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

Crystals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 974
Author(s):  
Shuai Wang ◽  
Yufeng Guo ◽  
Kuo Liu ◽  
Zhuang Yang ◽  
Yajing Liu ◽  
...  
Keyword(s):  
Liquid Phase ◽  
Alkali Metal ◽  
Alkali Metals ◽  
Iron Ore ◽  
Coal Ash ◽  
Pulverized Coal ◽  
Efficient Production ◽  
Material Base ◽  
Deposit Formation ◽  
Rotary Kilns

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.

Corrosion of Superheaters and Reheaters of Pulverized-Coal-Fired Boilers, II

1961 ◽  
Vol 83 (4) ◽  
pp. 468-474 ◽  
Author(s):  
Carl Cain ◽  
Wharton Nelson
Keyword(s):  
High Temperature ◽  
Liquid Phase ◽  
Gas Phase ◽  
Coal Ash ◽  
Pulverized Coal ◽  
Corrosion Mechanism ◽  
Fireside Corrosion ◽  
Factors Affecting ◽  
Ferritic Alloys ◽  
Tube Metal

This paper deals with studies of high-temperature fireside corrosion of reheater and superheater tubes in pulverized-coal-fired boilers. Factors affecting the temperature range and rate of corrosion by molten complex alkali sulfates are described. The influence of sulfides, produced by reaction of complex sulfates with tube metal, on corrosion rate is discussed. The similarity of coal-ash to oil-ash corrosion mechanism is brought out. Methods for distinguishing liquid phase from gas-phase corrosion on ferritic alloys are presented.

Experiment and Mechanism Study on the Effect of Coal Ash on the Capture of Alkali Metals in Zhundong Coal

2017 ◽  
Author(s):  
Hu Xinglei
Keyword(s):  
Alkali Metal ◽  
Quantum Chemical Calculation ◽  
Quantum Chemical ◽  
Alkali Metals ◽  
Coal Ash ◽  
Maximum Efficiency ◽  
Chemical Calculation ◽  
Reaction Interface ◽  
Zhundong Coal ◽  
High Alkali

A large number of Xinjiang Zhundong coal was found in China. Its high content of alkali metals can cause serious fouling/slagging problems which may lead to economic losses. It is significant to control the release of alkali metals from Zhundong coal during the combustion. Si-Al additives are used to capture Na released from the Zhundong coal. In this work, a combination of experimental research and quantum chemical calculation was used to study the effect of coal ash on the capture of alkali metal in Zhundong high alkali Coal and the related mineral evolution mechanism during melting processes. The experiments were done with Zhundong coal/coal ash mixtures at 900–1200°C. The behavior mechanism of coal ash capturing alkali metals was analyzed from the perspective of mineral microstructure features by using XRD, ICP and quantum chemical calculation methods. The results show that during the process of combustions, complex chemical reactions occur among minerals after sodium is released from the coal and captured by the coal ash. The coal ash’s ability to capture sodium in Zhundong high alkali coal rises firstly, and then gradually decreases with the rise of temperature. It shows the best capture performance for sodium at 1000∼1100°C. The maximum efficiency of sodium absorption can reach to 50.6%. The coal ash shows a rather high efficiency compared with other additives. Furthermore, metals in Zhundong coal have opposite directions of migration. The Na, K, Al, Ca, and Mg migrated to the coal ash far away from the reaction interface, and the Fe and Mn were moved to the coal from the reaction interface. The original minerals of Zhundong coal mainly include calcium sulfate hydrate, quartz and kaolinite. Investigating the capture mechanism, it indicates that O (26) and O (22) in kaolinite have electrophilic reaction with Na+ and K+ easily, which would promote the rupture of aluminum-oxygen bonds. The O2- of alkali metal or alkaline earth metal oxide would easily have nucleophilic reaction with Si (6) and Si (8) and prompt the rupture of bridging oxygen bonds (Si-O-Si). Kaolinite would be transformed into some other minerals that contains Na+ or K+ which have trend to form eutectics or evaporate into the flue gas easily, the degree of fouling and slagging on heating surface can be reduced based on these two most easily reaction paths.

