超临界锅炉高温受热面内壁氧化皮的形成及剥落机理研究

基于华能沁北电厂2~#机组高温再热器下弯头连续四次氧化皮脱落的检查结果,分析超临界机组再热器管内壁氧化皮生成及剥落的机理。分析结果表明:受热面在高温运行状态下,氧化皮的形成速率取决于受热面管壁温度。造成管壁氧化皮剥落的主要因素为金属基体与氧化皮的温差及温升、温降速率。从锅炉运行中受热面温度控制、受热面温度波动控制等几个方面,提出了预防和减少锅炉高温受热面管内氧化皮形成及剥落的措施。     

给水加氧处理引发蒸汽通道氧化皮剥落的机理

提出用“环境破坏说”来阐释锅炉给水加氧处理（0T）引发蒸汽通道氧化皮剥落的机理,即高温蒸汽通道双层金属氧化皮中的次层尖晶石化合物可与高温含氧蒸汽反应生成气态羟基氧化铬,导致蒸汽中氢电导率显著升高．双层氧化皮界面由于铬蒸发散逸形成空穴,随着空穴逐步增多,双层氧化皮界面结合强度逐步降低,最终发生灾难性的氧化皮剥落事故．“环境破坏说”还可以预测运行锅炉采用OT工艺可能带来的风险：采用给水加氧处理的起始时间距锅炉投运时间越长,风险越大;蒸汽含氧量越高,风险越大;蒸汽参数越高,风险越大．新建锅炉投运后越早采用OT工艺,风险就越小．     

超(超)临界锅炉高温受热面蒸汽氧化皮的生长与剥落特性

阐述了超(超)临界锅炉高温受热面蒸汽氧化皮的晶粒特点,重点分析了铁素体钢和奥氏体钢蒸汽氧化皮的结构特征及其生成和脱落现律.指出高温受热面蒸汽氧化皮的产生是不可避免的,应进一步研究各种运行条件对氧化皮程度、结构形态和剥落时机的影响,以便从机组的运行方式、检修策略和控制理念等各方面来预测和防止氧化皮的危害.     

300MW机组锅炉高温受热面氧化皮剥落特性分析

通过宏观形貌、氧化皮厚度、金相等多方面分析,对某电厂国内300MW机组锅炉高温受热面氧化皮进行了来源分析;通过机组投产以来检修情况和各受热面历次检修氧化皮堆积趋势,结果表明：锅炉高温受热面存在管内氧化皮大面积剥落现象,其中后屏过热器和末级过热器极为严重,高温受热面的氧化皮来源于TP347HFG管的生成和剥落。     

超临界机组锅炉滑停对氧化脱落的影响

当前由上海锅炉厂生产的350 MW超临界锅炉在进行滑停和正常停炉过程中,高温受热面奥氏体不锈钢材质,从高温降至低温时,对管壁内生成的氧化皮脱落情况进行对比分析发现:随着锅炉累计运行时间逐渐增长,锅炉高温受热面管壁内形成的氧化皮也逐步增厚,由于氧化皮与受热面管材的膨胀系数不同,温度变化率超出允许范围时,氧化皮会从管屏金属内壁上剥脱,一旦大量氧化皮集中剥落,就会在受热面弯头处堵塞管道引起爆管等等问题。文中就超临界锅炉在滑停过程中氧化皮脱落现象进行了探讨,并提出了锅炉滑停过程中的防控措施。     

350 MW超临界机组锅炉氧化皮防治技术研究

为减少350 MW超临界机组因锅炉氧化皮脱落而引起的堵塞爆管问题,针对某电力公司8台超临界煤粉锅炉的结构型式及运行工况展开调查研究,分析结构设计对锅炉高温受热面蒸汽侧氧化皮的影响,发现烟温偏差的叠加效应是引起高温再热器汽温偏差大和局部氧化皮生成过快的主要原因,针对锅炉高温受热面的SA-213TP347H不锈钢管材的金属壁温适用范围进行对比,确定其最佳金属壁温报警值为600℃;通过对锅炉给水加氧设备进行改造,控制给水含氧量在10~20μg/L范围内,确保高温受热面蒸汽侧含氧量为零。实践证明,采取上述氧化皮防治措施后,锅炉氧化皮堆积数量同比减少85%以上。     

