CME 384- POWER PLANT ENGINEERING

UNIT I COAL BASED THERMAL POWER PLANTS

Rankine cycle – improvisations, Layout of modern coal power plant, Super Critical
Boilers, FBC Boilers, Turbines, Condensers, Steam & Heat rate, Subsystems of thermal power
plants – Fuel and ash handling, Draught system, Feed water treatment. Binary Cycles and
Cogeneration systems.

UNIT II DIESEL, GAS TURBINE AND COMBINED CYCLE POWER PLANTS

Otto, Diesel, Dual & Brayton Cycle Analysis & Optimisation. Components of Diesel and
GasTurbine power plants. Cycle Power Plants. Integrated Gasifier based Combined Cycle
systems.

UNIT III NUCLEAR POWER PLANTS

Basics of Nuclear Engineering, Layout and subsystems of Nuclear Power Plants, Working
of Nuclear Reactors : Boiling Water Reactor (BWR), Pressurized Water Reactor (PWR),
Canada Deuterium- Uranium reactor (CANDU), Breeder, Gas Cooled and Liquid Metal Cooled
Reactors. Safety measures for Nuclear Power plants.

UNIT IV POWER FROM RENEWABLE ENERGY

Hydro Electric Power Plants – Classification, Typical Layout and associated components
including Turbines. Principle, Construction and working of Wind, Tidal, Solar Photo Voltaic
(SPV), Solar Thermal, Geo Thermal, Biogas and Fuel Cell power systems.

UNIT V ENERGY, ECONOMIC AND ENVIRONMENTAL ISSUES OF POWER

PLANTS

Power tariff types, Load distribution parameters, load curve, Comparison of site selection
criteria, relative merits & demerits, Capital & Operating Cost of different power plants. Pollution
control technologies including Waste Disposal Options for Coal and Nuclear Power Plants.

TEXT BOOKS:
1. Nag.P.K , “ Power Plant Engineering”, Third Edition, Tata McGraw Hill Publishing Company
Ltd,2008
REFERENCE BOOKS:

1. El-Wakil.M.M, ”Power plant technology”, Tata McGraw Hill Publishing Company Ltd, 2010

2. Godfrey Boyle, “Renewable Energy”, Open University, Oxford University Press in Association
with the open university,2004

3. Thomas C Elliot, kao Chen and Robert C Swanekamp, “Power Plant Engineering”, Second
Edition, Standard Handbook of McGraw-Hill, 1998
 UNIT 1
COAL BASED THERMAL
POWER PLANTS
Introduction to power plant engineering

A power plant is an industrial facility used to generate electric power with the help of one or
more generators which converts different energy sources into electric power.

A power plant or a power generating station is basically an industrial location that is utilized
for the generation and distribution of electric power in mass scale, usually in the order of
several 1000 Watts. These are generally located at the sub-urban regions or several kilometers
away from the cities or the load centers, because of its requisites like huge land and water
demand, along with several operating constraints like the waste disposal etc.

Electricity is produced at an electric power plant. Some fuel source, such as coal, oil, natural
gas, or nuclear energy produces heat. The heat is used to boil waterto create steam. The steam
under high pressure is used to spin a turbine.

For this reason, a power generating station has to not only take care of efficient generation but
also the fact that the power is transmitted efficiently over the entire distance and that’s why,
the transformer switch yard to regulate transmission voltage also becomes an integral part of
the power plant.

At the center of it, however, nearly all power generating stations has an AC generator or an
alternator, which is basically a rotating machine that is equipped to convert energy from the
mechanical domain (rotating turbine) into electrical domain by creating relative motion
between a magnetic field and the conductors.

Thermal power plant

A thermal power station or a coal fired thermal power plant is the most conventional method
of generating electric power with reasonably high efficiency. It uses coal as the primary fuel
to boil the water available to superheated steam for driving the steam turbine.

The steam turbine is then mechanically coupled to an alternator rotor, the rotation of which
results in the generation of electric power. Generally in India, bituminous coal or brown coal
are used as fuel of boiler which has volatile content ranging from 8 to 33% and ash content 5
to 16 %. To enhance the thermal efficiency of the plant, the coal is used in the boiler in its
pulverized form.

In coal fired thermal power plant, steam is obtained in very high pressure inside the steam
boiler by burning the pulverized coal. This steam is then super heated in the super heater to
extreme high temperature. This superheated steam is then allowed to enter into the turbine, as
the turbine blades are rotated by thepressure of the steam.

The turbine is mechanically coupled with alternator in a way that its rotor will
rotate with the rotation of turbine blades. After entering into the turbine, the steam pressure
suddenly falls leading to corresponding increase in the steam volume. After having imparted
energy into the turbine rotors, the steam is made to pass out of the turbine blades into the
steam condenser of turbine. In the condenser, cold water at ambient temperature is circulated
withthe help of pump which leads to the condensation of the low pressure wet steam.
 In thermal power plants, the heat energy obtained from combustion of solid
fuel (mostly coal) is used to convert water into steam, this steam is at high pressure and
temperature. This steam is used to rotate the turbine blade turbine shaft is connected to the
generator.

Fig. A typical thermal power plant

Fig. Components of a thermal power plant

Fig. Layout of a basic thermal power plant

 Fig. Layout of a modern thermal power plant

Fig. The four circuits of modern thermal power plant

A steam power plant, also known as thermal power plant, is using steam as working fluid.
Steam is produced in a boiler using coal as fuel and is used to drive the prime mover, namely,
the steam turbine. In the steam turbine, heat energy is converted into mechanical energy which
is used for generating electric power. Generator is an electro-magnetic device which makes the
power available in theform of electrical energy.

The layout of the steam power plant consists of four main circuits. These are:
1. Coal and ash circuit
2. Air and flue gas circuit
3. Water and steam circuit and
4. Cooling water circuit

1. Coal and ash circuit

Coal from the storage yard is transferred to the boiler furnace by means of coal handling
equipment like belt conveyor, bucket elevator, etc., ash resulting from the combustion of coal
in the boiler furnace collects at the back of the boiler and is removed to the ash storage yard
through the ash handling equipment.

Ash Disposal:

Indian coal contains 30% to 40% ash. A power plant of 100MW 20 to 25 tonnesof hot ash per
hour. Hence sufficient space near the power plant is essential to dispose such large quantities
of ash.
 2. Air and Flue gas circuit

Air is taken from the atmosphere to the air preheater. Air is heated in the air preheater by the
heat of flue gas which is passing to the chimney. The hot air is supplied to the furnace of the
boiler.

The flue gases after combustion in the furnace, pass around the boiler tubes. The flue gases
then passes through a dust collector, economizer and pre-heater before being exhausted to the
atmosphere through the chimney. By this method the heat of the flue gases which would have
been wasted otherwise is used effectively. Thus the overall efficiency of the plant is
improved.

Air Pollution:

The pollution of the surrounding atmosphere is caused by the emission of objectionable

gases and dust through the chimney. The air pollution and smoke cause nuisance to people
surrounding the planet.

3. Feed water and steam flow circuit

The steam generated in the boiler passes through super heater and is supplied to the steam
turbine. Work is done by the expansion of steam in the turbine and the pressure of steam is
reduced. The expanded steam then passes to the condenser, where it is condensed.

The condensate leaving the condenser is first heated in a l.p. water heater by using the steam
taken from the low pressure extraction point of the turbine. Again steam taken from the high
pressure extraction point of the turbine is used for heating the feed water in the H.P water
heater. The hot feed water is passing through the economizer, where it is further heated by
means of flue gases. Thefeed water which is sufficiently heated by the feed water heaters and
economizer is then fed into the boiler.

4. Cooling water circuit

Abundant quantity of water is required for condensing the steam in the condenser. Water
circulating through the condenser may be taken from various sources such as river or lake,
provided adequate water supply is available from the river or lake throughout the year.

If adequate quantity of water is not available at the plant site, the hot water from the
condenser is cooled in the cooling tower or cooling ponds and circulated again.

Advantages of thermal power plants

1) Initial cost is low compared with hydro-plant.

2) The power plant can be located near load center, so the transmissionlosses are
considerably reduced.
3) The generation of power is not dependent on the nature’s mercy likehydro plant.
4) The construction and commissioning of thermal plant requires less periodof time than a
hydro plant.

Disadvantages of thermal power plants

1) It pollutes the atmosphere due to production of large amount of smokeand fumes.

2) It is costlier in running cost as compared to hydroelectric plants.
3) The heated water that comes from thermal power plant has an adverseeffect on the
lives in the water and disturbs the ecology.
Rankine cycle

The Rankine cycle is a model used to predict the performance of steam turbinesystems. It was
also used to study the performance of reciprocating steam engines. The Rankine cycle is an
idealized thermodynamic cycle of a heat enginethat converts heat into mechanical work while
undergoing phase change.

