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JP5576593B2 - Method for removing N2O in exhaust gas - Google Patents

Method for removing N2O in exhaust gas Download PDF

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JP5576593B2
JP5576593B2 JP2008024798A JP2008024798A JP5576593B2 JP 5576593 B2 JP5576593 B2 JP 5576593B2 JP 2008024798 A JP2008024798 A JP 2008024798A JP 2008024798 A JP2008024798 A JP 2008024798A JP 5576593 B2 JP5576593 B2 JP 5576593B2
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JP2009183828A (en
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統一郎 佐々木
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Metawater Co Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/064—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof containing iron group metals, noble metals or copper
    • B01J29/072—Iron group metals or copper
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8621—Removing nitrogen compounds
    • B01D53/8625—Nitrogen oxides
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
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    • B01D2251/208—Hydrocarbons
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/20738—Iron
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/50—Zeolites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2257/00—Components to be removed
    • B01D2257/40—Nitrogen compounds
    • B01D2257/402—Dinitrogen oxide
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
    • B01J2229/10—After treatment, characterised by the effect to be obtained
    • B01J2229/18—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself
    • B01J2229/186—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself not in framework positions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
    • B01J37/0027—Powdering
    • B01J37/0036—Grinding
    • 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
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)
    • 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
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/20—Capture or disposal of greenhouse gases of methane

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Description

本発明は、下水汚泥焼却炉などの排ガス中のN2O除去方法に関するものである。 The present invention relates to a method for removing N 2 O in exhaust gas such as a sewage sludge incinerator.

下水汚泥焼却炉、火力発電所のボイラー排ガス、自動車排ガス等には、少量のN2O（亜酸化窒素）が含まれている。N2Oは温室効果ガスのひとつであり、地球温暖化係数が３１０であって、炭酸ガスの３１０倍の地球温室効果をもたらす。このため地球温暖化防止の観点から、大気中へのN2O排出量の削減が強く求められている。 A small amount of N 2 O (nitrous oxide) is contained in sewage sludge incinerators, boiler exhaust gas from thermal power plants, automobile exhaust gas, and the like. N 2 O is one of the greenhouse gases, has a global warming potential of 310, and produces a global greenhouse effect 310 times that of carbon dioxide. For this reason, from the viewpoint of preventing global warming, there is a strong demand for reducing N 2 O emissions into the atmosphere.

そこで従来から排ガス中のN2O除去方法として、N2O分解触媒を用いてN2Oを還元除去する方法が提案されている。例えば特許文献１，２，３には、ゼオライトに鉄や鉄イオンを担持させた鉄−ゼオライト系触媒を用いてN2Oを還元除去する方法が開示されている。このような鉄−ゼオライト系触媒は、排ガス中のNOX、SOXなどによる触媒活性の低下が少ないと説明されている。 Thus, as a method for removing N 2 O in exhaust gas, a method of reducing and removing N 2 O using an N 2 O decomposition catalyst has been proposed. For example, Patent Documents 1, 2, and 3 disclose a method for reducing and removing N 2 O using an iron-zeolite catalyst in which iron or iron ions are supported on zeolite. Such iron - zeolite based catalysts is described with a decrease in NO X, SO X such as by catalytic activity in the exhaust gas is small.

上記の鉄−ゼオライト系触媒は３５０〜５００℃程度の温度域において使用されるものであるが、特許文献４にはより低温域において使用できるN2O分解触媒が開示されている。このN2O分解触媒はアルミナまたはゼオライト担体にRh、Ir、Pd、Pt、Ruなどの貴金属を担持させたもので、４００℃以下でN2Oを分解することができると説明されている。 The iron-zeolite catalyst is used in a temperature range of about 350 to 500 ° C., but Patent Document 4 discloses an N 2 O decomposition catalyst that can be used in a lower temperature range. This N 2 O decomposition catalyst is one in which a noble metal such as Rh, Ir, Pd, Pt, or Ru is supported on an alumina or zeolite carrier, and it is described that N 2 O can be decomposed at 400 ° C. or lower.

