Thermal Power Plant

Prepared By:Vivek Pathak

INTRODUCTION

Talking of a thermal power, a number of major parameters need to be considered. Firstly, selecting a suitable site for a thermal pant is of utmost importance.

The thermal plant consumes huge amount of fuel principally coal.

It is estimated that for every megawatt produced, a plant needs more than 10,000 tons of coal.

Arrangement must exist to bring the coal from mines and store the coal.

Secondly, in the Thermal power plant layout, there must be provision to dispose of large quantities of ash generated.

It is estimated that for storage of coal, ash disposal building of the plant itself and residential space for workers etc you would need   approximately 3 acres of land for every megawatt generated.

Lastly you need huge quantities of water to run the plant. A perennial water source like a river nearby is needed to run a thermal power plant.

INTRODUCTORY OVERVIEW

A thermal power station is a power plant in which the prime mover is steam driven.

Water is heated, turns into steam and spins a steam turbine which drives an electrical generator.

After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated.

The greatest variation in the design of thermal power stations is due to the different fuel sources.

Energy Conversion Process in Thermal Power Plants

Chemical Energy isConverted into ThermalEnergy by Combustion

In Boiler

Thermal Energy isConverted into

Mechanical EnergyIn Turbine

Mechanical Energy isConverted into

Electrical Energy In Generator

Chemical

Energy

Fuel

Thermal

Energy

Mechanical

Energy

Electrical

Energy

Energy Conversion . . .

Fuel, Air and water produce steam in the boiler by combustion

Steam of high temperature and pressure is expended from high pressure to low pressure in the turbine

Thermal energy is converted into kinetic energy and finally mechanical energy

This mechanical energy derives the generator to produce electricity

Thermal Power Plant can work in two Manners

1. Production of electricity

2. Production of electricity with production of steam for the use in industry e.g. paper mills, textile mills, sugar mills, refineries

Processing of Power Plant

Turbine Grid Water

Fuel

Steam

Waste Gases

Exhaust Steam

Generator

Boiler

Efficiency

Efficiency = Heat Equivalent of Electrical output / Heat of Combustion

Normally η = 29%

Losses:

1. Boiler House Losses:

a. To Dry Fuel Gases 5%

b. To moisture in gases 5%

c. To ash and unburnt carbon 1%

d. To radiation and leakage 2.5%

e. Unknown losses 2.5%

TOTAL 16%

Efficiency. . .

2. Turbine Losses:

a. Heat rejection to Condenser 54%

3. Alternator or Generator Loss 1%

TOTAL 55%

Grand Total 71%

So Efficiency = (100% - Losses)

= 100% - 71% = 29%

Merits of Thermal Power Plant

Fuel is cheaper* Less space is required The initial cost is less Plant can be located near the load centre Turbine can work at 25% overload continuously A portion of steam can be used in various industries

Demerits of Steam Power Plant

Maintenance and operating costs are high Pollution of atmosphere is one of the major

problems Water is required in huge quantity Handling of coal and disposal of ash are

difficult tasks It requires long time for installation Efficiency falls quickly below 75%

Site Selection

Availability of Coal (Fuel) Proper arrangement for ash disposal Nature of the land Location from load centre Availability of water Transport facilities Availability of labor

Main Circuits of Thermal Power Plant

Coal and Ash Circuit Air and Gas circuit Feed Water and Steam circuit Cooling Water circuit

Coal and Ash Circuit

Coal from the storage is fed to the boiler through coal handling equipment for the generation of steam.

Ash produced due to combustion of coal is removed to ash storage through ash-handling system

Air and Gas Circuit

Air is supplied to the combustion chamber of the boiler either through forced draught or induced draught fan or by using both.

The dust from the air is removed before supplying to the combustion chamber.

The exhaust gases carrying sufficient quantity of heat and ash are passed through the air-heater.

