A steady-state heat-transfer model for solids deposition from waxy mixtures in a pipeline

• We present a mathematical model for solids deposition from paraffinic mixtures in a pipeline.
• The model is based on steady-state heat-transfer considerations.
• The predicted deposit thickness increases in the hot flow regime and decreases in the cold flow regime.
• The cold flow regime involves two-phase flow with wax crystals suspended in the liquid phase.
• The modeling approach and predictions will be useful to flow assurance engineers.

A steady-state heat-transfer model is presented for the formation of a deposit-layer from wax–solvent ‘waxy’ mixtures in a pipeline under turbulent flow. The waxy mixture is taken to enter the pipeline under the single-phase hot flow regime (where the average mixture temperature is higher than its wax appearance temperature, WAT) and, upon gradual cooling, the mixture transitions into the cold flow regime (where its average temperature is lower than its WAT). The cold flow regime is characterized by two-phase flow, in which solid particles are suspended in the liquid phase. The effect of deposit aging is incorporated via a shear-induced deformation approach proposed in the literature. The model predictions are reported for the deposit thickness, waxy mixture temperature, pressure drop and the rate of heat loss in the hot flow and cold flow regimes for a range of inlet mixture temperature, surrounding temperature, and the Reynolds number. The predicted deposit thickness is shown to increase axially in the hot flow regime, to reach a maximum as the liquid temperature approaches the WAT of the wax–solvent mixture, and to decrease gradually to zero in the cold flow regime. The trends in the model predictions compare satisfactorily with those reported from bench-scale experimental studies as well as the predictions from an unsteady state moving boundary problem formulation.