2007 PROJECT DOCUMENT ON EXERGY

Exergy Analysis of Thermal Power Plant

NOMENCLATURE

HPT : High pressure turbine

IPT : Intermediate pressure turbine

LPT : Low pressure turbine

BFP : Boiler feed pump

LPH : Low pressure heater

HPH : High pressure heater

FRS : Feed water regulating station

GSC : Gland steam cooler

P.L.F : Plant load factor

CEP : Condensate extraction pump

Ψ : Exergy

ηI : First law efficiency

ήII : Second law efficiency

W : Work done in kw

I destroyd = To ˙Sgen : Irreversibility destroyed or exergy l

∑n k=1 (1 – (÷ Tk))Qk : Exergy summation supplied through heat transfer

Tk : Temperature of heat source/sink at which

heat is transferred or rejected

Qk : Heat transfer rate in kW

Ψw : Work done by the system

Sgen : Entropy generated in kW/K

.m : Mass inlet or exit rate in kg/s

.s : Entropy inlet or exit rate in kW/K

p : Pressure in bar

h : enthalpy in kJ/kg

H : enthalpy in MW

Department of Mechanical Engg, SVIST, Kadapa. Page 1


s : entropy in kJ/kg-K

S : entropy in MW/K

To : atmospheric temperature in K

mg : mass of gases in kg/s

gi : gas inlet

go : gas outlet

ms : mass of steam in kg/s

mw : mass of water in kg/s

SH : super-heater

mb : mass of boiler in kg/s

bi : boiler inlet

bo : boiler outlet



CONTENTSABSTRACT.................................................................................................................................................................................................................................................... 8

CHAPTER 1................................................................................................................................................................................................................................................... 9

1.0 INTRODUCTION TO RTPP............................................................................................................................................................................................................. 9

1.1 GENERAL………………………………………………………………………………………………………………………………………………………….9

1.2 LOCATION…………………………………………………………………………………………………………………………………………………….…..9

1.3 RAWMATERIAL……………………………………………………………………………………………………………………………………...…...……..11

1.4 COMBUSTION PROCESS……………………………………………………………………………………………………………………………………….11

1.5 OPERATIONAL DATA…………………………………………………………………………………………………………………......................................11

CHAPTER 2................................................................................................................................................................................................................................................. 13

2.1 RANKINE CYCLE.......................................................................................................................................................................................................................... 13

2.2 REGENERATIVE CYCLE.............................................................................................................................................................................................................. 15

2.3 .REHEAT CYCLE........................................................................................................................................................................................................................... 17

2.4 TYPICAL VALUES OF EFFICIENCIES...................................................................................................................................................................................... 20

2.5 FACTORS INCREASING THE THERMAL CYCLE EFFICIENCY............................................................................................................................................20

2.6 PLANT LOSSES.............................................................................................................................................................................................................................. 22

CHAPTER 3................................................................................................................................................................................................................................................. 23

3.0 INTRODUCTION TO EXERGY.....................................................................................................................................................................................................23

3.1 ENERGY.......................................................................................................................................................................................................................................... 23

3.2 EXERGY.…………………………………………….……………………………………………………………………………………………………………24

3.3 APPLICATIONS OF THE SECOND LAW OF THERMO DYNAMICS……………………………………………………………………….…..…………..28

3.4 WORK DONE……………………………………………………………………………………………………………………..………………….…………..30

3.5 LAWS OF THERMO DYNAMICS…………………………………………………………………………………………..……………………….…………..32

3.6 LAW OF DEGRADIATION ENERGY……………………………………………………………………………..……………………………………………33

CHAPTER 4................................................................................................................................................................................................................................................. 34

4.0 DATA COLLECTION..................................................................................................................................................................................................................... 34

4.1TECHNICAL DATA......................................................................................................................................................................................................................... 34

4.2 GENERAL DATA………………………………………………………….…………………………………………………………………………………….34

4.3 HEAT RATE VALUES……………………………………………….…………………………………………………………………………………………..37

CHAPTER 5................................................................................................................................................................................................................................................. 40

5.0 COMPONENTS ON WHICH ANALYSIS IS MADE...................................................................................................................................................................40

5.1 BOILER............................................................................................................................................................................................................................................ 40

5.2 TYPES OF BOILERS...................................................................................................................................................................................................................... 40

5.3 SUPER HEATER............................................................................................................................................................................................................................. 41

5.4 CONDENSER.................................................................................................................................................................................................................................. 42

5.5 TYPES OF CONDENSERS…………………………………………………………………………………………………………………………………...….44

5.6 COOLING TOWER……………………………….……………………………………………………………………………………… ………………...……45

5.7 TYPES OF COOLING TOWERS…………………………………………………………………………………………………………………………...…….46

5.8 CONDENSATE EXTRACTION PUMP…………………………………………………………………………………………………..………………………48

5.9 EJECTORS…………………………………………………………………………………………………………………………………..…………..…………48

5.10 FEED WATER HEATER…………………………………………………………………………………………………………………………………...……49

5.11 DEAREATOR…………………………………………………………………………………...………………………………………………………..………50



5.12 BOOSTER PUMP…………………………………………………………………………………………………………………....………………………….. 51

5.13 BOILER FEED WATER PUMP……………………………………………………………………………………………….………………………………...51

5.14 ECONOMISER………………………………………………………………………………………………….……………………………………………….52

5.15 ELECTRO STATIC PRECIPITATORS……………………..…………………………………………………………………………………………………..53

5.16 BOILER REHEATER…………………………………………………………………………..………………………………………………………………...54

CHAPTER6.................................................................................................................................................................................................................................................. 56

6.0 TABLES AND CALCULATIONS.................................................................................................................................................................................................. 56

6.1 ENTHALPY AND ENTROPY OF THE COMPONENTS........................................................................................................................................................... .56

6.2 THERMO DYNAMIC EXTRACTION OF STEAM AT TURBINES………………………………………………………………………………..…… 79

6.3 TABULATED VALUES OF TURBINE………………………………………………………………………………………………………………………….81

CHAPTER 7…………………………………………………………………………………………………………………………………………..…………………...83

7.0 EXERGY AND ENERGY ANALYSIS ON THE COMPONENTS…………………………………………………………………………………….………...83

7.1 EXERGY ANALYSIS…………………………………………………………………………………………………………………………..………………….83

7.2 ENERGY ANALYSIS………………………………………………………………………………………………………………………...……………………90

7.3 TABLES OF THE EXERGY, ENERGY EFFICIENCIES AND LOSSES………………………………………………………………………………………..95

CHAPTER 8…………………………………………………………………………………………………………………………………………….…………………97

8.0 COMPARISONOF GRAPHS BETWEEN EXERGY AND ENERGY…………………………………………………………………..………………………97

8.1 EXERGY DESTRUCTION GRAPH………………………………………………………………………………………………………………………….…. 97

8.2 TURBINE EFFICIENCY AND DESTRUCTION GRAPH……………………………………………………………………………………………………... 97

8.3 EXERGY VS ENERGY GRAPH………………………………………………………………………………………………………....................................….98

8.4 COMPARISON GRAPH………………………………………………………………………………………………………………..…………….…………....98

CHAPTER 9………………………………………………………………………………………………………………………………………………………………99

9.0 CONCLUSION…………………………………………………………………………………………………………………………….……………...……….99

9.1 RECOMMENDATIONS FOR FURTHER STUDIES………………………………………………………………………………………………….….....….100

CHAPTER 10 ………………………………………………………………………………………………………………………………………………………..…101

10.0 BIBLOGRAPHY……………………………………………………………………………………………………………………………………..…………..101



LIST OF FIGURES

Figure 1 : Layout of Thermal power plant

Figure 2.1( a) : Rankine cycle

Figure 2.1(b) : T-S diagram Figure 2.1 (c) : P-V diagram

Figure 2.2 (a) : Regenerative cycle

Figure 2.2 (b) : T-S diagram

Figure 2.3 (a) : Reheat cycle

Figure 2.3 (b) : T-S diagram

Figure 2.3.2 : Line diagram of 210 MW thermal power plant

Figure 2 .6(a) : Single steam cycle diagram

Figure 2.6 (b) : Heat balance diagram

Figure 3.1 (a) : Thermal energy

Figure 5.2.1 : Fire tube boiler

Figure 5.2.2 : Water tube boiler

Figure 5.3 : Super-heater

Figure 5.4.1.3 : Condenser

Figure 5.5.1 : Jet condenser

Figure 5.6.2 : Cooling water operation

Figure 5.7.1 : Natural draught cooling tower

Figure 5.7.2 : Induced draught cooling tower

Figure 5.7.3 : Dry cooling tower system

Figure 5.9 (a) : Ejector line diagram



Figure 5.9(b) : Ejector

Figure 5.10.1 : Low pressure feed-heaters

Figure 5.13(a) : Boiler feed pump

Figure 5.14(a) : Economizer line diagram

Figure 5.14 (b) : Economizer

Figure 5.16 : Boiler Re-heater



LIST OF TABLES

Table 1.5.1 : Power generation data

Table 4.3 : Heat rate values

Table 6.1.1 : Enthalpy and entropy values of components

Table 6.2.1 : Thermodynamic extractions at turbines

Table 6.3 : High pressure Turbine

Table 6.4 : Intermediate pressure turbine

Table 6.5 : Low pressure turbine

Table 7.3.1 : First law and second law efficiencies

Table 7.3.2 : Energy and exergy losses

LIST OF GRAPHS

Graph 8.1 : Exergy destruction

Graph 8.2 : Turbine exergy efficiency and destruction

Graph 8.3 : Exergy vs energy efficiency

Graph 8.4 : Comparison charts



ABSTRACT

EXERGY ANALYSIS OF THERMAL POWER PLANT (RTPP)

The energy supply to the demand narrowing down day by

day around the world, the growing demand of the power has made the power plants of scientific

interest, but most of the power plants are designed by the energetic performance criteria based on

the first law of thermodynamics only. The real useful energy loss cannot be identified by the first

law of thermodynamics, because it does not differentiate between the quality and quantity of

energy. The project on Exergy Analysis was undertaken on Rayalaseema Thermal Power

Project located in Kadapa, Andhra Pradesh. The capacity of the plant is 5×210 MW.

