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. T he amount of energy saving depends on the thermodynamic parameters of the s ystems to be compared and can be presented in a closed formula. For the par ticular case of cogeneration in a steam turbine a thorough thermodynamic an alysis on the basis of exergy losses reveals the reasons For the higher eff iciency. It is due to the facts that on producing the useful heat e a trans fer 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 cy cle and that separate power production is avoided altogether. This leads to a rational allocation of primary energy and in turn of emissions to the co upled energy forms. (C) 2000 Editions scientifiques et medicales Elsevier S AS.