Is bioethanol a sustainable energy source? An energy-, exergy-, and emergy-based thermodynamic system analysis

Biofuels are widely seen as substitutes for fossil fuels to offset the imminent decline of oil production and to mitigate the emergent increase in GHG emissions. This view is, however, based on too simple an analysis, focusing on only one piece in the whole mosaic of the complex biofuel techno-system, and such partial approaches may easily lead to ideological bias based on political preference. This study defines the whole biofuel techno-system at three scales, i.e., the foreground production (A), the background industrial network (B, including A), and the supporting Earth biosphere (C, including B). The thermodynamic concepts of energy, exergy and emergy measure various flows at these three scales, viz. primary resources, energy and materials products, and labor and services. Our approach resolves the confusion about scale and metric: direct energy demand and direct exergy demand apply at scale A; cumulative energy demand and cumulative exergy demand apply at scale B; and energy is applied at scale C, where it is named emergy, while exergy also can be applied at scale C. This last option was not examined in the present study.The environmental performance of the system was assessed using a number of sustainability indicators, including resource consumption, input renewability, physical benefit, and system efficiency, using ethanol from corn stover in the US as a technology case. Results were compared with available literature values for typical biofuel alternatives. We also investigated the influence of methodological choices on the outcomes, based on contribution analysis, as well as the sensitivity of the outcomes to emergy intensity. The results indicate that the techno-system is not only supported by commercial energy and materials products, but also substantially by solar radiation and the labor and services invested. The bioethanol techno-system contributes to the overall supply of energy/exergy resources, although in a less efficient way than the process by which the Earth system produces fossil fuels.Our results show that bioethanol cannot be simply regarded as a renewable energy resource. Furthermore, the method chosen for the thermodynamic analysis results in different outcomes in terms of ranking the contributions by various flows. Consequently, energy analysis, exergy analysis, and emergy analysis jointly provide comprehensive indications of the energy-related sustainability of the biofuel techno-system. This thermodynamic analysis can provide theoretical support for decision making on sustainability issues.     

Constructing a network of the social-economic consumption system of China using extended exergy analysis

The prominent conflict between consumption and environmental resources is acknowledged as a significant force in affecting the social-ecological community balance. The whole process of resource allocation, utilization, efficiency and outcome are crucial clues in uncovering the structural and functional characteristics in complex consuming systems. Herein, network relationship provides a system-oriented modeling technique for examining the structure as well as flow of materials or energy from an input–output perspective. Meanwhile, extended exergy, the only currently available thermodynamic based metric for social-economic environmental impacts associated with energy consumption, manpower and monetary operation as well as environmental emission, is an extension of the labor theory of value and a possible sustainability metric. The core purpose of this research is to construct a network of the social-economic consumption system of China using extended exergy analysis to explain the interrelationship among different sectors within a thermodynamic metric. Therefore, we firstly make a database of extended exergy accounting in the Chinese consumption system. Data are available for 2007, which can be divided into seven sectors based on the reclassification of the regularly published 42-sector Input–Output Table, namely, (1) Agriculture, (2) Extraction, (3) Conversion, (4) Industry, (5) Transportation, (6) Tertiary, and (7) Domestic sectors. Then we will construct an extended exergy network to gain insight into the thermodynamic distribution within sectoral criterion. Lastly, the network results and indicator analysis are explained for China's social metabolism maintained by a large quantity of energy, resources, and labor, as well as the environmental costs, within an exergy foundation.     

Thermodynamic analysis of wind energy

Wind energy is assessed thermodynamically, from resource and technology perspectives. The thermodynamic characteristics of wind are considered. Wind speed is affected by air temperature and pressure and has an effect on wind turbine performance, based on wind chill effect and Bernoulli's equation. The wind chill effect leads to temperature differences that suggest enthalpy and entropy components must be considered in a thermodynamic analysis. The wind pressure effect based on Bernoulli's equation affects the entropy of wind. These components have not previously been considered in evaluations of wind turbine efficiency for electricity generation. A new efficiency formula for wind energy systems is described, which provides important information about the system. It is seen that average differences between energy and exergy efficiencies are approximately 40% at low wind speeds and up to approximately 55% at high wind speeds. Copyright © 2005 John Wiley & Sons, Ltd.     

