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steam power plant
BABA HIRA SINGH BHATTAL INSTITUTE OF
ENGINEERING AND TECHNOLOGY LEHRAGAGA-
148031 DISTT.SANGRUR (Pb.)
By :-Rakesh kumar
Assistant professor
Electrical Engineering Department.
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Essentials of Steam Power Plant Equipment
A steam power plant must have following equipment :
(a) A furnace to burn the fuel.(b) Steam generator or boiler containing water.
Heat generated in the furnace is utilized to
convert water into steam.
(c) Main power unit such as an engine or
turbine to use the heat energy of steam and
perform work.
(d) Piping system to convey steam and water.
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The flow sheet of a thermal power plant
consists of the following four main circui ts :(a) Feed water and steam flow circuit.
(b) Coal and ash circuit.
(c) Air and gas circuit.(d) Cooling water circuit.
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A steam power plant using steam as working
substance works basically on Rankine cycle.
Steam is generated in a boiler, expanded in theprime mover and condensed in the condenser
and fed into the boiler again.
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The different types of components used in steam
power plant
(a) High pressure boiler.
(b) Prime mover .
(c) Condensers and cooling towers .
(d) Coal handling system .
(e) Ash and dust handling system .
(f) Draught system .
(g) Feed water purification plant .(h) Pumping system .
(i) Air preheater, economizer, super heater, feed
heaters.
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Types of steam Generators Horizontal vertical or inclined.
Fire tube or water tube.
Externally fired or internally fired.
Forced circulation and natural circulation.
High pressure or low pressure boiler.
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Daltons law The partial pressure pressure of each
constituent is that pressure which the gas
would exert if it occupied alone that volumeoccupied by the mixture at the sametemperature.
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Factors that should be considered while
selecting the boiler Working pressure and quality of steam
required.
Steam generation rate.
Floor area available.
The portable load factor.
Erection facilities.
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Properties of good steam generators It should be absolutely reliable.
It should occupy minimum space.
It should be light in weight.
Capable of quick starting.
Erection of boiler should be simple.
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Steam Power Plants are Classified as
1.By fuel.
2.By prime mover.3.By cooling tower.
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Steam Power Plants are also Classified as;
Central stations; the electrical energy available fromthese stations is meant for sale to the consumers who
wish to purchase it.
I ndustr ial/ captive power stations; this type of
power station is run by the manufacturing company for
its own use and its output is not available for general
sale.
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Jet condenser; low manufacturing cost. Lowupkeeps, requires small floor space and more
auxiliary power required.
surface condenser; high manufacturing cost.high upkeeps, requires large floor space and less
auxiliary power required.
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Feed water heating improves overall plant
efficiency.
Quantity of steam produced by the boiler isincrease.
Thermal stress due to cold water entering the
boiler drum are avoided.Chance of boiler corrosion are decrease.
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Dust collectorsare Classified as;
Mechanical dust collectors;
(a)Wet type(scrubbers).Spray type, packed type and impingement type.
(b) Dry type.
Gravitational separators, cyclone separators,electricaldust collectors;Rod type and plate type.
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DIFFERENT TYPES OF BOILERS USED IN
STEAM POWER PLANTS
horizontal, vertical or inclined.
fire tube and water tube .
Externally or internally fired.
Forced or natural circulation.
High pressure or low pressure.
Stationary or portable.
Single-tube and multi-tube.
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or ng agram ermapower station.
S T bi P Pl
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C
saturatedwater
hot gases
SteamTurbine
Gen
compressedwater
superheatedsteam
Condenser
Pump
cooling watersaturatedsteam
Steam Generator(Boiler / Furnace)
Steam Turbine Power Plant
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Superheated steam then flows through the
turbine. After doing work in the turbine the
pressure of steam is reduced. Steam leavingthe turbine passes through the condenser
which is maintained the low pressure of
steam at the exhaust of turbine.
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Steam pressure in the condenser depends uponflow rate and temperature of cooling water andon effectiveness of air removal equipment.
