Methane | Research & Encyclopedia Articles

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Methane Summary

Methane

The hydrocarbon methane (CH₄) is the major component of natural gas (around 90 percent) that is found in oil and gas wells throughout the world. Since the beginning of time, methane has also been produced by a number of biological sources—both natural and human—by the decomposition of organicmaterial. From 1800 to 2000, atmospheric concentrations of methane, which are approximately 0.00017 percent, have grown around 150 percent. However, the patterns of methane emission is highly irregular and, for reasons yet unclear, the rate of increase slowed considerably from 1980 to 2000. The major natural releases of methane are from wetlands (marsh gas) and termites; the major human releases are from energy use, rice paddies, gaseous emissions from animals, human/animal wastes, landfills and biomass burning. Methane research is proceeding in two major directions: the energy course, looking for ways to make bioconversion of wastes to methane more economically attractive as an alternative fuel; and the environmental course, looking for ways to limit its release into the atmosphere since it is a much more potent greenhouse gas than carbon dioxide—a thermogenic effect four to six times that of carbon dioxide. The shared goal is finding ways to "harvest" for energy production much of the methane now being released into the atmosphere.

Molecular structure of methane. (Gale Group)

In the energy sector, many coal mines are looking at ways to put the methane produced as a result of the mining process to work instead of venting it into the atmosphere. The U.S. Environmental Protection Agency estimates that up to 40 percent of the methane that migrates to the atmosphere can be used for power generation (electricity and heat), injection into pipeline systems, methanol production, or onsite applications like coal drying. Besides methane sales revenue and greenhouse gas reductions, the removal of methane from coal seams could serve the vital function of decreasing the risk to workers of firedamp—methane-air mixtures igniting inadvertently.

A researcher checks a sealed poy of methane in Kajima Corp.'s newly developed system designed to break down organic waste. (Corbis-Bettmann)

Other energy sector concerns are methane emissions from unburned fuel, and from natural gas leaks at various stages of natural gas production, transmission and distribution. The curtailment of venting and flaring stranded gas (remotely located natural gas sources that are not economical to produce liquefied natural gas or methanol), and more efficient use of natural gas have significantly reduced atmospheric release. But growth in natural gas production and consumption may reverse this trend. Methane has the highest ratio of hydrogen to carbon of any fossil fuel (4:1), so switching to natural gas is increasingly seen as an attractive option for cleaner air and carbon dioxide reduction.

Unlike natural gas production, the biological production of methane is attractive from a sustainability perspective. Whereas the methane that sits in underground natural gas reservoirs is finite, the methane production from biological sources is potentially very large as well as renewable. Anaerobic bacteria digestion of organic materials, in the absence of air, can produce a biogas that is 60 to 70 percent methane (state-of-theart systems have reported producing 95 percent pure methane), the rest being carbon dioxide and other trace gases. Burning this gas can provide energy for cooking and space heating, or electricity generation.

Bioconversion of manure-to-methane is accomplished with biogas devices called digesters: organic material fed into the digester tank is heated to increase the natural decomposition rate by microorganisms, and then a pipe carries the biogas to where it will be used. There is an outlet for digested residues that usually are used as fertilizer. Several demonstration projects are taking place that are showcasing the technology. The Mason Dixon Dairy located in Gettysburg, Pennsylvania, produces enough methane from cow manure to meet its power needs, with excess power sold to the local utility. However, wide-scale development is unlikely because the low margins characteristic of farming do not support the additional capital investment to build such an operation.

Landfill gas-to-energy is another promising way to reduce atmospheric release and provide inexpensive energy to local industry and communities. Boilers for steam heat, hot water and the generation of electricity can be designed to burn a blended fuel or fueled exclusively on landfill gas. Because large-scale landfill methane recovery projects are most economical when an industrial facility is located nearby, landfill gas-to-energy projects are few and can only provide a limited amount of energy.

Controlling methane release from wetland, rice paddies and gaseous emissions from animals is more problematic. The release from rice paddies and wet lands is slow, intermittent and takes place over a wide geographic area, and thus very difficult to control. Gaseous emissions from agricultural animals contribute to atmospheric accumulation of methane due to fermentative digestion that produces methane inthe rumen (stomach). Although the rate of release is highly variable, affected by factors such as quantity and quality of feed, body weight, age and exercise, beef cattle and draught animals are suspected of contributing around 50 percent, dairy cows around 20 percent, and sheep around 10 percent. Higher quality feed standards, which increase the efficiency of nutrient use, are being recommended as a way to curtail these emissions.

Methane from renewable biological sources will never be a major energy resource, yet it can be a valuable addition to the energy supply mix. Nevertheless, whether methane comes from fossil fuel reservoirs or from bioconversions, it is certain to provide useful energy for many years to come.