JP3544384B2

JP3544384B2 - Boiler start control device

Info

Publication number: JP3544384B2
Application number: JP29063793A
Authority: JP
Inventors: 克己下平; 幸穂深山; 幹夫山中
Original assignee: Babcock Hitachi KK
Current assignee: Mitsubishi Power Ltd
Priority date: 1993-11-19
Filing date: 1993-11-19
Publication date: 2004-07-21
Anticipated expiration: 2019-07-21
Also published as: JPH07139703A

Description

【０００１】
【産業上の利用分野】
本発明は、ボイラ装置において、その起動を制御するボイラ起動制御装置に関する。
【０００２】
【従来の技術】
ボイラの起動は起動準備完了後、バーナに点火し、ボイラの昇温、昇圧を開始する。この時、ボイラ装置の各部が過熱したり、肉厚部に過大な熱応力が発生したりすることのないように適切な制御を行う必要がある。一方、点火から通気、併入に至る間に投入される燃料は直接発電に寄与しないため、極力削減することが求められる。
前記のような要求を満たすための手段として、本出願人は特開昭６１−２４９０５号の発明などを提案している。図８は前記特開昭６１−２４９０５で提案した貫流ボイラ起動装置の系統図である。同図において、ボイラの火炉炉壁を構成する水壁１への給水はボイラ給水ポンプ３により行われ、節炭器６で予熱された後、バーナ２により加熱される。給水が水壁１で加熱されて気水分離器４で気水混合物が蒸気と水とに分離される。気水分離器４からの蒸気は過熱器５で加熱され、過熱蒸気によりタービン発電機７が駆動される。過熱器５とタービン発電機７の間に過熱器５からタービン発電機７への蒸気量を加減するタービン加減弁８が介在する。また、燃料流量調節弁９は火炉２に供給される燃料投入量を調整するものであり、過熱器バイパス弁１０は気水分離器４からの蒸気を、またタービンバイパス弁１１は過熱器５からの蒸気をそれぞれコンデンサ（図示せず）などに逃がすための弁である。
【０００３】
前記本発明者らの特許出願では、過熱器５からタービン発電機７へ供給される蒸気の圧力を検出する蒸気圧力検出器１２、当該蒸気の温度を検出する蒸気温度検出器１３、昇圧完了時における過熱器５からタービン発電機７へ供給される蒸気の圧力の目標値を設定する蒸気圧力目標値設定器１４、同じく昇温完了時における過熱器５からタービン発電機７へ供給される蒸気の温度の目標値を設定する蒸気温度目標値設定器１５、気水分離器４の肉厚部の熱応力を抑制するための飽和温度変化率制限値を設定する飽和温度変化率制限値設定器１６、過熱器５の出口ヘッダの肉厚部の熱応力を抑制するための過熱器出口蒸気温度変化率制限値を設定する過熱器出口蒸気温度変化率制限値設定器１７、該設定器１７からの入力をもとに、蒸気圧力変化率目標値ａと過熱器５の出口蒸気温度変化率目標値ｂを演算する変化率目標値演算器１８、前記目標値ａ、ｂを入力して、これらを実現する最少の燃料投入量とタービンバイパス弁１０通過蒸気流量および過熱器バイパス弁１１通過蒸気流量の組み合わせを演算し、さらに算出された各流量を得るために必要な燃料流量調節弁９、タービンバイパス弁１０および過熱器バイパス弁１１の各弁開度信号ｃ、ｄ、ｅをそれぞれ演算する最適操作量演算器１９を設けることを提案した。
【０００４】
【発明が解決しようとする課題】
上記従来技術において、変化率目標値演算器１８における、蒸気圧力変化率目標値ａおよび過熱器５出口蒸気温度変化率目標値ｂの算出は、昇圧完了時における蒸気圧力目標値と現在の蒸気圧力の差および昇温完了時の過熱器５出口蒸気温度目標値と現在の過熱器５出口蒸気温度の差および熱応力を抑制するための蒸気圧力制限値と飽和温度変化率制限値を考慮するのみであり、その演算結果である蒸気圧力変化率目標値ａと過熱器５出口蒸気温度変化率目標値ｂが、現在のプラント状態において実現可能であるという保証はなかった。このため、最適操作量演算器１９における演算が発散する、あるいは前記各種の弁の開度が負の値となるなどの物理的に不適切な演算結果が出力される可能性があった。
本発明の目的はボイラ起動制御において、蒸気圧力および蒸気温度の各変化率目標値に基づき制御する場合に、各変化率目標値が現在のボイラ状態で実現可能な範囲に納まるように修正し、後段に配置される最適操作量演算器の演算の安定化を図ることである。
【０００５】
【課題を解決するための手段】
本発明の上記目的は次の構成によって達成される。
