12916392 Fuels and Combustion

8/14/2019 12916392 Fuels and Combustion

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Engineering ChemistryEngineering Chemistry

CODE NO: 07CODE NO: 07

I B.TECHI B.TECHMECHNICAL ENGINEERINGMECHNICAL ENGINEERING

Unit No: VIIIUnit No: VIII

Nos. of slides:Nos. of slides:


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Engineering/AppliedEngineering/Applied

ChemistryChemistryFUELS & COMBUSTIONFUELS & COMBUSTION

Term: 2008-09Term: 2008-09

Unit-VIII Power Point PresentationsUnit-VIII Power Point Presentations

Text Books:Text Books: A text book of Engineering ChemistryA text book of Engineering Chemistry

by Jain & Jain,by Jain & Jain, Chemistry of Engineering Materials byChemistry of Engineering Materials by

C.P. Murthy, C.V. Agarwal and A. NaiduC.P. Murthy, C.V. Agarwal and A. Naidu


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INDEXINDEX

UNIT-VIII PPTSUNIT-VIII PPTSSrl. Module as per Lecture PPTSrl. Module as per Lecture PPT

No. Session Planner No. Slide No.No. Session Planner No. Slide No.--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

1. L-1 L1-1 to L1-191. L-1 L1-1 to L1-19

2. L-2 L2-1 to L2-282. L-2 L2-1 to L2-28

3. L-3 L3-1 to L3-183. L-3 L3-1 to L3-18

4. L-4 L4-1 to L4-184. L-4 L4-1 to L4-18

5. L-5 L5-1 to L5-195. L-5 L5-1 to L5-196. L-6,7 L6,7-1 to L6,7-336. L-6,7 L6,7-1 to L6,7-33


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Fuels have beenFuels have been

classified according toclassified according to

their:their:

1. Occurrence (and preparation), and1. Occurrence (and preparation), and

2. The state of aggregation.2. The state of aggregation.


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According to the firstAccording to the first

classification, we have:classification, we have:

A. natural or primary fuels, which areA. natural or primary fuels, which arefound in nature as such e.g., wood,found in nature as such e.g., wood,peat, coal, petroleum, natural gas etc.peat, coal, petroleum, natural gas etc.

B. artificial or secondary fuels are thoseB. artificial or secondary fuels are thosewhich are prepared from the primarywhich are prepared from the primary

fuels. For example, charcoal, coke,fuels. For example, charcoal, coke,

kerosene, diesel, petrol, coal gas, oilkerosene, diesel, petrol, coal gas, oilgas, producer gas, blast furnace gas,gas, producer gas, blast furnace gas,etc.etc.


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The second classification isThe second classification is

based upon their state ofbased upon their state of

aggregation like:aggregation like: a) Solid fuels;a) Solid fuels;

b) Liquid fuels, andb) Liquid fuels, and c) Gaseous fuels.c) Gaseous fuels.


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Type of fuelType of fuel

Wood, peat, lignite,Wood, peat, lignite,dung, bituminous coaldung, bituminous coal

and anthraciteand anthracite

coal,Char coal, coke etc.coal,Char coal, coke etc.


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LiquidLiquid

Crude oil, Petrol,Crude oil, Petrol,diesel and variousdiesel and various

other fractions ofother fractions ofpetroleumpetroleum


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GaseousGaseous

Natural gasCoal gas, oilNatural gasCoal gas, oilgas, bio gas, water gasgas, bio gas, water gas

etc.etc.


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AnalysisAnalysisofof

coalcoal


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Proximate analysisProximate analysis


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Proximate analysis involvesProximate analysis involves

in the followingin the followingdeterminationsdeterminations::

MoistureMoisture

Volatile matterVolatile matter

AshAsh

Fixed carbonFixed carbon


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Moisture:Moisture:

Percentage of Moisture = __Percentage of Moisture = __Loss in weight__Loss in weight__X 100X 100

Weight of coal takenWeight of coal taken


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Volatile Matter:Volatile Matter:

The dried sample of coal left in theThe dried sample of coal left in thecrucible in (1) is then covered with acrucible in (1) is then covered with a

lid and placed in an electric furnacelid and placed in an electric furnace

or muffle furnace, maintained at 925or muffle furnace, maintained at 925+ 20C. The crucible is taken out of+ 20C. The crucible is taken out of

the oven after 7 minutes of heating.the oven after 7 minutes of heating.

