The Design And Optimization Study Of A350MW Supercritical W-shaped Boiler With Impellerless Flat Burner

The research object is a new-designed350MW supercritical down-fired boiler,and using FLUENT software to get the reasonable burner arrangement and operationparameters.At the beginning, three kinds of burner type were arranged. The first type is thevent air nozzles located near the furnace center. The secondary type is vent airnozzles located near the primary air nozzles and the primary air nozzles located nearthe furnace center. The third burner arrangement type adopted the"multiple-injection multi-stage combustion" technology. By analyzing the results ofnumerical simulation, and took the comprehensive consideration of flow field andtemperature field in furnace, the third one is the suitable burner arrangement type.When the burner arrangement type is settled, four conditions of differenttertiary air angle0°,10°,20°and30°were arranged. With the increase of tertiary airangle, the impact of the ejector enhanced, and then the downstream depth increase,which will promote the pulverized coal combustion. With the increment of tertiaryair angle, the flame center of the furnace down, the flue gas temperature of the lowerfurnace increased, and then the furnace outlet flue gas temperature decrease. At thesame time, the oxygen content of the lower furnace decreased. When the tertiary airbeing0°and10°, the depth of flow fluid is short, and then will cause a shortresidence time for coal particles in the furnace, which will reduce the burnout rate.When the tertiary air increased to30°, the downstream scoured the front and rearwalls and hopper. So ultimately determine the reasonable tertiary air angle is20°,and we suggest not to exceeding30°.Under the reasonable tertiary air angle, four research conditions were set on thecondition of the certain sum of tertiary air and secondary air58.89%, change thesecondary air wind at a rate of15%,25%,28.35%and35%. With the increase ofsecondary air rate, high temperature furnace flame center fell down, and thepulverized coal particles were extended, and then the furnace outlet flue gastemperature was reduced, while O2concentration of outlet of the furnace and NOxconcentration changes small. When the secondary air rate is15%, the arch airflowwith weak rigidity cannot organize reasonable combustion in the certain furnacespace. When the secondary air being35%, the flame has a deep depth, therefore fluegas temperature is higher, which is easy to cause cold ash hopper slagging. Overallconsideration, the suitable secondary air ratio is28.35%.Under the optimized parameters, high temperature area appears in the center of the furnace; the arch airflow can shot to the central area of the hopper, and formedthe symmetrical temperature field, velocity field and atmosphere field; thetemperature and oxygen concentration in the area of front and rear walls and thehopper is low, which can effectively prevent slagging. Therefore under theoptimized parameters, the furnace can organize better combustion.