JP4226143B2

JP4226143B2 - Catalytic combustion apparatus and combustion control method thereof

Info

Publication number: JP4226143B2
Application number: JP15648699A
Authority: JP
Inventors: 徹生寺島; 清田口; 良隆川崎; 基啓鈴木; 次郎鈴木
Original assignee: Panasonic Corp; Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Corp; Panasonic Holdings Corp
Priority date: 1998-06-05
Filing date: 1999-06-03
Publication date: 2009-02-18
Anticipated expiration: 2019-06-03
Also published as: JP2000055312A

Description

【０００１】
【発明の属する技術分野】
本発明は、主に発熱源や暖房用などに用いられる、気体燃料または液体燃料を触媒燃焼させる触媒燃焼装置において、特に高温耐久性の向上と可変燃焼量幅の拡大技術に関するものである。
【０００２】
【従来の技術】
燃料に対して酸化活性を有する触媒体を用いてその表面で触媒反応を行う触媒燃焼装置は従来より多数提案されているが、その燃焼方式には図１に示すような予混合気型の構成が一般的であった。
【０００３】
図１に示す従来の予混合気型では、１の燃料供給バルブから供給された燃料ガスは、２の空気供給バルブより供給された空気と予混合室３で混合され、予混合気入口４から予熱バーナ５に送られる。予混合気は、点火装置６により点火され、予熱バーナ５に火炎を形成する。火炎により生じた高温の排気ガスは燃焼室７内に設けられた触媒体８を加熱しながら通過し、排気口９より排出される。触媒体８が昇温され、触媒活性温度となると、一旦燃料供給バルブ１により燃料の供給を停止し、予熱バーナ５に形成された火炎を消滅させる。その後、直ちに燃料を再供給することにより、触媒燃焼を開始する。触媒体８は高温状態となり、触媒体８上流に対向する位置に設けられたガラス１０を通して輻射放熱するとともに、排気ガスとして放熱することで加熱、暖房や乾燥を行っていた。上記予混合気型では、常に空気過剰率（燃料の完全酸化反応に必要な理論空気量に対する実空気量の比）１以上の予混合気が触媒体８に供給され、触媒体８は過剰な酸素が存在する雰囲気で使用されていた。
【０００４】
【発明が解決しようとする課題】
上記従来の触媒燃焼装置では、触媒体の反応中心位置で常に酸素が共存する高温雰囲気が形成され、触媒成分の熱劣化が避けられないものであった。一般的に燃焼用触媒としてはＰｔ，Ｐｄ，Ｒｈなどの白金族系金属が耐熱性や反応活性の点から用いられることが多いが、８００〜９００℃にも至る高温では、貴金属粒子の凝集や蒸散などによる活性点の減少により、長時間安定した燃焼性能を得ることが困難であった。予混合気型の触媒燃焼装置では、活性低下によって反応中心位置が触媒体の下流側へと移行し、完全燃焼が維持できなくなったり、上流側表面からの輻射熱を利用するものでは使用時間の増加とともに輻射熱量が低下することにもなる。
【０００５】
本発明は、このような従来の触媒燃焼装置の高温耐久性の問題と可変燃焼量幅の狭さを考慮し、高温耐久性の向上と可変燃焼量幅の拡大を実現できる触媒燃焼装置を提供することを目的とする。
【０００６】
【課題を解決するための手段】
第１の本発明は、上流側に設けられた、燃料と空気の混合気入口と、下流側に設けられた排ガス出口と、多数の連通孔を有する基材に酸化触媒を担持させた第一の触媒体が配置された一次燃焼室と、前記一次燃焼室の下流側に設けられた、混合気または空気の二次供給口と、その二次供給口の下流に設けられ、第二の触媒体が配置された二次燃焼室とを備え、
燃焼する際、燃焼初期に前記二次燃焼室の第二の触媒体が所定温度未満の場合、前記一次燃焼室の空気過剰率は、１以上として燃焼し、
前記二次燃焼室の第二の触媒体が所定温度以上に昇温すると、前記一次燃焼室の空気過剰率は、１未満として燃焼し、
前記第一の触媒体の酸化触媒は、ＰｔもしくはＲｈ、またはＰｔもしくはＲｈを主体とする材料で構成され、
前記第一の触媒体は、ＣｅＯ₂またはＺｒＯ₂の一方あるいは両者を主成分として含む触媒燃焼装置である。
又、第２の本発明は、前記所定温度とは、前記二次燃焼室における燃料成分が酸化される割合が、あるいは排ガス中における可燃成分濃度が、所定のレベルとなる温度である第１の本発明の触媒燃焼装置である。
又、第３の本発明は、前記第二の触媒体は、多数の連通孔を有する基材に酸化触媒を担持させたものである、第１または２の本発明の触媒燃焼装置である。
又、第４の本発明は、前記第一の触媒体の酸化触媒がＰｔを主体とする材料で構成され、前記第二の触媒体がＰｄを主成分とした材料で構成され、前記所定温度を５００℃とする第３の本発明の触媒燃焼装置である。
又、第５の本発明は、前記二次燃焼室に供給する空気は、前記二次燃焼室の排気ガスにより加熱されることにより予熱されることを特徴とする第１〜４のいずれかの本発明の触媒燃焼装置である。
又、第６の本発明は、前記混合気入口から供給される混合気の空気過剰率は、前記燃料の供給量の減少とともに減少させることを特徴とする第１〜４のいずれかの本発明の触媒燃焼装置である。
又、第７の本発明は、前記混合気入口から供給される混合気の燃料の供給量は実質上一定として空気量のみ増減させるとともに、少なくともその増減量相当分の空気を前記二次供給口から供給することを特徴とする第１〜４のいずれかの本発明の触媒燃焼装置である。
又、第８の本発明は、前記第一の触媒体の基材の熱伝導率が１０Ｗ／ｍ・℃以上であることを特徴とする第１〜４のいずれかの本発明の触媒燃焼装置である。
又、第９の本発明は、前記ＰｔまたはＰｔを主体とする酸化触媒を担持させた触媒体は、ＰｔまたはＰｔを主体とする酸化触媒層と、ＲｈまたはＰｄを主体とする酸化触媒層とが積層して設けられていることを特徴とする第１の本発明の触媒燃焼装置である。
又、第１０の本発明は、前記ＰｔまたはＰｔを主体とする酸化触媒層に対して積層される前記ＲｈまたはＰｄを主体とする酸化触媒層は、下流側に部分的に設けられていることを特徴とする第９の本発明の媒燃焼装置である。
又、第１１の本発明は、前記燃焼する際、前記一次燃焼室の空気過剰率を１未満として燃焼する方法として、
前記一次燃焼室の空気過剰率を変動させて、前記触媒体の近傍に設けられた温度検知部により前記触媒体の温度が最高となる空気過剰率を判定しておき、前記空気過剰率より低い空気過剰率領域で前記一次燃焼室の燃焼を行うことを特徴とする第１の本発明の触媒燃焼装置である。
【０００７】
又、第１２の本発明は、上流側に設けられた、燃料と空気の混合気入口と、下流側に設けられた排ガス出口と、多数の連通孔を有する基材に酸化触媒を担持させた第一の触媒体が配置された一次燃焼室と、前記一次燃焼室の下流側に設けられた、混合気または空気の二次供給口と、その二次供給口の下流に設けられ、第二の触媒体が配置された二次燃焼室とを備えた触媒燃焼装置の燃焼制御方法であって、
燃焼する際、燃焼初期に前記二次燃焼室の第二の触媒体が所定温度未満の場合、前記一次燃焼室の空気過剰率は、１以上として燃焼し、
前記二次燃焼室の第二の触媒体が所定温度以上に昇温すると、前記一次燃焼室の空気過剰率は、１未満として燃焼し、
前記第一の触媒体の酸化触媒は、ＰｔもしくはＲｈ、またはＰｔもしくはＲｈを主体とする材料で構成され、
前記第一の触媒体は、ＣｅＯ₂またはＺｒＯ₂の一方あるいは両者を主成分として含む触媒燃焼装置の燃焼制御方法である。
【０００８】
【発明の実施の形態】
以下に本発明及び本発明に関連する発明の実施の形態について、図面を参照して説明する。
（実施の形態１）
図２は本発明に関連する発明の第一の実施の形態の要部断面図であり、その構成を作用とともに説明する。すなわち、１の燃料供給バルブから供給された燃料ガスは、空気供給バルブ２より供給された空気と予混合室３で混合され、混合気入口４から予熱バーナ５に送られる。混合気は、点火装置６により点火され、予熱バーナ５に火炎を形成する。火炎により生じた高温の排気ガスは一次燃焼室１１内に設けられた、ＰｔもしくはＲｈ、またはＰｔもしくはＲｈを主体とする酸化触媒を多数の連通孔を有する基材に担持させた、一次燃焼室としての第一の触媒体１２を加熱しながら通過し、二次混合気または空気の供給部１３から供給される混合気と混合され、下流の二次燃焼室１４を通過し、排気口９より排出される。第一の触媒体１２が昇温され、燃料に対する触媒活性温度となると、一旦燃料供給バルブ１により燃料の供給を停止し、予熱バーナ５に形成された火炎を消滅させる。その後、直ちに燃料を再供給することにより、触媒燃焼を開始するようになっている。第一の触媒体１２は高温状態となり、第一の触媒体１２上流に対向する位置に設けられたガラス１０を通して輻射放熱するとともに、排気ガスとして放熱することで加熱、暖房や乾燥を行う。
【０００９】
ここで、所定の条件を満足する場合、予混合室３に供給される燃料ガスと空気からなる混合気の空気過剰率は１未満となっており、第一の触媒体１２においては空気がやや不足する条件、すなわち還元雰囲気となっている。したがってここでの燃焼排ガスは、未燃焼の燃料ガス、部分酸化生成物としてのＣＯ、Ｈ₂、各種炭化水素と、完全燃焼生成物のＣＯ₂と水とＮ₂が含まれたものとなっている。この第一の触媒体１２通過後の排ガスに対して、二次混合気または空気の供給部１３から空気が供給される。空気の量は、二次燃焼室１４で完全燃焼させるために二次燃焼室１４の入口で空気過剰率１以上とすることが望ましい。図２に示す構成のように、二次燃焼室１４内には炎口１５が設けられており（炎口１５等で二次燃焼室が構成される）、ここに着火して（着火手段は特に図示せず）火炎を形成すると、未燃焼生成物や部分酸化生成物も完全燃焼され、排気口９からはクリーンな完全燃焼排ガスが放出されることになる。
【００１０】
なお、予熱バーナ５上に火炎を形成するのと同時に炎口１５にも火炎を形成し、即座に未燃焼生成物や部分酸化生成物の完全燃焼を実現することが可能となる。また、二次混合気または空気の供給部１３からは、空気のみの供給でもよいが、空気過剰な燃料と空気の混合気を供給してもよく、二次燃焼室１４での完全燃焼を維持するのに必要十分な燃料を追加供給することも可能である。
【００１１】
この条件で使用される第一の触媒体１２に担持される触媒成分は、少なくとも、ＰｔもしくはＲｈ、またはＰｔもしくはＲｈを主体とする酸化触媒であることが望ましく、この場合には熱劣化の抑制と可変燃焼量幅の拡大が同時に得られる。ここで、Ｐｔ又はＲｈを主体とするという意味は、少なくとも主に触媒反応に寄与する活性成分としてＰｔ又はＲｈが含まれているということを意味する。
【００１２】
また、本発明に関連する発明及び以下の本発明では、第一の触媒体に供給されるガスの空気過剰率λが１未満であるということを、空気過剰率λを燃焼量一定条件下で変動させて、触媒上流の最高温度（上流温度で代表されることが多い）が最も高くなる位置を空気過剰率が１近傍であるものと判定し、それよりも空気過剰率が低くなる領域で燃焼させるようにしている。通常ＰｔまたはＰｔを主体とする酸化触媒を用いた触媒燃焼では、燃焼量一定で空気過剰率λを変動させると、触媒最高温度は図５に示すように空気過剰率λ＝１近傍で最も高くなるため、適宜空気過剰率λを変化させ、触媒上流温度を図２に示す温度センサ２０等でモニターする操作を組み入れることにより、空気過剰率λを１未満に制御することが可能となる。なお、この構成に関する詳細な効果は後述する。
（実施の形態２）
本発明にかかる実施の形態は、基本構成と作用は実施の形態１と同様であるが、二次燃焼室１４の内部構成が異なる。したがってその構成の相違点を中心に作用とともに説明する。図３は、本発明第二の実施の形態の要部断面図である。二次燃焼室１４には、セラミックスハニカムにＰｄを担持した、二次燃焼室としての第二の触媒体１６を設置しており、その上流面近傍には電気ヒータ１７が添装されており、またその近傍には温度センサ１８が設置されている。
【００１３】
上記構成において、定常燃焼時には実施の形態１と同様に、未燃焼成分を含む排ガスが第二の触媒体１６に至り、ここで火炎を形成せずに触媒燃焼させることが可能となり、窒素酸化物の生成もなく、また希薄な可燃物濃度でも確実に酸化浄化することが可能となる。また、第二の触媒体１６近傍に電気ヒータ１７を添装して加熱することにより、第二の触媒体１６を常時活性温度以上に維持することが可能となる。特に炭化水素成分の中でも反応しにくいメタンが燃料成分や未燃焼成分として存在する場合には、図６に示すメタン酸化活性の温度依存性からも推測されるように、第二の触媒体１６を５００℃程度以上に維持することが必要となるが、この電気ヒータ１７によって、第一の触媒体１２での燃焼量に関わりなくその第二の触媒体１６の温度を制御できることから、常にクリーンな排ガスを確保することができる。このような加熱手段は本実施の形態のように電気加熱に限定されるものでなく、第二の触媒体１６の上流近傍に別途形成される火炎加熱手段を用いてもよい。
【００１４】
また、上記加熱手段を用いずに、低燃焼量時などのように、第二の触媒体が５００℃以下になり、浄化作用が不十分、すなわち燃焼率が９５％以下となるような条件下では、空気過剰率を１以上として完全燃焼させることも可能である。
【００１５】
また、一次燃焼室１１に供給される混合気の空気過剰率λを変化させて反応する燃料の割合を制御することにより、第一の触媒体１２の温度制御をするとともに第二の触媒体１６を５００℃以上に保持して二次燃焼を電気ヒータ１７無しに実現することも可能となる。すなわち、低燃焼量すなわち燃料供給速度が小さく第一の触媒体１２および第二の触媒体１６の温度が低くなる条件の場合に、一次燃焼室１１に対する混合気の空気過剰率λを意図的に低下させ、一次燃焼室１１における未燃焼分の割合を増加させ、それによって二次燃焼室１４において燃焼する量を増加させることにより、第二の触媒体１６の温度を高く維持することができる。また同様の効果は、燃焼量一定のままで一次燃焼室１１における空気過剰率λを増加させるとともに、少なくとも一次燃焼室１１における増量相当分の空気を二次燃焼室１４に減少供給することによっても得ることができる。あるいは、空気過剰率λを減少させるとともに、少なくとも一次燃焼室１１における減少相当分の空気を二次燃焼室１４に追加供給することによっても得ることができる。すなわち、一次燃焼室１１における空気過剰率λを比較的小さくなるように制御すると、第一の触媒体１２の温度は比較的低温となり、未燃成分量は第二の触媒体１６で完全燃焼されるようになり、第二の触媒体１６の温度は高温に維持されることになる。一方、一次燃焼室１１における空気過剰率λが比較的大きくなるように制御すると、第一の触媒体１２の温度が比較的高温となり、第二の触媒体１６も排ガスによって加熱されるため、第二の触媒体１６の温度も５００℃以上に保持することができる。
【００１６】
これらの操作は実施の形態１にも適用することが可能である。また、第一の触媒体１２の火炎予熱時など、第二の触媒体１６が十分に昇温していない場合には、二次混合気または空気の供給部１３から空気を追加供給して１以上としても、未燃焼成分を十分浄化することができない。そこで、第二の触媒体１６が浄化作用に十分な温度に至るまでの間は、電気ヒータ１７や別途設ける加熱バーナなどで予熱したり、あるいは予混合室３に供給する混合気の空気過剰率を１以上として、予熱バーナ５での完全燃焼火炎で加熱するなどの手段を用いることにより、燃焼初期からの完全浄化が可能となる。
【００１７】
ここで、上記浄化作用に十分な温度とは、少なくとも触媒でＣＯが９５％以上酸化されるか、排ガス中に含まれるＣＯ濃度が５０ppm以下となる温度（約２００℃以上）であり、好ましくは燃料成分が９５％以上酸化されるか、排ガス中に含まれる可燃成分濃度が１０００ppm以下となる温度（約５００℃以上）である。
【００１８】
なお、本実施の形態には第二の触媒体１６にＰｄを主体とする触媒を用いたが、空気過剰条件下でのメタン、ＣＯ，Ｈ₂の酸化活性に優れる、白金族系金属を無機酸化物に担持した触媒、遷移金属触媒、あるいは複合酸化物触媒などいずれから選択しても構わない。
【００１９】
なお、この構成に関する詳細な効果は後述する。
（実施の形態３）
本実施の形態は、基本構成と作用は実施の形態２と同様であるが、二次燃焼室１４、あるいは前記二次燃焼室１４から排気口９に至る沿道に排熱回収部１９を設けている点で構成が異なる。したがってその構成の相違点を中心に作用とともに説明する。図４は、本発明第三の実施の形態の要部断面図である。前記二次燃焼室１４から排気口９に至る沿道に設けられた排熱回収部１９は、二次燃焼室１４から得られる熱および排気ガスに含まれる熱を回収すると同時に二次混合気または空気の供給部１３から供給される空気または混合気を予熱し、第二の触媒体１６の加熱に必要とする熱量を大幅に低減することが可能となる。
【００２０】
【実施例】
以下、本発明の実施例７、及び本発明に関連する発明の実施例１〜６、８〜１０について述べる。
（実施例１）セラミックス製ハニカム（材質コージライト、４００セル／ｉｎｃｈ²、壁厚０．１５、φ５０、長さ２０）を、１０００℃で１時間予備焼成したＣｅ／ＢａＯ・Ａｌ₂Ｏ₃粉末１００ｇ、硝酸アルミニウム９水塩１０ｇ、水１３０ｇ、Ｐｔジニトロジアンミン塩水溶液をＰｔ換算で２ｇ、を加えてなるウォッシュコートスラリーＡに含浸し、乾燥後、５００℃で焼成して、Ｐｔ３ｇ／L（ハニカム嵩容積）相当担持することにより、第一の触媒体１２を形成した。
【００２１】
次に、セラミックス製ハニカム（材質コージライト、４００セル／ｉｎｃｈ²相当、壁厚０．１５、φ２０、長さ１０）を、１０００℃で１時間予備焼成した活性アルミナ粉末１００ｇ、硝酸アルミニウム９水塩１０ｇ、水１３０ｇ、Ｐｄジニトロジアンミン塩水溶液をＰｄ換算で２ｇ、を加えてなるウォッシュコートスラリーＢに含浸し、乾燥後、５００℃で焼成して、Ｐｄ３ｇ／L相当担持することにより、第二の触媒体１６を形成した。次に、図３に示す触媒燃焼装置に上記で得た第一の触媒体１２および第二の触媒体１６を装着した。燃料に都市ガス１３Ａを用い、一次燃焼室１１に供給される予混合気の空気過剰率λを０．９５とした。供給部１３からの予混合気又は空気の供給については、二次燃焼室１４へ予混合気又は空気を供給部１３から追加した後の混合気の総合の空気過剰率λが１．２となるようにした。第二の触媒体１６は、電気ヒータ１７を制御することにより、定常時に５００℃以上となるように設定されている
（実施例２）金属製ハニカム（材質ＦｅＣｒＡｌ、４００セル／ｉｎｃｈ²相当、壁厚０．１５、φ５０、長さ２０）を、実施例１で用いたものと同様のウォッシュコートスラリーＡに含浸し、乾燥後、５００℃で焼成して、Ｐｔ３ｇ／L相当担持することにより、第一の触媒体１２を形成した。次に、図３に示す触媒燃焼装置に、上記で得た第一の触媒体１２と実施例１と同様にして得た第二の触媒体１６を装着した。一次燃焼室１１に供給される予混合気の空気過剰率の制御、二次燃焼室１４に供給される空気供給量の制御、および第二の触媒体１６に対する温度制御は実施例１と同様に行った。
（実施例３）実施例１と同様に、第一の触媒体１２を形成した。次に図２に示す触媒燃焼装置に第一の触媒体１２を装着した。一次の混合気の空気過剰率は実施例１と同様に０．９５とした。炎口１５から二次燃焼室１４へ供給される都市ガスの燃焼量は４０ｋｃａｌ／ｈとし、都市ガスと空気からなる二次の混合気の空気過剰率は、一次燃焼室１１からの排気ガスと混合されて総合してλ＝１．２となるように設定した。
（実施例４）実施例１と同じ構成の触媒燃焼装置を用い、一次燃焼室１１においては、図１２、図１３に示すように燃焼量が小さくなるほど空気過剰率λが小さくなるように燃料供給量および空気供給量を制御した。二次燃焼室１４には、二次燃焼室１４入口で一次排ガスと混合された後の総合の空気過剰率λが１．２となるように空気供給量を制御した。
（実施例５）実施例１と同じ構成の触媒燃焼装置を用い、一次燃焼室１１に供給される都市ガス１３Ａを４００ｋｃａｌ／ｈ一定とし、一次燃焼室１１に供給される空気量を増減させた。二次燃焼室１４には、二次燃焼室１４入口で一次排ガスと混合された後の総合の空気過剰率λが１．２となるように空気供給量を制御した。
（実施例６）実施例１と同じ構成の触媒燃焼装置を用い、都市ガス１３Ａの供給量が１８０ｋｃａｌ／ｈ未満の場合には一次燃焼室１１に供給される混合気の空気過剰率λが１．２となるように空気量を制御し、１８０ｋｃａｌ／ｈ以上では空気過剰率λが０．９５となるように、かつ二次燃焼室１４では二次燃焼室１４入口で一次排ガスと混合された後の総合の空気過剰率λが１．２となるように空気供給量を制御した。
（実施例７）実施例１と同じ構成の触媒燃焼装置を用い、温度センサ１８が第二の触媒体１６の上流温度が２００℃になるのを検知するまでは、都市ガス１３Ａ＝４００ｋｃａｌ／ｈ、空気過剰率λ＝１．２の条件下で形成された火炎によって第一の触媒体１２を予熱し、２００℃になるのを検知した後は、一次燃焼室１１に供給される空気過剰率λが０．９５となるように空気供給量を制御した。定常時の一次燃焼室１１に供給される予混合気の空気過剰率の制御、二次燃焼室１４に供給される空気供給量の制御、および第二の触媒体１６に対する温度制御は実施例１と同様に行った。
（実施例８）セラミックス製ハニカム（材質コージライト、４００セル／ｉｎｃｈ²相当、壁厚０．１５、φ５０、長さ２０）を、実施例１で用いたのと同様のウォッシュコートスラリーＡに含浸し、乾燥後、５００℃で焼成して、Ｐｔ２ｇ／L相当担持し、次いで実施例１で用いたものと同様のウォッシュコートスラリーＢに含浸、乾燥後、５００℃で焼成することにより、図７に示すようなＰｄ１ｇ／Ｌ相当をＰｔ担持層上に積層担持させた第一の触媒体１２を形成した。次に、図３に示す触媒燃焼装置に上記で得た第一の触媒体１２および実施例１と同様にして得た第二の触媒体１６を装着した。一次燃焼室１１に供給される予混合気の空気過剰率の制御、二次燃焼室１４に供給される空気供給量の制御、および第二の触媒体１６に対する温度制御は実施例１と同様に行った。
（実施例９）セラミックス製ハニカム（材質コージライト、４００セル／ｉｎｃｈ²相当、壁厚０．１５、φ５０、長さ２０）を、実施例１で用いたのと同様のウォッシュコートスラリーＡに含浸し、乾燥後、５００℃で焼成して、Ｐｔ２．８ｇ／L相当担持し、次いで実施例１で用いたものと同様のウォッシュコートスラリーＢに上記ハニカム面の一端部を含浸させ、乾燥後、５００℃で焼成することにより、図８に示すようなＰｄ０．２ｇ／Ｌ相当をＰｔ担持層上に部分的に（端面より約３ｍｍの位置まで）積層担持させた第一の触媒体１２を形成した。次に、図３に示す触媒燃焼装置に上記で得た第一の触媒体１２および実施例１と同様にして得た第二の触媒体１６を装着した。一次燃焼室１１に供給される予混合気の空気過剰率の制御、二次燃焼室１４に供給される空気供給量の制御、および第二の触媒体１６に対する温度制御は実施例１と同様に行った。なお、Ｐｄの代わりにＲｈでもかまわない。
（実施例１０）セラミックス製ハニカム（材質コージライト、４００セル／ｉｎｃｈ²相当、壁厚０．１５、φ５０、長さ２０）を、５００℃で１時間予備焼成したＺｒＯ₂粉末１００ｇ、水１００ｇ、Ｐｔジニトロジアンミン塩水溶液をＰｔ換算で２ｇ、を加えてなるウォッシュコートスラリーＣに含浸し、乾燥後、５００℃で焼成して、Ｐｔ３ｇ／L（ハニカム嵩容積）相当担持することにより、第一の触媒体１２を形成した。次に、図３に示す触媒燃焼装置に上記で得た第一の触媒体１２および実施例１と同様にして得た第二の触媒体１６を装着した。一次燃焼室１１に供給される予混合気の空気過剰率の制御、二次燃焼室１４に供給される空気供給量の制御、および第二の触媒体１６に対する温度制御は実施例１と同様に行った。
（比較例１）実施例１と同様にして得たＰｔを担持した触媒体８を図１に示す構成の触媒燃焼装置に装着した。空気過剰率λ＝１．２一定とした。
（比較例２）セラミックス製ハニカム（材質コージライト、４００セル／ｉｎｃｈ²相当、壁厚０．１５、φ５０、長さ２０）を、１０００℃で１時間予備焼成したＣｅ／ＢａＯ・Ａｌ₂Ｏ₃粉末１００ｇ、硝酸アルミニウム９水塩１０ｇ、水１３０ｇ、Ｐｄジニトロジアンミン塩水溶液をＰｄ換算で２ｇ、を加えてなるウォッシュコートスラリーＤに含浸し、乾燥後、５００℃で焼成して、Ｐｄ３ｇ／L相当担持することにより、触媒体８を形成した。次に、比較例１と同様に図１に示す構成の触媒燃焼装置に上記で得た触媒体８を装着した。比較例１と同様に空気過剰率λを１．２に設定した。
（比較例３）比較例２における触媒体８と同様に形成した第一の触媒体１２、および実施例１と同様に形成した第二の触媒体１６を図３に示す構成の触媒燃焼装置に装着した。一次燃焼室１１に供給される予混合気の空気過剰率の制御、二次燃焼室１４に供給される空気供給量の制御、および第二の触媒体１６に対する温度制御は実施例１と同様に行った。
（比較例４）セラミックス製ハニカム（材質コージライト、４００セル／ｉｎｃｈ²相当、壁厚０．１５、φ５０、長さ２０）を、１０００℃で１時間予備焼成したＣｅ／ＢａＯ・Ａｌ₂Ｏ₃粉末１００ｇ、硝酸アルミニウム９水塩１０ｇ、水１３０ｇ、Ｐｄジニトロジアンミン塩水溶液をＰｄ換算で０．７ｇ、Ｐｔジニトロジアンミン塩水溶液をＰｔ換算で１．３ｇ加えてなるウォッシュコートスラリーＥに含浸し、乾燥後、５００℃で焼成して、Ｐｄ１ｇ／L、Ｐｔ２ｇ／Ｌ相当を同時担持することにより、第一の触媒体１２を形成した。次に実施例１と同様に第二の触媒体１６を形成した。次に、図３に示す構成の触媒燃焼装置に上記で得た第一の触媒体１２および第二の触媒体１６を装着した。一次燃焼室１１に供給される予混合気の空気過剰率の制御、二次燃焼室１４に供給される空気供給量の制御、および第二の触媒体１６に対する温度制御は実施例１と同様に行った。（比較例５）実施例２における第一の触媒体１２と同様に形成したＰｔを担持した触媒体８を用い、図１に示す構成の触媒燃焼装置に装着した。空気過剰率λ＝１．２と一定とした。
【００２２】
上記実施例１〜１０および比較例１〜５において、流れ方向の触媒層温度分布、触媒燃焼を開始するまでの予熱時間、予熱後および定常時の排ガス成分、および燃焼継続可能な最低燃焼量（低温限界燃焼量）等を調べた。流れ方向の触媒層温度分布は熱電対を走査することによって測定した。また、予熱時間は所定時間予熱後、再度混合気を供給し、触媒燃焼の開始の可否によって判断した。また、排ガス成分はＨＣ（全炭化水素）−ＣＯ−ＣＯ₂メータによって測定した。また、低温限界燃焼量は実施例１〜３、６〜９、比較例１〜４は空気過剰率λを一定とし、燃焼量を変化させて燃焼継続を６時間確認して判断した。実施例４は前記記載の方法で燃焼量を変化させた。燃焼寿命試験は、実施例１、２、９、１０および比較例１〜４について行った。実施例１、９および比較例１〜４では燃焼量（都市ガス供給量）４００ｋｃａｌ／ｈ条件下で、実施例１、２、１０および比較例５は５５０ｋｃａｌ／ｈ条件下で行った。触媒上流温度の経時変化は輻射温度計によって測定した。
［触媒上流温度経時変化］
図９、図１０に実施例１、２、９、１０および比較例１〜５の、各条件下における燃焼寿命試験最高１０００時間までの触媒上流温度の経時変化を示す。図９は、燃焼量４００ｋｃａｌ／ｈ条件下における結果である。空気過剰率１．２条件下で試験を行った比較例１、２では、初期より急激に上流温度の低下が観測され、顕著な劣化が見られた。比較例２では約１００時間経過後から触媒温度の上昇と下降を繰り返す、Ｐｄに固有の（または特徴的な）振動現象が観察された。一方、空気過剰率１未満で第一の触媒体１２を燃焼させた実施例１、９では、初期の触媒上流温度が１０５０℃と高温であるのにも関わらず、活性変化はわずかであり、還元状態ではＰｔが劣化しにくいことが判明した。しかしながらＰｄを主体とする第一の触媒体１２を用いて空気過剰率１未満で試験を行った比較例３では、５００時間までに触媒上流温度が極端に低下した。同様にその他の単独貴金属触媒粒子について試験したが、空気過剰率１未満における耐熱寿命の改善効果についてはＰｔが最も好ましかった。また、Ｒｈについては、本実施例における空気過剰率λ＝０．９５の条件下ではＰｔに劣るが、さらに低い空気過剰率条件下では、Ｐｔと同等の耐熱寿命性能を示した。本発明及び本発明に関連する発明にはＰｔもしくはＲｈ、またはＰｔもしくはＲｈを主体とする酸化触媒を燃焼室に用いることで空気過剰率が１未満における改善効果が得られるものといえる。また、ＰｔとＰｄを混合した比較例４はＰｄよりも耐久性に劣る結果となった。
【００２３】
図１０は、燃焼量を５５０ｋｃａｌ／ｈまで増加させた時の実施例１、２、１０および比較例５における燃焼寿命試験結果を示している。コージライト製ハニカムを用いた実施例１、１０では初期の触媒上流温度は１１５０℃に達した。実施例１では１０００時間までに触媒上流温度は約１００℃の低下したのに対し、実施例１０では、約５０℃の低下を示すのみであった。実施例１ではＰｔの担体にＣｅ・Ｂａ添加Ａｌ₂Ｏ₃を用いているのに対し、実施例１０ではＺｒＯ₂を用いている相違がある。この理由については現在明らかではないが、ＰｔとＺｒＯ₂の相互作用が関係あるものと推測される。同様の効果はＰｔの担体にＣｅＯ₂を用いた場合にも見られた。また、金属製ハニカムを用いた実施例２および比較例５の場合には、初期の触媒上流温度はコージライト製ハニカムの場合と比較して約１５０℃低下した１０００℃であった。比較例５では触媒上流温度は約８５０℃まで低下したのに対して、実施例２における触媒上流温度は初期と変化がなく、約１０００℃を維持した。コージライトに比較して熱伝導性に優れた耐酸化性金属製ハニカムを用い、それにＰｔを主体とした触媒を担持し、空気過剰率１未満で燃焼させることにより、より高い燃焼負荷（単位面積あたりの燃料供給量）で燃焼させることが可能となることがわかった。
［触媒層の流れ方向の温度分布］
また、実施例１と実施例２における、触媒層の流れ方向の温度分布（５５０ｋｃａｌ／ｈ条件下、および実施例１については４００ｋｃａｌ／ｈ条件下も図示）を図１１に示す。第一の触媒体１２の基材に金属製ハニカムを用いた実施例２では、コージライト製ハニカムを用いた実施例１に比べて温度分布が緩やかであった。すなわち、金属製ハニカムを用いることにより、コージライト製ハニカムに比べて最高温度の局所的高温化抑制しつつ、下流温度を高温化する事が出来る。第二の触媒体１６の最高温度は、第一の触媒体１２における下流温度の影響を直接的に受けるため、第二の触媒体の温度を５００℃以上に保つためには、本発明に関連する発明の実施例２のように、第一の触媒体の基材として、この分野で汎用されるコージライト（１〜２Ｗ／ｍ・℃）に比較して、本発明の実施例２で用いたような、金属などの熱伝導率が１０Ｗ／ｍ・℃以上の、熱伝導率が高い材料を用いることが有効であることが示された。金属ハニカム用の基材には、比較的耐酸化性に優れたＡｌを３％以上含むフェライト系ステンレスが好ましく、同様に熱伝導性がコージライト基材よりも高く、純アルミナ焼結体よりも耐熱衝撃性が高いＳｉＣなどのセラミックス基材を用いてもよい。
［予熱時間］
表１には、燃焼量２５０ｋｃａｌ／ｈ条件下、触媒燃焼を開始するのに要する最低の予熱時間を調べた結果を示す。
【００２４】
【表１】

