Fuel properties and combustion behaviors of fast torrefied pinewood in a heavily loaded fixed-bed reactor by superheated steam.

Superheated steam (SHS) was capable of fast and uniformly torrefying heavily loaded biomass. This work detailedly investigated the torrefied biomass in terms of fuel property and combustion behavior. The reactor chamber (300 ml) was fully loaded with pinewood pellets (160 g). Overall residence times were 20, 40 and 60 min (including preheating and holding periods) under 225, 275 and 325 °C. Biomass was estimated by elements, TG, FTIR, HHV, fuel property, combustion and pyrolysis behaviors, combustion kinetics and moisture reabsorption. Holding period as short as 2 min at 325 °C with a heating rate of 15 °C‧min was found to enhance energy density by 45% and generated homogeneous coal-like products with HHV of 26.76 MJ‧kg. Fixed carbon content increased to 64.84 wt%. The combustion activation energy increased to 79.66 kJ‧mol. Combustion indices and behaviors indicated that torrefied biomass had benign characteristics either for co-firing or as fuel. All suggests good potential of SHS torrefaction to obtain fuel alternatives.