超临界锅炉安全经济温度控制域的研究

超临界锅炉因高温管内氧化皮剥落堵塞导致超温爆管一直困扰许多大型火力发电厂安全生产。某些电厂常用降低主蒸汽温度的方法来降低管壁温度,达到减缓氧化皮生成、控制氧化皮剥落与阻塞、防止管道超温爆管的目的。本文基于超临界锅炉常用管材的特性分析,得到了管材的许用温度控制线,同时导出了不同效率下防止氧化皮产生的经济运行温度线,以此确立了超临界锅炉安全经济温度控制域,可为电厂降负荷提供理论指导。     

锅炉高温受热面管内氧化皮应力分析的一种解析方法

大型电站锅炉高温受热面管内氧化皮生长及脱落问题已成为影响锅炉安全运行的主要矛盾。介绍了一种锅炉高温受热面管内氧化皮应力分析解析方法,并针对某600 MW超临界电站锅炉末级过热器的TP347H和T91 2种管材进行了计算分析,得出了停炉过程中氧化皮的应力、应变状态和可能的失效模式。     

600MW超临界锅炉高温受热面蒸汽氧化初探

分析了600 MW超临界锅炉高温管屏蒸汽氧化及其氧化皮剥落的机理和影响因素,总结了氧化皮的产生、剥落和堆积堵塞对锅炉安全运行的危害,并从管材的选择及其热处理和锅炉设备的设计、运行等各环节提出了减缓氧化皮的产生、防止氧化皮集中脱落、避免因氧化皮堆积堵塞而导致锅炉高温管屏超温爆管的防控措施。     

1030MW超超临界锅炉高温受热面氧化皮大量生成及脱落的原因分析

本文借助某1030MW超超临界锅炉的生产实践,对高温受热面的爆管、脱落氧化皮形貌及能谱分析、氧化皮生成及脱落原因等方面的内容进行了详细阐述,本文对探索超(超)临界锅炉高温受热面氧化皮生成机理、氧化皮的生成和脱落的控制具有借鉴作用。     

Ashland锅炉药剂在长庆石化公司的工业应用

长庆石化公司1.4Mt/a催化裂化装置中压汽包由于蒸汽夹带盐分现象严重,蒸汽品质难以有效控制,影响装置和气压机长周期运行。分析认为,过热蒸汽中的钠离子、二氧化硅含量超标,是导致气压机组汽轮机叶片结垢的直接原因。所以,抑制饱和蒸汽夹带盐分,进一步降低蒸汽中钠离子和二氧化硅含量,优化过热蒸汽品质,是保证汽轮机稳定运行的重点。该装置于2009年开始使用美国Ashland公司锅炉药剂,在催化裂化中压汽包系统投加AMERZINE15除氧剂和DREWPHOS2600缓蚀阻垢剂,经过连续2年的运行,饱和蒸汽钠离子、二氧化硅含量分别由6130.75μg/L、811.16μg/L降低至12.25μg/L、7.86μg/L,过热蒸汽钠离子、二氧化硅含量分别由107.74μg/L、88.43μg/L降低至27.94μg/L、9.92μg/L,汽轮机主气门开度由100%降低至70%,并在保护锅炉内壁、避免溶解氧腐蚀、提升锅炉水汽品质、优化气压机运行工况等方面取得了良好效果。     

超临界机组的合金管蒸汽侧氧化膜生长与剥落研究进展

超临界机组高温合金管氧化膜剥落问题是困扰机组安全与经济运行的难题,严重制约了机组蒸汽参数和效率的提高。特别是,在超临界机组采用给水加氧处理方式(OT)后,奥氏体不锈钢管内壁氧化膜大面积剥落事故屡见不鲜,尤以TP347H合金管为甚。本文总结了近年来国内外针对超临界机组合金管氧化膜研究的进展及相关成果,首先介绍了超临界蒸汽环境中合金管氧化机理和原子迁移机制,综述了铁素体和奥氏体合金表面氧化膜的形貌特征,分析了蒸汽溶氧对氧化膜生长速率、形貌和缺陷的影响。氧化膜完整性是决定合金抗腐蚀性能的重要因素,但在机组运行过程中氧化膜应力破坏了氧化膜完整性。进一步总结了国内外氧化膜应力和剥落研究的数值分析及实验研究情况,为我国超临界机组氧化膜剥落故障诊断研究提供参考。     

