Study Of Low-NO_x Combustion Technology On A Tangential Boiler And A Down-Fired Boiler

Low-NO_x combustion and flue gas denitrification technology are the main strategies to lower NO_x emission in domestic thermal power units. With the implement of ultra-low emissions standards in coal-fired units, the above technologies are put forward to higher requirements. According to different coal and combustion system, it has important theoretical and engineering significance to study and establish an efficient, safe,economic low-NO_x combustion technology. In this study, a tangentially bituminous coal-fired boiler and a down-fired with lean coal boiler were taken as research objects.On the basis of the boiler characteristics, the numerical simulation study were done in different parameters of burner, secondary air and SOFA(Separated Over-Fire Air), and the effects of combustion and NO_x emissions were analyzed. On the premise of ensure the normal furnace operation parameters to reduce NO_x emissions as far as possible, and the optimal low-NO_x combustion retrofit scheme was put forward.At first, the original boiler conditions were analyzed by numerical method, and compared with the actual operation datum. The results suggested that the model was reasonable. According to characteristics of the tangential boiler, the original burners were replaced by horizontal bias burners, the tangential circle of secondary air was as same as primary air, and appropriate SOFA air rate and location were designed in low nitrogen combustion retrofit project to improve the furnace problems of high NO_x emissions, poor combustion stability and coking seriously. What's more, the NO_x can be reduced further or other combustion parameters can be optimized by adjusting the secondary air distribution and SOFA air jet angle in operation. In Down-fired boiler low-NO_x combustion design, by the comparison of parameters of different tertiary air arrangement,secondary air jet angle, SOFA air rate and angle, the original tertiary air was moved down,the A layer secondary air, tertiary air and F layer secondary air were down dip, and SOFA air was set in the upper furnace in low-NO_x combustion system. Compared with originalcondition, the low-NO_x combustion system could solve the problems of flame downthrust insufficiency, the high flue gas temperature in furnace exit and high NO_x emissions effectively.According to the hot test results after retrofitting, the tangential boiler combustion parameters was stable and furnace temperature distribution was relatively uniform, NO_x emissions were about 220mg/Nm3, a drop of about 65%, fly ash carbon content was between 3% ~ 4% and coking was improved obviously. The Down-fired boiler NO_x emissions reduced about 50%, a slight drop in flue gas temperature and a slight increase of fly ash carbon content, overall boiler efficiency change was not big, and the low-NO_x combustion effect was good.