Environmental impact reduction using exergy-based methods

Exergy-based methods (exergetic, exergoeconomic and exergoenvironmental analyses) are powerful tools for developing, evaluating and improving energy-conversion systems. In an exergoeconomic analysis, thermodynamic inefficiencies -represented by exergy destruction -are used together with investment cost to calculate the "cost-optimal" alternative for the overall plant. Analogously, in an exergoenvironmental analysis, the aim is to reduce the total environmental impact. Normally, exergoeconomic and exergoenvironmental analyses are conducted independently of each other. Thus, until now, the improvement of a plant has been considered in terms of reduction of either costs or environmental impact. To simultaneously decrease the investment costs and the component-related (manufacturing or constructionrelated) environmental impacts, their relationship with exergy destruction must be studied in parallel. This paper examines the relationship between exergoeconomic and exergoenvironmental data under various plant operating conditions. A combined-cycle power plant is analyzed and options for a simultaneous improvement from the economic and environmental viewpoints are discussed.

Energy, 2011

The analysis framework introduced in this paper utilizes the recognition that exergy is a form of environmental free energy to provide a fundamental basis for valuing environmental interactions independent from their secondary impacts (e.g., global warming, photochemical smog). In order to extend exergy to analyze environmental interactions, modifications are required to the traditional representation of the environment and definition of the dead state used in technical exergy analysis. These are accomplished through a combination of logical extensions and use of non-equilibrium thermodynamic principles. The framework is comprised of two separate components: (1) environmental exergy analysis and (2) anthropocentric sensitivity analysis. Environmental exergy analysis is based on fundamental thermodynamic principles and analysis techniques. It extends the principles of technical exergy analysis to the environment in order to quantify the locations, magnitudes, and types of environmental impactdstate change, alteration of natural transfers, and destruction change. Anthropocentric sensitivity analysis is based on the concepts of anthropocentric value and anthropocentric sensitivity. It enables the results of environmental exergy analysis to be interpreted for decision making, but at the expense of introducing some subjectivity into the framework. A key attribute of the framework is its ability to evaluate and compare the environmental performance of energy systems on a level playing field, regardless of the specifics of the systemsdresources, by-products, sizes, time scales.

An exergoenvironmental analysis is conducted at the component level of a system and identifies (a) the relative importance of each component with respect to environmental impact, and (b) options for reducing the environmental impact associated with the overall system. In an exergoenvironmental analysis, a onedimensional characterization indicator is obtained using a Life Cycle Assessment (LCA). An index (a single number) describes the overall environmental impact associated with system components and exergy carriers. It should be emphasized that the evaluation of environmental impacts will always be subjective to some degree and associated with some uncertainties. Exergoenvironmental analysis identifies the magnitude, location and causes of thermodynamic inefficiencies and environmental impacts. The information supplied by such exergy-based methods is very useful in understanding the operation of energy conversion systems and in developing strategies for improving them. The paper presents the exergoenvironmental analysis applied to a gas-turbine cogeneration system (the CGAM problem that is used here as an example), and discusses the effect of the Eco-indicator used in an exergoenvironmental analysis on the conclusions obtained from the analysis. Five indicators are used here to conduct the LCA: Eco-indicator 95, Eco-indicator 99, Cumulative Exergy Consumption, a method developed at the Center Environmental Studies of the University of Leiden (The Netherlands), and ECOfactor 2006.

Journal of Industrial Ecology, 2008

Life-cycle assessment is an established tool for industrial ecology. An analysis of the energy use in the chemical and other energy-intensive industries is still under discussion in this field. We argue that the concept of exergy can play a role in industrial ecology, using a recent Norwegian power production policy question as illustration. The question is whether to build a standard natural gas-or a hydrogen-fired gas-turbine combined-cycle power plant to meet increased needs for electricity in Norway. Several indicators are relevant for this discussion, and we calculate three based on exergy calculations, as proposed in the literature. The indicators are exergy renewability, exergy efficiency, and environmental compatibility. We show how these indicators can be used to evaluate paths for sustainable power production in two gas-fired combined-cycle power plants. We found that the two plants in question were equivalent, as judged by their exergy renewability and their environmental compatibility, but not by their exergy efficiency. This indicator favored the standard power plant, possibly in combination with carbon dioxide (CO 2 ) sequestration in a depleted gas reservoir. The analysis suggested that the present situation for power production in gas-fired combined-cycle power plants is such that one may have to choose in general between power production with a high exergy efficiency, but low renewability indicator, or the opposite, low exergy efficiency and high renewability indicator. The general importance of exergy analysis was demonstrated by this example. It enables communication between different professional groups. The technological details, understood by the engineers, can be transposed to meaningful aggregated indicators for decision makers.

Wiley Interdisciplinary Reviews: Energy and Environment, 2012

This study discusses what exergy analysis brings new to the system design, analysis, assessment, and improvement of energy systems. It also presents how efficiencies are defined for performance assessment. Case studies are given to explain how system exergy analysis is performed, and its efficiencies are evaluated for comparison. Exergy destruction rates for each component of the systems are also studied and presented to investigate the possibilities for determining the magnitudes and improving the performance.

