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SUSHIL LAMBA
MECHANICAL ENGINEERING
PART 2 IDD
ROLL NO. 10406EN008
IIT (BHU) VARANASI
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ACKNOWLEDGEMENT
With profound respect and gratitude, I take the opportunity to
convey my thanks to complete the training here. I do extend
my heartfelt thanks to Mr. Manmohan Singh for providing me
this opportunity to be a part of this esteemed organization. I
am extremely grateful to all the technical staff of BTPS / NTPCfor 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. I would also like to thank the training incharge of IIT (BHU)
Varanasi and all the faculty members of Mechanical
Engineering Department for their effort of constant co-
operation, which have been a significant factor in theaccomplishment of my industrial training.
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CERTIFICATE
This is to certify that Sushil Lamba, student of Mechanical
Engineering Dual Degree (IDD),Part 2, IIT (BHU) Varanasi, has
successfully completed his training at National Thermal Power
Station, Badarpur, New Delhi for 5 weeks from 28th May to 30th
June 2012. He has completed the whole training as per the
report submitted.
Training Incharge
NTPC
Badarpur, New Delhi
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TRAINING AT BTPS
I was appointed to do 6 weeks training at this esteemed organization
from 28th
May to 7th
July 2012. I was assigned to visit various division
of the plant, which were:
1. Boiler Maintenance Department (BMD I/II/III)
2. Plant Auxiliary Maintenance (PAM)
3. Turbine Maintenance Department (TMD)
These 6 weeks training was a very educational adventure for
me. It was really amazing to see the plant by yourself and learn
how electricity, which is one of our daily requirements of life, is
produced. This report has been made by my experience at
BTPS. The material in this report has been gathered from my
textbook, senior student reports and trainers manuals andpower journals provided by training department. The
specification and principles are as learned by me from the
employees of each division of BTPS.
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INDEX
S.No. Contents Page No.
1. BASIC STEPS OF ELECTRICITY GENERATION 05
2. BASIC POWER PLANT CYCLE 08
3. BOILER MAINTAINANCE DEPARTMENT (BMD) 14
4. PLANT AUXILIARY MAINTAINANCE (PAM) 19
5. TURBINE MAINTAINANCE DEPARTMENT (TMD) 26
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BASIC STEPS OF ELECTRICITY GENERATION
1. Coal to steam.
2. Steam to Mechanical Power.
3. Mechanical power to electrical power.
COAL TO STEAM
Coal from the coal wagons is unloaded in the coal handling plant. This coal is
transported up to the raw bunkers with the help of belt conveyors. Coal is
transported to Bowl Mills by Coal Feeders. The coal is pulverized in the Bowl Mill,
where it is ground to powder form. The mill consists of a round metallic table in
which coal particles fall. This table is rotated with the help of a motor. There are
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three large steel rollers, which are spaced 1200
apart. When there is no coal, these
rollers do not rotate but when the coal is fed to the table it packs up between
roller and table and thus forces the rollers to rotate. Coal is crushed by the
crushing action between the rollers and the rotating table. This crushed coal is
taken away to the furnace through the coal pipes with the help of hot and cold air
mixture from P.A. Fan.
P.A. Fan takes atmospheric air, a part of which is sent to the Air-Preheaters for
heating while a part goes directly to the mill for temperature control.
Atmospheric air from the F.D. Fan is heated in the air heaters and sent to the
furnace as combustion air.
Water from the boiler feed pump passes through the economizer and reaches the
boiler drum. Water from the drum passes through down comers and goes to the
bottom ring header. Water from the bottom ring header is divided to all the four
sides of the furnace. Due to heat and density difference, the water rises up in the
water wall tubes. Water is partly converted to steam as it rises up in the furnace.
This steam and water mixture is again taken to the boiler drum where the steam
is separated from the water.
Water follows the same path while the steam is sent to the super heaters for
superheating. The super heaters are located inside the furnace and the steam is
superheated(5400
C) and finally it goes to the turbine.
