Calorific value refers to the total heat released when a fuel is completely burned. There are two types of calorific values for fuels containing hydrogen: higher (gross) calorific value and lower (net) calorific value. The higher calorific value includes the latent heat released from condensation of water vapor in the combustion products, while the lower calorific value does not include this latent heat as it escapes with the gases. The lower calorific value can be calculated by subtracting the latent heat of vaporization of hydrogen from the gross calorific value. Dulong's formula can also be used to theoretically calculate the calorific value based on the fuel's carbon, hydrogen, oxygen,

1. Calorific value
GCV & HCV

2. 2
CALORIFIC VALUE
• It is defined as “the total amount of heat liberated
,when a unit mass of fuel is burnt completely”.
• It is used to identified “the Efficiency of a Fuel “.
•Wood has calorific value of 17 Kj/g.
•The amount of heat can be measured by the
following units :
calorie,
kilocalorie,
British Thermal Unit (B.T.U),
Centigrade Heat Unit (C.H.U).

3. 3
TYPES OF CALORIFIC VALUES
With fuels containing hydrogen, two calorificvalues are
distinguished,
Higher Or Gross Calorific Value
Lower Or Net Calorific Value

4. 4
Higher Calorific Value
• It is defined as
• “the total amount of heat liberated ,when a unit mass of fuel
is burnt completely
• The product of the combustion are cooled to room
temperature”.
• When a Fuel containing hydrogen is burnt, the hydrogen is
converted into steam.
• If the combustion products are cooled to room temperature
,the steam gets condensed into water and latent heat is
evolved.
• The latent heat of condensation of steam is also included in
gross calorific value.
• A good Fuel posses HCV

5. 5
Lower Calorific Value
• It is defined as
• “the net heat produced ,when a unit quantity of the fuel is
completely burnt
• The product of the combustion are allowed to escape”.
• Under normal working conditions, water vapours produced
during combustion are not condensed and escape as such
along with the hot gases.
• Hence lesser amount of heat is available, which is called
Lower or net calorific value.

6. Calculation of Net calorific value
Net calorific value=gross calorific value-latent heat of water vapours
Ncv=Gcv-weight of hydrogen x 9 x latent heat of water vapours
Latent heat of water vapours is 587 kcal/kg
Hydrogen in the fuel reacts with oxygen to give water
H2 + 1/2 O2 → H2O
2H = 1/2O2 = H2O
2parts = 16parts = 18parts
1parts = 8parts = 9parts
Thus,
NCV=GCV-0.09H*587
where H-% of Hydrogen in the Fuel
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7. Theoretical Calculation Of Calorific Value
Dulong’SFormula :
• If both hydrogen and oxygen are present, it may be
assumed that all the oxygen are already combined with 1/8
of its weight of hydrogen to form water.
• This fraction is then deducted from the hydrogen content of
the fuel in the calculation.
• Thus for a fuel containing carbon, hydrogen, oxygen and
sulphur, the calorific value of the fuel is given by DULONG
FORMULA
Calorific value =1/100[8080 C + 34500 {H − O/8 } +2240 S] kcal/kg
where C, H, O, S refer to % of carbon, hydrogen, oxygen and sulphur
respectively.
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8. ANY DOUBT ???????
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9. Let us discuss few multiple choice questions
• Que1.Agood fuel possess:
a. Net calorific value
b. Lower calorific value
c. Higher calorific value
d. Both (a) and (b)
• Ans (c)
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10. • Que2. Latent heat of water vapours is
a. 578 kcal/kg
b. 587 kcal/kg
c. 598 kcal/kg
d. None of these
• Ans (b)
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11. By
Kishore thangapandi
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