Fossil Fuels

 

Fossil fuels are fuels formed by the anaerobic (absence of oxygen) decomposition of buried dead organisms such as plants, animals, and bacteria.  Example fossil fuels include: coal, oil, and natural gas.  The formation process occurs over an exceptionally long time - the age of the organisms and their resulting fossil fuels is typically millions of years, but can even be orders of magnitude greater than this.  Therefore, fossil fuels are not classed as a renewable energy resource; once they have been consumed, there isn’t any more left. One particular problem here is that oil is also used to make many useful products such as plastics and other synthetics and so needs to be conserved.  Technically speaking, one could argue that if we wait long enough, more coal seams and oil fields will be formed and therefore fossil fuels are renewable.  This process, however, takes millions of years (longer than the human race has even existed so far) and so, for all practical purposes, fossil fuels are considered finite.

 

Formation

 

Pressure, heat, and a great deal of time go into the formation of fossil fuels.  In this process, the remains of plants and animals that have settled in large quantities, the majority of which include organisms such as phytoplankton and zooplankton, undergo the gradual and complex process of anaerobic decomposition. Typically, this ancient material accumulates on the bottom of a seabed or lake and over time mixes with silt and mud to form layers with additional sediment forming on top, effectively sealing the organic remains.  With increasing pressure and heat, the organic material is broken down and chemically altered into the simpler form of hydrocarbons (organic compounds consisting entirely of hydrogen and carbon). These hydrocarbon chains occur in varying forms ranging from simple configurations to complex compounds.

 

Combustion

 

The chemical energy stored within fossil fuels is released through combustion and that is still how the majority of the world’s energy requirements are met.  These fuels contain a high percentage of carbon and hydrogen and so release carbon dioxide and water when burned.  Of course, energy production is an absolute necessity to our way of life, but the use of fossil fuels is not only unsustainable but also damaging to the environment.

 

In preparation for combustion in fossil fuel power stations, coal will typically be crushed into a fine dust first but oil and gas can be burnt directly.  The heat from this combustion is used to heat water and produce steam.  The steam is then used to turn turbines connected to generators that create electrical power.

 

Refining

 

When taken from the ground, oil is unprocessed and contains a mixture of varying hydrocarbon molecules.  This naturally occurring substance is known as crude oil or, also, petroleum.  Crude oil is often thought of as being a black liquid but can actually vary in colour, from clear to black, and also varies in viscosity, from water-like to almost solid.  To make use of all these different hydrocarbons and produce something useful, crude oil needs to be refined - a process in which the hydrocarbons are separated.  The primary technique used to do this is called fractional distillation.  Due to their chain lengths and molecular configurations, different hydrocarbons usually have distinct boiling points allowing them to be separated by distillation.  In the distillation process, crude oil is heated and vaporised.  As the vapour rises up through the fractional distillation column it cools and passes through trays designed to collect liquids.  When a substance within the vapour reaches a height in the column equal to its boiling temperature it cools and condenses into a liquid where it is collected.  This method is used to collect each fraction at corresponding heights and temperatures within the column.  The fractions may then be stored or go on to further chemical processing.  In chemical processing one fraction is converted into another.  This may be done by: breaking long hydrocarbon chains into shorter ones (known as cracking); combining shorter chains into longer ones (known as unification) ; or, rearranging chains in the desired manner (known as alteration).

 

At the end of the distillation process crude oil has been used to produce a whole range of useful materials such as:

 

Petroleum gas - used for heating, cooking, and making plastics.

 

Naptha or ligroin - an intermediate that can be converted into gasoline.

 

Gasoline (petrol) - motor fuel.

 

Kerosene - used as jet fuel, tractor fuel, or making other products.

 

Gas oil or diesel distillate - diesel fuel, heating oil, or making other products.

 

Lubricating oil - motor oil, grease, and other lubricants.

 

Heavy gas or fuel oil - industrial fuel, or making other products.

 

Residuals - coke, asphalt, tar, wax, or making other products.

 

 

 : :  Fossil Fuels