A Methodology to Simulate the Impact of Tube Fouling on Steam Generator Performance With a Thermal-Hydraulic Code

ABSTRACT

Corrosion product deposits in the secondary side of nuclear plant steam generators may result in tube fouling. Tube fouling is a deposit that is influential for the heat exchanges between the primary and the secondary circuits. It may cause a steam pressure decrease and a power reduction. This paper presents a methodology to simulate the impact of tube fouling on steam generator performances. Simulations are performed with ThermoHYdraulique des Composants, which is Electricité de France reference code for the three-dimensional (3D) modeling of two-phase thermal-hydraulic flows in whole nuclear components such as steam generators. Tube fouling induces an additional thermal resistance on tubes. This resistance is supposed to correspond to the conductive resistance of a dense deposit by using the Maxwell model for a continuous solid phase with inclusions. As fouling deposit thicknesses are not uniformly distributed on the tube bundle, several thermal resistance distributions are investigated. In most cases, tube fouling concentrated in the hot leg is the most influential distribution. Nevertheless, for a large amount of deposits, tube fouling uniformly distributed in both hot and cold legs becomes more influential. This simulation series is an initial step. The strategy to improve the thermal resistance model is discussed.     

过热油田注汽锅炉过热器爆管原因分析及对策

过热油田注汽锅炉在油田应用之初,出现两起过热器爆管事故,不仅影响锅炉安全运行,而且因停炉造成一定的经济损失。通过对锅炉受热面炉管发生爆管的机理分析,针对两起爆管事故,找出原因并制定相应的对策。分析表明,该过热器爆管事故是锅炉火量与水量不匹配、过热器管壁结盐及介质滞流等引起炉管过热导致的。通过采取加强对过热器及分离器运行状态的监测,优化锅炉调试、运行流程等对策,一年多来锅炉运行状况良好,验证了过热器爆管原因分析和对策的有效性。     

蒸汽发生器管板和下封头局部热处理工艺研究

本文建立了远红外加热器作用下管板结构和管板与下封头结构的三维局部热处理数值分析模型。讨论了管板加热过程中温度场分布的特点，以及加热器布置位置对温度场的影响。研制了相应的程序，具有较好的通用性和精确性。用该模型对蒸汽发生器管饭与下封头焊缝局部热处理温度场进行了分析计算，确定了热处理温度场分布特征，得出了远红外加热器的合理布置方式和保温功率。计算结果与测试结果吻合较好。     

Theoretical and Experimental Investigation of Subcooled Flashing Flow through Simulated Steam Generator Tube Cracks

Flow models and experiments were developed to predict the choking flow of subcooled flashing water through steam generator tube crack. Experiments were conducted for vessel pressures up to 7 MPa with various subcoolings through 7 sets of simulated crack geometries with channel length to diameter ratios from 1.3 to 2, and channel length of 1.3 mm. Mass flux data with respect to subcooling are presented for all seven sets of crack specimens. As the subcooling increased for each specimen the mass flux increased. In general as the mass flux increased the area of the specimens increased. Experimental data were compared with homogeneous equilibrium and non-equilibrium mechanistic models for two-phase choking flow. A comparison of the model results with experimental data shows that the homogeneous equilibrium-based models grossly underpredict choking flow rates in such geometries, while homogeneous non-equilibrium models greatly increase the accuracy of the predictions.     

新型水火管蒸汽锅炉汽水分离特点与效果

提出十分简单的汽水分离措施,使蒸汽湿度低于0.5%。我国标准规定水火管锅炉和锅壳锅炉的蒸汽湿度不应大于4%,是明显偏高,建议对此给予修改。     

锅炉排汽管口裂纹原因及处理方法

针对某一发电锅炉排汽管口裂纹,分析了造成缺陷的原因及处理方法,并提出了防止出现这种缺陷的措施。     

蒸汽发生器流量分配板和管子支撑板的对中

介绍了在秦山二期蒸汽发生器制造中流量分配板和管子支撑板与管板对中校验过程     

Effect of Two-Phase Natural Circulation Distortion on Tube Failure in Steam Boilers

Two different cases of evaporator tube ruptures in power station boilers due to natural circulation distortion are presented. The first case discussed concerns a 110-MW, unit boiler with bottom evaporation tubing inclined at 15° to the horizontal. At the high heat fluxes present in the furnace, subcooled boiling occurs in inclined tubes. For these inclinations an insufficient flow rate causes local heat transfer deficiencies due to vapor-water separation. The introduction of internally finned tubes eliminates local heat transfer deficiencies and prevents further tube failures. The second case is that of circulation interruption due to blowdown during start-up. The water level in the drum of this second 110-MW, unit boiler was controlled by inlet header blowdown during start-up. Thus, natural circulation was interrupted, causing local overheating of evaporator tubing. The event was identified by an increase of the tube rupture frequency. After changing the blowdown procedure, the interruptions of natural circulation were avoided and the tube failure frequency decreased substantially.     