実施例１では、第一の触媒体１２と触媒体８が同じ組成である比較例１に比べて大幅に予熱時間が短縮された。第一の触媒体１２が予熱される速度は大差ないか、あるいは実質燃焼量は比較例１のほうが高いのにも関わらず、還元雰囲気によって触媒上での反応性が向上し、より短時間で触媒燃焼の開始が可能となったものと推測される。また、実施例８、９のように、Ｐｔ層とＰｄ層を積層した第一の触媒体１２を用いた場合は、さらに大幅に短縮された。比較例３の結果からわかるように、Ｐｄ単独では、実施例１のＰｔに比べて、還元雰囲気でもより短持間で触媒燃焼を開始することが可能であった。燃焼寿命については前記のようにＰｄ単独の比較例３、あるいはＰｔとＰｄが同一層内に存在する比較例４では充分でなく、したがって本発明に関連する発明の実施例８、９のようにＰｄ層をＰｔ層と積層して設けた第一の触媒体１２を還元雰囲気で用いることにより、長寿命化および予熱時間の短縮化が可能となる。同様の効果はＲｈを用いた場合でも見られた。また、図８に示すように、Ｐｄ層またはＲｈ層は温度が低く劣化が過小となる下流側に部分的に設けるほうが、燃焼寿命的にもコスト的にも有利となる。
［低温限界燃焼量］
次に本発明に関連する発明の実施例１、２および比較例１、２、３において低温限界燃焼量を測定した結果を表２に示す。
【００２５】
【表２】

