Exergy Resources Research Articles

Hybrid power energy system optimization by exergoeconomic and environmental models for an enhanced policy and sustainable management of exergy resources

Recent attention to global warming has increased interest in sustainable technology. The current issues are the reduction of emissions and cost. Innovative hybrid systems that combine fossil fuel and renewable energy sources need to be developed. The optimization of these systems is essential to ensure the continuity of load supply and to decrease the cost of energy production. This work presented a novel optimisation method for exergy resource distribution within hybrid power systems based on exergoeconomic and environmental performance. Three optimization models were proposed: the first one focuses on minimizing exergy input, the second one considers the minimization of the production cost and the last model aims to minimize the CO2 emissions. Tunisia was selected as a case study. The findings demonstrate that using model 1 results in gains in natural gas consumption, production costs, and CO2 emissions of 75 kWhex/kWhex, 0.015 €/kWhex, and 0.12 kg CO2/kWhex, respectively. Furthermore, when model 2 is used, these gains amount to 49 kWhex/kWhex, 0.035 €/kWhex, and 0.159 kg CO2/kWhex. And finally, when model 3 is used, there will be 2.49 kWhex/kWhex, 0.015 €/kWhex, and 0.168 kg CO2/kWhex. It is concluded that the second model is more suitable for the resources strategy in Tunisia; it affords a minimum cost with a moderated exergy input and CO2 emissions.

Multilevel optimization framework to support self-sustainability of industrial processes for energy/material recovery using circular integration concept

Climate change, resource scarcity, waste reduction, and the lack of sustainability in process industries are vital concerns that civilization confronts. The process integration methodology may aid such sustainability. In this study, a novel chemical exergy resource recovery network is proposed for optimal energy and waste recovery in high-salinity-gradient chemical industries using a pressure-retarded osmosis membrane while indicating a self-sustainability and allocation in complex industrial networks. The mathematical programming paradigm is expressed as a multilevel optimization model to introduce novel ideas for explicitly modeling the trade-offs between waste and energy flows in circular integration while demonstrating industrial network’s environmental impact assessment. This problem is decomposed into two subproblems (SPs) that must be addressed sequentially. The first SP is designed to decrease the total cost of the network while reducing external resource use. The second SP formulates a mixed-integer nonlinear programming model with the objective of minimizing the environmental effects and exergy consumption rate of the network. A case study of a naphthalene-methaforming plant demonstrates the efficacy of the proposed methodology. The results showed that using a tri-level optimization technique, a considerable improvement in flowrate, total annualized cost, and energy recovery is obtained while limiting the network's environmental impact. The operating phase accounts for approximately 75% of the global warming potential output. The proposed tri-level approach based on Benders’ decomposition approach reduced the overall cost of the network by 19.29%, and 47.42 MW net power is recovered in the case study. In addition, the circular exergy use rate and environmental factor were reduced from 400 to 0.037 MW and from 2.569 to 1.481 kgCO2/year, respectively, using the tri-level decomposition approach.

Extended exergy accounting for smelting and pressing of metals industry in China

Rapid expansion, relative shortage resources supply and environmental impact threat the sustainable development of the smelting and pressing of metals sector. Fluxes of energy, materials, environmental remediation expenses, labor, and capital were quantified by Joules based on the second-law thermodynamics during years 1992–2015. The accounting method that quantifies the component of the extended exergy fluxes and the proportion in the total inputs was used to analyze this energy-intensive industry. Net per-capita exergy resource input and labor production efficiency are described the conversion of natural resource exergy to economic output and labor efficiency. The results showed the following: (1) the smelting and pressing of metals sector expands rapidly; the ferrous metals industry accounts the large part of the overall metals industry and the nonferrous metals industry grows faster than the ferrous metals industry. Natural resource exergy, especially energy exergy, dominates the investments of the metals industry. (2) Capital exergy and labor exergy decrease in the smelting and pressing of metals industry, while they increase in the nonferrous metals industry and decrease in the ferrous metals industry. Environmental exergy declines in both the nonferrous metals and ferrous metals industries. (3) The comparison of the nonferrous metals and ferrous metals industries with China as a whole, conducted by applying the two indicators for efficiency, shows that the two industries are exceeding the whole country in efficiency and have made great progress. In addition, the extended exergy analysis of smelting and pressing of metals industry is helpful in the identification of resource consumption and environmental cost in sustainable development view.

