May 2014

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1. Define the terms “tar sands” and “shale oil”. (4 marks).

Tar sands and shale oil are two unconventional sources of oil that cannot be exploited using the traditional methods of drilling an oil well into a deposit and allowing natural pressure to bring the oil to the surface as the hydrocarbons are trapped in the pores and cracks of a rock. Shale oil is an immature hydrocarbon: kerogen found in fine grained sedimentary rocks whereas tar sands are mature hydrocarbons and consist of sedimentary rocks mixed with tar oil, asphalt or bitumen. 

For both tar sands and shale oil, briefly describe how oil is obtained from the raw material and list the main environmental impacts. (7 marks) 

To extract shale oil the keragen-rich rock is heated to 500oC in the absence of oxygen in a process known as retorting. To extract the hydrocarbons from tar sands, ***** or open pit mining takes place. Oil is recovered by washing the sands with hot water. 

Large areas are devegetated such as in the example of the Alberta tar sands, Canada where huge swathes of boreal forest have been cut down. This destroys habitats and also decreases the potential of the land for carbon sequestration. 

A huge volume of water is required for the processing and afterwards large toxic wastepools are produced which if a leak occurs can pollute nearby bodies of water destroying habitats and making water sources unsafe to drink.

Exploiting these resources further contributes to global climate change as when burned greenhouse gases are produced. Unconventional sources of fossil fuels furthers the fossil fuel lock-in.

2. Describe the main features of a proton exchange membrane fuel cell, including the two main inputs to the cell and the two main outputs from the cell and a brief description of how it works. (7 marks).

A PEM cell is usually used as part of a "gas battery" and works by splitting hydrogen into its protons and neutrons when hydrogen enter the cell. Protons can diffuse across the membrane, however electrons are repelled from the anode and so move around the cell . On the other side air is inputted and the electrons react with the oxygen to produce water and heat. It is this heat that provides the energy for the cell. 

Give two sources for large-scale generation of hydrogen for use in the hydrogen economy and name the technique/method involved. (4 marks)

Electrolysis of water can be used to produce hydrogen and oxygen by connecting water with an electrolyte to allow free flow of electrons to a DC current. Hydrogen ions are attracted to the negative anode and negative oxygen ions are attracted to the positive cathode. Gasification of solid fuels such as carbon and biomass can be used which involves two stages of reactions:

C+H20= C0+H2


3. Describe (with a sentence on each) the technologies that are used to control the following pollutants from coal fired power plants: SOx, NOx, particulate matter, CO2. (8 marks) 



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