Effects Of Air Supply On Flow Characteristics Of 600MW Down-fired Boiler With Swirl Burners

The down-fired boiler has been designed to burn hard coal,and now it has developed into one of the main types of anthracite fired boilers in China.However,many problems have been found in the actual operation of the down-fired boiler.There are many problems in down-fired boiler with swirl burners,such as pulverized-coal ignition,burnout and NOx emission characteristics of the down-fired boiler.When a down-fired boiler with central air swirl burner is mixed with bituminous coal,there are some problems,such as burner nozzle burning loss,SCR inlet flue gas temperature too high and NOx generation too high.In order to master the influence of air distribution on the single-phase flow characteristics of a 600 MW flame boiler with a new combustion organization.By establishing a single-phase cold-modeling experimental system and using a constant-temperature hot wire anemometer to study the air flow characteristics in the down-fired boiler.In this paper,the flow field in the furnace,the downward of the main air flow on the arch and the coupling of multiple complex jets are studied by the method of single-phase cold-modeling experiment,so as to optimize the flow field in the furnace and determine the best angle of staged air and the best OFA ratios.When the staged air downward angle are 0° and 10°,the downward depth of air flows on the arch is short and the flow field is "backward" due to the lifting effect of the staged air.The single-phase cold-modeling experiment of staged air declination results show that the staged air downward angle of 25°,the main air flow on the arch flows down to below Y / Y0 = 0.47,the secondary air under arch,vent air and staged air flow on the arch mix with the main air flow on the arch at Y / Y0 = 0.63,Y / Y0 = 0.19 and Y / Y0 = 0.4,all of which play a strong ejection role,at the same time,the basic symmetrical flow field is formed in the furnace.When the staged air downward angle of the staged air is 40° and 55°,the staged air is not easy to mix with the main air flow on the arch and can not play the role of ejection.Considering the velocity decay of air flows from the arches,the symmetry of flow field in the furnace and the downward depth of air flows at front wall and rear wall sides at different staged air ratio,it is considered that the staged air downward angle is 25° which is more suitable for the actual operation of the boiler.With the increase of the OFA ratios,the downward depth of the main air flow on the side arches of the front and rear walls decreases gradually.When the OFA ratios is 0% and 10%,the flow field in the furnace is symmetrical,and the main air flow on the arch has a large downward depth;When the OFA ratios is 16.3% and 20%,the former shows the sign of flow field deflection,while the latter has good flow field symmetry.In these two conditions,the main air flow on the arch has little difference in the depth of downward,which can reach the area near Y / Y0 = 0.443;At OFA ratios is 25%,the flow field symmetry in the furnace is good,the air volume and wind speed of all levels of air are too small,and the injection effect on the main air flow on the arch is weak.The main air flow on the arch turns upward at the position Y / Y0 = 0.32.When the OFA ratios is 20%,it can not only reduce NOx emission,but also ensure the symmetrical and the downward depth of the main airflow.Therefore,the best OFA ratios is determined to be 20%.