JP2006183628A - Exhaust emission treatment method and urea scr type automobile exhaust emission treatment device - Google Patents
Exhaust emission treatment method and urea scr type automobile exhaust emission treatment device Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 28
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 title claims description 11
- 239000004202 carbamide Substances 0.000 title claims description 11
- 239000003054 catalyst Substances 0.000 claims abstract description 83
- 230000003647 oxidation Effects 0.000 claims abstract description 59
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 59
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims abstract description 36
- 229910021529 ammonia Inorganic materials 0.000 claims abstract description 17
- 239000000126 substance Substances 0.000 claims abstract description 8
- 239000007789 gas Substances 0.000 abstract description 96
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 abstract description 42
- 239000000203 mixture Substances 0.000 abstract description 6
- 230000009467 reduction Effects 0.000 abstract description 3
- 238000006243 chemical reaction Methods 0.000 description 25
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 6
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 5
- 239000003638 chemical reducing agent Substances 0.000 description 5
- CPLXHLVBOLITMK-UHFFFAOYSA-N Magnesium oxide Chemical compound [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 4
- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 229910044991 metal oxide Inorganic materials 0.000 description 4
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 4
- 230000007423 decrease Effects 0.000 description 3
- 150000004706 metal oxides Chemical class 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 238000006722 reduction reaction Methods 0.000 description 3
- WTHDKMILWLGDKL-UHFFFAOYSA-N urea;hydrate Chemical compound O.NC(N)=O WTHDKMILWLGDKL-UHFFFAOYSA-N 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 239000002131 composite material Substances 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 229910052741 iridium Inorganic materials 0.000 description 2
- GKOZUEZYRPOHIO-UHFFFAOYSA-N iridium atom Chemical compound [Ir] GKOZUEZYRPOHIO-UHFFFAOYSA-N 0.000 description 2
- 239000000395 magnesium oxide Substances 0.000 description 2
- 229910000510 noble metal Inorganic materials 0.000 description 2
- 229910052763 palladium Inorganic materials 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 2
- ATRRKUHOCOJYRX-UHFFFAOYSA-N Ammonium bicarbonate Chemical compound [NH4+].OC([O-])=O ATRRKUHOCOJYRX-UHFFFAOYSA-N 0.000 description 1
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910021536 Zeolite Inorganic materials 0.000 description 1
- XHCLAFWTIXFWPH-UHFFFAOYSA-N [O-2].[O-2].[O-2].[O-2].[O-2].[V+5].[V+5] Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[V+5].[V+5] XHCLAFWTIXFWPH-UHFFFAOYSA-N 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- -1 alumina Chemical class 0.000 description 1
- 239000001099 ammonium carbonate Substances 0.000 description 1
- 235000012501 ammonium carbonate Nutrition 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 238000010531 catalytic reduction reaction Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000001784 detoxification Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- 229910052680 mordenite Inorganic materials 0.000 description 1
- QGLKJKCYBOYXKC-UHFFFAOYSA-N nonaoxidotritungsten Chemical compound O=[W]1(=O)O[W](=O)(=O)O[W](=O)(=O)O1 QGLKJKCYBOYXKC-UHFFFAOYSA-N 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 238000003672 processing method Methods 0.000 description 1
- 238000000746 purification Methods 0.000 description 1
- 238000011946 reduction process Methods 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- 239000010948 rhodium Substances 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 230000002459 sustained effect Effects 0.000 description 1
- 239000004408 titanium dioxide Substances 0.000 description 1
- 229910001930 tungsten oxide Inorganic materials 0.000 description 1
- 229910001935 vanadium oxide Inorganic materials 0.000 description 1
- 239000010457 zeolite Substances 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/12—Improving ICE efficiencies
Landscapes
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
- Exhaust Gas After Treatment (AREA)
Abstract
Description
本発明は、自動車の排ガス処理方法及びそれを用いるための自動車排ガス処理装置に関するものである。 The present invention relates to an automobile exhaust gas treatment method and an automobile exhaust gas treatment apparatus using the same.
従来、自動車排ガス中の窒素酸化物（ＮＯｘ）を浄化する排ガス処理方法として、排ガスを脱硝触媒に接触させその中のＮＯｘをＮ2に変換し無害化する排ガス処理方法、特に排ガスを前段の酸化触媒に接触させその中のＮＯをＮＯ2に変換したのち、その中へ還元剤のアンモニアや尿素などを混合し、この混合ガスを後段の脱硝触媒に接触させＮＯ2をＮ2に変換して無害化したガスを大気中に排出する処理方法がよく知られている（例えば、特許文献１、２参照）。 Conventionally, as an exhaust gas treatment method for purifying nitrogen oxides (NOx) in automobile exhaust gas, an exhaust gas treatment method in which exhaust gas is brought into contact with a denitration catalyst and NOx in the exhaust gas is converted to N 2 to render it harmless, in particular, exhaust gas is oxidized in the previous stage. After contacting the catalyst and converting NO therein to NO 2 , a reducing agent such as ammonia or urea is mixed therein, and this mixed gas is contacted with a denitration catalyst at the subsequent stage to convert NO 2 into N 2. A processing method for discharging detoxified gas into the atmosphere is well known (see, for example, Patent Documents 1 and 2).