Flue gases from the furnace are extracted by induced draft fan, which maintains
balance draft in the furnace with forced draft fan. These flue gases emit their heat
energy to various super heaters in the pent house and finally through air
preheaters and goes to electrostatic precipitators where the ash particles are
extracted. Electrostatic Precipitator consists of metal plates, which are electrically
charged. Ash particles are attracted on these plates, so that they do not passthrough the chimney to pollute the atmosphere. Regular mechanical hammer
blows cause the accumulation of ash to fall to the bottom of the precipitator
where they are collected in a hopper for disposal.
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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 emergency) and through
control valves that automatically regulate the supply of steam to the turbine. Stopvalve and control valves are located in a steam chest and a governor, driven from
the main turbine shaft, operates the control valves to regulate the amount of
steam used( This depends upon the speed of the turbine and the amount of
electricity required from the generator).
Steam from the control valve 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 bladesmounted on a disc secured to the turbine shaft. The second ring turns the shafts
as a result of a force of steam. The stationary and moving blades together
constitute a stage of turbine and in practice many stages are necessary, so that
the cylinder contains a number of tings of stationary blades with rings of moving
blades arranged between them. The steam passes through each stage in turn until
it reaches the end of the high-pressure cylinder and in its passage some of its heat
energy is changed into mechanical energy.
The steam leaving the high pressure cylinder goes back to the boiler for reheating
and returns by a further pipe to the 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 opposite directions through the rows of turbine
blades through an arrangement called the 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. Because of this expansion the
blades are much larger and longer towards the low pressure ends of the turbine.
MECHANICAL POWER TO ELECTRICAL POWER
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On large turbines, it becomes economical to increase the cycle efficiency by using
reheat, which is a way of partially overcoming temperature limitations. By
returning partially expanded steam, to a reheat, the average temperature at
which the heat is added, is increased and, by expanding this reheated steam to
the remaining stages of the turbine, the exhaust wetness is considerably less than
it would otherwise be conversely, if the maximum tolerable wetness is allowed.
The initial pressure of the steam can be appreciably increased.
Bleed steam extraction: For regenerative system, nos. of non-regulated
extractions is taken from HP,IP turbine.
Regenerative heating of the boiler feed water is widely used in modern power
plants; the effect being to increase the average temperature at which heat is
added to the cycle, thus improving efficiency.
FACTORS AFFECTING THERMAL CYCLE EFFICIENCY
Thermal cycle efficiency is affected by following:
1. Initial steam pressure.
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range the cycle can operate over is quite small: turbine entry temperatures are
typically 565C (the creep limit of stainless steel) and condenser temperatures are
around 30C. This gives a theoretical Carnot efficiency of about 63% compared
with an actual efficiency of 42% for a modern coal-fired power station. This low
turbine entry temperature (compared with a gas turbine) is why the Rankine cycle
is often used as a bottoming cycle in combined-cycle gas turbine power stations.
The working fluid in a Rankine cycle follows a closed loop and is reused
constantly. The water vapor with entrained droplets often seen billowing from
power stations is generated by the cooling systems (not from the closed-loop
Rankine power cycle) and represents the waste heat energy (pumping and
condensing) that could not be converted to useful work in the turbine. Note that
cooling towers operate using the latent heat of vaporization of the cooling fluid.While many substances could be used in the Rankine cycle, water is usually the
fluid of choice due to its favorable properties, such as nontoxic and nonreactive
chemistry, abundance, and low cost, as well as its thermodynamic properties.
One of the principal advantages the Rankine cycle holds over others is that during
the compression stage relatively little work is required to drive the pump, the
working fluid being in its liquid phase at this point. By condensing the fluid, the
work required by the pump consumes only 1% to 3% of the turbine power andcontributes to a much higher efficiency for a real cycle. The benefit of this is lost
somewhat due to the lower heat addition temperature.Gas turbines, for
instance, have turbine entry temperatures approaching 1500C. Nonetheless, the
efficiencies of actual large steam cycles and large modern gas turbines are fairly
well matched.
