Research On The Characteristic Of High Temperature Corrosion Of Water Wall Tube In Coal-combustion Boiler

In recent years,the environmental protection consciousness gradually has been strengthened and coal-fired power plants have been transformed by“ultra-low emissions”.In the process of reducing the generation of nitrogen oxides,the transform causes anoxic combustion in the near wall of water wall tube to form a strong reducing atmosphere.Sulfur in the coal is converted to hydrogen sulfide in the atmosphere,and hydrogen sulfide can cause serious high temperature corrosion of water wall tube.Corrosion led to the thickness of water wall tube to be thinner,which seriously affects the safety and economy of power plant operation.Therefore,it is necessary to study the high temperature corrosion of water wall tube.Aiming at supercritical and ultra-supercritical coal-fired units high temperature corrosion problems,the relevant scientific research is carried out,including three parts,respectively the experiment study on the gas composition distribution near the water wall tube,water wall mechanism study of high temperature corrosion rate,research on mathematics model of high temperature corrosion and life assessment of water wall tubes.In the part of the experiment study of gas composition distribution,to deal with the high temperature corrosion of the water wall in a 630MW supercritical tangential firing boiler,combustion optimization test is carried out.The influence of different types of air volume on the gas composition（O₂,CO and H₂S）and the influence of different types of air volume on the thermal efficiency of the boiler and the concentration of NOx are emphasized.In the experiment,the oxygen content,secondary air distribution,CCOFA air volume,SOFA air volume and CFS air volume test are respectively carried out.High temperature corrosion experiment of water wall tube materials 12Cr1MoVG and15CrMoG are made in the tube furnace.The experiment simulate the condition of reducing atmosphere（"H₂S+O₂+N₂","CO+N₂"and"H₂S+CO+N₂"）,temperature（400℃）and deposit near the water wall.Under the theoretical guidance of accelerated corrosion test,the high temperature corrosion behavior of alloy under 10 working conditions is studied in detail.Weight gain method is employed to gain the corrosion dynamic curves.Furthermore,the micro-morphology,element compositions and chemical composition of corrosion products are analyzed by SEM,EDS and XRD.Based on the physical chemistry mechanism and mathematical derivation,a one-dimensional mathematical model of high temperature corrosion of water wall is established.In the process of mathematical modeling,the influence of H₂S gas concentration near the water wall,temperature of tube wall and thickness of water wall tube to high temperature corrosion is high spot reviews.And H₂S gas diffusion coefficient in the corrosion product layer and intrinsic chemical reaction rate are involved in model.In the end,the relationship between the average corrosion rate of corrosion layer and the corrosion time is established.The wall safety factorλis introduced at the same time,and the pipeline life evaluation criterion is set up.Finally,a prediction case is given based on the measured data of the power plant,which provides a reference for the monitoring of high temperature corrosion of water wall tubes.