PREFACE

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 either drives

an electrical generator or does some other work, like ship propulsion. After it passes

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

heated; this is known as a Rankine cycle. 

Almost all coal, nuclear, geothermal, solar thermal electric, and waste incineration plants, as well

as many natural gas power plants are thermal. Natural gas is frequently

combusted in gas turbines as well as boilers.

Commercial electric utility power stations are most usually constructed on a very

large scale and designed for continuous operation. Electric power plants typically

use three-phase or individual-phase electrical generators to produce alternating current

(AC) electric power at a frequency of 50 Hz or 60 Hz (hertz, which is an AC sine

wave per second) depending on its location in the world.

CONTENTS

1. Introduction………………………………….02

2. Need For thermal power generation……..04

3. Classification………………………………..05

4. Basic definitions…………………………….07

5. Functioning of thermal power plant……...11

6. ADVANTAGES……………………………...17

7. DISADVANTAGES…………………………18

8. Future Prospects……………………………19

9. BIBLIOGRAPHY……………………………21

CHAPTER 1

INTRODUCTION

Almost all coal, nuclear, geothermal, solar thermal electric, and waste incineration plants, as well

as many natural gas power plants are thermal. Natural gas is frequently combusted in gas

turbines as well as boilers. The waste heat from a gas turbine can be used to raise steam, in

a combined cycle plant that improves overall efficiency. Power plants burning coal, oil,

or natural gas are often referred to collectively as fossil-fuel power plants. Some biomass-fueled

thermal power plants have appeared also. Non-nuclear thermal power plants, particularly fossil-

fueled plants, which do not use cogeneration, are sometimes referred to as conventional power

plants.

In thermal power stations, mechanical power is produced by a heat engine that

transforms thermal energy, often from combustion of a fuel, into rotational energy. Most thermal

power stations produce steam, and these are sometimes called steam power stations. Not all

thermal energy can be transformed into mechanical power, according to the second law of

thermodynamics. Therefore, there is always heat lost to the environment. If this loss is employed

as useful heat, for industrial processes or district heating, the power plant is referred to as a

cogeneration power plant or CHP (combined heat-and-power) plant. In countries where district

heating is common, there are dedicated heat plants called heat-only boiler stations. An important

class of power stations in the Middle East uses by-product heat for the desalination of water.

Commercial electric utility power stations are most usually constructed on a very large scale and

designed for continuous operation. Electric power plants typically use three-phase or individual-

phase electrical generators to produce alternating current (AC) electric power at a frequency of

50 Hz or 60 Hz (hertz, which is an AC sine wave per second) depending on its location in the

world. Other large companies or institutions may have their own usually smaller power plants to

supply heating or electricity to their facilities, especially if heat or steam is created anyway for

other purposes. Shipboard steam-driven power plants have been used in various large ships in the

past, but these days are used most often in large naval ships. Such shipboard power plants are

general lower power capacity than full-size electric company plants, but otherwise have many

similarities except that typically the main steam turbines mechanically turn the

propulsion propellers, either through reduction gears or directly by the same shaft. The steam

power plants in such ships also provide steam to separate smaller turbines driving electric

generators to supply electricity in the ship. Shipboard steam power plants can be either

conventional or nuclear; the shipboard nuclear plants are mostly in the navy. There have been

perhaps about a dozen turbo-electric ships in which a steam-driven turbine drives an electric

generator which powers an electric motor for propulsion.

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 either drives an electrical generator or

does some other work, like ship propulsion. After it passes through the turbine, the steam

is condensed in a condenser and recycled to where it was heated; this is known as a Rankine

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

sources. Some prefer to use the term energy center because such facilities convert forms

of heat energy into electrical energy.

History

Reciprocating steam engines have been used for mechanical power sources since the 18th

Century, with notable improvements being made by James Watt. The very first commercial

central electrical generating stations in New York and London, in 1882, also used reciprocating

steam engines. As generator sizes increased, eventually turbines took over they encres the hose

power.

CHAPTER 2

NEED FOR THERMAL POWER GENERATION

Scarcity of water resources: Water resources are not abundantly available and are

geographically unevenly distributed. Thus hydel power plants cannot be installed with

ease and are limited to certain locations.

Widely available alternate flues: Many alternate fuels such as coal, diesel, nuclear fuels,

geo-thermal energy sources, solar-energy, biomass fuels can be used to generate power

using steam cycles.

