基于计算机的电厂锅炉监控系统外文翻译、中英文翻译、外文文献翻译
基于计算机的电厂锅炉监控系统外文翻译、中英文翻译、外文文献翻译,基于,计算机,电厂,锅炉,监控,系统,外文,翻译,中英文,文献
附录A 译文
基于计算机的电厂锅炉监控系统
J Taler1, BWeglowski1, W Zima1*, P Duda1, S Gradziel1,T Sobota1,A Cebula1,and D Taler2
工艺和电力工程研究所,克拉科夫大学,波兰
AGH科技大学,波兰
接受时间:2007.2.2, 公布时间(经修改)2007.10.24
摘要
以计算机为基础的锅炉性能监测系统的开发,首要进行热工计算,测量各种温度,热通量,压力和燃料,分析数据,这些数据被用来进行传热分析,以便控制蒸发器,电炉,以及流量等。
一个新的工艺技术热通量管,用来确定所吸收的热通量。通量管安装在不同级别的锅炉中,其工作条件类似于水墙管。热通量测量燃煤蒸汽锅炉是目前比较好的选择。
锅炉负荷是变化的,水循环必须不能超出一定范围。迅速增加的压力可能会导致水因过渡沸腾而使水冷壁无法保护炉墙,而迅速下降的压力,导致锅炉系统中的锅炉蒸发器所有要素迅速下降。这两种情况下会导致水循环流动停滞 ,导致管道开裂。两个流量计组装在210(蒸汽能力 210X103千克/小时)锅炉自然水循环过程中进行。根据这些测量,压力改变时锅炉过热器最高速度应被限制。
根据实时计算,燃烧室可以实时确定需要多少热流量转移到电站锅炉蒸发器。此外, 表面清洁度,选择性吹灰,也可用在具体的问题中介绍。锅炉监控系统也提供详细的锅炉效率的变化和经营状况,在后一阶段对特定吹灰序列进行分析和优化。
本文还分析了在启动和关闭的锅炉时,锅炉气鼓中的压力
关键词:电站锅炉,热通量的测量,蒸发器,水循环,性能和热应力监测
1 绪论
电站锅炉关闭和启动进程,以及锅炉负荷的变化过程中,不容许锅炉应力超过限制,而至关重要的是水循环要时刻保持着。迅速增加的压力可能会导致水因过渡沸腾而使水冷壁无法保护炉墙,而迅速下降的压力,导致锅炉系统中的锅炉蒸发器所有要素迅速下降,这两种情况下会导致流动停滞水循环中的蒸发器,导致管道开裂。因此,在210(锅炉容量为 210X103千克/小时的生活蒸汽,9.8兆帕的压力和530到545的温度)锅炉自然水循环过程中要组装两个流量计。根据水循环参数确定一个锅炉蒸发器的最大压力。
控制的主要任务是锅炉负荷变化限制在标准范围内。比如说锅炉汽鼓,特别是汽鼓和锅炉管道的连接处,特别要强调在这些连接处,同等的分配压力,因为他们在很大程度上,对锅炉汽包的加热和冷却率有影响。锅炉制造商建议的具体加热和冷却率是有所保留的,锅炉汽鼓,往往可能是比建议的大些。通过提高利用率的这种方法,锅炉瞬变的时间可缩短。
监测的任务还包括锅炉监测范围内很多的其他参数,包括影响其效率和安全性的参数。目前提出了一种系统,可以在线监测的运行条件下的蒸发器。其基本内容是一套原始热通量管用来确定温度和热负荷分布的高度锅炉燃烧室。重要的是检测正常运行的蒸发器和燃烧室。所得结果也可以用来监测流通水蒸汽混合物和沉积物在水冷壁管内表面的沉积多少。该系统辅以测量蒸汽水的流量,控制循环系统,锅炉的在线模式也应考虑到由于系统的可变性,可能会导致空气过量的问题,这直接影响锅炉效率。其解决的办法,可减少相应的供给,如鼓风量和相应开关的开通量,同时利用热通量管设在不同的层次。空气分配应确保排放的氮氧化物和内含易燃物、内含容粉煤灰低于允许的水平。那个正确的估计程度的结渣中的锅炉燃烧室也非常重要。时间变化的分庭墙结渣系数,随着变化的水体流向 ,其它系统可可根据程序自动激活并运行,包括送煤机、除渣机和鼓风机。
