To clarify the in-furnace combustion characteristics of a 29 MW industrial pulverized coal hot-water boiler using centrally fuel-rich swirl combustion technology, a full-scale numerical model of the boiler furnace and burner was established and validated against industrial test data. The effects of the separated secondary air ratio and flue gas recirculation ratio on the flow field, temperature distribution, gas-species distribution, NOX formation, and furnace outlet parameters were investigated under full-load conditions. The validation results showed that the average deviation between the simulated and measured flue gas temperatures in the burner region was 9.8%, and the deviations in furnace outlet O2 concentration, NOX concentration, and combustible content in fly ash were 1.0%, 10.5%, and 11.3%, respectively, indicating that the numerical model was reliable. The results showed that the separated secondary air ratio significantly affected the central recirculation zone, flame morphology, and combustion completeness. Excessively high or low separated secondary air ratios were unfavorable for stable combustion and burnout, whereas a separated secondary air ratio of 55.4% produced a more reasonable high-temperature-zone distribution and more uniform furnace heating. Increasing the flue gas recirculation ratio shifted the central recirculation zone upward, reduced the high-temperature-zone area and flame filling degree, weakened coal burnout, and decreased NOX emissions. When the flue gas recirculation ratio was 30%, the NOX concentration and flue gas temperature at the furnace outlet decreased by 19% and 31 K, respectively, while the O2 concentration and combustible content in fly ash increased by 0.55 and 12.03 percentage points, respectively. Overall, the optimal separated secondary air ratio was 55.4%; the flue gas recirculation ratio should be controlled below 20% when boiler efficiency and burnout are prioritized, and above 25% when NOX reduction is the primary objective.
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