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 MBEL down-fired pulverized-coal 300 MW, 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.
展开▼