本発明に関連する発明の実施例１および比較例３では、低温限界燃焼量が最も小さかった。これは空気過剰率の減少により流速が小さくなるとともに、それ以上にＰｔやＰｄが還元的に活性化されている、あるいは燃焼機構が異なっているためと考えられる。同様に金属基材を用いた実施例２でも同様の構成で空気過剰率λ＝１．２条件下の比較例４に比べて格段に低温限界が低温化した。すなわち、空気過剰率１未満で燃焼させることによりＴＤＲが拡大できるものと考えられる。
【００２６】
次に本発明に関連する発明の実施例１と実施例４について比較する。実施例４では図１２に示すように一次燃焼室１１入口における空気過剰率が燃焼量の低下とともに低下するように制御されているため、低燃焼量になるほど未燃焼成分の割合が増加し、第二の触媒体１６で燃焼する。そのため、実施例１に比較して低い燃焼量では第一の触媒体１２の上流温度は低下し、第二の触媒体１６の温度は上昇した。このような制御を用いることにより、ヒータなどの加熱手段を用いることなく、未燃焼成分やＣＯの浄化が可能となった。低温限界燃焼量は、実施例４では実施例１と比較して触媒上流温度が低下するにもかかわらず、実施例１と同じく６０ｋｃａｌ／ｈであった。これは、実施例４では、実施例１よりも６０ｋｃａｌ／ｈにおける一次燃焼室１１入り口における空気過剰率が低くなるように制御されているため、燃焼率および触媒上流温度は低下するが、図１３に示すように、低温限界燃焼量も空気過剰率λの減少に伴い低下するためである。
【００２７】
実施例５では、燃焼量を４００ｋｃａｌ／ｈと略一定であり、空気過剰率を変化させて第一の触媒体１２における実質燃焼量および触媒温度を制御しているため、第一の触媒体１２と第二の触媒体１６の最高温度は、空気過剰率λに応じて図１４に示すように変化した。第二の触媒体１６は、５００℃以上に昇温されているため、空気過剰率の変化に伴う未燃焼成分やＣＯの排出は見られず、実施例４と同様に外部の加熱手段を用いずにクリーンな燃焼を行うことが可能となった。
【００２８】
実施例６では、第一の触媒体１２の最高温度は、図１５に示す燃焼量依存性を示したが、それに伴う未燃焼成分やＣＯの発生は観察されなかった。実施例６では、第一の触媒体１２の最高温度が８５０℃以下になる燃焼量１８０ｋｃａｌ／ｈ未満では、一次の混合気の空気過剰率λが１．２となるように制御されているため、第二の触媒体１６の最高温度が５００℃以下でも排ガスはクリーンであった。貴金属触媒の劣化は温度の影響を大きく受ける。８５０℃以下ではＰｔの熱劣化も大幅に抑制されるため、空気過剰率λが１以上であっても燃焼寿命についての問題は軽減される。一方、１８０ｋｃａｌ／ｈ以上になると、第二の触媒体１６の最高温度は未燃焼成分の浄化を十分に行うことができる５００℃以上となっているため、実施例６の方法をもちいても実施例１の特徴を活かしつつ、加熱手段を持ちいることなくクリーンな排ガスを得ることができ、触媒の高温耐久性の高い触媒燃焼装置を構成することができる。なお、実施例６では１８０ｋｃａｌ／ｈを境として空気過剰率を変化させたが、この値は装置の構成にしたがって、同様の主旨が達成できれば任意に設定できる。
［ＣＯ排出量］
図１６には、実施例１、３、７および比較例１における第一の触媒体１２の予熱時から予熱後触媒燃焼を開始するまでのＣＯの排出量の変化を示している。実施例１では第二の触媒体１６をＣＯを十分に酸化する温度（約２００℃）まで予熱してから予熱バーナ５に着火するとＣＯは浄化されるが、この操作を加えないと比較的多量のＣＯの発生が見られた。したがって結果的に第二の触媒体１６を予熱する時間を加えなくてはならなかった。比較例１は空気過剰率λ＝１．２で形成される火炎のため、着火時わずかにＣＯの排出が見られるのみであるが、前記のように触媒燃焼開始可能な状態になるまでには時間を要した。実施例３では予熱バーナ５に着火されるのと同時に炎口１５にも火炎が形成されるため、ＣＯの排出量は比較例１に比べてやや増加するのみであった。実施例７では、火炎予熱は空気過剰率λ＝１．２で行われるため、立ち上げ時のＣＯの排出は通常の火炎燃焼のレベルと同じであり、かつ触媒燃焼開始時にはすでに第二の触媒体１６が２００℃に到達したことを温度センサ１８が検知し、空気過剰率０．９５に設定されることになるため、速やかに触媒燃焼が開始された。上記のように実施例７の構成をとることにより、速やかにかつＣＯの排出量を極力抑制しながら触媒燃焼を開始することができた。なお、温度センサ１８が検知する温度は最低限ＣＯが酸化される温度以上であればよく、５００℃程度など温度を高く設定してスリップするメタン等の酸化を行ってもよい。
［定常燃焼時におけるＣＯ排出量］
また、表３には、実施例１〜６、８、９および比較例１、３、５の場合の２５０ｋｃａｌ／ｈ条件下定常燃焼時におけるＣＯの排出量について示した。
【００２９】
【表３】

