Analytical Modelling to Reduce Erosion in a Refinery Overhead Vapour Line

Streamlines on short arm including pipes to condensers in the original overhead line

Detail of flow velocity through the original overhead line

Streamline showing swirling flow generated in the main T junction of the proposed overhead line

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PDL Engineering Group has a wealth of experience in applying advanced engineering software to solve challenging technical problems.

Recently the team provided steady state multiphase analysis of the flow balance and erosion behaviour of a client’s existing and proposed design overhead vapour line of a crude distillation unit at a refinery.

The original vapour line carried a range of hydrocarbons from the top of the crude tower through water wash injections into a series of condensers and onto an overhead drum. The condensers were split into two banks; the short arm which fed into six  condensers, each with two inlets and outlets; and the long arm which fed into 24  condensers each with a single inlet and outlet.

The proposed design replaced a section of pipe from the top of the crude tower to the condenser inlets using larger diameter pipes and a T pipe junction to try and reduce the flow velocity through the line.

The PDL team used Computational Fluid Dynamics (CFD) to understand the flow behaviour including velocity and turbulence across the condensers through to the overhead drum, and also analysed the droplet fate (destination) using a particle track analysis to show the droplet distribution up to the inlet of each condenser bundle.

The analytical model was created in ANSYS SpaceClaim and the analysis was undertaken in ANSYS Fluent V2020R2 to create a detailed mesh within the pipework using 4.8 million elements for the original geometry and 4.9 million elements for the proposed geometry. All the work was checked and verified using standard PDL check sheets developed in accordance with BS EN ISO 9001:2015.

The analysis team provided an erosion map of the vapour line from the outlet of the crude tower to the inlet of each condenser bundle, and assessed the erosion damage from the collision of droplets sized 952, 600 and 300 µm on the internal walls of the overhead line. Areas susceptible to erosion were identified for efficient maintenance monitoring.

The team identified that the proposed T junction created unsatisfactory swirling flow pattern. Further work will be undertaken to reduce the line pressure drop and turbulent flow. Four proposed geometry solutions developed with the project team, will be compared to understand the most effective solution. Using PDL analysis capabilities, the optimised design will be delivered in a short space of time, supporting our customer to meet tight project timescales.

To find out more about the PDL team’s proven track record see their case studies.

Telephone: + 44 (0) 1 434 609 473

Email:  solutions@pdl-group.com

Website: www.pdl-group.com

Published: 21st April 2023