1. Badarpur Thermal Power Station
INDUSTRIAL TRAINING REPORT
SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE AWARD OF THE DEGREE
BACHELOR OF TECHNOLOGY
(MECHANICAL ENGINEERING)
At
SAM HIGGINBOTTOM INSTITUTE
OF
AGRICULTURE, TECHNOLOGY & SCIENCE
SUBMITTED BY:
AYUSH KHARE
TRAINING INCHARGE:
G.D. SHARMA
SNR. MANAGER
NTPC, BADARPUR
2. DECLARATION
I, Mr. AYUSH KHARE ,hereby declare that this industrial training report is the
record of authentic work carried out by me during the period from 02 june 2015
to 20 june 2015 in NTPC BADARPUR under the super vision of my training
incharge Mr. G.D. SHARMA(SN. MANAGER , TRAINING CENTRE, NTPC BADARPUR).
NAMEOF STUDENT: AYUSH KHARE
SIGNATURE:
3. TRAINING AT BTPS
I was appointed to do 6 week training at this esteemed organization from 02nd
June to 20th
June, 2015. I was assigned to visit various division of the plant, which
were:
Boiler Maintenance Department (BMD I/II/III)
Plant Auxiliary Maintenance (PAM)
These 3 weeks training was a very educational adventure for me. It was really
amazing to see the plant by yourself and learn how electricity, which is one of our
daily requirements of life, is produced.This report has been made by my
experience at BTPS. The material in this report has been gathered from my
textbook, senior student reports and trainers manuals and power journals
provided by training department. The specification and principles are as learned
by me from the employees of each division of BTPS.
AYUSH KHARE
4. ACKNOWLEDGEMENT
I would like to express my deepest appreciation to all those who provided me the
possibility to complete my industrial training. A special gratitude I give to our
Training incharge , Mr. G.D. SHARMA(SNR. HR MGR.), whose contribution in
stimulating suggestions and encouragement, helped me to coordinate in my
training period.
Furthermore I would also like to acknowledge with much appreciation the crucial
role of the employee of Other sections who gave the permission to use all
required equipment and the necessary materials to complete the task . A special
thanks goes to my team mate, who help me to assemble the parts and gave
suggestion about the task . . I have to appreciate the guidance given by other
supervisor as well as the panels especially in our training period that has
improved our presentation skills and knowledge.
A special thanks to Mr. A.K. SHARMA ( DGM, BMD ) For his guidance and care in
NTPC.
Last but not least, many thanks to NTPC , who give
me opportunity to complete my industrial training in such wonderful working
environment,in achieving my goal.
I am extremely grateful to all the technical staff of BTPS / NTPC for their co-
operation and guidance that has helped me a lot during the course of training. I
have learnt alot working under them and I will always be indebted of them for
this value addition in me.
I would also like to thank the training incharge of SHIATS, Allahabad and all the
faculty members of Mechanical Engineering Department for their effort of
constantco-operation,which have been a significant factor in the accomplishment
of my industrial training.
5. CONTENTS
ABOUT NTPC
ABOUT BTPS
INTRODUCTION TO THERMAL POWER PLANT
ENVIRONMENT POLICY
POLLUTION CONTROL SYSTEM
BASIC STEPS OF ELECTRICITY GENERATION
RANKINE CYCLE
BOILER MAINTENANCE DEPARTMENT
PLANT AUXILIARY MAINTENANCE
6. ABOUT NTPC
NTPC is the largest thermal power generating company of India, public sector
company. It was incorporated in the year 1975 to accelerate power development
in the country as a wholly owned company of Government of India. At presents,
Government of India holds 89.5% of the total equity shares of the company and
the balance 10.5% is held by FIIs, Domestic Banks, Public and others. With in a
span of 31 years, NTPC has emerged as a truly national power company, with
power generating facilities in all the major regions of the country.
NTPC’s core business is engineering, construction and operation of power
generating plants and consultancy to power utilities in India or abroad.
The total installed capacity of the company is 31134MW (including JVs) with 16
coal based and 7 gas based stations, located across the country. In addition under
JVs, 7 stations are coal based & another station uses naptha/LNG as fuel. The
company has set a target to have an installed power generating capacity of
1,28,000 MW by the year 2032. The capacity will have a diversified fuel mix
comprising 56% coal, 16% Gas, 11% Nuclear and 17% Renewable Energy
Sources(RES) including hydro. By 2032, non-fossil fuel based generation capacity
shall make up nearly 28% of NTPC‟s portfolio. NTPC has been operating its plants
at high efficiency levels. Although the company has 17.75% of the total national
capacity, it contributes 27.40% of total power generation due to its focus on high
efficiency.
7. In October 2004, NTPC launched its Initial Public Offering (IPO) consisting of
5.25% as fresh issue and 5.25% as offer for sale by Government of India. NTPC
thus became a listed company in November 2004 with the Government holding
89.5% of the equity share capital. In February 2010, the Shareholding of
Government of India was reduced from 89.5% to 84.5% through Further Public
Offer. The rest is held by Institutional Investors and the Public.
Technological Initiatives
Introduction of steam generators (boilers) of the size of 800 MW.
Integrated Gasification Combined Cycle (IGCC) Technology.
Launch of Energy Technology Centre - A new initiative for development of
technologies with focus on fundamental R&D.
The company sets aside up to 0.5% of the profits for R&D.
Roadmap developed for adopting µClean Development.
Mechanism to help get / earn µCertified Emission Reduction.
8. Corporate Social Responsbilities
As a responsible corporate citizen NTPC has taken up number of CSR
initiatives.
NTPC Foundation formed to address Social issues at national level.
NTPC has framed Corporate Social Responsibility Guidelines committing up to
0.5% of net profit annually for Community Welfare.
The welfare of project affected persons and the local population around NTPC
projects are taken care of through well drawn Rehabilitation and Resettlement
policies.
The company hasalso taken up distributed generation forremoterural areas.
Partnering government in various initiatives
Consultantrole tomodernize andimprovise severalplantsacrossthe country.
Disseminate technologies to other players in the sector.
Consultant role ³Partnership in Excellence´ Programmefor improvementof PLF
of 15 Power Stations of SEBs.
Rural Electrification work under Rajiv Gandhi Garmin Vidyutikaran.
Environment management
Allstations ofNTPCareISO14001 certified.
Various groupsto careof environmentalissues.
TheEnvironment Management Group.
Ash tilizationDivision.
AfforestationGroup.
Centre for Power Efficiency & EnvironmentProtection.
Group onCleanDevelopmentMechanism.
NTPC is the second largestowner of trees in the country after the Forest
department
9. Vision
“To be the world’s largest and best power producer, powering India’s growth.”
Mission
“Develop and provide reliable power, related products and services at
competitive prices, integrating multiple energy sources with innovative and eco-
friendly technologies and contribute to society.”
Core Values – BE COMMITTED
B Business Ethics
E Environmentally & Economically Sustainable
C Customer Focus
O Organizational & Professional Pride
M Mutual Respect & Trust
M Motivating Self & others
I Innovation & Speed
T Total Quality for Excellence
T Transparent & Respected Organization
E Enterprising
D Devoted
10. Journey Of NTPC
NTPC was set up in 1975 with 100% ownership by the Governmentof India. In
the last 30 years, NTPC has grown into the largest power utility in India.
In 1997, Government of India granted NTPC status of Navratna being one of
the nine jewels of India, enhancing the powers to theBoard of Directors.
NTPC became a listed company with majority Government ownership of
89.5%.