すなわち、蒸気温度変化率目標値および蒸気圧力変化率目標値を設定する第１の手段と、蒸気温度変化率および蒸気圧力変化率を制御する第２の手段を有するボイラ装置において、少なくともこのボイラの所定部の蒸気温度および蒸気圧力を入力として、現在のボイラ状態で実現可能な、少なくとも蒸気温度変化率の上下限値と実現可能な蒸気圧力変化率の上下限値を算出し、第１の手段から出力された変化率目標値を、前記実現可能な変化率に基づいて修正し、前記第２の手段へ出力する第３の手段を設け、該第３の手段は実現可能な範囲内に修正された蒸気温度変化率も入力として実現可能な蒸気圧力変化率の上下限値の演算を行うことを特徴とするボイラ起動制御装置である。
【０００６】
【作用】
本発明によれば、第３の手段により現在のボイラ状態で実現可能な蒸気圧力変化率の上下限値および蒸気温度変化率の上下限値を算出し、変化率目標値演算器からの出力である蒸気圧力変化率目標値と過熱器出口蒸気温度変化率目標値が、前記算出した現在のボイラ状態において実現可能な上下限値の範囲内にあるか否かを検査し、範囲外にある場合は、実現可能な変化率目標値の組み合わせとなるよう、第１の手段から出力された蒸気圧力、蒸気温度等の変化率目標値を、前記実現可能な変化率に基づいて修正し、蒸気圧力、蒸気温度等の変化率を制御する第２の手段へ出力する。こうして、蒸気圧力変化率目標値、蒸気温度変化率目標値等が、現在のプラント状態において実現可能であることが保証され、後段に配置される例えば燃料弁、過熱器バイパス弁、タービンバイパス弁等の最適操作量の演算の安定化が達成される。
このとき、第３の手段が実現可能な範囲内に修正された蒸気温度変化率も入力として実現可能な蒸気圧力変化率の上下限値の演算を行うことで、蒸気圧力変化率目標値と蒸気温度変化率目標値がそれぞれの実現可能な上下限値の間に矛盾が生じることがなくなる。
【０００７】
【実施例】
本発明の実施例を図面と共に説明する。
図１に示す実施例において、図８と同じ機能を達成する部材には同一番号を付けてその説明を省略する。図１には、現在の発電機出力を検出する発電機出力検出器２０、タービン加減弁８の開度を検出するタービン加減弁開度検出器２１、燃焼装置の仕様によって定められる燃料流量の下限値を設定する燃料流量下限値設定器２２および次に述べる変化率目標値修正器３０を設けている。
変化率目標値修正器３０は変化率目標値演算器１８と最適操作量演算器１９の間に介在し、蒸気圧力検出器１２、蒸気温度検出器１３、発電機出力検出器２０、タービン加減弁開度検出器２１、燃料流量下限値設定器２２の出力に基づいて、後に述べる手順により、蒸気圧力変化率目標値ａと過熱器５出口蒸気温度変化率目標値ｂが現在のボイラ状態において実現可能な組み合わせとなるように、そのいずれか、あるいは両方を変更して最適操作量演算器１９へ出力するものである。
【０００８】
すなわち、変化率目標値修正器３０は現在のボイラ状態において実現可能な蒸気圧力変化率と過熱器５出口蒸気温度の範囲を求め、変化率目標値演算器１８の出力である蒸気圧力変化率目標値ａと過熱器５出口蒸気温度変化率目標値ｂが求めた範囲内にあるか否かを検討し、範囲内にない場合には、蒸気圧力変化率目標値ａと過熱器５出口蒸気温度変化率目標値ｂが現在のボイラ状態において実現可能な組み合わせとなるように、そのいずれか、あるいは両方を変更して最適操作量演算器１９へ出力する。変化率目標値修正器３０によって修正された蒸気圧力変化率目標値ａ’と過熱器５出口蒸気温度変化率目標値ｂ’は最適操作量演算器１９に入力され、該目標値ａ’、ｂ’を実現するための最適な操作量の組み合わせが算出される。変化率目標値ａ’およびｂ’の値は変化率目標値修正器３０によって実現可能な範囲内に保たれるため、最適操作量演算器１９では常に最適な操作量の組み合わせが算出される。
【０００９】
次に、変化率目標値修正器３０のアルゴリズムについて説明する。本出願人は特開昭６１−２４９０５号において前記の構造を持つボイラにおいて蒸気圧力変化率ｄＰ／ｄｔおよび過熱器５の出口蒸気温度変化率ｄＴ／ｄｔは次の式（１）と式（２）によりそれぞれ求められることを示した。
【数１】

【００１０】
但し、式中の記号は以下のように定義する。
Ａ：過熱器の伝熱面積（ｍ^２）
Ｇ_ＷＷ：水壁１への給水量（ｋｇ／ｓ）
Ｇ_ｅ：水壁１の蒸発量（ｋｇ／ｓ）
ｈ’（Ｐ）：飽和水エンタルピ（ｋｃａｌ／ｋｇ）（Ｐの関数）
ｈ”（Ｐ）：飽和蒸気エンタルピ（ｋｃａｌ／ｋｇ）（Ｐの関数）
Ｈ（Ｐ，Ｔ）：過熱器５の出口蒸気エンタルピ（ｋｃａｌ／ｋｇ）（Ｐ，Ｔの関数）
ｄＨ／ｄｔ：過熱器５の出口蒸気エンタルピ変化率（ｋｃａｌ／ｋｇｓ）
Ｈ_ｉ：過熱器５の入口蒸気エンタルピ（ｋｃａｌ／ｋｇ）
Ｈ_ＷＷ：水壁１の出口流体エンタルピ（ｋｃａｌ／ｋｇ）
Ｈ_ＥＣＯ：節炭器６の出口給水エンタルピ（ｋｃａｌ／ｋｇ）
Ｐ：蒸気圧力（ｋｇ／ｃｍ^２）
ｄＰ／ｄｔ：蒸気圧力変化率（ｋｇ／ｃｍ^２ｓ）
Ｑ（ｘ）：水壁１の熱吸収量（ｋｃａｌ／ｓ）（ｘの関数）
Ｔ：過熱器５の出口蒸気温度（℃）
ｄＴ／ｄｔ：過熱器５の出口蒸気温度変化率（℃／ｓ）
ｖ（Ｐ，Ｔ）：過熱器５内蒸気の平均比容積（ｍ^３／ｋｇ）
Ｖ：過熱器５の内容積（ｍ^３）
ｘ：燃料流量（ｋｇ／ｓ）
α：過熱器５の平均熱貫流率（ｋｃａｌ／ｍ^２ｓ℃）
