In the United States, power is generated from various sources. In 2014 alone, 4,093 billion KWh units were produced. The majority of these came from fossil fuels while renewable energy sources accounted for around 17%. The high percentage of fossil fuels used for electric power generation as compared to renewable energy sources leads to a more a pronounced environmental impact. The table below shows the percentage of the total power produced by the four major energy sources in 2014.
Negative effects of power production
Coal power production
Coal is a fossil fuel that is combusted in steam boilers to generate steam for driving steam turbines. Fossil energy is stored in chemical bonds in hydrocarbons. When the fuels are combusted, the bonds are broken down with release of carbon and methane gases into the atmosphere. Carbon is discharged from the fuels in the form of carbon dioxide or carbon monoxide. It is estimated that 3.2 billion tons of carbon dioxide are produced annually with 2.5metric tons emanating from fossil fueled power plants (Green Energy Choice par.3).
Carbon and methane are greenhouse gases and their presence in the atmosphere causes the greenhouse effect. Greenhouse effect occurs when a gas layer forms around the earth’s atmosphere and traps reflected heat from the surface of the earth preventing it from escaping into space. The heat accumulates in the atmosphere leading to global warming, which has numerous negative effects on the environment. Higher global temperatures lead to melting of polar ice and the subsequent rise in sea levels. Reduction of the polar ice threatens animal species that live on ice habitats such as the polar bear. Also, rising sea levels displace people living in coastal regions and cause encroachment of dry land by sea water (Green Energy Choice par.5).
Other minor environmental impacts of coal combustion include discharge of combustion waste products such as soot and ashes, also referred to as particulate matter, into the atmosphere, which can cause respiratory problems in humans (Green Energy Choice par.7).
Natural gas is a gaseous fossil fuel formed by the pressurization of organic matter under intense heat for thousands of years. The gas can be used for electric power generation in three ways; through combustion in steam boilers that drive steam turbines, burning the fuel in combustion turbines, and burning the fuel in combustion turbines and using the flue gases to produce steam for driving steam turbines (EDF Energy par. 2 ).
The use of natural gas for power production is accompanied by several environmental impacts. Toxic emissions, such as nitrogen oxides and carbon dioxide, are the major challenge in natural gas use. Combustion of natural gas also produces methane, but in lower quantities as compared to other fossil fuels such as coal and heavy fuel oil. Methane is emitted when the fuel is not burnt completely or when leakages occurs during transportation.
Also natural gas extraction involves fracking, whereby pressurized fluids are pumped into natural gas wells in order to fracture shale rocks so that natural gas can seep from reservoirs and into the well. Fracking has been condemned by environmental activists worldwide because of the potential danger of ground water contamination (EDF Energy par. 12).
Natural gas fueled power plants require water to cool the boilers and the whole energy generating system. Removal of water from water bodies can adversely affect aquatic life such as killing fish, which would further affect the human population which depends on the water sources.
Cooling water in natural gas plant accumulates chemical substances with continued use. To avoid damage to the system through corrosion, the water is discharged to water bodies and replaced with fresh water. The pollutants in the discharged water make it toxic and harmful to aquatic life.
Environmental impacts of nuclear power generation
Nuclear energy is produced when radioactive materials such as radium go through fission chain reaction and release thermal energy. The produced energy is used to generate steam, which is then used for power production.
Nuclear energy, as opposed to fossil fuels, does not cause the discharge of toxic or greenhouse gases into the environment. The major risk associated with nuclear power plants is the danger of reactor accidents which would cause leakage and spillage of radioactive materials into the environment. In the case of a catastrophic nuclear reactor accident, the damage caused by the ensuing contamination would be so great that it can render the surrounding region inhabitable for several decades. The worst recorded nuclear power plant accident occurred in Chernobyl, Ukraine in 1986. The subsequent fallout affected Ukraine, Belarus, and Russia. The accident caused the death of 31 people working on the plant and displaced 350,400 people. It cost the Ukrainian government 18 billion rubles to contain the contamination. Long term effects of the accident include children born with disabilities and high cases of cancer (U.S. Environmental Protection Agency par. 9).
