Research Papers

Coal Ash Deposition on Nozzle Guide Vanes—Part I: Experimental Characteristics of Four Coal Ash Types

[+] Author and Article Information
J. P. Bons

Department of Mechanical and Aerospace Engineering,
Ohio State University,
Columbus, OH 43235

N. P. Padture

Department of Materials Science Engineering,
Ohio State University,
Columbus, OH 43235

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received August 31, 2011; final manuscript received September 1, 2011; published online November 8, 2012. Editor: David Wisler.

J. Turbomach 135(2), 021033 (Nov 08, 2012) (9 pages) Paper No: TURBO-11-1199; doi: 10.1115/1.4006571 History: Received August 31, 2011; Revised September 01, 2011

An accelerated deposition test facility was operated with four different coal ash species to study the effect of ash composition on deposition rate and spatial distribution. The facility seeds a combusting (natural gas) flow with 10–20 micron mass mean diameter coal ash particulate. The particulate-laden combustor exhaust is accelerated through a rectangular-to-annular transition duct and expands to ambient pressure through a nozzle guide vane annular sector. For the present study, the annular cascade consisted of two CFM56 aero-engine vane doublets, comprising three full passages and two half passages of flow. The inlet Mach number (0.1) and gas temperature (1100 °C) are representative of operating turbines. Ash samples were tested from the three major coal ranks: lignite, subbituminous, and bituminous. Investigations over a range of inlet gas temperatures from 900 °C to 1120 °C showed that deposition increased with temperature, though the threshold for deposition varied with ash type. Deposition levels varied with coal rank, with lignite producing the largest deposits at the lowest temperature. Regions of heightened deposition were noted; the leading edge and pressure surface being particularly implicated. Scanning electron microscopy was used to identify deposit structure. For a limited subset of tests, film cooling was employed at nominal design operating conditions but provided minimal protection in cases of severe deposition.

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Fig. 1

Volcanic ash deposition damage to high pressure turbine rotor (from Kim et al. [2])

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Fig. 2

Schematic of TuRFR showing primary flow path, particulate, fuel, and film cooling insertion points

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Fig. 3

Cutaway of TuRFR measurement and viewing area

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Fig. 4

Particle size distribution for all tested ash types

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Fig. 5

Side by side comparison of (a) bituminous, (b) PRB, (c) JBPS, and (d) lignite coal ash deposits. Test conditions in Table 2.

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Fig. 6

Sixty seconds into JBPS subbituminous fly ash test- 1044 °C; see Table 2

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Fig. 7

JBPS fly ash ∼1056 °C, 11 min into test

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Fig. 8

Surface metrology of vanes with JBPS ash deposit. Compare to Fig. 5(c).

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Fig. 9

Thickness comparison at (a) leading edge, (b) 37% chord, (c) 53% chord

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Fig. 10

Volcanic ash deposits on pressure surface of NGVs (from Chambers [16])

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Fig. 11

SEM photo of (a) bituminous ash deposit and (b) JBPS ash deposit (black background is epoxy filler, test conditions are presented in Table 2)

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Fig. 12

EDS micrographs of JBPS fly ash, showing concentrations of Si, Al, and Ca (350 μm × 450 μm)

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Fig. 13

Comparison of bituminous fly ash tests (a) film cooling, (b) nonfilm cooling

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Fig. 14

Comparison of lignite fly ash tests (a) film cooling, (b) nonfilm cooling




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