Energy analysis presents only quantities results while

Exergy analysis presents qualitative results about actual energy consumption. The main objective

is to analyze the system components separately and to identify and quantify sites having largest

energy and exergy efficiency losses . It also presents major losses of available energy at super-

heater, boiler and turbine section. Exergy destruction and energy loss comparison charts are

drawn for different components. The results are tabulated and graphs are plotted to show

correlation between various parameters. This project would also throw light on the scope for

further research and recommendations for improvement in the further existing plant.

CHAPTER-1

1.0 INTRODUCTION TO R.T.P.P



1.1 General

Rayalaseema thermal power project (R.T.P.P),is one of the major generation

unit, developed in A.P., to meet the growing demand for power, the project envisaged the

installation of 2×210MW coal based thermal generation units under stage I. The first 210MW

unit for commercial operation was started on 25 Nov1994 and the second unit on 30 Mar 1995.

The plant has another 2 × 210MW coal based thermal generation units under stage II. In the

stage 2, the third Unit was started on 24 Jan 2007 and the fourth unit is under construction.

1.2 Location

The R.T.P.P. project is located at a distance of 8km from Muddunur railway

station of south central railway on Chennai-Mumbai railway line. The site is selected at an

adequate distance from the residential areas and it has an area of 2600 Acres. The water

requirements for the project are met from Mylavaram reservoir across river Penna, which is 23

KM away from the power plant.

1.2.1 LAYOUT OF THERMAL POWER PLANT



Figure 1.0 Layout of Thermal power plant

1.3 Raw material



1.3.1 Coal:

The project gets its coal from singareni collieries by wagons. The coal used

in R.T.P.P. is bituminous coal. It is similar to lignite and contains 50% less moisture than lignite.

It also contains less ash than lignite and it is used either in the form of pulverized or briquettes

state. The coal from singareni is of inferior quality with ash average content varying between

45%-50%. The uncrushed coal is stocked in stockyard and crushed coal in separate yard.

1.3.2 Furnace oil and diesel oil:

Light diesel oil is used for firing and heavy furnace oil is used for flame

support and stabilization. Storage capacity: Heavy furnace oil: two tanks of 4150 kilo liter each.

Light diesel oil: two tanks of 800 kilo liter each.

1.3.3 Water:

The water requirement of the project is met from Mylavaram reservoir and

Brahma sagar dam across Penna River situated at a distance of 23 KM. A gravity pipeline is laid

to draw 25 cusecs of water from the reservoir.

1.4 Combustion Process

Pulverized coal after burning in furnace generates ash, out of which 20%

ash will be bottom ash and 80%will be fly ash. The combustion product of furnace is let into the

electro static precipitators to entrap dust and gases emission is let into the atmosphere through

220mt chimney.

1.5 Operational Data

The project has faced some troubles during construction, testing and

commissioning. After some modification and alterations, tremendous improvement in

availability and plant load factor was achieved during the last three years at R.T.P.P. The year

wise operations from 1995 onwards show the performance details of the plant and are given in

table below.

1.5.1 POWER GENERATION DATA:



Year Generation(MW) P.L.F (%) Achievements

1994-1995

1995-1996

1996-1997

1997-1998

1998-1999

1999-2000

2000-2001

2001-2002

2002-2003

2003-2004

2004-2005

2005-2006

2006-2007

2007-2008

2008-2009

2009-2010

2010-2011

2011-2012

2012-2013(feb)

1327.5041

2436.5355

2982.5728

3365.0559

3500.3542

3475.3821

3400.8030

3488.8235

3401.5830

3353.782

3095.562

3300.568

3293.670

3146.896

3357.265

3365.0559

3466.0559

3293.670

2436.5355

53.25

66.2

81.07

91.46

94.88

94.46

92.43

94.83

92.20

91.16

84.45

90.98

89.52

85.30

91.25

87.83

93.02

90.32

93.45

─

─

─

─

Gold medal

Gold medal

Gold medal

All India first

All India first

Gold medal

─

─

−

_

Silver medal

_

−

−

−



CHAPTER-2

2.0 WORKING CYCLES

The fundamental forms of energy with which thermal stations are

principally concerned are heat and work. Heat produces work and this work is further converted

into electrical energy through a medium .i.e. electrical generator. For the purpose of

understanding of thermal plants, the phenomenon of thermodynamics vapor power cycles is

explained here under:

1. Rankine cycle

2. Regenerative cycle

3. Reheat cycle



2.1 Rankine cycle:

Rankine cycle is theoretical cycle on which steam turbine (or engine)

works.

Fig.2.1(a) Rankine cycle

Fig.2.1(b) T-S Diagram Fig.2.1(c) P-V Diagram

It comprises of following process:

Process1-2: Reversible adiabatic or isentropic expansion in the turbine

Process2-3: Constant pressure condensation or heat rejection process

Process3-4: Isentropic pumping process in the feed pump.

Proces4-5: Constant pressure heat supplied in the boiler.



2.1.1 Effect of operating conditions on Rankine cycle efficiency

The Rankine cycle efficiency can be improved by increasing average

temperature at which heat is supplied, decreasing or reducing the temperature at which heat is

rejected. This can be achieved by making suitable changes in the condition of steam generation

or condensation, as discussed below:

2.1.2 Increasing boiler pressure

By increasing the boiler pressure the cycle tends to raise and reach

maximum value at a boiler pressure about 166bar.

2.1.3 Super heating

If the steam is superheated before allowing it to expand, the Rankine

cycle efficiency may be increased. The use of superheated steam also ensures longer turbine

blade life because of the absence of erosion from high velocity water particles that are suspended

in wet vapor.

2.1.4 Reducing condenser pressure

The thermal efficiency of the cycle can be improved by reducing the

condenser pressure, especially in high vacuum. But the increase in efficiency is obtained at the

increased cost of condensation apparatus. The thermal efficiency of the Rankine cycle is

improved by the following methods.

1 By regenerative feed heating.

2. By reheating of steam.

3. By water extraction.

4. By using binary vapor.

2.2 REGENERATIVE CYCLE

In the Rankine cycle it is observed that the condensate, which is fairly

at low temperature, has an irreversible mixing with hot boiler water and this result in decrease of



cycle efficiency. Methods are therefore adopted to heat the feed water from the hot well of

condenser irreversibly by interchanging of heat with in the system and thus improving the cycle

efficiency. This heating method is called regenerative feed heat and the cycle is called

regenerative cycle.

The principle of regeneration can be practically utilized by extracting

steam from turbine at several locations and supply it to the regenerative heater. The most

advantageous condensate heating temperature is selected depending on the throttle conditions

and this determines the number of heaters to be used. Figure shows the layout of condensing

steam power plant in which a surface condenser is used to condense all the steam that is not

extracted for feed water heating. The turbine is double extracting and boiler is equipped with a

super heater.

. Fig.2.2(a) Regenerative cycle



Fig:2.2(b) T-S DIAGRAM

M1=mass of high pressure steam extracted for HP heater per kg of steam flow

M2= mass of low pressure steam extracted for LP heater per kg of steam flow

1-M1-M2=mass of steam entering into the condenser per kg of steam flow.

2.2.1 Advantages of regenerative cycle

The heating process in the boiler tends to become reversible.

The thermal stresses set up in the boiler are minimized this is due to the fact that

temperature ranges in the boiler are reduced.

The thermal efficiency is improved because the average temperature of heat addition to

the cycle is increased.

2.3 REHEAT CYCLE

Fig:2.3(a) REHEAT CYCLE

The efficiency of the ordinary Rankine cycle can be improved by increasing

the pressure and temperature of the steam entering into the turbine. As the initial pressure

increases, the expansion ratio in the turbine also increase and the steam become quite wet at the

end of expansion. This is not desirable because the increased moisture content of steam causes

corrosion of turbine blades and increases losses. This reduces the efficiency.

