JP2004092992A - Device and method for calculating heat flux of furnace heat transfer tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device for calculating a heat flux of a furnace heat transfer tube capable of obtaining calculation results more precisely than a conventional one with less calculator resources. <P>SOLUTION: A device for calculating a heat flux of a boiler is equipped with plural groups of heat absorption panels forming a tertiary superheater and a secondary reheater downstream of a flow direction of combustion gas generated in a furnace. In this device, each one of lattice is produced to a flow path between a pair of heat absorption panels corresponding to the tertiary superheater and the secondary reheater in a separating direction (step 102). Numeric calculation formulae relating to heat transfer with flow rate and temperature of combustion gas adjacent to each heat absorption panel, and outer surface temperature of the heat absorption panel as variables are applied to each lattice, so that numeric calculation is repeated by using calculation results of the other lattice (step 106). <P>COPYRIGHT: (C)2004,JPO

Description

但し、Ｑ_ｃは対流による熱伝達量、αおよびβは経験定数、｜Ｖ_ｇ｜及びＴ_ｇは、それぞれ、吸熱体壁に隣接するガスの絶対流速及び温度、Ｔ_ｗは壁の外表面温度、Ａ_ｃは伝熱面積、であることを特徴とする。
【００１０】
請求項４記載の発明は、火炉で発生した燃焼ガスの流れ方向下流側に複数群の吸熱体を設けてなるボイラーの熱流束計算を行う装置において、ボイラーに対して複数の離散化領域を生成する離散化領域生成手段と、前記離散化領域生成手段が生成した各離散化領域に対して、熱解析に係る複数の数値計算式を適用し、他の領域に対する計算結果を用いながら全離散化領域に対する数値計算を繰り返し行う第１の数値計算手段と、所定の熱解析に係る数値計算式を複数の不活性かつ所定の大きさを有する微小の粒子モデルに対して適用し、数値計算を行う第２の数値計算手段と、前記第１の数値計算手段による数値計算に対して、前記第２の数値計算手段による計算結果を結合させる結合手段とを備えることを特徴とする。
【００１１】
請求項５記載の発明は、火炉で発生した燃焼ガスの流れ方向下流側に複数群の吸熱体を設けてなるボイラーの熱流束計算を行う方法において、各１対の吸熱体間の流路に対して該吸熱体の離間方向に各１個の離散化領域を対応させた複数の離散化領域（以下、第１の離散化領域）を生成するとともに、ボイラーの他の領域に対して複数の離散化領域（以下、第２の離散化領域）を生成する離散化領域生成過程と、前記離散化領域生成過程で生成された各離散化領域に対して、熱解析に係る複数の数値計算式を適用し、他の領域に対する計算結果を用いながら全離散化領域に対する数値計算を繰り返し行う数値計算過程とを有することを特徴とする。
【００１２】
請求項６記載の発明は、前記数値計算過程で、前記第２の離散化領域の各々に対して、熱解析に係る第１の複数の数値計算式を適用し、他の領域に対する計算結果を用いながら全離散化領域に対する数値計算を繰り返し行うとともに、前記第１の離散化領域の各々に対して、該各吸熱体に隣接する燃焼ガスの流速及び温度並びに該吸熱体の外表面温度を変数とする熱伝達に係る数値計算式を含む第２の複数の数値計算式を適用し、他の領域に対する計算結果を用いながら数値計算を繰り返し行うことを特徴とする。
【００１３】
請求項７記載の発明は、火炉で発生した燃焼ガスの流れ方向下流側に複数群の吸熱体を設けてなるボイラーの熱流束計算を行う方法において、ボイラーに対して複数の離散化領域を生成する離散化領域生成過程と、前記離散化領域生成過程で生成された各離散化領域に対して、熱解析に係る複数の数値計算式を適用し、他の領域に対する計算結果を用いながら全離散化領域に対する数値計算を繰り返し行う第１の数値計算過程と、所定の熱解析に係る数値計算式を複数の不活性かつ所定の大きさを有する微小の粒子モデルに対して適用し、数値計算を行う第２の数値計算過程と、前記第１の数値計算過程での数値計算に対して、前記第２の数値計算過程で求められた計算結果を結合させる結合過程とを有することを特徴とする。
【００１４】
【発明の実施の形態】
以下、図面を参照して、本発明による火炉伝熱管の熱流束計算装置の一実施の形態について説明する。本実施の形態の計算装置は、コンピュータ及びその周辺装置と、そのコンピュータで実行されるプログラムとから構成されるものである。
【００１５】
図１は、本実施の形態のプログラムによる処理の流れを示すフローチャートである。本実施の形態における熱流束計算処理では、まず、モデルの幾何学的形状を表すデータをコンピュータによって作成する（ステップ１０１）。ステップ１０１では、例えば、操作者が汎用のＣＡＤ（計算機支援製図）プログラム等を用いてボイラを構成する各構成要素を表す直交座標系における３次元座標を作成する。
【００１６】
ここで、図２及び図３を参照して、本実施の形態が計算の対象とするボイラの構造について説明する。図２はボイラの炉１の上部の断面構造を示す側面図、図３は図２に示す炉１の上部を上面から見た断面平面図である。燃料噴射装置や空気量調整装置からなり、空気と燃料を混合して燃焼させる装置（バーナ）は矢印１０の方向に設けられている。そのバーナで燃焼された燃焼ガスの流れの向きは、矢印１１ａ、１１ｂ、及び１１ｃで表される向きである。
【００１７】
火炉２内には、二次過熱器３、三次過熱器４、及び、二次再熱器５が設けられている。二次過熱器３、三次過熱器４、及び、二次再熱器５は、複数の鋼管を複数管寄せに平板状（板型）の形状をなすように取り付けることで組み立てられている。図２及び図３に示す例では、奥行き（図３の左右方向）約２４メートの火炉２内に、８枚の二次過熱器３と、４４枚の三次過熱器４と、６４枚の二次再熱器５とが設けられている。
【００１８】
また、二次過熱器３、三次過熱器４、及び、二次再熱器５よりも燃焼ガスの流れの下流方向に、一次再熱器６及び一次過熱器７と、そのさらに下流方向に節炭器８が設けられている。この場合、一次再熱器６は、上部再熱器６ａと下部再熱器６ｂとから構成されている。一次過熱器７は、上部過熱器７ａと下部過熱器７ｂとから構成されている。節炭器８は、ボイラの燃焼ガスが持つ熱を回収してボイラ水を加熱する給水加熱器をなすもので、一次パス８ａと二次パス８ｂとから構成されている。
【００１９】
さて、図１のステップ１０１では、上記のように図２及び図３に示した炉１の上部の構成と、図２及び図３に図示していない炉１のバーナ等の下部の構成との両方に対応したモデルを表す座標データが作成される。次に、ステップ１０１で作成されたモデルを、複数の小領域に離散化するメッシュの作成処理が行われる（図１のステップ１０２）。この場合、メッシュは、複数の３次元の空間格子（離散化領域）から構成される。
【００２０】
ここで、図４を参照して、本発明が特徴とするメッシュの作成方法について説明する。図４（ａ）は、図２に示す二次過熱器３、三次過熱器４、及び、二次再熱器５に対するメッシュ作成例を示す図である。但し、図４（ａ）は、図２の紙面裏側から見た方向で図示している。
【００２１】
各二次過熱器３、各三次過熱器４、及び、各二次再熱器５は、それぞれ、図示するようにＸ−Ｙ平面に対して複数の格子に分割される。Ｚ方向に対しては、各過熱器及び過熱器の厚さに対応する１つの格子、又は厚さを複数に分割する複数の格子が作成される。
【００２２】
各二次過熱器３、各三次過熱器４、及び、各二次再熱器５以外の火炉２内の空間に対しては、図示していない複数の格子が作成される。但し、各三次過熱器４の相互間の空間と、各二次再熱器５の相互間の空間については、本実施の形態では特に次の条件に従ってメッシュ分割がなされるようになっている。すなわち、各三次過熱器４間の空間については、例えば図４（ａ）及び（ｂ）に示す格子Ｇ４ａ及びＧ４ｂのように、離間方向（この場合、Ｚ方向）に、ただ１個の格子のみが作成されるようにメッシュ分割がなされるようになっている。各二次再熱器５間の空間については、同様にして、例えば図４（ａ）及び（ｃ）に示す格子Ｇ５ａのように、離間方向（この場合、Ｚ方向）に、ただ１個の格子のみが作成されるように、メッシュ分割がなされるようになっている。
【００２３】
以上のようにしてメッシュの作成処理（図１のステップ１０２）が終了すると、次に、作成したメッシュに対応させて解析条件の設定処理が行われる（ステップ１０３）。ステップ１０３では、ＣＦＤによる熱解析で用いるために求められた、燃焼における化学反応、対流による熱伝達、揮炎、不揮炎、ガス輻射、壁面輻射等の輻射熱等の複数の物理量の変化を表す複数の離散化方程式を設定するとともに、物性値、各種境界条件等を表す条件データや、軌跡解析を行う際の粒子についての条件の設定等が行われる。
【００２４】
本実施の形態におけるボイラの熱解析の基礎技術は、従来の技術の欄に示した公報に記載されているように、公知の技術である。一方、ＣＦＤによる流体解析については、種々の物理モデルの解析に適用可能な汎用の流体解析用プログラムが実用化され、市販されている。本実施の形態は、一部の離散化方程式に新規な数値計算式を採用するとともに、燃焼の灰分に対応する粒子解析の解析条件に新規な設定を採用するものである。一方、その他の解析手法については、公知の手法が利用可能である。
【００２５】
以下では、本実施の形態が特徴とする一部の離散化方程式の設定に係る構成と、粒子解析の設定に係る一部の構成について詳細に説明する。但し、前提として、本実施の形態のＣＦＤによる流体解析を、市販の流体解析用プログラムを用いて実現することとし、上述した新規な構成については、その市販の流体解析用プログラムに対してその特徴部分を適用する場合の構成について説明することとする。具体的には、市販の流体解析用プログラムとして、米国ＦＬＵＥＮＴ　ＩＮＣ．の汎用熱流体解析プログラムおよびＳＴＡＲ−ＣＤ等を使用することとする。熱流体解析プログラムＦＬＵＥＮＴは、離散化モデルとして有限体積法を用いるプログラムであり、圧縮性又は非圧縮性の熱流動解析、化学反応と燃焼の解析、輻射及び流体−固体伝熱連成解析等の数値流体力学（ＣＦＤ）による解析を実行可能とするものである。
【００２６】
さて、ステップ１０３における解析条件の設定では、一例として次のように設定を行うことができる。乱流モデルとして、二方程式乱流モデル一つであるｋ−εモデルを用いる。灰分に対応する粒子の直径については、通常、５０μｍ程度に設定するのに対して、１μｍ一定とするように設定し、粒子の状態については、不活性状態（高温下で蒸発や化学変化しない特性）に設定する。これらの設定は、各粒子の軌跡を求める計算によって、各メッシュに対する熱流動等に係る計算の収束性が低下することを防止するためのものである。
【００２７】
また、三次過熱器４及び二次再熱器５については、それらに関する対流伝熱に対応する離散化方程式を次のように設定した。すなわち、本実施形態では、三次過熱器４及び二次再熱器５について、複数の吸熱体（過熱器及び再熱器の伝熱管部分）相互間の空間に単一の格子のみを設定している。そのため、吸熱体間の対流伝導の解析精度を向上させるためにその新規な方程式を採用したのである。
【００２８】
通常、伝熱壁面要素に対するガス側対流熱伝達は、強制対流熱伝達に関する一般形である次式（１）によって表すことができる。
【数３】

