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Apr 3, 2010

COAL FIRED POWER PLANTS


Coal-Fired Power Plant:
 
 How a Coal-fired Power Plant works:
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. 


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