Microscopic investigation of unburnt char in fly ash

Shibaoka, Michio

doi:10.1016/0016-2361(85)90227-3

Cited by 58 publications

(17 citation statements)

References 5 publications

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“…A number of studies (Nandi et al, 1977;Shibaoka, 1985;Vleeskens et al, 1993) have shown that inertinite-and vitrinite-group macerals differ in resistance to combustion. Inertinite, primarily the higher reflecting forms, fusinite and secretinite, but also including other inertinite macerals, is more resistant to combustion than the vitrinitegroup macerals, especially in pulverized fuel combustion systems.…”

Section: Coal Petrologymentioning

confidence: 99%

Elemental and mineralogical anomalies in the coal-hosted Ge ore deposit of Lincang, Yunnan, southwestern China: Key role of N2–CO2-mixed hydrothermal solutions

Dai

Wang

Ward

et al. 2015

International Journal of Coal Geology

157

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Section: Coal Petrologymentioning

confidence: 99%

Elemental and mineralogical anomalies in the coal-hosted Ge ore deposit of Lincang, Yunnan, southwestern China: Key role of N2–CO2-mixed hydrothermal solutions

Dai

Wang

Ward

et al. 2015

International Journal of Coal Geology

157

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“…Although numerous papers report on the characterization of commercial or pilot-scale residues [15][16][17], few studies have focused on the late stages of char combustion under carefully controlled conditions. Among those, Nandi and Vleeskins [ 18] have investigated the fuel-related factors determining the degree of coal burnout in a drop tube furnace.…”

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confidence: 99%

Near-extinction and final burnout in coal combustion

Hurt

Davis

1994

Symposium (International) on Combustion

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The authors prefer an oral presentation and publication in the proceedings volume E. Experimental Data and Intet-pretation; D. Experimental Methodologies (6.2) Coal and Organic Solids Combustion Word count , body 3501 wds nomenclature table 126 wds (18 lines x 7 wds/line) references 336 wds (48 lines x 7 wds/line) dk ABSTRACTThe late stages of char combustion have a special technological significance, as carbon conversions of 99% or greater are typically required for the economic operation of pulverized coal fired boilers. In the present article, two independent optical techniques are used to investigate near-extinction and final burnout phenomena for Illinois #6 and Pittsburgh #8 bituminous coals. Captive particle image sequences, combined with in situ optical measurements on entrained particles, provide dramatic illustration of the asymptotic nature of the char burnout process. Single particle combustion to complete burnout is seen to comprise two distinct stages: (1) a rapid high-temperature combustion stage, consuming about 70% of the char carbon and ending with near-extinction of the heterogeneous reactions due to a loss of global particle reactivity, and (2) a final burnout stage occurring slowly and at lower temperatures. For particles containing mineral matter, the second stage can be further subdivided into: (2a) late char combustion, which begins after the nearextinction event, and converts carbon-rich particles to mixed particle types at a lower temperature and a slower rate; _d (2b) decarburization of ash u the removal of residual carbon inclusions from inorganic (ash) frameworks in the very late stages of combustion. This latter process can be extremely slow, requiring over an order of magnitude more time than the primary rapid combustion stage. For particles with very little ash, the loss of global reactivity leading to early near-extinction is clearly related to changes in the carbonaceous char matrix, which evolves over the course of combustion due to simultaneous oxidation and heat treatment. Current global kinetic models used for the prediction of char combustion rates and carbon burnout in boilers do not predict the asymptotic nature of char combustion. More realistic models accounting for the evolution of char structure are needed to make accurate predictions in the range of industrial interest. DISCLAIMERThis report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Governmen...

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“…The classification of fly ash carbons has gone through a number of iterations through the years [60][61][62][110][111][112][113][114][115]. Based on those discussions, and on the philosophy behind coke petrography [116], Hower et al [117] developed a system suitable for the bituminouscoal-derived fly ashes of the eastern US.…”

Section: Fly-ash Carbon Morphologymentioning

confidence: 99%

Progress in energy and combustion science

1984

Progress in Energy and Combustion Science

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a b s t r a c tThe control of mercury in the air emissions from coal-fired power plants is an ongoing challenge. The native unburned carbons in fly ash can capture varying amounts of Hg depending upon the temperature and composition of the flue gas at the air pollution control device, with Hg capture increasing with a decrease in temperature; the amount of carbon in the fly ash, with Hg capture increasing with an increase in carbon; and the form of the carbon and the consequent surface area of the carbon, with Hg capture increasing with an increase in surface area. The latter is influenced by the rank of the feed coal, with carbons derived from the combustion of low-rank coals having a greater surface area than carbons from bituminous-and anthracite-rank coals.The chemistry of the feed coal and the resulting composition of the flue gas enhances Hg capture by fly ash carbons. This is particularly evident in the correlation of feed coal Cl content to Hg oxidation to HgCl 2 , enhancing Hg capture. Acid gases, including HCl and H 2 SO 4 (at small concentrations) and the combination of HC1 and NO 2 , in the flue gas can enhance the oxidation of Hg.In this presentation, we discuss the transport of Hg through the boiler and pollution-control systems, the mechanisms of Hg oxidation, and the parameters controlling Hg capture by coal-derived fly ash carbons.

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Microscopic investigation of unburnt char in fly ash

Cited by 58 publications

References 5 publications

Elemental and mineralogical anomalies in the coal-hosted Ge ore deposit of Lincang, Yunnan, southwestern China: Key role of N2–CO2-mixed hydrothermal solutions

Elemental and mineralogical anomalies in the coal-hosted Ge ore deposit of Lincang, Yunnan, southwestern China: Key role of N2–CO2-mixed hydrothermal solutions

Near-extinction and final burnout in coal combustion

Progress in energy and combustion science

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