Settling and Re-Entrainment of Wax Particles in Near-Gelling Systems

Under near-gelling conditions, the precipitated wax particles can settle down due to gravity and form a bed at the bottom of the pipeline. During restart, the settled waxy bed can increase the pressure drop significantly, and the necessity for pigging and/or addition of chemicals has to be determined to re-entrain settled wax particles. A laboratory-scale flow loop, first of its kind, has been built and used to understand the settling and re-entrainment behavior. The experimental results confirmed the settling of precipitated wax in a pipe under quiescent conditions when the oil temperature falls between wax appearance temperature and pour point. During restart, complete re-entrainment was attained after reaching a critical flow rate. Solid transport models were able to predict reasonably good results in agreement with experiments. This work emphasizes the importance of understanding the behavior of waxy crude oil during production shutdown and design appropriate startup strategies. (c) 2017 American Institute of Chemical Engineers AIChE J, 64: 765-772, 2018