Analysis on the existing problems and countermeasures of boiler low-nitrogen burner after renovation
- Author:Shenzhen Zhongli Weiye Electromechanical Equipment Co., Ltd.
- Origin:Shenzhen Zhongli Weiye Electromechanical Equipment Co., Ltd.
- Time of issue:2021-05-28 14:41
Analysis on the existing problems and countermeasures of boiler low-nitrogen burner after renovation
In recent years, my country's environmental pollution has been serious, and smog has caused a certain degree of impact on all aspects of people's life and work. Under the strict requirements of the national environmental protection policy, power companies attach great importance to energy conservation and emission reduction, and formulate and implement reasonable and effective measures. For a long time in the future, my country will still mainly use coal-fired generator sets to generate electricity, but the boilers of many power generation companies cannot meet the current national environmental protection requirements. Therefore, coal power generation enterprises must comply with the national
Boiler optimization and transformation shall be carried out according to the required pollutant emission limit, and a series of environmental protection measures shall be actively adopted. Boiler renovation adopts low-nitrogen combustion technology, which can not only greatly reduce NO emissions, but also improve the stability and safety of boiler work, while saving costs.
1. Status of NO governance
The harm of NO, the formation mechanism of NO in the combustion process of coal-fired power generation and the technology of reducing NO have been fully studied at home and abroad , which can be divided into three types: thermal NO, fuel NO and fast NO; among them, fuel NO. Type NO accounts for about 80-90%, which is the main object of various low-NO technology control; followed by thermal type, mainly due to the local high temperature in the furnace, the amount of fast type NO generated is very small. The control method of NO can be divided into treatment before combustion, treatment during combustion and treatment after combustion. Pre-combustion denitrification refers to the conversion of fuel into low-nitrogen fuel, which is complicated in technology, difficult and costly, so it is currently in the research stage; denitrification in combustion mainly includes: one is to inhibit the formation of NO in combustion, and the other is to reduce the formation of NO. NO; post-combustion denitrification mainly refers to flue gas denitrification: including selective catalytic reduction, selective non-catalytic reduction, etc.
At present, it has been recognized by everyone and has been widely used in various coal-fired unit boilers. TheNO reduction method is mainly the low-nitrogen combustion technology of denitrification during combustion and the flue gas denitration technology of denitrification after combustion; denitrification during combustion is based on The low-nitrogen combustion technology adopted for the formation mechanism of NO is mainly: low-oxygen combustion, air staged combustion, fuel staged combustion, flue gas recirculation, etc. The main mechanism of this technology is to arrange the burners vertically to form redox, main reduction, There are three burnout zones. For a four-corner tangentially fired boiler, two zones, the near-wall zone and the central zone, can be formed by the horizontal double zone arrangement, so that fuel and air distribution can be divided, classified, low-temperature, and low-oxygen combustion in the furnace to reduce coal consumption.NO production during powder combustion.
2. Analysis of the problems and causes after the application and transformation of low-nitrogen combustion technology
The application of low-nitrogen combustion technology in a large number of coal-fired boilers in power plants has proved that this technology is very effective in reducing NO production. However, in actual work, due to the different types of coal used in boilers and different boiler models, the amount of NO produced is also different, and the resulting problems are also different.
2.1 Increase in ash and slag combustibles, resulting in reduced furnace efficiency
After the modification of the low-nitrogen burner, the production of NO is greatly reduced, but when the same type of coal is used, the increase in the combustible matter of fly ash is also larger. The main reason is that the low-nitrogen combustion technology uses a low-temperature and low-oxygen combustion method, the temperature of the main combustion area will drop a lot, and the ignition of pulverized coal will be controlled and delayed, and the amount of oxygen in the ignition area will be reduced, so that the pulverized coal is burned. The ember capacity is reduced, the combustion process is prolonged, and the fly ash and slag are more combustible. During the renovation of some boilers, the area of the primary and secondary air nozzles and the burnout air nozzles of the burner has changed, resulting in a delay in the mixing of the primary air and the secondary air, which is not conducive to the ignition and combustion of the pulverized coal airflow.
2.2 The steam parameters deviate from the design value, the amount of desuperheating water increases or the reheater overheats
After the boiler adopts the air-classified low-nitrogen combustion technology, on the one hand, the combustion is delayed, the flame center moves up, the flue gas temperature at the furnace outlet rises, and the superheated steam temperature and reheated steam temperature of the boiler rise. The problem that the temperature exceeds the design value is exacerbated, and the amount of overheating and dewarming water increases.On the other hand, the temperature of the main combustion zone decreases, and the temperature distribution in the furnace is more uniform. The contamination and slagging of the original furnace water wall will be improved. The water wall absorbs heat, the furnace outlet flue temperature decreases, and the superheater temperature The temperature rise of the reheater increases and the temperature rise of the reheater decreases. For the original problem of the superheated steam temperature and the low reheated steam temperature, the over-design value cannot be reached.
After the transformation of the low-nitrogen combustion technology, there are many problems that the amount of desuperheating water in the boiler superheater increases. Due to the longer process of pulverized coal combustion and the use of exhausted air, the temperature of the flue gas at the furnace outlet becomes higher. When the temperature of the furnace becomes lower, the radiant heat absorption of the water wall of the furnace will decrease, and the heat absorption of the heating surface forming convection will increase, which will increase the amount of desuperheating water in the superheater.
