基于計算機的電廠鍋爐監(jiān)控系統(tǒng)外文翻譯、中英文翻譯、外文文獻翻譯

基于計算機的電廠鍋爐監(jiān)控系統(tǒng)外文翻譯、中英文翻譯、外文文獻翻譯,基于,計算機,電廠,鍋爐,監(jiān)控,系統(tǒng),外文,翻譯,中英文,文獻 附錄A 譯文 基于計算機的電廠鍋爐監(jiān)控系統(tǒng) J Taler1, BWeglowski1, W Zima1*, P Duda1, S Gradziel1,T Sobota1,A Cebula1,and D Taler2 工藝和電力工程研究所，克拉科夫大學(xué)，波蘭 AGH科技大學(xué)，波蘭 接受時間：2007.2.2， 公布時間（經(jīng)修改）2007.10.24 摘要 以計算機為基礎(chǔ)的鍋爐性能監(jiān)測系統(tǒng)的開發(fā)，首要進行熱工計算，測量各種溫度，熱通量，壓力和燃料，分析數(shù)據(jù)，這些數(shù)據(jù)被用來進行傳熱分析，以便控制蒸發(fā)器，電爐，以及流量等。 一個新的工藝技術(shù)熱通量管，用來確定所吸收的熱通量。通量管安裝在不同級別的鍋爐中，其工作條件類似于水墻管。熱通量測量燃煤蒸汽鍋爐是目前比較好的選擇。 鍋爐負荷是變化的，水循環(huán)必須不能超出一定范圍。迅速增加的壓力可能會導(dǎo)致水因過渡沸騰而使水冷壁無法保護爐墻，而迅速下降的壓力，導(dǎo)致鍋爐系統(tǒng)中的鍋爐蒸發(fā)器所有要素迅速下降。這兩種情況下會導(dǎo)致水循環(huán)流動停滯 ，導(dǎo)致管道開裂。兩個流量計組裝在210（蒸汽能力 210X103千克/小時）鍋爐自然水循環(huán)過程中進行。根據(jù)這些測量，壓力改變時鍋爐過熱器最高速度應(yīng)被限制。 根據(jù)實時計算，燃燒室可以實時確定需要多少熱流量轉(zhuǎn)移到電站鍋爐蒸發(fā)器。此外， 表面清潔度，選擇性吹灰，也可用在具體的問題中介紹。鍋爐監(jiān)控系統(tǒng)也提供詳細的鍋爐效率的變化和經(jīng)營狀況，在后一階段對特定吹灰序列進行分析和優(yōu)化。 本文還分析了在啟動和關(guān)閉的鍋爐時，鍋爐氣鼓中的壓力 關(guān)鍵詞：電站鍋爐，熱通量的測量，蒸發(fā)器，水循環(huán)，性能和熱應(yīng)力監(jiān)測 1 緒論 電站鍋爐關(guān)閉和啟動進程，以及鍋爐負荷的變化過程中，不容許鍋爐應(yīng)力超過限制，而至關(guān)重要的是水循環(huán)要時刻保持著。迅速增加的壓力可能會導(dǎo)致水因過渡沸騰而使水冷壁無法保護爐墻，而迅速下降的壓力，導(dǎo)致鍋爐系統(tǒng)中的鍋爐蒸發(fā)器所有要素迅速下降，這兩種情況下會導(dǎo)致流動停滯水循環(huán)中的蒸發(fā)器，導(dǎo)致管道開裂。因此，在210（鍋爐容量為 210X103千克/小時的生活蒸汽，9.8兆帕的壓力和530到545的溫度）鍋爐自然水循環(huán)過程中要組裝兩個流量計。根據(jù)水循環(huán)參數(shù)確定一個鍋爐蒸發(fā)器的最大壓力。 控制的主要任務(wù)是鍋爐負荷變化限制在標(biāo)準(zhǔn)范圍內(nèi)。比如說鍋爐汽鼓，特別是汽鼓和鍋爐管道的連接處，特別要強調(diào)在這些連接處，同等的分配壓力，因為他們在很大程度上，對鍋爐汽包的加熱和冷卻率有影響。鍋爐制造商建議的具體加熱和冷卻率是有所保留的，鍋爐汽鼓，往往可能是比建議的大些。通過提高利用率的這種方法，鍋爐瞬變的時間可縮短。 監(jiān)測的任務(wù)還包括鍋爐監(jiān)測范圍內(nèi)很多的其他參數(shù)，包括影響其效率和安全性的參數(shù)。目前提出了一種系統(tǒng)，可以在線監(jiān)測的運行條件下的蒸發(fā)器。其基本內(nèi)容是一套原始熱通量管用來確定溫度和熱負荷分布的高度鍋爐燃燒室。重要的是檢測正常運行的蒸發(fā)器和燃燒室。所得結(jié)果也可以用來監(jiān)測流通水蒸汽混合物和沉積物在水冷壁管內(nèi)表面的沉積多少。該系統(tǒng)輔以測量蒸汽水的流量，控制循環(huán)系統(tǒng)，鍋爐的在線模式也應(yīng)考慮到由于系統(tǒng)的可變性，可能會導(dǎo)致空氣過量的問題，這直接影響鍋爐效率。其解決的辦法，可減少相應(yīng)的供給，如鼓風(fēng)量和相應(yīng)開關(guān)的開通量，同時利用熱通量管設(shè)在不同的層次?？諝夥峙鋺?yīng)確保排放的氮氧化物和內(nèi)含易燃物、內(nèi)含容粉煤灰低于允許的水平。那個正確的估計程度的結(jié)渣中的鍋爐燃燒室也非常重要。時間變化的分庭墻結(jié)渣系數(shù)，隨著變化的水體流向 ，其它系統(tǒng)可可根據(jù)程序自動激活并運行，包括送煤機、除渣機和鼓風(fēng)機。 比較，計算和測量過熱蒸汽質(zhì)量流量，燃燒室壁平均結(jié)渣一定程度的時間。這樣吹灰器可以充分自動化的運行在一個燃燒室，因此也會充分使用吹灰器并增加水冷壁壽命。在線計算燃燒室實時熱流量，其流量是轉(zhuǎn)移到電站鍋爐蒸發(fā)器?；谀芰科胶?，計算電站鍋爐蒸發(fā)器的過熱蒸汽質(zhì)量流量。 一些調(diào)查人員已促成各種方面的熱性能和剩余壽命理論研究來監(jiān)測發(fā)電廠。檢測熱信號的在線檢測被許多論文中被認可[5，6]，用于在線檢測疲勞退化程度的有限元的疲勞監(jiān)測系統(tǒng)顯示在參考[7]，文件[ 8 ]介紹了實際已經(jīng)執(zhí)行部分在線監(jiān)測的發(fā)電廠。 2 熱負荷測量燃燒室壁 由于測量高溫?zé)煔鈺r有很多困難的，鍋爐燃燒室在熱負荷運行，對其檢測，用測溫用儀器如圖1。熱負荷的密度吸收熱通量，其定義是：同比熱流量吸收爐墻表面積熱量，溫度測量器的插入前端（如圖1中1處），溫度測量選擇四個鎳鎳鉻熱電偶（外直徑鞘相當(dāng)于1毫米） ，放置在洞內(nèi)，插入到平行軸，避免錯誤造成的熱傳導(dǎo)沿軸的滑動空隙流出。這種分配原因是溫度保持不變， 20毫米寬槽，是溫度計所在，是涵蓋了3毫米耐熱金屬板材，預(yù)防被焚燒（圖1）。中心被填充20g鋼，導(dǎo)熱系數(shù)K的確定 K(T)=53.26-0.0235684TW/(mk) （1） 插入是否能夠安全工作，計算方法采用有限元方法演算。平均壓力假設(shè)為P=11 MPa和系統(tǒng)的溫度被假設(shè)為T=370攝氏度，利用軟件，參考[10] 可等于118兆帕的壓力，而最大應(yīng)力在假定負荷等于73兆帕。因此，最大應(yīng)力低于允許值。圖中Ⅰ，我水冷壁管;Ⅱ， 離心管;Ⅲ，耐熱金屬薄膜覆蓋;Ⅳ，管以外的鍋爐，以及1-5個位置 圖1 熱負荷測量。 Fig.1 Heat load measuring inser 2.1 熱負荷能力說明 為了確定水冷壁熱負荷的供給，溫度T1、T2、T3、和T4四點測得測量值。熱分布計算使用方法為有限容量的CFD軟件[ 11 ]。平均溫度差 （2） 由于對稱性的溫度測量器插入，只有插入一半的截面，插入表面的密度變化的熱通量取決于結(jié)渣因子C ，其中的變化顯著的位置。插入表面上的分散熱通量密度接近使用步驟線。后表面插入和管完全絕緣。管的內(nèi)表面屬于第三種邊界條件，需要的知識有熱傳熱系數(shù)A和平均溫度等假定，熱負荷可以表示為一個函數(shù)的測量溫度差 （3） 其中溫差有公式2獲得。 溫度T1、T2、T3、和T4四點計算使用CFD軟件[ 11 ]在熱負荷q及傳熱系數(shù)和溫度介質(zhì)假設(shè)的前提下Tm為320度。結(jié)果的數(shù)值計算 近似使用的功能（ 3 ）通過最小二乘法。常數(shù)A和B ，其中取決于傳熱系數(shù)A對內(nèi)表面的插入深度。 a=8367.9549W/m2 b=5357.8165W/(m2k) for a=6800.9789W/m2 b=5432.89W/(m2k) for a=4899.9549W/m2 b=5519.0645W/(m2k) for 分析的變化，證明，傳熱系數(shù)A的內(nèi)表面的管道有一個輕微影響熱負荷值q。這略微令人吃驚的結(jié)果可以解釋事實上，當(dāng)值的減小，導(dǎo)致溫度通過厚度的壁。同時，減少系數(shù)原因增加了插入溫度對一側(cè)的爐，而這反過來又造成減少熱傳導(dǎo)k確定由方程（ 1 ）和增加的溫度通過減少厚度的墻。這兩個相反的現(xiàn)象。 （4） 方程（ 4 ）得出的假設(shè)，即插入的內(nèi)部表面是干凈的，沒有殘留的低導(dǎo)熱系數(shù)（鍋爐規(guī)模或鐵的氧化物）的表面。如果內(nèi)部表面插入覆蓋規(guī)模沉積，然后增加插入溫度前表面，反過來又造成增加周圍熱流在減少。為了證明正確的熱負荷q在測量時，當(dāng)插入內(nèi)表面上沉積特征的規(guī)模使低導(dǎo)熱系數(shù)積累，計算溫度分布，插入清潔內(nèi)表面和骯臟的內(nèi)表面那樣，用流利溫度測量器插入位于十五點四米水平的正面墻上密度吸收熱通量流Q計算 運用這些數(shù)據(jù)，一是插入時沒有任何沉積物，另一個是有一點厚度的沉積物d=0.5毫米，兩者進行比較，計算如下 （6） 表1在橫截面的特征點的溫度 Table 1 Temperatures at the characteristic points of thecross-section 溫度 無沉積物溫度 標(biāo)準(zhǔn)溫度 有沉積物溫度 T1 404.43 405.1 642.00 T2 402.05 402.4 636.58 T3 365.59 366.8 600.86 T4 363.99 364.1 596.36 T5 318.2 318.2 344.65 分析結(jié)果證明，標(biāo)準(zhǔn)溫度相對與有沉積物的溫度更接近與無沉積物的溫度，假設(shè)有沉積物溫度為T，根據(jù)公式4密度的熱流Q計算 （7） 所獲得熱負荷價值和公式6所的結(jié)果非常的相似q=220135.9W/m2 沉積物對熱負荷的測量沒有不良影響。 2.2 熱負荷測量 所描述的傳感器被安裝在210鍋爐的燃燒事的水冷壁的前端，4個傳感器安裝在不同的高度，12.6，15.4，19.3，23m。實時計算，傳感器的熱負荷Q可以顯示在監(jiān)視器上。熱負荷的參數(shù)連續(xù)函數(shù)如圖2（a）。分析數(shù)字證明，最高值出現(xiàn)的熱負荷略高于刻錄機. 受影響最大的是在15。4米處。如圖2（b）選定的測量和計算結(jié)果：（a）測量溫度的歷史和熱負荷計算的測量插入位于高度為15.4米，和（ b ）熱載荷分布1 - 4 測量刀片，第一和第二兩排燃燒器位置，分別在高度為10.4和12.6米。 圖2（a）溫度和熱流量隨時間變化圖，（b）傳感器高度和熱流量關(guān)系 Fig 2 (a) temperature and heat flux variation with time, (b) the sensor height and the relationship between heat flux 3 鍋爐水循環(huán)系統(tǒng)的測量 鍋爐的啟動和關(guān)閉過程，以及鍋爐負荷的變化中，不超過允許應(yīng)力，而水循環(huán)基本維持在一定的范圍，迅速增加的壓力可能會導(dǎo)致水因過渡沸騰而使水冷壁無法保護爐墻，而迅速下降的壓力，導(dǎo)致鍋爐系統(tǒng)中的鍋爐蒸發(fā)器所有要素迅速下降。這兩種情況下會導(dǎo)致水循環(huán)流動停滯 ，導(dǎo)致管道開裂。210鍋爐實際水循環(huán)中水流率連續(xù)測量兩次（從總的10 ）。降液管的外徑二百七十三毫米和壁厚25 mm。流量計安裝在高度為10.5和11.5 m處。在穩(wěn)態(tài)鍋爐運行（鍋爐效率之間波動180-210X103 千克/小時）,和流通計算分析如圖，速度在下降管中介于1.6和1.8米/秒，而流通比率約為8到9。在此基礎(chǔ)上測量水的流量及其變化范圍，允許的最大壓力變化率被確定為的DP / dt的蒸發(fā)器（以避免停滯的水循環(huán)蒸發(fā)器） 。測量水的流速（1.6到1.8米/秒）和壓力p =10.79兆帕，開始的時候，的允許壓力應(yīng)降低到范圍從0.023到0.027兆帕/ s（圖4 （ a ） ） 。因制造商的建議在鍋爐汽包降低壓力，定為2K/分。 圖3測量水流速度 Fig 3 Measured water velocity histories 圖4 減壓比例： （a）允許壓力降率近似值以及（b）時間與壓力下降率之間的關(guān)系 Fig 4 Decompression ratio of: (a) allow the approximation of pressure drop rate and (b) pressure drop in the rate of time and the relationship between 壓力降低率的測量目的是蒸發(fā)器中的水循環(huán)圖4（b） 。分析證明，如果加熱鍋爐汽包和冷卻速度不超過制造商建議，就沒有不穩(wěn)定的風(fēng)險。 4 熱工檢測 下面談?wù)摰腻仩t效率的缺陷，燃料和生活蒸汽大規(guī)模流動以及爐結(jié)焦的因素是討論的細節(jié)。當(dāng)煤燃燒，一小部分的灰會造成沉積，高溫結(jié)渣是為熔融形成，部分熔融沉積爐墻壁和其他表面。污染影響對流換熱吸收，如過熱器和再熱器，渣和污染關(guān)鍵是影響燃煤電站鍋爐可靠性和可用性。然而，鍋爐表面存在的渣僅是一小部分，沉積是多方面的，污染以間接的形式影響高蒸汽和煙氣溫度，它們所造成的低質(zhì)量流量飽和蒸汽由蒸發(fā)器溫度進入對流表面，造成溫度過熱蒸汽增加，并保持恒定的高溫度的，所以鍋爐必須定期除渣，例如，煙氣溫度離開煙囪過熱，就應(yīng)該開始吹灰，吹氣時，達到一定壓力值，說明已經(jīng)結(jié)渣和污染狀況，但這些跡象可能造成一定錯誤，墻吹灰器是最常用的一個除渣工具，每天一次和三次，后者使用頻率可能是令人驚訝。必須最大限度地吸收熱量，以防止有時再熱蒸汽溫度過熱。基于計算機的鍋爐性能監(jiān)控，在爐膛和對流表面檢測溫度，壓力，流動和氣體分析的數(shù)據(jù)被用來執(zhí)行傳熱分析爐膛和對流，由測量值說明表面清潔度，風(fēng)機順序可根據(jù)實際優(yōu)化，清潔的要求，而不是固定時間，鍋爐監(jiān)控系統(tǒng)還提供細節(jié)的變化，鍋爐效率和吹灰條件，可事后分析與優(yōu)化。 4.1 鍋爐效率 鍋爐效率的計算采用在線模式。注意鍋爐效率隨時間的變化，可以改變參數(shù)，如質(zhì)量流量，空氣供應(yīng)，以提高效率，確定熱效率首先是基于熱值和煤量。 （8） 介質(zhì)全部熱量（水和水蒸汽），隨煤和空氣進如鍋爐的熱量，損失的熱量。 （9） 損失有以下集中一，干煙氣損失;二，未燃盡氣體損失;三，可燃的煤粉煤灰;四，燃燒爐底灰;五，輻射和下落不明的損失;六，合理的熱損失在爐底灰。 4.2 燃料質(zhì)量流量和蒸汽爐膛結(jié)渣的因素 穩(wěn)定狀態(tài)條件基于鍋爐效率評估在線模式下，煤炭質(zhì)量流量將取決于鍋爐熱效率如圖5（ a ） 圖5控制質(zhì)量和能量平衡 Fig 5 to control the quality and energy balance （a）鍋爐： 1 ，鍋爐; 2第一階段過熱; 3 ，第二階段過熱; 4 ，最后過熱; 5第一階段保溫; 6 ，第二階段保溫 (b)鍋爐蒸發(fā)器： 1 ，滾筒; 2 ，下降管; 3 ，蒸發(fā)器; 4 ，水冷壁 ; 5 ，第一階段過熱; 6 ，第二次現(xiàn)階段過熱; 7 ，最后過熱; 8，第一次階段保溫; 9，第二階段保溫 （10） 經(jīng)過一些變換方程，繼獲得公式 （11） 計算實際空氣流動的公式 （12） 質(zhì)量和體積流量上根據(jù)煙氣計算出來的。方程（ 11 ）只適用于穩(wěn)態(tài)條件下燃料質(zhì)量流量，鍋爐蒸發(fā)器負荷從質(zhì)量和能量平衡角度考慮，圖5（b） （13） （14） 由公式13和14得到 （15） 結(jié)渣C因子估方程 （18） 活蒸汽流量米計算利用方程（ 15 ），作為結(jié)渣因子c.取決于鍋爐孔板在出口流量實測流量 4.3燃料質(zhì)量流量 蒸汽質(zhì)量流量從鍋爐蒸發(fā)器開始，質(zhì)量和能在量整個蒸發(fā)器多少可以控制，這是水和水蒸汽混合。 （17） （18） 結(jié)合質(zhì)量守恒和能量守恒定律 （19） 從條件中饒了質(zhì)量是確定的 （20） 計算熱流量是方程（19）是一個功能。計算燃料質(zhì)量流量的情況，可以用非線性方程（ 20 ）解決，運用區(qū)間搜索或反復(fù)，例如，牛頓迭代法。 4.3 結(jié)果 基于計算機的在線監(jiān)測系統(tǒng)，檢測鍋爐的性能，如上文所述安裝在210電站鍋輸入數(shù)據(jù)運行監(jiān)測列于表2 。