JP4804640B2

JP4804640B2 - Exhaust gas treatment method

Info

Publication number: JP4804640B2
Application number: JP2001112202A
Authority: JP
Inventors: 幸介山下; 智昭田中
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2001-04-11
Filing date: 2001-04-11
Publication date: 2011-11-02
Anticipated expiration: 2021-04-11
Also published as: JP2002310573A

Description

【０００１】
【発明の属する技術分野】
高炉・電気炉・転炉等の精錬炉により製造された炭素を含有した粗溶湯を真空下において精錬する工程において、精錬炉から発生する排ガスを処理する方法に関する。
【０００２】
【従来の技術】
真空精錬炉においては、通常精錬炉で発生する排ガスを１段の冷却装置にて冷却し、集塵・真空排気装置に流す。また、排ガスの熱容量が大きい場合等は、１段の冷却装置８を図２に示す如く大型化（即ち冷却能力を大きく）し、冷却装置後の排ガス温度の低減を図っているが、冷却装置の圧力損失も大きくなるため、冷却装置前後のダクトにバイパスダクトを設置している例が見られる（特開平６−１７１１５号公報、特開２０００−２２７２８４号公報）。即ち、図３に示すように、精錬工程の前半で必要真空度が低く排ガス処理流量の大きい場合は、バイパスダクト７のダンパー９を閉じるか開度を小さくし、主に冷却装置８に排ガスを流す。精錬工程の後半で必要真空度が高く排ガス流量が小さくなると、バイパスダクト７のダンパー９の開度を大きくし、バイパスダクトに多くの排ガスを流して、冷却装置８の圧力損失を小さくする。
【０００３】
【発明が解決しようとする課題】
排ガス中のダスト濃度の増加、高温化・流量の増加といった、より排ガス処理システムにとって負荷の高い条件となると、従来の様に冷却装置の前より直接排ガスをバイパスさせる方法では下記の問題が判明した。即ち、ダストがバイパスダクト内に堆積し、流路を閉塞させる。ダストがバイパスダクト合流後に設置された集塵機５・真空排気装置６へ多量に流入し、ダスト負荷の増加をもたらす。高温排ガスに曝されるバイパスダクトは、温度負荷の耐熱対策として耐火物被覆或いは水冷化が必要であり、また流量を制御するダンパーは水冷化等の耐熱対策が同様に必要となり、初期設備投資の増加及びメンテナンスコストの増大といった課題が発生する。こうした問題を回避しようとすると、バイパスダクトに流入させる排ガスは、充分に温度・流量が低下し、ダスト濃度も低いレベルになってから増加せざるを得ない。しかしながら、これでは、排ガスの高流量時の根本的な圧損低減対策となり得ない。
【０００４】
本発明は、溶湯を真空精錬するプロセスにおいて、排ガス処理装置内の圧力損失を低くし、精錬炉内の真空度を高位に維持することによって、精錬時間が短縮によるエネルギー・用役原単位の削減、及び鉄・クロム等の有価元素の酸化ロスの減少、耐火物寿命の向上、生産能率の上昇等を図ることを課題とする。
【０００５】
【課題を解決するための手段】
上記課題を達成するための本発明の要旨は次の通りである。
（１）溶湯の真空脱ガス装置から発生する排ガスを２段以上の冷却装置にて冷却し、
１段目の冷却装置を煙管式に比べて圧損の低い水管式とし、２段目の冷却装置を水管式に比べて高い冷却能を有する煙管式とし、
且つ１段目と２段目の冷却装置問のダクトからバイパスダクトを分岐し、最終段の冷却装置の後方で集塵機前のダクトに接続し、
前記バイパスダクトに開閉弁或いは流量調節弁を設置し、
２段目の冷却装置後の温度、精錬炉内の真空度、或いは該温度と真空度の両方に基づき前記開閉弁又は流量調節弁の開度を制御して、
前記真空度が２００〜３５０Ｔｏｒｒの精錬初期から中期に比べて、前記真空度が３０〜５０Ｔｏｒｒの精錬中期から末期の前記開閉弁或いは流量調節弁の開度を大きくして、
前記集塵機前で、排ガスの上限温度を前記集塵機の許容温度である１２０〜１４０℃とする、
ことを特徴とする排ガス処理方法。
【０００６】
【発明の実施の形態】
本発明は、精錬初期から中期において、高温・高濃度ダスト・高流量の排ガスを低真空で処理しつつ、精錬中期から末期においては、低温・低濃度ダスト・低流量の排ガスを高真空で処理するための方法である。
【０００７】
以下本発明の実施例を示す図１を用いて説明する。真空精錬炉１から出た排ガス１１は、ダクト２を通って、１段目の排ガス冷却装置３に入り冷却及び粗粒ダストが除塵される。更に、２段目の排ガス冷却装置４に入り冷却及び除塵される。充分に冷却された排ガス１１は乾式集塵機５によって除塵されて真空排気装置６で吸引されて系外に放出される。ここで、１段目と２段目の排ガス冷却装置の間の排気ダクト２からバイパスダクト７を分岐して、集塵機前の排気ダクト２に合流させる。バイパスダクト７内に開閉弁或いは流量調節弁９を設け、精錬炉１内の真空度計１３及び集塵機前の排気ダクトに設けた温度計１４の検出装置から得られたデータを基に、制御装置１５で演算を行い、開閉弁或いは流量調節弁（可動ダンパー）９を調節する。