Also, nuclear energy is accompanied with the problem of nuclear waste disposal. The waste has to be disposed in special structures to avoid contamination. Most nuclear fuel waste products are stored in airtight steel and concrete containers filled with water. The wastes accumulate continuously which creates the need for the expansion of the waste storage capacity.
Nuclear power plants require large amounts of water to cool the reactors. Therefore, the plants have to be situated near a water body such as a lake or a large river. The plants draw a large amount of water from these water bodies which adversely affect aquatic life and plants. Also, nuclear plants discharge water contaminated with salts and heavy metals. The waste water is also at a higher temperature and contains traces of radioactive elements such as tritium. When this wastewater is drained to water bodies, it harms aquatic life or causes abnormal microbial activities which adversely affect the quality of water (U.S. Environmental Protection Agency par. 9).
Hydropower plants convert potential energy of water stored in elevated dams to kinetic energy, which is then used to drive turbines coupled to generators.
Hydro power is a form of renewable energy which means it has minimal environmental impacts. The major drawback of hydro power comes from the construction of dams which acts as a water reservoir and creates the required water head with enough potential energy. Construction of dams leads to flooding of land which has several negative environmental impacts. Large dams destroy forests, encroach on agricultural land, wildlife habitats, and ruins scenic lands. Huge dams, such as the Three Gorges Dam in China, can displace entire communities.
Also, hydropower dams negatively affect aquatic life. The turbines in power stations kill fish and other small organisms when the water hits the turbine blades. Dams also cause water stagnation, which leads to sediments and nutrient accumulation. The high nutrient levels encourage water weeds and algae to grow, which may choke out aquatic life and water plants. The decomposition of such weeds through microbial activity reduces the level of dissolved oxygen in the water and causes the emission of methane, a greenhouse gas (Union of Concerned Scientists par. 6). Dams also cause water loss through evaporation at a faster rate than it’s replenished by the inflowing rivers.
In addition, holding too much water in dams may cause downstream rivers to dry out, which may adversely affect plants and animals that depend on the water. Also, reservoirs cause low water temperatures, which when coupled with the low oxygen levels threaten downstream aquatic life.
Greenhouse gases are emitted from hydropower plants during the actual plant construction and dismantling. These gases are also emitted during the plant’s operation. The total greenhouse gases produced during a plant’s construction, operation, and dismantling is referred to as life-cycle greenhouse emissions. The amount of the emissions depends on the reservoir size and the size of land flooded by the reservoir. Small river run-off plants produce about 0.03 pounds of carbon dioxide per kWh while large plants produce 0.06 pounds per kWh (Union of Concerned Scientists par. 5).
Mitigation of environmental impacts of power generation technologies
Environmental impacts of coal reduction involves reducing carbonaceous gases and particulate matter emission.
Figure 1: Schematic diagram of a coal power plant. Source: U.S. Environmental Protection Agency
Greenhouse emissions from coal power plants can be reduced through the use of efficient turbines and combustion systems. Efficient power production will lower emissions per kWh generated. Alternatively, carbon capture and storage (CCS) can be used to remove carbonaceous compounds from the flue gases before discharging them into the atmosphere. CCS is a new technology which is in the nascent stages of development.
The flue gases from coal power stations also contain particulate matter. Particulate matter is removed by installing electrostatic precipitators or dust collectors. Dust collectors increase the quality of gases released from industrial processes by removing suspended particles in gases. Dust collectors are designed to support high flow rates of flue gases. The dust collector system consists of blower, a dust filter, a system to clean the filter, and a dust removal system. An electrostatic precipitator removes particulates from flowing flue gases through the use of induced electric charge. Precipitators attract particles of gases flowing through their chambers and make them stick on energized surfaces.
Figure 2: Image of a dust collector. Source: Green Energy Choice
Figure 3: Schematic diagram of an electrostatic precipitator. Source: Green Energy Choice.
