One of the easiest ways to understand bitumen is to compare it to its cousin, conventional crude oil. Whereas conventional crude oil flows freely, bitumen does not. At room temperature it looks like cold molasses, and must be either heated or diluted before it flows. Like all petroleum, both conventional crude and bitumen are made up of hydrocarbons (i.e., organic compounds containing only carbon and hydrogen. However, compared to conventional crude oil, bitumen contains more carbon than hydrogen, as well as many more impurities, such as nitrogen, sulphur and heavy metals. In order to produce synthetic crude, these impurities must be removed and the carbon-hydrogen imbalance corrected. (See also Oil Sands.)
Canada’s bitumen reserves — the oil sands — are located in three parts of Alberta: Athabasca, Cold Lake and Peace River. The Wabiskaw-McMurray deposit (in the Athabasca oil sands area) surrounding Fort McMurray is largest and nearest the surface. The Athabasca River cuts a channel through parts of the oil sands, and Aboriginal people used the tarry bitumen to caulk canoes before the first Europeans arrived in the late 18th century.
Upon their arrival, the Europeans found other uses for bitumen, including asphalt. Streets in several Alberta cities as well as in Ottawa were paved with bitumen in the 1920s, and both the International Bitumen Company and Abasand Oils Ltd produced asphalt from the Athabasca sands in the 1930s.
Since the late 19th century, people have schemed to tap the petroleum wealth of the oil sands. In 1967 Great Canadian Oil Sands Ltd, now part of Suncor Energy Inc, opened the first commercial upgrading plant. Syncrude Canada Ltd opened in 1978, and in the late 1990s, a series of new projects followed: Canadian Natural Resources Ltd constructed the Horizon Project, Shell developed Albian Sands and Petro-Canada began producing from its Fort Hills project.
In the 1920s, chemist Dr. Karl Clark of the Alberta Research Council developed the hot-water process, a method of extracting bitumen from oil sand. Clark’s method is still used today.
Oil sand, as mined commercially, contains an average of 10-12 per cent bitumen, 83-85 per cent mineral matter and 4-6 per cent water. A film of water coats most of the mineral matter, and this property permits extraction by the hot-water process.
During the hot-water process the oil sand is mixed with water in either a processing drum or pipeline. Droplets of bitumen separate from the grains of sand and attach themselves to tiny air bubbles which help the bitumen float upwards. The mixture — called slurry — is sent to separation vessels where the bitumen-rich froth is skimmed from the top. This froth generally contains about 65 per cent oil, 25 per cent water and 10 per cent solids. When the coarse sand settles it is pumped to disposal sites.
Generally, 88-95 per cent of the bitumen in the mined oil sand is recovered. Coarse sand from the primary separators is used to build dikes, forming the large ponds — called tailings ponds — needed to contain the materials remaining in the water after the bitumen has been separated from the sand. In these ponds the fine particles settle slowly, eventually producing clarified water that is reused in the extraction process. The fine particles do not consolidate to their original density, so every cubic metre of oil sand mined creates slightly more material (1.4 m3) for disposal.
In addition to tailings ponds, the large amounts of water and energy used in the bitumen extracting process are cause for environmental concern. Alternatives to these processes continue to be investigated.
After the bitumen is extracted from the oil sand it still requires extra processing, or upgrading, before it can be sold to refineries and turned into products such as fuel. Upgrading is done by coking the bitumen, hydro-processing it, or a combination of the two.
During coking, carbon is removed from the heavy components (called fractions) of bitumen. Coking involves thermally cracking the heavy fractions at 468-498° C to produce lighter fractions (e.g., gasoline, fuel gas) and petroleum coke (some of which may be used as fuel).
When bitumen is hydro-processed, hydrogen is added. Compared to coking, hydro-processing offers higher liquid yields, better distillate qualities and lower emission levels of sulphur dioxide, but at much greater expense.