JP4864231B2

JP4864231B2 - Denitration catalyst structure and exhaust gas denitration method using the same

Info

Publication number: JP4864231B2
Application number: JP2001171588A
Authority: JP
Inventors: 泰良加藤; 尚美今田
Original assignee: Babcock Hitachi KK
Current assignee: Mitsubishi Power Ltd
Priority date: 2001-06-06
Filing date: 2001-06-06
Publication date: 2012-02-01
Anticipated expiration: 2021-06-06
Also published as: JP2002361098A

Description

【０００１】
【発明の属する技術分野】
本発明は、脱硝用触媒構造体およびこれを用いた排ガス脱硝方法に係り、特に２５０℃以下の低温性能に優れた脱硝用触媒構造体およびこれを用いた排ガス脱硝方法に関する。
【０００２】
【従来の技術】
アンモニア（ＮＨ₃）等を還元剤とした選択的接触還元脱硝法は、発電所、各種工場、ディーゼルエンジンなどから排出される排煙中の窒素酸化物（ＮＯｘ）の処理方法として広く実用化されており、特に火力発電所における排煙脱硝法の主流となっている。ＮＨ₃を還元剤とした選択的接触還元脱硝法では、一般に、バナジウム（Ｖ）、モリブデン（Ｍｏ）またはタングステン（Ｗ）の酸化物を活性成分とした酸化チタン（ＴｉＯ₂)系触媒を板状、ハニカム状、粒状などに成形し、この触媒成形体を充填した脱硝触媒層にＮＨ₃と共に排ガスを導入し、２５０〜４００℃の温度域で排ガスに含まれるＮＯｘを還元、無害化するものであり、処理温度３５０℃近辺の中温脱硝が主流となっていた。
【０００３】
ところで近年、省エネルギーの観点から、脱硝反応温度を低温化することへの要望が高まっている。特に、ボイラのように高温の排ガス源を容易に得られない産業排ガスや、ごみ焼却炉排ガス、廃熱回収ボイラ（ＨＲＳＧ）出口ガス等の脱硝処理では、排ガスを脱硝反応温度、例えば３５０℃まで加熱するためには多くのエネルギーを必要とし、また環境上の問題が発生するおそれもあるために、低温活性の高い脱硝触媒および脱硝技術への要望が高まっており、プラズマや無機燐を用いる方法等も検討されている。
【０００４】
このような背景の下、本発明者らは、金属酸化物を脱硝活性成分とする触媒を用いた排ガス脱硝方法に加え、被処理ガス中の二酸化窒素（ＮＯ₂）濃度を高めて触媒の低温活性を向上させる方法、およびこの方法と、バグフィルタに脱硝触媒成分を担持した高活性の触媒とを組み合わせた脱硝方法を提案した。このような従来技術に関するものとして、例えば特開平９−２９０１３６号公報等が挙げられる。
【０００５】
【発明が解決しようとする課題】
しかしながら、バナジウム（Ｖ）、モリブデン（Ｍｏ）、タングステン（Ｗ）等を活性成分とする脱硝触媒を用いる方法は、反応温度が２５０℃以下になると急激に脱硝活性が低下し、例えば１５０℃で運転しようとすると３５０℃で運転する場合の約１０倍の触媒量が必要となるなど実用性に欠けるという問題があった。一方、脱硝触媒成分をバグフィルタに担持した触媒と被処理ガス中のＮＯ₂濃度をコントロールする（増加させる）技術とを組合わせた方法は低温における触媒単位面積当たりの性能が優れているので触媒使用量は少なくなるが、触媒面積を大きくしようとすると装置が大きくなって設置場所が制約される等の問題があり、広く実用化されるまでには至っていない。
【０００６】
本発明の課題は、上記従来技術の問題点に鑑み、少ない触媒量で高い脱硝活性が得られると共に、設置スペースの制約をなくして実用性の高い、コンパクト、かつ例えば２００℃以下の低温活性に優れた脱硝用触媒構造体およびこれを用いた排ガス脱硝方法を提供することにある。
【０００７】
【課題を解決するための手段】
上記課題を解決するため、本発明者は、各種触媒構造と脱硝活性との関係等について鋭意研究した結果、脱硝触媒成分を担持した網状の触媒シートを順次一方向に連続２回、逆方向に連続２回、繰り返し折り曲げて所定長さの平面部が段差部の間隔を保って幾重にも重なるように形成した断面凹凸状の触媒シート成形体の前記平面部相互間に金属、セラミックスまたは有機樹脂の平板または網状物を断面波形に成形したスペーサを挟持させ、該スペーサと前記触媒シートの平面部との隙間および該隙間から前記触媒シートの平面部を透過して隣接するスペーサと触媒シート平面部との間の隙間に到るガス流路を形成することにより、脱硝用触媒と排ガスとの接触効率が向上し、高活性の脱硝用触媒構造体が得られること、およびこの脱硝用触媒構造体を用いた排ガス脱硝方法において、触媒構造体に流入する排ガス中のＮＯ₂濃度を高めて脱硝活性を向上させる方法とを組み合わせることにより、処理温度２００℃以下でも排ガス中のＮＯｘが効率よく分解、除去されることを見出し、本発明に到達した。
【０００８】
すなわち、本願で特許請求する発明は、以下のとおりである。
（１）無機繊維または有機繊維製の織布または不織布シートに脱硝触媒成分を担持した、ガス透過性の触媒シートを順次一方向に連続２回、逆方向に連続２回、折り返す操作を繰り返して所定長さの平面部が段差部の間隔を保って複数重なるように形成した断面凹凸状の触媒シート成形体の前記平面部相互間に金属、セラミックスまたは有機樹脂の平板を断面波形に成形したスペーサを挟持させ、該スペーサと前記触媒シートの平面部との隙間および該隙間から前記触媒シート平面部を透過して隣接するスペーサと触媒シート平面部との間の隙間に到るガス流路を形成したことを特徴とする脱硝用触媒構造体。
【０００９】
（２）前記断面波形のスペーサが、金属、セラミックスまたは有機樹脂からなる平板状網状物の成形体であることを特徴とする上記（１）に記載の脱硝用触媒構造体。
（３）前記断面波形のスペーサに、脱硝触媒成分を担持させたことを特徴とする上記（１）または（２）に記載の脱硝用触媒構造体。
（４）前記脱硝触媒成分が、チタン（Ｔｉ）、モリブデン（Ｍｏ）、タングステン（Ｗ）およびバナジウム（Ｖ）の酸化物のうち少なくとも一種を含有することを特徴とする上記（１）〜（３）の何れかに記載の脱硝用触媒構造体。
