energy and exergy analysis

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					                                         The Joint Graduate School of Energy and Environment (JGSEE)
                                                            Seminar Course, November 2010 - January 2011

       Energy and exergy analysis in various components of Thermal Power
                                  Plants (TPPs)

                                      Muhammad Penta Helios
 The Joint Graduate School of Energy and Environment, King Mongkut’s University of Technology Thonburi, Thailand

Abstract: In this paper, the energy and exergy analysis which is taken data from 2 coal fired-thermal
power plants (TPPs), especially coal fired power plant in Turkey, are conveyed. This study of energy
and exergy analysis consider some thermodynamics variables, namely heating value, enthalpy,
pressure, temperature reference, entropy, and mass flow rate as directive to analyze energy and
exergy in each component. The main purposes in this paper are to describe the improvement of
energy and exergy quantity in each of components and also to know where the largest energy and
exergy losses has been occured based on first law of thermodynamics and second law of
thermodynamics. According to degree of entropy and exergy theoritically, the energy and exergy
comparison of two power plants can be accurately calculated if all of parameters that is used,
notably life time of each component and necessity input of technology, should be known.

           1.    INTRODUCTION                             whereas 20% of electricity is compensated
                                                          from different sources such as hydraulic,
      The most important aspect which is                  nuclear, wind, solar, geothermal, and biogas
analyzed and discussed as a major economical              [1]. Beside that, in another journal state the
and environmental aim in power plant is                   depletion of fossil fuel reserves and
energy. In daily activity, energy, especially             environmental concerns such as climate
electricity, is continuously increased from year          changes, the growth in oil demand is expected
to year in which ordinarily people used it for            to 47% between 2003 and 2030, 91,6% natural
lighting, heating, and cooling load in the                gas and 94,7% for coal [2].
building. Electricity as commercial energy                     In thermal power plants, boiler is the main
product is one of the most important indicator            component that gains more heat from
showing the prosperity development of                     combustion of fuel in the furnace where heat
countries and living standards of communities.            energy was converted to be mechanical energy
As an indicator, electricity has closest relation         during the process occured. When the energy
between population growth of human where it               is transfered during the process, amount of
involves urbanization, industrializing, and               energy will be lost in each of components, it is
technologic development as triggers increasing            usually caused by irreversibilities and thermal
of energy consumption. Globally, if we noticed            losses such as leakage of heat by conduction,
electricity usage, we could find that electricity         convection and radiation. To know that, it
is hold role in energy consumption in each of             usually can be known by energy analysis based
countries. Based on the data, In the world                on     first    law     of     thermodynamics.
80 % of electricity is approximately produced             Conventionally, Energy analysis only can
from fossil fuels (coal, petroleum, fuel oil,             measure quantity of energy but it can not
natural gas) fired thermal power plants (TPPs),           characterize the irreversibility of the process

                                           The Joint Graduate School of Energy and Environment (JGSEE)
                                                              Seminar Course, November 2010 - January 2011

       Figure.1. Simplified mass flow diagram for one of the investigated coal fired thermal power plants [6]

and quality of energy [3] within the system.                 turbines, condenser, heaters, pumps, and pipe)
Therefore, the energy concept alone is                       in Catalagzi, Turkey’s power plant [5]. Erdem.
insufficient to describe some important view                 et al analyzed the irreversibilities, exergy
points on energy utilization and needs second                performance for main components (boiler,
law of thermodynamics which is known by                      steam turbine, condenser, pump, feed water
exergy as more accurate calculation. Exergy                  heater) of thermal power plant in Turkey and
analysis is appeared as the best approaching                 also comparisons between the actual design
method where energy as the most valuable                     and simulated results. As shown in fig. 1,
object should be utilized rightly to give more               commonly a power plant includes the main
improvement in potensial work and heat                       component such as high, intermediate, and low
recycle.                                                     pressure turbin groups (HPT, IPT, and LPT,
     In this study, an exergy analysis is used               respectively), a boiler (B), several Pumps (P),
to indicate exergy and exergy destruction of                 a deaerator (D), a generator (G), a condenser
energy. From literature sources, some of paper               (C), low and high pressure feed water heater
concerning energy and exergy performances of                 groups (LPH and HPH) [6]. Regulagadda
fired thermal power plants [4-8]. Aljundi                    estimated the value of exergy for the plant
determined the location of most energy and                   under various operating conditions, including
exergy losses for Al-Hussein thermal power                   pressures, temperatures, and flow rates, in
plant in Jordan through energy and exergy                    order to determine the parameters that
analyses and, investigated the effects of                    maximize plant performance being installed by
variation of the reference ambient conditions                Tecpro Power Systems Ltd., Chennai, India [7].
on exergetic performance [4]. Kopac used                     Almost the same Saidur. et al conducted
exergy concept to find effects of ambient                    exergy and energy calculation of power plant
temperature of power plant components (boiler,               components (combustor, boiler and heat