この方法は、選択的接触還元（Ｓｅｌｅｃｔｉｖｅ Ｃａｔａｌｙｔｉｃ Ｒｅｄｕｃｔｉｏｎ：以下ＳＣＲと略す）として知られ、特に還元剤に尿素を用いる尿素ＳＣＲは脱硝効率が高いことから、ディーゼルエンジン搭載自動車の排ガス処理方法として地球環境保護の観点から近年注目されるようになった。 This method is known as selective catalytic reduction (hereinafter abbreviated as SCR). In particular, urea SCR using urea as a reducing agent has high denitration efficiency. In recent years, it has attracted attention from the viewpoint of protection.
ＳＣＲにおいては、排ガスを先ず酸化触媒に接触させてその中のＮＯをＮＯ2に変換するが、その際、ほぼ等モルの割合のときに高い脱硝効果が得られるのでＮＯとＮＯ2の割合をほぼ等モルに調節することが望ましい（特許文献３参照）。 In SCR, exhaust gas is first brought into contact with an oxidation catalyst to convert NO therein to NO 2. At that time, a high denitration effect is obtained at an approximately equimolar ratio, so the ratio of NO and NO 2 is increased. It is desirable to adjust to approximately equimolar (see Patent Document 3).
しかしながら、通常用いられる酸化触媒の酸化効率は、排ガス温度が低いと著しく低くなり、排ガス温度が高いと極度に高くなる傾向があり、ＮＯとＮＯ2の割合を所望のほぼ等モルの範囲内に調節することは非常にむずかしい。
一般に、酸化触媒においては、低い排ガス温度（例えば、始動時などの運転時）でのＮＯ2転換率の向上が望まれ、低温側に広い活性温度域を有する酸化触媒の開発がなされている。
However, the oxidation efficiency of the oxidation catalyst that is usually used tends to be extremely low when the exhaust gas temperature is low, and extremely high when the exhaust gas temperature is high, so that the ratio of NO and NO 2 falls within the desired approximately equimolar range. It is very difficult to adjust.
In general, in an oxidation catalyst, it is desired to improve the NO 2 conversion rate at a low exhaust gas temperature (for example, during operation such as starting), and an oxidation catalyst having a wide active temperature range on the low temperature side has been developed.
ＳＣＲにおいても、低温での活性化向上が大きな課題となっており、ＮＯとＮＯ2をほぼ等モルにし得る低温側での活性を有する酸化触媒に対する要望があるが、低温での活性向上を重視すると、排気ガス温度が高く、ＮＯ排出量の多い高負荷領域では、酸化触媒のＮＯからＮＯ2への転換率が高すぎ、ＮＯｘ浄化率が低下するという問題を生じる。 Even in SCR, improvement of activation at low temperature is a big issue, and there is a demand for an oxidation catalyst having activity on the low temperature side that can make NO and NO 2 almost equimolar, but importance is attached to improvement of activity at low temperature. Then, in a high load region where the exhaust gas temperature is high and the amount of NO emission is large, there is a problem that the conversion rate of NO from the oxidation catalyst to NO 2 is too high and the NOx purification rate decreases.
したがって、排気ガス温度が低温から高温まで変化しても、ＳＣＲ入口でのＮＯとＮＯ2のモル比を１：１から大きく逸脱しないように調整する技術が求められている。 Therefore, there is a need for a technique for adjusting the molar ratio of NO and NO 2 at the SCR inlet so as not to deviate significantly from 1: 1 even when the exhaust gas temperature changes from a low temperature to a high temperature.
酸化触媒組成の調整や使用条件（排気再循環量ほか）の調整でＮＯとＮＯ2の割合をその所望の範囲内に調節し得ることも知られているが、排ガスを高温下で運転したときにＮＯとＮＯ2をほぼ等モル内に調節するための実用的な方法は知られていない。 It is also known that the ratio of NO and NO 2 can be adjusted within the desired range by adjusting the oxidation catalyst composition and conditions of use (exhaust gas recirculation amount, etc.), but when operating exhaust gas at high temperatures In addition, there is no known practical method for adjusting NO and NO 2 within an equimolar amount.
本発明は、このような事情のもとで、自動車排ガス中の窒素酸化物をＳＣＲ法により処理するに当り、ＮＯとＮＯ2との生成割合をほぼ等モルにし、後続の還元処理段階における脱硝率を向上させることを目的としてなされたものである。 Under the circumstances, the present invention has a denitration rate in the subsequent reduction process step by setting the generation ratio of NO and NO 2 to be approximately equimolar when the nitrogen oxide in the automobile exhaust gas is processed by the SCR method. It was made for the purpose of improving the rate.
本発明者らは、ＳＣＲ法における脱硝率を向上させるために、窒素酸化物の酸化段階における生成ガス中のＮＯとＮＯ2のモル比がほぼ等しくなるように調整する方法について鋭意研究を重ねた結果、酸化処理に先立って排ガスの一部を分流し、それを酸化触媒に接触させてその中のＮＯをＮＯ2に変換したのち、未処理の排ガスと合流させ、その際の分流量を調節して処理した排ガスと未処理の排ガスとの混合ガス中のＮＯとＮＯ2とのモル比がほぼ等モルになるようにすれば、その目的を達成し得ることを見出し、この知見により本発明をなすに至った。 In order to improve the denitration rate in the SCR method, the present inventors have made extensive studies on a method of adjusting the molar ratio of NO and NO 2 in the product gas in the oxidation stage of nitrogen oxides to be approximately equal. As a result, a part of the exhaust gas is diverted prior to the oxidation treatment, and it is brought into contact with the oxidation catalyst to convert NO therein to NO 2 , and then merged with the untreated exhaust gas, and the flow rate at that time is adjusted. It is found that the object can be achieved if the molar ratio of NO and NO 2 in the mixed gas of the treated exhaust gas and the untreated exhaust gas is substantially equimolar. It came to make.