The crucible is cooled first in air, thenThe crucible is cooled first in air, theninside desiccators and weighed again.inside desiccators and weighed again.

Loss in weight is reported as volatileLoss in weight is reported as volatile

matter on percentage-basis.matter on percentage-basis.


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Volatile Matter:Volatile Matter:

Percentage of volatile matter =Percentage of volatile matter = Loss_in _weight_due_to_removal_of_volatile_matterLoss_in _weight_due_to_removal_of_volatile_matter XX100100

Weight of coal sample takenWeight of coal sample taken


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AshAsh::

The residual coal in the crucible inThe residual coal in the crucible in

(2) is then heated without lid in a(2) is then heated without lid in a

muffle furnace at 700 + 50 C for muffle furnace at 700 + 50 C for

hour. The crucible is then taken out,hour. The crucible is then taken out,cooled first in air, then in desiccatorscooled first in air, then in desiccators

and weighed. Hearing, cooling andand weighed. Hearing, cooling and

weighing is repeated, till a constantweighing is repeated, till a constantweight is obtained. The residue isweight is obtained. The residue isreported as ash on percentage-basis.reported as ash on percentage-basis.


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AshAsh::

percentage of ash =percentage of ash =__Weight of ash left____Weight of ash left__X 100X 100



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4. Fixed carbon:4. Fixed carbon:

Percentage of fixed carbon =Percentage of fixed carbon =100 - % of (Moisture + Volatile matter +100 - % of (Moisture + Volatile matter +

ash)ash)


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Importance of proximateImportance of proximateanalysis:analysis:

Proximate analysis provides followingProximate analysis provides following

valuable informations in assessingvaluable informations in assessingthe quality of coal.the quality of coal.


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1.1. MoistureMoisture

Moisture is coal evaporates during theMoisture is coal evaporates during theburning of coal and it takes some of theburning of coal and it takes some of the

liberated heat in the form of latent heat ofliberated heat in the form of latent heat of

evaporation. Therefore, moisture lowersevaporation. Therefore, moisture lowersthe effective calorific value of coal.the effective calorific value of coal.

Moverover, it quenches the fire in theMoverover, it quenches the fire in the

furnace, hence, lesser, the moisturefurnace, hence, lesser, the moisture

content, better the quality of coal as acontent, better the quality of coal as afuel. However, presence of moisture, up tofuel. However, presence of moisture, up to

10%, produces a more uniform fuel-bed10%, produces a more uniform fuel-bed

and less of fly-ash.and less of fly-ash.


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2.2. Volatile matterVolatile matter::

a high volatile matter content means thata high volatile matter content means thata high proportion of fuel will distil over asa high proportion of fuel will distil over asgas or vapour, a large proportion of whichgas or vapour, a large proportion of which

escapes unburnt, So, higher volatileescapes unburnt, So, higher volatilecontent in coal s undesirable. A highcontent in coal s undesirable. A high

volatile matter containing coal burns withvolatile matter containing coal burns witha long flame, high smoke and has lowa long flame, high smoke and has low

calorific value. Hence, lesser the volatilecalorific value. Hence, lesser the volatilematter, better the rank of the coal.matter, better the rank of the coal.


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A high volatile matter content meansA high volatile matter content meansthat high-proportion of fuel will be distilledthat high-proportion of fuel will be distilled

and burned as a gas or vapour. Theand burned as a gas or vapour. The

volatile matter present in the coal ay bevolatile matter present in the coal ay be

as high as 50%. The volatile matteras high as 50%. The volatile matterpresent in the coal may be combustiblepresent in the coal may be combustible

gases or non-combustible gases. Thegases or non-combustible gases. The

presence of non-combustible gases ispresence of non-combustible gases is

always undesirable, as they do not add toalways undesirable, as they do not add to

heat value, but increases the volume ofheat value, but increases the volume of

the furnace required.the furnace required.


