Comminution Theory of Superfine Pulverized Coal Based on Fractal Analysis of Aggregate Structures

Liu, Jiaxun; Zhang, Hai; Liu, Jianguo; Jiang, Xiumin

doi:10.1021/acs.energyfuels.6b02097

Cited by 14 publications

(6 citation statements)

References 52 publications

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“…Huffman et al found that thiophene sulfur could be converted completely into sulfate; namely, the sulfur compounds could be thoroughly cleaved during electrochemical oxidation. In terms of biological desulfurization, the 4S pathway of sulfur-specific dibenzothiophene degradation has been widely accepted. − Although the conditions mentioned above are different from the superfine comminution, similar significant chemical microstructure changes due to the mechanochemical effect like free radicals, aromatic sheets, carbon skeletons, etc., have been observed for superfine pulverized coal. ,, In addition, during the process of comminution, continuous exertion of stress can promote the damage of chemical bonds and thus reduce the reaction energy barriers. Then, both ring opening and chain dissociation are possible by the mechanical stretching of molecules. ,, Therefore, the C–S cleavages in thiophene are possible during the superfine comminution.…”

Section: Results and Discussionmentioning

confidence: 99%

“…56−58 Although the conditions mentioned above are different from the superfine comminution, similar significant chemical microstructure changes due to the mechanochemical effect like free radicals, aromatic sheets, carbon skeletons, etc., have been observed for superfine pulverized coal. 32,59,60 In addition, during the process of comminution, continuous exertion of stress can promote the damage of chemical bonds and thus reduce the reaction energy barriers. Then, both ring opening and chain dissociation are possible by the mechanical stretching of molecules.…”

Section: Resultsmentioning

confidence: 99%

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Chemical Properties of Superfine Pulverized Coal Particles. Part 4. Sulfur Speciation by X-ray Absorption Near-Edge Structure Spectroscopy

et al. 2020

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Exploring the transformation mechanisms of sulfur during the superfine comminution plays a crucial role in constructing a coal macromolecular model and developing clean coal technologies. In this work, the occurrences of sulfur in raw coal were quantitatively analyzed by X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS). The sulfur forms in two typical rank coals were compared, and the influence of particle size on the transformation of sulfur was elucidated. Furthermore, the mechanochemical effect on sulfur speciation during the superfine comminution was focused on. The final results indicate that HN coal contains more thiophene with ring structures, while sulfate is the dominant sulfur form in NMG coal. In addition, pyrite can be easily oxidized to sulfate and elemental S, while sulfide, sulfoxide, and sulfone are susceptible to transformation to thiophene during the coalification. It is worth noticing that during the superfine comminution, the organic sulfur shows a decreasing trend, while the inorganic sulfur shows the opposite, suggesting that a conversion from organic to inorganic sulfur exists due to the mechanochemical effect. In addition, two conversion pathways of sulfur are concluded, i.e., sulfide → sulfoxide → sulfone and thiophene → sulfoxide → sulfone → sulfate, which further elucidate the sulfur transformation mechanisms in coal. As the particle size decreases, there is an evident decline for sulfide and thiophene, while pyrite, elemental S, and sulfate generally increase. As for sulfoxide and sulfone, different tendencies are observed in HN and NMG coals due to the complex oxidation processes. The combined application of XANES and XPS is recommended for better characterization of the sulfur speciation and distribution due to the different probing depths in coal particles. This research provides a comprehensive understanding of the mutual transformation between organic and inorganic sulfur in coal. The elucidation of sulfur migration pathways can further promote the exploitation of more valuable desulfurization methods.

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Section: Results and Discussionmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Chemical Properties of Superfine Pulverized Coal Particles. Part 4. Sulfur Speciation by X-ray Absorption Near-Edge Structure Spectroscopy

et al. 2020

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“…The cleavage reaction is dominant, leading to the cracks of aromatic pieces in small HN coal, which decrease the g values. On the contrary, the coalescence reaction prevails in NMG coal that has more donable aliphatic chains with high activity, 32 and thus, the delocalization of electrons over aromatic rings rather than aliphatics increases the g values in small particles. In addition, the comminution-induced stronger oxidation effect introduces the dominant oxidative environment in NMG smaller coal, increasing g values of Lorentzian 1 and 3 components with the decline of particle size.…”

