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Annals of the Assembly for International Heat Transfer Conference 13

ISBN 1-56700-225-0 / CD 1-56700-226-9

Volumes per year:

various

Year 2006

DOI: 10.1615/IHTC13.p11

EVALUATION OF A DIFFUSION-BASED MODEL TO PREDICT WAX DEPOSITION IN PETROLEUM PIPELINES

M. I. Romero
Department of Mechanical Engineering, PUC/Rio, Rio de Janeiro, RJ, Brazil

A. T. Leiroz
Department of Mechanical Engineering, PUC/Rio, Rio de Janeiro, RJ, Brazil

A. O. Nieckele
Department of Mechanical Engineering, PUC/Rio, Rio de Janeiro, RJ, Brazil

L. F. A. Azevedo
Department of Mechanical Engineering, PUC-Rio, Rio de Janeiro, Brazil

ABSTRACT

Deposition of high molecular weight paraffins on the inner wall of subsea production and transportation pipelines continues to be a critical operational problem faced by the petroleum industry. Molecular diffusion, Brownian diffusion, shear dispersion and gravity settling are some of the possible mechanism responsible for wax deposition. Although, molecular diffusion is employed in the vast majority of the deposition models available in the literature, it is still not clear which one is the most relevant mechanism. A two-dimensional deposition model employing molecular diffusion of liquid paraffin in mineral oil as the only deposition mechanism was developed. The predictions of the model were compared with experimental data in order to assess the relevance of molecular diffusion as a deposition mechanism. The experiments were conducted in a channel where a transverse temperature gradient was imposed in order to promote the diffusive mass flux. In the simulation model, the mass, momentum, energy and concentration equations were solved by a finite difference method. The heat losses to the ambient as well as the paraffin latent heat were considered. A moving mesh was employed to account for the reduction of the flow cross section due to the paraffin deposition. The results obtained showed significant differences between experiments and computation, indicating that molecular diffusion might not be the only relevant mechanism responsible for wax deposition, as accepted in the literature.