Prediction of Flow-Accelerated Corrosion/Erosion in High-Speed Ejectors Using a CFD Model

In high-velocity ejector systems containing liquid droplets, ejector walls are sometimes damaged by flow-accelerated corrosion/erosion. Velocity, droplet size, impact angle etc. are the most important parameters affecting flow-accelerated (FA) corrosion/erosion. In our plant operation, we had experienced FA corrosion/erosion and consequent failure even with very low impact angle. To understand the leak/ failure, we have adopted the Euler-Euler multiphase model-based CFD approach. In the Euler-Euler multiphase model, the liquid droplets are modelled as dispersed phase while the gas-steam is modelled as a continuous phase. To capture the droplet dynamics very accurately, appropriate correlations for drag, lift and wall lubrication force have been chosen. In CFD simulations we have observed liquid film formation at the ejector wall. The liquid film moves along the ejector wall creates a very high wall shear-stress. In the location of high wall shear-stress, one can expect high FA corrosion/erosion and consequent leak. Qualitative comparison of the X-ray image of the actual equipment with the CFD results for wall-shear stress shows very good agreement in terms of predicting leak location. Moreover, we have varied the droplet size and the liquid fraction in the upstream of the ejector. Qualitatively we have observed that with increase in droplet size the material removal rate increases, however, the affected area of the leak decreases. The more liquid in the system increases the wall-shear stress very rapidly. The present CFD model is useful for predicting the leak-prone location and taking predictive actions (e.g. cladding the wall with a high-grade material).