More than 85 percent of source of electricity ( electric power generated) in North America is produced by AC generators that are driven by steam turbines. Of this amount, more than 65 percent of the steam is produced by burning of fossil fuels, primarily coal and natural gas. The below chart illustrates the distribution of energy sources for electrical power generation in the United States. The proportions hold for North America and many European countries as well.
Coal is the dominant fossil fuel consumed to produce steam, accounting for more than 50 percent of all energy consumed. Despite its reputation as a constant threat to its neighbors, nuclear energy accounts for only about 20 percent of the energy consumed for electric power generation. The nuclear reactors function only as steam generators. Natural gas is in third place among energy sources for steam generation. Oil is also a fossil fuel accounting for only about 3 percent of the energy consumed for electric generation, but most of it is used to power gas turbines in turbine generators or as fuel for the diesel engines in engine–generator sets.
Coal remains the dominant fuel worldwide for producing the steam required for electric power generation, despite efforts toward using the so-called renewable resources: water power, wind power, and solar power. Coal retains its importance because it is plentiful and relatively inexpensive and because many industrialized countries have adequate domestic sources. The United States, for example, does not have to depend on foreign source of electricity for coal.
The burning of coal, oil, and natural gas provides 85 percent of the world’s commercial energy and 80 percent of all human-caused carbon dioxide emissions. Energy demand has nearly doubled in the past 30 years, and it is expected to increase another 60 percent by 2020. At present only about 10 percent of the world’s total energy is supplied by renewable energy, although in some countries its use is said to be growing rapidly. This figure is comparable to the approximately 10 percent figure for North America.
Hydroelectric power dominates among the renewable sources, but such alternative sources as wind turbines, solar cells, biomass fuels, and hydrogen fuel cells still account for only a few percentage points. Nevertheless, some studies have predicted that renewable energy source of electricity could provide half the world’s energy needs by 2050.
The burning of fossil fuels has been identified as the source of most of the world’s pollutants—sulfur dioxide, nitrogen dioxide, particulates, and ozone. These emissions have been blamed for air pollution, smog, and acid rain, and they have been identified as a major cause of death and serious health problems. However, motor vehicles produce far more of these pollutants than electric power plants.
Because it is easier to focus on power plants than vehicles, citizen groups, environmentalists, and health professionals have demanded more government regulations to control and possibly eliminate objectionable emissions from power plants. Despite the fact that the electric power industry has done much to reduce its emissions over the past 20 years, primarily as a result of new plant construction, friction between the government and the industry still exists.
Some power plant owners have argued that some pollution control regulations are excessive, impractical, and too costly to implement in older plants. They say that compliance would be so expensive that they would either have to shut down the plants or raise electric rates. They add that by shutting down the plants they would deprive many people living nearby of a reliable local power source, and that low-income families would be unable to pay the higher rates.
Some have said that the obvious solution is to build more nuclear power plants because they do not produce pollutants, but this argument does not seem to be a viable option. Nuclear power plants have long been controversial because they pose a threat to public safety and health due to the possibility of nuclear accidents caused by equipment failure or operator error. This hazard was amply demonstrated by the well-publicized reactor meltdown at Chernobyl in the Ukraine and the many casualties it caused.
More recently, the public has become alarmed over the accumulation of spent nuclear fuel at existing nuclear power plants and the hazards that are presented by transporting large quantities of radioactive waste material from those sites over the nation’s highways to a storage facility in the Nevada desert.
Another serious consideration has been the security at commercial nuclear plants, because of the threat of terrorist attacks on the reactors that could release radioactive materials into the air. All of these factors have led to more legal constraints on the operation of existing nuclear plants and any construction of new ones, along with pressure to decommission more existing plants.
As a result of all of this controversy, natural gas is reemerging as the fuel of choice for new power plants in the United States because its combustion by-products are lower in polluting gases and particulates than coal-fired plants. This means that the scrubbing and filtering systems need not be as comprehensive as those required for coal-fired plants.
Federal laws prohibiting the use of both natural gas and petroleum products as fuels for source of electricity were passed during the energy crisis of the 1970s. That prohibition was only lifted years later, in 1987. Many of the new power plants being built or planned will be capable of generating steam from either natural gas or coal. The choice will depend on the price and availability of natural gas.
Despite high hopes for the renewables, the most important of these sources, hydroelectric generation, has proven to be unreliable in times of drought. Moreover, environmental concerns about the damming of bodies of water large enough to produce electric power reliably and cost-effectively have led to public protests against new dam construction. Here again, there is pressure to decommission many existing dams to improve the water flow in rivers and restore now submerged lands to a natural condition.
Complaints about the unsightly appearance of wind turbines and the threats they present to migrating birds have cast a shadow on that technology. Hopes for economical power generation from large arrays of solar panels have been dashed, and research into source of electricity by ocean waves and tides has yet to prove its viability.
Coal-fired, hydroelectric, and nuclear power plants remain the most economical sources for electric generation on an hourly basis for 24-hr periods. Because oil-fueled turbine and diesel engine generators have a higher hourly cost, their operation is reserved for peak periods or as backup when other power plants are offline for repairs.
Newer technologies have been introduced to correct the pollutant emissions from existing coal-fired power plants. Improved fabric filters and electrostatic precipitators are removing particulates, the dust and smoke that affect air quality. An electrostatic charge is applied to the particulates in precipitators, and the particulates are then passed through an electric field where they are attracted to collecting electrodes. The electrodes are then mechanically jolted, causing the particulates to drop into collecting hoppers.
Various flue-gas desulfurization (FGD) processes including lime/limestone wet scrubbers and dry scrubbers are being installed to remove sulfur dioxide, the industrial pollutant that forms acid rain. In addition, catalytic reduction systems (SCRs) are reducing the emission that reacts with sunlight to create ground-level ozone, or smog .
References :
- Handbook of Electrical Design Details(HEDD),