How does a coal-fired power plant work?
The following describes the key components in coal-fired generation. For oil-fired or natural gas-fired generation, the basic process remains the same.
- Coal supply — After haulers drop off the coal, a set of crushers and conveyors prepare and deliver the coal to hoppers at the power plant. The coal flows from the hopper and is crushed to a few inches in size.
- Coal pulverizer — Conveyor belts dump coal into a pulverizer, which grinds the coal to a fine powder. Hot air from nearby fans blows the powdered coal into large boilers.
- Boiler — The boiler walls are lined with many kilometres of pipe filled with water. As soon as the coal enters the boiler, it instantly catches fire and burns with high intensity. The temperatures inside the furnace may climb to 1,300° C. This heat quickly boils the water inside the pipes, changing it into steam.
- Precipitators and stack — As the coal burns, it produces emissions (carbon dioxide, sulphur dioxide and nitrogen oxides) and ash. The gases, together with the lighter ash (fly ash), are vented from the boiler up the stack. Large air filters called electrostatic precipitators remove nearly all the fly ash before it is released into the atmosphere. The heavier ash (bottom ash) collects in the floor of the boilers and is removed. Scrubbers and other pollution control equipment are used to reduce emissions into the air.
- Turbine and generator — Meanwhile, steam moves at high speed to the turbines. These massive drums have hundreds of blades turned at an angle, like the blades of a fan. As jets of high-pressure steam emerge from the pipes, they propel the blades, causing the turbine to spin rapidly. A metal shaft connects the turbine to a generator. As the turbine turns, it causes an electro-magnet to turn inside coils of wire in the generator. The spinning magnet puts electrons in motion inside the wires, creating electricity.
- Condenser and cooling water system — Next, the steam exits the turbines and passes over cool tubes in the condenser. The condenser captures the used steam and converts it back to water. The cooled water is then pumped back to the boiler to repeat the heating process. At the same time, water is piped from a reservoir or river to keep the condenser constantly cool. This cooling water, now warm from the heat exchange in the condenser, is released from the plant.
- Water purification — To reduce corrosion, plants purify water for use in the boiler tubes. Wastewater is also treated and pumped out to holding ponds.
- Ash systems — Ash is removed from the plant and hauled to disposal sites or ash lagoons. Fly ash is also sold for use in manufacturing cement.
- Transformer and transmission lines — Transformers increase the voltage of the electricity generated. Transmission lines then carry the electricity at high voltages from the plant to substations in cities and towns.
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