比较,计算和测量过热蒸汽质量流量,燃烧室壁平均结渣一定程度的时间。这样吹灰器可以充分自动化的运行在一个燃烧室,因此也会充分使用吹灰器并增加水冷壁寿命。在线计算燃烧室实时热流量,其流量是转移到电站锅炉蒸发器。基于能量平衡,计算电站锅炉蒸发器的过热蒸汽质量流量。
一些调查人员已促成各种方面的热性能和剩余寿命理论研究来监测发电厂。检测热信号的在线检测被许多论文中被认可[5,6],用于在线检测疲劳退化程度的有限元的疲劳监测系统显示在参考[7],文件[ 8 ]介绍了实际已经执行部分在线监测的发电厂。
2 热负荷测量燃烧室壁
由于测量高温烟气时有很多困难的,锅炉燃烧室在热负荷运行,对其检测,用测温用仪器如图1。热负荷的密度吸收热通量,其定义是:同比热流量吸收炉墙表面积热量,温度测量器的插入前端(如图1中1处),温度测量选择四个镍镍铬热电偶(外直径鞘相当于1毫米) ,放置在洞内,插入到平行轴,避免错误造成的热传导沿轴的滑动空隙流出。这种分配原因是温度保持不变, 20毫米宽槽,是温度计所在,是涵盖了3毫米耐热金属板材,预防被焚烧(图1)。中心被填充20g钢,导热系数K的确定
K(T)=53.26-0.0235684TW/(mk) (1)
插入是否能够安全工作,计算方法采用有限元方法演算。平均压力假设为P=11 MPa和系统的温度被假设为T=370摄氏度,利用软件,参考[10] 可等于118兆帕的压力,而最大应力在假定负荷等于73兆帕。因此,最大应力低于允许值。图中Ⅰ,我水冷壁管;Ⅱ, 离心管;Ⅲ,耐热金属薄膜覆盖;Ⅳ,管以外的锅炉,以及1-5个位置
图1 热负荷测量。
Fig.1 Heat load measuring inser
2.1 热负荷能力说明
为了确定水冷壁热负荷的供给,温度T1、T2、T3、和T4四点测得测量值。热分布计算使用方法为有限容量的CFD软件[ 11 ]。平均温度差 (2)
由于对称性的温度测量器插入,只有插入一半的截面,插入表面的密度变化的热通量取决于结渣因子C ,其中的变化显着的位置。插入表面上的分散热通量密度接近使用步骤线。后表面插入和管完全绝缘。管的内表面属于第三种边界条件,需要的知识有热传热系数A和平均温度等假定,热负荷可以表示为一个函数的测量温度差
(3)
其中温差有公式2获得。
温度T1、T2、T3、和T4四点计算使用CFD软件[ 11 ]在热负荷q及传热系数和温度介质假设的前提下Tm为320度。结果的数值计算
近似使用的功能( 3 )通过最小二乘法。常数A和B ,其中取决于传热系数A对内表面的插入深度。
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
分析的变化,证明,传热系数A的内表面的管道有一个轻微影响热负荷值q。这略微令人吃惊的结果可以解释事实上,当值的减小,导致温度通过厚度的壁。同时,减少系数原因增加了插入温度对一侧的炉,而这反过来又造成减少热传导k确定由方程( 1 )和增加的温度通过减少厚度的墙。这两个相反的现象。
(4)
方程( 4 )得出的假设,即插入的内部表面是干净的,没有残留的低导热系数(锅炉规模或铁的氧化物)的表面。如果内部表面插入覆盖规模沉积,然后增加插入温度前表面,反过来又造成增加周围热流在减少。为了证明正确的热负荷q在测量时,当插入内表面上沉积特征的规模使低导热系数积累,计算温度分布,插入清洁内表面和肮脏的内表面那样,用流利温度测量器插入位于十五点四米水平的正面墙上密度吸收热通量流Q计算
运用这些数据,一是插入时没有任何沉积物,另一个是有一点厚度的沉积物d=0.5毫米,两者进行比较,计算如下
(6)
表1在横截面的特征点的温度
Table 1 Temperatures at the characteristic points of thecross-section
温度
无沉积物温度
标准温度
有沉积物温度
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
