This document is a summer training report submitted by Awnish Anand, a 3rd year mechanical engineering student at SMIC Hyderabad, after completing a 4-week internship at the National Thermal Power Corporation (NTPC) plant in Barh, Bihar from June 1-31, 2016. The report provides an overview of NTPC, details about the Barh Super Thermal Power Plant where the training took place, and describes the basic steps of electricity generation from coal as observed during the internship. It also includes sections on maintenance departments at the plant and the Rankine cycle of thermal power generation.

1. 1
Summer Training Report
June
2016
SUBMITTED BY:
AWNISH ANAND
ROLL NO- 137W1A03D1
3rd
YEAR B.TECH
MECHANICAL ENGINEERING
SMIC, HYDERABAD.

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ACKNOWLEDGEMENT
With profound respect and gratitude, It is my fortune to be a part of NTPC
summer training programme at Barh, and I would like to thank for the same.
I am extremely grateful to all the technical staffs of BSTPP/NTPCfor their
co-operation and guidance that has helped me a lot during the training. I have
learnt a lot working under them and I will always be indebted to them for this
value addition in me .
I would also like to thank all the faculty members of mechanical enginnering
department for their effort of constant co-operation, which have been a signifiacant
role in my industrial training.
At last I want to convey my regards to all the people invoved in the training
session, who helped me in accomplishing it in such a wonderful way.
AWNISH ANAND
(SMICH)
ST.MARY’S INTEGRATED CAMPUS,
HYDERABAD.

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CERTIFICATE
This is to certify that AWNISH ANAND, student of 3rd year B.Tech
Mechanical Enginnering, (SMIC)ST.MARY’S INTEGRATED CAMPUS,
HYDERABAD,has successfully completed his Industrial Training at National
Thermal Power Corporation, Barh for 4 week from 1st JUNE to 31ST JUNE 2016.
He has completed the hole training at per the training report submitted by him.
Training Incharge
NTPC,
Barh,Bihar

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TRAINING AT BSTPP
I was appointed to do 4 week training at this esteemed organization from 1st JUNE
to 31st JUNE,2016
These 4 week training was a very educational adventure for me. It was really
amazing to learn how electricity,which is our daily requirement is produced .
The report has been made by my experience at BSTPP. The material in this report
has been gathered from my textbook ,senior student reports, and power journals
available. The specification and principles are as learned by me from the
employees of each division of BSTPP.
AWNISH ANAND

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INDEX
 ABOUT NTPC
 ABOUT BSTPP
 BASIC STEPS OF ELECTRICITYGENERATION
 RANKINE CYCLE
 BOILER MAINTAINANCE DEPARTMENT
 PALNT AUXILLARY MAINTAINANCE
 TURBINE MAINTAINANCE DEPARTMENT
 MAINTAINANCE PLANNING DEPARTMENT
 COAL HANDLING DEPARTMENT

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7. 7
ABOUT NTPC
NTPC is the india’s largest thermal power generation public sectorundertaking
company with a power generating capacity of 45,548 MW. It was founded in 1975
to accelerate power development in the country as a wholly owned company of
government of india. At presesnt, government of india holds 75.96% equity shares
in NTPC. LIC is the largest non-promotorshareholder in the company.
NTPC’s corebusiness is engineering, construction and operation of power
generating plants and providing consultancy to power utilities in India and abroad.
The total installed capacity of the company is 45,548 MW with 25 coal based and
7 gas based power plants including 9 coalbased (owned through JVs).
NTPC has adopted a multiapronged growth strategy which includes capacity
addition through green field projects, expansion of exisiting stations, joint
ventures, subsidiaries and takeover of stations.

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NTPC has set new benchmarks for the power industry both in the area of power
construction and operation. NTPC has undertaken massive aforestation in the
vicinity of the plants. Plantations have increased forest area and reduced barren
land. The massive aforestation by NTPC in and around its Ramagundam Power
station (2600) have contributed reducing the temperature in the areas by about
3degrees.
The company has also ventured into oil and gas explorationand coalmining
activities. Although the company has approx. 16% of the total national capacity it
contributes to over 25% of the total power generation due to its focus on operating
its power at higher efficiency levels (approx.80.2% against national PLF rate
64.5%).
In May 2010, NTPC is listed among one of the 7 MAHARATNA companies by
the UnionGovernment of India.

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TechnologicalInitiatives
 Introduction of steam generators (boilers) of the size of 800MW.
 Integrated Gasification Combined (IGCC) technology.
 Roadmap developed for adopting ‘clean development’
 The company sets aside upto 0.5% of the profits for R&D.
 Launch of energy technology centre – a new initiative for the development
of technologies with focus on fundamental R&D.
Partnering government in various initiatives
 Consultant role to modrnize and improvise several plants across the
country.
 Disseminate technologies to other players in the sector
 Rural electrification work under Rajiv Gandhi Gramin Vidyutikaran.
Environment Management
 All stations of NTPC are ISO 14001 certified.
 Groups are appointed to take care of the environment.
 Ash utilization division.
 Afforstation group.
 Centre for power efficiency & environment protection.
 NTPC is the second largest owner of the trees in the country after the forest
department.

