8.2 Energy resources  (Page 3/5)

Coal in south africa

The following advertisement appeared in a local paper:

1. "Coal is as old as the hills, and just as natural." Is this statement TRUE? Motivate your answer by referring to how coal is formed.
2. Coal is a non-renewable energy source. Quote a statement from the advertisement that gives an indication that coal is non-renewable. Give a reason for your choice.
3. Is coal actually a healthy source of energy? Motivate your answer by referring to all influences that coal and coal mining have on both humans and the environment.
4. Why is coal used as a primary energy source in South Africa?

(DoE Exemplar Paper 2, Grade 11, 2007)

Energy resources and their uses: oil

Oil is another product of the lithosphere which is very important in meeting our fuel needs.

How oil is formed

Oil is formed in a very similar way to coal, except that the organic material is laid down in oceans . Organisms such as zooplankton and algae settle to the ocean floor and become buried under layers of mud. Over time, as these layers of sediment accumulate and the heat and pressure also increase, the organic material changes to a waxy material called kerogen . Eventually, with continuing heat and pressure, liquid and gas hydrocarbons are formed. These hydrocarbons are lighter than rock and therefore move upwards through the rock layers before being trapped by an impermeable layer. Here the oil will slowly accumulate until there is enough that it can be accessed by oil rigs and other equipment. Crude oil or petroleum , is actually a mixture of hydrocarbons (mostly alkanes) of different lengths, ranging from 5 carbons to 18 carbons in the hydrocarbon chain. If the mixture contains mostly short hydrocarbons, then it is a gas called natural gas . As the hydrocarbon chains in the mixture become longer, the product becomes more and more solid. Coal is made up of the longest hydrocarbons. For more information on hydrocarbons, refer to Grade 12.

Extracting oil

When enough oil has accumulated in a well, it becomes economically viable to try to extract it either through drilling or pumping . If the pressure in the oil reservoir is high, the oil is forced naturally to the surface. This is known as primary recovery of oil. If the pressure is low, then pumps must be used to extract it. This is known as secondary recovery . When the oil is very difficult to extract, steam injection into the reservoir can be used to heat the oil, reduce its viscosity and make it easier to extract.

While most of South Africa's oil is imported and then processed at a refinery in either Durban, Cape Town or Sasolburg, some is extracted from coal, as discussed in "Energy resources and their uses" .