JPWO2003067046A1

JPWO2003067046A1 - Discharge gas purifier

Info

Publication number: JPWO2003067046A1
Application number: JP2003566375A
Authority: JP
Inventors: 滋田丸; 秀男木村; 由美草薙
Original assignee: Furrex Co Ltd
Current assignee: Furrex Co Ltd
Priority date: 2002-02-07
Filing date: 2003-02-07
Publication date: 2005-06-02
Also published as: WO2003067046A1; AU2003207183A1

Abstract

筒状外側電極２０と、筒状外側電極２０内に挿入されて、その筒状外側電極内周面との間に環状間隙を形成する外周面を持つ筒状誘電体２３と、筒状誘電体２３を挟んで前記筒状外側電極２０に対向する内側電極２５と、外側電極２０および内側電極２５間に放電電圧を印加する電源とからなる放電式ガス浄化装置である。筒状誘電体２３はセラミックスよりなっている。内側電極２５は放電電圧印加時に筒状誘電体２３内周面全周に亘って接触する誘電体と、この導電体と電源とを接続する接続手段とからなっている。そして、導電体は放電電圧印加時にその導電体の熱膨張によって前記セラミックスの内周面に加えられる圧力を緩和するように調整可能に構成されている。A cylindrical outer electrode 20, a cylindrical dielectric 23 having an outer peripheral surface inserted into the cylindrical outer electrode 20 and forming an annular gap between the inner peripheral surface of the cylindrical outer electrode, and a cylindrical dielectric 23 is a discharge-type gas purifier comprising an inner electrode 25 facing the cylindrical outer electrode 20 with a power supply for applying a discharge voltage between the outer electrode 20 and the inner electrode 25. The cylindrical dielectric 23 is made of ceramics. The inner electrode 25 includes a dielectric that contacts the entire inner peripheral surface of the cylindrical dielectric 23 when a discharge voltage is applied, and connection means that connects the conductor and a power source. The conductor is configured to be adjustable so as to relieve the pressure applied to the inner peripheral surface of the ceramic due to thermal expansion of the conductor when a discharge voltage is applied.