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ABOUT BSTPP
(Barh Super Thermal PowerProject)
Barh Super Thermal Power Station is located in Barh of Bihar state. It is a coal
operated power plant that delivers its power from 5 units each having 660 MW
with a nameplate capacity of 3,300MW.
The 1,980 MW (3×660 MW) Barh stage- 1 is being built by Russian firm
Technopromexport(TPE) which is delayed due to agreement issues and
1,320MW(2×660 MW) Barh stage -2 extension is being built by BHEL.
Bihar’s share is 1183 MW from NTPC Barh (26% from stage-1 and 50% from
stage -2).
Prime minister Atal Bihari Vajpayee, had laid the foundation of the main plant of
stage -1 of NTPC Barh on March 6,1999. Later on Shushil kkumar shinde had
inaugrated the main plant house of stage -2 on May 29, 2006.
Project Cost
The plant is to produce3,300 MW of power at a costof Rs 26,000 crore. The total
approved costof stage -1 has Rs 8,692 crore and that of stage -2 is Rs 7,688.12
crore.

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BASIC STEPS OF ELECTIRCITY GENERATION;
 Coal to steam
 Steam to mechanical power
 Mechanical to electrical power
COAL TO ELECTRICITY: BASICS
The basic steps in the generation of coal to electricity are shown below.
Coal to Steam
Coal from the coal wagons is unloaded in the handling plant. A empty wagon
weights about 15 tons rotated through 165˚ through which the coal comes out with
the help of gates. Gates are of two types :- BOXN (having the doors sideways) and
BOBR (gates are top and bottom). This coal is transported to to the raw coal
bunkers with the help of belt conveyors whose speed is about 3 m/s . As the coal
has so many impuritites so suspended magnets, metal detectors,inline metal
separators are used to count out the impurities. Coal is tronsported to bowl mills by

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coal feeders. The coal is pulverised in the bowl mill, where it is ground to powder
form. Coal is crushed by the crushing action of the rollers or hammers which
reduce the size of the coal at about 20 mm. This crushed coal is taken away to the
furnace through coal pipes with the help of P.A fan with compressionratio <1.2.
P.A (primary air) fan takes atmospheric air, a part of which is used to warm
the air in air preheater for better economy. Priamry air then passes through the coal
pulverizers and carries the coal dust to the burners for the injection into the
furnace. Warm air is supplied to the coalto make it dry and increase the
pressure of the coaldust. Secondary air is mixed with the primary air flow in the
burners.
The I.D (induced draft) fan assists the F.D fan by drawing out the combustible
gases from the furnace,maintaining a slightly negative pressure in side the furnace
less than the atmospheric pressure to avoid leakage of combustion products from
the boiler casing.
Pulverized coalis air-blown into the furnace through burners located at the four
corners, or along one wall, or two opposite walls, and it is ignited to rapidly burn,
forming a large fireball at the center. Water from the boiler pump passes through
economizer where it is warmed up and reaches the boiler drum. Water from the
drum passes through down comers and goes to the bottom ring header. From the
bottom ring header it is divided into all four sides of the furnace.
Thermal radiation of the fireball that is developed due to combustion of coal
in the furnace heats the water that circulates through the boiler tubes near the
boiler perimeter. And due to density differnce waterrises up in the water wall
tubes. Water is partly converted to steam and the cobination of steam and water re-
enters the steam drum. The water in the steam drum again returned to the
downcomers . this cycle continues till the whole water is converted into steam.
This process is natural or sometimes pump is also used.
But in case of Once Through Boiler no drum is used it directly converts all
the water into steam .

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The saturated steam is supplied to the superheaters coils which hang in the
hottest part of the furnace and they are superheated upto 540˚C to supply it to the
turbines.
Note- APH is Air preheater.
Flue gases from the furnace are extracted by I.D fan, which maintain balance draft
in the furnace (-5 to -10 mm of wel) with force draft fan. Flue gases emit their
energy to vairous superheaters in the pent house and finally pass through air-
preheaters and goes to electrostatic precipitators.
 An electrostatic precipitator consisits a row of thin vertical wires, and
followed by a stack of large flat metal plates oriented vertically which are
placed 1 to 18 cm apart.
 Air stream flows horizontally through the spaces between the wires and then
passes through the plates
 An electic coronadischarge developed ,due to a negative voltage of several
thousand volts between wire and plate, ionizes the air.
 Therefore the ionized particles are diverted to the grounded plates thus
removed from the air.

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STEAM TO MECHANICAL POWER
From the boiler, a steam pipe conveys steam to the turbine through a stop valve
(which can be used to shut-off the steam in case of an emergency) and through
control valves that automatically regulate supply of the steam to the turbine. Stop
valves to regulate the supply of the steam used. (this depends on th speed of the
turbine and the amount of electricity required from generator).
Steam from the controlvalve enters the high pressure cylinder of the turbine,
where it passes through a ring of stationary blades fixed to the cylinder wall. These
act as nozzles and direct the steam into a second ring of moving blades mounted on
the disc secured to the turbine shaft. The second ring turns the shaft as a result of
the force of steam. The stationary and moving blades together constitute a stage of
turbine and in practice manty stages are necessary, so that the cylinder contains a
number of rings of statiionary blades with ring of moving blades arranged between
them. The steam passes through each stage in turn until it reaches at the end of the
high-pressure cylinder and in its passage some of its heat energy is vhanged into
mechanical energy.
The steam leaving the high pressure cylinder goes back to the
boiler for reheating and returns by a furthur pipe to intermediate pressure cylinder.
Here it passes through another series of stationary and moving blades.
Finally, the steam is taken to the low-pressure cylinders, each
of which enters at the centre flowing outwards in the oppositedirections through
the rows of turbine the rows of turbine blades through an arrangement called
‘Double Flow’ –to the extremities of the cylinder. As the steam gives up its heat
energy to drive the turbine, its temperature and pressure fall and it expands.
Beacause of this expansion the blades are much larger towards the low pressure
ends of the turbine.

