Exergy Accounting Research Articles

Exergetic assessment of energy systems on North Sea oil and gas platforms

Oil and gas platforms in the North Sea region are associated with high power consumption and large CO2-emissions, as the processing and utility plants suffer from significant changes in production rates and performance losses over the field lifespan. In this paper, a generic model of the overall offshore system is described: its thermodynamic performance is assessed by performing an exergy accounting and rules of thumb for oil and gas platforms are derived. Simulations are built and conducted with the tools Aspen Plus®, Dynamic Network Analysis and Aspen HYSYS®. 62–65% of the total exergy destruction of an offshore platform is attributable to the power generation and waste heat recovery system, and 35–38% to the oil and gas processing. The variability of the feed composition has little effect on the split of the thermodynamic irreversibilities between both plants. The rejection of high-temperature gases from the utility and flaring systems is the major contributor to the exergy losses. These findings suggest to focus efforts on a better use of the waste heat contained in the exhaust gases and on the ways in which the gas compression performance can be improved.

Extended exergy analysis of Turkish transportation sector

This work presents an analysis of the different modes of the Turkish transportation sector along the guidelines of the Extended Exergy Accounting (EEA) method. The results refer to year 2006 because that was the most complete and sufficiently disaggregated database available. The evaluation of the transportation sector leads to the calculation of its extended exergetic efficiency (EEAeff) and requires the inclusion of all commercial and private transportation services (passengers and goods) as well as of all services directly related to transportation (post, cargo, pipeline transport, etc.). The environmental remediation costs (EEEnv) of sectoral solid waste and gas emissions (direct and indirect) are obtained in accordance with the original calculation procedure, without recurring to the conversion of monetary into exergetic costs. The resulting EEAeff of the sector is 0.36, which is rather low (in the EE sense), because of the sector’s largely unsustainable structure: fossil-fuelled road transportation widely prevails, which not only destroys a very high percentage of the incoming exergy, but is also affected by quite large CO2-equivalent emissions that demand for a high EEEnv.

Energy Intensity of the Catalan Construction Sector

SummaryWe used a thermodynamic framework to characterize the resource consumption of the construction sector in 2001 in Catalonia, the northeast region of Spain. The analysis was done with a cradle‐to‐product life cycle approach using material flow analysis (MFA) and exergy accounting methodologies to quantify the total material and energy inputs in the sector. The aim was to identify the limitations of resource metabolism in the sector and to pinpoint the opportunities for improved material selection criteria, processing, reuse, and recycling for sustainable resource use. The results obtained from MFA showed that nonrenewables such as minerals and natural rocks, cement and derivatives, ceramics, glass, metals, plastics, paints and other chemicals, electric and lighting products, and bituminous mix products accounted for more than 98% of the input materials in the construction sector. The exergy analysis quantified a total 113.1 petajoules (PJ) of exergy inputs in the sector; utilities accounted for 57% of this exergy.Besides exergy inputs, a total of 6.85 million metric tons of construction and demolition waste was generated in 2001. With a recycling rate of 6.5%, the sector recovered 1.3 PJ of exergy. If the sector were able to recycle 80% of construction and demolition waste, then exergy recovery would be 10.3 PJ. Hence the results of this analysis indicate that improvements are required in manufacturing processes and recycling activities, especially of energy‐intensive materials, in order to reduce the inputs of utilities and the extraction of primary materials from the environment.

A Thermodynamically Correct Treatment of Externalities with an Exergy-Based Numeraire

The concept of “sustainable development” implies that the environmental externalities unavoidably generated by human activities be reduced to a minimum: In fact, the very definition of “sustainability” leads—as it will be briefly discussed in the paper—to a physically measurable upper limit for untreated discharges. Since the current state of affairs on Earth is far from being sustainable, any proposal for a future scenario that is not substantiated by an accurate assessment of the effects of the environmental externalities is devoid of real sense and ought not to be pursued. The present paper illustrates the application of Extended Exergy Accounting (EEA) to the quantification of such externalities. The exergy flow diagrams of EEA include non-material and non-energetic production factors like labor, and capital and environmental remediation costs, providing a quantitative measure of the amount of primary resources that are cumulatively used in the production of a good or service, and it is shown to provide a wealth of quantitative information to energy managers and planners.

