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7/29/2019 SE Mech Thermo II Chapter 2 Fuels and Combustion
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Fuels and Combustion
S. Y. B. Tech. Mech. Engg.
Fuels & Combustion
ME0207 SEM-IV Applied ThermodynamicsII
Applied ThermodynamicsII
S.Y. B. Tech.
ME0207 SEMIV
Mechanical Engineering
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Fuels and Combustion
S. Y. B. Tech. Mech. Engg.
Outline
Types of Fuels, Higher Calorific value and Lower Calorific value,
Calorimeters to measure the calorific values Bomb and
Boys calorimeters.
Calorific value at constant pressure and constant volume.
Combustion reactions- Mass and Volume basis,
Stoichiometric Air : Fuel ratio,
Exhaust Gas Analysis Orsat Apparatus and Gas Chromatography.
Actual A/F ratio, Excess Air supplied.
Gravimetric analysis and volumetric analysis.
ME0207 SEM-IV Applied ThermodynamicsII
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Introduction
Fuel : A Combustible Substance, containing Carbonas a mail constituent, which, on
proper burn ing, releases large amount of heat, that can be used for domestic
and industr ial purposes.
Combustion : The atoms of Carbon, Hydrogen, etc.combine with atoms ofOxygen,
and L iberate Heat at a Rapid Rate, due to Rearrangement Of Valence
Electrons, i.e. forming New Compounds.
HeatProductsOxygenFuels
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Classification of Fuels
Fuels
Primary Fuels Secondary Fuels
Natural Fuels Derived Fuels
LiquidSolid Gaseous
Crude
Oil
Wood,
Coal,
Lignite
Natural
Gas
LiquidSolid Gaseous
Petrol,
Kerosene,
Diesel
Coke,
Charcoal
Coal Gas,
Water Gas,
Bio Gas
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Fuels and Combustion
S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Liquid Fuels
Usage
Used extensively in Industrial Applications.
Examples
Furnace Oil
Light Diesel Oil
Petrol
Kerosene
Ethanol
LSHS (Low Sulphur Heavy Stock)
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Liquid FuelsProperties
A. Density : Ratio of the Fuel Mass to its Volume @ 15 C,
Unit :( kg / m3 )
Useful for determining Fuel Quantity And Quality.
B. Sp. Gravity : Ratio of the Weight of Oil Volume to the Weight of
Equal Water Volume@ given temperature.
Specific Gravity of Water = 1!!
Measured by using Hydrometer.
Fuel oil type LDO
(Light Diesel Oil)
Furnace oil LSHS
(Low Sulphur Heavy Stock)
Specific
Gravity
0.85-0.87 0.89-0.95 0.88-0.98
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Liquid FuelsProperties
C. Viscosity : Measure ofFuels Internal Resistance to Flow.
Most important Characteristic for Storage and Use.
asTemperature .
D. Flash Point : Lowest Temperature at which a fuel can be heated so that the
Vapour Gives off Flashes when an Open Flame passes over it.
Flash point ofFurnace Oil = 66oC
E. Pour Point : Lowest Temperature at which a fuel can Flow.
Indication of temperature at which Fuel can be Pumped.
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Liquid FuelsProperties
F. Sp. Heat : kJ needed to raise temperature of1 kg of Oil by 1 C.
Unit : ( kJ / kg. C )
Indication of the Energy Required to Heat thegiven Quantity
of Oil to a Desired Temperature.
G. Calorific Value : Total Quantity of Heat Liberated, when a Unit Mass of Fuel
Burns Completely.
Unit :( kJ / kg ).Solid & Liquid Fuels.
( kJ / m3 ).Gaseous Fuels
Useful for determining Fuel Quantity And Quality.
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Liquid FuelsProperties
H igher Calori fi c Value (HCV) :
Total Amount of Heat produced when Unit Mass of Fuel is Burnt
Completely, and the Products of Combustion are Cooled to Ambient
Temperature.
i.e. Vapour Content in the Products of Combustion are Fully Condensed.
IfC Carbon %, H Hydrogen %, O Oxygen %, S Sulphur % :
kg
kJS
OHCHCV 9160
8000,43,1000,35
100
1
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Liquid FuelsProperties
Lower Calor if ic Value (LCV) :
Total Amount of Heat produced when Unit Mass of Fuel is Burnt
Completely, and the Products of Combustion are Permitted to Escape.
kg
kJHHCVLCV 2460
100
9
IfC Carbon %, H Hydrogen %, O Oxygen %, S Sulphur % :
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Liquid FuelsProperties
H. Sulphur Content : Depends Largely on Source of Crude Oil and Less on
the Refining Process.