Calculating the chemical exergy of materials

AbstractModern society requires large amounts of materials which lead to emissions of greenhouse gases. Effective climate policy should focus on not just energy efficiency but material efficiency as well. Exergy analysis is a powerful metric used to identify opportunities for efficiency improvement in industrial resource flow systems. Exergy offers a single unified measure of energy and material resources and indicates the real thermodynamic value of these resources, but the method suffers from a lack of comprehensive specific material chemical exergy datasets. The variety of different materials used in the global resource supply chain necessitates a combination of exergy calculation approaches. These approaches are combined into a single exergy calculator tool with over 1400 substances in the dataset. The chemical exergy values computed for key materials typically differ by less than 10% from values estimated in literature. The calculator is used in a case study of the upstream global material supply chain in 2013. The exergy resource map is visualized in a Sankey diagram and is found to be 72% resource efficient with 170 EJ of combined exergy losses and destruction. Further analysis is conducted on the refining, utilities, and industry sectors which are found to be 72%, 44%, and 50% resource efficient, respectively. Their combined losses and destruction are 15, 101, and 54 EJ, respectively. This study and the calculator developed provide a comprehensive dataset of chemical exergy values for a wide range of materials and can be applied in a variety of studies using exergy analysis.

Temporal-spatial exergy resource characteristics for 5th-generation district heating and cooling system

Temporal-spatial exergy resource characteristics for 5th-generation district heating and cooling system

Raw material use in a battery electric car – a thermodynamic rarity assessment

The transition to full electromobility must be carefully evaluated, as large amounts of strategic metals will be required, for which there is presently little to no recovery or recycling (e.g. gold, silver, tantalum or cobalt). In this study, we perform a comprehensive metal assessment of two passenger cars (conventional and battery electric models) in terms of mass and thermodynamic rarity. Thermodynamic rarity is based on the property of exergy and is defined as “the amount of exergy resources needed to obtain a mineral commodity from average crustal concentration using the best available technology” (measured in kJ). Thus, the thermodynamic rarity approach assigns a greater exergetic value to scarce (understood as having a relative low average crustal concentration) and difficult-to-extract minerals. Of the 60 metals analyzed, almost 50 metals have been identified within the studied cars, representing 800 (conventional) and 1,200 kg (battery electric), showcasing the fact that a car constitutes a “road mine”. Furthermore, given that the technology behind battery electric cars is in development, three generations of Li-ion batteries were analyzed to study the effect on resource use of a metal changing composition over time. Albeit the battery modules of the three generations present a similar mass content (approximately 70 kgs), the thermodynamic rarity decreases from 275 to 100 Gigajoules, due to the reduced proportion of cobalt, which is by far the most exergetic metal within the battery. Additionally, with the thermodynamic rarity approach, the most exergy intensive parts within a battery electric car have been identified – the high-voltage battery modules, the electric drive, the power module, the charger, the electrical air conditioning compressor and the electromechanical brake servo – providing an indicator facilitating proactive mid- to long-term ecodesign measures and recycling strategies.

Classification of geothermal resources in Indonesia by applying exergy concept

Indonesia is well-known for its reputation for possessing the world's largest geothermal potential, which has been characterized by high temperature geothermal resources' concentration. The geothermal energy potential of Indonesia has been estimated to be 28,617 MW, which is about 40% of the world's geothermal potential. However, only about 4.5% is being utilized as electrical energy supply in this country. This paper comprises the Indonesian geothermal resources, based on their capability of doing work and efficiency. In this study, currently operating geothermal power plants in Indonesia have been classified, based on the exergy concept and the Specific Exergy Index (SExI). The results of SExI values show that nine geothermal fields are classified as high exergy resource with their SExI values exceeding 0.5, and two remaining power plants with SExI values between 0.05 and 0.5 are classified as medium geothermal resources.

Life-cycle greenhouse gas emissions assessment and extended exergy accounting of a horizontal-flow constructed wetland for municipal wastewater treatment: A case study in Chile

The life-cycle greenhouse gaseous emissions and primary exergy resources consumption associated with a horizontal subsurface flow constructed wetland (HSSF) were investigated. The subject of study was a wetland for municipal wastewater treatment with a 700-person-equivalent capacity. The effects of two types of emergent aquatic macrophytes (Phragmites australis and Schoenoplectus californicus) and seasonality on greenhouse gas (GHG) gas emissions, the environmental remediation cost (ERC) and the specific environmental remediation cost (SERC) were assessed. The results indicate that GHG emissions per capita (12–22kgCO2eq/p.e/yr) and primary exergy resources consumed (24–27MJ/m3) for the HSSF are lower than those of a conventional wastewater treatment plant (67.9kgCO2eq/p.e/yr and 96MJ/m3). The SERC varied between 176 and 216MJ/kg biological oxygen demand (BOD5) removal, which should be further reduced by 20% for an improved BOD5 removal efficiency above 90%. The low organic matter removal efficiency is associated with a high organic load and low bacterial development. Seasonality has a marked effect on the organic removal efficiency and the SERC, but the macrophyte species does not.