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MECHANICALTO ELECTRICAL POWER
Athe blades of the turbine rotate, the shaft of the generator, which is coupled to the
turbine, also rotates. It results in the rotaition of the coil of the generator, which
causes induced electricity to be produced.
BASIC POWER PLANT CYCLE
The thermal power plant uses a dual plant
uses a dual (vapour+liquid) phase cycle to enable the working fluid to be used
continuously. The cycle uses Modified Rankine cycle which includes superheating
of steam, regenerative feed water heating and reheating of steam.

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On large turbines, it is economical to increase the cycle efficiency by using reheat,
which is a way of partially overcoming temperature limitations. By returning
partially expanded steam, to reheat, the average temperature at which the heat
added, is increased and, by expanding this reheated system to the remaining stages
of the turbine, the exhaust wetness is relatively less than otherwise be conversly, if
the maximum tolerable wetness is allowed, the initial pressure of the steam can be
appreciably increased.
Bleed Steam Extraction :- For regenerative system, no. of non-regulated
extractions are taken from HP,IP turbine.
FACTORS AFFECTING THE CYCLE EFFICIENCY
 Initial steam pressure.
 Initial steam temperature.
 On reheat cycle , whether used or not
 Condenser pressure
 Regenerative feed water heating.

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RANKINE CYCLE
The rankine cycle is a themodynamic cycle which converts heat into work. The
heat is supplied externally to a closed loop, which usually uses water as the woking
fluid. This cycle generates about 80% of all electric power used throughout the
world, including virtually all solar thermal, biomass, coal and nuclear power
plants. It is named after william john Mcquorm Rankine, a Scottish polymath.
DESCRIPTION
A Rankine cycle describes a
model of the operation of steam heat engines most commonly found in power
plants. Common heat sources for power plants are natural gas, coal, oil and
nuclear.
The Rankine cycle is sometimes reffered to as a practical carnot cycle as when an
efficient turbine is used the TS diagram will begun to resemble the carnot cycle.
The main difference is that a pump is used to pressurize the liquid instead of gas.
This requires about 1/100th i.e 1% as much energy as that compressing a gas in
compressor(as in Carnot cycle).
The efficiency of Rankine cycle is limited by the working fluid. Without going
supercritical the temperature range the cycle can operate over is quite small,
turbine entry temperatures are typically 565˚C and condenser temperatures are
around 30˚C. This gives a theoritical Carnot efficiency of around 63% compared
with an actual efficiency of 42% for a modern coal-fired power station. This low

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turbine entry temperature is why the Rankine cycle is often used as a bottoming
cycle.
The working fluid in a Rankine cycle follows a closed loop and is re-used
constantly. The water vapour and entrained droplets often seen billowing from
power stations is generated by the cooling systems(not from the closed loop
Rankine cycle) and represents the waste heatthat could not be converted to a useful
work.
Note that cooling towers operate using the latent heat of vapourization of the
cooling fluid. The white billowing clouds that form in cooling tower operation are
the result of water droplets which are entrained in the cooling tower air flow, it is
not, as commonly thought, steam. We can use any substancein place of water but
we are taking water because of the following properties :
 Non-toxic
 Less specific gravity so less pump work is required.
 Cheaply available.
 High latent heat of vapourization.
 Unreactive in nature.
One of the benefits with water is that during the compressionstage relatively little
work is required to drive the pump, due to the working fluid being in its liquid
phase at this point. By condensing the fluid to liquid, the work required by the pum
will only consume 1 to 3% of turbine power .
PROCESSESOF A RANKINE CYCLE
There are 4 processesin the Rankine cycle operating between pressures of 0.06bar
and 50bar.

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Process1-2:The working fluid is pumped from low to high pressure, as the
fluid is a liquid at this stage the pump requires little input energe.
Process2-3:The high pressure liquid enters a boiler where it is heated at
constant pressure by an external heat sourceto becomea dry saturated vapour.
Process3-4:The dry saturated vapour expands through a turbine generating
power. This decreases the temperature and pressure of the vapour, and some
condensation may occus.
Process4-1:The wet vapour then enters a condenserwhere it is condensed at a
constant pressure and temperature to become a saturated liquid. The pressure
and temperature of the condenser is fixed by the temperature of the cooling
coils as the liquid as the fluid is under going a phase change.
In an an ideal Rankine cycle the pump and the turbine would be isentropic i.e the
pump and turbine would generate no entropy and hence maximize the net work
output. Processes 1-2 and 3-4 would be represented by vertical lines and more
closely resemble that of the Carnot cycle.

