Abstract
Wax deposition is a hot and difficult topic in waxy crude oil transportation. Wax molecular diffusion is recognized to play a crucial role in wax deposition. Empirical correlations of Hayduk-Minhas and Wilke-Chang are widely used to calculate the wax molecular diffusivity. However, they are developed based on binary solutions and underestimate the diffusion coefficient of wax components. To address this issue, wax deposition experiments with different crude oils were conducted in cold-finger apparatus. The temperature distribution was obtained by computational fluid dynamics software of Fluent and the characteristics of wax deposit were investigated. In addition, the wax molecular diffusion process under saturated and partial saturated conditions were theoretically elucidated. It was found that the bulk temperature, deposition duration and carbon number distribution of wax molecules can significantly influence the total wax content and wax precipitation properties of wax deposits. Moreover, the wax molecular diffusivity experimentally calculated based on the Fick's first law were found larger than that obtained by correlations of Hayduk-Minhas and Wilke-Chang. A new correlation calculating the wax diffusion in crude oil was developed and verified with experiments. Good agreement between predicted and experimental values was observed with maximum relative deviation being 12.52% and mean absolute error being 8.90%. This new correlation is suitable in wax molecular diffusivity calculation for crude oils. • Highly paraffinic crude oils under saturated and partial saturated conditions were used in the wax deposition experiments. • Wax precipitation characteristics and morphologies of the wax deposits were compared and analyzed. • The wax molecular diffusion process was theoretically elucidated and the wax molecular diffusivity was calculated. • A new correlation for predicting wax molecular diffusivity in crude oil was developed and verified with experiments.
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