Numerical Simulation Of A Low NO_x Natural Gas Burner

Nitrogen oxide,as the main atmospheric pollutant,has great harm to the environment,with more and more stringent NO_x emission standards in steel industry in recent years,it is urgent to reduce NO_x emission.Compared with other low nitrogen combustion technology,the design of the new low nitrogen burner has more advantages in the economy and operation.In this paper,A low NO_x air multistage burner is studied based on air-staging combustion technology;Fluent software is used for numerical analysis of the burner;In order to prove the accuracy of the numerical model,the burner thermal test was carried out under the same combustion conditions as the numerical simulation;On this basis,numerical model is used to analyze the influence of parameters such as multistage air distribution ratio,different air excess coefficient,air preheating temperature and flue gas circulation amount on the combustion condition and NO_x of the burner.The numerical results show that:（1）when the area of the primary and secondary tuyere of the burner is increased by 20 %,When the ratio of the sum of the first and second stage air volume to the total air volume increases from 15.4 % to 17.8 %,the NO_x concentration decreases from 124mg/m³ to 53 mg/m³（converted into 8 % O₂ concentration）.But the area is increased by 30 %,the NO_x concentration increases to 95 mg/m³,instead of decreasing.While the area of the primary and secondary tuyere is decreased by 20 %,the NO_x concentration increases to 351 mg/m³.Finally,the optimal area of the primary and secondary tuyere is the area which increased by 20 %,in that case,the ratio of primary and secondary air to tertiary air of the burner is 21.68 %,and the NO_x concentration is 53 mg/m³;（2）Reducing the air excess coefficient can also reduce the generation of NO_x.When the air excess coefficient is about 1.1,the production of NO_x is relatively low,which is 53 mg/m³,under the condition of ensuring the full combustion of fuel;（3）The NO_x concentration increases with the increasing of air preheating temperature.When the air preheating temperature increases from 25 ℃ to 700 ℃,the NO_x concentration in the flue gas increases to1221 mg/m³,but the increase of the air preheating temperature can improve the temperature uniformity of the combustion chamber to some extent;（4）When the air is preheated,Adopting the flue gas circulation to reduce the NO_x.With the increase of flue gas circulation volume,the NO_x concentration gradually decreases.When the air preheating temperature is 450 ℃,the ratio of flue gas circulation volume to natural gas flow volume reach to 25:75,and the NO_x concentration can be reduced to less than 130 mg/m³.（5）After preheating the air,the optimal air coefficient will decrease with the increase of preheating temperature.When the preheating temperature is 450 ℃,the optimal air coefficient is 0.9.