ABSTRACT
Oil sands deposits in northern Alberta contain more hydrocarbons than all OPEC reserves combined. The amount recoverable using the existing technology is slightly larger than the total oil reserves of Saudi Arabia. Today, the total production of oil from oil sands amounts to over 20% of Canadian oil consumption, threequarters of which is from open pit mining; the remainder comes from in situ recovery. Clark’s hot water extraction process and its modifications have been used to separate bitumen from the oil sand ore. In this process, the mined oil sand is mixed with hot water and the digested slurry is fed into large gravity separation vessels, where bitumen is recovered as a froth product in a process
similar to flotation. The froth produced as such typically contains ca. 60% bitumen, 30% water, and 10% solids. The froth is cleaned by adding a diluent (an organic liquid mixture, such as naphtha) to provide a density difference between the water and hydrocarbon phases and to reduce the viscosity of the froth. The diluted bitumen is then fed through a two-stage centrifuge (at ca. 250 x and 2500 x g, respectively) to remove coarse particles in the first stage by scroll machines and the remaining fine solids and finely dispersed water droplets in the second stage by disc centrifuges. (Inclined plate settlers and/or third-stage centrifuges are also used in commercial operations.) Collectively called froth treatment, this process produces a product still containing ~ 2% water and 0.5% solids.
