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Unit 1-Thermal Power Plants

Steam power plant

Layout

Boilers

Pulverized coal burners

Fluidized bed combustion

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Power generating units aremega projects

Require huge capital

investment

Require natural resourceslike, fossil fuels

Large amount of water

Changes the local ecosystem

Huge Impacts on theEnvironment and Health

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Coal Mining

Surface Mining Strip Mining

Underground Mining

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Air Quality Around the coal based plants the ambient concentrations of

Sulphur Dioxide, Oxides of Nitrogen and SPM are high.

Epidemiological Studies have shown that of the area surroundingcoal based thermal plants, population living within a 2 -5 km radiusof the plant suffers from respiratory disorders .

Two other gases, carbon dioxide and ozone are emitted. The highamount of carbon dioxide emission from thermal power plantscontribute to global warming leading to climate change issignificant Ground level ozone, which is formed due to photolyticreactions of NOx and its impacts are under study

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Fly ash contains a

toxic brew of

dangerouschemicals and is

the largest

contributor tomercury pollution

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Composition of Fly ash

It contains as main chemical components SiO2

(51.4 wt%), Al2O3 (22.1 wt%) and Fe2O3 (17.2wt%; ignited weight basis). As commonly observed,many toxic elements and heavy metals are highlyenriched in the fly ash relative to the original coal.For example, considerable amounts of Be (16.4

ppm), Cu (106 ppm), Zn (578 ppm), As (40.4ppm), Cd (2.6 ppm), Hg (18 ppm), Pb (71 ppm),and U (21.8 ppm) is found in Fly ash.

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Water slurry is used to take the ash from the powerplant to the ash pond for disposal.

Water slowly seeps into the ground while carrying with it

the ash leach ate. Water may contain harmful heavymetals like boron, which have a tendency to leach outover a period of time.

When fly ash comes into contact with water, leachesinto groundwater supplies which get polluted and

unsuitable for domestic use. The release of ash pond decant into the local water

bodies- water dries up, dust nuisance, increasesturbidity, decreases primary productivity, affects fishesand other aquatic biota

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Coal Power Plant Operation

Steam Turbine GeneratorIs a series of steam turbines interconnected to each other

and then a generator

Steam CondenserSteam enters from the turbine generator and is pumped

into the bottom of the condenser, where pumps recyclethe condensed steam from the feedwater

StackReleases process emissions.

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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 a process

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Introduction

BURNERWATER

SOURCE

BRINE

SOFTENERS

CHEMICAL FEED

FUELBLOW DOWN

SEPARATOR

VENT

VENTEXHAUST GASSTEAM TOPROCESS

STACK DEAERATOR

PUMPS

Figure: Schematic overview of a boiler room

BOILER

ECO-

NOMI-

ZER

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Types of Boilers

1. Fire Tube Boiler

2. Water Tube Boiler

3. Packaged Boiler

4. Fluidized Bed (FBC) Boiler

5. Stoker Fired Boiler

6. Pulverized Fuel Boiler

7. Waste Heat Boiler

8. Thermic Fluid Heater (not a boiler!)

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Type of Boilers

1. Fire Tube Boiler

Relatively small steamcapacities (12,000

kg/hour)

Low to medium steam

pressures (18 kg/cm2)

Operates with oil, gas

or solid fuels

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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

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Type of Boilers

3. Packaged Boiler

Oil

Burner

To

Chimney

Comes in complete

package

Features

High heat transfer Faster evaporation

Good convective

heat transfer

Good combustion

efficiency High thermal

efficiency

Classified based on

number of passes

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Type of Boilers

4. Fluidized Bed Combustion

(FBC) Boiler

Particles (e.g. sand) are suspended in high

velocity air stream: bubbl ing f lu id ized bed

Combustion at 840 950 C

Capacity range 0,5 T/hr to 100 T/hr

Fuels: coal, washery rejects, rice husk, bagasseand agricultural wastes

Benefits: compactness, fuel flexibility, higher

combustion efficiency, reduced SOx & NOx

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Type of Boilers

4a. Atmospheric Fluidized Bed

Combustion (AFBC) Boiler

Most common FBC boiler that uses preheated

atmospheric air as fluidization and combustion air

4b. Pressurized Fluidized Bed

Combustion (PFBC) Boiler

Compressor supplies the forced draft and

combustor is a pressure vessel

Used for cogeneration or combined cycle powergeneration

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Type of Boilers

4c. Atmospheric Circulating Fluidized

Bed Combustion (CFBC) Boiler

Solids lifted from bed,

rise, return to bed

Steam generation inconvection section

Benefits: more

economical, better space

utilization and efficientcombustion

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Type of Boilers

5. Stoke Fired Boilers

a) Spreader stokers

Coal is first burnt in suspension then in

coal bed

Flexibility to meet load fluctuations

Favored in many industrial applications

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Type of Boilers

5. Stoke Fired Boilers

b) Chain-grate or traveling-grate stoker

Coal is burnt on moving

steel grate

Coal gate controls coal

feeding rate

Uniform coal size for

complete combustion

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Type of Boilers

Tangential firing

6. Pulverized Fuel Boiler

Pulverized coal powder blown with combustion

air into boiler through burner nozzles Combustion

temperature at 1300 -

1700 C

Benefits: varying coalquality coal, quick

response to load

changes and high pre-

heat air temperatures

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Type of Boilers

(Energy

Machine India)

8. Thermic Fluid Heater

Control

panel

Blower

motor

unit

Fuel oil

filter

Exhaust

Insulated

outer wall

1. Thermic

fluid heated

in the heater

2. Circulated

to userequipment

User equipment

3. Heat transfer

through heat

exchanged

4. Fluid

returned to

heater