Dry natural gas is sent through pipelines to underground storage fields or to distribution companies and then to consumers. In places where natural gas pipelines are not available to take away associated natural gas produced from oil wells, the natural gas may be reinjected into the oil-bearing formation, or it may be vented or burned flared. Reinjecting unmarketable natural gas can help to maintain pressure in oil wells to improve oil production.
Coalbed methane can be extracted from coal deposits before or during coal mining, and it can be added to natural gas pipelines without any special treatment. Most of the natural gas consumed in the United States is produced in the United States. Some natural gas is imported from Canada and Mexico in pipelines. A small amount of natural gas is also imported as liquefied natural gas. Natural gas explained. What is energy? Units and calculators.
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Diesel fuel. Heating oil. In a final process step called "pressure-swing adsorption," carbon dioxide and other impurities are removed from the gas stream, leaving essentially pure hydrogen. Steam reforming can also be used to produce hydrogen from other fuels, such as ethanol, propane, or even gasoline.
In partial oxidation, the methane and other hydrocarbons in natural gas react with a limited amount of oxygen typically from air that is not enough to completely oxidize the hydrocarbons to carbon dioxide and water. With less than the stoichiometric amount of oxygen available, the reaction products contain primarily hydrogen and carbon monoxide and nitrogen, if the reaction is carried out with air rather than pure oxygen , and a relatively small amount of carbon dioxide and other compounds.
Subsequently, in a water-gas shift reaction, the carbon monoxide reacts with water to form carbon dioxide and more hydrogen. Almost half of this was used by industry, a quarter by the residential sector, and the rest divided evenly between commercial users and electric utilities. Gas is used in homes for space and water heating and cooking. Nearly two-thirds of American homes are heated with gas. The best home furnaces are over 90 percent efficient at extracting heat from the gas.
There is increasing interest by utilities in using gas to generate electricity. Gas turbines, derived from jet engines, use the hot gases from fuel combustion directly, rather than using the heat to make steam, like in coal plants. After the hot gas is used to drive the jet engine turbine, it is used to boil water into steam, which then drives a steam turbine.
Combined cycle turbines can be over 50 percent efficient at converting gas into electricity, compared to about 33 percent for steam turbines.
Although natural gas is a fossil fuel and so is made up mostly of carbon, global warming emissions from gas are much less than coal or oil. Compared to coal, gas produces 43 percent fewer carbon emissions for each unit of energy produced, and 30 percent less than oil.
Gas also produces no solid waste, unlike the massive amounts of ash from a coal plant, and very little sulfur dioxide and particulate emissions. On the other hand, the combustion of gas still produces nitrogen oxides, a cause of smog and acid rain. Natural gas is a powerful greenhouse gas with lower carbon emissions. Natural gas methane is much more effective than carbon dioxide at trapping heat in the atmosphere, 58 times more effective on a pound-for-pound basis. Methane concentrations have increased eight times faster than carbon dioxide, doubling since the beginning of the industrial age.
Natural gas use has accounted for about 10 percent of all global warming emissions. The market for gas continues to expand rapidly.
In , gas added one million new customers in the US. As utilities anticipate electric utility restructuring, they are buying more gas turbines as well as more gas — gas sales to electric utilities rose by seven percent between and This growth is due to new gas turbines, which are cheaper to install than coal plants and easier to site and get permits for, and the currently low cost of gas.
Provided gas prices stay low; this trend will continue. Even a better technology for converting gas to electricity is rapidly approaching the market, the fuel cell.
Fuel cells convert gas directly into power without combustion. The combination of compress ion and high temperature causes the carbon bond s in the organic matter to break down. This molecular breakdown produces thermogenic methane—natural gas. Methane , probably the most abundant organic compound on Earth, is made of carbon and hydrogen CH4. Natural gas deposits are often found near oil deposits.
Deeper deposits—formed at higher temperatures and under more pressure—have more natural gas than oil. The deepest deposits can be made up of pure natural gas. Natural gas does not have to be formed deep underground, however.