選定的結(jié)果與使用本系統(tǒng)中顯示圖6和7。 表2輸入數(shù)據(jù)和鍋爐運行檢測結(jié)果 Table 2 Input data and the results of monitoring powerboiler operation 數(shù)據(jù) 結(jié)論 蒸汽壓力 蒸汽溫度 空氣溫度 給水溫度 出口溫度煙氣 相對濕度 含氧量 凈熱值寬 在燃料灰分含量 煤粉燃燒燃料 煙氣一氧化碳百分比 水流速度 插入點放在四個傳感器溫度 蒸汽質(zhì)量流量 水保溫 質(zhì)量流量的排污 水流重 汽包壓力 噴水溫度 引水溫 鍋爐效率 過量空氣計算 鍋爐熱功率 燃料質(zhì)量流量 燃氣流量 在燃燒室出口燃燒氣體溫度 結(jié)渣的因素 燃燒室熱負荷 蒸汽質(zhì)量流量 空氣損失量 燃料損失量 圖6 （ a ）鍋爐效率（ b ）和燃料質(zhì)量流量 Fig.6(a)Boiler efficiency(b)and fuel mass flow 圖7在爐膛出口燃燒氣體溫度（ a ）和質(zhì)量流量（ b ） Fig.7 Combustion gas temperature(a)and mass flow(b)at the furnace chamber outlet 圖8 鍋爐汽包的加熱和冷卻： （a） 溫度和壓力的歷史（ b ）在鍋爐啟動時熱負荷和壓力分布。 Figure 8 Boiler heating and cooling: (a) the history of temperature and pressure (b) start in the boiler heat load and pressure distribution. 圖9鍋爐汽包降交界處：（a）應(yīng)力集中點（點P）和（b）周向應(yīng)力 Figure 9 down at the junction of boiler drum: (a) stress concentration point (point P) and (b) circumferential stress 計算機在在線檢測下，并繪出圖形，進行監(jiān)測選定的參數(shù)，結(jié)渣的因素確定方程（ 16 ）取決于清潔燃燒爐墻和范圍從0.5至0.72 。 5 強度條件的控制 對210鍋爐下降管強度進行計算，考慮鍋爐汽包加熱/冷卻速度，確保壓力平衡210鍋爐加熱和冷卻在圖8（a）中顯示。 計算的溫度和應(yīng)力場進行了一個邊緣降。鍋爐汽包材質(zhì)是K22M鋼，其外徑一千八百八十零毫米和壁厚90 mm.Downcomers與外直徑102毫米，壁厚6毫米考慮到這些因素，鼓飽和壓力才能確定，根據(jù)溫度的變化（圖8（a）項）。 減少內(nèi)部的熱負荷，啟動鍋爐是在圖8 （ b ）項。鍋爐鼓降交界處周向應(yīng)力的變化是在圖（a），鍋爐汽包內(nèi)表面點應(yīng)力變化圖（ b ）證明，鍋爐啟動和關(guān)閉最大應(yīng)力點的應(yīng)力約束低于允許值，計算表明，如果制造鍋爐汽包加熱和冷卻率超過建議值，沒有超過允許應(yīng)力和不會造成造成不穩(wěn)定的水循環(huán)。鍋爐啟動和關(guān)閉程序是一個重要組成部分，即鍋爐汽包不能超過允許溫度變化的最小和最大值，分析這一數(shù)字表明，在最初的熱化階段，允許利率上升是由于承擔(dān)鍋爐啟動程序.開始啟動過程中，密集的蒸汽冷凝發(fā)生在鍋爐汽包中。 圖10 210鍋爐的鍋爐汽包升溫速率和壓力 Figure 10 210 boiler drum boiler heating rate and pressure 6 結(jié)論 基于計算機的性能監(jiān)控鍋爐系統(tǒng)基于鍋爐在線檢測的模式，檢測溫度，壓力，熱通量，流量。這些數(shù)據(jù)被用來進行傳熱分析，以便控制蒸發(fā)器，電爐，以及流量等。為了控制水循環(huán)，流量計安裝在210鍋爐兩下降管中，并在此基礎(chǔ)上計算水流通.測量水的速度，最大允許壓力，變化中的蒸發(fā)器，防止水蒸汽停滯 ，分析強調(diào)鍋爐運行可得出結(jié)論，如果鍋爐汽包超過制造商建議的加熱和冷卻利率，但不能超過允許壓力.利用有限元方法，由210鍋爐下降管的壓力分析，人們可以看到，鍋爐汽包在在一個允許的速率v=2K/min和冷卻速率在v=2K/min，溫度差異，達到約60 K,超過制造商的允許標(biāo)準(zhǔn).這是由于啟動過程，鍋爐汽包只是部分裝滿了水。該系統(tǒng)開發(fā)的監(jiān)測熱流量和強度，通過適當(dāng)?shù)姆峙淇諝忮仩t可提高鍋爐效率，使氣體排放和粉煤灰等可燃元素不超過允許值。此外，該系統(tǒng)可定期確定以下參數(shù)：燃料質(zhì)量流量，空氣流通，煙氣流動，煙氣溫度.它允許評估燃燒室一定程度的污染. 燃燒室結(jié)渣因素，計算和測量鍋爐質(zhì)量效率。改變水的質(zhì)量流量，以并改變排煙溫度，第二階段的蒸汽過熱器，可以形成根自動激活系統(tǒng)的爐渣和鼓風(fēng)機。高精度測量水冷壁熱負荷，鍋爐燃燒水冷壁溫度變化（燃燒和煙氣溫度監(jiān)測）。測量結(jié)果也可用于控制的流通汽水和內(nèi)表面沉積的規(guī)模，對水冷壁檢測.可用于燃燒室分析。 附錄B 外文文獻 Computer system for monitoring power boiler operationJ Taler1,B We glowski1,W Zima1*,P Duda1,S Gra dziel1,T Sobota1,A Cebula1,and D Taler21Institute of Process and Power Engineering,Cracow University of Technology,Krako w,Poland2AGH University of Science and Technology,Krako w,PolandThe manuscript was received on 2 February 2007 and was accepted after revision for publication on 24 October 2007.DOI:10.1243/09576509JPE419Abstract:The computer-based boiler performance monitoring system was developed to per-form thermal-hydraulic computations of the boiler working parameters in an on-line mode.Measurements of temperatures,heat flux,pressures,mass flowrates,and gas analysis datawere used to perform the heat transfer analysis in the evaporator,furnace,and convection pass.A new construction technique of heat flux tubes for determining heat flux absorbed bymembrane water-walls is also presented.Flux tubes mounted at different levels in the boilerwork at similar conditions as water-walls tubes.The current paper presents the results ofheat flux measurement in coal-fired steam boilers.During changes of the boiler load,the necessary natural water circulation cannot beexceeded.A rapid increase of pressure may cause fading of the boiling process in water-walltubes,whereas a rapid decrease of pressure leads to water boiling in all elements of the boilersevaporator water-wall tubes and