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REAL RANKINE CYCLE ;- Rankine cycle with superheat.
I
In a real Rankine cycle the compressionby the pump and the expansion in the
turbine are not isentropic. In other words, the processes are non-revresible and
entropy is incresed during the two processes. This somewhat increases the power
consumption during pump work from turbine thus deacreases turbine power
output.
In particular the efficiency of the steam turbine will be limited by water droplet
formation. As the water condenses, water droplets hit the turbine blades at high
speed causing pitting and erosion, gradually decreasing the life of the turbine
blades and efficiency of the turbine. The easiest way to overcome this problem is
to superheat the the steam. On the T-S diagram above, state 3 is above a two phase
region of steam and water so after expansiom the steam will be very wet by
superheating , state 3 will move to the right of the diagram and hence producea
dryer steam after expansion.

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Rankine Cycle With Reheat
In this variation, two turbines work in series. The first accepts vapour from the
boiler at high pressure. After the vapour has passed through the first turbine, it re-
enters the boiler and is reheated to superheated temperature before passing through
the second, low pressure turbine. Among other advantages this prevents the vapour
from condensing during its expansion which can seriously damage the turbine
blades, and improves the efficiency of the cycle. Some steps are :
 Lowering the condenserpressure.
 Increasing the temperature of the steam while entering the turbine.
 Large variation in pressure between boiler and condenser.
 Implementation of reheat and regenerative system in the cycle.

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Regenerative Rankine Cycle
The regenerative cycle isso named because after emerging from the condenser the
working fluid is heated by the steam tappd from the hot portion of the cycle. In the
diagram shown, the fluid at 2 is mixed with the fluid at 4 (both at the same
pressure) to end up with the saturated liquid at 7. The regenerative rankine cycle is
commonly used in real power stations.
Another variation sends bleed steam from between turbine stages to feedwater
heaters to preheat the water on its way from condenser to boiler.
Regeneration increases the cycle heat input temperature by eliminating the addition
of heat to the feed water heater from boiler that are at relatively low temperatuture
with repect to bleed steam.

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1. BOILER MAINTAINANCE DEPARTMENT.
Boilerand Its Description
The boiler is a ractangular furnace about 50 ft (15 m) on a snd 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 water circulation rate due to fireball in the boiler tubes near boiler
perimeter, is three to four times the throughput and is typically driven by pump.
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 seperated from the water inside a
drum at the top of the furnace.
The steam generating boiler has to purity steam turbine that drives the electric
generator.
The generator includes includes the economiser, the steam drum, the chemical
dosing equipment, and the furnace with its steam generating tubes and the
superheater coils. Drums are located outside the boiler since the inside the
bolier is high and if drum is located inside the boiler the water from steam drum
finds difficult to come down to bottomheader for the cycle to be repeated.
Necessary safety valves are located at suitable points to avoid excessive boiler
pressure. The air and flue gas path equipment include: forced draft fan, air
preheater, boile furnace, induced draft fan,fly ash collector (electrostatic
precipitator and baghouse) and the flue gas stack.
For units over about 210 MW capacity, redundancy of the key components is
provided by installing duplicates of the FD fan, APH, flyash 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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AUXILIARIES OF THE BOILER
1. FURNACE
2.
 Furnace is primary part of boile where the chemical energy of the fuel is
converted into thermal energy by combustion. Furnace is designed for
efficient and complete combustion.
3. BOILER DRUM
 Drum is fusion welded design with welded hemispherical dished ends. It is
provided with stubs for welding all the connecting tubes, i.e dowmcomers,
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

25. 25
reduce the dissolved solid contents of the steam below the prescribed limit
of 1 ppm and also take care of sudden change of steam demand for boiler.
 The secondarysage of two opposite banks of closely spaced thin corrugated
sheets, which direct the steam and force the remaining entrained water
against the corrugated plates. Since the velocity is relatively low this water
does not get picked up again but runs down the plates off the second stage of
the two steam outlets.
 From the seconddaryseparators the steam flows uwards to the series of
screen dryers, extending in layers across the length of the steam drum. These
screens perform the final stage of the separation.
 Once the inside boiler or steam generator, the process ofadding the latent
heat of vapourisation 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 ecocomiser. From economiser it passes to the steam drum. Once the
water enters the steam drum it goes down 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 density difference.
 The seam/vapour is passed through a series of steam and water separators
and then dryers inside the steam drum. The steam separetors 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.
 The boiler furnace auxillary eqipment includes coalfeed nozzles and igniter
guns, sootblowers, water lancing and observation ports for the observation
of the furnace interior. Furnace explosion due to any accumilatin of
combustible gas after a tripout are avoided by flishing out such gases from
the combustion zone before igniting the coal.

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 The steam drum has airvents 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 generating tubes. This dry steam flows to super
heater coils. No need of stem drums in geothermal plants since they use
naturally occuring steam sources.
 Heat exchangers may be used where the geothermal steam is very corosive
or contains excessive suspended solids.
4. REHEATER AND SUPERHEATER
 Reheater and super heater are a set of tubes located in the boiler. Steam
from water walls through steam drum passes to superheater where it is
heated above saturated temperature.
 They are generally made up of ferritic steel (upto 12% Cr) and austenitic
stainless steel (upto 25% Cr) to allow for a temperature rise upto 50˚C.
 The superheated steam flows through the main steam piping to the high
pressure turbine. The exhaust steam coming out of H.P turbine passes
through the reheat tubes before introduced to I.P and L.P turbines.

