No abstract

A pulverised solid fuel particle in a hot gas stream appears to have different characteristic behaviours at several stages, including heat-up, release of volatile matter, gas phase and solid combustion. The characteristics of these stages may vary distinctly depending on devolatilisation rate, the particle temperature history and its chemical and physical properties. Biomass particles manifest different combustion behaviour from that of burning coal particles under the same combustion conditions because they contain more volatiles (less fixed carbon), and they have a relatively lower particle density due to their fibrous structure. This paper presents an experimental study of burning behaviour of different types of biomass particles (torrefied wood, coffee waste and sewage sludge). The main experimental parameters-gas temperatures of 1,090 K and 1,340 K, and O2 concentrations ranging from 10% to 40%-were employed to investigate the burning of biomass through a directobservation approach using a high-speed photography technique at 7,000 frames/s. In the case of firing/co-firing, biomass particles must be larger than the coal particles in order to

No abstract

Torrefactionis a promising method for improving the quality of pulverised solid fuel, as itincreases the flame stability,radiative heat transfer and energy density of the fuel.Raw sewage sludge contains less fixed carbon and more ash compounds than other biomasses; consequently, it has poorenergy quality witha long ignition delay and forms arelatively low, sooty flame. In this study,we directly investigate the combustion behavioursof particles with varying degrees of torrefaction by burning them at 1340 K.Thetorrefied particles were prepared at different temperatures(473 K or 573 K) for different residence times (10minor 30min).The experimental parameters examined were the size range of the particles (150-215μmand 255-300 μm)and the O 2 percentage(10-40%).The particles wereentrained from a 3 cold carrier gas into a hot gas stream, igniting a volatile flame that was extinguished a few millisecondslater. These temporal variations in the burning particles weredetected byin-situ high speed photography (7000 frames/s).Thetorrefactiondegree affected the flame structure and varied the ignition delay, due to the mismatched reactivity and soot formation at rapid heating rates. The mosttorrefied sludge particlesexhibited a relatively luminous volatile cloudand a large flame, while preserving the duration of volatile combustion. These observations confirm theimproved pulverised combustion of the torrefied sludge particles. We also obtained valuable flame parameters (radius, intensity and combustion time) of the differentlytorrefied sludge particles.

No abstract