超临界水氧化环境中高氧高盐及流动耦合作用下镍基合金的腐蚀机理研究

Supercritical water oxidation is a promising technology for hazardous wastes and sludge treatment, which can remove organic pollutants rapidly, efficiently and thoroughly. It is a key technology which is able to extricate the difficult position of organic pollution problem in China. However, the severe corrosion problem of materials is a bottleneck which limits the development of such technology. In supercritical water oxidation environment, there are few relevant researches about the effect of salt deposition layer on the surface of equipment tubes and effect of high-speed flow of the medium, which can significantly affect the corrosion mechanism of materials. In this project, the precipitation behavior of inorganic salts on the surface of samples in supercritical water oxidation environment is studied, and the shielding effect of the deposited layer on diffusion behavior of corrosion products and dissolved oxygen is also analyzed in order to obtain the corrosion mechanism of Ni-based alloys in the surface microenvironment under the sediment layer. In addition, the effect of high flow rate effect on the corrosion behavior of Ni-based alloys was obtained by analyzing the law of turbulence and diffusion of corrosion products and dissolved oxygen in supercritical water oxidation environment. In the end, the corrosion mechanism of Ni-based alloys with the multiple effects of high concentration of oxygen, high concentration of salt and high velocity of medium in supercritical water oxidation environment is obtained. The project aims at figuring out the key factors which affect the equipment corrosion significantly and providing a useful method for improving the reliability and safety of supercritical water oxidation technology.

超临界水氧化技术是一种极具前景的危废、污泥处理技术，能够实现有机污染物快速、高效、彻底去除，是解决我国当前十分严峻的高浓有机污染物处理问题的重点发展技术，然而设备材料的严重腐蚀是限制该技术发展的瓶颈问题。在超临界水氧化环境中，无机盐在材料表面结晶及介质高速流动会显著影响材料的腐蚀机理，目前尚无相关研究报道。本项目通过研究超临界水氧化环境中无机盐在材料表面的结晶行为，分析沉积层对腐蚀产物、溶解氧扩散行为的屏蔽作用，获得沉积层下材料表面微环境中镍基合金的腐蚀机理；通过研究介质流动对腐蚀产物、溶解氧的湍流扩散作用规律及对无机盐在管道壁面结晶行为的影响规律，得到高流速作用对镍基合金的腐蚀行为影响机制。最终建立高氧、高盐及流动耦合作用下超临界水氧化环境中的镍基合金腐蚀机理模型，明确影响材料腐蚀的关键因素，指导建立腐蚀防控理论，为提高超临界水氧化技术的可靠性、安全性提供理论依据。

超临界水氧化(supercritical water oxidation, SCWO)是一种极具前景的高浓有机废水处理技术。设备材料的严重腐蚀是限制SCWO技术推广应用的瓶颈。本项目通过实验、理论分析与建模、数值模拟、热力学计算等手段，系统分析了影响镍基合金腐蚀行为的典型因素作用机制，得到以下创新性成果：1) 探究了镍基合金中镍、铬、铁元素在不同氧浓度下的稳定形态和溶解特性，揭示了镍基合金表面氧化膜在不同氧浓度下的破裂-再生机制，从而明晰了含高浓度溶解氧超临界水中镍基合金625、800的腐蚀机理。2) 探究了超临界水环境中无机盐结晶层存在条件下的无机盐结晶-腐蚀协同行为，通过分析垢下微环境中的溶解-传质-反应过程，在国际上首次提出了超临界水环境合金垢下腐蚀机制。3）通过高参数流动腐蚀实验装置建立了高雷诺数湍流流动环境，探究了超临界水环境镍基合金流动腐蚀行为，率先揭示了介质高流速作用下镍基合金的流动-腐蚀耦合作用机制。本项目的进行从机理层面解释了困扰本领域多年的高氧-高盐及流动超临界水氧化环境材料腐蚀严重的问题，创新性提出了超临界水环境镍基合金垢下腐蚀机制和流动促进腐蚀机制，为腐蚀防控技术和抗腐蚀新材料的开发提供了理论依据，有效解决了超临界水氧化技术商业化推广过程中面临的材料腐蚀问题，为工业废水、危废及污泥的妥善处理处置提供了新思路。同时，研究过程中创新性开发了国际领先的超临界水环境腐蚀-盐沉积-流动多因素耦合测试装置，获得多项国家发明专利授权，为后续超临界流体环境腐蚀测试提供了硬件基础。