To decrease operating economy :

1.After the heating surface is slagging, the heat transfer is deteriorated, the gas exhaust temperature is increased, and the heat efficiency of the boiler is reduced.

2. If the burner outlet slags, the airflow will deviate and the combustion will deteriorate, which may increase heat loss of the mechanical incomplete combustion heat loss and the chemical incomplete combustion.

3. If the boiler ventilation resistance increases, the power consumption of induced draft fan and forced draft fan of boiler will increase, thus the auxiliary power consumption rises. 

To affect boiler output: 

1.After the water-cooled wall slags, the evaporation capacity will decrease.

2. If the flue gas temperature at hearth outlet is increased, the temperature of the steam outlet will increase and the temperature of the pipe wall will increase, and the ventilation resistance will be enlarged, these may become the factors to limit the output.

To affect the safety of boiler operation: 

1. After slagging, the flue gas temperature and steam temperature at superheater both increase, in server circumstances, the pipe wall will be overheated.

2.The slagging is often not even, as a result, the heat deviation of superheater is increased, which brings adverse effect on water circulating safety of natural circulating boiler and heat deviation of water-cooled wall of forced circulating boiler.

3. When the slag at upper part of hearth drops out, it may smash water-cooled pipe of cold ash hopper, causing the fire in hearth to go out or the slagging opening to be blocked, and making the boiler stop operating.

4.If the operating time of deslagging is long, the cold air leakage to the hearth will be much more, making unstable combustion and fire going out. 

How to prevent coking in hearth:

1.Reasonbly adjust and mix the coal.

2.Reasonaly adjust the combustion, making flame distribute evenly and to prevent deviating.

3.Ensure proper excess air amount and prevent oxygen –deficient combustion.

4. Avoid overload operation of boiler.

5. Periodically remove ash and coke . 

6.Periodically verify the remote and local opening of primary and secondary damper baffle plate, to confirm the opening shall be consistent. 

7.Ensure the correct installation of burner.

8. Prevent boiler leakage.