The Structure of Submicron Ash from Combustion of Pulverized South African and Colombian Coals

Kauppinen, Esko I.; Lind, Terttaliisa; Valmari, T; Ylätalo, S; Jokiniemi, Jorma; Powell, Q.; Gurav, Abhijit; Kodas, Toivo T.; Mohr, Martin

doi:10.1007/978-1-4757-9223-2_31

Cited by 8 publications

(4 citation statements)

References 5 publications

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“…As the aggregate grows, however, it may be swept out of the boundary layer and into the "bulk" gas, where it may coagulate with aggregates produced from other coal particles. Kauppinen et al (1995) concluded that this secondary aggregation was responsible for the fairly broad submicron particulate size distribution obtained in their measurements of ash sampled from a full scale boiler burning 2 different bituminous coals and is consistent with the structures observed in this study.…”

Section: Bench Scale Experiments Utilizing Controlled Composition Aersupporting

confidence: 86%

The Effect of Chemical Composition on the Fractal-Like Structure of Combustion-Generated Inorganic Aerosols

Liu¹,

Srinivasachar²,

Helble³

2000

Aerosol Science and Technology

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ABSTRACT. The morphology of submicron ame-generated inorganic aerosols is known to be fractal-like with reported fractal exponents ranging from 1.1 -2.5 for different materials. This wide range represents a correspondingly broad variation in structure and suggests that chemical composition might affect the nal structure of ame-generated materials, a prospect of considerable importance in studies of submicron particulate penetration through electrostatic precipitators. To investigate this, the morphology of ame-generated submicron aerosols was studied by characterizing both y ash generated in a pilot scale coal combustor and controlled composition inorganic aerosols generated in a bench scale at ame burner. Fly ash generated during combustion of 2 bituminous coals at 2 different ame temperatures was found to be fractal-like with fractal exponents of 1.9 -2 and fractal prefactors of 1.1 -1.5. In addition, y ash samples collected at the inlet and outlet of an attached pilot scale electrostatic precipitator yielded no difference in particle morphology, indicating a lack of structure-dependent penetration. Flame-generated silica, magnesia, sodium-doped silica, and magnesium-doped silica produced under identical conditions in an invariant premixed ame were also fractal-like in structure with fractal exponents of 1.7 -1.8 and fractal prefactors of 1.6 -1.8. No dependence of these structural parameters on chemical composition, ame residence time, or particle number density was observed over the ranges considered. Changing chemical composition did, however, lead to order of magnitude changes in primary particle diameter without any corresponding change in aggregate structure. Findings from both systems are consistent with a growth process governed in the late stages by cluster-cluster aggregation and indicate that for ame synthesized materials produced in the overall decreasing temperature gradient characteristic of coal combustors and industrial ame reactors, the aerosol aggregate structure will not be affected by changes in chemical composition under conditions of coalescence-limited growth.¤ Corresponding author. 460 B. B. Liu et al.

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Section: Bench Scale Experiments Utilizing Controlled Composition Aersupporting

confidence: 86%

The Effect of Chemical Composition on the Fractal-Like Structure of Combustion-Generated Inorganic Aerosols

Liu¹,

Srinivasachar²,

Helble³

2000

Aerosol Science and Technology

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“…Large ash particles (>2 μm) correspond to ash resulting from mechanisms which include coal or char fragmentation, structural disintegration of the char, − coalescence of ash on the surface of a char particle or within the particle, ,− fragmentation of minerals due to inorganic reaction, ,, shedding of ash particles from the surface of chars during combustion, ,, and ash cenosphere formation . Fine ash particles (<2 μm), result from mechanisms that include vaporization, condensation and aggregation of volatile ash components, ,,,− chemical reaction of mineral grains, , convective transport of organically bound and possibly small-grained inorganic material away from coal particle during coal devolatilization, fragmentation of coal and char particles and excluded minerals due to thermal shock, ,, rapid evolution of gases during mineral decomposition, secondary fragmentation of char particles that produces very fine ash particle, ,, and ash cenosphere breakage to produce fine particles. , …”

Section: Introductionmentioning

confidence: 99%

The Effect of Pressure on Ash Formation during Pulverized Coal Combustion

Bryant

Wall

2000

Energy Fuels

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A bituminous coal with a size faction of 63−90 μm was combusted under oxidizing atmosphere (air) in a drop tube furnace (DTF) and a pressurized drop tube furnace (PDTF) at a gas temperature of 1573 K and pressures of 0.1, 0.5, 1.0, and 1.5 MPa. Ash generated at high pressure was found to be much finer than ash generated at low pressure due to the differences in char structure. Pressure influcences ash formation by its effect on the structure of char particles after devolatilisation. Char samples produced at high pressure have higher proportions of porous char particles which fragment to form finer ash particles. This study confirms and elaborates upon previous studies relating the structure and morphologies of char to ash formation.

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“…The large size ash particles (>2 μm) are formed by mechanisms such as coal or char fragmentation and the structural disintegration of char, − coalescence of ash on the surface of a char particle or within a char particle, ,, fragmentation of minerals due to inorganic reaction, ,, shedding of ash particles from the surface of chars during combustion, ,,, and cenosphere formation . The small size mode, size less than 2 μm, is referred to as fine ash particles (including fume) and results from mechanisms such as ash species vaporization, condensation, and aggregation, ,,,− chemical reaction of mineral grains to form fume particles, , convective transport of organically bound and possibly small-grained inorganic material away from the coal particle during coal devolatilization, thermal shock of coal particle or excluded minerals, ,, rapid evolution of gases during mineral decomposition, char secondary fragmentation, and busting of cenosphere to produce fine particles. , …”

Section: Introductionmentioning

confidence: 99%

Ash Liberation from Included Minerals during Combustion of Pulverized Coal: The Relationship with Char Structure and Burnout

Wall

Liu

et al. 1999

Energy Fuels

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The Structure of Submicron Ash from Combustion of Pulverized South African and Colombian Coals

Cited by 8 publications

References 5 publications

The Effect of Chemical Composition on the Fractal-Like Structure of Combustion-Generated Inorganic Aerosols

The Effect of Chemical Composition on the Fractal-Like Structure of Combustion-Generated Inorganic Aerosols

The Effect of Pressure on Ash Formation during Pulverized Coal Combustion

Ash Liberation from Included Minerals during Combustion of Pulverized Coal: The Relationship with Char Structure and Burnout

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