JP4093121B2

JP4093121B2 - Exhaust gas outlet temperature control method and apparatus for temperature reduction tower

Info

Publication number: JP4093121B2
Application number: JP2003163458A
Authority: JP
Inventors: 康雄鶴屋
Original assignee: IHI Corp
Current assignee: IHI Corp
Priority date: 2003-06-09
Filing date: 2003-06-09
Publication date: 2008-06-04
Anticipated expiration: 2023-06-09
Also published as: JP2004361059A

Description

【０００１】
【発明の属する技術分野】
本発明は、ごみ処理施設やセメントプラント等の燃焼炉を有する燃焼設備において、排ガスを所要の設定温度まで減温させるために用いられる減温塔の排ガス出口温度制御方法及び装置に関するものである。
【０００２】
【従来の技術】
ごみ処理施設やセメントプラント等の燃焼炉を有する燃焼設備において、ダストを含んだ排ガスの温度を減温する方法としては、排ガスに直接水を噴射して水の蒸発潜熱によって減温する方法がある。
【０００３】
近年、ごみ処理施設においてはダイオキシンの再合成防止の観点から、排ガスの温度を低下させる要求が多く発生しており、特に排熱ボイラを設置しないごみ処理施設の場合には、減温塔を設置して、高温の排ガスをダイオキシンの再合成が防止できる低温まで減温することが要求されている。
【０００４】
このため、従来より例えば、塔状容器内に排ガスを流入して冷却水を噴射することにより排ガスを冷却するようにしてある減温塔において、上部位置に噴射ノズルを設けた塔状容器と、塔状容器頂部の排ガス入口の上側に、一側より導入される排ガスをガイドベーンで周方向に分散させるようにし且つ底面中央部にガスの出口を設けた分散室と、分散室のガスの出口と塔状容器の排ガス入口との間に設けた垂直方向に延びる多数の細いガス流路を形成させる絞り部とからなるガス導入部を構成したものがある（例えば、特許文献１参照）。
【０００５】
【特許文献１】
特開２００２−２１９３２３号公報
【０００６】
【発明が解決しようとする課題】
上記特許文献１では、燃焼炉から導かれた排ガスは、先ず、ガス導入部の分散室内にてガイドベーンに邪魔されて、その流線が左右方向（周方向）に分散された後、絞り部に向かうようになり、次いで、該絞り部に形成された垂直方向に延びる多数の細い流路を通過することにより、流れ方向が垂直方向下向きに整流された状態になって、塔状容器の頂部中央の排ガス入口より塔状容器内に流入されるようになる。これにより、塔状容器内に流入する排ガスは、周方向に均等に且つ塔状容器中心部を垂直方向下向きに流されることから、噴射される冷却水と排ガスとの効率的な熱交換が行われ、このため冷却水はすべて蒸発させられ、ダストと共に塔状容器内壁面に付着することが防止されるとしている。
【０００７】
上記特許文献１による減温塔では、高温の排ガスを２５０℃程度まで減温する際には有効であった。
【０００８】
しかし、特許文献１の減温塔で排ガスを２５０℃以下の温度に減温しようとした場合には、排ガスの最終到達温度と水温とが近付くために完全蒸発を行わせることが困難であるという問題を有していた。
【０００９】
更に、上記特許文献１に示す如く従来の減温塔では、噴射ノズルを塔状容器上部の１個所（周方向には複数備えられているが、上下方向には１段）に設けている。そして、例えば９００℃の排ガスをダイオキシンの再合成が防止できる１８０℃程度まで減温する場合には、減温塔の出口温度を検出し該出口温度が１８０℃になるように流量制御弁の開度を調節して前記噴射ノズルの噴射量を制御する。しかし、このとき、減温塔に１段のみ設けている噴射ノズルと流量制御弁は、小噴射量から大噴射量まで調節できるよう元々大容量に構成しているために、出口温度の変化に応じて流量制御弁の開度を微調節しても、水の噴射量が大きく変化してしまい、このための応答遅れによる調整過剰によって出口温度を例えば１８０℃の設定温度に精度良く保持することができない。
【００１０】
また、特に、前記した如く減温塔上部の高さ方向１段に噴射ノズルを設けた構成では、噴射ノズルから大量の水を噴射したときに、水滴が微粒とならずに塊を生じたまま落下し易く、塊となった水滴は完全な蒸発が行われ難い。
【００１１】
上記したように、従来の減温塔では、排ガスの最終到達温度と水温とが近付くこと、水噴射の応答遅れ、噴射した水が塊を形成し易いこと等が相俟って、噴射した水の完全蒸発が行われず、そのために排ガス中のダストが湿りを生じ、湿ったダストは減温塔内下部に付着堆積する問題を生じる。更に、このような湿ったダストは、輸送や貯留時等のトラブルの原因となる。従って、従来の減温塔では１８０℃前後のような低温域まで排ガスを減温することは実際上問題を有していた。
【００１２】
本発明は、排ガス中のダストに湿りを生じさせることなく、減温塔出口の排ガス温度を設定温度に精度良く調節できるようにした減温塔の排ガス出口温度制御方法及び装置を提供しようとするものである。
【００１３】
【課題を解決するための手段】
請求項１に記載の発明は、ガス導入口から排ガスを導入してガス導出口から導出する減温塔の前記ガス導入口側に、各々に流量調整弁を備えた噴射ノズルをガスの流動方向に所要の間隔を隔てて２段に設け、更にガス導出口に排ガス温度を検出する温度検出器を設け、一方の噴射ノズルに備えた流量調整弁は、短い時間間隔に設定した狭幅検出時間内における温度検出器の検出温度の平均値の変化に基づいて開度を調節し、他方の噴射ノズルに備えた流量調整弁は、長い時間間隔に設定した広幅検出時間内における検出温度の平均値の変化に基づいて開度を調節して、ガス導出口の排ガス温度を設定温度に保持することを特徴とする減温塔の排ガス出口温度制御方法、に係るものである。
【００１４】
請求項２に記載の発明は、ガス導入口から排ガスを導入してガス導出口から導出する減温塔の前記ガス導入口側に、各々に流量調整弁を備えた噴射ノズルをガスの流動方向に所要の間隔を隔てて２段に設け、更にガス導出口に排ガス温度を検出する温度検出器を設け、一方の噴射ノズルに備えた流量調整弁は、温度検出器の検出温度に基づいて設定された流量調整範囲内で開度を調節し、他方の噴射ノズルに備えた流量調整弁は、前記一方の流量調整弁の開度が流量調整範囲の限界に達したときに温度検出器の検出温度に基づいて開度を調節して、ガス導出口の排ガス温度を設定温度に保持することを特徴とする減温塔の排ガス出口温度制御方法、に係るものである。
