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Research Papers

Anode Fuel and Steam Recycling for Internal Methane Reforming SOFCs: Analysis of Carbon Deposition

[+] Author and Article Information
Valérie Eveloy

Department of Mechanical Engineering, The Petroleum Institute, P.O. Box 2533, Abu Dhabi, United Arab Emiratesveveloy@pi.ac.ae

Currently, the preferred SOFC electrolyte material is dense yttria (Y2O3)-stabilized zirconia (ZrO2) (YSZ). In conjunction with YSZ, a porous nickel-zirconia (NiZrO2) cermet is the most common anode material, while the cathode is typically a lanthanum manganite (LaMnO3) based material (3).

Steam-to-carbon ratios (S:Cs) of 1–3 are typically employed to avoid coking on conventional nickel-based anodes (3).

J. Fuel Cell Sci. Technol 8(1), 011006 (Nov 03, 2010) (8 pages) doi:10.1115/1.4002230 History: Received January 06, 2010; Revised June 21, 2010; Published November 03, 2010; Online November 03, 2010

Anode fuel and steam recycling are explored as possible mitigation strategies against carbon deposition in an internal methane reforming solid oxide fuel cell (IR-SOFC) operated at steam-to-carbon ratios (S:Cs) of 0.5–1. Using a detailed computational fluid dynamics model, the cell behavior and spatial extent of carbon deposits within the anode are analyzed based on a thermodynamic analysis accounting for both the cracking and Boudouard reactions for fuel and steam recycling fractions of up to 90% (mass percent). At temperatures close to 1173 K, 50% fuel recycling is found to be an effective mitigation strategy against carbon deposition, with only a minor portion of the cell inlet affected by coking. Steam recycling reduces the extent of carbon deposits by a magnitude comparable to that obtained using fuel recycling, provided that recycling ratios on the order of 25% higher than that for fuel recycling are applied. Steam recycling could therefore be considered advantageous in terms of reduced overall mass flow. The mitigating effect of fuel recycling on the susceptibility to coking at the cell inlet is found to be through the direction of the cracking reaction, while steam recycling has a positive (but slightly less effective) impact on both the Boudouard and cracking reactions. The results suggest that partial anode gas recycling could help extend the operational range of IR-SOFCs to lower fuel humidification levels than typically considered, with reduced thermal stresses and risks of carbon deposits, while reducing system cost and complexity in terms of steam production.

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References

Figures

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Figure 1

GIR-SOFC configuration, with cell geometry dimensions given in (19)

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Figure 2

Numerically predicted profile of coefficient γ along the cell length direction as a function of the fuel recycling ratio (Rf) for an inlet fuel xH2O/xCH4 ratio of 1 (GIR/DIR boundary)

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Figure 3

Numerically predicted profile of coefficient γ along the cell length direction as a function of the steam recycling ratio (Rs) for an inlet fuel xH2O/xCH4 ratio of 1 (GIR/DIR boundary)

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Figure 4

Numerically predicted profile of coefficient γ along the cell length direction as a function of the fuel recycling ratio (Rf) for an inlet fuel xH2O/xCH4 ratio of 0.5 (GIR)

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Figure 5

Numerically predicted profile of coefficient γ along the cell length direction as a function of the steam recycling ratio (Rs) for an inlet fuel xH2O/xCH4 ratio of 0.5 (GIR)

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Figure 6

Numerically predicted profile of coefficient α along the cell length direction as a function of the fuel recycling ratio (Rf) for an inlet fuel xH2O/xCH4 ratio of 0.5 (GIR)

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Figure 7

Numerically predicted profile of coefficient α along the cell length direction as a function of the steam recycling ratio (Rs) for an inlet fuel xH2O/xCH4 ratio of 0.5 (GIR)

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Figure 8

Numerically predicted profile of coefficient β along the cell length direction as a function of the fuel recycling ratio (Rf) for an inlet fuel xH2O/xCH4 ratio of 0.5 (GIR)

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Figure 9

Numerically predicted profile of coefficient β along the cell length direction as a function of the steam recycling ratio (Rs) for an inlet fuel xH2O/xCH4 ratio of 0.5 (GIR)

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Figure 10

Numerically predicted profile of the water-gas-shift reaction kinetics along the cell length direction as a function of the fuel recycling ratio (Rf) for an inlet fuel xH2O/xCH4 ratio of 0.5 (GIR)

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Figure 11

Numerically predicted profile of the water-gas-shift reaction kinetics along the cell length direction as a function of the steam recycling ratio (Rs) for an inlet fuel xH2O/xCH4 ratio of 0.5 (GIR)

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Figure 12

Numerically predicted profile of the methane steam reforming reaction kinetics along the cell length direction as a function of the fuel recycling ratio (Rf) for an inlet fuel xH2O/xCH4 ratio of 0.5 (GIR)

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Figure 13

Numerically predicted profile of the methane steam reforming reaction kinetics along the cell length direction as a function of the steam recycling ratio (Rs) for an inlet fuel xH2O/xCH4 ratio of 0.5 (GIR)

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