JP2007273311A - Operation method of solid-oxide fuel cell - Google Patents

Operation method of solid-oxide fuel cell Download PDF

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JP2007273311A
JP2007273311A JP2006098510A JP2006098510A JP2007273311A JP 2007273311 A JP2007273311 A JP 2007273311A JP 2006098510 A JP2006098510 A JP 2006098510A JP 2006098510 A JP2006098510 A JP 2006098510A JP 2007273311 A JP2007273311 A JP 2007273311A
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fuel electrode
fuel cell
oxide fuel
fuel
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Toru Yamamoto
融 山本
Yutaka Fuchino
裕 渕野
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Central Research Institute of Electric Power Industry
Kyushu Electric Power Co Inc
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Kyushu Electric Power Co Inc
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

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Abstract

<P>PROBLEM TO BE SOLVED: To provide an operating method of a solid oxide fuel cell capable of suppressing oxidation and deterioration of a fuel electrode in an inert gas purge after stopping the solid oxide fuel cell. <P>SOLUTION: Oxidation of the fuel electrode is prevented by purging by the gas in which a reducing gas of less than the explosion lower limit amount is added to the inert gas. By adding the reducing gas to the inert gas containing a slight amount of oxygen, oxygen partial pressure can be reduced, and by using this gas as a purge gas, oxidation and deterioration of the fuel electrode is suppressed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、固体酸化物形燃料電池の停止後の不活性ガスパージにおいて、燃料極の酸化及び劣化を防止して電池の耐久性を向上させる運転方法に関する。   The present invention relates to an operation method for improving the durability of a battery by preventing oxidation and deterioration of a fuel electrode in an inert gas purge after the solid oxide fuel cell is stopped.

燃料電池はイオン透過性を有する電解質薄膜の両面に空気極と燃料極を配置し、空気極側には酸化剤（例えば、空気）を、燃料極側には燃料（例えば、水素）を、それぞれ供給し、電気エネルギーを発生させる化学電池である。燃料電池は電解質の材料により分類されるが、固体酸化物形燃料電池（以下「ＳＯＦＣ」という。）の電解質材料は酸素イオン透過性を有する酸化物が用いられ、約７００〜１０００℃の高温で運転される。ＳＯＦＣでは空気極に供給された酸素が陰イオンとなって電解質を透過し、電解質と燃料極の境界面に到達し、燃料極に供給された燃料ガスは燃料極材料中を拡散して燃料極と電解質との境界面に達し、電解質を透過してきた酸素イオンと反応する。   In a fuel cell, an air electrode and a fuel electrode are arranged on both surfaces of an electrolyte thin film having ion permeability, an oxidant (for example, air) is provided on the air electrode side, and a fuel (for example, hydrogen) is provided on the fuel electrode side. A chemical battery that supplies and generates electrical energy. Fuel cells are classified according to the electrolyte material, but the oxide material of the solid oxide fuel cell (hereinafter referred to as “SOFC”) uses an oxide having oxygen ion permeability at a high temperature of about 700 to 1000 ° C. Driven. In SOFC, oxygen supplied to the air electrode becomes an anion and permeates the electrolyte, reaches the interface between the electrolyte and the fuel electrode, and the fuel gas supplied to the fuel electrode diffuses in the fuel electrode material and diffuses into the fuel electrode. It reaches the interface between the electrolyte and the electrolyte and reacts with oxygen ions that have permeated the electrolyte.

上記のような動作原理であることから、ＳＯＦＣの燃料極材料には、材料中を燃料ガスが容易に拡散できる多孔質であることが必要であり、４０％程度の気孔率を有している。また、燃料極と電解質の境界面での反応により発生した電子を外部に取り出すための導体の役目も果たすため、３００〜４００Ｓ／ｃｍ程度の導電率を有している。   Because of the operating principle as described above, the SOFC fuel electrode material must be porous so that the fuel gas can easily diffuse through the material, and has a porosity of about 40%. . In addition, it also has a conductivity of about 300 to 400 S / cm because it also serves as a conductor for taking out electrons generated by the reaction at the interface between the fuel electrode and the electrolyte.

これらの条件を満足し高い運転温度に耐える材料として、ＳＯＦＣの燃料極には通常、金属ニッケルの粉末と電解質材料の粉末とを混合焼結した、いわゆるサーメットが用いられている。   As a material that satisfies these conditions and can withstand a high operating temperature, a so-called cermet, in which metallic nickel powder and electrolyte material powder are mixed and sintered, is usually used for the SOFC fuel electrode.

