Investigation of the effect of inherent water content on the combustion characteristics of victorian brown coal in air and under oxy-fuel conditions

This paper details in-situ investigations into the effect of inherent moisture content (10-30 wt%) on the combustion characteristics of a Victorian brown coal in a Drop Tube Furnace (DTF). The effect of the following parameters was examined: particle size, furnace temperature and combustion atmosphere (air versus 27% oxygen (O₂) and 73% carbon dioxide (CO₂)). A high speed camera and a two-colour pyrometer were used for in-situ diagnostics. The particle temperature was found to be around 80°C lower in the combustion of wet coal (∼30 wt% water) versus dry coal (∼10 wt% water) for most of the conditions. And increase in coal water content caused an ignition delay and prolonged combustion. Devolatilisation followed by volatile combustion was observed in all cases. At higher temperatures, coal/char combusted simultaneously with the volatiles. Dry coal was found to be less sensitive than wet coal to changes in furnace temperature and particle size. Particle temperatures were matched in both the wet and dry case when air was replaced by 27% O₂ in CO₂. However, oxy-fuel combustion of wet coal resulted in a barely visible unstable flame.