Influence of fuel composition and flame temperature on the formation of thermal and fuel NOx in residual oil flames

A 900 kw model package boiler and a 20 kw laboratory tunnel furnace were used to study fuel and thermal NO, formation during heavy oil combustion. Package boiler results indicated that atomizer design, spray/ flow field interactions, and fuel composition were significant, dependent parameters. These effects were then investigated in detail in the laboratory furnace. One distillate and nine heavy oils were studied. Fuel NO.,., isolated with an argon/oxygen/carbon dioxide oxidant, was found to be a major source of NOx emissions. Fuel NOx formation increased approximately linearily with increasing nitrogen content from 0.05 to 0.79 wt. percent nitrogen. Fuel nitrogen oxidation was insensitive to temperature changes (over the theoretical temperature range of 2100 to 2500°K) except for one oil which exhibited a sudden increase at the highest temperature. Fuel NOx was insensitive to drop size, but thermal NOx increased with decreased mean droplet size. Percentage conversion of bound nitrogen decreased with increasing nitrogen content except for one oil containing substantial refractory nitrogen. Doping studies indicated that fuel sulfur can enhance fuel NOx formation and that nitrogen and hydrocarbon volatility are not first order parameters with a rapid mix burner under fuel-lean conditions.