【０００８】
なお、上記したバイパス経路は、集塵機前に合流させても良いし、集塵機後のダクトに繋ぎ込んでも良い。また、開閉弁或いは流量調節弁９は、図示の如くバイパス経路中と２段目の冷却装置後或いは集塵機後にも設置して両者を連動させて流量を制御しても良い。
【０００９】
真空精錬の初期から中期において、即ち溶湯中初期Ｃ＝０．４〜０．６重量％の溶鋼を真空下で吹酸脱炭処理する場合、排ガス流量及びダスト発生量は大きく且つ排ガス温度も高い。このため精錬炉内真空度は２００〜３５０Torr程度あるが、排ガス冷却装置及び集塵装置の圧力損失は各々５〜１５Torr程度あり、相対的に小さい圧力なので真空精錬上特に問題とならない。しかし、中期〜末期において、即ち溶湯Ｃ＝０．０１〜０．０５重量％の溶鋼を真空処理する場合、排ガス流量・ダスト発生量及び排ガス温度は低下し、真空度は精錬炉内に吹き込まれる攪拌用の不活性ガスの流量に依存した値となり、例えばＡＯＤ炉の場合３０〜５０Torrとなる。また、取鍋精錬における真空処理の様に攪拌ガスが少ない場合、真空度は更に高くなり溶湯中Ｃは０．０１％以下のレベルにまで処理され、排ガス流量・ダスト発生量及び排ガス温度は更に大きく低下し、真空度も数Torr以下の高真空となる。この様に中期から末期においては高真空処理となるため、煙管式の排ガス冷却装置及び乾式集塵機の圧力損失は精錬処理上大きな問題となる。そこで、従来は中期から末期にかけてバイパスダクトを設置し、煙管式の排ガス冷却装置及び乾式集塵機の圧力損失を回避していた。
【００１０】
しかし、ダスト発生及び排ガス流量の大きな真空排気処理においては、前述の問題は発生して有効にバイパスダクトを利用できなかった。そこで、本発明による装置構成及び処理方法によりこの課題を解決することができたのである。
本発明では、大流量・高温排ガスを１段目の冷却装置で処理するため、排ガス温度は低下してバイパスダクト内の熱負荷は大幅に緩和される。また、１段目の冷却装置はダスト除去の効果も持つため、バイパスダクト内のダスト詰まり、開閉弁或いは流量調整弁へのダスト付着が減少する。特に、除去されるダストは主に粗粒のダストであるため、ダストの詰まり・付着防止効果は更に大きくなる。
【００１１】
バイパスダクトに流す排ガス流量及びタイミングは、操業上必要とされる精錬炉内真空度及び設備保護上必要とされる乾式集塵機の耐熱温度を考慮した排ガス温度をパラメータとして決められる。よって、真空精錬の中期〜末期において、炉内真空度計１３及び排ガス温度計１４の検出値を制御装置１５に取り入れ、あらかじめセットされた必要真空度及び許容上限温度を計算しながら、開閉弁或いは流量調整弁９を制御する。バイパスダクトの流量制御弁を開く場合、２段目の冷却装置後の流量制御弁を全開のまま、全閉、或いは中間の開度としても良い。これらの排ガス流量調節弁の開度は、必要炉内真空度と実績炉内真空度、集塵機前許容上限温度と実績温度の相対的なバランスから決定される。
【００１２】
排ガス冷却装置の型式により冷却能力と圧力損失が異なる。その詳細な構造により多少の相違はあるが、一般的に煙管式の冷却装置は同一体積に対して冷却能力が大きいが圧力損失も大きい。一方、水管式の冷却装置は冷却能力はやや小さいが圧力損失も小さい。従来は図２の様に、大流量の排ガスを冷却する場合、８００〜１０００℃から乾式集塵機５の一般的な許容温度である１２０〜１４０℃へと１段の大型煙管式冷却装置８で冷却する必要があった。しかし、この場合極めて大きな圧力損失が生じ、操業上問題となっていた。本発明では、前述の目的で２段に冷却装置を設け、更に１段目は、圧力損失の小さい水管式の冷却装置とした。これによって、１段目以降のバイパスダクトによる圧力損失低減効果と１段目の冷却装置そのものの圧力損失の減少が図れる。
【００１３】
また、１段目の冷却装置３において、水管に蒸気・空気・窒素等の噴射媒体を吹き付け、水管上に付着したダクトを払い落とすダストブロアー１０を設置した。これにより、水管表面を常にダストフリーな状態とすることができ、冷却能力の維持、及び圧力損失の増加防止を図ることが可能となる。ダストブロアー１０は水管の前面・後面・中間位置或いはこれらの組合せ等必要に応じた組合せ配置とすることができる。
【００１４】
【実施例】
表１はＡＯＤにて真空精錬を行った場合の操業条件を示す表で、本発明の実施例を従来方式の比較例と共に示す。本発明のプロセス構成は、２段の排ガス冷却装置とし、１段目を水管式、２段目を煙管式とした。真空風ポンプとエジェクターを組み合わせた真空排気装置の前段にバグフィルター方式の乾式集塵機を設置し、真空排気装置の冷却水のダストによる汚濁を防止した。１段目と２段目の間の排気ダクトからバイパスダクトを集塵機の前に繋ぎ込み、そのダクト途中に開度制御可能なダンパ−を設置した。１段目の排ガス冷却装置の前後にダストブロアーを設置し、真空処理の合間に水管のダストを除去することとした。一方、従来方式の比較例としてのプロセス構成は、集塵機と真空排気装置は本発明と同様であるが、冷却装置は１段の大型の煙管式とし、その前後にバイパスダクトを配置した例（図３に示す例）を示す。