Thermodynamic analysis:

1-2: Isentropic compression process in the pump

2-3: Isobaric heat absorption process in the evaporator.

3-4: Isentropic expansion process in the expander.
4-1: Isobaric heat rejection process in the condenser.
The Rankine cycle is a model used to predict the performance of steam turbine systems. The
Rankine cycle is an idealized thermodynamic cycle of a heat engine that converts heat into
mechanical work while undergoing phase change.

Rankine cycle is a reversible cycle which has two constant pressures and two constant
temperature processes. Working fluid in Rankine cycle undergoes 4 processes, expansion
in turbine, heat addition in Boiler, heat rejection in Condenser and compression in pump.

The thermal efficiency improvement techniques of Rankine cycle are:

i. By decreasing average temperature at which heat is rejected from theworking fluid

(steam) in the condenser. (Lowering condenser Pressure)
ii. By increasing steam temperature entering the turbine.

Super critical boilers

A supercritical steam generator is a type of boiler that operates at supercritical pressure,

frequently used in the production of electric power. In contrast to a subcritical boiler in
which bubbles can form, a supercritical steam generator operates at pressures above the
critical pressure

Advantages of SC Technology

I ) Higher cycle efficiency means Primarily – less fuel consumption – less per MW
infrastructure investments – less emission – less auxiliary power consumption – less water
consumption

II ) Operational flexibility – Better temp. control and load change flexibility – Shorter start-
up time – More suitable for widely variable pressure operation 28

Economy

Higher Efficiency (η)

• Less fuel input.

• Low capacity fuel handling system
• Low capacity ash handling system.
• Less Emissions.

Approximate improvement in Cycle

• Efficiency Pressure increase: 0.005 % per bar

• Temp increase : 0.011 % per deg K
At supercritical pressures, steam turbine efficiency improves significantly compared to the
typical subcritical cycle. Ultra-supercritical steam conditions provide even greater efficiency
improvements. The combination of utilizing supercritical throttle pressures along with an
increase in throttle temperatures results in cost reductions in fuel usage and handling, flue gas
treatment and ash disposal. B&W's supercritical and ultra-supercritical boilers are designed to
takefull advantage of variable pressure turbine operation.
Specific advantages include:

• For a given output, lower fuel consumption, and thus lower carbonemissions, than
other less efficient systems
• The load change rate capability of the system is not restricted by theturbine
• Steam temperature at the inlet and outlet of the re heater is nearlyconstant over
a wide load range
• The boiler feed water pump power is significantly reduced at lower loads
• Short start up times
• Higher plant efficiency over the entire load range

Supercritical boilers have working range of pressure and temperature above

220.64 bars and 374°C (Critical pressure and temperature of water). There occurs no bubbles
formation in this type of boiler. Subcritical boilers works below critical pressure and
temperature.

Supercritical Pressure:

Critical point in water vapor cycle is a thermodynamic state where there is no clear
distinction between liquid and gaseous state of water. Water reaches to this state at a critical
pressure above 22.1 MPa and 3740C.

A steam boiler or steam generator is a closed vessel in which water is heated, vaporized
and converted into steam at a pressure higher than atmospheric pressure.

A Boiler is the biggest and most critical part of a thermal power plant.
Applications of Boiler:

• Operating steam engines.

• Operating steam turbines.

• Operating reciprocating pumps.

• Industrial process work in chemical engineering.

• For producing hot water required to be supplied to room in very cold areas.

• In thermal power stations.

• The heat content of the steam is large and thus it is suitable for process heating in
many industries like sugar mills, textile mills, dairy industry and also in chemical
industries.
Definition of some useful terms used in Boiler:

• Boiler shell: The boiler shell consists of a hollow cylindrical body made up of steel
plates riveted or welded together.

• Furnace: Furnace is that part of the boiler in which the fuel is conveniently burned to
produce heat. This heat is utilized in generating steam in the boiler.

• Grate: The grate is a space on which the fuel is burnt. It consist of a combination of
several cast-iron bars so arranged that the fuel may be placed on it. Some space is
always provided in between two consecutive bars so that may flow to the fuel from
below the great and ashes may drop into the ash pit provided beneath the Grate. Grate
may be circular or rectangular in shape.

• Grate area: The area of the great upon which the fuel burns is called great area. Grate
area is always measured in square meters.

• Heating surface: The heating surface is the surface of a boiler which is exposed to
hot gases on one side and water of the other.

• Water space and steam space: Water space is the volume of the boiler which is
occupied by water. The remaining space is called steam space because it is needed for
storage of steam in the boiler until it id s drawn off through the steam pipe.

• Flue gases: Flue gases are hot gases produced due to the combination of fuel in the
boiler furnace. Flue gas usually contains water vapor (H2O), Carbon dioxide (CO2),
Carbon monoxide (CO), Nitrogen (N2). Flue gas includes complete and incomplete
products of combustion of fuels.

Classifications or Types of Boiler:

There are large number of boiler designs, but they may be classified accordingto the following
ways:

According to the circulation of gases:

• Fire-tube boiler

• Water-tube boiler

Fire-tube boiler:

Fire tube boilers are those boilers in which hot gases produced by the combination of fuel in
the boiler furnace while on their way to chimney pass through a number of tubes (called fuel
tubes or smoke tubes) which are immersed in water.
Heat is transferred from the hot gasses to water through the walls of tubes.

Example of fire tube boilers are Cochran boiler, locomotive boiler etc. Fire tubes

boilers are also known as a smoke tube boiler.

Water-tube boiler:

Water-tube boilers are those boilers in which water flows through a number of tubes (called
water tubes) and the hot gases produced by the combustion of fuelin the boiler furnace while on
their way to chimney pass surrounding the tubes.

The heat from the hot gases is transferred to the water through the walls of the water tubes.
Examples of water tube boilers are Bab-cock and Wilcox boiler, Benson boiler, etc.

According to Circulation of water:

i. Free circulation

ii. Forced circulation

Free circulation:

In any water heating vessel heat is transmitted from one place to another not by condition but
by convection because water is a bad conductor of heat. Let vessel containing water be heated
at its bottom, as the water in the bottom portion is heated therefore its density becomes
reduced in comparison to the density of water in the upper portion of the vessel, as a result,
the less dense water at the bottom portion of the vessel rise up and comparatively more dense
and cold water at the upper portion of the vessel comes down to take its place and thus a
convection current is set up in the water until temperature off all water becomes the same.

The method of circulation of water described above is known as free circulation.

In boilers like Lancashire, Babcock, and Wilcox, etc. free circulation of water takes place.

Advantages of free circulation:

The advantages of free circulation are:

• Free circulation of water helps to maintain a uniform temperature true everywhere

within the boiler so that unequal expansion of various parts of the boiler is prevented.

• Free circulation of water facilities the escape of steam from the heating surface as soon
as it formed. If steam does not escape quickly after its formation the boilerplates do not
remain constantly in touch with water and as a result, theseplates may be overheated.

Forced Circulation:

In forced circulation, pumps are used to maintain the continuous flow of water in the boiler.
In such a case, the circulation of water takes place due to pressure created by the pump. The
forced circulation system is adopted in more high pressure, high capacity boilers of all of
which are water tube type boiler.

Advantages of forced circulation:

i. The rate of heat transfer from the flue gases to the water higher.

ii. Tubes having comparatively smaller diameters can be used. This reducesthe overall
weight of the boiler.
 iii. The number of boiler drums required may be reduced.

iv. Less scale formation in the boilers is required.

v. Steam can be quickly generated.

vi. The fluctuation of load can be easily met without taking the help of anycomplicated
controlled device.

vii. Chance of overheating of the boilerplates in minimum.

viii. Weight per unit mass of steam generated is less.

According to the number of tubes used:

According to the number of tubes, Boilers may be classified as:

i. Single tube boiler

ii. Multi-tube boiler

Single tube boiler:

Cornish boiler may be termed as a single tumbler boiler because it has only oneflue tube.

Multi-tube boiler:

Cochran boiler may be termed as multi-tube boiler because it has a number offlue tubes.

According to the nature of use:

According to nature use, boilers are classified as

1.Stationary boilers

2.locomotive boilers

3. Marine boilers.

Stationary boilers:

For the generation of thermal power and for process work (in chemical, sagerand textile
industries) boilers used are called stationary boiler.

Locomotive boilers:

Boilers used in locomotive steam engines are called locomotive boilers.

Marine boilers:

Boilers used in steamships are called marine boilers.

According to the nature of the fuels used:

1. Fuel-fired

2. Gas fired

3. Liquid fuel fired

4. Electrically fired

5. Nuclear fired

According to the pressure of the boiler:

1. High-pressure boiler

2. Medium-pressure boiler

3. Low-pressure boiler

High-pressure boiler:

The pressure of the boiler above 80 bar.