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 High reheating temperature improves the output and efficiency of a
power plant.
 Superheater and reheaters consisits of parallel mounted steel tubes, butt
welded and bent, with outside diameters of 38 to 76 mm.
 Superheater steam temperature an go upto 600˚C and 280 bar,
respectively.
 The reheat steam is at much lower pressure than the supeheated steam
but the temperature can be above superheated steam i.e 620˚C.
5. ECONOMIZER
 The functionof economizer is to absorb heat from the flue gases and add as a
sensible heat (only temperature changes no phase change) to the feed water
before the water enters the evaporaion circuit of the boiler.
6. AIR –PREHEATER

28. 28
 Air preheater absorbs waste heat from the flue gases and transfers it to
incoming cold air, by means of continuously rotating heat transfer element
of especially formed metal plates. Thousands of these high efficiency
elements are spaced and compactly arranged with 12 sections. Sloped
compartments of radially divided cylindrical shell called the rotor.
 The air preheater heating surface elements are provided with two types of
cleaning device, sootblowers to clean normal devices and washing devices
to clean the elements in some places where sootblowing is not possible.
7. PULVERIZER
 A pulverizer is a mechanical device for the grinding of many types of
materials. Forexample : used to pulverise coal in plant.
 Advantages
 Pulverized coalis used for large capacity plants.
 Increasing thermal efficiency .
 The combustion process is almost free from clinker and slag formation.
 The boiler can be easily started from condition in case of emergency.
 Greater surface area of coal per unit mass of coal allows faster
combustion as more coal isi exposed to heat and combustion.

29. 29
 The use of secondary air in the combustion chamber along with the
powdered coal helps in crating turbulence and therefore uniform mixing
occurs,also furnace size required is less as the coal powderis combusted
aquiring less volume.
2. Plant Auxiliary Maintainance
A.Water circulation system.
Theory of Circulation
Water flows through the heat absorption surface of the boiler that it be
evaporated into steam. In drum type units (natural and controled circulation),
the water is circulated from the drum where the steam is seperated and directed
to the superheater. The water leaves the drum through the furnace wall is at
saturation temprature. Heat absorbed in water wall is latent heat of
vapourisation creating a mixture of steam and water. The ratio of the weight of
water to the weight of steam in the mixture leaving the heat absorption surface
is called circulation ratio.
Types of boiler circulaton system
 Natural circulation system- carried out due to differnence in densities.
Water entring the steam drum flows through the downcomer and enters ring
heater at the bottom. The steam is separated and goes to supreheater to rotate
the H.P turbine.. Remaining water mixes with the the incoming water from
economize and cycle is repeated. Natural circulation is limited to the boiler
with drum operating pressure around 175 kg/cm.cm

30. 30
 Controlled circulation system-Beyond 80 kg/cm.cm of pressure, this
circulation is required to overcome the frictional losses. To regulate the flow
through tubes, orifices plates are used. This system is applicable to high sub
critical regions. (200 kg/cm.cm)
B. ASH HANDLING PLANT
The widely used ash and handling systems are:-
I. Mechanicalhandling system
II. Hydraulic system
III. Pneumatic system
IV. Steamjet system
 Fly ashcollection-fly ash is captured and removed from the flue gas by
electrostsatic precipitators or fabric bag filters located at the outlet of the
furnace and before the induced draft fan. The fly ash is periodically removed
from the collection hoppers below the precipitators or bag filters, the fly ash
is pneumatically transported to storage silos for subsequent transport by
trucks or railroad cars.
 Bottom Ash Collectionand Disposal
At the bottomof every boiler a hopper has been provided for collection of
ash at the bottom of the furnace. Some arrangements include to crush the
clinkers and conveying th crushed clinkers and bottom ash to a storage site.

31. 31
C. Water Treatment Plant
Water treatment in thermal poer plants are required to process the raw water
with a very less amount of dissolved solids known as ‘Demineralized water’.
Pretreatmentsection
Pretreatment section removes the suspended solids such as clay, slit, organic
and inorganic matter, plant and other microscopic organisms. The coarse
componenets like sand, slit, etc can be removed from the water by simple
sedimentaion.
Demineralization
This filterwater is used for demineralizng purposeand is fed to cation
exchanger bed, but enroute being first dechlorinated, which is either done by
passing through activated carbonfilter or injecting along the flow of wate,
an equivalent amount of sodium sulphite through some stoke pumps.
a) A Deaerator is a device is used to remove oxygen and other dissolved
gasesfrom the feedwater. Two tyoes ;- tray type and spray type.
b) Solubility os gases in a solution also decreases with the decrease in partial
preddure of the gas above solution. (Henery’s 1st
law)
c) Solubility of gases in solution decreases with the increase the temperature of
solution upto saturation temperature.(Henery’s 2nd
law).
d) Oxygen scavegning are also added to the feed water to remove oxygen and
prevent corrosion. Such as ; sodium sulfate (Na2SO3), hydrazine(N2H4).
The condensateplus makeup water flows through the deaerator that removes
dissolved air from water, furthur purifying and reducing its corrosiveness. The
water may be dosed following this point with Hydrazine (N2H4) an oxygen
removing chemical. It is also dosed with pH control agents such as ammonia or
morpholine to keep the acidity low.