これらの特許文献１〜４のN2O分解触媒はいずれも、４００℃程度の温度域において炭化水素やアンモニアなどの還元剤とN2Oとを反応させてN2Oを還元除去するものであり、その反応式は次のとおりである。
Ｎ２Ｏ＋1/4ＣＨ４→Ｎ２＋1/4ＣＯ２＋1/2Ｈ２Ｏ
Ｎ２Ｏ＋2/3ＮＨ３→4/3Ｎ２＋Ｈ２Ｏ Each of these N 2 O decomposition catalysts of Patent Documents 1 to 4 reacts a reducing agent such as hydrocarbon or ammonia with N 2 O in a temperature range of about 400 ° C. to reduce and remove N 2 O. Yes, the reaction formula is as follows.
N 2 O + 1 / 4CH 4 → N 2 +1/4 CO 2 + 1 / 2H 2 O
N 2 O + 2 / 3NH 3 → 4 / 3N 2 + H 2 O

このように還元剤の種類は特に限定されるものではないが、工業的には還元剤としてメタンを用いることが適切である。何故ならば、メタンは都市ガスの主成分であってどこでも容易に入手できるうえに、比較的安価であるため、他の還元剤に比較してランニングコストを抑制し易いためである。   Thus, the kind of reducing agent is not particularly limited, but industrially, it is appropriate to use methane as the reducing agent. This is because methane is a main component of city gas and can be easily obtained anywhere, and is relatively inexpensive, so that it is easier to suppress running costs compared to other reducing agents.

ところがメタン自体も温暖化係数が２１の温室効果ガスであるため、適切に使用しなければならない。すなわち、N2Oの分解率を高めるためには反応に十分な量のメタンを添加することが好ましいのであるが、添加量が過剰となると未反応のメタンが大気中に放出されてしまい、温室効果を生じる。また逆にメタン添加量が不足するとN2Oの分解が不十分となって、N2Oによる温室効果を生じる。 However, since methane itself is a greenhouse gas with a warming potential of 21, it must be used appropriately. That is, in order to increase the decomposition rate of N 2 O, it is preferable to add a sufficient amount of methane for the reaction. However, if the addition amount becomes excessive, unreacted methane is released into the atmosphere, and the greenhouse Produces an effect. Conversely, if the amount of methane added is insufficient, the decomposition of N 2 O will be insufficient and the greenhouse effect due to N 2 O will be produced.

しかも適切なメタン添加量は、排ガス温度や排ガス組成によって変動するため、これらを一定に維持することができる実験室においては正確に制御することができても、実際の排ガス処理設備においては排ガス温度や排ガス組成が運転中に大きく変動するため、適切なメタン添加量を正確に把握しにくいという問題がある。
特許第３５５０６５３号公報 特許第３６８１７６９号公報 特表２００５−５２７３５０号公報 特開２００６−２７２２４０号公報 Moreover, since the appropriate amount of methane varies depending on the exhaust gas temperature and exhaust gas composition, it can be accurately controlled in a laboratory where these can be maintained constant, but in an actual exhaust gas treatment facility, the exhaust gas temperature In addition, since the exhaust gas composition fluctuates greatly during operation, there is a problem that it is difficult to accurately grasp the appropriate methane addition amount.
Japanese Patent No. 3550653 Japanese Patent No. 3681769 JP 2005-527350 Gazette JP 2006-272240 A

したがって本発明の目的は上記した従来の問題点を解決し、排ガス温度や排ガス組成が大きく変動する場合にも、排ガス中のN2Oを分解することができ、しかも過剰のメタンが排出されることによる温室効果を防止することができる排ガス中のN2O除去方法を提供することである。 Therefore, the object of the present invention is to solve the above-mentioned conventional problems, and even when the exhaust gas temperature and the exhaust gas composition fluctuate greatly, N 2 O in the exhaust gas can be decomposed and excess methane is discharged. It is an object to provide a method for removing N 2 O in exhaust gas that can prevent the greenhouse effect.

