Exergy: Its Potential and Limitations in Environmental Science and Technology

Abstract

New technologies, either renewables-based or not, are confronted with both economic and technical constraints. Their development takes advantage of considering the basic laws of economics and thermodynamics. With respect to the latter, the exergy concept pops up. Although its fundamentals, that is, the Second Law of Thermodynamics, were already established in the 1800s, it is only in the last years that the exergy concept has gained a more widespread interest in process analysis, typically employed to identify inefficiencies. However, exergy analysis today is implemented far beyond technical analysis; it is also employed in environmental, (thermo)economic, and even sustainability analysis of industrial systems. Because natural ecosystems are also subjected to the basic laws of thermodynamics, it is another subject of exergy analysis. After an introduction on the concept itself, this review focuses on the potential and limitations of the exergy conceptin (1) ecosystem analysis, utilized to describe maximum storage and maximum dissipation of energy flows (2); industrial system analysis: from single process analysis to complete process chain analysis (3); (thermo)economic analysis, with extended exergy accounting; and (4) environmental impact assessment throughout the whole life cycle with quantification of the resource intake and emission effects. Apart from technical system analysis, it proves that exergy as a tool in environmental impact analysis may be the most mature field of application, particularly with respect to resource and efficiency accounting, one of the major challenges in the development of sustainable technology. Far less mature is the exergy analysis of natural ecosystems and the coupling with economic analysis, where a lively debate is presently going on about the actual merits of an exergy-based approach.

Design of Sustainable Biofuel Processes and Supply Chains: Challenges and Opportunities

“…EcoLCA quantifies ecological resource consumption using a hierarchy of thermodynamic metrics including energy, industrial cumulative exergy consumption (ICEC), and ecological cumulative exergy consumption (ECEC), as well as mass flow. However, while exergy-based methods for thermodynamic aggregation of natural resource consumption may provide useful insights, these methods have their own limitations and are debated in the literature [113][114][115][116][117][118][119][120]. Research on combining the best advantages of Process LCA and EIO-LCA has also resulted in Hybrid LCA approaches, which combine the details of Process LCA with the greater completeness of EIOLCA [121,122].…”

Urban Planning for a Renewable Energy Future: Methodological Challenges and Opportunities from a Design Perspective

“…In order to assess these new research directions, a group of researchers has mapped the current state of affairs in an overview article [27]. They distinguish four paths of development: ecosystem analysis, industrial system analysis, (thermo-)economic analysis based on extended exergy accounting (EEA) and environmental impact assessment, for example through the Cumulative Exergy Extraction from the Natural Environment (CEENE) approach.…”

“…They distinguish four paths of development: ecosystem analysis, industrial system analysis, (thermo-)economic analysis based on extended exergy accounting (EEA) and environmental impact assessment, for example through the Cumulative Exergy Extraction from the Natural Environment (CEENE) approach. The latter category aims at reconciling LCA, which is mainly focused on harmful emissions, with exergy by considering those negative environmental impacts in terms of their related exergy effects or through the exergetic cost of abating the emissions in case ( [27], pp. 2228-2229).…”

“…The authors argue that industrial system analysis and environmental impact assessment based on exergy have indeed a mature potential, while ecosystem analysis and thermo-economics remain controversial. Techniques like EEA or CEENE would moreover avoid the application of (subjective) weight factors, as occurs in LCA, through a unified comparison basis [27,28].…”

Exergy as a Measure of Resource Use in Life Cycle Assessment and Other Sustainability Assessment Tools

“…Others have suggested that LCA and exergy analysis complement each other (e.g., [40][41][42][43]. Exergy analysis can also be used as a stand-alone assessment tool, e.g., [29,[44][45][46][47], or linked to other environmental systems analysis tools, such as Strategic Environmental Assessment [48], besides its use as an engineering tool for analyzing and optimizing different types of processes [29,49]. This non-exhaustive list indicates that the applications of exergy analysis are numerous and that it is an established method in many areas.…”