What are the phenomena of afterburning in the tail flue?

Phenomenon 1: The flue gas temperature at the inlet of the boiler air preheater or the exhaust gas temperature rises sharply, exceeding normal values； 2. The temperature of the hot air rises sharply, exceeding normal levels ； 3. There is a monitoring and alarm system for hot spots in the secondary combustion of the air preheater, and the temperature difference between the flue gas at the inlet of the air preheater and the hot air at its outlet decreases or even becomes negative ； 4. Sudden fluctuations in furnace negative pressure ； 5. Re-combustion at the economizer, with abnormally rising temperature at the economizer outlet ； 6. Smoke and sparks may emerge from areas that are not airtight, such as manholes, inspection holes, and soot blowing holes, near the re-ignition point; the flue ducts, economizers or air preheaters’ ash hoppers, as well as the air preheater housings, may overheat and turn red, with a strong sense of thermal radiation present in the area around the re-ignition point. Handling 1: If secondary combustion occurs in the rear flue during boiler operation, the boiler must be stopped immediately; the supply and exhaust fans should be shut down, and all smoke and air dampers must be closed ； 2. Force steam soot blowers in the re-ignition zone to be used for fire suppression ； 3. If combustion occurs again at the economizer, start the electric feed water pump to supply water for cooling at a flow rate of 150 T/H ； 4. If there is re-ignition on the heating surfaces of the air preheater, it can still operate normally; raise the fan-shaped sealing plates, and if necessary, contact the maintenance team to retract all sealing devices in order to maintain normal operation of the air preheater ； The air preheater became stuck, causing the main drive motor and the auxiliary drive motor to trip; in addition to lifting the fan-shaped sealing plate and retracting all sealing devices, maintenance personnel were contacted to manually rotate the air preheater rotor continuously. Steam soot blowing from the air preheater is used to extinguish the fire; if this does not work, fire-fighting water from the air preheater is employed instead ； 5. When the feedwater temperature at the economizer outlet approaches the inlet temperature (re-combustion occurs at the economizer), and when the flue gas temperature at the air preheater inlet, the exhaust gas temperature, and the hot air temperature drop below 80°C, and no more flue gas or sparks emerge from the various manholes and inspection holes, then stop using steam for soot blowing or fire-fighting water. Open the manholes and inspection holes for inspection; once it is confirmed that re-ignition has ceased, open the flue drainage valve to drain the water accumulated in the flue, and then open the smoke and air dampers to facilitate ventilation ； 6. After the furnace has been fully cooled, proceed to the reburning area to check and ensure that there is no damage to the equipment; once all combustible materials accumulated on the heated surfaces have been completely removed, restart the boiler.