Chemical exergy input

The coal exergy flow, calculated on an higher heating value (HHV) basis, is constant (525.7 MW) and clearly dominates the input stream. Most of the exergy is conserved in the gas phase, as can be seen from the respective values of gas chemical exergy flow, which reflect the cold gas efficiency to a certain extent. 

However, the energy of the chemical input and output is not so easily defined. At a simple level we could say that it is the chemical energy of the H2, O2, and H2O that is in question. The problem is that chemical energy is not simply defined - and terms such as enthalpy, Helmholtz function, and Gibbs free energy are used. In recent years the useful term exergy has become quite widely used, and the concept is particularly useful in high-temperature fuel cells. There are also older (but still useful) terms such as calorific value. 

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