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JP3545691B2 - Operating method of exhaust gas purification device - Google Patents

Operating method of exhaust gas purification device Download PDF

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Publication number
JP3545691B2
JP3545691B2 JP2000294052A JP2000294052A JP3545691B2 JP 3545691 B2 JP3545691 B2 JP 3545691B2 JP 2000294052 A JP2000294052 A JP 2000294052A JP 2000294052 A JP2000294052 A JP 2000294052A JP 3545691 B2 JP3545691 B2 JP 3545691B2
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Japan
Prior art keywords
reduction catalyst
exhaust gas
nox storage
nox
reducing agent
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JP2000294052A
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Japanese (ja)
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JP2002097940A (en
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満 細谷
浩 平林
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Hino Motors Ltd
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Hino Motors Ltd
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Description

【0001】
【発明の属する技術分野】
本発明は、ディーゼルエンジンに用いる排気浄化装置の運転方法に関するものである。
【0002】
【従来の技術】
従来より、ディーゼルエンジンにおいては、排気ガスが流通する排気管の途中にNOx還元触媒を装備し、該NOx還元触媒の上流側に必要量の還元剤を添加して該還元剤をNOx還元触媒上で排気ガス中のNOx(窒素酸化物)と還元反応させることによりNOxの排出濃度を低減し得るようにしたものがある。
【0003】
他方、理論空燃比より大きな空燃比で希薄燃焼(リーンバーン)を行わせることにより大幅な燃費の向上を図り得ることが広く知られているが、このような希薄燃焼運転を行うことを想定したディーゼルエンジンに関してもNOxの排出濃度を低減することは重要な課題となっている。
【0004】
しかしながら、一般的に、希薄燃焼運転時における酸素過剰存在下では、NOx還元触媒上において、還元剤がNOxと反応するよりも先に酸素と反応してしまうので、希薄燃焼運転時における実用化レベルの高いNOx低減効果を得ることが難しかった。
【0005】
そこで、希薄燃焼運転時においてもNOxを低減し得る触媒として、排気ガス中の酸素濃度が高い希薄燃焼運転時にNOxを酸化して硝酸塩の状態で一時的に吸蔵し且つ排気ガス中の酸素濃度が低い理論空燃比運転時に還元剤の介在によりNOxを分解放出して還元浄化する性質を備えたNOx吸蔵還元触媒の実用化が現在検討されている。
【0006】
例えば、この種のNOx吸蔵還元触媒としては、白金・バリウム・アルミナ触媒や、イリジウム・白金・バリウム・アルミナ触媒などが前述した如き性質を有するものとして既に知られている。
【0007】
ただし、NOx吸蔵還元触媒に吸蔵されたNOxを放出させて該NOx吸蔵還元触媒の再生を図るのに際し、いちいち運転状態を希薄燃焼運転から理論空燃比運転に切り替えていたのでは、せっかくの希薄燃焼運転による燃費向上のメリットが損なわれてしまうため、希薄燃焼運転としたままでNOx吸蔵還元触媒の良好な再生を図り得るようにすることが望まれているが、希薄燃焼運転時における酸素過剰存在下では、排気ガス中の酸素濃度が高いために、前述したNOx還元触媒の場合と同様に、HCなどの還元剤がNOxと反応するよりも先に酸素と反応して消費されてしまい、これにより還元剤とNOxの反応選択性が低下してNOx吸蔵還元触媒の良好な再生を図ることができないという問題があった。
【0008】
そこで、本発明者らは、排気管の途中にNOx吸蔵還元触媒を装備した上、該NOx吸蔵還元触媒を迂回するようにバイパス流路を付設し、このバイパス流路側に排気ガスを切り替えて流しながら還元剤の添加を行い、該還元剤の添加量に対する相対的な空気過剰率を下げて還元剤とNOxの反応選択性を向上し、これによりNOx吸蔵還元触媒からNOxを積極的に分解放出させて該NOx吸蔵還元触媒の良好な再生を図り、その放出したNOxをNOx吸蔵還元触媒上で前記還元剤と反応させて還元浄化させることを創案するに到り、これを特願平11−328339号として既に出願している。
【0009】
【発明が解決しようとする課題】