Furnace Oil : 24 % Sulphur
Sulphuric Acid Corrosion! !
I. Ash Content : Inorganic Materials in Fuels.
Typically, 0.030.07 %.
Corrosion ofBurner Tips and Materials / Equipments
Damage@ High Temperatures.
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Liquid FuelsProperties
J. Carbon Residue : Tendency of Oil to Deposit a Carbonaceous Solid Residue
on a Hot Surface.
Residual Oil :> 1 % Carbon Residue
K. Water Content : Normally Low inFurnace Oil( < 1 % @ Refinery).
Available in Free / Emulsified Form
Can Damage Furnace Surface andImpact Flame.
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PropertiesFuel Oils
Furnace Oil L.S.H.S L.D.ODensity (Approx. g/cc at 15 C) 0.89-0.95 0.88-0.98 0.85-0.87
Flash Point (C) 66 93 66
Pour Point (C) 20 72 18
HCV (MJ/kg) 43.95 44.34 44.8
Sediment, % Wt. Max. 0.25 0.25 0.1
Sulphur Total, % Wt. Max. < 4.0 < 0.5 < 1.8
Water Content, % Vol. Max. 1.0 1.0 0.25
Ash, % Wt. Max. 0.1 0.1 0.02
Typical Specifications of Fuel Oils :
(Adapted From Thermax India Ltd.)
Liquid FuelsProperties
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Solid Fuels
Solid Fuels
Anthracite Bituminous Lignite
Hard,
Geologically the Oldest
Soft Coal,
Geologically the Youngest
SubClassif ication : 1. SemiAnthracite,
2. SemiBituminous,
3. SubBituminous, etc.
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Solid FuelsProperties
Physical Properties : Calorific Values (HCV / LCV).
Moisture Content.
Volatile Matter.
Ash Content.
Chemical Properties : Chemical Contents of :
Carbon,
Hydrogen,
Oxygen,
Sulphur.
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Solid FuelsProperties
Higher Calorific Values :
Parameter Lignite
(Dry Basis)
Indian
Coal
Indonesian
Coal
South African
Coal
HCV (MJ/kg) 18.84 16.74 21.0 25.1
A. Moisture Content : % of Moisture in Fuel( < 0.510 % ).
Heating Valueof Fuel.
Results in Weight Loss from Heated and then Cooled
Powdered Raw Coal.
B. Fixed Carbon : Fixed Carbon = 100( Moisture + Volatile Matter + Ash )
Carbon + (H2, O2, S,N2 Residues).
Responsible for Heat Generation during Combustion.
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C. Volatile Matter : Methane (CH3), Hydrocarbons (HC), Hydrogen (H2),
Carbon Monoxide (CO), etc.
Typically 2535 %.
Easy Ignition with Volatile Matter. Results in Weight Loss from Heated and then Cooled
Crushed Coal.
Solid FuelsProperties
D. Ash Content : Impuritythat will NOT Burn.
Typically 540 %.
Important for Design of Furnaces.
Ash Residue after Combustion.
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
1. Proximate Analysis : Determines only Fixed Carbon, Volatile Matter,
Moisture and Ash.
Useful to Find HCV.
Simple Analysis Equipment.
2. Ultimate Analysis : Determines all ofCoal Component :
i.e. C,H2, O2, S, and others.
Useful for Furnace Design
(Flame Temp + Flue Duct Design)
Laboratory Analysis.
Solid FuelsAnalysis
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Solid FuelsComposition
Fuel Moisture in
Dried Sample
(ppm)
C
(%)
H
(%)
N
(%)
O
(%)
Calorific Value
(MJ / kg)
Wood 25 50 6 0.5 43.5 16.7 18.8
Peat 25 57 5.7 2 35.3 17.3 22.6
Lignite 20 67 5 1.5 20.6 27.2 29.7
Bituminous 4 83 5 2 10 33.5 35.6
Anthracite 1.5 93 3 0.7 3 36.2 36.5
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Gaseous Fuels
Advantages of Gaseous Fuels :
Least amount of Handling.
Simplest Burners Systems.
Least Maintenance.
Environmental Benefits : Lowest Emissions.
