Electrical Power Generation Notes3

7/25/2019 Electrical Power Generation Notes3

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Vinayaka.B.G , Asst professor, E& E dept., BIET Davanagere

Unit3.a

HYDRO POWER GENERATION

a) Hydro Power Generation: Selection of site. Classification of hydro-electric plants. General

arrangement and operation. Hydroelectric plant power station structure and control.

(b) Thermal Power Generation: Introduction. Main parts of a thermal power plant. Working.

Plant layout

Hydro power station utilizes the potential energy of water at high level for

generation of electrical energy.

The energy of water utilized for hydropower generation may be kinetic or

potential energy. The ample quantity of water is used, where water flows from

higher level to lower level is passed through turbine. When water flows from higher

level to lower level the potential energy of water gets transformed into kinetic

energy. This kinetic energy used to rotate the turbine there by converting kinetic

energy into mechanical energy. This is further converted into electrical energy by

alternator coupled to the turbine.


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Advantages of hydroelectric power plant

1.

It requires no fuel as water is used for the generation of electrical energy

2.

Water reaches to power house site on its own so no transportation is required.

3.

It is quite neat and clean as no smoke or ash is produced.

4.

After use of electricity generation water can be used further for drinking and

irrigation.

5. Hydro power plants has high efficiency compared to thermal plants

6. Hydro power plants has longer life compared to thermal plants

7. It requires low maintenance.

8.

These are economical.9.

Hydro power plants are quick in start and shut down.

10.Running cost is low.

11.

Hydro power plants are multipurpose projects in addition to power generation

they are also useful for irrigation and flood control.

12.It offers more flexibility in operation and control.

Disadvantages

1. It requires high initial capital cost.

2. High time of construction period.

3.

Due to construction of dams and reservoirs, a large portion of area submerged

into water which leads environmental and other social problems.

4.

Hydro power generation dependent on availability of water. In low rain fall

years the power generation is small.


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SELECTION OF SITE

Factors considered for selection of site

i). Availability of water: Since the primary requirement of hydroelectric power

plant is availability of water. Such plants must be constructed where huge quantity

of water is available at good head.

ii)Storage of water:there are wide variations in water supply during the year. This

makes it necessary to store water by constructing a dam in order to ensure the

generation of power throughout year.

iii)Head of water: the availability of head depends upon topography of the area.For generating sufficient head the dam or reservoir should be constructed at hilly

area. Availability of head affects the cost & economy of power generation.

iv) Distance of power station site from load centres:the distance should be small

as possible so that the cost of transmission is low.

v) Accessibility of site: the site should be accessible by rail and road for

transmission of materials and men.

vi) Type of land:the land for construction must be capable of withstanding a heavy

foundation.

vii) The site selected such that it should not be in seismic zone otherwise any

happening creates flooding & damaging of dam.


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CLASSIFICATION OF HYDRO ELECTRIC POWER PLANTS

The classification of hydropower plants based upon

1) Quantity of water available

2)

Available of head

3)

Nature of load

1) Classification based upon quantity of water available

According to quantity of water available hydro power plants may be divided

into 3 groups

a)

Run off river plants without pondage

b)

Run off river plants with pondage

c)

Reservoir plants

a) Run-off river plants without pondage : As name indicates that these plants

are not provided with storage facilities. No dam is constructed across the river. The

plant uses water as it comes. There is no control of water flow. During rainy season

high water flow is available so some quantity of water wasted if load demand is low.

During low flow rates the generating capacity is low.


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b) Run-off river plants with pondage: The usefulness of runoff river plants is

increased by pondage.

Pondage permits the storage of water during off peak periods& use of this

water during peak periods. Depending upon size of pondage provide it may be

possible to meet hour to hour fluctuations for a week or longer period.

c) Reservoir plants:most of hydro power plants are belonging to this category.

