Cause analysis of boiler coking
1.Component damage causes coking
The degree of boiler rotation is related to the combustion airflow, but the experiment shows that the optimal combustion airflow is open airflow. However, the design of the burner is unreasonable and the adaptability of coal ash is poor. When the nozzle of the burner and the concentration distributor of the combustion chamber or pulverized coal are damaged, when the rigidity of the primary wind speed is reduced, resulting in shorter gas flow range, the occurrence of this phenomenon causes the destruction of the normal airflow required by the burner, and the formation of the fully diffused airflow. However, when the air flow leaves the burner, it expands and moves along the combustion wall, which, on the one hand, will lead to local temperature rise of the burner and, on the other hand, will lead to flame brush wall or combustion deflection.
2.Oxygen content
The oxygen content has a great relationship with the smoke temperature at the exit of the boiler furnace. When the oxygen concentration is low, the combustion effect of pulverized coal will be reduced, the burnout time of pulverized coal will be prolonged, and the flame center point will be moved up. The underburned part will be reburned as the airflow reaches the upper burnout area of the furnace. Because the non-rongfen part will burn in the burning-out zone, resulting in a significant increase in the temperature of the burning-out zone. With the reduction of oxygen content and the increase of load, the smoke temperature at the furnace outlet will significantly increase, thus causing coking. Therefore, the content of oxygen has a very big influence on the coking phenomenon of boiler.
3.Wind speed too fast
In general, the designed wind speed of the combustion nozzle of the boiler is 27m /s, and the wind speed of the air pipe is 29m /s. By measuring the inlet wind speed of the coal mill, it is found that the actual wind speed cannot be exactly the same as the designed value, thus leading to the outlet speed of the coal mill pipeline is 25m /s. In this way, the wind speed is 4 m/s lower than the design value, which leads to the increase of the flue gas return flow of the burner, causing the combustion in advance, and thus causing coking. Therefore, the wind speed should be monitored in real time to adjust the wind speed in time to avoid coking.
Improvement measures for boiler coking
1.Design overhaul
When the burner, heating surface and other factors that affect the power in the furnace are reformed, the design coal type and actual ratio shall be taken into comprehensive consideration, and the data analysis and calculation shall be carried out. The design scheme shall be improved through data analysis and calculation, so as to ensure the comprehensive adaptability of the boiler to different types of coal charcoal. When the design of the burner is improved, the boiler should be aerodynamic field test before use, check the installation Angle of the burner, and determine whether the boiler power field meets the design requirements and use requirements. At the same time, the central support components of the burner and nozzle castable and other numerical evaluation, and timely inspection and maintenance of the boiler unit, damaged members to replace or repair.
2.Reduce the swirl strength of the burner
In the process of combustion test, mainly to the nitrogen dioxide burner to consider, study the generation and stability, through contrast experiment analysis, in the process of burning hedge swirl burner not only to consider the stability of nitrogen dioxide and generation, should also be flammability of pulverized coal, the wastage of the burner, burning zone coking phenomenon such as comprehensive consideration. According to the actual situation, adjust the air volume at the position of 100mm to get the best effect.
3.Coal blending
When matching with combustion materials, coal types should be controlled. If mixing with melting point crossover or easy coking varieties, the boiler should be checked constantly. If the boiler has coking phenomenon, the ratio should be adjusted timely, and after cleaning the furnace, it should be mixed again according to the new ratio. In the allocation of pulverized coal proportion, the characteristics of various pulverized coal shall be fully considered, the proportion of pulverized coal shall be reasonably allocated, the proportion shall be timely adjusted according to the actual situation, the way of stratified combustion in the boiler shall be carried out to avoid boiler re-coking.
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