Fire Triangle - Produced Energy and Calorific Power

Produced Energy and Calorific Power

The quantity of energy produced by the reaction is higher than the quantity of energy requested to start it. The quantity of energy produced by the combustion is given in Joules (J); it is the enthalpy of the reaction. In the application domains (oven, burner, engine with internal combustion, fire-fighting), we use the notion of calorific power, what is basically the enthalpy of the chemical reaction per unit of weight of combustible or the obtained energy given by the combustion of one kilogram of combustible, expressed in kilojoules per kilogram (kJ/kg or kJ•kg-1). Combustion of hydrocarbon produces water in its vapor form. ; This water vapor contains huge amount of energy and this parameter has to be taken into account in a specific way to evaluate correctly the calorific power. We define: • Superior Calorific Power (SCP): « Quantity of energy produced during a complete combustion of a combustible unit, water vapor is said condensed and heat collected »2. • Inferior Calorific Power (ICP): « Quantity of energy produced during a complete combustion of a combustible unit, Water vapor is said non-condensed and heat not collected »3. Difference between ICP and SCP is the latent heat of water vaporization (Lv) multiplied by the quantity of produced vapor (m), what equals +/- 2 250 kJ•kg-1 (this value is influenced by pressure and temperature). We have the relation SCP = ICP + m•Lv.