Notes

Nonrenewable Resources and Fossil Fuels
Earth’s growing population needs sources of energy to support it. These can be categorized into two types:

Renewable energy sources that are available in abundance (such as solar and wind energy), or those that can be replaced over time by natural processes (such as trees); and
Nonrenewable energy sources that are available in limited or fixed supply, which cannot be replaced in our lifetime (or many, many lifetimes), such as coal, oil, and nuclear energy.
Countries choose their energy sources based on some clear factors: resource availability, technological capability, and the cost of extraction and transportation. Japan, for example, has no natural coal or oil deposits. It has invested heavily in nuclear energy as a primary power source.



Renewable Energy Sources
Sources of renewable energy can be further categorized into those that are available in abundance (and are relatively quick to renew) and those that are slower and require careful planning to ensure continued supply.

Abundant sources: Some natural sources have become more readily available as technological capabilities have increased. They include solar, wind, hydroelectric, geothermal, tidal, and wave energy. Each taps into energy that is constantly available and isn’t depleted by use.

Slower sources: Trees harvested for wood, as well as other plants and vegetation, are known as biomass. They can be replaced as a sustainable fuel source. However the rate of planting should match or preferably exceed the rate of consumption.

Nonrenewable Energy Sources
As the name implies, nonrenewable energy sources will run out and cannot be replaced in our lifetimes. They took millions of years to come to exist in their current form.

Most nonrenewable energy sources are fossil fuels. Some fossil fuels are coal, oil, and natural gas. They were formed from organic matter (animals, plants, algae, and plankton). This matter was buried in sediment and transformed under immense heat (50–150°C) and pressure under the Earth’s surface.

Nuclear energy is also considered to be a non-renewable energy source. The atomic energy released in the process is abundant. However, the raw materials needed to release that energy are limited in supply.

Fossil Fuels
These byproducts of fossilized organic matter are available in three different physical states; solid (coal), liquid (oil), and gas (natural gas). They were formed under the Earth’s surface. Hence they require intensive and often expensive extraction processes, such as drilling or mining.

Carbon is the common element in fossil fuels. The period during which fossil fuels were formed is called the Carboniferous period, as many coal formations were deposited in this period. This period ranges between 360 and 300 million years ago.

Burning these fossil fuels as an energy source produces carbon dioxide. Carbon dioxide is one of the greenhouse gases that contribute to the trapping of radiant heat from the Earth’s surface. This heat in turn raises planet-wide temperatures.

Burning coal has even greater impact on the atmosphere through the production of sulfur. The release of sulfur again increases air pollution.



Nuclear Energy
Nuclear energy itself is a renewable energy source. It results from the splitting, or fission, of uranium atoms. The uranium used in that process, however, is non-renewable.

Uranium is found in the mineral pitchblende (a mix of uranium oxides) all over the world. However, the production of nuclear energy requires a specific isotope, uranium-235. Nuclear energy produces radioactive waste that can be harmful to humans and to the environment.

Nuclear energy is considered to be a “cleaner” energy source. It doesn’t pollute the air or produce greenhouse gases. It does require complex processes to construct the reactors and to operate them safely.



Coal
Coal is a black, rock-like fossil fuel made up of different elements; namely carbon, hydrogen, oxygen, nitrogen, and amounts of sulfur that vary according to the type of coal. The precursor to coal is peat, a brown, soil-like substance. Peat consists of the same decomposed vegetable matter that accumulates in the absence of oxygen. Coal is formed under intense heat and pressure. Peat is found in water-saturated environments called peat bogs. Here it is cut, dried, and used for fuel.

Coal can be found throughout the world and in many of the continental 48 states of the United States. As a solid product, it can be shipped by truck, train, and boat. It can even be ground into a powder, mixed with water, and pumped through pipelines in slurry form.

The processes for extracting coal from the ground vary according to the type of coal being extracted.

Types of Coal
Coal is classified into four main types depending on two factors: the types and amounts of carbon contained in the coal, and the amount of heat energy each type can produce.

