Thermal Power plants

BY :-

SAI KUMAR,

VARUN,

(JNTUK).

• In India 65% of total power is generated by the Thermal Power Stations.

• In thermal generating stations coal, oil, natural gas are employed as primary sources of energy .

• A thermal power station basically work on the rankine cycle.

• Thermal power plant convert the heat energy of coal into electrical energy.

• Coal is burnt in a boiler which converts water into steam.

• The expansion of steam in turbine produces mechanical power which drives the alternator coupled to the turbine.

INTRODUCTION

SOURCES

• COAL SOURCE

• WATER SOURCE

• OIL SOURCE

• GAS SOURCE

A generating station which converts heat energy of coal combustion into electrical energy is known as thermal power station.

DEFINITION

OPERATION MECHANISM

• The coal is brought and crushed to powder, This is feed to boiler for producing heat .

• In Boiler the water is converted to steam.

• In super heater the moisture content is removed from the steam and that steam is called super heated steam.

• The superheated steam rotates the shaft of the High pressure turbine.

• The exhausted steam is sent to preheater and the steam then rotates the intermediate pressure (IP) turbine.

• The steam from the IP Turbine is then feed to low pressure turbine.

• The turbine shaft is connected to the Generator, which produces electric Power.

• The power generated is then transmitted .

GENERAL LAYOUT OF THERMAL POWER STATION

Schematic arrangement of steam power station

COAL HANDLING PLANTRaw coal wagon – Coal is brought to the site through a wagon as per the requirement.

Wagon tippler – The coal is unloaded from the wagon and is transported to crusher and for storage place through conveyor.

Junction tower - JTs are used where the conveyor has any angular deviation.

Primary crusher – The raw coal is crushed into fine pieces of 45mm grit. Primary crusher is also called Rotatory breaker since the coal is crushed by rotating plate.

The stone and unwanted coal are rejected

Secondary crusher – The fine pieces of coal is crushed into powder . (25 mm grit).

Junction Tower

Mill Bunker – The 25 mm grit coal is crushed into very fine powder for feeding the boiler . We will have a spare bunker for each boiler.

Boiler

Stack & Re claimer – It is used to store the powdered coal for

emergency purpose.

Atmospheric air –Through FD fan

PULVERIZING PLANT

• In modern thermal power plant , coal is pulverized

• ground to dust like size and carried to the furnace in a stream of hot air.

• Pulverizing is a means of exposing a large surface area to the action of oxygen and consequently helping combustion.

• Pulverizing mills are further classified as:

1. Contact mill

2. Ball mill

3. Impact mill

BOILER

• A boiler or steam generator is a closed vessel to which water under pressure, is converted into steam.

• It is one of the major components of a thermal power plant.

• Always designed to absorb maximum amount of heat released in the process of combustion.

SUPER HEATER & RE HEATERMOST OF THE MODERN BOILERS ARE HAVING SUPER HEATER AND RE HEATER ARRANGEMENT.

• Super heater is a component of a steam-generating unit in which steam, after it has left the boiler drum, is heated above its saturation temperature.

• The super heater may consist of one or more stages of tube banks arranged to effectively transfer heat from the products of combustion.

• Super heaters are classified as convection , radiant or combination of these.

Re heater : Some of the heat of superheated steam is used to rotate the turbine where it loses some of its energy. Re heater is also steam boiler component in which heat is added to this intermediate-pressure steam, which has given up some of its energy in expansion through the high-pressure turbine. The steam after reheating is used to rotate the second steam turbine where the heat is converted to mechanical energy. This mechanical energy is used to run the alternator, which is coupled to turbine , there by generating electrical energy.

DRAFT SYSTEM

• The circulation of air is caused by a difference in pressure, known as Draft.

• Draft is a differential pressure b/w atmosphere and inside the boiler.

• It is necessary to cause the flow of gases through boiler setting It may be –

1. Natural draft 2. Mechanical draft

STEAM TURBINE • A steam turbine converts heat energy of steam into mechanical energy and

drives the generator.

• It uses the principle that steam when issuing from a small opening attains a high velocity.

• This velocity attained during expansion depends on the initial and final heat content of the steam.

• This difference b/w initial and final heat content represents the heat energy converted into kinetic energy.

• These are of two types :-

1. Impulse turbine

2. Reaction turbine

ALTERNATOR

• Turbine and alternator are mechanical coupled with each other.

• Alternator convert mechanical energy of turbine into electrical energy.

• The electrical output from the alternator is delivered to the bus bar through transformer.

CONDENSER

• Which condenses the steam at the exhaust of turbine.

• It creates a very low pressure at the exhaust of turbine, this helps in converting heat energy of steam into mechanical energy in the prime mover.

• The condensed steam can be used as feed water to the boiler.

GENERATOR

• The Synchronus Generator is used to generate power by connecting the shaft of the Turbine to the shaft of the generator which create the magnetic flux producing Emf.

• The generated voltage will generally 33 KV to 11 KV max.

• the generated Voltage is stepped up by connecting Step up transformer and is also used for auxilliary purpose.

COOLING TOWER• Remove heat from the

water discharged from the condenser so that the water can be discharged to the river or re circulated and reused.

• Air can be circulated in the cooling towers through natural draft and mechanical draft.

ECONOMIZER

• Flue gases coming out of the boiler carry lot of heat.

• An economizer extracts a part of this heat from flue gases and uses it for heating feed water.

• This use of economizer results in saving coal consumption and higher boiler efficiency

AIR PREHEATER

• An air pre heater increases the temperature of air supplied for coal burning

• And it driven from the flue gases.

• Air is drown from the atmosphere by the force of draft fan.

• Air preheaters may be of three types

1. Plate type

2. Tubular type

3. Regenerative type

ASH HANDLING PLANT

• The percentage of ash in coal varies from 5% in good quality coal to about 40% in poor quality coal Power plants generally use poor quality of coal .

• thus amount of ash produced by it is pretty large .

• A modern 2000MW plant produces about 5000 tons of ash daily.

• The stations use some conveyor arrangement to carry ash to dump sites directly or for carrying and loading it to trucks and wagons which transport it to the site of disposal

UTILISATION OF SECONDARY RAW MATERIAL (ASH)

• Construction of embankments and fills.

• Construction of road in sub-base.

• Manufacture of cement.

• Manufacture of bricks/blocks.

• Agriculture as soil amendment/source of essential plant nutrients.

• The fuel used is quite cheap.

• Less initial cost as compared to other generating plants.

• It can be installed at any place irrespective of the existence of coal.

• The coal can be easily transported to the site

• It require less space as compared to Hydro power plants.

• Cost of generation is less than that of diesel power plants.

Advantages

DISADVANTAGES

• It pollutes the atmosphere due to production of large amount of smoke and fumes.

• It is costlier in running cost as compared to Hydro electric plants.

• Maintenance cost is more

REFERENCES:- TEXTBOOKS:

DR. KVSG MURALI KRISHNA,

WWW.GOOGLE.COM

WWW.SLIDESHARE.NET

Thank You