Section: Methodsmentioning

confidence: 99%

“…In addition, as depicted in Figure 4b, with the decline of particle size, there are generally decreasing tendencies of g values for coal extracts, except for the scattered NMG-thfl, which is due to the ultra-low extraction effect. The comminution-induced coalescence reaction contributes to higher aromaticity of small coal particles, 32 which introduces the decline of Gaussian-and Lorentzian 2-type g values with decreasing particle size. In addition, the small molecules like methoxybenzenes accumulated in small coal particles are susceptible to the solvent extraction, which lowers the g values of Lorentzian 1 and 3 types.…”

Section: Methodsmentioning

confidence: 99%

Solvent Extraction of Superfine Pulverized Coal. Part 2. Free-Radical Characteristics

2021

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To better explore coal macromolecular models from the extraction aspects, the behaviors of free radicals during the solvent extraction of superfine pulverized coal were studied. The electron paramagnetic resonance (EPR) method was employed to characterize the extracts and extraction residues (ERs) from the pyridine (PY) and tetrahydrofuran (THF) extraction processes. The EPR parameters of different paramagnetic centers were analyzed through the peak deconvolution, and the detailed extraction mechanisms were discussed. The result suggests that the particle size and polarity of the reagent have the combined influences on the free-radical characteristics during the extraction process. Compared to the raw coals (rcs), the free-radical concentrations of the ER show a similar level, while these are 1 order of magnitude lower for the extracts (about 6 to 9% of rcs). In addition, PY with higher polarity is prone to attack the non-covalent interactions like hydrogen bonds, which can extract more abundant molecule components connected by charge-transfer forces, resulting in 35.42% higher spin concentrations compared to the THF extracts. On the other hand, THF with an affinity with oxygen-containing groups can loosen the coal structure, which extracts more stable oxygenated compounds. In addition, THF can effectively target the π–π interactions, and the paramagnetic centers on these aromatic clusters can be better preserved due to the steric hindrance effect. The study sheds light on better elucidation of coal macromolecular structures, which provides support on better understanding coal pyrolysis and liquefaction behaviors.

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“…Coal fragmentation has a great influence on the physical characteristics (e.g., mechanical, wetting, adsorption, and permeation properties) and the chemical reactivity (e.g., reaction rate) and affects the coal conversion and utilization processes, 1 such as coal devolatilizaiton. The devolatilizaiton is a complex physical and chemical process during the initial stage of coal combustion.…”

Section: Introductionmentioning

confidence: 99%

Primary Fragmentation Behavior Investigation in Pulverized Coal Combustion with High-Speed Digital Inline Holography

Lin

Yao

et al. 2019

Energy Fuels

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Comprehension on the primary fragmentation of coal particles is important in understanding and optimizing practical coal combustion and creating credible combustion models. High-speed digital inline holography (DIH) at 6000 Hz is employed to investigate the primary fragmentation of China Ximeng lignite (90−154 μm) during coal devolatilization. The particle morphologies, 3D trajectories, and size evolutions of the parent coals as well as the corresponding fragments are captured by time-resolved holographic visualization. Three fragmentation modes, fragmentation at the particle center, exfoliation/fragmentation at the outer zone, and a hybrid fragmentation mode of both, are observed in this study. The particle morphologies show distinct appearances under the three different fragmentation modes. It is found that the pressure resulted from the volatile products inside particle under the mode of fragmentation at the particle center will accelerate or decelerate the fragments. Statistical result on particle sizes on the recorded 26 coal particles undergoing fragmentation indicates that small particles formed because of coal fragmentation, which occupy 17.1% in the range of 26−40 μm. It is also concluded that the flame temperature and particle residence time during coal devolatilization have an obvious influence on the possibility of coal fragmentation in the operating condition and target research region. Digital inline holography is demonstrated to be capable of in situ three-dimensional (3D) measurement of particle fragmentation during coal devolatilization.

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Comminution Theory of Superfine Pulverized Coal Based on Fractal Analysis of Aggregate Structures

Cited by 14 publications

References 52 publications

Chemical Properties of Superfine Pulverized Coal Particles. Part 4. Sulfur Speciation by X-ray Absorption Near-Edge Structure Spectroscopy

Chemical Properties of Superfine Pulverized Coal Particles. Part 4. Sulfur Speciation by X-ray Absorption Near-Edge Structure Spectroscopy

Solvent Extraction of Superfine Pulverized Coal. Part 2. Free-Radical Characteristics

Primary Fragmentation Behavior Investigation in Pulverized Coal Combustion with High-Speed Digital Inline Holography

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