In reheat cycle the steam is extracted from a suitable point in the turbine

and is reheated it with the support of flue gases in the boiler furnace. The main purpose of

reheating to increase the dryness fraction of steam passing through the lower stages of the



turbine. The increase in thermal efficiency due to reheat depends upon the ratio of reheat

pressure to the original pressure of steam. The main advantage of the reheat cycle is to reduce the

specific steam consumption and consequently reduces the size of the boiler and auxiliaries for

the same output.

Fig.2.3(b).T-S Diagram

Process 1-2: Expansion of steam in high –pressure turbine

2-3: Reheating of steam in a boiler

3-4: Expansion of steam in low –pressure turbine

4-5: Condensation process in the condenser

5-6: Pump wok

6-1: Heat supplied to the boiler

2.3.1 Advantages of reheating

There is an increased output of the turbine

Erosion and corrosion problems in the steam turbine are eliminated.

There is an improvement in the thermal efficiency of the turbines.

Final dryness fraction of the steam is improved.

There is an increase in the nozzle and blade efficiency.



2.3.2 LINE DIAGRAM OF 210 MW THERMAL POWER PLANT



Figure 2.3.2 Line Diagram of 210 MW Thermal power plant

2.4 Typical values of efficiency

Thermal efficiency = 30 to 40 %

Steam generator (boiler) efficiency = 75 to 90 %



Thermal cycle efficiency = 35 to 50 %

Internal efficiency of the turbine = 85 to 94 %

Mechanical efficiency of turbine = 99 to 99.5%

Generator efficiency = 68 to 98.5%

2.5 FACTORS FOR INCREASING THE THERMAL CYCLE EFFICIENCY

Thermal cycle efficiency is affected by following factors

Initial steam pressure

Initial temperature

Whether reheat is used or not ,and if used reheat pressure and temperature

Regenerative feed water- heating

2.5.1 INITIAL STEAM PRESSURE

At constant initial steam temperature, increase in initial steam

pressure ,means increase in saturation temperature of feed water or increase in mean temperature

at which heat is added to cycle .this will result in increase in thermal cycle efficiency. With

increase in the initial steam pressure at constant temperature and constant condenser pressure,

wetness of steam in the last stage of turbine increases, there by reducing internal efficiency of

these stages. Usually 1% moisture in the steam in particular stage results in 0.9 to 1.2%

reduction. Erosion becomes so severe that life of turbine is endangered .With increase in initial

steam pressure, blade height of initial stages gets reduced. If blade height of initial stage blades

are less than 25mm, this stage becomes very inefficient due to three dimensional flow and vortex

formation etc.some times this problem is overcome by partial admission in first or first few

stages.

2.5.2 INITIAL STEAM TEMPERATURE

As initial temperature increases, the thermal cycle efficiency

increases and hence from thermodynamics there is no upper limit for initial temperature.

Material considerations do restrict the initial steam temperature up to 400oC plain carbon steel

can be used and up to 480 oC low alloy steels can be used.

Above 480 oC and up to 600 oC heat resistant ferritic steels can be

used .It gives limiting value of initial steam temperature to be 565 oC .

During operation of power plants, it was found that plant outages due to boiler failure with initial



steam temperature 565 oC were enormous as compared with initial steam temperature 535 oC.

Now-a-days, practical limit for initial steam temperature is 535 oC to 540 oC. Above 540 oC

temperature, austenitic steels could be used, which have coefficient of thermal expansion and

lower thermal conductivity but poor machinability and weldability as compared to ferritic steels.

For these reasons use of austenitic steels is not preferred.

2.5.3 REHEAT

Reheating the steam after it as partially expanded, improves the

thermal cycle efficiency by 4% to5% as a more efficient cycle is added to original cycle. Reheat

reduces moisture in the last stage of turbine, the re by improving the internal efficiency of the

turbine. Reheating invariably complicates design of turbine, steam generators and their controls.

If the pressure drop in re-heater is more than 12-15%, almost all increase in efficiency is offset

by it.

2.5.4 CONDENSER PRESSURE

Condenser has a triple function in Rankine cycle, first is providing

heat sink, second is to provide very low vacuum and third is to preserve working fluid. Lower

condenser pressure implies lower mean temperature at which heat is rejected to sink, thereby

increasing the thermal efficiency cycle.

Condenser pressure is dependent on cooling water temperature and

to certain extent on cooling water flow rate. Since cooling water is usually taken from river, lake

or sea whichever is near by to thermal plant, we do not really have control on cooling water

temperature and hence on condenser pressure. In India, cooling water temperature usually ranges

between 24 oC to 36 oC giving condenser pressure of 0.06 to 0.12.ata

2.5.5 REGENERATIVE FEED WATER HEATING

In regenerative feed water heating part of steam is extracted after

partial expansion in the turbine and is used to heat up the feed water going to steam generator

(boiler). In this process the latent heat of liquidification of extracted steam is also utilized in

heating feed water, which otherwise would have been dumped in to the condenser, there by

increasing the cycle efficiency.

2.6 PLANT LOSSES

By fact the largest turbine house loss is the heat carried away in the

circulating water passing through the condenser .Figure shows a heat balance diagram for the



complete process of generation in the power generation in the power station .this simplified form

of heat balance in practice, when a test is carried out the losses are subdivided and circulated in

much greater detail than shown in the diagram. It does, however, show where the principle losses

occur and enable the question of efficiency to be studied more closely. The aim is to keep the

losses as small as possible by good operation.

Fig.2.6(a) Simple Steam Cycle Diagram

Fig.2.6(b) Heat Balance diagram

CHAPTER-3

3.0 INTRODUCTION TO EXERGY

3.1 Energy



The word energy derives from the Greek ἐνέργεια energeia, which possibly

appears for the first time in the work of Aristotle in the 4th century BCE.

Energy is defined as the ability to do work.

In the context of chemistry, energy is an attribute of a substance as a consequence of its atomic,

molecular or aggregate structure.

In biology, energy is an attribute of all biological systems from the biosphere to the smallest

living organism.

Internal energy is the sum of all microscopic forms of energy of a system.

Heat, a form of energy, is partly potential energy and partly kinetic energy. In the context of

physical sciences, several forms of energy have been defined. These include

Chemical energy

Electric energy

Radiant energy, the energy of electromagnetic

radiation

Nuclear energy

Magnetic energy

Elastic energy

Sound energy Fig: 3.1(a) THERMAL ENERGY

Thermal energy

Mechanical energy

Luminous energy

Mass (E=mc²)

These forms of energy may be divided into two main groups; kinetic

energy and potential energy. Other familiar types of energy are a varying mix of both

potential and kinetic energy, Energy may be transformed between different forms at

various efficiencies.

3.1.1Unit of Measure:

The energy is a scalar physical quantity. Joule is the (SI) unit of

measurement for energy. It is a derived unit of energy, work, or amount of heat. It is equal to the


http://en.wikipedia.org/wiki/File:Hot_metalwork.jpg


energy expended (or work done) in applying a force of one newton through a distance of one

meter. However energy is also expressed in many other units such as ergs, calories, British

Thermal Units, kilowatt-hours and kilocalories for instance. There is always a conversion factor

for these to the SI unit; for instance; one kWh is equivalent to 3.6 million joules.

3.2 Exergy:

The term availability was made popular in the united states by the M.I.T.

school of engineering the 1940’s. Today, an equivalent term, exergy, introduced in Europe in the

1950’s, has found global acceptance partly because it is shorter, it rhymes with energy and

entropy, and it can be adapted without requiring translation. In this text the preferred term is

exergy. Exergy is now recognized that it is an extremely fruitful theory. Exergy accounting is the

only way to accurately calculate the thermodynamic losses of a given process and to

unambiguously define a thermodynamic efficiency expressing its level of perfection. It also

allows for the evaluation of the thermodynamic quality of an energy system when considering

energy policies and economics, independent of the size, complexity and the nature of the

phenomena being looked at. That is why we devote particular care to exergy theory and to its

generalization.

. The quantity exergy is defined as:The amount of work which can be received from an energy carrier in a process that:

is reversible. takes place in an open system with stationary flow. exchanges heat only with the environment. is in balance with the environment at the end of the process.

The property exergy is the work potential of a system in a specified

environment and the maximum amount of useful work that can be obtained as the system is

brought to equilibrium with the environment. Unlike energy, the value of exergy depends on the

state of the environment as well as the state of the system. Therefore, exergy is a combination

property. The exergy of a system that is in equilibrium with its environment is zero. The state of

the environment is referred to as the “dead state” since the system is practically “dead” from a

thermodynamic point of view when it reaches that state. A system must go to the dead state at

the end of the process to maximize the work output can be explained as follows: if the system

temperature at final state is greater than (or less than) the temperature of the environment it is

in, we can always produce additional work by running a heat engine between these two levels.



If the final pressure is greater than the pressure of environment, we can

still obtain work by letting the system expand to the pressure of environment. If the final

velocity of the system is zero. We can catch that extra kinetic energy by a turbine and convert it

to rotating shaft work, and so on. No work can be produced from a system that is initially at the

dead state. The atmosphere around us contains a tremendous amount of energy. However, the

atmosphere is in the dead state, and the energy it contains has no work potential. Therefore, we

conclude that a system delivers the maximum possible work as it undergoes a reversible process

from the specified initial state to the state of its environment, that is, the dead state. This

represents the useful work potential of the system at the specified state and is called exergy. It is

important to realize that exergy does not represent the amount of work that a work-producing

device will actually deliver up on installation. Rather, it represents the upper limit on the amount

of work a device can deliver without violating any thermodynamic laws. There will always be a

difference, larger or small, between exergy and the actual work delivered by a device.

