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Int. J. Engg. Res. & Sci. & Tech. 2014 Arunesh Kumar et al., 2014

VARIATION OF BOILER EFFICIENCY WITHRESPECT TO BOILER LOADS BY INCREASING

OF EXCESS AIR

Arunesh Kumar1*, Abhishek Arya2 and Rahul Kumar Singh3

The main motive of this study is to identify maximum energy loss areas in any thermal powerstations and generate a plan to reduce them using energy and exergy analysis as the tools. Theenergy sources are decreasing down day by day around the world due to the growing demandand sometimes due to ageing of machinery. Most of the power plants are designed by theenergetic performance criteria based not only on the first law of thermodynamics, but the realuseful energy loss cannot be justified by the fist law of thermodynamics, because it does notdifferentiate between the quality and quantity of energy. The main objective of this paper is tosurvey the technical options for waste heat capture and consider in greater depth of Waste heatcapture method through the use of real life examples. Present study deals with the comparisonof energy and exergy analysis of thermal power plants stimulated by coal. Our national electricityrequirement is about 2100 MW against 1615 MW supply; this is evident of about 21% deficit interms of power requirements. In view of this situation, greater need of efficiency improvement ofa thermal power plants

Keywords: Energy, Exergy, Heat balance sheet, Thermal Power Station, Fuel

*Corresponding Author: Arunesh Kumar [email protected]

INTRODUCTIONPower plant is assembly of systems or

subsystems to generate electricity. Power plant

generates the electricity result of combustion of

fuel into mechanical work and is thermal energy.

The availability of electricity and its per capita

consumption shows index of national standard

of living in the present day and flourishing power

1 M.Tech Scholar (Thermal Engineering), Department of Mechanical Engineering, SCOPE Engineering College, Bhopal, India.2 Assistant Professor, Scholar, Department of Mechanical Engineering, SCOPE Engineering College, Bhopal, India.3 M.Tech Scholar, Department of Mechanical Engineering, SCOPE Engineering College, Bhopal, India.

Int. J. Engg. Res. & Sci. & Tech. 2014

ISSN 2319-5991 www.ijerst.comVol. 3, No. 4, November 2014

© 2014 IJERST. All Rights Reserved

Research Paper

generation. The role of efficiency monitoring lies

in maximizing generation from power plants. It

enhances energy efficiency of the power plant. In

order to keep maximum output from a given input,

the units must run at the maximum possible

efficiency. Power sector is one of the key sectors

contributing significantly to the growth of country’s

economy. Power sector needs a more useful role

308



to be played in defining, formulating and

implementing the research projects with close

involvement of all utilities like solar energy and

other various non conventional sources. The

increase in energy consumption, particularly in

the past several decades, has raised fears of

exhausting the globes reserves of coal, petroleum

and other resources in the future. The huge

consumption of fossil fuels has caused visible

damage to the environment in various forms.

Every year human activity dumps roughly 8 billion

metric tons of carbon into the atmosphere, 6.5

billion tons from fossil fuels and 1.5 billion from

deforestation At present India is sixth largest

country in the world in electricity generation,

having aggregate capacity of 177 GWs out of

which 65% is from thermal, 21% from hydro, 3%

from nuclear and the rest about 11% is from

renewable energy sources. Although over the

years, Indian power sector has experienced a five-

time increased in its installed capacity—a jump

from 30,000 MW in 1981 to over 176,990.40 MW

by 30 June 2014 but still there is a huge gap in

generation and demand in India hence need to

be establish more generation plants preferably

to be come f rom renewable sources by

governmental as well as various private

participation.

Process of Thermal Power Plants

The whole process comprises of generating heat

energy in the boiler and then converting heat

energy generated in the boiler into mechanical

energy in the turbine and further converting this

mechanical energy generated in the turbine into

electrical energy in the alternator. Coal will be

used as fuel in the boiler. The combustion of the

fuel generates the heat energy in the boiler. The

heat energy transfer to heat transfer area provided

in the different area like (bed coils, water wall,

steam drawn /mud drum economizer super

heater, air pre heater. This will be transferred to

the water which will pass through and steam is

generated and this steam will be further

superheated in the super heater so that dry

superheated steam will be generated. This steam

will be fed into the turbine and this steam expands

in the turbine and generates mechanical energy

will be converted in to electrical energy. The whole

process is comprises in Figure 1.