                                        The Joint Graduate School of Energy and Environment (JGSEE)
                                                           Seminar Course, November 2010 - January 2011

exchanger) in malaysia and made an                     For total required heat energy in the boiler can
association between exergy and energy cost             be determined from :
saving [8].                                             .                .
  The final result in this study is purposed to        Q b  m fuels .LHV                         (5)
describe overall efficiency that covers energy,        After all of equations found, overall thermal
energy losses, exergy and exergy destruction           efficency of the power plants can be calculated
and also to identify various factor that effects       as follows :
the value of exergy.                                         W net
                                                        th  .                                   (6)
2.       APPROACHING ENERGY                AND                 Qb
         EXERGY   FORMULATION               OF         The energy balance for a control volume
         POWER PLANT                                   system is given by :
                                                                 .                .                   .       .
     In this study, energy analysis is analyzed        E            i    Q  E o  W                                            (7)
by using temperature operation whereas,                     i                                 o

exergy is always evaluated with respect to a           2.2. Exergy efficiency analysis
reference environment. The input and output                 in second law of thermodynamics to earn
values of the plant components can be                  the equation of exergy, energy equation can be
established using the measured/calculated              combined with entropy equation. Hereby, The
thermodynamics variables such as enthalpy,             entropy balance for a control volume system is
pressure, temperature, entropy, and mass flow          shown in equation 8 :
                                                                                          .                               .
rate. Before analyzing energy and exergy
                                                              Q ..        .       Q
performance, the process in each of                      S    S gen  S o  
                                                        i T                    o T
components should be arranged by mass,                 i                o

energy and exergy balance for any control              The exergy balance for a control volume
volume at steady state condition with                  system is written as
neglecting potential and kinetic energy.                    .           T  .   .     .   .
   For control volume system mass balance,               Exi   1   Q k  Exo  W  Ex d (9)
                                                                    T 
                                                                 k 
we can follow the equation below :                      i                 k   o

     .                     .                           Where .the exergy rate of a stream is

 mi   mo
 i                 o
                                                       E x  m(e x )                                                              (10)

                                                       me x   m e x  e x                             
                                                        .                             .
                                                                     tm    ch
2.1. Energy efficiency analysis                                                                                                   (11)
     According to first law of thermodynamics,
generally, energy analysis uses turbin and             And the spesifik exergy is given by:
pump as indicator to find overall thermal              e x  h  h0   To s  s o 
                                                         tm                                                                       (12)
effiiency in power plant. Accordingly, the
power output of steam turbine is as follows :          Equation 10. can give more explanation about
Wt  mhin  hout 
 .        .
                                                       exergy destruction in each of components.
                                          (2)          Total exergy destruction rate in plant can be
and for the calculation of pump power can be           determined as sum of exergy destruction rates
simply given as following :                            of components :
Wp m
                  hin  hout                 (3)
                                                        .                                         .
                                                       E x D ,total   E x D ,i  E x D , B  E x D ,T  E x D ,C
                                                                                                                  .   .       .

                                                                        .           .                        (13)
From two equation above, net electrical power                          E x D,P  E x D,H
output is given by :
                                                       From the equation 11 and 13, the overall exergy
 .                     .       .
W net   W t  W p
                                                       efficiency .is given by
                                                                W net                             (14)
                                                              Ex            .
                                                                             m coal .e x
                                     The Joint Graduate School of Energy and Environment (JGSEE)
                                                        Seminar Course, November 2010 - January 2011

   Table 1. Exergy efficiency equations for main components of a thermal power plant. [6]

In equation 14. The value of spesific exergy is     get that purposes. In this section the
very changable depending on types of fuel and       framework will be described below.
chemical     compounds.      Besides    exergy          a. Determining the heat supply from fuel
destruction and exergy efficiency, the other                combustion.          Theoritically,        the
important value that should be known in                     stoichiometry combustion of coal is
exergy analysis is exergetic performance                   5.08C  2 H 2  6.08(O2  3.76 N 2 )  5.08CO2
coefficient, where it is defined as amount of
exergy loss rate per unit power output and it               2 H 2 O  22.86 N 2                      (16)
can be written as following equation :                  b. Mass balance as the first point is
      .                                                     measured to find the characteristic of
      E x D ,total                                          mass in which covers mass of fuels,
         .                               (15)             water, and steam.          Based on the
          W Net
                                                            formed, mass is categorized into three
                                                            types namely, solid, gas, and liquid.
                     3.   METHODS                       c. Measuring energy balance in each of
                                                            components (such as, boiler, turbin,
     In this paper, to earn the main point of               condenser and pump) to earn the
energy and exergy efficiency. It should be                  efficiency and energy losses.
arranged the best framework as a basic how to          d. Combining entropy and energy

