Eventos Anais de eventos
ENCIT 2022
19th Brazilian Congress of Thermal Sciences and Engineering
A CRITICAL EVALUTAION OF FICK’S VERSUS STEFAN MAXWELL DIFFUSION MODELS TO PREDICT WAX DEPOSITION
Submission Author:
Paulo Gustavo Cândido Oliveira , RJ
Co-Authors:
Paulo Gustavo Cândido Oliveira, ivan fernney ibanez aguilar, Felipe Fleming, Luis Fernando Alzuguir Azevedo, Angela Nieckele
Presenter: ivan fernney ibanez aguilar
doi://10.26678/ABCM.ENCIT2022.CIT22-0020
Abstract
When hydrocarbons flow along pipelines losing heat to the environment, solid paraffin particles are formed when the temperature falls below a certain threshold known as wax appearance temperature (WAT). These particles can change the liquid rheology, and oil-paraffin mixtures can present a non-Newtonian fluid behavior. The particles can also deposit on the inner walls of the pipelines, increasing the pumping power or completely obstructing the flow, resulting in a loss of several million dollars. Therefore, the ability to predict and control wax deposition in future events is important for designers and operators. The necessity of insulation and/or points for introducing PIGs to remove the deposit must be well planned by the pipeline designers, as well as the determination of proper frequency of wax mitigation techniques like mechanical removal or chemical treatment in offshore production. Although a large effort has been made by the scientific community aiming to improve the wax deposition prediction, most formulations are based on molecular diffusion models employing Fick’s law, valid for binary mixtures. However, in the petroleum industry, the hydrocarbon flow is a multicomponent solution. In this article, a new approach based on the Maxwell-Stefan model, compatible with multicomponent diffusion systems is proposed. The Maxwell-Stefan formulation has larger applicability limits when compared with Fick’s law, considering effects of complex interactions between the species. To determine the time and axial wax deposition thickness evolution, the flow was modelled as liquid/solid mixture and the conservation equations of energy, mass, linear momentum and species continuity were solved. The conservation equations were discretized with the finite volume method using the open-source software OpenFOAM®. In addition, the thermodynamic model employed is capable of predicting the growing and aging of the wax deposit with time and position. A critical evaluation of the performance of Fick and Maxwell-Stefan models is presented through comparison with experimental data.
Keywords
Wax deposition, Maxwell-Stefan, Fick's law, Pipeline, multicomponent diffusion
