EXPLORING THE EFFECTS OF EMPLOYING DIFFERENT SCALING CRITERIA ON SWIRL STABILIZED PULVERIZED COAL BURNER PERFORMANCE

The effects of employing different scaling criteria on the performance of swirl stabilised pulverised coal burners are presented. Two burner s were studied at 2.5 MW thermal input. The burners were scaled down f rom a 50 MW(t) reference case using both constant velocity and constan t residence-time scaling criteria. Coal particle size distribution was maintained constant at 75% < 75 mu m in both cases. Parametric studie s were performed on each burner under baseline high NOx and aerodynami cally air staged low NOx operation. Detailed in-flame measurements of temperature and gas composition were performed on both baseline flames . Results show that in the baseline firing mode, NOx emissions are con sistently higher for the constant velocity burner. Employing aerodynam ic air staging for NOx reduction by promoting penetration of the coal jet into the internal recirculation zone, resulted in significant NOx reduction in both burners. It was also observed that the normalised co al. injector insertion distance where aerodynamic air staging was achi eved was less for the constant velocity scaled flame. This is explaine d by the differing effects of the two scaling criteria on the turbulen t mixing process and two phase interactions.