The calorific value is the measurement of heat value or amount of energy produced and is either measured in gross calorific value or net calorific value.
Gross calorific value (GCV) or Higher Heating Value (HCV) is the amount of heat released by the complete combustion of a unit of fuel. It assumes all water vapour produced during combustion process is fully condensed.
Net Calorific Value (NCV) or lower heating value (LHV) or lower calorific value (LCV) is determined by subtracting the heat of vaporization of the water vapour from the higher heating value. It assumes water vapour leaves with the combustion products without fully being condensed. Fuel should be purchased based on NCV.
Conversion of GCV to NCV can be done with below formula :-
GCV = NCV + 584 ((9*H2%+M%)/100)
GCV, Gross calorific value of fuel, Kcal/Kg
NCV, Net Calorific Value of fuel, Kcal/Kg
H2%, Hydrogen Percentage by Weight in the fuel
M%, Moisture percentage by weight in the fuel
584,Latent heat corresponding to partial pressure of water vapor, Kcal/kg
Calculation of GCV of fuel:-
For calculation of GCV of fuel we need to analysis of fuel and get the constituent of fuel on weight basis. Based on the enthalpy of formation we may estimate calorific value of fuel.
C+ O2 —- CO2 + 8137.5Kcal/kg of carbon
H2 +.5O2—-H20 + 28905 Kcal/Kg of hydrogen
S +O2—SO2+ 2181 Kcal/kg of Sulphur
Consider a fuel contains carbon, hydrogen, Nitrogen, sulphur, oxygen as 86.5%, 12%, 0.9%, 0.2%, 0.4% respectively,
Then GCV of fuel can be calculated as follows :-
GCV of Fuel
GCV of Fuel
= ((8137.5*(86.5/100)+ (2181*(.2/100)) + (28905*2*((12/2)-(2*(.4/32)))/100)
=7038.9 + 4.3 + 3454 = 10497.2 Kcal/Kg
NCV of Fuel = GCV – (584 ((9*H2%+M%)/100)
=10430 – (584((9*12+0)/100))
= 10497.2- 630.7 = 9866.5 Kcal/kg
Impact of CO formation in Fuel:
In normal combustion Carbon is converted into CO2, but when there is deficit of oxygen CO is generated as below:-
C+ O2 —- CO2 + 8137.5 Kcal/kg of carbon
2C+O2—-2C0 +2430 Kcal/kg of carbon
This indicated loss of (8137.5 – 2430) = 5707.5 Kcal of heat per kg of carbon burnt in compared to carbon burnt with conversion as CO2. Hence CO generation must be avoided with calculated excess supply of oxygen for combustion.
Please find excel sheet for calculation of calorific value of fuel based on composition
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