At a time weighted with increasing concerns about the present and future

energetic, environmental and geopolitical challenges, it is particularly vital to prioritize our

technological choices towards a more rational use of our non-renewable as well as our renewable

resources. This implies improvements of both our methodological and technological tools. From

the methodological viewpoint a more rational and sustainable use of the available resources is

only possible if engineers, architects, industrialists and decision makers can rely on coherent

indicators among which the exergy efficiency is bound to play a major role. It is rather

disappointing that in this beginning of the 21st century a major part of the practitioners are still

using only performance indicators based exclusively on the First Law of thermodynamics. For

example, simple boilers for house heating are labelled with efficiencies very close to 100%

(apparent perfection!), while it is technologically possible, with each same unit of fuel, to

provide about twice as much heat. Conversely, the exergy efficiency allows a coherent ranking

of the technical options, with values always below 100%, independent of the domain and the

energy service supplied. From a technological standpoint, the notion of exergy also allows a

better characterization of the sources of internal losses, and therefore leads to better target

designs and retrofitted projects.



Exergy analysis is a tool for identifying the types, locations and

magnitudes of thermal losses. Identification and quantification of these losses allows us to

evaluate and improve the design of thermodynamic systems. Although the amount of energy

remains constant, our ability to use the energy decreases with time. In other words, the energy in

the system at the initial state has a greater potential for use than at the final state. Due to the

irreversibility’s occurring during this process, the energy's potential for use or the system's

exergy is reduced. Exergy is defined as the maximum theoretical work obtainable as the system

interacts with its surroundings and comes to equilibrium. Once a system is in equilibrium with its

surroundings, it is not possible to use the energy within the system to produce work. At this

point, the exergy of the system has been completely destroyed. The state in which the system is

in equilibrium with its surroundings is known as the dead state.

Recall that the exergy of a system is maximum amount of work that can

be obtained from a system. In order to quantify the exergy of a system, we must specify both the

system and the surroundings. The exergy reference environment is used to standardize the

quantification of exergy. The exergy reference environment or simply the environment is

assumed to be a large, simple compressible system. The temperature of the environment is

assumed to be uniform at to, and the pressure is assumed to be uniform at Po. Also, it is assumed

that the intensive properties of the environment are not significantly changed by any process.

Therefore, the environment is modeled as a thermal reservoir at To.

The work produced by a system cannot all be used for the desired

purpose. For example, when the gas in the piston cylinder device is expanding, some of the work

is required to compress the environment. We define environment work as the work done on or by

the environment. Since the environment is a simple compressible system and the pressure of the

environment is constant.

In thermodynamics, the exergy of a system is the maximum useful

work possible during a process that brings the system into equilibrium with a heat reservoir.

When the surroundings are the reservoir, exergy is the potential of a system to cause a change as

it achieves equilibrium with its environment. Exergy is the energy that is available to be used.

After the system and surroundings reach equilibrium, the exergy is zero. Energy is never

destroyed during a process; it changes from one form to another (see First Law of

Thermodynamics). In contrast, exergy accounts for the irreversibility of a process due to increase



in entropy (see Second Law of Thermodynamics). Exergy is always destroyed when a process

involves a temperature change. This destruction is proportional to the entropy increase of the

system together with its surroundings. The destroyed exergy has been called anergy For an

isothermal process, exergy and energy are interchangeable terms, and there is no anergy.

Exergy analysis is performed in the field of industrial ecology to use

energy more efficiently. The term was coined by Zoran Rant in 1956, but the concept was

developed by J. Willard Gibbs in 1873. Ecologists and design engineers often choose a reference

state for the reservoir that may be different from the actual surroundings of the system. Exergy is

a combination property of a system and its environment because unlike energy it depends on the

state of both the system and environment. The exergy of a system in equilibrium with the

environment is zero. Exergy is neither a thermodynamic property of matter nor a thermodynamic

potential of a system.

Exergy and energy both have units of joules. The Internal Energy of a

system is always measured from a fixed reference state and is therefore always a state function.

Some authors define the exergy of the system to be changed when the environment changes, in

which case it is not a state function. Other writers prefer a slightly alternate definition of the

available energy or exergy of a system where the environment is firmly defined, as an

unchangeable absolute reference state, and in this alternate definition exergy becomes a property

of the state of the system alone. The term exergy is also used, by analogy with its physical

definition, in information theory related to reversible computing. Exergy is also synonymous

with: availability, available energy, exergic energy, essergy (considered archaic), utilizable

energy, available useful work, maximum (or minimum) work, maximum (or minimum) work

content, reversible work, and ideal work.

The exergy destruction of a cycle is the sum of the exergy destruction

of the processes that compose that cycle. The exergy destruction of a cycle can also be

determined without tracing the individual processed by considering the entire cycle as a single

process and using one of the exergy destruction equations. ---Information found in

thermodynamics by Yunus A. Cengel

3.3 Application of the second law of thermodynamics



Exergy uses system boundaries in a way that is unfamiliar to many.

We imagine the presence of a Carnot engine between the system and its reference environment

even though this engine does not exist in the real world. Its only purpose is to measure the results

of a "what-if" scenario to represent the most efficient work interaction possible between the

system and its surroundings.

If a real-world reference environment is chosen that behaves like an

unlimited reservoir that remains unaltered by the system, then Carnot's speculation about the

consequences of a system heading towards equilibrium with time is addressed by two equivalent

mathematical statements. Let B, the exergy or available work, decrease with time, and Stotal, the

entropy of the system and its reference environment enclosed together in a larger isolated

system, increase with time.

3.3.1 Engineering applications

Application of exergy to unit operations in chemical plants was

partially responsible for the huge growth of the chemical industry during the 20th century.

During this time it was usually called availability or available work. As a simple example of

exergy, air at atmospheric conditions of temperature, pressure, and composition contains energy

but no exergy when it is chosen as the thermodynamic reference state known as ambient.

Individual processes on Earth like combustion in a power plant often eventually result in

products that are incorporated into a large atmosphere, so defining this reference state for exergy

is useful even though the atmosphere itself is not at equilibrium and is full of long and short term

variations.

If standard ambient conditions are used for calculations during plant

operation when the actual weather is very cold or hot, then certain parts of a chemical plant

might seem to have an exergy efficiency of greater than 100% and appear on paper to be a

perpetual motion machine! Using actual conditions will give actual values, but standard ambient

conditions are useful for initial design calculations .One goal of energy and exergy methods in

engineering is to compute what comes into and out of several possible designs before a factory is

built. Energy input and output will always balance according to the First Law of

Thermodynamics or the energy conservation principle.

Exergy output will not balance the exergy input for real processes

since a part of the exergy input is always destroyed according to the Second Law of



Thermodynamics for real processes. After the input and output are completed, the engineer will

often want to select the most efficient process. An energy efficiency or first law efficiency will

determine the most efficient process based on wasting as little energy as possible relative to

energy inputs. An exergy efficiency or second-law efficiency will determine the most efficient

process based on wasting and destroying as little available work as possible from a given input

of available work. Design engineers have recognized that a higher exergy efficiency involves

building a more expensive plant, and a balance between capital investment and operating

efficiency must be determined in the context of economic competition.

3.3.2 Quality of energy types

The ratio of exergy to energy in a substance can be considered a

measure of energy quality. Forms of energy such as macroscopic kinetic energy, electrical

energy, and chemical Gibbs free energy are 100% recoverable as work, and therefore have an

exergy equal to their energy. However, forms of energy such as radiation and thermal energy can

not be converted completely to work, and have exergy content less than their energy content. The

exact proportion of exergy in a substance depends on the amount of entropy relative to the

surrounding environment as determined by the Second Law of Thermodynamics. Exergy is

useful when measuring the efficiency of an energy conversion process. The exergetic, or

2nd Law, efficiency is a ratio of the exergy output divided by the exergy input. This formulation

takes into account the quality of the energy, often offering a more accurate and useful analysis

than efficiency estimates only using the First Law of Thermodynamics.

Work can be extracted also from bodies colder than the

surroundings. When the flow of energy is coming into the body, work is performed by this

energy obtained from the large reservoir, the surrounding. A quantitative treatment of the notion

of energy quality rests on the definition of energy. According to the standard definition, Energy

is a measure of the ability to do work. Work can involve the movement of a mass by a force that

results from a transformation of energy. If there is an energy transformation, the second principle

of energy flow transformations says that this process must involve the dissipation of some energy

as heat. Measuring the amount of heat released is one way of quantifying the energy, or ability to

do work and apply a force over a distance.

However, it appears that the ability to do work is relative to the

energy transforming mechanism that applies a force. This is to say that some forms of energy



perform no work with respects to some mechanisms, but perform work with respects to others.

For example, water does not have a propensity to combust in an internal combustion engine,

whereas gasoline does. Relative to the internal combustion engine, water has little ability to do

work that provides a motive force.