The storage facility is provided by forming a reservoir. Water is stored behind the

dam &it is possible to control the flow of water into the turbine & use it most

effectively. Storage of water increases firm capacity of plant. A storage plant which

has better capacity can be used efficiently throughout year. This plant can be used as

base load plant or peak load plant.

2) Classification according to availability of water head

a) Low head plants less than 30m

b)Medium head plants between 30 to 300 m

c)

High head plants more than 300 m

a)Low head plants:If the water head less than 30m the plant is called low head

plant.

The arrangement of low head plant is shown in figure. The necessary head is

created by constructing dam or barrage across the river. This type power plant is

situated nearer to the dam therefore no need of surge tank d. Only small quantity of

power can be generated.

Generally Francis, Kaplan or propeller turbines are used.


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b) Medium head plants:plants operate at head between 30 to 300 m are called

Medium head plants.

The arrangement of Medium head plant is shown in figure. The forebay isprovided at beginning of the penstock serves as water reservoir. The water is carried

from main reservoir to forebay through open canals reach the power house through

penstock. There is no need of surge tank as forebay acts itself as surge tank.

Generally Francis, Kaplan turbines are used.

c)High head plants: Plants operating at head 300 m above are called High

head plants.

The arrangement of High head plant is shown in figure. This plant consists of

reservoir, dam, tunnel, surge tank, penstock etc. here water is carried from main

reservoir by a tunnel up to surge tank and then from the surge tank into the power

house by penstock. The surge tank is needed to reduce the water hammer effects on

penstock.


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These plants are suited to work as base load plants, as they can generate firm

power throughout the year.

For heads above 500 meters Peltonwheels are used and for heads less than

500 metersFrancisturbines are used.

3) Classification according to Nature of Load

According to Nature of load hydro power plants are classified into

Base load plants

peak load plants

pumped storage plants

a) Base load plants: The plants operated on the base portion of the load curve

are called base load plants. These plants supply almost constant loadthroughout the year so load factor of such plants is high. Run-off river plants

without pondage & reservoir plants are used as base load plants.

b)Peak load plants: The plants operated on top portion of load curve are called

peak load plants. These plants supply peak load of the system. The load factor

of these plants is low since they operated only for short period. These plants

stores water during off peak periods and are run during peak periods. Run-off

river plants and reservoir plants with large capacity are used as peak load

plants.


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c) Pumped storage plants:

Pumped storage plants are special type of plants which are used to supply

peak loads. The arrangement of pumped storage plant is shown in figure.

During peak period, water drawn from the head water pond passes through

the penstock and generates power for supplying peak loads.

During off peak period the same water is pumped back from tail water

pond to head water pond.

A recent development in this field is use of reversible turbine-pump unit.

This unit can be used as turbine while generating power and as a pump

while pumping water to the head water pond.

These pumped storage plants are always interconnected with other plants

such as steam power plants.

Advantages of pumped storage plants

Operating cost of steam power plant decreases when working in

combination with pumped storage plants.

It increases the load factor of the steam power plant combined with it.

These plants pick up load rapidly.


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GENERAL LAYOUT AND CONTROL

The schematic arrangement of hydropower plant is shown in figure. The dam

is constructed across the river & water from catchment areacollects at back of dam

to form reservoir. A pressure tunnel takes water from reservoir to surge tank and

valve house.

The valve house is situated at the beginning of penstock. The valve house

contains main sluice valve and the automatic isolating valves. The main sluice

valves controls the flow of water to the power house & automatic isolating valves

cut off the supply of water when penstock bursts.

From the valve house water is then taken to the turbine through huge steel

pipes known as penstock. The water turbine converts hydraulic energy into a

mechanical energy. The turbine drives the alternator which is coupled to the shaft of

the turbine. The alternator converts mechanical energy into electrical energy. This

electrical energy is then transmitted to the load centres.

The water from the turbine collects in tail race. This tail race is then taken off

to the river.