Ｔ_Ｈ（ｘ）：過熱器５の入口燃焼ガス温度（℃）（ｘの関数）
Ｇ_ａｌｌ：全蒸気流量（ｋｇ／ｓ）
Ｇ_ＳＨ：過熱器５の通過蒸気流量（ｋｇ／ｓ）
（∂Ｐ／∂γ）_Ｐ，_Ｔ：圧力Ｐ、温度ＴにおけるＰの比重γに対する偏微分係数
（∂Ｐ／∂γ）_Ｐ，_Ｔ：圧力Ｐ、温度ＴにおけるＴのエンタルピＨに対する偏微分係数
【００１１】
式（１）および式（２）で操作可能な量は燃料流量ｘ、全蒸気流量Ｇ_ａｌｌ、過熱器５の通過蒸気流量Ｇ_ＳＨであり、これらに対して独立な、その他の値は全てプラントの仕様で定められる定数、あるいは計測により求められる量である。また、一般に燃料流量ｘの上限は負荷の関数として定められ、下限値は燃焼装置の仕様で定められる。
式（１）において、水壁１の熱吸収量Ｑ（ｘ）はその性質から燃料流量ｘに対して単調に増加することを考慮すると、蒸気圧力変化率ｄＰ／ｄｔは燃料流量ｘに対して単調に増加し、全蒸気流量Ｇ_ａｌｌに対して単調に減少することが分かる。従って蒸気圧力変化率ｄＰ／ｄｔが最大となるのは、燃料流量ｘが最大で、かつ、全蒸気流量Ｇ_ａｌｌが最小となる操作を行った場合である。
同様に式（２）において、過熱器５の入口燃焼ガス温度Ｔ_Ｈ（ｘ）が燃料流量ｘに対して単調に増加することを考慮すると、過熱器５の出口蒸気温度変化率ｄＴ／ｄｔは燃料流量ｘに対して単調に増加し、過熱器５の通過蒸気流量Ｇ_ＳＨに対して単調に減少することが分かる。従って、過熱器５の出口蒸気温度変化率ｄＴ／ｄｔが最大となるのは燃料流量ｘが最大で、かつ、過熱器５の通過蒸気流量Ｇ_ＳＨが最小となる操作を行った場合であり、過熱器５の出口蒸気温度変化率ｄＴ／ｄｔが最小となるのは燃料流量ｘが最小で、かつ、過熱器５の通過蒸気流量Ｇ_ＳＨが最大となる操作を行った場合である。
【００１２】
ところで、全蒸気流量Ｇ_ａｌｌおよび過熱器５の通過蒸気流量Ｇ_ＳＨは、それぞれ次式（３）、（４）のように定義される。
Ｇ_ＳＨ＝Ｇ_ＴＢ＋Ｇ_{ＴＢｂｙｐａｓｓ} （３）
Ｇ_ａｌｌ＝Ｇ_ＳＨ＋Ｇ_{ＳＨｂｙｐａｓｓ} （４）
但し、式中の記号を以下のように定義する。
Ｇ_ＴＢ：タービン加減弁通過蒸気流量（ｋｇ／ｓ）
Ｇ_{ＴＢｂｙｐａｓｓ}：タービンバイパス弁通過蒸気流量（ｋｇ／ｓ）
Ｇ_{ＳＨｂｙｐａｓｓ}：過熱器バイパス弁通過蒸気流量（ｋｇ／ｓ）
ここでタービン加減弁通過蒸気流量Ｇ_ＴＢは発電機出力を制御するためにタービン側で独立に制御されるため、ボイラ起動制御装置において、制御対象とすることはできない。一方、タービンバイパス弁通過蒸気流量Ｇ_{ＴＢｂｙｐａｓｓ}、過熱器バイパス弁通過蒸気流量Ｇ_{ＳＨｂｙｐａｓｓ}はそれぞれタービンバイパス弁１１、過熱器バイパス弁１０の操作により制御可能である。式（４）から明らかなように、全蒸気流量Ｇ_ａｌｌと過熱器５の通過蒸気流量Ｇ_ＳＨは次の条件（５）を満たさなければならない。
Ｇ_ａｌｌ＞Ｇ_ＳＨ（５）
【００１３】
但し、最適操作量演算器１９における演算の合理性を保証するためには、この条件を燃料流量ｘの全域において満たす必要はなく、任意の一部分で満たせば十分である。燃料流量ｘが上限にある場合に該条件を満たすような蒸気圧力変化率ｄＰ／ｄｔを実現可能な該変化率ｄＰ／ｄｔの上限とする。すなわち、燃料流量ｘが上限値にある場合に、蒸気温度変化率目標値を満足する過熱器５の通過蒸気流量Ｇ_ＳＨを全蒸気流量Ｇ_ａｌｌの下限値と見なし、式（１）に代入して得られる蒸気圧力変化率ｄＰ／ｄｔを、実現可能な該変化率ｄＰ／ｄｔの最大値とする。任意の燃料流量ｘに対する、修正後の蒸気温度変化率目標値を満足する過熱器５の通過蒸気流量Ｇ_ＳＨは式（２）を該通過蒸気流量Ｇ_ＳＨについて解き、過熱器５の出口蒸気温度変化率ｄＴ／ｄｔに修正後の蒸気温度変化率を、燃料流量ｘに燃料流量ｘの上限値を代入することで求められる。
【００１４】
以上のことを整理すると、実現可能な過熱器５の出口蒸気温度変化率ｄＴ／ｄｔの上限値は、最大の燃料流量ｘすなわち燃料流量ｘの上限値、および、最小の過熱器５の通過蒸気流量Ｇ_ＳＨ、すなわちタービンバイパス弁１１を全閉とした過熱器５の通過蒸気流量Ｇ_ＳＨ（＝Ｇ_ＴＢ）を式（２）に代入することにより求められ、同じく下限値は、最小の燃料流量ｘすなわち燃料流量ｘの下限値、および、最大の過熱器５の通過蒸気流量Ｇ_ＳＨ、すなわちタービンバイパス弁１１を全開とした場合の過熱器５の通過蒸気流量Ｇ_ＳＨを式（２）に代入することにより求められる。
一方、実現可能な蒸気圧力変化率ｄＰ／ｄｔの上限値は、実現可能な上下限値の範囲内に修正された蒸気温度変化率目標値を燃料流量ｘの上限値において満足する過熱器５の通過蒸気流量Ｇ_ＳＨを全蒸気流量Ｇ_ａｌｌとし、最大の燃料流量ｘすなわち燃料流量ｘの上限値と共に式（１）に代入することにより求められ、同じく下限値は、最小の燃料流量ｘすなわち燃料流量ｘの下限値、および最大の全蒸気流量Ｇ_ａｌｌすなわち過熱器バイパス弁１０、タービンバイパス弁１１を共に全開とした場合の全蒸気流量Ｇ_ａｌｌを式（１）に代入することにより求められる。
