Experimental Investigations into Gas/Particle Flows in a Down-Fired Boiler: Influence of the Vent Air Ratio

To investigate the characteristics of air/particle flow in down-fired boilers, experiments were carried out using a particle dynamics anemometer (PDA) on a two-phase test facility of a small-scaled furnace for a down-fired pulverized-coal 300 MWe utility boiler. The experiments were carried out with four different vent air ratio settings. With these settings, the distributions of the mean velocity and the root-mean-square fluctuation velocity in the furnace were investigated. The results show that too large a vent air ratio will result in shortened fuel-rich flow penetration in the furnace. This results in an insufficient particle residence time in the furnace, which is disadvantageous for fuel ignition and causes burnout. Conversely, too low a vent air ratio leads to the possibility of slagging and high NOx emission. An optimized vent air ratio was chosen.