Theoretical And Experimental Study On Protection Against High Temperature Corrosion And Slagging For Water Wall Of 300 MW Low-NO_x Combustion Boiler

The high temperature corrosion and slagging for water wall of low-NO_X combustion boiler occur from time to time,directly endangering the safe and economic operation of the boiler.The high temperature corrosion and slagging for water wall of the boiler is directly related to the burner arrangement and the air distribution mode.Studying the methods of combustion organization adjustment and combustion conditions optimization of the boiler can effectively improve the high temperature corrosion and slagging.Therefore,in this paper,a 300 MW tangential low-NO_X combustion boiler of the power plant was taken as the research object,and the method of combining numerical simulation and experiment verification was used to deeply study the method of protection against high temperature corrosion and slagging for water wall.First of all,in this paper,numerical simulation was performed on the BMCR operating condition after low-NO_X combustion transformation,and the reliability of the model and calculation method was verified by experiments.Based on this,in order to solve the problem of high temperature corrosion and slagging for water wall of low-NO_X combustion boiler,according to the characteristics of the tangential combustion boiler,firstly,two combustion organization optimization design schemes were proposed around reducing the diameter of the imaginary tangential circle,and then numerical simulation was performed.The results of numerical simulation research showed that the tangent circle formed after the optimization of the combustion organization was more regular,which could effectively prevent uneven heating of the heated surface,the reducing atmosphere was significantly weakened,and the risk of high temperature corrosion and slagging was reduced accordingly.The combustion organization was adjusted according to the better one of the two combustion organization optimization design schemes,and the reliability of the numerical simulation results was further verified through experiments.Secondly,on the basis of combustion performance analysis,the effect of variable load on the performance of high temperature corrosion and slagging for water wall was studied.Under BMCR（full load）operating condition,the excess air coefficient was smaller,the NO_X concentration at the furnace outlet was lower,the temperature level in the furnace was higher,the near-wall area had a higher CO concentration,a lower O₂ concentration,and a higher H₂S concentration,and the performance of high temperature corrosion and slagging for water wall was enhanced.At 70%BMCR operating condition,the excess air coefficient was larger,the NO_X concentration at the furnace outlet was higher,the temperature level in the furnace was lower,the near-wall area had a lower CO concentration,a higher O₂concentration,and a lower H₂S concentration,and the performance of high temperature corrosion and slagging for water wall was weakened.Thirdly,because of the strongest performance of high temperature corrosion and slagging for water wall in BMCR operating condition,taking BMCR as an example,the effect of changing the air volume of separated over-fire air on the performance of high temperature corrosion and slagging for water wall was studied.When the SOFA wind rate was 20%,the NO_X concentration at the furnace outlet was 437.1 mg/Nm³,the near-wall area had a lower CO concentration,a higher O₂ concentration,and a lower H₂S concentration,the risk of high temperature corrosion and slagging for water wall was lower.When the SOFA wind rate were 25%and 30%,the NO_X concentration at the furnace outlet were385.6mg/Nm³ and 378.3 mg/Nm³,the near-wall area had a higher CO concentration,a lower O₂ concentration,and a higher H₂S concentration,and the risk of high temperature corrosion and slagging for water wall was high.Considering the performance of high temperature corrosion and slagging for water wall and the performance of NO_X generation,the SOFA wind rate could be set to 25%.Finally,the better one of the combustion organization optimization design schemes was applied in engineering,the SOFA wind rate was set to 25%and the SOFA was arranged in four layers,and used the same coal which used in the original operating condition of the low-NO_X combustion boiler for long-term operation.After four months of operation,the furnace was shut down and found that the high temperature corrosion and slagging for water wall in the same area have been significantly improved,which proved that this combustion optimization can significantly improve high temperature corrosion and slagging for water wall of the boiler.This research was scientific and effective.