【００１５】
【表１】

【００１６】
表１に示すように、精錬前半〜中期においては、両者はほぼ同様な操業条件である。但し、本発明では、１段目の冷却装置によって排ガス温度が低減されるため、バイパスダクトのダンパーを開け約３０％程度の排ガスをバイパスさせることができた。しかし比較例では、バイパスを使用すると高温の排ガスが流れるため集塵機前の温度が急激に上昇し、全くバイパスには流せなかった。この期間での真空度の冶金精錬効果への影響は前述したように大差はなかったが、比較例では冷却装置の煙管内へのダスト付着が増大したのに対し、本発明の冷却装置へのダスト付着は、１段目と２段目に付着が分散されていたと同時に、２段目の冷却装置の煙管内のダスト付着は排ガスが一部バイパスダクトに流れたため比較的軽微なものとなった。
【００１７】
精錬後期においては、排ガス流量・温度が大きく低減するため、両者ともバイパスダクトの使用が可能となる。しかし、本発明では、１段目の冷却装置によって排ガス温度が更に低減するため、バイパスダクトに流す排ガス流量を約７０％まで大幅に増加することができたのに対し、比較例では、精錬炉からの排ガス温度はまだ高いため、集塵機前での排ガス温度制約からバイパスダクトに大量に排ガスを流すことができず約３０％が限度であった。また、こうした操業を継続していると冷却装置自体が、本発明では１段目の冷却装置が毎ヒートダストブロアーでダスト除去され、且つ２段目の冷却装置も排ガスのバイパス比率が高いため、冷却装置本体の圧力損失が小さく抑制される。また、バイパス比率が高いためダクトを含めたシステム全体の圧力損失も小さくなる。これに対して比較例では、冷却装置本体及びシステム全体の圧力損失が大きくなり、結局表１に現れるような精錬炉内の真空度の差となった。
両者の真空度の差は、排ガス冷却装置の使用回数が増えれば増えるほど大きくなる。これは冷却装置の煙管内或いは水管表面に付着するダストの堆積量に大きな差があり、ヒート数が増えると更に差が増してゆくためである。
【００１８】
【発明の効果】
以上述べたように排ガス冷却装置を２段とし、２段目の前後にバイパスダクトを設置することにより、高い真空度を維持することができるようになった。この真空度の差により、本発明は脱炭効率が高くなり、精錬時間が短縮によるエネルギー・用役原単位の削減、及び鉄・クロム等の有価元素の酸化ロスの減少、耐火物寿命の向上、生産能率の上昇等多大なメリットがもたらされた。
【図面の簡単な説明】
【図１】本発明の実施例を示す排ガス処理設備のフローシートである。
【図２】従来装置１を示すフローシートである。
【図３】従来装置２を示すフローシートである。
【符号の説明】
１真空精錬炉２排気ダクト
３水管式ガス冷却装置４煙管式ガス冷却装置
５乾式集塵機６真空排気装置
７バイパス排気ダクト８大型煙管式ガス冷却装置
９開閉弁或いは流量調整弁１０ダストブロアー
１１排気ガス１２冷却水
１３真空度計１４温度計
１５制御装置[0001]
BACKGROUND OF THE INVENTION
The crude melt containing the produced carbon by refining furnace such as a blast furnace, electric furnace, converter furnace in the process of refining in a vacuum, about how that processes the exhaust gas generated from the smelting furnace.
[0002]
[Prior art]
In a vacuum smelting furnace, exhaust gas generated in a normal smelting furnace is cooled by a single-stage cooling device, and flows to a dust collection / evacuation device. In addition, when the heat capacity of the exhaust gas is large, the one-stage cooling device 8 is enlarged as shown in FIG. 2 (that is, the cooling capacity is increased) to reduce the exhaust gas temperature after the cooling device. Since the pressure loss also increases, examples in which bypass ducts are installed in the ducts before and after the cooling device are seen (Japanese Patent Laid-Open Nos. 6-17115 and 2000-227284). That is, as shown in FIG. 3, when the required vacuum is low and the