すなわち、本発明は、自動車排ガスを、酸化触媒に接触させてその中のＮＯの一部をＮＯ2に変換したのち、生成したＮＯとＮＯ2の混合ガスにアンモニア又はアンモニア発生物質を加えて、脱硝触媒と接触させ、ＮＯ及びＮＯ2をＮ2に変換して無害化する排ガス処理方法において、該排ガスを酸化触媒に接触させるに先立ってその排ガスの所定量を分流し、主流のみを酸化触媒と接触させてその中のＮＯの一部をＮＯ2に変換させたのち、分流した所定量の未処理の排ガスと合流させることにより、ＮＯとＮＯ2との割合をほぼ等モルに調節し、脱硝率を向上させることを特徴とする排ガス処理方法、及び内管部を主流通過部、外管部を分流通過部に形成した二重管からなる円筒状反応器、内管部に設けた円柱状酸化触媒層、酸化触媒層の前に配設され内管部及び外管部にそれぞれ連通した開口面積を調節可能に構成した開口部をもつ排ガス導入管、及び酸化触媒層の後に配設された内管部及び外管部の両方に導通したガス排出管を備えたことを特徴とする尿素ＳＣＲ型自動車排ガス処理装置を提供するものである。 That is, the present invention provides a vehicle emissions, after converting a portion of NO therein to NO 2 is brought into contact with the oxidation catalyst, the addition of ammonia or ammonia-generating substance in a mixed gas of the produced NO and NO 2, In an exhaust gas treatment method in which NO and NO 2 are converted into N 2 and made harmless by contacting with a denitration catalyst, a predetermined amount of the exhaust gas is diverted before contacting the exhaust gas with the oxidation catalyst, and only the main stream is oxidized catalyst some of NO therein in contact after was converted into NO 2, by merging the untreated exhaust gas diverted predetermined amount, adjusted to nearly equimolar ratio between NO and NO 2 and, An exhaust gas treatment method characterized by improving the denitration rate, and a cylindrical reactor composed of a double pipe in which the inner pipe portion is formed in the main flow passage portion and the outer pipe portion is formed in the branch flow passage portion, and a circle provided in the inner pipe portion Before the columnar oxidation catalyst layer and oxidation catalyst layer Exhaust gas introduction pipe having an opening configured to be adjustable so that the opening areas respectively connected to the inner pipe section and the outer pipe section can be adjusted, and both the inner pipe section and the outer pipe section disposed after the oxidation catalyst layer The present invention provides a urea SCR type automobile exhaust gas treatment apparatus including a gas exhaust pipe that is conducted.
次に、本発明方法をさらに詳細に説明する。
ＳＣＲ法により、ＮＯｘを含む自動車排ガスを無害化するには、この排ガスを先ず酸化条件下で酸化触媒と接触させて一部のＮＯをＮＯ2に変換し、次いでこれに還元剤例えばアンモニアＮＨ3又は尿素（ＮＨ2）2ＣＯ或いはその両方を加えて混合したのち、この混合ガスを脱硝触媒と接触させてＮＯ2をＮ2に変換する。
Next, the method of the present invention will be described in more detail.
In order to render automobile exhaust gas containing NOx harmless by the SCR method, this exhaust gas is first contacted with an oxidation catalyst under oxidizing conditions to convert a part of NO into NO 2 , and then to a reducing agent such as ammonia NH 3. or urea (NH 2) 2 CO or were mixed by adding both, to convert the mixed gas is brought into contact with the denitration catalyst to NO 2 to N 2.
この際の酸化触媒は、ＮＯをＮＯ2に酸化し得る能力を有するものであれば特に制限はなく、慣用されている酸化触媒の中から任意に選ぶことができる。このような酸化触媒としては、例えばアルミナ、チタニア、シリカ、シリカ−アルミナ、マグネシアなどの金属酸化物又は複合金属酸化物からなる多孔質担体に、白金、ロジウム、パラジウム、イリジウムなどの貴金属を担持させたものを挙げることができる。 The oxidation catalyst at this time is not particularly limited as long as it has an ability to oxidize NO to NO 2 , and can be arbitrarily selected from conventionally used oxidation catalysts. As such an oxidation catalyst, for example, a noble metal such as platinum, rhodium, palladium, iridium is supported on a porous carrier made of a metal oxide or composite metal oxide such as alumina, titania, silica, silica-alumina, magnesia. Can be mentioned.
