Alternative Energy Sources

Natural Gas

When oil exists below a certain depth, the heat of the earth breaks the molecules and it becomes natural gas; it is not necessarily found (in significant quantities) alongside oil. It is a simplest of the natural fuels, composed mainly of methane (CH4), the most basic hydrocarbon. When it is burned it releases carbon dioxide (CO2), water (2H2O) and energy.

It contains more energy per weight than any other fossil fuel and produces the least carbon dioxide which makes it very attractive for power companies concerned with climate change. Because there is more of it than oil, there has been a huge rush in recent years to build gas-powered power stations. New techniques such as combined-cycle power stations have been introduced. Unlike coal and oil stations which have to produce steam to turn turbines, gas can be used to directly turn the turbines. The exhaust heat is then captured and reused to produce steam for further power production. This technology can increase the efficiency of a fossil fuel from about 40% average to 80%.

Gas has many uses besides heating, cooking and power generation. Motor vehicles can be converted to run on it and it has long been used to create nitrogen fertilisers via the Haber-Bosch process. It is also the primary means of creating hydrogen at the moment (see Hydrogen).

LNG (Liquefied Natural Gas)

Unfortunately it is not so easy to transport gas as coal and oil, requiring either pipelines or LNG (liquid natural gas) ships. To liquefy natural gas, you need to cool it down to about -160°C where it will then occupy 1/640 (0.15%) of the original volume. Upon reaching its destination, it then has to be converted back to a gas by passing the liquid through vaporisers to warm it. Then it is transported through pipelines as normal gas. About a third of the original energy in the gas is lost in this double-conversion process.

Because of the dangers associated with it and the low temperatures needed, the transportation of LNG requires specially designed tankers, liquefaction plants and terminals. LNG is not explosive in its liquid state but, if it vaporises and mixes with air in the right proportions, it can ignite. As of yet, in nearly fifty years of use, there have been no major accidents with any tankers although there have been with incidents on shore. In recent years, 27 were killed in Algeria in 2004 at a liquefaction plant while, in the same year, 15 were killed in Belgium at an LNG pipeline.

Possibly the biggest danger involves the threat of terrorism. A successful attack on a tanker or terminal would be more likely to cause a massive fire rather than a massive explosion, and it may be that the biggest effect would be in closing down a terminal and a reduction in gas imports. In countries like the United States where land-based gas will soon decline, that in itself could be devastating.

Coal Gas

Coal gas can be converted to natural gas (methane) and it was this that formed the first use of gas in lighting (in Britain in 1785). However, this form of gas is not as efficient and clean as the gas which forms naturally underground. A tonne of coal can produce about 340 cubic meters of gas (29 GJ into approximately 13 GJ).

The Future of Gas

Gas production differs in several ways from oil. Being self-pressurised, it flows more easily which means that production is usually held at a plateau of about 80% of natural output for long periods. The problem then is that the production drops off rapidly, often with little warning. That is why the gas production profile is often referred to as a cliff rather than a peak.

As far as reserves are concerned, there is certainly more natural gas available than oil. Using data from the 2004 BP Statistical Review: