Numerical investigation of the process and flow erosion of flushing oil tank with nitrogen

• A CFD model coupling with VOF and DPM is used to investigate flow erosion.
• An initialization method for arranging particles initially is developed.
• The approach is validated with the comparison of measured and calculated erosion rate.
• Effects of operation and fluid parameters on flow erosion are discussed.
• Flow erosion is related to the emptying process of oil.

A computational fluid dynamic (CFD) model coupling with volume of fluid (VOF) method and discrete phase model (DPM) has been used to predict the flow erosion rate in an oil tank and blowdown pipe during the process of gas flushing. An initialization method by injecting particles from a tank wall is developed to construct the initialization distribution of residue particles. The flow field distribution of oil–gas–water flow and the erosion rate on the wall surface during emptying process can be captured under different operating conditions with different fluid parameters. The applicability of the approach is verified by comparing the simulated results with the measurements. The effects of fluid parameters such as gas inlet rate, oil density and viscosity, as well as the operating parameters such as residual oil level and residue particle diameter, are evaluated. In general, the required flushing time and erosion rate are all sensitive to fluid parameter changes and operating condition changes. It is found that the flow erosion is related to the emptying process of oil, which has a sharp rise in the end of the process. High inlet speed, large oil density, small oil viscosity, high oil level and large particle diameter can result in severe erosion.

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