The fate of shrinking boiler nose to improve the flow-field deflection and asymmetric combustion in a 600 MW_e supercritical down-fired boiler

The asymmetric upper furnace configuration effect (mainly relied on the short upper furnace and large boiler nose) and unreasonable burner designs are taken as potential major factors that favoring the asymmetric combustion formation in down-fired boilers. To determine the boiler nose's role in this aspect and weaken the boiler nose's effect, two boiler nose's depth shrunk settings of C_L = 0.199 and 0 were compared with the large design setup C_L = 0.298 within a 600 MW_e supercritical down-fired boiler. Numerical simulations on coal combustion were carried out for all three settings, plus full-load industrial-size measurements at the boiler's design setup. The boiler's design setup shows badly asymmetric combustion with poor burnout and high NO_x emissions, corresponding to its reported, severely deflected gas/particle flow field. Shrinking boiler nose attains limited improvements (such as shortening the front/rear downward coal/air penetration difference, redirecting a little the upward gas flow towards the upper furnace central part, and shrinking the gas-flow stagnation zone below boiler nose), but unfortunately, essentially fails to change the flow-field deflection pattern and meanwhile decreases the gas fullness in the upper furnace's top zone to generate a potential threat on steam parameters. The absence of effective improvements in asymmetric combustion and apparently shortened flame penetration finally develop a worsened burnout, decreased O₂ at the furnace outlet, and lowered NO_x emissions as C_L decreased. Findings in this work thus exclude boiler nose as a potential major factor that favoring the formation of flow-field deflection and asymmetric combustion and meanwhile, provide useful information that under the circumstances with a short upper furnace aggravating the asymmetric upper furnace configuration effect, a relatively large boiler nose should be used for maintaining (i) the boiler nose's suppression effect on the upward gas flow and (ii) gas fullness in the upper furnace's top zone.