【００１０】
（５）上記（１）〜（４）の何れかに記載の脱硝用触媒構造体を用いた排ガス脱硝方法において、前記触媒構造体を、該触媒構造体の触媒シートの平面部がガス流通方向に沿うように排ガス煙道内に設置し、被処理ガスを、前記触媒構造体の上流部で導入されるアンモニア（ＮＨ₃）と共に触媒構造体に流入させ、脱硝触媒の存在下前記アンモニアと接触させて被処理ガス中に含まれる窒素酸化物（ＮＯｘ）を還元処理することを特徴とする排ガス脱硝方法。
【００１１】
（６）前記脱硝用触媒構造体に流入する被処理ガス中の二酸化窒素（ＮＯ₂）濃度を増加させることを特徴とする上記（５）に記載の排ガス脱硝方法。
（７）前記被処理ガス中の二酸化窒素（ＮＯ₂）濃度を増加させる方法が、排ガス中にオゾン、硝酸、硝酸アンモニウムのような酸化剤を吹き込んで被処理ガスに含まれる一酸化窒素（ＮＯ）をＮＯ₂に酸化する方法、または前記被処理ガスを酸化触媒と接触させて被処理ガス中のＮＯをＮＯ₂に酸化する方法であることを特徴とする上記（６）に記載の排ガス脱硝方法。
【００１２】
【発明の実施の形態】
図１は、本発明の一実施例である脱硝用触媒構造体の説明図、図２は、図１の触媒構造体における排ガス流通状況を示す説明図である。図１において、この触媒構造体は、無機繊維または有機繊維製の織布または不織布シートに脱硝触媒成分を担持した、ガス透過性の触媒シート１を順次一方向に連続２回、逆方向に連続２回、繰り返し折り曲げて所定長さの平面部１１が段差部１２の間隔を保って複数重なるように形成した断面凹凸状の触媒シート成形体の前記平面部１１相互間に金属、セラミックスまたは有機樹脂の平板を断面波形に成形した入口部スペーサ２および出口部スペーサ３を挟持させ、入口部スペーサ２または出口部スペーサ３と前記触媒シート１の平面部１１との隙間および入口部スペーサ２と触媒シート１の平面部１１との間の隙間から前記触媒シート１の平面部１１を透過して出口部スペーサ３と触媒シート１の平面部１１との間の隙間に到るガス流路を形成したものである（図２参照）。
【００１３】
すなわち図１の触媒構造体は、無機または有機シート状物に脱硝触媒成分を担持した触媒シート１と、該触媒シート１の平面部１１を貫通してガスが流れるようにするための入口部スペーサ２および出口部スペーサ３とから主としてなり、触媒シート１に入口部スペーサ２および出口部スペーサ３が交互に挟まれて積層された構造になっている。
【００１４】
このような構成において、ＮＯｘを含む被処理排ガス８は、図２に示したように例えば還元剤としてのＮＨ₃と共に入口部スペーサ２と触媒シート１とで形成される間隙に流入したのち、触媒シート１の平面部１１の網目を貫通して出口部スペーサ３と触媒シート１の平面部１１とで形成される間隙に流れ、被処理排ガス８に含まれるＮＯｘは、図４に示したような触媒シート１に担持された脱硝触媒成分粒子１０の存在下、ＮＨ₃と効率よく接触、反応して無害な窒素と水に分解する。なお、図４中９は、繊維物質である。
【００１５】
本実施例によれば、被処理ガス８が触媒シート１の平面部１１の網目を貫通して流通するので、前記被処理ガス８と触媒粒子１０との接触効率が著しく向上し、触媒反応が促進される。
【００１６】
本実施例において、入口部スペーサ２および出口部スペーサ３にも触媒成分を担持させることが好ましい。これによって触媒シート１の平面部１１を通過する際だけでなく、入口部スペーサ２および出口部スペーサ３と触媒シート１とで形成された流路を通過する過程でも脱硝反応が進行し、より高い脱硝性能が得られる。
【００１７】
本発明において、触媒シートを構成するシート状物としては、例えば厚さ０．２〜６ｍｍのガス透過性の無機繊維または有機繊維製の織布または不織布シートが用いられる。無機繊維としてはガラス繊維、シリカ繊維、シリカアルミナ繊維など、有機繊維としてはフッ素樹脂繊維、ポリイミド樹脂繊維など使用温度で酸化による劣化を生じにくいものが用いられる。このようなシート状物に担持される脱硝触媒成分としては、酸化チタン、酸化バナジウム、酸化モリブデンおよび酸化タングステンのうち少なくとも１種を含むものが用いられ、好ましくは酸化チタンに活性成分として酸化バナジウム、酸化モリブデンまたは酸化タングステンを担持した触媒成分が用いられる。触媒成分の担持量は、例えば５０〜５００ｇ／ｍ²である。
【００１８】
本発明において、入口部スペーサおよび出口部スペーサとしては、例えば金属、セラミックスまたは有機樹脂製の薄板を波形に成形したもの、金属網、メタルラス、セラミックスからなる無機網状物等または有機網状物を波形に形成したものが使用されるほか、これらに上記脱硝用触媒成分を担持したものが使用される。波板状触媒、または波板状の網状物からなる触媒をスペーサとして用いることにより、同一触媒量における触媒構造体全体としての体積を小さくすることができるので、コンパクトな脱硝装置を実現することができる。
【００１９】
本発明において、スペーサの波形の寸法は特に限定されないが、波部の高さを２〜３０ｍｍとすることによりコンパクトな脱硝装置を構成し易くなる。スペーサの配置方向は、線条につけた波がガスの流通方向であること、すなわち各波形の稜線が被処理ガスの流通方向に沿うように配置することが好ましいが、スペーサが網状物からなる波形である場合には、ガス流が網目を貫通できるので配置方向はいずれの方向であってもよい。この場合、入口部スペーサの凸部または凹部に対し、出口部スペーサの凸部または凹部が、横方向から見て交差するように配置することにより、ガス流を乱して接触効率を高める効果とガスの均一攪拌効果の両方が期待できるのでより好ましい。
【００２０】
本発明の脱硝用触媒構造体を用いた排ガス脱硝方法において、脱硝用触媒構造体の上流側において排ガス中の二酸化窒素（ＮＯ₂）含有量を増加させることが好ましい。これによって触媒構造体の低温脱硝活性が向上する。
【００２１】
図３は、本発明の排ガス浄化方法に適用する脱硝装置の説明図である。図において、排ガス煙道４の所定位置に図１の脱硝用触媒構造体５が設置されており、この触媒構造体５の排ガス流通方向上流側には排ガス８の流通方向に沿って順次ＮＯ₂濃度の増加手段６およびＮＨ₃注入手段７が設けられている。
【００２２】
