STEAM PLANT

8/12/2019 STEAM PLANT

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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 cir cui 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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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 as1. 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. Low

upkeeps, 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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Schematic arrangement of equipment of a

steam power station.Coal received in coal storage yard of power

station is transferred in the furnace by coal

handling unit. Heat produced due to burning ofcoal is utilized in converting water contained in

boiler drum into steam at suitable pressure and

temperature. The steam generated is passedthrough the superheater.


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Superheated steam then flows through the

turbine. After doing work in the turbine the

pressure of steam is reduced. Steam leaving theturbine 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 upon flowrate and temperature of cooling water and oneffectiveness of air removal equipment. Watercirculating through the condenser may be taken

from the various sources such as river, lake or sea. Ifsufficient quantity of water is not available the hotwater coming out of the condenser may be cooled incooling towers and circulated again through the

condenser. Bled steam taken from the turbine atsuitable extraction points is sent to low pressure andhigh pressure water heaters.


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Air taken from the atmosphere is first passed

through the air pre-heater, where it is heated by

flue gases. The hot air then passes through thefurnace. The flue gases after passing over

boiler and superheater tubes, flow through the

dust collector and then through economiser, airpre-heater and finally they are exhausted to the

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 75 percentload.


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Advantages relating the steam in high pressure

steam plantTo maintain equal distribution of steam.

To maintain speed of steam turbine.

To maintain proper temperature.


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Mechanical equipment in Thermal

power station.

BOILER

ECONOMISER

TURBINE

SUPER HEATER

AIR PREHEATER

CONDENSER


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Superheater

The superheater consists of a superheater headerand superheater elements. Steam from the main

steam pipe arrives at the saturated steam chamber

of the superheater header and is fed into thesuperheater elements. Superheated steam arrives

back at the superheated steam chamber of the

superheater header 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 steam resultsin 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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Reheater

The reheater functions similar to the superheater

in that it serves to elevate the steam temperature.

Primary steam is supplied to 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 secondreheat cycle may also be provided.


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Soot Blowers

The fuel used in thermal power plants causes sootand 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 masstype depending upon the type of spray and nozzle

used.


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CondenserThe use of a condenser in a power plant is to

improve 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 softeningcapacity 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 will also 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 thesteam becomes hot and it has to be cooled as it

belongs to a closed system. The Cooling towers

do 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 being cooled isallowed 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 water temperatures and aremore cost effective and energy efficient than

most other alternatives. The smallest cooling

towers are structured for only 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 thelarger 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 the boiler.

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 on the total gain inefficiency. In turn this depends on the flue gas

temperature leaving the boiler and the feed

water inlet temperature.


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Air Pre-heater

The flue gases coming out of the economizer is

used to preheat the air before supplying it tothe combustion chamber. An increase in air

temperature of 20 degrees can be achieved by

this method. The pre heated air is used forcombustion 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

inTotal

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 in the boiler ordecreasing 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 the averagetemperature at which heat is rejected to thecooling medium. The average temperatureduring heat rejection can be decreased by

lowering the turbine exit pressure.


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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 reheatedafter 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 where it isreheated 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 of thecycle, can be increased by increasing thenumber of expansion and reheat stages. As the

number of stages is increased, the expansionand reheat processes approach an isothermalprocess at maximum temperature. Reheating

also decreases the moisture content at theturbine exit.


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Another way of increasing the thermal efficiency of

the Rankine cycle is by regeneration. During aregeneration process, liquid water (feed water)

leaving the pump is heated by some steam bled off

the turbine at some intermediate pressure in devicescalled 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 heater pressure. In closed feedwater heaters, heat is transferred from the

steam to the feed water without mixing.


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The production of more than one useful form ofenergy (such as process heat and electric power)

from the same energy source is called cogeneration.

Cogeneration plants produce electric power whilemeeting the process heat requirements of certain

industrial processes. This way, more of the energy

transferred to the fluid in the boiler is utilized for a

useful purpose. The faction 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 power plantcan be increased by using binary cycles or

combined cycles. A binary cycle is composed of

two separate cycles, one at high 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 AVAI LABI L I TY OF COAL.

Huge quanti ty of coal is required for large thermal

plants.

ASH DI SPOSAL FACIL I TIES.

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.

PUBL IC PROBLEMS.

SIZE OF THE PLANT.


