Oil Sands (a.k.a. Tar Sands)

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How do you separate bitumen from sand with the least energy cost?

Big Ideas: 
  • Using basic fluid physics to reduce energy cost

Why Oil Sands are Important

Oil sands are petroleum deposits in which very viscous, dense petroleum (called bitumen) is found in a mix of sand, clay and water. The bitumen is extracted, and then upgraded into synthetic crude oil. Synthetic crude oil from the oil sands becoming an important alternative to conventional crude oil as technology advances and conventional crude becomes scarcer. Currently there is estimated to be 1.75 trillion barrels (1 barrel = 117 L) of conventional crude oil deposits worldwide whereas the two largest oil sand deposits, found in Canada and Venezula, have a total of 3.6 trillion barrels. Canada is the largest supplier of crude oil to the United States, with most of this oil coming from Alberta's oil sands, which make up 44% of Canada’s total oil deposits.

 

Extraction and Processing

Due to the high viscosity of the bitumen, strip mining or in-situ techniques to reduce the viscosity are needed to extract the oil. In-situ techniques such as Cyclic Steam Stimulation and Steam Assisted Gravity Drainage are used when the bitumen is found at depths more that 75 m. In Alberta, strip mining is the most common technique as there is generally a shallow overburden (overburden is the topsoil, muskeg, sand, clay and gravel which lay over top of the bitumen). In strip mining operations hot water and chemicals such as caustic soda (NaOH) are added to the mined material to separate out the petroleum from the sand and clay in which it is found. After further excess water and solids have been removed from the separated petroluem, lighter petroleum products are added to the bitumen, or it is chemically separated to make the petroleum suitable for transportation 1. The petroleum is then upgraded by distillation, processed to improve the hydrogen-carbon ratio, and the contaminates such as sulphur are removed2.

 

Environmental Concerns

Though oils sands are becoming a very important source of energy, there are many environmental issues associated with extraction operations. There are concerns with the amount of toxic gases released into the air such as hydrogen sulphide (H2S), and the great amounts of water needed to extract the petroleum. It is estimated that for each barrel of oil extracted by strip mining, 7.5 to 10 barrels of water are used, of which only 40-70% can be recycled 3. There are also concerns about contaminated water sitting in tailings ponds leeching into nearby river systems. The deforestation and removal of overburden in strip mining processes are also a cause for concern. To date, 602 km2 have been disturbed, and as of December 2008 only 67 km2 have been reclaimed 4. A major concern with oil sands projects is the amount of carbon dioxide and other greenhouse gases emitted. The Canadian oil sands operation emits 40 million tons of CO2 annually, which is 0.1% of the global total and 5% of Canadian emissions, and this does not include the end-use burning of the oil produced.  By 2015 it is expected for this to rise to 8% of the total Canadian emissions. According to Cambridge Energy Research Associates, in 2009 the oil sands produced 5-15% higher CO2 emissions than conventional crude oil in the so-called “well-to-wheels” lifetime of the petroleum 5. Alberta's carbon offset program has been roundly criticized by the province's Auditor General6; none of the agricultural credits the auditors checked could be confirmed.

 

Oil Junkie's Last Fix7

Photo: http://www.flickr.com/photos/royaldutchshell/5484849587/in/set-72157626165407506/

Some Physics

To separate the bitumen from the sand, these are mixed with a great deal of water. The bitumen tends to rise, and the sand settles. In a vertical tube, the rising bitumen would collide with the falling sand, impeding the flow of both. A simple change in geometry - tiliting the vessel - allows the the lighter particles to flow up one side and the heavier to fall on the other, setting up a circulation that speeds the separation8 .  This is a neat idea that has been in use since the 1920s for separating blood components9. Follow the links for take-home experiments involving a simple demonstration using canola oil and water.

 

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