【００１５】
請求項３に記載の発明は、ガス導入口から排ガスを導入してガス導出口から導出する減温塔の前記ガス導入口側にガスの流動方向に所要の間隔を隔てて２段に配置した噴射ノズルと、噴射ノズルの夫々に設けた流量調整弁と、前記ガス導出口に設置した温度検出器と、該温度検出器の検出温度を入力し、短い時間間隔に設定した狭幅検出時間内における温度検出器の検出温度の平均値の変化に基づいて一方の流量調整弁の開度を調節し、且つ長い時間間隔に設定した広幅検出時間内における温度検出器の検出温度の平均値の変化に基づいて他方の流量調整弁の開度を調整するようにした制御器と、を備えたことを特徴とする減温塔の排ガス出口温度制御装置、に係るものである。
【００１６】
請求項４に記載の発明は、ガス導入口から排ガスを導入してガス導出口から導出する減温塔の前記ガス導入口側にガスの流動方向に所要の間隔を隔てて２段に配置した噴射ノズルと、噴射ノズルの夫々に設けた流量調整弁と、前記ガス導出口に設置した温度検出器と、温度検出器の検出温度に基づいて設定した流量調整範囲内で一方の流量調整弁の開度を調節し、且つ該一方の流量調整弁の開度が設定した流量制御範囲の限界に達したときに温度検出器の検出温度に基づいて他方の流量調整弁の開度を調節するようにした制御器と、を備えたことを特徴とする減温塔の排ガス出口温度制御装置、に係るものである。
【００１７】
請求項５に記載の発明は、前記各流量調整弁は、各噴射ノズルに水を供給する給水管の戻り管に設けていることを特徴とする請求項３または４に記載の減温塔の排ガス出口温度制御装置、に係るものである。
【００１８】
請求項６に記載の発明は、前記一方の流量調整弁は弁開度に対する噴射流量が小さい小流量調整弁であり、他方の流量調整弁は弁開度に対する噴射流量が大きい大流量調整弁であることを特徴とする請求項３〜５のいずれか１つに記載の減温塔の排ガス出口温度制御装置、に係るものである。
【００１９】
請求項７に記載の発明は、前記大流量調整弁は、小流量調整弁に対してガス導入口に近い位置に設けられていることを特徴とする請求項６に記載の減温塔の排ガス出口温度制御装置、に係るものである。
【００２０】
上記手段によれば、以下のように作用する。
【００２１】
温度検出器による検出温度が細かく変動する小さな変動に対しては、狭幅検出時間で捕えた検出温度の平均値によって一方の噴射ノズルに備えた流量調整弁を微調整して噴射ノズルによる噴射量を微調節し、一方、温度検出器による検出温度の大きな変動に対しては、広幅検出時間で捕えた検出温度の平均値によって他方の噴射ノズルに備えた流量調整弁を調節することで噴射ノズルの噴射量を大きな変化量でベースの調整を行うようにしたので、前記微調整とベースの調整が同時に行われることによって応答遅れを殆ど生じることなくガス導出口の排ガスの温度を精度良く設定温度に保持することができる。
【００２２】
一方の噴射ノズルに備えた流量調整弁は、温度検出器の検出温度に基づいて設定された流量調整範囲内で開度を調節し、他方の噴射ノズルに備えた流量調整弁は、前記一方の流量調整弁の開度が流量調整範囲の限界に達したときに温度検出器の検出温度に基づいて開度を調節するようにしたので、各流量調整弁の調節が１つの目標値に向かって制御されるようになり、よってガス導出口の排ガスの温度が変動することなく設定温度に精度良く制御されるようになる。
【００２３】
各流量調整弁を、各噴射ノズルに水を供給する給水管の戻り管に設けたことにより、噴射ノズルの入口圧力を安定させることができ、よって最大噴射量と最少噴射量の制御幅を広くでき、しかも全噴射域において微細な粒子による噴射が可能になってボタ落ちの問題を防止できる。
【００２４】
弁開度に対する噴射流量が大きい大流量調整弁をガス導入口に近い位置に設け、弁開度に対する噴射流量が小さい小流量調整弁をガス導入口から遠い位置に設けたことにより、噴射ノズルによる噴射水の完全蒸発が更に行われ易くなる。
【００２５】
【発明の実施の形態】
以下、本発明の好適な実施の形態を図面に基づいて説明する。
【００２６】
図１は本発明の減温塔の排ガス出口温度制御装置の実施の一形態を示すもので、図中１は減温塔であり、該減温塔１は、上部のガス導入口２から排ガス３を導入し、下部のガス導出口４から排ガス３を導出するようにしている。
【００２７】
前記減温塔１の上部位置には、上下に所要の間隔を隔てて配置した２段の噴射ノズル５，６を設けている。上下二段に設けられる噴射ノズル５，６の夫々は、減温塔１を取り巻くように複数配置されている。
【００２８】
上段の噴射ノズル５には、給水ポンプ７と圧力調節弁８とを有して一端が給水タンク９に連通した給水管１０の他端が接続されている。更に、噴射ノズル５に形成された図示しない旋回室（ワールチャンバー）には戻り管１０ａが接続されており、該戻り管１０ａに流量調整弁１１を設置することによりフローバックノズルを構成している。このとき、前記流量調整弁１１は、弁開度に対する噴射流量が大きい大流量調整弁１１Ｍとしている。
【００２９】
また、噴射ノズル６には、給水ポンプ１２と圧力調節弁１３とを有して一端が給水タンク９に連通した給水管１４の他端が接続されている。更に、噴射ノズル６に形成された図示しない旋回室（ワールチャンバー）には戻り管１４ａが接続されており、該戻り管１４ａに流量調整弁１５を設置することによりフローバックノズルを構成している。このとき、前記流量調整弁１５は、弁開度に対する噴射流量が小さい小流量調整弁１５Ｌとしている。前記戻り管１０ａと戻り管１４ａは一本に連通されて給水タンク９に導かれている。
【００３０】
前記フローバックノズルの構成は、大流量調整弁１１Ｍ及び小流量調整弁１５Ｌが全開のときには、圧力調節弁８，１３の下流に圧力が立たないために噴射ノズル５，６からは水が噴射されず、一方、大流量調整弁１１Ｍ及び小流量調整弁１５Ｌの開度を絞ると、その開度に応じて圧力調節弁８，１３の下流に圧力が立つことによって噴射ノズル５，６から水が噴射されるようになっている。
【００３１】
前記ガス導出口４には温度検出器１６が設置してあり、該温度検出器１６の検出温度１７は制御器１８に入力されている。
【００３２】
制御器１８は、前記噴射ノズル５，６に供給する水の圧力が所定の一定圧力に保持されるように前記各圧力調節弁８，１３を制御する。
【００３３】
一方、前記制御器１８は、温度検出器１６の検出温度１７に基づいて、大流量調整弁１１Ｍ及び小流量調整弁１５Ｌの開度を調節し、前記噴射ノズル５，６から減温塔１内に噴射する水の量を調節することにより、ガス導出口４の排ガス温度が所定の設定温度Ｔ（例えば１８０℃）になるように制御している。