THE FOUR PROCESSES IN RANKINE CYCLE
http://en.wikipedia.org/wiki/Creep_%28deformation%29http://en.wikipedia.org/wiki/Carnot_efficiencyhttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Combined_cyclehttp://en.wikipedia.org/wiki/Vaporhttp://en.wikipedia.org/wiki/Cooling_towerhttp://en.wikipedia.org/wiki/Heat_of_vaporizationhttp://en.wikipedia.org/wiki/Properties_of_water#Heat_capacity_and_heats_of_vaporization_and_fusionhttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Properties_of_water#Heat_capacity_and_heats_of_vaporization_and_fusionhttp://en.wikipedia.org/wiki/Heat_of_vaporizationhttp://en.wikipedia.org/wiki/Cooling_towerhttp://en.wikipedia.org/wiki/Vaporhttp://en.wikipedia.org/wiki/Combined_cyclehttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Carnot_efficiencyhttp://en.wikipedia.org/wiki/Creep_%28deformation%297/31/2019 Sushil Lamba
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There are four processes in the Rankine cycle. These states are identified by
numbers (in brown) in the above Ts diagram.
1. Process 1-2: The working fluid is pumped from low to high pressure. As thefluid is a liquid at this stage the pump requires little input energy.
2. Process 2-3: The high pressure liquid enters a boiler where it is heated atconstant pressure by an external heat source to become a dry saturated
vapor. The input energy required can be easily calculated usingmollier
diagram or h-s chart or enthalpy-entropy chart also known as steam
tables.
3. Process 3-4: The dry saturated vapor expands through a turbine,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.
4. Process 4-1: The wet vapor then enters a condenser where it is condensedat a constant temperature to become a saturated liquid.
In an ideal Rankine cycle the pump and 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 on theT-S
diagram and more closely resemble that of the Carnot cycle. The Rankine cycle
shown here prevents the vapor ending up in the superheat region after the
http://en.wikipedia.org/wiki/Mollier_diagramhttp://en.wikipedia.org/wiki/Mollier_diagramhttp://en.wikipedia.org/wiki/H-s_charthttp://en.wikipedia.org/wiki/Enthalpy-entropy_charthttp://en.wikipedia.org/wiki/Steam_tablehttp://en.wikipedia.org/wiki/Steam_tablehttp://en.wikipedia.org/wiki/Turbinehttp://en.wikipedia.org/wiki/Enthalpy-entropy_charthttp://en.wikipedia.org/wiki/Surface_condenserhttp://en.wikipedia.org/wiki/Boiling_pointhttp://en.wikipedia.org/wiki/Isentropichttp://en.wikipedia.org/wiki/T-S_diagramhttp://en.wikipedia.org/wiki/T-S_diagramhttp://en.wikipedia.org/wiki/T-S_diagramhttp://en.wikipedia.org/wiki/T-S_diagramhttp://en.wikipedia.org/wiki/Isentropichttp://en.wikipedia.org/wiki/Boiling_pointhttp://en.wikipedia.org/wiki/Surface_condenserhttp://en.wikipedia.org/wiki/Enthalpy-entropy_charthttp://en.wikipedia.org/wiki/Turbinehttp://en.wikipedia.org/wiki/Steam_tablehttp://en.wikipedia.org/wiki/Steam_tablehttp://en.wikipedia.org/wiki/Enthalpy-entropy_charthttp://en.wikipedia.org/wiki/H-s_charthttp://en.wikipedia.org/wiki/Mollier_diagramhttp://en.wikipedia.org/wiki/Mollier_diagram7/31/2019 Sushil Lamba
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expansion in the turbine,[1]
which reduces the energy removed by the
condensers.
Real rankine cycle (non-ideal)
Rankine cycle with superheat
In a real power plant cycle (the name 'Rankine' cycle used only for the ideal cycle),
the compression by the pump and the expansion in the turbine are not isentropic.
