Numerical simulation and optimization study on erosion characteristics of local structures in fly ash transportation pipelines

Pipeline failure occurs in various forms, and erosion wear is one of the most common failure modes in fly ash slurry transportation pipeline systems. Among them, reducers and elbows are high-risk structures for erosion wear. Affected by fluid flow regime, flow direction and pipeline structure change, the local erosion wear degree of the pipeline varies, which seriously restricts the transportation performance of the pipeline and greatly shortens its service life. To investigate the erosion characteristics of fly ash slurry on pipelines and the corresponding erosion protection measures, four 3D pipeline models combining horizontal reducers with 90° elbows were established using UnigraphicsNX. A pipeline transportation model of fly ash was built based on Fluent and solved by the DPM (Discrete Phase Model) multiphase flow model based on the Euler-Lagrange method. Using the Generic erosion model, the trajectory and erosion behavior of particles in solid-liquid two-phase flow were simulated by comprehensively considering impact angle, impact velocity and material properties. The influence laws of different inlet velocities and different diameter reduction modes on pipeline erosion characteristics were analyzed, and measures to reduce pipe wall erosion wear were proposed. The results show that: ① at low flow velocity, the pipeline structure with bottom-aligned diameter reduction is obviously superior to the coaxial diameter reduction in preventing local particle accumulation and resisting erosion; ② the maximum erosion rates of the four diameter reduction modes show basically the same variation law with the inlet flow velocity; ③ under the combined action of particle size and secondary flow, the erosion rate on the inner wall of the elbow is higher than that on the outer wall, but the erosion area is smaller; ④ reasonably increasing the curvature radius of the elbow can alleviate erosion wear of the elbow; ⑤ Adding suspending agents to increase slurry viscosity can effectively avoid particle impact on the pipe wall, thereby reducing erosion wear with the most significant effect.