一方、燃料電池を用いた発電装置では、火災や爆発の防止のため、停止後装置内に滞留している燃料を、不活性ガスを用いて押し出すこと（パージ）が行われる（特許文献１、２参照）。リン酸形燃料電池や固体高分子形燃料電池と異なり、ＳＯＦＣは燃料極に白金系の貴金属触媒を用いないため、特許文献１、２のようなパージ方法は不要であるが、停止直後の温度が高く、かつ、燃料極がニッケルを含むため下記のような課題がある。   On the other hand, in a power generation device using a fuel cell, in order to prevent a fire or an explosion, the fuel staying in the device after stopping is pushed out (purged) using an inert gas (Patent Document 1,). 2). Unlike phosphoric acid fuel cells and polymer electrolyte fuel cells, SOFC does not use a platinum-based noble metal catalyst for the fuel electrode. However, since the fuel electrode contains nickel, there are the following problems.

通常の不活性ガスには数〜数１０ｐｐｍの酸素が混入しており、これは酸素分圧１０−６ａｔｍ〜１０−４ａｔｍに相当する。この酸素分圧はパージ時の燃料極温度（約８００℃）においてニッケルが酸化する酸素分圧（約１０−１４ａｔｍ）を上回っているため、パージの際に停止直後の高温の燃料極中のニッケルが酸化されて導電率が低下し、同時に、酸化された燃料極は体積が膨張するため気孔率が低下して燃料極が劣化する。しかしながら、そのためにパージガスの純度を高めて酸素分圧を１０−１４ａｔｍ以下にすることは現実的ではない。このようにＳＯＦＣ停止後のパージにおいては、燃料極の酸化防止及び劣化防止がＳＯＦＣの運転における課題となっていた。
特開２００５−１５８２９８号公報 特開平８−２２２２５９号公報 Ordinary inert gas contains several to several tens of ppm of oxygen, which corresponds to an oxygen partial pressure of 10 −6 atm to 10 −4 atm. This oxygen partial pressure exceeds the oxygen partial pressure (about 10 −14 atm) at which the nickel is oxidized at the fuel electrode temperature (about 800 ° C.) at the time of purging. Nickel is oxidized to lower the conductivity, and at the same time, the volume of the oxidized fuel electrode expands, so that the porosity decreases and the fuel electrode deteriorates. However, it is not realistic to increase the purity of the purge gas to make the oxygen partial pressure 10 −14 atm or less. Thus, in purging after the stop of SOFC, prevention of oxidation and deterioration of the fuel electrode has been a problem in the operation of SOFC.
JP 2005-158298 A JP-A-8-222259

本発明が解決しようとする課題は、固体酸化物形燃料電池の停止後の不活性ガスパージにおいて、燃料極の酸化及び劣化を抑制することができる固体酸化物形燃料電池の運転方法を提供する。   The problem to be solved by the present invention is to provide a method for operating a solid oxide fuel cell capable of suppressing oxidation and deterioration of the fuel electrode in an inert gas purge after the solid oxide fuel cell is stopped.

本発明の運転方法は、不活性ガスに爆発下限量未満の還元性ガスを添加したガスによりパージすることで燃料極の酸化を防止することを特徴とする。   The operation method of the present invention is characterized in that oxidation of the fuel electrode is prevented by purging with a gas obtained by adding a reducing gas less than the lower explosion limit amount to an inert gas.

本発明は、微量の酸素を含む不活性ガスに還元性ガスを添加することで酸素分圧を下げることができることを示し、このガスをパージガスとして用いることをＳＯＦＣ燃料極の酸化を抑制する手段とするものである。   The present invention shows that an oxygen partial pressure can be lowered by adding a reducing gas to an inert gas containing a small amount of oxygen, and using this gas as a purge gas means to suppress oxidation of the SOFC fuel electrode To do.

まず、酸素を含むガスに還元性ガスを添加すると、酸素と還元性ガスが一部反応して平衡状態に達することにより、酸素分圧が低下する。例えば、酸素を含むガスに還元性ガスとして水素を添加すれば、式１の反応が起こる。
Ｈ２＋１／２Ｏ２＝Ｈ２Ｏ＋ΔＧ・・・・・式１ First, when a reducing gas is added to a gas containing oxygen, oxygen and the reducing gas partially react to reach an equilibrium state, thereby reducing the oxygen partial pressure. For example, when hydrogen is added as a reducing gas to a gas containing oxygen, the reaction of Formula 1 occurs.
H 2 + 1 / 2O 2 = H 2 O + ΔG Equation 1

ここで、ΔＧは反応により放出されるギブスの自由エネルギーである。この場合、平衡状態における酸素分圧Ｐ〔Ｏ２〕は式２で表される。
Ｐ〔Ｏ２〕＝（Ｐ〔Ｈ２Ｏ〕／Ｐ〔Ｈ２〕）２×ｅｘｐ（２ΔＧ／ＲＴ）・・・・・式２ Here, ΔG is the Gibbs free energy released by the reaction. In this case, the oxygen partial pressure P [O 2 ] in the equilibrium state is expressed by Equation 2.
P [O 2 ] = (P [H 2 O] / P [H 2 ]) 2 × exp (2ΔG / RT) Expression 2

ここで、Ｐ〔Ｈ２Ｏ〕は水蒸気分圧、Ｐ〔Ｈ２〕は水素分圧、ｅｘｐ（２ΔＧ／ＲＴ）は自然対数の底を基数とする指数関数、Ｒはガス定数、Ｔは絶対温度である。 Here, P [H 2 O] is the partial pressure of water vapor, P [H 2 ] is the partial pressure of hydrogen, exp (2ΔG / RT) is an exponential function with the base of the natural logarithm, R is a gas constant, and T is absolute Temperature.