いずれの場合も定常時のＣＯは通常の火炎燃焼に比べて微量であり、第二の触媒体１６が有効に作用していることが確認された。
【００３０】
なお、上記実施の形態３で記載したように、二次混合気または空気に対し、燃焼排ガスにより予熱する機構を設けると、実施例１などのような場合に第二の触媒体１６を予熱するのに必要な電力を大幅に減少させることが可能となった。また、実施例４の場合は、第一の触媒体１２での燃焼量を増加させることができるため、低温限界燃焼量をさらに低下させることが可能である。
【００３１】
なお、本実施例ではハニカム構造体に担持した触媒について述べたが、構造体の形状は、その他のいかなる形態の構造体でも同様の効果が発揮される。
【００３２】
また、本実施例１などでは一次燃焼室１１に供給される混合気の空気過剰率λを０．９５で一定値制御したが、空気過剰率１未満で触媒燃焼できる範囲であればどの値に設定しても問題はない。また、二次燃焼室１４に供給される混合気の総合の空気過剰率λは、１．２に設定したが、目的の達せられる空気過剰条件（好ましくはλ＞１）であればよい。また、拡散空気などで十分に可燃排ガス成分が酸化可能な場合は総合の空気過剰率λ≦１であってもよい。
【００３３】
また、本構成は燃焼量一定条件下で空気過剰率λを変化させ、触媒最高温度が極大を示す位置から空気過剰率を判断するようになっているが、それ以外に第一の触媒体の排ガス中のＨ₂、ＣＯ、炭化水素濃度などを化学的に検知する機構などを用いても対応可能となる。
【００３４】
【発明の効果】
以上の説明より明かなように、本発明によれば、８００℃以上の燃焼条件下における燃焼用触媒の劣化を抑制するとともに、ＴＤＲ（可変燃焼量幅）が大きく、かつ排ガスがクリーンな触媒燃焼装置とそれに用いる燃焼用触媒の提供が可能となる。
【図面の簡単な説明】
【図１】従来の触媒燃焼装置の要部断面図を示す。
【図２】本発明に関連する発明の一実施の形態における触媒燃焼装置の要部断面図を示す。
【図３】本発明の実施の形態における触媒燃焼装置の要部断面図を示す。
【図４】本発明の他の実施の形態における触媒燃焼装置の要部断面図を示す。
【図５】本発明に関連する発明の実施の形態１に示す、燃焼量一定条件下における触媒上流温度の空気過剰率λ依存性を示す。
【図６】本発明の一実施例に用いた第二の触媒のメタン酸化活性の温度依存性を示す。
【図７】実施例８に用いた第一の触媒体の断面図を示す。
【図８】実施例９に用いた第一の触媒体の断面図を示す。
【図９】本発明に関連する発明の実施例および比較例の寿命試験中の触媒上流温度の経時変化を示す。
【図１０】本発明に関連する発明の実施例および比較例の寿命試験中の触媒上流温度の経時変化を示す。
【図１１】本発明に関連する発明の実施例１、２における流れ方向の温度分布を示す。
【図１２】本発明に関連する発明の実施例１、４における燃焼量に対して制御される空気過剰率と触媒最高温度の関係を示す。
【図１３】空気過剰率と低温限界燃焼量との関係を示す。
【図１４】本発明に関連する発明の実施例５における第一の触媒体と第二の触媒体の最高温度の空気過剰率依存性を示す。
【図１５】本発明に関連する発明の実施例１、６および比較例１における触媒最高温度の燃焼量依存性を示す。
【図１６】本発明に関連する発明の実施例１、３、本発明の実施例７および比較例１における火炎予熱後に排出されるＣＯ濃度の経時変化について示す。
【符号の説明】
１燃料供給バルブ
２空気供給バルブ
３予混合室
４混合気入口
５予熱バーナ
６点火装置
７燃焼室
８触媒体
９排気口
１０ガラス
１１一次燃焼室
１２第一の触媒体
１３二次混合気または空気の供給部
１４二次燃焼室
１５炎口
１６第二の触媒体
１７電気ヒータ
１８温度センサ
１９排熱回収部
２０温度センサ[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a catalyst combustion apparatus for catalytic combustion of gaseous fuel or liquid fuel, which is mainly used for a heat source or heating, and particularly relates to a technique for improving high temperature durability and expanding a variable combustion amount range.
[0002]
[Prior art]
  A number of catalytic combustion apparatuses that perform catalytic reaction on the surface using a catalytic body that has an oxidizing activity for fuel have been proposed, and the combustion system has a premixed gas type configuration as shown in FIG. Was common.
[0003]
  In the conventional premixed gas type shown in FIG. 1, the fuel gas supplied from one fuel supply valve is mixed with the air supplied from the two air supply valves in the premixing chamber 3, and from the premixed gas inlet 4. It is sent to the preheating burner 5. The premixed gas is ignited by the ignition device 6 and forms a flame in the preheating burner 5. The high-temperature exhaust gas generated by the flame passes through the catalyst body 8 provided in the combustion chamber 7 while heating, and is discharged from the exhaust port 9. When the temperature of the catalyst body 8 is raised to the catalyst activation temperature, the fuel supply valve 1 temporarily stops the fuel supply, and the flame formed in the preheating burner 5 is extinguished. Thereafter, the fuel is resupplied immediately to start catalytic combustion. The catalyst body 8 is in a high temperature state and radiates and radiates heat through the glass 10 provided at a position facing the upstream side of the catalyst body 8, and heats, heats and dries by radiating heat as exhaust gas. In the premixed gas type, a premixed gas with an excess air ratio (ratio of the actual air amount to the theoretical air amount necessary for the complete oxidation reaction of fuel) of 1 or more is always supplied to the catalyst body 8, and the catalyst body 8 is excessive. It was used in an atmosphere where oxygen was present.
[0004]
[Problems to be solved by the invention]
  In the above-described conventional catalytic combustion apparatus, a high-temperature atmosphere in which oxygen always coexists is formed at the reaction center position of the catalyst body, and thermal deterioration of the catalyst components is inevitable. In general, platinum group metals such as Pt, Pd, and Rh are often used as combustion catalysts in terms of heat resistance and reaction activity. At high temperatures up to 800 to 900 ° C., It was difficult to obtain stable combustion performance for a long time due to a decrease in active sites due to transpiration. In a premixed gas type catalytic combustion device, the reaction center position moves to the downstream side of the catalyst body due to a decrease in activity, so that complete combustion cannot be maintained, or if the radiant heat from the upstream surface is used, the usage time increases. At the same time, the amount of radiant heat decreases.
[0005]
  The present invention provides a catalytic combustion apparatus capable of improving the high temperature durability and expanding the variable combustion amount width in consideration of the problem of high temperature durability of the conventional catalytic combustion device and the narrowness of the variable combustion amount range. The purpose is to do.
[0006]
[Means for Solving the Problems]
  FirstThe present invention provides a first catalyst body in which an oxidation catalyst is supported on a base material having a mixture inlet of fuel and air provided on the upstream side, an exhaust gas outlet provided on the downstream side, and a large number of communication holes. Is disposed downstream of the primary combustion chamber, and is provided downstream of the secondary supply port.The second catalyst body was placedA secondary combustion chamber,
  When burningWhen the second catalyst body in the secondary combustion chamber is lower than a predetermined temperature in the early stage of combustion, the excess air ratio in the primary combustion chamber burns as 1 or more,
  When the temperature of the second catalyst body in the secondary combustion chamber rises above a predetermined temperature,The primary combustion chamber is burned with an excess air ratio of less than 1,
  SaidOf the first catalyst bodyThe oxidation catalyst is composed of Pt or Rh, or a material mainly composed of Pt or Rh,
  SaidFirstThe catalyst body is CeO₂Or ZrO₂Is a catalytic combustion apparatus containing one or both of them as a main component.
According to a second aspect of the present invention, the predetermined temperature is a temperature at which a ratio at which the fuel component in the secondary combustion chamber is oxidized or a temperature at which the combustible component concentration in the exhaust gas reaches a predetermined level. It is the catalytic combustion apparatus of this invention.
  The third aspect of the present invention is the catalytic combustion apparatus according to the first or second aspect of the present invention, wherein the second catalyst body comprises an oxidation catalyst supported on a substrate having a large number of communicating holes.
According to a fourth aspect of the present invention, the oxidation catalyst of the first catalyst body is made of a material mainly containing Pt, the second catalyst body is made of a material mainly containing Pd, and the predetermined temperature is set. It is the catalytic combustion apparatus of 3rd this invention which makes 500 degreeC.
In the fifth aspect of the present invention, the air supplied to the secondary combustion chamber is preheated by being heated by the exhaust gas in the secondary combustion chamber. It is the catalytic combustion apparatus of this invention.
According to a sixth aspect of the present invention, the excess air ratio of the air-fuel mixture supplied from the air-fuel mixture inlet decreases with a decrease in the amount of fuel supplied. This is a catalytic combustion apparatus.
According to a seventh aspect of the present invention, the fuel supply amount of the air-fuel mixture supplied from the air-fuel mixture inlet is substantially constant, and only the air amount is increased or decreased, and at least the air corresponding to the increase / decrease amount is supplied to the secondary supply port. The catalytic combustion apparatus according to any one of the first to fourth aspects of the present invention, wherein the catalytic combustion apparatus is supplied from the first to fourth aspects.
The eighth aspect of the present invention is the catalytic combustion apparatus according to any one of the first to fourth aspects of the present invention, wherein the base substrate of the first catalyst body has a thermal conductivity of 10 W / m · ° C. or higher. It is.
According to a ninth aspect of the present invention, the catalyst body supporting the oxidation catalyst mainly composed of Pt or Pt includes an oxidation catalyst layer mainly composed of Pt or Pt, an oxidation catalyst layer mainly composed of Rh or Pd, Is a catalyst combustion apparatus according to the first aspect of the present invention.
In the tenth aspect of the present invention, the oxidation catalyst layer mainly composed of Rh or Pd laminated on the oxidation catalyst layer mainly composed of Pt or Pt is partially provided on the downstream side. A medium combustion apparatus according to a ninth aspect of the present invention.
The eleventh aspect of the present invention is a method for burning with the excess air ratio in the primary combustion chamber being less than 1 during the combustion.
The excess air ratio of the primary combustion chamber is changed, and the excess air ratio at which the temperature of the catalyst body becomes maximum is determined by a temperature detection unit provided in the vicinity of the catalyst body, and is lower than the excess air ratio. In the catalytic combustion apparatus according to the first aspect of the present invention, the primary combustion chamber is combusted in an excess air ratio region.
[0007]
  In the twelfth aspect of the present invention, an oxidation catalyst is supported on a base material having a mixture inlet of fuel and air provided on the upstream side, an exhaust gas outlet provided on the downstream side, and a large number of communication holes.FirstA primary combustion chamber in which a catalyst body is disposed; a secondary supply port for an air-fuel mixture or air provided downstream of the primary combustion chamber; and a second catalyst body provided downstream of the secondary supply port A combustion control method for a catalytic combustion apparatus comprising a secondary combustion chamber in which is disposed,
  When combusting, if the second catalyst body of the secondary combustion chamber is lower than a predetermined temperature at the initial stage of combustion, the excess air ratio of the primary combustion chamber burns as 1 or more,
  When the second catalyst body in the secondary combustion chamber is heated to a predetermined temperature or more, the excess air ratio in the primary combustion chamber burns as less than 1,
  The oxidation catalyst of the first catalyst body is composed of Pt or Rh, or a material mainly composed of Pt or Rh,
  The first catalyst body is CeO.₂Or ZrO₂This is a combustion control method for a catalytic combustion apparatus containing one or both of them as a main component.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
In the following, the present inventionAnd inventions related to the present inventionThe embodiment will be described with reference to the drawings.
(Embodiment 1)
  FIG. 2 shows the present invention.Inventions related toIt is principal part sectional drawing of this 1st embodiment, The structure is demonstrated with an effect | action. That is, the fuel gas supplied from one fuel supply valve is mixed with the air supplied from the air supply valve 2 in the premixing chamber 3, and sent from the mixture inlet 4 to the preheating burner 5. The air-fuel mixture is ignited by the ignition device 6 and forms a flame in the preheating burner 5. The high-temperature exhaust gas generated by the flame is provided in the primary combustion chamber 11 and is supported by Pt or Rh, or an oxidation catalyst mainly composed of Pt or Rh on a base material having a large number of communication holes. The first catalyst body 12 is heated and passed through, mixed with the secondary mixture or the air-fuel mixture supplied from the air supply unit 13, passes through the downstream secondary combustion chamber 14, and passes through the exhaust port 9. Discharged. When the temperature of the first catalyst body 12 is raised to the catalyst activation temperature for the fuel, the fuel supply valve 1 temporarily stops the supply of the fuel, and the flame formed in the preheating burner 5 is extinguished. Thereafter, the fuel is resupplied immediately to start catalytic combustion. The first catalyst body 12 is in a high temperature state, radiates and radiates heat through the glass 10 provided at a position facing the upstream side of the first catalyst body 12, and heats, heats, and dries by radiating heat as exhaust gas.
[0009]
  Here, when the predetermined condition is satisfied, the excess air ratio of the air-fuel mixture composed of the fuel gas and air supplied to the premixing chamber 3 is less than 1, and the air in the first catalyst body 12 is slightly air. Insufficient conditions, that is, a reducing atmosphere. Therefore, the combustion exhaust gas here is an unburned fuel gas, CO as a partial oxidation product, H₂, Various hydrocarbons and CO of complete combustion products₂And water and N₂Is included. Air is supplied from the secondary mixture or air supply unit 13 to the exhaust gas after passing through the first catalyst body 12. The amount of air is desirably an excess air ratio of 1 or more at the inlet of the secondary combustion chamber 14 in order to cause complete combustion in the secondary combustion chamber 14. As shown in FIG. 2, a flame port 15 is provided in the secondary combustion chamber 14 (a secondary combustion chamber is configured by the flame port 15 and the like), and ignited here (ignition means is When a flame is formed (unshown in particular), unburned products and partially oxidized products are completely burned, and clean complete combustion exhaust gas is discharged from the exhaust port 9.
[0010]
  At the same time as the flame is formed on the preheating burner 5, a flame is also formed in the flame opening 15, and it is possible to immediately realize complete combustion of the unburned product and the partially oxidized product. The secondary mixture or air supply unit 13 may supply only air, but may supply an air-excess fuel and air mixture, and maintain complete combustion in the secondary combustion chamber 14. It is also possible to supply additional fuel necessary and sufficient for this purpose.
[0011]
  The catalyst component supported on the first catalyst body 12 used under these conditions is preferably at least Pt or Rh, or an oxidation catalyst mainly composed of Pt or Rh. In this case, suppression of thermal deterioration And an expansion of the variable combustion range. Here, the meaning of being mainly composed of Pt or Rh means that Pt or Rh is contained as an active component that mainly contributes to the catalytic reaction.
[0012]
  In addition, the present inventionInventions related to the present invention and the following inventionsThen, the fact that the excess air ratio λ of the gas supplied to the first catalyst body is less than 1 means that the excess air ratio λ is varied under a constant combustion amount condition, and the maximum temperature upstream of the catalyst (at the upstream temperature). The position where the excess air ratio is the highest is determined to be near 1, and combustion is performed in a region where the excess air ratio is lower than that. Normally, in catalytic combustion using an oxidation catalyst mainly composed of Pt or Pt, when the excess air ratio λ is varied with a constant combustion amount, the maximum catalyst temperature is highest near the excess air ratio λ = 1 as shown in FIG. Therefore, it is possible to control the excess air ratio λ to less than 1 by appropriately changing the excess air ratio λ and incorporating an operation for monitoring the catalyst upstream temperature with the temperature sensor 20 shown in FIG. Detailed effects relating to this configuration will be described later.
(Embodiment 2)
  BookInventionThe basic configuration and operation of the embodiment are the same as those of the first embodiment, but the internal configuration of the secondary combustion chamber 14 is different. Therefore, it demonstrates with an effect | action centering on the difference of the structure. FIG. 3 is a cross-sectional view of the main part of the second embodiment of the present invention. The secondary combustion chamber 14 is provided with a second catalyst body 16 as a secondary combustion chamber in which Pd is supported on a ceramic honeycomb, and an electric heater 17 is attached in the vicinity of the upstream surface thereof. In the vicinity thereof, a temperature sensor 18 is installed.
[0013]
  In the above configuration, during steady combustion, as in the first embodiment, the exhaust gas containing unburned components reaches the second catalyst body 16, where it is possible to perform catalytic combustion without forming a flame, and nitrogen oxides. It is possible to reliably oxidize and purify even with a dilute combustible substance concentration. In addition, it is possible to keep the second catalyst body 16 at or above the activation temperature at all times by attaching and heating the electric heater 17 in the vicinity of the second catalyst body 16. In particular, when methane, which is difficult to react among hydrocarbon components, is present as a fuel component or an unburned component, the second catalyst body 16 is used as estimated from the temperature dependence of the methane oxidation activity shown in FIG. Although it is necessary to maintain the temperature at about 500 ° C. or higher, the temperature of the second catalyst body 16 can be controlled by the electric heater 17 regardless of the amount of combustion in the first catalyst body 12, so that it is always clean. Exhaust gas can be secured. Such a heating means is not limited to electric heating as in the present embodiment, and a flame heating means separately formed near the upstream of the second catalyst body 16 may be used.
[0014]
  Further, without using the heating means, as in the case of a low combustion amount, the second catalyst body has a temperature of 500 ° C. or lower, and the purification action is insufficient, that is, the combustion rate is 95% or lower. Then, it is possible to complete combustion with an excess air ratio of 1 or more.
[0015]
  Further, the temperature of the first catalyst body 12 is controlled and the second catalyst body 16 is controlled by changing the excess air ratio λ of the air-fuel mixture supplied to the primary combustion chamber 11 to control the ratio of the reacting fuel. Keeping the temperature above 500 ° C, the secondary combustion is an electric heater17It can also be realized without. That is, the air excess ratio λ of the air-fuel mixture with respect to the primary combustion chamber 11 is intentionally set under the condition that the low combustion amount, that is, the fuel supply speed is small and the temperature of the first catalyst body 12 and the second catalyst body 16 is low. The temperature of the second catalyst body 16 can be kept high by decreasing the ratio and increasing the proportion of the unburned portion in the primary combustion chamber 11, thereby increasing the amount of combustion in the secondary combustion chamber 14. The same effect can be obtained by increasing the excess air ratio λ in the primary combustion chamber 11 while keeping the combustion amount constant, and decreasingly supplying air corresponding to the increase in at least the primary combustion chamber 11 to the secondary combustion chamber 14. Obtainable. Alternatively, the excess air ratio λ can be reduced, and at least the air corresponding to the decrease in the primary combustion chamber 11 can be additionally supplied to the secondary combustion chamber 14. That is, the primary combustion chamber 11When the excess air ratio λ is controlled to be relatively small, the temperature of the first catalyst body 12 becomes relatively low, and the amount of unburned components is completely burned by the second catalyst body 16. The temperature of the second catalyst body 16 is maintained at a high temperature. On the other hand, if the excess air ratio λ in the primary combustion chamber 11 is controlled to be relatively large, the temperature of the first catalyst body 12 becomes relatively high and the second catalyst body 16 is also heated by the exhaust gas. The temperature of the second catalyst body 16 can also be maintained at 500 ° C. or higher.
[0016]
