What are the causes and treatment methods of slagging on the heating surface of coal-fired boilers?

Influencing factors of slagging on heating surface of boiler

(1) Ash characteristics of pulverized coal

Generally, the softening temperature ST of ash is used as the main indicator of slag formation. Coal with low ash melting point (ST<1200℃) is easy to slag. In addition, the slagging index also includes: silicon ratio, alkali-acid ratio, slagging index, limit viscosity and so on.

（2）Aerodynamic characteristics in the furnace

Improper air flow organization leads to flame center deviation, and the pulverized coal air flow flame adheres to the wall, causing local slagging of the water-cooled wall;

Improper air flow organization, forming flue gas retention vortex area and forming a reducing atmosphere (with CO), reducing the ash melting point and increasing the possibility of slagging.

Excess air coefficient: When the excess air in the furnace is too small, a reducing atmosphere may be generated, and the tendency of slagging will increase accordingly.

（3）Influence of boiler heat load

Boiler design heating load: The greater the heating load intensity, the higher the temperature of the burner area in the furnace, the coal ash reaches the molten state, and the possibility of slagging increases.

Boiler operation load: The higher the boiler operation heating load, the more heat is sent into the furnace and the greater the possibility of slagging.

（4）Influence of coal fineness

Coarse pulverized coal burns for a long time. When the proportion of coarse pulverized coal in the pulverized coal increases, it is easy to cause the flame to prolong and cause slagging on the heated surface at the outlet of the furnace.

Measures to prevent slagging on heated surface

(1) Prevent the temperature near the heated surface from being too high. Furnace design heating load intensity is reasonable, and reasonable furnace temperature is controlled; at the same time, sufficient heating surface is arranged to cool the flue gas to ensure that the molten ash has solidified before being close to the heating surface;

(2) Reasonably organize the airflow in the furnace, the burner layout is reasonable, the first and second air form a good airflow structure, ensure that the flame does not directly wash the heated surface; avoid excessively low air coefficient to produce a reducing atmosphere.

(3) Strengthen fuel management, do a good analysis of fuel ash composition and melting point, try to use design coal; avoid pulverized coal.

(4) Strengthen operation management, adjust combustion status in time, and blow dust and slag in time.