しかしながら、ディーゼルエンジンの排気ガス中には、燃料中の硫黄分に由来するSOが存在するため、このSOがNOx吸蔵還元触媒上でNOxと同様に酸化して硫酸塩となってしまうという不具合があり、この硫酸塩が硝酸塩と比べて安定であることからNOx吸蔵還元触媒が硫酸塩により被毒劣化し、これによりNOxの吸蔵が不可能となってNOx浄化率が低下するという問題に関しては未だ具体的な実用レベルの解決策が提案されていないのが実情である。
【0010】
ただし、硫酸塩による被毒を解消する手法自体は、理論空燃比より小さな空燃比でリッチ燃焼を行わせ且つ約600℃以上の高温雰囲気に保つことにより、NOx吸蔵還元触媒からSOを放出させてNOx吸蔵還元触媒の再生を図ることが知られているが、これをディーゼルエンジン側の運転制御で実現することは、黒煙の発生が不可避となってしまう運転領域でディーゼルエンジンを運転することを意味しているので、このような黒煙の発生を回避しつつディーゼルエンジン側の運転制御でNOx吸蔵還元触媒の脱硫処理の条件を整えることは現実的に難しいことであった。
【0011】
本発明は、上述の実情に鑑みてなされたものであり、ディーゼルエンジンの排気ガスをNOx吸蔵還元触媒で浄化するにあたり、該NOx吸蔵還元触媒の硫酸塩による被毒をディーゼルエンジン側の運転制御を行わずに解消し得るようにすることを目的としている。
【0012】
【課題を解決するための手段】
本発明は、ディーゼルエンジンからの排気ガスが流通する排気管の途中に、排気ガス中の酸素濃度が高い時にNOxを酸化して硝酸塩の状態で一時的に吸蔵し且つ排気ガス中の酸素濃度が低い時に還元剤の介在によりNOxを分解放出して還元浄化するNOx吸蔵還元触媒を装備し、該NOx吸蔵還元触媒に対し還元剤を適宜に添加し且つ前記NOx吸蔵還元触媒を適宜に迂回させて排気ガスを流し得るように構成した排気浄化装置の運転方法であって、通常はディーゼルエンジンの排気ガスをNOx吸蔵還元触媒に流し、これにより排気ガス中のNOxをNOx吸蔵還元触媒に吸蔵させてNOxの低減化を図る一方、定期的に排気ガスをNOx吸蔵還元触媒を迂回させて流しながら該NOx吸蔵還元触媒に還元剤を添加し、これによりNOx吸蔵還元触媒からNOxを積極的に分解放出させてNOx吸蔵還元触媒の再生を図り、更には、定期的にNOx吸蔵還元触媒に排気ガスを流しつつ還元剤を添加してNOx吸蔵還元触媒を所定温度以上に昇温させ且つその直後にNOx吸蔵還元触媒を迂回させて排気ガスを流しながら該NOx吸蔵還元触媒に再び還元剤を添加して脱硫処理を施すことを特徴とするものである。
【0013】
而して、ディーゼルエンジンの酸素濃度の高い排気ガスをNOx吸蔵還元触媒に流すと、排気ガス中のNOxがNOx吸蔵還元触媒に硝酸塩の状態で吸蔵され、これによりディーゼルエンジンの運転時における良好なNOxの低減化が図られることになる。
【0014】
また、定期的にNOx吸蔵還元触媒を迂回させて排気ガスを流しながらNOx吸蔵還元触媒に還元剤を添加すると、該還元剤の添加量に対する相対的な空気過剰率が低下して還元剤とNOxの反応選択性が向上し、これによりNOx吸蔵還元触媒からNOxを積極的に分解放出させて該NOx吸蔵還元触媒の良好な再生を図り、その放出したNOxをNOx吸蔵還元触媒上で前記還元剤と反応させて良好に還元浄化させることが可能となる。
【0015】
更には、NOx吸蔵還元触媒に排気ガスを流しつつ還元剤を添加すると、排気ガスが流通している酸素濃度の高い高温雰囲気下での還元剤の酸化反応による発熱でNOx吸蔵還元触媒が所定温度以上に昇温し、その直後にNOx吸蔵還元触媒を迂回させて排気ガスを流しながら該NOx吸蔵還元触媒に再び還元剤を添加すると、該還元剤の添加量に対する相対的な空気過剰率が低下して理論空燃比より小さな空燃比のリッチ雰囲気が実現されるので、NOx吸蔵還元触媒からSOを放出せるための条件がディーゼルエンジン側の運転制御を行わずに整うことになり、NOx吸蔵還元触媒が効率良く脱硫処理されて硫酸塩による被毒が解消されることになる。
【0016】
【発明の実施の形態】
以下本発明の実施の形態を図面を参照しつつ説明する。
【0017】
図1は本発明を実施する形態の一例を示すもので、図中1はディーゼルエンジンを示し、ここに図示しているディーゼルエンジン1では、ターボチャージャ2が備えられており、エアクリーナ3から導いた空気4が吸気管5を介し前記ターボチャージャ2のコンプレッサ2aへと送られ、該コンプレッサ2aで加圧された空気4が更にインタクーラ6へと送られて冷却され、該インタクーラ6から図示しないインテークマニホールドへと空気4が導かれてディーゼルエンジン1の各シリンダに導入されるようにしてある。
【0018】
また、このディーゼルエンジン1の各シリンダには、図示しない燃料タンクからの液体燃料(軽油)がディーゼルエンジン1の各シリンダ内に噴射されて燃焼されるようにしてあり、ディーゼルエンジン1の各シリンダから排出された排気ガス7がエキゾーストマニホールド8を介し前記ターボチャージャ2のタービン2bへと送られ、該タービン2bを駆動した排気ガス7が排気管9を介し車外へ排出されるようにしてある。
【0019】
そして、排気ガス7が流通する排気管9の途中には、排気ガス7中の酸素濃度が高い時にNOxを酸化して硝酸塩の状態で一時的に吸蔵し且つ排気ガス7中の酸素濃度が低い時に後述する還元剤10(軽油)の介在によりNOxを分解放出して還元浄化するNOx吸蔵還元触媒11が装備されており、該NOx吸蔵還元触媒11を迂回するように排気管9にバイパス流路12が付設されている。
【0020】
ここで、排気管9に対するバイパス流路12の分岐箇所には、排気管9を流れる排気ガス7を適宜にバイパス流路12側に切り替えて流し得るよう流路切換弁13,14が夫々設けられている。
