Prediction of Coal Primary Fragmentation and Char Particle Size Distribution in Fluidized Bed

Paprika, Milijana; Komatina, Mirko; Dakić, Dragoljub; Nemoda, Stevan

doi:10.1021/ef400875q

Cited by 24 publications

(22 citation statements)

References 26 publications

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“…The volatiles generated close to the center, start to move later, either towards the surface of already opened crack, depending on what is closer. -The existing pores and newly formed cracks are merging and connecting, leading in some cases to the fragmentation [6]. Similar spatial analysis has been conducted before [10,14,15], for example the calculation of Dacombe et al [15] taking into account only the thermal stress.…”

Section: Mechanism Of Primary Fragmentationmentioning

confidence: 85%

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Mechanism of primary fragmentation of coal in fluidized bed

Paprika¹,

Komatina

Mladenovic³

et al. 2016

THERM SCI

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In order to lay a foundation of a credible primary fragmentation model, a theoretical analysis of the thermo-mechanical processes in a devolatilizing solid fuel particle was carried out. The devolatilization model comprises heat transfer, chemical processes of generation of gaseous products of combustion (volatiles), volatile transfer, and solid mechanic processes. A spatial and temporal analysis of the stresses within the particle showed that the radial stress is caused primarily by the pressure of generated volatiles. This stress monotonously decreases from the particle center towards the particle surface, without changing its sign. The tangential stress is caused primarily by the thermal shock. Close to the surface, it changes its sign. In the particle cross-section, the radial stress prevails close to the particle center, whilst the tangential stress is dominant in the surface region. At the points where these stresses exceed the particle tensile strength, cracks occur. Cracks extend tangentially close to the surface, and radially close to the center of the particle.

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Section: Mechanism Of Primary Fragmentationmentioning

confidence: 85%

“…The resulting analysis of the stresses generated in the particle indicates the breakage mechanism and some basic geometric patterns of the primary fragmentation. The presented analysis and discussion were a base to a primary fragmentation model, described elsewhere [6].…”

Section: --------------mentioning

confidence: 99%

Mechanism of primary fragmentation of coal in fluidized bed

Paprika¹,

Komatina

Mladenovic³

et al. 2016

THERM SCI

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“…Primary fragmentation is commonly observed and studied in a fluidized bed combustion system. Many numerical and experimental studies have found that the extent of fragmentation is strongly dependent on the initial size of coal particle and coal ranks. − Various coal ranks can lead to differences in volatile-matter content, the hardness, and the strength of coal particles. Cui et al .…”

Section: Resultsmentioning

confidence: 99%

Influences of Coal Type and Particle Size on Soot Measurement by Laser-Induced Incandescence and Soot Formation Characteristics in Laminar Pulverized Coal Flames

et al. 2020

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This paper discussed the limitation of the laser-induced incandescence (LII) method for the measurement of soot in different laminar pulverized coal flames and explored the soot formation characteristic. Multiple methods, including digital photography, thermophoretic sampling, elastic laser scattering (ELS), and LII methods, were adopted to laboratory-scale laminar pulverized coal flames with different coal types (anthracite, lignite, and bituminous coal) and coal particle sizes (61−90, 90−100, and 100−154 μm). The flame structure, the morphology of dominant particles in different combustion regions, and the spatial distribution of soot and micron-sized carbonaceous particles were obtained and analyzed. The optical measurement and sampling results showed that the soot yield was so low that the LII signal from soot did not dominate in the detection area for anthracite, lignite, and the larger size fraction bituminous coal flames. In particular, a comparison of LII and scattering signals indicated that the vast majority of the LII signal was excited from char and unburned coal for anthracite flame, and char combustion was predominant during the combustion process. Moreover, the coal particles were more dispersed for the larger particle size fraction bituminous coal flames, which favored soot oxidation but did not favor local fuel-rich combustion and the formation of soot. Therefore, in the present study, the soot yield was high enough only in 61−90 μm bituminous coal flame, and the interference LII signal from char or unburned coal particles could be neglected by carefully controlling the laser fluence. It was also found that the LII signal intensity increased as the particle size of the pulverized coal jet decreased in the noncombustion case, which could be explained by the smaller total emission surface area with larger particle size. In addition, the temperature of heated coal particles was also lower as the coal particle size increased, which resulted in the weaker LII signal from coal particles. On the basis of this, a new phenomenon of primary fragmentation of coal particles in pulverized coal flames was observed for the first time by LII measurement, which could provide a potential method for the study of primary fragmentation for coal particles.

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“…Moreover, it is difficult to distinguish the type of luminous particle, such as parent coal particle, fragment and micron-sized soot aggregation. 15,32 classified the fragmentation modes of burning coal particles into three categories: exfoliation, fragmentation at the particle center, and fragmentation at the outer zone. These different modes cause diversity in the particle morphologies and fragmental characteristics.…”

Section: Resultsmentioning

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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Prediction of Coal Primary Fragmentation and Char Particle Size Distribution in Fluidized Bed

Cited by 24 publications

References 26 publications

Mechanism of primary fragmentation of coal in fluidized bed

Mechanism of primary fragmentation of coal in fluidized bed

Influences of Coal Type and Particle Size on Soot Measurement by Laser-Induced Incandescence and Soot Formation Characteristics in Laminar Pulverized Coal Flames

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

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