A Project report On EXERGY ANALYSIS OF STEAM POWER PLANT FOR DIFFERENT GRADES OF COAL Submitted in partial fulfillment of the requirement of National Institute Of Technology , Raipur For The Bachelor of Technology In MECHANICAL ENGINEERING Approved by Guided by Mr. S.Sanyal Mr. S. D. Patle Prof. & HOD, Associate Professor Mech. Engg. Department Mech.Engg.Department Submitted by
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A
Project report
On
EXERGY ANALYSIS OF STEAM POWER PLANT
FOR DIFFERENT GRADES OF COAL
Submitted in partial fulfillment of the requirement
of
National Institute Of Technology , Raipur
For
The Bachelor of Technology
In
MECHANICAL ENGINEERING
Approved by Guided by Mr. S.Sanyal Mr. S. D. Patle
Prof. & HOD, Associate Professor
Mech. Engg. Department Mech.Engg.Department
Submitted by
2
DEPARTMENT OF MECHANICAL ENGINEERING
NATIONAL INSTITUTE OF TECHNOLOGY,RAIPUR
CERTIFICATE
This is to certify that the project work titled �EXERGY ANALYSIS OF STEAM POWER PLANT FOR DIFFERENT GRADES OF COAL � submitted by Sumit Singh (08119079) , Manish Jain(08119039), Manish churendra (08119038) Aditya Gandharla (08119005), Lucky Jethani (08119037), Vikram Singh(08119067) Kamlesh Sahu(08119032), Poshak Chaudhary(08119049) students of B.Tech final Year of mechanical engineering during the academic year 2011-12 in partial fulfillment of the requirements for the award of the degree of bachelor of technology in mechanical engineering by National Institute of Technology, Raipur is a presentation of work done by them. This certification does not necessarily endorse or accept any statement made, opinion expressed or conclusion drawn as recorded in the report. However, it only signifies the acceptance of the report for the purpose for which it is submitted.
Approved by: Guided by:
Dr. S.Sanyal Dr.S.D Patle
Professor & Head Associate Professor,
Deptt. of Mechanical engg. Deptt. of Mechanical engg.
3
DECLARATION BY CANDIDATES
I the undersigned solemnly declare that the thesis entitled“EXERGY ANALYSIS OF STEAM
POWER PLANT FOR DIFFERENT GRADES OF COAL”is my own research work carried ou t
under the supervision of Dr.S.D.Patle,department of mechanical engineering , National institute of
technology Raipur (C.G) ,India.
I further declare that to the best of my knowledge and belief the thesis does not contain any part of
any work which has been submitted for the award of any other degree or certificate either this
institute or any other university/deemed university of India or any other country.
The Guide -Candidates
Dr. S.D.Patle
Associate professor
Department of mechanical engineering
National institute of technology Raipur (C.G)
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ACKNOWLEDGEMENT
Completing a task is never a single person’s effort.It is always the result of valuable contribution of
a group of individuals that helps in shaping & achieving the objective. We express our heartfull
thanks to those who have contributed greatly in accomplishing this task.
We express our deep sense of gratitude to Dr.S.D. Patle, Associate Professor
Mechanical engg. Deptt. Who has the attitude & substance of genius for his whole hearted
cooperation , valuable guidance, encouragement & suggestions throughout this project work which
were of immense help in successfully completion of this work. We also take this opportunity to
convey our deep gratitude to Dr.S.Sanyal,Professor & Head of Mechanical Engg. Deptt., for his
words of inspiration & encouragement and kind approval of the work.
5
ABSTRACT
This work is based on the application of second law of thermodynamics for energy efficient design
and operation of the conventional coal fired power generating station.the steam power plant has been
used for the analysis at present working condition.
The energy assessment must be made through the energy quantity as well as the quality
.but the usual energy analysis evaluates the energy generally on its quantity only. However ,the
exergy analysis assesses the energy on quantity as well as the quality . the primary objectives of this
project are to analyze the system components separately to identify and quantify the sites having
largest energy and exergy losses .in addition ,the effect of varying the reference environment state
on this analysis will also be presented the aim of the exergy analysis is to identify the magnitudes
and the locations of real energy losses to improve the existing systems processes or components
.This project deals with an energy and exergy analysis performed on an operating 250MW unit of
NTPC-SAIL power company limited ,Bhilai 3,(CG) India.
The exergy losses occurred in the various subsystems of the plant and their components have been
calculated using the mass ,energy and exergy balance equations.
The distribution of the exergy losses in several plant components during the real time plant running
conditions has been assessed to locate the process irreversibility.
