Impact Of Tertiary Air Declination Angle On Gas-solid Flow Characteristics In A DBEL Down-fired Boiler

In recent years, down-fired boilers have popularized well in China. However,actual operating results reveal that down-fired boilers suffer similarly from variousproblems. Based on the platform of CFD software Fluent6.3, gas-solid cold statenumerical simulation was performed on a600MW DBEL down-fired supercriticalutility boiler. And the gas-solid flow characteristics at different tertiary airinclination angles within a cold1:40-scaled model for the boiler were accuratelymeasured with a3D-PDA system.It can be found in good agreement by comparing the simulation andexperimental results. These two results both showed that an asymmetric flow field,with the gas/solid two-phase flow near the front wall penetrating much deeper thanthat near the rear wall appeared in the furnace. It’s more likely to slag on the wingand side walls and regions near the tertiary air vents of the rear wall.On the basis of simulation results, impacts of tertiary air declination angle ongas-solid flow characteristics were accurately measured aiming at building asymmetry flow field by inclining the tertiary air. The experimental results ofdifferent angles of0°,15°,30°and45°revealed that an asymmetric flow fieldappeared in the lower furnace and the downward airflow near the rear wall wasdirected upward much earlier than that near the front wall for all four settings.Vertical-velocity component, the decay of the maximum longitudinal-velocitycomponent, particle volume flow and particle number concentration turned to beasymmetric in the measurement cross-sections and the maximum velocity of thegas/solid two-phase flow near the rear wall decayed significantly faster that near thefront wall. As the tertiary air inclination angles increased, the flow-field deflectionbecame weakened but it can’t solve the flow-field deflection fundamentally. Soinclining the tertiary air can’t solve the problem of asymmetric flow fieldeffectively for this600MW DBEL down-fired utility boiler.The main two factors that favor the formation of the flow-field deflection in aDBEL down-fired boiler can be attributed to the asymmetric furnace structure andunreasonable combustion system. Considering great defects in the design of thefurnace structure and combustion system of the DBEL down-fired600MWsupercritical utility boiler, more research should be made further to solve theflow-field deflection.