An application of the extended exergy accounting method to the Turkish society, year 2006

The Turkish society is analyzed, on the basis of a 2006 database, by means of the EEA (Extended Exergy Accounting) method. A brief synthesis of EEA is also presented, with the purpose of clarifying some of the issues related to its accounting technique. The system to be analyzed is assumed to be at steady state, and the input and output fluxes of matter and energy are expressed in terms of their respective exergy content. This study is intended to provide support for possible structural interventions aimed at the improvement of the degree of sustainability of the Country: since EEA allows for the conversion of the so-called “externalities”, i.e., of the immaterial fluxes of labour, capital and environmental remediation, into their exergetic equivalents, a more comprehensive and deeper insight of the resource consumption and of the environmental impact becomes possible. As usual in EEA analyses, the Turkish society has been modelled as an open thermodynamic system interacting with two “external” systems, namely “Environment” and “Abroad”, and consisting itself of seven internal subsystems: Extraction-, Conversion-, Transportation-, Agricultural-, Industrial-, Tertiary- and Domestic sector.

An exergy-based Ecological Indicator as a measure of our resource use footprint

The concept of 'Ecological Indicator' (EI) is critically analysed to define the properties it ought to possess and to demonstrate that indicators based solely on material–and energy balances do not comply with the necessary properties. It is argued that exergy destruction and exergy of discharge, both acceptable thermodynamic indicators, cannot provide information on the human–specific impact of a pollutant (neither of them measures toxicity and non–energetic externalities). A recently proposed method, Extended Exergy Accounting (EEA), which includes in the exergy flow diagrams non–material and non–energetic production factors like labour, capital and environmental remediation costs, is shown to provide a proper measure of the amount of primary exergy resources consumed in the life–cycle of a material or immaterial commodity.

Extended exergy accounting applied to the flaring practice in oil fields

An original procedure based on the Extended Exergy Accounting method is described and implemented in this paper. The goal is the quantification of the environmental externality linked to the chemical pollutants released by an elevated flare stack (SOx and NOx). The extended exergy calculations provide a measure of both the exergy flux released into the environment by the stack and its 'cost' in primary resource equivalents. Idealised processes are assumed for the effluent treatment, but nevertheless, it is shown that the inclusion of the environmental externality bears a non–negligible influence on the final resource cost. As a further example of application, it is shown that both the environmental damage and the product costs can be reduced if hot gas recycling is enforced.

基于生命周期的户用沼气系统可用能核算——以广西恭城瑶族自治县为例

Biogas-linked agro-ecosystem can bring in economic and environmental benefits via integrated resource utilization,which provides an energy consuming pattern that has prominent advantages in relieving energy shortage and reducing environmental pollution.It is important to make clear how materials and energy convert in the agro-ecosystem,because the facts could suggest us how to improve the performance of the agro-ecosystem and get more benefits.Exergy of a system in a certain environment is defined as the amount of work that can be extracted from the system,which can be regarded as a uniform measure for different forms of energy and different states of matter.This paper presents an exergy-based life cycle accounting method for household biogas system.The proposed method is applied to a case study of Gongcheng as a National Eco-agriculture Demonstration County due to its demonstration status of biogas-linked agro-ecosystem in China.It has a high popularization rate of household biogas system.The typical household biogas system of Gongcheng is supposed to have three stages,i.e.,construction,operation and utilization.We calculate the exergy input-output of each subsystem and hereby analyze the exergy efficiency of the whole agro-ecosystem.The results show that,the exergy input of the system is 1.06×108kJ/a while the exergy output(mainly in the form of biogas residue) is 5.00×107kJ/a,with the exergy conversion rate being 48.82%.The exergy utilization rate is 21.60%,and biogas contributes more than biogas residue and biogas slurry.The exergy of system emission reaches 3.42×105kJ/a,which mainly comes from the biogas combustion.Major conclusions are as follows:(1) Compared with the traditional agro-ecosystem,biogas-linked agro-ecosystem has a longer utilization chain for agricultural wastes,which takes in nonrenewable resources and outputs renewable resources.Therefore,household biogas system is an effective measure in relieving energy shortage and reducing environmental pollution in rural area and realizing the sustainable development.(2) The exergy efficiency of the household biogas system is at a low level,and still needs to be promoted.Improving the process technology and optimizing the fermentation condition may be a choice to increase the exergy conversion rate.Meanwhile,technological innovation in the multi-purpose use of biogas residue and biogas slurry can increase the exergy utilization rate.(3) The exergy-based life cycle accounting method of household biogas system in this paper extends the application of exergy accounting,and fills in the gap of household biogas research field.The method may help us understand the household biogas system more clearly and directly in energy conversion and utilization mode.As a result,it is convenient to find out the weak points of the agro-ecosystem that waste more energy and seek for optimal solutions accordingly.

