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• A novel low-NO x technology is proposed for a down-fired boiler with swirl burners. • Gas/particle flow characteristics are studied under two combustion technologies. • Downward depth of gas/particle flows improves for the improved boiler. • Primary air is effectively ejected by burner secondary air for the novel technology. • Turbulent intensity in the recirculation region increases for the improved boiler. To confirm the validity and progressiveness of the eccentric-swirl-secondary-air combustion technology (ESSACT) in improving the economic and environmental performance of the down-fired boiler (DFB) with swirl burners, the gas/particle (GP) cold-modelling experiments are conducted by using a particle dynamic analyzer (PDA) measurement system in a 1:10 scale model of 300-MW e DFB applying original Babcock & Wilcox combustion technology (BWCT) and novel ESSACT, respectively. The distributions of average velocity, fluctuation velocity and particle size are compared and analyzed under the two combustion technologies in this study, in addition to the decay of particle volume flux and the jet trajectory of downward GP flows. In comparison with the BWCT, the rotation intensity of the burner secondary air is greatly weakened, and the vertical velocities of downward GP flows decay more slowly under the ESSACT. Although the recirculation regions are both formed below the arches under the two combustion technologies, the horizontal velocities and the horizontal fluctuation velocities of GP flows in the recirculation regions are both larger for the ESSACT, which benefits pulverized coal ignition. The particle size distributions under the two combustion technologies reveal that the mixing between the primary air and burner secondary air is obviously delayed and the burner secondary air effectively ejecting the primary air downward is realized by the ESSACT, which is advantageous to improve pulverized coal burnout and inhibit NO x formation. In addition, the maximum particle volume flux in the lower part of the lower furnace under the ESSACT is obviously higher than that under the BWCT, and the downward depth of GP flows and the space utilization ratio in the lower furnace increase for the original BW DFB retrofitted by the ESSACT. [ABSTRACT FROM AUTHOR]

Fuel rich/lean combustion is an important means of reducing NO x in coal-fired boilers. The mass ratio of pulverized-coal in fuel-rich flow to that in fuel-lean flow (MRL) is a key parameter in fuel rich/lean combustion that affects the gas/particle flow characteristics and in turn the coal ignition and NO x formation. In this work, using a 1:40 scale model furnace and a particle dynamics anemometer measurement system, the effects of various MRLs (6:4, 7:3, 8:2 and 9:1) on the gas/particle flow characteristics in a 600 MWe down-fired boiler incorporating multiple-injection and multiple-staging were studied. The results demonstrate that airflows injected from the front-arch burners flow downwards along the front wall and then turn upward in the furnace center zone, forming a U-shaped flow pattern. Increasing the MRL significantly raises the maximum particle volume flux under the fuel-rich flow nozzle, which favors advanced pulverized-coal ignition and improves the fuel rich/lean combustion in the boiler. The velocity decay of the downward gas/particle flow is also accelerated. The particle volume flux in the hopper zone is gradually reduced while the location of the maximum particle volume flux gradually moves away from the hopper declined wall. This scenario avoids the downward flame flushing the furnace hopper and prevents both hopper wall overheating and tube bursts in the actual down-fired boiler. Based on these results, an MRL of 9:1 is recommended as optimal. [ABSTRACT FROM AUTHOR]