downcomers.Both cases can cause flow stagnation in thewater circulation leading to pipe cracking.Two flowmeters were assembled on central downco-mers,and an investigation of natural water circulation in an OP-210 boiler(with steam capacityof 210?103kg/h)was carried out.On the basis of these measurements,the maximum rates ofpressure change in the boiler evaporator were determined.The on-line computation of the conditions in the combustion chamber allows for real-timedetermination of the heat flowrate transferred to the power boiler evaporator.Furthermore,with a quantitative indication of surface cleanliness,selective sootblowing can be directed atspecific problem areas.A boiler monitoring system is also incorporated to provide details ofchanges in boiler efficiency and operating conditions following sootblowing,so that the effectsof a particular sootblowing sequence can be analysed and optimized at a later stage.The current paper also presents an analysis of stresses occurring in the boiler drum and thedowncomer junction during-start up and shut-down of the boiler.Keywords:power boiler,heat flux measurement,evaporator,natural water circulation,performance and thermal stress monitoring1INTRODUCTIONPower boiler shut-down and start-up processes,aswell as boiler load changes,should be carried outsuch that no allowable stresses in the boiler areexceeded,while the essential natural circulation ismaintained at all times.A rapid increase of pressure may cause fading ofthe boiling process in water-wall tubes,whereas arapid decrease of pressure leads to water boiling inall elements of the boilers evaporator water-walltubes and downcomers.Both cases can cause flowstagnation in water circulation in the evaporatorthat leads to pipe cracking.Thus,the flowmeterswere assembled on two downcomers of the OP-210boiler(theboilercapacityis210?103kg/hoflive steam with 9.8 MPa pressure and 54052108Ctemperature).An investigation of natural water circu-lation was carried out and the maximum rates of*Corresponding author:Institute of Process and Power Engineer-ing,Cracow University of Technology,AL.Jana Pawla II 37,Krako w 31-864,Poland.email:zimamech.pk.edu.pl13JPE419#IMechE 2008Proc.IMechE Vol.222 Part A:J.Power and Energypressurechangeintheboilerevaporatorweredetermined.Stresses are mainly controlled by the so-called cri-terion elements that limit the rate of boiler loadchanges.One such elements is the boiler drum,andin particular its connection with the downcomers.The distribution of equivalent and circumferentialstresses for these connections depends,to a largeextent,on the boiler drums heating and coolingrates.The boiler manufacturers reserve the right torecommend the specific heating and cooling ratesfor boiler drums,that often could be larger.Byincreasing such rates the operation time of a boilerunder transient conditions can be shortened.The monitoring of an operating boiler also includesthe monitoring of a wide range of other parametersthat affect its efficiency and safety.The current paper presents a system that allowson-line monitoring of operating conditions for anevaporator.Its basic element is a set of original heatflux tubes used to determine the temperature andheat load distribution along the height of the boilerscombustion chamber.This heat distribution is veryimportant for the proper operation of the evaporatorand combustion chamber 14.The obtained resultscould also be used to monitor the circulation ofwatervapour mixture and the scale deposition onthe inner surfaces of waterwall tubes.The system issupplemented by measurements of water mass flowcirculating in the boilers evaporator from two centraldowncomers.The monitoring of thermal-flow conditions of aboiler in