【0021】
また、排気管9におけるNOx吸蔵還元触媒11の入側には、噴射ノズル15が配設されており、該噴射ノズル15と所定場所の還元剤タンク16(燃料タンクと兼用することも可)との間が還元剤供給管17により接続されていると共に、前記噴射ノズル15と所定場所のエアタンク18との間が空気導入管19により接続されており、前記還元剤供給管17の途中の送給ポンプ20を駆動して還元剤タンク16内の還元剤10を噴射ノズル15に導くことにより該噴射ノズル15からNOx吸蔵還元触媒11の入側に向け還元剤10を噴霧し得るようにしてある。また、還元剤10の量が少ないと霧化しづらい為、霧化させるためのアシストとして、前記空気導入管19の途中の開閉弁21を開けて少量の加圧空気を噴射ノズル15に導くことも可能な構造となっている。
【0022】
尚、図中22は排気管9の下流側に備えたマフラを示す。
【0023】
而して、ディーゼルエンジン1の運転時に、流路切換弁13を開け且つ流路切換弁14を閉じて酸素濃度の高い排気ガス7をNOx吸蔵還元触媒11に流すと、排気ガス7中のNOxが硝酸塩の状態で吸蔵され、これによりディーゼルエンジン1の希薄燃焼運転時における良好なNOxの低減化が図られることになる。
【0024】
そして、このようなNOxの吸蔵を約30秒〜3分程度続けた後に、流路切換弁14を開け且つ流路切換弁13を閉じて排気ガス7をバイパス流路12側へ迂回させて流し、送給ポンプ20の駆動により還元剤タンク16から還元剤10を導き、必要に応じ開閉弁21を開けて少量の加圧空気を霧化のアシストとしてエアタンク18から導く等して噴射ノズル15からNOx吸蔵還元触媒11の入側に還元剤10を噴霧する。
【0025】
このようにすれば、還元剤10の添加量に対する相対的な空気過剰率が低下して還元剤10とNOxの反応選択性が向上し、これによりNOx吸蔵還元触媒11からNOxが積極的に分解放出されて該NOx吸蔵還元触媒11の良好な再生が図られ、その放出したNOxがNOx吸蔵還元触媒11上で前記還元剤10と反応して還元浄化されることになる。
【0026】
更に、約10〜30時間(高負荷運転で約10〜15時間、中負荷運転で約20〜30時間)に一回程度の割合で定期的に以下に詳述する如きNOx吸蔵還元触媒11の脱硫処理を施すようにする。
【0027】
即ち、流路切換弁13を開け且つ流路切換弁14を閉じて排気ガス7をNOx吸蔵還元触媒11に流しつつ還元剤10を前述と同様にしてNOx吸蔵還元触媒11の入側に噴霧して添加し、これにより排気ガス7が流通している酸素濃度の高い高温雰囲気下での還元剤10の酸化反応による発熱でNOx吸蔵還元触媒11を約650〜700℃に昇温させ、その直後に流路切換弁14を開け且つ流路切換弁13を閉じて排気ガス7をバイパス流路12側へ迂回させて流しながらNOx吸蔵還元触媒11に再び還元剤10を添加する。
【0028】
このようにすれば、還元剤10の添加量に対する相対的な空気過剰率が低下して理論空燃比より小さな空燃比のリッチ雰囲気が実現されることになるので、NOx吸蔵還元触媒11からSOを放出させるための条件がディーゼルエンジン1側の運転制御を行わずに整うことになり、NOx吸蔵還元触媒11が効率良く脱硫処理されて硫酸塩による被毒が解消されることになる。
【0029】
ここで、NOx吸蔵還元触媒11の脱硫処理に関しては、図2に示す如く、前述した如き還元剤10の二段添加による脱硫処理を1サイクルとして約15分間程度に亘り数サイクル繰り返すモードを予め設定しておき、NOx吸蔵還元触媒11における大半の硫酸塩をSOとして放出させて被毒劣化を十分に回復させるようにすることが好ましい。
【0030】
従って、本形態例によれば、ディーゼルエンジンの排気ガスをNOx吸蔵還元触媒で浄化するにあたり、該NOx吸蔵還元触媒の硫酸塩による被毒をディーゼルエンジン側の運転制御を行わずに解消することができるので、NOx吸蔵還元触媒を使用した排気浄化装置のディーゼルエンジンへの適用を実現することができる。
【0031】
図3は本発明を実施する形態の別の例を示すもので、この形態例においては、前述した図1におけるNOx吸蔵還元触媒11を並列に対で設け、該各NOx吸蔵還元触媒11,11の夫々に対して適宜に排気ガス7を振り替えて流し得るよう排気管9を二つの分岐流路9A,9Bに分岐させて前記各NOx吸蔵還元触媒11,11に接続し且つその下流側で再び合流させてマフラ22に導くように構成してあり、前記各分岐流路9A,9Bの分岐箇所には、排気管9を流れる排気ガス7を各分岐流路9A,9Bに対し交互に切り替えて流し得るよう流路切換弁13,14が夫々設けられている。
【0032】
また、各NOx吸蔵還元触媒11,11の双方の入側には、図1の場合と同様に、噴射ノズル15が配設されており、該各噴射ノズル15,15の何れに対しても、還元剤タンク16内の還元剤10を送給ポンプ20,20の駆動により還元剤供給管17,17を介して導き且つ必要に応じてエアタンク18の加圧空気を開閉弁21,21の開放により空気導入管19,19を介し少量導いて各NOx吸蔵還元触媒11,11の入側に還元剤10を選択的に噴霧し得るようにしてある。
【0033】
而して、このようにNOx吸蔵還元触媒11を並列に対で設けた場合には、流路切換弁13を開け且つ流路切換弁14を閉じて排気ガス7を分岐流路9Aに流し、該分岐流路9AのNOx吸蔵還元触媒11により排気ガス7中のNOxを硝酸塩の状態で吸蔵させている間に、排気ガス7の流量が制限されている分岐流路9B側のNOx吸蔵還元触媒11を再生したり、脱硫処理を施したりするといった具合に、常にNOx吸蔵還元触媒11,11のうちの何れか一方を使用可能な状態として連続的にNOxの低減化を図ることができるわけであるが、斯かる構成の排気浄化装置の場合にも、本発明の運転方法を同様に適用できることは当然である。