Anthracite
This type of coal has the highest heating value (20–28 million British Thermal Units (BTU)/ton). It contains 86–97 percent carbon. Its high heat value and clean burning profile makes it particularly suited for the metals industry. It is, however, hard to ignite and difficult to work. The burnt coal ash has to be separated from the burning coal by means of a grate.

Anthracite accounts for only one percent of the amount of coal mined nationwide. Deposits of anthracite are found in northern Pennsylvania. The deposits are typically found at the lowest depths (around 1,000 feet) and may require deep mine shafts for extraction.


Bituminous
Bituminous coal is softer than anthracite. It burns with a smokier yellow flame as a result of its high sulfur content. It has a lower carbon content (45–80 percent) and produces less heat at 19–32 million BTU/ton.

This type of coal is the most commonly found of US coal deposits. It is found mostly in the Appalachian mountains, the Great Plains, and the Colorado Plateau. It is used primarily to generate electricity in coal-fired power stations. It is also converted to coke for use in the steel industry.

It is found at shallower depths than anthracite and may be extracted through strip mining or mine shafts. As the oldest coal type found in the United States, bituminous coal makes up about 45 percent of national coal production.

Subbituminous
As its name suggests, subbituminous coal is close in type to bituminous coal. It is typically dull black in color with a lower carbon content (35–45 percent) and a lower heat value (16–24 million BTU/ton).

The primary attraction of subbituminous coal is that it typically has a lower sulfur content, so it burns more cleanly than bituminous coal. It produces less heat. It is found closer to the surface, which facilitates less expensive shallow mining. The lower cost of extraction makes it very attractive to the electricity generating industry. For this reason, subbituminous coal makes up 47 percent of US coal production.




Lignite
This type of coal is found closest to the surface. It can be extracted by open strip mining at the lowest extraction cost. Lignite coal’s proximity to the surface means that the deposits received the least amount of heat and pressure during formation. As a result, the coal has the lowest carbon content (20–35 percent). It only produces 9–17 million BTU/ton of heat value.

As the youngest of the coal types, lignite is soft and brown. It comprises primarily compressed, dehydrated wood material. It is closest in composition to peat. It is often referred to as brown coal and is used mainly in electricity generation.

Lignite accounts for only seven percent of US coal production. Lignite deposits can be found in Texas, Montana, North Dakota, and the Gulf Coast region.

Side Effects
Coal mining is dirty and dangerous work. Deep mines operate under constant risk of collapse. They are also a risk of fire if any of the combustible gases that are found in coal deposits ignite.

Burning coal to produce energy also has negative effects on the environment:

Mining subterranean coal exposes sulfide minerals to water and air. This oxidation produces acid rock drainage (ARD), which introduces both acidity and dissolved metals into local water sources. It harms fish and aquatic life, and raises the toxicity of the water supply.
Carbon dioxide emissions contribute to climate change and acid rain. If the coal has high sulfur content, such as bituminous coal, that sulfur will contribute to higher pollution levels.



Natural Gas and Oil
Coal supplies are estimated to last for about another 300 years. The future for the other two fossil fuels—natural gas and oil—is not so positive. Natural gas, based on known deposits, is estimated to last for about 70 years.

Crude oil has become increasingly difficult to extract. It now requires deeper and more remote drilling platforms to reach new oil reserves. Some reserves may be too difficult to reach and extract based on current engineering capabilities. Even then, many energy analysts believe that we have already passed “peak oil.” Peak oil is the point at which the maximum rate of oil extraction is reached. They forecast that there may be as little as 50 years of oil left.

Natural Gas
Coal’s composition is dominated by carbon. Similarly, the fossil fuel natural gas consists mainly of methane. Methane is a compound with one carbon atom and four hydrogen atoms. It was formed in the same type of process as coal: Decaying remains of plants and animals were buried by sand and silt and transformed by pressure and heat.

As it formed, natural gas moved into cracks and spaces in the surrounding rock. This movement happened along the smaller spaces (pores) in sedimentary rock formations such as sandstone and shale.

It is the presence of natural gas around coal deposits that can place mining operations at high risk of fires and explosions.