汽轮机高压缸蒸汽激励故障分析与诊断

当机组运行工况恶化而产生非平稳,非线性的振动时,综合应用新兴的小波分析和经典的频谱分析等信号处理技术可以获得丰富的诊断信息。针对兰州西固热电厂５号汽轮机组高压缸大修后的振动现象,描述了汽轮机蒸汽激励故障征兆及其产生原因,指出了减振措施及故障的排除方法。     

采用小管径受热面的大型燃机联合循环余热锅炉设计

介绍PG9171E型燃机联合循环自然循环余热锅炉的方案设计,总结该型自然循环余热锅炉的设计特点及采用小管径蒸发受热面的优点,指出我国余热锅炉的市场正在逐渐扩大,我国自己设计的自然循环余热锅炉性能先进,完全可以满足市场需求。表4     

蒸汽发生器制造的质量管理

蒸汽发生器是核电站核岛中较复杂的设备,而质量管理是核岛设备制造管理的主要内容。本文介绍了哈尔滨锅炉厂有限责任公司承制的首台蒸汽发生器项目质量管理体系的建立及实施过程。     

蒸汽空气预热器对余热锅炉有效输出热量的影响

垃圾焚烧发电产生的烟气中含有大量SOx、HCl、水分和灰分。在锅炉系统采用传统的方法将空气预热器和省煤器布置在一起:一方面易引起尾部受热面空气预热器的低温腐蚀;另一方面烟气中大量的水分和灰分可导致尾部受热面的严重积灰,从而造成设备的损坏。采用单独布置的蒸汽空气预热器,可避免上述问题的发生。蒸汽空气预热器越来越多地应用于垃圾焚烧发电厂,但其采用汽包和汽机一抽的高温蒸汽加热冷空气,导致了余热锅炉有效输出热量的变化,同时造成电厂热经济性的下降。     

喷嘴结构对涡流管性能的影响

采用FLUENT数值模拟方法,对不同喷嘴流道数涡流管进行三维数值模拟,得到喷嘴流道数目对涡流管制冷效应、制热效应及分离效应的影响规律,并对3流道渐缩型喷嘴、直线型喷嘴和阿基米德型喷嘴涡流管的性能、压力场及速度场进行模拟分析。结果表明:3流道喷嘴涡流管具有最佳能量分离性能;当模拟入口总压为3 MPa、冷端出口静压为2.5 MPa时,涡流管制冷效应随冷流率的增大而减小,制热效应及分离效应随冷流率的增加呈现先增加后减小趋势;相比直线型喷嘴和阿基米德型喷嘴,渐缩型喷嘴涡流管能量分离效果最佳;配有渐缩型喷嘴涡流管能获得更大的压力、切向速度和轴向速度。     

锅炉化学清洗介质的选择

正确选择锅炉化学清洗介质，是确定化学清洗方案的关键环节。通过分析影响锅炉化学清洗介质选择的因素，并列举了主要的清洗介质的特点和清洗工艺参数，以避免在选择锅炉化学清洗介质时可能出现的失误。     

直流盘管式蒸汽锅炉管子泄漏失效分析

某酒店的立式强制循环盘管式直流锅炉,频繁出现盘管泄漏事故,在对该炉的结构和使用情况进行详细分析的基础上,对泄漏部位进行了检查和分析,确定吸氧电化学腐蚀、汽蚀和流动加速腐蚀是造成事故的主要原因,并有针对性地提出了防护和改进措施。     

汽轮机性能老化对排汽压力影响的研究

从汽轮机组和凝汽器的热平衡入手,对汽轮机性能老化后低压缸排汽点变动方向进行了研究。结果表明,汽轮机性能老化后,其排汽压力略有升高,这就提醒我们,在凝汽器运行工况分析时应考虑这一因素。     

带补燃余热锅炉的研制

介绍了燃-蒸联合循环余热锅炉补燃装置的分类及布置形式,重点介绍了带内补燃装置的余热锅炉的设计特点,对余热锅炉设计及选型具有参考作用。     

换热表面结垢对U型管蒸汽发生器传热性能的影响分析

U型管蒸汽发生器的壳侧沉积了来自二回路系统中的腐蚀产物,结垢导致热量聚积在金属换热管上,容易造成垢下热点腐蚀,危害设备安全。为了明确结垢对蒸汽发生器传热性能的影响,本研究基于仿真平台APROS建立了U型管蒸汽发生器的分布式模型,并根据已公开论文中的数据进行了模型准确性验证;推导了污垢热阻与表面换热系数之间的关系式,分析了不同结垢厚度、位置对U型管蒸汽发生器换热区域的传热管壁面温度、流体温度、传热系数、热流密度等的影响程度。研究结果表明：随着结垢程度的加剧,蒸汽发生器的换热效率不断降低,出口蒸汽品质不断下降;结垢对沸腾段换热效率的影响比对过冷段换热效率的影响更大。     

某核电堆型蒸汽发生器排污系统设计改进

根据全范围事故分析结果,在发生蒸汽发生器传热管破裂(SGTR)事故中,为使发生故障的蒸汽发生器水位不会上升太快,需通过蒸汽发生器排污系统排污管线来控制故障蒸发器的水位和压力。通过对蒸汽发生器排污系统进行设计改进,提高系统的设计标准,将破损蒸汽发生器内漏液排向内置换料水箱,使破损蒸汽发生器降压,同时限制破损蒸汽发生器水位,防止破损蒸汽发生器满溢,满足蒸汽发生器排污系统在设计基准事故工况下承担安全功能的要求。改进后的蒸汽发生器排污系统满足国内三代核电技术的要求,为国内三代核电的安全性提供理论依据。     

蒸汽发生器水位SDRNN优化自抗扰控制

针对蒸汽发生器(SG)水位控制过程存在的主要问题,引入水位自抗扰控制(ADRC)方案.通过扩张状态观测器实时估计系统内、外扰动,并采用前馈方式予以动态补偿,同时依据状态误差矢量进行非线性反馈调节,缓解控制系统快速与超调之间的矛盾.并引入二阶对角递归神经网络(SDRNN)动态辨识SG Jacobian信息,实时优化自抗扰控制器参数.分别在水位、蒸汽和给水扰动下进行SG水位仿真实验,并对比了前馈串级PI控制与SDRNN-ADRC控制的响应曲线.结果表明:在扰动工况及控制对象参数时变下,此SG水位控制系统的控制响应迅速、超调小且稳态误差小,具有优良的动、静态性能.