Optimizing the Combustion of Low-Quality Coal by the Wall Wind Auxiliary Combustion Method in a Tangentially Fired Utility Boiler

摘要

Adopting the low NOx combustion technologies in tangentially fired utility boilers, burners cannot maintain flame stability, coal adaptability, or high combustion efficiency. Generally, high-temperature corrosion and slagging occurs, especially when burning low-volatile coal or anthracite. Thus, a wall wind auxiliary combustion system is developed. Here, a part of the corner secondary air is transformed into wall wind, which is then directed vertically into the furnace through the water-cooled walls, thereby optimizing the combustion organization of the corner injections downstream. Pre-modification and post-modification results are compared by simulation in a 600 MWe boiler. The results show that wall wind prevents the injection downstream from skewing into the wall. As such, the high-temperature area near the water-cooled walls disappears and the flame center moves downwards. The combustion efficiency is also improved. The wall wind maintains oxidization near the water-cooled walls, thereby reducing the risk of high-temperature corrosion and slagging. Finally, the average NO concentration at furnace outlet is reduced by 10%. In the industrial application of this technology, the outlet steam temperature of the low temperature superheater decreases up to 20 K, and the NOx emission at boiler outlet decreases up to 20%, which is consistent with the simulation results.