分析结果证明,标准温度相对与有沉积物的温度更接近与无沉积物的温度,假设有沉积物温度为T,根据公式4密度的热流Q计算
(7)
所获得热负荷价值和公式6所的结果非常的相似q=220135.9W/m2
沉积物对热负荷的测量没有不良影响。
2.2 热负荷测量
所描述的传感器被安装在210锅炉的燃烧事的水冷壁的前端,4个传感器安装在不同的高度,12.6,15.4,19.3,23m。实时计算,传感器的热负荷Q可以显示在监视器上。热负荷的参数连续函数如图2(a)。分析数字证明,最高值出现的热负荷略高于刻录机. 受影响最大的是在15。4米处。如图2(b)选定的测量和计算结果:(a)测量温度的历史和热负荷计算的测量插入位于高度为15.4米,和( b )热载荷分布1 - 4 测量刀片,第一和第二两排燃烧器位置,分别在高度为10.4和12.6米。
图2(a)温度和热流量随时间变化图,(b)传感器高度和热流量关系
Fig 2 (a) temperature and heat flux variation with time, (b) the sensor height and the relationship between heat flux
3 锅炉水循环系统的测量
锅炉的启动和关闭过程,以及锅炉负荷的变化中,不超过允许应力,而水循环基本维持在一定的范围,迅速增加的压力可能会导致水因过渡沸腾而使水冷壁无法保护炉墙,而迅速下降的压力,导致锅炉系统中的锅炉蒸发器所有要素迅速下降。这两种情况下会导致水循环流动停滞 ,导致管道开裂。210锅炉实际水循环中水流率连续测量两次(从总的10 )。降液管的外径二百七十三毫米和壁厚25 mm。流量计安装在高度为10.5和11.5 m处。在稳态锅炉运行(锅炉效率之间波动180-210X103 千克/小时),和流通计算分析如图,速度在下降管中介于1.6和1.8米/秒,而流通比率约为8到9。在此基础上测量水的流量及其变化范围,允许的最大压力变化率被确定为的DP / dt的蒸发器(以避免停滞的水循环蒸发器) 。测量水的流速(1.6到1.8米/秒)和压力p =10.79兆帕,开始的时候,的允许压力应降低到范围从0.023到0.027兆帕/ s(图4 ( a ) ) 。因制造商的建议在锅炉汽包降低压力,定为2K/分。
图3测量水流速度
Fig 3 Measured water velocity histories
图4 减压比例: (a)允许压力降率近似值以及(b)时间与压力下降率之间的关系
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
压力降低率的测量目的是蒸发器中的水循环图4(b) 。分析证明,如果加热锅炉汽包和冷却速度不超过制造商建议,就没有不稳定的风险。
4 热工检测
下面谈论的锅炉效率的缺陷,燃料和生活蒸汽大规模流动以及炉结焦的因素是讨论的细节。当煤燃烧,一小部分的灰会造成沉积,高温结渣是为熔融形成,部分熔融沉积炉墙壁和其他表面。污染影响对流换热吸收,如过热器和再热器,渣和污染关键是影响燃煤电站锅炉可靠性和可用性。然而,锅炉表面存在的渣仅是一小部分,沉积是多方面的,污染以间接的形式影响高蒸汽和烟气温度,它们所造成的低质量流量饱和蒸汽由蒸发器温度进入对流表面,造成温度过热蒸汽增加,并保持恒定的高温度的,所以锅炉必须定期除渣,例如,烟气温度离开烟囱过热,就应该开始吹灰,吹气时,达到一定压力值,说明已经结渣和污染状况,但这些迹象可能造成一定错误,墙吹灰器是最常用的一个除渣工具,每天一次和三次,后者使用频率可能是令人惊讶。必须最大限度地吸收热量,以防止有时再热蒸汽温度过热。基于计算机的锅炉性能监控,在炉膛和对流表面检测温度,压力,流动和气体分析的数据被用来执行传热分析炉膛和对流,由测量值说明表面清洁度,风机顺序可根据实际优化,清洁的要求,而不是固定时间,锅炉监控系统还提供细节的变化,锅炉效率和吹灰条件,可事后分析与优化。
