Promotion of Anthracite Burnout for a 300 MW_e Down-Fired Boiler with a Novel Combustion Technology

摘要

Eccentric-swirl-secondary-air combustion technology (ESSACT) has been applied to a 300 MWe anthracite- and down-fired boiler with swirl burners. To improve burnout performance of the retrofitted boiler, the effects of primary air ratios on flow and combustion characteristics are investigated via cold-model aerodynamic experiments and industrial experiments. When primary air ratios are 17.09 and 19.08%, a deflective flow field occurs, and with increasing the primary air ratio from 21.11 to 24.75%, a symmetrical "W" flow field is formed. With increasing the primary air ratio from 17.09 to 24.75%, the maximum dimensionless vertical velocity of air flow near the front wall increases linearly from 0.364 to 0.521. Accordingly, the penetration depth in the real boiler increases by approximately 2.88 m. For a primary air ratio of 18.47%, the temperatures at the burner exit and in the furnace hopper near the front and rear walls are both seriously asymmetrical and the combustion path of pulverized coal particles by the rear wall is relatively short. When the primary air ratio increases from 21.18 to 23.85%, the combustion in the furnace is relatively symmetrical. The pulverized coal ignition distances are shortened continuously and are all within 1.2 m, and the temperature near the water-cooled wall in the furnace hopper increases by approximately 80 degrees C; the combustion path of pulverized coal particles increases continuously. When the combustion symmetry property, unburned combustible in fly ash, and NOx emissions are taken into account, the primary air ratio of 22.96% is preferable for the retrofitted down-fired boiler. In comparison to the original boiler, unburned combustible in fly ash decreases by 33.4% and NOx emissions decrease by 43.8%. In comparison to the preliminary application of ESSACT, unburned combustible in fly ash further decreases by 12.7% on the basis of a large reduction of NOx.