Gaseous Fuels
Naturally Found From Solid Fuel From Petroleum
Natural Gas,
Methane, etc.
LPG, Refinery Gas,
Oil Gasification
From Coal,
From Biomass,
From Industrial Wastes
From ChemicalFermentation
Processes
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Gaseous FuelsProperties
LPG : Propane + Butane +Unsaturates,
Lighter C2andHeavier C5Fractions
LPG Vapour is Denser than Air! !
Safety Issues : Leaking Gases can flow to Long Distances.
LNG : Methane (CH4)of95 %.
Remaining 5 % (Ethane + Propane + Butane + Pentane + Nitrogen +
Carbon Dioxide + other gases.
High Calorific Value.
No requirement for Storage Facility.
No Sulphur Content.
Readily mixes with Air without Smoke / Soot.
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Fuel Gas RelativeDensity
Higher HeatingValue
(MJ / Nm3)
Air / FuelRatio
(m3/ m3 )
FlameTemp.
(oC)
Flamespeed
(m / sec)
Natural Gas 0.6 39.14 10 1954 0.290
Propane 1.52 93.0 25 1967 0.460
Butane 1.96 119.3 32 1973 0.870
Fuel Oil Coal Natural GasCarbon 84 41.11 74
Hydrogen 12 2.76 25
Sulphur 3 0.41 -Oxygen 1 9.89 Trace
Nitrogen Trace 1.22 0.75
Ash Trace 38.63 -
Water Trace 5.98 -
Gaseous FuelsProperties & Comparison
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Liquid Fuels V/s. Solid Fuels
Advantages ofLiquid Fuels over Solid Fuels :
1. Higher Calorific Values.
2. Economy in Space.
3. Cleanliness of the Surrounding.
4. Easy Control in Combustion.
5. Elimination of Wear & Tear of Grate.
6. Easy Handling and Supply.
7. Easy Starting and Stopping.
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Gaseous Fuels V/s. Solid Fuels
Advantages ofGaseous Fuels over Solid Fuels :
1. Easy Production and Distribution.
2. Remote and Easy Control on Combustion.
3. Easy in Smoke and Ash Disposal.
4. Cleanliness.
5. Gasification helps for Reuse of Low Grade Solid Fuels.
6. Complete Combustion without Pollution is possible.
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Calorimeters
Calorimeter : Device used for Calorimetry,
i.e. Science ofMeasuring The Heat ofChemical reaction (or Physical
Changes) as well as Heat Capacity.
Calorimeter: Calor(Latin) meaningHeat!!
Simple Calorimeter : Thermometer attached to an Insulated Container.
Enthalpy Change,Hper mole of A
in a Reaction between A and B
Initial and Final Temperatures,T.
TCmQEnergy p ,
molesofNo
QmoleperH
.
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Bomb Calorimeter
The BOMB inside is a Steel
Vessel, capable of withstanding
High Pr. ( @ 100 atm ) of the inside
gas.
It should also capable to withstand
the Explosive Forces of the
Burning Reagents after Bombing.
BOMB Rigid Vessel.
Const. Vol. Calorimeter! !
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Principle :
A Known Mass of Fuel is Burnt.
The Quantity of Heat Liberated is
Absorbed in Water.
Thus, Quantity of Heat Produced
per Unit Mass is calculated.
Bomb Calorimeter
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Bomb Calorimeter
Heat Balance :
Heat given by the Fuel due to Combustion
+ Heat given by the Combustion of the
Fuse Wire
= Heat absorbed by the Water + Bomb
Calorimeter.
TCmmCVmHCVm Pcffwf )()()(
C i
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Bomb Calorimeter
TCmmCVmHCVm Pcffwf )()()(
FuelofMassmf
WireFuseofMassmfw
rCalorimeteinWaterofMassmw
rCalorimeteofEquivalentWatermc
RiseeTemperaturWaterT
FuelofValueCalorificHigherHCV
WireFuseofValueCalorificCV
f
fwPcf
m
CVmTCmmHCV
)()(
F l d C b i
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Bomb Calorimeter
Water Equivalent of Calorimeter :
Burning a Fuel ofKnown Calorific Value.
Standard Fuels :
1. Benzoic Acid (CV = 111.2 MJ / kg)
2. Naphthalene (CV = 170.32 MJ / kg)
To avoid Radiation Losses;
Tis Restricted to 3 C.