【0034】
尚、本発明の排気浄化装置の運転方法は、上述の形態例にのみ限定されるものではなく、本発明の要旨を逸脱しない範囲内において種々変更を加え得ることは勿論である。
【0035】
【発明の効果】
上記した本発明の排気浄化装置の運転方法によれば、ディーゼルエンジンの排気ガスをNOx吸蔵還元触媒で浄化するにあたり、該NOx吸蔵還元触媒の硫酸塩による被毒をディーゼルエンジン側の運転制御を行わずに解消することができるので、NOx吸蔵還元触媒を使用した排気浄化装置のディーゼルエンジンへの適用を実現することができるという優れた効果を奏し得る。
【図面の簡単な説明】
【図1】本発明を実施する形態の一例を示す概略図である。
【図2】脱硫処理のモードのタイムスケジュールを示す図である。
【図3】本発明を実施する形態の別の例を示す概略図である。
【符号の説明】
1 ディーゼルエンジン
7 排気ガス
9 排気管
10 還元剤
11 NOx吸蔵還元触媒
[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an operation method of an exhaust gas purification device used for a diesel engine.
[0002]
[Prior art]
Conventionally, in a diesel engine, a NOx reduction catalyst is provided in the middle of an exhaust pipe through which exhaust gas flows, and a required amount of a reducing agent is added to an upstream side of the NOx reducing catalyst so that the reducing agent is placed on the NOx reducing catalyst. There is an apparatus in which the reduction concentration of NOx can be reduced by causing a reduction reaction with NOx (nitrogen oxide) in exhaust gas.
[0003]
On the other hand, it is widely known that a lean burn can be performed at a higher air-fuel ratio than the stoichiometric air-fuel ratio to significantly improve fuel efficiency. However, it is assumed that such a lean-burn operation is performed. Reducing the NOx emission concentration has become an important issue for diesel engines as well.
[0004]
However, in general, in the presence of excess oxygen during the lean burn operation, the reducing agent reacts with oxygen on the NOx reduction catalyst before reacting with NOx. It was difficult to obtain a high NOx reduction effect.
[0005]
Therefore, as a catalyst capable of reducing NOx even during the lean burn operation, NOx is oxidized during the lean burn operation in which the oxygen concentration in the exhaust gas is high and temporarily stored in the form of nitrate, and the oxygen concentration in the exhaust gas is reduced. At present, practical use of a NOx storage-reduction catalyst having a property of decomposing and releasing NOx to reduce and purify by intervening a reducing agent during operation at a low stoichiometric air-fuel ratio is being studied.
[0006]
For example, as this type of NOx storage reduction catalyst, a platinum-barium-alumina catalyst, an iridium-platinum-barium-alumina catalyst, etc. are already known as having the above-mentioned properties.
