Study On Flow Accelerated Corrosion Hydrodynamics Process Of Supercritical Unit

The continuous improvement of the unit parameters of the thermal system of the power plant makes the pipeline wall thinning phenomenon caused by flow accelerated corrosion(Flow Accelerated Corrosion,FAC),which seriously threatens the safety of the power plant.Due to the particularity of the thermal cycle system of the power plant,the working conditions of the flow accelerated corrosion position are mostly high temperature and high pressure environment,which results in the very strict requirements for the experimental equipment,and it is difficult to carry out the flow accelerated corrosion experiments and tests.Therefore,it is a very effective and feasible means to continuously verify the FAC prediction and mechanism analysis by experts and scholars.The numerical simulation model is established in COMSOL software,select the hole plate and bend where the flow accelerated corrosion is violent as the research object.The medium is single-phase flow and two-phase flow with different vapor content,select the euler-euler model,using the wall function method to obtain the size and distribution of shear force at the wall,further calculate the mass transfer coefficient and iron ion at different temperature and p H values,through the FAC corrosion model.According to the calculation and analysis of the results obtained from the simulation of the hole plate model,it is found that when the aperture ratio of the single-phase flow medium is unchanged,the corrosion rate of the downstream flow of the plate accelerates the hole plate along the downstream distance of the plate increases first and then decreases,and the corrosion of the lower wall surface of the hole plate is the most serious.When the medium in the pipeline is two-phase flow,the distribution law of accelerated downstream flow of the hole plate is similar to that of single-phase flow.Due to the existence of water vapor,the accelerated corrosion rate of the downstream flow of the hole plate increases to varying degrees,and the accelerated corrosion rate in the upper wall increases the most.Changing the temperature is found that the temperature flows in the range of 100 to 150℃ and the two-phase flow with vapor content between 0.3% and 0.5%.On the contrary to the viscosity of the medium,the temperature increases the viscosity of the medium and the temperature,and the temperature will increase the solubility of iron ions in the medium.Therefore,the FAC rate is maximum when the medium is 150℃ and contains 0.5% vapor flow.By calculating the 90°bending model,it was found that when the medium contained water vapor,the distribution of the viscosity size inside the bend was similar to that of the water vapor content,and the viscosity size in the bend was obviously affected by the water vapor content.At the inner bend of the bend will produce two extreme points,the second extreme point is large.When the medium is a two-phase flow,the shear force of the sliding ratio and the influence of water vapor is greater than the influence of the viscosity of the wall,and the increase is obvious at the first extreme point.When the solubility of the medium is certain,the water vapor content of the two-phase flow is changed that with the vapor content of the two-phase flow,the FAC rate of the two-phase flow is more and more obvious,reaching the maximum when the vapor content is 0.5%.After that,the vapor content continues to increase,and the increase effect begins to decrease.When the vapor content increases to 1%,the FAC rate of the two-phase flow slows down to be similar to the single-phase flow.