NTPC becomes third largest by Market Capitalization of listed companies.
The company rechristened as NTPC Limited in line with its changing business
portfolio and transforms itself from a thermal power utility to an integrated
power utility.
National Thermal Power Corporation is the largest power generation company
in India. Forbes Global 2000 for 2008 ranked it 411th in the world.
National Thermal Power Corporation is the largest power generation company
in India. Forbes Global 2000 for 2008 ranked it 317th in the world.
NTPC has also set up a plan to achieve a target of 50,000 MW generation
capacity.
NTPC has embarked on plans to become a 75,000 MW company by 2017.
11. ABOUT BTPS
BADARPUR THERMAL POWER STATION was established on 1973 and it was the
part of Central Government. On 01/04/1978 is was given as No Loss No Profit
Plant of NTPC. Since then operating performance of NTPC has been considerably
above the national average. The availability factor for coal stations has increased
from 85.03 % in 1997-98 to 90.09 % in 2006-07, which compares favorably with
international standards. The PLF has increased from 75.2% in1997-98 to 89.4%
during the year 2006-07 which is the highest since the inception of NTPC.
Badarpur thermal power station started with a single 95 mw unit. There were 2
more units(95MWeach) installedin next2 consecutiveyears.Nowit
hastotalfiveunitswith total capacityof 720MW. Ownership of BTPS was
transferred to NTPC with effect from 01.06.2006 through GOIs Gazette
Notification .
The power is supplied to a 220 KV network that is a part of the northern grid. The
ten circuits through which the power is evacuated from the plant are:
1. Mehrauli
2. Okhla
3. Ballabgarh
4. Indraprastha
5. UP (Noida)
6. Jaipur
12. Badarpur thermal power station started working in 1973 with a single 95 mw unit.
Therewere 2 more units (95 MW each) installed in next 2 consecutive years. Now
it has total fiveunits with total capacity of 720 MW. Ownership of BTPS was
transferred to NTPC witheffect from 01.06.2006 through GOIs Gazette
Notification .Given below are the details of unit with the year they are installed.
It supplies power to Delhi city. It is one of the oldest plant in operation. Its 100
MW units capacity have been reduced to 95 MW. These units have indirectly fired
boiler, while 210 MW units have directly fired boiler. All the turbines are of
Russian Design. Both turbine and boilers have been supplied by BHEL. The boiler
of Stage-I units are of Czech. design. The boilers of Unit 4 and 5 are designed by
combustion engineering (USA). The instrumentation of the stage I units and unit 4
are of The Russian design. Instrumentation of unit5 is provided by M/S
Instrumentation Ltd. Kota, is of Kent design.
In 1978 the management of the plant was transferred to NTPC, from CEA. The
performance of the plant increased significantly, and steadily after take over by
NTPC till 2006, but now the plant is facing various issues.
Being an old plant, Badarpur Thermal Power Station (BTPS) has little automation.
Its performance is deteriorating due to various reasons, like aging, poor quantity
and quality of cooling water etc. Itreceive cooling water fromAgra Canal, which is
an irrigation canal from Yamuna river. Due to rising water pollution, the water of
Yamuna is highly polluted. This polluted water when goes into condenser,
adversely affect life of condenser tubes, resulting in frequent tube leakages. This
dirty water from tube leakages, gets mixed into feed water cycle causes
numerous problems, like frequent boiler tube leakages, and silica deposition on
turbine blades.
Apart from poor quality, the quantity of water supply is also erratic due to lack of
co-ordination between NTPC and UP irrigation which manages Agra Canal.
The quality of the coal supplied has degraded considerably. At worst times, there
were many unit tripping owing to poor quality. The poor coal quality also put
burdens on equipment, like mills and their performance also goes down.The coal
for the plant is fetched from far away, that makes the total fuel cost double of
13. coal cost at coalmine. This factor, coupled with low efficiency due to aging and old
design makes electricity of the plant costlier.
Address Badarpur, New Delhi – 110044
Telephone (STD – 011) - 26949523
Fax 26949532
Installed Capacity 720 MW
Deeated Capacity 705 MW
Location NEW DELHI
Coal Source Jharia Coal Fields
Water Source Agra Canal
Benefeciary States Delhi
Unit Sizes 395MW
2210MW
Units Commissioned Unit I- 95 MW - July 1973
Unit II- 95 MW - August 1974
Unit III- 95 MW - March 1975
Unit IV - 210 MW - December 1978
Unit V - 210 MW - December 1981
Transfer of BTPS to NTPC Ownership of BTPS was transferred to NTPC with effect
from01.06.2006 through GOIsGazetteNotification.
14. INTRODUTION TO THERMAL POWER PLANT
We are well aware that electricity is a form of energy. There are number of
methods by which electricity can be produced, but most common method of
production of electrical energy is to rotate a conductor in a magnetic field
continuously cutting of magnetic lines will cause E.M.F. to be generated at the
ends of conductor. If these terminals are connected through load then electricity
will start flowing through that conductor.
Now let us see what we are doing in Thermal Power Station for the purpose of
production of Electricity. Actually speaking we are doing conversion of energies
from form to another form, and our ultimate aim is to get Electrical energy.
For this purpose the rotation movement is required to rotate the magnetic
field so that it may cut the stationery conductors of the machine. To be more
precise this rotational or mechanical energy is derived from a machine to which we
call Turbine which is actually capable enough to convert heat energy to rotational
energy.
For obtaining heat energy we have to make use of the chemical energy, to
which we call fossil fuel i.e. coal, oil, gas etc. This is achieved in a plant to which
we call furnace or sometimes Boiler.
For transportation of heat energy from furnace to turbine inlet, we require a
medium and we have chosen water as media. This water is converted into steam in
furnace. Quality of steam is always monitored properly process of Electrical
generation.
So we see that the rotational movement required to rotate the magnetic field
of the electric generator is produced by the steam turbine. The power to the steam
turbine is given by steam generator in the form of high pressure and high
temperature steam.
The steam after doing work on the turbine shaft is condensed and condensate is
pumped back into Boiler as high pressure and low temperature water, by means
of Boiler feed pump.
15. PARTS OF A POWER PLANT
1. Cooling tower
2. Cooling water pump
3. Transmission line (3-phase)
4. Unit transformer (3-phase)
5. Electric generator (3-phase)
6. Low pressure turbine
7. Condensate extraction pump
8. Condenser
9. Intermediate pressure turbine
10. Steam governor valve
11. High pressure turbine
12. Deaerator
13. Feed heater
14. Coal conveyor
15. Coal hopper
16. Pulverised fuel mill
17. Boiler drum
18. Ash hopper
19. Super heater
20. Forced draught fan
21. Reheater
22. Air intake
23. Economiser
24. Air preheater
25. Precipitator
26. Induced draught fan
27. Flue Gas
16. 1. Cooling Tower
Cooling towers are heat removal devices used to transfer process waste heat to
the atmosphere. Cooling towers may either use the evaporation of water to
remove process heat and cool the working fluid to near the wet-bulb air
temperature or in the case of closed circuit dry cooling towers rely solely on air to
cool the working fluid to near the dry-bulb air temperature. Common applications
include cooling the circulating water used in oil refineries, chemical plants, power
stations and building cooling. The towers vary in size from small roof-top units to
very large hyperboloid structures that can be up to 200 meters tall and 100
meters in diameter, or rectangular structures that can be over 40 meters tall and
80 meters long. Smaller towers are normally factory-built, while larger ones are
constructed on site. The absorbed heat is rejected to the atmosphere by the
evaporation of some of the cooling water in mechanical forced-draft or induced
22 Draft towers or in natural draft hyperbolic shaped cooling towers as seen at
most nuclear power plants.
