The Deposit Formation Mechanism in Coal-Fired Rotary Kiln for Iron Ore Pellet Production: A Review

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.

Research on the ring formation mechanism of magnesian flux pellets in rotary kiln

“…Production processes of pellets mainly included shaft furnace, belt roaster and grate rotary kiln 7 – 9 . Grate rotary kiln was compatible with a variety of fuels for heating 10 . Moreover, China is rich in coal resources, with an output accounting for about 60% of total pellet production 11 .…”

Influence of Solid Waste Material Content on the Properties of Steel Slag-Waste Clay Brick Ceramic Bricks

“…With the increase in WCB content, the water absorption rate of ceramics initially exhibits a significant decrease followed by a slight increase within a narrow range. This phenomenon can be attributed to the relatively high concentration of alkali metal elements in the ceramic body at low WCB content, resulting in excessive liquid phase formation during sintering and leading to the over burning of ceramic tiles [39]. Consequently, this results in higher water absorption rates and lower fracture modules.…”

Effects of Pellet Basicity on the Simulated Deposit Formation in Coal-Fired Rotary Kilns for Iron Ore Pellet Production

“…The characterization of the deposits showed that the main mineralogical phases include hematite, silicate, and some minor glass phases. − Some studies have found differences in the mechanism of deposit formation in different parts of the rotary kiln. , The primary manner to form the deposits near the burner zone in the rotary kiln was the hematite crystallization and diffusion, while the liquid phases played a secondary role in the deposit formation. Furthermore, bentonite and coal ash contain high SiO 2 , Al 2 O 3 , Na 2 O, and K 2 O, which will promote the generation of liquid phases and intensify the deposition phenomenon. ,, In addition, insufficient combustion of pulverized coal caused partial zones of the reduction atmosphere in the rotary kiln, resulting in the generation of Fe 2+ , and formed low-melting-temperature compounds with veinstone minerals such as SiO 2 and CaO Al 2 O 3 . − It has been found that the deposition phenomenon became more severe in rotary kilns for producing fluxed iron ore pellets. , Unfortunately, the effects of the basicity of iron ore pellets on the deposition formation mechanism are still not fully understood. Thus, it is necessary to study the deposit formation mechanism during the production of fluxed iron ore pellets by the grate-kiln process.…”

“…27−29 It has been found that the deposition phenomenon became more severe in rotary kilns for producing fluxed iron ore pellets. 30,31 Unfortunately, the effects of the basicity of iron ore pellets on the deposition formation mechanism are still not fully understood. Thus, it is necessary to study the deposit formation mechanism during the production of fluxed iron ore pellets by the grate-kiln process.…”