American Electric Power

A two-phase, reacting flow CFD code was used in the design and evaluation of NOx control strategies for two pulverized coal utility boilers. The effects of furnace staging, burner alterations, and water injection were assessed in these furnaces. CFD analysis was shown to be a useful tool in optimizing NOx reduction while minimizing adverse effects such as increases in furnace CO emission and carbon in fly ash. The first boiler evaluated was a 265 MW B&W subcritical, opposed-wall fired, unstaged furnace. Furnace CFD simulations identified locations of highest flue gas mass flows and highest CO and O2 concentrations and were used to identify OFA port locations for maximum NOx reduction. Simulations of an OFA and burner alteration configuration that has been subsequently installed predicted a 34 % reduction in NOx emission with minimal changes in furnace exit CO and unburned carbon in fly ash. Plant CEMS data confirmed the accuracy of the modeling results for both the pre-retrofit and the post-retrofit operations The second furnace analyzed was a 153 MW B&W subcritical, roof-fired furnace. This furnace is equipped with 10 multi-tip burners and 10 NOx ports located below the burners. A CFD analysis predicted that a 23 % decrease in NOx emission with little adverse effect on furnace exit CO or carbon in fly ash was achievable through a combination of deeper staging and burner alterations. Further CFD analysis identified high NOx production zones in the downstream part of the combustion zone. It was predicted that selectively attacking these regions with water injection could further lower furnace NOx emission to a level 37 % below the current baseline operating condition. In designing an effective water injection such as this, it is crucial that NOx production zones in the downstream portion combustion field be identified, since these regions are most likely to produce NOx that will not be reduced before exiting the furnace