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Components of hydroelectric power plant

The following are the main components of a typical hydroelectric power plant

a) Reservior

b)

Dam

c)

Trash rack

d) Power tunnel

e) Forebay

f) Surge tank

g)

Penstock

h)

Spill way

i) Power house

j)

Draft tube

k)

Tail race

a) Reservoir: The main purpose of the reservoir is to store water during rainy

season & supply water during dry season which may be used to generateelectricity & irrigation purpose. A reservoir can be either natural or artificial.

b)Dam: The dam is constructed across the river to provide a necessary head to the

turbine. It is very important component in high & medium head plants. The

main function of the dam is to increase the height of the water level behind it,

which ultimately increases reservoir capacity. Dams are built in concrete or rockfill. The type of the dam depends on topography of area.

c) Trash rack: The trash rack is provided to stop entry of debris (impurities or

floating materials) which might damage the gates & turbine runners. It is mesh

like structure made up of steel bars & is placed across the intake i.e entrance of

the gate.


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d) Power tunnel: Power tunnel carries water from reservoir to the surge tank.

e) Fore bay: It is regulating water reservoir. When load on the turbine is reduced

then it stores water and it provides water when load is increased. It can be

consider as surge reservoir. It may be pond behind the dam or enlarge section of

canal spread out

f) Surge tank:

it is an additional storage space located at beginning of penstock.

It is usually provided for high head plants.

The surge tank controls the pressure variation in the penstock and there by

controls the water hammer effects.

When load on the turbine decreases ( or during load rejection) the turbine

gates are closed by governer mechanism which results high pressure

above the normal known as water hammer, so water at lower end of the

penstock rushes back to the surge tank hence water level rises in surge

tank.

When load on turbine increases the additional water releases into the

turbine hence water level in surge tak reduces. So surge tank regulates the

water flow into the turbine.


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g) Penstock:

A pipe between surge tank and turbine is known as penstock.

Penstock carry water from surge tank ( or forebay) to turbine

These are usually made up of steel or reinforced concrete.

For low head plants concrete penstocks are used.

For high head plants steel penstocks are used.

When distance between forebay and power house is short separate

penstocks are used for each turbine.

h) Spill way:

This is considered as safety valves for a dam.

The spill way discharges excess of water in the reservoir beyond the

permissible level.

i) Power house:

It is generally located at the foot of the dam.

The location of the power house should be such as to use maximum

possible head at turbines.

Power house consists of turbine, alternator & some auxiliary equipment.

Power house divided into sub structure, Intermediate structure, Super

structure.

Substructure supports the hydraulic and electric equipment.

Super structure to house & to protect this equipment.

j) Draft tube:

It is an air tight pipe attached to the runner & discharging water from

turbine to the tail race.

These draft tubes are usually used for reaction turbines.

k) Tail race:

The water after passing through the turbine is discharged to the tail race. A tail race is open channel carry water away from power house.


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WATER HAMMER AND ITS EFFECTS

There is a sudden increase of pressure in the penstock due to sudden

decrease in the water flow to the turbine when gates admitting to the turbines

are closed owing to the action of the governor. This happens when load decreases. This sudden rise of pressure in the

penstock above the normal due to reduced load on the generator is called

water hammer.

Water hammer leads to damage of penstock.

The effect of water hammer can be prevented by constructing surge tank in

between the reservoir and power house.

HYDROPOWER STATION STRUCTURE

The power house may be broadly divided into three subdivisions,

(a) Substructure

(b) Intermediate structure

(c) Superstructure

Substructure:

The part of the power house which extends from the top of the draft tube to the

soil or rock is known as substructure.

It serves support the equipment & to provide necessary passage for water ways.

It mainly consists of foundation of a building, draft tubes, water ways etc..

Substructure is generally concrete block with passage & water ways moulded

in it.

The structural functions of substructure are.

To safely carry the superimposed loads of machines and other

structures.

To act as transition foundation member, this distributes heavy

machine loads on the soil such that the obtainable ground pressure is

within safe limits.


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Intermediate structure:

The part of the power house which extends from the top of the draft tube-to

top of the generator foundation is known as intermediate structure.