  These operations can also be applied to the first embodiment. Further, when the second catalyst body 16 is not sufficiently heated, such as during the flame preheating of the first catalyst body 12,Secondary mixture or airEven if air is additionally supplied from the supply unit 13 to be 1 or more, unburned components cannot be sufficiently purified. Therefore, until the second catalyst body 16 reaches a temperature sufficient for the purification action, the electric heater17Combustion by using a means such as preheating with a separately provided heating burner or the like, or using a means of heating with a complete combustion flame in the preheating burner 5 with an excess air ratio of the mixture supplied to the premixing chamber 3 being 1 or more Complete purification from the beginning is possible.
[0017]
  Here, the temperature sufficient for the purification action is a temperature (about 200 ° C. or higher) at which CO is at least 95% oxidized by the catalyst or the CO concentration contained in the exhaust gas is 50 ppm or lower, preferably It is a temperature (about 500 ° C. or more) at which the fuel component is oxidized by 95% or more or the concentration of the combustible component contained in the exhaust gas is 1000 ppm or less.
[0018]
  In the present embodiment, a catalyst mainly composed of Pd is used as the second catalyst body 16, but methane, CO, H in an excess air condition are used.₂The catalyst may be selected from a catalyst having a platinum group metal supported on an inorganic oxide, a transition metal catalyst, a composite oxide catalyst, and the like that are excellent in oxidation activity.
[0019]
  Detailed effects relating to this configuration will be described later.
(Embodiment 3)
  This embodiment has the same basic configuration and operation as in the second embodiment, but is provided with an exhaust heat recovery unit 19 along the secondary combustion chamber 14 or along the road from the secondary combustion chamber 14 to the exhaust port 9. The configuration is different. Therefore, it demonstrates with an effect | action centering on the difference of the structure. FIG. 4 is a cross-sectional view of an essential part of the third embodiment of the present invention. The exhaust heat recovery unit 19 provided along the road from the secondary combustion chamber 14 to the exhaust port 9 recovers the heat obtained from the secondary combustion chamber 14 and the heat contained in the exhaust gas, and at the same time secondarymixtureQi orSkyThe air or air-fuel mixture supplied from the air supply unit 13 is preheated, and the amount of heat required for heating the second catalyst body 16 can be greatly reduced.
[0020]
【Example】
  Hereinafter, Example 7 of the present invention and Examples 1 to 6 and 8 to 10 of the invention related to the present invention will be described.
(Example 1) Ceramic honeycomb (material cordierite, 400 cells / inch)²Ce / BaO.Al pre-fired with wall thickness of 0.15, φ50, length 20) at 1000 ° C. for 1 hour₂O_Three100 g of powder, 10 g of aluminum nitrate 9 hydrate, 130 g of water, and 2 g of Pt dinitrodiammine salt aqueous solution were added to impregnate Washcoat Slurry A, dried, baked at 500 ° C., and Pt 3 g / L ( The first catalyst body 12 was formed by supporting the honeycomb bulk volume).
[0021]
  Next, ceramic honeycomb (material cordierite, 400 cells / inch²Equivalent, wall thickness 0.15, φ20, length 10) 100 g of activated alumina powder pre-fired at 1000 ° C. for 1 hour, aluminum nitrate 9 hydrate 10 g, water 130 g, Pd dinitrodiammine salt aqueous solution 2 g in terms of Pd, The second catalyst body 16 was formed by impregnating into the washcoat slurry B to which was added, followed by drying and calcining at 500 ° C. to carry the equivalent of Pd3 g / L. Next, the first catalyst body 12 and the second catalyst body 16 obtained above were mounted on the catalytic combustion apparatus shown in FIG. The city gas 13A was used as the fuel, and the excess air ratio λ of the premixed gas supplied to the primary combustion chamber 11 was set to 0.95. SupplyPartFor supplying the premixed gas or air from 13, supply the premixed gas or air to the secondary combustion chamber 14.PartThe total air excess ratio λ of the air-fuel mixture after adding from 13 was set to 1.2. The second catalyst body 16 is set to be 500 ° C. or higher in a steady state by controlling the electric heater 17.
(Example 2) Metal honeycomb (material FeCrAl, 400 cells / inch)²Corresponding wall thickness 0.15, φ50, length 20) is impregnated in the same washcoat slurry A as used in Example 1, dried, fired at 500 ° C., and supported by Pt 3 g / L Thus, the first catalyst body 12 was formed. Next, the first catalyst body 12 obtained above and the second catalyst body 16 obtained in the same manner as in Example 1 were attached to the catalytic combustion apparatus shown in FIG. The control of the excess air ratio of the premixed gas supplied to the primary combustion chamber 11, the control of the amount of air supplied to the secondary combustion chamber 14, and the temperature control for the second catalyst body 16 are the same as in the first embodiment. went.
(Example 3) In the same manner as in Example 1, a first catalyst body 12 was formed. Next, the first catalyst body 12 was attached to the catalytic combustion apparatus shown in FIG. The excess air ratio of the primary air-fuel mixture was set to 0.95 as in Example 1. The amount of combustion of the city gas supplied from the crater 15 to the secondary combustion chamber 14 is 40 kcal / h, and the excess air ratio of the secondary mixture composed of city gas and air is the exhaust gas from the primary combustion chamber 11. A total of λ = 1.2 was set by mixing.
(Embodiment 4) Using the catalytic combustion apparatus having the same configuration as that of Embodiment 1, in the primary combustion chamber 11, as shown in FIGS. 12 and 13, fuel is supplied so that the excess air ratio λ decreases as the combustion amount decreases. The volume and air supply were controlled. The amount of air supplied to the secondary combustion chamber 14 was controlled so that the total excess air ratio λ after mixing with the primary exhaust gas at the inlet of the secondary combustion chamber 14 was 1.2.
(Example 5) A catalytic combustion apparatus having the same configuration as that of Example 1 was used, the city gas 13A supplied to the primary combustion chamber 11 was kept constant at 400 kcal / h, and the amount of air supplied to the primary combustion chamber 11 was increased or decreased. . The amount of air supplied to the secondary combustion chamber 14 was controlled so that the total excess air ratio λ after mixing with the primary exhaust gas at the inlet of the secondary combustion chamber 14 was 1.2.
(Embodiment 6) When the catalytic combustion apparatus having the same configuration as that of Embodiment 1 is used and the supply amount of the city gas 13A is less than 180 kcal / h, the excess air ratio λ of the air-fuel mixture supplied to the primary combustion chamber 11 is 1. The amount of air was controlled to be .2 so that the excess air ratio λ was 0.95 at 180 kcal / h or more, and the secondary combustion chamber 14 was mixed with the primary exhaust gas at the inlet of the secondary combustion chamber 14. The air supply amount was controlled so that the total air excess ratio λ afterwards became 1.2.
(Embodiment 7) Using the catalytic combustion apparatus having the same configuration as that of Embodiment 1, until the temperature sensor 18 detects that the upstream temperature of the second catalyst body 16 becomes 200 ° C., the city gas 13A = 400 kcal / h After the first catalyst body 12 is preheated by the flame formed under the condition of the excess air ratio λ = 1.2 and the temperature reaches 200 ° C., the excess air ratio supplied to the primary combustion chamber 11 The air supply amount was controlled so that λ was 0.95. The control of the excess air ratio of the premixed gas supplied to the primary combustion chamber 11 at constant time, the control of the amount of air supplied to the secondary combustion chamber 14, and the temperature control for the second catalyst body 16 are performed in the first embodiment. As well as.
(Example 8) Honeycomb made of ceramics (material cordierite, 400 cells / inch)²Corresponding wall thickness of 0.15, φ50, length 20) is impregnated in the same washcoat slurry A as used in Example 1, dried, calcined at 500 ° C., and supported by Pt 2 g / L. Next, the same washcoat slurry B as used in Example 1 was impregnated, dried, and then fired at 500 ° C., whereby Pd 1 g / L equivalent as shown in FIG. 7 was laminated and supported on the Pt support layer. A first catalyst body 12 was formed. Next, the first catalyst body 12 obtained above and the second catalyst body 16 obtained in the same manner as in Example 1 were attached to the catalytic combustion apparatus shown in FIG. The control of the excess air ratio of the premixed gas supplied to the primary combustion chamber 11, the control of the amount of air supplied to the secondary combustion chamber 14, and the temperature control for the second catalyst body 16 are the same as in the first embodiment. went.
(Example 9) Honeycomb made of ceramics (material cordierite, 400 cells / inch)²Corresponding wall thickness 0.15, φ50, length 20) was impregnated in the same washcoat slurry A as used in Example 1, dried and fired at 500 ° C., equivalent to Pt 2.8 g / L Next, one end of the honeycomb surface was impregnated in the same washcoat slurry B as used in Example 1, dried, and then fired at 500 ° C., whereby Pd 0.2 g / kg as shown in FIG. A first catalyst body 12 in which the L equivalent was partially supported on the Pt support layer (up to a position of about 3 mm from the end face) was formed. Next, the first catalyst body 12 obtained above and the second catalyst body 16 obtained in the same manner as in Example 1 were attached to the catalytic combustion apparatus shown in FIG. The control of the excess air ratio of the premixed gas supplied to the primary combustion chamber 11, the control of the amount of air supplied to the secondary combustion chamber 14, and the temperature control for the second catalyst body 16 are the same as in the first embodiment. went. Rh may be used instead of Pd.
(Example 10) Ceramic honeycomb (material cordierite, 400 cells / inch)²Equivalent wall thickness 0.15, φ50, length 20) ZrO pre-fired at 500 ° C. for 1 hour₂100 g of powder, 100 g of water, and 2 g of Pt dinitrodiammine salt aqueous solution are added to impregnate washcoat slurry C, dried, fired at 500 ° C., and supported by Pt 3 g / L (honeycomb bulk). Thus, the first catalyst body 12 was formed. Next, the first catalyst body 12 obtained above and the second catalyst body 16 obtained in the same manner as in Example 1 were attached to the catalytic combustion apparatus shown in FIG. The control of the excess air ratio of the premixed gas supplied to the primary combustion chamber 11, the control of the amount of air supplied to the secondary combustion chamber 14, and the temperature control for the second catalyst body 16 are the same as in the first embodiment. went.
(Comparative Example 1) A catalyst body 8 carrying Pt obtained in the same manner as in Example 1 was mounted on a catalytic combustion apparatus having the structure shown in FIG. The excess air ratio λ = 1.2 was constant.
(Comparative Example 2) Ceramic honeycomb (material cordierite, 400 cells / inch²Equivalent wall thickness 0.15, φ50, length 20), pre-fired at 1000 ° C. for 1 hour, Ce / BaO · Al₂O_Three100 g of powder, 10 g of aluminum nitrate 9-hydrate, 130 g of water, and 2 g of Pd dinitrodiammine salt aqueous solution are added to impregnate Washcoat Slurry D, dried, fired at 500 ° C., and Pd equivalent to 3 g / L The catalyst body 8 was formed by carrying | supporting. Next, as in Comparative Example 1, the catalyst body 8 obtained above was attached to the catalytic combustion apparatus having the configuration shown in FIG. As in Comparative Example 1, the excess air ratio λ was set to 1.2.
(Comparative Example 3) A first catalyst body 12 formed in the same manner as the catalyst body 8 in Comparative Example 2 and a second catalyst body 16 formed in the same manner as in Example 1 are used in the catalytic combustion apparatus having the configuration shown in FIG. Installed. The control of the excess air ratio of the premixed gas supplied to the primary combustion chamber 11, the control of the amount of air supplied to the secondary combustion chamber 14, and the temperature control for the second catalyst body 16 are the same as in the first embodiment. went.
Comparative Example 4 Ceramic honeycomb (material cordierite, 400 cells / inch²Equivalent wall thickness 0.15, φ50, length 20), pre-fired at 1000 ° C. for 1 hour, Ce / BaO · Al₂O_Three100 g of powder, 10 g of aluminum nitrate 9-hydrate, 130 g of water, 0.7 g of Pd dinitrodiammine salt aqueous solution in terms of Pd, and 1.3 g of Pt dinitrodiammine salt aqueous solution in terms of Pt were impregnated and dried. Thereafter, the first catalyst body 12 was formed by firing at 500 ° C. and simultaneously supporting Pd 1 g / L and Pt 2 g / L. Next, a second catalyst body 16 was formed in the same manner as in Example 1. Next, the first catalyst body 12 and the second catalyst body 16 obtained above were mounted on the catalytic combustion apparatus having the configuration shown in FIG. The control of the excess air ratio of the premixed gas supplied to the primary combustion chamber 11, the control of the amount of air supplied to the secondary combustion chamber 14, and the temperature control for the second catalyst body 16 are the same as in the first embodiment. went. (Comparative Example 5) A catalyst body 8 carrying Pt formed in the same manner as the first catalyst body 12 in Example 2 was used and mounted on a catalytic combustion apparatus having the structure shown in FIG. The excess air ratio λ was constant at 1.2.
[0022]
  In the above Examples 1 to 10 and Comparative Examples 1 to 5, the catalyst layer temperature distribution in the flow direction, the preheating time until the start of catalytic combustion, the exhaust gas components after preheating and in steady state, and the minimum combustion amount that can continue combustion ( Low temperature limit combustion amount) was investigated. The catalyst layer temperature distribution in the flow direction was measured by scanning a thermocouple. The preheating time was determined based on whether or not the catalyst combustion could be started after supplying the air-fuel mixture again after preheating for a predetermined time. The exhaust gas component is HC (total hydrocarbons) -CO-CO₂Measured with a meter. Further, the low-temperature limit combustion amount was determined by checking the continuation of combustion for 6 hours by changing the combustion amount in Examples 1 to 3 and 6 to 9 and Comparative Examples 1 to 4 while keeping the excess air ratio λ constant. In Example 4, the amount of combustion was changed by the method described above. The combustion life test was conducted for Examples 1, 2, 9, 10 and Comparative Examples 1-4. In Examples 1 and 9 and Comparative Examples 1 to 4, the combustion amount (city gas supply amount) was 400 kcal / h, and in Examples 1, 2, 10 and Comparative Example 5, the conditions were 550 kcal / h. The time-dependent change of the catalyst upstream temperature was measured with a radiation thermometer.
[Catalyst upstream temperature change with time]
  9 and 10 show changes over time in the catalyst upstream temperature of Examples 1, 2, 9, 10 and Comparative Examples 1 to 5 up to a maximum of 1000 hours in the combustion life test under each condition. FIG. 9 shows the results under the condition of a combustion amount of 400 kcal / h. In Comparative Examples 1 and 2, which were tested under an excess air ratio of 1.2, a drop in the upstream temperature was observed abruptly from the initial stage, and significant deterioration was observed. In Comparative Example 2, a vibration phenomenon specific to (or characteristic to) Pd was observed in which the catalyst temperature repeatedly increased and decreased after about 100 hours had elapsed. On the other hand, in Examples 1 and 9 in which the first catalyst body 12 was burned at an excess air ratio of less than 1, the change in activity was slight despite the initial catalyst upstream temperature being as high as 1050 ° C. It was found that Pt hardly deteriorates in the reduced state. However, in Comparative Example 3 in which the test was performed at an excess air ratio of less than 1 using the first catalyst body 12 mainly composed of Pd, the catalyst upstream temperature was extremely lowered by 500 hours. Similarly, other single noble metal catalyst particles were tested, and Pt was most preferred for improving the heat resistance life when the excess air ratio was less than 1. Further, Rh was inferior to Pt under the condition of excess air ratio λ = 0.95 in this example, but exhibited a heat resistant life performance equivalent to that of Pt under a lower excess air ratio condition. The present inventionAnd inventions related to the present inventionIt can be said that an improvement effect when the excess air ratio is less than 1 can be obtained by using an oxidation catalyst mainly composed of Pt or Rh or Pt or Rh in the combustion chamber. Moreover, the comparative example 4 which mixed Pt and Pd brought a result inferior to durability rather than Pd.
[0023]
  FIG. 10 shows combustion life test results in Examples 1, 2, 10 and Comparative Example 5 when the combustion amount is increased to 550 kcal / h. In Examples 1 and 10 using a cordierite honeycomb, the initial catalyst upstream temperature reached 1150 ° C. In Example 1, the catalyst upstream temperature decreased by about 100 ° C. by 1000 hours, whereas Example 10 showed only a decrease of about 50 ° C. In Example 1, Ce / Ba-added Al was added to the Pt support.₂O_ThreeWhereas ZrO is used in Example 10.₂There is a difference using. The reason for this is currently not clear, but Pt and ZrO₂This interaction is presumed to be related. A similar effect is obtained by adding CeO to the Pt carrier.₂It was also seen when using. In the case of Example 2 and Comparative Example 5 using a metal honeycomb, the initial catalyst upstream temperature was 1000 ° C., which was about 150 ° C. lower than that of the cordierite honeycomb. In Comparative Example 5, the catalyst upstream temperature decreased to about 850 ° C., whereas the catalyst upstream temperature in Example 2 remained unchanged from the initial value, and was maintained at about 1000 ° C. Higher combustion load (unit area) is achieved by using an oxidation-resistant metal honeycomb having superior thermal conductivity compared to cordierite, carrying a catalyst mainly composed of Pt and burning it with an excess air ratio of less than 1. It was found that the fuel can be burned with the fuel supply amount).
[Temperature distribution in the flow direction of the catalyst layer]
  FIG. 11 shows the temperature distribution in the flow direction of the catalyst layer in Example 1 and Example 2 (under the condition of 550 kcal / h and for Example 1 under the condition of 400 kcal / h). In Example 2 in which a metal honeycomb was used as the base material of the first catalyst body 12, the temperature distribution was gentler than in Example 1 in which a cordierite honeycomb was used. That is, by using the metal honeycomb, the downstream temperature can be increased while suppressing the local high temperature at the highest temperature compared to the cordierite honeycomb. Since the maximum temperature of the second catalyst body 16 is directly affected by the downstream temperature in the first catalyst body 12, in order to keep the temperature of the second catalyst body at 500 ° C. or higher, the present invention is used.Related to the inventionAs in Example 2, as a base material for the first catalyst body, compared to cordierite (1-2 W / m · ° C.) widely used in this field, it was used in Example 2 of the present invention. It has been shown that it is effective to use a material having a high thermal conductivity such as a metal having a thermal conductivity of 10 W / m · ° C. or higher. The base material for the metal honeycomb is preferably a ferritic stainless steel containing 3% or more of Al having relatively excellent oxidation resistance. Similarly, the thermal conductivity is higher than that of the cordierite base material, and higher than that of the pure alumina sintered body. A ceramic substrate such as SiC having high thermal shock resistance may be used.
[Preheating time]
  Table 1 shows the result of examining the minimum preheating time required for starting catalytic combustion under the condition of a combustion amount of 250 kcal / h.
[0024]
[Table 1]