Towards a coherent multi-level framework for resource accounting

With increasing resource scarcity and environmental impacts resulting from inefficient resource utilisation, accounting for resource consumption along the life cycle of a product or service becomes critical for designing production–consumption systems. This work aims at developing a coherent framework for resource accounting to support the evaluation of alternatives for production and consumption activities. The framework provides an understanding of resource utilisation at unit, process, inter-process and production–consumption levels within a system. The multilevel characteristic of this framework allows a comprehensive and holistic view of a system with the potential to reveal how decisions at one level would affect other levels of the system. Based on such a multilevel view, a unique adaptation of the Cumulative Exergy Resource Accounting method is proposed to quantify resource consumption associated with both technological and natural processes. This work also differentiates between and accounts for the operational resource consumption in resource extraction, agriculture and manufacturing and for the capital resource consumption for providing machinery and infrastructure. This is a practical framework for resource accounting that can be used by process engineers and local planners to support decision making regarding alternative system designs, gain insights on the performance of a production system and devise design options including retrofits for improving the overall resource efficiency of a system. By revealing the resource consumption through each system layer, the framework provides a robust and transparent way to capture effects of decision making during design or retrofitting of processes in order to find the most efficient design options. In addition, the framework can be applied to support research in other areas such as those addressing the social, cultural and business perspectives of resource management. Finally, a case study on the production and consumption of sugarcane ethanol is used to illustrate the features of the proposed framework. The framework proved useful in assessing the effects of design decisions at the various levels, such as choosing between molecular sieve and azeotropic distillation at the unit level, adoption of water recycling at the process level, and bagasse exchange flows at inter-process level. The proposed systematic approach has given insights into how changes in resource consumption occur at different levels.

Exploitation of humid air latent heat by means of solar assisted heat pumps operating below the dew point

Nowadays, the exploitation of environmental exergy resources for heating purposes (solar energy, convection heat transfer from ambient air, moist air humidity condensation) by means of properly designed heat pump systems is a possible opportunity. In particular, the use of direct expansion solar assisted heat pumps (DX-SAHP) is investigated in this study, when a bare external plate (the solar collector) is kept at temperatures lower than the dew point temperature of ambient air, so that condensation takes place on it.The potential of this technology is settled and an instrumented prototype of a small DX-SAHP system is used to verify the actual performance of the system, in terms of specific thermal energy delivered to the user, efficiency and regulation capabilities. Results clearly show that the contribution of the condensation is significant (20%–30% of the total harvested energy) overnight or in cloudy days with very low or no solar irradiation, and must be taken into account in a system model devoted to describe the DX-SAHP behavior. During daytime, the percentage gain decreases but is still consistent. By investigating along these lines, the heat due to condensation harvested by the collector is found to be a function of the dew-point temperature alone.

Comparison Based on Exergetic Analyses of Two Hot Air Engines: A Gamma Type Stirling Engine and an Open Joule Cycle Ericsson Engine

In this paper, a comparison of exergetic models between two hot air engines (a Gamma type Stirling prototype having a maximum output mechanical power of 500 W and an Ericsson hot air engine with a maximum power of 300 W) is made. Referring to previous energetic analyses, exergetic models are set up in order to quantify the exergy destruction and efficiencies in each type of engine. The repartition of the exergy fluxes in each part of the two engines are determined and represented in Sankey diagrams, using dimensionless exergy fluxes. The results show a similar proportion in both engines of destroyed exergy compared to the exergy flux from the hot source. The compression cylinders generate the highest exergy destruction, whereas the expansion cylinders generate the lowest one. The regenerator of the Stirling engine increases the exergy resource at the inlet of the expansion cylinder, which might be also set up in the Ericsson engine, using a preheater between the exhaust air and the compressed air transferred to the hot heat exchanger.