Locating and Using Natural Gas
Energy companies turn to the services of geologists. The geologists identify rock formations that are ideal for natural gas deposits. Those formations can be on land or deep under the ocean floor.

Once extracted, natural gas is highly portable. It can be piped into storage containers. These containers can feed residential supplies for heating and cooking. It can also be burned as a fuel source to produce electricity.

Natural gas is odorless and colorless. Gas suppliers add a harmless chemical called mercaptan. It gives the gas a distinct odor in case of gas leaks. The smell is similar to rotten eggs.

Fracking
Extracting natural gas is not as simple as drilling a well and pumping out the gas. There may be pockets or reservoirs of gas. However, the majority of natural gas deposits have to be extracted from sedimentary rock or shale. This extraction is achieved by a process called hydraulic fracturing, or “fracking” for short.

The gas is dispersed throughout the rock. The most cost-effective way of releasing it is to fracture the rock. It is done using a mixture of water, chemicals, and sand under high pressure.

Over the last three decades, the technological capability of this process has increased significantly. Now the vertical wells are just the entry point. The drilling can proceed in any direction once the correct depth has been reached.



Dangers of Fracking
Fracking may be cost effective and highly lucrative for some landowners, if they are lucky enough to sell the mineral rights below their land. The process in itself has generated strong criticism.

There are up to 600 different chemicals in the “fracking fluid” used to disrupt the sedimentary rock or shale. They includes known carcinogens such as lead, mercury, and formaldehyde.
It can take between one and eight million gallons of water to complete each fracturing project.
Methane gas can leak from the well. It can contaminate local groundwater and drinking water sources.
Waste fluid from the fracking projects is left to evaporate in open surface pits. It leads to the release of harmful volatile organic compounds (VOCs) into the atmosphere.
Drilling in shale deposits has also been linked to localized earthquakes. Earthquakes have been seen in areas that are not linked to natural seismic fault lines.

Crude Oil
Oil was created as a fossil fuel by the same type of process that created coal and natural gas. It can be found in large underground reservoirs on land (as in the large Middle Eastern oil fields). It can also be found on the ocean floor, such as in the North Sea or the Gulf of Mexico.

There are many stories of oil bubbling up through the surface driven by subterranean pressure. These stories may suggest that oil is easy to extract. In reality, high demand and consumption levels are forcing energy companies into more extreme environments. They have even covered areas such as the Arctic Circle to find new deposits.

Oil deposits are measured in terms of barrels that contain 42 gallons of crude oil. However, they ultimately produce up to 45 gallons of refined petroleum products.



Oil Products
Oil may be a fossil fuel, but it would be incorrect to treat it as one homogeneous liquid. There are many different types of oil based on some unique factors: the geographical point of extraction and the relative viscosity (how easily it flows), volatility (how quickly it evaporates), and toxicity (how poisonous the oil may be if it spills).

There are over 160 different types of oil traded for commercial use. There are, however, only three that are widely used for production, refinery, and consumption:

West Texas Intermediate (WTI) is the highest-grade crude oil. It is refined primarily into high-quality gasoline or petroleum products.
Brent Blend is a blend of crude oil from 15 fields in the North Sea. It is refined into gasoline and other distillates.
OPEC Blend represents the Organization of Petroleum Exporting Countries. It consists of seven different crude oils from all over the world.


Side Effects of Crude Oil
As a fuel source, oil can be distilled into gasoline, diesel oil, and heating oil. Further distillation can produce a myriad of products including lubricants, plastics, and clothing items.

However, the side effects of oil production and consumption have proven to be very harmful to the environment:

Carbon dioxide emissions from gasoline engines contribute to the trapping of radiant heat from the Earth’s surface.
Poor safety and maintenance practices are a risk at oil drilling sites, both on land and at sea. They may lead to spills that harm ecosystems and pollute groundwater supplies.
The price of oil is a key driver in the health of global economies. Low oil prices can reduce transportation costs. On the other hand, they may also result in significant labor force reductions and business closures in the oil industry.


Nuclear Energy
Nuclear energy is not a fossil fuel. It is the energy that holds the nucleus of an atom together. As such, it could qualify as a renewable energy source under the same “abundant” classification as solar, wind, and water power.

