On the thermodynamics of cogeneration

Cogeneration of various energy forms in a single piece of equipment has the potential of saving primary energy in comparison to separate generation. The amount of energy saving depends on the thermodynamic parameters of the systems to be compared and can be presented in a closed formula. For the particular case of cogeneration in a steam turbine a thorough thermodynamic analysis on the basis of exergy losses reveals the reasons for the higher efficiency. It is due to the facts that on producing the useful heat a transfer of this heat over the temperature difference between the heat intake of the cycle and the temperature of the heat demand is replaced by a power cycle and that separate power production is avoided altogether. This leads to a rational allocation of primary energy and in turn of emissions to the coupled energy forms.