従って、パージガスとして用いられている不活性ガスに還元性ガスを適量添加することにより、パージガス中の酸素分圧を低下させることができる。例えば、一般の窒素ガスは多い場合に数１０ｐｐｍ程度酸素が混入しているが、水素を５％添加すると８００℃における酸素分圧は前記の式２により１０−２５ａｔｍ程度となり、停止直後のＳＯＦＣ燃料極と接触させても燃料極中のニッケルが酸化することはない。また、上記により水素添加したガスは空気と混合しても引火・爆発することはなく、パージガスの火災・爆発抑制効果は損なわれない。 Therefore, the oxygen partial pressure in the purge gas can be reduced by adding an appropriate amount of reducing gas to the inert gas used as the purge gas. For example, when there is a large amount of general nitrogen gas, oxygen is mixed in about several tens of ppm. However, when 5% of hydrogen is added, the oxygen partial pressure at 800 ° C. becomes about 10 −25 atm according to the above equation 2, and the SOFC immediately after stopping Nickel in the fuel electrode does not oxidize even when brought into contact with the fuel electrode. Further, the hydrogenated gas does not ignite or explode even when mixed with air, and the fire / explosion suppression effect of the purge gas is not impaired.

還元性ガスとしては、水素に限らず燃料電池の燃料として用いられるメタンやエタンなどのガスも用いることができる。   As the reducing gas, not only hydrogen but also gases such as methane and ethane used as fuel for the fuel cell can be used.

以上、説明した原理により、不活性ガスに爆発下限量未満の還元性ガスを添加したガスをパージガスとして用いれば、ＳＯＦＣ燃料極の酸化を防止し、燃料極の劣化を抑制できる。   As described above, if a gas obtained by adding a reducing gas less than the lower explosion limit amount to an inert gas is used as the purge gas, the oxidation of the SOFC fuel electrode can be prevented and the deterioration of the fuel electrode can be suppressed.

本発明は、不活性ガスに爆発下限量未満の還元性ガスを添加したガスによりパージすることでＳＯＦＣ燃料極の酸化および劣化を抑制することができる。   The present invention can suppress oxidation and deterioration of the SOFC fuel electrode by purging with an inert gas to which a reducing gas less than the lower explosion limit is added.

本発明の実施例として、水素を５％添加した窒素ガスによる燃料極の劣化防止効果について説明する。   As an embodiment of the present invention, the effect of preventing deterioration of the fuel electrode by nitrogen gas added with 5% of hydrogen will be described.

まず、ＳＯＦＣの燃料極材料として広く用いられているＮｉ／８ＹＳＺサーメットの試験片を、乾燥水素を１００ｍｌ／分を通じながら１０００℃、４８時間還元処理した後、四端子法により導電率を測定し、かさ密度の測定値と理論密度から気孔率を算出した。次に、還元処理後の燃料極材料を、３種類のガス（流量は何れも５０ｍｌ／分）において燃料電池の運転を想定した図１に示す温度パターンで加熱試験を行った後、還元処理後と同じ方法で、試験片の導電率及び気孔率を測定した。還元処理後と加熱試験後の燃料極材料の導電率（１０００℃における値）を表１に、気孔率を表２にそれぞれ示す。

Figure 2007273311
First, a Ni / 8YSZ cermet test piece widely used as a fuel electrode material for SOFC was subjected to reduction treatment at 1000 ° C. for 48 hours while passing dry hydrogen through 100 ml / min, and then the conductivity was measured by a four-terminal method. The porosity was calculated from the measured bulk density and the theoretical density. Next, the fuel electrode material after the reduction treatment was subjected to a heating test with the temperature pattern shown in FIG. 1 assuming the operation of the fuel cell in three kinds of gases (the flow rates are all 50 ml / min), and then after the reduction treatment. The electrical conductivity and porosity of the test piece were measured by the same method. Table 1 shows the conductivity (value at 1000 ° C.) of the fuel electrode material after the reduction treatment and after the heating test, and Table 2 shows the porosity.
Figure 2007273311

