Fossil Fuels Overview

Fossil Fuels are some of the most important energy sources in our world today. They are responsible for everything from heating our houses to fueling our automobiles. Coal, Oil or Petroleum, and Natural Gas are considered the three, basic fossil fuels. They are created by the fossilization of plants and animals. These decay, and revert into their most basic forms. Carbon in it's pure form is coal, and petroleum and natural gas are hydrocarbons (molecules formed primarily from hydrogen and carbon atoms) formed during the decaying
process. The only difference between natural gas and petroleum is their relative sizes. Since the natural gasses tend to be much smaller molecules, they are lighter, and exist in a gaseous state at room temperature, whereas petroleum molecules are heavier, and are liquid at room temperature. The premise behind the use of fossil fuels for energy conversion is the idea of combustion, more commonly called burning.  Combustion is the chemical process where molecules containing carbon are exposed to oxygen and heat, which creates a chain reaction, producing more heat to continue fueling the reaction.  The reaction will only cease when either the supply of oxygen or the supply of carbon runs out.  A simple, common example of this is the burning of methane, natural gas.  The process is shown below:

 

In this example, 4 molecules of methane and 7 molecules of oxygen react with heat to form 4 molecules of carbon dioxide and 6 molecules of water.  Carbon dioxide and water are often the result of combustion reactions.  This reaction is called exothermic, because it creates a large amount of heat, most commonly manifested in a flame.

Around 400,000 years ago in China, prehistoric man made one of the most important discoveries -- how to control fire.  The could then use fire to heat their homes, and also as a weapon.  This was the earliest use of combustion, the burning of wood to create heat for personal warmth.  For many, many centuries, this was the major source of heat and light. Eventually, people learned that burning fossil fuels was more efficient than wood, so they used oil to fuel their lamps, and coal to feed their fires. As technology advanced, so did the science of fossil fuels. Scientists had to find new and more efficient ways to produce power and later to produce electricity. The following sections discuss different fossil fuels used in this process.

Coal : 

In order to obtain coal for the purpose of energy conversion, it must first be mined. The coal we use today was originally formed between 100 and 300 million years ago, depending upon the quality. Huge deposits all over the world are mined, and the coal is shipped internationally. The first recorded coal mining occurred in China, in the twelfth century. Since then, the methods of mining coal have changed drastically. In the eighteenth century, most mining was done with picks, shovels, and wheelbarrows. Then, in the nineteenth century, with the advent of the mine cars, coal mining became much easier. Modern methods often include heavy machinery and explosives to more efficiently extract the coal. Not all mining is done underground, however. Today, nearly sixty percent of all coal mining is done on the surface, called strip mining.

 In order to use coal to produce electricity for modern uses, it is usually used as fuel for a steam engine. Basically, the coal is burned, producing heat. This heat is used to boil water, producing steam. This steam then turns a turbine, which is connected to a generator, which produces electricity.

 Crude oil (called "petroleum") is easier to get out of the ground than coal, as it can flow along pipes. This also makes it cheaper to transport. 

I ought to point out that some scientists are claiming that oil is not a 'fossil' fuel - that it is not the remains of prehistoric organisms after all. They claim it was made by some other, non-biological process. Currently this is not accepted by the majority of scientists, but you can find out more about the idea at space.com

Natural gas provides around 20% of the world's consumption of energy, and as well as being burnt in power stations, is used by many people to heat their homes.  It is easy to transport along pipes, and gas power stations produce comparatively little pollution.

Other fossil fuels are being investigated, such as bituminous sands and oil shale. The difficulty is that they need expensive processing before we can use them; however Canada has large reserves of 'tar sands' , which makes it economic for them to produce a great deal of energy this way. 

How it works: 

Coal is crushed to a fine dust and burnt.

Oil and gas can be burnt directly. 

The steam that has passed through the power station's turbines has to be cooled, to condense it back into water before it can be pumped round again. This is what happens in the huge "cooling towers" seen at power stations. 

Some power stations are built on the coast, so they can use sea water to cool the steam instead. However, this warms the sea and can affect the environment, although the fish seem to like it. 

  Advantages : 

• Very large amounts of electricity can be generated in one place using coal, fairly cheaply.
  
  
• Transporting oil and gas to the power stations is easy.
  
  
• Gas-fired power stations are very efficient.
  
  
• A fossil-fuelled power station can be built almost anywhere, so long as you can get large quantities of fuel to it. Didcot power station, in Oxfordshire, has a dedicated rail link to supply the coal.

 Disadvantages :

• Basically, the main drawback of fossil fuels is pollution.
  Burning any fossil fuel produces carbon dioxide, which contributes to the "greenhouse effect", warming the Earth.
  
  
• Burning coal produces more carbon dioxide than burning oil or gas.
  It also produces sulphur dioxide, a gas that contributes to acid rain. We can reduce this before releasing the waste gases into the atmosphere.
   
  
  
• Mining coal can be difficult and dangerous. Strip mining destroys large areas of the landscape.
  
  
• Coal-fired power stations need huge amounts of fuel, which means train-loads of coal almost constantly. In order to cope with changing demands for power, the station needs reserves.
  This means covering a large area of countryside next to the power station with piles of coal.

How a coal power station works ( video )

What is crude oil? ( video )