ntpc summer training report 2013
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Submitted by:
Sanket Kinage
B.Tech. 2nd Year
VT0733
IIT Jodhpur
Summer Training Report
20th May to 15thJune 2013
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ACKNOWLEDGEMENT
With profound respect and gratitude, I take the opportunityto convey my thanks to complete the training here.
I do extend my heartfelt thanks to Ms. Rachna Singh Bhal
for providing me this opportunity to be a part of this esteemed
organization.
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 a lot working
under them and I will always be indebted of them for this value
addition in me.
SANKET KINAGE
IIT JODHPUR
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INDEX
OVERVIEW ABOUT NTPC
VISION AND MISSION
ABOUT BTPS
NEED OF THERMAL POWER STATION
HOW COAL PRODUCES ELECTRICITY?
RANKINE CYCLE
BOILER MAINTENANCE DEPARTMENT
PLANT AUXILIARY MAINTENANCE
TURBINE MAINTENANCE DEPARTMENT
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OVERVIEW
Indias largest power company, NTPC was set up in 1975 toaccelerate power development in India. NTPC is emerging as a
diversified power major with presence in the entire value chain
of the power generation business. Apart from powergeneration, which is the mainstay of the company, NTPC has
already ventured into consultancy, power trading, ash
utilization and coal mining. NTPC ranked 337th in the 2012,
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Forbes Global 2000ranking of the Worlds biggest companies.NTPC became a Maharatna company in May, 2010, one of theonly four companies to be awarded this status.
The total installed capacity of the company is 41,184 MW(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 naphtha/LNG as fuel and 2
renewable energy projects. The company has set a target tohave an installed power generating capacity of1, 28,000 MWby the year 2032. The capacity will have a diversified fuel mixcomprising 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 NTPCs portfolio.
NTPC has been operating its plants at high efficiency levels.
Although the company has 17.75% of the total nationalcapacity, it contributes 27.40% of total power generation dueto its focus on high efficiency.
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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 listedcompany 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.
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VISION AND MISSION
VISIONTo be the worlds largest and best power producer,
powering Indiasgrowth.
MISSIONDevelop and provide reliable power, related products
and services at competitive prices, integrating multipleenergy sources with innovative and eco-friendly
technologies and contribute to society.
COREVALUESo
BE COMMITED
B Business EthicsE Environmentally & Economically SustainableC Customer FocusO Organizational & Professional PrideM Mutual Respect & TrustM Motivating Self & othersI Innovation & Speed
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T Total Quality for ExcellenceT Transparent & Respected OrganizationE EnterprisingD Devoted
ABOUT BTPS
Badarpur Thermal Power Station is located at Badarpur area inNCT Delhi. The Badarpur Thermal Power Station has aninstalled capacity of705 MW. It is situated in south east cornerof Delhi on Mathura Road near Faridabad. It was the first
central sector power plant conceived in India, in 1965. It wasoriginally conceived to provide power to neighboring states of
Haryana, Punjab, Jammu and Kashmir, U.P., Rajasthan, andDelhi. But since year 1987 Delhi has become its solebeneficiary. It was owned and conceived by Central Electric
Authority. Its construction was started in year 1968, and theFirst unit was commissioned in 26July 1973. The coal for theplant is derived from the Jharia Coal Fields. This wasconstructed under ownership of Central Electric Authority,
later it was transferred to NTPC.
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It supplies power to Delhi city. It is one of the oldest plant in
operation. Its 100 MW units capacity have been reduced to 95MW. These units have indirectly fired boiler, while 210 MWunits 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.
Installed capacity
StageUnit
Number
Installed Capacity
(MW)
Date of
Commissioning
Status
First 1 95 July, 1973 Running
First 2 95 August, 1974 Running
First 3 95 March, 1975 Running
Second 4 210 December, 1978 Running
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StageUnit
Number
Installed Capacity
(MW)
Date of
CommissioningStatus
Second 5 210 December, 1981Running
NEED OF THERMAL POWER STATION
Scarcity of water resources: Water resources are notabundantly available and are geographically unevenly
distributed. Thus hydro power plants cannot be installed with
ease and are limited to certain locations.
Widely available alternate flues: Many alternate fuels such as
coal, diesel, nuclear fuels, geo-thermal energy sources, solar-
energy, and biomass fuels can be used to generate power using
steam cycles.
Maintenance and lubrication cost is lower: Once installed,
these require less maintenance costs and on repairs.
Lubrication is not a major problem compared to hydro power
plant.
Coal is abundant: Coal is available in excess quantities in Indiaand is rich form of energy available at relatively lower cost.
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Working fluid remains within the system, and need not be
replaced every time thus simplifies the process.
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HOW COAL POWER PLANTS PRODUCE ELECTRICITY
The conversion from coal to electricity takes place in three stages.