Maintenance and lubrication cost is lower: Once installed, these require less

maintenance costs and on repairs. Lubrication is not a major problem compared to hydel

power plant.

Coal is abundant: Coal is available in excess quantities in India and is rich form of

energy available at relatively lower cost.

Working fluid remains within the system, and need not be replaced every time thus

simplifies the process.

CHAPTER 3

CLASSIFICATION

Thermal power plants are classified by the type of fuel and the type of prime mover Installed.

By fuel

Nuclear power plants use a nuclear reactor's heat to operate a steam turbine generator. 

Fossil fuelled power plants  may also use a steam turbine generator or in the case of natural

gas fired plants may use a combustion turbine. A coal-fired power station produces

electricity by burning coal to generate steam, and has the side-effect of producing a large

amount of carbon dioxide, which is released from burning coal and contributes to global

warming

Geothermal power plants use steam extracted from hot underground rocks.

Biomass Fuelled Power Plants may be fuelled by waste from sugar cane, municipal solid

waste, landfill methane, or other forms of biomass.

Solar thermal  electric plants use sunlight to boil water, which turns the generator.

By prime mover

Steam turbine  plants use the dynamic pressure generated by expanding steam to turn the

blades of a turbine

Gas turbine   plants use the dynamic pressure from flowing gases (air and combustion

products) to directly operate the turbine. 

Combined cycle  plants have both a gas turbine fired by natural gas, and a steam boiler

and steam turbine which use the hot exhaust gas from the gas turbine to produce

electricity

Reciprocating engines are used to provide power for isolated communities and are

frequently used for small cogeneration plants. Hospitals, office buildings, industrial

plants, and other critical facilities also use them to provide backup power in case of a

power outage

Microturbines ,   Stirling engine   and internal combustion reciprocating engines are low-

cost solutions for using opportunity fuels, such as landfill gas, digester gas from water

treatment plants and waste gas from oil production

Efficiency

Power is energy per unit time. The power output or capacity of an electric plant can be expressed

in units of megawatts electric (MWe). The electric efficiency of a conventional thermal power

station, considered as saleable energy (in MWe) produced at the plant busbars as a percent of the

heating value of the fuel consumed, is typically 33% to 48% efficient. This efficiency is limited

as all heat engines are governed by the laws of thermodynamics (See: Carnot cycle). The rest of

the energy must leave the plant in the form of heat. This waste heat can go through

a condenser and be disposed of with cooling water or in cooling towers. If the waste heat is

instead utilized for district heating, it is called cogeneration. An important class of thermal power

station is associated with desalination facilities; these are typically found in desert countries with

large supplies of natural gas and in these plants, freshwater production and electricity are equally

important co-products.

Since the efficiency of the plant is fundamentally limited by the ratio of the absolute

temperatures of the steam at turbine input and output, efficiency improvements require use of

higher temperature, and therefore higher pressure, steam. Historically, other working fluids such

as mercury have been experimentally used in a mercury vapor turbine power plant, since these

can attain higher temperatures than water at lower working pressures. However, the obvious

hazards of toxicity, and poor heat transfer properties, have ruled out mercury as a working fluid.

CHAPTER 4

BASIC DEFINITIONS

Steam is vaporized water and can be produced at 100’C at standard atmosphere. 

In common speech, steam most often refers to the visible white mist that condenses above

boiling water as the hot vapor mixes with the cooler air.

T urbine   A turbine is a rotary engine that extracts energy from a fluid or air flow and converts it

into useful work.

The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum,

with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they

move and impart rotational energy to the rotor. Early turbine exare windmills and waterwheels.

Fig Typical turbine

E lectric generator An electric generator is a device that converts mechanical energy to

electrical energy. A generator forces electrons in the windings to flow through the

external electrical circuit. It is somewhat analogous to a water pump, which creates a flow of

water but does not create the water inside. 

Fig Typical Generator

A boiler or steam generator is a device used to create steam by applyingheat energy to water.

Although the definitions are somewhat flexible, it can be said that older steam generators were

commonly termed boilers and worked at low to medium pressure

(1–300 psi/0.069–20.684 bar; 6.895–2,068.427 kPa), but at pressures above this it is more usual

to speak of a steam generator.

A boiler or steam generator is used wherever a source of steam is required. The form and size

depends on the application: mobile steam engines such as steam locomotives, portable engines

and steam-powered road vehicles typically use a smaller boiler that forms an integral part of the

vehicle;

Second law of thermodynamics  The second law of thermodynamics is an expression of the

universal principle of entropy, stating that the entropy of anisolated system which is not

in equilibrium will tend to increase over time, approaching a maximum value at equilibrium; and

that the entropy change dSof a system undergoing any infinitesimal reversible process is given

by δq / T, where δq is the heat supplied to the system and T is the absolute temperature of the

system. 

