Unit 3 Power Plant Engineering

8/4/2019 Unit 3 Power Plant Engineering

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Power Plant EngineeringUnit 3


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Sources of Energy

Conventional Energy Sources

Non-Conventional Energy Sources Renewable Energy sources

Non-Renewable Energy sources


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Energy Sources

Conventional Energy Source: thermal, nuclearenergy sources.

Non-Conventional Energy Source: Hydel, Wind,solar, Geo-thermal energy sources.

Renewable Energy Source: the sources of energywhich are inexhaustible. Available in abundant

quantity in the earth and they are continuouslyrestore in nature.

Non-Renewable Energy Sources: The energysources which are exhaustible. Fossil fuel &

nuclear power are the example of it.


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Classification of Power Plants

Thermal Power Plant

Hydro-Electrical Power Plant

Nuclear Power Plant

Diesel Power Plant

Gas Power Plant

Solar Energy Power Plant

Wind Energy Power Plant

Tidal Power Plant

Geo Thermal Power Plant

Bio Mass Energy Power Plant

Ocean Thermal Energy Conversion


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Thermal (Steam) Power Plants

Thermal power plant is to convert energy contained

in the fossil fuel into mechanical or electrical energy.

Coal is used as a fossil fuel for thermal power plant

2000 to 3000 tonnes of coal per day are required forthe 200MW capacity power plant.

Layout of thermal power plant

Coal & Ash circuit

Air & Gas circuit

Feed water & steam circuit

Cooling Water circuit.


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Thermal Power Plant


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Coal & Ash Circuit

Coal delivered by ships, trains or trucks to power station

Received in coal storage yard

Sized by crushers, breakers, etc.

Stored in stock yard(coal storage)

Transferred to the boiler furnace by conveyors, elevators

Ash is produced due to the combustion of coal in the furnace

of the boiler.

It is separated in ash precipitator and is mechanically removed.

Ash disposal is a serious problem because ash is coming out in

hot condition and it is highly corrosive

Thermal Power Plant


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Air & Gas Circuit

Air is essential for combustion of coal in the furnace.Atmospheric air is supplied to the furnace either induced draught (I.D) fan or

forced draught (F.D).

The air enters the pre-heater where the temperature of air slightly increased

due to the heat of exhaust gases.

The heated air is supplied to the combustion chamber in the furnace of the

boiler.

The hot flue gases leaving the furnace of the boiler flow over boiler tubes

where water is converted into steam and it passes through the dust

collector.

The hot flue gases pass through the economiser where feed water is pre-

heated.

The hot flue gases pass through the air-preheater where air is pre-heated.

Finally hot flue gases leaves to the atmosphere through chimeny.

Thermal Power Plant


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Feed Water and steam flow circuit

The feed water enters the boiler tubes in which water evaporates

into steam with the application of heat.

The steam is further heated in the super heaters.

The high pressure & temperature steam passes through the steam

turbine where thermal energy of steam is converted into mechanicalenergy and thus to electrical energy.

The exhaust steam flows into condenser. Steam is cooled and

condensed into water by the circulation of cooling water.

The condense water is pumped to the low pressure feed heater andhigh pressure feed heater thus the temperature of feed water get

increased.

The feed water passes through the economiser is further heated up

by the hot flue gases leaving the boiler.

The heated feed water is fed into the boiler.

Thermal Power Plant


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Cooling water circuit

cooling water is required to condense the steam in the condenser. Large quantities of water is required for the purpose.

Water is either taken from river or lake.

When the adequate water supply is not available, the water coming out

from the condenser is cooled either in cooling tower or in the cooling

pond.

Working Principle

It is known as steam power plant

The main element of power plant are boiler, turbine, condenser, feed

pump. Coal is burnt in the furnace of the boiler where hot flue gases flows

over the boiler and water is converted into superheated steam.

The high pressure & temperature steam passes through the steam turbine

where thermal energy of steam is converted into mechanical energy and

thus to electrical energy.

Thermal Power Plant


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Working Principle

The condense water is pumped to the low pressure feed heater and highpressure feed heater thus the temperature of feed water get increased.

The heated feed water is fed into the boiler.

Advantages of thermal power plant

Capital cost is more.

Takes less time for the construction of the power plant

Power developed is constant.

Can be located near to the load centers.

Disadvantages of thermal power plant

Discharge large quantities of SO2 .

Ash disposal is a serious problem.

Large quantities of cooling water required for condensing of steam.

Transportation of coal is very high.

Cost of production of electricity is very high.

Maintenance and operating cost are high.