The first law efficiency and the second law efficiency of the plant have also been calculated .the
comparison between the energy losses and exergy losses of the individual components of the plants
shows that maximum energy losses in present working condition occurred in the boiler. The real
losses of energy which has scope for the improvement are given as maximum exergy losses that
occurred in the combustor in boiler subsystem .
The results of the exergy analysis indicate that the boiler produces the highest exergy destruction.
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TABLE OF CONTENTS
Certificate 2
Declaration by the candidates 3
Abstract 4
Acknowledgement 5
Table of contents 6
List of figures 10
List of tables 12
Nomenclature 13
Subscript 14
Chapter 1 Introduction
1.1 Energy 15
1.1.1 The steady flow process 15
1.1.2 Energy efficieny of steady flow devices 16
1.2 Exergy 17
1.2.1 Definition of exergy 18
1.2.2 Exergy destruction 18
1.2.3 Mode of exergy transfer 19
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1.2.3.1 Exergy transfer by work 19
1.2.3.2 Exergy transfer by heat 20
1.2.4 Exergy transfer by mass 20
1.2.4.1 Physical Exergy 20
1.2.4.2. Exergy of kinetic energy 21
1.2.4.3. Exergy of potential energy 21
1.3 Exergy balance of a steady flow system 22
1.3.1 Exergy efficiency of steady flow device 23
1.4 Dead state 24
1.5 Exergy associated with fuel (coal) and flue gases 24
1.6 Power scenario in india 25
1.7 Objective of the study 26
Chapter2 Combustion calculation
2.1 Introduction 27
2.2 Calculation of chemical exergy of fuel 30
Chapter 3 problem formulation and plant description
3.1 Problem formulation 33
3.2 Data of different grades of coal 34
3.3 Power plant description and specification 35
3.3.1 Air fan 35
8
3.3.2 Air preheater 36
3.3.3 Boiler 37
3.3.4 Turbine 38
3.3.5 Deaerator 39
3.3.6 Condenser 41
Chapter4 Exergy analysis of components in the power plants
4.1 Boiler 44
4.2 Steam turbine 45
4.3 Air fan 46
4.4 Air preheater 47
4.5 Condenser 48
4.6 Feed water heater1 49
4.7 Deaerator 50
4.8 Condenser pump P1 51
4.9 Circulation pump 52
Chapter 5 Result and discussion
5.1 Analysis with a full load operation condition 53
5.2 Analysis of steam generator(boiler) 56
5.2.1 Effect of surrounding temperature on exergetic efficiency of the boiler 58
5.3 Analysis of turbine 59
5.3.1 Turbine efficiency variation with temperature 60
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5.4 Study of performance of boiler and air preheater with the usage of different grades of
coal in the power plant 60
Chapter6 C++ Programme coding for some iterative calculation
6.1 C++ programme coding for combustion calculation 71
6.2 C++ programme for calculation of chemical exergy of fuel 73
10
LIST OF FIGURES
Fig1.1 An Open system
Fig1.2 Total installed power generation capacity of india
Fig2.1 Combustion calculation of the fuel
Fig2.2 Calculation of chemical exergy of fuel
Fig3.1 Schematic diagram of the power plant
Fig3.2 The ideal rankine cycle(T s digram)
Fig3.3 Air fan
Fig 3.4 Air preheater
Fig 3.5 Boiler
Fig 3.6 Turbine
Fig 3.7 Deaerator
Fig4.1 Boiler
Fig 4.2 Turbine
Fig 4.3 Air fan
Fig 4.4 Air preheater
Fig 4.5 Condenser
Fig 4.6 Feed water heater
Fig4.7 Deaerator
Fig 4.8 Condenser pump P1
Fig4.9 Circulation pump
Fig 5.1 Graphical representation of exergetic efficiency of different units of the power plant
11
Fig5.2 Pie chart for exergy destruction in various components of the power plant.
Fig 5.3 Thermal and exergetic efficiency comparis
Fig5.4 Graphical representation of the variation of boiler exergetic efficiency with a variation in
reference temperature
Fig5.5 Graphical comparison of the thermal and exergetic efficiency of the turbine
Fig 5.6 Graphical representation of the variation of exergetic efficiency with variation in reference
temperature.
Fig5.7 Graphical representation of boiler efficiency v/s calorific value of coal
Fig 5.6 Graphical representation of air preheater exergetic efficiency v/s calorific value of coal
12
LIST OF TABLES
Table 3.1: Operating conditions of the power plant.
