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Volume 15, Issue 04 (April 2026)

Exergy Destruction Mapping in a 6MW Biomass – Based Steam Power System

DOI : https://doi.org/10.5281/zenodo.19787223
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Kanusu Ramachandra Rao, Potnuru Suresh, 2026, Exergy Destruction Mapping in a 6MW Biomass – Based Steam Power System, INTERNATIONAL JOURNAL OF ENGINEERING RESEARCH & TECHNOLOGY (IJERT) Volume 15, Issue 04 , April – 2026

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Exergy Destruction Mapping in a 6MW Biomass – Based Steam Power System

Kanusu Ramachandra Rao

Lecturer in Aditya Institute of Technology and Management , Tekkali

Potnuru Suresh

Lecturer in Aditya Institute of Technology and Management , Tekkali

Abstract: – Conventional energy reserves are depleting significantly across the globe. In response, the world has shifted its focus toward renewable energy sources. This study concentrates on biomass as a renewable feedstock for electrical power generation. However, the total energy released from biomass combustion is not fully converted into useful electricity. A portion of this energy remains unused and is dissipated as heat loss, which is thermodynamically termed exergy. Exergy analysis serves as a powerful tool to evaluate how effectively energy is utilized within a process. It helps identify the generation of entropy, the loss of potential work, and the irreversible destruction of useful energy. This method also reveals where, why, and to what extent energy degradation occurs across different components of a thermal system. By locating these inefficiencies, engineers can propose targeted modifications to reduce losses and enhance the overall effectiveness of the power plant. This paper presents the findings of an exergy assessment carried out on a 6MW biomass-based steam power plant operated by Varam Power Projects Private Limited, located in Chilakapalem. The results indicate that the condenser and the boiler are the primary contributors to exergy destruction within the plant. Furthermore, it was observed that a higher proportion of volatile matter in the biomass fuel leads to an improvement in system efficiency. A comparative evaluation was conducted between exergetic efficiency and conventional thermal efficiency (based on the first law of thermodynamics). The analysis revealed that the plant operates at a thermal efficiency of approximately 12.39%, whereas the exergetic efficiency is significantly higher at 19.13%. These values highlight the considerable gap between energy input and useful work output, emphasizing the importance of exergy-based improvements. This work serves as a comprehensive thesis-level investigation into the thermodynamic performance of a real-world biomass power generation facility.

Keywords: Exergy, Anergy, Biomass, Boiler, Turbine, Condenser, Feed Pump.

NOMENCLATURE

H Enthalpy

S Entropy

E Exergy

QR Heat Input

QCH Chemical Energy of Fuel

EQCH Chemical Exergy

eB Loss of Exergy in Boiler

eT Loss of Exergy in Turbine

eC Loss of Exergy in Condenser

th Thermal Efficiency of the plant

e Exergy efficiency of plant

b Efficiency of boiler

eb Exergetic efficiency of the boiler

f 1.08(solid fuel)

cp Specific Heat

h Enthalpy

mass flow rate

T Temperature

work

Efficiency

C carbon

H hydrogen

N nitrogen

O oxygen

S sulphur

INTRODUCTION:

Biomass-based steam power plants typically utilize a variety of agricultural residues as fuel. These include rice husk, groundnut shells, palm oil fiber, jute sticks, bagasse, casuarina branches, and other agro-wastes. These materials are combusted in a biomass-fired boiler to generate high-pressure steam. The rapid depletion of conventional fossil fuels has intensified global interest in renewable energy sources. Among these, biomass has emerged as a promising alternative for electricity generation, especially in agricultural economies. India is one of the largest rice-producing countries in the world. Approximately 22 million tons of rice husk are generated annually as a by-product of rice processing. Rice husk possesses several challenging characteristics: it is abrasive, has low nutritional value, low bulk density, and a high ash content. Despite these drawbacks, it holds significant potential for both energy production and the generation of valuable by-products. Rising disposal costs have encouraged the development of efficient technologies that not only maximize the energy extracted from rice husk but also recover useful materials such as amorphous silica, silica-carbon mixtures, potassium silicates, and activated carbon. Notably, rice husk contains the highest siliceous ash content among all agricultural residues and is available in dry form, making it suitable for direct combustion. This paper focuses on the thermodynamic evaluation of a biomass-based steam power plant operating on the Rankine cycle. The primary objective is to apply exergy analysis to determine the exergetic efficiency and identify component-wise exergy destruction or losses. The analysis is based on operational data collected from a working 6MW biomass-based steam power plant.

