Research About The Single Flow Performance For A 660MW Down-Fired Boiler With Over Fire Air

China's coal-dominated energy structure will not change in the future for a long period of time, and on the basis of energy consumption structure, most of the coal is used in power generation. In China's total power coal reserves, anthracite and lean coal take up a high proportion for more than 40%, down fired boiler is an ideal boiler for hard-to-burn coal. After the introduction of domestic in 1980s, this type of boiler has been greatly developed in China.In the practical operation of these boilers, there are some problems exist, and relevant departments have carried out some renovation. During the Period of the"Twelfth Five-Year Plan", the emission of nitrogen oxides (NOx) has been brought into the total control indicator system, but there is less research on the problem of NOx emissions for the down fired boilers. This paper is mainly about a low-NOx emission tecnology on down fired boilers.According to the problem of high NOx emissions of down fired boiler in a power plant. A 1:15 small scale model test facility was set up.By means of trajectory experiments,cold single-phase aerodynamic experiments,the optimal OFA air ratio and OFA nozzle angle were investigated.Total air ratio remains unchanged, the affect of the OFA ratio on flow field of lower furnace and region of OFA was investigated.With the OFA ratio increased, the penetration depth of fuel-rich flow decreased. When the ratio was more than 20%, the fuel-rich flow can only reach the upper area of the F–tier secondary air nozzles. With the OFA ratio increased, the OFA flow penetration gradually increased, and when the ratio was 10%, 15%, the jet could not reach the central region of the furnace. When the ratio was 20%, 25%, for the OFA momentum increased, the jet had sufficient rigidity and strength, which could reach the central of the furnace; OFA jet mixed with the upstream air in the centre of upper furnace.Keep the OFA ratio unchanged, when the OFA angle was 15°and 20°, the OFA jet mixed in the furnace centerline ,with the angle increased,the mixing point fell down; When the angle increased to 25°and 30°, with the increase of the angle, the horizontal momentum of OFA jet decreased, so the horizontal penetration decreased and could not reach the center of the furnace, OFA flow and upstream gas could't mix well, In addition, because the angle between the fuel-rich flow and OFA was too small, by the interference of OFA, the fuel-rich flow deflected to the furnace center, the depth of reach for the fuel-rich flow in the lower furnace decreased and the residence time for the coal in the furnace reduced. Taking into account the mixing point of OFA jet with the upstream gas in the furnace centerline, and ensure which should be as low as possible, and guarantee of the penetration depth of fuel-rich flow in the lower furnace, the best OFA angle should be 20°. So we can conclude that the OFA ratio and OFA angle has great influence on flow field of the furnace.