STEAM POWER PLANTS:

A thermal power station is a power plant in which the prime mover is steam driven.
Water is heated, turns into steam and spins a steam turbine which drives an electrical generator.
After it passes through the turbine, the steam is condensed in a condenser and recycled to where
it was heated; this is known as a Rankine cycle. The greatest variation in the design of thermal
power stations is due to the different fuel sources. Some prefer to use the term energy center
because such facilities convert forms of heat energy into electricity. Some thermal power plants
also deliver heat energy for industrial purposes, for district heating, or for desalination of water
as well as delivering electrical power. A large proportion of CO2 is produced by the worlds
fossil fired thermal power plants; efforts to reduce these outputs are various and widespread.

LAYOUT OF STEAM POWER PLANT:

The four main circuits one would come across in any thermal power plant layout are
- Coal and Ash Circuit
- Air and Gas Circuit
- Feed Water and Steam Circuit
- Cooling Water Circuit
Coal and Ash Circuit
Coal and Ash circuit in a thermal power plant layout mainly takes care of feeding the
boiler with coal from the storage for combustion. The ash that is generated during combustion
is collected at the back of the boiler and removed to the ash storage by scrap conveyors. The
combustion in the Coal and Ash circuit is controlled by regulating the speed and the quality of
coal entering the grate and the damper openings.
Air and Gas Circuit
Air from the atmosphere is directed into the furnace through the air preheated by the
action of a forced draught fan or induced draught fan. The dust from the air is removed before
it enters the combustion chamber of the thermal power plant layout. The exhaust gases from
the combustion heat the air, which goes through a heat exchanger and is finally let off into the
environment.
Feed Water and Steam Circuit
The steam produced in the boiler is supplied to the turbines to generate power. The
steam that is expelled by the prime mover in the thermal power plant layout is then condensed
in a condenser for re-use in the boiler. The condensed water is forced through a pump into the
feed water heaters where it is heated using the steam from different points in the turbine. To
make up for the lost steam and water while passing through the various components of the
thermal power plant layout, feed water is supplied through external sources. Feed water is
purified in a purifying plant to reduce the dissolve salts that could scale the boiler tubes.
Cooling Water Circuit
The quantity of cooling water required to cool the steam in a thermal power plant layout
is significantly high and hence it is supplied from a natural water source like a lake or a river.
After passing through screens that remove particles that can plug the condenser tubes in a
thermal power plant layout, it is passed through the condenser where the steam is condensed.
The water is finally discharged back into the water source after cooling. Cooling water circuit
can also be a closed system where the cooled water is sent through cooling towers for re-use in
the power plant. The cooling water circulation in the condenser of a thermal power plant layout
helps in maintaining a low pressure in the condenser all throughout.
All these circuits are integrated to form a thermal power plant layout that generates
electricity to meet our needs.
Advantages
Generation of power is continuous.
Initial cost low compared to hydel plant.
Less space required.
This can be located near the load centre so that the transmission losses are reduced.
It can respond to rapidly changing loads.
Disadvantages
Long time required for installation.
Transportation and handling of fuels major difficulty.
Efficiency of plant is less.
Power generation cost is high compared to hydel power plant.
Maintenance cost is high.

HYDEL POWER PLANTS

Hydroelectric power plants convert the hydraulic potential energy from water into electrical
energy. Such plants are suitable were water with suitable head are available. The layout
covered in this article is just a simple one and only cover the important parts of hydroelectric
plant.
LAYOUT OF HYDEL POWER PLANT:
(1) Dam
Dams are structures built over rivers to stop the water flow and form a reservoir. The
reservoir stores the water flowing down the river. This water is diverted to turbines in power
stations. The dams collect water during the rainy season and stores it, thus allowing for a steady
flow through the turbines throughout the year. Dams are also used for controlling floods and
irrigation. The dams should be water-tight and should be able to withstand the pressure exerted
by the water on it. There are different types of dams such as arch dams, gravity dams and
buttress dams. The height of water in the dam is called head race.

(2) Spillway
A spillway as the name suggests could be called as a way for spilling of water from
dams. It is used to provide for the release of flood water from a dam. It is used to prevent over
toping of the dams which could result in damage or failure of dams. Spillways could be
controlled type or uncontrolled type. The uncontrolled types start releasing water upon water
rising above a particular level. But in case of the controlled type, regulation of flow is possible.

(3) Penstock and Tunnels

Penstocks are pipes which carry water from the reservoir to the turbines inside power
station. They are usually made of steel and are equipped with gate systems. Water under high
pressure flows through the penstock. A tunnel serves the same purpose as a penstock. It is used
when an obstruction is present between the dam and power station such as a mountain.