4.1 锅炉效率
锅炉效率的计算采用在线模式。注意锅炉效率随时间的变化,可以改变参数,如质量流量,空气供应,以提高效率,确定热效率首先是基于热值和煤量。
(8)
介质全部热量(水和水蒸汽),随煤和空气进如锅炉的热量,损失的热量。
(9)
损失有以下集中一,干烟气损失;二,未燃尽气体损失;三,可燃的煤粉煤灰;四,燃烧炉底灰;五,辐射和下落不明的损失;六,合理的热损失在炉底灰。
4.2 燃料质量流量和蒸汽炉膛结渣的因素
稳定状态条件基于锅炉效率评估在线模式下,煤炭质量流量将取决于锅炉热效率如图5( a )
图5控制质量和能量平衡
Fig 5 to control the quality and energy balance
(a)锅炉: 1 ,锅炉; 2第一阶段过热; 3 ,第二阶段过热; 4 ,最后过热; 5第一阶段保温; 6 ,第二阶段保温
(b)锅炉蒸发器:
1 ,滚筒; 2 ,下降管; 3 ,蒸发器; 4 ,水冷壁 ; 5 ,第一阶段过热; 6 ,第二次现阶段过热; 7 ,最后过热; 8,第一次阶段保温; 9,第二阶段保温
(10)
经过一些变换方程,继获得公式
(11)
计算实际空气流动的公式
(12)
质量和体积流量上根据烟气计算出来的。方程( 11 )只适用于稳态条件下燃料质量流量,锅炉蒸发器负荷从质量和能量平衡角度考虑,图5(b)
(13)
(14)
由公式13和14得到
(15)
结渣C因子估方程
(18)
活蒸汽流量米计算利用方程( 15 ),作为结渣因子c.取决于锅炉孔板在出口流量实测流量
4.3燃料质量流量
蒸汽质量流量从锅炉蒸发器开始,质量和能在量整个蒸发器多少可以控制,这是水和水蒸汽混合。
(17)
(18)
结合质量守恒和能量守恒定律
(19)
从条件中饶了质量是确定的
(20)
计算热流量是方程(19)是一个功能。计算燃料质量流量的情况,可以用非线性方程( 20 )解决,运用区间搜索或反复,例如,牛顿迭代法。
4.3 结果
基于计算机的在线监测系统,检测锅炉的性能,如上文所述安装在210电站锅输入数据运行监测列于表2 。选定的结果与使用本系统中显示图6和7。
表2输入数据和锅炉运行检测结果
Table 2 Input data and the results of monitoring powerboiler operation
数据
结论
蒸汽压力
蒸汽温度
空气温度
给水温度
出口温度烟气
相对湿度
含氧量
净热值宽
在燃料灰分含量
煤粉燃烧燃料
烟气一氧化碳百分比
水流速度
插入点放在四个传感器温度
蒸汽质量流量
水保温
质量流量的排污
水流重
汽包压力
喷水温度
引水温
锅炉效率
过量空气计算
锅炉热功率
燃料质量流量
燃气流量
在燃烧室出口燃烧气体温度
结渣的因素
燃烧室热负荷
蒸汽质量流量
空气损失量
燃料损失量
图6 ( a )锅炉效率( b )和燃料质量流量
Fig.6(a)Boiler efficiency(b)and fuel mass flow
图7在炉膛出口燃烧气体温度( a )和质量流量( b )
Fig.7 Combustion gas temperature(a)and mass flow(b)at the furnace chamber outlet
图8 锅炉汽包的加热和冷却: (a) 温度和压力的历史( b )在锅炉启动时热负荷和压力分布。
Figure 8 Boiler heating and cooling: (a) the history of temperature and pressure (b) start in the boiler heat load and pressure distribution.