上記の課題を解決するためになされた本発明は、N2Oを含有する排ガスにメタンを添加し、N2O分解触媒を用いてN2Oを還元除去する排ガス中のN2O除去方法であって、N2O分解触媒を通過後のN2O濃度及びメタン濃度を測定し、これらの測定値に応じて、メタンによる温室効果とN 2 Oによる温室効果との和が極小になるようにメタン添加量を制御することを特徴とするものである。 The present invention has been made in order to solve the aforementioned problem, the addition of methane in exhaust gas containing N 2 O, N 2 O removal method in the exhaust gas to reduce and remove N 2 O using the N 2 O decomposition catalyst The N 2 O concentration and the methane concentration after passing through the N 2 O decomposition catalyst are measured, and the sum of the greenhouse effect due to methane and the greenhouse effect due to N 2 O is minimized according to these measured values. Thus, the methane addition amount is controlled.

なおメタン添加量は、N2O分解触媒の出口側の排ガスについて、温室効果ガス指数＝（メタン排出量×２１）＋（N2O排出量×３１０）の式によって定義される温室効果ガス指数を減少させるように制御されることが好ましい。 The amount of methane added is the greenhouse gas index defined by the formula of greenhouse gas index = (methane emissions × 21) + (N 2 O emissions × 310) for the exhaust gas on the outlet side of the N 2 O decomposition catalyst. It is preferable to be controlled so as to decrease.

N2O分解触媒としては、鉄−ゼオライト系触媒あるいは、アルミナまたはゼオライト担体に貴金属を担持させた触媒を使用することができる。また排ガスの種類は限定されるものではないが、代表的には下水汚泥焼却炉の排ガスである。 As the N 2 O decomposition catalyst, an iron-zeolite catalyst or a catalyst in which a noble metal is supported on an alumina or zeolite carrier can be used. The type of exhaust gas is not limited, but is typically exhaust gas from a sewage sludge incinerator.

本発明においては、N2O分解触媒を通過後のN2O濃度及びメタン濃度を測定し、これらの測定値に応じてメタンによる温室効果とN 2 Oによる温室効果との和が極小になるようにメタン添加量を制御する。好ましくは、N2O分解触媒を通過後の排ガスについて、温室効果ガス指数＝（メタン排出量×２１）＋（N2O排出量×３１０）の式によって定義される温室効果ガス指数を減少させるように制御する。このため、本発明によれば全体としての温室効果を極小とすることができる。しかもN2O濃度及びメタン濃度の測定を行っているので、排ガス温度や排ガス組成が運転中に大きく変動した場合にも、メタン添加量を最適に維持することができる。 In the present invention, the N 2 O concentration and the methane concentration after passing through the N 2 O decomposition catalyst are measured, and the sum of the greenhouse effect due to methane and the greenhouse effect due to N 2 O is minimized according to these measured values. Control the amount of methane added. Preferably, for the exhaust gas after passing through the N 2 O decomposition catalyst, the greenhouse gas index defined by the equation of greenhouse gas index = (methane emissions × 21) + (N 2 O emissions × 310) is decreased. To control. For this reason, according to this invention, the greenhouse effect as a whole can be made into the minimum. In addition, since the N 2 O concentration and the methane concentration are measured, the methane addition amount can be optimally maintained even when the exhaust gas temperature and the exhaust gas composition fluctuate greatly during operation.

以下に本発明の好ましい実施形態を示す。この実施形態ではN2Oを含有する排ガスは下水汚泥焼却排ガスであるが、排ガスの種類はこれに限定されるものではない。 Preferred embodiments of the present invention are shown below. In this embodiment, the exhaust gas containing N 2 O is sewage sludge incineration exhaust gas, but the type of exhaust gas is not limited to this.

図１は本発明の実施形態を示すブロック図であり、１は下水汚泥焼却炉、２は空気予熱器、３は第１加熱器、４は冷却塔、５はバグフィルタ、６は排煙処理塔（スクラバ）、７は第２加熱器、８は還元剤供給装置、９はN2O分解触媒、１０は煙突である。 FIG. 1 is a block diagram showing an embodiment of the present invention, wherein 1 is a sewage sludge incinerator, 2 is an air preheater, 3 is a first heater, 4 is a cooling tower, 5 is a bag filter, and 6 is a smoke treatment. A tower (scrubber), 7 is a second heater, 8 is a reducing agent supply device, 9 is an N 2 O decomposition catalyst, and 10 is a chimney.