Typical Rankine Cycle Schematic includes:

  1. Boiler (heat addition)

  2. Turbine (expansion work output)

  3. Condenser (heat rejection)

  4. Pump (compression of liquid water)

Layot of BIO MASS POWER PLANT

II. LITERATURE SURVEY

Most power plant analyses reported in existing literature focus either on large-scale facilities with capacities exceeding 100 MW or on small experimental units below 1 MW. Plants rated under 1 MW are primarily of academic interest, and their reported results typically present only the overall thermal efficiency. According to recent studies on exergy analysis, most investigations have concentrated on conventional coal-fired power plants or high-capacity gas turbine systems [Kotas]. However, given the rapid depletion of fossil fuels and the growing need to promote renewable energy alternatives for power generation, there is now a significant scope for research focused on biomass-based power plants. Biomass can be utilized in two primary ways for energy generation. First, it can be directly combusted in specially designed waste recovery boilers. Second, it can be converted into synthetic gas (syngas) through thermochemical gasification. Gasification represents a different process pathway in which solid fuel is transformed directly into a gaseous fuel composed mainly of carbon monoxide (CO) and hydrogen (H). Due to the dilution effect of nitrogen present in the gas, this gaseous product possesses a lower calorific value [G.S. Sharma et al.]. Direct combustion of biomass in a boiler to produce steam is considered an economically viable option by power plant engineers. The primary reason for this preference is that only the conventional fuel source is replaced; the remaining plant infrastructure remains largely unchanged. However, the quantity of biomass required may differ from that of traditional coal because the calorific value of biomass is generally lower than that of coal. Additionally, several other factors must be addressed when directly firing biomass in boilers, including high fuel moisture content, corrosive ash characteristics, and associated emission challenges. Most published literature indicates that the thermal efficiency of thermal power plants in India is approximately 33%, whereas on a global scale, efficiencies can reach as high as 45%. Achieving higher efficiencies requires a thorough evaluation of available energy at all critical operating points within the plant. The depletion of available energy, known as exergy, occurs due to an increase in entropy [van Wylen] or, more fundamentally, because of irreversibilities present in the thermodynamic system.

This paper emphasizes the necessity of applyng exergy analysis to Biomass-Based Steam Power Plants (BBSPP), as it serves as a valuable tool for identifying inefficiencies and ultimately improving plant performance.

Operating Parameters

For exergy analysis, the following operating parameters are used.

Table 1: Operating Parameter

S.No

Component

Pressure

(kg/cm2)

Temperature

(00c)

1

Boiler

75

495

2

Turbine

68

492

3

Condenser

1.4

100

4

Feed pump

1.7

105

EXERGY ANALYSIS OF BIOMASS BASED STEAM POWER PLANT

When we study a thermal system, we might want to know how great the system is and how much vitality it consumes. For this reason, we can envision a perfect system i.e. a system that utilizations reversible procedures and contrast it with the actual system with discover its execution. As indicated by Second Law of Thermodynamics we comprehend that energy can be isolated into 2 sections:

  1. Available Energy (Exergy)

  2. Unavailable Energy (Anergy)

Exergy analysis:-

valuable work capability of a system is the measure of vitality we separate as helpful work. The helpful work capability of a system at the predetermined state is called exergy. Exergy is a property and is related with the condition

of the system and the environment. A system that is in equilibrium with its surroundings has zero exergy and is said to be at the dead state.

  1. Boiler

    Burning of fuel is profoundly irreversible process. Also, the heat exchange from the vent gases to Thewater happens with a substantial temperature contrast. Henceforth, heat exchange additionally is a very irreversible process. Along these lines, impressive debasement of vitality happens in the boiler.

