Unit -2 Power PlantsUnit -2 Power Plants

Steam power plantSteam power plant Layout Layout Boilers Boilers Pulverized coal burnersPulverized coal burners Fluidized bed combustion Fluidized bed combustion

Power generating units Power generating units are mega projects are mega projects

Require huge capital Require huge capital investment investment

Require natural Require natural resources like, fossil resources like, fossil fuels fuels

Large amount of waterLarge amount of water Changes the local eco Changes the local eco

systemsystem Huge Impacts on the Huge Impacts on the

Environment and HealthEnvironment and Health

Coal MiningCoal Mining

Surface MiningSurface Mining Strip MiningStrip Mining

Underground Underground MiningMining

Air QualityAir Quality Around the coal based plants the ambient concentrations Around the coal based plants the ambient concentrations

of Sulphur Dioxide, Oxides of Nitrogen and SPM are high.of Sulphur Dioxide, Oxides of Nitrogen and SPM are high.

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

Two other gases, carbon dioxide and ozone are Two other gases, carbon dioxide and ozone are emitted. The high amount of carbon dioxide emission from emitted. The high amount of carbon dioxide emission from thermal power plants contribute to global warming leading thermal power plants contribute to global warming leading to climate change is significant Ground level ozone, which to climate change is significant Ground level ozone, which is formed due to photolytic reactions of NOis formed due to photolytic reactions of NOxx and its impacts and its impacts are under studyare under study

Fly ash contains Fly ash contains a toxic brew of a toxic brew of dangerous dangerous chemicals and is chemicals and is the largest the largest contributor to contributor to mercury pollutionmercury pollution

Composition of Fly ashComposition of Fly ash

It contains as main chemical components SiO2 It contains as main chemical components SiO2 (51.4 wt%), Al2O3 (22.1 wt%) and Fe2O3 (51.4 wt%), Al2O3 (22.1 wt%) and Fe2O3 (17.2 wt%; ignited weight basis). As (17.2 wt%; ignited weight basis). As commonly observed, many toxic elements commonly observed, many toxic elements and heavy metals are highly enriched in the and heavy metals are highly enriched in the fly ash relative to the original coal. For fly ash relative to the original coal. For example, considerable amounts of Be (16.4 example, considerable amounts of Be (16.4 ppm), Cu (106 ppm), Zn (578 ppm), As (40.4 ppm), Cu (106 ppm), Zn (578 ppm), As (40.4 ppm), Cd (2.6 ppm), Hg (18 ppm), Pb (71 ppm), Cd (2.6 ppm), Hg (18 ppm), Pb (71 ppm), and U (21.8 ppm) is found in Fly ash.ppm), and U (21.8 ppm) is found in Fly ash.

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

Water slowly seeps into the ground while carrying Water slowly seeps into the ground while carrying with it the ash leach ate. Water may contain with it the ash leach ate. Water may contain harmful heavy metals like boron, which have a harmful heavy metals like boron, which have a tendency to leach out over a period of time. tendency to leach out over a period of time. 

When fly ash comes into contact with water, When fly ash comes into contact with water, leaches into groundwater supplies which get leaches into groundwater supplies which get polluted and unsuitable for domestic use.  polluted and unsuitable for domestic use. 

The release of ash pond decant into the local The release of ash pond decant into the local water bodies- water dries up, dust nuisance, water bodies- water dries up, dust nuisance, increases turbidity, decreases primary increases turbidity, decreases primary productivity, affects fishes and other aquatic productivity, affects fishes and other aquatic biotabiota

Coal Power Plant OperationCoal Power Plant Operation

Steam Turbine Generator Steam Turbine Generator Is a series of steam turbines interconnected to each Is a series of steam turbines interconnected to each

other and then a generatorother and then a generator

Steam CondenserSteam CondenserSteam enters fSteam enters from the turbine generator and is pumped rom the turbine generator and is pumped

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

StackStackReleases process emissions.Releases process emissions.

What is a Boiler?

IntroductionIntroduction

• 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

IntroductionIntroduction

BURNERBURNERWATER WATER

SOURCESOURCE

BRINEBRINE

SOFTENERSSOFTENERSCHEMICAL FEEDCHEMICAL FEED

FUELFUELBLOW DOWN BLOW DOWN SEPARATORSEPARATOR

VENTVENT

VENTVENTEXHAUST GASEXHAUST GASSTEAM TO STEAM TO PROCESSPROCESS

STACKSTACK DEAERATORDEAERATOR

PUMPSPUMPS

Figure: Schematic overview of a boiler room

BOILERBOILER

ECO-ECO-NOMI-NOMI-ZERZER

Types of BoilersTypes 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!)

Type of BoilersType 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 BoilersType 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

Type of BoilersType 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

Type of BoilersType of Boilers

4. Fluidized Bed Combustion (FBC) Boiler• Particles (e.g. sand) are suspended in high

velocity air stream: bubbling fluidized bed

• Combustion at 840° – 950° C

• Capacity range 0,5 T/hr to 100 T/hr

• Fuels: coal, washery rejects, rice husk, bagasse and agricultural wastes

• Benefits: compactness, fuel flexibility, higher combustion efficiency, reduced SOx & NOx

Type of BoilersType 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 power generation

Type of BoilersType of Boilers

4c. Atmospheric Circulating Fluidized Bed Combustion (CFBC) Boiler

• Solids lifted from bed, rise, return to bed

• Steam generation in convection section

• Benefits: more economical, better space utilization and efficient combustion

Type of BoilersType 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

Type of BoilersType 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

Type of BoilersType 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 coal quality coal, quick response to load changes and high pre-heat air temperatures

Type of BoilersType 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 user

equipment

User equipment

3. Heat transfer through heat exchanged

4. Fluid returned to

heater