下水汚泥は下水汚泥焼却炉１において、重油その他の補助燃料を用いて焼却される。下水汚泥焼却炉１の燃焼温度は通常８００〜８５０℃の範囲である。下水汚泥焼却炉１としては例えば流動炉が用いられる。下水汚泥焼却炉１から排出されたN2Oを含有する８００〜８５０℃程度の高温の排ガスは、空気予熱器２に導かれて下水汚泥焼却炉１に供給される空気を予熱し、４００〜５５０℃で第１加熱器３に送られる。この第１加熱器３を通過した排ガスは３００℃程度まで降温し、冷却塔４において更に２００℃程度まで冷却されたうえで、バグフィルタ５において含有するダストを除去される。 The sewage sludge is incinerated in the sewage sludge incinerator 1 using heavy oil or other auxiliary fuel. The combustion temperature of the sewage sludge incinerator 1 is usually in the range of 800 to 850 ° C. For example, a fluidized furnace is used as the sewage sludge incinerator 1. The high-temperature exhaust gas of about 800 to 850 ° C. containing N 2 O discharged from the sewage sludge incinerator 1 preheats the air supplied to the sewage sludge incinerator 1 through 400 to 400 to It is sent to the first heater 3 at 550 ° C. The exhaust gas that has passed through the first heater 3 is cooled to about 300 ° C., further cooled to about 200 ° C. in the cooling tower 4, and the dust contained in the bag filter 5 is removed.

このように排ガスの温度を降下させるのは、バグフィルタ５が高温ガスを処理することができないためである。バグフィルタ５を通過して浄化された排ガスは排煙処理塔６に送られ、上方からの降水と接触して排ガス中のＳＯＸやＨＣｌを除去される。排煙処理塔６で水と接触した排ガスは温度が２０〜５０℃程度にまで低下している。前記したように、N2O分解触媒９には３００〜５００℃程度の温度が必要であるので、排煙処理塔６を出た排ガスは第２加熱器７と第１加熱器３とを通過することによってこの温度域まで再加熱される。 The temperature of the exhaust gas is lowered in this way because the bag filter 5 cannot process the high temperature gas. The exhaust gas purified through the bag filter 5 is sent to the flue gas treatment tower 6 and comes into contact with precipitation from above to remove SO X and HCl in the exhaust gas. The temperature of the exhaust gas that has come into contact with water in the flue gas treatment tower 6 is lowered to about 20 to 50 ° C. As described above, since the N 2 O decomposition catalyst 9 needs to have a temperature of about 300 to 500 ° C., the exhaust gas exiting the flue gas treatment tower 6 passes through the second heater 7 and the first heater 3. To reheat to this temperature range.

N2O分解触媒９としては、鉄−ゼオライト系触媒、またはアルミナまたはゼオライト担体に貴金属を担持させた触媒を用いることができるが、この実施形態ではゼオライトに鉄を担持させたものを用いた。具体的には、市販のアンモニウム・ゼオライトとFeSO4とを室温においてボールミルで撹拌混合し、得られた粉末をマッフル炉中で４００〜６００℃で仮焼し、さらにバインダを加えて直径２mm長さ５mmの円柱状に押し出し成形した鉄担持ゼオライトを使用した。なおバインダの種類は特に限定されるものではないが、例えばカオリンのような珪酸アルミニウム類を用いることができる。 As the N 2 O decomposition catalyst 9, an iron-zeolite-based catalyst or a catalyst in which a noble metal is supported on alumina or a zeolite carrier can be used. In this embodiment, a catalyst in which iron is supported on zeolite is used. Specifically, commercially available ammonium zeolite and FeSO 4 are stirred and mixed at room temperature with a ball mill, and the obtained powder is calcined at 400 to 600 ° C. in a muffle furnace, and further added with a binder to a diameter of 2 mm. An iron-carrying zeolite extruded into a 5 mm cylinder was used. The type of the binder is not particularly limited, and for example, aluminum silicates such as kaolin can be used.