表１から、窒素ガス雰囲気で加熱試験を行った燃料極材料の導電率は大きく低下しているのに対し、水素を５％添加した窒素ガス雰囲気で加熱試験を行った場合の導電率は低下していないことがわかる。

Figure 2007273311
From Table 1, the conductivity of the fuel electrode material subjected to the heating test in a nitrogen gas atmosphere is greatly reduced, whereas the conductivity when the heating test is performed in a nitrogen gas atmosphere to which 5% of hydrogen is added is reduced. You can see that they are not.
Figure 2007273311

表２から、窒素ガス雰囲気で加熱試験を行った燃料極材料の気孔率は低下しているのに対し、水素を５％添加した窒素ガス雰囲気で加熱試験を行った場合の気孔率は低下していないことがわかる。   From Table 2, the porosity of the fuel electrode material subjected to the heating test in a nitrogen gas atmosphere has decreased, whereas the porosity when the heating test has been performed in a nitrogen gas atmosphere to which 5% of hydrogen has been added has decreased. You can see that it is not.

これらのことから、本発明で提案する運転方法の一例として、水素を５％添加した窒素ガスを用いてＳＯＦＣ停止時のパージを行うと、燃料極の劣化を抑制できることが示された。   From these facts, it was shown that, as an example of the operation method proposed in the present invention, deterioration of the fuel electrode can be suppressed by purging when the SOFC is stopped using nitrogen gas added with 5% of hydrogen.

燃料電池の運転を想定した加熱試験の温度パターンを示す図である。It is a figure which shows the temperature pattern of the heating test supposing the driving | operation of a fuel cell.

Claims (3)

固体酸化物形燃料電池の停止後に固体酸化物形燃料電池内に滞留する燃料ガスを排出する際、不活性ガスに爆発下限量未満の還元性ガスを添加したガスによりパージすることを特徴とする固体酸化物形燃料電池の運転方法。   When the fuel gas staying in the solid oxide fuel cell is discharged after the solid oxide fuel cell is stopped, the fuel gas is purged with a gas obtained by adding a reducing gas less than the lower explosion limit to an inert gas. Operation method of solid oxide fuel cell. 不活性ガスが窒素ガスであることを特徴とする請求項１に記載の燃料電池の運転方法。   The method of operating a fuel cell according to claim 1, wherein the inert gas is nitrogen gas. 還元性ガスが水素ガスであることを特徴とする請求項１又は２に記載の燃料電池の運転方法。   3. The fuel cell operating method according to claim 1, wherein the reducing gas is hydrogen gas.
JP2006098510A 2006-03-31 2006-03-31 Operation method of solid-oxide fuel cell Pending JP2007273311A (en)

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2009096221A1 (en) * 2008-01-28 2009-08-06 Nippon Oil Corporation Indirect internally reforming solid oxide fuel cell and a method of stopping same
JP2010055910A (en) * 2008-08-28 2010-03-11 Hitachi Ltd Solid oxide fuel cell system and method for operating it
KR101342528B1 (en) 2012-05-22 2013-12-17 쌍용머티리얼 주식회사 Operation conditions for direct hydrocarbon solid oxide fuel cells
US8623562B2 (en) 2008-07-10 2014-01-07 Convion Oy Method and arrangement to reduce the consumption of safety gas in a fuel cell system

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH04324253A (en) * 1991-04-25 1992-11-13 Chubu Electric Power Co Inc Fuel cell

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH04324253A (en) * 1991-04-25 1992-11-13 Chubu Electric Power Co Inc Fuel cell

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2009096221A1 (en) * 2008-01-28 2009-08-06 Nippon Oil Corporation Indirect internally reforming solid oxide fuel cell and a method of stopping same
CN101953010A (en) * 2008-01-28 2011-01-19 吉坤日矿日石能源株式会社 Indirect internally reforming solid oxide fuel cell and a method of stopping same
CN101953010B (en) * 2008-01-28 2014-05-07 吉坤日矿日石能源株式会社 Indirect internally reforming solid oxide fuel cell and a method of stopping same
US8927166B2 (en) 2008-01-28 2015-01-06 Jx Nippon Oil & Energy Corporation Indirect internal reforming solid oxide fuel cell and method for shutting down the same
US9040206B2 (en) 2008-01-28 2015-05-26 Jx Nippon Oil & Energy Corporation Indirect internal reforming solid oxide fuel cell and method for shutting down the same
US8623562B2 (en) 2008-07-10 2014-01-07 Convion Oy Method and arrangement to reduce the consumption of safety gas in a fuel cell system
JP2010055910A (en) * 2008-08-28 2010-03-11 Hitachi Ltd Solid oxide fuel cell system and method for operating it
KR101342528B1 (en) 2012-05-22 2013-12-17 쌍용머티리얼 주식회사 Operation conditions for direct hydrocarbon solid oxide fuel cells

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