このような構成の装置により、ＮＯ₂濃度の増加手段６によってＮＯ₂濃度が、例えばＮＯとほぼ同一の濃度となるまで増加された窒素酸化物含有排ガス８はＮＨ₃注入手段７から注入される所定量のＮＨ₃と共に脱硝用触媒構造体５に流入し、排ガス中のＮＯ₂１モルとＮＯ１モルが２モルのＮＨ₃と素早く反応し、Ｎ₂とＨ₂Ｏとが生成する。
【００２３】
本発明において、排ガス中のＮＯ₂濃度を増加させる方法としては、例えば(1)オゾンの添加により排ガス中のＮＯの一部をＮＯ₂に酸化させる方法、(2)硝酸または硝酸アンモニウムを添加し、硝酸とＮＯからＮＯ₂を生成させる方法、(3)貴金属触媒などの酸化触媒を設置し、排ガス中のＮＯをＮＯ₂に酸化する方法または(4)排ガス中に外部からＮＯ₂を吹き込む方法を採用することができる。
【００２４】
排ガス中にオゾン、硝酸などの酸化剤が添加されるとこれが触媒と接触することにより排ガスに含まれるＮＯの一部は次の反応により酸化されてＮＯ₂が生成する。
【００２５】
Ｏ₃ ＋ＮＯ → ＮＯ₂＋Ｏ₂ (1) 式
２ＨＮＯ₃＋ＮＯ → ３ＮＯ₂＋Ｈ₂Ｏ (2) 式
ＮＨ₄ＮＯ₃＋ＮＯ → ＮＯ₂＋Ｎ₂＋２Ｈ₂Ｏ (3) 式
生成したＮＯ₂と残存するＮＯは等モルづつ２倍当量のＮＨ₃と反応し（下記、４式）、無害な窒素と水になる。下記４式の反応は通常の脱硝反応であるＮＯとＮＨ₃の反応（下記５式）に比べ極めて早く、例えば１５０〜２００℃の範囲における反応速度比は４〜５倍になる。
【００２６】
ＮＯ＋ＮＯ₂＋２ＮＨ₃ → ２Ｎ₂＋３Ｈ₂Ｏ (4) 式
ＮＯ＋ＮＨ₃＋Ｏ₂ → Ｎ₂＋ 3/2Ｈ₂Ｏ (5) 式
従って、本発明によれば、触媒構造体を図１に示したような特定構造にしたことによるコンパクト、かつ排ガスと脱硝触媒成分との接触効率向上効果と、排ガス中のＮＯ₂濃度増加による脱硝反応速度比増大効果との相乗効果により、例えば２００℃程度の低温であっても、従来技術を用いた３５０℃における脱硝処理の場合に比べてより少ない触媒量で効率よくＮＯｘを分解、処理することができる。
【００２７】
【実施例】
以下、具体的実施例を用いて本発明を詳細に説明する。
【００２８】
実施例１
酸化チタン粉末（比表面積：３００m²/g、ＳＯ₄含有量：３wt％）１．５kg、モリブデン酸アンモニウム((ＮＨ₄)₆・Ｍｏ₇Ｏ₂₄・４Ｈ₂Ｏ）１８８g 、メタバナジン酸アンモニウム（ＮＨ₄ＶＯ₃)１７５g 、および蓚酸（Ｈ₂Ｃ₂Ｏ₄・２Ｈ₂Ｏ）２２６g に水を加えて加熱、混練して粘土状物質を得た。これを３φの柱状に押し出し成形した後、流動層乾燥機で乾燥し、５００℃で２時間焼成し、得られた焼成物をハンマーミルを用いて１μm 以下の粒径が６０％以上の粉末となるように粉砕し、触媒粉末を得た。この触媒粉末１０kgを水５０kgに分散させて担持用触媒スラリとした。
【００２９】
これとは別に５００ｍｍ幅のポリイミド製不織布（厚み２ｍｍ、重量密度５２０g/m²）を用意し、これを上記スラリ中に浸漬した後１５０℃で乾燥し、触媒担持量４００g/m²の触媒担持フィルタ（触媒シート）を調製した。
【００３０】
これとは別に、厚さ０．２ｍｍ、５００ｍｍ幅のＳＵＳ４３０の平板に山高さ４ｍｍ、山底辺１２ｍｍの波形を多数形成し、長さ５００ｍｍに切断して入口部および出口部スペーサとし、このスペーサを挟みながら上記触媒シートを屏風状に折り曲げて積層し、枠に組み込んで図１のような触媒構造体を得た。
【００３１】
実施例２
実施例１のスペーサに代えて、厚さ０．２ｍｍのＳＵＳ製帯鋼をメタルラス加工した金属基板に、酸化チタン粉末２０kgにモリブデン酸アンモニウム((ＮＨ₄)₆・Ｍｏ₇Ｏ₂₄・４Ｈ₂Ｏ）を２．５kg、メタバナジン酸アンモニウム２．３３kg、蓚酸３．０kg、無機繊維（商品名カオウール）４．８kgとに水を加えてニーダで混練した、水分３３％の基材用ペーストをローラを用いて塗布し、その後、実施例１のスペーサと同様の山形を成形し、５００℃で２時間焼成したスペーサを用いた以外は、上記実施例１と同様にして実施例２の触媒構造体を得た。
【００３２】
実施例３
実施例１のポリイミド製不織布に代えて繊維径１０μm 、厚み０．５ｍｍのＥガラス繊維不織布を用いた以外は、上記実施例１と同様にして７０g/m²で触媒成分が担持された触媒シートを得た。
【００３３】
一方、繊維径９μm のＥガラス製繊維１４００本の撚糸を１０本／２５．４ｍｍの荒さで平織りした網状物にチタニア４０％、シリカゾル２０％、ポリビニールアルコール１％のスラリを含浸し、１５０℃で乾燥して剛性を持たせて触媒基材とし、この触媒基材二枚の間に上記実施例２で用いた基材用ペーストを置き、圧延ローラを通すことにより酸化チタン、酸化モリブデンおよび酸化バナジウムを活性成分とする厚み０．７ｍｍの板状触媒を得、これを加熱成形金型により実施例１のスペーサと同様の山形を成形し、５００℃で２時間焼成して入口部および出口部スペーサとし、このスペーサを挟みながら上記触媒シートを屏風状に折り曲げて図１に示したように複数積層し、枠に組み込んで実施例３の触媒構造体とした。
実施例４
実施例２で用いた厚さ０．２ｍｍのＳＵＳ製帯鋼をメタルラス加工した金属基板にプレス加工により実施例１のスペーサと同様の波形を形成して波形基材とし、この波形基材を実施例１の触媒シートの作成に用いた触媒スラリ中に浸漬した後、エアーブローしてラス目間の余剰スラリを吹き飛ばして網目を貫通させ、乾燥し、５００℃で２時間焼成し、得られた触媒担持網状スペーサを、実施例１で用いた触媒シートに挟みながら該触媒シートを屏風状に折り曲げて複数積層し、触媒枠に組み込んで実施例４の触媒構造体とした。
【００３４】
実施例５
実施例１で用いた触媒シートに代えて実施例３で用いた触媒シートを用いた以外は、上記実施例４と同様にして実施例５の触媒構造体とした。
【００３５】
比較例１
実施例３でスペーサとして使用した、成形前の厚み０．７ｍｍの板状触媒を加熱成形金型に供給して高さ３ｍｍの波形を多数形成したのち乾燥し、５００℃で２時間焼成し、得られた波形板状触媒を積層し、図５に示したような流路形状を有する、パラレルフロー形の触媒構造体とした。
【００３６】
実施例１〜５および比較例１の触媒構造体の性能を比較するため、実施例１〜５の触媒シートを５０cm²の大きさに切り出し、表１および表２に示す組成のガスＡおよびＢをフィルタ面に直交する方向に１m/min の速度で流しながら１８０℃における脱硝率を測定した。
【００３７】
【表１】

