换热表面析晶污垢附着与腐蚀行为相关性研究

Crystallization fouling is a kind of fouling investigated widely on heat transfer surfaces. The deep understanding on adhesion mechanism, especially in the adhesion of crystallization fouling and growing up lumpily, was not given in the literatures because of the complicate water quality. In the period of forming, on the one hand, the crystalline types were altered with the different ionic types and concentrations in the medium, on the other hand, the adhesion state was altered with different corrosive oxidation. The micro-bonding interface between crystallization fouling and heat transfer surface was investigated firstly in this project. The adhesion mechanism was paid more attention when investigating the effect of ionic types and concentrations on the forming of crystallization fouling in the medium. The coupling analysis on the corrosion behavior and the crystallization fouling adhesion was carried out based on the “bridging concept”. The corrosion resistance, corrosive product types and fouling adhesion on heat transfer surface were put into a comprehensive model to analyze. Through comparing the correlation of corrosive product types and fouling adhesion on the heat transfer surface used often and corrosion-resistant Ni-P-X deposit surface, the relationship model of corrosion resistance, corrosive product and fouling adhesion ability was established. The essential factors influencing the crystallization fouling adhesion were explained. The present investigation will not only provides a fundamental foundation with the formation and adhesion mechanism of crystallization fouling on the surfaces of heat transfer, but also provides fundamental guide with anti-fouling in the field of heat transfer.

析晶污垢是换热表面常研究的一种污垢类型，但其附着机理因水质等多方面的影响，在析晶污垢的附着及块状长大机制方面还缺少深入的认识。析晶污垢在形成过程中，一方面受工作介质中离子类型及浓度的影响改变晶型，另一方面换热表面受腐蚀氧化等的影响也在改变析晶污垢的附着状态。本项目从考虑析晶污垢与换热表面结合的微观界面入手，在研究工作介质中不同金属离子浓度及类型对析晶污垢形成影响的同时，更重点研究析晶污垢的附着机制，基于“桥接”概念，对换热表面腐蚀氧化行为与析晶污垢的附着进行耦合分析，将换热材质的耐蚀性、腐蚀产物的类型及污垢附着纳入到一个整体考虑，通过对比分析常用换热材质表面及耐蚀Ni-P-X系镀层换热表面腐蚀产物的类型及污垢附着的相关性，建立耐蚀性-腐蚀产物-污垢附着能力的关系模型，解明影响析晶污垢附着的本质因素。研究成果可为换热表面析晶污垢形成及粘附机理奠定理论基础，同时也为传热领域抑垢提供理论指导。

换热表面污垢问题在工业界至今仍没有得到很好的解决。析晶污垢在形成过程中，一方面受工作介质中离子类型及浓度的影响改变晶型，另一方面换热表面受腐蚀氧化等的影响也在改变析晶污垢的附着状态。本项目在开展时，以煤制焦系统中换热器表面析晶污垢与换热表面结合的微观界面入手，在研究工作介质中不同金属离子浓度及类型对析晶污垢形成影响的同时，更重点研究析晶污垢的附着机制，深入分析了焦化换热表面两侧换热介质(焦化气侧：H2S, HCN 和NH3，冷却水侧：Cl-离子、Ca2+离子、CO32+离子)在不同换热表面腐蚀作用下，污垢结合界面成键的不同及其所表现出的结合状态，发现了焦化换热介质在换热表面及其不同氧化产物上的附着机制。.为抑制析晶污垢的形成和附着，开发了三元Ni-W-P化学镀抗垢耐蚀镀层和制备了基于激光熔覆的镍基（Ni-Cr-Mo-Nb）和铁基（Fe-Cr-Ni）两种典型激光熔覆涂层。对比分析了常用换热材质表面及耐蚀Ni-P-X系镀层换热表面腐蚀产物的类型及污垢附着的相关性，建立了耐蚀性-腐蚀产物-污垢附着能力的关系模型，解明了影响析晶污垢附着的本质因素。另一方面，以超临界水为应用工况，发现了Ni-W-P镀层和激光熔覆层在超临界水高温氧化环境中的元素扩散分布规律和对应氧化产物的形成，阐释了主要氧化产物在所形成的致密氧化保护膜中对基体的保护作用，显示了氧化层对基体腐蚀的阻止和对污垢附着的减缓作用。本工作的完成为采用激光熔覆和化学镀以抑制焦化氛围下腐蚀污垢的附着提供了新方法，也为换热表面析晶污垢形成及粘附机理奠定了理论基础。