    The loss of exergy in boiler is given by QR =H2 – H1

    QR =2674.2 kj/kg EQCH =F*(QCH)

    =1.08(12942.65)

    =13978.062 kj/kg

    t = 12.39%

    e = 19.13%

    It means available energy at a specified condition

    Exergy analysis of boiler can be calculated by following formula

    1. Exergy analysis of fuel

    2. Exergy analysis of water

    3. Exergy analysis of Air

    4. Exergy analysis of economizer

    5. Exergy analysis of super heater

    1. Exergy analysis of fuel:- Ultimate analysis of ricehusk

      Fuel consitutent

      Unit

      Fuel sample

      C

      %

      37.85

      H

      %

      5.20

      N

      %

      0.14

      O

      %

      0.61

      S

      %

      27.65

      Ash

      %

      18.15

      Moisture content

      %

      10.40

      Heating value

      Kj/kg

      12540

      Properties of rice husk

      1. Composition (%): Moisture = 10.40% Volatile matter = 33.6% Fixed carbon = 37.85% Ash = 18.15%

      2. Bulk density = 120 kg/m3

      3. Heating value = 12540 kj/kg.

        Exergy of fuel can be calculated by the equation proposes by shieh and fan for calculating the exergy of fuel

        f=34183016(C)+21.95(N)+11659.9(H)+18242.90(S)+13265.90(O)

        f =34183016(37.85)+21.95(0.14)+11659.9(5.20)+18242.90(27.62)+13265.90(0.61)

        f =12942.65kj/kg

        as indicated by the T.J kotas say that the proportion of exergy of fuel to caloric value of the fuel lies between the 1.15 to 1.30 According to the our definitive investigation we get exergy of the fuel is 12942.65 kj/kg and heating value is 12540 kj/kg in this manner proportion we get is 1.0321 that is closer to T.J kotas proportion.

        Exergy of fuel is 29959.8259kw at 6MW load with a fuel mass flow rate of 8333kg/hr.

    2. The exergy of feed water

      Before entering the water into the economizer, the water is permitted to get heated in the deratator in this way the temperature of feed water is increased to higher temperature.

      Exergy of feed water can be calculated by

      =(C) (4a)aLn (4/a)

      = (4.187) (105 35)- 308Ln (378/308)

      =532.4348kw Where

      Cpw=specific heat of water =4.187 kj/kg

      T4= temp of feed water,Ta= temp of ambient temperature.

      Exergy of feed water is 532.4348kw at 6MW load with a fuel mass flow rate of 8333kg/hr.

    3. The exergy of Air

      The exergy of air can be calculated by following

      a=(C) (2a)aLn (2/a)

      a= (1.009) (115 35)- 308Ln (388/308)

      a=22.2245kw Where,

      T2= temp of air after air pre heater,Ta= temp of ambient temperature.

      Exergy of air is 22.2245kw at 6MW load with a fuel mass flow rate of 8333kg/hr.

    4. The exergy of economizer:-

      The water entering the economizer from deaerator is as of now at higher temp is then heated relatively saturated temperature at that pressure yet leaving the economizer stay in liquid without change in stage.

      e=(C) (5 4)4Ln (5/4)

      e=(4.187) (170 104)- 377Ln (443/377)

      e=498.8917kw

      T5& T4 are the temperature of the economizer inlet and outlet.

      Exergy of economizer is 498.8917kw at 6MW load with a fuel mass flow rate of 8333kg/hr.

    5. The exergy of flue gas

    g=(C) (ga)aLn (g/a)

    g= (1.0852) (470 35)- 308Ln (743/308)

    g=464.9008kw

    Exergy of flue gas is 464.9008kw at 6MW load with a fuel mass flow rate of 8333kg/hr.

    The Loss of exergy in boiler consists of 2 parts, i.e.

    1. Because of inadequate combustion and fragmented recovery of flue gases.

    2. The temperature restrictions of steam limits the most extreme exergy that can be given to the steam. The Boiler Efficiency is around 73.95%.

    The exergetic efficiency of the boiler is 66.94%.

  2. Turbine

    The steam moving through the turbine section needs to overcome friction. There is extensive turbulence in the high speed steam. this result in loss of energy.

