Methane, CH4, is a common gas here on earth. It is found in the atmosphere, buried in garbage dumps, and deep in the ground, often in combination with petroleum where it is generally known as natural gas. It comes from anaerobic decomposition of organic matter by bacteria and, as such, is the principal gas in animal (including human, of course) enteric emissions. Grazing cattle are a major source! Human-influenced sources include landfills, leakage from natural gas and petroleum systems, agricultural activities, coal mining, stationary and mobile combustion, wastewater treatment, and certain industrial process.
Methane is both a fuel and a potent greenhouse gas, roughly 20 times more potent than CO2 pound for pound, although it does not stay in the atmosphere as long, 12 years versus 100 (these are average lifetimes) for CO2. Methane is also one the commonest fuels and is rising in importance because it burns cleanly compared to coal in the sense that its burning or oxidation products are only H2O and CO2 and per energy output, methane burning produces less CO2 than coal burning. I'll have more to say about this later in the column.
In this column I will describe the several sources and uses of methane now and in the near future as well as describe its contribution to global warming. There was little use of natural gas until pipelines for its transport were built. Although one of the first lengthy pipelines was built in 1891, it was 120 miles long and carried gas from fields in central Indiana to Chicago, there were very few pipelines built until after World War II in the 1940s.
Improvements in metals, welding techniques and pipe making during the War made pipeline construction more economically attractive. After World War II, the U.S. began building its pipeline network. Throughout the 1950s and 1960s, thousands of miles of pipeline were constructed throughout the United States. Today, the U.S. pipeline network, laid end-to-end, would stretch to the moon and back twice. Pipelines are still being built and they have a profound impact on local areas that had little natural gas supply prior to the pipeline. An example of this just recently occurred in eastern Ohio. It drew little fanfare, but with the flip of a switch last week, natural gas from Colorado and Wyoming began flowing into Clarington, Ohio through the new $4.4 billion Rockies Express pipeline. Robert Black, president of Waterville Gas Co., said even the partial amount of Rockies Express gas that began flowing to western Ohio in June had an immediate impact on prices. Rates charged locally by Columbia Gas of Ohio were $1.43 per 100 cubic feet in July 2008; 94 cents in January; 68 cents in July 2009; and will be 49 cents next month.
Internationally there are many natural gas pipelines connecting the fields of gas wells with customers. The ones from Russia to Ukraine and Europe are often in the news. A consortium of gas and pipeline companies wishes to build a long pipeline from northern Canada to northern U.S. Natural gas needs to be liquefied cryogenically for economic shipping in bulk across oceans. Most ports in the United States will not accept such ships because of the potential danger of massive fires and explosions of the liquid natural gas. Specialized port facilities need to be built to safely handle LNG (Liquefied Natural Gas) and the ships that carry it. So now with easy availability we have found many uses for methane or natural gas. I will describe those uses later in this column, but first I will discuss its greenhouse gas characteristics, since it is second only to CO2 in effectiveness at warming the atmosphere.
In order, Earth's most abundant greenhouse gases are:
▪ water vapor
▪ carbon dioxide
▪ nitrous oxide [N2O]
▪ ozone [O3]
▪ CFCs [chlorinated fluorocarbons]
Each of the greenhouse gases has a unique infrared absorption spectra and each have bands in their spectra that overlap with those of other gases so that it is complicated to determine the net greenhouse effect for mixtures. Methane (CH4) is a greenhouse gas that remains in the atmosphere for approximately 9-15 years. Chemical reaction with OH in the atmosphere is the dominant removal mechanism.
Methane is over 20 times more effective in trapping heat pound for pound in the atmosphere than carbon dioxide (CO2) over a 100-year period and is emitted from a variety of natural and human-influenced sources. Human-influenced sources include landfills, natural gas and petroleum systems, agricultural activities, especially ruminant digestion and manure management associated with domestic livestock, coal mining, stationary and mobile combustion, wastewater treatment, and certain industrial processes. Methane emission levels from a source can vary significantly from one country or region to another, depending on climate, industrial and agricultural production characteristics, energy types and usage, and waste management practices. For example, temperature and moisture have a significant effect on the anaerobic digestion process, which is the key biological process that causes methane emissions in both human-related and natural sources.
The historical record, based on air bubbles trapped in ice cores, shows that methane is at its highest abundance now in at least the last 400,000 years. Since 1750, global average atmospheric concentrations of methane have increased from approximately 700 to 1,745 parts per billion by volume in 1998. Over the past decade methane concentrations have continued to increase, but the rate of increase has slowed.
The four largest U.S. sources of methane going into the atmosphere are enteric fermentation in livestock, landfills, natural gas systems, and coal mining. Globally, livestock are the largest source of methane from human-related activities. Livestock production can also result in emissions of nitrous oxide, a very potent greenhouse gas, and carbon dioxide, the most abundant greenhouse gas. Fortunately, there are ways to reduce greenhouse gas emissions from livestock production through management strategies that improve production efficiency and result in lower emissions per unit of milk or meat produced.
