Comparisons of ash particle properties under air and oxy coal combustion in a 25kW one-dimensional down fired furnace

A 25kW one-dimensional down fired furnace was operating in air (O ₂/N₂) and oxy (O₂/CO₂) combustion conditions respectively. A typical Chinese bituminous coal was burned in this experiment. The furnace operation can be switched between air and oxy comditions freely. The real flue gas recycling was performed but not one through system. The recycle ratio defined as the mass fraction of recycled flue gas to the whole flue gas amount is 77.8% (dry basis) here. Comparisons of ash particle properties under these two different combustion conditions were carried out in this work. The particle matters were sampled in flue gas cooling zone(Port 10) by a self-desighed two stages nitrogen dilution water cooled sampling probe. The fly ash particle size distribution results meatured by mastersizer 2000 show that the fly ash formed under oxy combustion condition is smaller than those formed under air combustion condition. The elements mass fraction of PM ₁ show different characteristics under these two conditions.The microscopic analysis confirm differences between air and oxy coal combustion considering burning bulk atmosphere, heat transfer, molecule diffusion and radiation.