Study Of Forming Mechanism And Blockage Discipline Of Oxide Skin In High-temperature Tube Of Supercritical Boiler

The unit parameters such as steam temperature and pressure are increased substantially with the progress of (ultra-)supercritical power generation technology. The high temperature steam side oxidation is arisesed in the boiler heating surfaces and resulting series of safety problems, including the tube explosion of superheater and reheater which caused by peeling oxide skin blocking the tube lead to over temperature. This is one of the main problems impact safe operation of (ultra-)supercritical boiler.In order to solve the problems of tube explosion caused by oxide skin blocked to occurs over temperature, the paper tightly around the start of these aspects of oxide formation, spalling mechanism, flow law and control measures in (ultra-)supercritical boiler high temperature heating surface. Through the based on the analysis about disposal of typical supercritical boiler heating surface, material of heat pipe and operating characteristics, different oxide skin and pipe are collected as sample from scene of power plant. The oxide formation and spalling mechanism of (ultra-)supercritical boiler high temperature heating surface are found by analysing composition and structure of oxide skin and microstructure and micro-area composition of the pipe burst mouth, using energy chromatograph, X-ray diffraction, optical microscope and scanning electron microscopy. The results showed that at high temperature operation conditions, the iron in metal matrix react with infiltrated oxygen atoms to generate for the inner FeO oxidation layer, so that oxide film change from the 2-layer into a 3-layer membrane. The inside high-temperature oxide membrane is unstable and decompose easily. The inner oxide skin spall and scale off easily under the action of thermal stress. The parts easy to accumulate oxide skin are found by studying the oxide skin flow law in (ultra-)supercritical boiler high temperature heating surface pipe. It will provide guidance and reference for power plant maintenance work.In this paper, the measures are proposed to prevent and reduce oxide skin formation and spalling from the boiler operation, equipment design, material selection and transformation, as well as surface treatment and chemical cleaning and other aspects on (ultra-)supercritical boiler high temperature heating surface. These control measures can effectively reduce the safe operation problems which long-term difficulties power plant brought from oxide skin formation and spalling, and improve the reliability of the unit.