the on-line mode should also take intoaccount the variability of the excess air number,which directly influences the boiler efficiency.Itsvalue can be reduced by means of the appropriateair distribution(primary,secondary,and over-firedair(OFA)nozzles)while using the heat flux tubeslocated at different levels.Air distribution shouldensure the emission of NOxand the content of flam-mable elements in fly-ash below allowable levels.Thecorrect estimation of the degree of slagging in theboilers combustion chamber is also very important.Time changes of the chamber wall slagging coeffi-cient,along with changes of water mass flows toinjection attemperators,and the temperature of fluegas can be the basis for an automatic activation ofslag and ash blowers in the boiler.Comparing the computed and measured super-heated steam mass flowrate,the average slaggingdegree of a combustion chamber wall is determinedin the on-line mode.This allows for full automationof soot blowers operating in a combustion chamber,therefore reducing the medium usage in soot blowersand increasing the water-wall lifetime.Theon-linecomputationofthecombustionchamberallowsforreal-timeheatflowratedetermination,whichis transferred to the power boiler evaporator.Based onthe energy balance for the power boiler evaporator,the superheated steam mass flowrate is computed(takingintoaccountthewaterflowrateforattemperators).Several investigators have contributed to variousaspects of thermal performance and remnant lifemonitoring of power plants.The monitoring of thermal conditions in powerplants is considered in many papers 5,6.Afinite-element-basedfatiguemonitoringsystemdeveloped for on-line monitoring of fatigue degra-dation of components used in various plants isshown in reference 7.Paper 8 describes practicalexamples where component life monitoring hasbeen implemented on power plants.The results offull-scale investigations on fouling in convective bun-dles of coal-fired boilers are presented in paper 9.2HEAT LOAD MEASUREMENT OF THECOMBUSTION CHAMBER WALLSDue to the difficulties occurred while measuring thehigh temperature of flue gas,the measurement ofthe heat load of the boilers combustion chamberusing the thermometric inserts presented in Fig.1was proposed.The heat load is the density of theabsorbed heat flux,defined as the ratio of the heatflowrate absorbed by the wall to the projected wallsurface area,and was determined on the basis oftemperature measurement of the insert located onFig.1Heat load measuring insert:I,waterwall pipe;II,eccentric pipe;III,heat resistant metal sheetingcover;IV,pipe leading the thermoelementsoutside the boiler,and 15 location of thethermoelements14J Taler,B We glowski,W Zima,P Duda,S Gra dziel,T Sobota,A Cebula,and D TalerProc.IMechE Vol.222 Part A:J.Power and EnergyJPE419#IMechE 2008its front side(points I to IV in Fig.1).The insert wasmade of carbon steel,and the temperature wasmeasured using four Ni-NiCr thermocouples(outsidediameter of the sheath equalling 1 mm),placed inholes located parallel to the axis of the insert toavoid errors caused by heat conduction along theaxis of the thermoelement outputs.This distributionof the openings causes the temperature of the ther-moelement to remain constant,and assures thatheat flows neither in nor out of the point in whichthe temperature is measured.The thermoelementsare led out at the back of the tubes.A 20 mm widegroove,in which the thermoelements are located,iscovered by a 3 mm heat resistant metal sheet pre-venting burning of the thermoelements(Fig.1).The insert was made of 20G steel,for which thethermal conductivity k was determined by theexpressionkT 53:26?0:02376224?T W=mK1To check whether the insert was able to work