Environmental Engineering Reference
In-Depth Information
These days, natural gas is as highly prized as oil, mainly as a fuel for electricity
generation and heating. Natural gas is transported through high-pressure pipelines or by
ship in the form of liquefied natural gas (LNG). Its main advantages over coal and oil are
its cleanliness (it releases only carbon dioxide and water on combustion) and relative ease
of transportation. The United States was the world's largest producer of natural gas until
1982, when it was surpassed by the USSR. In the last decade, the United States has been
catching up again, thanks to a recent boom in shale gas.
Coal: The Mainstay of the Industrial Age
In the West most people instinctively associate coal with a bygone age: smokestacks, sooty
factory towns, workers toiling in pits and blazing ironworks. There is a general assumption
that we have moved on to cleaner and more sophisticated fuels. Yet the coal age never
really ended. It is true that the energy mix diversified during the twentieth century as first
oil, then natural gas, nuclear and renewable energies became commercially competitive.
Yet coal has hung doggedly in there and remains the principal fuel of industrial production.
It is just that production has become invisible for many in the West, as it now
predominantly takes place in the East. The global economy would grind to a halt without
coal,asitisbyfarthemostimportantsourceofenergyforelectricitygeneration.Moreover,
in the short term at least, its importance is likely to grow. As oil and gas supplies dwindle,
we are likely to see a renaissance of coal precede a renaissance of renewables.
Coal is a sedimentary rock, composed primarily of carbon, as well as other minerals,
including sulphur. It is formed through a process known as carbonization: leaves and
branches fall and are compressed, first forming peat, then various qualities of coal, then
graphite, and finally, under the right conditions, diamonds. Peat takes several thousand
years to form, while anthracite, the most carbon- and energy-dense of the coal varieties,
is formed over many millions of years. Graphite and diamonds are made of pure carbon
and are not used as fuels. This is not just because of their rarity or usefulness for other
applications, but because their molecular bonds are too tight to allow for easy combustion.
Table 2.3.
Energy content of different fossil fuels compared with air-dried wood
Fuel
Energy content
Poor brown coal or peat
> 8 MJ/kg
Brown coal (lignites)
> 14.7 MJ/kg
