sushil lamba

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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%29


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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_diagram


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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_a


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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/Turbine


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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/Superheat


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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.
http://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Combustionhttp://en.wikipedia.org/wiki/Boilerhttp://en.wikipedia.org/wiki/Recuperatorhttp://en.wikipedia.org/wiki/Flue_gashttp://en.wikipedia.org/wiki/Flue_gas_stackhttp://en.wikipedia.org/wiki/Flue_gas_stackhttp://en.wikipedia.org/wiki/Chimneyhttp://en.wikipedia.org/wiki/Ducthttp://en.wikipedia.org/wiki/Ducthttp://en.wikipedia.org/wiki/Chimneyhttp://en.wikipedia.org/wiki/Flue_gas_stackhttp://en.wikipedia.org/wiki/Flue_gas_stackhttp://en.wikipedia.org/wiki/Flue_gashttp://en.wikipedia.org/wiki/Recuperatorhttp://en.wikipedia.org/wiki/Boilerhttp://en.wikipedia.org/wiki/Combustionhttp://en.wikipedia.org/wiki/Air


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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_energy


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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_law


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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.

sushil lamba

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