In other words, these processes are non-reversible and entropy is increased
during the two processes. This somewhat increases the power required by thepump and decreases the power generated by the turbine.
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 turbine blades
and efficiency of the turbine. The easiest way to overcome this problem is by
superheating the steam. On the Ts diagram above, state 3 is above a two phase
region of steam and water so after expansion the steam will be very wet. By
superheating, state 3 will move to the right of the diagram and hence produce adrier steam after expansion.
Rankine cycle with reheat
http://en.wikipedia.org/wiki/Rankine_cycle#endnote_Van_Wyllen_ahttp://en.wikipedia.org/wiki/Rankine_cycle#endnote_Van_Wyllen_ahttp://en.wikipedia.org/wiki/Rankine_cycle#endnote_Van_Wyllen_ahttp://en.wikipedia.org/wiki/Pumphttp://en.wikipedia.org/wiki/Turbinehttp://en.wikipedia.org/wiki/Entropyhttp://en.wikipedia.org/wiki/Power_%28physics%29http://en.wikipedia.org/wiki/Ts_diagramhttp://en.wikipedia.org/wiki/File:Rankine_cycle_with_superheat.jpghttp://en.wikipedia.org/wiki/Ts_diagramhttp://en.wikipedia.org/wiki/Power_%28physics%29http://en.wikipedia.org/wiki/Entropyhttp://en.wikipedia.org/wiki/Turbinehttp://en.wikipedia.org/wiki/Pumphttp://en.wikipedia.org/wiki/Rankine_cycle#endnote_Van_Wyllen_a7/31/2019 Sushil Lamba
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In this variation, two turbines work in series. The first accepts vapor from the
boiler at high pressure. After the vapor has passed through the first turbine, it re-
enters the boiler and is reheated before passing through a second, lower pressure
turbine. Among other advantages, this prevents the vapor from condensing
during its expansion which can seriously damage the turbine blades, and
improves the efficiency of the cycle, as more of the heat flow into the cycle occurs
at higher temperature.
Regenerative Rankine cycle
The regenerative Rankine cycle is so named because after emerging from the
condenser (possibly as a sub cooled liquid) the working fluid is heated by steam
tapped from the hot portion of the cycle. On 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. This is called "direct contact heating". The Regenerative Rankine cycle
(with minor variants) is commonly used in real power stations.
Another variation is where bleed steam from between turbine stages is sent to
feedwater heaters to preheat the water on its way from the condenser to the
boiler. These heaters do not mix the input steam and condensate, function as an
ordinary tubular heat exchanger, and are named "closed feedwater heaters".
The regenerative features here effectively raise the nominal cycle heat input
temperature, by reducing the addition of heat from the boiler/fuel source at the
relatively low feedwater temperatures that would exist without regenerative
feedwater heating. This improves the efficiency of the cycle, as more of the heat
flow into the cycle occurs at higher temperature.
http://en.wikipedia.org/wiki/Turbinehttp://en.wikipedia.org/wiki/Vaporizationhttp://en.wikipedia.org/wiki/Boilerhttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Subcooled_liquidhttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Feedwater_heaterhttp://en.wikipedia.org/wiki/Feedwater_heaterhttp://en.wikipedia.org/wiki/Steamhttp://en.wikipedia.org/wiki/Subcooled_liquidhttp://en.wikipedia.org/wiki/Condensationhttp://en.wikipedia.org/wiki/Boilerhttp://en.wikipedia.org/wiki/Vaporizationhttp://en.wikipedia.org/wiki/Turbine7/31/2019 Sushil Lamba
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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 required for the steam turbine that drives the electrical generator.
A steam generator includes an economizer, a steam drum, and the furnace with
its steam generating tubes and 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 (AP), 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 forced and induced draft fans, air
preheaters, and fly ash collectors. On some units of about 60 MW, two boilers per
unit may instead be provided.