Applying bottom-up analysis to identify the system boundaries of non-energy use data in international energy statistics

Data on the non-energy use of fossil fuels in energy statistics are subject to major uncertainties. We apply a simple bottom-up methodology to recalculate non-energy use for the entire world and for the 50 countries with the highest consumption of fossil fuels for non-energy purposes. We quantify worldwide non-energy use in the year 2000 to be 24±2 exajoules (EJ), thereby accounting for 6% of the global total primary energy supply (TPES). Our bottom-up estimates are in line with data from international energy statistics for the entire world and for 14 individual countries. Our estimates exceed official non-energy use data for 22 countries, whereas they are lower than official data in the case of 14 countries. Inconsistent system boundaries of non-energy use data in international energy statistics can explain parts of the observed deviations. We regard our bottom-up methodology as reliable albeit being attached with uncertainties. We recommend its use for energy statisticians and greenhouse gas (GHG) inventory makers to generate a shortlist of countries, for which efforts should be made to clarify and improve the quality of non-energy use data in national and international energy statistics.     

The additional benefits of energy efficiency investments—a systematic literature review and a framework for categorisation

Investments in industrial energy efficiency are essential for meeting future energy needs. Nevertheless, the industrial sector’s current efforts in energy efficiency investments are insufficient. Additional benefits of energy efficiency investments have been suggested to improve the financial attractiveness of energy efficiency investments. Yet, previous research indicates that not all benefits are included when investment opportunities are evaluated, leading to an underestimation of what a firm will gain from the investment. Additionally, previous research lacks conceptual frameworks for describing these additional benefits at an early stage in the investment process. Moreover, various benefit terms are found in currently existing research, but there are a lack of definitions and distinctions attributed to these terms. Therefore, this paper provides a systematic review on the benefit terms of energy efficiency investments, establishes non-energy benefits as the term most relevant for such investments and provides a new definition of the concept. Further, a new framework for categorising non-energy benefits to enable them to be included during the investment process is developed, in which the level of quantifiability and time frame of the non-energy benefits are taken into account. Including non-energy benefits in the investment process can make energy efficiency investments more attractive and increase their priority against other investments. Moreover, non-energy benefits can reinforce drivers as well as counterbalance known barriers to energy efficiency investments. Acknowledging non-energy benefits can thus contribute to an increased adoption level for energy efficiency investments.     

An outlook for sustainable forest bioenergy production in the Lake States

The Lake States region of Minnesota, Wisconsin and Michigan offers significant potential for bioenergy production. We examine the sustainability of regional forest biomass use in the context of existing thermal heating, electricity, and biofuels production, projected resource needs over the next decade including existing forest product market demand, and impacts on price and feasibility. Assuming $36 per dry tonne at roadside, 4.1 million dry tonnes of forest biomass could be available region-wide. However, less is likely available due to localized environmental and forest cover type constraints, and landowner willingness to harvest timber. Total projected demand of 5.7 million dry tonnes, based on current and announced industry capacity, exceeds estimates of biomass availability, which suggests that anticipated growth in the forest-based bioeconomy may be constrained. Attaining projected demand will likely require a combination of higher cost feedstocks, integration of energy and non-energy uses, and careful management to meet environmental constraints. State distinctions in biomass harvest guidelines and the propensity for third-party forest certification will be critical in providing environmental safeguards. The cumulative effect of policy initiatives on biomass competition are discussed in the context of an emerging Lake States bioeconomy.     