このＮＯをＮＯ2に変換する反応は、酸素の存在下、一般に２００℃程度以上の温度で行われる。次いで、このようにして生成したＮＯ2は、アンモニアと混合したのち、混合ガスを脱硝触媒と接触させると、反応式
８ＮＨ3＋６ＮＯ2 → １２Ｈ2Ｏ＋７Ｎ2
に従って、ＮＯ2をＮ2に変換して無害化する。
The reaction for converting NO to NO 2 is generally performed at a temperature of about 200 ° C. or higher in the presence of oxygen. Next, the NO 2 produced in this way is mixed with ammonia, and then the mixed gas is brought into contact with a denitration catalyst. Then, the reaction formula 8NH 3 + 6NO 2 → 12H 2 O + 7N 2
Accordingly, NO 2 is converted to N 2 and rendered harmless.
また、上記のアンモニアの代りに尿素水を用いることができるが、この場合、尿素水は排ガス中において、反応式
（ＮＨ2）2ＣＯ＋Ｈ2Ｏ → ２ＮＨ3＋ＣＯ2
に従って加水分解し、アンモニアを生成し、これによってＮＯ2が還元される。
この際の脱硝触媒としては、ＮＣＲ法において通常用いられている脱硝触媒、いわゆるＳＣＲ触媒を用いる。
In addition, urea water can be used in place of the above ammonia. In this case, the urea water is a reaction formula (NH 2 ) 2 CO + H 2 O → 2NH 3 + CO 2 in the exhaust gas.
To produce ammonia, which reduces NO 2 .
As the denitration catalyst at this time, a denitration catalyst generally used in the NCR method, a so-called SCR catalyst is used.
自動車排ガス中には、いわゆるＮＯｘが含まれるが、ディーゼルエンジンの排気ガスでは、ＮＯｘの大半がＮＯである。ところで、ＳＣＲ法、特に尿素を還元剤として用いる場合には、ＮＯとＮＯ2の割合を１：１付近にしたときに最も効率よく無害化が行われるので、先ずこの排ガスを酸化触媒に接触させ、その中のＮＯの一部を反応式
２ＮＯ＋Ｏ2 → ＮＯ2 （１）
に従ってＮＯ2に変換させて、ＮＯとＮＯ2との１：１の混合ガスを生成させたのち、これに還元剤としてアンモニア又はアンモニア発生物質を加えて脱硝触媒と接触させ、反応式
ＮＯ＋ＮＯ2＋２ＮＨ3 → ２Ｎ2＋３Ｈ2Ｏ （２）
に従って窒素と水に変換し、無害化する方法である。
Although so-called NOx is contained in automobile exhaust gas, most of NOx is NO in the exhaust gas of a diesel engine. By the way, when the SCR method, particularly urea is used as a reducing agent, the detoxification is most efficiently performed when the ratio of NO and NO 2 is close to 1: 1, so this exhaust gas is first brought into contact with the oxidation catalyst. , A part of NO in the reaction formula 2NO + O 2 → NO 2 (1)
By conversion to NO 2 in accordance with one of NO and NO 2: After to produce a first mixed gas, to which ammonia or ammonia-generating substance is contacted with a denitrification catalyst added as the reducing agent, reaction equation NO + NO 2 + 2NH 3 → 2N 2 + 3H 2 O (2)
According to the method, it is converted into nitrogen and water and detoxified.
この第一段階の反応（１）における酸化触媒としては、例えば白金、パラジウム、イリジウム、ロジウムなどの貴金属を、アルミナ、チタニア、シリカ−アルミナ、マグネシアのような金属酸化物又は複合金属酸化物あるいはコージェライトからなる多孔質担体に担持したものが用いられる。この反応（１）は、通常２００〜３００℃の温度で進行する。 Examples of the oxidation catalyst in the first stage reaction (1) include noble metals such as platinum, palladium, iridium and rhodium, metal oxides such as alumina, titania, silica-alumina, magnesia, composite metal oxides, and cordiers. Those supported on a porous carrier made of light are used. This reaction (1) usually proceeds at a temperature of 200 to 300 ° C.
また、第二段階の反応（２）における脱硝触媒としては、例えば酸化バナジウム、酸化タングステン、二酸化チタンなどが用いられるが、そのほかに鉄や銅によってイオン変換されたゼオライト例えばＺＳＭ−５、モルデナイト、ホージャサイトなどが用いられる。この反応（２）は、通常３００〜５５０℃の温度で進行する。この反応（２）においては、アンモニアを用いることが必要であるが、アンモニアガスを用いる代りに、この反応条件下でアンモニアを発生する物質、例えばアンモニア水、尿素、炭酸アンモニウムなどを用いることもできる。 In addition, as the denitration catalyst in the second stage reaction (2), for example, vanadium oxide, tungsten oxide, titanium dioxide or the like is used. In addition, zeolite ion-converted with iron or copper, for example, ZSM-5, mordenite, fauja Sites are used. This reaction (2) usually proceeds at a temperature of 300 to 550 ° C. In this reaction (2), it is necessary to use ammonia. Instead of using ammonia gas, a substance that generates ammonia under the reaction conditions, such as aqueous ammonia, urea, ammonium carbonate, etc., can also be used. .
ところで、前記反応式（２）から分るように、このＳＣＲ法では、ＮＯとＮＯ2との割合が１：１近傍において最も効率よく反応することが知られている。しかしながら、排ガスの温度が高すぎると、前記反応式（１）におけるＮＯ2への変換率が大きくなり、ＮＯｘの低減効果が低下する。 By the way, as can be seen from the reaction formula (2), in this SCR method, it is known that the reaction is most efficiently performed when the ratio of NO to NO 2 is in the vicinity of 1: 1. However, if the temperature of the exhaust gas is too high, the conversion rate to NO 2 in the reaction formula (1) increases, and the NOx reduction effect decreases.
