The Burning Velocity of Pulverised Biomass: The Influence of Particle Size

The use of pulverised biomass as a replacement for coal in power generation is a major source of renewable electricity in the UK. However, there is little data on flame propagation rates for pulverised biomass and this makes it difficult to design burners and model these flames using the traditional burning velocity approach. An ISO 1 m3 dust explosion vessel was modified to enable constant pressure spherical expanding turbulent flame speeds, ST, to be measured for pulverised biomass. The turbulence generated by the new dust injection system was calibrated using turbulent and laminar gas explosions and this enabled the dust laminar flame speed, SL, to be determined from ST. The burnt gas expansion ratio, EP, was determined from the peak pressure rise and this enabled the laminar burning velocity, Su, to be determined from the measured ST. The results showed for a range of biomass that the peak ST was in the range 3–5.5 m/s. The laminar burning velocity for 26 biomass and two coal samples and were very low at 0.1 – 0.2 m/s for the most reactive mixture, depending on the biomass particle size.