2. Cooling Water Pump
It pumps the water from the cooling tower which goes to the condenser.
3. Three phase transmission line
Three phase electric power is a common method of electric power transmission.
It is a type of polyphase system mainly used to power motors and many other
devices. A three phase system uses less conductive material to transmit electric
power than equivalent single phase, two phase, or direct current system at the
same voltage. In a three phase system, three circuits reach their instantaneous
peak values at different times. Taking current in one conductor as the reference,
the currents in the other two are delayed in time by one-third and two-third of
one cycle .This delay between “phases” has the effect of giving constant power
transfer over each cycle of the current and also makes it possible to produce a
rotating magnetic field in an electric motor. At the power station, an electric
generator converts mechanical power into a set of electric currents, one from
each electromagnetic coil or winding of the generator. The current are sinusoidal
functions of time, all at the same frequency but offset in time to give different
phases. In a three phase system the phases are spaced equally, giving a phase
17. separation of one-third of one cycle. Generators output at a voltage that ranges
from hundreds of volts to 30,000 volts.
4. Unit transformer (3-phase)
At the power station, transformers step-up this voltage to one more suitable for
transmission. After numerous further conversions in the transmission and
distribution network the power is finally transformed to the standard mains
voltage (i.e. the “household” voltage). The power may already have been split
into single phase at this point or it may still be three phase. Where the step-down
is 3 phase, the output of this transformer is usually star connected with the
standard mains voltage being the phase- 23 neutral voltage. Another system
commonly seen in North America is to have a delta connected secondary with a
center tap on one of the windings supplying the ground and neutral. This allows
for 240 V three phase as well as three different single phase voltages( 120 V
between two of the phases and neutral , 208 V between the third phase ( or wild
leg) and neutral and 240 V between any two phase) to be available from the same
supply.
5. Electrical generator
An Electrical generator is a device that converts kinetic energy to electrical
energy, generally using electromagnetic induction. The task of converting the
electrical energy into mechanical energy is accomplished by using a motor. The
source of mechanical energy maybe water falling through the turbine or steam
turning a turbine (as is the case with thermal power plants). There are several
classifications for modern steam turbines. Steam turbines are used in our entire
major coal fired power stations to drive the generators or alternators, which
produce electricity. The turbines themselves are driven by steam generated in
"boilers “or "steam generators" as they are sometimes called. Electrical power
stations use large steam turbines driving electric generators to produce most
(about 86%) of the world‟s electricity. These centralized stations are of two types:
fossil fuel power plants and nuclear power plants. The turbines used for electric
power generation are most often directly coupled to their-generators .As the
generators must rotate at constant synchronous speeds according to the
frequency of the electric power system, the most common speeds are 3000 r/min
18. for 50 Hz systems, and 3600 r/min for 60 Hz systems. Most large nuclear sets
rotate at half those speeds, and have a 4-pole generator rather than the more
common 2-pole one.
6. Low Pressure Turbine
Energy in the steam after it leaves the boiler is converted into rotational energy as
it passes through the turbine. The turbine normally consists of several stages with
each stages consisting of a stationary blade (or nozzle) and a rotating blade.
Stationary blades convert the potential energy of the steam into kinetic energy
and direct the flow onto the 24 rotating blades. The rotating blades convert the
kinetic energy into impulse and reaction forces, caused by pressure drop, which
results in the rotation of the turbine shaft. The turbine shaft is connected to a
generator, which produces the electrical energy. Low Pressure Turbine (LPT)
consists of 4x2 stages. After passing through IntermediatePressureTurbinesteam
is passed through LPT which is made up of two parts- LPC REAR & LPC FRONT. As
water gets cooler here it gathers into a HOTWELL placed in lower parts of turbine.
7. Condensation Extraction Pump
A Boiler feed water pump is a specific type of pump used to pump water into a
steam boiler. The water may be freshly supplied or returning condensation of
the steam produced by the boiler. These pumps are normally high pressure
units that use suction from a condensate return system and can be of the
centrifugal pump type or positive displacement type. Construction and
operation: Feed water pumps range in size up to many horsepower and the
electric motor is usually separated from the pump body by some form of
mechanical coupling. Large industrial condensate pumps may also serve as the
feed water pump. In either case, to force the water into the boiler, the pump
must generate sufficient pressure to overcome the steam pressure developed
by the boiler. This is usually accomplished through the use of a centrifugal
pump. Feed water pumps usually run intermittently and are controlled by a
float switch or other similar level-sensing device energizing the pump when it
detects a lowered liquid level in the boiler. Some pumps contain a two-stage
switch. As liquid lowers to the trigger point of the first stage, the pump is
activated. If the liquid continues to drop, (perhaps because the pump has
failed, its supply has been cut off or exhausted, or its discharge is blocked) the
second stage will be triggered. This stage may switch off the boiler equipment
19. (preventing the boiler from running dry and overheating), trigger an alarm, or
both.
8. Condenser
The steam coming out from the Low Pressure Turbine (a little above its boiling
pump) is brought into thermal contact with cold water (pumped in from the
cooling tower) in the condenser, where it condenses rapidly back into water,
creating near Vacuum-like conditions inside the condenser chest.
9. Intermediate Pressure Turbine
Intermediate Pressure Turbine (IPT) consists of 11 stages. When the steam has
been passed through HPT it enters into IPT. IPT has two ends named as FRONT &
REAR. Steam enters through front end and leaves from Rear end.
10.Steam Governor Valve
Steam locomotives and the steam engines used on ships and stationary
applications such as power plants also required feed water pumps. In this
situation, though, the pump was often powered using a small steam engine that
ran using the steam produced by the boiler a means had to be provided, of
course, to put the initial charge of water into the boiler (before steam power was
available to operate the steam-powered feed water pump).The pump was often a
positive displacement pump that had steam valves and cylinders at one end and
feed water cylinders at the other end; no crankshaft was required. In thermal
plants, the primary purpose of 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 so that it may be reused in the steam
generator or boiler as boiler feed water. By condensing the exhaust steam of a
turbine at a pressure below atmospheric pressure, the steam pressure drop
between the inlet and exhaust of the turbine is increased, which increases the
amount heat available for conversion to mechanical power. Most of the heat
liberated due to condensation of the exhaust steam is carried away by the cooling
20. medium (water or air) used by the surface condenser. Control valves are valves
used within industrial plants and elsewhere to control operating conditions such
as temperature, pressure, flow and liquid level by fully or partially opening or
closing in response to signals received from controllers that compares a “set
point” to a 26 “process variable” whosevalue is provided by sensors that monitor
changes in such conditions. The opening or closing of control valves is done by
means of electrical, hydraulic or pneumatic systems.
11.High Pressure Turbine
Steam coming from Boiler directly feeds into HPT at a temperature of 540°C and
at a pressure of 136 kg/cm2. Here it passes through 12 different stages due to
which its temperature goes down to 329°C and pressure as 27 kg/cm2. This line is
also called as CRH – COLD REHEAT LINE. It is now passed to a REHEATER where its
temperature rises to 540°C and called as HRH-HOT REHEATED LINE.