[0007]
However, in order to release the NOx stored in the NOx storage reduction catalyst and to regenerate the NOx storage reduction catalyst, it is necessary to switch the operation state from the lean burn operation to the stoichiometric air-fuel ratio operation every time. Since the merit of improving fuel economy by driving is impaired, it is desired to be able to achieve good regeneration of the NOx storage-reduction catalyst while operating in lean burn mode. Below, the oxygen concentration in the exhaust gas is high, so that the reducing agent such as HC reacts with oxygen before reacting with NOx and is consumed as in the case of the NOx reduction catalyst described above. As a result, there is a problem in that the reaction selectivity between the reducing agent and NOx is reduced, and good regeneration of the NOx storage reduction catalyst cannot be achieved.
[0008]
Therefore, the present inventors provided a NOx storage reduction catalyst in the middle of the exhaust pipe, provided a bypass flow path so as to bypass the NOx storage reduction catalyst, and switched exhaust gas to the bypass flow path side to flow. While reducing the addition of the reducing agent, the excess air ratio relative to the amount of the reducing agent is reduced to improve the reaction selectivity between the reducing agent and NOx, whereby NOx is actively decomposed and released from the NOx storage reduction catalyst. Thus, the NOx storage reduction catalyst is satisfactorily regenerated, and the released NOx is reacted with the reducing agent on the NOx storage reduction catalyst to reduce and purify the NOx storage reduction catalyst. 328339.
[0009]
[Problems to be solved by the invention]
However, since the exhaust gas from diesel engines, because of the presence of SO 2 derived from sulfur in the fuel, resulting in a sulfate this SO 2 is oxidized as with NOx on the NOx storage reduction catalyst There is a problem, and since the sulfate is more stable than the nitrate, the NOx storage reduction catalyst is poisoned and deteriorated by the sulfate, thereby making it impossible to store NOx and reducing the NOx purification rate. In fact, no practical solution has been proposed yet.
[0010]
However, the method itself for eliminating poisoning by sulfate is to release SO 2 from the NOx storage reduction catalyst by performing rich combustion at an air-fuel ratio smaller than the stoichiometric air-fuel ratio and maintaining a high temperature atmosphere of about 600 ° C. or higher. It is known that the NOx storage reduction catalyst is regenerated by operating the diesel engine. However, realizing this through operation control on the diesel engine side requires operating the diesel engine in an operation region where black smoke is inevitable. Therefore, it is practically difficult to adjust the conditions for the desulfurization treatment of the NOx storage reduction catalyst by operation control on the diesel engine side while avoiding the generation of such black smoke.
[0011]
The present invention has been made in view of the above-mentioned circumstances, and in purifying exhaust gas of a diesel engine with a NOx storage reduction catalyst, the operation control of the NOx storage reduction catalyst by poisoning by sulfates on the diesel engine side is performed. The purpose is to be able to resolve without doing.
[0012]
[Means for Solving the Problems]
The present invention oxidizes NOx in the middle of an exhaust pipe through which exhaust gas from a diesel engine flows when the oxygen concentration in the exhaust gas is high, temporarily stores NOx in a state of nitrate, and reduces the oxygen concentration in the exhaust gas. It is equipped with a NOx storage-reduction catalyst that decomposes and releases NOx by the interposition of a reducing agent when the temperature is low to reduce and purify it. The reducing agent is appropriately added to the NOx storage-reduction catalyst, and the NOx storage reduction catalyst is appropriately bypassed. An operating method of an exhaust gas purifying apparatus configured to allow exhaust gas to flow therethrough. Usually, the exhaust gas of a diesel engine is caused to flow to a NOx storage reduction catalyst, whereby NOx in the exhaust gas is stored in the NOx storage reduction catalyst. While reducing NOx, a reducing agent is added to the NOx storage-reduction catalyst while the exhaust gas is flowed periodically bypassing the NOx storage-reduction catalyst. The NOx storage reduction catalyst is actively decomposed and released from the storage reduction catalyst in order to regenerate the NOx storage reduction catalyst. Further, a reducing agent is added to the NOx storage reduction catalyst by periodically adding exhaust gas to the NOx storage reduction catalyst to set the NOx storage reduction catalyst to a predetermined value. The method is characterized in that the temperature is raised to a temperature higher than or equal to the temperature, and immediately after that, a reducing agent is again added to the NOx storage reduction catalyst while exhaust gas is bypassed to bypass the NOx storage reduction catalyst to perform desulfurization treatment.
[0013]
Thus, when exhaust gas having a high oxygen concentration of the diesel engine is passed through the NOx storage reduction catalyst, NOx in the exhaust gas is stored in the NOx storage reduction catalyst in the form of nitrate, whereby good NOx during operation of the diesel engine is obtained. NOx can be reduced.