Medium-pressure boiler:

It has a working pressure of steam from 20 bar to 80 bar. It is used for power generation or
process heating.

Low-pressure boiler:

This type of boiler produces steam at 15-20 bar pressure. This is used for process heating.

According to the position of the axis of the boiler shell:

According to the position of the axis of the boiler shell,

1. Vertical boiler

2. Horizontal boiler

Vertical boiler:

If the boiler axis is vertical, it is called a vertical boiler. Eg. Cochran Boiler

Horizontal boiler:

If the boiler axis is horizontal, it is called a horizontal boiler.Eg. Lancashire boiler.

Fire Tube Boiler Schematic Diagram:
Water Tube Boiler Schematic Diagram:

Types of Fuel Used in Boiler:

The fuel has been categorized in three formats:

Solid Fuels:

Wood, Coal, Briquettes (a block of compressed coal dust), Pet Coke, Rice Husk.

Liquid Fuels:

LDO (Light Diesel Oil), Furnace oil.

Gaseous Fuels:

LPG (Liquified Petroleum Gas), LNG (Liquified Natural Gas), PNG (Piped NaturalGas) can
be used to carry out the combustion for a specific purpose.

The Necessity of Boiler:

• The most common function for any boiler, whether it is an industrial or residential
boiler, is to serve as the central heating mechanism for a home, business facility,
hospital, commercial complex, etc.

• No matter what setting they are used in, boilers operate with the same basic functions
and mechanisms that work together to create a contained, heat- generating combustion
process.

• Boilers draw natural gas from gas lines running through our streets and use this gas to
 fuel the combustion process for heat creation and distribution throughouta building.

• The boiler system relies on a burner to initiate the combustion process, and thenheat in the
form of steam or hot water moves through the system using pumps, radiators, and heat
exchangers.

• Boiler manufacturers are making use of rapidly improving technology to build

equipment that is cost-efficient, environmentally friendly, and powerful.

Cochran boiler:

Cochran Boiler is a vertical drum axis, natural circulation, natural draft, low pressure,
multi-tubular, solid fuel fired, fire tube boiler with internally fired furnace. It is the
modified form of a simple vertical boiler. In this boiler, thefire tubes are placed horizontally.

A vertical boiler with horizontal fire-tubes is a type of small vertical boiler, used to generate
steam for small machinery. It is characterized by having many narrow fire-tubes, running
horizontally. Boilers like this have been widely used on ships as either auxiliary or donkey
boilers.
The Main parts of Cochran boiler are:

1. Shell

2. Grate

3. Combustion chamber

4. Fire tubes

5. Fire hole

6. Firebox (Furnace)

7. Chimney

8. Man Hole

9. Flue pipe

1. Shell:
The main body of the boiler is known as a shell.

It is hemispherical on the top, where space is provided for steam.

This hemispherical top gives a higher volume to area ratio which increases the steam
capacity.

2. Grate:
The area where the fire is placed known as a grate.

It is placed at the bottom of the furnace where coal is burnt.

3. Combustion Chamber:

It is lined with fire bricks on the side of the shell to prevent overheating of theboiler.

Hot gases enter the fire tubes from the flue pipe through the combustionchamber.

The combustion chamber is connected to the furnace.

4. Fire Tubes:

There are various fire tubes whose one end is connected to the furnace andother to the
chimney.

A number of horizontal fire tubes are provided, thereby the heating surface isincreased.
 5. Fire Hole:

The small hole is provided at the bottom of the combustion chamber to placefuel is known as
a fire hole.

6. Fir Box (Furnace):

It works as a mediator of fire tubes and combustion chamber.

It is also dome-shaped like the shell so that the gases can be deflected back tillthey are passed
out through the flue pipe to the combustion chamber.

7. Chimney:
It is provided for the exit of flue gases to the atmosphere from the smokebox.

8. Man Hole:

It is provided for the inspection and repair of the interior of the boiler shell.

9. Flue Pipe:

It is a short passage connecting the firebox with the combustion chamber.

Working Principle of Cochran Boiler:

The Cochran boiler works as same as other fire tube boiler.First, the coal is placed at the grate through
the fire hole then the air is entering into the combustion chamber through the atmosphere and fuel is
sparked through fire hole then flue gases start flowing into the hemispherical dome-shaped
combustion chamber. This flue gases further moves into the fire pipes. And then the heat is exchanged
from flue gases to the water into the fire tubes. The steam produce collected into the upper side of the
shell and taken out by when the required pressure generated and then the flue gases now send to the
chimney through a firebox where it leaves into the atmosphere. Now, this process repeats and runs
continuously. The steam generates used intothe small industrial processed.

Various boiler mounting and accessories are attached to the boiler for itsefficient working:

1. Pressure Gauge: It measures the pressure of steam inside the boiler.

2. Safety Valve: It blows off the extra steam when the steam pressure inside theboiler reaches
above safety level.

3. Water level Indicator: The position of the water level in the Cochran boiler isindicated
by the water level indicator.

4. Stop Valve: Stop valve is used to transfer steam to the desired location whenit is required.
Otherwise, it stops the steam in the boiler.
5. Blow off Valve: It is used to blow off the settle down impurities, mud, andsediments
present in the boiler water.

The application of Cochran boiler are:

• Variety of process applications in industries

• Chemical processing divisions

• Pulp and Paper manufacturing plants

• Refining units

Besides, they are frequently employed in power generation plants where large quantities of
steam (ranging up to 500 kg/s) having high pressures i.e. approximately 16 mega pascals (160
bar) and high temperatures reaching up to550 °C are generally required.

Features of Cochran boiler:

• In the Cochran boiler, any type of fuel can be used.

• It is best suitable for small capacity requirements.

• It gives about 70% thermal efficiency with coal firing and about 75%thermal
efficiency with oil firing.

• The ratio of the grate area to the heating surface area varies from 10: 1 to25:1

The advantages of Cochran Boiler:

• Low floor area required.

• Low initialization cost.

• It is easy to operate.

• Transport from one place to another is very easy.

• It has a higher volume to area ratio.

Disadvantages of Cochran Boiler:

• Low steam generation rate.

• Limited pressure handles capacity.

• It is difficult to inspect and maintain.

Babcock and Wilcox boiler

The Babcock and Wilcox boiler are also is known as Longitudinal Drum Boiler or Horizontal
Tubes Boiler it is water tube boiler in water tube boiler water remains inside the tube and
hot gases are remains outside the tubes.
According to their name this boiler is known as Babcock and Wilcox boiler.
This is a water tube boiler, used in steam power plants. In this type of boiler,water is
circulated inside the tubes and hot gases flow over the tubes.

This is a Horizontal drum axis, natural draft, natural circulation, multitubular,stationary, high
pressure, solid fuel fired, externally fired Water tube boiler.

A Babcock and Wilcox Boiler Parts or Construction consists of:

• Drum

• Water Tubes

• Uptake and Down take header

• Grate

• furnace

• Baffles

• Super heater

• Mud box

• Inspection Door

• Water Level Indicator

• Pressure Gauge

Drum:

This is a horizontal axis drum which contains water and steam.

Water tubes:

Water tubes are placed between the drum and furnace in an inclined position(at an angle

of 10 to 15 degrees) to promote water circulation.

Uptake and Down take Header:

This is present at the front end of the boiler and connected to the front end ofthe drum. It transports
the steam from the water tubes to the drum. And this is present at the rear end of the boiler and
connects the water tubes to therear end of the drum. It receives water from the drum.

Grate:

Coal is fed to the grate through the fire door.

Furnace:

The furnace is kept below the uptake-header.

Baffles:

The fire-brick baffles, two in number, are provided to deflect the hot flue gases.

Super heater:

It increases the temperature of saturated steam to the required temperaturebefore discharging

it from the steam stop valve.

Mud Box:

This is used to collect the mud present in the water.

Mud box is provided at the bottom end of the down-take header.

Inspection Door:

Inspection doors are provided for cleaning and inspection of the boiler.

Water Level Indicator:

The water level indicator shows the level of water within the drum.

Pressure Gauge:

The pressure gauge is used to check the pressure of steam within the boilerdrum.

Working Principle of Babcock and Wilcox Boiler:

The working of Babcock and Wilcox boiler is first the water starts to come in the water tubes
from the drum through down take header with the help of a boiler feed pump which continues
to feed the water against the drum pressure. The water present in the inclined water tubes gets
heated up by the hot flue gases produced by the burning of coal on the fire grate.

These fuel gases are uniformly heated the water tube with the help of a baffle plate which
works deflect the flues gas uniform throughout the tubes which absorbed the heating
maximum from the flue gases. As the hot flue gases come in contact with water tubes, It
exchanges the heat with heater and converts into the steam.

Continuous circulation of water from the drum to the water tubes and water tubes to the drum
is thus maintained. The circulation of water is maintained by convective current and it’s
known as Natural Circulation. The Steam generated is moved upward, due to density
difference and through the up-take header; it gets collected at the upper side in the boiler
drum.

