Research On The Failure Of Oxide Scale In The(Ultra-)Supercritical Boiler

As the contradiction between China’s economic development and environmental protection is increasingly intensified,in the face of the shortage of fossil energy and the gradual deterioration of the environment,the development and utilization of new energy power generation technologies is imminent.However,at present,coal-fired thermal power generating units in China’s generating units still occupy a high proportion,and vigorously developing(ultra-)supercritical thermal power units has become the current trend.With the improvement of the unit parameters,the high-temperature heating surface materials of the boiler will face more severe tests.High temperature pipeline metal reacts with superheated steam to generate a certain thickness of oxide scale.The presence of oxide scale will affect the heat transfer of high temperature pipeline and cause the pipeline metal to overheat.The peeled scale will cause high temperature pipeline blockage and tube explosion.The erosion of steam turbine components poses a great threat to the safe operation of the unit.Based on the characteristics of scale and heat transfer characteristics in high temperature tubes of(ultra-)supercritical boilers,this paper uses finite element numerical simulation to study the problem of scale failure in high temperature tubes.The main work and conclusions of the paper are as follows:(1)Based on the existing research at home and abroad,the generation and failure behavior of the steam-side oxide scale was analyzed.The steam scale growth and shedding mechanisms of ferritic and austenitic metal pipes were compared.It was found that the metal oxidation kinetics,scale morphology,and the elemental composition of the pipe material had a great effect on the scale formation and shedding.(2)Based on the heat transfer method and actual operating parameters of a1000 MW ultra-supercritical boiler high temperature pipeline,the finite element thermal analysis method was used to numerically simulate the high temperature pipeline,and the effect of the scale thickness on the steam side on the temperature field of the pipeline was studied.The simulation results show that as the scale thickness increases,the temperature of the pipe matrix gradually increases,and the temperature at the interface between the scale and the pipe matrix is most sensitive to the change of the scale thickness,and the temperature of each interface has a linear relationship with the thickness of the scale.In the case of scale buildup,this article assumes the thermal conductivity of the scale,and finds that the thickness of the scale that has not fallen off under the same operating conditions is different,but the tube wall temperature when the scale of the scale is 4W/(m·K)The temperature rise at the highest point is basically the same.Judging from this,the thermal conductivity of the deposited oxide scale is closest to the actual situation when 4W/(m·K)is taken.(3)Through the heat-structure coupling,the simulation results of the temperature field are applied to the nodes as the thermal load of the structural analysis to solve the structure.It was found that under high load operation,as the thickness of the scale increases,the stress of the scale and the stress difference at the interface between the scale and the substrate gradually decrease,and the scale is not easy to fall off at high temperatures.The accumulation of scale on the pipeline will cause a vicious cycle of oxidation on the steam side of the pipeline-warming of the wall-rapid oxidation on both sides of the pipe-overtemperature.