Water circulating through the condenser may be
taken from the various sources such as river, lakeor sea. If sufficient quantity of water is notavailable the hot water coming out of thecondenser may be cooled in cooling towers andcirculated again through the condenser.
Bled steam taken from the turbine at suitableextraction points is sent to low pressure and highpressure water heaters.
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Air taken from the atmosphere is firstpassed through the air pre-heater, where it is
heated by flue gases. The hot air then passesthrough the furnace.
The flue gases after passing over boiler andsuperheater tubes, flow through the dust
collector and then through economiser, airpre-heater and finally they are exhausted tothe atmosphere through the chimney.
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Disadvantage of steam power plant
Maintenance and operating cost are high.
Long time required for erection and putting into
action . Large quantity of water is required.
Great difficulty experienced in coal handling .
Efficiency decreases rapidly below about 75percent load.
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Mechanical equipment in Thermal
power station.
BOILER
ECONOMISER
TURBINE
SUPER HEATER
AIR PREHEATER
CONDENSER
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SuperheaterThe superheater consists of a superheater
header and superheater elements. Steam from
the main steam pipe arrives at the saturated
steam chamber of the superheater header and is
fed into the superheater elements.
Superheated steam arrives back at the
superheated steam chamber of the superheaterheader and is fed into the steam pipe to the
cylinders. Superheated steam is more expansive.
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Advantages of superheated steamCapacity to do work is increased without
increasing its pressure.
High temperature of super heated steamresults in an increase in thermal efficiency.
Heat losses due to condensation of stem on
cylinder walls are avoided to a great extent.
Does not produce corrosion effect on
turbine.
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Superheater It is a heating device.
It is used to raise temp of steam at const
pressure.
It removes even last traces of moisture.
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Classification of super heaterConvection.
Radiation.
Combination of convection and radiation.
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ReheaterThe function of reheater is similar to the
superheater in that it serves to elevate the
steam temperature. Primary steam is suppliedto the high pressure turbine.
After passing through the high pressure
turbine, the steam is returned to the steam
generator for reheating (in a reheater) after
which it is sent to the low pressure turbine. A
second reheat cycle may also be provided.
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Soot BlowersThe fuel used in thermal power plants causes
soot and this is deposited on the boiler tubes,
economizer tubes, air pre heaters, etc.
This drastically reduces the amount of heat
transfer of the heat exchangers. Soot blowers
control the formation of soot and reduce its
corrosive effects.
The types of soot blowers are fixed type, which
may be further classified into lane type and
mass type depending upon the type of spray and
nozzle used.
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Condenser
The use of a condenser in a power plant is toimprove the efficiency of the power plant by
decreasing the exhaust pressure of the steam
below atmosphere.
Another advantage of the condenser is that the
steam condensed may be recovered to provide a
source of good pure feed water to the boiler and
reduce the water softening capacity to a
considerable extent. A condenser is one of the
essential components of a power plant.
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Functions of Condensers
The main purposes of the condenser are to
condense the exhaust steam from the turbine
for reuse in the cycle and to maximize turbine
efficiency by maintaining proper vacuum. As the operating pressure of the condenser is
lowered (vacuum is increased), the enthalpy
drop of the expanding steam in the turbine willalso increase. This will increase the amount of
available work from the turbine (electrical
output).
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Cooling TowerThe importance of the cooling tower is felt
when the cooling water from the condenser has
to be cooled.
The cooling water after condensing the steam
becomes hot and it has to be cooled as it
belongs to a closed system. The Cooling towersdo the job of decreasing the temperature of the
cooling water after condensing the steam in the
condenser.
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Cooling Towers have one function :
Remove heat from the water discharged
from the condenser so that the water can bedischarged to the river or re-circulated and
reused.
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A cooling tower extracts heat from water by
evaporation. In an evaporative cooling
tower, a small portion of the water beingcooled is allowed to evaporate into a moving
air stream to provide significant cooling to
the rest of that water stream.
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Cooling Towers are commonly used to
provide lower than ambient watertemperatures and are more cost effective and
energy efficient than most other alternatives.