【００３８】
【表２】

これとは別に実施例１〜５のスペーサおよび比較例１の触媒を２０ｍｍ×１００ｍｍに切り出し、これらテストピースの表１および表２に示すガスに対する脱硝活性を表３の条件で測定した。
【００３９】
【表３】

実施例１〜５および比較例１の触媒を用いてＳＶ＝２０，０００ h^-1、１８０℃で脱硝処理した場合の脱硝率を試算し、結果を表４に示した。
【００４０】
【表４】

表４の結果から分かるように、各実施例触媒の脱硝性能は、比較例１に比べて高く、１８０℃という低温でも実用に耐え得る性能を有していることが分かる。特に、ＮＯ₂／ＮＯモル比を１近くに維持した場合（表２のガス組成）では、その性能が飛躍的に向上し、本発明の触媒構造体と、被処理ガス中のＮＯ濃度を増加させてＮＯ₂／ＮＯモル比を調節する方法とを組み合わせた脱硝方法は低温脱硝に適することが分かる。
【００４１】
【発明の効果】
本願の請求項１に記載の発明によれば、触媒構造体をコンパクト化できるうえ、被処理ガスが触媒シートの平面部を貫通して流通するので、被処理ガスと脱硝触媒との接触効率が向上する。
【００４２】
本願の請求項２に記載の発明によれば、上記発明の効果に加え、被処理ガスの均一攪拌効果が向上する。
【００４３】
本願の請求項３に記載の発明によれば、上記発明の効果に加え、同一体積内の触媒量が増加するので、脱硝効率がより向上するとともに、同一触媒量であれば、触媒構造体全体としての体積をよりコンパクトにすることができる。
【００４４】
本願の請求項４に記載の発明によれば、上記発明の効果に加え、特定成分の脱硝触媒成分による脱硝性能が発揮される。
【００４５】
本願の請求項５に記載の発明によれば、特定構造の触媒構造体を用いることにより排ガス中のＮＯｘを効率よく分解除去することができる。
【００４６】
本願の請求項６に記載の発明によれば、特定構造の触媒構造体を用いることによる接触効率の向上と、排ガス中のＮＯ₂濃度を増加させることによる、脱硝反応速度増大効果との相乗効果により、低温でも高い脱硝性能を実現することができ、例えば反応温度２００℃以下の低温脱硝においても、従来技術における３５０℃の場合と同程度の触媒量で済むコンパクトな脱硝装置が実現できる。
【００４７】
本願の請求項７に記載の発明によれば、上記発明と同様の効果が得られ、例えば排ガスの予熱など無駄なエネルギー消費を低減でき、地球環境の保護に大きく寄与することができる。
【図面の簡単な説明】
【図１】本発明の一実施例である脱硝用触媒構造体を示す説明図である。
【図２】図１の触媒構造体におけるガス流れ方向を示す説明図。
【図３】本発明の排ガス脱硝方法に適用される排ガス脱硝装置を示す説明図。
【図４】本発明の触媒構造体における触媒シートの一部を拡大した模式図。
【図５】従来技術の断面形状および外寸法を示す説明図。
【符号の説明】
１…触媒シート、２…入口部スペーサ、３…出口部スペーサ、４…煙道、５…触媒構造体、６…ＮＯ₂濃度増加手段、７…ＮＨ₃注入手段、８…排ガス流、９…繊維物質、１０…脱硝触媒成分粒子、１１…触媒シートの平面部、１２…触媒シートの段差部。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a denitration catalyst structure and an exhaust gas denitration method using the same, and more particularly to a denitration catalyst structure excellent in low temperature performance of 250 ° C. or less and an exhaust gas denitration method using the same.
[0002]
[Prior art]
The selective catalytic reduction denitration method using ammonia (NH ₃ ) as a reducing agent has been widely put into practical use as a method for treating nitrogen oxides (NOx) in flue gas discharged from power plants, various factories, diesel engines, etc. In particular, it has become the mainstream of flue gas denitration methods in thermal power plants. In the selective catalytic reduction denitration method using NH ₃ as a reducing agent, a titanium oxide (TiO ₂ ) -based catalyst containing an oxide of vanadium (V), molybdenum (Mo) or tungsten (W) as an active component is generally plate-shaped. It is formed into a honeycomb shape, granular shape, etc., and exhaust gas is introduced into the denitration catalyst layer filled with this catalyst molded body together with NH ₃ , and NOx contained in the exhaust gas is reduced and rendered harmless in a temperature range of 250 to 400 ° C. Yes, medium-temperature denitration around 350 ° C was the mainstream.
[0003]
Incidentally, in recent years, from the viewpoint of energy saving, there is an increasing demand for lowering the denitration reaction temperature. In particular, in the denitration treatment of industrial exhaust gas that cannot easily obtain a high-temperature exhaust gas source such as a boiler, waste incinerator exhaust gas, and waste heat recovery boiler (HRSG) outlet gas, the exhaust gas is reduced to a denitration reaction temperature, for example, 350 ° C. Since heating requires a lot of energy and environmental problems may occur, there is an increasing demand for a low-temperature active denitration catalyst and denitration technology. A method using plasma or inorganic phosphorus Etc. are also being studied.
[0004]
Under such a background, the present inventors have increased the concentration of nitrogen dioxide (NO ₂ ) in the gas to be treated in addition to the exhaust gas denitration method using a catalyst containing a metal oxide as a denitration active component, thereby reducing the temperature of the catalyst. A method for improving the activity and a denitration method combining this method with a highly active catalyst in which a denitration catalyst component is supported on a bag filter have been proposed. As such a prior art, for example, JP-A-9-290136 can be cited.
[0005]
[Problems to be solved by the invention]
However, the method using a denitration catalyst containing vanadium (V), molybdenum (Mo), tungsten (W), etc. as the active component, the denitration activity rapidly decreases when the reaction temperature is 250 ° C. or lower, for example, operating at 150 ° C. When trying to do so, there was a problem of lack of practicality, for example, about 10 times as much catalyst amount as when operating at 350 ° C. was required. On the other hand, the method combining the catalyst having the denitration catalyst component supported on the bag filter and the technology for controlling (increasing) the NO ₂ concentration in the gas to be treated has excellent performance per unit area of the catalyst at low temperature. Although the amount of use is reduced, there is a problem that if the catalyst area is increased, the apparatus becomes larger and the installation location is restricted, so that it has not yet been put into practical use.
[0006]
In view of the above-mentioned problems of the prior art, the object of the present invention is that high denitration activity is obtained with a small amount of catalyst, and that there is no restriction on installation space, high practicality, compactness, and low temperature activity of, for example, 200 ° C. or less. An object of the present invention is to provide an excellent denitration catalyst structure and an exhaust gas denitration method using the same.