In case of reaction turbine unit, the intermediate structure contains scroll case,

which feeds water to the turbine

In case of impulse turbine intermediate structure contains pipes supplying

water to the jets.

The generator foundation rests on the scroll case which is embedded in

concrete. Other galleries and chambers also rest on this foundation.

Superstructure:

The part of the power house above the generator floor right up to the roof is

known as superstructure.

This structure houses for generator & power house equipment including

switch board.

This part provides walls and roofs to power station and also provides an

overhead travelling crane.

This overhead travelling crane helps for handling heavy machine parts during

installation and repair.


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QUESTIONS

1 Discuss the advantages and disadvantages of hydroelectric power plants.

[Dec 09,4M]2 Mention the factors to be considered for the selection of site for a hydroelectric

power plant. [Dec 08, June

10][6 M]

OR

What are the factors to be considered while selecting a site hydro power station?

[Dec 11](5M)]

3 Classify hydroelectric power plants based on i) Water flow regulation , ii) head, iii)

load. [June09][4M]

OR

How do you classify the hydroelectric plants explain clearly? [Dec 11,5M]

4 Discuss the classification of hydroelectric power plants. Explain high head and base

load power plant. [Dec 09,8M]

5 Explain with neat sketch the working of medium head power plant [June 09][6 M]

6 With a neat sketch , explain the function of pumped storage plant [June 08, 12] [4M]

ORExplain with diagram the principle of operation of pumped storage plant. How does it

help to take sudden peak load in a power system? [Dec 08, 12](6 M)]

7 With neat schematic diagram, explain the essential elements of hydroelectric power

plant.

[Dec 10, 11, june12]( 8M)

OR

Explain general arrangement & operation of a hydroelectric power plant.

[ June 08](8 M)

8 What is meant by water hammer with a neat sketch, explain the function of surge

tank. [Dec 11](7 marks)

Describe the features of the substructure & super structure of a hydroelectric power

station. [jan 08,12] [4marks]

Discuss the power station structure and control in hydroelectric power plant.

[june11](5 marks)


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TRASH RACK

PENSTOCK

SPILL WAYS


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SURGE TANK

TAIL RACE

Generator


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UNIT 3.b

THERMAL POWER PLANT

Syllabus:Introduction. Main parts of a thermal power plant. Working. Plant layout.

A generating station which converts heat energy of coal combustion into

electrical energy is known as thermal power station or steam power station.

In this power station the steam is produced in the boiler by using heat of

coal combustion. The steam is then expanded in steam turbine which drives the

alternator. The alternator converts mechanical energy of the turbine into electrical

energy. The exhaust steam gets condensed in the condenser and fed back into the

boiler again, completing the cycle of the power station, this principle is called

Rankine cycle.

Thermal power plants are usually constructed where coal and water are

available in abundance.

Now a days these power plants with small capacity (up to 30MW) are

installed in various industries like paper industries, textile mill, sugar industries etc.


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ADVANTAGES OF THERMAL POWER PLANT

1. The fuel (coal) used is quite cheap.

2.

Less initial cost compared to other generating stations.

3. It can be installed at any place irrespective of existence of coal. The coal can

be transported to the site of plant by rail or road.

4. It requires less space compared to hydroelectric plant.

5. Cost of generation is lesser than that of diesel power plant

DIS ADVANTAGES

1. It pollutes the atmosphere due to production of large amount of smoke and

fumes.

2. Running cost is high compared to hydroelectric power plant.

3.

Great difficulties experienced in coal handling and ash disposal.

FACTORS CONSIDERED FOR SELECTION OF SITE

i.

Availability of fuel: The thermal power plants should be located near the coalmines so that transportation cost is reduced.

ii.

Availability of water: Large quantity of water required for condenser so such

plants are located near the water resources.

iii.

Transportation facilities: Adequate transportation required for transporting

material and machines. So plants should be well connected to rail and road.