AUXILIARIES OF THE BOILER
http://en.wikipedia.org/wiki/Superheathttp://en.wikipedia.org/wiki/Economizerhttp://en.wikipedia.org/wiki/Steam_drumhttp://en.wikipedia.org/wiki/Furnacehttp://en.wikipedia.org/wiki/Safety_valvehttp://en.wikipedia.org/wiki/Flue_gashttp://en.wikipedia.org/wiki/Centrifugal_fanhttp://en.wikipedia.org/w/index.php?title=Air_Preheater&action=edit&redlink=1http://en.wikipedia.org/wiki/Electrostatic_precipitatorhttp://en.wikipedia.org/wiki/Dust_collector#Fabric_filtershttp://en.wikipedia.org/wiki/Flue_gas_stackhttp://en.wikipedia.org/wiki/Megawatthttp://en.wikipedia.org/wiki/Megawatthttp://en.wikipedia.org/wiki/Flue_gas_stackhttp://en.wikipedia.org/wiki/Dust_collector#Fabric_filtershttp://en.wikipedia.org/wiki/Electrostatic_precipitatorhttp://en.wikipedia.org/w/index.php?title=Air_Preheater&action=edit&redlink=1http://en.wikipedia.org/wiki/Centrifugal_fanhttp://en.wikipedia.org/wiki/Flue_gashttp://en.wikipedia.org/wiki/Safety_valvehttp://en.wikipedia.org/wiki/Furnacehttp://en.wikipedia.org/wiki/Steam_drumhttp://en.wikipedia.org/wiki/Economizerhttp://en.wikipedia.org/wiki/Superheat7/31/2019 Sushil Lamba
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1. FURNACEFurnace 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 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.
2. BOILER DRUMDrum 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 risers discharge into steam a mixture of water, steam, foam and sludge.
Steam must be separated from the mixture before it leaves the drum. The
functions of a boiler drum are as following:
1. To store water and steam efficiently to meet varying load requirement.2. To aid in circulation.3. To separate vapour or steam from the water-steam mixture, discharged
by the risers.
4. To provide enough surface area for liquid- vapour disengagement.5. To maintain certain desired ppm in the drum water by phosphate
injection and blowdown.
3. WATER WALLSWater 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.
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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 tubes at the top are grounded in
four rows at a wider pitch forming the grid tubes.
4. REHEATERPower plant furnaces may have a reheater section containing tubes heated
by hot flue gases outside the tubes. Exhaust steam from the high pressure
turbine is passed through these heated tubes to collect more energy before
driving the intermediate and then low pressure turbines.
5. SUPERHEATERFossil fuel power plants can have a superheater and/or re-heater section in the
steam generating furnace. In a fossil fuel plant, after the steam is conditioned by
the drying equipment inside the steam drum, it is piped from the upper drum
area into tubes inside an area of the furnace known as the superheater, which has
an elaborate set up of tubing where the steam vapor picks up more energy from
hot flue gases outside the tubing and its temperature is now superheated above
the saturation temperature. The superheated steam is then piped through themain steam lines to the valves before the high pressure turbine.
Nuclear-powered steam plants do not have such sections but produce steam at
essentially saturated conditions. Experimental nuclear plants were equipped with
fossil-fired super heaters in an attempt to improve overall plant operating cost.
6.ECONOMIZERAn economizer is a heat exchanger which raises the temperature of the
feedwater leaving the highest pressure feedwater heater to about the
saturation temperature corresponding to the boiler pressure. This is done
by the hot flue gases exiting the last superheater or reheater at a
temperature varying from 3700
C to 5400
C. By utilizing these gases in
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heating feedwater, higher efficiency and better economy are achieved and
hence the heat exchanger is called economizer.
Economizer tubes are commonly 45-70 mm in outside diameter and are
made in vertical coils of continuous tubes connected between inlet andoutlet headers with each section formed into several horizontal paths
connected by 1800
vertical bends. The coils are installed at a pitch of 45 to
50 mm spacing, which depends on the type of fuel and ash characteristics.