F l d C b ti
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Boys Gas Calorimeter
Used to measure CV of Gaseous Fuel.
Gaseous Fuel + Air mixture flows down from
the Top of the Container .
Gas Supply with
Flow Measurement
Cooling Coil
Condensate Flow
Cooling Water InCooling Water Out
Burner
Container
Air
Steamin the exhaust,due to the Combustion
of H2, Condenses over the Cooling Coils.
Outer Casing of the Container is Insulated,
to avoid Radiation Losses.
F l d C b ti
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Boys Gas Calorimeter
].[
3
g' mconsumed,GasofVol.V ].[kg,circulatedWaterofMassmw
].[. C,circulatedWaterofRiseTempTw
][ waterofcm
,AtmosphereaboveGasofr.Phw
][ waterofcmPr.Barometerhb
].[ Csupplied,GasofTemp.Tg'
760
6.1315.273'
w
b
g
gg
hh
TVV
.@ NTP
F l d C b ti
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Boys Gas Calorimeter
760
6.1315.273'
w
b
g
gg
hh
TVV
g
wpw
V
TCmHCV
wpwg TCmHCVV
Energy Balance :
F els and Comb stion
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Principles of Combustion
Combustion : Rapid Oxidation of a Fuel!!
Carbon : (a) CO2
(b) CO
Complete Combustion : Total Oxidation of Fuel
i.e. Adequate Supply of Oxygen required.
Air :20.9% Oxygen, 79% Nitrogen + others (by vol.)
Nitrogen : (a) Combustion Efficiency.
(b) Forms NOx@ High Temperatures.
Heat Production
Fuels and Combustion
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
3 Tsfor Combustion Optimization :
1T) Temperature
2T) Turbulence
3T) Time
Principles of Combustion
Water Vapor :
1. ByProduct of burning Fuel having H2.
2. Heat from the Flue Gases.
Oxygen :Key To Combustion!!
Fuels and Combustion
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Principles of Combustion
Stoichiometric Air : Fuel Ratio :Perfect Amount ofOxygen
for Complete Combustion of Fuel!!
Rich Mixture :Excess Fuel!!
Lean Mixture :Excess Air (or Oxygen)!! O2in Exhaust!!
CO in Exhaust!!
Fuels and Combustion
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Combustion
C, H2, S + O Combustion + Heat
22 COOC
A. Carbon Carbon Dioxide :
)44()32()12( kgkgkg .Mole. Wt. basis
2COofkgOofkg3
8Cofkg1
3
112
CO2OC 22
B. Carbon Carbon Monoxide :
)56()32()24( kgkgkg .Mole. Wt. basis
COofkgOofkg3
4Cofkg1
3
72
Fuels and Combustion
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Combustion
222 CO2OCO
C. Carbon Monoxide Carbon Dioxide :
)88()32()56( kgkgkg .Mole. Wt. basis
2COofkgOofkg7
4
COofkg1 7
112
O2HOH 2222
D. Hydrogen Water / Steam :
)36()32()4( kgkgkg .Mole. Wt. basis
OHOofkgH 222 ofkg98ofkg1
Fuels and Combustion
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Combustion
22 OSOS
E. Sulphur Sulphur Dioxide :
)64()32()32( kgkgkg .Mole. Wt. basis
222 ofkg21ofkg1 SOOofkgH
Fuels and Combustion
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Combustion of Hydrocarbon Fuels
OHqCOpOyHCx nn 22222
.where x, y, p, & qare Const.
OHnCOnOn
HC nn 22222 12
13
Solving for x, y, p,& qin terms ofn :
OHCOOHC 2222210 11102
130
e.g. for n= 10 :
OHCOOHC 2222210 2220312
Fuels and Combustion
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Stoichiometric Combustion
Oxygenper kg of Fuel,
for Complete Combustion :
S
OHC
88
2
8
100
1
Air contains 23 %by mass ofOxygen.
kg of Air required, per kg of Fuel,
for Complete Combustion : 23
100
88
2
8
100
1
S
OHC
S
OHC
88
2
8
23
1
Fuels and Combustion
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Orsat Apparatus
Used for Volumetric Analysis ofDry Flue Gases.
3 Flasks for the Selective
Absorption ofCO2, O2 and CO.
May have 4th Flasks with
Calcium Chloride / Silica Gel to
make the Incoming Flue Gases
Completely Dr y.
