Study on Gas/particle Flows in a Down-Fired Boiler with Swirl Burners: Influence of Different Outer Secondary Air Vane Angle

Abstract

The gas-solid multi-phase flow is measured in a 300MW down-fired bolier cold model with swirl burners by two-dimensional phase Doppler velocimetry(PDA), concluded the influence of different outer secondary air vane angles on the multi-phase flow characteristics in the furnace. For vane angles of 25°, the vertical direction average velocity is high and fluctuating velocity is low, the reach of the downward airflow is deeper, primary air and secondary air mix slowly, the horizontal direction average velocity is high and fluctuating velocity is low, solid phased particles spread slowly and mix with the rewind air weakly, this is against to the ignition of pulverized coal. For vane angles of 35°, the vertical direction average velocity decrease and decay faster, fluctuating velocity increase slightly, the horizontal direction average velocity and fluctuating velocity increased slightly, solid phased particles spread quickly and mixed with the rewind air quickly, the ignition of pulverized coal increase. For vane angles of 55°, the recirculation zone appear in the burner nozzle region, the vertical direction fluctuating velocity increase significantly, average velocity decrease and decay quickly, the downward airflow turn upwards before mixing with gas, the horizontal direction average velocity high and fluctuating velocity is higher, solid phased particles spread more quickly, mixed with the rewind air more quickly, this will erode the water wall and throat, cause the water wall slagging. Considering various factors, the best outer secondary air vane angle is 35° in the operation of boiler.