7.AIR PREHEATERAn air preheater (APH) is a general term to describe any device designed to heat
air before another process (for example, combustion in a boiler) with the primary
objective of increasing the thermal efficiency of the process. They may be used
alone or to replace a recuperative heat system or to replace a steam coil.
The purpose of the air preheater is to recover the heat from the boiler flue gas
which increases the thermal efficiency of the boiler by reducing the useful heat
lost in the flue gas. As a consequence, the flue gases are also sent to the flue gas
stack (or chimney) at a lower temperature, allowing simplified design of the
ducting and the flue gas stack. It also allows control over the temperature ofgases leaving the stack (to meet emissions regulations, for example).
8.PULVERIZER
Pulverizer is a mechanical device for the grinding of many types of materials. Forexample, they are used to pulverize coal for combustion in the steam generating
furnaces of the fossil fuel power plants.
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TYPES OF PULVERIZERS
1. BALL AND TUBE MILLS
A 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 f up to five diameters in length used
for finer pulverization of ore, rock and other such materials, thematerials mixed with water is fed into the chamber from one end, and
passes out the other end as slime.
2. BOWL MILLIt uses tires to crush coal. It is of two types; a deep bowl mill and the
shallow mill.
3. PLANT AUXILIARY MAINTAINENCE (PAM)1. ASH HANDLING PLANT
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HYDRAULIC ASH HANDLING SYSTEM IS USED AT BADARPUR THERMAL
POWER STATION
Boilers having pulverized coal have dry bottom furnaces. The large ashparticles are collected under the furnace in a water filled ash hopper. Fly
ash is collected in dust collectors with either an electrostatic precipitator
or a bag house. A pulverized coal boiler generates approximately 80% fly
ash and 20% bottom ash. Ash must be collected and transported from
various points of the plants like economizer, air heater, and precipitator.
Pyrites, which are rejects from the pulverizers, are disposed with the
bottom ash system. Three major factors should be considered for ash
disposal systems.
1. Plant Site.2. Fuel source.
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3. Environmental regulation.Needs for water and land are important considerations for many ash
handling systems. Ash quantities to be disposed depend on the kind of
fuel source. Ash storage and disposal sites are guided by environmentalregulations.
The sluice conveyor system is the most widely used for bottom ash
handling, while the hydraulic vacuum conveyor is the most frequently
used for fly ash systems.
Bottom ash and slag may be used as filling material for road
construction. Fly ash can partly replace cement for making concrete.
Bricks can be made with fly ash. These are durable and strong.
4. WATER TREATMENTAs the types of boiler are not alike their working pressure and operating
conditions vary and so do the types and methods of water treatment.
Water treatment plants used in thermal power plants are designed to
process the raw water to water with 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.
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The type of demineralization process chosen for power station depends on three
main factors:
1. The quality of the raw water.2. The degree of de-ionization i.e. treated water quality.3. Selectivity of resins.
Water treatment process is generally made up of two sections:
a. Pretreatment section.b. Demineralization section.
PRETREATMENT SECTION
Pretreatment plant removes the suspended solids such as clay, silt, organicand 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
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sedimentation. Finer particles, however, will not settle in any reasonable time
and must be flcculated to produce the large particles, which are settleable.
Long term ability to remain suspended in water is basically a function of both
size and specific gravity.
DEMINERALIZATION
This filter water is now used for demineralizing purpose and is fed to cation
exchanger bed, butr 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
maater from raw water, is now detrimental to action resin and must be
eliminated before its entry to this bed.
A DM plant generally consists of cation, anion and mixed bed exchangers. The
final water from this process consists essentially of hydrogen iosn 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 storage is essential as the DM plaant may be
down for maintenance. Fot this purpose, a storage tank is installed from which
the 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 stee. Sometimes, asteam
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. 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
condeser itself.
