Optimisation d'une cellule élementaire de SOFC pour un fonctionnement en reformage interne progressif sans dépôt de carbone

SOFC optmisation for a gradual internal reforming operation without carbon deposition

• Auteur / Autrice : Jean-Marie Klein
• Direction : Yann Bultel, Samuel Georges
• Type : Thèse de doctorat
• Discipline(s) : Génie des procédés
• Date : Soutenance en 2008
• Etablissement(s) : Grenoble INPG

Mots clés

Mots clés contrôlés

Catalyse hétérogène

Spectroscopie d'impédance

Piles à combustible à oxyde solide

Résumé

La pile à combustible est un générateur électrochimique au rendement énergétique élevé qui convertit directement l’énergie chimique en énergie électrique. La température de fonctionnement élevée de la SOFC peut permettre l’utilisation de combustibles variés tels que le gaz naturel constitué en grande partie de méthane. En effet, le méthane peut être alors reformé au cœur de l’anode pour former l’hydrogène in situ. Le matériau d’anode le plus abouti est un cermet composé de nickel et de zircone (Ni-YSZ). Le verrou technologique principal à lever lors d’une alimentation par des hydrocarbures sur ce type de matériau concerne le dépôt de carbone empoisonnant l’activité électrocatalytique de l’anode. La démarche générale a été d’étudier par une approche de modélisation le comportement d’une cellule dite à architecture classique en reformage interne direct et suivant le principe du reformage interne progressif décrit pour la première fois au LEPMI par Philippe Vernoux en 1998. Une architecture innovante a ensuite été étudiée, ce qui a mené à la conception d’une cellule de SOFC permettant le fonctionnement en reformage interne progressif sans dépôt de carbone (120 heures).

Ln recent years, fuel cell technology has attracted considerable attention from several fields of scientific research. Fuel cells are highly efficient in terms of energy conversion. They emit little noise, and are non¬polluting. Solid oxide fuel cells (SOFCs) development is particularly import~nt for stationary applications due to their high operating temperature (800-1000°C). Natural gas appears to be a fuel of great interest for SOFC systems. The principal component of natural gas is methane, which can be converted into hydrogen by Direct Internai Reforming (DIR) within the SOFC anode. Unfortunately, internai steam reforming in SOFC leads to inhomogeneous temperature distributions according to the endothermicity of this reaction and the exothermicity of the electrochemical processes. This results in thennal induced stresses and may lead to mechanical failure of the cermet anode. To avoid this problem, Graduai Internai Reforming (GIR) can be used. GIR is based on local coupling between steam reforming and hydrogen oxidation. The steam required for the reforming reaction is obtained by the hydrogen oxidation. However, with GIR, Boudouard and cracking reactions can involve a risk of carbon formation. To cope with carbon formation a new cell configuration is studied. This configuration combines a catalyst layer (0. 1 %Ir-CeOz) with a classical anode, allowing GIR without coking. This study proposes simulations, using the CFD software package developed by CFD Research Corporation, of the behavior of a planar SOFC using GIR. A thermodynamic study based on the partial pressure distributions in the cell is carried out to investigate the occurrence of carbon forn1ation. Based on these simulation results a planar SOFC has been developed and experimental tests have been done. Polarization curves were established for many ratios CHJHzO. The various behaviors of the cell were analysed by impedance spectroscopy and gas chromatography. Finally the cell was tested for 120 hours under pure methane. As expected, the current density was higher with CHJH20 mixtures than with hydrogen and was finally found to increase with the CH4/HzO ratio. A stable operation of the cell was finally observed during 120 hours, which tends to prove the viability of the GIR without coking in this new cell configuration.