Description

技術分野
本発明は放電式ガス浄化装置、特にＮＯｘなどの自動車用排気ガスの浄化に好適な装置に関する。
背景技術
従来の放電式ガス浄化装置としては特開平５−１２５９２８号公報、または特開平７−１９７８０６公報に示すものが公知となっている。
前者の特開平５−１２５９２８号公報に係る放電式ガス浄化装置では、棒状の導電性金属からなる第１電極の外周を有機ガラスやセラミックなどの誘電体で被覆し、その外周を比較的大きな間隔をあけて筒状の導電性金属からなる第２電極で包囲し、第２電極の内壁に雌ねじ状のスパイラル溝を形成し、コロナ放電を用いて排気ガスを浄化する装置である。
この装置では棒状の導電性金属の外周を誘電体で密着被覆している。しかしながら、導電性金属と誘電体の熱膨張率は大きく異なるため、棒状の導電性金属に高電圧をかけて放電すると、その放電に伴って導電性金属が高温になり、誘電体との熱膨張率の差により誘電体が内側から大きな応力を受けて破壊する現象が起きる。従って、この装置は棒状の導電性金属にアーク放電またはグロー放電からアーク放電に至る直前の遷移域の高電圧をかける放電装置には適用することができない。
また、後者の特開平７−１９７８０６公報に示す放電式ガス浄化装置は、中心に位置する棒状電極を芯線とその芯線と筒状誘電体との間に充填した多数の粒状導電体から構成し、棒状電極の外周を円筒状電極で包囲し、円筒状電極と筒状誘電体との間でプラズマ放電を起こす排ガス浄化装置である。
この装置も筒状誘電体内に砂の粒子程度の細かな導電性粒子を密着充填して芯線と密着させているから、前記従来例の場合と同様に芯線に例えばグロー放電からアーク放電へ移行する直前の遷移域の高放電電圧を印加して放電すると、その放電に伴って導電性粒子が高温になり、誘電体との熱膨張率の差により誘電体が内側から大きな応力を受けて破壊する現象が起きる。
本発明は上記のような従来の問題点を解決するもので、その目的は外周を誘電体で包囲した金属製の電極に前記遷移域の高放電電圧を印加して高温下において放電しても誘電体が金属製の電極の熱膨張によって破損することのない放電式ガス浄化装置を提供することにある。
発明の開示
上記の目的を達成するため、本発明は、筒状外側電極と、前記筒状外側電極内に挿入されて前記筒状外側電極内周面との間に環状間隙を形成する外周面を持つ筒状誘電体と、前記筒状誘電体を挾んで前記筒状外側電極に対向する内側電極と、前記外側電極および内側電極間に放電電圧を印加する電源とからなる放電式ガス浄化装置において、前記筒状誘電体はセラミックスよりなり、前記内側電極は放電電圧印加時に前記筒状誘電体内周面全周に亘って接触する導電体と、前記導電体と前記電源とを接続する接続手段とからなり、前記導電体は放電電圧印加時に前記導電体の熱膨張によって前記セラミックスの内周面に加えられる圧力を緩和するように調整可能に構成されてなるのである。
このような構成により、内側電極に高電圧を印加して外側電極との間においてアーク放電またはアーク放電に至る直前のグロー放電からアーク放電への遷移域の放電を行い内側電極が高温に加熱されてもセラミックに大きな応力がかかることが無く、長期間の放電によっても誘電体が破損することなく効率よい放電を維持することができる。
好ましくは、前記調整可能な構成とするために、前記内側電極の前記導電体を径方向に圧縮可能な炭素繊維体から形成し、前記炭素繊維体を前記筒状誘電体の軸線に沿って配設された金属製軸状部材と前記筒状誘電体との間に介装することである。
更に好ましくは、前記炭素繊維体を炭素繊維からなる不織布から構成し、この不織布を前記金属製軸状部材に渦巻状に巻き付けることである。そして好ましくは、この不織布のカサ密度を約９０〜１８０ｇ／ｍ^３とすることである。
また好ましくは、前記調整可能な構成とするために、前記内側電極の前記導電体が水などの導電性液体からなり、前記導電性液体が前記内側電極の前記筒状誘電体内に充填されるとともに前記筒状誘電体の外部との間で循環されるように構成することである。
また、本発明の好ましい形態では、前記筒状誘電体の外周面を、軸線方向に伸びる稜線を持つ複数の山形凸面と、相隣る両山形凸面の対向する両斜面によって谷形凹面とが形成されるように周方向に沿って配列することによって、前記軸線方向に直交する断面が環状の波形となるように形成することである。
これによって、例えば山形凸面の頂部と外側電極の内周面との間隔が５ｍｍ程度の場合、自動車の排気ガスの初期の放電処理時において排気ガス中に多量の水分が含まれていても、その水分が山形凸面に集中することなく谷形凹面を通ることによって両電極間の短絡が防止されて良好な放電処理が可能となる。また、環状の波形形状により、山形凸面を環状に結んで形成される滑らかな筒状内側電極の場合と比べて谷形凹面の存在により環状空隙の断面積が増大し、そのぶん単位時間内に処理されるガスの流量を増大させることができる。
発明を実施するための好適な形態
第１図は本発明の好適な実施例に係る放電式排気ガス浄化装置を示し、この装置１は、放電器２と、その放電器２の近傍に配置された電源としての交流電源３とを備えている。放電器２は、ステンレス鋼（例えば、ＪＩＳＳＵＳ３０４）より構成されたハウジング４を有し、そのハウジング４は、横断面四角形で、且つ両端に四角形のフランジ５、６を有する筒状ハウジング本体７と、一方のフランジ５に四角形のポリアミド１２製絶縁パッキン８を介して四角形のフランジ９を取付けられたガス入口形成体１０と、他方のフランジ６に四角形のポリアミド１２製絶縁パッキン１１を介して四角形のフランジ１２を取付けられたガス出口形成体１３とを有する。
ガス入口形成体１０は四角錐台形中空部１４を有し、その中空部１４の大開口縁側に前記四角形のフランジ９が連設され、また中空部１０の小開口縁側に横断面円形の入口筒１５が連設される。ガス出口形成体１３は四角錐台形中空部１６を有し、その中空部１６の大開口縁側に前記四角形のフランジ１２が連設され、また中空部１６の小開口縁側に横断面円形の出口筒１７が連設される。
ガス入口形成体１０のフランジ９内周縁に、中央に貫通孔１８を有する四角形の板状支持部１９が連設され、その貫通孔１８の内周縁に、ステンレス鋼（例えば、ＪＩＳＳＵＳ３０４）より構成された横断面円形の筒状外側電極２０の一端外周縁が固着され、その外側電極２０はハウジング本体７内に配置される。その外側電極２０の長さはハウジング本体７の長さの２分の１よりも短い。
第２図にも示すように、ハウジング本体７内において、ガス出口形成体１３と外側電極２０の端面との間に、ステンレス鋼（例えば、ＪＩＳＳＵＳ３０４）よりなる支持部材２１が底壁上に設置され、その支持部材２１の短円筒形保持部２２に横断面ほぼ円形の筒状誘電体２３の一端部側が支持される。誘電体２３の他端部側は外側電極２０内に挿入され、その誘電体２３の挿入長さは外側電極２０の長さの３分の２程度である。これにより外側電極２０内に存する誘電体２３の外周面と外側電極２０の内周面との間には環状間隙２４が形成される。
誘電体２３内に、内側電極２５が配置され、その内側電極２５は誘電体２３を挟んで外側電極２０に対向し、且つその誘電体２３内周面全周に亘って接触する。
第３図に明示するように誘電体２３は、セラミックス（例えば、２ＭｇＯ・２Ａｌ_２Ｏ_３．５ＳｉＯ_２）よりなる筒状セラミックス本体２６と、前記環状間隙２４を形成すべく、筒状セラミックス本体２６の外周面を被覆する筒状外側ガラス層（例えば、うわぐすり）２７とを有し、また筒状セラミックス本体２６の内周面に、内側電極２５との接触面を形成する筒状内側ガラス層（例えば、うわぐすり）２８を有する。筒状セラミックス本体２６の筒状外側ガラス層２７により被覆される外周面は、軸線方向に延びる稜線を持つ複数の山形凸面２９を、相隣る両山形凸面２９の対向する両斜面によって谷形凹面３０が形成されるように、周方向に沿って配列することによって形成され、前記軸線方向に直交する断面が環状の波形に形成されている。
前記山形凸面の頂点と前記筒状外側電極２０の内周面との間の間隙は４〜６ｍｍ、好ましくは５ｍｍで、前記谷形凹面の底部と前記筒状外側電極２０の内周面との間の間隙は７〜９ｍｍ、好ましくは８ｍｍで、前記頂部と前記底部との間隙は２〜４ｍｍ、好ましくは３ｍｍである。
内側電極２５は、金属（例えば、ＪＩＳＳＵＳ３０４）よりなる軸状部材３１と、その軸状部材３１および誘電体２３間に充填された導電性の炭素繊維集合体３２とよりなる。炭素繊維集合体３２は、実施例では炭素繊維（商品名カイノール）よりなる不織布を軸状部材３１外周面に渦巻状に巻付けて形成されており、そのカサ密度は約９０〜１８０ｇ／ｍ^３である。軸状部材３１の両端部は、誘電体２３両端の開口を閉鎖する、セラミックス（例えば、２ＭｇＯ・２Ａｌ_２Ｏ_３・５ＳｉＯ_２）よりなる蓋板３３に支持されており、その軸状部材３３の、ガス出口側の端部は蓋板３３より突出する。
交流電源３の一方の端子に接続されたリード線３４がハウジング本体７の天井壁に設けられた絶縁筒３５を通されて、軸状部材３１の端部に接続され、また他方の端子はアース線３６を介して接地される。また外側電極２０と電気的に接続されたガス入口形成体１０がアース線３７を介して接地されている。これにより外側、内側電極２０、２５間に放電電圧を印加することができる。
ガス出口形成体１３の中空部１６周壁にガス分析器３８の採取管３９が貫通保持されている。ガス分析器３８としては、ＨＯＲＩＢＡＰＯＲＴＡＢＬＥＧＡＳＡＮＡＬＹＺＥＲ型番ＰＧ−２４０が用いられている。
以下、ガソリンエンジンから排出された排気ガス中に含まれるＮＯｘの浄化について説明する。
［例−Ｉ］
第４図に示すように、排気量６６０ｃｃのガソリンエンジン４０の排気管４１に、１つの放電器２におけるハウジング４の入口筒１５を導入管４２を介して接続した。次いで、ガソリンエンジン４０をエンジン回転数１０００ｒｐｍにて運転して、排気管４１、放電器２の前記環状間隙２４等を流通した排気ガス中のＮＯｘ濃度をガス分析器３８により測定した。このＮＯｘ濃度を放電処理前ＮＯｘ濃度とする。
その後、交流電源３により内、外側電極２０、２５間に、２０ｋＶ、１ｋＨｚの高放電電圧を印加した。これにより環状間隙２４に放電（グロー放電）が発生し、その放電は、環状間隙２４を形成する外側電極２０内周面ほぼ全体および誘電体２３外周面ほぼ全体、つまり各山形凸面２９の表面ほぼ全体に亘って発生しており、面放電を呈しており、この放電状態は環状間隙の入口側から出口側に向かって螺旋状に旋回した。このような放電を約１０分間行い、その間に排気ガス中のＮＯｘ濃度をガス分析器３８により測定した。このＮＯｘ濃度を放電処理後ＮＯｘ濃度とする。
交流電源３による高放電電圧の印加を中断し、次いでガソリンエンジン４０をエンジン回転数１５００ｒｐｍ、全負荷の条件で運転すると共に前記同様に放電処理前ＮＯｘ濃度の測定を行い、その後交流電源３による前記と同一条件での高放電電圧の印加を行うと共に前記同様に放電処理後ＮＯｘ濃度の測定を行った。これをエンジン回転数２４００ｒｐｍについても行った。表１は測定結果を示す。
【表１】

