--- The following actions would be accompanied along with MFT:
1.Main feeding material is cut off.
2.The limestone system is cut off.
3.The under-bed ignition system is cut off.
4.All the air flow control should be changed to be manually, and the last position should be kept.
5.Unless the air fan is cut off by itself, all the air fans should be changed to be of manually controlled, and the last position should be kept. Under the premise that the air fan cut off by itself, the air fan would follow the logical control procedures.
6.The automatically controlling of the induced draft fan would be limited by the output signal of the combustion controlling, make sure that the furnace pressure would not exceed the limited.
7.Unless the boiler is in hot state and it is restarted, the logic of “the specified boiler blowing” would be established.
8.The time and reason for the MFT action is printed by printer.
--- All the following conditions would cause MFT:
1. The MFT bottom is pressed.
2. The bed temperature is higher than 1050℃ (the signal comes from the combustion controlling system).
3. The logic controlling power is off.
4. One of the two logic controlling indicates that the outlet pressure of furnace is too high +2500Pa (delay).
5. One of the two logic controlling indicates that the outlet pressure of furnace is too low -2500Pa (delay).
6.One of the two logic controlling indicates that the drum water level is too high (250mm higher than the normal water level) (delay).
5.One of the two logic controlling indicates that the drum water level is too low (200mm lower than the normal water level) (delay).
6.The induced draft fan is under voltage trip.
7.The primary air fan and the secondary air fan are under voltage trip.
8.The total air flow is too low, it is less than 25% (with delay) (the signal comes from the combustion controlling system).
9.The power of the combustion controlling system is off (the signal comes from the combustion controlling system).
10.The ratio between the air and the material is less than the minimum value (the signal comes from the combustion controlling system).
11.The bed temperature is lower than 800℃, and the under-bed igniter is under use.
12.The back-feeding air fan is under voltage trip.
13.The steam turbine is cut off.
--- Treatment after MFT
1.If it is not caused by the tripping operation of the induced draft fan, the primary air fan and the secondary fan or not by the DSC fault, it can be treated according to the following principles.
(1) Adjust the air fan damper and maintain the negative pressure of furnace to be normal.
(2) Adjust the water flow and maintain the drum water level to be normal.
(3) Find out the real reason of MFT quickly.
(4) If the reason of MFT cannot be found or the problem cannot be solved for short time, the boiler should be stopped and maintain the boiler in the state of hot standby.
(5) If the reason of MFT is found and it is cleared in short time, the boiler operation could be recovered by hot state starting.
2. If it is caused by the tripping operation of the induced draft fan, the primary air fan and the secondary fan or by the DSC fault, the local bed material accumulation or the fluid stagnation should also be considered except for treating according to the above principles. And the phenomenons are as follows:
(1) The difference between one or several bed temperature indication and other bed temperature indications are relatively large.
(2) All the bed pressure indications are static readings (the normal bed pressure indications are fluctuant reading).
3. Steps for automatic bed material fluidization:
(1) The boiler air flow should be manually controlled.
(2) Open the general door for the primary air quickly, then return it back to the original position and observe that whether the bed pressure indication is normally or not.
(3) If it is still no effect after being repeated for 3 times within 10 minutes, further measures should be taken to start the fluidization of bed material, that is, emission of bed material, until the satisfactory effect is achieved.
(4) Change the boiler air flow adjustment to be automatically.