If “energy” is defined as the ability to do work then a consequence

of this simple example is that water has no energy — according to this definition. Nevertheless,

water, raised to a height, does have the ability to do work like driving a turbine, and so does have

energy.

This example means to demonstrate that the ability to do work can be

considered relative to the mechanism that transforms energy, and through such a conversion

applies a force. From this observation we might wish to use the word “quality”, and the term

“energy quality” to characterize the energetic differences between substances and their

propensities to perform work given a specific mechanism. That is the abilities of different energy

forms to flow and be transformed in certain mechanisms. With this lexicon, we can say that

energy quality is mechanism-relative, and the energy efficiency of a mechanism is energy

quality-relative – an internal combustion engine running on water has nearly 0% efficiency since

it has the propensity to transform little or no water-energy into thermal-energy. In order to clarify

things here we might think of this as the “water-efficiency”. The mechanism of interest is also

our system of reference, such that the choice of energy quality specifies a certain system of

reference. Thus with respects to the internal combustion system of reference, it has a low “water-

efficiency”.

3.4 WORKDONE

Work done during a process depends on its initial state, final state, and

the process itself. That is, work = f(initial state, process, final state)If the initial state has been

specified, then work is only a function of process and the final state. Previously, it was shown

that reversible process between two selected states gives the maximum work output.

System exchanges work, heat, and mass with its surroundings during a process. If the system

reaches a state which is in equilibrium with its surroundings, then the system can not exchanges

work, heat, and mass with its surroundings. This state is called a dead state and its properties are

denoted by subscript 0, such as pressure P0 and temperature T0. At the dead state: A system is at

the same temperature and pressure of its surroundings. It has no kinetic or potential energy



relative to its surroundings. It does not react with the surroundings. There are no unbalanced

magnetic, electrical and surface tension effects between the system and its surroundings.

For example, gas expands in a cylinder to do work on its surroundings. If

the pressure in the cylinder reaches the pressure in its surroundings, no more work can be done

by the cylinder. That means the cylinder reaches its dead state, and the work done by this

cylinder reaches its maximum value. Therefore, a system will deliver the maximum possible

work if it undergoes a reversible process from the specified initial state to its dead state. This

work represents the useful work potential of the system at the specified initial state and is called

exergy of the specified initial state.

3.4.1 REVERSIBLE WORK

W rev (reversible work): the maximum amount of useful work that

can be produced (or the minimum work that needs to be supplied) as a system undergoes a

process between the specified initial and final states. This is the useful work output obtained,

when the process between the initial and final states is executed in a totally reversible

manner. When the final state is the dead state, the reversible work equals exergy.

3.4.2 IRREVERSIBLE WORK

Irreversible work or Irreversibility is defined as the difference

between the reversible work and the useful work. It is expressed as

I = Wrev,out - Wu, out or I = Wu, in - Wrev,in

Where W rev is the reversible work and Wu is the useful work. The definitions

of reversible work and the usefully work are given below. When gas expands in a cylinder to do

work, it needs to expend some work on pushing the atmospheric air out of the way. This part of

work cannot be recovered and utilized, and is called surrounding work, which is the work done

by or against the surroundings during a process.

Reversible work is defined as the maximum amount of useful work that

can be produced (or the minimum work consumed) as a system undergoes a process between the

specified initial and final states. A system can contain energy in numerous forms such as kinetic

energy, potential energy, internal energy, flow work and enthalpy.

Exergy is the useful work potential of energy, and the exergy of a system is

the sum of the exergies of different forms of energy it contains.

3.5 THE LAWS OF THERMODYNAMICS



Energy can neither be created nor destroyed, In all energy

transformations, energy quality will be consumed .These are Natural Laws, i.e. they are

fundamental and cannot be negotiated. On the other hand, if somebody find out something that

might falsify them, they will cease to be fundamental.

The First Law tells us that energy can be neither created nor destroyed.

(The production or consumption of energy is impossible. Anyone who speaks about 'energy

production’ or 'energy consumption' is probably ignorant about the First Law). This means that

the amount of energy in the universe is constant. So, the First Law tells us something about the

state of the universe and all processes in it.

The Second Law tells us that the quality of a particular amount of

energy i.e. the amount of work, or action, that it can do, diminishes for each time this energy is

used. This is true for all instances of energy use, physical, metabolic, interactive, and so on.

This means that the quality of energy in the universe as a whole, is constantly diminishing. All

real processes are irreversible, since the quality of the energy driving them is lowered for all

times.

Thus, the Second Law tells us about the direction of the universe and all

processes, namely towards a decreasing exergy content of the universe. Processes that follow this

general principle will be preferred. Some people seem to think that this law should be revoked...

But perhaps they are misled by their notion of entropy. The usable energy in a system is called

exergy, and can be measured as the total of the free energies in the system. Unlike energy,

exergy can be consumed.

To more easily understand the concept

of exergy, you can consider this picture as an analogy:

Likewise we can’t extract paste completely from a

tube we can’t utilize energy completely from a source

means there must be some losses during the process

or a work being done and most of the losses is due to entropy which we can’t avoid completely.

Furthermore, it is not defined in far-from-equilibrium systems, as living

systems and other organized systems. The first law of thermodynamics was stated in terms of

cycles first and it was shown that the cyclic integral of heat is equal to the cyclic integral of



work. When the first law was applied for thermodynamic process, the existence of a property,

the internal energy was found. Similarly, the second law was also first stated in terms of cycles

executed by systems. When applied to process, the second law also leads to the definition of a

new property, known as entropy. If first law is said to be the law of internal energy, then second

law may be stated to be the law of entropy. In fact, thermodynamics is the study of three E’s,

namely, energy, equilibrium and entropy.

3.6 LAW OF DEGRADATION OF ENERGY

The available energy of a system decreases as its temperature or

pressure decreases and approaches that of the surroundings. When heat is transferred from a

system, its temperature decreases and hence the quality of its energy deteriorates.

The degradations more for energy loss at a higher temperature than that at a lower temperature.

Quantity wise the energy loss may be the same, but quality wise the losses are different. While

the first law states that energy is always conserved quantity wise , the second law emphasizes

that energy always degrades quality wise. When a gas is throttled adiabatically from a high to a

low pressure , the enthalpy(or energy per unit mass) remain the same, but there is a degradation

of energy or available work.

The same holds good for pressure drop due to friction of a fluid

flowing through an insulated pipe. If the first law is the law of conservation of energy, the

second law is called the law of degradation of energy. Energy is always conserved, but its

quality is always degraded.

CHAPTER-4

4.0 DATA COLLECTION



The following data is collected for calculation of heat rate and

performance of steam turbine and heat balance of regenerative cycles.

4.1 Technical data of 210 MW Turbine

Main steam pressure = 150 kg/cm2

Main steam temperature = 535 oC

Reheat steam temperature = 535 oC

Full load steam flow = 641 TPH

Back pressure range = 0.03 ata to 0.12 ata

No. of extractions = 6

No. of stages High Pressure Turbine = 1X25

Intermediate Pressure Turbine = 2X20

Low Pressure Turbine = 2X8

Last stage blade height = 661.4 mm

Over all length = 16.175 meter

Width = 10.6 meter

Weight of the turbine = 480 tons

Frequency band = 47.5 to 51.5 HZ

Pressure & Temp variations AS per IEC recommendations

4.2 GENERAL DATA

4.2.1 CONSTRUCTION

Three-cylinder reheat condensing turbine

Single-flow HP turbine with 25 reaction stages Type H30-25-2

Double –flow IP turbine with 20 reaction stages per flow Type M30-20

Double –flow LP turbine with 8 reaction stages per flow Type N30-2×5

2 Main stop and control valve Type EV 160

2 Reheat stop and control valves Type IV320

2swing check valves in cold reheat line DN450

2Bypass stop and control valves DN200



Extraction swing check valves

Extraction 1: No valve

Extraction 2: swing check valve with auxiliary actuator, 1 swing check valve




Extraction 6: No valve

4.2.3 SPEED CYCLE/SEC

Rated speed 50cycles/s ~ 3000 RPM

4.2.4 STEAM PRESSURES: In bar

Initial steam 147

Before 1st HP drum stage 132.6

HP cylinder exhausts 39.23

IP cylinder stop valve inlet 34.13

Extraction 6(HPH-6) 39.23

Extraction 5(HPH-5) 16.75

Extraction 4(D/A) 7.06

Extraction 3(LPH-3) 2.37



LP cylinder exhausts 0.1187

4.2.5 STEAM TEMPERATURES: In oC

Initial steam 535

IP cylinder stop value inlet 535



HP cylinder exhausts 343

Extraction 6 343

Extraction 5 433

Extraction 4 316

Extraction 3 200

Extraction 2 107

Extraction 1 62

LP cylinder exhausts 49

4.3 HEAT RATE VALUES

S.