In Example 1, the preheating time was significantly shortened as compared with Comparative Example 1 in which the first catalyst body 12 and the catalyst body 8 had the same composition. Although the speed at which the first catalyst body 12 is preheated is not much different or the substantial combustion amount is higher in Comparative Example 1, the reactivity on the catalyst is improved by the reducing atmosphere, and in a shorter time. It is presumed that catalytic combustion can be started. Further, when the first catalyst body 12 in which the Pt layer and the Pd layer were laminated as in Examples 8 and 9, the length was further shortened. As can be seen from the results of Comparative Example 3, Pd alone was able to start catalytic combustion in a shorter atmosphere in a reducing atmosphere as compared with Pt of Example 1. As described above, the combustion life of Comparative Example 3 containing Pd alone or Comparative Example 4 where Pt and Pd are present in the same layer is not sufficient as described above.Related to the inventionBy using the first catalyst body 12 provided with the Pd layer laminated with the Pt layer as in Examples 8 and 9 in a reducing atmosphere, it is possible to extend the life and shorten the preheating time. Similar effects were seen when Rh was used. Further, as shown in FIG. 8, it is more advantageous in terms of combustion life and cost to partially provide the Pd layer or the Rh layer on the downstream side where the temperature is low and deterioration is excessive.
[Low temperature limit combustion amount]
Next, the present inventionInventions related toTable 2 shows the results of measuring the low-temperature limit combustion amount in Examples 1 and 2 and Comparative Examples 1, 2 and 3.
[0025]
[Table 2]