STAGE 1:
The first conversion of energy takes place in the
boiler. Coal is burnt in the boiler furnace to produce
heat. Carbon in the coal and Oxygen in the air
combine to produce Carbon Dioxide and heat.
STAGE 2:The second stage is the thermodynamic process. The
heat from combustion of the coal boils water in the
boiler to produce steam. In modern power plant, boilers
produce steam at a high pressure and temperature. The
steam is then piped to a turbine. The high pressure steam
impinges and expands across a number of sets of blades in
the turbine. The impulse and the thrust created rotates the
turbine. The steam is then condensed to water and
pumped back into the boiler to repeat to the cycle. This
cycle in ideal case is known as Rankine cycle.
STAGE 3:
In the third stage, rotation of the turbine rotates the
generator rotor to produce electricity based of Faradays
Principle of electromagnetic induction.
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RANKINE CYCLE
The Rankine cycle is an idealized thermodynamic cycle of
a heat engine that converts heat into mechanical work.
The heat is supplied externally to a closed loop, which
usually uses water as the working fluid. The Rankine
cycle, in the form of steam engines generates about 90% of
all electric power used throughout the world.
GENERAL LAYOUT OF THE FOUR MAIN DEVICES
USED IN THE RANKINE CYCLE
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THERE ARE FOUR PROCESSES IN THE RANKINE CYCLE.
Process 1-2: The working fluid is pumped from low to highpressure. As the fluid is a liquid at this stage the pumprequires little input energy.
Process 2-3: The high pressure liquid enters a boiler where itis heated at constant pressure by an external heat source to
become a dry saturated vapor. The input energy required
can be easily calculated using steam tables.
Process 3-4: The dry saturated vapor expands through aturbine, generating power. This decreases the temperature
and pressure of the vapor, and some condensation may
occur. The output in this process can be easily calculated
using the Enthalpy-entropy chart or the steam tables. Ideally
this process is isentropic i.e. entropy of steam doesnt changeduring this process, but in actual case there is increase in
entropy of steam due to irreversibility and hence work
extracted from turbine is less than the work in ideal case.
Process 4-1: The wet vapor then enters a condenser where itis condensed at a constant pressure to become saturated
liquid.
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POWER PLANT CYCLE OR REAL RANKINE CYCLE
In a real power plant cycle (the name 'Rankine' cycle used
only for the ideal cycle), the compression by the pump andthe expansion in the turbine arenot isentropic. In otherwords, these processes are non-reversible and entropy is
increased during the two processes. This somewhat
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increases the power required by the pump and decreases
the power generated by the turbine.
Isentropic efficiency of the Turbine is defined as the ratio
of the work extracted out of turbine to the ideal workconsidering isentropic process.
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GENERAL LAYOUT OF STEAM POWER PLANT
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BOILER MAINTENANCE DEPARTMENT
Boiler and Its Description
The boiler is a rectangular furnace about 50 ft (15 m) on a side
and 130 ft (40 m) tall. Its walls are made of a web of high
pressure steel tubes about 2.3 inches (60 mm) in diameter.
Pulverized coal is air-blown into the furnace from fuel nozzles
at the four corners and it rapidly burns, forming a large fireball
at the centre. The thermal radiation of the fireball heats the
water that circulates through the boiler tubes near the boiler
perimeter. The water circulation rate in the boiler is three to four
times the throughput and is typically driven by pumps. As the
water in the boiler circulates it absorbs heat and changes into
steam at 700 F (370 C) and 3,200 psi (22.1MPa). It is separated
from the water inside a drum at the top of the furnace.
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Boiler Side of the Badarpur Thermal Power Station,
New Delhi
The saturated steam is introduced into superheat pendant tubes
that hang in the hottest part of the combustion gases as they exit
the furnace. Here the steam is superheated to 1,000 F (540 C)
to prepare it for the turbine. The steam generating boiler has to
produce steam at the high purity, pressure and temperature
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required for the steam turbine that drives the electrical
generator.
The generator includes the economizer, the steam drum, the
chemical dosing equipment, and the furnace with its steam
generating tubes and the superheater coils. Necessary safety
valves are located at suitable points to avoid excessive boiler
pressure. The air and flue gas path equipment include: forced
draft (FD) fan, air preheater (APH), boiler furnace, induced draft
(ID) fan, fly ash collectors (electrostatic precipitator or
baghouse) and the flue gas stack.
For units over about 210 MW capacity, redundancy of key
components is provided by installing duplicates of the FD fan,
APH, fly ash collectors and ID fan with isolating dampers. On
some units of about 60 MW, two boilers per unit may instead be
provided.
