Phenomenon of sharply decreasing of load: 

1. The boiler steam pressure rises sharply. 

2. The steam flow rate decreases. 

3. The water level of steam drum rises instantaneously and then rises.

4. The temperature of superheated steam rises. 

5. The indication of voltmeter and ammeter fluctuates.

6. The  indication of electrical load gauge decreases suddenly. 

7. The indication of steam flow meter suddenly decreases.

8. In serious case, the control valve of the drum and the header at the outlet of the superheated steam header acts . 

Causes: 

1. The power system is in failure and generator and system are disconnected. 

2. The main transformer is in failure.

3. The generator is in failure. 

4. The steam turbine is in failure. 

5. The steam consumption of heat user decreases suddenly. 

6. The heating pipe network is in failure. 

Treatment: 

1. According to the load decreasing, reduce significantly the coal-feeding, decrease the primary  air volume properly, maintain the normal combustion of fluidized bed. When necessary, the automatic control of negative pressure of boiler hearth, the automatic control of boiler combustion and the automatic control of water level of drum are adjusted from "automatic " to "manual". 

2. Appropriately reduce the secondary air volume, adjust the air distribution ratio of the upper and lower secondary air. 

3. Appropriately reduce the air volume and air pressure of returns. 

4. If the steam pressure exceeds the limit, it is required to open the air bleeding valve of the superheater and maintain the normal steam pressure of boiler.

5. According to the changes of outlet temperature of the superheated steam, adjust the attemperation water valve of the superheater. When necessary, the main steam temperature automatic control is changed from "automatic" to "manual".

6. According to the indication of steam drum water level gauge, steam flow meter and feed water flow meter, keep the water level of steam drum slightly below the normal water level, for fear that the load of boiler increases. When necessary, the automatic control  of boiler steam drum water level when necessary adjustment from "automatic" to "manual". 

7. If the control valve of the boiler has acted, and cannot back to its seat when the steam pressure of boiler decreases below the working pressure, the measures shall be taken in order to  make it back to its normal position.