【作者】 张乃强；

【导师】 徐鸿；

【作者基本信息】 华北电力大学 ， 热能工程， 2012， 博士

【摘要】 超超临界发电是国际上先进的洁净煤燃烧技术之一,主要是通过提高主蒸汽温度和压力来提高转换效率,进而实现节能减排。超临界水处于临界点以上,其密度、扩散系数、粘度、介电常数、溶解度等物性较亚临界发生了明显变化。加氧处理是国内外超临界电站广泛采用的给水处理方式之一,因此锅炉管材料处于溶氧超临界水中。近年来锅炉管氧化层生长过快出现剥落现象较为普遍,导致爆管事故频发,原因复杂。溶解氧对超临界水中金属氧化机理影响的研究将有助于揭示氧化层生成机理,进而为预防锅炉管爆管提供理论依据。因此开展电站锅炉管氧化层在溶氧超临界水中生长机理的研究,意义重大。论文对铁素体钢T24、铁马氏体钢P92和奥氏体钢Super304H、TP347HFG、HR3C五种钢种在550℃和600℃,25MPa超临界水中进行了氧化试验研究。为了研究溶解氧对氧化过程的影响,溶解氧浓度分别控制为无氧、100ppb、300ppb和2000ppb。氧化时间分别为200h、400h、600h、800h和1000h。得到了不同温度和不同溶解氧浓度超临界水环境中五种材料的氧化动力学曲线。分析了氧化物表面形貌和成份,观察了氧化层横截面结构和元素分布。分析研究了温度、溶解氧、铬含量、水环境等因素对氧化过程的影响,其中溶解氧对氧化增重和裂纹有明显影响。研究中发现加氧处理抑制腐蚀的作用机理在超临界水环境中是不适用的。分析了水的扩散系数、溶解度等对氧化过程的影响。基于溶解氧在不同工况下对电站系统管道的作用不同,提出了一种针对火力发电机组给水处理新工艺。该工艺在精处理后母管或除氧器下降管加氧气,在高压加热器后、省煤器前加联胺,除掉氧气。该给水处理工艺既可以抑制低压加热器和高压加热器中的流动加速腐蚀,又可降低溶解氧对超临界水中金属氧化的加速影响。铁素体钢和铁马氏体钢在超临界水中生成均匀的双层结构的氧化层,由于超声波在两层中的传播速度不同,因此提出了一种超声波测量氧化层厚度的修正方法,该方法可以更准确的测量锅炉管内壁氧化层厚度。更多还原

【Abstract】 Ultra supercritical power generation is one of the most advanced clean coal technologies. Operating the water medium in the supercritical state in ultra supercritical (USC) power plant improves the energy conversion efficiency and fuel usage, thus a reduction of pollutant emissions. In comparison to the subcritical state, the physical properties of the water medium including density, diffusion coefficient, kinematic viscosity and dielectric constant change more greatly when it works above the thermodynamic critical point. Oxygenated treatment (OT) is widely used in USC power plant. So the materials of boiler tube are working in supercritical water (SCW) with dissolved oxygen (DO).In recent years, the tube explosion resulting from the excessively growth rate and all-pervading exfoliation of oxide scale occurs frequently. The reasons for this appearance is rather complex. Consequently, the research on growth mechanism of oxide scale of boiler tube in supercritical water with dissolved oxygen has important significant and academic value。The corrosion experiments of the ferritic (T24), ferritic-mantensitic (P92) and austenitic steel (Super304H, TP347HFG, HR3C) were investigated in supercritical water at the temperature of550℃and600℃under a pressure of25MPa. To probe the influence of DO content on corrosion, the DO contents were controlled at0,100,300and2000ppb, respectively. The exposure time were200,400,600,800and1000h. After obtaining the weight gain curves under different conditions, the surface morphologies and composition were observed using SEM and EDS technologies. At the same time, the cross structures and element distribution of the oxide scales were analyzed.The influences of Cr concentration, temperature, DO and water on oxidation were also investigated. The results indicated DO can have an obvious effect on weight gain and exfoliation of oxide scale. FAC avoided in OT method proposed by EPRI was proved to be non-controlled in SCW. The growth and exfoliation mechanism of oxide scale was changed when the water was present. So the influence of diffusion coefficient and solubility on oxidation were also discussed in this paper.Based on the different effect of DO on corrosion of tubes under different operating conditions, a new treatment method of feed water was proposed. In this method, the oxygen was fed in the site of the main pipe after precision treatment or the vertical pipe after the deareator, and the diamide was fed in the site of the pipe after high pressure heater and before economizer. The oxygen and diamide were reacted each other in the pipe. The deareated water was fed into the tube of the boiler. The treatment method proposed in this study can avoid of the occurring of FAC in high and low pressure heaters, as well as can decrease the corrosion of boiler tubes enhanced by DO in SCW.Based on observations on the uniform dual-layered structure oxide scale formed on ferritic and ferritic-martenistic steels, a correction method of the thickness of the oxide scale on the boiler tube using supersonic measurement system was proposed because of the different propagation velocity of supersonic in the above two layers. The more accurate thickness of oxide scale on boiler tube can be measured by this method.更多还原