Download Thermal Power Station

Thermal Power Station
turbine
boiler
Chemical
generator
Heat
Heat
Kinetic
Kinetic
electrical
energy
Electrical
turbines
steam
boiler
generator
condenser
electrical
energy
Nuclear Power
Nuclear power stations operate similarly to thermal power
stations, but instead of burning fossil fuels to produce heat, a
nuclear reaction takes place inside a reactor.
Reactor
Nuclear
Turbine
Heat
Heat
Kinetic
Generator
Kinetic
Electrical
Uranium is a fuel used in nuclear power stations.
It is non-renewable, so it will eventually run-out.
However, it has the advantage that a small amount of Uranium can
produce huge amounts of energy.
1 kg of Coal
1 kg Uranium
30 MJ
5,000,000 MJ
The major disadvantage of nuclear power is that the waste
produced is radioactive.
It has to be stored underground in lead and concrete containers
for thousands of years.
Chain Reactions
Uranium
Nucleus
Neutrons
+
Neutron
ENERGY
Fission
Products
A neutron is fired at a Uranium nucleus causing it to split-up into fragments.
The splitting of the Uranium nucleus is called fission, so we call the fragments
fission products.
When the Uranium nucleus splits energy is released (which heats water in boiler).
More neutrons are also released which can go on to split more Uranium nuclei.
Control rods are used in nuclear reactors to absorb some of these new neutrons
preventing too much energy being released in a short time.
Yellow Book
Power Stations – Page 79
Q12, Q13, Q16, Q18, Q20, Q24
Hydroelectric Power Station
high level reservoir
water flow
low level
reservoir
turbine + generator
transmission
reservoir
lines
transformer
generator
water flow
turbine
Water is stored at a height behind a dam.
The water is allowed to flow down to a lower level.
Potential
Kinetic
The water flows through a turbine spinning the blades which then
turns the generator.
Kinetic
Electrical
Pumped Hydroelectric Power
In a pumped hydroelectric power station water can be pumped
back-up from the low level reservoir to the higher level.
This usually happens throughout the night when the demand for
electricity is lower.
In the morning when we wake up and there is a demand for
electricity, the water is allowed to flow back down again to
generate the electricity we need.
Potential Energy
EP  m g h
EP
÷
m
g
h
x
Example 1
A dam stores 1.2 x 1010 kg of water and is 430 m above the
turbine of a hydroelectric scheme.
(a)
Calculate the potential energy of the water in the dam.
(b) The pipe delivers 1,280 kg of water to the turbine every
second. Calculate the energy delivered to the power
station in one second.
(a)
(b)
EP  ?
m  1.2  1010 kg
h  430 m
g  10 N kg-1
 1.2  1010  10  430
EP  5.16  1013 J
EP  ?
m  1,280 kg
h  430 m
g  10 N kg-1
EP  m g h
 1,280  10  430
EP  5.5  10 6 J
EP  m g h


So there are 5.5 x 106 J of energy produced in one second.
That means 5.5 x 106 J per second.
But since
1 Watt  1 Joule per second
The power output is 5.5 x 106 W, or 5.5 MW.
Question 1
A dam releases 750 kg of water down a pipe every second. The
dam is 620 m above the turbine.
(a)
Calculate the potential energy of this amount of water at
the start.
4,650,000 J = 4.65 MJ
(b) Calculate the power output of the power station if it were
only 50% efficient.
4.65 MJ = 4.65 MW
50% of 4.65 MW = 2.325 MW
Yellow Book
Energy Conversions – Page 83
Q48 and Q51
Efficiency
When an energy transfer takes place some energy is always
wasted or degraded through heat.
For example, in a lamp
Electrical
Light + Heat
“Energy in” is the electrical energy.
“Energy out” is the light energy.
“Wasted energy” is the heat energy.
If an energy transfer is efficient then only a small amount of
energy is wasted.
Most of the “energy in” is changed to useful “energy out”.
Eout
÷
Ein
Eff
Quantity
Unit
Energy Out ( Eout )
Joules ( J )
Efficiency ( Eff )
NO UNIT
Energy In ( Ein )
Joules ( J )
x
Some energy is always wasted so the efficiency is always less than 1.
Sometimes the efficiency is written as a percentage, for example
1 can be written as 100%
0.75 can be written as 75%
0.37 can be written as 37%
( decimal is multiplied by 100 to give percentage )
Example 1
A nuclear power station produces 1,500 MJ of electrical energy.
This requires 5,000 MJ of heat energy from the reactor.
Calculate the efficiency of the power station.
Eff  ?
Eff 
Eout  1,500 MJ
 1,500  106 J
Eout
Ein
1,500
5,000
Eff  0.3 ** NO UNIT **

Ein  5,000 MJ
 5,000  10 6 J
% efficiency  0.3 100
 30%
Efficiency can also be calculated from input and output powers.
Pout
÷
Pin
Eff
Quantity
Unit
Power Out ( Pout )
Joules ( J )
Efficiency ( Eff )
NO UNIT
Power In ( Pin )
Joules ( J )
x
A thermal power station has a percentage efficiency of 33%.
It produces 600 MW of electrical power.
How much power needs to be produced in the boiler?
Eff  33 %
 0.33
Pout  600 MW
Pin  ?
Pin 
Pout
Eff
600  10 6

0.33
Pin  1,800 MW
Yellow Book
Efficiency – Page 80
Q25 (a), (d) and (f)
Q28, Q30, Q31, Q33, Q34, Q36