Discussion on reducing N0x emission index by low nitrogen burner

　　China is a major producer and consumer of coal. At present, coal provides 75% of China's primary energy. In the foreseeable decades, coal will remain the main energy source in China.Coal-fired thermal power is the main component of China's installed power generation capacity, accounting for about 70% of the total power generation capacity.NOx emissions in the power industry are more than 50% of the total NOx emissions in the country, mainly from various coal-fired boilers.NOx emissions from coal-fired power plants have not been effectively controlled.Coal power plant by coal changeful, depth peak adjustment and other external disturbance factors, the boiler NOx excessive, economic decline has become a common problem.At present, there are two methods to reduce NOx emission in flue gas: low nitrogen combustion and flue gas denitration.Among them, low nitrogen combustion in the furnace can reduce NOx emissions in flue gas by more than 50%, and the cost is only about 10% of the flue gas denitrification.Power plant boiler with low NOx combustion technology is a low cost, quick effect and is suitable for the situation of our country, effective measures to control NOx emissions, it includes the low NOx burner technology, low excess air coefficient in the furnace operation, the air gradation combustion technology and grade of fuel burning technology and flue gas recycling technology, etc., at the same time to consider boiler running economy, security, and the optimal combination of NOx removal efficiency.Among them, the classification and grading of fuel air low NOx combustion technology, which is the process of pulverized coal combustion reaction chemical equivalent ratio control at lower levels, and try to reduce the pulverized coal flame temperature, low temperature, strong reducing atmosphere can be formed of pulverized coal burning environment, effectively reduce the nitrogen element in coal to the NO conversion rate and reduce the thermal type NO generation.NOx emissions can be reduced to 250 ~ 280 mg/m3 on 200 ~ 600 MW units burning bituminous coal or lignite.This paper discusses the effect of low nitrogen combustion technology on reducing NOx emission by taking the transformation of low nitrogen burner for 300 MW boiler in datang taiyuan no.2 thermal power plant as an example.Reducing NOx emission by vertical air grading in 1 furnace air grading combustion is one of the most commonly used low NOx combustion technologies.Classification for the basic principle of combustion air: the quantity of air required for the combustion can be divided into two level into the furnace, the main combustion zone excess air coefficient in 0.8 ~ 1, under the condition of fuel in the first burning, burning velocity and temperature is reduced, delayed the combustion process, a large amount of nitrogen in reducing atmosphere group and NOx reaction, improve the NOx conversion rate of N2, reduced NOx generation in this area.The remaining air required for combustion is fed into the furnace chamber through the exhaust air nozzle (OFA) arranged above the main burner. After the exhaust air is fed into the furnace, it becomes an oxygen-rich combustion zone.The air quantity is more, but because of the low flame temperature, and precipitation of most of the nitrogen in the coal group in the main combustion zone reaction has been finished, NOx generation, at the same time, the air into the remaining in the pulverized coal coke burning fully, ensure the high combustion efficiency of pulverized coal, in the end, the vertical air grading combustion inside the furnace can reduce NOx generation 30% ~ 40%.In the use of deep air fractional combustion, because the excess air coefficient in the main combustion area is much less than 1, combustion is carried out in the case of much lower than the theoretical air volume, although conducive to the suppression of NOx generation, but a large number of incomplete combustion products, resulting in combustion efficiency and easy to cause slags and heating surface corrosion.Therefore, it is necessary to properly organize reasonable air fractional combustion, while ensuring the reduction of NOx emissions while fully considering the boiler operation economy and safety reliability.The combination of vertical fractional combustion of air and tint combustion technology can enhance the reducing atmosphere in the main burner area, which is more conducive to the reaction between NO and the reducing n-containing group, improve the reduction rate of NO, and better play the performance of tint combustion technology in reducing NOx emissions.At the same time, the concentrated pulverized coal airflow causes the ignition of pulverized coal airflow to advance, and the residence time of pulverized coal particles increases in the high-temperature combustion area, which is conducive to ensuring the coke in the coal particles to fully burn out.Thin pulverized coal air flow in the lateral concentrated pulverized coal and air flow into the, to ensure the combustion in the main combustion zone overall excess air coefficient is less than 1 reducing atmosphere, but of slagging and high-temperature corrosion of furnace is seen in near wall area for oxidizing atmosphere, raise the melting point of ash particles near wall area, and effectively reduce the near wall area, the concentration of corrosive gas in flue gas, to prevent the high temperature corrosion of furnace slagging and water-cooled wall.In view of the problem of pulverized coal burners wear in the actual operation of the boiler, the pulverized coal burners in the low NOx combustion system transformation project are analyzed