ここに、Ｎ_ｕはＮｕｓｓｅｌｔ数（ヌッセルト数）、Ｒ_ｅはＲｅｙｎｏｌｄｓ数（レイノルズ数）、Ｐ_ｒはＰｒａｎｄｔｌ数（プラントル数）で、ａ，ｂ，ｃは何れも係数を表す。
【００２９】
但し、熱流体解析プログラムＦＬＵＥＮＴでは、伝熱壁面要素に対するガス側対流熱伝達が、式（１）で表されるのではなく、伝熱壁面要素に出来る温度境界層内の壁面温度勾配の形である次式（２）で表される。
【数４】

ここに、ｑ_ｃは対流熱伝達による吸収熱流束、λ_ｇおよびＴ_ｇはガスの熱伝導率及び温度、ｘは対流伝熱面から距離を示す。
【００３０】
そのため、従来は、対流熱伝達量を正しく評価するには伝熱壁面要素に隣接するガス流路に対して温度境界層を正しく計算出来る程度まで細かくメッシュ切りを行う必要があった。しかし、三次過熱器４、二次再熱器５等は、片炉でも数十枚のパネルで構成されており、この領域での温度境界層を解くには火炉幅方向（図３の左右方向）のメッシュ数を数百個にする必要がある。そうすると火炉全体では１０００万を越える膨大なメッシュ数になる。これは現状の計算機設備で例えば１ケースあたり１年程度の計算時間を要することになり、実用的でない。そこで、今回対象としている三次過熱器４や二次再熱器５に対してパネル間（吸熱体間）ガス要素１個でも対流熱伝達量を正しく評価出来るように、過熱器や再熱器に対するガス側対流熱伝達係数Ｒ_ｃの式として、下記Ｇｒｉｍｉｓｏｎの式を適用することにした。
【００３１】
【数５】

ここに、Ｆ_ａは管群の形状因子、λ_ｇｍはガスの熱伝導率、ｄは管直径を示す。
【００３２】
次に、式（１）と式（２）との関係と同様にして、式（３）を変形するとこで、次式（４）を作成した。そして、ステップ１０３では、この経験式である式（４）を、三次過熱器４及び二次再熱器５についての対流熱伝達を計算するための方程式として設定した。汎用熱流体解析プログラムでは、式（４）に基づいてユーザーサブルーチンを作成した。
【００３３】
【数６】

