Evidence that wax deposition is a phase transition rather than a molecular diffusion phenomenon

• Published in: Fuel (Guildford) Vol. 313; p. 122940
• Main Authors: van der Geest, Charlie, Bizarre, Letícia, Melchuna, Aline, Pinheiro, Ivanei F., Guersoni, Vanessa C.B.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.04.2022; Elsevier BV
• Subjects: Boundary conditions; Cold flow; Deposition; Diffusion; Experimental data; Flow assurance; Fluid flow; Heat transfer; Low temperature resistance; Mass transfer; Molecular diffusion; Phase transition; Phase transitions; Predictions; Reynolds number; Simulators; Thermal resistance; Thickness; Wax deposition; Waxes; Waxy crude oil; Molecular diffusion; Flow assurance; Wax deposition; Waxy crude oil; Phase transition
• ISSN: 0016-2361; 1873-7153
• DOI: 10.1016/j.fuel.2021.122940

Over the past five decades, wax deposition has been widely considered a mass transfer-controlled phenomenon. Despite the highly inaccurate predictions, engineers cannot accurately predict the final thickness of the deposit, the hypothesis that wax deposition is a mass transfer phenomenon was not commonly questioned, but this has recently changed. This paper shows evidence that wax deposition is limited by phase transition (heat transfer), by analyzing a vast experimental matrix previously presented in the literature and clearly showing that the thickness decreases as the Reynolds number increases, which cannot be explained by molecular diffusion alone, also by showing that the Reynolds number does not influence the ratio between the deposit’s thermal resistance and the total thermal resistance (dimensionless temperature) for all cold flow experiments, which is further evidence of phase transition. When comparing the limits of the molecular diffusion approach with the experimental data, without any fitting parameter, one observes that not only the experimental data cannot be predicted, but the trend is also incorrect. When using the phase transition model (heat transfer), the accuracy in the thickness prediction is high, which is evidence that what limits the wax deposition is the phase transition. This shows that heat transfer equations can accurately predict wax deposition thickness. Since all wax deposition simulators have the heat transfer calculations, to improve their predictions, one must only implement a single boundary condition. [Display omitted] •Molecular Diffusion is not the dominant mechanism in wax deposition.•Phase transition (Heat Transfer) is the dominant mechanism in wax deposition.•All evidence shows a constant temperature of the interface (Phase Transition!).