Thermal Power Plant

H d El i P Pl


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Hydro-Electric Power Plants

H d El i P Pl


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Layout of Hydro-Electric Power Plant

Catchment area

Reservoir

Dam

Trash racks

Gate valve

Surge tank

Penstock

Inlet valve(Nozzle)Water turbine

Draft tube

Tail race

Power house



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Working principle

The source of energy is water

Water at higher altitude possess potential energy.

When water falls from higher level to lower level its potential energy is

converted into kinetic energy.

Then the kinetic energy is converted into mechanical energy.

The mechanical energy is drawn by allowing the water to flow through the

hydraulic turbine.

The mechanical energy is utilised to run the electric generator to produce the

electricity.



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Advantage of Hydro-electric power plant

No consumption of energy of raw material

It is cheapest in source of energy

Useful life of plant is 100 years

Free from environment pollutionMaintenance cost is very less

Disadvantage of Hydro-electric power plant

Capital cost is high compare to TPP

Takes longer time for construction of plant

Largely depends on the nature

Requires longer transmission line to transmit power to load centre



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Diesel Power Plants

Diesel power are more suitable for medium output power plantand have capacities upto 5MW.

Main components of diesel power plant

Diesel engine

Engine air intake system

Fuel system

Exhaust system Cooling system

Lubrication system

Engine starting system

Di l P Pl t


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Diesel Power Plants


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Diesel Power Plants

Working Principle

In diesel engine, air first compressed to a high pressure and

temperature.

A metered quantity of fuel in the form of fine sprays is injected

into the hot compressed air by the fuel injector.

The temperature at the end of compression is sufficient to self-

ignite the fuel and the combustion process begins.

The combustion products expand doing work.

Exhaust of the products then takes place at the end of which

fresh air is taken into the cylinder and the cycle repeats itself.


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Gas Turbine Power Plants

Gas power plant are used for smaller capacities.

It has found application in ship, aircraft engines and locomotives.

Main components of gas turbine power plant

Low pressure compressor(LPC)

Compression is carried out in two stages

Low pressure stage

High pressure stage

An intercooler is provided in between the two stages

The atmospheric air enters the low pressure its pressure is

increased

Air at the exit of LPC is hot due to its pressure rise


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Intercooler

An intercooler is provided in between the two stages of compression

in order to minimize the power required for compression at the

higher stages.

The hot compressed air from LPC enter the intercooler where theheat of the compressed air is removed.

The cooling medium used in the intercooler is water.

High Pressure Compressor

The cooled air coming out of the intercooler is further compressed

in the HPC.

The pressure and temperature of air further increases in HPC.

Nearly 66% of the power developed by high pressure turbine is used

to run the compressor


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Regenerator

The air from HPC enters the regenerator before it enters into

the combustion chamber.

In this, air is preheated by the exhaust gases coming out of the

turbine.

It is used to make use of this heat.

Combustion chamber

The hot air from regenerator mixes with fuel and the fuel is

burnt in the combustion chamber.

The fuel used in the gas turbine is coal gas.

The products of combustion enters into the HP turbine.


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High pressure turbine

The hot combination gases expand in the HP turbine.

Almost 65-70% of the total power is developed in this stage.

The power is used to drive the HP compressor and LP

compressor.

The compressors mounted on the same shaft as that of the turbine

shaft.

Low pressure turbine and reheater

The expanded gases coming out of the HP turbine is again burntin the reheater by adding some amount of fuel and the products

of combustion is allowed to expand in the LP turbine.

The remaining 35% of the power developed in this stage used to

generate electrical power.


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Working Principle

The atmospheric air enter the compressor where it is

compressed to a high pressure and temperature.

The hot air then enters into the combustion chamber and mixes

with the fuel and the fuel is burnt.

The product of combustion expand in the turbine and thus

mechanical energy is produced.

Part of this mechanical energy is used in driving the

compressor mounted on the same shaft.

The remaining part of this mechanical energy is utilized for

producing electric power.


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N l P Pl


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Nuclear Power Plants

Nuclear power plant consist of two main circuits

Primary circuitSecondary circuit

Important elements in primary circuit

Nuclear reactor

Nuclear reactor is an apparatus in which heat is produced due to nuclear

fission chain.

To control and sustain chain reaction , the nuclear fuel should be placed in

a nuclear reactor.

The main function of the nuclear reactor is to control the emission and

absorption of neutrons.

Nuclear reactor may be different types

Pressurized water reactor

Boiling water reactor

Fast breedor reactor

N l P Pl


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Reactor core It consists of fuel rods and assemblies

All reactors have a central core in which nuclear fission occurs.

