Basic effects on NO_x emissions in air staging and reburning at a bench-scale test facility

Investigations on air staging and fuel staging were carried out with an electrically heated tube reactor. The effects of stoichiometry and residence time in the fuel-rich zone and the effects of temperature were evaluated for air staging with different coals and, in the case of reburning, for different gaseous reburn fuels. The results show the strong influence of residence time and stoichiometry, which may not be considered independently. The effects of temperature depend on the stoichiometric parameters. In air-deficient conditions, given by air staging and fuel staging, the NO_x emission decreased with increasing temperature, whereas in oxygen-rich conditions the opposite trend occurred. In pulverized bituminous coal combustion, reburning is superior to air staging. While minimum NO_x emissions of ∼250 mg m^-3_s could be achieved with air staging, reburning brought about values ∼200 mg m^-3_s. For brown coal combustion, the minimum emissions far below 200 mg m^-3_s with air staging could not be achieved with reburning.