Pulverised wood combustion in a vertical furnace: Experimental and computational analyses

Experimental and numerical investigations of pulverised wood flames in a laboratory vertical furnace are carried out. The aims are to study the fundamental structures of pulverised wood flames, to identify the basic reasons that cause the emissions of unburned volatiles and particles, and to provide experimental data for model validations. Three different fuel particles are investigated; the particle effective diameter ranges from 0.02mm to 1.2mm and the length is about 5 times the diameter. Rather high emission of unburned hydrocarbons and carbon monoxide are recorded in the experiments. It is found that pulverised wood flames have similarities to gas premixed flames; distinct zones are found in pulverised wood flames – preheat zone, drying and devolatilization zone, oxidation zone and post-flame zone. The mechanism of heat transfer to the preheat zone of pulverised wood flames is rather different from the gas flames. The former is by virtue of radiation from the walls and the flames to the fuel particles; the latter is by diffusion (molecular and turbulent diffusion) from the reaction zone. This makes the emissions from pulverised wood flames rather sensitive to the particle size and combustor/burner configurations. An important feature of pulverised wood flames found in the experiments is the effect of particle devolatilization on the dispersion of the particles. A model is developed to account for this dispersion effect.