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Eulerian Model to Predict Asphaltene Deposition Process in Turbulent Oil Transport Pipelines Hadi Seyyedbagheri, and Behruz Mirzayi Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b01273 • Publication Date (Web): 06 Jul 2017 Downloaded from http://pubs.acs.org on July 8, 2017
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Energy & Fuels
Eulerian Model to Predict Asphaltene Deposition Process in Turbulent Oil Transport Pipelines Hadi Seyyedbagheri, Behruz Mirzayi* Chemical Engineering Department, University of Mohaghegh Ardabili, P.O. Box 179, Ardabil, Iran *Corresponding Author, Email:
[email protected] Tel: +98-45-33512910; Fax +98-45-33512904
Abstract In this paper, Eulerian approach was applied to model asphaltene deposition process in turbulent production pipeline. In addition to common mechanisms like drag, lift, gravity and molecular diffusion the most effective deposition mechanisms such as eddy diffusion, turbophoresis and thermophoresis were considered over a wide range of asphaltene particle size (i.e. 1 nm-100 μm). Modeling results showed that for small submicron particles (20). Morevere, refering to the results reported by Guha23, it can be obseved that for not too high inertia particles (𝜏𝑝+ 30).23 Considering that the particles used in this study have a relaxation time in the range of 𝜏𝑝+ 10 μm) take a different velocity and leave the eddy ahead of eddy life time. 5.2. Asphaltene deposition velocity Using the numerical solution of Eq. 28 for different size of asphaltene particles, as shown in Figure 3, the dimensionless asphaltene deposition velocity versus particle size can be obtained. In this figure the calculated deposition velocity curve is divided into two sections, the first section belongs to the particle size of less than 1 μm. In this section only the diffusion is the dominant deposition mechanism where the deposition velocity decreases with increasing the ACS Paragon Plus Environment
Energy & Fuels
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particle size. This reduction is attributed to the inverse effect of particles size on Brownian diffusion coefficient. In other words, Brownian diffusion is important for extremely small particles and it can be deduced form Eq. 3 that this mechanism can be neglected as the particle size becomes larger. The second section concerns the large particles with high inertia (i.e. large relaxation time). For large particles, molecular diffusion mechanism practically has no significant effect and as shown in Figure 3 a little increase in particle size caused that the deposition velocity increased by 2-3 times. This finding reveals that other deposition mechanisms play a significant role in the second section. To our knowledge from literature there are two dominate mechanisms i.e. eddy diffusion and turbophoresis that influence the particle deposition for large particles.1,
19
As a result, with the increasing of particle size and
disappearance of Brownian diffusion the particles will be moved under the influence of eddy diffusion and turbophoresis mechanisms, which make the deposition velocity increases by the particle size (or relaxation time). The result is consistent with the results depicted in Figure 2. The effect of temperature gradient on asphaltene deposition was also illustrated in Figure 3. This figure shows that the temperature gradient and consequently the thermophoresis mechanism has no significant effect on the asphaltene particle deposition. This is attributed to the extremely low value of thermal diffusion coefficient (DT) for small particle in liquids, which is of the order of magnitude of ~10-12. In this regard, previously, Eskin et al. showed that asphaltene deposition was not influenced strongly by temperature gradient.39 5.3. Effect of oil flow velocity The effect of oil velocity on the asphaltene deposition rate in the production pipeline is given in Figure 4. According to this figure, in the wide range of asphaltene particle sizes, increasing oil velocity always leads to increase of deposition velocity. The reason is that for extremely small particles (dp