Combustion Reaction of Pulverized Coal on the Deposit Formation in the Kiln for Iron Ore Pellet Production

2016 ◽  
Vol 30 (7) ◽  
pp. 6123-6131 ◽  
Author(s):  
Shuai Wang ◽  
Yu-Feng Guo ◽  
Feng Chen ◽  
Yu He ◽  
Tao Jiang ◽  
...  
Keyword(s):  
Iron Ore ◽  
Pulverized Coal ◽  
Combustion Reaction ◽  
Deposit Formation ◽  
Pellet Production ◽  
Iron Ore Pellet

Room Temperature Alkali Metal Reduction of Carbon Dioxide

2020 ◽  
Author(s):  
Lucas A. Freeman ◽  
Akachukwu D. Obi ◽  
Haleigh R. Machost ◽  
Andrew Molino ◽  
Asa W. Nichols ◽  
...  
Keyword(s):  
Alkali Metal ◽  
Alkali Metals ◽  
Room Temperature ◽  
Chemical Reduction ◽  
Bond Cleavage ◽  
Open Shell ◽  
Metal Reduction ◽  
One Pot ◽  
Earth Abundant ◽  
Electron Reduction

The reduction of the relatively inert carbon–oxygen bonds of CO<sub>2</sub> to access useful CO<sub>2</sub>-derived organic products is one of the most important fundamental challenges in synthetic chemistry. Facilitating this bond-cleavage using earth-abundant, non-toxic main group elements (MGEs) is especially arduous because of the difficulty in achieving strong inner-sphere interactions between CO<sub>2</sub> and the MGE. Herein we report the first successful chemical reduction of CO<sub>2</sub> at room temperature by alkali metals, promoted by a cyclic(alkyl)(amino) carbene (CAAC). One-electron reduction of CAAC-CO<sub>2</sub> adduct (<b>1</b>) with lithium, sodium or potassium metal yields stable monoanionic radicals clusters [M(CAAC–CO<sub>2</sub>)]<sub>n</sub>(M = Li, Na, K, <b> 2</b>-<b>4</b>) and two-electron alkali metal reduction affords open-shell, dianionic clusters of the general formula [M<sub>2</sub>(CAAC–CO<sub>2</sub>)]<sub>n </sub>(<b>5</b>-<b>8</b>). It is notable that these crystalline clusters of reduced CO<sub>2</sub> may also be isolated via the “one-pot” reaction of free CO<sub>2</sub> with free CAAC followed by the addition of alkali metals – a reductive process which does not occur in the absence of carbene. Each of the products <b>2</b>-<b>8</b> were investigated using a combination of experimental and theoretical methods.<br>

scholarly journals Spotlight on Alkali Metals: The Structural Chemistry of Alkali Metal Thallides

Crystals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 1013
Author(s):  
Stefanie Gärtner
Keyword(s):  
Crystal Structure ◽  
Alkali Metal ◽  
Crystal Structures ◽  
Alkali Metals ◽  
Valence Electron ◽  
Oxidation States ◽  
Valence Electron Concentration ◽  
Base Metals ◽  
Charge Balancing

Alkali metal thallides go back to the investigative works of Eduard Zintl about base metals in negative oxidation states. In 1932, he described the crystal structure of NaTl as the first representative for this class of compounds. Since then, a bunch of versatile crystal structures has been reported for thallium as electronegative element in intermetallic solid state compounds. For combinations of thallium with alkali metals as electropositive counterparts, a broad range of different unique structure types has been observed. Interestingly, various thallium substructures at the same or very similar valence electron concentration (VEC) are obtained. This in return emphasizes that the role of the alkali metals on structure formation goes far beyond ancillary filling atoms, which are present only due to charge balancing reasons. In this review, the alkali metals are in focus and the local surroundings of the latter are discussed in terms of their crystallographic sites in the corresponding crystal structures.

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