exhaust gas treatment flow rate is large in the first half of the refining process, the damper 9 of the bypass duct 7 is closed or the opening degree is reduced, and the exhaust gas is mainly supplied to the cooling device 8. Shed. When the required degree of vacuum is high and the exhaust gas flow rate is reduced in the second half of the refining process, the opening degree of the damper 9 of the bypass duct 7 is increased, a large amount of exhaust gas is caused to flow through the bypass duct, and the pressure loss of the cooling device 8 is reduced.
[0003]
[Problems to be solved by the invention]
When the conditions are higher for the exhaust gas treatment system, such as increasing the dust concentration in the exhaust gas, increasing the temperature and increasing the flow rate, the following problems have been found in the conventional method of bypassing the exhaust gas directly before the cooling device as before. . That is, dust accumulates in the bypass duct and closes the flow path. A large amount of dust flows into the dust collector 5 and the vacuum exhaust device 6 installed after joining the bypass duct, resulting in an increase in dust load. Bypass ducts exposed to high-temperature exhaust gas need to be covered with refractory or water-cooled as a heat-resistant measure against temperature load, and dampers that control the flow rate require heat-resistant measures such as water-cooling as well. Problems such as an increase and an increase in maintenance costs occur. In order to avoid such a problem, the exhaust gas flowing into the bypass duct must be increased after the temperature and flow rate have sufficiently decreased and the dust concentration has reached a low level. However, this cannot be a fundamental measure for reducing pressure loss at a high flow rate of exhaust gas.
[0004]
In the process of vacuum refining of molten metal, the present invention reduces the energy and utility unit by reducing the refining time by reducing the pressure loss in the exhaust gas treatment device and maintaining the vacuum in the refining furnace at a high level. And reduction of oxidation loss of valuable elements such as iron and chromium, improvement of refractory life, increase of production efficiency, and the like.
