Aerodynamic characteristics within a cold small-scale model for a down-fired 350 MWe utility boiler applying a multiple-injection and multiple-staging technology: Effect of the staged-air declination angle

This work presents an experimental staged-air angle optimization for a forthcoming ultra-low NOx retrofit within a down-fired pulverized-coal 350 MWe utility boiler. By recording aerodynamic field measurements within a small-scale model of the furnace, cold airflow experiments were conducted at seven different angle settings of 0°, 15°, 30°, 35°, 40°, 45° and 50°. At the four smaller angle settings, a deflected flow field characterized by the downward airflow near the front wall reversing upward far earlier than that near the rear wall, developed in the lower furnace. Accordingly, in the furnace throat region overfire air penetrated much further near the front arch than near the rear arch. Certain cross-sectional velocity component distributions and the decaying in airflows displayed poor symmetries along the furnace center. With increasing the angle from 0° to 35°, the flow-field deflection weakened continually. At the three larger angle settings, a well-formed symmetric flow field appeared in the lower furnace and the furnace throat region. Increasing the staged-air angle decreased sharply the difference in the downward airflow reach near the front and rear walls initially in the range of 0–45° but then varied it slightly in the angles of 45–50°. An optimal staged-air declination angle of 45° was recommended according to the present experiment results.

► Asymmetric combustion and high NOx emissions are found in down-fired boilers.
► With focus on this subject, a new combustion technology has been developed.
► Cold airflow experiments were conducted to establish an optimal staged-air angle with this technology.
► An optimal setting of staged-air angle was found at 45°.