Effect of burner location on flow-field deflection and asymmetric combustion in a 600 MWe supercritical down-fired boiler

Abstract

To evaluate the burner location's role on the flow-field deflection and asymmetric combustion that occurring in a 600MWe supercritical down-fired boiler, cold-modeling gas/particle flow experiments and numerical simulations on coal combustion were performed with varying the furnace arch's burner location. Meanwhile, full-load industrial-size measurements at the boiler's design setup were performed to uncover the asymmetric combustion characteristics and verify the simulation validity. The boiler's design setup displayed a severely deflected gas/particle flow field with (i) a large downward gas/particle flow penetration difference appearing in the front- and rear-half sides and (ii) the upward flow fully deflecting towards the front-half side. Accordingly, a badly asymmetric combustion performance (much lower gas temperature levels appearing in the front-half side than in the rear-half side) occurred with poor burnout and high NOx emissions. The calculated coal/air penetration and flow-field deflection extent were found to be shallower than the cold-modeling experimental versions, despite the consistent flow-field deflection pattern respectively gained by the two methods. Positioning burners towards the front/rear wall greatly improved the flow-field deflection in the form of apparently decreasing the aforementioned penetration difference and redirecting the upward gas/particle flow in the furnace’s central part. Consequently, asymmetric combustion sharply weakened to increase burnout and reduce NOx emissions. In contrast, moving burners towards the furnace centerline aggravated the flow-field deflection and asymmetric combustion to worsen the furnace performance in burnout and NOx production. These results suggest that in the absence of coal/air distribution with varying burner location, the local high gas temperatures incurred by asymmetric combustion facilitate the NOx production. Finally, burners are recommended to position towards the front/rear wall as much as possible for weakening the flow-field deflection and asymmetric combustion if a lowered manufacturing cost requires a short upper furnace where the asymmetric upper furnace configuration effect is aggravated.