[0005]
[Means for Solving the Problems]
The gist of the present invention for achieving the above object is as follows.
(1) Cool the exhaust gas generated from the vacuum degassing device of the molten metal with a cooling device of two or more stages,
The first-stage cooling device is a water tube type having a lower pressure loss than the smoke tube type, and the second-stage cooling device is a smoke tube type having a higher cooling capacity than the water tube type,
And the bypass duct is branched from the ducts of the first and second stage cooling devices, and connected to the duct before the dust collector behind the last stage cooling device,
Install an on-off valve or flow control valve in the bypass duct,
Based on the temperature after the second stage cooling device, the degree of vacuum in the refining furnace, or both the temperature and degree of vacuum, the opening degree of the on-off valve or the flow control valve is controlled,
The opening degree of the on-off valve or the flow control valve is increased from the middle to the last stage of refining at a vacuum level of 30 to 50 Torr compared to the middle and last stage of the refining at a vacuum degree of 200 to 350 Torr,
Before the dust collector, the upper limit temperature of the exhaust gas is 120 to 140 ° C. which is the allowable temperature of the dust collector ,
An exhaust gas treatment method characterized by that.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The present invention treats high-temperature, high-concentration dust and high-flow exhaust gas at low vacuum from the beginning to the middle of refining, and treats low-temperature, low-concentration dust and low-flow exhaust gas at high vacuum from the middle to the end of refining. it is a way for.
[0007]
Hereinafter, an embodiment of the present invention will be described with reference to FIG. The exhaust gas 11 emitted from the vacuum refining furnace 1 passes through the duct 2 and enters the first-stage exhaust gas cooling device 3 to cool and remove coarse dust. Furthermore, it enters into the second stage exhaust gas cooling device 4 and is cooled and dedusted. The exhaust gas 11 that has been sufficiently cooled is removed by the dry dust collector 5, sucked by the vacuum exhaust device 6, and discharged outside the system. Here, the bypass duct 7 is branched from the exhaust duct 2 between the first-stage and second-stage exhaust gas cooling devices, and is joined to the exhaust duct 2 in front of the dust collector. On-off valve or flow control valve 9 is provided in the bypass duct 7, and the control device is based on the data obtained from the vacuum gauge 13 in the refining furnace 1 and the thermometer 14 detection device provided in the exhaust duct before the dust collector. The calculation is performed at 15 to adjust the on-off valve or the flow control valve (movable damper) 9.
[0008]
The bypass path described above may be merged before the dust collector, or may be connected to a duct after the dust collector. Further, as shown in the figure, the on-off valve or the flow rate adjusting valve 9 may be installed in the bypass path and after the second stage cooling device or after the dust collector, and the flow rate may be controlled by linking them together.
[0009]
From the initial to the middle of vacuum refining, that is, when blown acid decarburization treatment of molten steel with initial C = 0.4 to 0.6% by weight in the melt is performed under vacuum, the exhaust gas flow rate and dust generation amount are large and the exhaust gas temperature is also high. . For this reason, the degree of vacuum in the refining furnace is about 200 to 350 Torr, but the pressure loss of the exhaust gas cooling device and the dust collector is about 5 to 15 Torr, respectively. However, in the middle to the end, that is, when the molten steel of molten metal C = 0.01 to 0.05% by weight is vacuum-treated, the exhaust gas flow rate / dust generation amount and exhaust gas temperature are lowered, and the degree of vacuum is blown into the refining furnace. The value depends on the flow rate of the inert gas for stirring, and is, for example, 30 to 50 Torr in the case of an AOD furnace. In addition, when the amount of agitation gas is small as in vacuum treatment in ladle refining, the degree of vacuum is further increased and C in the molten metal is processed to a level of 0.01% or less, and the exhaust gas flow rate / dust generation amount and exhaust gas temperature are further increased. It is greatly reduced, and the degree of vacuum becomes a high vacuum of several Torr or less. As described above, since high vacuum processing is performed from the middle to the final stage, the pressure loss of the flue gas exhaust gas cooling device and the dry dust collector is a serious problem in the refining process. Therefore, conventionally, bypass ducts were installed from the middle to the end to avoid pressure loss of the flue gas type exhaust gas cooling device and the dry dust collector.
