Low nitrogen combustion retrofit and operation optimization adjustment of boiler in thermal power plant
The emission of nitrogen oxides (NOx) in the process of low nitrogen combustion poses a threat to the ecological environment and human health. By adopting professional methods to carry out low nitrogen combustion transformation and operation optimization adjustment of the boiler, NOx emission can be effectively controlled, production efficiency can be improved, and environmental and ecological problems can be reduced. This paper briefly analyzes the current situation of low nitrogen combustion technology, and puts forward the transformation scheme and optimized operation process of low nitrogen burner.
China attaches great importance to the emission of air pollutants from thermal power plants and has issued various laws, regulations and prevention policies. In addition to considering economic benefits, thermal power plants also consider environmental issues in the development process, consider how to reduce the emission of air pollutants, and propose effective implementation methods. In fact, the transformation of power plant boiler can effectively control NOx emission, reduce environmental and air pollution, and achieve environmental benefits and objectives.
1、 Current status of low nitrogen combustion technology.
Reducing NOx emission can effectively control air pollution. In terms of production process, low nitrogen combustion technology is mainly used, with flue gas denitration as auxiliary. Among these factors, the generation mechanism of nitrogen is related to low nitrogen combustion technology, and the main components are low oxygen combustion and flue gas recirculation. The burners are arranged longitudinally to promote the formation of three plates in the oxidation-reduction zone, the main reduction zone and the burn-out zone. This process can also place the burners in appropriate positions according to different boiler conditions, so as to facilitate the combustion of organic dyes and air distribution in the boiler at low temperature and low oxygen, and achieve zoning and classification, so as to effectively control the NOx emission, so as to achieve a good clean combustion effect.
2、 Transformation scheme of low nitrogen burner.
1. Select burner.
According to the actual needs, a scientific low nitrogen burner transformation plan is formulated as a reference to optimize it. Horizontal and vertical thick and thin burners are widely used in China. The former is mainly used to separate the pulverized coal in the horizontal direction and separate its concentration from its dilution, which is widely used in the desulfurization work in the furnace. In the desulfurization work in the furnace, the jet is inclined to the center of the furnace, which has a strong effect of direct entrainment and air bag coal. The vertical bias burner is the same as its principle, but the use process is the opposite. It is mainly responsible for the vertical pulverized coal separation, and the implementation effect is very good. The selection of burner type should not be blind. In addition to isolating the thick and thin pulverized coal in the furnace, the separation ratio and various parameters should be fully understood. It is strictly prohibited to have low nitrogen residue in the furnace.
2. Transformation of main burner.
For the transformation of the main burner, not only the standard height of the main burner should be determined, but also the positions of the air ducts and bellows of the four bellows should be fixed scientifically, and all nozzles and elbows should be replaced to ensure that all components can meet the standard. The last layer is in the form of an axially inserted plasma burner. It can also convert the remaining primary air burner into a thick and thin burner, which can be concentrated at the top and diluted at the bottom or concentrated at the bottom and diluted at the top. In this context, the use effect of high heat-resistant steel plate is good. The secondary air nozzles in the middle of the fourth layer are kept closed, and the remaining secondary air nozzles are replaced. The arrangement of the wall air nozzles should also be considered to ensure that there is sufficient oxygen on the surface layer of the water wall, so as to avoid excessive furnace temperature due to insufficient oxygen, resulting in excessive furnace temperature, slagging and corrosion. In addition, the remaining secondary air nozzles need to be changed to make the jet direction change, and the angle of the primary air and other secondary air nozzles should be controlled in order to fully mix the oxygen-deficient fuel in the early stage and the oxygen supply in the later stage.
3. Scientific design of OFA nozzle and secondary air.
Although the boiler combustion system is relatively complex, the OFA nozzle has a relatively simple structure and is widely favored in the industry. In practical application, it is necessary to apply OFA nozzle again on the basis of the original system, give full play to its advantages, take into account the tangency, effectively control the air flow in the furnace, and make the furnace outlet temperature normal. Assuming that the original OFA nozzle size, wind speed setting, air volume and other indicators can not meet the requirements of low-nitrogen combustion technology transformation, the heat-resistant version can be directly blocked, and it can also be subject to secondary transformation. A large proportion of secondary air is arranged at the upper end of the burner, which is conducive to the classification of air in the furnace, reducing nitrogen oxides, and enabling the boiler to fully burn. In the secondary air design, the location and area of the burnout zone should also be considered.
3、 The optimized operation scheme of nitrogen combustion.
1. Optimize and adjust the boundary wind of primary and secondary air.
The change of air flow has a certain impact on the concentration of nitrogen oxides. If the air flow is too large, the furnace oxygen content and the concentration of nitrogen oxides are low. According to the adjustment of the operation status of each power supply and the comparison of air distribution methods such as positive and negative pagoda, it can be seen that the air distribution operation of negative pagoda produces less nitrogen oxides and has no impact on the atmosphere. Starting from the equivalent indicators of nitrogen oxides and boiler combustion efficiency, the secondary air opening of each layer shall not exceed 70%, and the secondary air opening of the upper layer and the weekly opening of each layer shall be between 35% and 15% - 20% respectively.
2. Adjust the burner swing angle and burnout air.
It is very important to study the formation of nitrogen oxides in the process of low nitrogen combustion and to adjust the burner swing angle and burnout air. Adjusting the swing angle of the burnout air to make the furnace tilt upward can not only avoid the deviation of the furnace temperature on both sides, but also obtain a better swing angle and shorten the operation time. The optimized adjustment of the burnout air is to increase the area of the burnout air baffle according to the specific operation conditions while stabilizing the total composition of the boiler, so as to effectively control the emission of nitrogen oxide and fly ash parameters.
3. Adjust the oxygen content in the furnace.
In fact, scientifically adjusting the oxygen content of the furnace can also optimize the operation process of low nitrogen combustion. Control the oxygen content of furnace gas to avoid the generation of excessive nitrogen oxides. Under the condition of low oxygen content, a small amount of nitrogen oxide will be produced in the furnace. The experimental results show that if the oxygen content in the furnace is too low, the combustible of fly ash will increase. Therefore, the oxygen content in the furnace should be controlled scientifically between 2.5% and 3.5%. While effectively controlling the emission of nitrogen oxides from thermal power plants, the boiler combustion efficiency should also be considered.
4. Conclusion
The low nitrogen combustion transformation project of thermal power plant boiler has high technical content, high technical standards, high professional requirements and complex implementation process, which can significantly improve the boiler combustion efficiency, effectively control the emission of nitrogen oxides, and improve the daily work and service quality of thermal power plant. With the improvement of environmental awareness, relevant employees should protect the quality of the ecological environment, upgrade and transform the low nitrogen combustion of the boiler according to the external conditions, make it meet the requirements of process production and social development, improve equipment performance, and achieve production and environmental benefits.