表１から明らかなように、エンジン回転数の上昇に伴いＮＯｘ濃度が高くなり、それに応じてＮＯｘ除去率は低下するが、それでもエンジン回転数２４００ｒｐｍにてＮＯｘ除去率４４％は実用レベルであることが判る。
［例−ＩＩ］
第５図に示す大型放電器２は、１つの入口筒１５および１つの出口筒１７を有するハウジング４内に、外側電極２０、誘電体２３および内側電極２５よりなる複数、実施例では３つの放電ユニット４３を水平面上において並列に配置し、相隣る両放電ユニット４３間に隔壁４４を設けたものである。ガソリンエンジン４０から排出される排気ガスは三分割されて各放電ユニット４３により放電処理され、各放電ユニット４３を経た処理済排気ガスの合計ＮＯｘ濃度がガス分析器３８によって測定される。
ＮＯｘ濃度測定を行うべく、排気量２５００ｃｃのガソリンエンジン４０の排気管４１に大型放電器２におけるハウジング４の入口筒１５を導入管４２を介して接続した。そして、ガソリンエンジン４０を運転してエンジン回転数１６００ｒｐｍ、全負荷およびエンジン回転数２０００ｒｐｍ、全負荷について前記同様の方法でＮＯｘ濃度測定を行った。表２は測定結果を示す。
【表２】

