Calorific Value

Detail about GCV and HCV

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 calorific values 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 H 2 + 1/2 O 2 → H 2 O 2H = 1/2O 2 = H 2 O 2parts = 16parts = 18parts 1parts = 8parts = 9parts Thus, NCV=GCV-0.09H*587 where H-% of Hydrogen in the Fuel 6 Image size 210x302

7. Theoretical Calculation Of Calorific Value Dulong’S Formula : 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 . 7

8. ANY DOUBT ??????? 8

9. Let us discuss few multiple choice questions Que1 .Agood fuel possess: Net calorific value Lower calorific value Higher calorific value Both (a) and (b) Ans (c) 9

10. Que2 . Latent heat of water vapours is 578 kcal/kg 587 kcal/kg 598 kcal/kg None of these Ans (b) 10

11. By Kishore thangapandi 11