【００３４】
図１の構成において、噴射ノズル５，６よりも上流側の給水管１０，１４に、流量調整弁１１，１５を設置することも可能であるが、このようにした場合には、噴射ノズル５，６入口の圧力の一定保持が難しく、そのために最大噴射量と最少噴射量の制御幅が狭く制限され、しかも噴射量が小さい時にボタ落ちを生じる問題がある。これに対し、前記したように噴射ノズル５，６の戻り管１０ａ，１４ａに大流量調整弁１１Ｍ及び小流量調整弁１５Ｌを設置したフローバックノズルの構成によれば、噴射ノズル５，６の入口圧力を安定させることができ、よって最大噴射量と最少噴射量の制御幅を広くでき、しかも全噴射域において微細な粒子による噴射が可能になってボタ落ちの問題を防止できる。従って、図１の構成によれば、減温塔１によって高温の排ガス３を減温するのに好適に用いることができる。
【００３５】
また、噴射ノズル５，６に、専用の給水ポンプ７，１２を備えた独自の給水管１０，１４を接続して給水を行うようにしたので、１つの給水ポンプを供用した場合のように一方の噴射ノズルを噴射したときの圧力の変動の影響を他方の噴射ノズルが受けるという問題を防止でき、噴射ノズル５，６に対する給水の圧力の変動を更に低減できる。
【００３６】
次に、図１に示した構成において減温塔の出口温度を制御する２つの制御方法について説明する。
【００３７】
第１の制御方法について図１及び図２を参照して説明する。図２は、ガス導出口４の排ガス３の温度が変動したときの検出温度と時間との関係を模式的に表わした線図であり、図中Ｔは設定温度（例えば１８０℃）である。
【００３８】
制御器１８は、前記温度検出器１６の検出温度１７を入力しており、図２に示す如く、短い時間間隔に設定した狭幅検出時間Ｓ₁内における温度を検出してその平均値Ｔ₁を求めている。一方、長い時間間隔に設定した狭幅検出時間Ｓ₂内における温度を検出してその平均値Ｔ₂を求めている。
【００３９】
そして、狭幅検出時間Ｓ₁で検出した検出温度１７の平均値Ｔ₁の比較的小さい変化幅の変化に対しては小流量調整弁１５Ｌの開度を微調節して噴射ノズル６による噴射量を調整する。
【００４０】
一方、狭幅検出時間Ｓ₂で検出した検出温度１７の平均値Ｔ₂の比較的大きな変化幅の変化に対しては大流量調整弁１１Ｍの開度を調整することにより噴射ノズル６の噴射量を調整する。
【００４１】
図３は上記第１の制御方法を実施した小流量調整弁１５Ｌの弁開度Ａと、大流量調整弁１１Ｍの弁開度Ｂとを示したものであり、小流量調整弁１５Ｌの弁開度Ａは大きく変動しており、大流量調整弁１１Ｍの弁開度Ｂは小さい変動となっている。
【００４２】
上記した第１の制御方法によれば、温度検出器１６による検出温度１７が細かく変動する小さな変動に対しては、狭幅検出時間Ｓ₁で捕えた検出温度１７の平均値Ｔ₁によって小流量調整弁１５Ｌが図３に示す弁開度Ａの如く大きく変化（噴射流量の変化は小さい）されて噴射ノズル６の噴射量を微調整する。
【００４３】
一方、温度検出器１６による検出温度１７の大きな変動に対しては、広幅検出時間Ｓ₂で捕えた検出温度１７の平均値Ｔ₂によって大流量調整弁１１Ｍが図３に示す弁開度Ｂの如く小さく変化（噴射流量の変化は大きい）されて噴射ノズル５による大きな変化量での調整（ベースの調整）を行うようにしたので、微調整とベースの調整が同時に行われることによって応答遅れを殆ど生じることなくガス導出口４の排ガス３の温度を精度良く設定温度Ｔに保持することができる。
【００４４】
第２の制御方法について図１及び図４を参照して説明する。図４は、大流量調整弁１１Ｍ及び小流量調整弁１５Ｌの、開度と噴射流量との関係を模式的に表わした線図であり、大流量調整弁１１Ｍは弁開度に対する噴射流量が大きく、小流量調整弁１５Ｌは弁開度に対する噴射流量が小さくなっている。
【００４５】
更に、この場合の制御器１８’は、小流量調整弁１５Ｌによる開度を、例えば４０％〜６０％の範囲とする設定流量範囲Ｘを設定するようにしており、また、大流量調整弁１１Ｍの開度を前記設定流量範囲Ｘより大きい、例えば２０％〜８０％の使用範囲で制御するようにしている。
【００４６】
そして、制御器１８’は、前記温度検出器１６による検出温度１７が変化すると、検出温度１７が設定温度Ｔ（例えば１８０℃）になるように、まず小流量調整弁１５Ｌの開度を調節する。このとき、小流量調整弁１５Ｌは弁開度に対する噴射流量が小さいので、検出温度１７の小さな変化に対して精度良く追従し、微調整を効果的に実施できる。
【００４７】
一方、検出温度１７の変化が大きくなると、小流量調整弁１５Ｌに設定した設定流量範囲Ｘでは調節できない限界（４０％以下、及び６０％以上）になる。このように、小流量調整弁１５Ｌの開度が設定流量範囲Ｘの限界に達すると、制御器１８’は、前記温度検出器１６の検出温度１７に基づいて、大流量調整弁１１Ｍの開度を調節範囲Ｙ₁及びＹ₂内で調節し、検出温度１７が設定温度Ｔ（例えば１８０℃）になるように制御する。
【００４８】
上記した第２の制御方法によれば、小流量調整弁１５Ｌと大流量調整弁１１Ｍとの調節が１つの目標値に向かって制御されるようになるので、ガス導出口４の排ガス３の温度が変動することなく設定温度に精度良く制御されるようになる。
【００４９】
尚、図１の形態では戻り管１０ａ，１４ａに流量調整弁１１，１５を設けたフローバックノズルの構成とした場合について説明したが、戻り管を備えることなく、給水管に流量調整弁を設置した場合にも、前記フローバックノズルの構成による効果は期待できないが、２段に設けた噴射ノズルによる噴射を別個に制御することによって得られる効果は発揮することができる。
【００５０】
また、前記形態では、大流量調整弁１１Ｍをガス導入口２に近い上段に設け、小流量調整弁１５Ｌをガス導入口２から遠い下段に設けた場合について説明したが、大流量調整弁１１Ｍと小流量調整弁１５Ｌは上下を逆転して設けてもよく、また流量調整弁１１と流量調整弁１５を同等の性能（開度に対する噴射流量）を有したものとしてもよい。
【００５１】
更に、本発明は上記形態例にのみ限定されるものではなく、本発明の要旨を逸脱しない範囲内において種々変更を加え得ることは勿論である。
【００５２】
【発明の効果】
本発明によれば、以下の如く優れた効果を奏し得る。
【００５３】