第１加熱器３によって３００〜５００℃の温度域まで加熱された排ガスが上記のN2O分解触媒９に入る手前部分に、還元剤供給装置８が設置されており、還元剤としてメタンガスを排ガス中に添加している。メタンガスが添加された排ガスはN2O分解触媒９を通過する間に、Ｎ２Ｏ＋1/4ＣＨ４→Ｎ２＋1/4ＣＯ２＋1/2Ｈ２Ｏの反応によりN2Oを還元除去することができる。 A reducing agent supply device 8 is installed in the front part where the exhaust gas heated to a temperature range of 300 to 500 ° C. by the first heater 3 enters the N 2 O decomposition catalyst 9, and methane gas is exhausted as the reducing agent. It is added inside. While the exhaust gas to which methane gas has been added passes through the N 2 O decomposition catalyst 9, N 2 O can be reduced and removed by a reaction of N 2 O + 1 / 4CH 4 → N 2 + 1 / 4CO 2 + 1 / 2H 2 O. .

前記したように排ガス温度や排ガス組成は大きく変動するため、メタンガスの最適な添加量を決定することは容易ではない。そこで本発明では、N2O分解触媒９の出口側にN2O濃度検出器１１及びメタン濃度検出器１２を設置し、N2O分解触媒９を通過後のN2O濃度及びメタン濃度を測定し、これらの測定値に応じてメタン添加量を制御する。具体的な制御方法は次の通りである。 As described above, since the exhaust gas temperature and the exhaust gas composition largely fluctuate, it is not easy to determine the optimum addition amount of methane gas. Accordingly, in the present invention, the N 2 O concentration detector 11 and the methane concentration detector 12 installed on the outlet side of the N 2 O decomposition catalyst 9, the N 2 O concentration and the methane concentration after passing the N 2 O decomposition catalyst 9 Measure and control the amount of methane added according to these measurements. A specific control method is as follows.

図２のグラフに示されるように、N2O分解触媒９の入口側における排ガス中のメタン濃度を増加させて行くと、N2O分解触媒９を通過後の排ガス中のN2O濃度は低下して行くが、あるレベルに達するとそれ以上は低下しない。これに対して、N2O分解触媒９の入口側における排ガス中のメタン濃度を増加させて行くと、N2O分解触媒９を通過後の排ガス中のメタン濃度は増加して行く。なおこのグラフは、グラフ中に記載された特定条件下における測定結果を示したものであって、排ガス条件が変化すると当然ながら数値は変化するが、全体的な傾向は変わらない。 As shown in the graph of FIG. 2, when the methane concentration in the exhaust gas at the inlet side of the N 2 O decomposition catalyst 9 is increased, the N 2 O concentration in the exhaust gas after passing through the N 2 O decomposition catalyst 9 is It goes down, but when it reaches a certain level, it doesn't drop any further. In contrast, when gradually increasing the methane concentration in the exhaust gas at the inlet side of the N 2 O decomposition catalyst 9, the methane concentration in the exhaust gas after passing the N 2 O decomposition catalyst 9 increases. This graph shows the measurement results under the specific conditions described in the graph. Naturally, the numerical value changes when the exhaust gas conditions change, but the overall trend does not change.

図２のグラフから分かるように、単に排ガス中のN2O濃度を低下させるためにはメタン添加量を単純に増加させればよいが、必要以上に添加してもN2O濃度を低下させる効果は飽和に達し、逆にメタンが大気中に排出されることによる温室効果が高まることとなる。そこで、温室効果ガス指数＝（メタン排出量×２１）＋（N2O排出量×３１０）の式によって温室効果ガス指数を定義する。この指数はメタンとN2Oとによる温室効果を総合的に評価したものであって、その値が極小になるようにメタン添加量を制御すれば、過剰のメタン添加による温室効果も考慮した制御が可能となる。このような演算及び制御は制御手段１３によって行われる。 As can be seen from the graph of FIG. 2, in order to simply reduce the N 2 O concentration in the exhaust gas, the methane addition amount may be simply increased, but even if it is added more than necessary, the N 2 O concentration is reduced. The effect reaches saturation, and conversely, the greenhouse effect is increased due to the emission of methane into the atmosphere. Therefore, the greenhouse gas index is defined by the formula of greenhouse gas index = (methane emission amount × 21) + (N 2 O emission amount × 310). This index is a comprehensive evaluation of the greenhouse effect due to methane and N 2 O. If the amount of methane added is controlled so that the value is minimized, the control considering the greenhouse effect due to excess methane addition is also taken into account. Is possible. Such calculation and control are performed by the control means 13.

