Research On Mitigating High Temperature Corrosion Of Furnace Water Wall For 1000 MW Dual Tangential Boiler

In order to respond to China’s policy of energy conservation and emission reduction and reduce NO_x emissions from coal-fired power plants,large boilers widely use deep staged combustion technology.But his technology makes the main combustion area of the furnace in a strong reducing atmosphere,causing serious high-temperature corrosion of the water wall of the furnace,endangering the safe and stable operation of the boiler.Therefore,under the premise of ensuring low NO_x emissions,reducing the corrosion of the furnace water wall has important safety significance and economic benefits.Aiming at the problem of high temperature corrosion in the hot corner area of the dual tangential boiler,this paper takes a1000 MW ultra-supercritical dual tangential boiler as the research object.Starting from the idea of reducing the concentration of reducing gas near the water wall,numerical simulation methods are used to carry out the following work:Simulation and verification of the corrosion situation of the target boiler,research on mitigation of high temperature corrosion of furnace water wall based on combustion optimization,research on mitigation of high temperature corrosion of furnace water wall based on near-wall air technology,research on coordinated combustion optimization and combination of near-wall air to mitigate corrosion.In the simulation and verification of the original working conditions of the target boiler,the distribution characteristics of the furnace flue gas velocity field,temperature field and gas component field and the distribution of the corrosion area are analyzed.The results show that there is a considerable proportion of the corrosion area on each wall.The total corrosion area obtained later is 840.40 m~2,accounting for 24.30%of the entire furnace inspection area.Anoxic combustion and flue gas deflection in the main combustion area are the main reasons for high temperature corrosion in the hot corner area of the dual tangential boiler.The accuracy of the numerical simulation is verified from the three aspects:Corrosion area,gas composition of measuring hole and furnace outlet parameters.Based on the combustion optimization technology,five combustion optimization schemes(variable excess air coefficient,variable SOFA volume,variable primary and secondary air ratio,variable secondary air vertical ratio,and variable secondary air horizontal ratio)are designed.The water wall corrosion area,combustion conditions and furnace outlet parameters of the working conditions change.The results show that the combustion optimization technology has limitations in mitigating the high temperature corrosion problem.It can only reduce the limited area of the corrosion area,and will lead to an increase in NOx emissions at the furnace outlet.However,the regular triangle air distribution and increasing cold corner secondary air not only have a certain anti-corrosion effect,but the corrosion area is also reduced to 759.02 m~2 and 764.08 m~2 respectively.Meanwhile,the NO_x emissions at the furnace outlet slightly is increased by 20.9 mg/m~3 and 6.4 mg/m~3 respectively.These two schemes can be combined with the near-wall wind scheme to jointly mitigate the high temperature corrosion problem of the furnace.Based on near-wall wind technology,a set of near-wall air layout scheme was designed according to the corrosion area,and the corrosion mitigation effects,effects on combustion and furnace outlet parameters of different air intake methods and air volumes were explored.The results show that both the near-wall air taken from SOFA and the secondary air of the furnace can effectively mitigate the high temperature corrosion,and the anti-corrosion effect of the near-wall air taken from SOFA is slightly better for the same wall-mounted air volume.If the near-wall air is taken from SOFA,when the near-wall air rate is less than 3.24%,the pulverized coal burnout effect becomes better as the adhering air volume increases;when the near-wall air rate is greater than 4.17%,the pulverized coal burnout effect increases with the near-wall air volume increasing.The NO_x emissions at the furnace outlet increase with the increase of the near-wall air volume.If the near-wall air is taken from the secondary air of the furnace,with the increase of the near-wall air volume,the burnout effect of pulverized coal will become worse,resulting in a gradual increase in the CO and combustible content at the furnace outlet,and a continuous decrease in NO_x emissions at the furnace outlet.In the research on corrosion mitigation of the coordinated combustion optimization and the combination scheme of near-wall wall,the coordinated combustion optimization technology is based on the working condition of SOFA whose near-wall air rate is 4.17%.The results show that the optimal combination scheme of near-wall and combustion optimization can further improve the anti-corrosion effect.The working condition combines the two combustion optimization methods,the regular triangle air distribution and increasing cold corner secondary air,which has the best anti-corrosion effect,reducing the total corrosion area to 23.09 m~2,which is only 2.75%of the original working condition,accounting for less than 1%of the entire inspection area,basically eliminating the corrosion area.At the same time,the working condition also has a high pulverized coal burnout rate and low pollutant emissions,the fly ash combustible content is only 0.271%,and the NO_x mass concentration is only 256.3mg/m~3.