温度検出器による検出温度が細かく変動する小さな変動に対しては、狭幅検出時間で捕えた検出温度の平均値によって一方の噴射ノズルに備えた流量調整弁を微調整して噴射ノズルによる噴射量を微調節し、一方、温度検出器による検出温度の大きな変動に対しては、広幅検出時間で捕えた検出温度の平均値によって他方の噴射ノズルに備えた流量調整弁を調節することで噴射ノズルの噴射量を大きな変化量でベースの調整を行うようにしたので、前記微調整とベースの調整が同時に行われることにより、応答遅れを殆ど生じることなくガス導出口の排ガスの温度を精度良く設定温度に保持することができる。
【００５４】
一方の噴射ノズルに備えた流量調整弁は、温度検出器の検出温度に基づいて設定された流量調整範囲内で開度を調節し、他方の噴射ノズルに備えた流量調整弁は、前記一方の流量調整弁の開度が流量調整範囲の限界に達したときに温度検出器の検出温度に基づいて開度を調節するようにしたので、各流量調整弁の調節が１つの目標値に向かって制御されるようになり、よってガス導出口の排ガスの温度が変動することなく設定温度に精度良く制御されるようになる。
【００５５】
各流量調整弁を、各噴射ノズルに水を供給する給水管の戻り管に設けたことにより、噴射ノズルの入口圧力を安定させることができ、よって最大噴射量と最少噴射量の制御幅を広くでき、しかも全噴射域において微細な粒子による噴射が可能になってボタ落ちの問題を防止できる。
【００５６】
弁開度に対する噴射流量が大きい大流量調整弁をガス導入口に近い位置に設け、弁開度に対する噴射流量が小さい小流量調整弁をガス導入口から遠い位置に設けたことにより、噴射ノズルによる噴射水の完全蒸発が更に行われ易くなる。
【図面の簡単な説明】
【図１】本発明の減温塔の排ガス出口温度制御装置の実施の一形態を示すブロック図である。
【図２】ガス導出口の排ガスの温度が変動したときの検出温度と時間との関係を模式的に表わした線図である。
【図３】小流量調整弁の弁開度と大流量調整弁の弁開度とを実測した値の線図である。
【図４】大流量調整弁及び小流量調整弁の、開度と噴射流量との関係を模式的に表わした線図である。
【符号の説明】
１減温塔
２ガス導入口
３排ガス
４ガス導出口
５噴射ノズル
６噴射ノズル
１０給水管
１０ａ戻り管
１１流量調整弁
１１Ｍ大流量調整弁
１４給水管
１４ａ戻り管
１５流量調整弁
１５Ｌ小流量調整弁
１６温度検出器
１７検出温度
１８制御器
１８’ 制御器
Ｓ₁ 狭幅検出時間
Ｓ₂ 広幅検出時間
Ｔ設定温度
Ｔ₁ 平均値
Ｔ₂ 平均値
Ｘ設定流量範囲[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas outlet temperature control method and apparatus for a temperature reducing tower used for reducing the temperature of exhaust gas to a predetermined set temperature in a combustion facility having a combustion furnace such as a waste treatment facility or a cement plant.
[0002]
[Prior art]
As a method of reducing the temperature of exhaust gas containing dust in a combustion facility having a combustion furnace such as a waste treatment facility or cement plant, there is a method of injecting water directly into the exhaust gas and reducing the temperature by the latent heat of evaporation of water. .
[0003]
In recent years, waste treatment facilities have been increasingly demanded to reduce the temperature of exhaust gas from the viewpoint of preventing dioxin resynthesis, and in particular in the case of waste treatment facilities that do not have a waste heat boiler, a temperature reducing tower is installed. Therefore, it is required to reduce the temperature of the high-temperature exhaust gas to a low temperature at which dioxin resynthesis can be prevented.
[0004]
Therefore, conventionally, for example, in a temperature reducing tower that cools exhaust gas by injecting exhaust gas into the tower and injecting cooling water, a tower container provided with an injection nozzle at the upper position; A dispersion chamber in which the exhaust gas introduced from one side is dispersed in the circumferential direction by a guide vane on the upper side of the exhaust gas inlet at the top of the tower, and a gas outlet is provided at the center of the bottom, and the gas outlet of the dispersion chamber There is a gas inlet that includes a plurality of narrow gas passages extending in the vertical direction that are provided between the tower and the exhaust gas inlet of the tower-like container (see, for example, Patent Document 1).