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Schematic diagram of a coal-fired power plant steam
generator
Specifications of the boiler
1.Main Boiler (AT 100% LOAD):i. Evaporation 700 tons/hr
ii. Feed water temperature 247C
iii. Feed water leaving economizer 276C
2.Steam Temperature:
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i. Drum 341Cii. Super heater outlet 540C
iii. Reheat inlet 332Civ. Reheat outlet 540C
3.Steam Pressure:
i. Drum design 158. 20
kg/cm2ii. Drum operating 149.70
kg/cm2iii. Super heater outlet 137.00
kg/cm2iv. Reheat inlet 26.35 kg/cm2v. Reheat outlet 24.50 kg/cm2
4.Fuel Specifications
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A) Coali. Fixed Carbon 38%
ii. Volatile Matter 26%
iii. Moisture 8.0%
iv. Ash 28%
v. Grind ability 55HGI
vi. High Heat 4860 Kcal/Kg
vii. Coal size to Mill 20 mm
B)Oili. Low Heat value 10000 kcal/kg
ii. Sulphur 4.5% w/w
iii. Moisture 1% w/w
iv. Flash point 660
C.
v. Viscosity 1500 redwood at 37.80
C.
vi. Sp. Weight 0.98 at 380
C.
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5.Heat Balance
i. Dry gas loss 4.63%
ii. Carbon loss 2%
iii. Radiation loss 0.26%
iv. Unaccounted loss 1.5%
v. H2
in air and H2O in fuel 4.9%
vi. Total loss 13.3%
vii. Efficiency 86.7%
AUXILIARIES OF THE BOILER
1.Furnace Furnace is primary part of boiler where the chemical
energy of the fuel is converted to thermal energy by
combustion. Furnace is designed for efficient and complete
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combustion. Major factors that assist for efficient
combustion are amount of fuel inside the furnace and
turbulence, which causes rapid mixing between fuel and
air. In modern boilers, water furnaces are used.
2.Boiler drum Drum is of fusion-welded design with welded
hemispherical dished ends. It is provided with stubs for
welding all the connecting tubes, i.e. downcomers, risers,
pipes, saturated steam outlet. The function of steam drum
internals is to separate the water from the steam generated
in the furnace walls and to reduce the dissolved solid
contents of the steam below the prescribed limit of 1 ppm
and also take care of the sudden change of steam demand
for boiler.
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The secondary stage of two opposite banks of closely spaced
thin corrugated sheets, which direct the steam and force the
remaining entertained water against the corrugated plates.
Since the velocity is relatively low this water does not get
picked up again but runs down the plates and off the second
stage of the two steam outlets.
From the secondary separators the steam flows upwards to
the series of screen dryers, extending in layers across the
length of the drum. These screens perform the final stage of
the separation.
Once water inside the boiler or steam generator, the process
of adding the latent heat of vaporization or enthalpy is
underway. The boiler transfers energy to the water by the
chemical reaction of burning some type of fuel.
The water enters the boiler through a section in the
convection pass called the economizer. From the
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economizer it passes to the steam drum. Once the water
enters the steam drum it goes down the down comers to the
lower inlet water wall headers. From the inlet headers the
water rises through the water walls and is eventually
turned into 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 once again enters the steam
drum.
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External View of an Industrial Boiler at BTPS, New
Delhi
The steam/vapour is passed through a series of steam and
water separators and then dryers inside the steam drum.
The steam separators and dryers remove the water droplets
from the steam and the cycle through the water walls is
repeated. This process is known as natural circulation.
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The boiler furnace auxiliary equipment includes coal feed
nozzles and igniter guns, soot blowers, water lancing and
observation ports (in the furnace walls) for observation of
the furnace interior. Furnace explosions due to any
accumulation of combustible gases after a tripout are
avoided by flushing out such gases from the combustion
zone before igniting the coal.
The steam drum (as well as the superheater coils and
headers) have air vents and drains needed for initial start-
up. The steam drum has an internal device that removes
moisture from the wet steam entering the drum from the
steam generating tubes. The dry steam then flows into the
superheater coils. Geothermal plants need no boiler since
they use naturally occurring steam sources.
Heat exchangers may be used where the geothermal steam
is very corrosive or contains excessive suspended solids.
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Nuclear plants also boil water to raise steam, either directly
passing the working steam through the reactor or else using
an intermediate heat exchanger.
3.Water walls Water flows to the water walls from the boiler drum by
natural circulation. The front and the two side water walls
constitute the main evaporation surface, absorbing the bulk
of radiant heat of the fuel burnt in the chamber. The front
and rear walls are bent at the lower ends to form a water-
cooled slag hopper. The upper part of the chamber is
narrowed to achieve perfect mixing of combustion gases.
The water wall tubes are connected to headers at the top
and bottom. The rear water wall tubes at the top are
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grounded in four rows at a wider pitch forming g the grid
tubes.
