Oil sand kicks into high gear

Mechanical Engineering, Dec 1998 by Valenti, Michael

New extraction technologies have turned a sticky mixture into a profitable energy source.

BENEATH THE WINDSWEPT soil of the Canadian province of Alberta lies an unlikely-looking treasure. It is a thick, viscid mixture of bitumen, sand, clay, and water called oil sand that resembles asphalt to the untrained eye. However, to Syncrude Canada Ltd. and Suncor Energy Inc., both headquartered in Fort McMurray, Alberta, it looks like gold. These two Canadian companies extract the bitumen from the sand, and upgrade it to light crude oils that are used to make fuels, petrochemicals, and lubricants.

Cutting-edge technologies and the rising value of light crude oils have ushered in an era of new investment in Alberta's oil sand extraction, with the major players embarking on ambitious programs that will more than double production in the next century.

Earlier in this century, oil sand was regarded more as a geological curiosity than as a valuable natural resource, because the high costs of mining oil sand and processing it hampered commercial-scale extraction. More recently, new extraction techniques and a rise in the price of light crude oils have made it more economical to extract the bitumen from sand and upgrade it into a light crude oil. In 1979, Syncrude and Suncor spent $25 (Canadian) to extract each barrel of oil from oil sand; by 1998, they halved that to approximately $13 (Canadian) per barrel.

Both companies mine the Athabasca Oil Sands in Alberta. As it was for the Beatles, 1964 proved to be a watershed year for oil sand extraction. Great Canadian Oil Sands Ltd., as Suncor was then known, began construction of its $240 million oil sand extraction plant, designed to produce 45,000 barrels of oil per day, and Syncrude Canada Ltd. was incorporated to exploit Alberta's oil sand deposits. Suncor completed the plant in 1967 and today produces more than 90,000 barrels of sweet crude oil, sour crude oil, and diesel fuel per day.

By 1978, Syncrude began producing from the Athabasca oil sand deposit a light, sweet crude oil called Syncrude Sweet Blend (SSB), which is used to make diesel, automotive, and aviation fuels, as well as industrial lubricants and petrochemicals. Syncrude produces 215,000 barrels of SSB daily.

Because of the technical improvements developed by these companies, oil sand extraction is a major component in Canada's energy industry, producing enough oil to meet 17 percent of the country's petroleum needs and accounting for 13 percent of all oil produced in Canada.

FIRST, You DIG

Oil extraction begins with mining techniques, specifically, removing the layers of earth and overburden (a thick layer of clay, silt, and gravel) to expose the oil-laden sand. At its Mildred Lake mine, Syncrude uses two 8750 walking draglines made by Marion Power Shovel, and two 2750 walking draglines made by Marion's parent company, Bucyrus International Inc. in Milwaukee, all 28,000horsepower machines, to dig out the oil sand. The walking draglines are equipped with 90-cubic-yard buckets on 360-foot booms. The dragline operator piles oil sand in windrows along the sides of the mine pit.

Four Krupp bucketwheel reclaimers scoop the oil sand from the windrows and deposit it onto conveyors that transport it to Syncrude's extraction plant. Three of the 12,000-hp reclaimers have wheels equipped with 14 buckets that each hold 3.1 cubic yards of sand. One has a "flying wheel" that carries 24 buckets, each capable of holding 1.8 cubic yards of sand. The conveyor belts carry more than 6,300 metric tons of oil sand per hour 31 miles from the mine and an additional 1.2 miles in the extraction plant.

EXTRACTING BLACK GOLD

Once inside the extraction plant, the oil sand is sent into large, horizontal, rotating drums called tumblers. Caustic soda, hot water, and steam are introduced to the oil sand, which is rotated to aerate the mixture. The slurry is then discharged onto vibrating screens that remove clay and rocks. The filtered slurry is diluted in pump boxes and pumped to the primary separation vessels, or PSVs.

Bitumen floats to the surface within the PSVs and is separated. The sand settles to the bottom of the PSVs and is pumped to tailings oil recovery (TOR) vessels. Much of the bitumen remaining in the sand is removed in the TOR vessels by a proprietary Syncrude technology. The bitumen separated in the TOR vessels returns to the separation vessels to improve its quality. The bitumen froth is then collected and deaerated. Naphtha is added to assist with the removal of the remaining solids and water in second-stage extraction.

Syncrude added an extraction auxiliary production system at the site in 1993. This system takes the crushed oil sand excavated by auxiliary production and sends it to a cyclofeeder, where it is mixed with caustic soda and water. Screens filter out oversize particles before the slurry is piped to the extraction plant, and to the PSVs for processing. The clay, hydrocarbons, sand, and water that remain after extraction are stored in a settling basin that measures 22 square kilometers. Water is removed and then reused as process water.