One of the goals in oil sands development is to process poorer quality oil sands while reducing energy consumption. To achieve this goal, it is necessary to optimize the two main stages of oil sands processing: extraction and froth treatment. The most common extraction process is hot water bitumen extraction where bitumen is produced in a froth consisting of bitumen, water, and inorganic solids. The froth is treated in a second stage to separate the bitumen. There are currently two commercialized froth treatment processes in Alberta, here termed the "Syncrude Process" and the "Albian Process". In the Syncrude process, the froth is diluted with naphtha to decrease the density and viscosity of the bitumen and to promote coalescence of emulsified water. Phase separation is achieved with centrifuging. The Albian process, a paraffinic solvent is added to the froth to reduce the bitumen density and viscosity, and to promote flocculation of the emulsified water and suspended solids. Some asphaltenes are also precipitated to achieve a product suitable for a conventional refinery. Phase separation is achieved with gravity settling.
In both processes, it is desirable to reduce energy costs and minimize the water and solids content of the product bitumen. In the past, research has aimed to optimize each stage in isolation. Now we are seeking to establish the relationship between bitumen extraction conditions and froth treatment effectiveness for different quality oil sands. Hence, the optimization of the overall process can be evaluated. In this work, the effect of shear conditions during bitumen extraction is considered. Overall bitumen recovery and the water and solids content of the product bitumen are determined for a low shear and a high shear extraction process.
A high quality (HQOS) and a low quality (LQOS) oil sand samples were obtained from Syncrude Canada Ltd. The bitumen, water, and solids contents were determined at the Syncrude Research Centre, as reported elsewhere(1), and are given in Table 1. Oil sand quality is assessed in terms of bitumen and fine solids content. Poorer quality oil sand froths have lower oil content and higher contents of water and solids.
Table 1. Oil sands composition Available in full paper)
Bitumen extractions were performed using a Batch Extraction Unit (BEU) or a Denver Cell (DC)following the Syncrude standard extraction procedures(1). The BEU is a low-shear laboratory approximation of the Clark hot water extraction process and typically produces a froth similar to that obtained from the traditional commercial process with conditioning and separation stages. The DC is a higher shear flotation apparatus and produces a froth that is more similar to that obtained from a commercial process with hydrotransport and separation stages. Extractions were performed at 50 and 80 °C and sodium hydroxide was added to improve the bitumen recovery. Subsamples of froth from the extractions were collected and assayed for oil, water and solid contents using the "Syncrude method"(2,3). Only primary froth was used for froth treatment experiments.