Towards the Evaluation of Environment and Business Trade-offs in Supply Chains

Supply chains (SCs) are one of the most environment impacting systems. Analysis of such systems should thus take into account not only performance but also environment indicators. The amount of energy consumed for producing goods and the total emissions of greenhouse gases (GHG) of an activity are examples of such indicators. This paper presents a framework for assessing performance as well as Global Warming Potential (GWP) and exergy indicators in SCs. In order, exergy accounting helps on finding reliable GWP indicators for different energy sources adopted in the supply chain. This framework supports the evaluation of supply chainsʼ business and environment indicators trade-offs using a unified model. A real case study is conducted to demonstrate the application of the proposed modeling technique.

Comparison of five exergoenvironmental methods applied to candidate energy systems for rural villages in developing countries

This paper tackles the environmental impact assessment of different energy systems for rural communities in developing countries. Ten systems are proposed, modelled, and assessed by five published methods: ReCiPe indicator combined with exergy, exergy wasted, thermo-ecological cost, extended exergy accounting, and extended thermoeconomics. All the methods constitute life cycle assessment (LCA) and mathematically take a similar form, combining an environmental impact assessment with exergetic analysis. Despite the inevitable difference of weighting between methods, most showed clear benefits to using responsibly grown Jatropha oil (rather than diesel) to generate electricity and all showed clear benefits of biogas over solar thermal or fuelwood heat. Analyses of error and sensitivity are presented at the end of the results and discussion section.

A revised calculation of the econometric factors α- and β for the Extended Exergy Accounting method

Extended Exergy Accounting (“EEA”) is a method to compute the space- and time integral of the primary exergy required to produce a good or a service: the extended exergy of a commodity measures its “embodied exergy”, including externalities (Labour, Capital and Environmental Costa). A crucial point of the method is the calculation of two econometric coefficients, commonly referred to as “ α” and “ β”,used to calculate the extended exergy equivalents of Labour and Capital respectively. In previous applications of the EEA method, these coefficients have been assigned approximate values estimated on the basis of global system considerations. In this paper, a novel procedure is described that leads to the calculation of “exact” values of both econometric coefficients, based on detailed exergy- and monetary balances of the Society to which the EEA is applied. It is shown that both α and β depend in a non-trivial way from the consumption patterns, the technological level and the life- and socio-economic standards of each Country. It is also shown that the values are substantially different for developed (OECD) and underdeveloped Countries, and representative samples of values are calculated and critically analysed. On the basis of these new model coefficients, the specific exergy equivalents of Labour (ee L) and of Capital (ee K) are calculated, and shown to differ from the values used in previous EEA calculations.

