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Research Papers

Time-Dependent Deposition Characteristics of Fine Coal Fly Ash in a Laboratory Gas Turbine Environment

[+] Author and Article Information
Robert G. Laycock

e-mail: laycockrobert@gmail.com

Thomas H. Fletcher

e-mail: tom_fletcher@byu.edu
Department of Chemical Engineering,
Brigham Young University,
Provo, UT 84602

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received November 9, 2011; final manuscript received December 5, 2011; published online November 1, 2012. Editor: David Wisler.

J. Turbomach 135(2), 021003 (Nov 01, 2012) (8 pages) Paper No: TURBO-11-1241; doi: 10.1115/1.4006639 History: Received November 09, 2011; Revised December 05, 2011

Time-dependent deposition characteristics of fine coal fly ash were measured in the Turbine Accelerated Deposition Facility (TADF) at Brigham Young University. Two samples of subbituminous coal fly ash, with mass mean diameters of 3 μm and 13 μm, were entrained in a hot gas flow with a gas temperature of 1288 °C and Mach number of 0.25. A nickel-based, superalloy metal coupon approximately 0.3 cm thick was held in a hot particle-laden gas stream to simulate deposition in a gas turbine. Tests were conducted with deposition times of 20, 40, and 60 min. Capture efficiencies and surface roughness characteristics (e.g., Ra) were obtained at different times. Capture efficiency increased exponentially with time, while Ra increased linearly with time. The increased deposition with time caused the surface temperature of the deposit to increase. The increased surface temperature caused more softening, increasing the propensity for impacting particles to stick to the surface. These data are important for improving models of deposition in turbines from syngas flows.

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Figures

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Fig. 1

Schematic of the TADF at BYU

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Fig. 2

Redesigned coupon holder

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Fig. 3

SiO2 faceplate protecting the redesigned coupon holder from high gas temperatures

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Fig. 4

Comparison of capture efficiencies obtained from tests on the original (old) TADF and the upgraded (new) TADF

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Fig. 5

Particle size distribution of fly ash used in this study

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Fig. 6

(a) Coupon and faceplate before any deposition occurred. (b) Coupon and faceplate after deposition. The circle represents the coupon area. Only ash deposited within this circle was used in calculating capture efficiencies.

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Fig. 7

(a) 3D surface map of the scan of test 3, (b) side view of the surface scan, (c) area used to determine Ra for test 3

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Fig. 8

Surface temperature maps at 10-min increments for test 3 (Tg = 1288 °C, Dp = 13 μm)

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Fig. 9

Increase of spatially averaged coupon surface temperature with respect to time

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Fig. 10

Time-dependent growth of capture efficiency. 95% confidence band is shown for the 13-μm fit.

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Fig. 11

Deposit thickness growth with respect to time. 95% confidence band is shown for the 13-μm fit.

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Fig. 12

Centerline-averaged surface roughness (Ra) development over time. 95% confidence band is shown for the 13-μm fit.

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Fig. 13

Increase in average Ps of the surface ash with time

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Fig. 14

Increase in the maximum Ps of the surface ash with time

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Fig. 15

Increase in the minimum Ps of the surface ash with time

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Fig. 16

Distribution of sticking probability for pixels over the observed face of the coupon as a function of time

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