Exergy analysis of construction material manufacturing processes and assessment of their improvement potentials

This study presents the application of exergy analysis in assessing how effectively resources are utilised in construction material manufacturing. The role of exergy is discussed from several key perspectives such as quality, energy conservation and process improvement potentials. Both primary and secondary processes (recycling) of nine major non–renewable construction materials (steel, aluminium, copper, cement, concrete, ceramic, glass, polypropylene and polyvinylchloride (PVC)) have been evaluated in this study. The outlined theoretical exergy efficiency approach assesses the improvement potentials of the present manufacturing processes. The large difference between theoretical and industrial exergy demand suggests that exergy resources are utilised very inefficiently in current technologies. The study reveals that more than 55% of exergy is being lost in current technologies even though a significant amount of waste heat is recovered in different segments of the case study processes. Thus, attention is required to reduce the specific exergy losses through improved process design and introduction of new technology.

Ecological accounting for China based on extended exergy

Abstract All recent analyses acknowledge that environmental resources are in short supply and that it is on them that “carrying capacity” calculations ought to be based. For the specific case of the Chinese society, which is undergoing an unprecedented period of continuous growth, it seems therefore mandatory to alleviate the conflict between high-speed development and available resources. This paper analyzes the variation of the natural resources input into China during years 2000–2007 using the exergy and extended exergy socio-economic metric. Fluxes of materials, labor, capital and environmental remediation expenses were quantified by a numeraire solidly rooted on a second-law metric, so that a new mode of ecological accounting that quantifies both the composition and the proportion of the extended exergy flows can shed light on the total available energy input into the Chinese society. Two new indicators, labor production efficiency and net pro-capite exergy resource input, are proposed to depict the contribution of economic, social and environmental aspects to the usual four production factors and to express the conversion results in transferring efficiency and quantity from material energy to economic output. “Social” extended exergy analysis, applied to each one of the seven sectors of the society, is suggested as an effective method to reveal the energy quality degradation in the resource conversion process at both national and sectoral levels. The comparison of social resource accounting among different societies by using these two indicators may provide useful additional information to evaluate the production conversion coefficients, to assess the environmental impacts and to diagnose possible ecological dysfunctions. In addition, the extended exergy analysis of the Chinese society is helpful in uncovering the long-term resource depletion and promoting efficiency of the resource transformation in the social–economic–environmental system, thus providing a holistic method and a systematic view for decision makers responsible for environmental management.

Corrigendum: The Mineral Question: How Energy and Technology Will Determine the Future of Mining

A concept has been mistakenly attributed to the authors of the book while it should have been attributed to the authors of an article in it. The reference of the following sentence should therefore be Valero et al.,2010 rather than Stanek et al.,2010."The exergy of mineral deposits can be referenced to a “zero level” state that corresponds to the average concentration of the elements of the ore in the crust." The References change also accordingly: Valero, Al., Valero, A., and Martínez, A.(2010).Inventory of the exergy resources on earth including its mineral capital. Energy 35, 989–995. doi:10.1016/j.energy.2009.06.036 Instead of Stanek, W., Valero,A., Valero,A., and Martínez, A.(2010).Inventory of the exergy resources on earth including its mineral capital. Energy 35, 989–995. doi:10.1016/j.energy.2009.06.036

Thermodynamic based resource classification of renewable geothermal energy in Nigeria

Geothermal resources are a source of renewable alternative energy, providing heat from below the Earth's surface. This is often regarded as “energy under our feet,” and has the potential to contribute significantly towards energy diversification and energy security. Geothermal heat has two primary applications: heating/cooling and electricity generation. As an oil-producing country with geopressured zones, Nigeria has considerable geothermal resource potential, with the capacity to reduce the overt dependence on fossil fuels. Categorizing and classifying her resource potential is of utmost importance. Temperature and enthalpy are two parameters that have been used previously to classify geothermal resources, but are inadequate for the purpose of estimating geothermal system potential. Two fluids (e.g., saturated water or saturated steam) can have the same temperature in different phases, with resulting differences in their ability to do work. The concept of exergy, based on the second law of thermodynamics, describes the maximum amount of useful work that can be extracted from a system and is widely used in the field for resource accounting. In this study, potential geothermal sites in Nigeria are classified based on their Specific Exergy Index. Data used were collated from published literature, although due to lack of a consistently developed and maintained database on geothermal resources in Nigeria, not all known areas may have been characterized here. Data obtained from the fields/sites (oil wells, natural gas, and geothermal) were classified using the exergy method. The results indicate that Nigeria's geothermal sites/fields are low exergy resources with the capacity to contribute to the nation's total energy use. Furthermore, the absence of a consistent geothermal database and coherent geothermal energy policies indicates that research and policy measures are needed to aid all stakeholders in developing the nation's geothermal resources.