Here the exhaust heat of the gases is given to the air then it is passed through the dust collectors where

most of the dust is removed before exhausting the gases to the atmosphere

Feed Water and Steam Circuit

The steam generated in the boiler is fed to the steam prime mover to develop the power

The steam coming out of the prime mover is condensed in the condenser and then fed to the boiler with the help of pump

The condensate is heated in the feed-heaters using the steam tapped from different points of the turbine

The feed water supplied from external source is passed through the purifying plant to reduce to reduce dissolve salts to an acceptable level

This purification is necessary to avoid the scaling of the boiler tubes

Cooling Water Circuit

The quantity of cooling water required to condense the steam is considerably high and it is taken from a lake, river or sea

. The water is pumped in by means of pumps and the hot water after condensing the steam is cooled before sending back into the pond by means of cooling towers

Major Parts of Steam Power Plant

1. Boilers 2. Superheater

3. Turbine 4. Condenser

5. Economizer 6. Air preheater

7. Induced Draft Fan 8. Forced Draft Fan

9. Chimney 10. Coal Handling Plant

11. Ash Handling Plant 12. Cooling Tower

13. Alternator 14. Evaporator

15. Pumps

1 .Boiler

Purpose: To produce steam under pressureTypes:1. Fire Tube Boiler: Hot gases of combustion are

inside the tubes and the tubes are surrounded by water

2. Water Tube Boiler: Water is inside the tube and hot gases are outside the tube

One of these are used according to the requirements

Fire Tube Boiler

Water Tube Boiler

Superheater

Device used to remove the traces of moisture from saturated steam leaving boiler tubes.

It also increase the temperature above saturation temperature

Classes:1. Radiant Superheater: Located in the furnace between the

furnace water walls and absorbs heat from the burning fuel through radiation

2. Convection Superheater: Located well back in boiler tube bank. It receives its heat from flue gases through convection.

Economizer

It absorbs heat from outgoing flue gases and used for raising the temperature of feed water coming from condenser

Economizer raises efficiency of boiler by 10 -12 % thus 5 – 15 % of fuel consumption is saved

Air Preheater

Air preheater is used to recover heat from flue gases since entire heat can’t be extracted by economizer

Boiler Efficiency is increased by 1% if the avg. air temp. is increased by 20°C

Steam Turbines

There are two types of steam turbines

1. Impulse type: Steam expands completely in the stationary nozzles, the pressure over the moving blades remains constant.

2. Reaction Type: Steam is expanded both in fixed blades (nozzles) and moving blades.

Coal Handling

1. Coal shouldn’t be exposed to air It pollutes the air and releases poisonous gases

like carbon monoxide

2. The coal from the heaps is moved into the plant by means of long conveyors that are electrically operated

There are many different types of conveyors and coal-handling devices like screwing conveyors, bucket elevators, grabbing bucket conveyors etc.

Coal Crusher

Before the coal is sent to the plant it has to be ensured that the coal is of uniform size so it is passed through the crushers

Rotary crushers are very commonly used for this purpose as they can provide a continuous flow of coal to the pulverizer

Coal Crusher. . .

Pulverizer

Are used to smash materials into tiny granular.

Most commonly used pulverizer is the Boul Mill

The arrangement consists of 2 stationary rollers and a power driven baul in which pulverization takes place as the coal passes through the sides of the rollers and the baul

THERMAL POWER PLANT LAYOUT

Installed Plant Capacity Of Thermal Power Plant In India

Installed Plant Capacity Of Thermal Power Plant In World

Rank Station Country Location Capacity (MW) Ref

1 Taichung Power Plant Taiwan 24°12 46″N 120°28 52″E′ ′ 5,500 [23]

2 Tuoketuo Power Station China 40°11 49″N 111°21 52″E′ ′ 5,400 [24][25][26]

3 Bełchatów Power Station Poland 51°15 59″N 19°19 50″E′ ′ 5,354 [27][28][29]

4= Guodian Beilun Power Station

China 29°56 37″N 121°48 57″E′ ′ 5,000 [30]

4= Waigaoqiao Power Station China 31°21 21″N 121°35 54″E′ ′ 5,000 [31][32]

4= Guohoa Taishan Power Station

China 21°52 00″N 112°55 22″E′ ′ 5,000 [33]

4= Jiaxing Power Station (zh) China 30°37 46″N 121°8 49″E′ ′ 5,000 [34]