In reactor fuel is used in the form of rods and the moderator surrounds the

fuel elements

Moderator

Fast neutrons are emitted after the fission of uranium atoms.

The fast neutrons are less effective in causing the fission of uranium 235

and try to escape from the reactor.

Moderator are used to reduce the speed of fast neutrons.

The commonly used moderator materials are graphite and heavy water.


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Reflector The main purpose of reflector is to turn back neutrons that escape from

the reactor core.

It surrounds the reactor core within the thermal shielding.

In actual practice, the same material can be used for both moderatorand reflector.

Control rods

The control rods are inserted into the reactor core from the top of the

reactor.

The function of the control rod is to absorb the excess neutrons and thechain reaction.

Control rod is used to start and stop nuclear chain reaction.


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Thermal shield The reactor is a source of instance radiations like gamma rays and fast

neutrons and these neutrons are very harmful to human life.

To prevent this, a thermal shield which surrounds the entire reactor core

is essential.

Concrete Shield

It absorbs the radiations emitted during emission fission.

The radiation are harmful for living organism

Coolant

The main purpose of coolant is to carry away the heat produced in the

reactor.

The same heat carried by the coolant is used in the heat exchanger for

further utilization in power generation.


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Important Element in Secondary CircuitBoiler

The primary coolant in the primary circuit gets heated by absorbing

the fission energy in the reactor core and the some energy is utilized

in the heat exchanger to generate steam.Turbine

The generated steam then passes through a steam turbine where the

thermal energy of steam is further used for generating electric

power.

Condenser and feed pump

The steam coming out of the turbine is condensed in the condenser

and the condensate is supplied back to the boiler with the help of

feed pump.


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Advantages Floor space requirement are very less as compared to other power plant of

the same capacity

As very small amount of fuel is needed for nuclear power plant, fuel

transportation and storage cost are minimised.

Nuclear power plant can be located at any place, so they can be established

near rural areas to develop that area.

Power transmission losses are minimised by locating the power plant near

load centres.

Disadvantage

Initial Cost is very high

Disposal of radioactive waste is a serious problem

Cooling water requirements are more

Well trained and highly specialised people are not available in NPP.


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Working Principle

Matter consists of minute particles known as atom.

The atom consists of enormous amount of binding energy

Controlled fission of heavier unstable atom such as U235, Th23

This heat energy is utilised to produce steam in heat exchangers and

the steam is passed through the turbine generator set up to produce

electricity.


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Pump Pump are hydraulic machine which convert mechanical energy into

hydraulic energy.

A pump is define as a device, when driven from some extended sources,

lifts water from a lower level to a higher level.

Pump are classified into two types

Reciprocating Pump

Centrifugal Pump The pump which lift water or a liquid from a lower level to a higher level

by the action of sucking the liquid into the cylinder and pushing out the

liquid from the cylinder by the reciprocating motion of piston is known as

reciprocating pump.

The pump which lift water from lower level to a higher level by the actionof centrifugal force which is created by the rotation of impeller in the liquid

is known as centrifugal pump.

Reciprocating pump are called as positive displacement pump.

Centrifugal pump are called as rotodynamic pump.


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R i i P


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Reciprocating Pump

R i i P


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Working Priniciple of Reciprocating Pump

Let the crank be initially at its extreme left position. Now the crank is driven at

an uniform speed by an electric motor.

When the crank start rotating from =0 to 180, the piston moves outwards and

creates a partial vacuum in the cylinder.

The atmospheric pressure acting on the water surface in the sump, forces water to

enter into suction pipe.

The water rises in the suction pipe and forces the suction valve to open and enters

the cylinder. It is called as suction stroke.

When the piston is at the extreme right position =180 the cylinder is full of

water, the suction valve is closed and the delivery valve is just at the point of

opening.

When the crank start rotating from =180 to 360 , the piston moves inwardsand creates a partial vacuum in the cylinder.

The movement of piston right to left increases the pressure of water in the

cylinder to raise above atmospheric, due to which the suction valve closes and

the delivery valve opens. The water then rises in the delivery pipe and supplied

to the upper tank. This is knows as delivery stroke

Reciprocating Pump

R i i P


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Types of Reciprocating Pump

According to Action of Water Single & double acting pump

According to number of cylinder

Single, Double, Triple cylinder pump

According to Existence of air vessels

Without air vessels & without air vessels

Advantages.

It does not need priming.

It has more efficiency.