4.Reheater Reheater is used to raise the temperature of steam from
which a part of energy has been extracted in highpressure
turbine. This is another method of increasing the cycle
efficiency. Reheating requires additional equipment i.e.
heating surface connecting boiler and turbine pipe safety
equipment like safety valve, non return valves, isolating
valves, high pressure feed pump, etc: Reheater is composed
of two sections namely the front and the rear pendant
section, which is located above the furnace arc between
water-cooled, screen wall tubes and rear wall tubes.
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Tubes of a reheater
5.Superheater Whatever type of boiler is used, steam will leave the water
at its surface and pass into the steam space. Steam formed
above the water surface in a shell boiler is always saturated
and become superheated in the boiler shell, as it is
constantly. If superheated steam is required, the saturated
steam must pass through a superheater. This is simply a
heat exchanger where additional heat is added to the steam.
In water-tube boilers, the superheater may be an additional
pendant suspended in the furnace area where the hot gases
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will provide the degree of superheat required. In other
cases, for example in CHP schemes where the gas turbine
exhaust gases are relatively cool, a separately fired
superheater may be needed to provide the additional heat.
6.Economizer The function of an economizer in a steam-generating unit
is to absorb heat from the flue gases and add as a sensible
heat to the feed water before the water enters the
evaporation circuit of the boiler. Earlier economizer were introduced mainly to recover the
heat available in the flue gases that leaves the boiler and
provision of this addition heating surface increases the
efficiency of steam generators. In the modern boilers used
for power generation feed water heaters were used to
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increase the efficiency of turbine unit and feed water
temperature.
An economizer
Use of economizer or air heater or both is decided by the
total economy that will result in flexibility in operation,
maintenance and selection of firing system and other
related equipment. Modern medium and high capacity
boilers are used both as economizers and air heaters. In low
capacity, air heaters may alone be selected.
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Stop valves and non-return valves may be incorporated to
keep circulation in economizer into steam drum when
there is fire in the furnace but not feed flow. Tube elements
composing the unit are built up into banks and these are
connected to inlet and outlet headers.
7.Air preheater Air preheater absorbs waste heat from the flue gases and
transfers this heat to incoming cold air, by means of
continuously rotating heat transfer element of specially
formed metal plates. Thousands of these high efficiency
elements are spaced and compactly arranged within 12
sections. Sloped compartments of a radially divided
cylindrical shell called the rotor. The housing surrounding
the rotor is provided with duct connecting both the ends
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and is adequately scaled by radial and circumferential
scaling.
An air preheater
Special sealing arrangements are provided in the provided
in the air preheater to prevent the leakage between the air
and gas sides. Adjustable plates are also used to help the
sealing arrangements and prevent the leakage as expansion
occurs. The air preheater heating surface elements are
provided with two types of cleaning devices, soot blowers
to clean normal devices and washing devices to clean the
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element when soot blowing alone cannot keep the element
clean.
8.Pulverizer
A pulverizer is a mechanical device for the grinding of
many types of materials. For example, they are used to
pulverize coal for combustion in the steam-generating
furnaces of the fossil fuel power plants.
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A PulverizerTypes of Pulverizer
i. Ball and Tube millsA ball mill is a pulverizer that consists of a horizontal
cylinder, up to three diameters in length, containing a
charge of tumbling or cascading steel balls, pebbles or steel
rods.
A tube mill is a revolving cylinder of up to five diameters in
length used for finer pulverization of ore, rock and other
such materials; the materials mixed with water is fed into
the chamber from one end, and passes out the other end as
slime.
ii. Bowl millIt uses tires to crush coal. It is of two types; a deep bowl mill
and the shallow bowl mill.
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An external view of a Coal Pulverizer
Advantages of Pulverized Coal Pulverized coal is used for large capacity plants.
It is easier to adapt to fluctuating load as there are no
limitations on the combustion capacity.
Coal with higher ash percentage cannot be used without
pulverizing because of the problem of large amount ash
deposition after combustion.
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Increased thermal efficiency is obtained through
pulverization.
The use of secondary air in the combustion chamber along
with the powered coal helps in creating turbulence and
therefore uniform mixing of the coal and the air during
combustion.
Greater surface area of coal per unit mass of coal allows
faster combustion as more coal is exposed to heat and
combustion.
The combustion process is almost free from clinker and slag
formation.
The boiler can be easily started from cold condition in case
of emergency.
Practically no ash handling problem.
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The furnace volume required is less as the turbulence
caused aids in complete combustion of the coal with
minimum travel of the particles.
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PLANT AUXILIARY MAINTENANCE
1. Water circulation system
Theory of CirculationWater must flow through the heat absorption surface of the
boiler in order that it be evaporated into steam. In drum type
units (natural and controlled circulation), the water is circulated
from the drum through the generating circuits and then back to
the drum where the steam is separated and directed to the super
heater. The water leaves the drum through the down corners at
a temperature slightly below the saturation temperature. The
flow through the furnace wall is at saturation temperature. Heat
absorbed in water wall is latent heat of vaporization creating a
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mixture of steam and water. The ratio of the weight of the water
to the weight of the steam in the mixture leaving the heat
absorption surface is called circulation ratio.