Figure 1: General Layout of Thermal Power

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Aim

The main analysis of the study is to find out those

areas where energy losses are occurring

maximum and modified them for efficient and

effective improvement in thermal power station.

Objectives

The object to satisfy this are

• To conduct energy calculation of the overall

plant and determine the efficiencies and energy

losses of all the major components on the

power station.

• Select and modified the areas where energy

losses are being experienced.

• Determine the costs and payback periods for

the new technologies suggested for efficiency

improvements.

Types of Fuel Used in Boiler

There are many type of fuel used in boiler to

generate necessary heat (Table 1).

of the it’s thermal energy is converted into

mechanical energy which is further used forgeneration electric power. The steam coming outof the steam turbine is condensed in thecondenser and condensate is supplied back tothe boiler with the help of the feed pump and cycleis repeated.

The function of the boiler is to generate thesteam .The function of condenser is to condensethe steam coming out of steam turbine at lowpressure. The function of the steam turbine is toconvert part of heat energy of steam intomechanical energy. The function of feed pump isto raise the pressure of the condensate from thecondenser pressure (0.015 bar ) to boilerpressure (200 bar). The other components likeeconomizer, super heater and steam feedheaters are used in the primary circuit to increasethe overall efficiency of the thermal power plant.

Fuel GCV(Kcal/kg)

Coal

a) Bituminous 4,500 to 6,500

b) Anthracite 6,500 to 7,700

c) Lignite 3,500 to 4500

Furnace oil 10,500 to 11,700

Natural Gas 8,200 to 8,600 KCal/Nm3

Agro fuels 3,100 to 4,500

Kerosene 11,100 11,100

LPG 11,600 to 11,700 KCal/Kg

Working of Thermal Power Plant

Steam is generated in the boiler of the thermal

power plant using the heat of the fuel burned in

the combustion chamber. The steam generated

is passed through steam turbine where the part

Figure 2: working of Thermal Power Plant

HISTORICAL PROSPECTIVEThe scenario of energy in thermal power plant

are discussed that fossil fuels contribute 80%,

renewable Energy resources contribute 14% and

nuclear 6% of world annual energy use. These

numbers will soon change as the world’s

populat ion grows, energy demand rises,

inexpensive oil and gas deplete, global warming.

Effects continue to rise and urban pollution

worsens the living conditions. The development

Table 1: Various Types of Fuels Used in Boiler

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Table 2: Heat Balance Sheet

Steam GrossS.No. Bioler Generation Calorific Boiler Fuel

Load TPH Value Efficiency ConsumptionKcal/kg. kg/s

1 60 81 3300 80.6 19.44 4.58 0 4.58 0

2 65 87.75 3300 81.7 20.77 4.58 0 4.58 0

3 70 94.5 3300 82.3 22.21 4.58 0 4.58 0

Theoreticalair

Requirementk g

Excessair

req.@0%

Total airreq.@0%excess

air

oxygen@0%

excessairk g

Table 3: Standard Values Table 4: Efficiency Of Boiler With DifferentBoiler Loads And 0% Excess Air

Grass calorific value of coal 3300 kcal/kg

Feed water temperature 180oc

% of oxygen in flue gases 5.5

% of co2 in flue gases 11

Flue gas temperature 1400C

% Hydrogen in fuel 1.2

Ambient air temperature 350C

Humidity of air 0.018 kg/kg of dry air

Theoretical air required for boiler 4.58 kg/kg of coal

Actual mass of air supplied 5.95 kg/kg of coal

Specific heat of superheated steam 0.45k cal/kg,k

Boiler pressure 96 bar

Steam temperature 3800c

Enthalpy of steam 3060 kj/kg

Enthalpy of feed water temperature 763.22kj/kg

Table 5: Efficiency of Boiler With Different Boiler Loads and 20% Excess Air



1 60 81 3300 80.12 19.44 4.58 0.91 5.49 0.209

2 65 87.75 3300 81.2 20.77 4.58 0.91 5.49 0.209

3 70 94.5 3300 81.82 22.21 4.58 0.91 5.49 0.209

Theoreticalair

Requirementk g

Excessair

req.@0%


air

oxygen@0%

excessairk g

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1 60 81 3300 79.82 19.44 4.58 1.37 5.95 0.31