(4) Surge Tank

Surge tanks are tanks connected to the water conductor system. It serves the purpose of
reducing water hammering in pipes which can cause damage to pipes. The sudden surges of
water in penstock is taken by the surge tank, and when the water requirements increase, it
supplies the collected water thereby regulating water flow and pressure inside the penstock.

(5) Power Station

Power station contains a turbine coupled to a generator. The water brought to the power
station rotates the vanes of the turbine producing torque and rotation of turbine shaft. This
rotational torque is transferred to the generator and is converted into electricity.
 The used water is released through the tail race. The difference between head race and
tail race is called gross head and by subtracting the frictional losses we get the net head
available to the turbine for generation of electricity.

Advantages
Water the working fluid is natural and available plenty.
Life of the plant is very long.
Running cost and maintenance are very low.
Highly reliable.
Running cost is low.
Maintenance and operation costs are very less.
No fuel transport problem.
No ash disposal problem.
Disadvantages
Initial cost of plant is very high.
Power generation depends on quantity of water available which depends on rainfall.
Transmission losses are very high.
More time is required for erection.

DIESEL POWER PLANTS

Diesel power plants produce power from a diesel engine. Diesel electric plants in the
range of 2 to 50 MW capacities are used as central stations for small electric supply networks
and used as a standby to hydroelectric or thermal plants where continuous power supply is
needed. Diesel power plant is not economical compared to other power plants.
The diesel power plants are cheaply used in the fields mentioned below.
1. Mobile electric plants
2. Standby units
3. Emergency power plants
4. Starting stations of existing plants
5. Central power station etc.
LAYOUT OF DIESEL POWER PLANT:

Figure shows the arrangements of the engine and its auxiliaries in a diesel power plant.
The major components of the diesel power plant are:
1) Engine
Engine is the heart of a diesel power plant. Engine is directly connected through a gear box to
the generator. Generally two-stroke engines are used for power generation. Now a days,
advanced super & turbo charged high speed engines are available for power production.
2) Air supply system
Air inlet is arranged outside the engine room. Air from the atmosphere is filtered by air filter
and conveyed to the inlet manifold of engine. In large plants supercharger/turbocharger is used
for increasing the pressure of input air which increases the power output.
3) Exhaust System
This includes the silencers and connecting ducts. The heat content of the exhaust gas is utilized
in a turbine in a turbocharger to compress the air input to the engine.
4) Fuel System
Fuel is stored in a tank from where it flows to the fuel pump through a filter. Fuel is injected to
the engine as per the load requirement.
5) Cooling system
This system includes water circulating pumps, cooling towers, water filter etc. Cooling water
is circulated through the engine block to keep the temperature of the engine in the safe range.
6) Lubricating system
Lubrication system includes the air pumps, oil tanks, filters, coolers and pipe lines. Lubricant
is given to reduce friction of moving parts and reduce the wear and tear of the engine parts.
7) Starting System
There are three commonly used starting systems, they are;
1) A petrol driven auxiliary engine
2) Use of electric motors.
3) Use of compressed air from an air compressor at a pressure of 20 Kg/cm.

8) Governing system
The function of a governing system is to maintain the speed of the engine constant irrespective
of load on the plant. This is done by varying fuel supply to the engine according to load.

Advantages
Diesel power plants can be quickly installed and commissioned.
Quick starting.
Requires minimum labour.
Plant is smaller, operate at high efficiency and simple compared to steam power plant.
It can be located near to load centres.

Disadvantages
Capacity of plant is low.
Fuel, repair and maintenance cost are high.
Life of plant is low compared to steam power plant.
Lubrication costs are very high.
Not guaranteed for operation under continuous overloads.
Noise is a serious problem in diesel power plant.
Diesel power plant cannot be constructed for large scale.
NUCLEAR POWER PLANTS
Nuclear power is the use of sustained or controlled nuclear fission to generate heat
and do useful work. Nuclear Electric Plants, Nuclear Ships and Submarines use controlled
nuclear energy to heat water and produce steam, while in space, nuclear energy decays naturally
in a radioisotope thermoelectric generator. Scientists are experimenting with fusion energy for
future generation, but these experiments do not currently generate useful energy.
Nuclear power provides about 6% of the world's energy and 13–14% of the world's
electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear
generated electricity.
Also, more than 150 naval vessels using nuclear propulsion have been built. Just as
many conventional thermal power stations generate electricity by harnessing the thermal
energy released from burning fossil fuels, nuclear power plants convert the energy released
from the nucleus of an atom, typically via nuclear fission.

