In case of the following circumstances, the boiler shall be emergency shutdown: 

1. The DCS signal disappears. 

2. The boiler is full of water, the water level exceeds the visible water level of the upper part of the drum water level gauge, but the water level still cannot be seen after emergency draining. 

3. When the tube of the heating surface bursts, and the normal water level of the boiler cannot be maintained. 

4. All the level meters are damage. 

5. The boiler steam and water pipe bursts and threat the safety of equipment and personnel. 

6. The pressure exceeds the acting pressure of the safety valve, but the safety valve does not act, and the depressurization of air bleeding valve is not sufficient or the air bleeding valve cannot be opened. 

7. The returns feeder and combustion chamber of fluidized bed seriously coke and cannot  maintain the operation. 

8. The main rotating equipment is in failure, it endangers the equipment and personal safety. 

9. The fuel re-burns in the tail of the flue , so that the temperature of exhaust smoke rises abnormally.