11.Deaerator
A Deaerator is a device for air removal and used to remove dissolved gases (an
alternate would be the use of water treatment chemicals) from boiler feed water
to make it noncorrosive. A dearator typically includes a vertical domed deaeration
section as the deaeration boiler feed water tank. A Steam generating boiler
requires that the circulating steam, condensate, and feed water should be devoid
of dissolved gases, particularly corrosive ones and dissolved or suspended solids.
The gases will give rise to corrosion of the metal. The solids will deposit on the
heating surfaces giving rise to localized heating and tube ruptures due to
overheating. Under some conditions it may give rise to stress corrosion cracking.
Deaerator level and pressure must be controlled by adjusting control valves the
level by regulating condensate flow and the pressure by regulating steam flow. If
operated properly, most deaerator vendors will guarantee that oxygen in the
deaerated water will not exceed 7 ppb by weight (0.005 cm3/L).
21. 12.Feed water heater
A Feed water heater is a power plant component used to pre-heat water
delivered to a steam generating boiler. Preheating the feed water reduces the
irreversibility involved in steam generation and therefore improves the
thermodynamic efficiency of the system. This reduces plant operating costs and
also helps to avoid thermal shock to the boiler 27 metal when the feed water is
introduced back into the steam cycle. In a steam power (usually modelled as a
modified Rankine cycle), feed water heaters allow the feed water to be brought
up to the saturation temperature very gradually. This minimizes the inevitable
irreversibility associated with heat transfer to the working fluid (water).
13.Coal conveyor
Coal conveyors are belts which are used to transfer coal from its storage place to
Coal Hopper. A belt conveyor consists of two pulleys, with a continuous loop of
material- the conveyor Belt – that rotates about them. The pulleys are powered,
moving the belt and the material on the belt forward. Conveyor belts are
extensively used to transport industrial and agricultural material, such as grain,
coal, ores etc.
14.Coal Hopper
Coal Hoppers are the places which are used to feed coal to Fuel Mill. It also has
the arrangement of entering Hot Air at 200°C inside it which solves our two
purposes:-
1. If our Coal has moisture content then it dries it so that a proper combustion
takes place.
2. It raises the temperature of coal so that its temperature is more near to its
Ignite Temperature so that combustion is easy.
22. 16. Pulverized Fuel Mill
A pulveriser is a device for grinding coal for combustion in a furnace in a fossil fuel
power plant.
17. Boiler drum
Steam Drums are a regular feature of water tube boilers. It is reservoir of
water/steam at the top end of the water tubes in the water-tube boiler. They
store the steam generated in the water tubes and act as a phase separator for the
steam/water mixture. The difference in densities between hot and cold water
helps in the accumulation of the “hotter”- water/and saturated –steam into
steam drum. Made from high-grade steel (probably 28 stainless) and its working
involve temperature of 390°C and pressure well above 350psi (2.4MPa). The
separated steam is drawn out from the top section of the drum. Saturated steam
is drawn off the top of the drum. The steam will re-enter the furnace in through a
super heater, while the saturated water at the bottom of steam drum flows down
to the mud-drum /feed water drum by down comer tubes accessories include a
safety valve, water level indicator and fuse plug.
18. Ash Hopper
A steam drum is used in the company of a mud-drum/feed water drum which is
located at a lower level. So that it acts as a sump for the sludge or sediments
which have a tendency to accumulate at the bottom.
23. 19. Super Heater
A Super heater is a device in a steam engine that heats the steam generated by
the boiler again increasing its thermal energy. Super heaters increase the
efficiency of the steam engine, and were widely adopted. Steam which has been
superheated is logically known as superheated steam; non- superheated steam is
called saturated steam or wet steam. Super heaters were applied to steam
locomotives in quantity from the early 20th century, to most steam vehicles, and
also stationary steam engines including power stations.
20. Force Draught Fan
External fans are provided to give sufficient air for combustion. The forced
draught fan takes air from the atmosphere and, warms it in the air preheater for
better combustion, injects it via the air nozzles on the furnace wall.
21. Reheater
Reheater is a heater which is used to raise the temperature of steam which has
fallen from the intermediate pressure turbine.
22. Air Intake
Air is taken from the environment by an air intake tower which is fed to the fuel.
23. Economizers
Economizer, or in the UK economizer, are mechanical devices intended to reduce
energy consumption, or to perform another useful function like preheating a
fluid. The term economizer is used for other purposes as well-Boiler, power plant,
heating, ventilating and air-conditioning. In boilers, economizer are heat
exchange devices that heat fluids , usually water, up to but not normally beyond
24. the boiling point of the fluid. Economizers are so named because they can make
use of the enthalpy and improving the boiler‟s efficiency. They are devices fitted
to a boiler which save energy by using the exhaust gases from the boiler to
preheat the cold water used to fill it (the feed water). Modern day boilers, such as
those in cold fired power stations, are still fitted with economizer which is
decedents of Green‟s original design. In this context there are turbines before it is
pumped to the boilers. A common application of economizer in steam power
plants is to capture the waste heat from boiler stack gases (flue gas) and transfer
thus it to the boiler feed water thus lowering the needed energy input , in turn
reducing the firing rates to accomplish the rated boiler output . Economizer lower
stack temperatures which may cause condensation of acidic combustion gases
and serious equipment corrosion damage if care is not taken in their design and
material selection.
24. Air Preheater
Air preheater is a general term to describe any device designed to heat air before
another process (for example, combustion in a boiler). The purpose of the air
preheater is to recover the heat from the boiler flue gas which increases the
thermal efficiency of the boiler by reducing the useful heat lost in the flue gas. As
a consequence, the flue gases are also sent to the flue gas stack (or chimney) at a
lower temperature allowing simplified design of the ducting and the flue gas
stack. It also allows control over the temperature of gases leaving the stack.
25. Precipitator
An Electrostatic precipitator (ESP) or electrostatic air cleaner is a particulate
device that removes particles from a flowing gas (such as air) using the force of an
induced electrostatic charge. Electrostatic precipitators are highly efficient
filtration devices, and can easily remove fine particulate matter such as dust and
smoke from the air steam. ESPs continue to be excellent devices for control of
many industrial particulate emissions, including smoke from electricity-generating
utilities (coal and oil fired), salt cake collection from black liquor boilers in pump
25. mills, and catalyst collection from fluidized bed catalytic crackers from several
hundred thousand ACFM in the largest coalfired boiler applications. The original
parallel plate-Weighted wire design (described above) has evolved as more
efficient (and robust) discharge electrode designs, today focus is on rigid
discharge electrodes to which many sharpened spikes are attached , maximizing
corona production. Transformer –rectifier systems apply voltages of 50-100
Kilovolts at relatively high current densities. Modern controls minimize sparking
and prevent arcing, avoiding damage to the components. Automatic rapping
systems and hopper evacuation systems remove the collected particulate matter
while on line allowing ESPs to stay in operation for years at a time.
26. Induced Draught Fan
The induced draft fan assists the FD fan by drawing out combustible gases from
the furnace, maintaining a slightly negative pressure in the furnace to avoid
backfiring through any opening. At the furnace outlet and before the furnace
gases are handled by the ID fan, fine dust carried by the outlet gases is removed
to avoid atmospheric pollution. This is an environmental limitation prescribed by
law, which additionally minimizes erosion of the ID fan.