表２から明らかなように、大型放電器２はその浄化処理能力が大であることから、大量のＮＯｘが効率良く除去されることが判る。
なお、３つの放電ユニット４３を直列に連結した大型放電器２はＮＯｘ浄化能が低い。これは、放電処理経路が長いことから、ＮＯｘの分解だけでなくその合成が行われているものと考えられる。
［例−ＩＩＩ］
第６図に示すように、排気量６６０ｃｃのガソリンエンジン４０の排気管４１に、１つの放電器２におけるハウジング４の入口筒１５を導入管４２を介して接続し、また出口筒１７に３元触媒式触媒コンバータ４５を導入管４６を介して接続した。次いで、ガソリンエンジン４０をエンジン回転数２０００ｒｐｍにて運転して、排気管４１、放電器２の前記環状間隙２４等を流通してガス出口形成体１３内に到った排気ガス中のＮＯｘ濃度をガス分析器３８により測定した。このＮＯｘ濃度を放電処理前ＮＯｘ濃度とする。
その後、交流電源３により内、外側電極２０、２５間に、２０ｋＶ、１ｋＨｚの高放電電圧を印加した。これにより、前記同様に環状間隙２４に放電が発生した。この放電を約１０分間行い、その間にガス出口形成体１３内の排気ガス中のＮＯｘ濃度をガス分析器３８により測定した。このＮＯｘ濃度を放電処理後ＮＯｘ濃度とする。同時に、触媒コンバータ４５を通過した排気ガス中のＮＯｘ濃度をガス分析器３８により測定した。このＮＯｘ濃度を触媒作用後ＮＯｘ濃度とする。このような測定を２回行って表３の結果を得た。
【表３】

