How does a thermal power plant work?
In thermal generating plants, fuel is converted into thermal energy to heat water, making steam. The steam turns an engine (turbine), creating mechanical energy to run a generator. Magnets turn inside the generator, producing electric energy.
From fuel to electric energy
This diagram shows the basic steps in converting fossil fuels to thermal power.
Coal, oil and gas are used to make thermal electricity. They all work basically the same way (with a few exceptions: for example, in an oil- or gas-fired plant, fuel is piped to the boiler).
- Coal supply — After haulers drop off the coal, a set of crushers and conveyors prepare and deliver the coal to the power plant. When the plant needs coal, coal “hoppers” crush coal to a few inches in size and conveyor belts bring the coal inside.
- Coal pulverizer — The belts dump coal into a huge bin (pulverizer), which reduces the coal to a fine powder. Hot air from nearby fans blows the powdered coal into huge furnaces (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. Huge 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 bottom of the boilers and is removed.
- Turbine and generator — Meanwhile, steam moves at high speed to the turbines, massive drums with 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.
- Condensers and cooling water system — Next, the steam exits the turbines and passes over cool tubes in the condenser. The condensers capture the used steam and transform 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 condensers constantly cool. This cooling water, now warm from the heat exchange in the condensers, 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. 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.
Types of thermal plants
Many of Canada’s large thermal plants use a simple-cycle process to generate electricity. Fuel is burned to heat water to create steam, and much of the heat is vented as hot air or steam. While these conventional thermal plants use less fuel than plants in the past to generate the same amount of power, they still lose energy in the form of exhaust heat or steam.
Some thermal plants have been converted from simple cycle to combined-cycle generation, a form of more advanced thermal technology. These plants capture waste heat from exhaust gases to produce more electricity and to use fuel more efficiently. Gas-fired combined cycle plants have a heat conversion efficiency of about 60 per cent, compared to 35 per cent for conventional simple-cycle plants.
Cogeneration is another important innovative thermal technology, which is increasing in use. Cogeneration plants produce electricity and usable heat or steam from a single fuel source such as natural gas. A cogeneration plant captures heat that would be otherwise wasted to provide heat or steam to a building or facility.
previous | next