JP2004255324A

JP2004255324A - Flue gas denitrification apparatus

Info

Publication number: JP2004255324A
Application number: JP2003050432A
Authority: JP
Inventors: Satoshi Shishido; 聡宍戸; Toshimichi Wada; 敏通和田
Original assignee: Babcock Hitachi KK
Current assignee: Mitsubishi Power Ltd
Priority date: 2003-02-27
Filing date: 2003-02-27
Publication date: 2004-09-16

Abstract

<P>PROBLEM TO BE SOLVED: To provide a denitrification apparatus having a duct structure which does not form a low flow velocity region on the inlet duct side of a honeycomb outlet and makes the flow velocity distribution on the inlet of a denitrification catalyst layer as uniform as possible. <P>SOLUTION: This denitrification apparatus is constituted so that an inlet duct into which exhaust gas flows is vertically connected with a catalyst duct in which the denitration catalyst is arranged, on a bend part. Therein, the inlet duct is constituted so that the flow velocity distribution of the exhaust gas in the inlet duct satisfies the following relation (1) on the basis of the distance from an inlet duct bottom surface part: VL > VAVL (1), wherein, VL is the average flow velocity (m/s) within the range of 5% of duct height from the duct bottom surface part and VA is duct average flow velocity (m/s). <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【０００１】
【発明の属する技術分野】
本発明は排煙脱硝装置に係り、特に脱硝装置入口ダクト構造に特徴を有する排煙脱硝装置に関するものである。
【０００２】
【従来の技術】
ボイラ等の燃焼装置から排出される排ガス中の窒素酸化物（ＮＯｘ）を除去する装置の一つとして、排ガス流中に脱硝触媒層を配置する排煙脱硝装置が主として火力発電所用の大型ボイラ等に設置されている。図４は、従来の脱硝装置の構成を示す説明図である。この装置は、排ガスが流入する入口ダクト１と脱硝触媒を配置した触媒ダクト６とを、ベンド部２で直交するように接続し、ベンド部外側ケーシングを、ベンド部出口ダクトと入口ダクトの床面の延長線の交点Ｘと、ベンド部出口ダクトの延長線と入口ダクトの天井部との交点Ｙの間に差し渡すように配置し、かつ触媒ダクト内の整流格子の配置位置を、その排ガス流入面が入口ダクト床面とほぼ同一となるように構成したものである。ボイラ等の燃焼装置を出た排ガスＧは、入口ダクト１を経て、アンモニアのような還元剤混入装置（図示省略）から還元剤を混入された後、排ガスダクトの途中に形成したベンド部２に至り、その流れを９０度変更して下降し、触媒ダクト６の触媒層４に流入して脱硝されたのち出口ダクト５に至る。この種の脱硝装置において、特に石炭焚きボイラ等では、ダクトおよび触媒層の灰堆積が問題になるが、灰堆積は、触媒層上の偏流や脱硝装置の圧損上昇を引き起こし、脱硝触媒の劣化及びプラントの運転に影響を与える。そこで入口ダクト内にダストの堆積がなく、脱硝触媒入口における流速分布が均一となるダクト構造が望まれていた。
【０００３】
【特許文献１】特開平０１−１２７０２９号公報
【０００４】
【発明が解決しようとする課題】
上記従来技術においていては、触媒層上の流れの均質化は不充分であり、特に触媒層上での整流格子の上面位置が入口ダクト１と一致しているため、慣性力により入口ダクト側部分に排ガスが触媒層ダクトに流入しにくく、触媒層上で低流速域を生じさせ、入口ダクト１の底面や、触媒層上に灰の堆積を生じるという問題があった。
【０００５】
本発明の課題は、上記従来技術の欠点を解消し、整流格子出口の入口ダクト側に低流速領域を生じることなく、脱硝触媒層入口の流速分布が可及的に均一になるようなダクト構造を有する脱硝装置を提供することにある。
【０００６】
【課題を解決するための手段】
上記課題を解決するため、本願で特許請求される発明は下記のとおりである。
（１）排ガスが流入する入口ダクトと脱硝触媒を配置した触媒ダクトとを、ベンド部で直交するように接続することにより構成された脱硝装置において、前記入口ダクト内の排ガスの流速分布が、該入口ダクト底面部からの距離をもとに下記数式１を満足するように入口ダクトを構成したことを特徴とする排煙脱硝装
置。
【数式１】
ＶＬ＞ＶＡ
ＶＬ；ダクト底面部からのダクト高さの５％の範囲内の排ガスの平均流速（ｍ／ｓ）
ＶＡ；ダクト内の排ガスの平均流速（ｍ／ｓ）
（２）前記入口ダクトの流速分布を達成するように、該入口ダクト内に抵抗体を設置したことを特徴とする（１）記載の排煙脱硝装置。
（３）前記抵抗体が多孔板、円管または整流板である（２）記載の排煙脱硝装置。
【０００７】
本発明においては、図１に示すように、ダクト１の底面部からの高さ方向の距離が入口ダクト高さの５％の範囲において、その範囲の排ガスの平均流速Ｈが入口ダクト内の排ガス平均流速より高くなるようにダクトを構成する。そのようにダクトを構成するには、例えば図２に示すように、ダクト１内の底面部に近接する部分を除き排ガス流路断面に多孔板９を設ける。そうすることにより、入口ダクト底面部のガス流量が増加し、この入口ダクト底面部の流量増加は、触媒層４上の入口ダクト側部分の排ガス流入流量の増加となるので、従来技術において課題となっていた触媒層上の低流域の発生を防止することができ、同時に、入口ダクト底面部の灰の堆積も防止できる。図３は、図２の実施例において、整流格子３の構造を入口ダクト端部からベンド部端部Ｘに向けて徐々に高くした場合の実施例を示す図である。この実施例によれば、触媒層上の偏流を防止し、流速分布をより均一にすることができる。
【０００８】
【発明の実施の形態】
以下、本発明を実施例により具体的に説明する。
実施例１、２および比較例１、２
図１に示した基本ダクト構造を有する試験装置を用い、入口ダクト１に設置する多孔板９の大きさおよび設置位置を変化させ、触媒層４の直上の流速分布を測定し、偏流の有無とダクトへのダスト堆積状況を調べた。その結果を表１に示す。表中、実施例１は、入口ダクト１の底面部流速が平均流速より高い場合、比較例１および２は、同底面部流速が平均流速よりそれぞれ低い場合および同じ場合である。
【０００９】
【表１】