表３において、「放電」の欄のＮＯｘ除去率は放電処理前および放電処理後の両ＮＯｘ濃度を用いて求められたものであり、また「触媒」の欄の最終ＮＯｘ除去率は放電処理前ＮＯｘ濃度および触媒作用後ＮＯｘ濃度を用いて求められたものである。
表３から明らかなように、放電式排気ガス浄化装置１を用いることによって排気ガス中のＮＯｘを５４％以上除去することができ、また触媒コンバータ４５を併用することによって排気ガス中のＮＯｘを９７％以上除去することができる。
なお、本発明における好適な放電状態は、前記外側電極と前記筒状誘電体との間の環状空隙において単なるグロー放電をさせることではなく、グロー放電からアーク放電に至る直前の遷移域の放電状態とすることである。
本発明は上記の実施例以外にも種々の変更が可能であり、例えば、筒状セラミックス本体２６を耐熱高強度セラミックスである９４．７７ｗｔ％のＡｌ_２Ｏ_３と１．７２ｗｔ％のＣａＯと３．５１ｗｔ％のＳｉＯ_２とよりなるアルミナ系セラミックス、或いはＡｌ_２Ｏ_３を９２ｗｔ％含有した碍子用セラミックスを用いれば筒状セラミックス本体２６の外側および内側のガラス層２７，２８を被覆しないでもよい。
さらに内側電極２５の炭素繊維集合体３２の代わりに、筒状セラミックス本体２６内に水などの導電性液体を充填し、その水を筒状セラミックス本体の内外に循環するようにし、この循環する導電性液体の量を調整することによって軸状部材３１等の熱膨張により筒状セラミックス本体２６の内面に加えられる応力を緩和することができる。
以上、本発明の好適な実施形態に基づいて説明してきたが、上記した発明の実施の形態は、本発明の理解を容易にするためのものであり、本発明を限定するものではない。
産業上の利用可能性
本発明によれば、前記のように構成することによって、内側電極に高電圧を印加して外側電極との間においてアーク放電またはアーク放電に至る直前のグロー放電からアーク放電への遷移域の放電を行い内側電極が高温に加熱されてもセラミックに大きな応力がかかることが無く、長期間の放電によっても誘電体が破損することがなく、自動車の排気ガスのような被処理ガス中の有害成分を効率よく除去することが可能な放電式ガス浄化装置を提供することができる。
【図面の簡単な説明】
第１図は本発明の実施例に係る放電式ガス浄化装置の要部破断正面図である。
第２図は第１図の装置において内部電極を構成する筒状誘電体およびその支持構造を示す斜視図である。
第３図は第１図の３−３線拡大断面図である。
第４図は本発明の実施例に係る放電式ガス浄化装置をガソリンエンジンの排気系に接続した状態を示す説明図である。
第５図は本発明の実施例に係る放電式排気ガス浄化装置をガソリンエンジンの排気系に接続した第２例を示す説明図である。
第６図は本発明の実施例に係る放電式排気ガス浄化装置をガソリンエンジンの排気系に接続した第３例を示す説明図である。TECHNICAL FIELD The present invention relates to a discharge type gas purification device, and more particularly to a device suitable for purification of automobile exhaust gas such as NOx.
2. Description of the Related Art As a conventional discharge type gas purification apparatus, those disclosed in Japanese Patent Application Laid-Open No. 5-125828 or Japanese Patent Application Laid-Open No. 7-197806 are known.
In the former discharge type gas purification apparatus according to Japanese Patent Laid-Open No. 5-125828, the outer periphery of the first electrode made of a rod-like conductive metal is covered with a dielectric such as organic glass or ceramic, and the outer periphery is relatively large. This is an apparatus that is surrounded by a second electrode made of a cylindrical conductive metal, forms a female threaded spiral groove on the inner wall of the second electrode, and purifies exhaust gas using corona discharge.
In this apparatus, the outer periphery of a rod-shaped conductive metal is tightly coated with a dielectric. However, the coefficient of thermal expansion between the conductive metal and the dielectric material is greatly different. Therefore, when a high voltage is applied to the rod-shaped conductive metal and discharged, the conductive metal becomes high temperature along with the discharge, and the thermal expansion with the dielectric Due to the difference in rate, a phenomenon occurs in which the dielectric material is broken by receiving a large stress from the inside. Therefore, this device cannot be applied to a discharge device that applies a high voltage in a transition region immediately before an arc discharge or a glow discharge to an arc discharge to a rod-shaped conductive metal.
Moreover, the latter discharge type gas purification apparatus shown in JP-A-7-197806 is composed of a core electrode and a number of granular conductors filled between the core wire and the cylindrical dielectric, This is an exhaust gas purifying apparatus that surrounds the outer periphery of a rod-shaped electrode with a cylindrical electrode and causes plasma discharge between the cylindrical electrode and a cylindrical dielectric.
Since this device is also closely packed with fine conductive particles, such as sand particles, in a cylindrical dielectric and is in close contact with the core wire, the core wire is shifted from, for example, glow discharge to arc discharge as in the conventional example. When discharging by applying a high discharge voltage in the immediately preceding transition region, the conductive particles become high temperature with the discharge, and the dielectric is damaged by a large stress from the inside due to the difference in thermal expansion coefficient with the dielectric. A phenomenon occurs.
The present invention solves the above-mentioned conventional problems, and its purpose is to apply a high discharge voltage in the transition region to a metal electrode whose outer periphery is surrounded by a dielectric material and discharge at a high temperature. An object of the present invention is to provide a discharge type gas purification apparatus in which a dielectric is not damaged by thermal expansion of a metal electrode.
DISCLOSURE OF THE INVENTION To achieve the above object, the present invention provides an outer peripheral surface that forms an annular gap between a cylindrical outer electrode and an inner peripheral surface of the cylindrical outer electrode that is inserted into the cylindrical outer electrode. A discharge type gas purifying apparatus comprising: a cylindrical dielectric having an inner electrode; an inner electrode sandwiching the cylindrical dielectric and facing the outer cylindrical electrode; and a power source for applying a discharge voltage between the outer electrode and the inner electrode. In the above, the cylindrical dielectric is made of ceramics, and the inner electrode contacts the entire circumference of the cylindrical dielectric body when a discharge voltage is applied, and the connecting means for connecting the conductor and the power source The conductor is configured to be adjustable so as to relieve the pressure applied to the inner peripheral surface of the ceramic due to thermal expansion of the conductor when a discharge voltage is applied.
With such a configuration, the inner electrode is heated to a high temperature by applying a high voltage to the inner electrode and discharging between the outer electrode and an arc discharge or a transition region from the glow discharge just before reaching the arc discharge to the arc discharge. However, no great stress is applied to the ceramic, and an efficient discharge can be maintained without damaging the dielectric due to a long-term discharge.
Preferably, in order to achieve the adjustable configuration, the conductor of the inner electrode is formed of a carbon fiber body that is compressible in the radial direction, and the carbon fiber body is disposed along the axis of the cylindrical dielectric. It is to interpose between the metal shaft-shaped member provided and the cylindrical dielectric.
More preferably, the carbon fiber body is composed of a nonwoven fabric made of carbon fibers, and the nonwoven fabric is wound around the metal shaft-like member in a spiral shape. And preferably, the bulk density of this nonwoven fabric shall be about 90-180 g / m < ³ >.
Preferably, in order to achieve the adjustable configuration, the conductor of the inner electrode is made of a conductive liquid such as water, and the conductive liquid is filled in the cylindrical dielectric of the inner electrode. It is configured to circulate between the outside of the cylindrical dielectric.
Further, in a preferred embodiment of the present invention, the outer peripheral surface of the cylindrical dielectric is formed with a plurality of chevron convex surfaces having ridge lines extending in the axial direction and valley concave surfaces by the opposing slopes of the adjacent two chevron convex surfaces. As described above, by arranging along the circumferential direction, the cross section perpendicular to the axial direction is formed into an annular waveform.
Thus, for example, when the distance between the top of the convex surface of the chevron and the inner peripheral surface of the outer electrode is about 5 mm, even if a large amount of moisture is contained in the exhaust gas during the initial discharge treatment of the automobile exhaust gas, Short circuit between the two electrodes is prevented by allowing the moisture to pass through the valley-shaped concave surface without concentrating on the convex surface of the mountain-shaped, so that a favorable discharge treatment is possible. In addition, due to the annular corrugated shape, the cross-sectional area of the annular gap increases due to the presence of the valley-shaped concave surface compared to the case of the smooth cylindrical inner electrode formed by connecting the convex convex surfaces annularly, and within that unit time The flow rate of the gas to be processed can be increased.
FIG. 1 shows a discharge-type exhaust gas purifying apparatus according to a preferred embodiment of the present invention. This apparatus 1 is disposed in the vicinity of a discharger 2 and the discharger 2. And an AC power source 3 as a power source. The discharger 2 has a housing 4 made of stainless steel (for example, JIS SUS304). The housing 4 has a rectangular cross section and a cylindrical housing body 7 having