The smallest cooling towers are structured foronly a few litres of water per minute while the
largest cooling towers may handle upwards of
thousands of litres per minute. The pipes are
obviously much larger to accommodate this
much water in the larger towers and can
range up to 12 inches in diameter.
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Advantages of regenerative cycle Improve overall plant efficiency.
Protect boiler corrosion.
Avoid the thermal stresses due to cold water
entering the boiler .
Increased the quantity of steam produced by
boiler.
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Function of economizer To extract a part of heat from the fuel gas
coming out of the boiler.
To use heat for heating feed water to theboiler.
To increases the efficiency of boiler.
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The economizer is a feed water heater,
deriving heat from the flue gases. The
justifiable cost of the economizer depends onthe total gain in efficiency. In turn this
depends on the flue gas temperature leaving
the boiler and the feed water inlettemperature.
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Air Pre-heater
The flue gases coming out of the economizer
is used to preheat the air before supplying itto the combustion chamber. An increase in
air temperature of 20 degrees can be
achieved by this method. The pre heated airis used for combustion and also to dry the
crushed coal before pulverizing.
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Advantages of mechanical handlingHigher reliability.
Less labour required.
Operation is easy and smooth.
Economical for large capacity plant.
Losses in transport are minimised.
Easily started.
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Disadvantages of mechanical handlingNeed continuous maintenance and repair.
Capital cost of plant is increased.
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Working diagram Thermal
power station.
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Side view Thermal power station.
Steam Turbine Power PlantTotal
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C
saturatedwater
Gen
compressedwater
superheatedsteam
cooling water
PumpSteamTurbine
Condenser
Steam Generator
Steam Turbine Power Plant
saturatedsteam
hot gases
Heat
WorkoutTotal
Workin
in
Total
Loss???Where???
A di t th
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R. Shanthini 15Aug 2010
According to the2ndLaw of Thermodynamics
when heat is converted into work,part of the heat energy must be wasted
Power generation
type
Unit size
(MW)
Energy wasted
(MW)
Diesel engine 10 - 30 7 22
Gas Turbine 50 - 100 36 78
Steam Turbine 200 - 800 120
560Combined (ST & GT) 300 - 600 150 380
Nuclear (BWR & PWR) 500 - 1100 330 760
9-1
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The Simple Ideal Rankine Cycle
The McGraw-Hill Companies, Inc.,1998
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How can We Increase the Efficiency of the
Rankine cycle?
Rankine cycle efficiency can be increased by
increasing average temperature at which
heat is transferred to the working fluid inthe boiler or decreasing the average
temperature at which heat is rejected from
the working fluid in the condenser. That is,
the average fluid temperature should be as
high as possible during heat addition and as
low as possible during heat rejection.
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The three ways by which eff iciency of the
Rankine cycle can be increased are :
(a) Lowering the condenser pressure.
(b) Superheating the steam to high
temperatures.
(c) Increasing the boiler pressure.
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The thermal efficiency of the Rankine cyclecan be increased by increasing the averagetemperature at which heat is added to the
working fluid and/or by decreasing theaverage temperature at which heat isrejected to the cooling medium. The averagetemperature during heat rejection can be
decreased by lowering the turbine exitpressure.
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Consequently, the condenser pressure of most
vapor power plants is well below theatmospheric pressure. The average
temperature during heat addition can be
increased by raising the boiler pressure or bysuperheating the fluid to high temperatures.
There is a limit to the degree of superheating,
however, since the fluid temperature is notallowed to exceed a metallurgically safe value.
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Superheating has the added advantage of
decreasing the moisture content of the steam at
the turbine exit. Lowering the exhaust pressure
or raising the boiler pressure, however, increases
the moisture content. To take advantage of the
improved efficiencies at higher boiler pressures
and lower condenser pressures, steam is usually
reheated after expanding partially in the high-
pressure turbine.
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This is done by extracting the steam after
partial extraction in the high-pressure
turbine, sending it back to the boiler whereit is reheated at constant pressure, and
returning it to the low-pressure turbine for
complete expansion to the condenser
pressure.