Types of Boiler Circulating System
i. Natural circulation system
ii. Controlled circulation systemiii. Combined circulation system
i. Natural Circulation SystemWater delivered to steam generator from feed water is at a
temperature well below the saturation value corresponding to
that pressure. Entering first the economizer, it is heated to about
30-40
C below saturation temperature. From economizer thewater enters the drum and thus joins the circulation system.
Water entering the drum flows through the down corner and
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enters ring heater at the bottom. In the water walls, a part of the
water is converted to steam and the mixture flows back to the
drum. In the drum, the steam is separated, and sent to
superheater 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. Thus the hydrostatic head available
will not be able to overcome the frictional resistance for a flow
corresponding to the minimum requirement of cooling of water
wall tubes. Therefore natural circulation is limited to the boiler
with drum operating pressure around 175 kg/ cm2.
ii. Controlled Circulation System
Beyond 80 kg/ cm2 of pressure, circulation is to be assisted with
mechanical pumps to overcome the frictional losses. To regulate
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the flow through various tubes, orifices plates are used. This
system is applicable in the high sub-critical regions (200 kg/
cm2).
2. Ash handling plant
The widely used ash handling systems are:i. Mechanical Handling System
ii. Hydraulic System
iii. Pneumatic System
iv. Steam Jet System
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Ash Handling System at Badarpur Thermal Power
Station, New Delhi
The Hydraulic Ash handling system is used at the Badarpur
Thermal Power Station.
Hydraulic Ash Handling System
The hydraulic system carried the ash with the flow of water with
high velocity through a channel and finally dumps into a sump.
The hydraulic system is divided into a low velocity and high
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velocity system. In the low velocity system the ash from the
boilers falls into a stream of water flowing into the sump. The
ash is carried along with the water and they are separated at the
sump. In the high velocity system a jet of water is sprayed to
quench the hot ash. 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 fuel
system can also be quenched and washed by using the high
velocity system. The advantages of this system are that its clean,
large ash handling capacity, considerable distance can be
traversed, 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 bag filters (or sometimes
both) located at the outlet of the furnace and before the induced
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draft fan. The fly ash is periodically removed from the collection
hoppers below the precipitators or bag filters. Generally, the fly
ash is pneumatically transported to storage silos for subsequent
transport by trucks or railroad cars.
Bottom Ash Collection and DisposalAt the bottom of every boiler, a hopper has been provided for
collection of the bottom ash from the bottom of the furnace. This
hopper is always filled with water to quench the ash and clinkers
falling down from the furnace. Some arrangement is included to
crush the clinkers and for conveying the crushed clinkers and
bottom ash to a storage site.
3. Water treatment plant
As the types of boiler are not alike their working pressure and
operating conditions vary and so do the types and methods of
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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 demineralized 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.
A water treatment plant
The type of demineralization process chosen for a power station
depends on three main factors:
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i. The quality of the raw water.
ii. The degree of de-ionization i.e. treated water quality.
iii. Selectivity of resins.
Water treatment process is generally made up of two sections:
Pretreatment section.
Demineralization section
Pretreatment SectionPretreatment plant removes the suspended solids such as clay,
silt, organic and inorganic matter, plants and other microscopic
organism. The turbidity may be taken as two types of suspended
solid in water; firstly, the separable solids and secondly the non-
separable solids (colloids). The coarse components, such as sand,
silt, etc: can be removed from the water by simple sedimentation.
Finer particles, however, will not settle in any reasonable time
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and must be flocculated to produce the large particles, which are
settle able. Long term ability to remain suspended in water is
basically a function of both size and specific gravity.DemineralizationThis filter water is now used for demineralizing purpose and is
fed to cation exchanger bed, but enroute being first
dechlorinated, which is either done by passing through activated
carbon filter or injecting along the flow of water, an equivalent
amount of sodium sulphite through some stroke pumps. The
residual chlorine, which is maintained in clarification plant to
remove organic matter from raw water, is now detrimental to
action resin and must be eliminated before its entry to this bed.
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A demineralization tank
A DM plant generally consists of cation, anion and mixed bed
exchangers. The final water from this process consists essentially
of hydrogen ions and hydroxide ions which is the chemical
composition of pure water. The DM water, being very pure,
becomes highly corrosive once it absorbs oxygen from the
atmosphere because of its very high affinity for oxygen
absorption. The capacity of the DM plant is dictated by the type
and quantity of salts in the raw water input. However, some
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storage is essential as the DM plant may be down for
maintenance. For this purpose, a storage tank is installed from
which DM water is continuously withdrawn for boiler make-
up. The storage tank for DM water is made from materials not
affected by corrosive water, such as PVC. The piping and valves
are generally of stainless steel. Sometimes, a steam blanketing
arrangement or stainless steel doughnut float is provided on top
of the water in the tank to avoid contact with atmospheric air.