27. Flue gas stack
A Flue gas stack is a type of chimney, a vertical pipe, channel or similar structure
through which combustion product gases called flue gases are exhausted to the
outside air. Flue gases are produced when coal, oil, natural gas, wood or any
other large combustion 31 device. Flue gas is usually composed of carbon dioxide
(CO2) and water vapour as well as nitrogen and excess oxygen remaining from the
intake combustion air. It also contains a small percentage of pollutants such as
particulates matter, carbon mono oxide, nitrogen oxides and sulphur oxides. The
flue gas stacks are often quite tall, up to 400 meters (1300 feet) or more, so as to
disperse the exhaust pollutants over a greater area and thereby reduce the
concentration of the pollutants to the levels required by government's
environmental policies and regulations. The flue gases are exhausted from stoves
ovens, fireplaces or other small sources within residential abodes, restaurants,
hotels through other stacks which are referred to as chimneys.
26. VARIOUS CYCLES AT POWER STATION
PRIMARY AIR CYCLE
SECONDARY AIR CYCLE
COAL CYLCE
ELECTRICITY CYCLE
FLUE GAS CYCLE
CONDENSATE CYCLE
FEED WATER CYCLE
STEAM CYCLE
PRIMARY AIR CYCLE
P A FAN
COLD AIR DUCT APH
STEAL AIR F AN HOT AIR DUCT
PULVERISER
27. SECONDRY AIR CYCLE
FD FAN
SCAPH
APH
WIND BOX
BOILER
IGNITER FAN
SCANNER AIR FAN
W
I
N
D
B
O
X
SCANNER COOLING
33. ENVIRONMENT POLICY
While leading the nation’s power generation league, NTPC has remained
committed to the environment. It continues to take various pro-active measures
for protection of the environment and ecology around its projects.
NTPC was the first among power utilities in India to startEnvironment Impact
Assessment (EIA) studies and reinforced it with Periodic Environmental Audits.
Enviroment Policy & Management
For NTPC, the journey extends much beyond generating power. Right fromits
inception, the company had a well defined environment policy. More than just
generating power, it is committed to sustainable growth of power.
NTPC has evolved sound environmentpractices.
National EnvironmentPolicy
The Ministry of Environment and Forests and the Ministry of Power and NTPC
were involved in preparing the draftEnvironment Policy (NEP) which was later
approved by the Union Cabinet in May 2006.
34. Since its inception NTPC has been at the forefrontof Environmentmanagement.
In November 1995, NTPCbroughtout a comprehensivedocument entitled ‘NTPC
EnvironmentPolicy and EnvironmentManagement System. Amongstthe guiding
principles adopted in the document are the company's pro-activeapproach to
environment, optimum utilisation of equipment, adoption of latest technologies
and continual environmentimprovement. The policy also envisages efficient
utilisation of resources, thereby minimising waste, maximising ash utilisation and
ensuring a green belt all around the plant for maintaining ecological balance.
35. Environment Management, Occupational Health and Safety
Systems
NTPC has actively gone for adoption of the best international practices on
environment, occupational health and safety areas. The organisation has pursued
the EnvironmentalManagement System(EMS) ISO 14001 and theOccupational
Health and Safety Assessment SystemOHSAS 18001atits different
establishments. As a result of pursuing thesepractices, all NTPC power stations
have been certified for ISO 14001& OHSAS 18001 by reputed national and
international certifying agencies.
Pollution Control Systems
While deciding the appropriate technology for its projects, NTPC integrates many
environmental provisions into the plant design. In order to ensure that NTPC
complies with all the stipulated environment norms, following state-of-the-art
pollution control systems / devices have been
installed to control air and water pollution:
• Electrostatic Precipitators
• Flue Gas Stacks
• Low-NOX Burners
• Neutralisation Pits
• Coal Settling Pits / Oil Settling Pits
• DE & DS Systems Cooling Tower
36. • Ash Dykes & Ash Disposal Systems
• Ash Water Recycling System
• Dry Ash Extraction System (DAES)
• Liquid Waste Treatment Plants & Management System
• Sewage Treatment Plants & Facilities
• Environmental Institutional Set-up
Following are the additional measures taken by NTPC in the area of Environment
Management:
• Environment Management During Operation Phase
• Monitoring of Environmental Parameters
• On-Line Data Base Management
• Environment Review
• Upgradation & Retrofitting of Pollution Control Systems
• Resources Conservation
• Waste Management
• Municipal Waste Management
• Hazardous Waste Management
• Bio-Medical Waste Management
• Land Use / Bio-diversity Reclamation of Abandoned Ash Green Belts,
Afforestation & Energy Plantations.
37. BASIC STEPS OF ELECTRICITY GENERATION
The complete and complex process of electricity generation in TPS can be divided
into four major cycles for the sakeof simplicity. The main systems arediscussed in
these cycles in a step by step manner and some useful drawings are also
enclosed. The four cycles are:
1. Coal Cycle
2. Oil Cycle
3. Air and Flue Gas Cycle
4. Steam Water Cycle
OR
1. Coal to steam.
2. Steam to mechanical power.
3. Mechanical power to electrical power.
COAL TO ELECTRICITY: BASICS
38. The simplest of the above four cycles is the coal cycle. In this cycle as explained
earlier crushed coal of about 20mm is transported by conveyor belts to the coal
mill bunkers. From here the coal goes to coal mills through raw coal feeders. In
the coal mills the coal is further pulverized (crushed) to powder form. The
temperature of the coal mills are maintained at 180-200 degree centigrade by a
suitable mixture of hot & cold air.
The air comes from Primary Air fans (P.A FANS) which are 2 in Nos. - A&B. The
outlet duct after combining gets divided into two. One duct goes to the Air
Heaters (A.H- A&B) where primary air is heated by the hot flue gases in a Heat
Exchanger. This duct provides hot air & the other one provides cold primary air. A
suitable mixture of this hot & cold air is fed to the coal mills to maintain their
temperature. This is done to remove moisture of coal. More over this primary air
is also used for transportation of powdered coal from coal mills to the four
corners of the boiler by a set of four pipes. There are six coal mills – A, B, C, D,
E&F and their outlets in the Boiler are at different elevations. The high
Temperature of the primary air does not allow the air coal mixture to choke the
duct from mill to boilers. A portion of the primary air is further pumped to high
pressure and is known as seal air. It is used to protect certain parts of mills like
bearings etc. where powered coal may pose certain problems in the functioning
of the mill. When the air coal mixture enters the boiler it catches fire in the firing
zone and some ash along with clinkers settles down. This is removed periodically
by mixing it with water to make slurry.
39.
40. Oil Cycle
In the oil cycle the oil is pumped and enters the boiler from four corners at three
elevations. Oil guns are used which sprays the oil in atomized form along with
steam so that it catches fire instantly. At each elevation and each corner there are
separate igniters which ignite the fuel oil. There are flame sensors which sense
the flame and send the information to the control roam.
Air & Flue Gas Cycle
For the proper combustion to take place in the boiler right amount of
Oxygen or air is needed in the boiler. The air is provided to the furnace in two
ways - Primary Air & Secondary Air. Primary air is provided by P.A. fans and
enters the boiler along with powdered coal from the mills. While the secondary
air is pumped through Forced Draft fans better known as F.D Fans which are also
two in numbers A&B. The outlet of F.D fans combine and are again divided into
two which goes to Steam coiled Air pre heaters (S.C.A.P.H) A&B where its
temperature is raised by utilizing the heat of waste steam. Then it goes to Air Pre
heater-A&B where secondary air is heated further utilizing the heat of flue gases.
The temperature of air is raised to improve the efficiency of the unit & for proper
combustion in the furnace. Then this air is fed to the furnace.
