Influence Of Vaneangle On Flow Field Of A Down-Fired Bioler With Swirl Burners

In China, with the national economy rapidly developing, the societydemands on more and more electricity, so that the capacity of power stationburning lean coal or anthracite leaps quickly. Down-fired boiler specially suits forlarge scale burning lean coal or anthracite power station, because of adoptinglong-flame, air zoning and high concentration factor of pulverized coal. Atpresent, more than eighty down-fired boilers are operating in many Chineselarge-scale power stations. Many operation experiences are accumulated in China,but the research of down-fired boiler is not in-depth enough. Indeed, there are notmany lucubrate results on the down-fired boiler adopting swirl burners.A pilot-scale of 1:4 of a swirl burner used in down-fired boiler and a scale of1:10 of down-fired boiler model with swirl burners were designed and producedaimed at a full-scale utility boiler for cold experimentation by modeling theory.Using an IFA300 constant temperature anemometer system, the air flowcharacteristic of the outlet of the swirl burner and the inner of the furnace werestudied to analyze the influence of different outer secondary air vane angles onthe flow characteristics in the furnace.Using an IFA300 constant temperature anemometer system, cold airexperiments on a quarter-scaled burner model were also carried out to investigatethe influence of various outer secondary air vane angles on the flowcharacteristics in the burner nozzle region. No central recirculation zone appearedfor vane angles of 25°and 32.5°. Most of the pulverized-coal was ignited in theexternal recirculation zone. For vane angles of 45°and 55°, a central recirculationzone could be observed, and air flow rigidity and axial velocities decreasedrapidly.Using an IFA300 constant temperature anemometer system, cold airexperiments on a scale-model of a down-fired pulverized-coal 300 MWe utilityboiler with swirl burners were performed to investigate the influence of outersecondary air vane angles on the flow characteristics in the furnace. For vaneangle of 20°, the reach of the downward airflow is deep and the mixing with ventair and staged-air is good, thereby favoring coal combustion, but at the expense airflow washing out at the entrance of the upper furnace. For vane angles of25°and 30°, the reach of the downward airflow is short, mixing with thestaged-air weakens, and thus the recirculation zone below the arches is small,although washing out at the entrance ceases. The reach of the airflow furthershortens, and the mixing of the airflow and vent air is weaker for a 35°vaneangle. At even larger vane angles of 40°and 50°, the recirculation zone appearsin the burner nozzle region, and the airflow is directed upwards near the burnernozzle 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 asoptimal in the operation of the boiler.