[0005]
[Patent Document 1]
JP-A-2002-219323 [0006]
[Problems to be solved by the invention]
In Patent Document 1, the exhaust gas guided from the combustion furnace is first obstructed by the guide vanes in the dispersion chamber of the gas introduction unit, and the streamline is dispersed in the left-right direction (circumferential direction), and then the throttle unit. Then, the flow direction is rectified downward in the vertical direction by passing through a large number of thin channels extending in the vertical direction formed in the throttle portion, and the top of the columnar vessel It flows into the tower-like container from the central exhaust gas inlet. As a result, the exhaust gas flowing into the tower vessel is made to flow evenly in the circumferential direction and vertically downward in the center of the tower vessel, so that efficient heat exchange between the injected cooling water and the exhaust gas is performed. For this reason, all the cooling water is evaporated and prevented from adhering to the inner wall surface of the tower container together with dust.
[0007]
The temperature reducing tower according to Patent Document 1 is effective in reducing the temperature of high-temperature exhaust gas to about 250 ° C.
[0008]
However, when trying to reduce the temperature of the exhaust gas to a temperature of 250 ° C. or less with the temperature reducing tower of Patent Document 1, it is difficult to perform complete evaporation because the final temperature of the exhaust gas approaches the water temperature. Had a problem.
[0009]
Furthermore, as shown in Patent Document 1, in the conventional temperature reducing tower, the injection nozzle is provided at one place (a plurality of nozzles are provided in the circumferential direction but one stage in the vertical direction) at the upper part of the tower-like container. For example, when the temperature of the exhaust gas at 900 ° C. is reduced to about 180 ° C. at which dioxin resynthesis can be prevented, the outlet temperature of the temperature reducing tower is detected and the flow control valve is opened so that the outlet temperature becomes 180 ° C. The injection amount of the injection nozzle is controlled by adjusting the degree. However, at this time, the injection nozzle and flow control valve provided in only one stage in the temperature reducing tower are originally configured to have a large capacity so that they can be adjusted from a small injection amount to a large injection amount. Accordingly, even if the opening degree of the flow control valve is finely adjusted, the water injection amount changes greatly, and the outlet temperature is accurately maintained at a set temperature of, for example, 180 ° C. due to over-adjustment due to the response delay. I can't.
[0010]
In particular, in the configuration in which the injection nozzle is provided in the first stage in the height direction at the top of the temperature reducing tower as described above, when a large amount of water is injected from the injection nozzle, the water droplets remain agglomerated without becoming fine particles. It is easy to fall, and the water droplets which become a lump are hard to be completely evaporated.
[0011]
As described above, in the conventional temperature reducing tower, the final reached temperature of the exhaust gas approaches the water temperature, the response delay of the water injection, the fact that the injected water easily forms a lump, etc. As a result, the dust in the exhaust gas is moistened, causing the problem that the moist dust adheres to and accumulates in the lower part of the temperature reducing tower. Further, such wet dust causes troubles during transportation and storage. Therefore, in the conventional temperature reducing tower, it has been a problem in practice to reduce the temperature of exhaust gas to a low temperature range such as around 180 ° C.
[0012]
The present invention seeks to provide an exhaust gas outlet temperature control method and apparatus for a temperature reducing tower that can accurately adjust the exhaust gas temperature at the outlet of the temperature reducing tower to a set temperature without causing the dust in the exhaust gas to become wet. Is.
[0013]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided an injection nozzle provided with a flow rate adjusting valve on each side of the gas introduction port of the temperature reducing tower that introduces the exhaust gas from the gas introduction port and leads out from the gas discharge port. Are provided in two stages with a required interval, and further provided with a temperature detector for detecting the exhaust gas temperature at the gas outlet, and the flow rate adjusting valve provided on one of the injection nozzles has a narrow detection time set at a short time interval The flow rate adjustment valve provided in the other injection nozzle adjusts the opening based on the change in the average value of the detected temperature of the temperature detector in the inside, and the average value of the detected temperature within the wide detection time set at a long time interval The exhaust gas outlet temperature control method for a temperature-decreasing tower is characterized in that the opening degree is adjusted based on the change of the temperature to maintain the exhaust gas temperature at the gas outlet at a set temperature.
[0014]
According to the second aspect of the present invention, there is provided an injection nozzle provided with a flow rate adjusting valve on each side of the gas introduction port of the temperature reducing tower that introduces exhaust gas from the gas introduction port and leads out from the gas discharge port. The temperature sensor that detects the exhaust gas temperature is provided at the gas outlet, and the flow rate adjustment valve on one of the injection nozzles is set based on the temperature detected by the temperature detector. The flow rate adjustment valve in the other injection nozzle adjusts the opening within the specified flow rate adjustment range, and the temperature detector detects when the opening of the one flow rate adjustment valve reaches the limit of the flow rate adjustment range. The present invention relates to an exhaust gas outlet temperature control method for a temperature-decreasing tower, wherein the exhaust gas temperature at the gas outlet is maintained at a set temperature by adjusting the opening degree based on the temperature.
[0015]
The invention described in claim 3 is arranged in two stages at a predetermined interval in the gas flow direction on the gas inlet side of the temperature reducing tower that introduces exhaust gas from the gas inlet and leads out from the gas outlet. Within the narrow detection time set in a short time interval by inputting the injection nozzle, the flow rate adjusting valve provided for each of the injection nozzle, the temperature detector installed at the gas outlet, and the temperature detected by the temperature detector Based on the change of the average value of the detected temperature of the temperature detector at the time, the opening of one flow rate adjustment valve is adjusted, and the change of the average value of the detected temperature of the temperature detector within the wide detection time set at a long time interval And an exhaust gas outlet temperature control device for a temperature-decreasing tower, characterized in that the controller is configured to adjust the opening of the other flow rate adjustment valve based on the above.
[0016]
The invention according to claim 4 is arranged in two stages at a predetermined interval in the gas flow direction on the gas inlet side of the temperature reducing tower that introduces exhaust gas from the gas inlet and leads out from the gas outlet. An injection nozzle, a flow adjustment valve provided for each of the injection nozzles, a temperature detector installed at the gas outlet, and one of the flow adjustment valves within a flow adjustment range set based on the detection temperature of the temperature detector. Adjusting the opening and adjusting the opening of the other flow control valve based on the temperature detected by the temperature detector when the opening of the one flow control valve reaches the limit of the set flow control range And an exhaust gas outlet temperature control device for a temperature-decreasing tower, characterized in that the controller is provided.
[0017]
The invention according to claim 5 is characterized in that each flow rate adjusting valve is provided in a return pipe of a water supply pipe for supplying water to each injection nozzle. The present invention relates to an exhaust gas outlet temperature control device.
