Phenomenon: 

1. The temperature of exhaust gas is abnormally higher than the feed water flow.

2. The negative pressure of the flue and hearth changes acutely. 

3. The hot air temperature rises and exceeds the specified value. 

4. Blake gas emits from the chimney  (without ESP). 

5. Spark emits from the place of the flue that has not been sealed strictly. 

6. In serious case, the explosion door of flue acts.  

Causes: 

1. The induced draft air amount is  too large and the negative pressure is too large. 

2. The cyclone separator is not normal, a lot of un-burnt fuel is carried into the flue. 

3. The air volume is not sufficient or the air distribution is not reasonable. 

4. Low load operation time is too long, the gas speed is too low, and a lot of combustibles accumulate in the flue. 

Treatment: 

1. If the gas temperature abnormally rises, firstly the causes shall be ascertained and the accuracy of the instrument indication shall be verified. 

2. Highlight the combustion adjustment to maintain stability of combustion. 

3. Keep the operation parameters stable. 

4. If the temperature of the exhaust gas is over 190 ℃, the instruction shall be asked for disconnecting the ESP, if the exhaust gas temperature continues to rise to 220 ℃, immediately stop the boiler, close the damper baffles and the hole doors.

5. When the temperature drops, and confirm there is no fire, the induced draft fan can be started for ventilation for 5-10 minutes to exhaust the accumulated ash and then restarted.