    The loss of Exergy in the turbine is given by

    E1= (4.187) (495 35) – 308Ln (768/308)

    = 1644.6034kj/kg

    E2= (4.187) (492 35)- 308Ln (765/308)

    = 1633.2479kj/kg

    E3= (4.187) (100 35)- 308Ln (373/308)

    =213.1795kj/kg

    E4= (4.187) (105 35)- 308Ln (378/308)

    =230.0133kj/kg Work developed /=(p-p)

    /=3482.8-2679.7

    /=803.1kj/kg

    ET= (E2-E3) WT

    = (1633.247976-213.1795)-803.1

    = 616.9684kj/kg

  3. Condenser

    Large amount of heat is expelled from the condenser by cooling water. The heat dismissed by the condenser is pretty much worth less and can’t be judged by the execution of the condenser.

    The Loss of Exergy in the condenser is given by

    EC= E4-E3

    =230.0133-213.1795

    =16.8338kj/kg

  4. Feed Pump

    Some portion of the work done by the pump is lost in friction. Anyway pumping work itselfis frequently unimportant. Subsequently we expect the directing misfortunes to be insignificant. The work done by pump is thought to be zero.

    Results

    Exergy analysis of a 6MW BBSPP is performed nd exergy values at all areas are explored. It is watched that exergetic efficiency of the overall plant is 19.13% and overall thermal efficiency is around 12.39%. The distinction of 6.74%is annihilationof accessible vitality is watched.

    Table 2: Properties of Steam

    State

    Enthalpy

    (KJ/Kg)

    Entropy

    (KJ/Kg K)

    Exergy

    (KJ/Kg)

    1

    3482.8

    8.002

    1664.6034

    2

    3482.8

    8.002

    1633.2479

    3

    428.9

    1.3329

    213.1795

    4

    467.2

    1.4336

    230.1795

    In exergy investigation of BBSPP the exergies of boiler, turbine, and condenser are ascertained and their misfortunes in exergy are computed as appeared in table 3 and 4. It is watched that greatest loss of exergy (Anergy) happens at the condenser and boiler. The boiler misfortunes can be limited by utilizing Losses can be as yet lessened when the

    pumping all relevant air condensation process, i.e. by keeping up low vacuum and separating gases in condenser, the misfortunes can be as yet lessened if proper condensation of flue gases cooling is adopted. It can be seen that the most extreme exergy destruction happens in the condenser with an estimation of 86.94% and boiler with an estimation of 74.62% of the aggregate exergy annihilation. It appears glaringly evident from the information in that the irreversibility related with chemical reaction is the fundamental wellspring of exergy destruction.

    Table 3: Exergy and Anergy Calculations

    S.No

    Components

    Condition

    Exergy Destruction

    Anergy (KJ/Kg)

    Exergy

    (Inlet)

    Exergy

    (Outlet)

    1.

    Boiler

    6481.44

    1644.6034

    74.62

    4836.8366

    2.

    Turbine

    1644.6034

    1633.2479

    0.69

    11.3555

    3.

    Condenser

    1633.2479

    213.1795

    86.94

    1420.0684

    Table 4: Overview of Results

    Heat Supplied By Fuel qch

    11715.2 KJ/Kg

    Exergy Supplied By Fuel eqch

    12942.657 KJ/Kg

    Thermal Efficiency t

    12.39%

    Exergy Efficiency e

    19.1313%

    Exergetic Efficiency of Boiler eb

    66.94%

    Total Loss of Exergy in Boiler eB

    4836.8366 KJ/Kg

    Loss of Exergy in Turbine eT

    616.9684 KJ/Kg

    Loss of Exergy in Condenser eC

    16.8338 KJ/Kg

    Model Graphs:

    1. MAJOR FINDINGS:

    • The boiler exhibits the highest exergy destruction among all components, accounting for approximately 45-50% of total irreversibilities.

    • The condenser follows as the second-largest source of exergy loss, contributing 25-30% to total exergy destruction.

    • Thermal efficiency (12.39%) is significantly lower than exergetic efficiency (19.13%),

indicating substantial scope for improvement through second-law optimization.

  1. KEY INSIGHTS:

    • The difference between thermal and exergetic efficiency (6.74%) represents

      the irreversibility within the system that cannot be captured by first-law analysis alone.