【００１０】
ここでＶＬは入口ダクト底面部からダクト高さの５％の範囲における平均流速。ＶＡは入口ダクト平均流速である。ξは流速変動係数で、流速分布のばらつき度合いを表すものであり、数式２で定義される。
【００１１】
【数式２】
ξ＝σ／Ｖａ ×１００（σ：標準偏差、Ｖａ：平均流速）
比較例１では、入口ダクト１および触媒層６上で灰の堆積１０および触媒層上の偏流が確認された。比較例２では、灰堆積はみられなかったものの、触媒層上の偏流が確認された。これに対し、実施例１では、灰の堆積および触媒層上の偏流がみられず、流速分布が最も均一であることが確認された。
実施例２
図３に示すように、整流格子３の構造を入口ダクト側の端部からベンド部端部Ｘに向けて徐々に高くした以外は実施例１と同様にした。この整流格子の構造は特開２００２−３９５２４で提案されている。この実施例によれば、流速変動係数（ξ）が７％に向上した以外は実施例１と同様であった。
【００１２】
【発明の効果】
請求項に記載の本発明によれば、入口ダクト底面部のガス流速をダクト全体の平均流速より速くすることにより、触媒層４に対して可及的に均一に排ガスが流入し、これにより触媒層４の排ガス接触面積が有効に利用され、触媒全体の性能を高めることができる。
【００１３】
また触媒層４に形成されるガス流路と、触媒層４に入る直前の排ガスの流れが可及的に一致していることにより、例えば排ガス流中にフライアッシュ、未燃分等のダストを含有する場合、触媒にこのダストが衝突して触媒を摩耗させ、また先端部にこのダストが付着堆積して排ガスの流入を阻害することがないので、触媒寿命を長くすることができる。
【００１４】
さらに触媒層４に入る排ガス流れが均一になることにより、脱硝装置入口水平ダクト底面部におけるダストの堆積を防止し、ダストの堆積による偏流や、その偏流による触媒層上での流速の不均一並びに触媒層前流側で注入される還元剤の不均一および触媒層上での灰堆積を防止することができる。
【図面の簡単な説明】
【図１】本発明の構成を示す脱硝装置の説明図。
【図２】本発明の実施例における脱硝装置の説明図。
【図３】本発明の他の実施例における脱硝装置の説明図。
【図４】本発明の比較例を示す従来の脱硝装置の説明図。
【図５】本発明の比較例を示す脱硝装置の説明図。
【図６】従来の脱硝装置を示す説明図。
【符号の説明】
１…入口ダクト、２…ベンド部、３…整流格子、４…触媒層、５…出口ダクト、６…触媒層ダクト、７…入口ダクト流速分布、８…触媒層上流速分布、９…多孔板、１０…灰堆積、１１…還元剤注入装置、Ｇ…排ガス。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a flue gas denitration apparatus, and more particularly to a flue gas denitration apparatus characterized by a duct structure at an entrance of the denitration apparatus.
[0002]
[Prior art]
As one of devices for removing nitrogen oxides (NOx) in exhaust gas discharged from a combustion device such as a boiler, a flue gas denitration device in which a denitration catalyst layer is arranged in an exhaust gas flow is mainly used for a large-scale boiler for a thermal power plant. It is installed in. FIG. 4 is an explanatory diagram showing a configuration of a conventional denitration apparatus. In this apparatus, an inlet duct 1 into which exhaust gas flows and a catalyst duct 6 in which a denitration catalyst is disposed are connected so as to be orthogonal to each other at a bend portion 2, and a bend portion outer casing is connected to a bend portion outlet duct and a floor surface of the inlet duct. And the intersection of the extension line of the bend outlet duct and the intersection Y of the ceiling of the inlet duct, and the position of the rectifying grid in the catalyst duct is determined by the The surface is configured to be substantially the same as the entrance duct floor surface. Exhaust gas G exiting a combustion device such as a boiler passes through an inlet duct 1 and is mixed with a reducing agent from a reducing agent mixing device (not shown) such as ammonia (not shown). Then, the flow is changed by 90 degrees and descends, flows into the catalyst layer 4 of the catalyst duct 6, is denitrated, and then reaches the outlet duct 5. In this type of denitration apparatus, particularly in a coal-fired boiler or the like, ash accumulation in the duct and the catalyst layer poses a problem. Affects plant operation. Therefore, a duct structure that does not accumulate dust in the inlet duct and has a uniform flow velocity distribution at the inlet of the denitration catalyst has been desired.
[0003]
[Patent Document 1] Japanese Patent Application Laid-Open No. 01-127029
[Problems to be solved by the invention]
In the above prior art, the homogenization of the flow on the catalyst layer is insufficient. In particular, since the upper surface position of the rectifying grid on the catalyst layer coincides with the inlet duct 1, the inlet duct side portion is caused by inertial force. However, there is a problem in that the exhaust gas hardly flows into the catalyst layer duct, causing a low flow velocity region on the catalyst layer, and depositing ash on the bottom surface of the inlet duct 1 and on the catalyst layer.