Table 3.2 Grades of coal
Table 3.3 Composition of designed coal
Table 5.1 Exergy efficiency and exergy destruction calculation
Table 5.2 Boiler efficiency variation with temperature
Table 5.3 Exergy destruction and exergetic efficiency at different reference temperatures in the
turbine
Table5.4 Exergy destruction and exergetic efficiency of the boiler for different grades of coal.
Table5.5 Exergy destruction and exergetic efficiency of air preheater for different coal grades
Table 5.6 Exergy analysis for temperature (To)=298k.
Table 5.7 Exergy analysis for temperature (To)=283k.
Table 5.8 Exergy analysis for temperature (To)=288k.
Table 5.9 Exergy analysis for temperature (To)=293k.
Table 5.10 Exergy analysis for temperature (To)=303k.
Table 5.11 Composition of grades of coal used for analysis in the project
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NOMENCLATURE
C Carbon [%]
Cp Specific heat [kJ/kg K]
e Specific exergy [kJ/kg]
E Time rate of exergy [MW]
FWH Feed Water Heater
�I Energy efficiency [%]
�II Exergy efficiency [%]
h Specific enthalpy [kJ/kg]
LHV Lower heating value [kJ/kg]
� Time rate of mass [kg/s]
n Excess air
N Nitrogen [%]
O Oxygen [%]
P Pressure [kPa]
Q Time rate of heat loss [MW]
S Sulphur [%]
s Specific entropy [kJ/kg]
T Temperature [ºC]
W. Time rate of work [MW]
W Water [%]
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SUBSCRIPT
a Air
B Boiler
CH Chemical
CV Control volume
D Destruction
DG Dry gas
ECO Economizer
EVA Evaporator
G Combustion gas
i Inlet
KN Kinetic
o Outlet
P Product
PH Physical
PT Potential
R.H Re-heater
S.H Super-heater
ST Steam turbine
th Theoretic
WG Wet gas
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CHAPTER 1
INTRODUCTION
1.1 ENERGY
The concept of energy was first introduced in mechanics by newton when he hypothesized about
kinetic and potential energies .however the emergence of energy as unifying concepts in physics was
not adopted until the middle of 19th
Century and was considered one of the major scientific achievements in that century .The concept of
energy is so familiar to us today that it is intuitively obvious ,yet we have difficulty in defining it
exactly . Energy is a scalar quantity that can not be observed directly but can be recorded and
evaluat4ed by indirect measurements .The absolute value of energy of system is difficult to measure
, whereas its energy change is rather easy to calculate .In our life the example for energy are endless.
The sun is the major source of the earth’s energy .It emits a spectrum of energy that travels across
space as electromagnetic radiation. Energy is also associated with the structure of matter and can be
released by chemical and atomic reactions .Through out history ,the emergence of civilization has
been characterized by the discovery and effective application of energy to society’s needs.
One of the most fundamental law of nature is the conservation of energy principle . It simply state
that during an interaction ,energy can change from one form to another but the total amount of
energy remains constant.
That is , energy can not be created or destroyed.
1.1.1The steady -flow process
The terms steady and uniform are used frequently in engineering , and thus it is important to have a
clear understanding of their meanings. The terms steady implies no change with time .The term
uniform ,however implies no change with location over a specified region .A large number of
engineering devices operate for long periods of time under the same conditions , and they are
classified as steady flow devices. Process involving such devices can be represented reasonably well
by a somewhat idealized process ,called a steady flow process.
16
Assumptions:
The following assumptions are made in the system analysis:
The mass flow through the system remain constant.
Fluid is uniform in composition.
The only interaction between the system and surrounding are work and heat.
The state of fluid at any point remain constant with time.
The steady flow equation
(u1+p1v1+V12 /2 +gZ1)+δQ/δm = (u2+p2v2+V2
2 /2 +gZ2)+ δw/δm 1.1
The steady flow energy equation
m[u1+p1v1+V12 /2 +gZ1]+Q =m [u2+p2v2+V2
2 /2 +gZ2]+ W 1.2
where; m;mass (kg/sec)
u1 and u2; Internal energy at inlet and outlet(kj/kg)
V1 and V2; velocities of fluid at inlet and outlet (m/sec)
Z1 and Z2 ; elevation at inlet and outlet(metre)
Q; heat transfer rate at inlet and outlet(kwatt)
W;work transfer rate at inlet and outlet(kwatt)
1.1.2Energy efficiency of steady flow devices
Efficiency is one of the most frequently used terms in thermodynamics , and it indicates ,how well
an energy conversion or transfer process is accomplished . Efficiency is also one of the most
frequently misused term in thermodynamics and a source of misunderstanding . The performance or
efficiency, in general, can be expressed in terms of desired output and the required input.
