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Research Papers: Gas Turbines: Coal, Biomass, and Alternative Fuels

Independent Effects of Surface and Gas Temperature on Coal Fly Ash Deposition in Gas Turbines at Temperatures up to 1400 °C

[+] Author and Article Information
Robert Laycock

Chemical Engineering Department,
Brigham Young University,
350 CB,
Provo, UT 84602
e-mail: laycockrobert@gmail.com

Thomas H. Fletcher

Mem. ASME
Chemical Engineering Department,
Brigham Young University,
350 CB,
Provo, UT 84602
e-mail: tom_fletcher@byu.edu

1Corresponding author.

Contributed by the Coal, Biomass and Alternate Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received July 13, 2015; final manuscript received August 3, 2015; published online September 16, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(2), 021402 (Sep 16, 2015) (8 pages) Paper No: GTP-15-1277; doi: 10.1115/1.4031318 History: Received July 13, 2015; Revised August 03, 2015

Deposition of coal fly ash in gas turbines has been studied to support the concept of integrated gasification combined cycle (IGCC). Although particle filters are used in IGCC, small amounts of ash particles less than 5 μm in diameter enter the gas turbine. Previous deposition experiments in the literature have been conducted at temperatures up to about 1288 °C. However, few tests have been conducted that reveal the independent effects of gas and surface temperature, and most have been conducted at gas temperatures lower than 1400 °C. The independent effects of gas and surface temperature on particle deposition in a gas turbine environment were measured using the Turbine Accelerated Deposition Facility (TADF) at Brigham Young University. Gas temperatures were measured with a type K thermocouple and surface temperatures were measured with two-color pyrometry. This facility was modified for testing at temperatures up to 1400 °C. Subbituminous coal fly ash, with a mass mean diameter of 4 μm, was entrained in a hot gas flow at a Mach number of 0.25. A nickel base super alloy metal coupon 2.5 cm in diameter was held in this gas stream to simulate deposition in a gas turbine. The gas temperature (and hence particle temperature) governs the softening and viscosity of the particle, while the surface temperature governs the stickiness of the deposit. Two test series were therefore conducted. The first series used backside cooling to hold the initial temperature of the deposition surface (Ts,i) constant at 1000 °C while varying the gas temperature (Tg) from 1250 °C to 1400 °C. The second series held Tg constant at 1400 °C while varying Ts,i from 1050 °C to 1200 °C by varying the amount of backside cooling. Capture efficiency and surface roughness were calculated. Capture efficiency increased with increasing Tg. Capture efficiency also initially increased with Ts,i until a certain threshold temperature where capture efficiency began to decrease with increasing Ts,i.

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Figures

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Fig. 1

Schematic of the TADF at BYU

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Fig. 2

SiO2 faceplate protecting the coupon holder from high gas temperatures

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Fig. 3

Particle size distribution of the milled ash, Dp = 4 μm

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Fig. 4

(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. 5

Capture efficiency versus mass of ash delivered for Tg close to 1300 °C

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Fig. 6

Variation in capture efficiency with respect to gas temperature

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Fig. 7

Average surface roughness with respect to gas temperature

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Fig. 8

Deposit bulk density with respect to gas temperature

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Fig. 9

ESEM images of deposits from (a) test G3 (Tg = 1247 °C) and (b) test G8 (Tg = 1394 °C)

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Fig. 10

Increase in average surface temperature with respect to time for tests G3, G6, G8, and G9

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Fig. 11

Surface temperature profiles measured during test G8 (Tg = 1394 °C)

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Fig. 12

Photos of ash deposits collected from tests G3, G6, G8, and G9

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Fig. 13

Capture efficiency versus initial surface temperature of the coupon

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Fig. 14

Surface roughness versus initial surface temperature of the coupon

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Fig. 15

Deposit density versus initial surface temperature of the coupon

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Fig. 16

Photos of ash deposits collected from tests S4, S3, S6, and S14, respectively

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Fig. 17

Equilibration tube capture efficiency data

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