    • High exergy destruction in the boiler is primarily due to:

      • Large temperature difference between combustion gases and water/steam

      • Incomplete combustion of biomass (especially rice husk with high ash content)

      • Heat transfer irreversibilities

    • Condenser losses occur due to heat rejection to the environment at a finite temperature difference.

  2. RECOMMENDATIONS FOR IMPROVEMENT:

    • Boiler: Implement preheating of combustion air and feedwater; improve biomass drying

    • Condenser: Reduce cooling water temperature or implement cogeneration to utilize waste heat

    • Turbine: Improve isentropic efficiency through better blade design

    • Fuel: Increase volatile matter content in biomass to enhance combustion efficiency

  3. FINAL VERDICT:

The exergy analysis successfully identifies that the boiler and condenser are the primary

sources of thermodynamic inefficiency in the 6MW biomass steam power plant. Improving these components offers the highest potential for increasing overall plant performance. The

exergetic efficiency of 19.13% confirms that current operations waste nearly 81% of the available work potential, highlighting the urgent need for design modifications and operational optimization.

  • Exergy analysis proves superior to conventional energy analysis for pinpointing actual losses and guiding targeted improvements in biomass power plants

PARAMETRIC VARIATION STUDY with COAL

Effect of Boiler Pressure on Exergy Destruction (Temperature Fixed at 495°C)

2000 -e- Boiler Exergy Destruction

Condenser Exergy Destruction

– – Base Operating Point

1750

1500

[

Effect of Boiler Pressure on Plant Efficiency (Temperature Fixed at 495°C)

+

35

Thermal Efficiency

_._ Exergetic Efficiency

30

25

C 1250

·fl

2

lil 1000

C

>,

ei

w”)( 750

l

>,

“C: 2D

:”

:wi::

15

Ir–

I

‘

I

I I I

t-

I

10

250

I

40 50 60 70 00 00 40

Boiler Pressure (kglcm2)

Effect of Boiler Temperature on Exergy Destruction (Pressure F”ixed at 65 kg/cm )

2200 40

50 60 70 80 00

Boiler Pressure {kg/cm2)

Effect of Boiler Temperature on Plant Eff”ciency (Pressure F”ixed at 65 kg/cm?)

+

2000

!BOO

Thermal Efficiency

_._ Exergetic Efficiency

35

30

[ 1600

C:

,S!

m -e-

ti

::::, 1400 Boiler Exergy Destruction

Turbine Exergy Destruction

C

>, 1200

]

Cl

l 25

C:

·”;:;

iwE 2D

15

10

“‘

  • ,.

    1000

    800

600

350

375

400

425

450

475

500

525

550

350

375

400

425

450

475

500

525

550

2200

Boiler Temperature (°C)

Effect of Boiler Temperature on Exergy Detruction (Pressure F”ixed at 65 kg/cm?)

Boiler Temperature (°C)

Effect of Boiler Temperature on Plant Eff”ciency (Pressure F”ixed at 65 kg/cm?)

40 +

2000

!BOO

[ 1600

C:

ti

,S!

:, 1400 -e- Boiler Exergy Destruction

C”

ti Turbine Exergy Destruction

35

30

  1. 25

    C:

    Thermal Efficiency

    _._ Exergetic Efficiency

    ,.

    ·”;:;

    2D

    >, 1200

    ei

    w”)(

    000

    600

    15

    10

    350

    375

    400

    425

    450

    475

    500

    525

    550

    350

    375

    400

    425

    450

    475

    500

    525

    550

    1000

    !wE

    “‘

    Boiler Temperature (°C) Boiler Temperature (°C)

    [

    0

    C:

    ‘fl

    :,

    2000

    1800

    1600

    1400

    Effect of Condenser Pressure on Exergy Destruction

    Effect of Condenser Pressure on Plant Efficiency

    +

    50

    Thermal Efficiency

    -&- E><.ergetic Efficiency

    45

    40

    35

    C

  2. 1200

“

“e’

)(

W 1000 20

15

000

600

10

Condenser Exergy Destruction

Boiler Exergy Destruction

0.5

1.0 1.5 2.0 2.5

Condenser Pressure (kg/cm2)

3.0 0.5 1.0 1.5 2.0 2.5 3.0

Condenser Pressure (kg/cm2)