[0018]
According to a sixth aspect of the present invention, the one flow rate adjusting valve is a small flow rate adjusting valve having a small injection flow rate with respect to the valve opening degree, and the other flow rate adjusting valve is a large flow rate adjusting valve having a large injection flow rate with respect to the valve opening degree. The present invention relates to an exhaust gas outlet temperature control device for a temperature-decreasing tower according to any one of claims 3 to 5.
[0019]
The invention according to claim 7 is characterized in that the large flow rate adjusting valve is provided at a position close to the gas inlet with respect to the small flow rate adjusting valve. The present invention relates to an outlet temperature control device.
[0020]
According to the above means, it operates as follows.
[0021]
For small fluctuations in which the temperature detected by the temperature detector fluctuates finely, the flow rate adjustment valve provided on one of the injection nozzles is finely adjusted according to the average value of the detected temperatures captured in the narrow detection time, and the injection amount by the injection nozzle On the other hand, for large fluctuations in the detected temperature by the temperature detector, the injection nozzle is adjusted by adjusting the flow rate adjustment valve provided in the other injection nozzle according to the average value of the detected temperature captured in the wide detection time Since the base adjustment is performed with a large change in the injection amount of the gas, the fine adjustment and the base adjustment are performed at the same time, so that the exhaust gas temperature at the gas outlet is accurately set without causing a response delay. Can be held in.
[0022]
The flow rate adjustment valve provided in one of the injection nozzles adjusts the opening within a flow rate adjustment range set based on the temperature detected by the temperature detector, and the flow rate adjustment valve provided in the other injection nozzle Since the opening degree is adjusted based on the temperature detected by the temperature detector when the opening degree of the flow rate adjustment valve reaches the limit of the flow rate adjustment range, the adjustment of each flow rate adjustment valve is directed toward one target value. Therefore, the temperature of the exhaust gas at the gas outlet is controlled with high accuracy without fluctuation.
[0023]
By providing each flow control valve in the return pipe of the water supply pipe that supplies water to each injection nozzle, the inlet pressure of the injection nozzle can be stabilized, so the control range of the maximum injection amount and the minimum injection amount is widened. In addition, injection with fine particles is possible in the entire injection region, and the problem of dropping out can be prevented.
[0024]
By providing a large flow rate adjustment valve with a large injection flow rate with respect to the valve opening at a position close to the gas introduction port and a small flow rate adjustment valve with a small injection flow rate with respect to the valve opening at a position far from the gas introduction port, Complete evaporation of the jet water is further facilitated.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.
[0026]
FIG. 1 shows an embodiment of an exhaust gas outlet temperature control device for a temperature-decreasing tower according to the present invention. In FIG. 1, 1 is a temperature-decreasing tower, and the temperature-decreasing tower 1 is exhausted from an upper gas inlet 2. 3 is introduced, and the exhaust gas 3 is led out from the lower gas outlet 4.
[0027]
Two stages of injection nozzles 5 and 6 are provided at the upper position of the temperature-decreasing tower 1 so as to be vertically spaced apart from each other. Each of the injection nozzles 5 and 6 provided in the upper and lower two stages is arranged so as to surround the temperature reducing tower 1.
[0028]
The upper injection nozzle 5 is connected to the other end of a water supply pipe 10 having a water supply pump 7 and a pressure control valve 8 and having one end communicating with a water supply tank 9. Further, a return pipe 10a is connected to a swirl chamber (war chamber) (not shown) formed in the injection nozzle 5, and a flow back nozzle is configured by installing a flow rate adjusting valve 11 in the return pipe 10a. . At this time, the flow rate adjusting valve 11 is a large flow rate adjusting valve 11M having a large injection flow rate relative to the valve opening.
[0029]
The injection nozzle 6 is connected to the other end of a water supply pipe 14 having a water supply pump 12 and a pressure control valve 13 and having one end communicating with the water supply tank 9. Further, a return pipe 14a is connected to a swirl chamber (war chamber) (not shown) formed in the injection nozzle 6, and a flow back nozzle is configured by installing a flow rate adjusting valve 15 in the return pipe 14a. . At this time, the flow rate adjusting valve 15 is a small flow rate adjusting valve 15L having a small injection flow rate relative to the valve opening degree. The return pipe 10a and the return pipe 14a communicate with each other and are led to the water supply tank 9.
[0030]
The flow-back nozzle is configured such that when the large flow rate adjusting valve 11M and the small flow rate adjusting valve 15L are fully open, no pressure is established downstream of the pressure adjusting valves 8, 13, so that water is injected from the injection nozzles 5, 6. On the other hand, when the opening degree of the large flow rate adjustment valve 11M and the small flow rate adjustment valve 15L is reduced, water is supplied from the injection nozzles 5 and 6 due to the pressure rising downstream of the pressure adjustment valves 8 and 13 according to the opening degree. It comes to be injected.
[0031]
A temperature detector 16 is installed at the gas outlet 4, and a detected temperature 17 of the temperature detector 16 is input to a controller 18.
[0032]
The controller 18 controls the pressure control valves 8 and 13 so that the pressure of water supplied to the injection nozzles 5 and 6 is maintained at a predetermined constant pressure.
[0033]
On the other hand, the controller 18 adjusts the opening degree of the large flow rate adjusting valve 11M and the small flow rate adjusting valve 15L based on the detected temperature 17 of the temperature detector 16, and the inside of the temperature reducing tower 1 from the injection nozzles 5 and 6. By adjusting the amount of water injected to the exhaust gas, the exhaust gas temperature at the gas outlet 4 is controlled to a predetermined set temperature T (for example, 180 ° C.).
[0034]
In the configuration of FIG. 1, the flow rate adjusting valves 11 and 15 can be installed in the water supply pipes 10 and 14 upstream of the injection nozzles 5 and 6. In this case, the injection nozzle 5 Therefore, it is difficult to keep the pressure at the 6 inlets constant, and therefore, the control range of the maximum injection amount and the minimum injection amount is narrowly limited, and there is a problem that the dropout occurs when the injection amount is small. In contrast, according to the configuration of the flowback nozzle in which the large flow rate adjusting valve 11M and the small flow rate adjusting valve 15L are installed in the return pipes 10a and 14a of the injection nozzles 5 and 6 as described above, the inlets of the injection nozzles 5 and 6 are used. The pressure can be stabilized, so that the control range of the maximum injection amount and the minimum injection amount can be widened, and injection with fine particles can be performed in the entire injection region, thereby preventing the problem of dropping out. Therefore, according to the configuration of FIG. 1, it can be suitably used for reducing the temperature of the high temperature exhaust gas 3 by the temperature reducing tower 1.