[0010]
However, in the vacuum evacuation process in which dust is generated and the exhaust gas flow rate is large, the above-mentioned problems occur and the bypass duct cannot be used effectively. Therefore, this problem can be solved by the apparatus configuration and processing method according to the present invention.
In the present invention, since the large flow rate / high temperature exhaust gas is processed by the first stage cooling device, the exhaust gas temperature is lowered, and the heat load in the bypass duct is greatly reduced. In addition, since the first stage cooling device also has an effect of dust removal, dust clogging in the bypass duct and adhesion of dust to the on-off valve or flow rate adjusting valve are reduced. In particular, since the dust to be removed is mainly coarse dust, the effect of preventing dust clogging and adhesion is further increased.
[0011]
The flow rate and timing of the exhaust gas flowing through the bypass duct are determined using the exhaust gas temperature in consideration of the vacuum level in the refining furnace required for operation and the heat resistance temperature of the dry dust collector required for equipment protection. Therefore, in the middle to the last stage of vacuum refining, the detected values of the in-furnace vacuum gauge 13 and the exhaust gas thermometer 14 are taken into the control device 15 to calculate the required vacuum degree and the allowable upper limit temperature set in advance. The flow regulating valve 9 is controlled. When the flow control valve of the bypass duct is opened, the flow control valve after the second-stage cooling device may be fully opened, or may be fully closed or an intermediate opening degree. The opening degree of these exhaust gas flow rate control valves is determined from the relative balance of the required in-furnace vacuum degree and the actual furnace vacuum degree, the allowable upper limit temperature before the dust collector and the actual temperature.
[0012]
The cooling capacity and pressure loss differ depending on the type of exhaust gas cooling system. Although there are some differences depending on the detailed structure, generally a flue-tube type cooling device has a large cooling capacity but a large pressure loss with respect to the same volume. On the other hand, the water tube type cooling device has a small cooling capacity but a small pressure loss. Conventionally, as shown in FIG. 2, when cooling a large amount of exhaust gas, it is cooled from 800 to 1000 ° C. to 120 to 140 ° C., which is a general allowable temperature of the dry dust collector 5, by a single large smoke tube type cooling device 8. There was a need to do. However, in this case, an extremely large pressure loss occurred, which was an operational problem. In the present invention, a cooling device is provided in two stages for the above-mentioned purpose, and the first stage is a water tube type cooling device with a small pressure loss. Thereby, the pressure loss reduction effect by the bypass duct after the first stage and the pressure loss of the first stage cooling device itself can be reduced.
[0013]
Further, in the first-stage cooling device 3, a dust blower 10 was installed that sprayed an injection medium such as steam, air, and nitrogen on the water pipe and wiped off the duct adhering to the water pipe. As a result, the surface of the water tube can always be in a dust-free state, and it is possible to maintain the cooling capacity and prevent an increase in pressure loss. The dust blower 10 can be arranged in combination such as the front surface, the rear surface, the intermediate position of the water pipe, or a combination thereof as required.
[0014]
【Example】
Table 1 shows the operating conditions when vacuum refining is performed with AOD, and examples of the present invention are shown together with comparative examples of conventional systems. The process configuration of the present invention was a two-stage exhaust gas cooling device, the first stage being a water pipe type and the second stage being a smoke pipe type. A bag filter type dry dust collector was installed in front of the vacuum exhaust system that combined the vacuum air pump and ejector to prevent contamination of the vacuum exhaust system by cooling water dust. A bypass duct was connected in front of the dust collector from the exhaust duct between the first stage and the second stage, and a damper whose opening degree could be controlled was installed in the middle of the duct. A dust blower was installed before and after the first stage exhaust gas cooling device, and dust in the water pipe was removed between vacuum treatments. On the other hand, the process configuration as a comparative example of the conventional method is the same as that of the present invention in the dust collector and the vacuum exhaust device, but the cooling device is a one-stage large smoke tube type, and an example in which bypass ducts are arranged before and after (see FIG. 3).
