Experimental investigation of gas/particle two-phase flow characteristics in a down-fired boiler by PDA measurements

Abstract

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-MWe 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 NOx 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.