1. The MFT acts and alarms is given. 

2. All the coal feeders trip, and the ignition system is removed, and the fast closing valves of fuel-oil are closed. 

3. The bed temperature and bed pressure drop. 

4. The steam temperature and steam pressure drop, and steam flow reduces sharply, and the steam drum water level drops firstly and then rises. 

Causes: 

1. The removing buttons of main fuel of two boilers are pressed at the same time. 

2. The bed temperature is higher than 1050 ℃ ( the signals come from the combustion control system). 

3. The pressure of outlet of the hearth is high high level +2500 Pa ( select two from three). 4. The pressure of outlet of the hearth is low low level -2500 Pa ( select two from three). 

5. The water level of boiler drum is high high value ( higher than normal water level by 250mm) ( select two from three). 

6. The water level of boiler drum is low low value( lower than the normal water level by 200mm) ( select two from three). 

7. The induced draft fans all trip. 

8. The primary fan trips. 

9. The returns fans all trip. 

Treatment after MFT acts: 

1. Because of the failure of induced draft fan, the primary and secondary fan trip and DCS system, it can be treated according to the following principles: 

(1) Regulating the rotating speed of the fan in order to maintain normal negative pressure of boiler hearth. 

(2) Adjust the flow of feed water in order to keep the water level of steam drum normal.

(3) Quickly indentify the causes of acting of MFT. 

(4) If the causes of acting of MFT are difficult to identify or eliminate in a short time, the boiler shall be stopped and the boiler shall be in hot standby state. 

(5) If the causes of acting of MFT can be identified and eliminated, the boiler operation can be recovered when the hot start is pressed. 

(6)If the boiler is stopped due to re-combustion at tail flue, ventilation is forbidden and the running of all the fans shall be stopped. 

2. If the failure is caused by the tripping of induced draft fan, the primary and secondary fan trip and DCS system, in condition to treating according to the above principles, the local accumulation and fluidizing and stagnating of the bed materials shall be considered. 

The Phenomenon is as follows: 

(1) The display value of one or more bed temperature differs greatly with that of other bed temperature. 

(2) All the display value of bed pressure is static readings( the normal display value of bed pressure is fluctuation reading). 

3. Checking steps of the material fluidization:

(1) Adjust the air volume of boiler to manual operating mode. 

(2) Quickly increase the rotating speed of the primary air fan, to make the air flow of the primary air fan exceed the fluidization air volume, and then recover to normal fluidized air volume, observe whether the display of bed pressure returns to normal or not. 

(3) If there is not effect after the above mentioned methods have been repeated for three times in 10 minutes, the further measures of discharging the bed materials shall be taken to fluidize the bed materials until the satisfied effect is reached.