Thermodynamic analysis of the main devices for thermal energy upgrading

Abstract

The problem of using low-level energies is a general one, in the light of the amount of thermal waste in numerous sectors. It is important both in the utilization of new energy sources available in thermal form (e.g., low-enthalpy geothermal and solar energies) and in the industrial field. The upgrading of low-level energy can be achieved either by means of absorption and resorption cycles or by heat transformers or by their combinations. Steam recompression is a particular case, but by no means a negligible one. Indeed, vent steam, for example, is probably one of the largest untapped sources of industrial waste energy. On the basis of a general definition of efficiency examined in a previous paper, in this note, the relative entropy production and the exergy efficiency of the various upgrading techniques are considered. Besides, the possibilities and the convenience of recompressing vent steam are examined.