Abstract
The deposit-forming problem is one of the main bottlenecks restricting the yield and production benefit of iron ore pellets produced by coal-fired rotary kilns. In order to implement measures to ensure the efficient production of pellets by coal-fired rotary kilns, the mechanism and influencing factors on the deposit formation were reviewed. The pellet powder and coal ash come together to form the material base of the deposit. Meanwhile, the local reducing atmosphere caused by the continued combustion of residual carbon increases the FeO content, resulting in the formation of low-melting-point silicates. Moreover, alkali metal elements in coal ash can also promote liquid phase formation to cause serious deposit aggregation problems. During high-temperature roasting, the liquid phase corrodes the surface of the refractory brick to form the initial deposit, whereafter, it binds the pellet powder and coal ash from the material layer, which causes the deposit to accumulate continuously. The deposit formation of coal-fired rotary kilns is the result of interaction between many factors, which includes the quality of the green pellets, the composition of coal ash, the combustion efficiency of pulverized coal, roasting temperature, FeO content and alkali metal input. Finally, it is recommended that some measures to mitigate deposit formation can be adopted, such as increasing the compression strength of preheated pellets, choosing high-quality raw materials with low alkali metals, improving the combustion of pulverized coal.
Highlights
As an important component of ironmaking charge, pellets are characterized by their high grade, uniform particle size, better strength and metallurgical performance than natural lump ores and sinters; the advantages in environmental protection and energy conservation are especially obvious [1]
Based on the previous work carried out by our research group, this paper summarized the formation mechanism and influencing factors of deposit formation in a coal-fired rotary kiln, and put forward the prospect of the development direction to prevent deposit forming
The residual coal ash produced by pulverized coal combustion is driven air to the kiln tail, which makes the deposit in the K4-K7 region contain more c components, while the chemical composition of the deposit in the K1-K3 region is to pellets
Summary
As an important component of ironmaking charge, pellets are characterized by their high grade, uniform particle size, better strength and metallurgical performance than natural lump ores and sinters; the advantages in environmental protection and energy conservation are especially obvious [1]. The incomplete burnt pulverized coal containing residual carbon and a large amount of coal ash was mixed with preheated pellet powder, which would produce local reducing atmosphere to form low-melting-temperature compounds by residual carbon combustion during the roasting process [9,10]. These compounds are usually composed of Fe, Ca, Si, Al, K and Na, which have melting temperatures below 1673 K [11] and melt into the liquid phase in the high-temperature region of the rotary kiln [12,13].
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