Effect of different inner secondary-air vane angles on combustion characteristics of primary combustion zone for a down-fired 300-MWe utility boiler with overfire air
Zhengqi Li and
Applied Energy, 2016, vol. 182, issue C, 29-38
To achieve significant reductions in NOx emissions without increasing the levels of unburnt carbon in the fly ash, a new combustion system was applied to a 300-MWe Babcock & Wilcox (B&W) down-fired boiler installed with swirl burners. The unit featured introduced overfire air (OFA) and decreased outlet area of the inner and outer secondary-air ducts of the swirl burners. Full-scale measurements (adjusting the inner secondary-air vane angle to 35°, 45°, and 55°) revealed that the influence of the high-temperature recirculating region under the arch upon the combustion and NOx emission characteristics of the boiler is greater than that of the high-temperature flue gas entrained by the swirl burner itself. The ignition distance of the coal/air flow is reduced by at least 1.8m compared with that of the original combustion system. For the inner secondary-air vane angle of 35°, the coal/air flow ignites earlier than for the vane angles of 45° and 55°. The measurements of the gas species concentrations in the zone near the sidewall indicates that at inspection port 1, the coal flame of the burners does not spread across the entire furnace cross-section for all three vane angles; however, for the vane angle of 35° the flame is spread across the entire furnace cross-section at inspection port 2. For this optimal (35°) inner secondary-air vane angle, the NOx emissions and carbon content in the fly ash reached levels of 674mg/m3 (6% O2), and 11.4%, respectively, achieving a significant NOx reduction of 51.9% without increasing the levels of unburnt carbon in the fly ash.
Keywords: Down-fired boiler; Swirl burner; Vane angles; Overfire air; Pulverized coal combustion; NOx emissions (search for similar items in EconPapers)
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