N DESI

UNIT UNIT-1 UNIT UNIT



O DESCRIPTION UNIT GN

VAL

UES

-1

FULL

LOA

D

PART

LOAD

-2

FULL

LOA

D

-2

PAR

T

LOA

D

1 Load MW 210 212.0 197.3 215.5 180

2 Feed water flow(Hr avg) TPH 636.7

4

703.1 656.7 718.8 628.6

3 RH spray TPH 0 9.6 0.0 18.1 1.8

4 Main steam flow TPH 636.7

4

670.6 642.4 672.2 562.1

5 Main steam pressure before

strain

Kg/

cm2

150 152.1 148 152.1 153.1

6 Main steam temp before

Esv1/Esv2

oC 535 537.6 536.2 536.5 537.4

7 HP turbine 1.stage balding

pressure

Kg/

cm2

134.2

3

133.2 125.9 132.6 114.9

8 CRH steam pressure at HPT

exhaust

Kg/

cm2

38.56 37.2 34.7 38.6 33.5

9 CRH steam temperature At HPT

exhaust

oC 342.4 342.8 339.3 345.2 333.5

1

0

HRH steam pressure at IPT inlet Kg/

cm2

35/36 36.1 33.7 37.5 32.6

1

1

HRH steam temperature at IPT

inlet

oC 535 540.7 535.4 536.4 536.6

1

2

LP turbine exhaust hood

temperature

oC 42.1 48.6 47.7 49.7 47.1

1

3

HPH 5 inlet feed water

temperature

oC 168 170.6 167.4 169.6 162.8



1

4

HPH 6 outlet feed water

temperature

oC 244.8 233.1 232.8 235.3 234.8

1

5

HPH 6 inlet feed water

temperature

oC 201.2 200.1 196.7 200.6 194.6

1

6

HPH 6 inlet feed water pressure Kg/

cm2

185.4

2

181.3 181.6 185.8 181.4

1

7

HPH 6 outlet feed water pressure Kg/

cm2

184.5

6

185.1 177.8 184.5 180.2

1

8

Economizer inlet feed water

temp(L/R)

oC 244.8 233.1 233.3 233.9 233.5

1

9

CW temp at condenser

I/L-O/L(L/R)

oC 27/36 29/39 29.2/38.

9

31.1/4

0

32/39.

4

2

0

Steam pressure at ejector nozzle Kg/

cm2

7.5 10.0 10.0 10.2 11

2

1

No 6 extraction steam pressure Kg/

cm2

36.91 37.1 34.6 34.7 33.6

2

2

No 6 extraction steam

temperature

oC 340.7 346.9 343.6 350.5 340.7

2

3

IP casing exhaust steam

temperature

oC 314.8 336.8 332.3 342.6 325.9

2

4

HPH 6 drip temperature oC 206 205.5 201.9 207.4 199.8

2

5

IP casing exhaust steam pressure Kg/

cm2

7.2 7.7 7.2 7.8 7.4

2

6

Steam temperature at ejector

nozzle

oC 200 199.8 198.7 266.7 217



CHAPTER-5

5.0 COMPONENTS ON WHICH ANALYSIS IS MADE



5.1 Boiler

A boiler is a closed vessel in which water or other fluid is heated. The

pressure vessel in a boiler is usually made of steel (or alloy steel), or historically of wrought iron.

Stainless steel is virtually prohibited (by the ASME Boiler Code) for use in wetted parts of

modern boilers, but is used often in super-heater sections that will not be exposed to liquid boiler

water. The source of heat for a boiler is combustion of any of several fuels, such as wood, coal,

oil, or natural gas. Electric steam boilers use resistance- or immersion-type heating elements.

Nuclear fission is also used as a heat source for generating steam, either directly (BWR) or, in

most cases, in specialized heat exchangers called "steam generators" (PWR). Heat recovery

steam generators (HRSGs) use the heat rejected from other processes such as gas turbines.

5.2 Types of Boilers inlet conditions

5.2.1 Fire Tube Boiler

In fire tube boiler, hot gases pass through

the tubes and boiler feed water in the shell side is converted into

steam. Fire tube boilers are generally used for relatively small

steam capacities and low to medium steam pressures. As a

guideline, fire tube boilers are competitive for steam rates up to

12,000 kg/hour and pressures up to 18 kg/cm2. Fire tube boilers

are available for operation with oil, gas or solid fuels. For

economic reasons, most fire tube boilers are nowadays of

“packaged” construction (i.e. manufacturers shop erected) for all fuels.

Outlet conditions

Fig:5.2.1 FIRE TUBE BOILER


157.8 bar,574k

146 bar,613k


5.2.2 Water Tube Boiler

In water tube boiler, boiler feed water flows through the tubes and

enters the boiler drum. The circulated water is heated by the combustion gases and converted

into steam at the vapor space in the drum. These boilers are selected when the steam demand as

well as steam pressure requirements are high as in the case of process cum power boiler / power

boilers.

5.3 Super heater

A super heater is a Fig:5.2.2WATER TUBE BOILER

device used to convert saturated steam or

wet steam into dry steam used in steam

engines or in processes, such as steam

reforming. A component of a boiler system that

heats the steam produced above its

saturation temperature to prevent it

condensing, and in case of a steam engine Fig: 5.3 SUPER HEATER

to improve its efficiency.

Superheated steam is steam at a temperature that is higher than its

vaporization (boiling) point at the absolute pressure where the temperature measurement is

taken; Saturated steam is, in contrast to superheated steam, steam that is in equilibrium with

heated water at the same pressure, i.e., it has not been heated past the boiling point for that

pressure. The main advantages of using a super heater are reduced fuel and water consumption

but there is a price to pay in increased maintenance costs. In most cases the benefits outweighed

the costs and super heaters were widely used. Without careful maintenance super-heaters are

prone to a particular type of hazardous failure in the tube bursting at the U-shaped turns in the

super-heater tube.

5.4 CONDENSER



When the steam has completed its work in the turbine and before it can

be returned to the boiler, it must be changed back into water. This is the duty the condenser must

perform as efficiency as possible and, for this reason, it is the largest and most important of the

heat exchangers in a power station. The heat in the exhaust steam cannot be converted into

mechanical energy and must be transferred from the steam to the cooling water. The way in

which the condenser carries describe in this lesson.

5.4.1 Principle of condenser:

5.4.1.1 Volume of steam:

If water is put into a closed and heated, a quantity of heat known as

sensible heat is required to bring the water to boiling point and if further heat is added to convert

the water into steam this is known as latent heat. The volume of the steam formed is far greater

than that of the water and consequently the pressure in the vessel rises. Thus the application of

the latent heat has caused an increase in pressure.

5.4.1.2 Removal of heat:

Now reverse the process and remove some heat by cooling the vessel.

During this cooling the latent heat is removed from the steam from which is reduced to water

with a consequently fall in pressure. This removal of latent heat happens on a very large scale in

a turbine condenser. Inlet conditions

5.4.1.3 Condenser pressure:

The condenser is an

airtight vessel where the steam exhaust from the

turbine is cooled and condenser. The

condensation is so complete that the pressure

inside the condenser is reduced below that of the

atmosphere and this condition is referred to as

vacuum in the condenser Fig: 5.4.1.3 Condenser


0.089 bar,320 k


To maintain this low pressure condition it is essential that any air or

other incondensable gases, passing into the condenser with the steam must be continuously

removed and, in addition to condensing the steam, the condenser must separate these gases from

the steam for discharge by an ejected or air pump.

5.4.2 Purpose of condenser:

5.4.2.1 Saving of steam:

By using a condenser there is a big reduction in the amount of a steam

required to generate each unit of electricity. In a turbine without a condenser the lowest pressure

to which the steam can be expanded is that of the atmosphere. It can be said that in this case the

back pressure against which the steam is exhausted is atmospheric pressure. Atmospheric

pressure is equivalent to the pressure which would support a column of mercury approximately

30 inches high. This is usually abbreviated to 30 inches Hg. being the chemical symbol for

mercury.

If the last stage of the turbine were under vacuum and the back pressure

reduced by a condenser to 2 inches Hg. Then the steam would be able to continue its expansion

from 30 inches Hg. Down to 2 inches Hg during this expansion each pound of steam is capable,

in a 9000lb/in2 turbine with a back pressure of 1.5 inches Hg the steam dose nearly 30% of its

work as it expand below atmospheric pressure. Thus the use of a condenser brings a considerable

saving.

5.4.2.2 Conservation of pure feed water:

Very large quantities of steam pass through a turbine, for example, a

500 MW machine on full load uses over 3,000,000 lbs/hr. it would, of course, be not only very

wasteful but impracticable to allow this vast amount of steam to be exhausted to a atmosphere.

By using a condenser the exhaust steam is changed back to water which is removed from the

condenser for continuous use in the power station heat cycle. This water is known as condensate

5.4.2.3 Deaeration of make-up water:

Due to leakage and necessary blowing down of boilers some of the

water used in the power station heat cycle is lost and must be replaced. This water, which is

known as make-up water, is generally supplied from reserve feed water tanks and, being in

contact with the air, contains dissolved oxygen. If this oxygen were not removed it would cause

corrosion in boilers and pipe work. The best way of releasing this oxygen is to bring the water to



boiling point and for this purpose the condenser can be employed. The make-up water is

introduced into the condenser where it is brought to boiling point and the dissolved oxygen

released ready for removal together with any air and other gases which may be in the condenser.