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The average temperature during the reheatprocess, and thus the thermal efficiency ofthe cycle, can be increased by increasing thenumber of expansion and reheat stages. As
the number of stages is increased, theexpansion and reheat processes approach anisothermal process at maximum
temperature. Reheating also decreases themoisture content at the turbine exit.
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Another way of increasing the thermal
efficiency of the Rankine cycle is by
regeneration. During a regeneration process,
liquid water (feed water) leaving the pump
is heated by some steam bled off the turbine
at some intermediate pressure in devices
called feed water heaters.
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The two streams are mixed in open feed
water heaters, and the mixture leaves
as a saturated liquid at the heaterpressure. In closed feed water heaters,
heat is transferred from the steam to
the feed water without mixing.
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The production of more than one usefulform of energy (such as process heat and
electr ic power) f rom the same energy source
is cal led cogeneration. Cogeneration plantsproduce electric power while meeting the
process heat requirements of certain
industr ial processes.
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This way, more of the energy
transferred to the fluid in the boiler
is utilized for a useful purpose. Thefaction of energy that is used for
either process heat or power
generation is called the utilization
factor of the cogeneration plant.
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The overall thermal efficiency of a powerplant can be increased by using binary
cycles or combined cycles. A binary cycle
is composed of two separate cycles, one athigh temperatures (topping cycle) and the
other at relatively low temperatures.
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The most common combined cycle is the gas-steam combined cycle where a gas-turbinecycle operates at the high-temperature rangeand a steam-turbine cycle at the low-temperature range. Steam is heated by thehigh-temperature exhaust gases leaving the
gas turbine. Combined cycles have a higherthermal efficiency than the steam- or gas-turbine cycles operating alone.
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Selection of plant site
The selection of plant site for thermal power
plant compared with hydro-power plant is
more difficult as it involves number offactors to be considered for its economic
justification.
A few important factors to be considered forthe selection of thermal power plants.
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Selection of plant site
AVAI LABI L I TY OF COAL.
Huge quantity of coal is required for
large thermal plants.ASH DI SPOSAL FACIL I TI ES.
SPACE REQUIREMENT.
NATURE OF LAND.
AVAI LABI L I TY OF WATER.
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Selection of plant site
TRANSPORT FACIL I TYIES.
AVAI LABI L I TY OF LABOUR.
PUBLIC PROBLEMS.SIZE OF THE PLANT.
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Nowadays, the environment protection has
become a crucial problem and theauthorities are requested to set increasingly
more str ingent l imits , one of which is the
emissions from the industr ial plants of solidparticulate and other gaseous pollutants.
ABOUT ELECTROSTATIC
PRECIPITATOR
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ABOUT ELECTROSTATIC PRECIPITATOR
Electrostatic precipitator (ESP) is a widely
used device in so many different domainsto remove the pollutant particulates,
especially in industr ial plants.
What is ESP
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HOW ESP WORKS
Generally, the processes of
electrostatic precipitator are known as
three main stages: particle charging,
transport and collection.
Main process of ESP
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Schematic of wire-plate ESP
Schematic of wire-plate electrostatic
precipitator
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Mechanism of ESP
Mechanism of electrostatic precipitator
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PROCESS OF Particle charging
Particle charging is the first and
foremost beginning in processes.
As the voltage applied on precipitator
reach threshold value, the space inside
divided into ionization region and driftregion.
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The electric field magnitude around thenegative electrode is so strong that the
electrons escape from molecule.
Under the influence of electric field, the positive
ions move towards the corona, while the
negative ions and electrons towards thecollecting plates.
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Particle transport
I n the moving way, under the inf luence ofelectr ic field, negative ions cohere and charge the
particles, make the particles be forced towards
collecting-plate.
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Particle collectionAs soon as the particles reach the plate,
they will be neutralized and packed by
the succeeded ones subsequently. Thecontinuous process happens, as a result,
particles are collected on the collecting
plate.
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72
What is a Boiler?
Introduction
Vessel that heats water to become hot water
or steam
At atmospheric pressure water volume
increases 1,600 times
Hot water or steam used to transfer heat to aprocess
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The boiler is a rectangular furnaceabout 50 feet (15 m) on a side and 130 feet
(40 m) tall. Its walls are made of a web ofhigh pressure steel tubes about 2.3 inches
(58 mm) in diameter.