ここに、Ｑ_ｃは対流による熱伝達量、αおよびβは経験定数である。｜Ｖ_ｇ｜及びＴ_ｇは、それぞれ、吸熱体壁（パネルあるは吸熱板）に隣接するガスの絶対流速および温度、Ｔ_ｗは壁の外表面温度を示す。Ａ_ｃは伝熱面積を表す。
【００３４】
壁の外表面温度Ｔ_ｗは本来対流熱伝達に火炉からの輝炎およびパネル内ガスからの輻射熱伝達を含めた壁面吸熱量Ｑ及び管内流体温度Ｔ_ｌと連成して求めなければならない。すなわち、ｈを管内流体から管外表面までの熱通過係数、Ａを伝熱面積とすると壁の外表面温度Ｔ_ｗは次式で表せる。
【数７】

【００３５】
ここで、図５及び図６を参照して、三次過熱器４及び二次再熱器５に適用する物理モデルと、ステップ１０６における数値計算の手法について説明する。図５は、火炉２内における吸熱板（三次過熱器４及び二次再熱器５）に対する熱流束を示す模式図である。図６は、図５に示す物理モデルに対応する平面図である。
【００３６】
図６において、火炉２内には、三次過熱器４又は二次再熱器５に対応する１つの壁面構成要素２０が設けられている。この壁面構成要素２０に対しては、壁面構成要素番号ｎ、壁要素番号ｋ、壁温度Ｔ_ｗｋ、流体温度Ｔ_ｓｎ、壁熱伝導率λ_ｗｎ、壁厚みδ_ｗｎが定義されているものとする。
【００３７】
図６において、壁面構成要素ｎの中の要素番号ｋでの吸収熱流束ｑ_ｋは、次式で表すことができる。
【数８】

ここに、ｑ_ｒｋ＝［火炎からの輻射＋不輝炎からの輻射＋壁面からの輻射］であり、ｑ_ｃｋ＝［ガス要素ｊと壁面要素ｋとの間の対流熱伝達］である。この熱流束ｑ_ｒｋは、公知のＤＯ（Ｄｉｓｃｒｅｔｅ　Ｏｒｄｉｎａｔｅ）モデルによる輻射計算で求めることができる。
【００３８】
そして変数ｑ_ｃｋは下式（７）で表される。
【数９】

【００３９】
但し、熱流束ｑ_ｒｋの輻射計算に必要な温度Ｔ_ｗｋは、式（６）と下式（８）で計算される値を考慮する。
【数１０】

【００４０】
ここで、ステップ１０６における各メッシュに対する数値計算における繰り返し回数を考慮して、式（６）を以下のように考える。但し、添字ＮはＮ回目の繰り返し数を示す。
【数１１】

【００４１】
さらに、式（８）を以下のように考える。
【数１２】

この関係式から壁温度Ｔ_ｗｋは、Ｎ回目の繰り返し計算における吸収熱流束ｑ^Ｎ _ｋから求められることが分かる。
【００４２】
残りの式（８）と式（７）との関係から、式（９）は以下のように書くことができる。
【数１３】

【００４３】
つまり、Ｎ＋１回目の繰り返し計算における吸収熱流束ｑ_ｋ ^Ｎ＋１は、Ｎ回目の繰り返し計算における吸収熱流束ｑ_ｋ ^Ｎの関数となる。ここで、汎用熱流体解析プログラムでは、図１のステップ１０３において、吸収熱流束ｑ_ｋ ^Ｎ＋１を境界条件として入力する。
【００４４】
なお、係数α，β_ｋ，δ_ｗｎは、全て定数とすることができる。また、計算（物理）モデルは、例えば、図６に示すように、２次元で左側が吸気口、右側が排気口で、領域内に壁が１枚あるようなものとすることができる。
【００４５】
以上に説明したように、三次過熱器４及び二次再熱器５に関する対流伝熱を示す離散化方程式等の設定を含む、各種解析条件の設定を終了させた後（図１のステップ１０３）、解析に関して初期条件の設定処理が行われる（ステップ１０４）。ステップ１０４では、数値計算に用いられる各種変数の初期値の設定等が行われる。
【００４６】
次に、運転状態等に応じ、必要に応じて解析制御パラメータの調整が行われる（ステップ１０５）。ここでは、例えば燃料の投入量を表すパラメータ等に対して時間的変化を与えることができる。
【００４７】
次に、各メッシュに対して設定された複数の方程式の解を算出する数値計算が実行される（ステップ１０６）。すなわち、公知の手法を用いて燃焼反応に係る解が求められるとともに、オイラー法、ルンゲ−クッタ法、線形多段階法等の解法を用いて熱流束等の熱解析に係る解が、各格子に対して求めれる。ステップ１０６では、例えば、図５及び図６を参照して説明した三次過熱器４及び二次再熱器５に関する対流伝熱を示す離散化方程式を解き、各格子に対して熱流束を求める数値計算が実行されることになる。
【００４８】
次に、ステップ１０６で求めた解を用いて、各粒子に対して、粒子に対して設定された方程式の解を求める数値計算が実行される（ステップ１０７）。汎用熱流体解析プログラムでは、ステップ１０７において、運動量に係る方程式等を解くことで各粒子の軌跡解析を行うとともに、以下に示す熱解析に係る方程式を解くことで粒子の熱伝達と輻射熱に係る解が求められる。
【００４９】
【数１４】

ここに、ｍ_ｐは粒子の質量、ｃ_ｐは粒子の熱容量、Ａ_ｐは粒子の表面積、Ｔ∞はステップ１０６で求めた局所温度、ｈは対流熱伝達係数、ε_ｐは粒子の放射率、σはボルツマン定数、θ_Ｒは輻射温度（｛Ｉ／（４σ）｝^１／４；ただしＩは放射強度強度）である。
【００５０】
次に、ステップ１０６で用いる各メッシュの境界条件を、ステップ１０７で求めた各粒子に対する数値計算結果に基づいて更新する処理が行われる（ステップ１０８）。汎用熱流体解析プログラムでは、ステップ１０８において、次の熱流量Ｑに係る方程式が解かれ、熱流量Ｑが次のステップ１０６の数値計算においてエネルギー・バランスのエネルギのわき出し源あるいは吸い込み源として用いられる。
【００５１】
【数１５】

