The effect of impellers layout on mixing time in a large-scale crude oil storage tank

This paper reports the results of a study on the effect of the position of impellers on homogenization time in a large scale 19,000 m3 crude oil storage tank. Based on the good agreement found between the predicted and the site measured results for an existing tank equipped by a single impeller, the hydrodynamics of the flow generated by two, three and five side entry impellers arranged in two different orientations is theoretically studied. In order to achieve this, an in-house CFD code with the ability of simultaneous solving of continuity and Reynolds-averaged Navier-Stokes (RANS) equations is used. The RNG (renormalization group) version of the k-ε turbulence model is applied for turbulence modeling. The fluid region is divided into a large number of control volumes (580,000 to 900,000), and the MFR (multiple frames of reference) model is used for impeller modeling. The velocity distribution inside the tank for two different types of impellers layouts is investigated and the crude oil mixing time for these two arrangements is compared. The results show when the impellers are placed close to each other in one bottom quarter of the tank, mixing is more efficient in comparison with the distributed arrangement. When the tank is equipped with two and three impellers, the mixing performance is quite different in the two different orientations. However, in the five impellers cases, no considerable difference is observed except at the beginning and finishing parts of homogenization.