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventor has conducted intensive research on the relationship between various catalyst structures and denitration activity, and as a result, the reticulated catalyst sheet carrying the denitration catalyst component has been sequentially and continuously applied twice in one direction and in the opposite direction. Metal, ceramics, or organic resin between the planar portions of the catalyst sheet molded body having a concave-convex cross section formed by repeatedly bending twice and continuously so that the planar portions of a predetermined length overlap with each other while maintaining the gap between the stepped portions. A spacer formed by flattening a flat plate or a net of a cross-sectional waveform is sandwiched, and a gap between the spacer and the planar portion of the catalyst sheet and a planar portion of the catalyst sheet passing through the planar portion of the catalyst sheet from the gap are adjacent to each other. By forming a gas flow path leading to the gap between the NOx catalyst and the NOx removal catalyst, the contact efficiency between the exhaust gas and the exhaust gas is improved, and a highly active catalyst removal structure for NOx removal can be obtained. In the exhaust gas denitration method using the structure, by combining a method of improving the denitration activity by increasing the NO ₂ concentration in the exhaust gas flowing into the catalyst structure, NOx in the exhaust gas even processing temperature 200 ° C. or less efficiently As a result, the present invention has been reached.
[0008]
That is, the invention claimed in the present application is as follows.
(1) Repeat the operation of turning a gas-permeable catalyst sheet carrying a denitration catalyst component on a woven or non-woven sheet made of inorganic fiber or organic fiber in succession twice in one direction and twice in the opposite direction. A spacer in which a flat plate of metal, ceramics, or organic resin is formed into a cross-sectional corrugation between the flat portions of a catalyst sheet molded body having a concavo-convex shape formed so that a plurality of flat portions having a predetermined length are overlapped with a gap between stepped portions. To form a gas flow path that reaches the gap between the spacer and the flat surface of the catalyst sheet through the gap of the flat surface of the catalyst sheet and the gap between the adjacent spacer and the flat surface of the catalyst sheet. A catalyst structure for denitration characterized by the above.
[0009]
(2) The catalyst structure for denitration as described in (1) above, wherein the spacer having a corrugated cross section is a molded product of a flat network made of metal, ceramics or organic resin.
(3) The denitration catalyst structure according to (1) or (2), wherein a denitration catalyst component is supported on the spacer having a corrugated cross section.
(4) The above (1) to (3), wherein the denitration catalyst component contains at least one of titanium (Ti), molybdenum (Mo), tungsten (W) and vanadium (V) oxides. ) The catalyst structure for denitration according to any one of the above.
[0010]
(5) In the exhaust gas denitration method using the denitration catalyst structure according to any one of (1) to (4), the planar structure of the catalyst sheet of the catalyst structure has a gas flow direction. The gas to be treated is introduced into the catalyst structure together with ammonia (NH ₃ ) introduced upstream of the catalyst structure and brought into contact with the ammonia in the presence of a denitration catalyst. An exhaust gas denitration method comprising reducing a nitrogen oxide (NOx) contained in the gas to be treated.
[0011]
(6) The exhaust gas denitration method according to (5), wherein the concentration of nitrogen dioxide (NO ₂ ) in the gas to be treated flowing into the denitration catalyst structure is increased.
(7) A method for increasing the concentration of nitrogen dioxide (NO ₂ ) in the gas to be treated is a method in which an oxidizing agent such as ozone, nitric acid, or ammonium nitrate is blown into the exhaust gas to contain nitrogen monoxide (NO) contained in the gas to be treated. The exhaust gas denitration method according to (6) above, wherein the process gas is oxidized to NO ₂ or the process gas is brought into contact with an oxidation catalyst to oxidize NO in the process gas to NO _2. .
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an explanatory view of a denitration catalyst structure according to an embodiment of the present invention, and FIG. 2 is an explanatory view showing an exhaust gas distribution state in the catalyst structure of FIG. In FIG. 1, this catalyst structure comprises a gas-permeable catalyst sheet 1 carrying a denitration catalyst component on a woven or non-woven sheet made of inorganic fibers or organic fibers, successively in one direction twice in succession and continuously in the opposite direction. Metal, ceramics, or organic resin between the planar portions 11 of the catalyst sheet molded body having a concavo-convex shape formed by repeatedly bending twice and forming a plurality of planar portions 11 having a predetermined length with the gap of the stepped portion 12 therebetween. The inlet portion spacer 2 and the outlet portion spacer 3, which are formed into a corrugated cross section, are sandwiched between the inlet portion spacer 2 or the outlet portion spacer 3 and the flat portion 11 of the catalyst sheet 1, and the inlet portion spacer 2 and the catalyst sheet. A gas flow path that passes through the flat portion 11 of the catalyst sheet 1 from the gap between the flat portion 11 and the flat portion 11 and reaches the gap between the outlet spacer 3 and the flat portion 11 of the catalyst sheet 1. It is obtained by forming (see FIG. 2).
[0013]
That is, the catalyst structure shown in FIG. 1 includes a catalyst sheet 1 carrying a denitration catalyst component on an inorganic or organic sheet, and an inlet spacer for allowing gas to flow through the flat portion 11 of the catalyst sheet 1. 2 and the outlet portion spacer 3. The inlet portion spacer 2 and the outlet portion spacer 3 are alternately sandwiched and stacked on the catalyst sheet 1.
[0014]