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A boiler should ful f i l l the fol lowing requi rements
(a)Safety : The boiler should be safe under
operating conditions.
(b) Accessibility : The various parts of the
boiler should be accessible for repair and
maintenance.
(c) Capacity : The boiler should be capable of
supplying steam according to the requirements.
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(d) Efficiency : To permit efficient operation, the boiler
should be able to absorb a maximum amount of heatproduced due to burning of fuel in the furnace.
(e) It should be simple in construction and its
maintenance cost should be low.
(f) Its initial cost should be low.
(g) The boiler should have no joints exposed to flames.
(h) The boiler should be capable of quick starting and
loading.
I t d ti
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Introduction
BURNERWATER
SOURCE
BRINE
SOFTENERSCHEMICAL FEED
FUELBLOW DOWN
SEPARATOR
VENT
VENTEXHAUST GASSTEAM TOPROCESS
STACK DEAERATOR
PUMPS
Figure: Schematic overview of a boiler room
BOILER
ECO-
NOMI-
ZER
T f B il
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Types of Boilers
1. Fire Tube Boiler
2. Water Tube Boiler
3. Packaged Boiler4. Fluidized Bed (FBC) Boiler
5. Stoker Fired Boiler
6. Pulverized Fuel Boiler7. Waste Heat Boiler
8. Thermic Fluid Heater (not a boiler!)
What Type of Boilers Are There?
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The boilers can be classif ied according to the
following cr iter ia.According to flow of water and hot
gases :
(a) Water tube(b) Fire tube.
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Type of Boilers
1. Fire Tube Boiler
Relatively small steam
capacities (12,000 kg/hour)
Low to medium steam
pressures (18 kg/cm2)
Operates with oil, gas or solid
fuels
T f B il
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Type of Boilers
2. Water Tube Boiler
Used for high steam demand
and pressure requirements
Capacity range of 4,500
120,000 kg/hour
Combustion efficiency
enhanced by induced draft
provisions Lower tolerance for water
quality and needs water
treatment plant
3. Packaged Boiler
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Oil
Burner
To
Chimney
Comes in complete package Features
High heat transfer
Faster evaporation
Good convective heattransfer
Good combustion efficiency
High thermal efficiency
Classified based on number ofpasses
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Working of power plant
Pulverized coal is air-blown into thefurnace from fuel nozzles at the four
corners and it rapidly burns, forming a
large fireball at the center. The thermal
radiation of the fireball heats the waterthat circulates through the boiler tubes near
the boiler perimeter.
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The water circulation rate in the boileris three to four times the throughput and
is typically driven by pumps. As the
water in the boilercirculates it absorbsheat and changes into steam at 700 F
(371 C) and 3,200 psi
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The water enters the boiler through a
section in the convection pass called the
economizer. From the economizer it
passes to the steam drum. Once thewater enters the steam drum it goes down
to the lower inlet water wall headers.
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From the inlet headers the water rises
through the water walls and is eventuallyturned into steam due to the heat being
generated by the burners located on the
front and rear water walls (typically). As
the water is turned into steam/vapor in the
water walls, the steam/vapor once again
enters the steam drum.
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The steam/vapor is passed through a series of
steam and water separators and then dryersinside the steam drum.
Thesteam separatorsand dryers remove
water droplets from the steam and the cyclethrough the water walls is repeated. This process
is known as natural circulation.
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super heaterFossil fuel power plants can have a super
heaterand/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 insidean area of the furnace known as the super
heater,
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which has an elaborate set up of tubing where
the steam vapor picks up more energy from
hot flue gases outside the tubing and itstemperature is now superheated above the
saturation temperature. The superheated
steam is then piped through the main steam
lines to the valves before the high pressure
turbine.