Anti-priming pipe inside the drum which works separates the moisture from the steam and
sends it’s to the superheated. The super heater receives the water-free steam from an anti-
priming pipe. It increases the temperature of the steam to the desired level and transfers it to
the main stream stop valve of the boiler. The superheated steam stop valve is either collected
in a steam drum or sends it’s inside the steam turbine for electricity generation.
Applications:

To produce high-pressure steam in power generation industries.

Advantages:

• The overall efficiency of this boiler is high.

• The steam generation rate is higher about 20 ton per hour at pressure 10to 20 bars.

• The tubes can be replaced easily.

• The boiler can expand and contract freely.

• It is easy to repair maintenance and cleaning.

Disadvantages:

• It is less suitable for impure and sedimentary water, as a small deposit of scale may
cause the overheating and bursting of tubes. Hence, water treatment is very essential
for water tube boilers.

• Failure in feed water supply even for a short period is liable to make the boiler
overheated. Hence the water level must be watched very carefully during the operation
of a water tube boiler.

• The maintenance cost is high.

Lancashire boiler
Lancashire Boiler is a horizontal type and stationary fire tube boiler. This boiler was
invented in the year 1844, by William Fairbairn. This is an internally fired boiler because the
furnace uses to present inside the boiler.

Lancashire boiler is a horizontal drum axis, natural circulation, natural draft, two-tubular,
low pressure, stationary, fire tube boiler with furnace located internally. Its main purpose is to
create steam and then this steam is used to drive steam turbines for power generation. It has
high thermal efficiency and it is about 80 to 90 percent. It is mostly used in locomotive
engines and marines etc.

Construction

1. Safety valve:

It is used to blow off the steam when the pressure of the steam inside the boilerexceeds the working
pressure.

2. Water Level Indicator:

It indicates the level of water in the boiler. It is placed in front of the boiler. Twowater level
indicators are used in the boiler.

3. Pressure gauge:

The function of the pressure gauge is to indicate the pressure of the steam insidethe boiler.

4. Steam stop valve:

Its function is to stop and allows the flow of steam from the boiler to the steampipe.

5. Feed check valve:

It stops and allows the flow of water inside the boiler.

6. Blow off Valve:

Its function is to remove the sediments or mud periodically that is collected atthe bottom of
the boiler.

7. Manhole:

It is a hole provided on the boiler so that a man can easily enter inside the boiler for the
cleaning and repairing purpose.

8. Fusible plug:

It is used to extinguish the fire inside the boiler when the water level inside the boiler falls to
an unsafe level and prevents an explosion. It also prevents the damage that may happen due
to the explosion.

9. Grate:

It is a platform that is used to burn solid fuel.

10. Fire door:

It is used to ignite the fuel present inside or outside the boiler.

11. Ash pit:

It is used to collect the ash of the fuel after the fuel is burnt.

WORKING

Lancashire boiler consists of a horizontal cylindrical shell filled with watersurrounding

two large fire tubes.

The cylindrical shell is placed over brickwork which creates several channels for the
flow of hot flue gases.

Solid fuel is provided by the fire door which then burnt over grate at the front end of
each fire tube.

A small arc shape brickwork is provided at the end of the grate to deflectthe flue gases
upward and prevent the entry of burning coal and ashes into the interior part of the fire
tubes.

The fire tubes are slightly conical at the rear end to increase the velocity of hot flue
gases.

When hot flue gases are allowed to pass through the downward channel at the front
end of the fire tubes. Now, these gases pass through the side
channel towards the rear end of the fire tube and finally escape outthrough the chimney.

There are dampers at each side channel to regulate the airflow.

The feed check valve is used to feed the water uniformly to the boiler shell.

Once the boiler is at quickly, water converts into steam by absorbing the heat from the
flue gases. This steam is stored at the upper portion of the boiler where the anti-
priming pipe separates the water from steam. Thus the steam stop valve receives the
dry steam for various purposes.

A manhole is provided at the top and bottom of the shell to allow a man to enter into
the boiler and clean it.

A blow-off valve is provided to remove the mud that has settled down. It is also used
to clean the boiler.

Advantages

It has high thermal efficiency; the thermal efficiency is about 80 to 90%.

It is easy to operate.

It can easily meet the load requirement.

 Easy to maintain.

Generate a large amount of steam and hence more reliable.

Low consumption of electricity due to natural circulation.

Disadvantages

It is a low-pressure type boiler, so high-pressure steam is not produced.

Tedious maintenance of brickwork.

It has a limited grate area due to the small diameter of the flue tubes.

The steam production rate is low. It is about 9000 kg/hr

Corrosion occurs in the water legs.

Area of Application the Lancashire boiler is used to drive steam turbines, locomotives,
marines, etc. it is used in industries like paper industries, textile industries, sugar industries,
tire industries, and Etc.
FBC Boiler (Fluidized Bed Combustion)

A bed of solid particles is said to be fluidized when the pressurized fluid (liquid or gas) is
passed through the medium and causes the solid particles to behave like a fluid under certain
conditions.

Fluidization causes the transformation of the state of solid particles from staticto dynamic.

Fluidized Bed Combustion is the ignition of a solid fuel under the conditionsmentioned above.

Bubbling FBC is used for Fuels with lower heating values such as Rice Husk.Under

such sort, the main factors leading to fluidization are as follows:

• Solid Fuel

• Particle Size

• Air Fuel Mixture

Fluidized Bed Combustion takes place when the forced draught fan supplies air to the
Furnace of the Boiler. In the furnace, and is (used for Bubbling phenomenon) placed on the
Bed and is heated before fluidization, the air enters the bed from the nozzles fitted on the
Furnace Bed. And above the nozzles; thesand opposes the upward motion of the air.

But at sufficient velocities, when the pressure applied by the air becomes equal to the weight
of the sand, fluidization of the sand occurs.Now the fuel supplied by fuel conveyor is fed to
the preheated bubbling sand and gets combusted away. This phenomenon also ensures
complete combustionof the Fuel.

The heat released during combustion heats up the surrounding boiler tubes and
generates steam. The major advantages of Bubbling Fluidized Bed Combustion are the
enhanced thermal efficiency, easy ash removal.
Another type is the Circulating Fluidized Bed Combustion; it is applied to fuels with
higher heating values such as Petcoke.In this, the unburned fuel is fed again to the furnace
with the help of a Forced Draught fan and ducts, ensuring enhanced combustion and higher
heating and provides excellent fuel flexibility.Also, the fluidizing velocity of Air in CFBC
is comparatively higher than that of BFBC. One of the major drawbacks is the power
consumption.

The motors installed in the Forced Draught Fan consume more power than the one installed
in the same capacity Boiler’s ( wood/coal fired) Forced Draught Fan, because of elevated
levels of draught requirement to create fluidization.

Condensers

In thermal power plants, the purpose of a surface condenser is to condense the exhaust steam
from a steam turbine to obtain maximum efficiency, and also to convert the turbine
exhaust steam into pure water (referred to as steam condensate) so that it may be
reused in the steam generator or boileras boiler feed water.

Steam Condenser of Turbine. Steam condenser is a device in which theexhaust steam from
steam turbine is condensed by means of cooling water.Condensation of steam in a closed
system, creates an empty place byreduction of volume of the low pressure steam

A condenser's function is to allow high pressure and temperature refrigerant vapor to

condense and eject heat. There are three main types: air-cooled,evaporative, and water-cooled
condensers.

The purpose of the condenser is to receive the high-pressure gas from the compressor and
convert this gas to a liquid. It does it by heat transfer, or the principle that heat will
always move from a warmer to a cooler substance.
Air cooled condenser

An air cooled condenser (ACC) is a direct dry cooling system where steam is condensed
inside air-cooled finned tubes. The cool ambient air flow outside the finned tubes is what
removes heat and defines the functionality of an ACC
Water cooled condenser
Evaporative condenser

Surface condenser
Coal Handling
Belt conveyor

Screw conveyor

Helical conveyor

Skip hoist
Ash handling systems

Ash handling refers to the method of collection, conveying, interim storage and load out of
various types of ash residue left over from solid fuel combustion processes. The most
common types of ash resulting from the combustion of coal, wood and other solid fuels.

Ash handling system are generally divided into three types fly ash handling system, bottom
ash handling system and ash slurry disposal system.

Ash handling refers to the method of collection, conveying, interim storage and load out of
various types of ash residue left over from solid fuel combustion processes.

The most common types of ash resulting from the combustion of coal, wood and other solid
fuels.

o bottom ash

o bed ash

o fly ash

o ash clinkers

Ash handling systems may employ different forms of pneumatic ash conveying or
mechanical ash conveyors.A typical ash handling system may employ vacuum pneumatic ash
collection with ash conveying from several ash pick up stations and resulting in delivery to an
ash storage silo for interim holding prior to load out for disposal or reuse. Pressurized
pneumatic ash conveying may also be employed.

