Session: 09-10-02: Hydrogen Production, Storage, and Integrated Hydrogen Energy Systems II

Paper Number: 163913

Defining Useful Exergetic Efficiencies in Energy-Intensive Chemical Processes 

The exergetic efficiency, the best variable to characterize the thermodynamic performance of an energy-conversion system or a system component, has been discussed in many previous publications. The purpose of using an exergetic efficiency is not only to objectively evaluate how well the system operates from the thermodynamic viewpoint but also to identify opportunities for improving the system performance, initially from the thermodynamic viewpoint in an exergetic analysis and, subsequently from the cost and environmental impact viewpoints in an exergoeconomic analysis and an exergoenvironmental analysis. 

However, in defining the exergetic efficiency of a component of a system, the purpose of the component has not always been considered appropriately, mainly when dealing with energy-intensive chemical processes. This, combined with the fact that often, two or even more definitions of efficiency appear to be reasonable or acceptable, has led to confusion and misuse in the definition of energetic efficiencies in the literature. In addition, the definition of exergetic efficiencies based on total exergies has the disadvantage of not allowing the comparison of efficiency values for dissimilar components.

Finally, the splitting of physical and chemical exergies into thermal, mechanical, reactive, and non-reactive exergies, as well as the application of the advanced exergy-based methods (in which the exergy destruction is split into endogenous, exogenous, avoidable, and unavoidable parts) offer new opportunities to define more precise and more meaningful and useful efficiencies and to allow the comparison of efficiencies of dissimilar components. It should be noted that it is not possible to automatically define meaningful and useful exergetic efficiencies because the purpose of using a component in an energy-conversion system could take different expressions depending on the system in which the component is being used and its integration with other components. This becomes particularly clear in energy-intensive chemical processes.

The presentation will discuss a general approach and the primary considerations for defining exergetic efficiencies. This approach, which improves previous developments by the author and other coworkers, is based not only on the avoidance of using absolute exergy values and the use of exergy differences in defining efficiencies but also on a more detailed consideration of the purpose of each component and on the splitting of exergy destruction into endogenous, exogenous, avoidable, and unavoidable parts. In addition, if deemed appropriate, the constituents of a gas mixture are considered separately in the efficiency definition, depending on whether they are desired. In the presentation, examples will be presented from processes that are currently discussed in the literature and deal with the synthesis of ammonia and methanol as well as the production of hydrogen. 

Presenting Author: George Tsatsaronis Technical Univ Of Berlin

Presenting Author Biography: George Tsatsaronis was the Bewag Professor of Energy Engineering and Protection of the Environment at the Technical University of Berlin from May 1994 until March 2024. He received a Diploma in mechanical engineering (NTU Athens, Greece) as well as an MBA, a Ph.D. in combustion, and a Dr Habilitatus Degree in Thermoeconomics, all from the RWTH Aachen University, Germany. In the time period 1982-1994, he was employed as a full professor at two US Institutions (Desert Research Institute and Tennessee Tech University). Since November 2023, he has been a member of the Governing Board of the Aristotle University of Thessaloniki, Greece.

His areas of interest include exergy-based methods, the design, analysis, and optimization of energy conversion systems, decarbonization methods, power plant technology, energy storage, production, and transportation, as well as the use of hydrogen. He contributed significantly to the fundamentals of exergy-based methods.

He co-authored the book Thermal Design and Optimization (Wiley, 1996). He is an Honorary Editor or Associate Editor of several International Journals, served as chairman or co-chairman of 22 international conferences, and received many international awards and recognitions, including two Doctoris Honoris Causa (from the NTU Athens, Greece, and the Polytechnic University of Bucharest, Romania), two honorary professorships from China (North China University of Electric Power, and Zhejiang University of Technology) as well as the George Westinghouse Gold Medal, the Edward F. Obert Best Paper Award, and the James Harry Potter Gold Medal all from the American Society of Mechanical Engineers.

Authors:

George Tsatsaronis Technical Univ Of Berlin