5.5 Types of condensers:

Steam can be condensate by using either the jet or the surface type of condenser.

1. Jet condenser

2. Surface condenser

5.5.1 Jet condenser:

The simplest method is to mix the steam with a spray of water in a closed

vessel. The water will remove the heat from the steam by

direct contact and the steam will condense. This method is

used in the jet condenser which is illustrated in figure.

In a power station the condensate is

returned to the boiler and must be absolute pure. If a jet

condenser were used the cooling water, which is mixed

with the condensate would have to be equally pure.

Because very large quantities of cooling water required,

this type of Condenser is not a practical proposition for

power plant. It was, however, the first type of condenser

ever to be fitted to a steam turbine. A new development for

jet type condenser is in conjunction with the dry cooling

Fig:5.5.1 Jet condenser

tower installation at rudely power station, where the

cooling tower becomes a tube heat exchanger instead

of the condenser.

5.5.2 Surface condenser:

Where water is available in

large quantities it is usually very impure, for example,

sea water and river water, but such impurities have

little effect upon its cooling properties.



This suggests a condenser with two entirely separate water system, steam

being condensed on the outside of surface which is kept cool by an abundant supply of water

flowing on the inside. Such an arrangement is known as a surface condenser and the cooling

surface consist of small diameter tubes as shown in figure. In this case the purity of the cooling

water does not matter because apart from any leakages which may occur it is never in contact

with the condensate.

5.6 COOLING TOWER

5.6.1 Cooling water:

When power station are built beside river which cannot supply

sufficient water to condense the turbine exhaust steam by using a once through system, cooling

tower are used in conjunction with a closed circuit system to cool the circulating water.

5.6.2 Principles of operation:

Cooling water is pumped from

the turbine condenser by the tower pump to the cooling

tower. Inside the tower the water passes through

sprinklers, and sprays out in fine drops. The water than

fall as droplets, passing over pickings where it is made

to present a greater surface area to the cooling air. The

water then falls into the cooling tower pond. Air is

drawn in near the bottom of the tower, either by natural

draught or by a fan. The air passes up the tower and

cools the water as it does so. Any water droplets which

have been carried up by the air are Fig: 5.6.2 Cooling water operation

removed by the water droplet eliminator screen.

5.6.3 The theory of cooling:

As a water droplet fall through the tower, air flows past it and cooling

takes place in three ways:

A small proportion of heat is lost from the droplet by radiation of heat from its

surface.



Approximately a quarter to one third of the heat transferred is by conduction and

convection between the water and the air; the amount of heat transferred depends

on the temperature of water and air.

The remainder of the great transfer is by evaporation. As the air evaporates some

of the water into vapor, the remaining water therefore has a lower heat content

than it had originally, and is also at a lower temperature.

The amount of evaporation which takes place depends on a number of

factors; these include the total surface area the water present to the air, and the amount of air

flowing. The greater the air flow, the greater the cooling achieved.

5.7 Types of cooling towers:

There are several types of cooling tower based on two air and water

system. They can be natural or forced draught cooled, and can be wet towers or dry tower. Figure

illustrates two of these types.

5.7.1 Natural drought cooling tower

The modern natural draught tower is

usually of the concrete hyperbolic pattern. The term

hyperbolic refers to the fact that the side of the tower has

the form of a hyperbola. In this type of tower, air moves

upwards, because of the chimney effect created by the

difference in density between the warm moist air inside the

tower and the colder, denser sir outside. Hyperbolic towers

are best suited to regions with high Fig: 5.7.1 Natural drought cooling tower

humidity, populated areas, and where land prices are high.

The height of the exhaust from these tower supports to

prevent the formation of fog along the ground.



5.7.2 Induced drought cooling tower

Induced draught towers, using fans either to force or to induce the

movement of air, first came into use in the 1930s. In a forced

draught tower, the fan is at the bottom and pushes the air up through

the tower. In an induced draught tower the fan is at top and pulls the

air up. One of the main problems with forced draught towers is

recirculation; vapor leaving the tower at low velocity tends to re

enter the tower, with the result that the wet bulb temperature of

entering air is increased and performance of the tower is impaired.

A combination of natural and mechanical Draught cooling can be

seen in the assisted draught tower. The fans, in this case, support to

increase the air flow. With this arrangement it is estimated that a Fig: 5.7.2Induced drought

single tower will provide the cooling for at least 660MW of plant cooling tower

and, although its base diameter will be about 140 m, its appearance from a distance will be little

different from a single natural draught tower with a capacity of 250MW. Compare this with a

500MW unit which requires two natural draught tower 115 m high by 90 m diameter.

5.7.3Dry cooling tower system

Dry cooling tower first made their

appearance in hungry during the 1950s, but it was not

until 1962that the CEGB brought one of these towers

into operation, on a 120MW unit. Figure shows a

schematic layout of a dry cooling tower system. In

principle, it is simply a water to air surface heat

exchanger, like a motor car radiator, the air being

induced to flow through the radiator by the tower

chimney effect. Fig:5.7.3Dry cooling tower system

In the closed circuit, cooled water after passing through the water

turbine from the heat exchanger in the cooling tower is sprayed through nozzle into the direct

contact condenser, where exhaust steam from the turbine is condensed by direct contact. The

cooling water and condensate mixture passes to the CW pump, which delivers most of it through

the discharge culvert to the heat exchangers. The remainder is taken by the extraction pumps and



delivered through the feed heating system to the boiler. As you will appreciate, all the water used

is of condensate quality.

5.8 Condensate Extraction Pump

The condensate water is drawn from the condenser by the extraction pump

and sent to the low pressure feed heaters. This is how we begin to get the water back to the boiler

so that the whole process can start again. The pump which removes the water from the hot-well,

called condensate at this point, is the pump you are referring to. It is a high volume, low pressure

pump and it may have one or more stages. It only raises the pressure enough to get the water out

of the condenser and into the system which pipes it to the feed pump.

5.9 Ejectors

Operation of Ejectors is based upon Bernoulli’s Principle which states: -

‘When the speed of a fluid increases its pressure decreases and vice versa’. The principle is

demonstrated by air moving over the top of a piece of paper is moving quicker than the air

underneath. Thus, the local pressure on the top surface of the paper is less than on the underside.

The resulting pressure imbalance causes the paper to rise. An ejector or steam ejector, is a type

of pump that uses the Venturi effect of a converging-diverging nozzle to convert the pressure

energy of a motive fluid to velocity energy which creates a low pressure zone that draws in and

entrains a suction fluid. After passing through the throat of the injector, the mixed fluid expands

and the velocity is reduced which results in recompressing the mixed fluids by converting

velocity energy back into pressure energy. The motive fluid may be a liquid, steam or any other

gas. The entrained suction fluid may be a gas, a liquid, slurry, or a dust-laden gas stream. The

adjacent diagram depicts a typical modern ejector. It consists of a motive fluid inlet nozzle and a

converging-diverging outlet nozzle. Water, air, steam, or any other fluid at high pressure

provides the motive force at the inlet.

The Venturi effect, a particular case of Bernoulli's principle, applies to the

operation of this device. Fluid under high pressure is converted into a high-velocity jet at the

throat of the convergent-divergent nozzle which creates a low pressure at that point. The low

pressure draws the suction fluid into the convergent-divergent nozzle where it mixes with the

motive fluid.

The seals around the rotating shaft on steam turbines are many in several

ways but all leak a small amount of steam to the atmosphere. To capture this steam, many of the


Inlet Pressure 18.63bar Temperature 320K

Outlet Pressure 17.65 bar Temperature 325K


seals have small condensers to capture this steam. mall

heat exchanger used to condense the steam that leaks past

the first section of seals on

the shaft of a steam turbine. Specifically, if the turbine

exhausts into a vacuum system, it is necessary to inject

sealing steam into the seals in order to keep the low

pressure end of the turbine from drawing in atmospheric

air. Fig: 5.9(a) Ejector Line diagram

This sealing steam

from the low pressure end and the normal leakage

from the high pressure end would tend to leak out and

blow toward the bearing housing. In order to reduce

the chance of this leakage causing an accumulation of

water in the lube oil system, we use a gland steam

condenser to draw a very slight vacuum (typically 2 or

3 in-Hg) at the outer section of the shaft seals. The

gland condenser uses cooling water to condense this Fig: 5.9(b) Ejectors

steam to water which is usually lost to sewer.

5.10 Feed water heater

Feed water heaters are used within a power plants thermal cycle to

improve overall efficiency. The number and placement of feed water heaters are determined

during the original plant design and are highly integrated with the overall performance of the

steam turbine. Feed water heaters preheat the boiler feed water prior to it entering the boiler for

steam generation. The heat used to increase the feed water temperature comes directly from the

thermal cycle, as steam extracted from various turbine sections. The feed water heaters in a

power plant are either LP or HP shell and tube heat exchangers. From an efficiency standpoint,

the primary means of improving the operation of such heat exchangers is to maintain their

operational effectiveness. Feed water heating surface could be added to improve efficiency.

However, the costs associated with either increasing the heat transfer surfaces of existing heaters,



or adding additional heaters for efficiency purposes only, is prohibitive due to the small

incremental reductions in heat rate that would be obtained.

