1. Oxygen-deficient combustion, incomplete combustion of coal powder
From curve of oxygen, oxygen run, generally between 3% and 6.0%, can meet the needs of the boiler combustion, and higher carbon content of slag CO concentration no abnormal rise trend at the same time, eliminate the possibility of reducing fire.
The coal powder is thick and incomplete
Through sampling and testing of coal powder, it was found that the coal powder in the system of a, b and c was thicker. The design value of coal powder fineness R90=25%, and the actual R90 is around 30%. After the overhaul in 2011, the screen mesh of the wooden block separator was replaced, which was badly worn in two years of operation. The entry of debris into the coarse powder separator (axial type) affected the separation effect of coal powder. The steel ball of coal mill does not sieve the ball for a long time. There is a large deviation in the opening degree of the baffle of the coarse powder separator due to the impact of coal powder air flow and the overhaul process. The above three conditions are the main reason for the thick coal powder. The coarse coal powder is one of the reasons for the increase of carbon content in slag.
3. Air distribution difference of burner
N burner after modification, the unit in the normal operation of the burner air distribution mode is: a layer and seven secondary air door fully open, two to six layer secondary throttle opening is 50%, SOFA damper according to unit load switch (full four layer burning air door open), to control NOx concentration in 300 mg/m3. After the amount of slag rises, the secondary air doors of the second to the sixth floors are fully opened, and the SOFA air doors of the first floor are always fully closed. The remaining three SOFA air doors are checked according to the load switches of the unit. After 10 days' test, there was no significant change in the carbon content of slag, but the average concentration of NOx increased to 370mg/m3, which basically eliminated the increase in the carbon content of slag caused by wind distribution.
Low nitrogen burner wear
Through the concept of the burner area fire hole found that some low nitrogen pulverized coal burner air roots have Mars, certain areas of low nitrogen combustion chamber wall often appear obvious coke phenomenon, which determine low nitrogen burner wear more serious.
Causes of wear of horizontal thick and light burners: the contact area between the burners and coal powder is generally thinned and partially grinded after being washed by a wind powder airflow. The grinding position is concentrated on the lower end face of the nozzle, which is mainly when the upper end of the primary air nozzle is in operation, when the air flow turns in the joint part of the nozzle and the square pipe, the erosion of the lower end face of the nozzle is intensified. The wear of the blunt body of the nozzle is mainly concentrated on the "thick side", which is related to the high concentration of coal powder (the "weak side").
Endogenous wind membrane type burner abrasion reasons: micro oil ignition burner enrichment separation plant is located in the middle burner, during the operation of small oil gun, coal and oil in internal mixing burner to burn (heat load exceeds the yield temperature of the metal parts), lead to low nitrogen deformation loss items within the burner. N around the burner wear, coking, resulting in pulverized coal air flow disorder, pulverized coal into the center of the flame burning, all can't eventually led to the incomplete combustion loss increase, this is one of the main cause of the high carbon content of slag. It can also explain the increase of carbon content in fly ash.