Emissions from beef cows are high for a number of reasons: beef cows are very large animals; diets, consisting mainly of forages of varying quality, are generally poorer than in the dairy or feedlot sectors; the level of management is typically not as good as for dairy animals; and the beef cow population is very large. Better grazing management and dietary supplementation have been identified as the most effective ways to improve efficiency and reduce emissions from this sector because they improve animal nutrition and reproductive efficiency. Also grazing land should be better fertilized. Landfills are the largest human-related source of methane in the U.S., accounting for 34 % of all methane emissions. Methane is generated in landfills and open dumps as waste decomposes under anaerobic conditions. The amount of methane created depends on the quantity and moisture content of the waste and the design and management practices at the site. The EPA has established a voluntary program to reduce methane emissions from landfills. This program, known as the Landfill Methane Outreach Program (LMOP), works with companies, utilities, and communities to encourage the use of landfill gas for energy. The implementation of similar technologies to capture and utilize methane (usually for energy) from coal mines, and manure management on commercial farms is making some progress. Methane, or natural gas, is a hugely important source of energy. When it burns, the products are CO2 and H2O just as in coal or petroleum burning. However, natural gas contains no dangerous heavy metals and burns very cleanly without any ash. Therefore, natural gas would be a far better fuel for electricity production than coal if it were available in huge quantities and a low enough price. Today, natural gas produces about 23% of all the energy in the U.S. (the same as coal) and about 30% of natural gas is used for electricity generation. The rest goes to residential and commercial building heating and industrial use.
Many coal burning plants can be retrofitted to burn natural gas and thereby reduce CO2 emissions since natural gas produces 43% less CO2 than the average coal type per energy unit generated from combustion. While a vast improvement over coal (and oil), it is not a sustainable solution to global warming, air pollution and resource depletion. But advanced electric generation technology like combined-cycle gas turbines and fuel cells show that natural gas will be an important way to reduce the environmental impacts of electricity in the short run, perhaps until about 2040. Natural gas reserves are dwarfed by coal reserves in the US, but are still expected to be able to supply the nation for 60 years or more. What makes estimating difficult is that new supplies are still being discovered. Worldwide this is even truer. The former Soviet Union is anticipated to have huge supplies, up to ten times as much as the US, especially in Siberia. Major finds have been found recently in Indonesia, Mexico, and North Africa. Estimates of worldwide gas reserves range from 120 to 175 years of supply, but some predict that with improved extraction methods, it could be three times higher.
A new source for natural gas is deep shale. Shale gas has become an increasingly more important source of natural gas in the United States over the past decade, and interest has spread to potential gas shales in Canada, Europe, and China. It is possible that shale gas will supply as much as half the natural gas production in North America by 2020 if the extraction process can be made sufficiently environmentally benign. Because shales ordinarily have insufficient permeability to allow significant flow to a well bore, most shales are not commercial sources of natural gas unless the shale can be fractured in situ. Shale gas has been produced for years from shales with natural fractures. However, the shale gas boom in recent years widely reported in the news media has been due to modern technology in hydraulic fracturing to create extensive artificial fractures around well bores. Horizontal drilling is often used with shale gas wells, with lateral lengths up to 5,000 feet within the shale, to create maximum borehole surface area in contact with the shale.
Today, most hydrogen needed for industrial processes, especially in oil refining, is produced from natural gas, the fossil fuel with the largest number of hydrogen atoms per carbon atom. Industry is exploring a variety of ways to produce hydrogen from renewable resources so that in the future another need for fossil fuels will disappear and the attendant production of CO2 from fossil fuel combustion will disappear. The process for making hydrogen from CH4 is called steam-methane reforming and this process produces about 95% of the hydrogen used in the U.S. A great amount of carbon dioxide is an end product of this reforming process and therefore hydrogen production is another important source of this greenhouse gas. Methane is versatile enough to be used as a fuel for automobiles. Honda is producing the 2010 Civic GX that is fueled by compressed natural gas for nearly zero emissions of any harmful or air polluting gas except carbon dioxide. Over the years many service vehicles have been powered by natural gas and this use of natural gas as a transport fuel in urban areas with high air pollution is a good use for natural gas. But with global warming increasingly forcing the elimination of CO2 emissions, natural gas as a transportation fuel has a limited future.
Natural gas has also been considered as a fuel to make electricity in fuel cells, even for an electric car. Honda has been doing research and development on such a car. Electric utilities have experimented with natural gas fuel cells to generate electricity. The cost has remained much too high for commercial applications, plus the emphasis now on reducing CO2 emissions has slowed R&D on new uses of CH4 as a fuel including for fuel cells.
I'll close this column with a word about methane trapped in the ground in the frozen arctic regions of Canada and Siberia. It is known that huge quantities of CH4 produced by anaerobic decomposition of organic matter has accumulated in the frozen ground. As this region of the earth has warmed considerably in the last couple of decades, scientists have observed methane emissions. This situation is potentially a heat induced feedback mechanism; heat produces methane emissions and those emissions produce more heat which continues the cycle until the buried methane is gone. This mechanism has not been included in the various climate models the world's scientists are using because good quantitative information is lacking. But it worries the scientists!