% N2 = 100(% CO2+ % O2 + % CO)
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Orsat Apparatus
F lask A Solution :NaOH+ KOH
1 part of KOH
+ 2 parts of Water, by wt.
CO2 Absorption.
F lask B Solution :Pyrogalic Acid
5 gm Pyrogalic Acid in 15 cc Water
+ 120 gm KOH in 80 cc Water.
O2 Absorption.
F lask C Solution :Cuprous Chlor ide
CuO dissolvedin 20 times by wt.
ofConc. HCLtill Colourless.
CO Absorption.
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Orsat Apparatus
Initially, all 3 Valves, x, y& zClosed.
3 Way Valve is Open. Aspirator Bottle moved
on to fill the Eudiometer till ZERO Markw.r.t.
Outside Water Level.Valves
Flue Gas
Inlet
3Way Valve
Aspirator
Bottle
Eudiometer
3 Way Valve is Closed. Valve xfor Flask AOpened. Aspirator Bottle moved up-and-down
for Complete Absorption ofCO2 in the Flask.
Aspirator Bottle lowered for Flue Gases to come
back to Eudiometer. Valve xfor Flask AClosed.
Aspirator Bottle set such that Eudiometer Mark
matcheswith Water Level.
hforEudiometer Mark % CO2.
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ue s d Co bus o
S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Orsat Apparatus
Process repeated in Flask B for O2and Flask Cfor CO.
Remainder % N2.
Valves
Flue Gas
Inlet
3Way Valve
Aspirator
Bottle
Eudiometer
Order for Selective Absorption : 1. CO2.
2. O2.
3. CO
Order for Selective Absorption
type of Absorber implemented.
Eudiometer Capacity = 100 cc
Water Bath : To maintain Temp. Const.
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Orsat Apparatus
Fuels and Combustion
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Example 1A coal sample has a following composition by mass :
C = 90 %, H = 3 %, S = 1 %, O = 2 %, N = 2 %, and the remaining is ash.Find the HCV and LCV of the fuel.
kg
kJ
SO
HCHCV
1.35524
6.915.3932500,31
191608
23000,43,190000,35
100
1
91608
000,43,1000,35100
1
.ANS
Fuels and Combustion
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Example 1.cntd.
kg
kJ
HHCVLCV
9.34859
24603100
91.35524
2460100
9
.ANS
Fuels and Combustion
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Example 2The following observations were made during the test for finding the lower calorific value
of a solid fuel with the help of Bomb Calorimeter :Mass of fuel in crucible = 0.78 gm.
Mass of fuse wire = 0.02 gm.
CV of fuse wire = 6500 kJ / kg.
Mass of water in the calorimeter = 1.88 kg.
Water equivalent of calorimeter = 0.37 kg.
Temp. rise = 3 C.Assume the fuel contains 90 % Carbon, 4 % Hydrogen, the rest being ash.
kg
kJHCV
HCV
HCV
TCmmCVmHCVm Pcffwf
98.36066
325.2187.4100013078.0
3187.437.088.16500
1000
02.0
1000
78.0
)()()(
.ANS
Fuels and Combustion
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
kg
kJ
HHCVLCV
38.35181
24604100
998.36066
2460100
9
.ANS
Example 2.cntd.
Fuels and Combustion
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
Example 3The following observations were made during the test for finding the calorific value of a
gaseous fuel with the help of Boys Gas Calorimeter :Gas burnt = 60 lit.
Gas Pressure = 4 cm of water above atm.
Barometer reading = 750 mm of Hg.
Temp. of gas = 30 C.
Water circulated through the calorimeter = 20 kg.
Temp. rise for water = 10 C.Condensate collected during the test = 60 gms.
Find the HCV and LCV of the fuel at NTP.
3
'
05356.0
.56.53
760
6.13
40750
)3015.273(
15.27360760
6.1315.273
m
lit
hh
TVV
w
b
g
gg
Fuels and Combustion
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S. Y. B. Tech. Mech. Engg.ME0207 SEM-IV Applied ThermodynamicsII
kg
NTP@gasofmperformedCondensate3
12.1
05356.01
100060
Example 3.cntd.
NTPm
kJ
V
TCm
HCVg
wpw
@15634
0535.0
10418720
3.ANS
kg
kJ
vapourby waterawaycarriedHeatHCVLCV
8.12878
246012.115634
.ANS
Fuels and Combustion
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