In such a configuration, the exhaust gas 8 to be treated containing NOx flows into a gap formed by the inlet spacer 2 and the catalyst sheet 1 together with NH ₃ as a reducing agent, for example, as shown in FIG. The NOx contained in the treated exhaust gas 8 passes through the mesh of the flat portion 11 of the sheet 1 and flows into a gap formed by the outlet portion spacer 3 and the flat portion 11 of the catalyst sheet 1 as shown in FIG. In the presence of the denitration catalyst component particles 10 supported on the catalyst sheet 1, it efficiently contacts and reacts with NH ₃ to decompose into harmless nitrogen and water. In addition, 9 in FIG. 4 is a fiber substance.
[0015]
According to the present embodiment, the gas to be treated 8 flows through the mesh of the flat portion 11 of the catalyst sheet 1, so that the contact efficiency between the gas to be treated 8 and the catalyst particles 10 is remarkably improved, and the catalytic reaction is improved. Promoted.
[0016]
In the present embodiment, it is preferable that the inlet spacer 2 and the outlet spacer 3 are also loaded with catalyst components. As a result, not only when passing through the flat portion 11 of the catalyst sheet 1, but also in the process of passing through the flow path formed by the inlet portion spacer 2, the outlet portion spacer 3 and the catalyst sheet 1, the denitration reaction proceeds and is higher. Denitration performance is obtained.
[0017]
In the present invention, as the sheet-like material constituting the catalyst sheet, for example, a gas-permeable inorganic fiber or organic fiber woven or non-woven sheet having a thickness of 0.2 to 6 mm is used. As the inorganic fiber, glass fiber, silica fiber, silica alumina fiber or the like is used, and as the organic fiber, a material that hardly causes deterioration due to oxidation at a use temperature, such as a fluororesin fiber or a polyimide resin fiber, is used. As the denitration catalyst component supported on such a sheet-like material, one containing at least one of titanium oxide, vanadium oxide, molybdenum oxide and tungsten oxide is used, preferably vanadium oxide as an active component in titanium oxide, A catalyst component carrying molybdenum oxide or tungsten oxide is used. The supported amount of the catalyst component is, for example, 50 to 500 g / m ² .
[0018]
In the present invention, as the inlet portion spacer and the outlet portion spacer, for example, a metal, ceramic or organic resin thin plate formed into a corrugated shape, a metal net, a metal lath, an inorganic net made of ceramics, or an organic net into a corrugated shape In addition to those formed, those carrying the above-mentioned denitration catalyst component are used. By using a corrugated catalyst or a catalyst made of corrugated mesh as a spacer, the volume of the entire catalyst structure in the same catalyst amount can be reduced, so that a compact denitration device can be realized. it can.
[0019]
In the present invention, the corrugated dimension of the spacer is not particularly limited, but it becomes easy to construct a compact denitration apparatus by setting the height of the wave portion to 2 to 30 mm. The arrangement direction of the spacer is preferably such that the wave applied to the filament is the gas flow direction, that is, the ridgeline of each waveform is along the flow direction of the gas to be treated. In this case, since the gas flow can penetrate the mesh, the arrangement direction may be any direction. In this case, by arranging the convex portion or the concave portion of the outlet portion spacer so as to intersect the convex portion or the concave portion of the inlet portion spacer as viewed from the lateral direction, the gas flow is disturbed and the contact efficiency is improved. It is more preferable because both the homogeneous stirring effect of gas can be expected.
[0020]
In the exhaust gas denitration method using the denitration catalyst structure of the present invention, it is preferable to increase the nitrogen dioxide (NO ₂ ) content in the exhaust gas upstream of the denitration catalyst structure. This improves the low-temperature denitration activity of the catalyst structure.
[0021]
FIG. 3 is an explanatory view of a denitration apparatus applied to the exhaust gas purification method of the present invention. In the figure, the denitration catalyst structure 5 of FIG. 1 is installed at a predetermined position of the exhaust gas flue 4, and NO ₂ is sequentially disposed in the exhaust gas flow direction upstream side of the catalyst structure 5 along the flow direction of the exhaust gas 8. Concentration increasing means 6 and NH ₃ injecting means 7 are provided.
[0022]
With the apparatus having such a configuration, the nitrogen oxide-containing exhaust gas 8 whose NO ₂ concentration has been increased by the NO ₂ concentration increasing means 6 until it becomes substantially the same as NO, for example, is injected from the NH ₃ injection means 7. It flows into the denitration catalyst structure 5 together with a predetermined amount of NH ₃ , and 1 mol of NO _{2 and} 1 mol of NO in the exhaust gas react rapidly with 2 mol of NH ₃ to produce N ₂ and H ₂ O.
[0023]
In the present invention, as a method of increasing the NO ₂ concentration in the exhaust gas, for example, (1) a method of oxidizing a part of NO in the exhaust gas to NO ₂ by adding ozone, (2) adding nitric acid or ammonium nitrate, A method of generating NO ₂ from nitric acid and NO, (3) a method of installing an oxidation catalyst such as a noble metal catalyst and oxidizing NO in exhaust gas to NO ₂ or (4) a method of blowing NO ₂ from the outside into the exhaust gas Can be adopted.
[0024]
When an oxidizing agent such as ozone or nitric acid is added to the exhaust gas, it comes into contact with the catalyst, so that a part of NO contained in the exhaust gas is oxidized by the following reaction to generate NO ₂ .
[0025]
O ₃ + NO → NO ₂ + O ₂ (1) Formula ₂ HNO ₃ + NO → 3NO ₂ + H ₂ O (2) Formula NH ₄ NO ₃ + NO → NO ₂ + N ₂ + 2H ₂ O (3) The generated NO ₂ remains. NO reacts with 2 equivalents of NH _{3 in} equimolar amounts (below 4 formulas) to form harmless nitrogen and water. The reaction of the following four formulas is extremely faster than the reaction of NO and NH ₃ (the following five formulas), which is a normal denitration reaction.
