Fuels Fire Power Plants




Fire is a phenomenon of combustion, usually the reaction of a substance with oxygen, producing heat, light, and gases. It has been used for entertainment, religious ceremonies, destruction, and energy. Typical fires involve wood, paper, or hydrocarbon fuels combining with oxygen in air, but many substances such as metals burn in atmospheres of chlorine or fluorine.

Fire, considered by ancient Greeks to be one of the four elements, has been worshiped and is often invoked in religious ceremonies. Fires provide a source of energy as well as adding to the entertainment of an evening at home or around a campfire.

The fire from candles has provided light for centuries. Capillary action carries melted wax along the wick from the candle to the flame. As the wax burns, it produces a characteristic teardrop-shaped flame as air is heated and expands, moving upward. In the microgravity of space, candle flames slightly influenced by gravity are round or dome-shaped.

Oxidation is a chemical process in which the substance being oxidized loses electrons to another substance that is simultaneously reduced. Magnesium metal burns vigorously in air, producing flames and magnesium oxide. The flames produced in this reaction are caused by heating magnesium oxide particles until they incandesce, radiating visible light. Similarly, when a hydrocarbon fuel burns, particles of carbon incandesce, emitting light and passing into the surrounding air as smoke.

Efficient and complete combustion of a hydrocarbon such as methane yields carbon dioxide and water:

CH 4 + 2 O 2 → CO 2 + 2 H 2 O + heat

Incomplete combustion caused by insufficient oxygen yields water and carbon monoxide or carbon in place of carbon dioxide. Small amounts of carbon monoxide in air are probably harmless, but carbon particles form soot, which often contains dangerous polycyclic hydrocarbons and may carry dangerous gases into the alveoli of lungs. Carbon monoxide is a colorless, odorless, poisonous gas. Furnaces are designed to burn natural gas with a blue flame, indicating production of little carbon, and probably little carbon monoxide.

Power Plants

Fire also provides energy for power plants. Energy is defined as the ability to do work, power is defined as the rate of doing work. An incandescent light bulb is rated in terms of power. A 100-watt bulb uses power at the rate of 100 watts. Power is commonly measured in watts or joules. One watt is equivalent to 1 joule per second, so a 100-watt incandescent bulb would use 100 joules of energy per second. Burning the electrical bulb for ten hours uses 1 kilowatt-hour of energy at the rate of 100 watts per hour. Homeowners purchase electrical energy, not power.

Power plants typically consist of a generator to produce electricity and a power source to operate the generator. The source of energy may be nuclear reactions or fossil fuels such as natural gas, oil, or coal. The fuel may be burned to boil water, producing steam, or burned in a diesel or internal combustion engine to turn the generator. Most thermal power plants burn fuel to boil water, forming steam, then pass the steam through turbines that spin generators, producing electricity.

The location of power plants is determined in part by the need for electricity, the availability of fuel, and water for cooling. The Four Corners power plant located at the junction of Colorado, New Mexico, Arizona, and Utah is one of the largest plants in the United States. It burns 28,000 tons of coal per day and produces 2,040,000,000 watts of power. Located far from urban areas, the plant's emissions originally seemed to pose less danger to humans than urban plants, but environmental concerns soon demanded more stringent emission controls. Emissions from the plant, located in a rural area, are now more carefully controlled, fuel from nearby coal mines is readily available, and cooling water from nearby rivers makes the energy-generation process more efficient.

Electrical energy is fed into power transmission grids that span several states. A number of power plants produce electricity that goes into the grids and is used by consumers many miles away. Distribution of alternating current allows the voltage to be stepped up by passage through transformers prior to distribution. High-voltage electricity can be transmitted more efficiently than low voltages, and the voltage is reduced through step-down transformers and transferred to distribution grids before use by consumers.

Nuclear power plants use fissionable materials such as uranium-235 as sources of energy. In the core of a nuclear power plant, rods of uranium dioxide (UO 2 ) are placed in a matrix containing moderators such as heavy water or graphite that slow neutrons so they can be captured. The neutrons impact uranium nuclei, splitting them to release lighter nuclei and converting a small amount of mass to energy. In order for a chain reaction to occur, a critical mass of fissionable material must be present.

Nuclear power plants are designed to prevent accidents such as meltdown by careful control of fuel-rod placement and positioning of control rods made of boron or other materials that have high affinity for neutrons. If the core of the reactor should become overheated, the fuel rods are automatically pulled out of the reactor and the control rods drop in, cutting the supply of neutrons. In addition, the core of the reactor is positioned over a number of separate wells into which components would fall, separating the fissionable materials to less than a critical mass.

Fusion promises to provide a nearly inexhaustible supply of hydrogen fuel as well as less radioactive waste, but temperatures of fusion reactions are too high for present materials, and the huge amounts of energy needed to start fusion reactions would explode or melt any known construction materials. The fires of nuclear fusion in our Sun provided energy for early humans long before they discovered the art of combustion.

SEE ALSO Chemical Reactions ; Chemistry and Energy ; Explosions ; Fossil Fuels .

Dan M. Sullivan

Bibliography

Bodansky, David (1996). Nuclear Energy: Principles, Practices, and Prospects. Woodbury, NY: American Institute of Physics.

Termeulen, Heinz (2001). One Hundred Years of Power Plant Development. New York: American Society of Mechanical Engineers.



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