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Nowadays, the environment protection has

become a crucial problem and the authoritiesare requested to set increasingly more stringent

limits , one of which is the emissions from the

industrial plants of solid particulate and other

gaseous pollutants.

Background

ABOUT ELECTROSTATIC

PRECIPITATOR


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ABOUT ELECTROSTATICPRECIPITATOR

Electrostatic precipitator (ESP) is a widely

used device in so many different domainsto remove the pollutant particulates,

especially in industrial 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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To characterize all these stages determines to

take a great number of basic phenomena into

account from a physical point of view whenthey occurred.

Introduction

These are stages interacted that originated

from the complexity of the processes of

precipitator.


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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 the collecting plates.


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Particle transport

In the moving way, under the influence of electricfield, 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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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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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 TO

PROCESS

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

Type of Boilers


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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

THERMAL POWER PLANT


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THERMAL POWER PLANT

AUXILIARIES

FD fans.

ID fans.

Boiler feed Water pumps.

Condensate extraction pumps.

Circulation Cooling Water Pumping system.

Cooling Towers .

CT Fans. PA fans.

Coal Mills.


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Working of power plant

Pulverized coalis air-blown into the furnace from fuelnozzles at the four corners and it rapidly burns, forming a

large fireball at the center. Thethermal radiationofthe fireball heats the water that circulates through the boiler

tubes near the boiler perimeter. The water circulation rate in

the boiler is three to four times the throughput and is

typically driven by pumps. As the water in the boilercirculates it absorbs heat 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. Fromthe economizer it passes to the steam drum.Once the water enters the steam drum it goes down

to the lower inlet water wall headers. From the inletheaders the water rises through the water walls and

is eventually turned into steam due to the heat being

generated by the burners located on the front andrear 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 steamand water separators and then dryers inside the

steam drum. The steam separatorsand dryers

remove water droplets from the steam and the cyclethrough the water walls is repeated. This process is

known as natural circulation.
http://en.wikipedia.org/wiki/Steam_separatorhttp://en.wikipedia.org/wiki/Natural_circulationhttp://en.wikipedia.org/wiki/Natural_circulationhttp://en.wikipedia.org/wiki/Steam_separator


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super heaterFossil fuel power plants can have a super

heater and/or re-heater section in the steam

generating furnace. In a fossil fuel plant, afterthe steam is conditioned by the drying

equipment inside the steam drum, it is piped

from the upper drum area into tubes inside anarea 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_cycle


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For best efficiency, the temperature in the

condenser must be kept as low as practical inorder to achieve the lowest possible pressure in

the condensing steam. Since the condenser

temperature can almost always be keptsignificantly below 100 C where the vapor

pressureof water is much less than atmospheric

pressure, the condenser generally works undervacuum.Thus leaks of non-condensible air intothe closed loop must be prevented.
http://en.wikipedia.org/wiki/Vapor_pressurehttp://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_pressure


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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/Brass


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The condenser tubes are made of brass or

stainless steel to resist corrosion from eitherside. Nevertheless they may become internally

fouled during operation by bacteria or algae in the

cooling water or by mineral scaling, all of whichinhibit heat transfer and reduce

thermodynamic efficiency. Many plants

include an automatic cleaning system that circulatessponge 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 from thehigh pressure turbine is rerouted to go inside

the re heater tubes to pickup more energy to go

drive intermediate or lower pressure turbines.


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Non toxic 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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The major sources for air pollution are I-stackgases, discharge by thermal power plant, industrialenterprise and exhaust gases emitted byautomobiles.

The basic pollutants from nuclear power plantare;

Strontium 90, Strontium 89,

Bita and gama active aerosols

I odine isotopes

Radio-active inert gases


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Acid rain; the rain which contain acid as its constituents,brings all the acid down from high above the environment.

Contaminant; it is the another name of pollution. It isundesirable substances which may be physical, chemical orbiological.

Pollutant; these are undesirable substances present in the

environment these can be NO2, SO2, CO2,smoke,salt, bacteria.


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Radium

Thorium

Uranium

Plutonium.

The basic radio active pollutants


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Wet scrubbers; used for removal of gases.

Electrostatic precipitator.

Bag house filters useful in removing thepalticulate matters where low sulphur coal is

used.

Fossil fuel fault system; to discharge solidwaste such as calcium and magnesium.

The solid waste disposal equipment


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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 the effect ofdischarge 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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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.

Incremental rate curve shows that asoutput power increases, cost of plant also

increases.


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