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iv.

Cost and type of land: Cost of land should be reasonable, further extensions if

necessary should be possible.

v.

Nearness to the load centre: In order to reduce the transmission cost the

plants should be located near the load centres.

vi.

Distance from populated area: Plants should be located at a considerable

distance due to pollution from thermal plants.

vii. Initial cost: Initial cost should be low.

viii.

Site selection also depends on Magnitude and nature of load to be handled.


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THERMAL POWER PLANT LAYOUT:


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WORKING OF THERMAL POWER PLANT

Steam power plants operate on Rankine cycle. Steam generated in the boiler,

expanded in prime mover, which produces mechanical power driving the

alternator which is coupled to the turbine.

The steam after expansion in the turbine and is condensed in a condenser this

condensed steam is fed into boiler again, however in practice a large number of

modifications and improvements have been made to improve the efficiency of the

plant.

The schematic layout of modern thermal power plant is as shown in figure.

The plant can be divided into 4 main parts

Fuel and Ash circuit

Air and Gas circuit

Feed water and Steam circuit

Cooling water circuit

Fuel and Ash circuit:

It comprises coal storage, coal handling, free space of boiler, ash handling

and ash storage.

The coal is stored in coal storage and is fed to the combustion chamber of

boiler through coal handling equipments.

Ash is produced as a result of combustion and collects at the back of the

boiler and is removed to the ash storage through ash handling equipment.


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Air and Gas circuit:

It comprises induced draught fan ( ID fan), Forced draught fan (FD fan), air

preheater, economiser, super heater and combustion chamber of boiler(

furnace).

Air is drawn from the atmosphere by a FD fan or ID fan through a air

preheater.

In air preheater air is heated by the heat of the flue gases which are passing to

the chimney.

The flue gases passing around the boiler and super heater tubes are drawn by

ID fan through dust collector, economiser, air preheater and finally exhausted

to the atmosphere.

Feed water and steam circuit:

It comprises water space of boiler, super heater, turbine, condenser, low

pressure and high pressure feedwater heaters, deaerator, economiser.

Wet steam from the boiler is further heated in super heater before supplied

to the turbine. This super heated steam expanded in the turbine to run it.

The steam after turbine passes to the condenser where it is condensed.

The condensate (water) leaving the condenser is first heated in the LP heater

using steam taken from low pressure extraction point of the turbine.

Some part of the water is lost while passing through different components ofthe system. Adding make up water in the feedwater system to compensate

this loss.

This feedwater again heated by HP (high pressure) heater using steam taken

from high pressure extraction point of the turbine.

This hot feed water is passed to the boiler through economiser where it is

further heated by flue gasses.


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Cooling Water circuit :

Cooling water circuit comprises of the condenser and cooling towers (or spray

ponds).

A large quantity of cooling water required to condensate the steam in the

condenser.

The cooling water after passing through the condenser fed back to the river.

If adequate quantity of water is not available then cooling tower and cooling

ponds are used.

MAIN PARTS OF THERMAL POWER PLANT

1) BOILER:

Boiler is a device which produces the steam.

It is one of the major equipment in thermal power plant.

It is cylindrical drum made up of steel.

There are two types of boilers

Fire tube boiler

Water tube boiler

Fire tube boiler: In this type of boiler, tubes containing hot combustion

gases which are surrounded by water, that is hot gases are inside the tubes

and water is outside.

Advantages of Fire tube boilers:

Compact in size

low initial cost

reliable in operation

Quick respond to load change

Disadvantages: more likely to explode and cannot withstand high pressure.


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Water tube boiler: In this type water is through the tubes and hot gases are

outside the tubes. These water tube boilers have more advantages than fire

tube boilers.

Advantages of water tube boiler are

High pressure can be obtained

Safety in operation

2) SUPER HEATER:

Super heater is a heat exchanger in which heat is transferred to the saturated

steam to increase its temperature.

Super-heated steam contains more heat than saturated steam.