[0035]
In addition, since the unique water supply pipes 10 and 14 provided with the dedicated water pumps 7 and 12 are connected to the injection nozzles 5 and 6 to perform water supply, as in the case where one water supply pump is used. The problem that the other injection nozzle is affected by the fluctuation of the pressure when the injection nozzle is injected can be prevented, and the fluctuation of the pressure of the water supply to the injection nozzles 5 and 6 can be further reduced.
[0036]
Next, two control methods for controlling the outlet temperature of the temperature reducing tower in the configuration shown in FIG. 1 will be described.
[0037]
The first control method will be described with reference to FIG. 1 and FIG. FIG. 2 is a diagram schematically showing the relationship between the detected temperature and time when the temperature of the exhaust gas 3 at the gas outlet 4 varies, where T is a set temperature (for example, 180 ° C.).
[0038]
The controller 18 receives the detected temperature 17 of the temperature detector 16, detects the temperature within the narrow detection time S ₁ set at a short time interval, and averages the value T _{1 as shown in FIG.} Seeking. On the other hand, an average value T ₂ is obtained by detecting the temperature within the narrow detection time S ₂ set at a long time interval.
[0039]
Then, for a relatively small change in the average value T ₁ of the detected temperature 17 detected in the narrow detection time S ₁ , the amount of injection by the injection nozzle 6 is finely adjusted by opening the small flow rate adjusting valve 15L. Adjust.
[0040]
On the other hand, for a relatively large change in the average value T ₂ of the detected temperature 17 detected in the narrow width detection time S ₂ , the injection amount of the injection nozzle 6 is adjusted by adjusting the opening of the large flow rate adjusting valve 11M. Adjust.
[0041]
FIG. 3 shows the valve opening A of the small flow rate adjusting valve 15L and the valve opening B of the large flow rate adjusting valve 11M in which the first control method is implemented, and the small flow rate adjusting valve 15L is opened. The degree A greatly fluctuates, and the valve opening degree B of the large flow rate adjusting valve 11M has a small fluctuation.
[0042]
According to the first control method described above, a small flow rate is detected by the average value T ₁ of the detection temperature 17 captured in the narrow detection time S ₁ for small fluctuations in which the detection temperature 17 by the temperature detector 16 fluctuates finely. The adjustment valve 15L is greatly changed (a change in the injection flow rate is small) as the valve opening A shown in FIG. 3 to finely adjust the injection amount of the injection nozzle 6.
[0043]
On the other hand, for large fluctuations in the detected temperature 17 by the temperature detector 16, the average value T ₂ of the temperature detected 17 captured by the wide detection time S ₂ is a high flow rate regulating valve 11M of the valve opening B shown in FIG. 3 Since the adjustment (base adjustment) is carried out with a large change amount by the injection nozzle 5 (base adjustment), the response delay is reduced by performing the fine adjustment and the base adjustment at the same time. The temperature of the exhaust gas 3 at the gas outlet 4 can be accurately maintained at the set temperature T with almost no occurrence.
[0044]
The second control method will be described with reference to FIGS. FIG. 4 is a diagram schematically showing the relationship between the opening degree and the injection flow rate of the large flow rate adjustment valve 11M and the small flow rate adjustment valve 15L. The large flow rate adjustment valve 11M has a large injection flow rate with respect to the valve opening degree. The small flow rate adjusting valve 15L has a small injection flow rate with respect to the valve opening.
[0045]
Further, the controller 18 ′ in this case is configured to set a set flow rate range X in which the opening degree by the small flow rate adjustment valve 15L is in a range of 40% to 60%, for example, and the large flow rate adjustment valve 11M. Is controlled in a use range larger than the set flow rate range X, for example, 20% to 80%.
[0046]
Then, the controller 18 ′ first adjusts the opening of the small flow rate adjusting valve 15L so that when the detected temperature 17 by the temperature detector 16 changes, the detected temperature 17 becomes a set temperature T (for example, 180 ° C.). . At this time, since the small flow rate adjusting valve 15L has a small injection flow rate with respect to the valve opening, it can accurately follow a small change in the detected temperature 17 and effectively perform fine adjustment.
[0047]
On the other hand, when the change of the detected temperature 17 becomes large, it becomes a limit (40% or less and 60% or more) that cannot be adjusted in the set flow rate range X set in the small flow rate adjusting valve 15L. Thus, when the opening degree of the small flow rate adjusting valve 15L reaches the limit of the set flow rate range X, the controller 18 ′ opens the opening degree of the large flow rate adjusting valve 11M based on the detected temperature 17 of the temperature detector 16. Is adjusted within the adjustment ranges Y ₁ and Y ₂ , and the detected temperature 17 is controlled to be a set temperature T (for example, 180 ° C.).
[0048]
According to the second control method described above, the adjustment of the small flow rate adjusting valve 15L and the large flow rate adjusting valve 11M is controlled toward one target value, so that the temperature of the exhaust gas 3 at the gas outlet 4 is increased. Can be accurately controlled to the set temperature without fluctuation.
[0049]
In the embodiment shown in FIG. 1, the flow back nozzle is provided with the flow rate adjusting valves 11 and 15 in the return pipes 10a and 14a. However, the flow rate adjusting valve is installed in the water supply pipe without providing the return pipe. Even in this case, the effect of the configuration of the flowback nozzle cannot be expected, but the effect obtained by separately controlling the injection by the injection nozzles provided in two stages can be exhibited.
[0050]
In the above embodiment, the case where the large flow rate adjusting valve 11M is provided in the upper stage close to the gas inlet 2 and the small flow rate adjusting valve 15L is provided in the lower stage far from the gas inlet 2 has been described. The small flow rate adjusting valve 15L may be provided upside down, and the flow rate adjusting valve 11 and the flow rate adjusting valve 15 may have equivalent performance (injection flow rate relative to the opening).
[0051]
Furthermore, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention.
[0052]
【The invention's effect】
According to the present invention, the following excellent effects can be obtained.
