The Effect of Oil Sands Bitumen Extraction Conditions on Froth Treatment Performance

Abstract

Abstract Further development of oil sand deposits requires processing poorer quality oil sands while maximizing bitumen recovery, minimizing the water and solids content of the product bitumen, and minimizing overall energy consumption. Bitumen recovery requires two stages: extraction and froth treatment. This work focuses on the effect of process conditions in the Clark Hot Water Bitumen Extraction Process on froth treatment effectiveness. Laboratory approximations are used to represent the two commercialized froth treatment processes in Alberta:the "Syncrude Process," which is dilution with an aromatic solvent followed by centrifugation; and,the "Albian Process," which is dilution with a paraffinic solvent followed by gravity settling. Parameters considered are oil sand quality, extraction shear, extraction temperature, NaOH addition during extraction, froth treatment temperature, and froth treatment residence time. It was found that reduced extraction temperature results in lower bitumen recovery at least for low quality oil sands. Higher shear extraction may improve bitumen recovery, but decreases froth treatment effectiveness. For paraffinic solvent-based froth treatments, the addition of NaOH during extraction may be required to obtain optimum froth treatment of low quality oil sands. Introduction The Canadian oil industry is producing about 1 million barrels of bitumen and synthetic crude oil per day from oil sands and the production is expected to rise to 2 million barrels per day by 2012(1). Currently, both in situ and surface mining operations contribute almost equally to the total production. However, the production of synthetic crude from surface-mined oil sands is expected to take the lead in the next decade(2). Expansions of existing oil sand facilities are already underway and the addition of new facilities are planned within the next decade. There are two main stages to oil sand processing: extraction and froth treatment. The most common extraction process is hot water bitumen extraction. The oil sand is conditioned with hot water, either in a process vessel (conditioning drum) usually with NaOH added, or more recently in a pipeline (hydrotransport) usually with a smaller amount of NaOH added. During conditioning, the slurry is aerated and, ideally, the bitumen separates from the sand, and attaches to and spreads on the air bubbles. Water is added to the slurry, which is subsequently sent to a separation vessel. The bitumen- coated air bubbles are carried upwards to form a froth that is rich in bitumen. The froth also contains free water, emulsified water, and suspended solids(3, 4). The froth is collected in two stages yielding a primary and a secondary froth. For high-quality oil sands, a typical primary froth composition is approximately 66 wt% oil, 25 wt% water, and 9 wt% solids. A typical secondary froth has lower oil content (approximately 24 wt%) and higher water and solids contents (59 wt% and 17 wt%, respectively). Poorer quality oil sand froths have lower oil content and higher water and solids contents(5).