Calculation And Analysis On High-temperature Heating Surfaces Thermal Deviation Of Supercritical Boiler

supercritical and ultra-supercritical thermal power generating units have gradually been main parts of thermal power industry, whose high-temperature heating surfaces are paid more and more attention by researchers and operators because of overheating tube rupture. Usual thermal deviation methods take no account of influence above, so the methods cannot assess the security of high-temperature heating surfaces. Taking one 600MW supercritical power plant as an example, the impact of oxide scale on thermal deviation is researched to analyze the safety of high-temperature heating surfaces in operation.In this paper, the forming mechanism of thermal deviation is analyzed from the following two aspects:flue gas heat deviation, steam flow distribution deviation. As for final superheater, a thermal deviation model is established based on existing method, and a integrated thermal deviation software is compiled. This software is utilized to research the flow distribution and thermal deviation between tube panels and tubes in a panel, and calculate the wall temperature of key points and other points along the tube, which is useful to analyze the impact of oxide scale on thermal deviation.Then this paper analyzes the forming mechanism and damage of oxide scale, establishes oxide scale growth prediction model by considering the interaction effect of oxide scale growth and tube wall temperature, and works out thickness of oxide scale along tube. Thus, the impact of oxide scale on flow distribution, thermal deviation and tube wall temperature is calculated aimed at safety analysis, and this paper also analyzes the impact from the aspect of creep rupture life.The result shows, steam-side oxide scale increase the tube wall temperature and affect flow distribution between tube panels and tubes in a panel. The former shortens creep rupture life, the latter decreases thermal deviation between tube panels, but enlarges thermal deviation tubes in a panel. Therefore, Carrying on a security appraisal to high-temperature heating surfaces of supercritical and ultra-supercritical boilers by thermal deviation method should consider oxide scale and its influence on tube wall temperature and bearing life.Research results in this paper can be used to further improve thermal deviation methods of high-temperature heating surfaces, and also can be used to assess security of high-temperature heating surfaces in operation.