Coarse ash material such as bottom ash is most often crushed in clinker grinders (crushers)
prior to being transported in the ash conveyor system. Very finely sized fly ash often accounts
for the major portion of the material conveyed in an ash handling system. It is collected from
baghouse type dust collectors, electrostatic precipitators and other apparatus in the flue gas
processing stream.
Ash mixers (conditioners) and dry dustless telescopic devices are used to prepare ash for
transfer from the ash storage silo to transport vehicles.

Mechanical Ash handling system:

In this system ash cooled by water seal falls on the belt conveyor and is carried out
continuously to the bunker.
Hydraulic ash handling system
Pneumatic ash handling system

In this system ash from the boiler furnace outlet falls into a crusher where a lager ash particles
are crushed to small sizes. The ash is then carried by a high velocityair or steam to the point of
delivery. Air leaving the ash separator is passed through filter to remove dust etc. So that the
exhauster handles clean air which will protect the blades of the exhauster.
Boiler Draught

Boiler draught is defined as the small difference between the pressure of outside cold atmospheric air
and that of gases within a furnace or chimney. The draught is necessary to force air through the fuel
grate to help in proper combustion of fueland to remove the products of combustion.

Boiler draught is defined as the difference between absolute gas pressure at any point in a flow
passage and the ambient (same elevation) atmospheric pressure. Draught is achieved a small pressure
difference which causes the flow of air or gas totake place. It is measured in millimeter (mm) or water.

The draught is one of the most essential systems of the thermal power plant which support the
required quantity of air for combustion and removes the burnt products from the system. To move the
aid through the fuel bed and to produce a flow of hot gases through the boiler economizer, preheated
and chimney require a difference ofpressure.

This difference of pressure to maintaining the constant flow of air anddischarging the gases through the
chimney to the atmosphere is known as draught. Draught can be achieved by the use of chimney, fan,
steam or air jet or a combination of these.

When the draught is produced with the help of chimney only, it is known as Natural Draught and
when the draught is produced by any other means except chimney it is known as Artificial Draught.

Purpose of Boiler Draught

To provide an adequate supply of air for fuel combustion.

For throw out the exhaust gases of combustion from
the combustion chamber.

To discharge these gases to the atmosphere through thechimney.

Measurement of Draught

The amount of draught produce depends upon:

1) The nature and depth of fuel at the furnace.

2) Design of combustion chamber or firebox.

3) The rate of combustion required.

4) Resistance is allowed in the system due to baffles, tubes,superheaters,

economizers, air pre-heaters etc.
Classification of Boiler Draught

Types of Boiler Draught

In general, the draughts may be classified into the following twotypes,

Natural Draught

Artificial Draught

Natural Draught

Natural draught system employs a tall chimney as shown in the figure. The chimney is a
vertical tubular masonry structure or reinforced concrete. It is formed for enclosing a column
of flue gasesto produce the draught.
Advantages of Natural Draught

It does not require any external power for producing thedraught.

The capital investment is less. The maintenance cost is low as there is no mechanical
part.

Chimney keeps the flue gases at a high place in the atmosphere which prevents the
contamination of the atmosphere.

It has a long life.

Disadvantages of Natural Draught

The maximum pressure available for producing natural draught by the chimney is
hardly 10 to 20 mm of water under the normalatmospheric and flue gas temperatures.

The available draught reduces with increases in outside air temperature and for
generating enough draught, the exhaust gases have to be discharged at relatively high
temperatures resulting in the loss of overall plant efficiency. Thus maximum
utilization of Heat is not possible.

Artificial or Mechanical Draught

It has been seen that the draught produced by the chimney is affected by the atmospheric
conditions. It has no flexibility, poor efficiency and tall chimney are required. In most of the
modern power plants, the draught applied must be freedom of atmospheric condition, and It
should have more flexibility (control) to bear the fluctuation loads onthe plant.

Today’s steam power plants requiring 20 thousand tons of steam perhour would be impossible
to run without the aid of draft fans. A chimney of a reasonable height would be incapable of
improving enough draft to eliminate the huge volume of air and gases ( 400 x 103 m 3 to 800
x 10 3 m 3 per minutes). The further advantages of fans are to reduce the height of the
chimney needed.

The draught required in the actual power plant is sufficiently high (300 mm of water) and to
meet high draught requirements, some other system must be used, known as artificial draught.
The artificial is produced by a fan and it is known as dan (mechanical) draught. Mechanical
draught is preferred for central power stations.
Advantages of Artificial or Mechanical Draught

It is more economical and its control is easy.

The desired value of draught can be produced by mechanical means which cannot
produce by means of natural draught.

It increases the rate of combustion by which low-grade fuel canalso be used.

It reduces the smoke level and increases the heat transfer co- efficient no flue gases
side thus increases the thermal efficiencyof the boiler.

In mechanical draught, it saves the energy and the heat of flue gases can be best
utilized by it.

In this way, it reduces fuel consumption and makes boiler operation cheaper.

It reduces the height of chimney which now is only controlled by the requirement of
pollution norms.

Disadvantages of Artificial or Mechanical Draught

The initial cost of mechanical draught system is high.

Running cost is also high due to the requirement of electricity but that is easily
compensated by the savings in fuel consumption.

Maintenance cost is also at a higher rate.

Noise level of boiler is also high due to noisy fan/blower etc.

Types of Artificial or Mechanical Draught

The following are the two types of Artificial or Mechanical draught:

Steam jet draught

Mechanical or fan draught

1. Steam Jet Draught

It is a very simple and easy method of producing artificial draughtwithout the need for an
electric motor. It may be forced or induced depending on where the steam jet is installed.
Steam under pressureis available in the boiler.

When a small position of steam is passed through a jet or nozzle, pressure energy converts to
kinetic energy and steam comes out witha high velocity. This high-velocity steam carries, along
with it, a large mass of air or flue gases and makes it flow through the boiler. Thus steam jet
can be used to produce draught and it is a simple and cheapmethod.

Actually the steam jet is directed towards a fix direction and carries all its energy in kinetic
form. It creates some vacuum in its surrounding and attracts the air of flue gases either by
carrying alongwith it.
 Types of Steam Jet Draught

The following are the main two types of steam jet draught:

1) Induced steam jet draught.

2) Forced steam jet draught.

1. Induced Steam Jet Draught

The jet of steam is turned into a smoke box or chimney. The kinetic head of the steam is high
but static head is low i.e., it produces a partial vacuum which brings the air through the grate,
ash pit, flues and then to motor box and chimney.

This type of induced steam jet draught arrangement is used in locomotive boilers. Here the
steam jet is absorbing the exhaust gases through boiler so it is Induced Steam Jet Draught.
2. Forced Steam Jet Draught

Steam from the boiler after having been throttled to a gauge pressure of 1.5 to 2 bar is supplied
to the jet or nozzle installed in the ash pit.The steam rising out of nozzles with a great velocity
drags air by the fuel bed, furnace, flue passage and then to the chimney. Here the steam jet is
pushing or forcing the air and flue gases to flow through boiler hence it is forced steam jet
draught.

Advantages of Induced Steam Jet Draught

1) It is quite simple and cheap.

2) The induced steam jet draught has the capability of using low-grade fuels.

3) It occupies very less space.

4) It is quite simple and cheap.

5) The initial cost is low.

6) Maintenance cost is low.

7) Exhaust steam from the steam engine or turbine can be usedeasily in the steam jet
draught.

Disadvantages of Steam Jet Draught

1) It can operate only when some steam is generated.

2) Draught produced very low.

2. Mechanical or Fan Draught

The draught, produced by means of a fan or blower, is known as mechanical draught or fan
draught. The fan used is, generally, of centrifugal type and is driven by an electric motor.

In an induced fan draught a centrifugal fan is placed in the path of the flue gases before they
enter the chimney. It draws the flue gases from the furnace and forces them up through the
chimney. The actionof this type of draught is similar to that of the natural draught.
In case of forced fan draught, the fan is placed before the grate, and the air is forced into the
grate through the closed ash pit.

Types of Mechanical or Fan Draught

The following are the three types of mechanical or fan draught:

1. Induced draught.

2. Forced draught.

3. Balanced draught.
1. Induced draught

In induced draught, the blower is placed near the base of the chimney instead of near the grate.
The air is absorbed in the system by decreasing the pressure through the system below the
atmosphere. The induced draught fan sucks the burned gases from the furnace and the
pressure inside the furnace is reduced below atmosphere and includes the atmospheric air to
flow through the furnace.

This draught system is known as positive draught system or forced draught system because
the pressure and air are forced to flow through the system.