Nuclear energy is classified as a nonrenewable energy source, because the energy is released when uranium atoms split. As uranium atoms split easily, it the most used fuel source. Nuclear energy is the result of this splitting, or fission.

Uranium is a common element found all over the world. Uranium-235 is a specific type of uranium used to produce nuclear energy. Uranium-235 is a rare element.

Only one percent of global uranium deposits consist of uranium-235.

Uranium Mining and Enrichment
Traditional uranium mining involves grinding the mineral and mixing it with water to produce a slurry. This slurry is then leached with sulfuric acid to dissolve the uranium oxides. A new method, called in situ leaching, is in practice in uranium mining. This method involves injecting the groundwater into the uranium ore without any major ground disturbance or crushing of the mined ore.

The dissolved uranium is filtered and separated by ion exchange. When dried, it becomes a uranium oxide concentrate called yellowcake.

The amount of uranium-235 in the yellowcake has to be raised from 0.7 percent to between 3.5 and 5 percent. For this purpose, the uranium is converted into gaseous form (uranium hexafluoride). It is processed through centrifuges that separate the uranium-235 isotope from uranium-238 (which then becomes depleted uranium). Afterward, it can be introduced into the nuclear energy production process.



Nuclear Fission
The enriched uranium is then transported to a fuel fabrication plant. The plant converts it into uranium dioxide powder, which is formed into fuel pellets. The pellets are then heated to make a hard ceramic material. It forms fuel rods, which are grouped together to form fuel assemblies.

In nuclear power plants, those fuel assemblies are immersed in water. Some are designed as boiling water reactors, and others are designed as pressurized water reactors. The high pressure prevents the water in the reactor from boiling. The superheated water is used to boil water in a secondary system.

When the uranium atoms are bombarded with neutrons, fission occurs. Fission releases energy, which heats the water. The assemblies can be inserted or withdrawn to slow or accelerate the fission reaction.

Other than the nuclear component, the energy production process is very similar to traditional fossil-fuel power stations. The heat produced by the fission turns the water into steam that drives a turbine. The turbine spins a generator to produce electricity.


Clean Energy
Advocates of nuclear energy production argue that their power plants produce clean energy. The steam is recycled in a cooling tower that either returns the water to the reactor or evaporates into the atmosphere.

There is no air pollution or production of greenhouse gases that can contribute to climate change. As such, the power plants can be built in rural or urban areas without inflicting the same damage on the local environment as drilling or strip mining. It doesn’t require the transportation of fossil fuels.

There are currently 99 commercial nuclear reactors in the United States. They account for about 20 percent of the nations total electricity generation.




Radioactive Waste
All electricity generation plants produce waste. Nuclear power plants produce a smaller quantity by volume: 27 tons of used fuel as compared to 400,000 tons of ash from a coal-fired power station. However, the used fuel from the nuclear plant is both radioactive and highly toxic.

Fuel rods are recycled and re-used to reduce the amount of high-level waste (HLW) produced. The waste must then be reprocessed and stored in vast water tanks. This method protects the environment from radioactive isotopes.

It can take 40 to 50 years before the radioactivity levels have fallen to a point where the fuel can be safely handled. It is then placed in corrosion-resistant containers and can be stored deep underground in stable rock structures.High-Risk Energy Production
Clean energy may be an attractive proposition for countries that don’t have vast reserves of fossil fuel sources. However, nuclear energy production is not without considerable risk.

Reactor malfunctions demonstrated the catastrophic risks that nuclear energy production presents. This risk was seen at Three Mile Island in Pennsylvania in 1979, Chernobyl in Russia in 1986, and, most recently, Fukushima in Japan in 2011.

When cooling processes fail, the reactors can overheat in a meltdown scenario. A meltdown can release radioactive coolant liquid into local water sources and radioactive gases into the atmosphere. Gases are released as part of the steam clouds generated by the meltdown.

This release of radioactive elements can do irreparable harm to the environment. It can affect local water supplies, wildlife, and plants. It can render land surrounding the power plants uninhabitable.