Fossil Fuels

Fossil-fuelled generating stations burn coal, oil or natural gas to generate electricity.

The Nanticoke Generating Station
The Nanticoke Generating Station on the shores of Lake Erie is the largest coal-fired power plant in North America. When running at capacity the station can meet up to 20% of Ontario’s electricity demands.

In the case of a coal-fired generating station, the coal is stored in large coal piles just outside the station. From there, the coal is brought into the station on a conveyor belt where it is fed into large pulverizers that crush the coal into a fine powder. Large fans blow the coal powder into a giant furnace where it is burned giving off vast amounts of heat. The temperature in the furnace can reach over 3,000oC.

The furnace is surrounded by tubes filled with water. The immense heat from the burning coal turns the water in the tubes into steam. The steam is then transferred under pressure at high speed through large pipes to a turbine where it pushes the turbine’s blades causing them to spin. From there, the process is the same as in a nuclear or hydroelectric generating station: the turbine spins the generator producing electricity.

The steam is condensed back to water using cooling water, usually from a nearby lake or river. It is then pumped back into the water tubes surrounding the furnace to continue the process.

Fossil-fuelled power plants play an important role because, unlike nuclear stations, they are able to quickly adjust to changes in electricity demand. Their output can easily be increased to help meet periods of peak demand.

coal power plant
Diagram of a coal power plant.

Burning fossil fuels to generate electricity creates a number of byproducts that impact the environment. This includes gases like sulfur dioxide (SO2) and nitrous oxide (N2O) which contribute to smog and acid rain. Some of Ontario’s coal-fired generation stations use special technologies that can reduce or almost eliminate these pollutants.

Another gas that is released when burning coal is carbon dioxide (CO2), which is a greenhouse gas. Greenhouse gases trap heat in the earth’s atmosphere and can cause temperatures on the earth’s surface to rise. This effect is known as global warming.

carbon cycle
The carbon cycle.

The carbon cycle shown above is the process through which carbon is cycled through the air, ground, plants, animals, and fossil fuels. Carbon is stored in fossil fuels, over millions of years. When these fuels are burned, the carbon dioxide stored in them is released back into the air.

History of Fossil Fuels

There are two theories on the origins of fossil fuels. One theory states that they formed over hundreds of millions of years from the fossilized remains of dead plants and animals subjected to intense heat and pressure in the Earth’s crust. This is known as the biogenic theory and was first introduced by Mikhail Lomonosov in 1757. The second theory is called the abiogenic petroleum origin and it states that natural petroleum was formed from deep carbon deposits, perhaps dating to the formation of the Earth. The abundance of hydrocarbons elsewhere in the solar system is taken as evidence that there may be a great deal more petroleum on Earth than was previously thought.

Fossil fuels have been used as a fuel source for hundreds of years — in fact, the industrial revolution was powered by coal. Coal is responsible for the way of life you now enjoy. Its discovery led to the development of the steam engine and the internal combustion engine which revolutionized manufacturing, transportation and electricity production through the use of thermal electric generating stations. Fossil fuels are also used to make a wide variety of products including plastic which, like the automobile, has become a key component of modern society. Fossil fuels and their by-products are also used in the manufacture of paints, cosmetics, soaps, shampoo, lubricants, asphalt and countless other products.

However there is documentation that, as early as the 16th century, the environmental impact of burning fossil fuels was becoming evident. Factories burned coal to power steam engines, steel mills burned coal to make steel, and people in the cities used coal to heat their homes. The poor air quality in many large European cities was far beyond what we can even imagine today.

Fossil Fuel Challenges

The burning of fossil fuels produces around 6.3 billion metric tonnes of carbon dioxide (CO2), a greenhouse gas, per year. It is estimated that natural processes of the Earth can only absorb about half of that amount, resulting in a net increase of 3.2 billion tonnes of atmospheric carbon dioxide per year which many scientists believe leads to global warming.

coal power plant
The output of a coal power plant in a single day.

The burning of fossil fuels also adds sulfur dioxide (SO2) and other gases into the atmosphere, creating acid precipitation which is harmful to plants and aquatic life, and particulate emissions (fly ash in figure above) which are harmful when breathed in. Oil spills, both large and small, are not uncommon and have disastrous environmental results. All you need do is walk down a paved street after it has rained. You can often see the shiny rainbow effect of oil on the surface of the water. More than likely that oil came from a leak in an automobile. Now think about the millions of automobiles on the roads today and you can see the scale of the problem.

Over the past 30 years, oil companies, automotive companies and electric generating utilities have placed a great deal of effort into lessening the environmental impact of burning and using fossil fuels. Many oil tankers now have double hulls to reduce oil spills, automobile companies are steadily increasing the fuel efficiency of vehicles, and electric generating utilities have installed scrubbers on their smoke stacks to reduce the CO2 and SO2 released into the atmosphere. A technique called carbon sequestration is now being studied which involves the capture of CO2, converting it into a liquid state and pumping it back underground where it came from.

One of the biggest challenges to solving the carbon dioxide problem is the sheer volume of fossil fuels we extract and use each year. Each of these activities produces CO2 and despite recent fossil fuel price increases, we consume more and more each year. Although in the 1970s many scientists warned about the possibility of running out of fossil fuels, studies now indicate that natural gas and oil will last well into this century, and coal could last for hundreds of years at currently projected rates of consumption. The Athabasca Tar Sands in Alberta cover an area roughly the size of the State of Florida and contain an enormous amount of oil which, with the greatly increased price of oil, has now become economically feasible to extract. With scientists warning that the Earth is not only getting warmer but global warming is happening much faster than anticipated, the question is not whether or not we are running out of fossil fuels, but rather can we afford to burn them at our present rate.

Athabasca tar sands
The Athabasca tar sands in Alberta contain enormous amounts of oil.

Natural gas presents a source of energy with significantly reduced acid gas and particulate emissions compared to coal. However, the greenhouse gas emissions are similar to those from coal generation so this source still presents a concern in this regard. Additionally gas must be transported via pipelines and tankers much like oil, making its security of supply susceptible to the market and political factors. Since 2002, natural gas has tripled in price.

Sources:

Canadian Energy Research Institute, World Energy: The Past and Possible Futures, p. 75
www.cna.ca/english/pdf/Studies/CERI/CNA_CERI07_EN.pdf.
Ontario Power Generation, http://www.opg.com/communities-and-partners/teachers-and-students/Documents/grade9student.pdf.