【００１５】
以上のアルゴリズムに基づいて構成した変化率目標値修正器の系統図を図２に示す。関数発生器３１は図３に示す特性を備えた関数発生器であり、発電機出力検出器２０の出力を受けて、現時点で投入可能な燃料流量の上限値を出力する。関数発生器３２は図４に示す特性を備えていて、蒸気圧力検出器１２の出力を受けて、タービン加減弁８が全開の時に得られる蒸気流量を出力する。関数発生器３３は図５に示す特性を備えたものであり、タービン加減弁開度検出器２１の出力を受けて、タービン加減弁８の有効ポート面積比を出力する。また、乗算器３４は２つの関数発生器３２、３３の出力を乗算することにより、タービン加減弁８を通過する蒸気流量を算出する。関数発生器３５は図６に示す特性を備えており、蒸気圧力検出器１２の出力を受けて、タービンバイパス弁１１を全開にした場合にタービンバイパス弁１１を通過する蒸気の流量を出力する。関数発生器３６は図７に示す特性を備えたものであり、蒸気圧力検出器１２の出力を受けて、過熱器バイパス弁１０を全開した場合に過熱器バイパス弁１０を通過する蒸気の流量の合計を出力する。
【００１６】
蒸気温度変化率上下限値演算器３７は蒸気圧力検出器１２の検出値、過熱器出口蒸気温度検出器１３の検出値、関数発生器３１からの現時点で投入可能な燃料流量の上限値、燃料流量下限値設定器２２による設定値、乗算器３４から出力されるタービン加減弁通過蒸気流量、関数発生器３５から出力されるタービンバイパス弁１１全開時通過蒸気流量を入力として、式（２）に基づき、現在のボイラ状態で実現可能な、過熱器５出口における蒸気温度変化率の上限値および下限値を演算することができる。また範囲制限器３８は蒸気温度変化率上下限値演算器３７で算出された上下限値に基づいて、蒸気温度変化率目標値ｂが上下限値内に収まるように修正する。
【００１７】
蒸気圧力変化率上下限値演算器３９は蒸気圧力検出器１２の検出値、過熱器出口温度検出器１３の検出値、関数発生器３１からの現時点で投入可能な燃料流量の上限値、燃料流量下限値設定器２２による設定値、乗算器３４から出力されるタービン加減弁通過蒸気流量、関数発生器３５から出力されるタービンバイパス弁１１全開時通過蒸気流量、範囲制限器３８により実現可能な範囲内に修正された蒸気温度変化率目標値ｂ’を入力として、式（１）に基づき、現在のボイラ状態で実現可能な蒸気圧力変化率の上下限値を演算する。また、範囲制限器４０は蒸気圧力変化率上下限値演算器３９で算出された上下限値に基づいて、蒸気圧力変化率目標値ａが上下限値内に収まるように修正する。
【００１８】
以上により、変化率目標値修正器３０から出力される、修正された、蒸気圧力変化率目標値ａ’および蒸気温度変化率目標値ｂ’の組み合わせは、常に実現可能な範囲内に保たれる。こうして、最適操作量演算器１９における演算が発散したり、算出された操作量が、物理的に不可能な値となるなどの不都合な事態を防止し、確実に正しい解を得ることが保証され、燃料流量調節弁９、過熱器バイパス弁１０、タービンバイパス弁１１等の最適操作量の演算の安定化が達成される。
【００１９】
【発明の効果】
本発明によれば、最適操作量演算器に入力される、蒸気圧力変化率目標値、蒸気温度変化率目標値等は、それぞれの実現可能な上下限値の間に矛盾が生じることがなく、かつそれぞれ常に実現可能な値に保たれ、後段に配置される燃料弁、蒸気流量弁等の最適操作量の演算の安定化が達成される。
【図面の簡単な説明】
【図１】本発明の一実施例に係るボイラ起動制御装置の系統図。
【図２】図１に示す変化率目標値修正器３０の系統図。
【図３】図２に示す関数発生器３１の特性図。
【図４】図２に示す関数発生器３２の特性図。
【図５】図２に示す関数発生器３３の特性図。
【図６】図２に示す関数発生器３５の特性図。
【図７】図２に示す関数発生器３６の特性図。
【図８】従来技術によるボイラ起動制御装置の系統図。
【符号の説明】
１…水壁、２…バーナ、３…ボイラ給水ポンプ、４…気水分離器、
５…過熱器、６…節炭器、７…タービン発電機、８…タービン加減弁、
９…燃料流量調節弁、１０…過熱器バイパス弁、１１…タービンバイパス弁、
１２…蒸気圧力検出器、１３…蒸気温度検出器、
１４…蒸気圧力目標値設定器、１５…蒸気温度目標値設定器、
１６…飽和温度変化率制限値設定器、
１７…過熱器出口蒸気温度変化率制限値設定器、
１８…変化率目標値演算器、１９…最適操作量演算器
２０…発電機出力検出器、２１…タービン加減弁開度検出器、
２２…燃料流量下限値設定器、３０…変化率目標値修正器、
３１〜３３、３５、３６…関数発生器、３４…乗算器、
３７…蒸気温度変化率上下限値演算器、３８、４０…範囲制限器、
３９…蒸気圧力変化率上下限値演算器[0001]
[Industrial applications]
The present invention relates to a boiler activation control device for controlling activation of a boiler device.
