Observations of Heterogeneity in Large Pulverized Coal Particles

Gibbins, Jon; Beeley, T.J.; Crelling, John C.; Scott, Andrew C.; Skorupska, N.; Williamson, James M.

doi:10.1021/ef980161c

Cited by 12 publications

(6 citation statements)

References 5 publications

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“…Therefore, it is reasonable to conclude that ash has an impact on the physical structure of the residual char. This observation supports the conclusion of Gibbins et al . that both coal maceral and ash should be considered to provide reasonable explanation to pf coal combustion behavior.…”

Section: Resultssupporting

confidence: 91%

“…In investigating the heterogeneity of large pf coal particles during the devolatilization process, Gibbins and his colleagues found some synergic effects during devolatilization, and suggested that the ability of using relatively pure macerals (from hand-picking, or micronizing, demineralization, and density separation) to represent actual pf combustion behavior may be limited. In their study, a wide range of particle mineral content was also observed, and the minerals were generally well dispersed and frequently associated with the inertinite maceral.…”

Section: Introductionmentioning

confidence: 99%

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Swelling and Char Structures from Density Fractions of Pulverized Coal

Lucas

Strezov

et al. 2003

Energy Fuels

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Char samples are prepared in a drop tube furnace (DTF) in a nitrogen atmosphere using density-separated coal samples of two Australian coals. The structure and morphology of the char samples are analyzed under a scanning electron microscope (SEM). The porosities of individual chars are determined through image processing of the SEM images. The char particle size distribution (PSD) is analyzed using a Malvern Laser Sizer and through image analysis. The results demonstrate the heterogeneity of the char structures and morphology among the density fractions of the same coal. For both coals, porous chars with a cenospheric structure (Group I chars) are generated in the coal samples of low density (F1.25 and S1.25-F1.30). Solid char structures (Group III chars) are formed from the high density coal samples (S1.35-F1.50 and S1.50). The medium density samples contain different types of chars with a moderate porosity and wall thickness. The weight loss, swelling ratio, and the porosity decrease with increasing parent coal density. Results of size fraction samples suggest that a larger swelling occurs in DTF when the particle size decreases. Mechanisms for the formation of different char structures from different density fractions are discussed, and influences of the presence of ash on char structure formation, in addition to the dominant role of maceral compositions reported in previous works, are identified.

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Section: Resultssupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Swelling and Char Structures from Density Fractions of Pulverized Coal

Lucas

Strezov

et al. 2003

Energy Fuels

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“…Pulverized coal is a mixture of heterogeneous particles . The chemical and physical properties of coal, such as H/C ratio, ash content, internal surface area and sulfur content, may depend on the initial particle size, but particle-to-particle differences between particles of equal size exist.…”

Section: Resultsmentioning

confidence: 99%

Effects of Pressure and Oxygen Concentration on the Combustion of Different Coals

et al. 1998

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A pyrometric method was used for simultaneous in situ measurement of the temperature and size of individual coal particles in a pressurized entrained flow reactor. Several series of measurements were made in the gas temperature range 1150-1270 K to study the effects of pressure (0.2-1.0 MPa) and oxygen volume fraction (3-30 vol %) on the particle temperature and size distributions and on the mean degree of burnoff at well-defined residence times. The fuels used in the experiments varied strongly in their reactivity: lignite from France (Gardanne), high-volatile bituminous (hvb) coals from Germany (Westerholt, Go ¨ttelborn) and Poland (mixture), and anthracite from Germany (Niederberg). Milled fuel was sieved into nominal-size fractions in the range from 75 to 180 µm. The strongest increase in combustion rate at increased pressure occurred for anthracite, which was the least reactive among the fuels studied. This is shown by increasing the mass-loss rate and increasing particle temperatures. Pressure had no effect on the combustion of the lignite sample, the most reactive fuel studied. Some evidence of swelling of hvb coal particles was observed during the early stages of combustion. The particle size remained roughly unchanged until the degree of burnoff exceeded 90%, whereafter the particle size started to decrease due to fragmentation. Experimental results from particle temperature measurements at various oxygen concentrations are compared with literature data. Results from in situ particle measurements including size and temperature recording have not been presented previously at elevated pressures for such a wide range of coals. Measurements on combustion rates, particle temperatures and particle sizes were analyzed with a single-particle combustion model. The effect of pressure on the surface reaction kinetics for an anthracite was found to be small compared to the oxygen content and temperature.

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“…These coal blocks were prepared by mounting in resin followed by drying. The blocks were polished using a Struers TegraForce-1 polishing machine, followed by maceral group analyses using a 500 point-count method [43]. The block-examining equipment was a Leica DM4500P petrography microscope [42], which has a 50Â lens and a 10Â internal.…”

Section: Petrographic Analysismentioning

confidence: 99%