Efficiency = Desired output/Required input 1.3
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1.2EXERGY
Exergy analysis has sparked interest in the scientific community to take a closer look at the energy
conversation devices and to develop new techniques to better utilize the existing limited resources.
First law of thermodynamics deal with the quantity of energy and asserts that energy cannot be
created or destroyed .This law merely serves as a necessary tool for the bookkeeping of energy
during a process and offers no challenges to the engineer. The second law, however, deals with the
quality of energy. More specifically, it is concerned with the degradation of energy during a process
, the entropy generation , and the lost opportunities to do work. The second law of thermodynamics
has proved to be a very powerful tool in the optimization of complex thermodynamic systems . we
examine the performance of engineering devices in light of the second law of thermodynamics. we
start our discussion with the introduction of exergy (also called availability)which is the maximum
useful work that could be obtained from the system at a given state in a specified environment ,and
we continue with the reversible work, which is the maximum useful work that can be obtained as a
system undergoes a process between two specified state . Next we discuss the irreversibility (also
called the exergy destruction or lost work),which is the wasted work potential during a process as a
result of irreversibilities , and be defined as second law efficiency .We then develop the exergy
balance relation and apply to closed systems and control volumes.
When a new energy source, such as geothermal well ,is discovered ,the first thing the
explorers do is estimate the amount of energy contained in the source .This information alone,
however ,is of little value in deciding whether to build a power plant on that site .what we really
need to know is the work potential of the source-that is ,the amount of energy we can extract as
useful work .T he rest of the energy will eventually be discarded as waste energy and is not worthy
of our consideration .Thus ,it would be very desirable to have a property to enable us to determine
the useful work potential of a given amount of energy at some specified state.
This property is Exergy ,which is also called the availability or available energy. The work
potential of the energy contained in a system at a specified state is simply the maximum useful work
that can be obtained from the system. You will recall that the work done during a process depends
on the initial state, the final state, and the process path. That is,
18
Work = f (initial state, process path, final state)
Despite the rapid developments in renewable energy utilization, it can be estimated that, fossil fuel
dependency will continue for decades. Lignite is one of the most widely used fossil fuels in Turkey
due to its vast reserves. According to IEA, approximately 65% of the total energy demand is met by
coal in India. However, because of the environmental effects and combustion difficulties of the low
grade lignite, an improved method for its better utilization is required. As a result, pre-treatment of
coal is widely used for lowering the combustion emissions.
The aim of this study is to study a coal based thermal power plant and perform an exergy analysis
based on the second law of thermodynamics to evaluate the exergetic efficiency and exergy
destruction of the overall plant and each of its components, and to identify the extent and exact
location of the exergy destruction in the system. Finally, the power plant is modeled assuming
various types of coal that are currently employed in real thermal power plants. The results are
compared in terms of energy generation, exergetic efficiency and CO2 emissions for each type of
coal.
1.2.1Definition of exergy
It is the maximum possible useful work that could be obtained from the system at a given state in
specified environment. The work potential of the energy contained in a system at a specified state
is simply the maximum useful work that can be obtained from the system.Work output is
maximized when the process between two specified states is executed in a reversible manner, as
therefore, all the irreversibilities are disregarded in determining the work potential.
1.2.2Exergy destruction
Irreversibilities such as friction , mixing, chemical reaction, heat transfer through a finite
temperature difference, unrestrained expansion, non quasieqilibrium compression or expantion
always generate entropy and anything that generate entropy always destroys exergy.The exergy
destroyed is proportional to the entropy generated , it is expressed as
Xdestroyed = (T0S) >0 1.4
Note that exergy destroyed is a positive quantity for any actual process and becomes zero for
reversible process. Exergy destroy represent the lost work potential and is also called the
irreversibility or lost work for the decrease of exergy and the exergy destruction is applicable to any
19
kind of system undergoing any kind of process since any system and its surroundings can be
enclosed by a sufficiently large arbitrary boundary across which there is no heat, work and mass
transfer, and thus, any system and its surrounding constitute an isolated system. No actual process is
truly reversible and thus, some exergy is destroyed during a process .Therefore, the exergy of the
universe which can be considered to be an isolated system is continuously decreasing. The more
irreversible a process is , the larger the exergy destruction during that process. No exergy is
destroyed during a reversible process.
Xdestroyed =0 1.5
The decease of exergy principle does not imply that the exergy of system can not increase. The
exergy change of a system can be positive or negative during a process but the exergy destroyed can
not be negative.
