How a Coal-fired Power Plant works ~ Process Control

Coal Fired Power Plant Process

1. Coal Supply

Coal from the mine is delivered to the coal hopper, where it is crushed to five centimetres (2 inches) in size.
The coal is processed and delivered by a conveyor belt to the generating plant.

2. Pulverizer

The coal is then pulverized, or crushed, to a fine powder, mixed with air and blown into the boiler, or furnace for combustion.

3. Boiler

The coal / air mixture ignites instantly in the boiler.
Millions of litres of purified water are pumped through tubes inside the boiler.
Intense heat from the burning coal turns the purified water in the boiler tubes into steam, which spins the turbine (see number four) to create electricity.

4. Precipitator, stack

Burning coal produces carbon dioxide (CO2), sulphur dioxide (SO2) and nitrogen oxides (NOx).
These gases are vented from the boiler.
Bottom ash, which is made of coarse fragments that fall to the bottom of the boiler, is removed.
Fly ash, which is very light, exits the boiler along with the hot gases.
An electrostatic precipitator (a huge air filter) removes 99.4 per cent of fly ash before the flue gases are dispersed into the atmosphere.

5. Turbine, generator

Water in the boiler tubes picks up heat from the boiler and turns into steam.
The high-pressure steam from the boiler passes into the turbine (a massive drum with thousands of propeller blades).
Once the steam hits the turbine blades, it causes the turbine to spin rapidly.
The spinning turbine causes a shaft to turn inside the generator, creating an electric current.

6. Condensers and the cooling water system

Cooling water is drawn into the plant and circulated through condensers, which cools steam discharged from the turbine.
Steam from the turbine also passes through the condensers in separate pipes from cooling water.
The cold water is warmed by the steam, which condenses back into pure water and circulates back to the boiler to begin the process of generating electricity again.
Cooling water, now warm from the heat exchange in the condensers, is released from the plant.

7. Water treatment plant: water purification

To reduce corrosion, water must be purified for use in the boiler tubes.
Other wastewater systems within the plant collect water used to clean pipes and other equipment, and sludge from the water purification process and other processes.
Waste water is pumped out of the plant and into the holding ponds.

8. Precipitator, Ash systems

Ash that builds up on the precipitator's plates is vibrated off and collected in large hoppers or bins.
Fly ash and bottom ash are removed from the plants and hauled to disposal sites or ash lagoons.
Depending on the market demand, fly ash produced from TransAlta's three plants is sold to the cement industry for construction.

9. Substation, transformer, transmission lines

Once the electricity is generated, transformers increase the voltage so it can be carried across the transmission lines.
Once electricity is delivered to substations in cities and towns, the voltage flowing into the distribution lines is reduced, and then reduced again to distribute electricity to customers.

Process Control