【作者】 高玲；

【导师】 周克毅；

【作者基本信息】 东南大学 ， 动力工程及工程热物理， 2016， 硕士

【摘要】 超临界和超超临界电站锅炉高温受热面布置在高温烟气区,蒸汽温度最高,经常发生超温或爆管事件,严重影响机组安全运行。本文针对常规热偏差分析方法的不足,采用数值计算方法研究高温受热而的热偏差和金属温度分布,及其对蒸汽侧氧化膜的分布和脱落的影响,对提高高温受热面的安全性具有重要意义。论文研究以某600MW超临界锅炉末级过热器为对象,在分析热偏差影响因素及常规热偏差方法特点的基础上,选用CFD方法计算分析单个管屏的各热力参数及热偏差的分布。建模时,按屏的原始尺寸,在Workbench软件环境下进行网格划分,基于RNG k-ε流动模型建立了烟气横掠末级过热器管屏的数值计算模型。然后在Fluent软件平台下完成了50%、75%和100%负荷工况下的稳态模拟计算,并将计算结果与锅炉热力计算结果进行了整体比较,确定了所建模型的正确性。在此基础上,利用计算数据分析了末级过热器管屏的蒸汽温度、金属温度和烟气温度分布,以及各管的换热和热偏差分布特点,由此得到同屏各管蒸汽侧氧化膜的生长规律。结果表明,数值计算模型比常规热偏差分析更能准确地反映受热面的换热及各热力参数分布,是分析超临界和超超临界锅炉高温受热面安全性的-‘种重要方法。为分析高温受热面蒸汽侧氧化膜脱落问题,论文研究基于稳态数值模型及其计算结果,依据过程动态特征的分析对前述数值模型烟气侧进行了适当简化,分别计算了三种参数阶跃扰动情况下同屏各管沿管长方向金属壁温的动态响应,即蒸汽入口温度扰动、烟气入口温度扰动和蒸汽入口流量扰动。动态计算数据反映,进口蒸汽温度扰动对管屏各管内壁金属温度变化影响最大,出口蒸汽温度变化值和内壁金属温度变化值与蒸汽入口温度变化值基本相等,各管之问存在一定差异。进口烟气温度扰动和进口蒸汽流量扰动对管屏各管内壁金属温度变化的影响相对较小；在进口蒸汽温度扰动时,越靠近进口处的内壁金属温度变动速度越快。因此,实际运行中要结合管内蒸汽侧氧化膜的厚度分布分析各扰动下氧化膜发生脱落的可能性。论文研究所得到的计算数据及各参数的分布规律为后续进一步研究同类锅炉高温受热面蒸汽氧化膜的生长和脱落提供了重要数据,同时也为现场优化运行方式,确保高温受热面的安全运行提供了指导。更多还原

【Abstract】 The high temperature heating surface of supercritical and ultra-supercritical power plant boiler is arranged in the high temperature gas region. Qvertemperature tube-burst accident which affects the safe operation of the unit seriously often occurs on because of highest temperature steam. Contrary to the defect of conventional analysis of thermal deviation, using the numerical method to study temperature distribution of metal, thermal deviation of high temperature heating surface and its impact on the distribution and fall-off situation of oxide scale has great significance for improving the security of high-temperature heating surface significantly.This paper chooses the finishing super-heater of a 600MW boiler as the research project. Based on the analysis of factors affecting thermal deviation and features of conventional analysis of thermal deviation, using CFD numerical method to analyze distribution of thermal deviation and thermal parameters of a single tube screen. Based on its original size,using RNG k-ε flow model to establish the heat transfer model of gas horizontally sweeping the finishing super-heater tube bundle, using the Workbench internal software for meshing. Then completing the steady-state’s numerical simulation in Fluent software platform by 50%,75% and 100% load conditions and comparing the results with boiler thermodynamic calculation results integrally to determine the validity of the established model. On this basis, using the datas of calculation to analyze steam temperature, metal temperature and flue gas temperature distribution of the finishing super-heater tube screen and features of each tube’s heat transfer and thermal deviation, to obtain the growth law of the steam side oxide scale on each tube in the same screen. The results show that comparing with conventional analysis of thermal deviation the numerical model reflects the distribution of thermal parameters and heat transfer more acurratly. It’s an important method to analyze the safety of supercritical and ultra-supercritical boiler’s temperature heating surface.For analyzing the falling off of steam side oxide scale on high-temperature heating surface, the study based on steady-state calculation results taking appropriate simplified assumptions to the model in accordance with analysis of dynamic characteristics. Simulating the the metal wall temperature’s dynamic response along the tube length direction of each tube which in the same screen,the simulation is in three cases which using steam inlet temperature disturbances, flue gas inlet temperature disturbances and steam inlet flow disturbances as parameters. Dynamic calculations reflect that inlet steam temperature perturbations has the most impacts on each tube screen tube wall metal temperature changes. The temperature change of the steam outlet, the inner wall of the metal and the steam inlet is substantially equal. There are some differences between different tubes, flue gas inlet temperature disturbances and steam inlet flow disturbances have less impacts. When the inlet steam temperature disturbances, closer to the inlet the metal temperature of the inner wall change faster. Therefore, in actual operation we should analyze the possibility of the falling off of steam side oxide scale on high-temperature heating surface combining with the thickness distribution and different disturbance conditions.The calculated data and distribution of the parameters in the papers provides important data for further study on growth and fall off of similar boiler’s steam side oxide scale on high-temperature heating surface, but also for on-site optimization operation mode and providing guidance to ensure the safe operation of high temperature heating surface.更多还原