DM water make-up is generally added at the steam space of the
surface condenser (i.e., the vacuum side). This arrangement not
only sprays the water but also DM water gets deaerated, with the
dissolved gases being removed by the ejector of the condenser
itself.
4. Draught system
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A natural draught system
Induced Draft SystemIn this system, the air is admitted to natural pressure difference
and the flue gases are taken out by means of Induced Draught
(I.D.) fans and the furnace is maintained under vacuum.
An induced draught system
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Balanced Draught SystemHere a set of Induced and Forced Draft Fans are utilized in
maintaining a vacuum in the furnace. Normally all the power
stations utilize this draft system.
5. Industrial fans
ID FanThe induced Draft Fans are generally of Axial-Impulse Type.
Impeller nominal diameter is of the order of 2500 mm. The fan
consists of the following sub-assemblies:
Suction Chamber
Inlet Vane Control
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Impeller
Outlet Guide Vane Assembly
An ID fan
FD FanThe fan, normally of the same type as ID Fan, consists of the
following components:
Silencer
Inlet Bend
Fan Housing
Impeller with blades and setting mechanism
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An FD fan
The centrifugal and setting forces of the blades are taken up by
the blade bearings. The blade shafts are placed in combined
radial and axial anti-friction bearings, which are sealed off to
the outside. The angle of incidence of the blades may be adjusted
during operation. The characteristic pressure volume curves of
the fan may be changed in a large range without essentially
modifying the efficiency. The fan can then be easily adapted to
changing operating conditions.
The rotor is accommodated in cylindrical roller bearings and an
inclined ball bearing at the drive side absorbs the axial thrust.
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Lubrication and cooling these bearings is assured by a combined
oil level and circulating lubrication system.
Primary Air FanPA Fan if flange-mounted design, single stage suction, NDFV
type, backward curved bladed radial fan operating on the
principle of energy transformation due to centrifugal forces.
Some amount of the velocity energy is converted to pressure
energy in the spiral casing. The fan is driven at a constant speed
and varying the angle of the inlet vane control controls the flow.
The special feature of the fan is that is provided with inlet guide
vane control with a positive and precise link mechanism.
It is robust in construction for higher peripheral speed so as to
have unit sizes. Fan can develop high pressures at low and
medium volumes and can handle hot-air laden with dust
particles.
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Primary air fan
6. Compressor house
Instrument air is required for operating various dampers,
burner tilting, devices, diaphragm valves, etc: in the 210 MW
units. Station air meets the general requirement of the power
station such as light oil atomizing air, for cleaning filters and for
various maintenance works. The control air compressors and
station air compressors have been housed separately with
separate receivers and supply headers and their tapping.
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A compressor house
Instrument Air SystemControl air compressors have been installed for supplying
moisture free dry air required for instrument used. The output
from the compressors is fed to air receivers via return valves.From the receiver air passed through the dryers to the main
instrument airline, which runs along with the boiler house and
turbine house of 210 MW units. Adequate numbers of tapping
have been provided all over the area.
Air-Drying Unit
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A 95 MW Generator at BTPS, New Delhi
CompoundingSeveral problems occur if energy of steam is converted in single
step and so compounding is done. Following are the type of
compounded turbine:
i. Velocity Compounded TurbineLike simple turbine it has only one set of nozzles and
entire steam pressure drop takes place there. The kinetic
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MAIN TURBINE
The 210MW turbine is a cylinder tandem compounded type
machine comprising of H.P. and I.P and L.P cylinders. The H.P.
turbine comprises of 12 stages the I.P turbine has 11 stages and
the L.P has four stages of double flow. The H.P and I.P. turbine
rotor are rigidly compounded and the I.P. and L.P rotor by lens
type semi flexible coupling. All the 3 rotors are aligned on five
bearings of which the bearing number is combined with thrust
bearing.
The main superheated steam branches off into two streams from
the boiler and passes through the emergency stop valve and
control valve before entering the governing wheel chamber of
the H.P. Turbine. After expanding in the 12 stages in the H.P.
turbine then steam is returned in the boiler for reheating.
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The reheated steam from boiler enters I.P. turbine via the
interceptor valves and control valves and after expanding enters
the L.P stage via 2 numbers of cross over pipes.
In the L.P. stage the steam expands in axially opposed direction
to counteract the thrust and enters the condenser placed directly
below the L.P. turbine. The cooling water flowing through the
condenser tubes condenses the steam and the condensate the
collected in the hot well of the condenser.
The condensate collected the pumped by means of 3x50% duty
condensate pumps through L.P heaters to deaerator from where
the boiler feed pump delivers the water to the boiler through H.P.
heaters thus forming a closed cycle.