5.10.1 Low Pressure Feed Heaters

Feed-water from the condensate extraction pumps passes through five

low pressure feed heaters. Steam is used to heat the feed-water. After the fifth feed-heater, the

feed-water is at around 160°C. A feed-water heater is a power plant component used to pre-heat

water delivered to a steam generating boiler In a steam power plant, feed-water heaters allow

the feed-water to be brought up to the saturation temperature very gradually.

These feed heaters are increasing the water temperature before this

water returns to the boiler. Low Pressure Heater: A heater located between the condensate pump

and either the boiler feed pump . It normally extracts steam from the low pressure turbine. High

Pressure Heater: A heater located downstream of the boiler feed pump. Typically, the tube side

design pressure is at least 100 kg/cm2, and the steam source is the high pressure turbine.

The heating process by means of extraction steam is referred to as

being regenerative. The feed- heaters are an integral portion of the

power plant thermodynamic cycle. Normally, there are multiple

stages of feed-water heating. Each stage corresponds to a turbine

extraction point. These extraction points occur at various stages of

the expansion of steam through the turbines. The presence of the

heaters in the cycle enhances the thermal efficiency of the power

plant; the greater the number of extraction stages, the lower the

amount of thermal energy required to generate a given amount of

electrical energy. Fig: 5.10.1 Low Pressure Feed Heaters

5.11 De-aerator

From the low pressure feed heaters the water passes through the de-

aerator before going to the high pressure feed heaters. A de-aerator is a device that is widely used

for the removal of oxygen and other dissolved gases from the feed water to steam-generating

boilers. In particular, dissolved oxygen in boiler feed waters will cause serious corrosion damage

in steam systems by attaching to the walls of metal piping and other metallic equipment and

forming oxides (rust). Dissolved carbon dioxide combines with water to form carbonic acid that



causes further corrosion. Most de-aerators are designed to remove oxygen down to levels of 7

ppb by weight (0.005 cm³/L) or less as well as essentially eliminating carbon. In the de-aerator,

the gases are removed from the water to limit corrosion or rusting of the steel tubing that carries

the water back to the boiler and lines the boiler.

5.12 Booster pump

A Booster pump is a machine which will increase the pressure of a

gas. It is similar to a gas compressor, but generally a simpler mechanism which often has only a

single stage of compression, and is used to increase pressure of an already pressurized gas.

Booster pumps are designed to smooth out water pressure in areas where the flows are highly

variable. Booster pumps are usually piston or plunger type compressors. A single-acting, single-

stage booster is the simplest configuration, and comprises a cylinder, designed to withstand the

operating pressures, with a piston which is driven back and forth inside the cylinder. The

cylinder head is fitted with supply and is charge ports, to which the supply and discharge hoses

or pipes are connected, with a non-return valve on each, constraining flow in one direction from

supply to discharge. When the booster is inactive, and the piston is stationary, gas will flow from

the inlet hose, through the inlet valve into the space between the cylinder head and the piston. If

the pressure in the outlet hose is lower, it will then flow out and to whatever the outlet hose is

connected to. This flow will stop when the pressure is equalized, taking valve opening pressures

into account.

5.13 Boiler Feed Pump

A boiler feed-water pump is a specific

type of pump used to pump feed water into a steam boiler. The

water may be freshly supplied or returning condensate produced

as a result of the condensation of the steam produced by the

boiler. These pumps are normally high pressure units that take

suction from a condensate return system and can be of the Fig: 5.13(a) Boiler Feed Pump

centrifugal pump type or positive displacement type.

The boiler feed pump pumps water into the boiler, overcoming the boiler

pressure of 160 bar to achieve it. The pump is driven by a steam turbine and runs at 7,500

revolutions per minute. The boiler feed pumps consume a


http://en.wikipedia.org/wiki/Reciprocating_compressor

http://en.wikipedia.org/wiki/Gas_compressor

http://en.wikipedia.org/wiki/Gas

http://en.wikipedia.org/wiki/Pressure


large fraction of the auxiliary power used internally within a power plant. Boiler feed pumps

pressurize and force feed water through the HP feed water heaters and boiler. Boiler feed pumps

can require power in excess of 10 Mon a 500-MW power plant, therefore the maintenance on

these pumps Fig: 5.13(b) Boiler Feed Pump

should be rigorous to ensure both reliability and high-efficiency operation.

Boiler feed pumps wear over time and subsequently operate below the original design

efficiency. The most pragmatic remedy is to rebuild a boiler feed pump in an overhaul or

upgrade. The overhaul of the pumps is justifiable in the industry and can yield heat rate

reductions estimated to be in the of range 25-50 Btu/kWh.

5.14 Economizer

Fig: 5.14(a) Economizer line diagram Fig: 5.14(b) Economizer

Flue gases leaving the super-heater and re-heater still contain useful

energy. Water from the high pressure feed heaters is heated in the economizer from 252°C to

292°C before it continues to the steam drum. Having given up its last heat in the boiler, the flue

gases move on to the air heater. The economizer makes use of the heat energy that is still in the

flue gas to increase the temperature of the feed water further before it goes to the steam drum. In

boilers, economizers are heat exchange devices that heat fluids, usually water, up to but not


Inlet conditions163.7 bar, 518k

Outlet conditions157.89 bar,574k


normally beyond the boiling point of that fluid. Economizers are so named because they make

use of the enthalpy in fluid streams that are hot, but not hot enough to be used in a boiler, thereby

recovering more useful enthalpy and improving the boiler's efficiency. They are a device fitted to

a boiler which saves energy by using the exhaust gases from the boiler to preheat the cold water

used to fill it.

An economizer is employed to utilize the waste heat generated from the

combustion process to improve overall efficiency in the boiler. Flue gas exiting the combustion

chamber is still very hot and can be used as a pre- heater for the feed water. The economizer used

for these boilers is a horizontal counter current shell and tube heat exchanger. Feed water enters

finned tubes while hot flue gases pass over the outside. This allows for the recovery of energy

which would otherwise be wasted.

5.15 ELECTROSTATIC PRECIPITATORS

5.15.1 Introduction to ESP

A device which separates particles from a gas stream by passing the carrier

gas between pairs of electrodes across which a unidirectional, high-voltage potential is placed.

The particles are charged before passing through the field and migrate to an oppositely charged

electrode. These devices are very efficient collectors of small particles, and their use in removing

particles from power plant plumes and in other industrial applications are widespread. An

electrostatic precipitator (ESP) is a particle control device that uses electrical forces to move the

particles out of the flowing gas stream and onto collector plates. The particles are given an

electrical charge by forcing them to pass through a corona, a region in which gaseous ions flow.

The electrical field that forces the charged particles to the walls comes from

electrodes maintained at high voltage in the center of the flow lane. Once the particles are

collected on the plates, they must be removed from the plates without re entraining them into the

gas stream. This is usually accomplished by knocking them loose from the plates, allowing the

collected layer of particles to slide down into a hopper from which they are evacuated. Some

precipitators remove the particles by intermittent or continuous washing with water.



5.16 Boiler Re-heater

Power plant furnaces may have a re-

heater section containing tubes heated by hot flue gases

outside the tubes. Exhaust steam from the high pressure

turbine is passed through these heated tubes to collect

more energy before driving the intermediate and then low

pressure turbines. After expanding through the high

pressure turbine the exhaust steam is returned to the boiler

at 360°C and 42 bar pressure for reheating before being

used in the intermediate pressure turbine. The re-heater

reheats the steam from a temperature of 360°C back to 568°C. Fig: 5.16 Boiler Re-heater

5.17 STEAM TURBINES

5.17.1 INTRODUCTION

Steam turbine is a rotating machine which converts heat energy of steam to mechanical

energy. In India, steam turbines of different capacities varying from 15MW to 500MW are

employed in the field of thermal power generation. The design, material, auxiliary systems etc

vary widely from each other depending on the capacity of the sets

.

5.17.2 Development of steam turbines

Historically, first steam turbine was produced by Hero, a Greek philosopher, in 120 B.C.

In 1629, an Italian named Bean actually anticipated the boiler-steam turbine combination that is

a major source of power today. Charles Parsons introduced first practical steam turbine in 1884,

which was also of the reaction type. Just after the five years, in 1889, Gustav de Laval produced

the first practical impulse turbine.

5.17.3 Working principle of steam turbine

When the steam is allowed to expand through a narrow orifice, it assumes kinetic energy

at the expense of enthalpy (heat energy). This kinetic energy of steam is charged to mechanical

(rotational) energy through the impact (impulse) a reaction of steam against the blades. It should

be realized that the blade of the turbine obtains no moving force from the static pressure of the


http://www.draxgroup.plc.uk/explore_drax/power_station/?id=1897





steam or from any impact of the steam jet. The blades are designed in such a way, that the steam

will guide on and off the blade without any tendency to strike it.

As the steam moves over the blade, its direction is continuously changing and centrifugal

pressure exerted as the result is normal to the blade surface at all points. The total motive force

acting on the blades is thus the resultant of all the centrifugal forces plus change of momentum.

This causes the rotational motion of blades.


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2007 PROJECT DOCUMENT ON EXERGY