[0002]
[Prior art]
After the start-up of the boiler is completed, the burner is ignited, and the temperature and pressure of the boiler are started. At this time, it is necessary to perform appropriate control so that each part of the boiler device is not overheated or excessive thermal stress is generated in the thick part. On the other hand, since the fuel injected during the period from ignition to ventilation and combined use does not directly contribute to power generation, it is required to reduce as much as possible.
As a means for satisfying the above requirements, the present applicant has proposed the invention of Japanese Patent Application Laid-Open No. 61-24905. FIG. 8 is a system diagram of a once-through boiler starting device proposed in the above-mentioned Japanese Patent Application Laid-Open No. 61-24905. In the figure, water is supplied to a water wall 1 constituting a furnace wall of a boiler by a boiler feed pump 3, preheated by a economizer 6, and then heated by a burner 2. The feed water is heated by the water wall 1 and the steam-water mixture is separated by the steam-water separator 4 into steam and water. The steam from the steam separator 4 is heated by the superheater 5 and the superheated steam drives the turbine generator 7. A turbine control valve 8 for controlling the amount of steam from the superheater 5 to the turbine generator 7 is interposed between the superheater 5 and the turbine generator 7. The fuel flow control valve 9 is for adjusting the amount of fuel supplied to the furnace 2, the superheater bypass valve 10 is for the steam from the steam separator 4, and the turbine bypass valve 11 is for the superheater 5. Is a valve for allowing the steam of the gas to escape to a condenser (not shown) or the like.
[0003]
In the patent application of the present inventors, a steam pressure detector 12 for detecting the pressure of steam supplied from the superheater 5 to the turbine generator 7, a steam temperature detector 13 for detecting the temperature of the steam, , A steam pressure target value setting unit 14 for setting a target value of the pressure of steam supplied from the superheater 5 to the turbine generator 7 at the same time. A steam temperature target value setting device 15 for setting a target temperature value, and a saturation temperature change rate limit value setting device 16 for setting a saturation temperature change rate limit value for suppressing thermal stress in a thick portion of the steam separator 4. A superheater outlet steam temperature change rate limit value setting device 17 for setting a superheater outlet steam temperature change rate limit value for suppressing a thermal stress in a thick portion of an outlet header of the superheater 5; Steam pressure change based on input A change rate target value calculator 18 for calculating a rate target value a and a target steam temperature change rate b of the outlet of the superheater 5; inputting the target values a and b; A combination of the steam flow rate passing through the bypass valve 10 and the steam flow rate passing through the superheater bypass valve 11 is calculated, and the fuel flow rate control valve 9, the turbine bypass valve 10, and the superheater bypass valve 11 required to obtain each calculated flow rate are calculated. It has been proposed to provide an optimal manipulated variable calculator 19 for calculating each of the valve opening signals c, d, and e.
[0004]
[Problems to be solved by the invention]
In the above prior art, the calculation of the steam pressure change rate target value a and the steam temperature change rate target value b at the outlet of the superheater 5 in the change rate target value calculator 18 is based on the steam pressure target value at the time of completion of the pressure increase and the current steam pressure. Only the difference between the target steam temperature at the outlet of the superheater 5 and the current steam temperature at the outlet of the superheater 5 at the completion of the temperature rise, and the steam pressure limit value and the saturation temperature change rate limit value for suppressing the thermal stress. Therefore, there is no guarantee that the steam pressure change rate target value a and the steam temperature change rate target value b at the outlet of the superheater 5, which are the calculation results, can be realized in the current plant state. Therefore, there is a possibility that a calculation result in the optimum operation amount calculator 19 is diverged or a physically inappropriate calculation result such as a negative value of the opening degree of the various valves is output.
An object of the present invention is to control the steam rate and the steam temperature based on the respective change rate target values in the boiler start-up control, so that each change rate target value is corrected to fall within a range achievable in the current boiler state, It is an object of the present invention to stabilize the operation of an optimal manipulated variable operation unit arranged at a subsequent stage.
[0005]
[Means for Solving the Problems]
The above object of the present invention is achieved by the following configuration.
That is, in a boiler apparatus having first means for setting a steam temperature change rate target value and a steam pressure change rate target value, and second means for controlling a steam temperature change rate and a steam pressure change rate, at least the boiler A first means for calculating at least upper and lower limit values of a steam temperature change rate and a feasible steam pressure change rate which can be realized in the current boiler state by inputting a steam temperature and a steam pressure of a predetermined portion; modify the output rate of change target value, and modified based on the achievable rate of change, said third means for outputting provided to the second means, in the means of the third feasible range The boiler activation control device is characterized in that it calculates upper and lower limits of a steam pressure change rate that can be realized also as an input of the steam temperature change rate .