32. 32
Steam condensing
The condenser condensesthe steam from the exhaust of the turbine into
liquid to allow it to be pumped. If the condenser can be made cooler, the
pressureof the exhaust steam is reduced and efficiency of the cycle increases.
Diagram of a typical water-cooled surfacecondenser.
The surfacecondenser is a shell and tube heat exchanger in which cooling
water is circulated through the tubes.[7][11][12][13] The exhaust steam from the
low pressureturbineentersthe shell where it is cooled and converted to
condensate(water) by flowingover the tubes as shown in the adjacent
diagram. Such condensersuse steam ejectors or rotary motor-driven exhausts
for continuousremovalof air and gases from the steam side to
maintainvacuum.
For best efficiency, the temperaturein the condenser mustbe kept as low as
practical in order to achieve the lowest possible pressurein the condensing
steam. Since the condenser temperaturecan almost alwaysbe kept
significantly below 100 °C where the vapor pressure of water is muchless
than atmospheric pressure, the condenser generally worksunder vacuum.
Thus leaks of non-condensibleair into the closed loop mustbe prevented.
Typically the cooling water causes the steam to condenseat a temperatureof
about 35 °C (95 °F) and that creates an absolute pressure in the condenser of
about 2–7 kPa(0.59–2.07inHg), i.e. a vacuum of about −95 kPa(−28 inHg)
relative to atmosphericpressure. The large decrease in volumethat occurs

33. 33
when water vapor condensesto liquid creates the low vacuum that helps pull
steam through and increase the efficiency of the turbines.
The limiting factor is the temperatureof the cooling water and that, in turn, is
limited by the prevailingaverage climatic conditionsat the power plant's
location (it may be possible to lower the temperaturebeyond the turbine
limits duringwinter, causing excessive condensation in the turbine). Plants
operating in hot climates may have to reduceoutputif their sourceof
condenser cooling water becomes warmer; unfortunately this usually
coincides with periodsof high electrical demand for air conditioning.
The condenser generally useseither circulating cooling water from a cooling
tower to reject waste heat to the atmosphere, or once-through water from a
river, lake or ocean.
The heat absorbed by the circulating cooling water in the condenser tubes
mustalso be removed to maintain the ability of the water to cool as it
circulates. This is doneby pumpingthewarm water from the condenser
through either naturaldraft, forced draftor induced draft coolingtowers (as
seen in the image to the right) that reducethe temperatureof the water by
evaporation, by about 11 to 17 °C (20 to 30 °F)—expelling waste heat to the
atmosphere. The circulation flow rate of the cooling water in a 500 MW unitis
about 14.2 m³/s(500 ft³/sor 225,000USgal/min) at fullload.
The condenser tubesare madeof brass or stainless steel to resist corrosion
from either side. Nevertheless, they may become internally fouled during
operation by bacteria or algae in the cooling water or by mineral scaling, all of
which inhibit heat transfer and reduce thermodynamicefficiency. Many plants
includean automatic cleaning system that circulates spongerubber balls
through the tubes to scrubthem clean without the need to take the system off-
line.
The cooling water used to condensethe steam in the condenser returnsto its
sourcewithout having been changed other than having been warmed. If the
water returnsto a local water body (rather than a circulating cooling tower),
it is often tempered with cool 'raw' water to preventthermal shock when
discharged into that body of water .
Another form of condensingsystem is the air-cooled condenser. The process
is similar to that of a radiator and fan. Exhaust heat from the low pressure
section of a steam turbine runsthrough the condensingtubes, the tubes are
usually finned and ambientair is pushed through the finswith the help of a

34. 34
large fan. The steam condensesto water to be reused in the water-steam
cycle. Air-cooled condenserstypically operate at a higher temperaturethan
water-cooled versions. Whilesaving water, the efficiency of the cycle is
reduced (resultingin morecarbon dioxideper megawatt-hour of electricity).
From the bottom of the condenser, powerful condensatepumps recyclethe
condensed steam (water) back to the water/steam cycle.
Boiler make-up water treatment plant and storage
Since there is continuouswithdrawalof steam and continuousreturn
of condensate to the boiler, losses dueto blowdown and leakageshave to be
madeup to maintain a desired water level in the boiler steam drum. For this,
continuousmake-up water is added to the boiler water system. Impuritiesin
the raw water inputto the plantgenerally consist of
calcium and magnesium salts which imparthardness to the water. Hardness
in the make-up water to the boiler willform deposits on the tube water
surfaceswhich will lead to overheating and failureof the tubes. Thus, the salts
have to be removed from the water, and that is doneby a water
demineralizingtreatmentplant (DM). A DM plantgenerally consists of cation,
anion, and mixed bed exchangers. Any ions in the final water from this process
consist essentially of hydrogen ionsand hydroxideions, which recombineto
form purewater. Very pureDM water becomes highly corrosiveonce it
absorbs oxygen from the atmosphere because of its very high affinity for
oxygen.
The capacity of the DM plantis dictated by the type and quantity of salts in the
raw water input. However, somestorage is essential as the DM plantmay be
down for maintenance. For this purpose, astorage tank is installed from
which DM water is continuously withdrawn for boiler make-up. The storage
tank for DM water is madefrom materials notaffected by corrosivewater,
such as PVC. The pipingand valvesare generally of stainless steel. Sometimes,
a steam blanketing arrangementor stainless steel doughnutfloat is provided
on top of the water in the tank to avoid contact with air. DM water make-up is
generally added at the steam space of the surfacecondenser (i.e., the vacuum
side). This arrangementnot only spraysthe water but also DM water gets
deaerated, with the dissolved gases being removed by a de-aerator through an
ejector attached to the condenser.