CHAPTER 5

FUNCTIONING OF THERMAL POWER PLANT:

In a thermal power plant, one of coal, oil or natural gas is used to heat the boiler to convert the

water into steam. The steam is used to turn a turbine, which is connected to a generator. When

the turbine turns, electricity is generated and given as output by the generator, which is then

supplied to the consumers through high-voltage power lines.

Fig steam power generation –

Typical diagram of a coal-fired thermal power station

1. Cooling tower 10. Steam Control valve 19. Superheater

2. Cooling water pump 11. High pressure steam

turbine

20.Forced draught

(draft) fan

3. transmission line (3-phase) 12. Deaerator 21. Reheater

4. Step-up transformer (3-

phase) 13. Feed water heater 22. Combustion air intake

5. Electrical generator (3-

phase)14. Coal conveyor 23. Economiser

6.Low pressure steam turbine 15. Coal hopper 24. Air preheater

7. Condensate pump 16. Coal pulverizer 25. Precipitator

8. Surface condenser 17. Boiler steam drum26.Induced draught

(draft) fan

9.Intermediate pressure steam

turbine18. Bottom ash hopper 27. Flue gas stack

Detailed process of power generation in a thermal power plant:

Water intake: Firstly, water is taken into the boiler through a water source. If water is

available in a plenty in the region, then the source is an open pond or river. If water is

scarce, then it is recycled and the same water is used over and over again.

Boiler heating: The boiler is heated with the help of oil, coal or natural gas. A furnace is

used to heat the fuel and supply the heat produced to the boiler. The increase in

temperature helps in the transformation of water into steam.

Steam Turbine: The steam generated in the boiler is sent through a steam turbine. The

turbine has blades that rotate when high velocity steam flows across them. This rotation

of turbine blades is used to generate electricity.

Generator: A generator is connected to the steam turbine. When the turbine rotates, the

generator produces electricity which is then passed on to the power distribution systems.

Special mountings: There is some other equipment like the economizer and air pre-

heater. An economizer uses the heat from the exhaust gases to heat the feed water. An air

pre-heater heats the air sent into the combustion chamber to improve the efficiency of the

combustion process.

Ash collection system: There is a separate residue and ash collection system in place to

collect all the waste materials from the combustion process and to prevent them from

escaping into the atmosphere.

Apart from this, there are various other monitoring systems and instruments in place to keep track of the

functioning of all the devices. This prevents any hazards from taking place in the plant.

A   Rankine cycle   with a two-stage   steam turbine   and a single feedwater heater.

The second law of thermodynamics states that any closed-loop cycle can only convert a fraction

of the heat produced during combustion into mechanical work. The rest of the heat, called waste

heat, must be released into a cooler environment during the return portion of the cycle. The

fraction of heat released into a cooler medium must be equal or larger than the ratio ofabsolute

temperatures of the cooling system (environment) and the heat source (combustion furnace).

Raising the furnace temperature improves the efficiency but also increases the steam pressure,

complicates the design and makes the furnace more expensive. The waste heat cannot be

converted into mechanical energy without an even cooler cooling system. However, it may be

used in cogeneration plants to heat buildings, produce hot water, or to heat materials on an

industrial scale, such as in some oil refineries, cement plants, and chemical synthesis plants.

Typical thermal efficiency for electrical generators in the electricity industry is around 33% for

coal and oil-fired plants, and up to 50% for combined-cycle gas-fired plants 

CHAPTER 6

ADVANTAGES

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

transported to the site of the plant by rail or road.

It requires less space as compared to Hydro power plants.

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

This plants can be quickly installed and commissioned and can be loaded when compare

to hydel power plant

It can meet sudden changes in the load without much difficulty controlling operation to

increase steam generation

Coal is less costlier than diesel

Maintenance and lubrication cost is lower

CHAPTER 7

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.

well, stations always take up room for the environment which could be cultivated for the

use of growing food etc. which is a great disadvantage is our day and age, as food is

necessary to live.

However, this could create more jobs for a lot of people thus increasing in a good way

our current economic situation which by is failing miserably.

Over all capital investment is very high on account of turbines, condensers, boilers

reheaters etc .maintenance cost is also high on lubrication, fuel handling, fuel processing.