その後、排ガスは第２加熱器７を通過し、熱交換を行ったうえで煙突から放出される。このように本発明によれば、N2O分解触媒９を通過後のN2O濃度及びメタン濃度を測定し、これらの測定値に応じてメタン添加量を制御するので、排ガス温度や排ガス組成が変動しても常にメタン添加量を最適に制御し、N2Oの分解を行うことができる。しかも上記した温室効果ガス指数を用いることにより、全体としての温室効果を極小とすることができる。 Thereafter, the exhaust gas passes through the second heater 7 and is discharged from the chimney after heat exchange. As described above, according to the present invention, the N 2 O concentration and the methane concentration after passing through the N 2 O decomposition catalyst 9 are measured, and the amount of methane added is controlled according to these measured values. Even if fluctuates, the amount of methane added can always be optimally controlled to decompose N 2 O. In addition, by using the above-mentioned greenhouse gas index, the overall greenhouse effect can be minimized.

以下に、本発明の効果を確認した実験結果を示す。
使用したN2O分解触媒は、前記した実施形態において用いたものと同じ、直径２mm、長さ５mmの円柱状に押し出し成形した鉄担持ゼオライトであり、これをカラム内部に充填し、排ガスを模擬したガスをSV＝1100ｈ−1で流した。 Below, the experimental result which confirmed the effect of this invention is shown.
The N 2 O decomposition catalyst used is an iron-carrying zeolite extruded in a cylindrical shape with a diameter of 2 mm and a length of 5 mm, which is the same as that used in the above-described embodiment. Gas was flowed at SV = 1100 h −1 .

ドライガスの組成は酸素５％、残部窒素であり、これに５００ppmのN2Oと１０％の水蒸気を添加した。水蒸気濃度を１０％としたのは、実設備における水蒸気濃度の上限値と一致させたものである。メタン添加量を様々に変化させながら、N2O分解触媒を通過後のN2O濃度及びメタン濃度を測定し、排ガスの温室効果ガス排出量（炭酸ガスへの換算値）を算出して図３のグラフに示した。 The composition of the dry gas was 5% oxygen and the balance nitrogen, and 500 ppm N 2 O and 10% water vapor were added thereto. The water vapor concentration of 10% is made to coincide with the upper limit value of the water vapor concentration in the actual equipment. While varying the amount of methane added, measure the N 2 O concentration and methane concentration after passing through the N 2 O decomposition catalyst, and calculate the greenhouse gas emissions (converted value to carbon dioxide) of the exhaust gas. This is shown in the graph of FIG.

このグラフに示されるように、メタン添加量の増加とともに温室効果ガス排出量は急激に減少するが、この実験条件下においては、メタン濃度が５００ppmを越えると逆に増加する傾向を示す。このためこの実験においては、触媒出口側のメタン濃度が５００ppmになるようにメタン添加量を制御することによって、温室効果ガス排出量を最も少なくすることが可能となる。   As shown in this graph, the greenhouse gas emissions rapidly decrease with the increase in the amount of methane added. However, under this experimental condition, when the methane concentration exceeds 500 ppm, it tends to increase. For this reason, in this experiment, it is possible to minimize the amount of greenhouse gas emissions by controlling the amount of methane added so that the methane concentration on the catalyst outlet side is 500 ppm.