[0005]
An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide a duct structure in which the flow velocity distribution at the entrance of the denitration catalyst layer is made as uniform as possible without generating a low flow velocity area on the inlet duct side of the flow straightening grid outlet. It is to provide a denitration apparatus having the following.
[0006]
[Means for Solving the Problems]
The invention claimed in the present application to solve the above problems is as follows.
(1) In a denitration apparatus configured by connecting an inlet duct into which exhaust gas flows and a catalyst duct in which a denitration catalyst is arranged so as to be orthogonal to each other at a bend portion, the flow velocity distribution of exhaust gas in the inlet duct is A flue gas denitration apparatus characterized in that the inlet duct is configured so as to satisfy the following equation 1 based on the distance from the bottom of the inlet duct.
[Formula 1]
VL> VA
VL; average flow velocity (m / s) of exhaust gas within 5% of the duct height from the bottom of the duct
VA; average flow velocity of exhaust gas in duct (m / s)
(2) The flue gas denitration apparatus according to (1), wherein a resistor is installed in the inlet duct so as to achieve the flow velocity distribution of the inlet duct.
(3) The flue gas denitration apparatus according to (2), wherein the resistor is a perforated plate, a circular tube, or a rectifying plate.
[0007]
In the present invention, as shown in FIG. 1, when the distance in the height direction from the bottom surface of the duct 1 is 5% of the height of the inlet duct, the average flow rate H of the exhaust gas in that range is reduced by the exhaust gas in the inlet duct. Configure the duct to be higher than the average flow velocity. In order to form such a duct, for example, as shown in FIG. 2, a perforated plate 9 is provided in the cross section of the exhaust gas flow path except for a portion near the bottom surface in the duct 1. By doing so, the gas flow rate at the bottom of the inlet duct increases, and the increase in the flow rate at the bottom of the inlet duct increases the flow rate of exhaust gas flowing into the inlet duct side portion on the catalyst layer 4. It is possible to prevent the generation of a low flow area on the catalyst layer, which has been formed, and at the same time, it is possible to prevent the accumulation of ash on the bottom of the inlet duct. FIG. 3 is a view showing an embodiment in which the structure of the flow regulating grid 3 is gradually increased from the end of the inlet duct toward the end X of the bend in the embodiment of FIG. According to this embodiment, the drift on the catalyst layer can be prevented, and the flow velocity distribution can be made more uniform.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described specifically with reference to examples.
Examples 1 and 2 and Comparative Examples 1 and 2
Using the test device having the basic duct structure shown in FIG. 1, the size and position of the perforated plate 9 installed in the inlet duct 1 were changed, and the flow velocity distribution immediately above the catalyst layer 4 was measured. The dust accumulation on the duct was investigated. Table 1 shows the results. In the table, Example 1 is the case where the bottom surface flow velocity of the inlet duct 1 is higher than the average flow velocity, and Comparative Examples 1 and 2 are the cases where the bottom surface flow velocity is lower than the average flow velocity and the same.
[0009]
[Table 1]

