Methane, Biogas and Natural Gas

Natural gas is a fossil fuel which consists mostly of methane. It can be found in oil fields, natural gas fields and coal beds.

Non-fossil gasses rich in methane are produced by the anaerobic decay of non-fossil organic material and are called biogases. Sources include cattle flatulence (17% - 600 litres per cow per day), landfills (from food decay), sewage, swamps and marshes. It can be explosive.

Chemical reactions in industry and nature, for instance volcanoes can also produce methane. In some volcanoes methane and oxygen react, giving off carbon dioxide. Some bacteria and deep-water corals live on methane.

Methane is a hydrocarbon with chemical formula CH₄. It is naturally odourless though often a strong smell is added in the interests of safety. It is a greenhouse gas. When it is burnt in an atmosphere containing oxygen, one molecule of methane releases one molecule of carbon dioxide (CO₂) and two molecules of water (H₂O) in the form of steam. The amount of methane in the (dry) atmosphere varies but it is typically 1.745 ppm - 149% higher than before the industrial revolution. It is 23 times more powerful a greenhouse gas than CO₂ but there is more than 2,000 times as much carbon dioxide in the atmosphere. It contributes about 20% of the greenhouse effect compared to 60% for CO2. According to ice cores from the Vostok station in East Antarctica, the atmospheric concentration of methane is higher now than it has been in the past 420,000 years. There was a great deal more when the supercontinent Pangaea in the Triassic Period 245 to 202 million years ago, however.

A lot of methane is believed to be trapped at high pressure on the bottom of the ocean. It is possible that the sudden release of large amounts of methane form such sources into the atmosphere could cause rapid global warming, which may have happened 55 million years ago. This could happen again if global warming heats the oceans enough.

Natural gas is mostly transported by pipeline. Methane can be transported in refrigerated or liquid form. If there is a leak the liquid will be heavier than air, but the gas will be lighter than air.

This article relates to a news wire in the October 06 Environmental Roundup.

Index of topics in this series.

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