                                                 The Joint Graduate School of Energy and Environment (JGSEE)
                                                                    Seminar Course, November 2010 - January 2011

            equation to get exergy equation. Finally,           e. Ash fusion temperatures
            exergy balance as a main point can be                  (slagging predictors)
            calculated.                                         Table 3. Energy efficiency results for the main
                                                                         component of two thermal power
      4.     RESULTS AND DISCUSSION                                      plants.
                                                                        Spesific analytical point        Can-PP    Ca-PP

     In this section, the data of two power                     Heat supplied to boiler (kW)             379,443   416,020

plants selected from references [6] are shown                   Turbin power output total (kW)           165,085   161,263
in Table 2.                                                     Power consumption of pumps               5260      3670
                                                                Heat transfer rate at LPH (kW)           37,900    41,445
Table 2. Technical data of two coal-fired
                                                                Heat transfer rate at HPH (kW)           35,940    44,027
           power plants in Turkey.
                                                                Rejected heat rate from condenser (kW)   196,615   205,961
              Technical data            Can-PP         Ca-PP
                                                                Thermal efficiency (%)                   42.12     37.88
Total power (MW)                        320        300
Unit number                             2          2            Table 4. Exergy efficiency results of two
Unit power (MW)                         160        150                   thermal power plants.
                                                                        Spesific analytical point        Can-PP    Ca-PP
Main steam pressure (bar)               172        136.3
                                                                Fuel exergy (kW)                         421,891   447,888
Main steam temperature (oC)             540        538
                                                                Total exergy loss (kW)                   239,770   270,288
Main steam flowrate (t/h)               456.2      480
                                                                Exergy loss per unit power               1.50      1.72
Reheat pressure (bar)                   39.7       39.33
                                                                Exergy efficiency (%)                    37.88     35.19
Reheat temperature (oC)                 540        538
Reheat flowrate (t/h)                   405.6      415               Table 3. shows the difference result of
Low/high pressure pre-heater number     4/2        3/2          energy two power plants, where the energy
Condenser temperature ( C)o
                                        42.7       38.7         consumption of components is different.
Condenser cold water temperature (oC)   30.7       22           Logically, if heating value of coal in can is
Condenser cold water flowrate (t/h)     15,800     20,000       smaller than catalagzi power plant, it should be
Flue gas temperature (oC)               138        157
                                                                the energy efficiency of catalagzi is greater
Coal type                               Lignite    Hard coal
                                                                than can power plant. So, It indicates that the
LHV (kJ/kg)                             10,884     12,979
                                                                plant design and main equipment life time
                                                                affected the amount of energy in each
Can = Can Power plant
Ca = Catalagzi Power plant                                      component. Beside that, table 4. shows the
                                                                difference of exergy efficiency, where the fuel
From data in table 2. The yellow highlight                      exergy that was gained by catalagzi is greater
shows the differences of power plants design                    than can power plant. But, if it is looked from
and requirements for input of each component.                   total exergy loss in the table, the lower exergy
Beside that, the green highlight gives more                     efficiency in can power plant was caused by
information that for fuel combustion, it should                 energy loss in a component in low pressure
be analyzed characteristic of coal by using                     heater (LPH) groups. (stated data from table 6
some of requirement below.                                      in reference [6]).
a. Rank of coal                                                 As mentioned before, this study involves
   (Anthracite, Bituminous, Sub-bituminous,                     reference temperature as aspect analysis of
   Lignite, Peat).                                              energy and exergy. the reference temperature
b. Proximate analysis                                           does not have an effect on the energy
   (Btu, Moisture, Ash, Volatiles, Fixed                        efficiency, but it affects the exergy efficiency.
   Carbon).                                                     The performance of the system depends on the
c. Ultimate analysis                                            surrounding of the system [7]. In quantify the
   (Carbon, Hydrogen, Sulfur, Nitrogen, Ash,                    exergy of a system, reference temperature
   Moisture, Oxygen)                                            must be specified both the system and
d. Ash analysis                                                 surroundings. It is assumed intensive
   (SiO2, Al2O3, Fe2O3, CaO, MgO, Na2O,                         properties are not significantly changed by any
   K2O, P2O5, TiO2).                                            process [4]. From the two statements above,

                                             The Joint Graduate School of Energy and Environment (JGSEE)
                                                                Seminar Course, November 2010 - January 2011

reduction of energy and exergy value in power
plant was occured, because amount of energy                 Figure. 2. Effect of reference environment temperature
                                                                       on total exergy destruction rate in major plant
must be released in to the environment as a                            components.
consequency of operation process in reference               To get the correlation between percent exergy
temperature. It can be proved by data results in            efficiency      and     reference environment
table 5 below. (stated data from reference [5])             temperature can be used the data in table 7 to
Table 5. Variation of energy and exergy                     illustrate in fig. 4 below.
         efficiencies with the reference                    Table 7. Major sources of percentage exegy
         temperature                                                  efficiency in any various reference
                                                                      environment temperature.
Temperature   Exergy efficiency       Energy efficiency
   (K)              (%)                     (%)
                                                           Temperature        Boiler         Condenser      Turbine
   273             25.397                  30.12              (K)              (%)             (%)           (%)
   283             25.392                  30.12              283.15          50.33            20.18         75.34
   293            25.3884                  30.12              288.15          49.45            21.76         75.01
   303             25.385                  30.12              293.15          48.57            23.69         74.68
   313            25.3806                  30.12              298.15          47.68            26.11         74.36
   323             25.376                  30.12              303.15          46.80            29.19         74.03
                                                              308.15          45.92            33.25         73.71
In addition, this section described association               313.15          45.03            38.84         73.39
of exergy destruction and reference                           318.15          44.15            47.02         73.08
environment temperature in any major source.
All data are represented by table 6 and
shown by fig. 2.
Table 6. Major sources of exergy destruction
         in any various reference environment

Temperature   Boiler        Condenser        Turbine
   (K)        (MW)           (MW)             (MW)
  283.15      115.72          22.34           18.75
  288.15      117.33          20.38           19.09
  293.15      118.93          18.41           19.42
  298.15      120.54          16.45           19.75
  303.15      122.15          14.48           20.09
  308.15      123.75          12.52           20.42
  313.15      125.36          10.56           20.76
  318.15      126.96          8.59            21.09         Figure. 3. Effect of reference environment temperature
                                                                       on the exergy efficiency in major plant

                                                                           5. CONCLUSIONS

                                                               In this study, energy and exergy analysis

                                      The Joint Graduate School of Energy and Environment (JGSEE)
                                                         Seminar Course, November 2010 - January 2011

                                                      h     enthalpy (kJ kg-1)
                                                     LHV lower heating value (kJ kg-1)
                                                     s      entropy (kJ kg-1 K-1)
                                                     T      temperature (K or oc)
                                                     W      electrical power output (kW)
                                                     Q      heat transfer rate (kW)

                                                     Greek letters

                                                           energy efficiency
                                                           exergy efficiency
                                                           exergetic performance coefficient

                                                                     9.   REFERENCES

                                                     [1] Statistical Review of World Energy, The
                                                         British Petroleum Company, 2007.
                                                     [2] Som,        S.K.,     Datta,      A.,2008.
                                                         Thermodynamic irreversibilities and
                                                         exergy balance in combustion processes.
                                                         Progress in Energy and Combustion
                                                         Science 34, 351-376.
                                                     [3] Lior, N. and N. Zhang (2007). "Energy,
                                                         exergy, and Second Law performance
                                                         criteria." Energy 32(4): 281-296.
                                                     [4] Aljundi, I. H. (2009). "Energy and exergy
                                                         analysis of a steam power plant in
                                                         Jordan." Applied Thermal Engineering
                                                         29(2-3): 324-328.
                                                     [5] Kopac, Mehmet and A. Hilalci (2007).
                                                         “Effect of ambient temperature on the
                                                         efficiency of the regenerative and reheat
                                                         Catalagzi power plant in Turkey. Applied
                                                         Thermal Engineering 27: 1377-1385.
                                                     [6] Erdem, H. H., A. V. Akkaya, et al. (2009).
                                                         "Comparative energetic and exergetic
       7.   ACKNOWLEDGEMENTS                             performance analyses for coal-fired
                                                         thermal power plants in Turkey."
                                                         International Journal of Thermal Sciences
                                                         48(11): 2179-2186.
                                                     [7] Regulagadda, P., I. Dincer, et al. "Exergy
                                                         analysis of a thermal power plant with
                                                         measured boiler and turbine losses."
            8.   NOMENCLATURE                            Applied Thermal Engineering 30(8-9):
.                                                        970-976.
Ex     exergy transfer rate (kW)
.                                                    [8] Saidur, R. et al.(2010). “Energy, exergy
ex     spesific exergy (kJ kg-1)                         and economic analysis of industrial
E xD   exergy destruction rate (kW)                      boilers.” Energy Policy 38 : 2188-2197.


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