Thermodynamic parameters for energy sustainability of urban areas

This paper presents some thermodynamic indicators useful for energy planning of urban areas, and for defining the scenarios of integrated low environmental impact energy strategies and actions in an urban area. It is based on the results of the energy balance of a reference volume obtained by the Geographical Information System (GIS) techniques applied to the built-up area studied. The defined parameters allow evaluation of the sustainability of energy use in an urban area and its areal distribution in different building meshes superimposed on the area considered, using entropy.     

Optimization method for metal-forming processes

The paper presents a general-purpose optimization method for metal-forming processes by plastic deformation based on their modelling as thermodynamic processes with entropy generation minimization. To this purpose, equations have been formulated describing a thermodynamic system consisting of two subsystems: a tool and a workpiece which is a basic feature of each metal-forming process. A mathematical model of the thermodynamic system has been derived based on fundamental equations in continuum mechanics related to a deformable solid and the basic laws of thermodynamics. The mathematical model describes the phenomena related to the thermomechanical strength of the tool; the energy balance of the system; displacements and deformation in the tool–workpiece system due to mechanical and temperature factors, etc. On the basis of the second law of thermodynamics, entropy generation has been defined as a generalized optimization criterion and its functional has been synthesized containing the tensor functions of stresses and of strain velocities, the scalar functions of temperatures and the relative velocities of the two media. A summarized algorithm for entropy generation minimization has been proposed and illustrated by a numerical example.     

Growth curves and sustained commissioning modelling of renewable energy: Investigating resource constraints for wind energy

Several recent studies have proposed fast transitions to energy systems based on renewable energy technology. Many of them dismiss potential physical constraints and issues with natural resource supply, and do not consider the growth rates of the individual technologies needed or how the energy systems are to be sustained over longer time frames. A case study is presented modelling potential growth rates of the wind energy required to reach installed capacities proposed in other studies, taking into account the expected service life of wind turbines. A sustained commissioning model is proposed as a theoretical foundation for analysing reasonable growth patterns for technologies that can be sustained in the future. The annual installation and related resource requirements to reach proposed wind capacity are quantified and it is concluded that these factors should be considered when assessing the feasibility, and even the sustainability, of fast energy transitions. Even a sustained commissioning scenario would require significant resource flows, for the transition as well as for sustaining the system, indefinitely. Recent studies that claim there are no potential natural resource barriers or other physical constraints to fast transitions to renewable energy appear inadequate in ruling out these concerns.     

A Second Law analysis of the optimum design and operation of thermal energy storage systems

Second Law analysis techniques based on the minimization of entropy generation are applied to the optimal design and operation of a sensible heat thermal energy storage system in which the storage element is both heated and cooled by flowing streams of gases. The results of this study show that (1) an entire operational cycle, which consists of a storage process and a removal process, must be considered (as opposed to the storage process alone) in order to optimize the design and performance of such a system; and (2) a typical optimum system destroys approximately 70–90% of the entering availability and, therefore, has an extremely low thermodynamic efficiency.     

Development and performance analysis of a new solar tower and high temperature steam electrolyzer hybrid integrated plant

In this article, an extensive thermodynamic performance assessment for the useful products from the solar tower and high-temperature steam electrolyzer assisted multigeneration system is performed, and also its sustainability index is also investigated. The system under study is considered for multi-purposes such as power, heating, cooling, drying productions, and also hydrogen generation and liquefaction. In this combined plant occurs of seven sub-systems; the solar tower, gas turbine cycle, high temperature steam electrolyzer, dryer process, heat pump, and absorption cooling system with single effect. In addition, the energy and exergy performance, irreversibility and sustainability index of multigeneration system are examined according to several factors, such as environment temperature, gas turbine input pressure, solar radiation and pinch point temperature of HRSG. Results of thermodynamic and sustainability assessments show that the total energetic and exergetic efficiency of suggested paper are calculated as 60.14%, 58.37%, respectively. The solar tower sub-system has the highest irreversibility with 18775 kW among the multigeneration system constituents. Solar radiation and pinch point temperature of HRSG are the most critical determinants affecting the system energetic and exergetic performances, and also hydrogen production rate. In addition, it has been concluded that, the sustainability index of multigeneration suggested study has changed between 2.2 and 3.05.     

