Achieving cold flow conditions for 'waxy' mixtures with minimum solid deposition

The terms hot flow and cold flow refer to the bulk temperature of a 'waxy' crude oil being above and below its wax appearance temperature (WAT), respectively. The deposit thickness is reported to decrease substantially when the crude oil in a pipeline is in the cold flow regime. However, achieving cold flow of a 'waxy' crude oil would invariably involve solid deposition on the cooling surface. This study investigates a novel methodology for accomplishing cold flow condition without any significant deposition in the hot flow regime. The solid deposition from wax-solvent mixtures was studied using both cold-finger and flow-loop apparatuses. Experiments were performed with a 10 mass% wax-solvent mixture by maintaining constant cooling rates of 0.05-0.38 degrees C min(-1) in decreasing the average temperature of the wax-solvent mixture from (WAT+ 20) degrees C to the four final mixture temperatures below WAT. The effect of cooling rate was investigated on the temperature difference between the mixture and the coolant as well as the extent of wax deposition. It was found that the temperature difference and the deposit mass increase with the cooling rate. With a constant temperature difference, no deposition was observed above the WAT. The experimental results of this study are corroborated by both cold finger and flow loop studies. Experiments with both apparatuses gave similar results; however, the deposit mass was much lower in the flow-loop apparatus, due to turbulent flow conditions, compared to the laminar conditions for the cold-finger experiments. The results indicate that the deposition in the hot flow regime could be decreased substantially, or even be avoided, when the waxy mixture is cooled at a low cooling rate.