Corrosion characteristics of a nickel-base alloy C-276 in harsh environments

The oxidation behaviors of alloy C-276 in two harsh environments: high-temperature air and supercritical water (SCW), respectively representing the working conditions of the external and internal surfaces of reactors for SCW gasification biomass to produce H₂, were investigated. In two environments, all oxidation kinetics followed parabolic laws, while the corrosion rate of alloy C-276 exposed to supercritical water gasification (SCWG) environments was 2.5–3 times higher than that in high-temperature air. The oxide scale formed in air at 500 °C consisted of an outer Fe-rich layer (Fe₂O₃ and NiCr₂O₄) and an inner layer of Cr₂O₃ and NiCr₂O₄, while the outer Fe-rich layer disappeared as the temperature increased to 550 °C. Compared to the scales formed on nickel-base alloys in near-pure SCW, the absence of NiO and Ni(OH)₂ phases within the scales formed on the C-276 samples in present SCWG environment may be due to higher molar proportion of hydrogen.     

电站锅炉省煤器设计与改造对过热汽温的影响

根据锅炉蒸发受热面工质侧产汽量与过热汽温之间的内在依赖关系 ,从热量和质量平衡原理出发 ,讨论了自然循环锅炉给水温度不变而省煤器出口水温偏离设计值时对过热汽温间接的影响规律。在电站锅炉尾部受热面的改造或设计中 ,为考虑其它因素而不得不改变省煤器的吸热量时 ,建议将锅炉烟气侧热力计算与工质侧的吸热产汽量计算结合起来 ,验算省煤器出口水温的变化对炉膛蒸发受热面工作以及过热汽温的影响。     

Thermal degradation of alloy CCA617 in pure steam at 750 and 850°C

Oxidation and oxidation-induced microstructure evolution of CCA617 alloy was studied in pure steam at 750 and 850°C. Results showed that the alloy was oxidised approximately following a parabolic law. Temperature increase greatly promoted the external and internal oxidation. A single (Cr, Mn)₂O₃ layer with distribution of minor TiO₂ and MnCr₂O₄ formed at 750°C whereas a duplex oxide scale formed at 850°C consisting of a thin MnTiO₃ outer layer and a thicker (Cr, Mn)₂O₃ inner layer. TiO₂ and Al₂O₃ were formed internally especially along grain boundaries. Intragranular Mo-rich M₂₃C₆ type carbides were also observed. The carbides dissolved into the matrix as oxidation progressed. Based on detailed compositional and microstructural characterisation of the oxidised alloy, the mechanisms of external and internal oxidation as well as dissolution of the intragranular carbides are presented.     

过热蒸汽喷水混合装置的节能效益分析

依据热力学的基本原理,分析了实现蒸汽喃水混合装置节能的原理,提出了该装置的应用条件,应用喷水混合装置节省用汽的实质是利用蒸汽的潜热,对于示很好利用蒸汽潜热的用热系统,在对生产工艺无影响的情况下,该技术具有一定的应用价值,由于该装置本身并不能提供能源,相反在喷水混合过程中不可逆损失较大,所以即使在未完全利用蒸汽潜热的场合,它也不一定是节能的最佳手段。     

锅炉高温受热面蒸汽侧氧化膜在线监测技术研究

建立了高温受热面炉内壁温在线监测模型、氧化膜生长模型、氧化膜应力在线监测计算模型和氧化膜脱落评估模型等.在此基础上,开发了锅炉高温受热面蒸汽侧氧化膜管理系统,并利用该系统对某600MW超临界锅炉高温受热面炉内管壁温度和蒸汽侧氧化膜厚度及应力状态进行实时计算与分析.结果表明:利用该系统可以减小沿烟道宽度方向的热偏差,有效降低偏差屏的炉内温度,减缓管内氧化膜生成速率;通过对温度变化速率、氧化膜应力状态的实时监测,可以积极预防氧化膜的脱落和堆积.     