したがって、本発明においては、酸化触媒を通過するに先立って、排ガス流を分流し、酸化触媒に接触する排ガス流量を制御し、酸化触媒通過後に再び未処理の排ガスと合流して、ＮＯとＮＯ2の混合割合が１：１近傍の混合ガスを形成させることが必要である。このようにして形成されたＮＯとＮＯ2の割合が１：１近傍の混合ガスは、次いでアンモニア又はアンモニア発生物質と混合し、脱硝触媒と接触することにより窒素と水とに変換され、無害化される。
このようにして９０％又はそれ以上の変換率で排ガス中のＮＯｘを除去することができる。
Therefore, in the present invention, before passing through the oxidation catalyst, the exhaust gas flow is diverted, the flow rate of the exhaust gas in contact with the oxidation catalyst is controlled, and after passing through the oxidation catalyst, the untreated exhaust gas is joined again, and NO and NO It is necessary to form a mixed gas in which the mixing ratio of 2 is close to 1: 1. The gas mixture in which the ratio of NO and NO 2 formed in this way is close to 1: 1 is then mixed with ammonia or an ammonia-generating substance, and converted into nitrogen and water by contacting with a denitration catalyst, making it harmless. Is done.
In this way, NOx in the exhaust gas can be removed at a conversion rate of 90% or more.
図１は、酸化触媒と排ガスとの接触温度ｘと脱硝触媒に導入するときの排ガス中のＮＯ2／（ＮＯ＋ＮＯ2）比との関係を示すグラフであり、網掛け範囲はＮＯとＮＯ2の割合がほぼ等モル（１：１）の範囲である。 FIG. 1 is a graph showing the relationship between the contact temperature x between the oxidation catalyst and the exhaust gas and the NO 2 / (NO + NO 2 ) ratio in the exhaust gas when introduced into the denitration catalyst, and the shaded range is NO and NO 2 . The ratio is in the range of approximately equimolar (1: 1).
図中の実線は、低温においてもＮＯからＮＯ2への転換が行われる組成の酸化触媒Ａについての温度に対するＮＯ2／（ＮＯ＋ＮＯ2）の転換率の変化を示したものであり、同じく点線はより高温でＮＯとＮＯ2とが等モルになるような性能をもつ別個の組成の酸化触媒Ｂについての温度に対するＮＯ2／（ＮＯ＋ＮＯ2）の転換率の変化を示したものであって、いずれも本発明方法を用いない場合のものである。
この図から分るように、いずれの触媒を用いても、低温から高温までの広い温度範囲にわたってＮＯとＮＯ2との割合を適正な範囲に調整することはできない。
一方、破線は触媒Ａを用いて本発明方法を行い、ＮＯとＮＯ2を等モルに制御した場合を示す。
The solid line in the figure shows the change in the conversion rate of NO 2 / (NO + NO 2 ) with respect to the temperature for the oxidation catalyst A having a composition in which conversion from NO to NO 2 is performed even at low temperatures. The change in the conversion rate of NO 2 / (NO + NO 2 ) with respect to temperature for an oxidation catalyst B having a separate composition having the performance of equimolar NO and NO 2 at higher temperatures, Is the case where the method of the present invention is not used.
As can be seen from this figure, no matter which catalyst is used, the ratio of NO and NO 2 cannot be adjusted to an appropriate range over a wide temperature range from low temperature to high temperature.
On the other hand, the broken line shows the case where the method of the present invention is performed using the catalyst A and NO and NO 2 are controlled to be equimolar.
この図から分るように、従来方法においてはアイドリングの多い都市内走行などでは酸化触媒温度が低いために、比較的低温で活性化し、ＮＯ／（ＮＯ＋ＮＯ2）比がほぼ０．５になる酸化触媒の使用が望ましいが、その場合には触媒温度が上昇する運転条件においては、ＮＯ／（ＮＯ＋ＮＯ2）比が０．５を超え、その状態で脱硝触媒と接触するので脱硝効率が低下し、脱硝されない多量のＮＯｘが大気中に排出されることになる。 As can be seen from this figure, in the conventional method, since the oxidation catalyst temperature is low when traveling in a city with a lot of idling, it is activated at a relatively low temperature, and the NO / (NO + NO 2 ) ratio becomes approximately 0.5. Although it is desirable to use a catalyst, in that case, the NO / (NO + NO 2 ) ratio exceeds 0.5 under the operating conditions in which the catalyst temperature rises, and the NOx removal efficiency decreases because it contacts with the NOx removal catalyst in that state, A large amount of NOx that is not denitrated is discharged into the atmosphere.