[0006]
[Action]
According to the present invention, the upper and lower limits of the steam pressure change rate and the steam temperature change rate that can be realized in the current boiler state by the third means are calculated, and the output from the change rate target value calculator is calculated. If the target steam pressure change rate target and the superheater outlet steam temperature change rate target value are within the range of the upper and lower limits achievable in the current boiler state calculated above, and are out of the range, Corrects the change rate target values, such as the steam pressure and the steam temperature, output from the first means based on the achievable change rate so as to be a combination of the achievable change rate target values, , And outputs to the second means for controlling the rate of change of the steam temperature and the like. In this way, it is guaranteed that the steam pressure change rate target value, the steam temperature change rate target value, and the like can be realized in the current plant state, and for example, a fuel valve, a superheater bypass valve, a turbine bypass valve, etc. Stabilization of the calculation of the optimal operation amount is achieved.
At this time, the steam pressure change rate corrected within the range achievable by the third means is also input and the upper and lower limit values of the steam pressure change rate which can be realized are calculated, whereby the steam pressure change rate target value and the steam pressure change rate are calculated. There is no inconsistency between the target temperature change rate and the respective achievable upper and lower limits.
[0007]
【Example】
An embodiment of the present invention will be described with reference to the drawings.
In the embodiment shown in FIG. 1, members that achieve the same functions as those in FIG. 8 are given the same numbers, and descriptions thereof are omitted. FIG. 1 shows a generator output detector 20 for detecting the current generator output, a turbine control valve opening detector 21 for detecting the opening of the turbine control valve 8, and a lower limit of the fuel flow rate determined by the specifications of the combustion device. A fuel flow rate lower limit value setter 22 for setting a value and a change rate target value corrector 30 described below are provided.
The change rate target value corrector 30 is interposed between the change rate target value calculator 18 and the optimum manipulated variable calculator 19, and has a steam pressure detector 12, a steam temperature detector 13, a generator output detector 20, a turbine control valve. The steam pressure change rate target value a and the steam temperature change rate target value b at the outlet of the superheater 5 are realized in the current boiler state by the procedure described later based on the outputs of the opening degree detector 21 and the fuel flow rate lower limit value setting unit 22. One or both of them are changed so as to be a possible combination and output to the optimum manipulated variable calculator 19.
[0008]
That is, the change rate target value corrector 30 determines the range of the steam pressure change rate and the steam temperature at the outlet of the superheater 5 that can be realized in the current boiler state, and obtains the steam pressure change rate target output from the change rate target value calculator 18. It is examined whether the value a and the target steam temperature change rate b at the outlet of the superheater 5 are within the determined range. If not, the target steam pressure change rate target value a and the steam temperature at the outlet of the superheater 5 are determined. One or both of them are changed and output to the optimal manipulated variable calculator 19 so that the change rate target value b becomes a combination feasible in the current boiler state. The steam pressure change rate target value a ′ corrected by the change rate target value corrector 30 and the steam temperature change rate target value b ′ at the outlet of the superheater 5 are input to the optimum manipulated variable calculator 19, and the target values a ′, b The optimum combination of the operation amounts for realizing 'is calculated. Since the values of the change rate target values a ′ and b ′ are kept within a range achievable by the change rate target value corrector 30, the optimum operation amount calculator 19 always calculates the optimum combination of the operation amounts.
[0009]
Next, the algorithm of the change rate target value corrector 30 will be described. The applicant has disclosed in Japanese Patent Application Laid-Open No. 61-24905 that the steam pressure change rate dP / dt and the steam temperature change rate dT / dt at the outlet of the superheater 5 in the boiler having the above-described structure are expressed by the following equations (1) and (2). ).
(Equation 1)

[0010]
However, the symbols in the formula are defined as follows.
A: Heat transfer area of superheater (m ² )
G _WW : Water supply amount to water wall 1 (kg / s)
G _e: amount of evaporation of the water wall 1 (kg / s)
h ′ (P): enthalpy of saturated water (kcal / kg) (function of P)
h "(P): saturated steam enthalpy (kcal / kg) (function of P)
H (P, T): steam enthalpy at exit of superheater 5 (kcal / kg) (function of P, T)
dH / dt: change rate of steam enthalpy at the outlet of the superheater 5 (kcal / kgs)
H _i: the superheater 5 inlet steam enthalpy (kcal / kg)
H _WW: water wall 1 of the outlet fluid enthalpy (kcal / kg)
_HECO : Water enthalpy at the outlet of the economizer 6 (kcal / kg)
P: Steam pressure (kg / cm ² )
dP / dt: steam pressure change rate (kg / cm ² s)
Q (x): heat absorption of water wall 1 (kcal / s) (function of x)
T: Outlet steam temperature of superheater 5 (° C)
dT / dt: change rate of steam temperature at outlet of superheater 5 (° C./s)
v (P, T): average specific volume of steam in the superheater 5 (m ³ / kg)
V: Internal volume of superheater 5 (m ³ )
x: fuel flow rate (kg / s)
α: average heat transmission rate of the superheater 5 (kcal / m ² s ° C)
_TH (x): temperature of the combustion gas at the inlet of the superheater 5 (° C.) (a function of x)
G _all : Total steam flow rate (kg / s)
G _SH : Steam flow rate through superheater 5 (kg / s)
(∂P / ∂γ) _P , _T : Partial derivative of pressure P and specific gravity γ of P at temperature T (∂P / ∂γ) _P , _T : Partial derivative of pressure T and enthalpy H of T at temperature T [0011]
The quantities that can be operated in the formulas (1) and (2) are the fuel flow rate x, the total steam flow rate G _all , and the steam flow rate G _SH passing through the superheater 5. Is a constant determined by the specification of, or an amount determined by measurement. In general, the upper limit of the fuel flow rate x is determined as a function of the load, and the lower limit is determined by the specifications of the combustion device.