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divided at the horizontal centerline. Its halves are bolted together
for easy access. The cylinder contains fixed blades, vanes and
nozzles that direct steam into the moving blades carried by the
rotor. Each fixed blade set is mounted in diaphragms located in
front of each disc on the rotor, or directly in the casing. A disc
and diaphragm pair a turbine stage. Steam turbines can have
many stages. A rotor is a rotating shaft that carries the moving
blades on the outer edges of either discs or drums. The blades
rotate as the rotor revolves. The rotor of a large steam turbine
consists of large, intermediate and low-pressure sections.
In a multiple-stage turbine, steam at a high pressure and high
temperature enters the first row of fixed blades or nozzles
through an inlet valve/valves. As the steam passes through the
fixed blades or nozzles, it expands and its velocity increases. The
high velocity jet of stream strikes the first set of moving blades.
The kinetic energy of the steam changes into mechanical energy,
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causing the shaft to rotate. The steam that enters the next set of
fixed blades strikes the next row of moving blades.
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As the steam flows through the turbine, its pressure and
temperature decreases while its volume increases. The decrease
in pressure and temperature occurs as the steam transmits
energy to the shaft and performs work. After passing through
the last turbine stage, the steam exhausts into the condenser or
process steam system.
The kinetic energy of the steam changes into mechanical energy
through the impact (impulse) or reaction of the steam against
the blades. An impulse turbine uses the impact force of the steam
jet on the blades to turn the shaft. Steam expands as it passes
through thee nozzles, where its pressure drops and its velocity
increases. As the steam flows through the moving blades, its
pressure remains the same, but its velocity decreases. The steam
does not expand as it flows through the moving blades.
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STEAM CYCLE
The thermal (steam) power plant uses a dual (vapor+liquid)
phase cycle. It is a closed cycle to enable the working fluid
(water) to be used again and again. The cycle used is Rankine
cycle modified to include superheating of steam, regenerative
feed water heating and reheating of steam.
MAIN TURBINE
The 210 MW turbine is a tandem compounded type machine
comprising of H.P. and I.P. cylinders. The H.P. turbines comprise
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of 12 stages, I.P. turbine has 11 stages and the L.P. turbine has 4
stages of double flow.
The H.P. and I.P. turbine rotors are rigidly compounded and the
L.P. motor by the lens type semi flexible coupling. All the three
rotors are aligned on five bearings of which the bearing no. 2 is
combined with the thrust bearing
The main superheated steam branches off into two streams from
the boiler and passes through the emergency stop valve and
control valve before entering the governing wheel chamber of
the H.P. turbine. After expanding in the 12 stages in the H.P.
turbine the steam is returned in boiler for reheating.
The reheated steam for the boiler enters the I.P> turbine via the
interceptor valves and control valves and after expanding enters
the L.P. turbine stage via 2 nos of cross-over pipes.
In the L.P. stage the steam expands in axially opposite direction
to counteract the trust and enters the condensers placed below
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the L.P. turbine. The cooling water flowing throughout the
condenser tubes condenses the steam and the condensate
collected in the hot well of the condenser.
The condensate collected is pumped by means of 3*50% duty
condensate pumps through L.P. heaters to deaerator from where
the boiler feed pump delivers the water to boiler through H.P.
heaters thus forming a close cycle.
The Main Turbine
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TURBINE CYCLE
Fresh steam from the boiler is supplied to the turbine through
the emergency stop valve. From the stop valves steam is supplied
to control valves situated in H.P. cylinders on the front bearing
end. After expansion through 12 stages at the H.P. cylinder,
steam flows back to the boiler for reheating steam and reheated
steam from the boiler cover to the intermediate pressure turbine
through two interceptor valves and four control valves mounted
on I.P. turbine.
After flowing through I.P. turbine steam enters the middle part
of the L.P. turbine through cross-over pipes. In L.P. turbine the
exhaust steam condenses in the surface condensers welded
directly to the exhaust part of L.P. turbine.
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from deaerator through a collection where pressure of steam is
regulated.
From the condenser, condensate is pumped with the help of
3*50% capacity condensate pumps to deaerator through the
low-pressure regenerative equipments.
Feed water is pumped from deaerator to the boiler through the
H.P. heaters by means of 3*50% capacity feed pumps connected
before the H.P. heaters.
SPECIFICATIONS OF THE TURBINE
Type: Tandem compound 3 cylinder reheated type. Rated power:210 MW. Number of stages:12 in H.P., 11 in I.P. and 4*2 in L.P.
cylinder.
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Rated steam pressure:130 kg /sq. cm before entering thestop valve.
Rated steam temperature:535C after reheating at inlet. Steam flow: 670T / hr. H.P. turbine exhaust pressure: 27 kg /sq. cm., 327C Condenser back pressure:0.09 kg /sq. cm. Type of governing:nozzle governing. Number of bearing:5 excluding generator and exciter.