It requires comparatively more space and more skilled operating staff as the operations

are complex and required precise execution

A large number of circuits makes the design complex

Starting of a thermal power plant takes fairly long time as the boiler operation and steam

generation process are not rapid and instantaneous

CHAPTER 8

FUTURE PROSPECTS

Effective Use of Fossil Fuels and Reduction in CO2  Emissions by Improving the

Efficiency of Thermal Power Generation

At present, thermal power generation accounts for approximately 70% of the total amount of

electricity produced around the world. However, thermal power generation, which uses fossil

fuels, causes more CO2 emissions than other power generation methods. In order to reduce

CO2emissions per unit power produced, Toshiba Group is developing next-generation thermal

power technologies aimed at improving plant efficiency and commercializing the

CCS*1 (CO2 capture and storage) system.

To improve the efficiency of thermal power generation, it is of vital importance that the

temperature of the steam or gas used to rotate the turbines is raised. Toshiba Group is working on

the development of ultra-high-temperature materials and cooling technologies in order to

commercialize an A-USC*2 system (Advanced Ultra-Super Critical steam turbine system) more

efficient than previous models, which is designed to increase steam temperature from 600°C to

above the 700°C mark. In the area of combined cycle power generation using a combination of

gas and steam turbines, we are also engaged in jointly developing a power generation system

designed to increase gas temperature to the level of 1,500°C with the U.S. Company General

Electric, which is starting commercial operation in July 2008 in Japan.

Accelerating the Development of CO2 Capture and Storage Technology

The Key to Realizing Next-generation Power Generation System

Toshiba Group is engaged in the development of CO2 capture and storage (CCS) technology

designed to separate and capture CO2 emitted from thermal power plants and other such facilities

and then store it underground. More specifically, this development is aimed at commercializing

CCS technology. In order to commercialize this technology, it is essential that we develop a

system that makes it possible to separate and capture CO2 without reducing the economic

performance of a power plant. In the course of its basic research, Toshiba Group has developed a

high-performance absorbent that minimizes the energy consumption required for the CO2 capture

process. Experiments conducted using small-scale test equipment have confirmed that its level of

performance is the best in the industry.

Preventive Maintenance Technologies That Support the Long-term, Stable

Operation of Facilities and Extension of the Service Life of High-temperature

Gas Turbine Parts

The use of combined cycle power generation facilities using gas turbines is increasing year by

year for the purpose of achieving the reduction in CO2 emissions required to create a low-carbon

society, increasing energy use efficiency and improving economic performance. Toshiba Group

is developing various technologies that support the long-term, stable operation of facilities.

In order to analyze and assess high-temperature gas turbine parts, which are used in harsh

environments and to determine their remaining service lives based on the level of degradation,

we developed a technology for making highly accurate diagnoses by combining a number of

methods, including the finite element method (FEM) and methods for testing cleavage strength,

tensile strength, durability and fatigue strength. We are also working to commercialize service

life extension and repair technologies aimed at recycling gas turbine rotor/stator blades and

extending their service lives. Based on the BLE (Blade Life Extension™) concept unique to our

company group, we repeatedly reuse old rotor blades that meet our repair standards instead of

simply discarding them. The repair and recycling of these parts not only reduces running costs

and improves economic performance, but also effectively minimize the environmental impact.

Fig- Concept of the BLE Process

BIBLIOGRAPHY

1.  British Electricity International (1991).Modern Power Station Practice: incorporating

modern power system practice (3rd Edition (12 volume set) ed.). Pergamon. ISBN 0-08-

040510-X.

2. Babcock & Wilcox Co. (2005).Steam: Its Generation and Use (41st edition ed.). ISBN 0-

9634570-0-4.

3.  Thomas C. Elliott, Kao Chen, Robert Swanekamp (coauthors) (1997).Standard

Handbook of Powerplant Engineering (2nd edition ed.). McGraw-Hill

Professional.ISBN 0-07-019435-1.

4. Air Pollution Control Orientation Course from website of the Air Pollution Training

InstituteAir Pollution Control Orientation Coursefrom website of the Air Pollution

Training Institute

5.  Fundamentals of Steam Power by Kenneth Weston,

6. First  and second lectures by S. Banerjee on "Thermal Power Plants"

7. www.cognizance.org.in/main/pages/technovision

8. cleantechnica.com/.. -thermal-electricity

9. www.britannica.com/. -Thermal-Power-Generation-Technology