square flanges

5 and 6 at both ends. A gas inlet forming body 10 having a square flange 9 attached to one flange 5 via a square polyamide 12 insulating packing 8 and a square flange 12 having a square polyamide 12 insulating packing 11 attached to the other flange 6. And a gas outlet forming body 13 to which a flange 12 is attached.
The gas inlet forming body 10 has a quadrangular frustum-shaped hollow portion 14, the square flange 9 is continuously provided on the large opening edge side of the hollow portion 14, and an inlet tube having a circular cross section on the small opening edge side of the hollow portion 10. 15 is continuously provided. The gas outlet forming body 13 has a quadrangular frustum-shaped hollow portion 16, the square flange 12 is continuously provided on the large opening edge side of the hollow portion 16, and the outlet tube having a circular cross section on the small opening edge side of the hollow portion 16. 17 is continuously provided.
A rectangular plate-like support portion 19 having a through hole 18 in the center is connected to the inner peripheral edge of the flange 9 of the gas inlet forming body 10, and the inner peripheral edge of the through hole 18 is made of stainless steel (for example, JIS SUS304). The outer peripheral edge of one end of the cylindrical outer electrode 20 having a circular cross section is fixed, and the outer electrode 20 is disposed in the housing body 7. The length of the outer electrode 20 is shorter than one half of the length of the housing body 7.
As shown also in FIG. 2, a support member 21 made of stainless steel (for example, JIS SUS304) is installed on the bottom wall between the gas outlet forming body 13 and the end face of the outer electrode 20 in the housing body 7. The one end side of the cylindrical dielectric 23 having a substantially circular cross section is supported by the short cylindrical holding portion 22 of the support member 21. The other end side of the dielectric 23 is inserted into the outer electrode 20, and the insertion length of the dielectric 23 is about two thirds of the length of the outer electrode 20. Thereby, an annular gap 24 is formed between the outer peripheral surface of the dielectric 23 existing in the outer electrode 20 and the inner peripheral surface of the outer electrode 20.
An inner electrode 25 is disposed in the dielectric 23, the inner electrode 25 is opposed to the outer electrode 20 with the dielectric 23 interposed therebetween, and is in contact with the entire inner peripheral surface of the dielectric 23.
Dielectric 23, as best shown in Figure 3, the ceramic _{_{(e.g., 2MgO · 2Al 2 O 3 .5SiO}} 2) a tubular ceramic body 26 made of, so as to form the annular gap 24, the cylindrical ceramic body 26 A cylindrical outer glass layer (for example, glaze) 27 that covers the outer peripheral surface of the cylindrical ceramic body, and a cylindrical inner glass that forms a contact surface with the inner electrode 25 on the inner peripheral surface of the cylindrical ceramic body 26. It has a layer (eg, glaze) 28. The outer peripheral surface covered with the cylindrical outer glass layer 27 of the cylindrical ceramic body 26 has a plurality of mountain-shaped convex surfaces 29 having ridge lines extending in the axial direction, and valley-shaped concave surfaces due to both opposing slopes of the two mountain-shaped convex surfaces 29 adjacent to each other. 30 is formed by arranging along the circumferential direction, and a cross section perpendicular to the axial direction is formed in an annular waveform.
The gap between the apex of the chevron convex surface and the inner peripheral surface of the cylindrical outer electrode 20 is 4 to 6 mm, preferably 5 mm, and the bottom of the valley-shaped concave surface and the inner peripheral surface of the cylindrical outer electrode 20 The gap between them is 7-9 mm, preferably 8 mm, and the gap between the top and the bottom is 2-4 mm, preferably 3 mm.
The inner electrode 25 includes a shaft-shaped member 31 made of metal (for example, JIS SUS304) and a conductive carbon fiber aggregate 32 filled between the shaft-shaped member 31 and the dielectric 23. In the embodiment, the carbon fiber assembly 32 is formed by winding a nonwoven fabric made of carbon fiber (trade name Kynol) around the outer peripheral surface of the shaft-shaped member 31 in a spiral shape, and its bulk density is about 90 to 180 g / m ^3. It is. Both end portions of the shaft-shaped member 31 are supported by a cover plate 33 made of ceramics (for example, 2MgO · 2Al ₂ O ₃ · 5SiO ₂ ) that closes the openings at both ends of the dielectric 23. The gas outlet side end protrudes from the cover plate 33.
A lead wire 34 connected to one terminal of the AC power source 3 is passed through an insulating cylinder 35 provided on the ceiling wall of the housing body 7 and connected to the end of the shaft-shaped member 31, and the other terminal is grounded. Grounded via line 36. Further, the gas inlet forming body 10 electrically connected to the outer electrode 20 is grounded via a ground wire 37. As a result, a discharge voltage can be applied between the outer and

inner electrodes

20 and 25.
A sampling tube 39 of the gas analyzer 38 is held through the peripheral wall of the hollow portion 16 of the gas outlet forming body 13. As the gas analyzer 38, HORIBA PORTABLE GAS ANALYZER model number PG-240 is used.
Hereinafter, purification of NOx contained in the exhaust gas discharged from the gasoline engine will be described.
[Example-I]
As shown in FIG. 4, the inlet cylinder 15 of the housing 4 in one discharger 2 is connected to an exhaust pipe 41 of a gasoline engine 40 having a displacement of 660 cc through an introduction pipe 42. Next, the gasoline engine 40 was operated at an engine speed of 1000 rpm, and the NOx concentration in the exhaust gas flowing through the exhaust pipe 41 and the annular gap 24 of the discharger 2 was measured by the gas analyzer 38. This NOx concentration is taken as the NOx concentration before the discharge treatment.
Thereafter, a high discharge voltage of 20 kV and 1 kHz was applied between the inner and