From the combustion chamber the fuel gases travel to the upper portion of
the boiler and give a portion of heat to the Platen Super Heater. Further up it comes
in contact with the Reheater and heats the steam which is inside the tubes of
reheater. Then it travels horizontally and comes in contact with Final Super Heater.
After imparting the heat to the steam in super heater flue gases go downward to the
Economizer to heat the cold water pumped by the Boiler Feed Pumps (B.F.P.)
these all are enclosed in the furnace. After leaving the furnace the fuel gases go to
the Air Heaters where more heat of the flue gases is extracted to heat primary and
secondary air. Then it goes to the Electrostatic Precipitators (E.S.P.) Stage A&B
where the suspended ash from the flue gases is removed by passing the fuel gas
between charged plates. Then comes the induced draft fan (I.D Fan) which sucks
air from E.S.P. and releases it to the atmosphere through chimney. The pressure
inside the boiler is kept suitably below the atmospheric pressure with the help of
1.0. Fans so that the flame does not spread out of the openings of boiler and cause
41. explosion. Further very low pressure in the boiler is also not desirable because it
will lead to the quenching of flame.
Steam Water Cycle
The most complex of all the cycles is the steam & water cycle. Steam is
the working substance in the turbines in all the thermal and nuclear power
plants. As there is very high temperature and pressure inside the boiler, initially
water has to be pumped to a very high pressure. Water has also to be heated to a
suitably high temperature before putting it inside the boiler so that cold water
does not cause any problem. Initially cold water is slightly heated in low
pressure heaters. Then it is pumped to a very high pressure of about 200
Kg/Cm2 by boiler feed pumps A & B. After this it is further heated in high
pressure heaters by taking the heat from the high pressure steam coming from
various auxiliaries and / or turbines. Then this water goes to the economizer
where its temperature is further raised by the flue gases.
This hot water then goes to the boiler drum. In the boiler drum there is very
high temperature and pressure. It contains a saturated mixture of boiling water and
steam which are in equilibrium. The water level in the boiler is maintained
between certain limit. From here relatively cold water goes down to the water
header situated at the bottom, due to difference in density. Then this cold water
rises gradually in the tubes of the boiler on being heated. The tubes are in the form
of water walls. These tubes combine at the top in the hot water header. From here
the hot water and steam mixture comes back to the boiler drum completing the
small loop.
From the boiler drum hot steam goes to platen super heater situated in the
upper portion of the boiler. Here the temperature of the steam is increased. Then it
goes to final super heater. Here its temperature is further increased.
The turbine is a three cylinder machine with high pressure (H.P),
intermediate pressure (I.P) & low pressure (L.P) casings taking efficiency into
account the .The turbine speed is controlled by hydro dynamic governing system.
The three turbines are on the same shaft which is coupled with generator. The
generator is equipped with D.C excitation system. The steam from the final super
heater comes by main steam line to the H.P turbine. After doing work in the H.P
turbine its temperature is reduced. It is sent back to the boiler by cold reheat line to
42. the reheater. Here its temperature is increased and is sent to the I.P turbine through
hot reheat line. After doing work in the I.P turbine steam directly enters L.P
turbine.
The pressure of L.P turbine is maintained very low in order to reduce the
condensation point of steam. The outlet of L.P turbine is connected with
condenser. In the condenser, arrangement is made to cool the steam to water. This
is done by using cold water which is made to flow in tubes. This secondary water
which is not very pure gains heat from steam & becomes hot. This secondary water
is sent to the cooling towers to cool it down so that it may be reused for cooling.
The water thus formed in the condenser is sucked by condensate water pumps
(C.W. PUMPS) and is sent to deaerator. A suitable water level is maintained in the
hot well of condenser.
Water or steam leakages from the system are compensated by the make up
water, line from storage tanks which are connected to the condenser. The pressure
in side condenser is automatically maintained less then atmospheric pressure and
large volume of steam condense here to form small volume of water. In the
deaerator the water is sprayed to small droplets & the air dissolved in it is removed
so that it may not cause trouble at high temperatures in the Boiler. Moreover, the
water level which is maintained constant in the deaerator also acts as a constant
water head for the boiler feed pumps. Water from deaerator goes to the Boiler feed
pumps after the heated by L.P. Heaters. Thus the water cycle in the boiler is
completed and water is ready for another new cycle. This is a continuous and
repetitive process.
44. RANKINE CYCLE
A Rankine cycle describes a model of the operation of steam heat engines most
commonlyfound in power generation plants. Common heat sources for power
plants using the Rankinecycle are coal, natural gas, oil, and nuclear.The Rankine
cycle is sometimes referred to as a practical Carnotcycle as, when an
efficientturbine is used, the TS diagramwill begin to resemble the Carnotcycle.
The main differenceis that a pump is used to pressurizeliquid instead of gas. This
requires about 1/100th (1%) asmuch energy as that compressing a gas in a
compressor (as in the Carnotcycle).The efficiency of a Rankine cycle is usually
limited by the working fluid.
Without the pressuregoing
super critical the temperature
range the cycle can operate
over is quite small,turbine
entry temperatures are
typically 565°C(the creep
limit of stainless steel)
andcondenser temperatures
are around 30C. This gives a
theoretical Carnotefficiency of around63% compared with an actual efficiency of
42% for a modern coal-fired power station. Thislow turbine entry temperature
(compared with a gas turbine) is why the Rankine cycle isoften used as a
bottoming cycle in combined cycle gas turbine power stations.Theworking fluid in
a Rankine cycle follows a closed loop and is re-used constantly. Thewater vapor
and entrained droplets often seen billowing from power stations is generated
bythe cooling systems (notfromthe closed loop Rankine power cycle) and
represents the wasteheat that could not be converted to useful work. Note that
cooling towers operate using the latent heat of vaporization of the cooling
fluid.The white billowing clouds that formin cooling tower operation are the
result of water droplets which are entrained in the cooling tower airflow it is not,
45. as commonly thought,steam. While many substances could be used in the
Rankine cycle, water is usually the fluidof choice due to its favorableproperties,
such as nontoxic and unreactive chemistry,abundance, and low cost, as well as its
thermodynamic properties.
One of the principal advantages it holds over other cycles is that during the
compressionstagerelatively little work is required to drivethe pump, due to the
working fluid being in itsliquid phase at this point. By condensing the fluid to
liquid, the work required by the pumpwill only consumeapproximately 1% to 3%
of the turbine power and so give a much higher efficiency for a real cycle.The
benefit of this is lost somewhatdue to the lower heat addition temperature. Gas
turbines,for instance, haveturbine entry temperatures approaching 1500°C.
Nonetheless, theefficiencies of steam cycles and gas turbines are fairly well
matched.
The Rankine cycle is a heat engine with a vapour power cycle. The common
working fluid is water. The cycle consists of four processes as shown in
46. 1 to 2: Isentropic expansion (Steamturbine)1 An isentropic process, in which the
entropy of working fluid remains constant.
2 to 3: Isobaric heatrejection (Condenser) An isobaric process, in which the
pressureof working fluid remains constant.
3 to 4: Isentropic compression (Pump)During the isentropic compression process,
external work is done on the working fluid by means of pumping operation.
4 to 1: Isobaric heatsupply (SteamGenerator or Boiler) During this process, the
heat fromthe high temperature sourceis added to the working fluid to convertit
into superheated steam.