In equation (1), considering that the heat absorption amount Q (x) of the water wall 1 monotonically increases from the fuel flow rate x due to its property, the steam pressure change rate dP / dt is It can be seen that it increases monotonically and monotonically decreases with respect to the total steam flow G _all . Therefore, the steam pressure change rate dP / dt becomes maximum when the operation is performed such that the fuel flow rate x is maximum and the total steam flow rate _Gall is minimum.
Similarly, in equation (2), considering that the inlet combustion gas temperature _TH (x) of the superheater 5 monotonically increases with respect to the fuel flow rate x, the exit steam temperature change rate dT / dt of the superheater 5 becomes It can be seen that it increases monotonically with the fuel flow rate x and decreases monotonously with the steam flow rate _GSH passing through the superheater 5. Accordingly, the rate of change of the outlet steam temperature dT / dt of the superheater 5 becomes maximum when the fuel flow rate x is maximum and the operation is such that the steam flow rate _GSH passing through the superheater 5 is minimum, and the outlet steam temperature change rate dT / dt of the superheater 5 is minimum is the minimum fuel flow rate x, and is when passing the steam flow rate G _SH superheater 5 performs an operation of the maximum.
[0012]
Incidentally, the total steam flow G _all and the passing steam flow G _SH of the superheater 5 are defined as in the following equations (3) and (4), respectively.
G _SH = G _TB + G _TBbypass (3)
G _all = G _SH + G _SHbypass (4)
However, the symbols in the formula are defined as follows.
G _TB : Steam flow rate through turbine control valve (kg / s)
G _TBbypass : Steam flow rate through turbine bypass valve (kg / s)
G _SHbypass : Steam flow rate through superheater bypass valve (kg / s)
Here, since the turbine governor valve passing steam flow G _TB which is controlled independently in the turbine side to control the generator output, the boiler startup control device, can not be controlled. On the other hand, the turbine bypass valve passing steam flow rate _GTBbypass and the superheater bypass valve passing steam flow rate _GSHbypass can be controlled by operating the turbine bypass valve 11 and the superheater bypass valve 10, respectively. As is clear from equation (4), the total steam flow G _all and the steam flow G _SH passing through the superheater 5 must satisfy the following condition (5).
G _all > G _SH (5)
[0013]
However, in order to guarantee the rationality of the calculation in the optimum manipulated variable calculator 19, it is not necessary to satisfy this condition in the entire area of the fuel flow rate x, but it is sufficient to satisfy this condition in any part. When the fuel flow rate x is at the upper limit, the steam pressure change rate dP / dt that satisfies the condition is set as the upper limit of the change rate dP / dt that can be realized. That is, when the fuel flow rate x is at the upper limit, the passing steam flow rate G _SH passing through the superheater 5 that satisfies the steam temperature change rate target value is regarded as the lower limit value of the total steam flow rate G _all and is substituted into the equation (1). The steam pressure change rate dP / dt obtained as described above is the maximum value of the change rate dP / dt that can be realized. The steam flow rate G _SH passing through the superheater 5 that satisfies the corrected steam temperature change rate target value for an arbitrary fuel flow rate x is obtained by solving Equation (2) for the steam flow rate G _SH and calculating the steam temperature at the outlet of the super heater 5. The corrected steam temperature change rate is obtained as the change rate dT / dt by substituting the upper limit value of the fuel flow rate x into the fuel flow rate x.
[0014]
Summarizing the above, the upper limit of the rate of change dT / dt of the outlet steam temperature of the superheater 5 that can be realized is the maximum fuel flow x, that is, the upper limit of the fuel flow x, and the minimum steam passing through the superheater 5. The flow rate G _SH , that is, the steam flow rate G _SH (= G _TB ) passing through the superheater 5 with the turbine bypass valve 11 fully closed, is obtained by substituting it into equation (2). the lower limit of x that fuel flow rate x, and, substituted passed steam flow rate G _SH maximum superheater _5, i.e. the passing steam flow G _SH superheater 5 when the turbine bypass valve 11 was fully opened to equation (2) It is required by doing.
On the other hand, the upper limit of the achievable steam pressure change rate dP / dt is determined by the superheater 5 that satisfies the target steam temperature change rate corrected within the achievable upper and lower limit values at the upper limit of the fuel flow rate x. The passing steam flow rate G _SH is defined as the total steam flow rate G _all and is obtained by substituting the maximum fuel flow rate x, that is, the upper limit value of the fuel flow rate x, into the equation (1). the lower limit of the flow rate x, and maximum total steam flow rate G _all ie superheater bypass valve 10, is the total vapor flow rate G _all in the case of a both fully open the turbine bypass valve 11 determined by substituting the equation (1).
