1.Characteristics of ash content in fuel:  the melting point of ash content in fuel is low and the ash content is high.

2.Aerodynamic characteristics inside boiler: If the excess air coefficient is too small, the combustion is incomplete, the reducing gas such as CO occurs in flue gas, thus making the melting point of ash reduce and increasing the possibility of slagging. If the excess air coefficient is too big, the flame kernel moves up, which may cause slagging at outlet of hearth. The big difference of air speed of each burner causes the flame to slant, making a certain wall slag. If the turbulent burner tunrs to a certain side, making this side boiler wall slag. The diameter of circle of contact of direct flow burner is big, the angle of flare of turbulent burner will be big. When “Wall-adherence” and “Trimming” phenomenon occur, the slagging will easily occur. 

3.When the air leakage from boiler is severe, air will leak from bottom of the boiler and the flame kernel will move up, so the hearth out will slag; if air leaks from air side of air preheater, then the air supply is not enough. If air leakage from the flue gas is more, then the induced draft fan will be over loaded, and is forced to reduce air supply, thus causing incomplete combustion and increasing possibility o slagging. 

4.If the boiler load is too high, the boiler temperature and hearth outlet gas temperature will rise both, thus increasing the possibility of slagging.