[0010]
Here, VL is the average flow velocity in the range of 5% of the duct height from the bottom of the inlet duct. VA is the average inlet duct velocity. ξ denotes a flow velocity variation coefficient, which represents the degree of variation in the flow velocity distribution, and is defined by Expression 2.
[0011]
[Formula 2]
ξ = σ / Va × 100 (σ: standard deviation, Va: average flow velocity)
In Comparative Example 1, ash deposition 10 on the inlet duct 1 and the catalyst layer 6 and drift on the catalyst layer were confirmed. In Comparative Example 2, although ash deposition was not observed, drift on the catalyst layer was confirmed. On the other hand, in Example 1, ash accumulation and drift on the catalyst layer were not observed, and it was confirmed that the flow velocity distribution was the most uniform.
Example 2
As shown in FIG. 3, the structure of the rectifying grid 3 was the same as that of Example 1 except that the structure of the rectifying grid 3 was gradually increased from the end on the inlet duct side to the bend end X. The structure of this rectifying grating has been proposed in JP-A-2002-39524. According to this example, it was the same as Example 1 except that the flow velocity variation coefficient (ξ) was improved to 7%.
[0012]
【The invention's effect】
According to the present invention, the exhaust gas flows into the catalyst layer 4 as uniformly as possible by making the gas flow velocity at the bottom of the inlet duct higher than the average flow velocity of the entire duct, whereby the catalyst The exhaust gas contact area of the layer 4 is effectively used, and the performance of the entire catalyst can be improved.
[0013]
In addition, since the gas flow path formed in the catalyst layer 4 and the flow of the exhaust gas immediately before entering the catalyst layer 4 match as much as possible, for example, dust such as fly ash and unburned matter is contained in the exhaust gas flow. When it is contained, the dust collides with the catalyst and wears the catalyst, and the dust does not adhere to and accumulate on the front end portion, thereby preventing the inflow of exhaust gas, thereby prolonging the life of the catalyst.
[0014]
Further, since the flow of exhaust gas entering the catalyst layer 4 becomes uniform, dust accumulation at the bottom of the horizontal duct at the entrance of the denitration apparatus is prevented, and drift due to dust accumulation and uneven flow velocity on the catalyst layer due to the drift are reduced. Non-uniformity of the reducing agent injected on the upstream side of the catalyst layer and ash accumulation on the catalyst layer can be prevented.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a denitration apparatus showing a configuration of the present invention.
FIG. 2 is an explanatory diagram of a denitration apparatus according to the embodiment of the present invention.
FIG. 3 is an explanatory view of a denitration apparatus according to another embodiment of the present invention.
FIG. 4 is an explanatory view of a conventional denitration apparatus showing a comparative example of the present invention.
FIG. 5 is an explanatory diagram of a denitration apparatus showing a comparative example of the present invention.
FIG. 6 is an explanatory view showing a conventional denitration apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Inlet duct, 2 ... Bend part, 3 ... Rectification grid, 4 ... Catalyst layer, 5 ... Outlet duct, 6 ... Catalyst layer duct, 7 ... Inlet duct flow velocity distribution, 8 ... Catalyst layer flow velocity distribution, 9 ... Perforated plate 10, ash deposition, 11: reducing agent injection device, G: exhaust gas.

Claims

In a denitration apparatus configured by connecting an inlet duct into which exhaust gas flows and a catalyst duct in which a denitration catalyst is arranged so as to be orthogonal to each other at a bend portion, the flow velocity distribution of exhaust gas in the inlet duct is reduced by the bottom surface of the inlet duct. A flue gas denitration apparatus, wherein the inlet duct is configured to satisfy the following equation 1 based on the distance from the section.
[Formula 1]
VL> VA
VL; average flow velocity (m / s) of exhaust gas within 5% of the duct height from the bottom of the duct
VA; average flow velocity of exhaust gas in duct (m / s)

2. The flue gas denitration apparatus according to claim 1, wherein a resistor is provided in the inlet duct so as to achieve the flow velocity distribution of the inlet duct.

3. The flue gas denitration apparatus according to claim 2, wherein the resistor is a perforated plate, a circular tube, or a current plate.