  The present inventionInventions related toIn Example 1 and Comparative Example 3, the low-temperature limit combustion amount was the smallest. This is presumably because the flow rate becomes smaller due to the decrease in the excess air ratio, and Pt and Pd are reductively activated more than that, or the combustion mechanism is different. Similarly, in Example 2 using a metal base material, the low temperature limit was remarkably lowered as compared with Comparative Example 4 with the same configuration and excess air ratio λ = 1.2. That is, it is considered that TDR can be expanded by burning at an excess air ratio of less than 1.
[0026]
  Next, the present inventionInventions related toExample 1 and Example 4 are compared. In the fourth embodiment, as shown in FIG. 12, the excess air ratio at the inlet of the primary combustion chamber 11 is controlled so as to decrease with a decrease in the combustion amount. Therefore, the proportion of unburned components increases as the combustion amount decreases. The second catalyst body 16 burns. Therefore, the upstream temperature of the first catalyst body 12 decreased and the temperature of the second catalyst body 16 increased at a low combustion amount as compared with Example 1. By using such control, unburned components and CO can be purified without using heating means such as a heater. The low temperature limit combustion amount was 60 kcal / h in Example 4 as in Example 1, although the catalyst upstream temperature was lower than that in Example 1. In Example 4, since the excess air ratio at the inlet of the primary combustion chamber 11 at 60 kcal / h is controlled to be lower than that in Example 1, the combustion rate and the catalyst upstream temperature are reduced. This is because the low-temperature limit combustion amount also decreases as the excess air ratio λ decreases.
[0027]
  In the fifth embodiment, the combustion amount is substantially constant at 400 kcal / h, and the substantial combustion amount and the catalyst temperature in the first catalyst body 12 are controlled by changing the excess air ratio. The maximum temperature of the second catalyst body 16 changed as shown in FIG. 14 according to the excess air ratio λ. Since the second catalyst body 16 is heated to 500 ° C. or higher, no unburned components and CO are discharged due to the change in the excess air ratio, and an external heating means is used as in the fourth embodiment. This makes it possible to perform clean combustion.
[0028]
  In Example 6, the maximum temperature of the first catalyst body 12 showed the combustion amount dependency shown in FIG. 15, but the generation of unburned components and CO associated therewith was not observed. In Example 6, since the excess air ratio λ of the primary air-fuel mixture is controlled to be 1.2 when the maximum temperature of the first catalyst body 12 is less than 850 ° C. and the combustion amount is less than 180 kcal / h. Even when the maximum temperature of the second catalyst body 16 was 500 ° C. or less, the exhaust gas was clean. The deterioration of the noble metal catalyst is greatly affected by temperature. At 850 ° C. or less, the thermal deterioration of Pt is greatly suppressed, so even if the excess air ratio λ is 1 or more, the problem regarding the combustion life is reduced. On the other hand, at 180 kcal / h or higher, the maximum temperature of the second catalyst body 16 is 500 ° C. or higher at which unburned components can be sufficiently purified. While utilizing the characteristics of Example 1, a clean exhaust gas can be obtained without having a heating means, and a catalyst combustion apparatus with high high-temperature durability of the catalyst can be configured. In Example 6, the excess air ratio was changed at 180 kcal / h as a boundary, but this value can be arbitrarily set according to the configuration of the apparatus as long as the same purpose can be achieved.
[CO emissions]
  FIG. 16 shows a change in the amount of CO emission from the time of preheating the first catalyst body 12 in Examples 1, 3, 7 and Comparative Example 1 until the start of catalytic combustion after preheating. In Example 1, the second catalyst body 16 is preheated to a temperature at which CO is sufficiently oxidized (about 200 ° C.) and then ignited in the preheating burner 5, but the CO is purified. The generation of CO was observed. Therefore, as a result, time for preheating the second catalyst body 16 had to be added. Since Comparative Example 1 is a flame formed with an excess air ratio λ = 1.2, only slight CO emissions are observed at the time of ignition. It took time. In Example 3, since the preheating burner 5 was ignited and a flame was formed in the flame opening 15 as well, the CO emission amount only increased slightly compared with Comparative Example 1. In Example 7, since the flame preheating is performed with the excess air ratio λ = 1.2, the CO emission at the time of start-up is the same as the level of the normal flame combustion, and at the start of the catalytic combustion, the second catalyst is already used. The temperature sensor 1 indicates that the medium 16 has reached 200 ° C.8Is detected and the excess air ratio is set to 0.95, so that catalytic combustion was started promptly. By adopting the configuration of Example 7 as described above, it was possible to start catalytic combustion promptly and while suppressing CO emission as much as possible. Temperature sensor 18The temperature to be detected may be at least equal to or higher than the temperature at which CO is oxidized, and oxidation such as methane that slips may be performed by setting the temperature high, such as about 500 ° C.
[CO emissions during steady combustion]
  Table 3 shows CO emissions during steady combustion under the conditions of 250 kcal / h in Examples 1 to 6, 8, and 9 and Comparative Examples 1, 3, and 5.
[0029]
[Table 3]