The function of super heater is to remove last traces of moisture (1 to 2 %)

from the saturated steam coming out of the boiler and to increase the turbine

internal efficiency.

Super heater is made up of group of tubes of special alloy steel. These tubes

are heated by the heat of the flue gases when they pass from the furnace to

the chimney.

Super heating raises the overall efficiency the thermal plant.

Advantages of super heater:

Steam condensation can be avoided

It increases the efficiency

It eliminates moisture

The additional heat imparted to vapour causes it to behave more likely

to perfect gas


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3) REHEATERS:

In addition to super heater modern power plant have reheater.

The function of reheater to bring the partially expanded steam back to super

heat temperature by passing it through the tubes of reheater.

4)

ECONOMISER:

It is a heat exchanger which increases the temperature of feed water by

utilizing the heat from flue gases thus the efficiency of thermal power plant

can be improved.

In an economiser a large number of thin walled tubes are placed between two

headers, feed water enters through one header and leaves through the other.

Economiser is used to extract the heat from the flue gases for heating the

feed water thus higher and better economy can be achieved.

Economiser increases the resistance of the flue gases and also reduces the

temperature hence induced draught fans are required in thermal plants.

5) AIR PREHEATER:

Air preheater is placed in between economiser and chimney

Air preheaters are used to extract the heat from the flue gases to heat the

air.


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The heat carried from the flue gases coming out of the economiser are

further utilized for further heating the air before supplying to the boiler.

It increases the temperature of the air; it has been found that increase of air

temperature by 200C increases the boiler efficiency by 1%.

Air preheaters are more economical with pulverised fuel boilers because

temperatures of flue gases are more and better for coal combustion.

Advantages of air preheater are

Improved combustion

Successful burning of low grade coal

Increased thermal efficiency

Increased steam generating capacity

6)

DRAUGHT SYSTEM:

The purpose of draught system is

Supply required amount of air to the furnace

To take flue gases from the boiler( furnace) through chimney

The difference in pressure is known as draught.

Draught can be produced by use of chimney, fans, steam or air jet or

combination of these.

Pressure difference is produced with the help of chimney only is called

natural draught.

Pressure difference is produced with the help of fans is called mechanical

draught.

In most modern power plants two types of fans are used namely

Induced draught fan

Forced draught fan


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7) CHIMNEY:

It is important component of thermal power plant.

Its main function is to discharge the flue gases to the atmosphere at a great

height.

It is tall structure which is open at the top.

Chimneys are made up of steel of bricks and concrete.

It also creates the draught which is necessary for efficient combustion.

8) TURBINE:

Steam turbine converts steam energy into mechanical energy.

The dry super-heated steam is fed to the steam turbine through main valve.

The heat energy of the steam when passing over the blades of the turbine is

converted into mechanical energy.

There are two types of turbine

Impulse turbine

Reaction turbine

Impulse turbine consists of number of nozzles, fixed and moving blades. The

steam expands in the stationary nozzles and attains a high velocity. Potential

energy of the steam converted into kinetic energy when passing through

these nozzles. The high velocity steam impacts on the moving blades giving

rise to impulsive force on them, thus turbine starts rotating.

In reaction turbine there are no nozzles but they have fixed and moving

blades, the steam pressure is gradually reduced in the blades as steam

passes through them.

9) CONDENSER:

Condenser is a device in which exhaust steam from the turbine is condensed.

The use of condenser improves the efficiency of the plant by decreasing the

exhaust pressure of steam below the atmosphere pressure.


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The condensed steam can be recovered for use as feed water to the boiler.

Air and non-condensable gases are also removed from the steam when it

passes through condenser.

There are two types of condenser

jet condenser

Surface condenser

In Jet condenser the exhaust steam and cooling water come in direct contact

with each other. Cold water is pumped from suitable source into condenser

where it comes in direct contact with steam & absorbs the heat from the

steam as a result the steam condenses into water. Here condensate cannot

be used as feed water.

