外加溶氧对锅炉过热器管内氧化皮生长及剥落的影响  

Effect of Adding Dissolved Oxygen Upon Formation and Exfoliation of Oxide Scale of Superheater Tube

作　　者：朱志平[1] 柳森[1] 郑敏聪[2] 

机构地区：[1]长沙理工大学化学与生物工程学院,湖南长沙410114 [2]国网安徽省电力公司电力科学研究院,安徽合肥230601

出　　处：《全面腐蚀控制》2016年第5期12-18,共7页Total Corrosion Control

基　　金：湖南省科技计划重点项目(2013GK2006);湖南省自然科学基金项目(09JJ6067)

摘　　要：火电厂超临界机组过热器管内氧化皮的生长与脱落问题是困扰全厂安全与经济运行的难题,而外加溶氧对锅炉过热器管内氧化皮生长及剥落是否有影响已经受到广泛关注。文章阐述了Fe系合金的氧化机理,给出的外加氧分压与蒸汽自身分解氧分压间的函数关系,表明随着外加溶氧的增大,蒸汽中总的氧分压增大,而蒸汽分解的氧分压减小,即外加溶氧抑制蒸汽分解的氧分压,从热力学角度证明外加溶氧对金属高温蒸汽氧化有贡献作用;探讨了不同的外加溶氧浓度下过热器管氧化皮形成过程中的形貌、厚度、成分等理化特性,分析了外加溶氧对氧化皮生长及剥落的影响,具体表现为:在外加溶氧状态下,氧化膜表面更容易形成不连续、疏松多孔的氧化物,氧化层外层氧化物内及内外层界面处有较多孔洞等缺陷,氧化层厚度也比不加氧的状态下的厚,且外加溶氧加快形成CrO_2(OH)_2,由于CrO_2(OH)_2的蒸发散逸在氧化层中形成空洞,破坏氧化皮的结构,此外,外加溶氧也促进了氧化皮外层生成不致密的Fe_2O_3氧化物。上述结果表明外加溶氧对过(再)热器管内壁氧化皮的生长及剥落有影响,为电厂水化学工况的改进提供技术参考。Formation and exfoliation of supercritical thermal power unit superheater tube seriously impact the safe and stable operation of power system. Besides, the consequence of adding dissolved oxygen has drawn wide attention due to its uncertainty influences. Through the analysis of the oxygen oxidation mechanism, this article introduces a functional relationship between the adding dissolved oxygen partial pressure and the oxygen partial pressure of steam decomposition. With the increasing of adding dissolved oxygen, the total oxygen partial pressure in steam increases. However the oxygen partial pressure of steam decomposition reduces, it means that the adding dissolved oxygen inhibit the oxygen partial pressure of steam decomposition. And it proves that the adding dissolved oxygen accelerated the oxidation of the metal according to the related thermodynamic theory. The morphology, thickness, composition and other physical and chemical properties in the process of superheater tubes oxide formation were investigated at different dissolved oxygen concentration. In addition, the impact of adding dissolved oxygen within the boiler superheater tubes oxide growth and exfoliation were analyzed. When we add dissolved oxygen, the surface of oxide film is easier to form discontinuous, loose and porous oxides. The outer oxide of oxide layer and the contact surface of inner and outer layers has massive holes and other defects, the thickness of oxide layer is thicker than without adding oxygen state, what＇ s more, the adding dissolved oxygen accelerate the formation of CrO2（OH）2. It also destroy the structure of scale because evaporation fugitive of CrO2（OH）2 form voids in oxide layer. In addition, adding dissolved oxygen is helpful to form loose oxide Fe2O3 on the outer layer. Therefore, it proves that the adding dissolved oxygen has an impact on growth and exfoliation of scale in the boiler superheater （reheater） tubes, which can make some guidance for the power plant to select water chemistry conditions.

关 键 词：超临界机组 过热器 氧化皮 生长及剥落 外加溶氧 水化学工况 

分 类 号：TK223.3[动力工程及工程热物理—动力机械及工程]