The future of exergy-based methods
George Tsatsaronis
Abstract
Exergy-based methods consist of at least an exergetic analysis, which can be combined with an economic analysis and a life cycle assessment in order to evaluate and improve energy-intensive processes. The author coined the term exergoeconomics in 1984 to replace the term thermoeconomics when exergy costing is used in the combination of an exergetic analysis with a cost analysis and to emphasize the role of exergy in the efforts to reduce the product cost. He also developed a general exergoeconomic methodology based on exergy-based variables and on appropriate definitions of the “product” and “fuel” for each component of an energy conversion system. These definitions and the application of exergoeconomics were generalized by A. Lazzaretto and the author in 2006 in an approach based on specific costs (SPECO approach). L. Meyer and the author coined the term exergoenvironmental analysis in 2009 for the combination of an exergy analysis with a life-cycle analysis when exergy is used to assign environmental impacts to streams. An exergoenvironmental analysis uses the methodological background of exergoeconomic methods. Starting in 2002, to reduce the limitations of the conventional exergy-based methods, and to facilitate system optimization, the author, and later in cooperation with T. Morosuk and co-workers at TU Berlin, developed the advanced exergy-based methods, which are based on the notion that the inefficiencies (exergy destruction and exergy loss), the costs, and the environmental impacts can be split into avoidable/unavoidable and endogenous/exogenous parts, to improve understanding of the formation process of inefficiencies, costs and environmental impacts within an energy conversion system,. As often happens, after their introduction, all the above terms and methods have been misused and misinterpreted by some other authors. This paper briefly reviews past contributions by the author and some other exergy practitioners and discusses future developments. It concludes, that the advanced exergy-based methods need further development to be generalized, and integrated and to reduce their subjectivity in addition to the efforts and time required for their application. Development of appropriate software and shortcut methods will facilitate their use by researchers and engineers in industry and the application of exergy-based methods in energy-intensive industrial processes for multiobjective optimization purposes.