In Surface condenser the exhaust steam and cooling water do not come

direct contact. The steam passes over the surface of tubes through which

cooling water is maintained.

The surface condenser is most commonly used because the condensate can

be used as feed water.

10) COOLING WATER SYSTEM:

A large source of water supply is not usually available near thermal power

plant. Therefore most power plants use closed cooling water system where

warm water coming out of the condenser cooled and reused.

Small plants use spray ponds and medium plants & large plants use cooling

towers.

Spray ponds: it consists of water tank, in which hot water coming from the

condenser is sprayed through nozzles at a suitable pressure. As spray of

water comprising extremely small droplets, comes in contact with cold

atmospheric air, it cools down and cold water collected at the bottom and

again pumped into condenser for circulation.


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Cooling tower:

A cooling tower is a steel or concrete hyperbolic structure having a

reservoir at the bottom for storage of cooled water.

Warm water led to the top, air flows from bottom to the top.

Water drops falling from the top comes in contact with air and get cooled.

This cooling water collected at the base of the tower is pumped to the

condenser and cycle repeats.

Cooling towers are classified as

o

Atmospheric (natural draught) Cooling tower.

o Mechanical draught cooling tower.

11) FEED WATER HEATERS:

The condensate leaving the condenser is used as feed water to the boiler

and also makeup water added.

These heaters are used to heat the feed water by means of bled steam

before supplied to the boiler.

It necessity to heat the feed water before supplying it to boiler for following

reasons.

Overall plant efficiency is improved

Thermal stresses due to cold water entering the drum of boiler is

avoided

There is an increase in the quantity of steam produced by the boiler

The dissolved oxygen & carbon dioxide which would otherwise cause

boiler corrosion are removed in the feed water heaters

There are two types of feed water heater

Open feed water


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Closed feed water

Large thermal plants uses two types of closed heaters

o

Low pressure heatero High pressure heater

In LP heater the feed water heated by the steam taken from low pressure

extraction point of the turbine.

In HP heater the feed water heated by the steam taken from high pressure

extraction point of the turbine.

12)

DE-AERATOR:

De-aerator is a special type of heater whose function is to expel the

dissolved oxygen and other gases from the feed water.

13) TURBO-ALTERNATOR:

Generators coupled directly to the steam turbines are called turbo-

alternators

High speed synchronous generators are used because efficiency of steam

turbines is high at high speed.

Speed of alternator is given by

rpm

For 50 Hz frequency the maximum speed is 3000 rpm for two pole p=2.

For 60 Hz frequency the maximum speed is 3600 rpm for two pole p=2.

Turbo-alternators have cylindrical rotor & therefore have uniform air gap.

Turbo- alternators are usually rated at 11 kV, 3 phase star connection of

stator windings.

Generally Turbo-alternators are rated at 0.8 power factor lagging.

Air cooling is used up to 40 MW above this hydrogen cooling is used.


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Indian thermal generators are

11kV, 50 MW;

11kV,100MW;

15.56 kV, 200 MW;

COAL HANDLING

Explain with line diagram fuel handling system of modern thermal power

plant

i)

Delivery of coal: The coal from supply points is delivered by ships or boats to

power stations situated near to sea or river whereas coal is supplied by rail or

trucks to the power stations which are situated away from sea or river.

June 2009, 10M


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ii) Unloading: The type of equipment to be used for unloading the coal received

at the power station depends on how coal is received at the power station. If

coal is delivered by trucks, there is noneed of unloading device as the trucks

may dump the coal to the outdoor storage. In case the coal is brought by

railway wagons, ships or boats, the unloading may be done by car shakes,

rotary car dumpers, cranes & grab buckets.

iii)

Preparation: Preparation is necessary when unsized coal is brought to the

site.