[0015]
FIG. 2 shows a system diagram of the change rate target value corrector configured based on the above algorithm. The function generator 31 is a function generator having the characteristics shown in FIG. 3 and receives the output of the generator output detector 20 and outputs the upper limit value of the fuel flow that can be injected at the present time. The function generator 32 has the characteristics shown in FIG. 4 and receives the output of the steam pressure detector 12 and outputs the steam flow obtained when the turbine control valve 8 is fully opened. The function generator 33 has the characteristics shown in FIG. 5 and receives the output of the turbine control valve opening degree detector 21 and outputs the effective port area ratio of the turbine control valve 8. Further, the multiplier 34 calculates a steam flow rate passing through the turbine control valve 8 by multiplying the outputs of the two function generators 32 and 33. The function generator 35 has the characteristics shown in FIG. 6, and receives the output of the steam pressure detector 12 and outputs the flow rate of steam passing through the turbine bypass valve 11 when the turbine bypass valve 11 is fully opened. The function generator 36 has the characteristics shown in FIG. 7, receives the output of the steam pressure detector 12, and controls the flow rate of the steam passing through the superheater bypass valve 10 when the superheater bypass valve 10 is fully opened. Print the sum.
[0016]
The steam temperature change rate upper / lower limit value calculator 37 detects the detected value of the steam pressure detector 12, the detected value of the superheater outlet steam temperature detector 13, the upper limit of the fuel flow rate that can be supplied at this time from the function generator 31, Inputting the set value by the flow rate lower limit setting unit 22, the steam flow rate through the turbine control valve output from the multiplier 34, and the steam flow rate when the turbine bypass valve 11 is fully opened output from the function generator 35, Based on this, the upper limit value and the lower limit value of the steam temperature change rate at the outlet of the superheater 5, which can be realized in the current boiler state, can be calculated. The range limiter 38 corrects the steam temperature change rate target value b based on the upper and lower limit values calculated by the steam temperature change rate upper and lower limit value calculator 37 so as to fall within the upper and lower limit values.
[0017]
The steam pressure change rate upper / lower limit value calculator 39 is a detection value of the steam pressure detector 12, a detection value of the superheater outlet temperature detector 13, an upper limit value of a fuel flow rate that can be supplied at the present time from the function generator 31, and a fuel flow rate. The set value set by the lower limit value setter 22, the steam flow rate through the turbine regulator valve output from the multiplier 34, the steam flow rate when the turbine bypass valve 11 is fully opened, output from the function generator 35, and the range achievable by the range limiter 38. Using the corrected steam temperature change rate target value b 'as an input, the upper and lower limits of the steam pressure change rate that can be realized in the current boiler state are calculated based on equation (1). The range limiter 40 corrects the steam pressure change rate target value a based on the upper and lower limit values calculated by the steam pressure change rate upper and lower limit value calculator 39 so as to fall within the upper and lower limit values.
[0018]
As described above, the corrected combination of the steam pressure change rate target value a ′ and the steam temperature change rate target value b ′ output from the change rate target value corrector 30 is always kept within a feasible range. . In this way, it is possible to prevent inconveniences such as divergence of the calculation in the optimum manipulated variable calculator 19 and the calculated manipulated variable becoming a physically impossible value, and it is ensured that a correct solution can be surely obtained. Thus, the calculation of the optimal operation amounts of the fuel flow control valve 9, the superheater bypass valve 10, the turbine bypass valve 11, and the like is stabilized.
[0019]
【The invention's effect】
According to the present invention, the target steam pressure change rate, the target steam temperature change rate, and the like, which are input to the optimal manipulated variable calculator, do not cause inconsistencies between the upper and lower limits that can be achieved. In addition, the values are always maintained at achievable values, and the calculation of the optimal operation amounts of the fuel valve, the steam flow valve, and the like arranged at the subsequent stage is stabilized.
[Brief description of the drawings]
FIG. 1 is a system diagram of a boiler activation control device according to one embodiment of the present invention.
FIG. 2 is a system diagram of a change rate target value corrector 30 shown in FIG.
FIG. 3 is a characteristic diagram of the function generator 31 shown in FIG.
FIG. 4 is a characteristic diagram of the function generator 32 shown in FIG.
FIG. 5 is a characteristic diagram of the function generator 33 shown in FIG. 2;
6 is a characteristic diagram of the function generator 35 shown in FIG.
FIG. 7 is a characteristic diagram of the function generator 36 shown in FIG.
FIG. 8 is a system diagram of a boiler start control device according to a conventional technique.
[Explanation of symbols]
1 ... water wall, 2 ... burner, 3 ... boiler feed pump, 4 ... steam-water separator,
5: superheater, 6: economizer, 7: turbine generator, 8: turbine control valve,
9: fuel flow control valve, 10: superheater bypass valve, 11: turbine bypass valve,
12: steam pressure detector, 13: steam temperature detector,
14: steam pressure target value setting device, 15: steam temperature target value setting device,
16: Saturation temperature change rate limit value setting device
17: Superheater outlet steam temperature change rate limit value setting device,
18: change rate target value calculator; 19: optimum manipulated variable calculator 20: generator output detector; 21: turbine control valve opening degree detector;
22: fuel flow rate lower limit value setting device, 30: change rate target value corrector,
31 to 33, 35, 36 ... function generator, 34 ... multiplier,
37: Steam temperature change rate upper / lower limit value calculator, 38, 40: Range limiter,
39… Steam pressure change rate upper / lower limit value calculator

Claims

In a boiler apparatus having first means for setting a steam temperature change rate target value and a steam pressure change rate target value, and second means for controlling a steam temperature change rate and a steam pressure change rate, at least a predetermined portion of the boiler With the steam temperature and the steam pressure as inputs, at least the upper and lower limits of the steam temperature change rate and the feasible steam pressure change rate that can be realized in the current boiler state are calculated, and output from the first means. A third means for correcting the set change rate target value based on the achievable change rate, and outputting the corrected change rate target value to the second means , wherein the third means is corrected within a achievable range. A boiler start-up control device for calculating upper and lower limits of a steam pressure change rate that can be realized also as a steam temperature change rate .