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4. INDUSTRIAL FANSID FAN
The Induced Draft Fans are generally of Axial-Impulse Type, Impeller nominal
diameter is of the order of 2500mm. The fan consists of the following sub-
assemblies:
1. Suction Chamber.2. Inlet Vane Control.3. Impeller.4. Outlet Guide Vane Assembly.
FD FAN
The fan normally of the same type as ID Fan, consists of the followingcomponents:
1. Silencer2. Inlet Bend.3. Fan Housing4. Impeller with blades and setting mechanism.
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, ehich are sealed off to the outside. The angle of incidence of the blades
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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 operation conditions.
The rotor is accomodated in cylindrical roller bearings and an inclined ball bearingat the drive side absorbs the axial thrust.
Lubrication and cooling these is assured by a combined oil level and circulating
lubrication system.
PA FAN
PA Fan if flange-mounted design, single suction, NDFV type, backward curved
blaede 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 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 airladen with dust particles.
5. COMPRESSOR HOUSEInstrument air is rewuired 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 compresssors and station air
compressors have been housed separately with separate receivers and supply
headers and their tapping..
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INSRUMENT AIR SYSTEM
Control 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 the boiler house and trubine house of
210 MW units. Adequate numbers of tapping have been provided all over the
area.
AIR-DRYING UNIT
Air contains moisture which tends to condense, and causes trouble in operation
of various devices by compreseed air. Therefore drying of air is accepted widely
in case of instrument air. Air drying consists of dual absorption towers with
embedded heaters for reactivation. The absoprtion towers are adequately filledwith specially selected silica gel and activated alumina while one tower is drying
the air.
SERVICE AIR COMPRESSOR
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The station air compressor is generally a slow speed horizontal double acting
stage type and is arranged for belt drive. The cylinder heads nad barrel are
enclosed in a jacket, which extends around the valve also. The intercooler is
provided between the low and high pressure cylinder which cools the air between
them and collect the moisture that condenses.
Air from the L.P. cylinder enters at one end of the intercooler and goes to the
opposite end where from it is discharged to the high pressure cylinder, cooling
water flows through the nest of the tubes and cools the air.A safety valve is set at
rated pressure.
Two selected swithces one with positions atuo load/unload nad another with
positions auto start/stop, non-stop have been provieded on the control panel of
the compressor. In auto start/stop position the compressor will start.
6. TURBINE MAINTENANCE DEPARTMENTA working fluid contains potential energy (pressure head) and kinetic energy
(velocity head). The fluid may be compressible or incompressible.
The types of turbines are:
IMPULSE TURBINES change the direction of flow of a high velocity fluid or gas jet.
The resulting impulse spins the turbine and leaves the fluid flow with diminished
kinetic energy. There is no pressure change of the fluid or gas in the turbine
blades (the moving blades), as in the case of a steam or gas turbine; the entire
pressure drop takes place in the stationary blades (the nozzles). Before reachingthe turbine, the fluid'spressure headis changed to velocity headby accelerating
the fluid with a nozzle. Pelton wheels and de Laval turbines use this process
exclusively. Impulse turbines do not require a pressure casement around the
rotor since the fluid jet is created by the nozzle prior to reaching the blading on
http://en.wikipedia.org/wiki/Potential_energyhttp://en.wikipedia.org/wiki/Head_%28hydraulic%29http://en.wikipedia.org/wiki/Kinetic_energyhttp://en.wikipedia.org/wiki/Compressibilityhttp://en.wikipedia.org/wiki/Incompressible_fluidhttp://en.wikipedia.org/wiki/Impulse_%28physics%29http://en.wikipedia.org/wiki/Nozzlehttp://en.wikipedia.org/wiki/Pelton_wheelhttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Pelton_wheelhttp://en.wikipedia.org/wiki/Nozzlehttp://en.wikipedia.org/wiki/Impulse_%28physics%29http://en.wikipedia.org/wiki/Incompressible_fluidhttp://en.wikipedia.org/wiki/Compressibilityhttp://en.wikipedia.org/wiki/Kinetic_energyhttp://en.wikipedia.org/wiki/Head_%28hydraulic%29http://en.wikipedia.org/wiki/Potential_energy7/31/2019 Sushil Lamba
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the rotor. Newton's second law describes the transfer of energy for impulse
turbines.