[0014]
Also, when a reducing agent is added to the NOx storage reduction catalyst while exhaust gas is flowed around the NOx storage reduction catalyst periodically, the relative excess ratio of air to the amount of the reducing agent decreases, and the reducing agent and NOx Of the NOx storage-reduction catalyst, whereby the NOx storage-reduction catalyst is actively decomposed and released to achieve good regeneration of the NOx storage-reduction catalyst, and the released NOx is reduced on the NOx storage-reduction catalyst by the reducing agent. And make it possible to favorably perform reduction purification.
[0015]
Furthermore, when the reducing agent is added while flowing the exhaust gas to the NOx storage-reduction catalyst, the NOx storage-reduction catalyst is heated to a predetermined temperature by the heat generated by the oxidation reaction of the reducing agent in a high-temperature atmosphere having a high oxygen concentration in which the exhaust gas flows. When the temperature is raised as described above, and immediately after that, the reducing agent is added again to the NOx storage reduction catalyst while flowing the exhaust gas while bypassing the NOx storage reduction catalyst, the relative excess air ratio with respect to the added amount of the reducing agent decreases. As a result, a rich atmosphere with an air-fuel ratio smaller than the stoichiometric air-fuel ratio is realized, so that the conditions for releasing SO 2 from the NOx storage reduction catalyst are set without performing the operation control on the diesel engine side, and the NOx storage reduction is performed. The catalyst is efficiently desulfurized and the poisoning by sulfate is eliminated.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0017]
FIG. 1 shows an example of an embodiment of the present invention. In the figure, reference numeral 1 denotes a diesel engine. In the diesel engine 1 shown here, a turbocharger 2 is provided, and the diesel engine 1 is led from an air cleaner 3. The air 4 is sent to the compressor 2a of the turbocharger 2 through the intake pipe 5, and the air 4 pressurized by the compressor 2a is further sent to the intercooler 6 where it is cooled. The air 4 is guided to each cylinder of the diesel engine 1.
[0018]
In each cylinder of the diesel engine 1, liquid fuel (light oil) from a fuel tank (not shown) is injected into each cylinder of the diesel engine 1 and burned. The discharged exhaust gas 7 is sent to a turbine 2b of the turbocharger 2 via an exhaust manifold 8, and the exhaust gas 7 driving the turbine 2b is discharged to the outside of the vehicle via an exhaust pipe 9.
[0019]
In the middle of the exhaust pipe 9 through which the exhaust gas 7 flows, when the oxygen concentration in the exhaust gas 7 is high, NOx is oxidized and temporarily stored in the form of nitrate, and the oxygen concentration in the exhaust gas 7 is low. A NOx storage reduction catalyst 11 that decomposes and releases NOx by intervening a reducing agent 10 (light oil), which will be described later, is provided. A NOx storage reduction catalyst 11 is provided in the exhaust pipe 9 so as to bypass the NOx storage reduction catalyst 11. 12 is attached.
[0020]
Here, flow path switching valves 13 and 14 are provided at branch points of the bypass flow path 12 with respect to the exhaust pipe 9 so that the exhaust gas 7 flowing through the exhaust pipe 9 can be appropriately switched and flown to the bypass flow path 12 side. ing.
[0021]
An injection nozzle 15 is provided on the exhaust pipe 9 on the inlet side of the NOx storage reduction catalyst 11, and the injection nozzle 15 and a reducing agent tank 16 at a predetermined location (which can also be used as a fuel tank). Is connected by a reducing agent supply pipe 17, and between the injection nozzle 15 and an air tank 18 at a predetermined location is connected by an air introduction pipe 19, and the supply of the reducing agent in the middle of the reducing agent supply pipe 17 is performed. By driving the pump 20 to guide the reducing agent 10 in the reducing agent tank 16 to the injection nozzle 15, the reducing agent 10 can be sprayed from the injection nozzle 15 toward the inlet side of the NOx storage reduction catalyst 11. If the amount of the reducing agent 10 is small, it is difficult to atomize. Therefore, as an assist for atomization, a small amount of pressurized air may be guided to the injection nozzle 15 by opening the on-off valve 21 in the middle of the air introduction pipe 19. It has a possible structure.
[0022]
In the drawing, reference numeral 22 denotes a muffler provided downstream of the exhaust pipe 9.
[0023]
When the exhaust gas 7 having a high oxygen concentration flows through the NOx storage reduction catalyst 11 by opening the flow path switching valve 13 and closing the flow path switching valve 14 during operation of the diesel engine 1, the NOx in the exhaust gas 7 is reduced. Is stored in the state of nitrate, whereby good reduction of NOx during lean combustion operation of the diesel engine 1 can be achieved.
[0024]
Then, after such NOx occlusion is continued for about 30 seconds to about 3 minutes, the flow path switching valve 14 is opened, the flow path switching valve 13 is closed, and the exhaust gas 7 is diverted to the bypass flow path 12 side to flow. By driving the feed pump 20, the reducing agent 10 is guided from the reducing agent tank 16, and the opening / closing valve 21 is opened as needed to guide a small amount of pressurized air from the air tank 18 as an assist for atomization. The reducing agent 10 is sprayed on the inlet side of the NOx storage reduction catalyst 11.