2 65 87.75 3300 81.02 20.77 4.58 1.37 5.95 0.31

3 70 94.5 3300 81.62 22.21 4.58 1.37 5.95 0.31

Theoreticalair

Requirementk g

Excessair

req.@0%


air

oxygen@0%

excessairk g




1 60 81 3300 79.52 19.44 4.58 1.83 6.41 0.42

2 65 87.75 3300 80.72 20.77 4.58 1.83 6.41 0.42

3 70 94.5 3300 81.32 22.21 4.58 1.83 6.41 0.42

Theoreticalair

Requirementk g

Excessair

req.@0%


air

oxygen@0%

excessairk g

of alternative energy sources and devices willemerge more rapidly to address the world’senergy and Environmental situation. Thus, theestablishment of a sustainable energy Is one ofthe most pressing tasks of humanity? With theexhaustion of Fossil resources, the energyeconomy will change to a chemical and anElectrical base. Mahindra Lalwani and Mool Singhrevealed that, India consumes 7% of coal of theworld where as China, US, Japan and Rest ofthe world consumes 43%, 9%, 4% and 20%,respectively. 68% of World’s consumption of coalfor the generation of electricity. Coal-firedGeneration increases by an annual average of2.3%, making coal the second fastest-growing

source for electricity generation.

METHODOLOGY ANDFORMULAE USEDPerformance of Steam Generator

Evaporation Rate

The quantity of water evaporated into steam per

hour is called the evaporation rate. It is expressed

as kg of steam/h, or kg of steam/h/m2 of heating

surface, or kg of steam/h/m3 of furnace volume,

or kg of steam/kg of fuel fired.

Equivalent Evaporation

It is the equivalent of the evaporation of 1 kg of

water at 100oC to steam at 100oC, it requires

2256.9 kJ = 2260 kJ.

Factor of Evaporation

The ratio of actual heat absorption above feed

water temperature for transformation to steam

(wet, dry, or superheated), to the latent heat of

steam at atmospheric pressure (1.01325 bar) is

known as factor of evaporation.

Then equivalent evaporation = Actual

evaporation × Factor of evaporation

where

me = [ (h1 – hf ) / hfg ]× ms = F × ms

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Heat Losses in a Boiler Plant

1. Heat used to generate steam, Q= ms (h1– hf )

2. Heat lost to flue gases.

The flue gases contain dry products of

combustion and the steam generated due to the

combustion of hydrogen in the fuel.

Heat lost to dry flue gases,

Q1= mg cpg(Tg – Ta )

mg = Mass of gases formed per kg of fuel

cpg = Specific heat of gases

Tg = Temperature of gases, oC

Ta = Temperature of air entering the

combustion chamber of the boiler, oC

3. Heat carried by steam in flue gases-

Q2= ms1(hs1– hf1)

ms1 = Mass of steam formed per kg of fuel

due to combustion of H2 in fuel

hf1= Enthalpy of water at boiler house

temperature

hs1= Enthalpy of steam at the gas temperature

and at the partial pressure of the vapor in the flue

gas

4. Heat loss due to incomplete combustion

If carbon burns to CO instead of CO2 then it is

known as incomplete combustion.

1 kg of C releases 10,200 kJ/kg of heat if it

burns to CO whereas it releases 35,000 kJ/kg if

it burns to CO2. if the percentages of CO and

CO2 in flue gases by volume are known, then

Mass of C burnt to 2

CO CCO

CO CO

CO, CO2 = % by volume of CO and CO2 in

flue gases

C = fraction of carbon in 1 kg of fuel

Heat lost due to incomplete combustion of

carbon per kg of fuel,

32

35,000 10,200CO C

QCO CO

32

24,800 /CO C

Q ki kg of fuelCO CO

5. Heat lost due to unburnt fuel

Q4 = mf1× C.V

mf1= Mass of unburnt fuel per kg of fuel burnt

6. Heat unaccounted

Q6= Q– (Q1+Q2+Q3+Q4+Q5)

Q = mf ×C.V

= Heat released per kg of fuel

Boiler Trial and Heat Balance Sheet

There are three purposes of conducting the boiler

trial.

1. To determine and check the specified

generating capacity. Of the boiler when

working at full load conditions.