[0015]
[Table 1]

[0016]
As shown in Table 1, in the first half to the middle of the refining, both have substantially the same operating conditions. However, in the present invention, since the exhaust gas temperature is reduced by the first-stage cooling device, the damper of the bypass duct can be opened and about 30% of the exhaust gas can be bypassed. However, in the comparative example, when the bypass was used, high temperature exhaust gas flowed, so the temperature in front of the dust collector rose rapidly and could not flow through the bypass at all. The influence of the degree of vacuum on the metallurgical refining effect during this period was not much different as described above, but in the comparative example, dust adhesion in the smoke pipe of the cooling device increased, whereas the effect on the cooling device of the present invention was increased. At the same time as dust adhesion was dispersed at the first and second stages, dust adhesion in the smoke pipe of the second stage cooling device was relatively minor because some exhaust gas flowed into the bypass duct. .
[0017]
In the latter stage of refining, since the exhaust gas flow rate and temperature are greatly reduced, both can use a bypass duct. However, in the present invention, since the exhaust gas temperature is further reduced by the first-stage cooling device, the exhaust gas flow rate flowing through the bypass duct can be significantly increased to about 70%, whereas in the comparative example, the refining furnace Since the exhaust gas temperature from the exhaust gas was still high, the exhaust gas could not flow in large quantities through the bypass duct due to the exhaust gas temperature restriction in front of the dust collector, and the limit was about 30%. In addition, if such operation is continued, the cooling device itself, in the present invention, the first-stage cooling device is dust-removed by each heat dust blower, and the second-stage cooling device also has a high exhaust gas bypass ratio, The pressure loss of the cooling device body is suppressed to a small level. Moreover, since the bypass ratio is high, the pressure loss of the entire system including the duct is also reduced. On the other hand, in the comparative example, the pressure loss of the cooling device main body and the entire system became large, resulting in a difference in the degree of vacuum in the refining furnace as shown in Table 1 after all.
The difference in the degree of vacuum between the two increases as the number of uses of the exhaust gas cooling device increases. This is because there is a large difference in the amount of dust deposited on the smoke pipe of the cooling device or on the surface of the water pipe, and the difference further increases as the number of heat increases.
[0018]
【The invention's effect】
As described above, the exhaust gas cooling device has two stages, and by installing bypass ducts before and after the second stage, a high degree of vacuum can be maintained. Due to this difference in the degree of vacuum, the present invention increases the decarburization efficiency, reduces the energy and utility intensity by shortening the refining time, reduces the oxidation loss of valuable elements such as iron and chromium, and improves the refractory life There were many advantages such as increased production efficiency.
[Brief description of the drawings]
FIG. 1 is a flow sheet of an exhaust gas treatment facility showing an embodiment of the present invention.
FIG. 2 is a flow sheet showing a conventional apparatus 1;
FIG. 3 is a flow sheet showing a conventional apparatus 2;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Vacuum refining furnace 2 Exhaust duct 3 Water pipe type gas cooling device 4 Smoke pipe type gas cooling device 5 Dry type dust collector 6 Vacuum exhaust device 7 Bypass exhaust duct 8 Large smoke pipe type gas cooling device 9 On-off valve or flow control valve 10 Dust blower 11 Exhaust gas 12 Cooling water 13 Vacuum gauge 14 Thermometer 15 Controller

Claims

The exhaust gas generated from the vacuum degassing device of the molten metal is cooled by two or more stages of cooling devices,
The first-stage cooling device is a water tube type having a lower pressure loss than the smoke tube type, and the second-stage cooling device is a smoke tube type having a higher cooling capacity than the water tube type,
And the bypass duct is branched from the ducts of the first and second stage cooling devices, and connected to the duct before the dust collector behind the last stage cooling device,
Install an on-off valve or flow control valve in the bypass duct,
Based on the temperature after the second stage cooling device, the degree of vacuum in the refining furnace, or both the temperature and degree of vacuum, the opening degree of the on-off valve or the flow control valve is controlled,
The opening degree of the on-off valve or the flow control valve is increased from the middle to the last stage of refining at a vacuum level of 30 to 50 Torr compared to the middle and last stage of the refining at a vacuum degree of 200 to 350 Torr,
Before the dust collector, the upper limit temperature of the exhaust gas is 120 to 140 ° C. which is the allowable temperature of the dust collector ,
An exhaust gas treatment method characterized by that.