これに対し、本発明方法においては、自動車排ガスが酸化触媒に接触するに先立って、その一部を分流し、主流を酸化触媒と接触した後で、分流と再び合流させることによりＮＯ／（ＮＯ＋ＮＯ2）比を常に０．５付近に調節するので（矢印で示す）、脱硝効率が常に高い条件に維持され、排ガスは、その中のＮＯｘが完全に除かれ無害化した状態で大気中に排出される。 In contrast, in the method of the present invention, a part of the automobile exhaust gas contacts with the oxidation catalyst prior to contact with the oxidation catalyst, and after contacting the main stream with the oxidation catalyst, it is recombined with the split flow to produce NO / (NO + NO 2 ) Since the ratio is always adjusted to around 0.5 (indicated by an arrow), the denitration efficiency is always maintained at a high level, and exhaust gas is exhausted into the atmosphere in a state where NOx in it is completely removed and rendered harmless Is done.
脱硝触媒に接触させる合流ガス中のＮＯ／（ＮＯ＋ＮＯ2）比を０．５付近に調節するには、例えば適当な位置にＮＯ2又はＮＯ濃度センサ及び温度センサを配置し、それらからの信号をコンピュータに入力して解析し、あらかじめ設定されている分流と主流との分配比をその情報に基づいて補正し、電子制御により操作される流量制御手段によって分流する量を変えることによって行う。この場合、温度が上昇すれば、分流する量を多くして主流中のＮＯのＮＯ2への変換量を少なくし、逆に温度が低下すれば分流する量を少なくして主流中のＮＯのＮＯ2への変換量を多くし、合流ガス中のＮＯとＮＯ2のモル比がほぼ等量になるように調節する。
このようにして、自動車排ガスの温度が変動しても、常に脱硝効率を最良の状態に保ち、排ガス中のＮＯｘを完全に無害化して大気中に排出することができる。
In order to adjust the NO / (NO + NO 2 ) ratio in the combined gas brought into contact with the denitration catalyst to around 0.5, for example, an NO 2 or NO concentration sensor and a temperature sensor are arranged at appropriate positions, and signals from them are sent. This is performed by inputting to a computer for analysis, correcting a distribution ratio between the divided flow and the main flow set in advance based on the information, and changing the amount of flow divided by the flow rate control means operated by electronic control. In this case, if the temperature rises, the amount to be diverted is increased to reduce the conversion amount of NO in the main stream to NO 2. Conversely, if the temperature is lowered, the amount to be diverted is decreased to reduce the amount of NO in the main stream. The amount of conversion to NO 2 is increased, and the molar ratio of NO and NO 2 in the combined gas is adjusted to be approximately equal.
In this way, even if the temperature of the automobile exhaust gas fluctuates, the NOx removal efficiency can always be kept in the best state, and NOx in the exhaust gas can be completely rendered harmless and discharged into the atmosphere.
次に添付図面に従って本発明装置を説明する。
図２は、本発明方法に用いるのに好適な排ガス処理装置の酸化反応器の１例を示す縦断面略解図である。この酸化反応器は、ガス導入部１、酸化触媒収納部２及びガス排出部３から構成されている。酸化触媒収納部２は、主流通過部を形成する内筒部４と分流通過部を形成する外筒部５からなり、この内筒部４及び外筒部５の前端はガス導入部１に、また後端はガス排出部３にそれぞれ開口している。内筒部４のほぼ中央部には酸化触媒層６が設けられ、ガス導入部１とガス排出部３に連通している。
Next, the apparatus of the present invention will be described with reference to the accompanying drawings.
FIG. 2 is a schematic longitudinal sectional view showing an example of an oxidation reactor of an exhaust gas treatment apparatus suitable for use in the method of the present invention. This oxidation reactor is composed of a gas introduction part 1, an oxidation catalyst storage part 2 and a gas discharge part 3. The oxidation catalyst storage unit 2 includes an inner cylinder part 4 that forms a main flow passage part and an outer cylinder part 5 that forms a diversion passage part, and the front ends of the inner cylinder part 4 and the outer cylinder part 5 are connected to the gas introduction part 1. In addition, the rear ends are open to the gas discharge portions 3 respectively. An oxidation catalyst layer 6 is provided substantially at the center of the inner cylinder portion 4 and communicates with the gas introduction portion 1 and the gas discharge portion 3.
自動車排ガスＡは、ガス導入部１に入り、ここで分流して、その一部は外筒部５に誘導され、残りは内筒部４に誘導される。内筒部４に誘導された主流は、酸化触媒層６を通って、その中のＮＯの一部がＮＯ2に変換され、ＮＯとＮＯ2の混合物となって、ガス排出部３に至り、ここで外筒部５を通って送られる未処理の排ガスと合流し、ＮＯとＮＯ2のほぼ等モルからなる混合ガスＢとなって排出され、後続の脱硝工程に供給される。外筒部５を通る分流の量は、流量制御弁７，７´によって制御され、排出部から排出される混合ガス中のＮＯとＮＯ2がほぼ等モルになるように調節される。 The automobile exhaust gas A enters the gas introduction part 1 and is divided here, part of which is guided to the outer cylinder part 5 and the rest is guided to the inner cylinder part 4. Mainstream induced in the inner cylinder portion 4 passes through the oxidation catalyst layer 6, a part of NO therein is converted to NO 2 and a mixture of NO and NO 2, reaches the gas discharge portion 3, Here, the untreated exhaust gas sent through the outer cylinder portion 5 is merged, discharged as a mixed gas B composed of substantially equimolar amounts of NO and NO 2 , and supplied to the subsequent denitration step. The amount of the diverted flow that passes through the outer cylinder portion 5 is controlled by the flow rate control valves 7 and 7 ′, and is adjusted so that NO and NO 2 in the mixed gas discharged from the discharge portion are approximately equimolar.
