the torrefied biofuel. In this article, properties of thermally treated biomass by DT and WT are summarized, and then the net energy content of torrefied biofuels is presented to evaluate the sustainability. The net energy content is expressed as a function of mass yield, and the optimum torrefaction condition with high net energy content can be evaluated by the relation for the net energy content.