Extended exergy accounting applied to biodiesel production

When evaluating the production of renewable energies such as biofuels, it is necessary to include in the assessment the resource inputs, capital, labor investment and environmental remediation costs. Extended Exergy Accounting (EEA) is a system analysis method that calculates, on the basis of detailed mass and exergy balances, the total amount of primary exergy resources necessary to obtain a product or service. The conceptual novelty of EEA is represented by the fact that it also includes externalities (capital, labor and environmental impact) measured in homogeneous units (Joules). As an illustration of EEA, we assess and compare the production of 1 ton of biodiesel from used cooking oil (UCOME) and rapeseed crops (RME). The extended exergy “content” of UCOME and RME are 51.90 GJ and 77.05 GJ respectively. The production of UCOME uses 25.15 GJ less resources (materials and energy) and requires lower total investments and environmental remediation costs than that of RME. On the other hand, UCOME requires 35% more workhours. In summary, the extended exergy of UCOME is about 1.5 the extended exergy content of RME. Thus, we can conclude that biodiesel production from UCO is less resource use intensive than the production from RME.

Physical geonomics: Combining the exergy and Hubbert peak analysis for predicting mineral resources depletion

This paper shows how thermodynamics and in particular the exergy analysis can help to assess the degradation degree of earth's mineral resources. The resources may be physically assessed as its exergy content as well as the exergy required for replacing them from a complete degraded state to the conditions in which they are currently presented in nature. In this paper, an analysis of the state of our mineral resources has been accomplished. For that purpose an exergy accounting of 51 minerals has been carried out throughout the 20th century. This has allowed estimating from geological data when the peak of production of the main mineral commodities could be reached. The obtained Hubbert's bell-shaped curves of the mineral and fossil fuels commodities can now be represented in an all-together exergy–time representation here named as the “exergy countdown”. This shows in a very schematic way the amount of exergy resources available in the planet and the possible exhaustion behaviour. Our results show that the peak of production of the most important minerals might be reached before the end of the 21st century. This confirms the Hubbert trend curves for minerals obtained by other authors using a different methodology. These figures may change, as new discoveries are made. However, assuming that these discoveries double, most of the peaks would only displace our concern around 30 years. This is due to our exponential demand growth. The exergy analysis of minerals could constitute a universal and transparent tool for the management of the earth's physical stock.

Extended-exergy analysis of the Chinese society

Extended-exergy analysis (EEA) for Chinese society was carried out in this paper to present a benchmarking case for future comparative studies in social systems ecology based on exergetic biophysics. For the EEA as an extension of labor theory of value and a possible sustainability metric, exergetic values were assigned to the production factors including labor, capital and environmental remediation costs. Also, the conversion coefficient of households sector was evaluated with the consideration of working hours, which significantly supplements the traditional energy and exergy accounting. The Chinese societal system was classified into seven sectors including the extraction, conversion, agriculture, industry, transportation, tertiary and households. The calculations of capital exergy and labor exergy were modified according to the special social–economic situation of China. A detailed accounting for the total societal extended-exergy use of China 2005 was conducted. Meanwhile, comparison of the net input exergy resources, extended-exergy capital, and labor of the total Chinese society during 2000–2005 was made to reveal the temporal changes using EEA. Finally, the EEA performances of China were compared with those of Norway, UK, Italy and the province of Siena to present solid foundation for energy strategy and identification of sustainable development mode.

Why Emergy- and Exergy Analysis are non-commensurable methods for the assessment of energy conversion systems

The paper discusses a fundamental incompatibility between Emergy- ('EMA') and Exergy ('EXA') Analysis. Both approaches quantify the resource consumption of physical systems by applying space- and time integrated energy input/output methods. A detailed theoretical analysis and two specific examples show that at least one of the claims made by EMA practitioners is based on a misinterpretation of the exergy accounting practices, that the claim that "emergy is embodied exergy" is inconsistent with EMA procedures, and that if these procedures were amended to correctly account for exergy flows, EMA would resemble Szargut's Cumulative Exergy Content method and/or Extended Exergy Accounting.