The arrangement of the system is shown in the figure. A stack or chimney is also in this
system as shown in the figure but its function is to discharge gases high in the atmosphere to
prevent the contamination. It is not much significant for producing draught, therefore, the
height of the chimney may not be very much.
3. Balanced Draught
It is always better to use a combination of forced draught and induced draught instead of forced
or induced draught alone. If the forced draught is applied alone, the furnace cannot be opened
for firing or inspection because high-pressure air inside the furnace will quickly try to blow
out and there is every possibility of blowing out the fire completely and furnace stops.

If the induced draught is used alone, then also furnace can not be opened either for firing
inspection because the cold air will try to rush into the furnace as the pressure inside the
furnace is under atmospheric pressure. This reduces the effective draught and dilutes the
combustion.

Comparison between Forced Draught and Induced Draught

Forced Draught Induced Draught

Fan or blower is placed beforethe grate Fan or blower is placed after thegrate

The pressure inside the flue The pressure inside the flue
gases is slightly more than gases is slightly less than
atmospheric pressure atmospheric pressure

Fan requires less power Fan requires more power

The flow of the flue gases through The flow of the flue gasesthrough
the boiler is moreuniform the boiler is less uniform

The danger of fire in case pfleakage No danger of fire in case ofleakage

of flue gases. of flue gases.
Boiler Feed Water Treatment

Boiler feed water is an essential part of boiler operations. The feed water is put into the steam
drum from a feed pump. In the steam drum the feed water is then turned into steam from the
heat. After the steam is used it is then dumped to the main condenser.

Boiler feed water

A boiler is a device for generating steam, which consists of two principal parts: the furnace,
which provides heat, usually by burning a fuel, and the boiler proper, a device in which the heat
changes water into steam. The steam or hot fluid is then recirculated out of the boiler for use in
various processes in heating applications.

The water circuit of a water boiler can be summarized by the following

:

The boiler receives the feed water, which consists of varying proportion of recovered
condensed water (return water) and fresh water, which has been purified in varying degrees
(make up water). The make-up water is usually natural water either in its raw state, or treated
by some process before use. Feed-water composition therefore depends on the quality
of the make-up water and the amount of condensate returned to the boiler. The steam, which
escapes from the boiler, frequently contains liquid droplets and gases. The water remaining in
liquid form at the bottom of the boiler picks up all the foreign matter from the water that was
converted to steam. The impurities must be blown down by the discharge of some of the water
from the boiler to the drains. The permissible percentage of blown down at a plant is strictly
limited by running costs and initial outlay. The tendency is to reduce this percentage to a very
small figure.
 Proper treatment of boiler feed water is an important part of operating and maintaining a boiler
system. As steam is produced, dissolved solids become concentrated and form deposits inside
the boiler. This leads to poor heat transfer and reduces the efficiency of the boiler. Dissolved
gasses such as oxygen and carbon dioxide will react with the metals in the boiler system and
lead to boiler corrosion. In orderto protect the boiler from these contaminants, they should be
controlled or removed, trough external or internal treatment.

Methods of feed water treatment

1. Filtration and ultrafiltration.

2. Ion exchange/softening.
3. Membrane processes such as reverse osmosis and
nanofiltration.
4. Deaeration/degasification.
5. Coagulation/chemical precipitation.

A boiler feed water treatment system might be made up of the technologies necessary to
remove problematic dissolved solids, suspended solids, and organic material, including any
number ofthe following:

i. Iron: either soluble or insoluble, iron can deposit on boiler parts and tubes, damage
downstream equipment, and affect the quality of certain manufacturing processes
ii. Copper: can cause deposits to settle in high-pressure turbines, decreasing their
efficiency and requiring costly cleaning orequipment change-outs
iii. Silica: if not removed to low levels, especially in high-pressure boilers, silica can
cause extremely hard scaling
iv. Calcium: can cause scaling in several forms depending on the chemistry of the boiler
feed water (e.g. calcium silicate, calciumphosphate, etc.)
v. Magnesium: if combined with phosphate, magnesium can stick to the interior of the
boiler and coat tubes, attracting more solidsand contributing to scale
vi. Aluminum: deposits as scale on the boiler interior and can react with silica to
increase the likelihood of scaling
vii. Hardness: also causes deposits and scale on boiler parts and piping
viii. Dissolved gasses: chemical reactions due to the presence of dissolved gases such as
oxygen and carbon dioxide can cause severe corrosion on boiler pipes and parts

Makeup water intake

Makeup water, or the water replacing evaporated or leaked water from the boiler, is first
drawn from its source, whether raw water, city water, city-treated effluent, in-plant wastewater
recycle (coolingtower blowdown recycle), well water, or any other surface water source.

Coagulation and chemical precipitation

After all the large objects are removed from the original water source, various chemicals are
added to a reaction tank to remove the bulk suspended solids and other various contaminants.
This process startsoff with an assortment of mixing reactors, typically one or two reactors that
add specific chemicals to take out all the finer particles in the water by combining them into
heavier particles that settle out. The most widely used coagulates are aluminum-based such as
alum and polyaluminum chloride.
Filtration and ultrafiltration

The next step is generally running through some type of filtration to remove any suspended
particles such as sediment, turbidity, and certain types of organic matter. It is often useful to
do this early on in the process, as the removal of suspended solids upstream can help protect
membranes and ion exchange resins from fouling later on in the pretreatment process.
Depending on the type of filtration used, suspended particles can be removed down to under
one micron.

Ion exchange softening

When pretreating boiler feed water, if there’s high hardness complexed with bicarbonates,
sulphates, chlorides, or nitrates, a softening resin can be used. This procedure uses a
strong acid exchange process, whereby resin is charged with a sodium ion, and as the hardness
comes through, it has a higher affinity for calcium, magnesium, and iron so it will grab that
molecule and release the sodium molecule into the water.

Dealkalization

After the softening process, some boiler feed water treatment systems will utilize
dealkalization to reduce alkalinity/pH, an impurityin boiler feed water that can cause foaming,
corrosion, and embrittlement. Sodium chloride dealkalization uses a strong anion exchange
resin to replace bicarbonate, sulfate, and nitrate for chloride anions. Although it doesn’t
remove alkalinity 100%, it does remove the majority of it with what can be an easy-to-
implement and economical process. Weak acid dealkalization only removes cations bound to
bicarbonate, converting it to carbon dioxide (and therefore requiring degasification). It is a
partial softening process that is alsoeconomical for adjusting the boiler feed water pH.

Reverse osmosis (RO) and nanofiltration (NF)

Reverse osmosis (RO) and nanofiltration (NF) are often used down the line in the boiler feed
water treatment system process so most of the harmful impurities that can foul and clog the
RO/NF membranes have been removed. Similar processes of separation, they both force
pressurized water through semipermeable membranes, trapping contaminants such as
bacteria, salts, organics, silica, and hardness, while allowing concentrated, purified water
through. Not always required in boiler feed water treatment, these filtration units are used
mostly with high-pressure boilers where concentration of suspended and dissolved solids
needs to be extremely low.

Deaeration or degasification

At this point in the boiler feed water treatment process, any condensate being returned to the
system will mix with the treated makeup water and enter the deaeration or degasification
process. Any amount of gasses such as oxygen and carbon dioxide can be extremely corrosive
to boiler equipment and piping when they attach to them, forming oxides and causing rust.
Therefore, removing these gases to acceptable levels (nearly 100%) can be imperative to the
service life and safety of the boiler system. There are several types of deaeration devices that
come in a range of configurations depending on the manufacturer, but generally, you might
use a tray-or spray-type deaerator for degasification or oxygen scavengers.
Distribution
After the boiler feed water has been sufficiently purified according to the boiler
manufacturer’s recommendation and other industry-wide regulations, the water is fed to the
boiler where it is heated and used to generate steam. Pure steam is used in the facility, steam
and condensate are lost, and condensate return is pumped back into the process to meet up
with the pretreated makeup water to cycle through pretreatment again.