ここに、ｍ_ｐバーは格子（コントロールボリューム）中の粒子の平均質量、ｍ_ｐ０は粒子の初期質量、ｃ_ｐは粒子の熱容量、ΔＴ_ｐは格子中の粒子の温度変化、Δｍ_ｐは格子中の粒子の質量変化、ｈ_ｆｇは放出された揮発物の潜熱、ｈ_{ｐｙｒｏｌ}は揮発物が放出されるときの熱分解の熱、ｃ_ｐ，ｉは放出された揮発物の熱容量、Ｔ_ｐは格子の出口上の粒子の温度、Ｔ_ｒｅｆはエンタルピに対する基準温度、ｍ_ｐ０ドットは追跡される粒子注入の初期流量率である。ここで、上述したように本実施の形態ではステップ１０３で粒子が不活性に設定されているので、式（１３）の右辺の大括弧の中の第２項は零となる。
【００５２】
次に、収束条件の判定処理が行われる（ステップ１０９）。ここでは、例えば、数値計算の繰り返し回数が予め設定した値に達したか否かが判定され、達した場合には収束条件が満足したと判定される。一方、ステップ１０９で収束条件が満たされない場合には反復してステップ１０６〜ステップ１０８の数値計算処理が実行される。
【００５３】
ステップ１０９で収束条件が満足されると、時刻ｔが所定の時間増分Δｔだけ進められる（ステップ１１０）。次に、終了条件の判定処理が行われる（ステップ１１１）。ここでは、例えば、時刻ｔが予め設定した値に達したかどうかの判定が行われる。そして、条件が満たされない場合はステップ１０５に戻って再度数値計算処理が実行され、条件が満たされた場合は計算結果の出力が行われて（ステップ１１２）、処理が終了する。
【００５４】
以上に説明した実施の形態を用いてボイラの熱解析を行った結果の一例を図７及び図８に示す。図７は三次過熱器の無次元化した全吸収熱量（吸収熱量／平均吸収熱量）のボイラ中心からの距離（図４のＺ方向の距離）による変化を示す図であり、図８は二次過熱器の無次元化した全吸収熱量のボイラ中心からの距離による変化を示す図であり、参考として示すものである。図７に示すように、解析値と実測値は、ボイラ中心付近において変化の傾向が一致している。上述したように、本発明が主要な特徴とする構成は、三次過熱器や二次再熱器の対するメッシュを各吸熱体に対応させて分割する構成と、吸熱体間の各１つの格子に対する対流熱伝達の解析に新規な方程式を導入する構成と、灰分に対応する粒子の大きさを初期設定時から微小な大きさに設定するとともに不活性な特性を有するものとして設定する構成である。なお、これらの構成を採用しなかった場合には、図７に示す特性が、解析値として中央部分が盛り上がり、左右が盛り下がった山形の曲線を描くものとなっていた。
【００５５】
【発明の効果】
以上説明したように、本発明によれば、メッシュ分割数の増加を主要部のみに限定することができ、またその場合の解析精度の向上を図ることができ、さらに灰分に対応する粒子の解析効率を向上させることができる。したがって、より少ない計算機資源で、精度が高い計算結果を算出する計算装置及び方法を、容易に構築することができる。
【図面の簡単な説明】
【図１】本発明による火炉伝熱管の熱流束計算装置の一実施の形態における処理の流れを示すフローチャート。
【図２】本発明の一実施の形態の解析対象とするボイラの構成の一部を示す側断面図。
【図３】図２に示す炉１の平面断面図。
【図４】図２及び図３に示す炉１におけるメッシュ分割例を示す図（図４（ａ））であり、図４（ｂ）が三次過熱器４間に作成された格子の拡大図、図４（ｃ）が二次再熱器５間に作成された格子の拡大図である。
【図５】三次過熱器４及び二次再熱器５がなす吸熱板（吸熱体）に適用する熱解析に係る物理モデルを示す模式図。
【図６】図５に示す模式図に対応する平面模式図。
【図７】図１に示す実施の形態による解析結果の一例を示す図。
【図８】図１に示す実施の形態による解析結果の一例を示す図。
【符号の説明】
１　炉
２　火炉
３　二次過熱器
４　三次過熱器
５　二次再熱器[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a heat flux of a furnace heat transfer tube suitable for use in calculating a heat flux of a furnace heat transfer tube which is a heat transfer tube of a superheater or a reheater provided in a furnace which is a part for burning fuel in a boiler. The present invention relates to a computing device and method.
[0002]
[Prior art]
A boiler may be provided with a plurality of stages of a superheater for absorbing combustion heat to heat saturated steam and a reheater for reheating turbine high-pressure exhaust and medium-pressure exhaust. . For a superheater or a reheater, it is important to design the heat exchanger in accordance with the amount of heat received in order to prevent damage to the heat transfer tube due to blasting due to excessive heat. In particular, for the superheater and reheater provided near the downstream side in the flow direction of the combustion gas generated in the furnace or the furnace, not only the heat transfer from the combustion gas but also the detailed heat Analysis is required.
[0003]
In recent years, the above-described thermal analysis has been performed by computational fluid dynamics (CFD; Computational Fluid Dynamics). CFD is a discipline that analyzes the motion of a fluid using a computer. Japanese Patent Application Laid-Open No. 2000-346304, "Method and Apparatus for Predicting Wall Temperature of Boiler Heat Transfer Tube", and Japanese Patent Application Laid-Open No. 9-133321, "Method and Apparatus for Predicting In-furnace State of Pulverized Coal Combustion Apparatus", etc. An example of a conventional technique in analysis is described.
[0004]
In the CFD analysis, a physical model formed by discretizing an analysis target into a plurality of regions is created. Each region is formed of a two-dimensional or three-dimensional polygonal or polyhedral region, and is defined by position data representing a grid, a cell, and the like, and condition data representing physical property values, various boundary conditions, and the like. For each region, an approximation formula (discretization equation) obtained by discretizing a general conservation equation (General {conservation} (transport) @equation) for mass, momentum, energy, and the like, and other equations are applied, and values are applied to each region. By obtaining the value, the value of the entire analysis object is obtained. Such a numerical solution is called a discretized numerical solution and includes a finite element method, a difference method, a finite volume method, and the like depending on the discretization method. The finite element method approximates the distribution of the physical quantity within the element by a polynomial function, and the difference method approximates the differentiation of the physical quantity by a difference equation. The finite volume method approximates the balance between the inflow and outflow of physical quantities at the boundary of the volume / area area (control volume; mesh (grid)).
[0005]
[Problems to be solved by the invention]
In CFD thermal analysis of boilers, it is necessary to solve multiple discretized equations representing multiple changes such as chemical reaction in combustion, heat transfer by convection, radiant heat such as flame, non-flame, gas radiation, wall radiation, etc. It becomes. 2. Description of the Related Art In recent boilers, the configuration of each section has been made more precise for higher efficiency and the like. Therefore, a more accurate thermal analysis is required, and a computer having a higher calculation capability is desired as a computer used for the thermal analysis.
[0006]
On the other hand, there is a certain limit in the computational resources used in practice, and in order to obtain a desired computation result in a practical time, there is a restriction that the number of divisions of the region must be limited to a predetermined value or less. Sometimes. However, in the design of a boiler, higher precision is required as described above. In particular, in the design of a heat transfer tube such as a superheater or a reheater, a problem caused by excessive heat is avoided. Therefore, it is required to establish a more accurate thermal analysis method.
[0007]
The present invention has been made in consideration of the above circumstances, and provides an apparatus and a method for calculating a heat flux of a furnace heat transfer tube, which can calculate a calculation result with higher accuracy than before using only a small amount of computer resources. The purpose is to:
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 is an apparatus for performing heat flux calculation of a boiler having a plurality of heat absorbers provided on a downstream side in a flow direction of a combustion gas generated in a furnace. A plurality of discretized regions (hereinafter, referred to as a first discretized region) in which one discretized region is made to correspond to the flow path between the heat absorbers in the separation direction of the heat absorber, and a boiler A discretized region generating means for generating a plurality of discretized regions (hereinafter, referred to as a second discretized region) with respect to another region; and a thermal analysis for each of the discretized regions generated by the discretized region generating device. And a numerical calculation means for repeatedly performing numerical calculations on all discretized regions using the calculation results for other regions by applying the plurality of numerical formulas according to the above.
[0009]
The invention according to claim 2 is characterized in that the numerical calculation means applies a first plurality of numerical calculation expressions relating to thermal analysis to each of the second discretized regions, and calculates a calculation result for another region. Numerical calculations are repeatedly performed for all the discrete regions while using, and for each of the first discrete regions, the flow velocity and temperature of the combustion gas adjacent to each of the heat absorbers and the outer surface temperature of the heat absorber are set as variables. It is characterized in that a second plurality of numerical formulas including a numerical formula relating to heat transfer are applied, and numerical calculations are repeatedly performed using the calculation results for other regions. In the invention according to claim 3, a numerical value 、 calculation formula relating to the heat transfer in the second plurality of numerical calculation formulas is:
(Equation 2)

