Wax Deposition in Laminar and Turbulent Flow in Pipelines

Abstract

Accurate prediction of wax deposition rates and deposited wax spatial distribution is invaluable information for the design of subsea lines. Unfortunately wax deposition mechanisms are still not fully understood. The present paper is part of an ongoing research program developed with the objective of identifying the relative importance of the different wax deposition mechanisms proposed in the literature. To this end, laboratory experiments conducted at controlled conditions were performed in a geometry formed by a rectangular channel having two glass walls and two heat exchanging walls. A laboratory solution of wax and solvent was pumped through the channel while the heat exchanging walls were cooled. The wax deposit formed was optically measured by a traversing microscope imaging the deposit through the glass walls. This setup allowed the determination of both, the temporal and spatial evolution of the wax deposit. Laminar and turbulent flow conditions were investigated. Numerical simulation of the equations governing conservation of mass, momentum, energy and concentration were solved for the channel configuration employing the known thermophysical properties of the solution used in the tests. A comparison of measured and predicted results yielded good agreement for the steady state distribution of the deposited wax for laminar flow conditions. The transient behavior of the deposit was, however, under predicted by the calculations. Turbulent flow predictions were obtained using Reynolds-averaged models. The simulations were able to predict the correct trends of thinner deposits when compared to laminar deposition.