Higher and Lower Calorific Values

HIGHER AND LOWER CALORIFIC VALUES

1. Higher (or) Gross calorific value (GCV)

It is defined as the total amount of heat produced, when a unit quantity of the fuel is completely burnt and the products of 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. Thus, the latent heat of condensation of steam is also included in gross calorific value.

2. Lower (or) Net Calorific Value (NCV)

It is defined as the net heat produced, when a unit quantity of the fuel is completely burnt and the products of combustion are allowed to escape.

ஃ NCV = GCV - Latent heat of condensation of water vapour produced.

= GCV – Mass of hydrogen × 9 × Latent heat of condensation of water vapour.

1 part by weight of H₂ produces 9 parts by weight of H₂O as follows. The latent heat of steam is 587 cal/gm.

= GCV – 0.09H × 587

where

H = % of H₂  in the fuel.