However, Q_cIs the amount of heat transfer by convection, α and β are empirical constants, | V_g| And T_gAre the absolute flow velocity and temperature of the gas adjacent to the heat absorber wall, respectively, T_wIs the outer surface temperature of the wall, A_cIs a heat transfer area.
[0010]
According to a fourth aspect of the present invention, there is provided an apparatus for calculating a heat flux of a boiler provided with a plurality of groups of heat absorbers on a downstream side in a flow direction of a combustion gas generated in a furnace, wherein a plurality of discretized regions are generated for the boiler. Applying a plurality of numerical formulas related to thermal analysis to each of the discretized regions generated by the discretized region generating means and the discretized regions generated by the discretized region generating means, and performing total discretization while using the calculation results for other regions. A first numerical calculation means for repeatedly performing numerical calculation on a region, and a numerical calculation formula related to a predetermined thermal analysis is applied to a plurality of inert and small particle models having a predetermined size to perform a numerical calculation. It is characterized by comprising a second numerical calculation means, and a coupling means for coupling a calculation result by the second numerical calculation means to a numerical calculation by the first numerical calculation means.
[0011]
According to a fifth aspect of the present invention, there is provided a method for calculating a heat flux of a boiler having a plurality of heat absorbers provided on a downstream side in a flow direction of a combustion gas generated in a furnace, wherein a flow path between each pair of heat absorbers is provided. On the other hand, a plurality of discretized regions (hereinafter, referred to as a first discretized region) in which each one of the discretized regions is made to correspond to the direction in which the heat absorber is separated are generated, and a plurality of discretized regions are formed with respect to other regions of the boiler. A discretized region generating step of generating a discretized region (hereinafter, referred to as a second discretized region); and a plurality of numerical calculation expressions related to thermal analysis for each of the discretized regions generated in the discretized region generating process. And a numerical calculation step of repeatedly performing numerical calculations on all discretized regions while using the calculation results for other regions.
[0012]
In the invention according to claim 6, in the numerical calculation process, a first plurality of numerical calculation expressions related to thermal analysis are applied to each of the second discretized regions, and calculation results for other regions are calculated. Numerical calculations are repeatedly performed for all the discrete regions while using, and for each of the first discrete regions, the flow velocity and temperature of the combustion gas adjacent to each of the heat absorbers and the outer surface temperature of the heat absorber are set as variables. A second plurality of numerical formulas including a numerical formula relating to heat transfer are applied, and the numerical calculation is repeatedly performed using the calculation results for other regions.
[0013]
According to a seventh aspect of the present invention, there is provided a method for calculating a heat flux of a boiler having a plurality of heat absorbers provided on a downstream side in a flow direction of a combustion gas generated in a furnace, wherein a plurality of discretized regions are generated for the boiler. Applying a plurality of numerical formulas relating to thermal analysis to each of the discretized regions generated in the discretized region generation process and the discretized regions generated in the discretized region generation process, A first numerical calculation process of repeatedly performing a numerical calculation on the activated region, and applying a numerical calculation formula related to a predetermined thermal analysis to a plurality of inert and small particle models having a predetermined size, and performing the numerical calculation. A second numerical calculation step to be performed; and a combining step of combining a calculation result obtained in the second numerical calculation step with the numerical calculation in the first numerical calculation step. .
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a heat flux calculation device for a furnace heat transfer tube according to the present invention will be described with reference to the drawings. The computing device according to the present embodiment includes a computer and its peripheral devices, and a program executed by the computer.
[0015]
FIG. 1 is a flowchart showing the flow of processing by the program according to the present embodiment. In the heat flux calculation process according to the present embodiment, first, data representing a geometric shape of a model is created by a computer (step 101). In step 101, for example, the operator creates three-dimensional coordinates in a rectangular coordinate system representing each component constituting the boiler using a general-purpose CAD (computer-assisted drafting) program or the like.
[0016]
Here, with reference to FIG. 2 and FIG. 3, a description will be given of the structure of the boiler to be calculated in the present embodiment. FIG. 2 is a side view showing a sectional structure of an upper part of the furnace 1 of the boiler, and FIG. 3 is a sectional plan view of the upper part of the furnace 1 shown in FIG. A device (burner) that includes a fuel injection device and an air amount adjusting device and mixes and burns air and fuel is provided in the direction of arrow 10. The direction of the flow of the combustion gas burned by the burner is the direction represented by arrows 11a, 11b, and 11c.
[0017]
In the furnace 2, a secondary superheater 3, a tertiary superheater 4, and a secondary reheater 5 are provided. The secondary superheater 3, the tertiary superheater 4, and the secondary reheater 5 are assembled by attaching a plurality of steel pipes to a plurality of headers so as to form a flat (plate) shape. In the example shown in FIG. 2 and FIG. 3, eight secondary superheaters 3, 44 tertiary superheaters 4, and 64 A secondary reheater 5 is provided.
[0018]
In addition, the primary reheater 6 and the primary superheater 7 are located downstream of the secondary superheater 3, the tertiary superheater 4, and the secondary reheater 5 in the flow direction of the combustion gas, and the nodes are further downstream thereof. A charcoal device 8 is provided. In this case, the primary reheater 6 includes an upper reheater 6a and a lower reheater 6b. The primary superheater 7 includes an upper superheater 7a and a lower superheater 7b. The economizer 8 serves as a feed water heater for recovering heat of the combustion gas of the boiler and heating the boiler water, and includes a primary path 8a and a secondary path 8b.
[0019]
Now, in step 101 of FIG. 1, the upper configuration of the furnace 1 shown in FIGS. 2 and 3 and the lower configuration of the burner and the like of the furnace 1 not shown in FIGS. Coordinate data representing models corresponding to both are created. Next, a process of creating a mesh for discretizing the model created in step 101 into a plurality of small regions is performed (step 102 in FIG. 1). In this case, the mesh is composed of a plurality of three-dimensional spatial grids (discrete areas).
[0020]
Here, with reference to FIG. 4, a method of creating a mesh which is a feature of the present invention will be described. FIG. 4A is a diagram showing an example of mesh creation for the secondary superheater 3, the tertiary superheater 4, and the secondary reheater 5 shown in FIG. However, FIG. 4A is shown in the direction viewed from the back side of the paper of FIG.
[0021]
Each secondary superheater 3, each tertiary superheater 4, and each secondary reheater 5 are each divided into a plurality of grids with respect to the XY plane as shown in the figure. In the Z direction, one grid corresponding to each superheater and the thickness of the superheater, or a plurality of grids that divide the thickness into a plurality is created.
[0022]
A plurality of grids (not shown) are created for spaces in the furnace 2 other than the secondary superheaters 3, the tertiary superheaters 4, and the secondary reheaters 5. However, in the present embodiment, the space between the tertiary superheaters 4 and the space between the secondary reheaters 5 are divided into meshes according to the following conditions. That is, as for the space between the tertiary superheaters 4, only one grid is provided in the separation direction (in this case, the Z direction), for example, as shown in grids G4a and G4b shown in FIGS. The mesh division is performed so that is created. Similarly, the space between the secondary reheaters 5 is only one in the separation direction (in this case, the Z direction), for example, as shown in a grid G5a shown in FIGS. 4 (a) and 4 (c). The mesh is divided so that only the grid is created.
[0023]
When the mesh creation processing (Step 102 in FIG. 1) is completed as described above, next, analysis condition setting processing is performed corresponding to the created mesh (Step 103). In step 103, changes in a plurality of physical quantities, such as radiant heat such as chemical reaction in combustion, heat transfer by convection, flame, non-flame, gas radiation, and wall radiation, which are obtained for use in thermal analysis by CFD, are represented. In addition to setting a plurality of discretization equations, condition data representing physical property values, various boundary conditions, and the like, setting of conditions for particles when performing trajectory analysis, and the like are performed.
[0024]
The basic technology of the thermal analysis of the boiler in the present embodiment is a known technology as described in the gazette shown in the section of the prior art. On the other hand, for fluid analysis by CFD, a general-purpose fluid analysis program applicable to the analysis of various physical models has been put to practical use and is commercially available. In the present embodiment, a new numerical formula is used for some of the discretization equations, and a new setting is used for the analysis condition of the particle analysis corresponding to the ash content of the combustion. On the other hand, as other analysis methods, known methods can be used.
[0025]
In the following, a configuration related to the setting of a part of the discretization equation and a configuration related to the setting of the particle analysis, which are features of the present embodiment, will be described in detail. However, it is assumed that the fluid analysis by the CFD of the present embodiment is realized by using a commercially available fluid analysis program, and the new configuration described above is characterized by the features of the commercially available fluid analysis program. A configuration in the case of applying a part will be described. Specifically, US commercially available Fluent Inc. , A general-purpose thermo-fluid analysis program, STAR-CD, and the like. The thermofluid analysis program FLUENT is a program that uses the finite volume method as a discretized model, and is capable of analyzing compressible or incompressible thermo-fluid analysis, analysis of chemical reactions and combustion, radiation and fluid-solid heat transfer coupled analysis, etc. An analysis by computational fluid dynamics (CFD) can be executed.
[0026]
By the way, in the setting of the analysis condition in step 103, the setting can be performed as follows as an example. As a turbulence model, a k-ε model, which is a two-equation turbulence model, is used. The diameter of the particles corresponding to the ash content is usually set to about 50 μm, but is set to be constant at 1 μm, and the state of the particles is in an inactive state (a property that does not evaporate or change chemically at high temperatures). ). These settings are for preventing the calculation of the trajectory of each particle from deteriorating the convergence of the calculation relating to the heat flow and the like for each mesh.
[0027]
For the tertiary superheater 4 and the secondary reheater 5, a discretization equation corresponding to convective heat transfer was set as follows. That is, in the present embodiment, for the tertiary superheater 4 and the secondary reheater 5, only a single grid is set in the space between the plurality of heat absorbers (heat transfer tube portions of the superheater and the reheater). I have. Therefore, the new equation was adopted in order to improve the analysis accuracy of the convective conduction between the heat absorbers.
[0028]
Generally, gas side convective heat transfer to a heat transfer wall element can be represented by the following equation (1), which is a general form for forced convective heat transfer.
(Equation 3)