[0025]
By doing so, the relative excess ratio of air to the amount of the reducing agent 10 is reduced, and the reaction selectivity between the reducing agent 10 and NOx is improved, whereby NOx is actively decomposed from the NOx storage reduction catalyst 11. The NOx storage-reduction catalyst 11 that is released is favorably regenerated, and the released NOx reacts with the reducing agent 10 on the NOx storage-reduction catalyst 11 to be reduced and purified.
[0026]
Further, the NOx storage-reduction catalyst 11 as described in detail below is periodically used at a rate of about once every about 10 to 30 hours (about 10 to 15 hours for high load operation, about 20 to 30 hours for medium load operation). A desulfurization treatment is applied.
[0027]
That is, while the flow path switching valve 13 is opened and the flow path switching valve 14 is closed, the reducing agent 10 is sprayed on the inlet side of the NOx storage reduction catalyst 11 in the same manner as described above while the exhaust gas 7 flows through the NOx storage reduction catalyst 11. The NOx storage reduction catalyst 11 is heated to about 650 to 700 ° C. by the heat generated by the oxidation reaction of the reducing agent 10 in a high-temperature atmosphere with a high oxygen concentration in which the exhaust gas 7 flows, and immediately thereafter. Then, while the flow path switching valve 14 is opened and the flow path switching valve 13 is closed, the reducing agent 10 is again added to the NOx storage reduction catalyst 11 while the exhaust gas 7 is bypassed and flows toward the bypass flow path 12.
[0028]
Thus, it means that the relative excess air ratio relative to the addition amount of the reducing agent 10 is realized rich atmosphere of a small air-fuel ratio than the stoichiometric air-fuel ratio decreases, SO 2 from the NOx storage-reduction catalyst 11 The condition for releasing the NOx is set without performing the operation control of the diesel engine 1, and the NOx storage reduction catalyst 11 is efficiently desulfurized and the poisoning by the sulfate is eliminated.
[0029]
Here, as for the desulfurization treatment of the NOx storage reduction catalyst 11, as shown in FIG. 2, a mode in which the desulfurization treatment by the two-stage addition of the reducing agent 10 as described above is defined as one cycle and repeated several cycles for about 15 minutes is preset. In addition, it is preferable to release most of the sulfate in the NOx storage reduction catalyst 11 as SO 2 so as to sufficiently recover the poisoning deterioration.
[0030]
Therefore, according to the present embodiment, when purifying the exhaust gas of the diesel engine with the NOx storage reduction catalyst, the poisoning of the NOx storage reduction catalyst by the sulfate can be eliminated without performing the operation control on the diesel engine side. Therefore, it is possible to realize application of the exhaust gas purification device using the NOx storage reduction catalyst to a diesel engine.
[0031]
FIG. 3 shows another embodiment of the present invention. In this embodiment, the NOx storage reduction catalysts 11 shown in FIG. The exhaust pipe 9 is branched into two branch passages 9A and 9B so that the exhaust gas 7 can be appropriately transferred and flowed to each of the NOx storage and reduction catalysts 11 and 11 and connected to the NOx storage reduction catalysts 11 and 11 again. It is configured to be joined and guided to the muffler 22. At the branch point of each of the branch flow paths 9A and 9B, the exhaust gas 7 flowing through the exhaust pipe 9 is alternately switched to each of the branch flow paths 9A and 9B. Flow path switching valves 13 and 14 are provided so that they can flow.
[0032]
An injection nozzle 15 is provided on both sides of each of the NOx storage reduction catalysts 11, 11 as in the case of FIG. The reducing agent 10 in the reducing agent tank 16 is guided through the reducing agent supply pipes 17, 17 by driving the feed pumps 20, 20, and pressurized air in the air tank 18 is opened by opening the on-off valves 21, 21 as necessary. A small amount of the reducing agent 10 is guided through the air introduction pipes 19, 19 so that the reducing agent 10 can be selectively sprayed on the inlet sides of the respective NOx storage reduction catalysts 11, 11.
[0033]
Thus, when the NOx storage reduction catalysts 11 are provided in a pair in parallel, the exhaust gas 7 flows through the branch flow passage 9A by opening the flow passage switching valve 13 and closing the flow passage switching valve 14, While the NOx in the exhaust gas 7 is stored in the state of nitrate by the NOx storage reduction catalyst 11 in the branch flow path 9A, the NOx storage reduction catalyst on the branch flow path 9B side where the flow rate of the exhaust gas 7 is restricted. For example, when one of the NOx storage reduction catalysts 11 is used, the NOx can be continuously reduced by regenerating or desulfurizing the NOx. However, it goes without saying that the operation method of the present invention can be similarly applied to the exhaust gas purification device having such a configuration.