  In either case, CO in a steady state was a very small amount as compared with normal flame combustion, and it was confirmed that the second catalyst body 16 was acting effectively.
[0030]
  As described in the third embodiment, when a mechanism for preheating the secondary mixture or air with combustion exhaust gas is provided, the second catalyst body 16 is preheated in the case of Example 1 or the like. It has become possible to greatly reduce the power required for this. In the case of Example 4, the amount of combustion in the first catalyst body 12 can be increased, so that the low temperature limit combustion amount can be further reduced.
[0031]
  In the present embodiment, the catalyst supported on the honeycomb structure has been described, but the same effect can be obtained with any other form of the structure.
[0032]
  In the first embodiment and the like, the air excess ratio λ of the air-fuel mixture supplied to the primary combustion chamber 11 is controlled to a constant value of 0.95. However, any value can be used as long as catalytic combustion is possible with an air excess ratio of less than 1. There is no problem even if it is set. In addition, the total excess air ratio λ of the air-fuel mixture supplied to the secondary combustion chamber 14 is set to 1.2, but it is sufficient that the excess air condition (preferably λ> 1) is achieved. Further, when the combustible exhaust gas components can be sufficiently oxidized with diffusion air or the like, the total excess air ratio λ ≦ 1 may be satisfied.
[0033]
  In this configuration, the excess air ratio λ is changed under a constant combustion amount condition, and the excess air ratio is determined from the position where the maximum catalyst temperature is maximum. H in exhaust gas₂It is also possible to use a mechanism that chemically detects CO, hydrocarbon concentration, and the like.
[0034]
【The invention's effect】
  As is clear from the above explanation, according to the present invention, catalytic combustion in which deterioration of the combustion catalyst under combustion conditions of 800 ° C. or higher is suppressed, TDR (variable combustion amount width) is large, and exhaust gas is clean. It is possible to provide a device and a combustion catalyst used therefor.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a main part of a conventional catalytic combustion apparatus.
FIG. 2Inventions related toThe principal part sectional drawing of the catalytic combustion apparatus in one embodiment is shown.
FIG. 3The fruitThe principal part sectional drawing of the catalytic combustion apparatus in embodiment is shown.
FIG. 4 is a cross-sectional view of a main part of a catalytic combustion apparatus according to another embodiment of the present invention.
FIG. 5 shows the present invention.Related to the inventionThe dependence of the catalyst upstream temperature on the excess air ratio λ under the constant combustion amount condition shown in Embodiment 1 is shown.
FIG. 6 shows the temperature dependence of the methane oxidation activity of the second catalyst used in one example of the present invention.
7 shows a cross-sectional view of the first catalyst body used in Example 8. FIG.
8 shows a cross-sectional view of the first catalyst body used in Example 9. FIG.
FIG. 9Inventions related toThe time-dependent change of the catalyst upstream temperature during the life test of an Example of this and a comparative example is shown.
FIG. 10 shows the present invention.Inventions related toThe time-dependent change of the catalyst upstream temperature during the life test of an Example of this and a comparative example is shown.
FIG. 11 shows the present invention.Inventions related toThe temperature distribution of the flow direction in Examples 1 and 2 is shown.
FIG. 12 shows the present invention.Inventions related toThe relationship between the excess air ratio controlled with respect to the combustion amount in Examples 1 and 4 and the maximum catalyst temperature is shown.
FIG. 13 shows the relationship between the excess air ratio and the low-temperature limit combustion amount.
FIG. 14 shows the present invention.Inventions related toThe dependence of the maximum temperature of the first catalyst body and the second catalyst body in Example 5 on the excess air ratio is shown.
FIG. 15 shows the present invention.Inventions related toThe combustion temperature dependence of the catalyst maximum temperature in Examples 1 and 6 and Comparative Example 1 is shown.
FIG. 16 shows the present invention.Inventions related

to

Examples

1, 3,Embodiment 7 of the present inventionAnd it shows about the time-dependent change of CO density | concentration discharged | emitted after the flame preheating in the comparative example 1. FIG.
[Explanation of symbols]
   1 Fuel supply valve
2 Air supply valve
3 Premixing chamber
4 Mixture inlet
    5 Preheating burner
    6 Ignition device
    7 Combustion chamber
    8 Catalyst body
    9 Exhaust port
  10 Glass
  11 Primary combustion chamber
  12 First catalyst body
  13 Supply of secondary mixture or airPart
  14 Secondary combustion chamber
  15 Flame mouth
  16 Second catalyst body
  17 Electric heater
  18 Temperature sensor
  19Waste heat recovery unit
  20 Temperature sensor

Claims

Arranged on the upstream side is a fuel / air mixture inlet, on the downstream side an exhaust gas outlet, and a first catalyst body in which an oxidation catalyst is supported on a substrate having a large number of communication holes. A primary combustion chamber, a secondary supply port of an air-fuel mixture or air provided downstream of the primary combustion chamber, and a secondary provided with a second catalyst body provided downstream of the secondary supply port A combustion chamber,
When combusting, if the second catalyst body of the secondary combustion chamber is lower than a predetermined temperature at the initial stage of combustion, the excess air ratio of the primary combustion chamber burns as 1 or more,
When the second catalyst body in the secondary combustion chamber is heated to a predetermined temperature or more, the excess air ratio in the primary combustion chamber burns as less than 1,
The oxidation catalyst of the first catalyst body is composed of Pt or Rh, or a material mainly composed of Pt or Rh,
The first catalyst body is a catalytic combustion apparatus containing one or both of CeO _{2 and} ZrO ₂ as a main component.

2. The catalytic combustion apparatus according to claim 1 , wherein the predetermined temperature is a temperature at which a fuel component in the secondary combustion chamber is oxidized or a concentration of a combustible component in the exhaust gas reaches a predetermined level.

The second catalyst body is obtained by supporting an oxidation catalyst on the substrate having a plurality of communication holes, the catalytic combustion apparatus according to claim 1 or 2.

The oxidation catalyst of the first catalyst body is composed of a material mainly composed of Pt, the oxidation catalyst of the second catalyst body is composed of a material mainly composed of Pd, and the predetermined temperature is 500 ° C. 3. The catalytic combustion apparatus according to 3.

The catalytic combustion apparatus according to any one of claims 1 to 4 , wherein the air supplied to the secondary combustion chamber is preheated by being heated by exhaust gas in the secondary combustion chamber.

The catalytic combustion apparatus according to any one of claims 1 to 4 , wherein the excess air ratio of the air-fuel mixture supplied from the air-fuel mixture inlet decreases with a decrease in the amount of fuel component supplied .

The supply amount of the fuel component of the air-fuel mixture supplied from the air-fuel mixture inlet is substantially constant, and only the air amount is increased or decreased, and at least the air corresponding to the increase / decrease amount is supplied from the secondary supply port. The catalytic combustion apparatus in any one of Claims 1-4 .

The catalytic combustion apparatus according to any one of claims 1 to 4 , wherein the thermal conductivity of the base material of the first catalyst body is 10 W / m · ° C or more.

The catalyst body carrying the oxidation catalyst mainly composed of Pt or Pt is provided by laminating an oxidation catalyst layer mainly composed of Pt or Pt and an oxidation catalyst layer mainly composed of Rh or Pd. The catalytic combustion apparatus according to claim 1.

The Pt or an oxidation catalyst layer mainly the Rh or Pd are stacked against oxidation catalyst layer mainly composed of Pt is as claimed in claim 9, wherein the are partially disposed downstream Medium combustion device.

As a method of burning with the excess air ratio of the primary combustion chamber being less than 1 during the combustion,
The excess air ratio of the primary combustion chamber is changed, and the excess air ratio at which the temperature of the catalyst body becomes maximum is determined by a temperature detection unit provided in the vicinity of the catalyst body, and is lower than the excess air ratio. The catalytic combustion apparatus according to claim 1, wherein the combustion in the primary combustion chamber is performed in an excess air ratio region.

Arranged on the upstream side is a fuel / air mixture inlet, on the downstream side an exhaust gas outlet, and a first catalyst body in which an oxidation catalyst is supported on a substrate having a large number of communication holes. A primary combustion chamber, a secondary supply port of an air-fuel mixture or air provided downstream of the primary combustion chamber, and a secondary provided with a second catalyst body provided downstream of the secondary supply port A combustion control method for a catalytic combustion apparatus comprising a combustion chamber,
When combusting, if the second catalyst body of the secondary combustion chamber is lower than a predetermined temperature at the initial stage of combustion, the excess air ratio of the primary combustion chamber burns as 1 or more,
When the second catalyst body in the secondary combustion chamber is heated to a predetermined temperature or more, the excess air ratio in the primary combustion chamber burns as less than 1,
The oxidation catalyst of the first catalyst body is composed of Pt or Rh, or a material mainly composed of Pt or Rh,
The combustion control method for a catalytic combustion apparatus, wherein the first catalyst body includes one or both of CeO _{2 and} ZrO ₂ as a main component.