Direct observations on the combustion characteristics of Miscanthus and Beechwood biomass including fusion and spherodization

The pyrolysis and combustion characteristics of two disparate kinds of pulverized biofuels, (i) Miscanthus which is an herbaceous biomass and (ii) Beechwood which is a woody biomass, were investigated at high heating rates and high temperatures. Both materials were burned in either raw or torrefied (at 275 °C for 30 min) states. The particles were in the nominal range of 160-200 μm, as classified by sieving. Single particles of raw and torrefied biomass, were injected in an electric drop-tube furnace heated to 1400 K. Their pyrolytic behavior in nitrogen was assessed by examining collected samples microscopically. Their combustion behavior in air was observed with high-resolution, high-speed cinematography. Ignition took place close to the injector tip at the top of the drop-tube furnace, immediately upon entering the radiation zone. Upon ignition, nearly-spherical volatile matter flames formed around individual particles and grew bigger with time. The volatile matter flames of torrefied biomass particles were brighter than those of raw biomass particles. A clear shape transformation of the initially needle-shaped particles became apparent. Softening, melting and shrinking during devolatilization were prevalent phenomena observed both by microscopy of collected samples under pyrolytic conditions and by direct observations on burning individual particles under oxidative conditions. Such effects were more pronounced in the case of Miscanthus than Beechwood biomass and, again, they were more pronounced in the case of torrefied than raw biomass. Char residues of torrefied biomass particles took much longer to burn than those of raw biomass particles.