Invariably, oil pump station piping layouts may contain multiple dead-legs brought about by closed valves at one end of side branches, while flows continue through the main runs. During the transportation of heavy crude through the pump station, these dead-legs will be filled with this crude. When a light crude batch is introduced next into the pipeline, following the heavy crude ahead, two phenomena will occur. First, contamination between batches at the interface of the two crudes will occur due to axial turbulent diffusion along the length of the pipeline itself. Second, as the light crude flows through the pump station, and passes by each dead-leg containing residual heavy crude from the preceding batch, the heavy crude trapped in these dead-legs will start to drain out into the passing light crude in the main run. This causes further contamination and spreading of the mixing zone between the two batches. The second source of contamination, which is addressed in this paper, could cause appreciable contamination particularly for large dead-leg sizes and numbers. A computational fluid dynamics (CFD) model has been developed to quantify the drainage rate of the contaminating crude into the main stream and its impact on widening the mixed zone (contamination spread) between the two batches. Two drainage mechanisms of the heavy crude in the dead-legs into the main stream of the light crude have been identified and quantified. Finally, potential innovations to mitigate contamination due to dead legs are presented and quantified for their respective effectiveness in minimizing the contamination spreads between batches of different crudes.

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