Disadvantages It operates at lower speed.

It is not able to discharge large quantities of liquid.

It is complicated in construction because of more number of parts.

Reciprocating Pump

R i i P


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Reciprocating Pump

C if l P


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Centrifugal PumpImpeller

The impeller is a wheel which has a series of backward curved vanes.

It is mounted on a shaft which is coupled to an electrical motor, it is enclosing

in the casing.

The fluid enters in the central portion known as the eye of the impeller and

flow out radially outward and it is then discharge around the entire

circumference into the casing.

Casing

It is an air tight chamber that surrounded the impeller

Volute casing

Diffuser casing

Strainer and foot valve

The lower end of the suction pipe is fitted with a strainer and foot valve.

The liquid first enters the strainer and it prevents the debris and impurities to

enter into the impeller.

The foot valve is of non return type and its permits the liquid to flow in theupward direction.

C if l P


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Suction PipeOne end of the suction pipe is connected to the strainer and foot valve

The other end is connected to the eye of the impeller.

A poorly designed suction pipe causes insufficient net positive head,

vibration, noise etc.,Delivery Pipe

A delivery pipe is connected to the flange of the casing and it delivers

the liquid to the upper pump.

The diameter of the suction and delivery pipe are usaully the same.Delivery valve

Nearer to the outlet of the pump on the delivery valve is fitted.

The function of delivery valve is to regulate the discharge from the

pump.

Centrifugal Pump

C t if l P


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Centrifugal Pump

C if l P


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Working Principle

The first step in the operation of centrifugal pump is priming

Priming is the process of filling up the suction pipe, casing and portion of

the delivery valve with the liquid which is to be pumped.

This is required to remove the air from the portion of pump.

If an impeller is made to rotate in the presence of air, only negligible

pressure will be developed. As a result no liquid is lifted up by the pump.

After priming the motor is started and the delivery valve is still kept closed

in order to reduce the starting torque of the motor.

The rotation of the impeller in the casing full of liquid produces a forced

vortex which imparts a centrifugal forces to the liquid and this result in anincreased pressure throughout the liquid mass.

Due to increase in pressure the liquid rushes out of the casing into the

delivery pipe and is discharged into the upper sump.

When the delivery valve is opened, the liquid is discharged through the

delivery pipe.

Centrifugal Pump

C if l P


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AdvantagesInitial Cost is low

It runs at much higher speed.

It is easy to install and maintain.

Efficiency is high.Discharge is high.

Disadvantages

It need to be primed

Centrifugal Pump

T bi


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In steam. Gas or hydroelectric power plant. The device that drivesthe generator is the turbine.

As the fluid passes through the turbine blades which are attached to

the shaft, the shaft rotates and the turbine produces the work.

Turbine is a prime mover in which rotary motion is obtained by the

gradual changes of momentum of fluid.

Turbines are classified into:

Steam turbine

Hydraulic turbine

Gas turbine.

Turbine

Hydraulic Turbine (Water Turbine)


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Machine Which converts hydraulic energy into mechanical energy.

Turbines are installed at place where a continuous supply of water under high

head is available.

Water is carried from the dam to the turbine through large pipes know as

penstock.

Hydraulic turbines are classified into following types:

According to the energy available at inlet

Impulse turbine

Reaction turbine

According to the direction of flow

Tangential flow turbine

Radial flow turbine Axial flow turbine

According to the head at inlet

Low head turbine

Medium head turbine

High head turbine



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Impulse turbineAll the hydraulic energy of water is converted into kinetic energy when

it enter the impulse turbine.

The jet of water from the nozzle strike against a number of buckets

fixed on the periphery of a wheel, called runner and do work over it.

Pelton Wheel

Water is conveyed from the reservoir to the turbine through penstock.

A powerful jet which comes out of the nozzle, impinges on the vane

provide on the periphery of the wheel.

The water after importing its energy to the turbine is discharged into

the tailrace.



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Reaction turbine

Water entering the turbine has got pressure as well as kinetic energy.

Only a part of available hydraulic energy is transformed into kinetic

energy before it enters the turbine under pressure.

A air tight casing is necessary for a reaction turbine.

Different types of reaction turbine

Francis Turbine

Kaplan Turbine

The water flows parallel to the axis of rotation.

The shaft of the turbine is vertical and lower end of the shaft is made

larger to form the boss or hub. A number of vanes are fixed to the boss.

The turbine is enclosed in a scrolling casing which receives water from

the main.

From the scrolling casing water is directed to the runner blades through


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Unit 3 Power Plant Engineering