Binary cycles
 Binary Cycle Power Plant

• Low to moderately heated (below 400°F) geothermal fluid and a secondary (hence,
"binary") fluid with a much lower boiling point that water pass through a heat
exchanger. Binary cycle power plants are closed-loop systems, and virtually nothing
(except water vapor) is emitted to the atmosphere.
• A binary cycle power plant is a type of geothermal power plant that allows cooler
geothermal reservoirs to be used than is necessary for dry steam and flash steam plants
• Binary Power Plants. Binary plants, like dry-steam and flash- steam plants, make use
of naturally sourced hot steam generated by activity from within the Earth's core. All
geothermal plants convert thermal energy to mechanical energy, then finally to electrical
energy.
• The vapor exiting the turbine is then condensed by cold air radiators or cold water and
cycled back through the heat exchanger. A binary vapor cycle is defined in
thermodynamics as a power cycle that is a combination of two cycles, one in a high
temperature region and the other in a lower temperature region
Cogeneration

• Cogeneration—also known as combined heat and power, distributed generation, or

recycled energy—is the simultaneousproduction of two or more forms of energy from
a single fuel source. Cogeneration power plants often operate at 50 to 70 percent
higher efficiency rates than single-generation facilities
• A conventional power plant makes electricity by a fairly inefficient process. A fossil
fuel such as oil, coal, or natural gas is burned in a giant furnace to release heat
energy. Cogeneration (the alternative name for CHP) simply means that the electricity
and heat are made at the same time.
• Cogeneration is a more efficient use of fuel because otherwise- wasted heat from
electricity generation is put to some productive use. This is also called combined heat
and power district heating. Small CHP plants are an example ofdecentralized energy.
• Cogeneration is the process of producing electricity from steam (or other hot gases)
and using the waste heat as steam in chemical processes. In contrast, a stand-alone
power-producing plant typically converts less than 40% of the heat energy of fuel (coal,
natural gas, nuclear, etc.) into electricity.
 UNIT 2
DIESEL, GAS TURBINE
ANDCOMBINED CYCLE
POWERPLANTS
Otto cycle
An Otto cycle is an idealized thermodynamic cycle that describes the functioning of a typical
spark ignition piston engine. It is the thermodynamic cycle most commonly found in
automobile engines.

The Otto Cycle describes how heat engines turn gasoline into motion. Like other thermodynamic
cycles, this cycle turns chemical energy into thermal energy and then into motion. The Otto
cycle describes how internal combustion engines (that use gasoline) work, like automobiles
and lawn mowers.
Diesel cycle

The Diesel cycle is a combustion process of a reciprocating internal combustion engine. In it,
fuel is ignited by heat generated during the compression of air in the combustion chamber,
into which fuel is then injected.
Dual cycle

The dual combustion cycle is a thermal cycle that is a combination of the Otto cycle and the
Diesel cycle. Heat is added partly at constant volume (isochoric) and partly at constant
pressure (isobaric), the significance of which is that more time is available for the fuel to
completely combust. Because of lagging characteristics of fuel this cycle is invariably used for
Diesel and hot spot ignition engines. It consists of two adiabatic and two constant volume and
one constantpressure processes.

The dual cycle consists of following operations:

Process 1-2: Isentropic compression

Process 2-3: Addition of heat at constant volume.
Process 3-4: Addition of heat at constant pressure.
Process 4-5: Isentropic expansion.
Process 5-1: Rejection of heat at constant volume.
Brayton cycle

The Brayton cycle is a thermodynamic cycle named after George Brayton that describes the
workings of a constant-pressure heat engine. The original Brayton engines used a
piston compressor and piston expander, but more modern gas turbine engines and air
breathing jet engines also followthe Brayton cycle.

Diesel engine power plant

A Diesel Power Plant is wherein the prime mover of an alternator is a diesel engine. Using
a diesel engine has its own pros and cons. Installation and operation are easier as compared to
other power plants.

In a diesel power station, diesel engine is used as the prime mover. The diesel burns inside
the engine and the products of this combustion act as the working fluid to produce
mechanical energy. The diesel engine drives alternator which converts mechanical energy into
electrical energy.

A Diesel power station (also known as Stand-by power station) usesa diesel engine as prime
mover for the generation of electrical energy. This kind of power station can be used to
produce limited amounts ofelectrical energy.
 Layout of Diesel Engine Power Plant

Components of Diesel Power Plants

Air Intake System.

Engine Starting system.
Fuel System.
Exhaust System.
Cooling System.
Lubricating System.

Air Intake System

This system supplies necessary air to the engine for fuel combustion. It consists of a pipe for
supplying of fresh air to the engine. Filters are provided to remove dust particles from air
because these particles canact as an abrasive in the engine cylinder.

Engine Starting System

For starting a diesel engine, initial rotation of the engine shaft is required. Until the firing
start and the unit runs with its own power. For small DG set, the initial rotation of the shaft is
provided by handlesbut for large diesel power station. Compressed air is used for starting.
Fuel Supply System

In fuel supply system there are one storage tank strainers, fuel transfer pump and all day fuel
tank. Storage tank where oil in stored.

Strainer: This oil then pump to dry tank, by means of transfer pump.

During transferring from main tank to smaller dry tank, the oil passes through strainer to
remove solid impurities. From dry tank to main tank, there is another pipe connection. This is
over flow pipe. This pipeconnection is used to return the oil from dry tank to main tank in the
event of over flowing.

From dry tank the oil is injected in the diesel engine by means of fuel injection pump.
Exhaust System

The exhaust gas is removed from engine, to the atmosphere by means of an exhaust system. A
silencer is normally used in this system to reduce noise level of the engine.

Cooling System

The heat produced due to internal combustion, drives the engine. But some parts of this heat
raise the temperature of different parts of the engine. High temperature may cause permanent
damage to the machine. Hence, it is essential to maintain the overall temperature ofthe engine
to a tolerable level.

Cooling system of diesel power station does exactly so. The cooling system requires a water
source, water source, water pump and cooling towers. The pump circulates water through
cylinder and head jacket. The water takes away heat from the engine and it becomes hot. The
hot water is cooled by cooling towers and is re-circulated forcooling.

Lubricating System

This system minimizes the wear of rubbing surface of the engine. Here lubricating oil is stored
in main lubricating oil tank. This lubricating oilis drawn from the tank by means of oil pump.
Then the oil is passed through the oil filter for removing impurities. From the filtering point,
this clean lubricating oil is delivered to the different points of the machine where lubrication
is required the oil cooler is provided in the system to keep the temperature of the lubricating
oil as low as possible.

Why diesel plants are not used for high capacity?

The mechanical power required for driving alternator comes from combustion of diesel.
As the diesel costs high, this type of power station is not suitable for producing
power in large scale in our country.

The advantages of diesel power stations include:

1. This is simple in design point of view.

2. Required very small space.
3. It can also be designed for portable use.
 4. It has quick starting facility; the small diesel generator set can bestarted within few
seconds.
5. It can also be stopped as when required stopping small
size diesel power station, even easier than it’s starting
6. As these machines can easily be started and stopped as whenrequired, there may
not be any standby loss in the system.
7. Cooling is easy and required smaller quantity of water in thistype power station.
8. Initial cost is less than other types of power station.
9. Thermal efficiency of diesel is quite higher than of coal.

Disadvantages

The cost of diesel is very high compared to coal. This is the main reason for which a
diesel power plant is not getting popularity over other means of generating power. In
other words the running cost of this plant is higher compared to steam and hydro power
plants.
The plant generally used to produce small power requirement.
Cost of lubricants is high.
Maintenance is quite complex and costs high.
Plant does not work satisfactorily under overload conditions fora longer period.

Applications of diesel engine power plant

• Diesel power plant is used for electrical power generation in capacities ranging
from 100 to 5000 H.P.
• They are commonly used for mobile power generation and are widely used in
transportation systems consisting of railroads, ships, automobiles, and airplanes.
• They can be used as standby power plants.
• They can be utilized as peak load plants for some other typesof power plants.
• For Industries where power requirement is small in the order of 500 kW, diesel
power plants become more economical dueto higher overall efficiency

Gas turbine power plant

The gas turbine is the engine at the heart of the power plant that produces electric current.

A gas turbine is a combustion engine that can convert natural gas or other liquid fuels to
mechanical energy. This energy then drives a generator that produces electrical energy. It
is electrical energy that moves along power lines to homes and businesses.

To generate electricity, the gas turbine heats a mixture of air and fuel at very high
temperatures, causing the turbine blades to spin. The spinning turbine drives a generator
that converts the energy into electricity.

The gas turbine can be used in combination with a steam turbine— in a combined-cycle
power plant—to create power extremely efficiently.
 1. Air-fuel mixture ignites.

• The gas turbine compresses air and mixes it with fuel that is then burned at
extremely high temperatures, creating a hot gas.

2. Hot gas spins turbine blades.

• The hot air-and-fuel mixture moves through blades in the turbine, causing them to
spin quickly.

3. Spinning blades turn the drive shaft.

• The fast-spinning turbine blades rotate the turbine drive shaft.

4. Turbine rotation powers the generator.

• The spinning turbine is connected to the rod in a generator that turns a large
magnet surrounded by coils of copper wire.

5. Generator magnet causes electrons to move and creates electricity.

• The fast-revolving generator magnet creates a powerful magnetic field that lines
up the electrons around the copper coils and causes them to move.
• The movement of these electrons through a wire is electricity.
Layout
The gas turbine is made up of the following components:

• An air compressor.
• A combustor.
• A power turbine, which produces the power to drive theair compressor and
the output shaft.

Compressor

Early gas turbines employed centrifugal compressors, which are relatively simple and
inexpensive. They are, however, limited to low pressure ratios and cannot match the
efficiencies of modern axial- flow compressors. Accordingly, centrifugal compressors are
used today primarily in small industrial units.