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Moverover, the volatile matter affects theMoverover, the volatile matter affects thefurnace volume and arrangement of heatingfurnace volume and arrangement of heatingspace. Thus, a furnace with small combustionspace. Thus, a furnace with small combustion

volume or of short flame travel is not suitable forvolume or of short flame travel is not suitable for

burning high volatile coals at high rates ofburning high volatile coals at high rates of

combustion, since a large proportion of volatilecombustion, since a large proportion of volatilematter will escape unburnt. On the other hand,matter will escape unburnt. On the other hand,

burning of low volatile coals necessarily requiresburning of low volatile coals necessarily requiresforced draught and the intensity of draughtforced draught and the intensity of draught

increases with the decrease in volatile matterincreases with the decrease in volatile matterpercentage.percentage.


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Volatile matter content is of specialVolatile matter content is of special

significance in coal gas manufacture and insignificance in coal gas manufacture and incarbonization plants, particularly when by-carbonization plants, particularly when by-product recovery is the main object. Thus,product recovery is the main object. Thus,

high-volatile matter containing coals do nothigh-volatile matter containing coals do notcake well; whereas medium-volatile mattercake well; whereas medium-volatile matter

content coals are capable of yielding hard andcontent coals are capable of yielding hard andstrong coke on carbonization. On the otherstrong coke on carbonization. On the other

hand, low-volatile matter containing coals dohand, low-volatile matter containing coals donot cake at all and consequently, they arenot cake at all and consequently, they are

totally unsuitable for coke making.totally unsuitable for coke making.


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3.3. Ash:Ash:

Ash is a useless, non-combustible matter,Ash is a useless, non-combustible matter,which reduces the calorific value of coal.which reduces the calorific value of coal.

Moverver, ash causes the hindrance toMoverver, ash causes the hindrance tothe flow of air and heat, thereby loweringthe flow of air and heat, thereby lowering

the temperature. Also, it often causesthe temperature. Also, it often causes

trouble during firing by forming clinkers,trouble during firing by forming clinkers,which block the interspaces of the grate,which block the interspaces of the grate,

on which coal is being burnt. This in-turnon which coal is being burnt. This in-turncauses obstruction to air supply; therebycauses obstruction to air supply; therebythe burning of coal becomes irregular.the burning of coal becomes irregular.


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3.3. Ash:Ash:

Hence, lower the ash content, better theHence, lower the ash content, better thequality of coal. The presence of ash alsoquality of coal. The presence of ash also

increases transporting, handling andincreases transporting, handling and

storage costs. It also involves additionalstorage costs. It also involves additionalcost in ash disposal. The presence ofcost in ash disposal. The presence of

ash also causes early wear of furnaceash also causes early wear of furnacewalls, burning of apparatus and feedingwalls, burning of apparatus and feeding

mechanism.mechanism.


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4.4. Fixed carbonFixed carbon::

Higher the percentage of fixed carbon,Higher the percentage of fixed carbon,greater is its calorific and better the qualitygreater is its calorific and better the qualitycoal. Greater the percentage of fixed carbon,coal. Greater the percentage of fixed carbon,smaller is the percentage of volatile matter.smaller is the percentage of volatile matter.This also represents the quantity of carbonThis also represents the quantity of carbon

that can be burnt by a primary current of airthat can be burnt by a primary current of airdrawn through the hot bed of a fuel. Hence,drawn through the hot bed of a fuel. Hence,high percentage of fixed carbon is desirable.high percentage of fixed carbon is desirable.The percentage of fixed carbon helps inThe percentage of fixed carbon helps in

designing the furnace and the shape of thedesigning the furnace and the shape of thefire-box, because it is the fixed carbon thatfire-box, because it is the fixed carbon thatburns in the solid state.burns in the solid state.