2.3 The internal combustion environment of the boiler is deteriorated, and the coal blending, air distribution and combustion stability become lower
Due to the use of low-temperature and low-oxygen combustion, the temperature of the furnace will drop, and the pulverized coal will be delayed to catch fire in the low-temperature and oxygen-deficient environment, and the ability to burn into ashes will also be weakened, and the combustion environment in the boiler will be worse than before the transformation.
The coal blending and air blending methods used before the boiler renovation are largely inapplicable, which will not only affect the various indicators of the boiler, but also reduce the ability of the boiler to stabilize combustion under low load.
2.4 The adaptability of the boiler to the type of coal becomes worse
After the retrofit of the low-nitrogen burner, vigorously optimizing and adjusting the combustion can well match the NO emission level and the boiler economy to a large extent. However, when the coal type of boiler changes, it will break the balance between the economic indicators and environmental indicators of the boiler at the beginning. If coal with high calorific value and high volatility is used, the emission concentration of NO will increase slightly, but it is easier to adjust and control; Difficult to control.
3 Coping strategies for the problems existing after the transformation of the boiler low-nitrogen burner
At present, the transformation of low-nitrogen burners in boilers of coal-fired power plants has not been completed, and the problems in the application of this technology are gradually exposed. In view of the existing problems, the following solutions are proposed :
3.1 Adequate assessment before retrofitting
Various emission indicators of boilers are very important, especiallythe emission concentration of NO is closely related to coal type, boiler selection, and burner type. For boilers in operation, the furnace type has been determined, but in recent years, coal-fired power plants have Therefore, before using the low-nitrogen combustion technology for transformation, the existing main coal types and commonly used coal types of the boiler should be fully evaluated. In the feasibility demonstration, due to the improper selection of coal types, there are many cases where the effect of NO emission reduction after the transformation is not obvious and new problems are caused. The second is to conduct a thorough test of the boilers in operation to fully evaluate the combustion performance, steam In terms of parameters, heating surface wall temperature, coking and slagging, operation adjustment, thermal automation, etc.,the scientific and reasonable transformation expectations are put forward, and the economic indicators and environmental protection indicators of the boiler are weighed to gradually solve the existing problems and prevent new problems from appearing.
3.2 Optimizing and adjusting, using scientific combustion methods
After the boiler's low-nitrogen burner is transformed, the type of the burner has been determined, but under different conditions of the boiler, the amount of NO produced by burning different types of coal will also be different. It can be seen that the operating mode of the boiler plays a leading role. . Therefore, in order to reduce NO emissions, the combustion method must be optimized and adjusted, and the operating economy should be taken into account to the greatest extent under the premise of meeting the environmental emission requirements.
3.2.1 Mixed combustion of stratified coal blending in the boiler
In the case of ensuring that the concentration of the exhaust gas meets the environmental protection requirements and the combustion is stable, the most economical coal should be used, and the stratified combustion in the furnace can not only ensure the stability of the boiler, but also control the production of NO.
3.2.2 Automatic control to optimize thermal
After the transformation with low nitrogen technology, the fuel combustion time in the boiler becomes longer, so the thermal control system and control curve should be optimized and adjusted. According to the problems that occur in the actual work of the boiler, the required control curve and control system should be optimized to improve its response capability under load.
3.2.3 Continuous combustion optimization adjustment
After the transformation of the low-nitrogen combustion technology of the boiler, in addition to the type of coal used, it is mainly related to the operation mode of the boiler. To explore and optimize, according to the optimization and adjustment test of boiler combustion, when the coal quality changes greatly, it generally takes nearly two months of adjustment to find out the law that takes into account both environmental protection emission indicators and operational economic indicators. Therefore, continuous combustion optimization and adjustment is essential.
It took a short time to transform the low-nitrogen burner of the boiler, and the problem was not fully exposed. At the same time, our understanding of the problem was not enough, and the experience in dealing with the problem was not enough. In order to alleviate the environmental protection pressure of coal-fired power plants and reduce the reduction of NO. Emission technology needs to be further researched and developed to reduce the environmental protection pressure of power plants. More importantly, the ability to deal with problems caused by the application of new emission reduction technologies and environmental protection facilities should be further improved, so as to contribute to the sustainable development of coal-fired power plants. Strive for greater environmental benefits.
Shenzhen Zhongli Weiye Electromechanical Equipment Co., Ltd., on the basis of absorbing domestic and foreign advanced technology and craftsmanship, has accumulated many years of wisdom and experience in burners, and the accuracy, stability and reliability of products are in an important position in China. Our company produces Zhongli Weiye brand burner has been gradually upgraded from the first generation product to the current third generation product, and is still developing higher-end products. It is an advanced ultra-low nitrogen burner enterprise in China.With advanced technology, excellent quality and perfect service, our company's products are in the forefront of the domestic super-burner industry and have become a well-known domestic brand. The leader, with innovation as a means, actively explores domestic and foreign markets .