上記の円筒状反応器は、その前部及び後部を外方に向って狭めた円錐台状に形成するとともに、その中に収納した円柱状酸化触媒層を前後に移動可能とし、円錐台内壁８と触媒層の円形側壁縁部９との間の間隙で形成される外筒部のガス通過断面積を変えることによって、分流の量を制御する構造とすることもできる。 The cylindrical reactor is formed in a truncated cone shape whose front and rear portions are narrowed outward, and the columnar oxidation catalyst layer accommodated therein can be moved back and forth, and the inner wall 8 of the truncated cone It is also possible to adopt a structure in which the amount of diversion is controlled by changing the gas passage cross-sectional area of the outer cylinder portion formed by the gap between the catalyst and the circular side wall edge 9 of the catalyst layer.
図３は、その構造の機能を示す説明図であり、実線は最も分流の量を多くした状態、破線は分流の量がほとんど零になるように制御した状態を示す。そして、触媒層の円形側壁縁部９が円錐台内壁８に当接すると、分流は零となり、排ガスはすべて酸化触媒層を通過するようになる。
このような円柱状酸化触媒層の移動による分流の量の制御は、前記したＮＯ2又はＮＯ濃度センサ及び温度センサからの情報に基づくコンピュータ処理により自動的に行うことができる。
FIG. 3 is an explanatory diagram showing the function of the structure, in which the solid line indicates the state where the amount of diversion is the largest, and the broken line indicates a state where the amount of diversion is controlled to be almost zero. When the circular side wall edge 9 of the catalyst layer comes into contact with the frustoconical inner wall 8, the shunt flow becomes zero, and all exhaust gas passes through the oxidation catalyst layer.
Such control of the amount of diversion by movement of the cylindrical oxidation catalyst layer can be automatically performed by computer processing based on the information from the NO 2 or NO concentration sensor and the temperature sensor.
本発明装置は、このようにして酸化反応器においてＮＯとＮＯ2とのモル比がほぼ１になるように調節された混合ガスに、アンモニア又はアンモニア発生物質例えば尿素を添加し、混合する混合槽（図示せず）、このようにしてアンモニア又はアンモニア発生物質を混合された混合ガスを脱硝触媒と接触させ、前記還元反応（２）を行わせるための還元反応器（図示せず）が配設されている。 The apparatus of the present invention is a mixing tank in which ammonia or an ammonia generating substance such as urea is added to and mixed with the mixed gas adjusted so that the molar ratio of NO to NO 2 is approximately 1 in the oxidation reactor. (Not shown), a reduction reactor (not shown) for bringing the ammonia or the mixed gas mixed with the ammonia generating substance into contact with the denitration catalyst and causing the reduction reaction (2) is provided. Has been.
図２及び図３における矢印は、酸化触媒層の通過前において分流され、通過後において合流されるガス流を示したものである。 The arrows in FIGS. 2 and 3 indicate the gas flows that are diverted before passing through the oxidation catalyst layer and merged after passing.
本発明方法の排ガス処理方法によれば、自動車排ガスを、酸化触媒に接触させてその中のＮＯをＮＯ2に変換したのち、その中へＮＨ3又は（ＮＨ2）2ＣＯを混合し、この混合ガスを脱硝触媒に接触させてＮＯ2をＮ2に変換して無害化する排ガス処理方法において、排ガス高温運転時にＮＯとＮＯ2との割合をほぼ等モルに調節できて、その結果、持続して高い脱硝効率を得ることができる。
さらに本発明装置の尿素ＳＣＲ型自動車排ガス処理装置によれば、排ガス高温運転時に、ＮＯとＮＯ2との割合をほぼ等モルに調節でき、持続して高い脱硝効率を実現することができる。
According to the exhaust gas treatment method of the present invention, after the automobile exhaust gas is brought into contact with an oxidation catalyst to convert NO therein to NO 2 , NH 3 or (NH 2 ) 2 CO is mixed therein, In the exhaust gas treatment method in which the mixed gas is brought into contact with the denitration catalyst to convert NO 2 into N 2 and detoxify, the ratio of NO and NO 2 can be adjusted to approximately equimolar during exhaust gas high-temperature operation, and as a result, sustained Thus, high denitration efficiency can be obtained.
Furthermore, according to the urea SCR type automobile exhaust gas treatment device of the present invention device, the ratio of NO and NO 2 can be adjusted to approximately equimolar during exhaust gas high temperature operation, and high denitration efficiency can be realized continuously.
次に、実施例により本発明を実施するための最良の形態を説明する。 Next, the best mode for carrying out the present invention will be described by way of examples.