Lubrication Oil: turbine oil 14 of IOC. Gland steam pressure:1.03 to 1.05 kg /sq. cm (Abs) Critical speed:1585, 1881, 2017. Ejector steam parameter:4.5 kg /sq. cm. Condenser cooling water pressure: 1.0 to 1.1 kg /sq.
cm.
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Condenser cooling water temperature:27000 cu. M/hr.
Number of extraction lines for regenerative heatingof feed water: seven.
TURBINE COMPONENTS
Casing.
Rotor.
Blades.
Sealing system.
Stop & control valves.
Couplings and bearings.
Barring gear.
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TURBINE CASINGS
HP Turbine Casings Outer casing: a barrel-type without axial or radial flange.
Barrel-type casing suitable for quick startup and loading.
The inner casing- cylindrically, axially split.
The inner casing is attached in the horizontal and vertical
planes in the barrel casing so that it can freely expand
radially in all the directions and axially from a fixed point
(HP- inlet side).
IP Turbine Casing: The casing of the IP turbine is split horizontally and is of
double-shell construction.
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Both are axially split and a double flow inner casing is
supported in the outer casing and carries the guide blades.
Provides opposed double flow in the two blade sections and
compensates axial thrust.
Steam after reheating enters the inner casing from Top &
Bottom.
LP Turbine Casing: The LP turbine casing consists of a double flow unit and has
a triple shell welded casing. The shells are axially split and of rigid welded construction.
The inner shell taking the first rows of guide blades is
attached kinematically in the middle shell.
Independent of the outer shell, the middle shell, is
supported at four points on longitudinal beams.
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In all the stages lashing wires are provided to adjust the
frequency of blades. In the last two rows, satellite strips are
provided at the leading edges of the blades to protect them
against wet-steam erosion.
BLADES Most costly element of the turbine.
Blades fixed in stationary part are called guide blades/
nozzles and those fitted in moving part are called
rotating/working blades.
Blades have three main parts:
oAerofoil: working part.
oRoot.
oShrouds.
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Shroud are used to prevent steam leakage and guide steam
to next set of moving blades.
VACUUM SYSTEMThis comprises of:
Condenser: 2 for 200 MW unit at the exhaust of LPturbine.
Ejectors:One starting and two main ejectors connected tothe condenser locared near the turbine.
C.W. Pumps: Normally two per unit of 50% capacity.
CONDENSERThere are two condensers entered to the two exhausters of the
L.P. turbine. These are surface-type condensers with two pass
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valves in the steam space level indicator for visual level
indication of heating steam condensate pressure vacuum gauges
for measurement of steam pressure, etc.
DeaeratorThe presence of certain gases, principally oxygen, carbon
dioxide and ammonia, dissolved in water is generally considered
harmful because of their corrosive attack on metals, particularly
at elevated temperatures. One of the most important factors in
the prevention of internal corrosion in modern boilers and
associated plant therefore, is that the boiler feed water should be
free as far as possible from all dissolved gases especially oxygen.
This is achieved by embodying into the boiler feed system a
deaerating unit, whose function is to remove the dissolved gases
from the feed water by mechanical means. Particularly the unit
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lubricating system with adequate protection to trip the pump if
the lubrication oil pressure falls below a preset value.
The high pressure boiler feed pump is a very expensive machine
which calls for a very careful operation and skilled maintenance.
Operating staff must be able to find out the causes of defect at
the very beginning, which can be easily removed without
endangering the operator of the power plant and also without
the expensive dismantling of the high pressure feed pump.
Function
The water with the given operating temperature should flow
continuously to the pump under a certain minimum pressure. It
passes through the suction branch into the intake spiral and
from there; it is directed to the first impeller. After leaving the
impeller it passes through the distributing passages of the
diffuser and thereby gets a certain pressure rise and at the same
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suction pressure which will remove the possibility of cavitation.
Therefore all the feed pumps are provided with a main shaft
driven booster pump in its suction line for obtaining a definite
positive suction pressure.
Lubricating Pressure
All the bearings of boiler feed pump, pump motor and hydraulic
coupling are force lubricated. The feed pump consists of two
radial sleeve bearings and one thrust bearing. The thrust bearing
is located at the free end of the pump.
High Pressure Heaters
These are regenerative feed waters heaters operating at high
pressure and located by the side of turbine. These are generally
vertical type and turbine based steam pipes are connected to
them.
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HP heaters are connected in series on feed waterside and by such
arrangement, the feed water, after feed pump enters the HP
heaters. The steam is supplied to these heaters to form the bleed
point of the turbine through motor operated valves. These
heaters have a group bypass protection on the feed waterside.
In the event of tube rupture in any of the HPH and the level of
condensate rising to dangerous level, the group protection
devices divert automatically the feed water directly to boiler,
thus bypassing all the 3 H.P. heaters.
An HP heater
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