NUMERICAL SIMULATION OF WAX DEPOSITION IN PETROLEUM LINES: ASSESSEMENT OF MOLECULAR DIFFUSION AND BROWNIAN DIFFUSION MECHANISMS / SIMULAÇÃO NUMÉRICA DA DEPOSIÇÃO DE PARAFINA EM DUTOS DE PETRÓLEO: AVALIAÇÃO DOS MECANISMOS DE DIFUSÃO MOLECULAR E DIFUSÃO BROWNIANA

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Wax deposition is one of the major critical operational problems in crude oil pipelines operating in cold environments. Therefore, accurate prediction of the wax deposition is crucial for the efficient design of subsea lines. Unfortunately, wax deposition is a complex process for which the mechanisms are still not fully understood. Aiming at the identification of the relative importance of the different deposition mechanisms, two of them were investigated: Molecular and Brownian Diffusion. To determine the amount of deposit, the conservation equations of mass, momentum, energy, concentration of the mixture and wax concentration outside the solution were numerically solved with the finite volume method. A non-orthogonal moving coordinate system that adapts to the wax interface deposit geometry was employed. Although for the laminar regime, the deposition profile predicted with the selected deposition mechanisms presented a reasonable agreement with available literature results for the steady state regime, a significant discrepancy was observed during the transient. The employment of the Brownian diffusion mechanism led to only a small improvement in the transient solution prediction in sub-cooled regions. The influence of the turbulent regime with the Molecular diffusion mechanism was also investigated by employing the Low Reynolds ê−turbulence model. The results obtained were physically coherent, presenting a smaller deposit thickness, since the region with temperature below the wax appearance temperature is smaller in the turbulent regime.

ASSUNTO(S)

brownian diffusion difusao molecular difusao browniana deposicao de parafina wax deposition simulacao numerica numerical simulation molecular diffusion

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