Where N_uIs the Nusselt number (nusselt number), R_eIs the Reynolds number (Reynolds number), P_rIs the Prandtl number (Prandtl number), and a, b, and c all represent coefficients.
[0029]
However, in the thermal fluid analysis program FLUENT, the gas-side convective heat transfer to the heat transfer wall element is not represented by the equation (1), but in the form of a wall temperature gradient in the temperature boundary layer that can be formed by the heat transfer wall element. It is represented by the following equation (2).
(Equation 4)

Where q_cIs the absorbed heat flux due to convective heat transfer, λ_gAnd T_gRepresents the thermal conductivity and temperature of the gas, and x represents the distance from the convective heat transfer surface.
[0030]
Therefore, conventionally, in order to correctly evaluate the convective heat transfer amount, it has been necessary to finely mesh the gas flow path adjacent to the heat transfer wall element to such an extent that the temperature boundary layer can be correctly calculated. However, the tertiary superheater 4, the secondary reheater 5 and the like are composed of dozens of panels even in a single furnace, and in order to solve the temperature boundary layer in this region, it is necessary to solve the temperature boundary layer in the furnace width direction (the horizontal direction in FIG. 3). ) Needs to have several hundred meshes. Then, the entire furnace has a huge number of meshes exceeding 10 million. This means that the current computer equipment requires a calculation time of, for example, about one year per case, which is not practical. Therefore, for the tertiary superheater 4 and the secondary reheater 5 targeted this time, the convection heat transfer amount can be correctly evaluated even with one gas element between panels (between heat absorbers). Gas side convection heat transfer coefficient R_cThe following Grimison equation was applied.
[0031]
(Equation 5)

Where F_aIs the form factor of the tube bank, λ_gmRepresents the thermal conductivity of the gas, and d represents the tube diameter.
[0032]
Next, the following equation (4) was created by modifying the equation (3) in the same manner as the relationship between the equations (1) and (2). Then, in step 103, the empirical equation (4) is set as an equation for calculating convective heat transfer for the tertiary superheater 4 and the secondary reheater 5. In the general-purpose thermo-fluid analysis program, a user subroutine was created based on equation (4).
[0033]
(Equation 6)