[0034]
Note that the method of operating the exhaust gas purification apparatus of the present invention is not limited to the above embodiment, and it is needless to say that various changes can be made without departing from the gist of the present invention.
[0035]
【The invention's effect】
According to the operation method of the exhaust gas purification apparatus of the present invention described above, when purifying the exhaust gas of the diesel engine with the NOx storage reduction catalyst, the poisoning of the NOx storage reduction catalyst by the sulfate is controlled on the diesel engine side. Therefore, it is possible to achieve an excellent effect that the application of the exhaust gas purification device using the NOx storage reduction catalyst to a diesel engine can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of an embodiment for carrying out the present invention.
FIG. 2 is a diagram showing a time schedule in a desulfurization processing mode.
FIG. 3 is a schematic diagram showing another example of the embodiment for carrying out the present invention.
[Explanation of symbols]
Reference Signs List 1 diesel engine 7 exhaust gas 9 exhaust pipe 10 reducing agent 11 NOx storage reduction catalyst

Claims (1)

ディーゼルエンジンからの排気ガスが流通する排気管の途中に、排気ガス中の酸素濃度が高い時にNOxを酸化して硝酸塩の状態で一時的に吸蔵し且つ排気ガス中の酸素濃度が低い時に還元剤の介在によりNOxを分解放出して還元浄化するNOx吸蔵還元触媒を装備し、該NOx吸蔵還元触媒に対し還元剤を適宜に添加し且つ前記NOx吸蔵還元触媒を適宜に迂回させて排気ガスを流し得るように構成した排気浄化装置の運転方法であって、通常はディーゼルエンジンの排気ガスをNOx吸蔵還元触媒に流し、これにより排気ガス中のNOxをNOx吸蔵還元触媒に吸蔵させてNOxの低減化を図る一方、定期的に排気ガスをNOx吸蔵還元触媒を迂回させて流しながら該NOx吸蔵還元触媒に還元剤を添加し、これによりNOx吸蔵還元触媒からNOxを積極的に分解放出させて該NOx吸蔵還元触媒の再生を図り、更には、定期的にNOx吸蔵還元触媒に排気ガスを流しつつ還元剤を添加してNOx吸蔵還元触媒を所定温度以上に昇温させ且つその直後にNOx吸蔵還元触媒を迂回させて排気ガスを流しながらNOx吸蔵還元触媒に再び還元剤を添加して脱硫処理を施すことを特徴とする排気浄化装置の運転方法。In the middle of an exhaust pipe through which exhaust gas from a diesel engine flows, NOx is oxidized when the oxygen concentration in the exhaust gas is high, temporarily stored in the form of nitrate, and reduced when the oxygen concentration in the exhaust gas is low. Is provided with a NOx storage reduction catalyst that decomposes and releases NOx to reduce and purify through the interposition of a NOx storage reduction catalyst, an appropriate amount of a reducing agent is added to the NOx storage reduction catalyst, and the exhaust gas is caused to flow around the NOx storage reduction catalyst appropriately. An operating method of an exhaust gas purifying apparatus configured to obtain the exhaust gas, wherein normally the exhaust gas of a diesel engine is caused to flow through a NOx storage reduction catalyst, whereby NOx in the exhaust gas is stored in the NOx storage reduction catalyst to reduce NOx. On the other hand, a reducing agent is added to the NOx storage-reduction catalyst while exhaust gas is flowed around the NOx storage-reduction catalyst at regular intervals. The NOx storage-reduction catalyst is regenerated by actively decomposing and releasing NOx from the medium. Further, a reducing agent is added to the NOx storage-reduction catalyst at a predetermined temperature by periodically flowing exhaust gas to the NOx storage-reduction catalyst. A method for operating an exhaust gas purifying apparatus, comprising raising the temperature and immediately after that, while passing exhaust gas while bypassing the NOx storage reduction catalyst, adding a reducing agent again to the NOx storage reduction catalyst to perform desulfurization treatment.
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JP4152833B2 (en) * 2003-07-30 2008-09-17 日産ディーゼル工業株式会社 Engine exhaust purification system
EP1691046B1 (en) 2003-09-19 2013-04-24 Nissan Diesel Motor Co., Ltd. Exhaust emission purification apparatus for an internal combustion engine
EP1669567B1 (en) 2003-09-19 2012-03-21 Nissan Diesel Motor Co., Ltd. Exhaust gas purification device of engine
EP2383444B1 (en) 2004-02-02 2012-12-19 Nissan Diesel Motor Co., Ltd. Exhaust emission purifying apparatus for engine
WO2005073527A1 (en) 2004-02-02 2005-08-11 Nissan Diesel Motor Co., Ltd. Device for purifying exhaust gas of internal combustion engine
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JP4972914B2 (en) 2005-11-21 2012-07-11 いすゞ自動車株式会社 Exhaust gas purification system regeneration control method and exhaust gas purification system
JP2009002225A (en) * 2007-06-21 2009-01-08 Hino Motors Ltd Exhaust emission control device
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