Flow-Field Deflection within a Cold Small-Scale Model for a Down-Fired 300 MWe Utility Boiler at Asymmetric Staged-Air Distribution

Abstract

Deflected flow fields and large combustion differences between zones near front and rear walls have been found in Mitsui Babcock Energy Limited (MBEL) down-fired pulverized-coal boilers under a symmetric air distribution. To eliminate or mitigate the flow-field deflection and achieve relatively symmetric combustion in these boilers, the distribution of the staged air between the front and rear walls was adjusted to construct an asymmetric staged-air distribution. Cold airflow experiments over a wide range of asymmetric staged-air distributions [viz., differences in the ratio of staged-air mass flux between the front and rear walls (R d ) of ―50, ―25, 0, 13, 25, and 50%] were conducted within a small-scale furnace of a MBELdown-fired pulverized-coal 300 MW e utility boiler. At settings of R d = ―50, ―25, 0, and 13%, there was a deflected flow field in the lower furnace, and this airflow was directed upward later near the front wall than near the rear wall. With R d increasing from -50 to 13%, the flow-field deflection weakened. For settings of R d = 25 and 50%, there was another flow-field deflection, with the downward airflow reversing direction earlier near the front wall than near the rear wall. With an increase in R d from 25 to 50%, the flow-field deflection became more pronounced. To establish a flow field along with an appropriate airflow reach for more economical operation, an optimal setting of R d = 13% was found for the staged-air distribution between the front and rear walls.