Where Q_cIs the amount of heat transfer by convection, and α and β are empirical constants. ｜ V_g| And T_gAre the absolute flow velocity and temperature of the gas adjacent to the heat absorbing body wall (panel or heat absorbing plate), respectively._wIndicates the outer surface temperature of the wall. A_cRepresents the heat transfer area.
[0034]
Wall outer surface temperature T_wIs the wall heat absorption Q and the fluid temperature T in the pipe, including the convection heat transfer including the radiant heat transfer from the furnace and the gas in the panel._lMust be linked with. That is, if h is the heat transfer coefficient from the fluid in the pipe to the outer surface of the pipe, and A is the heat transfer area, the outer surface temperature T of the wall_wCan be expressed by the following equation.
(Equation 7)

[0035]
Here, a physical model applied to the tertiary superheater 4 and the secondary reheater 5 and a numerical calculation method in step 106 will be described with reference to FIGS. FIG. 5 is a schematic diagram showing a heat flux with respect to the heat absorbing plates (the tertiary superheater 4 and the secondary reheater 5) in the furnace 2. FIG. 6 is a plan view corresponding to the physical model shown in FIG.
[0036]
In FIG. 6, one wall component 20 corresponding to the tertiary superheater 4 or the secondary reheater 5 is provided in the furnace 2. For this wall surface component 20, wall surface element number n, wall element number k, wall temperature T_wk, Fluid temperature T_sn, Wall thermal conductivity λ_wn, Wall thickness δ_wnIs defined.
[0037]
In FIG. 6, the absorbed heat flux q at the element number k in the wall surface component n_kCan be expressed by the following equation.
(Equation 8)

Where q_rk= [Radiation from flame + radiation from inflame flame + radiation from wall] and q_ck= [Convective heat transfer between gas element j and wall element k]. This heat flux q_rkCan be obtained by radiation calculation using a known DO (Discrete @ Ordinate) model.
[0038]
And the variable q_ckIs represented by the following equation (7).
(Equation 9)

[0039]
However, heat flux q_rkTemperature T required for radiation calculation_wkTakes into account the values calculated by equation (6) and equation (8) below.
(Equation 10)

[0040]
Here, Expression (6) is considered as follows, taking into account the number of repetitions in the numerical calculation for each mesh in step 106. Here, the subscript N indicates the number of repetitions for the Nth time.
[Equation 11]

[0041]
Further, Equation (8) is considered as follows.
(Equation 12)

From this relation, the wall temperature T_wkIs the absorbed heat flux q in the Nth iteration calculation^N _kIt can be seen from the above that it is required.
[0042]
From the relationship between the remaining equations (8) and (7), equation (9) can be written as:
(Equation 13)

[0043]
That is, the absorbed heat flux q in the (N + 1) th repetitive calculation_k ^{N + 1}Is the absorbed heat flux q in the Nth iteration calculation_k ^NIs a function of Here, in the general-purpose thermo-fluid analysis program, in step 103 of FIG. 1, the absorbed heat flux q_k ^{N + 1}Is input as the boundary condition.
[0044]
Note that the coefficients α, β_k, Δ_wnCan be all constants. In addition, the calculation (physical) model may be, for example, a two-dimensional model in which the left side is an intake port, the right side is an exhaust port, and there is one wall in the area, as shown in FIG.
[0045]
As described above, after completing the setting of various analysis conditions including the setting of the discretized equation indicating the convective heat transfer regarding the tertiary superheater 4 and the secondary reheater 5 (Step 103 in FIG. 1). A process for setting initial conditions for analysis is performed (step 104). In step 104, initial values of various variables used for numerical calculation are set.
[0046]
Next, the analysis control parameters are adjusted as necessary according to the operating state and the like (step 105). Here, for example, a temporal change can be given to a parameter or the like representing the amount of injected fuel.
[0047]
Next, numerical calculation for calculating solutions of a plurality of equations set for each mesh is executed (step 106). That is, a solution related to the combustion reaction is obtained using a known method, and a solution related to a heat analysis such as a heat flux using a solution such as an Euler method, a Runge-Kutta method, a linear multi-step method is applied to each lattice. Is required. In step 106, for example, the discretization equation showing the convective heat transfer regarding the tertiary superheater 4 and the secondary reheater 5 described with reference to FIGS. The calculation will be performed.
[0048]
Next, using the solution obtained in step 106, a numerical calculation is performed for each particle to obtain a solution of an equation set for the particle (step 107). In the general-purpose thermo-fluid analysis program, in step 107, the trajectory analysis of each particle is performed by solving an equation relating to momentum, and the solution relating to heat transfer and radiant heat of the particle is solved by solving an equation relating to the following thermal analysis. Is required.
[0049]
[Equation 14]

Where m_pIs the mass of the particle, c_pIs the heat capacity of the particles, A_pIs the surface area of the particle, T∞ is the local temperature obtained in step 106, h is the convective heat transfer coefficient, ε_pIs the emissivity of the particle, σ is Boltzmann's constant, θ_RIs the radiation temperature ({I / (4σ))}^1/4Where I is the radiation intensity).
[0050]
Next, a process of updating the boundary conditions of each mesh used in step 106 based on the numerical calculation result for each particle obtained in step 107 is performed (step 108). In the general-purpose thermo-fluid analysis program, in step 108, an equation relating to the next heat flow rate Q is solved, and the heat flow rate Q is used as an energy source or a suction source of energy balance in the numerical calculation in the next step 106. .
[0051]
[Equation 15]