outer electrodes

20 and 25 by the AC power source 3. As a result, a discharge (glow discharge) is generated in the annular gap 24, and the discharge is caused by almost the entire inner peripheral surface of the outer electrode 20 and almost the entire outer peripheral surface of the dielectric 23 that form the annular gap 24, that is, almost the surface of each convex surface 29. It occurred over the whole and exhibited surface discharge. This discharge state swirled spirally from the inlet side to the outlet side of the annular gap. Such discharge was performed for about 10 minutes, during which the NOx concentration in the exhaust gas was measured by the gas analyzer 38. This NOx concentration is taken as the NOx concentration after the discharge treatment.
The application of the high discharge voltage by the AC power supply 3 is interrupted, and then the gasoline engine 40 is operated at the engine speed of 1500 rpm and the full load, and the NOx concentration before the discharge treatment is measured in the same manner as described above. The high discharge voltage was applied under the same conditions as above, and the NOx concentration was measured after the discharge treatment in the same manner as described above. This was also performed for an engine speed of 2400 rpm. Table 1 shows the measurement results.
[Table 1]

As is apparent from Table 1, the NOx concentration increases as the engine speed increases, and the NOx removal rate decreases accordingly. However, the NOx removal rate of 44% is still at a practical level at the engine speed of 2400 rpm. I understand.
[Example-II]
A large-sized discharger 2 shown in FIG. 5 has a plurality of discharges composed of an outer electrode 20, a dielectric 23 and an inner electrode 25 in a housing 4 having one inlet tube 15 and one outlet tube 17, in the embodiment, three discharges. The units 43 are arranged in parallel on a horizontal plane, and a partition wall 44 is provided between the two discharge units 43 adjacent to each other. The exhaust gas discharged from the gasoline engine 40 is divided into three parts and discharged by each discharge unit 43, and the total NOx concentration of the processed exhaust gas that has passed through each discharge unit 43 is measured by the gas analyzer 38.
In order to measure the NOx concentration, the inlet cylinder 15 of the housing 4 in the large-sized discharger 2 was connected to the exhaust pipe 41 of the gasoline engine 40 having a displacement of 2500 cc through the introduction pipe 42. Then, the gasoline engine 40 was operated, and the NOx concentration was measured in the same manner as described above for the engine speed of 1600 rpm, the full load and the engine speed of 2000 rpm, and the full load. Table 2 shows the measurement results.
[Table 2]

As is clear from Table 2, the large-sized discharger 2 has a large purification treatment capacity, and thus it can be seen that a large amount of NOx is efficiently removed.
The large-sized discharger 2 in which the three discharge units 43 are connected in series has a low NOx purification capacity. This is considered to be because not only decomposition of NOx but also its synthesis is performed due to the long discharge treatment path.
[Example-III]
As shown in FIG. 6, the inlet cylinder 15 of the housing 4 in one discharger 2 is connected to an exhaust pipe 41 of a gasoline engine 40 having a displacement of 660 cc via an introduction pipe 42, and three outlets are connected to the outlet cylinder 17. A catalytic catalytic converter 45 was connected via an introduction pipe 46. Next, the gasoline engine 40 is operated at an engine speed of 2000 rpm, and the NOx concentration in the exhaust gas that has flowed through the exhaust pipe 41, the annular gap 24 of the discharger 2 and the like into the gas outlet forming body 13 is determined. Measurement was performed by a gas analyzer 38. This NOx concentration is taken as the NOx concentration before the discharge treatment.
Thereafter, a high discharge voltage of 20 kV and 1 kHz was applied between the inner and

outer electrodes

20 and 25 by the AC power source 3. As a result, discharge was generated in the annular gap 24 as described above. This discharge was performed for about 10 minutes, during which the NOx concentration in the exhaust gas in the gas outlet forming body 13 was measured by the gas analyzer 38. This NOx concentration is taken as the NOx concentration after the discharge treatment. At the same time, the NOx concentration in the exhaust gas that passed through the catalytic converter 45 was measured by the gas analyzer 38. This NOx concentration is defined as the NOx concentration after catalysis. Such measurement was performed twice to obtain the results shown in Table 3.
[Table 3]