An exergy-based analysis of the co-evolution of different species sharing common resources

We consider a set of species feeding on the same exergy resources. The balance equations for the allocation of such resources among the species result in a set of non linear differential equations describing the dynamics of each population. We address the important question of optimal exploitation of the incoming exergy resource at the species- and ecological niche level: more specifically, after a formal definition of the exergy effectiveness of the conversion for the overall system and for each species, we search for the – unique or multiple – set of values of the model parameters that may lead to a sustainable situation in which all of the species survive and – together – optimally exploit the incoming exergy flux. The analytical results will be discussed both qualitatively and, for a 2-species case, quantitatively.

Methodology for the physical and chemical exergetic analysis of steam boilers

This paper presents a framework of thermodynamic, energy and exergy, analyses of industrial steam boilers. Mass, energy, and exergy analysis were used to develop a methodology for evaluating thermodynamic properties, energy and exergy input and output resources in industrial steam boilers. Determined methods make available an analytic procedure for the physical and chemical exergetic analysis of steam boilers for appropriate applications. The energy and exergy efficiencies obtained for the entire boiler was 69.56% and 38.57% at standard reference state temperature of 25°C for an evaporation ratio of 12. Chemical exergy of the material streams was considered to offer a more comprehensive detail on energy and exergy resource allocation and losses of the processes in a steam boiler.

Classification of Geothermal Energy Resources in Japan Applying Exergy Concept

SUMMARY Higher demand for energy consumption and importance of environmental issues has encouraged researchers and policy makers to consider renewable energies more seriously. Geothermal resources are a green energy source that can make a considerable contribution in some countries. Japan has the third ranking geothermal energy potential, and its geothermal electricity production is currently eighth in the world. Since the nature of geothermal resources dictates its method of utilization, it is important to categorize available resources. There is no consensus on classification of geothermal resources. Most scientists, from geologist to engineers, agree on the term temperature. However, temperature or enthalpy alone cannot describe the nature of fluids; they can have same temperature with different phases, such as saturated water or saturated steam. Using exergy for resource classification benefits their comparison, according to their ability to do work. In this paper, exergetic classification of geothermal resources was applied to 18 under-operating geothermal power plants in Japan. Six geothermal fields have high exergy resources according to their SExI values in excess of 0.5. The remaining geothermal fields in Japan are classified in the medium resources zone. Classification results can be used by decision makers as a reference for future geothermal development. Copyright © 2012 John Wiley & Sons, Ltd.

An Exergy-Based Model for Population Dynamics: Adaptation, Mutualism, Commensalism and Selective Extinction

Following the critical analysis of the concept of “sustainability”, developed on the basis of exergy considerations in previous works, an analysis of possible species “behavior” is presented and discussed in this paper. Once more, we make use of one single axiom: that resource consumption (material and immaterial) can be quantified solely in terms of exergy flows. This assumption leads to a model of population dynamics that is applied here to describe the general behavior of interacting populations. The resulting equations are similar to the Lotka-Volterra ones, but more strongly coupled and intrinsically non-linear: as such, their solution space is topologically richer than those of classical prey-predator models. In this paper, we address an interesting specific problem in population dynamics: if a species assumes a commensalistic behavior, does it gain an evolutionary advantage? And, what is the difference, in terms of the access to the available exergy resources, between mutualism and commensalism? The model equations can be easily rearranged to accommodate both types of behavior, and thus only a brief discussion is devoted to this facet of the problem. The solution space is explored in the simplest case of two interacting populations: the model results in population curves in phase space that can satisfactorily explain the evolutionistic advantages and drawbacks of either behavior and, more importantly, identify the presence or absence of a “sustainable” solution in which both species survive.

Cumulative exergetic assessment of LPFO utilised steam boilers

This paper relates to a study on the energy and exergy resources, transfers, consumption and losses in the combustion and heat exchanging units of industrial steam boilers. Mass, energy and exergy analyses, which included the physical and chemical exergies of material streams, were used to investigate the energy resource utilisation of Low Pour Fuel Oil (LPFO) in industrial steam boilers. The chemical exergies of LPFO and the exhaust flue gases were determined as 44,566.66 and 147.97 kJ/kg, respectively, for LPFO undergoing complete combustion process. Higher evaporation ratios and energy consumption by steam were associated with reduction in heat loss. Lower exergy destruction was due to lower rapid changes in temperature potential for the generation of steam in the heat exchanging unit. The average energy and exergy efficiencies of the boilers are obtained as 69.54 and 38.5%, respectively. The exergy efficiencies obtained for the combustion and heat exchanging units for the boilers investigated are given as 55.35, 49.06 and 58.69 and 63.80%, respectively. The results obtained in this study could be applied for energy resources management and control of oil–fired industrial steam boilers.