なお、この実験では排ガス温度や排ガス組成を固定したが、本発明によれば排ガス温度や排ガス組成が変動しても常にメタン添加量を最適に制御し、全体としての温室効果ガスの排出量を極小とすることができる。   In this experiment, the exhaust gas temperature and the exhaust gas composition were fixed. However, according to the present invention, even if the exhaust gas temperature and the exhaust gas composition fluctuate, the methane addition amount is always optimally controlled to reduce the overall greenhouse gas emission amount. Can be minimal.

本発明の実施形態を示すブロック図である。It is a block diagram which shows embodiment of this invention. 触媒入口側におけるメタン濃度と、触媒出口側のN2O濃度及びメタン濃度との関係を示すグラフである。And methane concentration at the catalyst inlet side, is a graph showing the relationship between the N 2 O concentration and the methane concentration of the catalyst outlet. 触媒入口側におけるメタン濃度と、温室効果ガス排出量との関係を示すグラフである。It is a graph which shows the relationship between the methane density | concentration in a catalyst inlet side, and greenhouse gas discharge | emission amount.

符号の説明Explanation of symbols

１ 下水汚泥焼却炉
２ 空気予熱器
３ 第１加熱器
４ 冷却塔
５ バグフィルタ
６ 排煙処理塔
７ 第２加熱器
８ 還元剤供給装置
９ N2O分解触媒
１０ 煙突
１１ N2O濃度検出器
１２ メタン濃度検出器
１３ 制御手段 DESCRIPTION OF SYMBOLS 1 Sewage sludge incinerator 2 Air preheater 3 1st heater 4 Cooling tower 5 Bag filter 6 Smoke treatment tower 7 2nd heater 8 Reducing agent supply device 9 N 2 O decomposition catalyst 10 Chimney 11 N 2 O concentration detector 12 Methane concentration detector 13 Control means

Claims (5)

N2Oを含有する排ガスにメタンを添加し、N2O分解触媒を用いてN2Oを還元除去する排ガス中のN2O除去方法であって、N2O分解触媒を通過後のN2O濃度及びメタン濃度を測定し、これらの測定値に応じて、メタンによる温室効果とN 2 Oによる温室効果との和が極小になるようにメタン添加量を制御することを特徴とする排ガス中のN2O除去方法。 It was added methane gas containing N 2 O, an N 2 O removal method in the exhaust gas to reduce and remove N 2 O using the N 2 O decomposition catalyst, after passing through the N 2 O decomposition catalyst N Exhaust gas characterized by measuring 2 O concentration and methane concentration and controlling the amount of methane added so that the sum of the greenhouse effect due to methane and the greenhouse effect due to N 2 O is minimized according to these measured values N 2 O removal method. メタン添加量は、N2O分解触媒の出口側の排ガスについて、温室効果ガス指数＝（メタン排出量×２１）＋（N2O排出量×３１０）の式によって定義される温室効果ガス指数を減少させるように制御されることを特徴とする請求項１記載の排ガス中のN2O除去方法。 The amount of methane added is the greenhouse gas index defined by the equation of greenhouse gas index = (methane emissions × 21) + (N 2 O emissions × 310) for the exhaust gas on the outlet side of the N 2 O decomposition catalyst. 2. The method for removing N 2 O in exhaust gas according to claim 1, wherein the method is controlled so as to decrease. N2O分解触媒として、鉄−ゼオライト系触媒を使用することを特徴とする請求項１記載の排ガス中のN2O除去方法。 The method for removing N 2 O in exhaust gas according to claim 1, wherein an iron-zeolite-based catalyst is used as the N 2 O decomposition catalyst. N2O分解触媒として、アルミナまたはゼオライト担体に貴金属を担持させた触媒を使用することを特徴とする請求項１記載の排ガス中のN2O除去方法。 The method for removing N 2 O in exhaust gas according to claim 1, wherein a catalyst in which a noble metal is supported on alumina or a zeolite carrier is used as the N 2 O decomposition catalyst. 排ガスが下水汚泥焼却炉の排ガスであることを特徴とする請求項１記載の排ガス中のN2O除去方法。 The method for removing N 2 O in exhaust gas according to claim 1, wherein the exhaust gas is exhaust gas from a sewage sludge incinerator.
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