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Carbon and HydrogenCarbon and Hydrogen::

About 1 to 2 gram of accurately weighedAbout 1 to 2 gram of accurately weighed

coal sample is burnt in a current of oxygen incoal sample is burnt in a current of oxygen in

a combustion apparatus. C and H of the coala combustion apparatus. C and H of the coal

are converted into CO2 and H2Oare converted into CO2 and H2Orespectively. The gaseous products ofrespectively. The gaseous products ofcombustion are absorbed respectively incombustion are absorbed respectively in

KOH and CaCl2 tubes of known weights. TheKOH and CaCl2 tubes of known weights. The

increase in weights of these are thenincrease in weights of these are thendetermined.determined.


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Carbon and HydrogenCarbon and Hydrogen::

C + 02C + 02 CO2 : H2 + O2CO2 : H2 + O2 H2OH2O 2KOH + CO22KOH + CO2 K2CO3 + H2OK2CO3 + H2O

CaCl2 + 7 H2OCaCl2 + 7 H2O

CaCl2.7H2OCaCl2.7H2O


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Nitrogen:Nitrogen:

About 1 gram of accurately weighed powdered coalAbout 1 gram of accurately weighed powdered coalis heated with concentrated H2SO4 along withis heated with concentrated H2SO4 along withK2SO4 (catalyst) in a long-necked Kjeldahls flask.K2SO4 (catalyst) in a long-necked Kjeldahls flask.After the solution becomes clear, it is treated withAfter the solution becomes clear, it is treated withexcess of KOH and the liberated ammonia is distilledexcess of KOH and the liberated ammonia is distilledover and absorbed in a known volume of standardover and absorbed in a known volume of standardacid solution. The unused acid is then determined byacid solution. The unused acid is then determined byback titration with standard NaOH solution. From theback titration with standard NaOH solution. From thevolume of acid used by ammonia liberated,volume of acid used by ammonia liberated,

Th fTh t f


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The percentage ofThe percentage ofNitrogenNitrogen in coal isin coal is

calculated as follows:calculated as follows:

Percentage of N =Percentage of N = Volume of BaSo4 obtained X 32 X_100Volume of BaSo4 obtained X 32 X_100



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Sulphur:Sulphur:

Sulphur is determined from the washingsSulphur is determined from the washingsobtained from the known mass of coal, usedobtained from the known mass of coal, used

in bomb calorimeter for determination of ain bomb calorimeter for determination of acalorific value. During this determination, Scalorific value. During this determination, S

is converted in to Sulphate. The washingsis converted in to Sulphate. The washingsare treated with Barium chloride solution,are treated with Barium chloride solution,

when Barium sulphate is precipitated. Thiswhen Barium sulphate is precipitated. This

precipitate is filtered, washed and heated toprecipitate is filtered, washed and heated to

constant weight.constant weight.


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Sulphur:Sulphur:

Percentage of Sulphur =Percentage of Sulphur =__Weight of BaSO4 obtained X 32 X 100___Weight of BaSO4 obtained X 32 X 100_ Weight of coal sample taken in bomb X 233Weight of coal sample taken in bomb X 233


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4.Ash:4.Ash:

ash determination is carried out as inash determination is carried out as in

proximate analysis.proximate analysis.


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5.Oxygen:5.Oxygen:

It is obtained by difference.It is obtained by difference.

Percentage of Oxygen =Percentage of Oxygen =

100 percentage of (100 percentage of ( C + H + S + N +C + H + S + N +

AshAsh))


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Importance of ultimateImportance of ultimate

analysisanalysis::


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OxygenOxygen

Oxygen content decreases the calorific value ofOxygen content decreases the calorific value ofcoal. High oxygen-content coals are characterizedcoal. High oxygen-content coals are characterized

by high inherent moisture, low calorific value, andby high inherent moisture, low calorific value, and

low coking power. Moverover, oxygen is anlow coking power. Moverover, oxygen is an

combined form with hydrogen in coal and thus,combined form with hydrogen in coal and thus,hydrogen available for combustion is lesser thanhydrogen available for combustion is lesser thanactual one. An increase in 1% oxygen contentactual one. An increase in 1% oxygen content

decreases the calorific value by about 1.7% anddecreases the calorific value by about 1.7% and

hence, oxygen is undesirable. Thus, a good qualityhence, oxygen is undesirable. Thus, a good qualitycoal should have low percentage of oxygencoal should have low percentage of oxygen

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12916392 Fuels and Combustion