Natural gas plants
Scrubbers are used in natural gas plants to remove toxic and greenhouse emission. Chemical reagents are reacted with the constituents of the waste gases to form nontoxic gaseous products. Scrubbers are also used as heat exchangers to collect heat from waste gases. This improves efficiency and lowers the production cost of the plant.
Figure 4: Cutoff image of a gas scrubber. Source: Green Energy Choice.
Figure 5: Schematic diagram of a labeled natural gas power plant. Source: EDF Energy
The use of efficient natural gas to power plants, such as the one shown in the figure above, with a heat recovery system improves energy conversion efficiency and hence less fuel is spent per power unit produced. The use of efficient gas plants will reduce natural gas demand, which in turn will eliminate the need for fracking. Also, removal of heat from waste water before discharging it to water bodies through heat recovery systems will reduce the adverse effects of discharging hot water to water bodies.
The major consideration in hydropower plant construction is land usage. A hydro plant should use as little land as possible. This is achieved by locating plants in hilly regions with deep canyons that can hold a high water head. Flat areas require expansive land to hold the same amount of water. Locating plants in hilly regions reduce land required for the reservoirs and subsequently the amount of money required for purchasing the land from the individual owners. Minimal land use will also reduce other negative externalities such as water loss due to evaporation, emission of methane gas, and encroachment of agricultural land (Union of Concerned Scientists par 12).
Also, improvement of water quality is a factor which influences plant design. Water quality in hydro power plants is raised through aerating turbines or water intake design. The low dissolved oxygen levels in the water discharged from hydro plants can be raised by incorporating aerating turbines into the turbine system.
Figure 6: Diagram of a hydro power plant. Source: VOITH.
The aerating turbine is placed along the discharge pipe as shown in the diagram below.
Figure 7: Cross-section of an aerating turbine. Source: VOITH.
Control of dam outlets is done to prevent downstream water bodies such as rivers from drying up. To achieve this, dam operators are required to release a minimum amount of water to avoid hoarding all the water in the reservoirs and starving downstream water requirements.
Also, to avoid harm to aquatic life such as fish, the water is sieved off before it’s fed to the penstocks. Penstocks are large pipes that accelerate the speed of water, thereby converting potential energy in the water to kinetic energy. Strainers of different sizes are introduced at different stages of the water intake to avoid unwanted matter from getting into the turbines (Union of Concerned Scientists par. 14).
Nuclear power plants
Figure 8: Schematic diagram of a nuclear power plant. Source: U.S. Environmental Protection Agency
Nuclear power plants require large amounts of cooling water. The volume of water drawn from water sources can be minimized through recycling of the cooling water by circulating it in a closed loop in the plant.
The reactors are housed in airtight chambers which contain the radiation from the radioactive fuel elements. The rectors are enclosed in thick steel and concrete structures which prevent leakage of radioactive gases. In the United States, power plants are responsible for the disposal of waste materials that they produce. The specialized waste containers are located on the plant site and they are under the care of the plant operators (U.S. Environmental Protection Agency par. 3).
Nuclear plants have intricate automated fail-safe systems that remotely monitor plant parameters to avoid accidents from happening. A lot of investment is also done during plant design and construction to avoid radiation leakages and to ensure steam pressure containment (U.S. Environmental Protection Agency par. 5).
Figure 9: Exploded image of a nuclear waste container. Source: Nuclear Energy Institute
Figure 10: Nuclear waste containers in a nuclear power plant site. Source: Nuclear Energy Institute
Summary and conclusion
All energy production technologies are associated with external costs on the environment. To mitigate these externalities, investment grade modifications of the power generating systems are required. Plant modifications such gas scrubbers, dust collectors, electric precipitators, heat recovery devices, and cooling towers reduce environmental pollution. Also, some of the plant components, such as heat recovery devices reduce operational costs by improving efficiency. High plant efficiency reduces amount of greenhouse emission per unit of power produced and therefore lowers the environmental impact of the power production activities. Power producers are ethically and legally obligated to ensure that their activities do not pose harm to their employees, the larger population and to the environment even if it means sacrificing their profits.
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