In Table 3, the NOx removal rate in the “Discharge” column is obtained using both NOx concentrations before and after the discharge treatment, and the final NOx removal rate in the “Catalyst” column is before the discharge treatment. This is obtained using the NOx concentration and the post-catalytic NOx concentration.
As apparent from Table 3, 54% or more of NOx in the exhaust gas can be removed by using the discharge-type exhaust gas purification device 1, and NOx in the exhaust gas can be reduced by 97 by using the catalytic converter 45 in combination. % Or more can be removed.
The preferred discharge state in the present invention is not a simple glow discharge in the annular gap between the outer electrode and the cylindrical dielectric, but a discharge state in the transition region immediately before the glow discharge to the arc discharge. It is to do.
The present invention can be modified in various ways other than the above-described embodiments. For example, the cylindrical ceramic body 26 is composed of 94.77 wt% Al ₂ O ₃ and 1.72 wt% CaO ₃ which are heat resistant high strength ceramics. The glass layers 27 and 28 on the outer side and the inner side of the cylindrical ceramic body 26 may not be coated if alumina ceramics composed of .51 wt% SiO ₂ or ceramics containing 92 wt% Al ₂ O ₃ is used.
Further, instead of the carbon fiber aggregate 32 of the inner electrode 25, the cylindrical ceramic body 26 is filled with a conductive liquid such as water, and the water is circulated into and out of the cylindrical ceramic body, and this circulating conductive material is circulated. By adjusting the amount of the ionic liquid, the stress applied to the inner surface of the cylindrical ceramic body 26 due to thermal expansion of the shaft-shaped member 31 or the like can be relaxed.
As mentioned above, although demonstrated based on preferred embodiment of this invention, embodiment mentioned above is for making an understanding of this invention easy, and does not limit this invention.
INDUSTRIAL APPLICABILITY According to the present invention, an arc discharge from a glow discharge immediately before reaching an arc discharge or an arc discharge between the outer electrode by applying a high voltage to the inner electrode is configured as described above. Even if the inner electrode is heated to a high temperature when the inner electrode is heated to a high temperature, there is no significant stress applied to the ceramic, and the dielectric is not damaged by a long-term discharge. It is possible to provide a discharge gas purification apparatus capable of efficiently removing harmful components in the processing gas.
[Brief description of the drawings]
FIG. 1 is a fragmentary front view of a main part of a discharge gas purification apparatus according to an embodiment of the present invention.
FIG. 2 is a perspective view showing a cylindrical dielectric constituting an internal electrode and its supporting structure in the apparatus of FIG.
FIG. 3 is an enlarged sectional view taken along line 3-3 of FIG.
FIG. 4 is an explanatory view showing a state in which the discharge type gas purification apparatus according to the embodiment of the present invention is connected to the exhaust system of a gasoline engine.
FIG. 5 is an explanatory view showing a second example in which a discharge type exhaust gas purifying apparatus according to an embodiment of the present invention is connected to an exhaust system of a gasoline engine.
FIG. 6 is an explanatory view showing a third example in which the discharge type exhaust gas purifying apparatus according to the embodiment of the present invention is connected to the exhaust system of a gasoline engine.

Claims

A cylindrical outer electrode;
A cylindrical dielectric inserted into the cylindrical outer electrode and having an outer peripheral surface that forms an annular gap with the inner peripheral surface of the cylindrical outer electrode;
An inner electrode sandwiching the cylindrical dielectric and facing the cylindrical outer electrode;
A power supply for applying a discharge voltage between the outer electrode and the inner electrode;
In the discharge-type gas purification device consisting of
The cylindrical dielectric is made of ceramics,
The inner electrode includes a conductor that contacts the entire circumference of the cylindrical dielectric body when a discharge voltage is applied, and a connecting means that connects the conductor and the power source. A discharge-type gas purification apparatus configured to be adjustable so as to relieve pressure applied to the inner peripheral surface of the ceramic due to thermal expansion of the conductor.

The conductor of the inner electrode is made of a carbon fiber body that is compressible in the radial direction, and the carbon fiber body is a metal shaft-like member that constitutes the connecting means disposed along the axis of the cylindrical dielectric. 2. The discharge type gas purification apparatus according to claim 1, wherein the discharge type gas purification apparatus is interposed between the pipe and the cylindrical dielectric.

3. The discharge type gas purification apparatus according to claim 2, wherein the carbon fiber body is composed of a non-woven fabric made of carbon fiber, and the non-woven fabric is wound around the metal shaft member in a spiral shape.

The conductor of the inner electrode is made of a conductive liquid such as water, and the conductive liquid is filled in the cylindrical dielectric of the inner electrode and is circulated between the outside of the cylindrical dielectric. The discharge-type gas purification apparatus according to claim 1, wherein the discharge-type gas purification apparatus is configured as described above.

The outer peripheral surface of the cylindrical dielectric has a plurality of chevron convex surfaces having ridge lines extending in the axial direction along the circumferential direction so that valley concave surfaces are formed by the opposing slopes of the two chevron convex surfaces adjacent to each other. The discharge type gas purification apparatus according to any one of claims 1 to 4, wherein a cross section perpendicular to the axial direction is formed into an annular waveform by arranging the sections.

6. The discharge type gas purification apparatus according to claim 1, wherein an outer peripheral surface of the cylindrical ceramic is covered with a glass layer.

6. The discharge type gas purification apparatus according to claim 1, wherein an inner peripheral surface of the cylindrical ceramic is coated with a glass layer.

The cylindrical outer electrode has a cylindrical inner peripheral surface, and a gap between the apex of the convex convex surface of the cylindrical dielectric and the inner peripheral surface of the cylindrical outer electrode is 4 to 6 mm. 6. The gap between the bottom of the valley-shaped concave surface of the body and the inner peripheral surface of the cylindrical outer electrode is 7 to 9 mm, and the gap between the top and the bottom is 2 to 4 mm. Discharge gas purification device.

The discharge voltage is set so that discharge in a transition region immediately before glow discharge to arc discharge occurs in an annular gap between the outer electrode and the cylindrical dielectric. 5. The discharge type gas purification apparatus according to any one of 4 above.

5. The discharge type gas purification apparatus according to claim 1, wherein in the exhaust system of the gasoline engine, the annular gap is arranged upstream of the catalytic converter in the flow direction of the exhaust gas. 6. .