safely,computations using the finite-element method wereperformed.The pressure of the medium was assumedto be p 11 MPa and the temperature of the systemwas assumed to be T 3708C.The results of thosecomputations,carried out with the use of theANSYS software,are presented in reference 10.Allowablestressequals118 MPa,whereasthemaximumstressattheassumedloadequals73 MPa.Thus,the maximum stress is lower than theallowable one.2.1Description of the heat load determinationmethodIn order to determine the waterwall heat load depen-dency q q(DT),temperatures T1,T2,T3,and T4measured at four points of the front insert were used(Fig.1).The heat distribution was computed using themethod of finite capacity from the CFD software 11.DT is the average temperature differenceDT T1 T22?T3 T422Due to the symmetry of the temperature field in theinsert,only half of the cross-section of the insert wasanalysed.Changes of the density of the heat flux onthe surface of the insert and of the neighbouringtubes depend on the slagging factorc,which changessignificantly with location.The dispersion of the heatflux density on the surface of the insert and in thetube on the side of the furnace has been approxi-mated using a step line.The back surface of theinsert and the tubes was completely insulated.Onthe inside surface of the tube,the boundary conditionof the third kind,requiring the knowledge of the heattransfer coefficientaand the temperature of themedium Tmwas assumed.The heat load can be expressed as a function of themeasured temperature differenceq a b?DT3where the temperature difference DT is expressed byequation(2).Temperatures T1,T2,T3,and T4were computedusing the CFD software 11 for various values ofthe heat load q and the heat transfer coefficienta.The temperature of the medium was assumed to beTm 3208C.This is the temperature of the watervapour mixture in the evaporator of the OP-210boiler.The results of the numerical calculations wereapproximated using the function(3)by means ofthe least squares method.Constants a and b,whichdepend on the heat transfer coefficientaon theinside surface of the insert,equala 8367:9549W=m2;b 5357:8165W=m2Kfora 5000W=m2Ka 6800:9790W=m2;b 5432:89W=m2Kfora 10000W=m2Ka 4899:67W=m2;b 5519:0615W=m2Kfora 50000W=m2KThe analysis of the changes of the heat load q infunction DT proved that the heat transfer coeffi-cientaon the inside surface of the pipe has aminor influence on the heat load value q 10.This slightly surprising result can be explained bythe fact that when the value ofadecreases,the cir-cumferential heat flow from the front of the insertto its back side increases,which causes a drop inthe temperature through the thickness of the wall.Simultaneously,the reduction of theacoefficientcauses an increase of the insert temperature onthe side of the furnace,which in turn causesreduction of the thermal conductivity k determinedby equation(1)and increasing of the temperaturedrop through the thickness of the wall.Those twoopposite phenomena make q practically indepen-dent froma.For the on-line computations the following depen-dencyq q(DT)fora 10 000 W/(m2K)wasassumedq 6800:979 5432:89?DT W=m24Computer system for monitoring power boiler operation15JPE419#IMechE 2008Proc.IMechE Vol.222 Part A:J.Power and EnergyEquation(4)was derived with the assumption,thatthe interior surface of the insert is clean,and there areno residues of a low thermal conductivity coefficient(boiler scale or iron oxides)on the surface.If theinterior surface of the insert is covered with scaledeposition,then the temperature of the front surfaceof the insert increases,in turn causing the increase ofthe circumferential heat flux in the insert.To provethe correctness of the heat load q