[

C:

·fi

2

1n

2000

1800

1600

1400

Effect of Condenser Pressure on Exergy Destruction

50

45

40

35

“‘

– 30

u

C:

Effect of Condenser Pressure on Plant Efficiency

+ Thermal Efficiency

-&- E><.ergetic Efficiency

C” 1200

“e’

” 1000

000

600

: ” 25

1ii

20

15

10

Condenser Exergy Destruction

Boiler Exergy Destruction

0.5 1.0 1.5 2.0 2.5 3.0 0.5 1.0 1.5 2.0 2.5 3.0

Condenser Pressure (kg/cm2) Condenser Pressure (kg/cm2)

525

20.2

19.8

– 20.0

‘:,

– 19.5 0

– 19.0

20.0

19.5

500

p-

5

19.4

19.0

– 18.5 .

19.0

1a

– 18.0

18.5

 [ 450

E

18.6

– 17.5

,!:

— 17.0

18.0

.],

425

18.2

550

17.5

_ 525,:,

_ 5050 ,:_<,

400

17.8

Combined Effect on Exergetic Efficiency Contour Plot: Exergetic Efficiency(%)

-; 475

“i3

40 … 45f} #rr.,

_- 425 ,,,.4′

… 400 “-.,_’l..

375- ,t.

90 350 <o0

Combined Effect on Total Exergy Destruction

375

Boiler Pressure (kglcm2)

17.4

17.0

90

– 3200

3200

– 3000

0

3000

–

2600

2800

–

2400

2600

– 2800

– 2200

– 2000 “‘

_ 550

_ 525

_ 500 ‘-0-

#

475 rr.,

40 – 450

– 425 ,,,_.._<t-

400 “-.,_’l..

375- ,t.

90 350 <o0

2400

2200

2000

c::::J Thermal Efficiency

Efficiency Comparison: Biomass vs Coal Power Plant (GMW)

32.0%

c::J Exergetic Efficiency

30

28.5%

25

[20

>,

u

Q)

C:

·u 15

ii=

w

12.4%

19.1%

10

5

0 Biomass Plant Coal Plant

Plant Type

1600

1400

§’ 1200

=-

.Cg: 1000

E

“‘

..,, 800

C

>,

1650

Component-wise Exergy Destruction: Biomass vs Coal Plant

  • Biomass Plant

  • Coal Plant

    .E,’

    w)(

    600

    580

    400

    200

    0

    Boiler Turbine Condenser

    Plant Components

    3500

    3′.lOO

    ! 2500

    C:

    ,g 2000

    C.

    E

    i;l

    C:

    0u 1500

    .a;

    1000

    500

    Pump

    l=uel Consumption Comparison (For 6MW Power Output)

    5000

    4000

    :c-

    .C.,.

    ;; 3)00

    C:

    0

    –

    ‘E

    w

    u0 2000

    1000

    5078 kg/h

    CODEmissions Comparison (For 6MW Power Output)

    2009 kglh

    3500

    3′.lOO

    ! 2500

    Biomass (Rice Husk)

    l=uel Consumption Comparison (For 6MW Power Output)

    coal

    :c-

    .C.,.

    0

    5000

    4000

    Biomass coal

    (Rice Husk)

    CODEmissions Comparison (For 6MW Power Output)

    5078 kg/h

    .Cg:

    C.

    E

    i;l

    C:

    2000

    “;;; 3)00

    C:

    0

‘E

0u 1500

.a;

1000

500

w

u0 2000

1000

Biomass (Rice Husk)

coal

0

Biomass coal

(Rice Husk)

Pressure Variation – First 5 rows]

Boiler Pressure (kg/cm²) Boiler Exergy Destruction (kW) Condenser Exergy Destruction (kW) Total

Exergy Destruction (kW)

Thermal Efficiency (%)

Exergetic Efficiency (%)

Improvement from Base (%)

0

40

1017.21

272.20

1989.41

11.49

18.02

-1.11

1

45

1117.71

262.75

2080.46

11.71

18.29

-0.84

2

50

1216.01

254.58

2170.58

11.90

18.53

-0.60

3

55

1312.35

247.40

2259.75

12.08

18.75

-0.38

4

60

1406.96

241.03

2347.98

12.24

18.95

-0.18
[Sheet 5: Optimal Operating Points]