2. To determine the thermal efficiency of the

plant.

3. To draw up the heat balance sheet so that

suitable corrective measures may be taken

to improve the efficiency.

The following measurements should be

observed during the boiler trial.

1. The fuel supplied and its analysis.

2. Steam generated and its quality or superheat.

3. Flue gases formed from exhaust analysis.

4. Air inlet temperature and gases exhaust

temperature.

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5. Volumetric analysis of exhaust gases.

6. Mass of fuel left unburnt in ash.

7. Feed water temperature.

The Heat balance sheet is a symmetric

representation of heat released from burning of

fuel and heat distribution on minute, hour or per

kg of fuel basis.

RESULTS AND DISCUSSIONVardhman Group is a leading textile conglomerate

in India having a turnover of $1009 mn. Spanning

over 25 manufacturing facilities in five states

across India, the Group business portfolio

includes Yarn, Greige and Processed Fabric,

Sewing Thread, Acrylic Fiber and Alloy Steel.

Vardhman has evolved through history from a

small beginning in 1965 into a modern textile major

under the dynamic leadership of its chairman, S

P Oswal. His vision and insight has given

Vardhman an enviable position in the textile

industry. Under his leadership, Vardhman is

efficiently using resources to innovate, diversify,

integrate and build its diverse operations into a

dynamic modern enterprise.

Figure 3: Efficiency Versus Excess Air

Figure 4: Efficiency Vesus Excess Air



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steam generation also varies at different boiler

loads.

4. In this study show the variation of excess air

with fuel consumption and basically 40%

excess air use to reduce the loses and improve

boiler efficiency

5. In this study the calculation of efficiency based

on 20%, 30%, 40% excess air which gives the

excellent variation in boiler efficiency.

6. In this study we see that at minimum boiler

load the efficiency of boiler is minimum in range

which is show in graph and with the variation

of boiler load efficiency of boiler range also vary

which is clearly show in graph.

7. Boiler load and excess air variation help to

show the variation in the boiler efficiency. In

graph 1.1 we are see that at 0% excess air

the boiler efficiency range is maximum and at

40% excess air the boiler efficiency range is

minimum

REFERENCES1. Bejan (2002), “Fundamentals of Exergy

Analysis, Entropy Generation Minimization,

and the Generation of Flow Architecture”,

International Journal of Energy Research,

Vol. 26, No. 7, pp. 545-565.

2. Jin H, Ishida M, Kobayashi M and Nunokawa

M (1997), “Exergy Evaluation of Two Current

Advanced Power Plants: Supercritical

Steam Turbine and Combined Cycle”,

Trans. of ASME, Vol. 119, pp 250-256.

3. Naterer G F, Regulagadda P and Dincer I

(2010), “Exergy analysis of a thermal power

plant with measured boiler and turbine

Losses”, Applied Thermal Engineering, Vol.

30, pp. 970-976.

CONCLUSIONThe following conclusions have been drawn from

the experimental results:

This paper show the enervative ideas to

reduce losses of boiler and improve boiler

efficiency by using the variation of boiler load and

also percentage of excess air

We conclude the following point which points

show in paper and by using of heat balance sheet

clearly indicate unnecessary loss of heat. Give

some ideas to reduce unnecessary loses and

improve boiler efficiency.

1. This study shows the working process of

thermal power plants and indicates the

performance of boiler which can be improving

by using load variation.

2. This study show the performance of Vardhman

Yarns, Satlapur, Mandideep in which steam

generation has been done at a boiler pressure

of 96 bars and temperature approximately 380

degree Celsius.

3. In this study show the variation of fuel

consumption for various boiler loads and also


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4. Tekin T and Bayramoglu M (1998), “Exergy

Analysis of the Sugar Production Process

from Sugar Beets”, Int. J. of Energy

Research, Vol. 22, pp. 591-601.

5. Wiser Wendell H (2000), “Energy

Resources: Occurrence, Production,

Conversion, Use”, ISBM 0-387-98744-

4(Alk.Paper).

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Int. J. Engg. Res. & Sci. & Tech. 2014 Arunesh Kumar et al ... · PDF fileInt. J. Engg. Res. & Sci. & Tech. 2014 Arunesh Kumar et al., ... the overall efficiency of the thermal power