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Research Papers

In Situ Characterization of Ash Thermal Conductivity for Three Coal Types Formed Under Oxidizing and Reducing Conditions in a Laboratory Furnace

[+] Author and Article Information
D. Maynes

e-mail: maynes@byu.edu

M. R. Jones

Department of Mechanical Engineering,
Brigham Young University,
Provo, UT 84602

L. L. Baxter

Department of Chemical Engineering,
Brigham Young University,
Provo, UT 84602

1Corresponding author.

Manuscript received October 7, 2011; final manuscript received May 1, 2012; published online October 12, 2012. Assoc. Editor: Chenn Zhou.

J. Thermal Sci. Eng. Appl 4(4), 041002 (Oct 12, 2012) (11 pages) doi:10.1115/1.4006899 History: Received October 07, 2011; Revised May 01, 2012

This work presents in situ measurements of the effective thermal conductivity in particulate coal ash deposits under both reducing and oxidizing environments. Laboratory experiments generated deposits on an instrumented deposition probe of loosely bound particulate ash from three coals generated in a down-fired flow reactor with optical access. An approach is presented for making in situ measurements of the temperature difference across the ash deposits, the thickness of the deposits, and the total heat transfer rate through the ash deposits. Using this approach, the effective thermal conductivity was determined for coal ash deposits formed under oxidizing and reducing conditions. Three coals were tested under oxidizing conditions: two bituminous coals derived from the Illinois #6 basin and a subbituminous Powder River Basin coal. The subbituminous coal exhibited the lowest range of effective thermal conductivities (0.05–0.18 W/m K) while the Illinois #6 coals showed higher effective thermal conductivities (0.2–0.5 W/m K). One of the bituminous coals and the subbituminous coal were also tested under reducing conditions. A comparison of the ash deposits from these two coals showed no discernible difference in the effective thermal conductivity based on stoichiometry. All experiments indicated an increase in effective thermal conductivity with deposit thickness, probably associated with deposit sintering.

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References

Figures

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Fig. 4

Image of a typical ash deposit on the deposition probe

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Fig. 3

Image of test section portion of deposition probe without an ash deposit mounted in place below the reactor exit (top panel) and a schematic illustrating the locations of the internal thermocouples at the x = 0 and L (bottom panel)

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Fig. 2

Image of deposition probe mounted below the reactor exit with related instrumentation

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Fig. 1

Schematic illustration of the multifuel reactor

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Fig. 5

Image of nitrogen purged snorkel used for FTIR surface temperature measurements under reducing conditions

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Fig. 6

Distance from profilometer zero-point to deposition probe surface as a function of number of probe revolutions when the probe was clean and at a much later time when a typical ash deposit existed

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Fig. 8

Control volume enclosing the test section portion of the deposition probe used for analysis in determining ke

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Fig. 7

Probe surface temperature as a function of time (top panel) and tangential position, θ (bottom panel), at axial locations x/L = 0, 1/3, 2/3, and 1

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Fig. 9

Cooling-air temperature as a function of radial position, r/R, for a typical scenario at x/L = 0 and θ = 0 deg, 90 deg, and 180 deg, and at x/L = 1 at θ = 0 deg. The experimental data are shown by markers, and the lines indicate power law fits of the data of the form expressed in Eq. (5).

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Fig. 10

Results from two deposition experiments using the IL #6-I coal. Shown are the ash deposit thickness as a function of elapsed time (top panel); ash surface temperature and probe temperature at the same θ location as a function of deposit thickness (middle panel); and average heat flux as a function of deposit thickness (bottom panel).

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Fig. 11

Effective thermal conductivity of ash deposits as a function of deposit thickness for three coals formed under oxidizing conditions; bituminous IL #6-I (top panel), IL #6-II (middle panel), and subbituminous PRB (bottom panel). Results are shown for two experimental runs for each coal and both methods for estimating ke.

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Fig. 12

Effective thermal conductivity of ash deposits as a function of deposit thickness for bituminous IL #6-I (top panel) and subbituminous PRB (bottom panel) coals formed under both oxidizing and reducing conditions. The results correspond to the constant h method for estimating ke.

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