35. 35
Fuel preparationsystem
In coal-fired power stations, the raw feed coal from the coal storage area is
first crushed into small pieces and then conveyed to the coal feed hoppersat
the boilers. The coal is next pulverized into a very finepowder. The
pulverizersmay be ball mills, rotating drum grinders, or other typesof
grinders.
Some power stations burn fueloil rather than coal. The oil must keptwarm
(above its pour point)in the fueloil storage tanks to preventthe oil from
congealing and becoming unpumpable. Theoil is usually heated to about
100 °C before being pumped throughthe furnacefueloil spray nozzles.
Boilers in some power stations use processed naturalgas as their main fuel.
Other power stations may use processed naturalgas as auxiliary fuelin the
eventthat their main fuelsupply (coalor oil) is interrupted. In suchcases,
separate gas burnersareprovided on the boiler furnaces.
Barring gear[
Barringgear (or "turninggear") is the mechanism provided to rotate the
turbinegenerator shaft at a very low speed after unitstoppages. Once the unit
is "tripped" (i.e., the steam inlet valveis closed), the turbine coasts down
towardsstandstill. When it stopscompletely, there is a tendency for the
turbineshaft to deflect or bend if allowed to remain in oneposition too long.
This is because the heat insidethe turbine casing tendsto concentrate in the
top half of the casing, makingthe top half portion of the shaft hotter than the
bottom half. The shaft therefore could warp or bend by millionths of inches.
This small shaft deflection, only detectable by eccentricity meters, would be
enoughto cause damagingvibrations to the entire steam turbinegenerator

36. 36
unitwhen it is restarted. The shaft is therefore automatically turned at low
speed (about one percentrated speed)by the barring gear untilit has cooled
sufficiently to permita completestop.
Oil system
An auxiliary oil system pump isused to supply oil at the start-up of the steam
turbinegenerator. It suppliesthe hydraulicoil system required for steam
turbine'smain inlet steam stop valve, the governingcontrol valves, the
bearing and seal oil systems, the relevant hydraulicrelaysand other
mechanisms.
At a preset speed of the turbineduringstart-ups, a pump driven by the
turbinemain shaft takes over the functionsof the auxiliary system.
Generator cooling
While small generators may be cooled by air drawn throughfilters at the inlet,
larger units generally requirespecial cooling arrangements. Hydrogen gas
cooling, in an oil-sealed casing, is used because it has the highest known heat
transfer coefficient of any gas and for its low viscosity which
reduces windagelosses. This system requires special handlingduringstart-
up, with air in the generator enclosurefirst displaced by carbon
dioxidebefore filling with hydrogen. This ensuresthat the
highly flammable hydrogen doesnot mix with oxygen in the air.
The hydrogen pressureinside the casing is maintained slightly higher
than atmospheric pressure to avoid outside air ingress. The hydrogen mustbe
sealed against outward leakage where the shaft emerges from the casing.
Mechanical seals around theshaft are installed with a very small annular gap
to avoid rubbing between the shaft and the seals. Seal oil is used to prevent
the hydrogen gas leakage to atmosphere.
The generator also useswater cooling. Since the generator coils are at a
potential of about 22 kV, an insulating barrier such as Teflon is used to
interconnect the water line and the generator high-voltage windings.
Demineralized water of low conductivity is used.Itsthe importanceof
generator cooling.
Generator high-voltage system
The generator voltage for modern utility-connected generatorsranges
from 11 kV in smaller units to 30 kV in larger units. The generator high-
voltage leads are normally large aluminium channelsbecause of their high

37. 37
currentas compared to the cables used in smaller machines. They are
enclosed in well-grounded aluminiumbusductsand aresupported on
suitable insulators. The generator high-voltage leads are connected to step-
up transformers for connectingto a high-voltage electrical substation (usually
in the rangeof 115 kVto 765 kV)for further transmission by the local power
grid.
The necessary protection and meteringdevices are included for the high-
voltage leads. Thus, the steam turbinegenerator and the transformer form
one unit. Smaller unitsmay share a common generator step-up transformer
with individualcircuitbreakers to connectthe generators to a common bus.
Monitoring and alarm system
Most of the power plantoperational controlsare automatic. However, at
times, manualintervention may be required. Thus, the plant is provided with
monitorsand alarm systemsthat alert the plantoperators when certain
operating parametersare seriously deviatingfrom their normalrange.
Battery-suppliedemergency lighting and communication
A central battery system consisting of lead acid cell unitsis provided to supply
emergency electric power, when needed, to essential items such as the power
plant'scontrol systems, communication systems,generator hydrogen seal
system, turbine lube oil pumps, and emergency lighting. This is essential for a
safe, damage-freeshutdown of the unitsin an emergency situation
TURBINE MAINTAINANCE DEPARTMENT.
Steam turbine generator.