Xdestroyed, impossible <0 1.6
1.2.3Mode of exergy transfer
1.2.3.1Exergy transfer by work
Exergy is the useful work potential ,and the exergy transfer by work can simply be expressed
as:-
Xwork =W-Wsurr for boundary work 1.7
Xwork =W for other form of work 1.8
Where Wsurr =P0(V2-V1)
P0 is atmospheric pressure,and
V1 and V2 are the initial and final volumes of the system
Therefore,the exergy transfer with work such as shaft work and electrical work is equal to the work
W itself.in the case of a system that involves boundary work,such as piston cylinder devise ,the work
done to push the atmospheric air out of the way during expansion can not be transferred, and thus it
must be subtracted .also, during a compression process , part of the work is done by the atmospheric
air,thus we need to supply less useful work from a external source .
20
The work done by or against the atmospheric pressure has significance only for system whose
volume changes during the process.it has no significance for cyclic devices and system whose
boundary remain fixed during a process such as steady flow devices like turbine and heat exchanger
etc.
1.2.3.2Exergy transfer by heat
The work potential of the energy transfer form a heat source a temperature T is the maximum
work that can be obtained from that energy in a environment at temperature T0 and is equivalent to
the work produced by a carnot heat engine operating between the source and the environment
therefore,the carnot efficiency represents as:-
�c=(1-T0/T) 1.9
Therefore , heat transfer is always accompanied by exergy transfer.heat transfer Q at a location at
thermodynamic temperature T is always accompanied by exergy transfer Xheat is in the amount of
Xheat=(1- T0/T)Q 1.10
Where T0 =environment temperature
T=system temperature
Q=heat added or heat rejected
1.2.4Exergy transfer by mass
1.2.4.1Physical Exergy
It can be calculated :-
Xph=(h-h0)-T0(S-S0) 1.11
Where hand h0 are specific enthalpy at temperature Tand T0 respectively
S andS0 are specific entropy at temperature Tand T0 respectively
Xph is the physical exergy per unit mass
21
1.2.4.2. Exergy of kinetic energy
It is:-
Xke=KE=V2/2 1.12
Where V is the velocity of the system related to the environment
KE is the kinetic energy.
Xke=total Exergy of kinetic energy per unit mass
1.2.4.3.Exergy of potential energy
It is:-
Xpe=PE=gZ 1.13
Where g is the gravitational acceleration.
Z is the elevation of the system related to reference level in the environment .
PE is the potential energy.
Xpe is the exergy of potential energy per unit mass.
There for ,the exergies of kinetic and potential energies are equal to themselves ,and they are
entirely available for work
22
1.3Exergy balance of a steady flow system
Fig.1.1 An Open system
Let us consider , a steady state , control volume system .
Mass balance:
�1 = �2 = �
Energy balance:
(u1+p1v1+V12 /2 +gZ1)+ δQ/δm = (u2+p2v2+V2
2/2 +gZ2)+ δw/δm 1.14
Exergy balance:
Af1+δQ/δm(1-T0/T) = Af2 +δw/δm - dI/dm 1.15
Af1 +Ati = Af2 +Ato – T0(dσ/dm) 1.16
Specific flow availability, Af = h – T0S + V2/2 +gZ 1.17
printf("\n\nspecific heat of combustion gas=%f\n\n",Cc);
printf("\ndo you want to continue y/n: ");
ans=getche();
}
while(ans=='y');
}
75
REFERENCES
[1] P.K. Nag , (2008). “Power Plant Engineering”, by Tata McGraw-Hill Publishing Company Limited, 7 West Patel Nagar, New Delhi 110 008 [2] P.K. Nag , (2008). “Thermo dynamics”, by Tata McGraw-Hill Publishing Company Limited, 7 West Patel Nagar, New Delhi 110 008
[3] Research Paper on “Energy and Exergy Analysis of a Steam Power Plant in Egypt” by A. Rashad*, and A. El Maihy* , presented in 13th International Conference on AEROSPACE SCIENCES & AVIATION TECHNOLOGY.
[4] Energy and Exergy Analysis of a 500 KW Steam Power Plant at Benso Oil PalmPlantation (BOPP) by C. Mborah and E.K. Gbadam , Mechanical Engineering Department , University of Mines and Technology, Tarkwa, Ghana
[5] Book on “THERMODYNAMICS An engineering approach” 2008 by Yunus A. Cengel & Michael A Boles 6th Edn., McGraw Hill Companies, Inc., New York.
[6] O.P.Gupta “Elements of fuels,furnaces and refractory”s by khanna publication
[7] R.S.Khurmi “ Tables with Mollier diagram in si units ” by S.Chand and company limited