Direct optical observation of coal particle fragmentation behavior in a drop-tube reactor

Friedemann, Jan; Wagner, Andreas; Heinze, Armin; Krzack, Steffen; Meyer, Bernd

doi:10.1016/j.fuel.2015.11.007

Cited by 27 publications

(14 citation statements)

References 20 publications

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“…Fragmentation is reported to be caused either by thermal stresses due to intra-particle temperature gradients [11] or by internal pressure gradients from the volatiles emerging during devolatilisation [11,13] or a combination of both. Literature indicates that vitrinite-rich coals are prone to fragmentation [9,10,12,14] since vitrinite is one of the most brittle coal macerals [15]. Kim et al [14] and Friedmann et al [9,10] investigate the fragmentation behaviour of different coal type particles, and both indicate a higher fragmentation probability for anthracite-like coals (high vitrinite content).…”

Section: Heating Ratementioning

confidence: 99%

“…Kim et al [14] and Friedmann et al [9,10] investigate the fragmentation behaviour of different coal type particles, and both indicate a higher fragmentation probability for anthracite-like coals (high vitrinite content). Moreover, Friedmann et al [9,10] also indicate that fragmentation increases with increasing heating rates. Fragmentation due to thermal stresses significantly depends on the particle heating rates and the physical properties of the coal.…”

Section: Heating Ratementioning

confidence: 99%

“…For Bi below unity, the uniform temperature assumption is valid and only minor temperature gradients occur. Biot numbers of coal particles within the blast furnace raceway zone are around unity directly after injection, depending on the physical coal properties and particle size [10,16,17]. The external pyrolysis number (Py) compares the reaction and heat transfer time scales [31]:…”

Section: Heating Ratementioning

confidence: 99%

See 2 more Smart Citations

Suitability of pulverised coal testing facilities for blast furnace applications

Bösenhofer

Wartha

Jordan

et al. 2019

Ironmaking & Steelmaking

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Identifying coals suitable for blast furnace injection has become increasingly important due to rising injection rates. This review of traditional pulverised coal reactivity testing equipment reveals that no agreed-upon evaluation standard exists and that different reactor types are employed for testing. Therefore, reference blast furnace conversion conditions are defined, followed by a discussion of their influence on the coal conversion process as illustrated by conceptual conversion models. Critical process parameters are temperature, heating rate and pressure, while other effects can be calibrated. Evaluating the currently employed test equipment with regard to these process parameters shows that only specially designed drop-tube furnaces and flow reactors provide conversion conditions near to blast furnace conditions. For consistent injection coal testing, special reactors complying with the previously defined critical process parameters must be established.

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Section: Heating Ratementioning

confidence: 99%

Section: Heating Ratementioning

confidence: 99%

Section: Heating Ratementioning

confidence: 99%

See 1 more Smart Citation

Suitability of pulverised coal testing facilities for blast furnace applications

Bösenhofer

Wartha

Jordan

et al. 2019

Ironmaking & Steelmaking

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“…The fragmentation process of low rank lignite is more severe than that of anthracite, but the crushing process only occurs in the outer layer of the coal particles. Friedemann et al 18 used a high‐speed camera to study the fragmentation behavior of coal particles in a drop tube furnace. They found that increasing temperature and residence time of the particles in the furnace can increase their probability of fragmentation and the larger the particles with the higher probability.…”

Section: Introductionmentioning

confidence: 99%

The behavior of coal slime bursting in early stage combustion and induced pore structure change