The preparation (sizing) of coal can be achieved by

crushers,

sizers

dryers and

Magnetic separators.

iv) Transfer: After preparation coal is transferred to the outdoor storage by

means of the following systems:

1. Belt conveyors.

2. Screw conveyors.

3. Bucket elevators.

4. Grab bucket elevators.

5. Skip hoists.

6. Flight conveyor.

v)

Outdoor storage: the storage of coal is necessary because storage of cal

gives protection against interruption of coal supplies when there is delay of

transportation and also when prices are low the coal can be purchased and

stored for future use.


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Usual practice is to store the coal required for one month of operation of

power station in case it is situated at larger distance from coal mines.

Whereas coal is needed for 15 days is stored in case power station situated

near the coal mines.

vi)

Indoor storage or covered storage or live storage: This storage constitutes

coal requirements of the plant for a day.

vii)

In Plant Handling:This refers to handling of coal between the final storage

to the firing equipment. In plant handling may include the equipment such

as belt conveyors, screw conveyors, bucket elevators etc. to transfer the

coal. Weigh Lorries hoppers and automatic scales are used to record the

quantity of coal delivered to the furnace.

viii)

Weighing and measuring: It is necessary to weigh the coal because it gives

the idea of total quantity of coal consumed and coal supplied.

Coal weighing can be done by using

weigh bridge

belt and scale method

automatic recording system

ASH DISPOSAL:

A large quantity of ash is produced by steam power plant. Ash is produced

about 10 to 20% of the coal burnt.

Handling of ash is a problem because it is too hot and it is dusty and irritating.

Ash handling can be done by following systems

Mechanical handling system

Hydraulic handling system

Pneumatic system

Steam jet system


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Dust collection:

Dust may be defined as the solid matter in the flue gasses which is more than

0.001 mm and less than 0.1mm in diameter.

A quantity of dust in few gases largely depends on methods of firing.

Two types of dust collecting systems are used

oMechanic al dust collector

oElectrostatic precipitator.

electro static precipitator:

Electrostatic Precipitators: It has two sets of electrodes, insulated from each other

that maintain an electrostatic field between them at high voltage. The flue gases

are made to pass between these two sets of electrodes. The electric field ionises

the dust particle; that pass through it attracting them to the electrode of opposite

charge. The other electrode is maintained at a negative potential of 30,000 to

60,000 volts. The dust particles are removed from the collecting electrode by

rapping the electrode periodically.

The electrostatic precipitator is costly but has low maintenance cost and is

frequently employed with pulverised coal fired power stations for its effectiveness

on very fine ash particles and is superior to that of any other type.

June 2009, 6M


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QUESTIONS

1. Describe the schematic arrangement of a thermal power station. Briefly explain the

functions of each.

OR

With a schematic diagram, explain main parts and operation of a thermal power plant.

OR

With a neat block diagram, explain clearly main parts and operation of a thermal plant

OR

Draw the schematic layout of thermal power plant & explain functions of various

elements

OR

Discuss the function of elements present in thermal power plant and sketch the

structure of thermal power plant

2. Write a short notes on

i) Air preheater ii) Condensers

iii) Super heater and reheaters iv) Boiler v) Turbo generator

3. Discuss the functions condenser, cooling towers and economizer in a thermal power

station.

4. Write a brief note on i) super heater ii) air pre heater

5. Discuss the functions of the following in a thermal plant:

i)Condenser ii) cooling towers iii)Economizer

6. Explain with line diagram fuel handling system of modern thermal power plant

7. How the coal is utilized in power generation? Describe how it is handled in thermal power

station.

8. Explain with neat sketch, the working of electro static precipitator used for dust

collection in thermal plant.

9. Explainwith neat sketch, the working of electro static precipitator used for

dust collection in thermal plant.

Dec 2010, 10M

Dec 2009, 8M

Dec 2011, 7M

June 2011, 10M

Dec 2008, 8M

Dec 2011, 6M

June 2010, 8M

June 2009, 10M

June 2011, 5M

June 2009, 6M

June 08, 8M

June 12, 10M


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Electrical Power Generation Notes3

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Transcript of Electrical Power Generation Notes3