Experimental study on superheated steam generation by the reaction of high humidity hydrogen and oxygen in a model internal combustion steam generator

Internal combustion steam cycle (ICSC) is a novel steam power cycle using hydrogen as an energy carrier to produce superheated steam. High humidity hydrogen produced during fast hydrogen production process is directly used to produce superheated steam by combusting with stoichiometric oxygen without hydrogen storage. The ICSC efficiency is greatly affected by the content of non-condensable gas in superheated steam. In the present study, superheated steam generation by high humidity hydrogen was investigated in a model internal combustion steam generator. Effects of H₂O/H₂ molar ratio of humid hydrogen and velocity ratio of humid hydrogen to oxygen on non-condensable gas content, combustion efficiency, and mixing rate were evaluated. The results showed that the critical H₂O/H₂ ratio for the humid hydrogen humidity limit was 2.8. With increasing velocity ratio, mixing rate and combustion efficiency increased under the same H₂O/H₂ ratio. The H₂O/H₂ reaction rate monotonously decreased as the H₂O/H₂ ratio increased from 1.0 to 2.5, while the mixing rate increased along with the velocity ratio. The combustion efficiency initially increased and subsequently decreased, and the peak value was reached at a H₂O/H₂ ratio of 1.75. This result indicated that the humid H₂-O₂ combustion was controlled by diffusion under H₂O/H₂ ratios of 1.0 to 1.75, but turned to be controlled by chemical kinetics when the H₂O/H₂ ratio ranged between 1.75 and 2.5.     

An experimental study on combustion characteristics of flames in a coaxial flow with a stagnation point

By using a stagnation-point coaxial flow generated by a lower coaxial burner and an upper quartz plate, an inner (or outer) premixed flame influenced by outer (or inner) oxygen content is experimentally developed to simulate and study double-flame burning structures modified by interactions of flamelets in turbulent combustible flows. In the experiments, fuel-air and oxygen-nitrogen mixtures are therefore introduced into outer (or inner) and inner (or outer) flows, respectively. This experimental arrangement allows either the inner flame or the outer flame to be located at different planes by separately adjusting the compositions and injection velocities of the inner and outer flows. An inner (or outer) planar premixed flame with a small outer (or inner) lifted tail or an inner (or outer) nonplanar premixed flame and an outer (or inner) trumpet-shaped diffusion flame can be developed in the flow field. The lifted tail and the trumpet-shaped diffusion flame are stabilized along the interface between the inner and outer jets in the coaxial flow. The inner (or outer) premixed flame influenced by the outer (or inner) oxygen content may experience transports of mass and thermal diffusion parallel to the flame surface. It endures the flow stretch tangent to the flame surface. Furthermore, in the flow field, the directions of flow convection for both inner and outer flows are the same (both divergent). The combustion characteristics, including extinction, blow off, flashback, the transition from the flat flame to the hat-shaped flame, and the ignition and development of diffusion flame are reported and discussed. Finally, the measurements of flame shape and temperature distribution are involved.     

Superheated steam drying of sawdust in continuous feed spouted beds – A design perspective

Spouted bed drying technology shows promising results for the drying of unscreened sawdust in superheated steam. In this paper, the experiences from designing, running and evaluating two spouted bed continuous feed dryers are presented. Stable running conditions and drying results have been achieved. This has been particularly important for sawdust that will be compressed into pellets or briquettes. The spouted bed superheated steam dryer also shows high potential for energy efficient integration into sawmills. Our recommendation is thus, to use the outlet steam temperature as the control parameter for the outlet moisture content. A drying rate above and one below the fibre saturation level, can be identified. Visual observations through the viewing glass in the drying zone in both the dryers clearly showed that not all of the material participated in the spout at all times; there were, however, no indications of dead zones. A heat transfer analysis indicated that only about 70% of the surface area of the material was in thermal contact with the steam. This paper sums up the experiences regarding drying properties, control and system properties obtained when sawdust is dried using superheated steam as the drying medium. Further work on standardised dryers in series or in parallel is necessary to increase the capacity in the spouted bed dryer.