図２に示す構造において、ガス導入部寸法を内径１０ｍｍ、長さ５０ｍｍに、酸化触媒収納部寸法を円筒部内径６０ｍｍ、円筒部長さ６０ｍｍ、前端及び後端円錐台長さ３０ｍｍに、ガス排出部寸法を内径１０ｍｍ、長さ３０ｍｍに構成した酸化触媒装置内に径３０ｍｍ、長さ６０ｍｍの円柱状に形成した白金担持シリカ−アルミナ触媒を分流通過部間隙３ｍｍに保って収納した。
次いで、ディーゼルエンジンからの排出ガスを想定した温度３００℃で、ＮＯを６００ｐｐｍ、ＮＯ2を５０ｐｐｍ含む混合ガスを供給速度２リットル／秒で導入し、主流部と分流部の割合が２：１になるように流量制御弁７，７´を設定し、処理したところ、ＮＯとＮＯ2との含有比が約１：１の混合ガス排出部３から排出された。
次に、この混合ガスに、尿素水を混合ガス中のＮＯ及びＮＯ2を還元するのに必要な割合で添加し、混合したのち、一般に用いられているＳＣＲ触媒内蔵コンバータに約２７０℃で通したところ、混合ガス中のＮＯ及びＮＯ2では９０％以上の転換率で窒素と水蒸気に還元され、所期の成果を得た。
In the structure shown in FIG. 2, the gas introduction part has an inner diameter of 10 mm and a length of 50 mm, the oxidation catalyst storage part has a cylindrical part inner diameter of 60 mm, a cylindrical part length of 60 mm, and a front end and rear end truncated cone length of 30 mm. A platinum-supporting silica-alumina catalyst formed in a columnar shape having a diameter of 30 mm and a length of 60 mm was stored in an oxidation catalyst device having dimensions of an inner diameter of 10 mm and a length of 30 mm while maintaining a separation passage passage gap of 3 mm.
Next, a mixed gas containing 600 ppm NO and 50 ppm NO 2 was introduced at a supply rate of 2 liters / second at a temperature of 300 ° C. assuming exhaust gas from a diesel engine, and the ratio of the main flow part to the diversion part was 2: 1. The flow rate control valves 7 and 7 ′ were set and processed so that they were discharged from the mixed gas discharge portion 3 having a content ratio of NO and NO 2 of about 1: 1.
Next, urea water is added to this mixed gas at a ratio necessary for reducing NO and NO 2 in the mixed gas, and after mixing, it is passed through a converter with a built-in SCR catalyst at about 270 ° C. As a result, NO and NO 2 in the mixed gas were reduced to nitrogen and water vapor at a conversion rate of 90% or more, and the desired result was obtained.
本発明は、自動車排ガス中のＮＯｘを除去し、無害化するために有用である。 The present invention is useful for removing NOx from automobile exhaust gas and making it harmless.
１ ガス導入部
２ 酸化触媒収納部
３ ガス排出部
４ 内筒部
５ 外筒部
６ 酸化触媒層
７，７´流量制御弁
８ 円錐台内壁
９ 円形側壁縁部
DESCRIPTION OF SYMBOLS 1 Gas introduction part 2 Oxidation catalyst storage part 3 Gas discharge part 4 Inner cylinder part 5 Outer cylinder part 6 Oxidation catalyst layer 7,7 'flow control valve 8 Frustum inner wall 9 Circular side wall edge
Claims (3)
Claims that the front and rear parts of the cylindrical reactor are formed in a truncated cone shape that narrows outward, the columnar oxidation catalyst layer is movable back and forth, and the gas passage cross-sectional area of the outer tube part is adjustable. Item 3. An automobile exhaust gas treatment apparatus according to Item 2.
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| JP2010519458A (en) * | 2007-02-21 | 2010-06-03 | ボルボ ラストバグナー アーベー | Control method for controlling exhaust aftertreatment system and exhaust aftertreatment system |
| KR101057342B1 (en) | 2010-11-09 | 2011-08-22 | 주식회사 기스코 | The de-nox efficiency improvement at low temperature and yellow plume reduction system by fast scr |
| DE102012201809A1 (en) * | 2011-02-09 | 2012-09-13 | Honda Motor Co., Ltd. | EXHAUST GAS CLEANING SYSTEM FOR A COMBUSTION ENGINE |
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| JPS5529018A (en) * | 1978-08-18 | 1980-03-01 | Fuji Heavy Ind Ltd | Exhauster for internal combustion engine |
| JPH1026017A (en) * | 1996-07-09 | 1998-01-27 | Toyota Motor Corp | Emission control system for internal combustion engine |
| JP2004346794A (en) * | 2003-05-21 | 2004-12-09 | Mitsubishi Fuso Truck & Bus Corp | Exhaust emission control device for internal combustion engine |
| JP2005023921A (en) * | 2003-06-12 | 2005-01-27 | Hino Motors Ltd | Exhaust emission control device |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2010519458A (en) * | 2007-02-21 | 2010-06-03 | ボルボ ラストバグナー アーベー | Control method for controlling exhaust aftertreatment system and exhaust aftertreatment system |
| WO2008114834A1 (en) * | 2007-03-16 | 2008-09-25 | Toyota Jidosha Kabushiki Kaisha | Exhaust purification device for internal combustion engine |
| KR101057342B1 (en) | 2010-11-09 | 2011-08-22 | 주식회사 기스코 | The de-nox efficiency improvement at low temperature and yellow plume reduction system by fast scr |
| DE102012201809A1 (en) * | 2011-02-09 | 2012-09-13 | Honda Motor Co., Ltd. | EXHAUST GAS CLEANING SYSTEM FOR A COMBUSTION ENGINE |
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| JP4652047B2 (en) | 2011-03-16 |
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