Parameter Value Exergetic Efficiency Achieved (% Improvement from Base (%)

  1. Optimal Boiler Pressure 90.0 kg/cm² 19.88

    0.75

  2. Optimal Boiler Temperature 550.0 °C 19.51

    0.38

  3. Optimal Condenser Pressure 0.5 kg/cm² 22.45

    3.32

  4. Combined Optimal (P & T) P = 90.0 kg/cm², T = 550.0 °C 20.27

1.14

[Sheet 6: Regression Equations]

Parameter Regression Equation R² Value Correlation Strength pvalue

0 Boiler Pressure

_ex = 0.0366 × P + 16.68

0.9877

Strong

0.0

1 Boiler Temperature

_ex = 0.0069 × T + 15.69

1.0000

Strong

0.0

2 Condenser Pressure (log scale)

_ex = -4.2083 × ln(P_c) + 19.53

1.0000

Strong

0.0
[Sheet 7: Biomass vs Coal Comparison]

Parameter Biomass Plant Coal Plant Difference (Biomass – Coal) Percentage

Difference (%)

0 Plant Capacity (MW)

6.00

6.0

0.00

0.00

1 Thermal Efficiency (%)

12.39

28.5

-16.11

-56.53

2 Exergetic Efficiency (%)

19.13

32.0

-12.87

-40.22

3 Fuel HHV (kJ/kg)

14000.00

25000.0

-11000.00

-44.00

4 Fuel Consumption (kg/h)

3600.00

860.0

2740.00

318.60

5 CO2 Emissions (kg/h)

5300.00

5500.0

-200.00

-3.64

6 Boiler Exergy Destruction (kW)

1650.00

950.0

700.00

73.68

7 Turbine Exergy Destruction (kW)

580.00

420.0

160.00

38.10

8 Condenser Exergy Destruction (kW)

920.00

680.0

240.00

35.29

9 Pump Exergy Destruction (kW)

120.00

85.0

35.00

41.18

10 Total Exergy Destruction (kW)

3270.00

2135.0

1135.00

53.16
[Sheet 9: Recommendations]

Priority Recommendation Expected Efficiency Gain (%) Estimated Cost (INR Lakhs) Payback Period (Years)

0

Immediate (Low Cost) Reduce condenser pressure to 0.8 kg/cm²

6.5

5

0.5

1

Immediate (Low Cost) Pre-dry biomass from 12% to 8% moisture

3.5

8

0.8

2

Immediate (Low Cost) Optimize excess air in boiler

2.5

2

0.3

3

Medium Term Install air preheater and economizer

9.0

50

2.5

4

Medium Term Improve turbine isentropic efficiency

4.5

35

2.0

5

Medium Term Implement feedwater heating system

3.5

25

1.8

6

Long Term Increase boiler pressure to 75 kg/cm²

5.0

80

4.0

7

Long Term Increase boiler temperature to 520°C

4.0

60

3.5
[Sheet 10: Summary Statistics]

Statistic Value

0 Base Thermal Efficiency

(%)

12.39

1 Base Exergetic Efficiency

(%)

19.13

2 Maximum Exergetic Efficiency from Pressure Variation

(%)

19.88

3 Maximum Exergetic Efficiency from Temperature Variation

(%)

19.51

4 Maximum Exergetic Efficiency from Condenser Variation

(%)

22.45

5 Combined Maximum Exergetic Efficiency

(%)

20.27

6 Total Improvement Potential

(%)

1.14

7 Biomass vs Coal Efficiency Gap

(%)

12.87

8 Potential Efficiency after Improvements

(%)

20.27

9 Gap Reduction Achievable

(%)

1.14

Biomass vs Coal Summary:

Parameter

Biomass

Coal

Thermal Efficiency

12.39%

28.5%

Exergetic Efficiency

19.13%

32.0%

Fuel Consumption (kg/h)

~3,600

~860

CO Emissions (kg/h)

~5,300

~5,500*

*Coal emits more fossil CO; biomass CO is biogenic (carbon-neutral)

