Research On Coordinative Optimization Of Low NOx Combustion In A600MW Supercritical Unit

Environmental problem is an important issue relating to the national economy and people’s livelihood. As the requirements for environmental protection are increasingly strict, power plants need to take effective means of reducing NOx emissions. Air-staging combustion technology is widely used as a method for NOx control. However, the application of this approach could increase unburned carbon content in fly ash and enhance the tendency of high temperature corrosion due to the lower excess air ratio in the primary combustion region. Therefore, it is necessary to optimize the boiler operation parameters to reduce NOx emissions and water wall corrosion wastage with higher boiler efficiency at the same time.The paper was based on the experiment on a600MW supercritical pulverized coal boiler which adopted air-staging combustion technology. In order to research the water wall high temperature corrosion,88matrix-type arrangement measuring points were installed on the walls. Flue gas was obtained from the measuring points and the composition of gas was analyzed by flue gas analyzer. As a result, the relationship between O2concentration, CO concentration and H2S concentration near the water wall was found. According to the statistical law of data and the mechanism of high temperature corrosion, the judgment basis for high temperature corrosion was provided to judge the tendency of water wall high temperature corrosion.Under the premise that the judgment basis for high temperature corrosion had been provided, the main boiler operating parameters, including SOFA flow, SOFA running mode, SOFA jet height, furnace oxygen content, coal and boiler load, were changed to investigate the impacts of the adjustment of operating parameters on NOx emissions, boiler efficiency and water wall high temperature corrosion.The boiler operating parameters was coordinately optimized from three aspects of safety, economy and environment protection. Through the coordinative optimization of low NOx combustion, the formation concentration of NOx increased from317mg/m3to376mg/m3, but boiler efficiency increased by about0.4%and reheater cooling water flow decreased by about27.75t/h. Considering the heat loss caused by reheater cooling water, the gross power generation coal consumption reduced by2.3g/kWh or so. Owing to the significant reduction of the reducing atmosphere near the water wall, the risk of water wall high temperature corrosion effectively reduced.Taking out the increment in denitrification cost caused by the increase in NOx concentration, each unit could still save computable cost about10.14million RMB a year after the coordinative optimization of low NOx combustion. So, the coordinative optimization not only had significant direct economic benefits, but also had intangible economic benefits attributed to the reduction of the rist of water wall high temperature corrosion. In addition, the coordinative optimization of low NOx combustion from the three aspects of safety, economy and environment protection could not only respond positively to the national energy conservation and emission reduction policy, but also ensure the security of power supply. Thus, the coordinative optimization also had significant social benefits.