Exergy analysis of a combined engine-organic Rankine cycle configuration

This article presents an exergy analysis of a combined engine-organic Rankine cycle configuration (E-ORC) using the exergy topological method. A detailed roadmap of exergy flow is presented using an exergy destruction chart to clearly depict the exergy accounting associated with each thermodynamic process. The analysis indicates that an ORC combined with an engine not only improves the engine thermal efficiency but also increases the exergy efficiency. Different organic fluids are evaluated in this article. Depending on the organic fluid employed, the thermal and exergy efficiencies could be increased by approximately 10 per cent. Parameters such as the thermodynamic influence coefficient and degree of thermodynamic perfection are identified as useful design metrics to assist exergy-based design of devices. This article also examines the effect of the pinch-point temperature difference (PPTD) on the E-ORC performance. Results show that the lower the PPTD the higher the thermal and exergy efficiencies.

Exergy: Its Potential and Limitations in Environmental Science and Technology

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.

An examination of exergy destruction in organic Rankine cycles

The exergy topological method is used to present a quantitative estimation of the exergy destroyed in an organic Rankine cycle (ORC) operating on R113. A detailed roadmap of exergy flow is presented using an exergy wheel, and this visual representation clearly depicts the exergy accounting associated with each thermodynamic process. The analysis indicates that the evaporator accounts for maximum exergy destroyed in the ORC and the process responsible for this is the heat transfer across a finite temperature difference. In addition, the results confirm the thermodynamic superiority of the regenerative ORC over the basic ORC since regenerative heating helps offset a significant amount of exergy destroyed in the evaporator, thereby resulting in a thermodynamically more efficient process. Parameters such as thermodynamic influence coefficient and degree of thermodynamic perfection are identified as useful design metrics to assist exergy-based design of devices. This paper also examines the impact of operating parameters such as evaporator pressure and inlet temperature of the hot gases entering the evaporator on ORC performance. It is shown that exergy destruction decreases with increasing evaporator pressure and decreasing turbine inlet temperatures. Finally, the analysis reveals the potential of the exergy topological methodology as a robust technique to identify the magnitude of irreversibilities associated with real thermodynamic processes in practical thermal systems. Copyright © 2008 John Wiley & Sons, Ltd.

Extended Exergy Accounting as a general method for assessing the primary resource consumption of social and industrial systems

The method of Extended Exergy Accounting (EEA) is proposed as a paradigm for the evaluation of the equivalent primary resource consumption of 'Energy Systems'. In a 'system's approach', an energy system is an assembly of components that feed on primary energy sources to produce material or immaterial commodities.

Exergy and extended exergy accounting of very large complex systems with an application to the province of Siena, Italy

This paper describes the application of exergy and extended exergy analyses to large complex systems. The system to be analysed is assumed to be at steady state, and the input and output fluxes of matter and energy are expressed in units of exergy. Human societies of any reasonable extent are indeed Very Large Complex Systems and can be represented as interconnected networks of N elementary “components”, their Subsystems; the detail of the disaggregation depends on the type and quality of the available data. The structural connectivity of the “model” of the System must correctly describe the interactions of each mass or energy flow with each sector of the society: since it is seldom the case that all of these fluxes are available in detail, some preliminary mass- and energy balances must be completed and constitute in fact a part of the initial assumptions. Exergy accounting converts the total amount of resources inflow into their equivalent exergetic form with the help of a table of “raw exergy data” available in the literature. The quantification of each flow on a homogeneous exergetic basis paves the way to the evaluation of the efficiency of each energy and mass transfer between the N sectors and makes it possible to quantify the irreversible losses and identify their sources. The advantage of the EEA, compared to a classical exergy accounting, is the inclusion in the system balance of the exergetic equivalents of three additional “Production Factors”: human Labour, Capital and Environmental Remediation costs. EEA has an additional advantage: it allows for the calculation of the efficiency of the domestic sector (impossible to evaluate with any other energy- or exergy-based method) by considering the working hours as its product. As implied in the title, an application of the method was made to a model of the province of Siena (on a year 2000 database): the results show that the sectors of this Province have values of efficiency close to the Italian average, with the exception of the commercial and energy conversion sectors that are more efficient, in agreement with the rather peculiar socio-economic situation of the Province. The largest inefficiency is found to be in the transportation sector, which has an efficiency lower then 30% in EEA and lower than 10% in classical exergy accounting.