38. 38
The turbinegenerator consists of a series of steam turbines interconnected to
each other and a generator on a common shaft. There is a high pressure
turbineat one end, followed by an intermediate pressureturbine, two low
pressureturbines, and the generator. As steam movesthrough the system and
loses pressureand thermal energy it expandsin volume, requiringincreasing
diameter and longer blades at each succeedingstage to extract the remaining
energy. The entire rotating mass may be over 200 metrictons and 100 feet
(30 m) long. It is so heavy that it must be kept turningslowly even when shut
down (at 3 rpm)so that the shaft will not bow even slightly and become
unbalanced. This is so importantthat it is oneof only six functionsof blackout
emergency power batteries on site. Other functionsare emergency
lighting, communication, station alarms, generator hydrogen seal system, and
turbogenerator lube oil.
Superheated steam from the boiler is delivered through 14–16-inch(360–
410 mm)diameter pipingto the high pressureturbinewhere it falls in
pressureto 600 psi(4.1 MPa)and to 600 °F(320 °C)in temperaturethrough
the stage. It exits via 24–26-inch(610–660mm)diameter cold reheat lines
and passes back into the boiler where the steam is reheated in special reheat
pendanttubesback to 1,000 °F(540 °C). The hot reheat steam is conducted to
the intermediatepressureturbinewhere it falls in
both temperatureand pressure and exitsdirectly to the long-bladed low
pressureturbinesand finally exits to the condenser.

39. 39
The generator, 30 feet (9 m) longand 12 feet (3.7 m)in diameter, contains a
stationary stator and a spinningrotor, each containing miles of
heavy copper conductor—no permanentmagnets here. In operation it
generates up to 21,000 amperes at24,000volts AC(504 MWe)asit spinsat
either 3,000 or 3,600 rpm, synchronized to the power grid. The rotor spinsin
a sealed chamber cooled with hydrogen gas, selected because it has the
highest known heat transfer coefficient of any gas and for its
low viscosity which reduces windagelosses. This system requires special
handlingduringstartup, with air in the chamber first displaced by carbon
dioxidebefore filling with hydrogen. This ensuresthat the
highly explosive hydrogen–oxygen environmentisnot created.
The power grid frequency is 60 Hz across North America and 50 Hz
in Europe, Oceania, Asia (Korea and parts of Japan arenotable exceptions) and
parts of Africa. The desired frequency affects the design of large turbines,
since they are highly optimized for one particular speed.
The electricity flowsto a distribution yard where transformers increase the
voltage for transmission to its destination.
The steam turbine-driven generators have auxiliary systemsenabling them to
work satisfactorily and safely. The steam turbinegenerator being rotating
equipmentgenerally has a heavy, large diameter shaft. The shaft therefore
requires notonly supportsbutalso has to be kept in position while running.
To minimizethe frictional resistance to the rotation, the shaft has a number
of bearings. The bearing shells, in which the shaft rotates, are lined with a low
friction material like Babbitt metal. Oil lubrication is provided to further
reducethe friction between shaft and bearing surfaceand to limit the heat
generated.
Stack gas path and cleanup
As the combustion fluegas exits the boiler it is routed through a rotating flat
basket of metal mesh which picks up heat and returnsit to incomingfresh air
as the basket rotates. This is called the air preheater. The gas exiting the boiler
is laden with fly ash, which are tiny spherical ash particles. The fluegas
contains nitrogen along with combustion products carbon dioxide, sulfur
dioxide, and nitrogen oxides. The fly ash is removed by fabric bag
filters or electrostatic precipitators. Once removed, the fly ash byproductcan
sometimes be used in the manufacturingof concrete. This cleaning up of flue
gases, however, only occurs in plantsthat are fitted with the appropriate

40. 40
technology. Still, the majority of coal-fired power plantsin the world do not
have these facilities.[citation needed] Legislation in Europehas been efficient to
reducefluegas pollution. Japan has been usingfluegas cleaning technology
for over 30 yearsand the US has been doingthe same for over 25 years. China
is now beginning to grapplewith the pollution caused by coal-fired power
plants.
Where required by law, the sulfur and nitrogen oxide pollutants are removed
by stack gas scrubbers which use a pulverized limestoneor other alkaline wet
slurry to removethose pollutantsfrom the exit stack gas. Other devicesuse
catalysts to removeNitrousOxide compoundsfrom theflue gas stream. The
gas travelling up the fluegas stack may by this time have dropped to about
50 °C (120 °F). A typicalflue gas stack may be 150–180 metres(490–590ft)
tall to dispersethe remainingfluegas componentsin the atmosphere. The
tallest fluegas stack in the world is 419.7 metres(1,377 ft)tall at the GRES-
2 power plant in Ekibastuz, Kazakhstan.

41. 41
Induced Draft system
In this system the air is admitted to natural pressure difference and the flue gases
are taken out by means of Induced Draft (I.D) fans and the furnace is maintained
under vaccum.
Forced Draft System
A set of forced draft fans is made use of for supplying air to the furnace and so the
furnace is pressurized. The flue gases are taken out due to the pressure differnce
between the furnace and the atmosphere..
Balanced Draft System
Here a set of Induced and Forced Draft Fans are utilized in maintaining a vaccum
in the furnace. Normally all the power stations utilize this draft system.