Experimental investigations into gas/particle flows in a down-fired boiler: Influence of down-draft secondary air

Down-fired boiler operations suffer problems of high carbon content in the fly ash. This is because horizontally fed secondary air restrains the fuel-rich flow from penetrating into the lower levels of the furnace. Experiments were conducted on a small-scaled furnace for a down-fired pulverized-coal 300 MW _eutility boiler on a gas/solid two-phase test facility. Modifications to the furnace permitted secondary air to be directed downward giving five different F-tier secondary air angle settings. Investigations at various settings were performed to obtain distributions of the mean velocity, root-mean-square (rms) fluctuation velocity, particle size, particle volume flux, and particle number concentration within the furnace. Results show that, with increasing angle settings, greater depths were attained for both air and particles within the furnace and slip velocities also increased between air and particles. At a 25°angle setting, the particle residence time in the furnace can be increased, while slagging within the furnace hopper can be avoided.