Influnence Of Direct Flow Split Burner Arrangement On Aerodynamic In A Down-Fired Pulverized-Coal Boiler

With the rapid development of the national economy of China, the society demands of more electricity and the capacity of lean coal-fired and anthracite-fired power plants according to the power coal configuration increases quickly. The down-fired boilers could apply to large-scale low-grade coal fired (such as lean coal and anthracite) power plants with characteristics of long flame, air zoning and pulverized coal sectionalized combustion. Although more than eighty down-fired boilers have been on operation or bulding since the year of 1984,. When the technology was imported and abundant operational experience have been accumulated, the research of down-fired boilers is not deep enough especially on the research of the down-fired boiler adopting direct flow split burners.In this thesis, the aerodynamic fields in a 300MW down-fired boiler`s furnace, which is designed by MBEL company. To find why these furnaces are combustion instability, apt to fire extinguishing, slagging seriously in furnace, and later ignition, we studied on the single-phase cold model, which is built on the Similarity Theory in accordance with the ratio of 1:15 and an IFA300 constant-temperature anemometer system was used to measure the air velocity in the model.At angle settings of–10°and–5°, a deflected flow field appears in the lower furnace with the downward airflow near the front wall turns up earlier than that near the rear wall. With increasing the angle from–10°to–5°, the flow-field deflection weakens. At secondary-air angles of 0°and 5°, flow field deflection disappears in the furnace. The difference in the airflow reaches near the front and rear walls are small. At angle settings of–10°,–5°, and 0°, but not 5°, the transverse velocity components washing toward the wall in the region approaching the front and rear walls are large, which may cause slagging on the front and rear walls. For angles of 10°and 20°, the air flows to the center of the furnace, and avoids washing toward the wall, but a different deflected flow field forms. In considering a symmetric flow field and appropriate airflow reach, particularly if slagging is to be avoided on the front and rear walls and in the dry bottom hopper, an optimal angle setting of secondary air was found at 5°.At the arrangement of rich-lean-air, when the tertiary air rates of 0% and 4%, the transverse velocity components washing toward the wall in the region approaching the front and rear walls are large, which may cause slagging on the front and rear walls. With increasing of the tertiary air rate, the transverse velocity components washing toward the wall becomes decrease. When the tertiary air rates of 25%, the dimensionless depth that the downward flow reaches is more than 0.65, the fuel-rich flow penetrates the middle and lower parts of the dry bottom hopper and washes the hopper walls with high velocity particulate that may cause seious slagging. So in considering the appropriate airflow reach, particularly if slagging is to be avoided on the front and rear walls and in the dry bottom hopper, an optimal rate setting of the tertiary air was found at 5°.