How Do Fossil Fuels Provide Electricity?

Two-thirds of the electricity produced in the world comes from fossil-fuel generation. Fossil fuels include coal, oil and natural gas. They are formed from the organic remains of plants and animals that lived millions of years ago. Most often, fossil fuels are found under the earth's surface and must be extracted by digging or drilling. About half of the electricity used in the United States comes from burning coal, so a coal-fired power plant will serve to illustrate the principles of how fossil fuels produce electricity.

Combustion

• The fundamental process in producing electricity from fossil fuels is combustion. The coal, oil or gas is burned in a power plant, which is a machinery system for converting the energy stored in fossil fuels to mechanical or electrical energy. The byproducts of burning fossil fuels include carbon dioxide, sulfur dioxide, nitrous oxide, methane and particulate matter, all of which are harmful to the environment and particularly impact air quality.

Pulverized Coal

• Lumps of coal extracted from the earth in surface or underground coal mines are pulverized, or milled, to create a powder. Pulverized coal has more surface area than lumps of coal, so it burns more readily. The coal powder is blown into a combustion chamber (a boiler, essentially) where it mixes with oxygen and where it is burned at a very high temperature, producing hot gases.

Steam Turbine

• Inside the boiler are interconnected tubes filled with water. The hot gases generated by burning the coal heat the water in the tubes and turn it into steam. The steam, under high pressure, passes into a steam turbine, which in its most basic form is a cylindrical drum with blades attached to the outside. The turbine is mounted on a shaft. The steam shoots into the chamber containing the turbine, hits the blades and causes the turbine and the shaft to turn at high speeds. The steam then goes into a condenser where it turns back into water, which is directed back into the tubes to be used again. The heat released by the steam as it cools goes into a cooling tower, where it flows into the atmosphere.

Generator

• A generator is mounted at one end of the shaft. The generator consists of a system of wire coils. When the wires rotate in a strong magnetic field, electricity is produced. The electricity is transformed into high-voltage power and sent along transmission lines to our homes and businesses, where it is converted into lower voltages so that it can be used safely.

Variations

• Many variations exist on the process of burning fossil fuels to produce electricity. For example, an Integrated gasification combined cycle power plant turns coal into gas and removes the impurities from the gas before burning it to produce electricity as a means of reducing pollutants released into the air. In many natural gas generation plants, hot gases, not steam, are used to turn the turbines. Combined-cycle natural gas power plants use gas to turn a turbine and then redirect waste heat from that process to produce steam that runs a steam turbine, thereby increasing the efficiency of the process.