Wang

Liu

Yang

et al. 2022

Asia-Pacific J Chem Eng

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To conduct an in‐depth analysis of the bursting of coal slime in its early stage of combustion, a high‐speed camera was used to film the bursting process in a horizontal tube furnace. Three different types of coal slime with water contents of 5%, 10%, 15%, and 20% under different temperatures of 750°C, 850°C, and 950°C were tested. The behavior of coal slime bursting and the influence of water content and temperature were obtained. It appears that there is a critical water content and a deduced range to determine primary bursting intensity. The bursting intensity index (BII) increases with furnace temperature and water content. So a comprehensive consideration of temperature and water content is crucial for industrial design. To investigate influence induced by the bursting, analysis of the micromorphology and pore structure changes of the coal slime samples before and after bursting at 850°C has been done and shows that the coal slime structure after bursting changes greatly compared with the original state of the coal slime. The calculation results of the fractal dimension show that the pore structure of coal slime after bursting becomes more complicated, and the portion of pores in the coal slime generally increases after bursting.

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“…Significant experimental, numerical, or theoretical methods were conducted to understand the properties of granular coal, such as density, ash, and particle size effects on the fixed characteristics [7][8][9][10][11], coal particle moving [12], fragmentation behavior [13], coal combustion [14], etc. Adánez et al [7] conducted a series of experiments and proposed an equation to evaluate the transport velocities of sand and coal particles.…”

Section: Introductionmentioning

confidence: 99%

Experimental Investigation of Stress Rate and Grain Size on Gas Seepage Characteristics of Granular Coal

Hall

et al. 2017

Energies

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Coal seam gas, held within the inner pores of unmineable coal, is an important energy resource. Gas release largely depends on the gas seepage characteristics and their evolution within granular coal. To monitor this evolution, a series of experiments were conducted to study the effects of applied compressive stress and original grain size distribution (GSD) on the variations in the gas seepage characteristics of granular coal samples. Grain crushing under higher stress rates was observed to be more intense. Isolated fractures in the larger diameter fractions transformed from self-extending to inter-connecting pathways at a critical compressive stress. Grain crushing was mainly caused by compression and high-speed impact. Based on the test results of the original GSD effect, the overall process of porosity and permeability evolution during compression can be divided into three different phases: (1) rapid reduction in the void ratio; (2) continued reduction in the void ratio and large particle crushing; and (3) continued crushing of large particles. Void size reduction and particle crushing were mainly attributed to the porosity and permeability decreases that occurred. The performance of an empirical model, for porosity and permeability evolution, was also investigated. The predictive results indicate that grain crushing caused permeability increases during compression, and that this appeared to be the main cause for the predictive values being lower than those obtained from the experimental tests. The predictive accuracy would be the same for samples under different stress rates and the lowest for the sample with the highest proportion of large grain diameters.Significant experimental, numerical, or theoretical methods were conducted to understand the properties of granular coal, such as density, ash, and particle size effects on the fixed characteristics [7-11], coal particle moving [12], fragmentation behavior [13], coal combustion [14], etc. Adánez et al. [7] conducted a series of experiments and proposed an equation to evaluate the transport velocities of sand and coal particles. For coal blocks having larger particle diameters, the gas desorbs from its micropores, diffuses into macropores, and then seeps under a pressure gradient [15,16]. Hu et al. [17] experimentally and numerically investigated the scale effects and formation mechanism of gas releases from coal particles, and a bidisperse diffusion model was established to predict the experimental results; they found that the scale effects of gas releases from coal are controlled by the multi-scale pore structure of coal. In studies conducted using coal core samples as opposed to granular coal, it was found that under constant total stress conditions, the permeability for adsorbed gases increases when the pore pressure is reduced due to coal swelling [18][19][20], and decreases with increasing pore pressure due to matrix shrinkage [21].Gas permeability is also influenced by fracture geometry [6,22], fracture geometry and water-content [23], and the presen...

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Direct optical observation of coal particle fragmentation behavior in a drop-tube reactor

Cited by 27 publications

References 20 publications

Suitability of pulverised coal testing facilities for blast furnace applications

Suitability of pulverised coal testing facilities for blast furnace applications

The behavior of coal slime bursting in early stage combustion and induced pore structure change

Experimental Investigation of Stress Rate and Grain Size on Gas Seepage Characteristics of Granular Coal

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