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Research Papers: Fuel Combustion

Infiltration Velocity and Thickness of Flowing Slag Film on Porous Refractory of Slagging Gasifiers

[+] Author and Article Information
Ramalakshmi Krishnaswamy

Mechanical & Aerospace
Engineering Department,
West Virginia University,
Morgantown, WV 26506-6106

Tetsuya Kenneth Kaneko

Department of Materials Science & Engineering,
Carnegie Mellon University,
Pittsburgh, PA 15213

Bishal Madhab Mazumdar

Center for Study of Science,
Technology and Policy (CSTEP),
Dr. Raja Ramanna Complex,
Raj Bhavan Circle, High Grounds,
Bangalore 560001, India

Peter Rozelle

Office of Clean Energy Systems,
US Department of Energy,
FE-22/Germantown Building,
1000 Independence Avenue NW,
Washington, DC 20585

Seetharaman Sridhar

Warwick Manufacturing Group,
University of Warwick,
Coventry CV4 7AL, UK

John M. Kuhlman

Mechanical & Aerospace
Engineering Department,
West Virginia University,
ESB Rm. 317
Morgantown, WV 26506-6106

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received July 17, 2013; final manuscript received January 25, 2014; published online May 13, 2014. Assoc. Editor: Sarma V. Pisupati.

J. Energy Resour. Technol 136(3), 032203 (May 13, 2014) (9 pages) Paper No: JERT-13-1214; doi: 10.1115/1.4026918 History: Received July 17, 2013; Revised January 25, 2014

Two analytical formulations that describe the fluid interactions of slag with the porous refractory linings of gasification reactors have been derived. The first formulation considers the infiltration velocity of molten slag into the porous microstructure of the refractory material that possesses an inherent temperature gradient in the direction of infiltration. Capillary pressures are assumed to be the primary driving force for the infiltration. Considering that the geometry of the pores provides a substantially shorter length scale in the radial direction as compared with the penetration direction, a lubrication approximation was employed to simplify the equation of motion. The assumption of a fully developed flow in the pores is justified based on the extremely small Reynolds numbers of the infiltration slag flow. The second formulation describes the thickness of the slag film that flows down the perimeter of the refractory lining. The thickness of the film was approximated by equating the volumetric slag production rate of the gasification reactor to the integration of the velocity profile with respect to the lateral flow cross-sectional area of the film. These two models demonstrate that both the infiltration velocity into the refractory and the thickness of the film that forms at the refractory surface were sensitive to the viscosity of the fluid slag. The slag thickness model has been applied to predict film thicknesses in a generic slagging gasifier with assumed axial temperature distributions, using slag viscosity from the literature, both for the case of a constant slag volumetric flow rate down the gasifier wall, and for the case of a constant flyash flux distributed uniformly over the entire gasifier wall.

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Figures

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Fig. 2

Nondimensionalized plot of the viscosity of 100% coal feedstock slag with respect to the pore depth. Values in both the axes are in arbitrary units.

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Fig. 1

Schematic of gasifier showing z-coordinate system and typical slag thicknesses (exaggerated) for cooler temperatures near the bottom of the gasifier

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Fig. 3

Schematic of gasifier showing z-coordinate system and the distributed flyash flux, qf

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Fig. 4

Control volume of the distributed (uniform) flyash flux to the slag

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Fig. 5

Measured variation of slag viscosity with respect to temperature for eastern coal, western coal, eastern coal + petcoke, and western coal + petcoke

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Fig. 6

Sensitivity of the derived models to temperature for eastern coal, western coal, eastern coal + petcoke, and western coal + petcoke; thickness of the slag layer on the refractory lining of the gasifier walls in mm versus temperature

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Fig. 7

Assumed axial temperature distributions for a generic entrained-flow gasifier

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Fig. 8

Resulting axial slag viscosity distribution for a generic entrained-flow gasifier based on experimental data for an eastern coal and the assumed temperature profiles shown in Fig. 7

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Fig. 9

Predicted slag layer axial thickness distribution for a generic entrained-flow gasifier based on viscosity for an eastern coal (from Fig. 8)

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Fig. 11

Comparison of the three slag film thickness distributions, as predicted using the planar model and the two cylindrical coordinate models, with a constant gasifier temperature of T = 2000 K, and a uniform flyash flux to the slag; total flyash flux to slag = 0.000902 m3/s

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Fig. 12

Predicted slag film thickness distributions using planar model for three different constant gasifier temperatures, and a uniform flyash flux to the slag; total flyash flux to slag = 0.000902 m3/s. Viscosity of 0.67 Pa s corresponds to T = 2000 K (eastern coal in Fig. 5); 2.807 Pa s corresponds to T = 1823 K (eastern coal in Fig. 5); 7.86 Pa s corresponds to T = 1750 K (eastern coal in Fig. 5).

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Fig. 13

Predicted slag film thickness distributions using planar model for the two different gasifier axial temperature distributions shown in Fig. 8, for a uniform flyash flux to the slag; total flyash flux to slag = 0.000902 m3/s

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Fig. 10

Predicted slag film thickness distribution using planar model with a constant gasifier temperature of T = 2000 K, and a uniform flyash flux to the slag; total flyash flux to slag = 0.000902 m3/s

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