On the Dependencies of the Average Specific Heat Capacity of Flue Gas

The heat capacity of the flue gas is a basic property of a combustion process since it establishes the link between the energy balance and the combustion temperature. The dependencies of the average specific heat capacity on composition and temperature are thus of significance in interpreting differences in the achievable combustion temperature of different fuels. In this contribution, these dependencies are discussed and evaluated to provide simple correlations for use in practice. The correlations are applicable over the wide temperature range of 25…1600°C, while deviations at higher temperature are mainly due to dissociation of polyatomic gases. The provided correlations are also applicable if an oxygen carrier other than air is used, so that they are useful for a wide range of practical applications. This study also shows that the specific heat capacities of flue gases from different fuels are very similar, which is another reason – besides their similar "heat of oxidation" – why the adiabatic flame temperatures of different fuels are within a narrow range.