图9锅炉汽包降交界处:(a)应力集中点(点P)和(b)周向应力
Figure 9 down at the junction of boiler drum: (a) stress concentration point (point P) and (b) circumferential stress
计算机在在线检测下,并绘出图形,进行监测选定的参数,结渣的因素确定方程( 16 )取决于清洁燃烧炉墙和范围从0.5至0.72 。
5 强度条件的控制
对210锅炉下降管强度进行计算,考虑锅炉汽包加热/冷却速度,确保压力平衡210锅炉加热和冷却在图8(a)中显示。
计算的温度和应力场进行了一个边缘降。锅炉汽包材质是K22M钢,其外径一千八百八十零毫米和壁厚90 mm.Downcomers与外直径102毫米,壁厚6毫米考虑到这些因素,鼓饱和压力才能确定,根据温度的变化(图8(a)项)。 减少内部的热负荷,启动锅炉是在图8 ( b )项。锅炉鼓降交界处周向应力的变化是在图(a),锅炉汽包内表面点应力变化图( b )证明,锅炉启动和关闭最大应力点的应力约束低于允许值,计算表明,如果制造锅炉汽包加热和冷却率超过建议值,没有超过允许应力和不会造成造成不稳定的水循环。锅炉启动和关闭程序是一个重要组成部分,即锅炉汽包不能超过允许温度变化的最小和最大值,分析这一数字表明,在最初的热化阶段,允许利率上升是由于承担锅炉启动程序.开始启动过程中,密集的蒸汽冷凝发生在锅炉汽包中。
图10 210锅炉的锅炉汽包升温速率和压力
Figure 10 210 boiler drum boiler heating rate and pressure
6 结论
基于计算机的性能监控锅炉系统基于锅炉在线检测的模式,检测温度,压力,热通量,流量。这些数据被用来进行传热分析,以便控制蒸发器,电炉,以及流量等。为了控制水循环,流量计安装在210锅炉两下降管中,并在此基础上计算水流通.测量水的速度,最大允许压力,变化中的蒸发器,防止水蒸汽停滞 ,分析强调锅炉运行可得出结论,如果锅炉汽包超过制造商建议的加热和冷却利率,但不能超过允许压力.利用有限元方法,由210锅炉下降管的压力分析,人们可以看到,锅炉汽包在在一个允许的速率v=2K/min和冷却速率在v=2K/min,温度差异,达到约60 K,超过制造商的允许标准.这是由于启动过程,锅炉汽包只是部分装满了水。该系统开发的监测热流量和强度,通过适当的分配空气锅炉可提高锅炉效率,使气体排放和粉煤灰等可燃元素不超过允许值。此外,该系统可定期确定以下参数:燃料质量流量,空气流通,烟气流动,烟气温度.它允许评估燃烧室一定程度的污染. 燃烧室结渣因素,计算和测量锅炉质量效率。改变水的质量流量,以并改变排烟温度,第二阶段的蒸汽过热器,可以形成根自动激活系统的炉渣和鼓风机。高精度测量水冷壁热负荷,锅炉燃烧水冷壁温度变化(燃烧和烟气温度监测)。测量结果也可用于控制的流通汽水和内表面沉积的规模,对水冷壁检测.可用于燃烧室分析。
附录B 外文文献
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
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