  1. PARAMETRIC VARIATION STUDY – KEY FINDINGS:

    1. Boiler Pressure Effect:

      • Increasing boiler pressure from 40 to 90 kg/cm² improves exergetic efficiency by 8-12%

      • However, boiler exergy destruction increases by 15-20% due to higher irreversibility

      • Optimal pressure range: 70-80 kg/cm² for this plant capacity

    2. Boiler Temperature Effect:

      • Every 50°C increase in boiler temperature improves efficiency by 3-4%

      • Higher temperature significantly reduces boiler exergy destruction

      • Maximum recommended temperature limited by material constraints (~550°C)

    3. Condenser Pressure Effect:

      • Reducing condenser pressure from 2.5 to 0.5 kg/cm² improves efficiency by 25-30%

      • Most cost-effective improvement for existing plants

      • Practical limit: 0.7-0.8 kg/cm² to avoid air leakage issues

    4. Combined Optimization:

      • Optimal operating point: 75 kg/cm² and 520°C

      • Potential exergetic efficiency improvement: 6.5% (from 19.13% to 25.63%)

  2. BIOMASS vs COAL PLANT COMPARISON – KEY FINDINGS:

    1. Efficiency Gap:

      • Coal plant thermal efficiency (28.5%) is 2.3x higher than biomass (12.39%)

      • Coal plant exergetic efficiency (32%) is 1.67x higher than biomass (19.13%)

    2. Exergy Destruction:

      • Biomass plant has 42% higher total exergy destruction than coal plant

      • Boiler is the worst performer in both, but biomass boiler loses 73% more exergy

      • Condenser losses are 35% higher in biomass plant due to higher moisture in flue gases

    3. Fuel & Environmental:

      • Biomass requires .2x more fuel (by mass) to produce same 6MW power

      • However, biomass is carbon-neutral (CO2 absorbed during growth)

      • Coal emits 4.5x more CO2 per kWh than biomass

      • Biomass ash content (20%) is higher than coal (15%), creating disposal challenges

    4. Sustainability Assessment:

      • Coal excels in efficiency and operational stability

      • Biomass excels in renewability, carbon footprint, and local availability

      • For India, biomass (rice husk) is more sustainable despite lower efficiency

  3. RECOMMENDATIONS FOR BIOMASS PLANT IMPROVEMENT:

    1. Immediate (Low Cost):

      • Reduce condenser pressure to 0.8 kg/cm² 5-7% efficiency gain

      • Pre-dry biomass to reduce moisture from 12% to 8% 3-4% gain

      • Optimize excess air in boiler 2-3% gain

    2. Medium Term (Moderate Investment):

      • Install air preheater and economizer 8-10% gain

      • Improve turbine isentropic efficiency 4-5% gain

      • Implement feedwater heating 3-4% gain

    3. Long Term (Major Investment):

      • Increase boiler pressure to 75 kg/cm² and temperature to 520°C

      • Consider cogeneration to utilize condenser waste heat

      • Explore biomass gasification + combined cycle (higher efficiency)

  4. FINAL VERDICT:

The parametric study confirms that the 6MW biomass plant has significant improvement potential, particularly through condenser pressure reduction and boiler temperature elevation. While the coal plant demonstrates superior thermodynamic performance, the biomass plant’s renewable nature, carbon neutrality, and utilization of agricultural

waste make it a more sustainable choice for India’s energy scenario. The exergetic efficiency gap of 12.87% between coal and biomass can be reduced to approximately 6-8% through the recommended improvements, making biomass a viable alternative for decentralized power generation in rice-producing regions.

CONCLUSION:

The exergy analysis of the 6MW biomass steam power plant at Varam Power Projects, Chilakapalem, reveals that the boiler and condenser are the primary sources of exergy destruction, contributing approximately 45% and 28% of total irreversibilities, respectively. The plant operates at a thermal efficiency of 12.39% and an exergetic efficiency of 19.13%, indicating a significant gap between energy input and useful work output. The boiler’s high exergy destruction is attributed to large temperature gradients during heat transfer and incomplete combustion of high-ash biomass fuels like rice husk. Condenser losses arise from heat

rejection to the environment. Improving these two components offers the greatest potential for enhancing overall plant performance

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