For opposed wall-fired boilers, the dependency of NOx emission and burnout characteristics on swirl intensity is not straightforward during air-staged combustion. In this study, therefore, influences of swirl vane angle, primary zone stoichiometric ratio, and air staging level on NOx emission and burnout were evaluated experimentally in a laboratory-scale pulverized coal fired furnace. The NOx emission and burnout were a function of residence time in the primary combustion zone. Increasing of the residence time and decreasing of the primary zone stoichiometric ratio had a positive effect on NOx reduction and a negative effect on burnout. There was a tradeoff relationship between the NOx reduction and burnout performance. With controlling of the swirl vane angle, aerodynamic behaviors in the burner region had a strong impact on NOx emissions and burnout characteristics. From the effectiveness analysis of combustion modifications such as the primary zone stoichiometric ratio and swirl vane angle, the control of swirl vane angle was more effective than that in the control of the primary zone stoichiometric ratio. The optimum swirl vane angle should be adjusted with given combustion environments, especially in this research, it was 80 degrees, 45 degrees, and 60 degrees at no staging, air staging level 1, and air staging levels 2-4, respectively. (C) 2015 Elsevier B.V. All rights reserved.