Where m_pThe bar is the average mass of the particles in the grid (control volume), m_p0Is the initial mass of the particle, c_pIs the heat capacity of the particle, ΔT_pIs the temperature change of the particles in the lattice, Δm_pIs the mass change of the particles in the lattice, h_fgIs the latent heat of the released volatiles, h_pyrolIs the heat of pyrolysis when volatiles are released, c_{p, i}Is the heat capacity of the released volatiles, T_pIs the temperature of the particles on the outlet of the grid, T_refIs the reference temperature for enthalpy, m_p0The dot is the initial flow rate of the tracked particle injection. Here, as described above, in the present embodiment, since the particles are set to be inactive in step 103, the second term in the square bracket on the right side of Expression (13) becomes zero.
[0052]
Next, convergence condition determination processing is performed (step 109). Here, for example, it is determined whether the number of repetitions of the numerical calculation has reached a preset value, and if it has, it is determined that the convergence condition has been satisfied. On the other hand, when the convergence condition is not satisfied in step 109, the numerical calculation processing of steps 106 to 108 is repeatedly executed.
[0053]
When the convergence condition is satisfied in step 109, the time t is advanced by a predetermined time increment Δt (step 110). Next, a termination condition determination process is performed (step 111). Here, for example, it is determined whether or not the time t has reached a preset value. If the condition is not satisfied, the process returns to step 105 to execute the numerical calculation process again. If the condition is satisfied, the calculation result is output (step 112), and the process ends.
[0054]
FIGS. 7 and 8 show an example of a result of performing a thermal analysis of the boiler using the embodiment described above. FIG. 7 is a diagram showing the change of the dimensionless total absorbed heat (absorbed heat / average absorbed heat) of the tertiary superheater according to the distance from the boiler center (distance in the Z direction in FIG. 4), and FIG. It is a figure which shows the change by the distance from the boiler center of the dimensionless total absorbed heat of the superheater, and is shown as a reference. As shown in FIG. 7, the analysis value and the measured value have the same tendency of change near the boiler center. As described above, the main features of the present invention include a configuration in which a mesh for a tertiary superheater or a secondary reheater is divided corresponding to each heat absorber, and a configuration in which each mesh between the heat absorbers is divided. One is to introduce a new equation into the analysis of convective heat transfer, and the other is to set the size of the particles corresponding to the ash to a minute size from the time of initial setting and to set it as having an inert characteristic. When these configurations were not adopted, the characteristics shown in FIG. 7 were such that the analysis value represented a mountain-shaped curve in which the central portion was raised and the left and right were lowered.
[0055]
【The invention's effect】
As described above, according to the present invention, it is possible to limit the increase in the number of mesh divisions to only the main part, to improve the analysis accuracy in that case, and to analyze particles corresponding to ash. Efficiency can be improved. Therefore, it is possible to easily construct a computer and a method for calculating a highly accurate calculation result with less computer resources.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a flow of processing in an embodiment of a heat flux calculation device for a furnace heat transfer tube according to the present invention.
FIG. 2 is a side sectional view showing a part of a configuration of a boiler to be analyzed according to the embodiment of the present invention.
FIG. 3 is a plan sectional view of the furnace 1 shown in FIG.
4 is a diagram showing an example of mesh division in the furnace 1 shown in FIGS. 2 and 3 (FIG. 4A), and FIG. 4B is an enlarged view of a lattice created between the tertiary superheaters 4, FIG. 4C is an enlarged view of a grid created between the secondary reheaters 5.
FIG. 5 is a schematic diagram showing a physical model related to thermal analysis applied to a heat absorbing plate (heat absorbing body) formed by the tertiary superheater 4 and the secondary reheater 5;
FIG. 6 is a schematic plan view corresponding to the schematic diagram shown in FIG. 5;
FIG. 7 is a view showing an example of an analysis result according to the embodiment shown in FIG. 1;
FIG. 8 is a view showing an example of an analysis result according to the embodiment shown in FIG. 1;
[Explanation of symbols]
1 furnace
2 furnace
3 Secondary heater
4. Tertiary superheater
5 secondary reheater

Claims (7)

In a device for calculating the heat flux of a boiler provided with a plurality of heat absorbers on the downstream side in the flow direction of the combustion gas generated in the furnace,
A plurality of discretized regions (hereinafter, referred to as a first discretized region) in which one discretized region is made to correspond to a flow path between each pair of heat absorbers in a direction in which the heat absorbers are separated from each other are generated. A discretized area generating means for generating a plurality of discretized areas (hereinafter, referred to as a second discretized area) with respect to another area of the boiler;
For each discretized region generated by the discretized region generating means, a plurality of numerical formulas related to thermal analysis are applied, and numerical values for repeatedly performing numerical calculations for all discretized regions using calculation results for other regions A heat flux calculation device, comprising: calculation means. The numerical calculation means,
For each of the second discretized regions, applying a first plurality of numerical formulas related to thermal analysis, and repeatedly performing numerical calculations on all discretized regions while using the calculation results for other regions,
For each of the first discretized regions, a second formula including a numerical calculation formula relating to heat transfer with the flow velocity and temperature of the combustion gas adjacent to each heat absorber and the outer surface temperature of the heat absorber as variables. 2. The heat flux calculator according to claim 1, wherein a plurality of numerical formulas are applied, and the numerical calculation is repeatedly performed using the calculation results for other areas. Numerical expressions related to the heat transfer in the second plurality of numerical expressions,

Where _Qc is the amount of heat transfer by convection, α and β are empirical constants, | V _g | and T _g are the absolute flow velocity and temperature of the gas adjacent to the heat absorber wall, and _Tw is the outer surface temperature of the wall. , _Ac is the heat transfer area,
The heat flux calculation device according to claim 2, wherein In a device for calculating the heat flux of a boiler provided with a plurality of heat absorbers on the downstream side in the flow direction of the combustion gas generated in the furnace,
Means for generating a plurality of discretized regions for the boiler,
Applying a plurality of numerical calculation formulas related to thermal analysis to each of the discretized regions generated by the discretized region generating means, and repeatedly performing numerical calculations on all the discretized regions while using the calculation results for other regions. Numerical calculation means of 1,
A second numerical calculation unit that performs a numerical calculation by applying a numerical calculation formula related to a predetermined thermal analysis to a plurality of inert and small particle models having a predetermined size,
A heat flux calculating device, comprising: a coupling means for coupling a calculation result by the second numerical calculation means to a numerical calculation by the first numerical calculation means. In a method for calculating a heat flux of a boiler including a plurality of heat absorbers provided on a downstream side in a flow direction of a combustion gas generated in a furnace,
A plurality of discretized regions (hereinafter, referred to as a first discretized region) in which one discretized region is made to correspond to a flow path between each pair of heat absorbers in a direction in which the heat absorbers are separated from each other are generated. Generating a plurality of discretized regions (hereinafter, referred to as a second discretized region) with respect to other regions of the boiler;
A plurality of numerical formulas related to thermal analysis are applied to each of the discretized regions generated in the discretized region generation process, and numerical calculations are repeatedly performed on all the discretized regions while using the calculation results for other regions. A heat flux calculation method, comprising: a numerical calculation step. In the numerical calculation process,
For each of the second discretized regions, applying a first plurality of numerical formulas related to thermal analysis, and repeatedly performing numerical calculations on all discretized regions while using the calculation results for other regions,
For each of the first discretized regions, a second formula including a numerical calculation formula relating to heat transfer with the flow velocity and temperature of the combustion gas adjacent to each heat absorber and the outer surface temperature of the heat absorber as variables. 6. The heat flux calculation method according to claim 5, wherein a plurality of numerical formulas are applied, and the numerical calculations are repeatedly performed using the calculation results for other regions. In a method for calculating a heat flux of a boiler including a plurality of heat absorbers provided on a downstream side in a flow direction of a combustion gas generated in a furnace,
A discretized region generation process for generating a plurality of discretized regions for the boiler;
A plurality of numerical formulas related to thermal analysis are applied to each of the discretized regions generated in the discretized region generation process, and numerical calculations are repeatedly performed on all the discretized regions while using the calculation results for other regions. A first numerical calculation process;
A second numerical calculation process in which a numerical calculation formula related to a predetermined thermal analysis is applied to a plurality of inert and small particle models having a predetermined size, and a numerical calculation is performed,
A method of calculating the heat flux, the method further comprising: combining the calculation result obtained in the second numerical calculation step with the numerical calculation in the first numerical calculation step.

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