Characteristics of Char Gasification in Staged Oxygen-Enriched Combustion in a Down Flame Furnace

Staged oxygen-enriched combustion was carried out in a 20 kW down flame furnace (DFF). The experimental results were used to perform corresponding simulations. This paper proposes a refined char gasification model for accurately simulating the deep-staged combustion of pulverized coal at elevated oxygen concentrations. The following experimental conditions were used: burner stoichiometric ratio (SR) ranging from 0.696 (deep staged) to 1.200 (unstaged), O-2 concentrations ranging from 21 to 30 vol %, and burnout stream injection ratio (Ms) ranging from 0.28 to 0.45. According to the experimental results, as SR decreased from 1.200 to 0.696, the peak CO concentration increased from low to very high levels (above 12 vol % under normal air conditions). The elevated oxygen concentration (30 vol % O-2) further increased the peak CO concentration at SR = 0.696 to approximately 18 vol %. The reaction model in the simulation was refined on the basis of char gasification and then used to successfully reproduce the experimental results (especially the CO concentration profile). The influence of char gasification reactions on the staged oxygen-enriched combustion is investigated in detail. Furthermore, the pollutants formed are then presented by comparing the NO profiles between the experimental and simulation results.