According to the T-s diagram shown in Figure1(b), the work outputW1 during
isentropic expansion of steam in the turbine, and the work inputW2 during
isentropic compression of working fluid in the pump are:
W1 = m (h1 – h2) (1.1)
and
W2 = m (h4 – h3) (1.2)
Where m is the mass flow of the cycle and h1, h2, h3, h4 is enthalpy. Heat
supplied to the cycle (steam generator or boiler) Q1, and heat rejected from the
cycle (condenser) Q2, are:
Q1 = m (h1-h4) (1.3)
and
Q2 = m (h2-h3) (1.4)
The net work outputof the cycle is:
W = W1 – W2 (1.5)
The efficiency of the Rankine cycle is:
η = W/Q1 (1.6)
Q1 – Q2 – W = 0 (1.7)
47. And the thermal efficiency of the cycle will be:
η = W/Q1 = 1 – T2 / T1 (1.8)
Due to mechanical friction and other irreversibility’s, no cycle can achieve this
efficiency. The gross work outputof the cycle, i.e. the work done by the system
is:
Wg = W4-1 + W1-2 (1.9)
T-S DIAGRAM OF RANKINE CYCLE
In a real Rankine cycle,the compression by the pump and the expansion in the
turbine are not isentropic. In other words, theseprocesses arenon-reversibleand
entropy is increased during the two processes. This somewhatincreases the
power required by the pump and decreases the power generated by the turbine.
48. Thermal power plant based on a Rankine cycle
In a simple Rankine cycle, steam is used as the working fluid, generated from
saturated liquid water (feed-water). This saturated steam flows through the
turbine, whereits internal energy is converted into mechanical work to run an
electricity generating system. All the energy fromsteam cannot be utilized for
running the generating systembecauseof losses dueto friction, viscosity, bend-
on-blade etc. Most of the heat energy is rejected in the steam condenser. The
feed water brings the condensed water back to the boiler.
49. BOILER MANTENANCE DEPARTMENT
BOILER THEORY
Boiler systems are classified in a variety of ways. They can be
classified according to the end use, such as foe heating, power
generation or process requirements. Or they can be classified
according to pressure, materials of construction, size tube contents
(for example, waterside or fireside), firing, heat source or circulation.
Boilers are also distinguished by their method of fabrication.
Accordingly, a boiler can be pack aged or field erected. Sometimes
boilers are classified by their heat source. For example, they are
often referred to as oil-fired, gas-fired, coal-fired, or solid fuel –fired
boilers.
50. TYPES OF BOILER
Fire tube boilers : Fire tube boilers consistof a series of straight tubes that are
housed inside a water-filled outer shell. The tubes are arranged so that hot
combustion gases flow through the tubes. As the hot gases flow through the
tubes, they heat the water surrounding thetubes. The water is confined by the
outer shell of boiler. To avoid the need for a thick outer shell fire tube boilers are
used for lower pressureapplications. Generally, the heat input capacities for fire
tube boilers are limited to 50 mbtu per hour or less, but in recent years the size of
firetube boilers has increased.
Most modern fire tube boilers have cylindricalouter shells with a small round
combustion chamber located inside the bottom of the shell. Depending on the
construction details, these boilers havetubes configured in either one, two, three,
or four pass arrangements. Becausethe design of fire tube boilers is simple, they
are easy to constructin a shop and can be shipped fully assembled as a package
unit.
These boilers contain long steel tubes through which the hot gases fromthe
furnacepass and around which the hot gases fromthe furnacepass and around
which the water circulates. Fire tube boilers typically havea lower initial cost, are
more fuel efficient and are easier to operate, but they are limited generally to
capacities of 25 tonnes per hour and pressures of 17.5 kg per cm2.
51. Water tube boilers:
Water tube boilers are designed to circulate hot combustion gases
around the outsideof a large number of water filled tubes. The tubes extend
between an upper header, called a steam drum, and one or morelower headers
or drums. In theolder designs, the tubes were either straight or bent into simple
shapes. Newer boilers havetubes with complex and diversebends. Because the
pressureis confined inside the tubes, water tube boilers can be fabricated in
larger sizes and used for higher-pressureapplications.Smallwater tube boilers,
which have one and sometimes two burners, aregenerally fabricated and
supplied as packaged units. Because of their sizeand weight, large water tube
boilers are often fabricated in pieces and assembled in the field.
In water tube or “water in tube” boilers, the conditions arereversed
with the water passing through the tubes and the hot gases passing outside the
tubes. These boilers can be of a single- or multiple-drum type. They can be built to
any steam capacity and pressures, and havehigher efficiencies than fire tube
boilers.
Almost any solid, liquid or gaseous fuelcan be burntin a water tube boiler. The
common fuels are coal, oil, natural gas, biomass and solid fuels such as municipal
solid waste(MSW), tire-derived fuel (TDF) and RDF. Designs of water tube boilers
that burn these fuels can be significantly different.
Coal-fired water tube boilers are classified into three major categories: stoker
fired units, PC fired units and FBC boilers.
Packagewater tube boilers come in three basic designs: A, D and O type. The
names are derived fromthe general shapes of the tube and drum arrangements.
All havesteam drums for the separation of the steam fromthe water, and one or
more mud drums for the removalof sludge. Fuel oil-fired and natural gas-fired
water tube packageboilers are subdivided into three classes based on the
geometry of the tubes.
52. The “A” design has two small lower drums and a larger upper drumfor steam-
water separation. In the “D” design, which is the most common, the unit has two
drums and a large-volumecombustion chamber. The orientation of the tubes in a
“D” boiler creates either a left or right-handed configuration. For the “O” design,
the boiler tube configuration exposes the least amount of tube surfaceto radiant
heat. Rental units are often “O” boilers because their symmetry is a benefit in
transportation
“D” Type boilers:
“This design has the mostflexible design. They have a single steam drumand a
single mud drum, vertically aligned. The boiler tubes extend to one side of each
drum. “D” type boilers generally have moretube surfaceexposed to the radiant
heat than do other designs. “Packageboilers” as opposed to “field-erected” units
generally have significantly shorter fireboxes and frequently have very high heat
transfer rates (250,000btu per hour per sq foot). For this reason it is importantto
ensurehigh-quality boiler feedwater and to chemically treat the systems
properly. Maintenance of burners and diffuser plates to minimize the potential
for flame impingement is critical.
53. “A” type boilers:
This design is more susceptibleto tube starvation if bottom blows are not
performed properly because“A” type boilers havetwo mud drums symmetrically
below the steam drum. Drums are each smaller than the single mud drums of the
“D” or “O” type boilers. Bottom blows should not be undertaken at more than 80
per cent of the rated steam load in these boilers. Bottom blow refers to the
required regular blow down from the boiler mud drums to remove sludgeand
suspended solids.
AUXILIARIES OF THE BOILER
FURNACE
Furnace is primary part of boiler where the chemical energy of the fuel is
converted tothermal energy by combustion. Furnace is designed for efficient and
completecombustion. Major factors that assist for efficient combustion are
amount of fuel inside the furnace and turbulence, which causes rapid mixing
between fuel and air. Inmodern boilers, water furnaces are used.
54. BOILER DRUM
Drumis of fusion-welded design with welded hemisphericaldished ends. Itis
provided with stubs for welding all the connecting tubes, i.e. downcomers, risers,
pipes, saturated steam outlet. The function of steam druminternals is to separate
thewater fromthe steam generated in the furnacewalls and to reduce the
dissolved solidcontents of the steam below the prescribed limit of 1 ppm and also
take care of thesudden change of steam demand for boiler.