REACTION TURBINES develop torque by reacting to the gas or fluid's pressure or
mass. The pressure of the gas or fluid changes as it passes through the turbinerotor blades. A pressure casement is needed to contain the working fluid as it acts
on the turbine stage(s) or the turbine must be fully immersed in the fluid flow
(such as with wind turbines). The casing contains and directs the working fluid
and, for water turbines, maintains the suction imparted by the draft tube.Francis
turbines and most steam turbines use this concept. For compressible working
fluids, multiple turbine stages are usually used to harness the expanding gas
efficiently. Newton's third law describes the transfer of energy for reaction
turbines.
MAIN TURBINE
The 210MW turbine is a cylinder tandem compounded type machine comprising
of H.P., I.P. and L.P. cylinders. The H.P. turbine comprises of 12 stages, the I.P. 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.
The reheated steam from the 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
http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion#Newton.27s_second_lawhttp://en.wikipedia.org/wiki/Reaction_%28physics%29http://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Francis_turbinehttp://en.wikipedia.org/wiki/Francis_turbinehttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Newton%27s_laws_of_motion#Newton.27s_third_lawhttp://en.wikipedia.org/wiki/Newton%27s_laws_of_motion#Newton.27s_third_lawhttp://en.wikipedia.org/wiki/Steam_turbinehttp://en.wikipedia.org/wiki/Francis_turbinehttp://en.wikipedia.org/wiki/Francis_turbinehttp://en.wikipedia.org/wiki/Torquehttp://en.wikipedia.org/wiki/Reaction_%28physics%29http://en.wikipedia.org/wiki/Newton%27s_laws_of_motion#Newton.27s_second_law7/31/2019 Sushil Lamba
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cooling water flow through the condenser tubes condenses the steam and the
condensate 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 pumpdelivers the water to the boiler through H.P. heaters thus forming a closed cycle.
STEAM TURBINE
A steam turbine is a mechanical device that extracts thermal energy from
pressurized steam and converts it into useful mechanical work. From a
mechanical point of view, the turbine is ideal, because the propelling force is
applied directly to the rotating element of the machine and has not as in the
reciprocating engine to be transmitted through a system of connecting links,
which are necessary to transform a reciprocating motion into rotary motion. Here
since the steam turbine possesses for its moving parts rotating elements only if
the manufacture is good and machine is correctly designed, it ought to be free
from out of balance forces.
If the load in the turbine is kept constant the torque developed at the coupling is
also constant. A generator at a steady load offers a constant torque. Therefore, a
turbine is suitable for driving a generator, particularly as they are both high-speedmachines.
A further advantage of the turbine is the absence of internal lubrication. This
means that the exhaust steam is not contaminated with oil vapour and can be
condensed and fed back to the boilers without passing through the filters. It also
means that turbine is considerable saving in lubricating oil when compared with a
reciprocating steam engine of equal power.
A final advantage of the steam turbine and a very important one is the fact that aturbine can develop many times the power compared to a reciprocating engine
whether steam or oil.
OPEARTING PRINCIPLES
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A steam turbines two main parts are the cylinder and the rotor. The cylinder
(stator) is a steel or cast iron housing usually 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 rotating shaft that carries the moving
blades on the outer edge 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, the steam at a high pressure and high temperature
enters the first row of fixed blades or nozzles, it expands and its velocityincreases. The high cvelocity jet of stream strikes the first set of moving blades.
The kinetic energy of the steam changes into mechanical energy, causing the shaft
to rotate. The steam that enters the next set of fixed blades strikes the next row
of moving blades.