Factors Governing Friction Losses in Self‐lubricated Transport of Bitumen Froth: 1. Water Release

Department of Aerospace Engineering and Mechanics, University of Minnesota, 55455, Minneapolis, MN, USA
The Canadian Journal of Chemical Engineering (Impact Factor: 1.31). 09/2004; 82.

ABSTRACT S yncrude Canada Ltd. produces approximately 250,000 barrels of synthetic crude oil daily from the surface mineable portion of the Athabasca Oil Sands deposit located in northern Alberta, Canada. S y n c r u d e 's operation consists of mining, extraction, upgrading and utilities facilities. The extraction process involves mixing oil sand with water to form a dense slurry. The slurry is prepared for extraction in pipelines as it is being transported from the mine to the extraction plant. Bitumen, which is a very heavy crude (viscosity 5.5 Pa·s at 50ºC), is released from the oil sand and subsequently separated from the other oil sand constituents (sand and clay) in large gravity settling vessels. The product from the p r i m a ry settling vessels is known as bitumen froth and contains, on average, 60% bitumen, 30% water, and 10% solids (by mass). For Syncrude's Aurora mine, which is located 35 km from the existing froth treatment and upgrading facilities, bitumen froth is transported from the Aurora extraction facilities to the existing froth treatment plant via pipeline, using self-lubricated froth flow technology. This technology utilizes a type of flow that occurs under certain conditions when froth is flowing in a pipeline: water droplets dispersed in the bitumen-continu-ous froth migrate in the area of high shear near the pipe wall and coalesce to form a lubricating sheath that surrounds a bitumen-rich core. As a result, pipeline friction losses are orders of magnitude lower than would be predicted based on the apparent froth viscosity. Self-lubricated froth flow technology was developed by researchers at Syncrude and the University of Minnesota, and is described by Neiman et al. (1999) and Joseph et al. (1999). In the latter, results of flow experiments conducted in pipelines of 0.025 m, 0.05 m, and 0.6 m diameter are presented. It is shown that the pressure gradients measured for froth flow in different diameter pipelines can be represented using a modified Blasius equation, which is an empirical equation used to describe turbulent flow in a smooth pipe. In this paper, we will describe froth flow tests that were conducted in a 25 mm diameter pipeline loop at the University of Minnesota. We will look specifically at the effects of the froth water content on self-lubricated flow. Our attempts to measure the ratio of free water to dispersed water during a series of 25 mm pipeline flow loop tests will be presented. Finally, conditions required to initiate and to maintain self-lubricated flow in pipe flow and in a type of concentric cylinder viscome-ter referred to as a froth rheometer will be described. In Part 2 of this work (Sanders et al., 2004), we will describe the results of froth flow tests from which we determined that the lubricating water layer is separated from the pipe wall by a thin coating of bitumen. We Syncrude Canada Ltd. transports bitumen froth, a viscous intermediate product of the oil sand extraction process, 35 km via pipeline. Pipeline transport is feasible because some of the water that occurs naturally in the froth forms a thin lubricating layer around a bitumen-rich core, thereby greatly reducing friction losses and transportation costs. In this paper, the effect of froth composition (namely, water content) on the formation of the lubricating layer is reported. Tests were conducted with a 25 mm diameter pipe loop and a concentric cylinder froth rheometer. Measurements of pressure gradient and water holdup (free water fraction), along with visual observations, showed that froth containing a lower total water content yielded less free water to the lubricating layer. In the froth rheometer, the conditions for which stable, self-lubricated flow could be maintained were comparable to those required to maintain self-lubricated flow in the 25 mm pipe loop. Syncrude Canada Ltd. transporte de la mousse de bitume, un produit intermédiaire visqueux du procédé d'extraction des sables bitumineux, via un pipeline de 35 km. Le transport par pipeline est réalisable parce qu'une partie de l'eau qui est présente naturellement dans la mousse forme une fine couche lubrifiante autour du noyau riche en bitume, réduisant ainsi grandement les pertes de friction et les coûts de transport. Dans cet article, on décrit l'effet de la composition de la mousse (à savoir, la teneur en eau) sur la formation de la couche lubrifiante. Des essais ont été menés avec une boucle de conduite de 25 mm de diamètre et un rhéomètre de mousse à cylindre concentrique. Les mesures de gradient de pression et de rétention d'eau (fraction libre de l'eau), ainsi que les observations visuelles, montrent que la mousse contenant une plus faible teneur en eau totale produit moins d'eau libre pour la couche lubrifiante. Dans le rhéomètre pour mousse, les conditions pour lesquelles un écoulement stable auto-lubrifié peut être maintenu sont comparables à celles requises pour maintenir un écoulement auto-lubrifié dans la boucle de conduite de 25 mm.

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