The secondary stageof two oppositebanks of closely spaced thin corrugated
sheets,which direct the steam and forcethe remaining entertained water against
thecorrugated plates. Since the velocity is relatively low this water does not get
pickedup again but runs down the plates and off the second stage of the two
steam outlets.
Fromthe secondary separators thesteamflows upwards to the series of screen
dryers,extending in layers across thelength of the drum. These screens perform
the finalstageof the separation.
The water enters the boiler through a section in the convection pass called
theeconomizer. Fromthe economizer it passes to the steam drum. Once the
water entersthe steam drumit goes down the down comers to the lower inlet
water wall headers.Fromtheinlet headers the water rises through the water
walls and is eventually turnedinto steam due to the heat being generated by the
burners located on the front and rear water walls (typically). As the water is
turned into steam/vapour in the water walls,the steam/vapour onceagain enters
the steam drum.
Once water inside the boiler or steam generator, the process of adding the latent
heatof vaporization or enthalpy is underway. Theboiler transfers energy to the
water bythechemical reaction of burning sometype of fuel.
55. Air Preheater ( Tubular Type)
• Wasteheat recovery devicein which the air to on its way to the furnaceis
heated utilizing the heat of exhaust gases
• The function of air pre-heater is to increase the temperature of air before enters
the furnace.
• Itis generally placed after the economizer; so the flue gases passes through the
economizer and then to the air preheater.
56. • An air-preheater consists of plates or tubes with hot gases on one side and air
on the other.
• Itpreheats the to be supplied to the furnace. Preheated air accelerates the
combustion and facilitates the burning of coal.
Degree of Preheating depends on:
(i) Type of fuel,
(ii) Type of fuel burning equipment, and
(iii) Rating at which the boiler and furnaces are operated.
There are three types of air preheaters :
1. Tubular type
2. Plate type
3. Storage type.
Economizer
Function:
Itis a device in which the wasteheat of the flue gases is utilsed for heating the
feed water.
• To recover someof the heat being carried over by exhaustgases.
This heat is used to raisethe temperature of feed water supplied to the boiler.
57. Advantages:
i) The temperature rangebetween various parts of the boiler is reduced
which results in reduction of stresses dueto unequal expansion.
ii) If the boiler is fed with cold water it may result in chilling the boiler metal.
iii) Evaporativecapacity of the boiler is increased.
iv) Overall efficiency of the plant is increased.
58. Super heater
• The function of super heater is to increasethe temperature of the steam above
its saturation point.
• To superheatthe steam generated by boiler.
• Super heaters are heat exchangers in which heat is transferred to the saturated
steam to increase its temperature.
• Superheated steam has the following
Advantages :
i) Steam consumption of the engine or turbine is reduced.
ii) Losses due to condensation in the cylinders and the steam pipes are reduced.
iii)Erosion of turbine blade is eliminated.
iv) Efficiency of steam plant is increased.
Feed Pump
• The feed pump is a pump which is used to deliver feed water to the boiler.
• Doublefeed pump is commonly employed for medium sizeboilers.
• The reciprocating pump are continuously run by steam fromthe same boiler to
which water is to be fed.
• Rotary feed pumps are of centrifugal type and are commonly run either by a
small steam turbine or by an electric motor.
59. AIR PREHEATER
An air preheater (APH) is a general term used to describe any device designed to
heat air before another process (for example, combustion in a boiler) with the
primary objectiveof increasing the thermal efficiency of the process.
The purposeof the air preheater is to recover the heat fromthe boiler flue gas
which increases the thermal efficiency of the boiler by reducing the usefulheat
lost in the flue gas. As a consequence, the flue gases are also conveyed to the flue
gas stack (or chimney) at a lower temperature, allowing simplified design of the
conveyancesystemand the flue gas stack. Italso allows control over the
temperature of gases leaving the stack (to meet emissions regulations).
60. PULVERISER
A pulverizer or grinder is a mechanical device for the grinding of many different
types of materials. For example, a pulverizer mill is used to pulverizecoal for
combustion in the steam-generating furnaces of fossilfuel power plants.
61. PLANT AUXILIARY MAINTENANCE
WATER CIRCULATION SYSTEM
Water must flow through the heat absorption surface of the boiler in order that it
beevaporated into steam. In drum type units (natural and controlled circulation),
the water iscirculated from the drum through the generating circuits and then
back to the drum where thesteam is separated and directed to the super heater.
The water leaves the drum through thedown corners at a temperature slightly
below the saturation temperature. The flow throughthe furnace wall is at
saturation temperature. Heat absorbed in water wall is latent heat of vaporization
creating a mixture of steam and water. The ratio of the weight of the water to
theweight of the steam in the mixture leaving the heat absorption surface is
called circulationration ratio.
TYPES OF BOILER CIRCULATING SYSTEM
Natural circulation system
Controlled circulation system
Combined circulation system
NATURAL CIRCULATING SYSTEM
Water delivered to steam generator from feed water is at a temperature well
below thesaturation value corresponding to that pressure. Entering first the
economizer, it is heated to about 30-40C below saturation temperature. From
economizer the water enters the drum andthus joins the circulation system.
Water entering the drumflows through the down corner andenters ring heater at
the bottom. In the water walls, a part of the water is converted to steamand the
62. mixture flows back to the drum. In the drum, the steam is separated, and sent
tosuperheater for superheating and then sent to the high-pressure turbine.
Remaining water mixes with the incoming water from the economizer and the
cycle is repeated.
As the pressure increases, the difference in density between water and steam
reduces. Thusthe hydrostatic head available will not be able to overcome the
frictional resistance for a flow corresponding to minimum requirement of cooling
of water wall tubes.
ASH HANDLING PLANT
63. HYDRAULIC ASH HANDLING SYSTEM
The hydraulic system carried the ash with the flow of water with high velocity
velocity through a channel and finally dumps into sump. The hydraulic system is
divided into a low velocity and high velocity system. In the low velocity system the
ash from the boilers falls into astream of water flowing into the sump. The ash is
carried along with the water and they areseparated at the sump. In the high
velocity system a jet of water is sprayed to quench the hotash. Two other jets
force the ash into a trough in which they are washed away by the water into the
sump, where they are separated. The molten slag formed in the pulverized
fuelsystem can also be quenched and washed by using the high velocity system.
The advantagesof this system are that its clean, large ash handling capacity,
considerable distance can betraversed, absence of working parts in contact with
ash.
FLY ASH COLLECTION
Fly ash is captured and removed from the flue gas by electrostatic precipitators or
fabric bagfilters (or sometimes both) located at the outlet of the furnace and
before the induced draftfan. The fly ash is periodically removed from the
collection hoppers below the precipitatorsor bag filters. Generally, the fly ash is
pneumatically transported to storage silos for subsequent transport by trucks or
railroad cars.
BOTTOM ASH COLLECTION AND DISPOSAL
At the bottom of every boiler, a hopper has been provided for collection of the
bottom ashfrom the bottom of the furnace. This hopper is always filled with
water to quench the ash andclinkers falling down from the furnace. Some
arrangement is included to crush the clinkersand for conveying the crushed
clinkers and bottom ash to a storage site.
64. WATER PLANT TREATMENT
As the types of boiler are not alike their working pressure and operating
conditions vary andso do the types and methods of water treatment. Water
treatment plants used in thermal power plants used in thermal power plants are
designed to process the raw water to water with a very low content of dissolved
solids known as µdemineralized water. No doubt, this plant has to be engineered
very carefully keeping in view the type of raw water to the thermal plant, its
treatment costs and overall economics.
