Influence of the Outer Secondary Air Vane Angle on the Flow Field of a Down-Fired Pulverized-Coal 300 MWe Utility Boiler with Swirl Burners

摘要

Using an IFA300 constant temperature anemometer system, cold air experiments on a scale model of a down-fired pulverized-coal 300 MWe utility boiler with swirl burners were performed to investigate the influence of outer secondary air vane angles on the flow characteristics in the furnace. For a vane angle of 20°, the reach of the downward airflow is deep and the mixing with vent air and staged air is good, thereby favoring coal combustion but at the expense of airflow washing out at the entrance of the upper furnace. For vane angles of 25° and 30°, the reach of the downward airflow is short, mixing with the staged air weakens, and thus, the recirculation zone below the arches is small, although washing out at the entrance ceases. For a 35° vane angle, the reach of the airflow further shortens and the mixing of the airflow and vent air is weaker. At even larger vane angles of 40° and 50°, the recirculation zone appears in the burner nozzle region and the airflow is directed upward near the burner nozzle region, creating a short flame circulation. Considering all of the above, conditions with a vane angle setting in the range of 25° and 30° are considered as optimal in the operation of the boiler.