[0053]
For small fluctuations in which the temperature detected by the temperature detector fluctuates finely, the flow rate adjustment valve provided on one of the injection nozzles is finely adjusted according to the average value of the detected temperatures captured in the narrow detection time, and the injection amount by the injection nozzle On the other hand, for large fluctuations in the detected temperature by the temperature detector, the injection nozzle is adjusted by adjusting the flow rate adjustment valve provided in the other injection nozzle according to the average value of the detected temperature captured in the wide detection time Since the base is adjusted with a large change in the injection amount, the fine adjustment and the base adjustment are performed at the same time, so that the temperature of the exhaust gas at the gas outlet is accurately set with almost no response delay. Can be held at temperature.
[0054]
The flow rate adjustment valve provided in one of the injection nozzles adjusts the opening within a flow rate adjustment range set based on the temperature detected by the temperature detector, and the flow rate adjustment valve provided in the other injection nozzle Since the opening degree is adjusted based on the temperature detected by the temperature detector when the opening degree of the flow rate adjustment valve reaches the limit of the flow rate adjustment range, the adjustment of each flow rate adjustment valve is directed toward one target value. Therefore, the temperature of the exhaust gas at the gas outlet is controlled with high accuracy without fluctuation.
[0055]
By providing each flow control valve in the return pipe of the water supply pipe that supplies water to each injection nozzle, the inlet pressure of the injection nozzle can be stabilized, so the control range of the maximum injection amount and the minimum injection amount is widened. In addition, injection with fine particles is possible in the entire injection region, and the problem of dropping out can be prevented.
[0056]
By providing a large flow rate adjustment valve with a large injection flow rate with respect to the valve opening at a position close to the gas introduction port and a small flow rate adjustment valve with a small injection flow rate with respect to the valve opening at a position far from the gas introduction port, Complete evaporation of the jet water is further facilitated.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of an exhaust gas outlet temperature control device for a temperature reducing tower of the present invention.
FIG. 2 is a diagram schematically showing the relationship between the detected temperature and time when the temperature of the exhaust gas at the gas outlet changes.
FIG. 3 is a diagram of values obtained by actually measuring a valve opening degree of a small flow rate adjusting valve and a valve opening degree of a large flow rate adjusting valve;
FIG. 4 is a diagram schematically showing a relationship between an opening degree and an injection flow rate of a large flow rate adjustment valve and a small flow rate adjustment valve.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Temperature reducing tower 2 Gas introduction port 3 Exhaust gas 4 Gas outlet port 5 Injection nozzle 6 Injection nozzle 10 Water supply pipe 10a Return pipe 11 Flow control valve 11M Large flow control valve 14 Water supply pipe 14a Return pipe 15 Flow control valve 15L Small flow control valve 16 Temperature detector 17 Detection temperature 18 Controller 18 'Controller S ₁ Narrow detection time S ₂ Wide detection time T Set temperature T ₁ Average value T ₂ Average value X Set flow rate range

Claims

Two stages of injection nozzles each equipped with a flow rate adjusting valve are provided in the gas flow direction at a predetermined interval on the gas inlet side of the temperature reducing tower that introduces exhaust gas from the gas inlet and leads out from the gas outlet. In addition, a temperature detector for detecting the exhaust gas temperature is provided at the gas outlet, and the flow rate adjusting valve provided on one of the injection nozzles is used to detect the temperature detected by the temperature detector within the narrow detection time set at a short time interval. The opening is adjusted based on the change in the average value, and the flow rate adjustment valve on the other injection nozzle adjusts the opening based on the change in the average value of the detected temperature within the wide detection time set at a long time interval. Then, the exhaust gas outlet temperature control method for a temperature reducing tower, wherein the exhaust gas temperature at the gas outlet is maintained at a set temperature.

Two stages of injection nozzles each equipped with a flow rate adjusting valve are provided in the gas flow direction at a predetermined interval on the gas inlet side of the temperature reducing tower that introduces exhaust gas from the gas inlet and leads out from the gas outlet. In addition, a temperature detector for detecting the exhaust gas temperature is provided at the gas outlet, and the flow rate adjustment valve provided on one of the injection nozzles is opened within the flow rate adjustment range set based on the temperature detected by the temperature detector. The flow rate adjustment valve provided in the other injection nozzle adjusts the opening degree based on the detected temperature of the temperature detector when the opening degree of the one flow rate adjustment valve reaches the limit of the flow rate adjustment range. An exhaust gas outlet temperature control method for a temperature reduction tower, wherein the exhaust gas temperature at the gas outlet is maintained at a set temperature.

An injection nozzle arranged in two stages at a predetermined interval in the gas flow direction on the gas inlet side of the temperature reducing tower that introduces exhaust gas from the gas inlet and leads out from the gas outlet, and each of the injection nozzles The flow rate adjusting valve provided, the temperature detector installed at the gas outlet, and the detected temperature of the temperature detector within the narrow detection time set at a short time interval by inputting the detected temperature of the temperature detector The opening of one flow rate adjustment valve is adjusted based on the change in the value, and the flow rate of the other flow rate adjustment valve is adjusted based on the change in the average value of the detected temperature of the temperature detector within the wide detection time set at a long time interval. An exhaust gas outlet temperature control device for a temperature-decreasing tower, comprising: a controller configured to adjust an opening degree.

An injection nozzle arranged in two stages at a predetermined interval in the gas flow direction on the gas inlet side of the temperature reducing tower that introduces exhaust gas from the gas inlet and leads out from the gas outlet, and each of the injection nozzles Adjusting the opening of one flow rate adjustment valve within a flow rate adjustment range set based on the detected temperature of the flow rate adjusting valve, the temperature detector installed at the gas outlet, and the temperature detector; A controller that adjusts the opening of the other flow control valve based on the temperature detected by the temperature detector when the opening of the flow control valve reaches the limit of the set flow control range. An exhaust gas outlet temperature control device for a temperature-decreasing tower characterized by the above.

5. The exhaust gas outlet temperature control device for a temperature-decreasing tower according to claim 3, wherein each flow rate adjusting valve is provided in a return pipe of a water supply pipe that supplies water to each injection nozzle.

4. The one flow rate adjusting valve is a small flow rate adjusting valve having a small injection flow rate with respect to the valve opening degree, and the other flow rate adjusting valve is a large flow rate adjusting valve having a large injection flow rate with respect to the valve opening degree. The exhaust gas outlet temperature control device for a temperature reducing tower according to any one of -5.

The exhaust gas outlet temperature control device for a temperature-decreasing tower according to claim 6, wherein the large flow rate adjusting valve is provided at a position close to the gas inlet with respect to the small flow rate adjusting valve.