measurement in asituation,when the scale deposition characterizedby a low thermal conductivity coefficient accumu-lated on the interior surface of the insert,compu-tations of the temperature distribution for the cleanand dirty interior surface of the insert were carriedout,using FLUENT.Temperatures measured on the insert located at15.4 m level on the front wall of the evaporator ofthe OP-210 boiler:T1 405.1 8C,T2 402.4 8C,T3366.8 8C,T4 364.1 8C were used for verification.Temperature T5 318.2 8C of the external back sur-face(w 1808)of the insert was also known fromthe measurement.The density of the heat flux q,calculated fromequation(4),equals toq 6800:979 5432:89405:1 402:42?366:8 364:12?214888:7W=m25Measured temperatures for the clean insert formeda basis for the determination of the specific values ofthe heat load q,heat transfer coefficientaon theinterior surface of the insert,and the temperature ofthe medium Tm.Those values were derived usingthe control volume method,and FLUENT.The computations were carried out using the leastsquares method,for whichX5i1Tci?Ti2!min6andfollowingvalueswereobtained:q 220 135.3 W/m2,Tm 318.28C,anda 37 105.47 W/(m2K).Applying those values as data for FLUENT,thetemperature distributions at the cross-section of theinsert devoid of any residue and with scale depositionof thicknessd 0.5 mm(with the thermal conduc-tivity k 0.5 W/(mK)on the inside surface werecomputed.Thecomputedtemperaturesatthecharacteristic points of the cross-section are pre-sented in Table 1.Table 1 also contains,for the pur-pose of comparison,the measured temperatures.An analysis of the results proved that the measuredtemperatures Timatch the calculated temperaturesTcifor the clean insert.Assuming the calculated temperatures Tcifor theinsert with scale deposition to be the measured temp-eratures,the density of the heat flux q was calculatedusing equation(4)q 6800:979 5432:89642 636:582?600:86 596:362?227810:9W/m27The obtained value of the heat load agreed verywell the value derived from condition(6)equalling:q 220 135.3 W/m2.Accumulation of deposit onthe inside surface of the insert does not adverselyaffect the precision of the heat load measurement.2.2Results of the heat load measurementsThe described sensors in form of measuring insertswere installed on the middle tube of the frontwaterwall of the combustion chamber of the OP-210boiler.The inserts were mounted at four differentelevations:12.6,15.4,19.2,and 23 m.Real-time calcu-lations of heat load q can be displayed on the monitor.The values of the heat load for the determined discretepoints were approximated using the continuous func-tion(Fig.2(a).An analysis of the figure proves thatthe maximum values of heat load occur just above theburners.Changes to this heatload are determined con-tinuously with time.A sample history of the heat load,for the most thermally affected insert,at the level of15.4 m,is presented in Fig.2(b).Maximum heat loadvalues,occurring at this level are typical for steam boi-lers fuelled with pulverized coal 1.Since the heat flux measurements are carried out inthe on-line mode,heat flux distribution along the fur-nace height is known at any time.Table 1Temperatures at the characteristic points of thecross-sectionTemperatureCalculatedtemperature(cleaninsert)Tic(8C)MeasuredtemperatureTi(8C)Calculatedtemperature(insert withscaledeposition)Tic(8C)T1404.43405.1642.00T2402.05402.4636.58T3365.59366.8600.86T4363.99364.1596.36T5318.2318.2344.6516J Taler,B We glowski,W Zima,P Duda,S Gra dziel,T Sobota,A Cebula,and D TalerProc.IMechE Vol.222 Part A:J.Power and EnergyJPE419#IMechE 20083MEASUREMENT OF THE WATERCIRCULATION RATIO IN BOILEREVAPORATORBoiler start-up and shut-down processes,as well