[0026]
NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O (4) Formula NO + NH ₃ + O ₂ → N ₂ + 3 / 2H ₂ O (5) Therefore, according to the present invention, the catalyst structure is as shown in FIG. Due to the compact effect resulting from the specific structure and the synergistic effect of improving the contact efficiency between the exhaust gas and the denitration catalyst component and the effect of increasing the denitration reaction rate ratio by increasing the NO ₂ concentration in the exhaust gas, the temperature can be as low as about 200 ° C., for example. However, NOx can be efficiently decomposed and treated with a smaller amount of catalyst than in the case of the denitration treatment at 350 ° C. using the prior art.
[0027]
【Example】
Hereinafter, the present invention will be described in detail using specific examples.
[0028]
Example 1
Titanium oxide powder (specific surface area: 300 m ² / g, SO ₄ content: 3 wt%) 1.5 kg, ammonium molybdate ((NH ₄ ) ₆ · Mo ₇ O ₂₄ · 4H ₂ O) 188 g, ammonium metavanadate (NH ₄ VO ₃ ) 175 g and oxalic acid (H ₂ C ₂ O ₄ .2H ₂ O) 226 g were added with water, heated and kneaded to obtain a clay-like substance. This was extruded into a 3φ columnar shape, dried with a fluidized bed dryer, and fired at 500 ° C. for 2 hours. The obtained fired product was powdered with a particle size of 1 μm or less of 60% or more using a hammer mill. The catalyst powder was obtained by grinding. 10 kg of this catalyst powder was dispersed in 50 kg of water to obtain a catalyst slurry for support.
[0029]
Separately, a 500 mm wide polyimide non-woven fabric (thickness 2 mm, weight density 520 g / m ² ) was prepared, dipped in the slurry, dried at 150 ° C., and a catalyst supported amount of 400 g / m ² catalyst supported. A filter (catalyst sheet) was prepared.
[0030]
Separately, a SUS430 flat plate having a thickness of 0.2 mm and a width of 500 mm is formed with a plurality of corrugations having a height of 4 mm and a bottom of the mountain of 12 mm, and is cut into a length of 500 mm to form inlet and outlet spacers. The catalyst sheet was folded in a folding screen while being sandwiched and laminated into a frame to obtain a catalyst structure as shown in FIG.
[0031]
Example 2
In place of the spacer of Example 1, a metal substrate obtained by metallizing SUS steel strip having a thickness of 0.2 mm, titanium oxide powder 20 kg, ammonium molybdate ((NH ₄ ) ₆ · Mo ₇ O ₂₄ · 4H ₂ O ) 2.5 kg, ammonium metavanadate 2.33 kg, oxalic acid 3.0 kg, inorganic fiber (trade name Kao wool) 4.8 kg and water kneaded in a kneader. The catalyst structure of Example 2 was formed in the same manner as in Example 1 except that a chevron similar to the spacer of Example 1 was formed and the spacer fired at 500 ° C. for 2 hours was used. Obtained.
[0032]
Example 3
A catalyst sheet carrying a catalyst component at 70 g / m ² in the same manner as in Example 1 except that an E-glass fiber nonwoven fabric having a fiber diameter of 10 μm and a thickness of 0.5 mm was used instead of the polyimide nonwoven fabric of Example 1. Got.
[0033]
On the other hand, a net-like product obtained by plain weaving 10400 / 25.4 mm twisted yarns of 1400 E glass fibers having a fiber diameter of 9 μm was impregnated with a slurry of 40% titania, 20% silica sol, and 1% polyvinyl alcohol at 150 ° C The catalyst base material was dried to give rigidity, and the base material paste used in Example 2 was placed between the two catalyst base materials, and passed through a rolling roller to form titanium oxide, molybdenum oxide and oxide. A plate-like catalyst having a thickness of 0.7 mm containing vanadium as an active component is obtained, and this is formed into a chevron similar to the spacer of Example 1 by a thermoforming mold, and baked at 500 ° C. for 2 hours. As a spacer, the catalyst sheet was folded in a folding screen while sandwiching the spacer, and a plurality of layers were stacked as shown in FIG. 1 and assembled into a frame to obtain a catalyst structure of Example 3.
Example 4
A corrugated substrate is formed by forming a corrugated substrate similar to the spacer of Example 1 by pressing on a metal substrate obtained by metallizing the 0.2 mm thick SUS steel strip used in Example 2 and carrying out the corrugated substrate. After immersing in the catalyst slurry used in the preparation of the catalyst sheet of Example 1, air blown to blow off excess slurry between the laths to penetrate the mesh, dried, and fired at 500 ° C. for 2 hours to obtain A plurality of catalyst sheets were folded in a folding screen while sandwiching the catalyst-supporting mesh spacer between the catalyst sheets used in Example 1, and assembled into a catalyst frame to obtain a catalyst structure of Example 4.
[0034]
Example 5
A catalyst structure of Example 5 was obtained in the same manner as in Example 4 except that the catalyst sheet used in Example 3 was used instead of the catalyst sheet used in Example 1.
[0035]
Comparative Example 1
A plate-shaped catalyst having a thickness of 0.7 mm before molding, which was used as a spacer in Example 3, was supplied to a thermoforming mold to form a large number of corrugations having a height of 3 mm, dried, and then fired at 500 ° C. for 2 hours. The obtained corrugated plate catalyst was laminated to obtain a parallel flow type catalyst structure having a flow channel shape as shown in FIG.
[0036]
In order to compare the performance of the catalyst structures of Examples 1 to 5 and Comparative Example 1, the catalyst sheets of Examples 1 to 5 were cut into a size of 50 cm ² and gases A and B having the compositions shown in Tables 1 and 2 were used. Was measured at 180 ° C. while flowing at a speed of 1 m / min in a direction perpendicular to the filter surface.
[0037]
[Table 1]