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Condenser
The condenser condenses the steam from the
exhaust of the turbine into liquid to allow it
to be pumped. If the condenser can be madecooler, the pressure of the exhaust steam is
reduced and efficiency of the cycleincreases.
http://en.wikipedia.org/wiki/Rankine_cyclehttp://en.wikipedia.org/wiki/Rankine_cycle8/13/2019 Jagan Steam Power Plant
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For best efficiency, the temperature in the
condenser must be kept as low as
practical in order to achieve the lowest
possible pressure in the condensing
steam.
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Since the condenser temperature can almost
always be kept significantly below 100 C
where the vapor pressureof water is muchless than atmospheric pressure, the condenser
generally works under vacuum. Thus leaksof non-condensible air into the closed loop
must be prevented.
http://en.wikipedia.org/wiki/Vapor_pressurehttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Vacuumhttp://en.wikipedia.org/wiki/Vapor_pressurehttp://en.wikipedia.org/wiki/Vapor_pressurehttp://en.wikipedia.org/wiki/Vapor_pressure8/13/2019 Jagan Steam Power Plant
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The condenser generally uses either
circulating cooling water from a cooling
tower to reject waste heat to theatmosphere, or once-through water from a
river, lake or ocean.
http://en.wikipedia.org/wiki/Cooling_towerhttp://en.wikipedia.org/wiki/Cooling_towerhttp://en.wikipedia.org/wiki/Cooling_towerhttp://en.wikipedia.org/wiki/Cooling_towerhttp://en.wikipedia.org/wiki/Cooling_towerhttp://en.wikipedia.org/wiki/Brass8/13/2019 Jagan Steam Power Plant
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The condenser tubes are made of brass
or stainless steel to resist corrosionfrom 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.
http://en.wikipedia.org/wiki/Brasshttp://en.wikipedia.org/wiki/Stainless_steelhttp://en.wikipedia.org/wiki/Thermodynamic_efficiencyhttp://en.wikipedia.org/wiki/Thermodynamic_efficiencyhttp://en.wikipedia.org/wiki/Thermodynamic_efficiencyhttp://en.wikipedia.org/wiki/Thermodynamic_efficiencyhttp://en.wikipedia.org/wiki/Thermodynamic_efficiencyhttp://en.wikipedia.org/wiki/Stainless_steelhttp://en.wikipedia.org/wiki/Stainless_steelhttp://en.wikipedia.org/wiki/Stainless_steelhttp://en.wikipedia.org/wiki/Brass8/13/2019 Jagan Steam Power Plant
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Many plants include an automatic
cleaning system that circulates sponge
rubber balls through the tubes to scrub
them clean without the need to take the
system off-line.
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Re heaterPower plant furnaces may have a re heater
section containing tubes heated by hot flue
gases outside the tubes. Exhaust steam fromthe high pressure turbine is rerouted to go
inside the re heater tubes to pickup more
energy to go drive intermediate or lower
pressure turbines.
M i ll t t f t
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Nontoxic dust
Sulphurous anhydride
Carbon monoxide
Nitrogen dioxide
Soot (fly ash)
Hydrogen sulphide
Pollution can be define as the contamination of soil ,
air and water with undesirable amount of mater ial and
heat.
Main pollutants from a power system
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Acid rain; the rain which contain acid as itsconstituents, brings all the acid down from high
above the environment.
Contaminant; it is the another name of
pollution. It is undesirable substances whichmay be physical, chemical or biological.
Pollutant; these are undesirable substancespresent in the environment these can be NO2,SO2, CO2,smoke,salt, bacteria.
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Lot of heat is injected into biosphere from
thermal power plant, through exhaust gases
and waste water. The major problem is theeffect of discharge of large quantity of
heated wasted water into natural water
basins. Hot water raises the temperature
and disturbs the natural ecological balance
Bad effects of thermal pollution
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Greater reliability of supply to the consumers.
Avoid complete shut down.
The overall cost of energy per unit of an
interconnected system is less.
There is a more effective use of transmission
line facilities.
Less capital investment required.
Less expenses on supervision, operation and
maintenance.
Advantages of combined operation of plants
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Due to limited generating capacity diesel
power stations is not suitable for base load
plants.Nuclear power stations is not suitable for
peak load plants.
I ncremental rate curve shows that asoutput power increases, cost of plant
also increases.
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