asboiler load changes shall be carried out in such way,that no allowable stresses are exceeded,while theessential natural circulation is maintained at alltimes.A rapid increase of pressure may causefading of the boiling process in water-wall tubes,whereas a rapid decrease of pressure leads to waterboiling in all elements of the boilers evaporator water-wall tubes and downcomers.Both cases cancause flow stagnation in the water circulation in theevaporator that leads to pipe cracking.In orderto examine the actual natural circulation in the evap-orator of the OP-210 boiler,the rate of water flow ismeasured continuously on two(from the total often)downcomer tubes with an outer diameter of273 mm and wall thickness of 25 mm.The flow-meters were installed on the opposite sides of theboiler,at the height of 10.5 and 11.5 m.The flowmeterconsists of two main elements:a measuring devicemanufacturedbyTorbarTMandadifferentialpressure converter manufactured by YokogawaTM.Figure 3 shows the results from measurementstaken during a steady-state boiler operation(boilerefficiency fluctuated between 180210?103kg/h)and the computed circulation ratio.From the analysisof the diagram,the velocity in the downcomer tubesranges between 1.6 and 1.8 m/s,while the circulationratio is at about eight to nine.On the basis of themeasured water flowrate and its variability range,the maximum allowable pressure change rates havebeen determined for the dp/dt evaporator(in orderto avoid the stagnation of water circulation in theevaporator).For the measured water velocity in the downco-mers(w 1.61.8 m/s)andthepressurep 10.79 MPa(at the beginning of the shut-down pro-cess)the allowable pressure lowering rate shallrange from 0.023 to 0.027 MPa/s 12(Fig.4(a).The pressure lowering rate at the boiler drum,resulting from the manufacturers recommendations,is set at 2 K/min 10 and is lower than the allowableFig.2Selected measurement and calculation results:(a)measuredtemperaturehistoriesandcalculated heat load for the measuring insertlocated at the height of 15.4 m,and(b)heatloaddistributionalongthecombustionchamber:14 measurement inserts,I and II,two rows of burners located,respectively,atthe height of 10.4 and 12.6 mFig.3Measured water velocity histories in boilerdowncomers(a)and(b),and determinedcirculation multiplicity(c)Computer system for monitoring power boiler operation17JPE419#IMechE 2008Proc.IMechE Vol.222 Part A:J.Power and Energypressure lowering rate established with regard to thestability of the water circulation in the evaporator(Fig.4(b).The analysis proved that if the boiler drum heatingand cooling rates recommended by the manufacturerare not exceeded,there is no risk of instability ofwater circulation occurring in the evaporator.4MONITORING OF THERMAL-HYDRAULICOPERATING CONDITIONSIn the following the determination of boiler effi-ciency,fuel and live steam mass flows as well as fur-nace slagging factor will be discussed in details.When coal is burned,a relatively small portion ofthe ash will cause deposition problems.Due to thedifferences in deposition mechanisms involved,twotypes of high temperature ash deposition have beendefined as slagging and fouling.Slagging is the for-mation of molten,partially fused deposits on furnacewalls and other surfaces exposed to radiant heat.Fouling is defined as the formation of high tempera-ture bonded deposits on convection heat absorbingsurfaces,such as superheaters and reheaters,whichare not exposed to radiant heat 13,14.Slaggingand fouling conditions are critical factors influencingreliability and availability of a coal-fired utility boiler.However,boiler surface deposits have been,tra-ditionally,one of the most difficult operating vari-ables to