LAYOUT OF NUCLEAR POWER PLANT:

NUCLEAR REACTOR
A nuclear reactor is an apparatus in which heat is produced due to nuclear fission chain
reaction. Fig. shows the various parts of reactor, which are as follows:
1. Nuclear Fuel
2. Moderator
3. Control Rods
4. Reflector
5. Reactors Vessel
6. Biological Shielding
7. Coolant.

Nuclear reactor
1. Nuclear Fuel
Fuel of a nuclear reactor should be fissionable material which can be defined as an
element or isotope whose nuclei can be caused to undergo nuclear fission by nuclear
bombardment and to produce a fission chain reaction. It can be one or all of the following U233,
U235 and Pu239.
Natural uranium found in earth crust contains three isotopes namely U234, U235 and U238
and their average percentage is as follows:
U238 - 99.3%
U235 - 0.7%
U234 - Trace
 2. Moderator
In the chain reaction the neutrons produced are fast moving neutrons. These fast moving
neutrons are far less effective in causing the fission of U235 and try to escape from the reactor.
To improve the utilization of these neutrons their speed is reduced. It is done by colliding them
with the nuclei of other material which is lighter, does not capture the neutrons but scatters
them. Each such collision causes loss of energy, and the speed of the fast moving neutrons is
reduced. Such material is called Moderator.
The slow neutrons (Thermal Neutrons) so produced are easily captured by the nuclear fuel and
the chain reaction proceeds smoothly. Graphite, heavy water and beryllium are generally used
as moderator
3. Control Rods
The Control and operation of a nuclear reactor is quite different from a fossil fuelled (coal or
oil fired) furnace. The energy produced in the reactor due to fission of nuclear fuel during chain
reaction is so much that if it is not controlled properly the entire core and surrounding structure
may melt and radioactive fission products may come out of the reactor thus making it
uninhabitable. This implies that we should have some means to control the power of reactor.
This is done by means of control rods.
Control rods in the cylindrical or sheet form are made of boron or cadmium. These rods
can be moved in and out of the holes in the reactor core assembly. Their insertion absorbs more
neutrons and damps down the reaction and their withdrawal absorbs less neutrons. Thus power
of reaction is controlled by shifting control rods which may be done manually or automatically.

4. Reflector
The neutrons produced during the fission process will be partly absorbed by the fuel
rods, moderator, coolant or structural material etc. Neutrons left unabsorbed will try to leave
the reactor core never to return to it and will be lost. Such losses should be minimized. It is
done by surrounding the reactor core by a material called reflector which will send the neutrons
back into the core. The returned neutrons can then cause more fission and improve the neutrons
economy of' the reactor.
Generally the reflector is made up of graphite and beryllium.
5. Reactor Vessel
It is a. strong walled container housing the cure of the power reactor. It contains
moderator, reflector, thermal shielding and control rods.
 6. Biological Shielding
Shielding the radioactive zones in the reactor roan possible radiation hazard is essential
to protect, the operating men from the harmful effects. During fission of nuclear fuel, alpha
particles, beta particles, deadly gamma rays and neutrons are produced. Out of these gamma
rays are of main significance. A protection must be provided against them. Thick layers of lead
or concrete are provided round the reactor for stopping the gamma rays. Thick layers of metals
or plastics are sufficient to stop the alpha and beta particles.
7. Coolant
Coolant flows through and around the reactor core. It is used to transfer the large
amount of heat produced in the reactor due to fission of the nuclear fuel during chain reaction.
The coolant either transfers its heat to another medium or if the coolant used is water it takes
up the heat and gets converted into steam in the reactor which is directly sent to the turbine.
Advantages
Need less space.
Fuel consumption is small, hence transportation and storage charges are low.
Well suited for large power demands.
Less work men required.
Disadvantages
Capital cost very high.
Radioactive wastes, if not disposed properly have adverse effect on environment.
Maintenance cost high.

GAS TURBINE POWER PLANTS

A gas turbine, also called a combustion turbine, is a type of internal combustion engine.
It has an upstream rotating compressor coupled to a downstream turbine, and a combustion
chamber in-between.
Energy is added to the gas stream in the combustor, where fuel is mixed with air and
ignited. In the high pressure environment of the combustor, combustion of the fuel increases
the temperature. The products of the combustion are forced into the turbine section. There, the
high velocity and volume of the gas flow is directed through a nozzle over the turbine's blades,
spinning the turbine which powers the compressor and, for some turbines, drives their
mechanical output. The energy given up to the turbine comes from the reduction in the
temperature and pressure of the exhaust gas.