A Simulation Study Of The Effect Of Combined Closing-to-wall Air On The Corrosive Environment Of Water Wall And The Anlysis Of Anti-corrosion Effect

With the continuous improvement of energy saving and environmental protection requirements of thermal power units,thermal power units continue to develop towards large capacity and high parameters.Although the standard coal consumption of thermal power units is decreasing year by year and NOx emission is getting less and less,the high temperature corrosion of boiler water wall is becoming more and more serious.And the problem of high temperature corrosion of boiler water wall using swirl opposed combustion is particularly serious.In this paper,a new type of closing-to-wall air method and device was proposed for the problem of high temperature corrosion of waterwall side wall which appears in the large capacity power station boilers,the effect of the structure on the the corrosion environment in the furnace was numerically simulated,and the effect of the closing-to-wall air structure on the high temperature corrosion of the water wall side wall was qualitatively analyzed according to the numerical simulation results.Finally,the empirical formula was used to quantitatively predict the corrosion rate drop of the waterwall side wall.The specific work of this paper was as follows:Firstly,taking the boiler with the model of DG1900/25.4-?1 of a power plant as the research object,the corrosion environment of the boiler in 100%BMCR working condition was numerically simulated.The numerical simulation results of furnace velocity field,temperature field,O2 concentration field,CO concentration field,H2S concentration field,SO2 concentration field and NO concentration field in the original working condition were obtained.The causes of the high temperature corrosion of the water wall of the boiler were analyzed in detail based on the simulation results,and the numerical simulation results under the original working condition were compared with the actual operating data.The results showed that the error was within a reasonable range.Secondly,a new closing-to-wall air method and device was developed in this paper innovatively.The secondary air with higher temperature and lower pressure was combined with the compressed air with lower temperature and higher pressure,and then it was injected into the furnace to protect the waterwall of side wall.The numerical simulation and optimization of the operating parameters of the closing-to-wall air device was carried out,the results showed that it met the requirement when flow rate of the compressed air mass is 3kg/s and the flow rate of secondary air mass is 1.5kg/s.The compressed air temperature is increased from 300K to 342.1K,and the secondary air temperature is reduced from 612K to 483.8K.Thirdly,on the basis of the original structure of the DG1900/25.4-II 1 boiler,the closing-to-wall air device was simplified in this paper properly and added it to the original geometric model to realize the three-dimensional numerical simulation of the closing-to-wall air device that extends from the side wall to the furnace with the whole boiler furnace.The simulation results of the corrosion environment of the boiler after adding a layer of combined closing-to-wall air device and adding three-layer combined closing-to-wall air device were compared with the original operating conditions.The results showed that the reducing atmosphere of waterwall side wall of the boiler after adding the closing-to-wall air device was obviously improved,the temperature of the flue gas near the side wall of the water wall was significantly reduced,and the main combustion area of the furnace center was not influenced,while the NO emission was increased.Lastly,by comparing the temperature of the outer wall and the H2S concentration of the water wall side wall before and after the installation of the closing-to-wall air device,the avoidance of the high temperature corrosion effect of the water wall side wall of the combined closing-to-wall device was quantitatively predicted based on the empirical formula.The prediction results showed that the high temperature corrosion rate can be reduced by 34%by reducing the temperature of the water wall,and by reducing the H2S concentration,the high temperature corrosion rate can be reduced by 90%.