Energy, 2013

To develop approaches that effectively reduce engine environmental effect of aircrafts, it is necessary to understand the mechanisms that have enabled improvements in thermodynamic efficiency of aircraft engines. In the present work, a turboprop engine used in regional aircrafts that produces 1948 shp and 640 N.m torque is examined using exergo-environmental method. The results show compressor, combustion chamber, gas generator turbine, power turbine and exhaust nozzle create 9%, 69%, 13%, 7%, 2% of total environmental impact of the engine, respectively. According to rates, the compressor and gas turbine can be considered first to improve in case of component related environmental impact. Furthermore, total component related environmental impact for the turboprop engine is found to be 2.26 mPts/s for the constructional phase and 2.34 mPts/s for the operation/maintenance phases. Accordingly, it is suggested that, in order to estimate environmental impact metric of aircrafts, the exergo-environmental analysis can be employed for aircraft propulsion systems.

International Journal of Exergy, 2012

A thorough qualitative investigation of the relation between exergy losses and environmental problems has been conducted. Environmental effects being taken into account include climate change, acidification, eutrophication, disposal and dissipation. It is concluded that almost all environmental effects can be taken into account by studying the waste of feedstocks and energy caused by technological activities, like processes, and the emission and dispersion of pollutants. To underpin the qualitative investigation two case studies have been conducted: the production of aluminium and polystyrene. On the basis of the results of the case studies it can be made plausible that exergy losses and environmental impact are related. Exergy losses are a kind of environmental impact, whereas environmental impact is related to exergy loss. It is concluded that exergy loss is at least a qualitative measure that can be used in environmental policy making regarding technological processes. According to literature, exergy losses should be minimized to obtain a more sustainable development. During a follow-up study the relation between exergy and sustainability will be investigated in more detail, partly based on basic principles borrowed from nature. Apart from environmental impact also others aspects of sustainability, like economic and social aspects, will be taken into account.

2018

EXERGY ANALYSIS FOR INDUSTRIAL ENERGY ASSESSMENT Bader, Wayne Thomas University of Dayton, 2000 Advisor: Dr. J. Kelly Kissock Traditional approaches to improving energy efficiency often focus on leak-plugging and housekeeping efforts to avoid wasting energy. In many cases however, the way energy is used, rather than the amount used, is the primary cause of inefficiency. Exergy analysis provides a thermodynamic basis for optimizing energy systems. By considering the quality of energy as well as the quantity, the true thermodynamic efficiencies can be quantified and proper priorities for improvement projects can be established. In spite of its value for optimizing thermodynamic systems, exergy analysis has seen only limited use as a practical tool for industrial energy assessment. In this thesis, the energy and exergy efficiencies of two common industrial processes, air compression and aluminum melting, are developed. Methods for improving the processes are quantitatively discussed. F...

Environmental Science & Technology, 2012

Life Cycle Assessment (LCA) is a widely recognized, multicriteria and standardized tool for environmental assessment of products and processes. As an independent evaluation method, emergy assessment has shown to be a promising and relatively novel tool. The technique has gained wide recognition in the past decade but still faces methodological difficulties which prevent it from being accepted by a broader stakeholder community. This review aims to elucidate the fundamental requirements to possibly improve the Emergy evaluation by using LCA. Despite its capability to compare the amount of resources embodied in production systems, Emergy suffers from its vague accounting procedures and lacks accuracy, reproducibility, and completeness. An improvement of Emergy evaluations can be achieved via (1) technical implementation of Emergy algebra in the Life Cycle Inventory (LCI); (2) selection of consistent Unit Emergy Values (UEVs) as characterization factors for Life Cycle Impact Assessment (LCIA); and (3) expansion of the LCI system boundaries to include supporting systems usually considered by Emergy but excluded in LCA (e.g., ecosystem services and human labor). Whereas Emergy rules must be adapted to life-cycle structures, LCA should enlarge its inventory to give Emergy a broader computational framework. The matrix inversion principle used for LCAs is also proposed as an alternative to consistently account for a large number of resource UEVs.

2003

This s tudy focuses on the sustainability of different t echnological options for minimizing environmental impact. it is proposed that the c umulative c onsumption o f materials and utilities for construction a nd operation o f environmental t reatment systems can be quantified in terms of exergy. in addition, the exergy content of the emissions of a given production process, as well as the exe rgy of by-products of the treatment process, can b e quantified to d evelop an exergy balance, focused o n the treatment process. Furthermore, a methodology is proposed to compare the different process alternatives in two situations: the former considering that the main task of the process is to eliminate the exe rgy c ontent of a given emission, which is analyzed b y the ηd coefficient; and the latter considering that the main task of the process is to maximize the utilization of the exergy content of a given emission, which is analyzed b y the ηp coefficient. Three c ase studies are present...