An axial-flow compressor is the reverse of a reaction turbine. The blade passages,

which look like twisted, highly curved airfoils, must exert a tangential force on the fluid with
the pressures on one side of the blade higher than on the other. For subsonic flow, an increase
in pressure requires the flow area to also increase, thus reducing the flow velocity between
the blade passages and diffusing the flow. A row of compressor blades must be viewed as a
set of closely spaced, highly curved airfoil shapes with which airflow strongly interacts. There
will not only be a rise in pressure along the blades but a variation between them as well. Flow
friction, leakage, wakes produced by the previous sets of blades, and secondary circulation or
swirl flows all contribute to losses in a real unit. Tests of stationary blade assemblies, known
as cascades, can be performed in special wind tunnels, but actual blade arrangements in a
rotating assembly require special test setups or rigs.

Blades must be designed not only to have the correct aerodynamic shape but also to be light
and not prone to critical vibrations. Recent advances in compressor (and turbine) blade design
have been aided by extensive computer programs.
While moderately large expansion-pressure ratios can be achieved in a reaction-turbine stage,
only relatively small pressure increases can be handled by a compressor stage—typically
pressure ratios per stage of 1.35 or 1.4 to 1 in a modern design. Thus, compressors require more
stages than turbines. If higher stage pressure ratios are attempted, the flow will tend to separate
from the blades, leading to turbulence, reduced pressure rise, and a “stalling” of the
compressor with a concurrent loss of engine power. Unfortunately, compressors are most
efficient close to this so-called surge condition, where small disturbances can disrupt
operation. It remains a major challenge to the designer to maintain high efficiency without
stalling the compressor.

As the air is compressed, its volume decreases. Thus the annular passage area should also
decrease if the through-flow velocity is to be kept nearly constant—i.e., the blades have to
become shorter at higher pressures. An optimum balance of blade-tip speeds and airflow
velocities often requires that the rotational speed of the front, low- pressure end of the
compressor be less than that of the high-pressure end. This is achieved in large aircraft gas
turbines by “spooled” shafts where the shaft for the low-pressure end, driven by the low-
pressureportion of the turbine, is running at a different speed within the hollow high-pressure
compressor/turbine shaft, with each shaft having its own bearings. Both twin- and triple-spool
engines have beendeveloped.

Combustion chamber

Air leaving the compressor must first be slowed down and then split into two streams. The
smaller stream is fed centrally into a region where atomized fuel is injected and burned with a
flame held in place by a turbulence-generating obstruction. The larger, cooler stream is then
fed into the chamber through holes along a “combustion liner” (a sort of shell) to reduce the
overall temperature to a level suitable for the turbine inlet. Combustion can be carried out in
a series of nearly cylindrical elements spaced around the circumference of the engine called
cans, or in a single annular passage with fuel- injection nozzles at various circumferential
positions. The difficulty of achieving nearly uniform exit-temperature distributions in a short
aircraft combustion chamber can be alleviated in stationary applications by longer chambers
with partial internal reversed flow.

Turbine

The turbine is normally based on the reaction principle with the hot gases expanding through
up to eight stages using one- or two-spooledturbines. In a turbine driving an external load, part
of the expansion frequently takes place in a high-pressure turbine that drives only the
compressor while the remaining expansion takes place in a separate, “free” turbine connected
to the load.

High-performance aircraft engines usually employ multiple spools. A recent large aircraft-
engine design operating with an overall pressureratio of 30.5:1 uses two high-pressure turbine
stages to drive 11 high- pressure compressor stages on the outer spool, rotating at 9,860
revolutions per minute, while four low-pressure turbine stages drive the fan for the bypass air
as well as four additional low-pressure compressor stages through the inner spool turning at
3,600 revolutions per minute (see below). For stationary units, a total of three to five total
turbine stages is more typical.
High temperatures at the turbine inlet and high centrifugal blade stresses necessitate the use
of special metallic alloys for the turbine blades. (Such alloys are sometimes grown as single
crystals.) Blades subject to very high temperatures also must be cooled by colder air drawn
directly from the compressor and fed through internal passages. Two processes are currently
used: (1) jet impingement on the inside of hollow blades, and (2) bleeding of air through tiny
holes to form a cooling blanket over the outside of the blades.

Control and start-up

In a gas-turbine engine driving an electric generator, the speed must be kept constant
regardless of the electrical load. A decrease in load from the design maximum can be
matched by burning less fuel while keeping the engine speed constant. Fuel flow reduction
will lower the exit temperature of the combustion chamber and, with it, the enthalpy drop
available to the turbine. Although this reduces the turbine efficiency slightly, it does not affect
the compressor, which stillhandles the same amount of air. The foregoing method of control is
substantially different from that of a steam turbine, where the mass flow rate has to be
changed to match varying loads.

An aircraft gas-turbine engine is more difficult to control. The required thrust, and with it
engine speed, may have to be changed as altitude and aircraft speed are altered. Higher
altitudes lead to lower air-inlet temperatures and pressures and reduce the mass flow rate
through the engine. Aircraft now use complex computer-driven controls to adjust engine
speed and fuel flow while all critical conditions are monitored continuously.

For start-up, gas turbines require an external motor which may be either electric or, for
stationary applications, a small diesel engine.

Advantages

1. It is smaller in size and weight as compared to an equivalent steam power plant. For
smaller capacities, the size of the gas turbine power plant is appreciably greater than a
high-speed diesel engine plant, but for larger capacities, it is smaller in size than a
comparable diesel engine plant. If size and weight are themain consideration such as in
ships, aircraft engines and locomotives, gas turbines are more suitable.
2. The initial cost and operating cost of the gas turbine plant are lower than an
equivalent steam power plant.
3. The plant requires less water as compared to a condensingsteam power plant.
4. The plant can be started quickly and can be put on load in a veryshort time.
5. There are no standby losses in the gas turbine power plant whereas in steam power
plant these losses occur because the boiler is kept in operation even when the turbine is
not supplyingany load.
6. Maintenance cost of the gas turbine power plant is low and easier to maintain.
7. The lubrication of the plant is easy. In gas turbine plant, lubrication is needed mainly
in compressor, turbine main bearing and bearings of auxiliary equipment.
8. The plant does not require massive foundations and building.
9. There is a significant simplification of the plant over a steam plant due to the absence
of boilers with their feed water evaporator and condensing system.
Disadvantages

1. The significant part of the work developed by the turbine is used to derive the
compressor. Therefore, network output of the plant is low.
2. The temperature of the products of combustion becomes too high, so service
conditions become complicated even atmoderate pressures.

Applications

1. Gas turbine plants are used as standby plants for the

hydroelectric power plants.
2. Gas turbine power plants may be used as peak loads plant andstandby plants for
smaller power units.
3. Gas turbines are used in jet aircraft and ships. Pulverised fuel-fired plants are used
in a locomotive.

Combined cycle power plants

A combined cycle power plant is an assembly of heat engines that work in tandem from the
same source of heat, converting it into mechanical energy. On land, when used to make
electricity the most common type is called a combined cycle gas turbine plant.

A combined-cycle power plant uses both a gas and a steam turbine together to produce up to
50 percent more electricity from the same fuel than a traditional simple-cycle plant. The
waste heat from the gas turbine is routed to the nearby steam turbine, which generates extra
power

A Combined Cycle Power Plant produces high power outputs at high efficiencies (up to
55%) and with low emissions. In a Conventional power plant we are getting 33%
electricity only andremaining 67% as waste.

The major components of a combined cycle plant are a gas turbine, a heat recovery steam
generator, a steam turbine, and balance of plantsystems.
A combined-cycle power plant uses both a gas and a steam turbine together to produce up to
50 percent more electricity from the same fuel than a traditional simple-cycle plant. The waste
heat from the gasturbine is routed to the nearby steam turbine, which generates extra power.

Co-generations uses waste heat for many different processes, such as space heating or drying.
Combined-cycle power generation is a two- cycle electricity generation process that uses the
heat from the first cycle to run a second cycle.

Integrated Gasifier based Combined Cycle systems

An integrated gasification combined cycle is a technology that uses a high pressure Gasifier
to turn coal and other carbon based fuels into pressurized gas—synthesis gas. It can then
remove impurities from the syngas prior to the power generation cycle.

Integrated coal gasification combined cycle (IGCC) power plants are a next-generation
thermal power system with significantly enhanced power generation efficiency and
environmental performance due to its combination with coal gasification and the Gas Turbine
Combined Cycle (GTCC) system.
A combined-cycle power plant uses both a gas and a steam turbine together to produce up to
50 percent more electricity from the same fuel than a traditional simple-cycle plant. The
waste heat from the gas turbine is routed to the nearby steam turbine, which generates extra
power.