It can also be formed by tiny microorganisms called methanogen s. Methanogens live in the intestine s of animals including humans and in low-oxygen areas near the surface of the Earth. Landfill s, for example, are full of decomposing matter that methanogens break down into a type of methane called biogenic methane.
The process of methanogens creating natural gas methane is called methanogenesis. Although most biogenic methane escapes into the atmosphere , there are new technologies being created to contain and harvest this potential energy source. Some of the gas is able to rise through permeable matter, such as porous rock, and eventually dissipate into the atmosphere. However, most thermogenic methane that rises toward the surface encounters geological formations that are too impermeable for it to escape.
These rock formations are called sedimentary basin s. Sedimentary basins trap huge reservoirs of natural gas. In order to gain access to these natural gas reservoirs, a hole sometimes called a well must be drilled through the rock to allow the gas to escape and be harvested. Sedimentary basins rich in natural gas are found all over the world.
In the United States outside Alaska, basins are primarily around the states bordering the Gulf of Mexico, including Texas and Louisiana. Recently, the northern states of North Dakota, South Dakota, and Montana have developed significant drilling facilities in sedimentary basins.
Natural gas found in other geological settings is not always so easy or practical to extract. Biogas is a type of gas that is produced when organic matter decomposes without oxygen being present.
This process is called anaerobic decomposition , and it takes place in landfills or where organic material such as animal waste, sewage , or industrial byproduct s are decomposing. Biogas is biological matter that comes from plants or animals, which can be living or not-living. This material, such as forest residues, can be combusted to create a renewable energy source.
Biogas contains less methane than natural gas, but can be refined and used as an energy source. Deep Natural Gas Deep natural gas is an unconventional gas. While most conventional gas can be found just a few thousand meters deep, deep natural gas is located in deposits at least 4, meters 15, feet below the surface of the Earth. Drilling for deep natural gas is not always economically practical, although techniques to extract it have been developed and improved.
Shale Shale gas is another type of unconventional deposit. Shale is a fine-grained, sedimentary rock that does not disintegrate in water. Shale gas is considered an unconventional source because of the difficult processes necessary to access it: hydraulic fracturing also known as fracking and horizontal drilling. This allows gas to flow more freely out of the well. Tight Gas Tight gas is an unconventional natural gas trapped underground in an impermeable rock formation that makes it extremely difficult to extract.
Acidizing is similar to fracking. An acid usually hydrochloric acid is injected into the natural gas well. The acid dissolves the tight rock that is blocking the flow of gas. Coalbed Methane Coalbed methane is another type of unconventional natural gas. As its name implies, coalbed methane is commonly found along seams of coal that run underground.
Historically, when coal was mined, the natural gas was intentionally vented out of the mine and into the atmosphere as a waste product. Today, coalbed methane is collected and is a popular energy source. Gas in Geopressurized Zones Another source of unconventional natural gas is geopressurized zone s. These zones form when layers of clay rapidly accumulate and compact on top of material that is more porous, such as sand or silt. Because the natural gas is forced out of the compressed clay, it is deposited under very high pressure into the sand, silt, or other absorbent material below.
Geopressurized zones are very difficult to mine, but they may contain a very high amount of natural gas. In the United States, most geopressurized zones have been found in the Gulf Coast region. Methane Hydrates Methane hydrate s are another type of unconventional natural gas. Methane hydrates were discovered only recently in ocean sediments and permafrost areas of the Arctic. When environmental conditions change, methane hydrates are released into the atmosphere.
The United States Geological Survey USGS estimates that methane hydrates could contain twice the amount of carbon than all of the coal, oil, and conventional natural gas in the world, combined.
In ocean sediments, methane hydrates form on the continental slope as bacteria and other microorganisms sink to the ocean floor and decompose in the silt. However, if the water becomes warmer, the methane hydrates break down. This causes causes underwater landslides, and releases natural gas. The gas, trapped in a frozen lattice of water, is contained at a much higher density than it would be in its gaseous state.
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