Beyond thermoeconomics? The concept of Extended Exergy Accounting and its application to the analysis and design of thermal systems

Abstract

This paper presents a novel approach to the evaluation of energy conversion processes and systems, based on an extended representation of their exergy flow diagram. This approach is a systematic attempt to integrate into a unified coherent formalism both Cumulative Exergy Consumption and Thermo-economic methods, and constitutes a generalisation of both, in that its framework allows for a direct quantitative comparison of non-energetic quantities like labour and environmental impact (hence the apposition ‘Extended’). A critical examination of the existing state-of-the-art of energy- and exergy analysis methods and paradigms indicates that an extension of the existing ‘Design and Optimisation’ procedures to include explicitly ‘non-energetic externalities’ is indeed feasible. It appears that it can indeed be successfully argued that some of the issues that are difficult to address with a purely monetary theory of value can be resolved by Extended Exergy Accounting (‘EEA’ in the following) methods without introducing arbitrary assumptions external to the theory. In this respect, EEA can be regarded as a natural development of the economic theory of production of commodities, which it extends by properly accounting for the unavoidable energy dissipation in the productive chain. While a systematic description of the EEA theory is discussed in previous work by the same author, the present paper aims at a more specific target, and presents a formal representation of the application of EEA to a cogenerating plant based on a gas turbine process. It is shown that the solution indeed leads to an ‘optimal’ design, and that its formalism embeds even extended Thermo-economic formulations.