[0038]
[Table 2]

Separately, the spacers of Examples 1 to 5 and the catalyst of Comparative Example 1 were cut into 20 mm × 100 mm, and the denitration activity of these test pieces against the gases shown in Table 1 and Table 2 was measured under the conditions shown in Table 3.
[0039]
[Table 3]

The denitration rate in the case of denitration treatment at 180 ° C. with SV = 20,000 h ⁻¹ using the catalysts of Examples 1 to 5 and Comparative Example 1 was calculated, and the results are shown in Table 4.
[0040]
[Table 4]

As can be seen from the results in Table 4, the denitration performance of the catalyst of each example is higher than that of Comparative Example 1, and it can be seen that the catalyst can withstand practical use even at a low temperature of 180 ° C. In particular, when the NO ₂ / NO molar ratio is maintained close to 1 (the gas composition in Table 2), the performance is dramatically improved, and the catalyst structure of the present invention and the NO concentration in the gas to be treated are increased. It can be seen that the denitration method combined with the method of adjusting the NO ₂ / NO molar ratio is suitable for low-temperature denitration.
[0041]
【Effect of the invention】
According to the invention described in claim 1 of the present application, the catalyst structure can be made compact, and the gas to be treated flows through the flat portion of the catalyst sheet, so that the contact efficiency between the gas to be treated and the denitration catalyst is high. improves.
[0042]
According to invention of Claim 2 of this application, in addition to the effect of the said invention, the uniform stirring effect of to-be-processed gas improves.
[0043]
According to the invention described in claim 3 of the present application, in addition to the effect of the above invention, the amount of catalyst in the same volume is increased, so that the denitration efficiency is further improved. The volume can be made more compact.
[0044]
According to the invention described in claim 4 of the present application, in addition to the effects of the above invention, the denitration performance by the denitration catalyst component of the specific component is exhibited.
[0045]
According to the invention described in claim 5 of the present application, NOx in the exhaust gas can be efficiently decomposed and removed by using the catalyst structure having a specific structure.
[0046]
According to the invention described in claim 6 of the present application, there is a synergistic effect between the improvement of the contact efficiency by using the catalyst structure having the specific structure and the effect of increasing the denitration reaction rate by increasing the NO ₂ concentration in the exhaust gas. Thus, high denitration performance can be realized even at low temperatures. For example, even in low temperature denitration at a reaction temperature of 200 ° C. or lower, a compact denitration apparatus that requires a catalyst amount comparable to 350 ° C. in the prior art can be realized.
[0047]
According to the invention described in claim 7 of the present application, an effect similar to that of the above-described invention can be obtained. For example, useless energy consumption such as preheating of exhaust gas can be reduced, which can greatly contribute to protection of the global environment.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a denitration catalyst structure according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a gas flow direction in the catalyst structure of FIG.
FIG. 3 is an explanatory view showing an exhaust gas denitration apparatus applied to the exhaust gas denitration method of the present invention.
FIG. 4 is an enlarged schematic view of a part of the catalyst sheet in the catalyst structure of the present invention.
FIG. 5 is an explanatory diagram showing a cross-sectional shape and external dimensions of the prior art.
[Explanation of symbols]
1 ... catalyst sheet, 2 ... inlet spacer 3 ... outlet spacers, 4 ... flue, 5 ... catalyst structure, 6 ... NO ₂ concentration increasing means, 7 ... NH ₃ injection means, 8 ... exhaust gas stream, 9 ... Fiber material, 10 ... Denitration catalyst component particles, 11 ... Flat portion of catalyst sheet, 12 ... Stepped portion of catalyst sheet.

Claims

Repeat the operation of turning a gas-permeable catalyst sheet carrying a denitration catalyst component on a woven or non-woven sheet made of inorganic fiber or organic fiber in succession twice in one direction and twice in the opposite direction. A spacer formed by forming a flat plate of metal, ceramics, or organic resin into a cross-sectional corrugation is sandwiched between the flat portions of a catalyst sheet molded body having a concavo-convex cross section formed so that a plurality of flat portions are overlapped with a gap between the step portions. A gas flow path is formed between the spacer and the flat portion of the catalyst sheet, and through the gap through the catalyst sheet flat portion to reach a gap between the adjacent spacer and the catalyst sheet flat portion. A catalytic structure for denitration.

2. The catalyst structure for denitration according to claim 1, wherein the spacer having a corrugated cross section is a molded product of a flat network made of metal, ceramics or organic resin.

The catalyst structure for denitrification according to claim 1 or 2, wherein a denitration catalyst component is supported on the spacer having a corrugated cross section.

The denitration catalyst component contains at least one of oxides of titanium (Ti), molybdenum (Mo) tungsten (W), and vanadium (V), according to any one of claims 1 to 3. Catalyst structure for denitration.

5. The exhaust gas denitration method using the denitration catalyst structure according to claim 1, wherein the catalyst structure is treated with exhaust gas so that a catalyst sheet flat portion of the catalyst structure is along a gas flow direction. Nitrogen contained in the gas to be treated by allowing the gas to be treated to flow into the catalyst structure together with ammonia introduced in the upstream portion of the catalyst structure and contacting the ammonia in the presence of a denitration catalyst. An exhaust gas denitration method comprising reducing oxides.

6. The exhaust gas denitration method according to claim 5, wherein the concentration of nitrogen dioxide in the gas to be treated flowing into the denitration catalyst structure is increased.

A method of increasing the concentration of nitrogen dioxide in the gas to be treated is a method of oxidizing nitrogen monoxide contained in the gas to be treated into nitrogen dioxide by blowing an oxidizing agent such as ozone, nitric acid or ammonium nitrate into the exhaust gas, or The exhaust gas denitration method according to claim 6, wherein the process gas is brought into contact with an oxidation catalyst to oxidize nitrogen monoxide in the exhaust gas to nitrogen dioxide.