Phenomenon: 

1. The steam pressure and steam temperature drop. 

2. The hearth temperature drop. 

3. The air pressure of returns increases and the air pressure of returns decreases. 

4. The differential pressure of hearth drops. 

5. The boiler load sharply rises.

6. The ash cannot be discharged. 

Causes:

1. The heat resistant and wear-resistant materials in the cyclone separator fall off and block the ash-returning device. 

2. The air proportion ratio of air for returns and for loosening is not equal. 

3. The returns feeder and standpipe for returns are blocked, so the ash-discharged is too less, large amount of ash escapes from the central tube of the separator, thus causing serious wear of internal wall of central tube, 

4. The ventilation hood inside the returns feeder, the materials are poor fluidized. 

5. The coking at the return feeder is mainly because that the bed temperature in the main combustion chamber is too high and the circulation material fluidizing flow rate is too small. There shall be not air leakage inside the return feeder, otherwise the fluidizing flow rate of circulating materials significantly decreases, thus making the temperature inside the returns feeder rise and coke. 

Treatment: 

1. Adjust the upper and lower valves for air proportioning of air for returns, in order to make air amount proper and boiling normal. 

2. Manually dredge the blocking of the cyclone separator and ash storage bin to maintain normal ash-discharging. 

3. Adjust the air distribution ratio of air for blowing  and loosening of the returns feeder in order to  achieve satisfactory result of returns. 

4. Adjust the materials-discharging amount from the returns feeder and ash-returning storehouse channel, to keep smoothly materials discharging. 

5. After the temperature inside the boiler drops, adjust the coal-feeding amount and main the returns circulation normal.