Engineering sustainability: thermodynamics,energy systems,and the environment

Thermodynamic concepts have been utilized by practitioners in a variety of disciplines with interests in environmental sustainability, including ecology, economics and engineering. Widespread concern about resource depletion and environmental degradation are common to them all. It has been argued that these consequences of human development are reflected in thermodynamic parameters and methods of analysis; they are said to mirror energy transformations within society. ‘Exergy’, a quantity which follows from the First and Second Laws of Thermodynamics, has been viewed as providing the basis of a tool for resource and/or emissions accounting. It is also seen as indicating natural limits on the attainment of sustainability. The more traditional use of the exergy method is illustrated by a number of cases drawn from the United Kingdom energy sector: electricity generation, combined heat and power schemes, and energy productivity in industry. This indicates the scope for increasing energy efficiency, and the extent of exergetic ‘improvement potential’, in each of these areas. Poor thermodynamic performance is principally the result of exergy losses in combustion and heat transfer processes. However, the application of such thermodynamic ideas outside the sphere of engineering has its critics. The link between the efficiency of resource utilization, pollutant emissions, and ‘exergy consumption’ is only indirect, and generally provides an insufficient basis for environmental appraisal. Methods of energy and exergy analysis are, therefore, evaluated as appropriate measures of sustainability in and beyond the energy sector. Copyright © 2004 John Wiley & Sons, Ltd.     

Implementation of energy efficiency measures in compressed air systems: barriers,drivers and non-energy benefits

Increased global competition and resource scarcity drives industrial companies to cut costs. Energy can be a significant component of such cuts, particularly for energy-intensive companies. Improving energy efficiency in industry is complex, as it pertains to various energy-using processes that are heavily intertwined. One such process is the compressed air system (CAS), which is used in most industrial companies worldwide. Since energy efficiency improvement measures for various types of energy-using processes differ, technology-specific measures might encounter different barriers to and drivers for energy efficiency. The same applies to the non-energy benefits (NEBs) related to energy efficiency improvement measures; since measures vary between various energy-using processes, the perceived NEBs might be different as well. The aim of this paper is to study the barriers to, drivers for and NEBs of CAS energy efficiency improvement measures from the perspectives of three actors. Carried out as an interview study combined with a questionnaire, the paper merges the perspectives of users, audit experts and suppliers of CASs. The results showed that the major barriers are related to the investment, or are of an organisational character, and that organisational and economic factors seemed to be important for making positive decisions on energy efficiency investments and measures in CASs. Major NEBs for CASs include productivity gains and the avoidance of capital expenditures. The results of this study also address the importance of having a comprehensive approach to recognise additional effects of energy efficiency improvements in CASs.     

Exergy Analysis of Photo-Thermal Interaction Process between Solar Radiation Energy and Solar Receiver

A unified theory of non-equilibrium radiation thermodynamics is always in search as it is meaningful for solar energy utilization. An exergy analysis of photo-thermal interaction process between the solar radiation energy and solar receiver is conducted in this paper. The non-equilibrium radiation thermodynamic system is described. The thermodynamic process of photo-thermal interaction between the solar radiation and solar receiver is introduced. Energy, exergy and entropy equations for the photo-thermal process are provided. Formulas for calculating the optimum receiving temperatures of the solar receiver under both non-concentration and solar concentration conditions are presented. A simple solar receiver is chosen as the calculation example to launch the exergy analysis under non-concentration condition. Furthermore, the effect analysis of solar concentration on the thermodynamic performance of the solar receiver for solar thermal utilization is carried out. The analysis results demonstrate that both the output exergy flux and efficiency of the solar receiver can be improved by increasing the solar concentration ratio during the solar thermal utilization process. The formulas and results provided in this paper may be used as a theoretical reference for the further studies of non-equilibrium radiation thermodynamic theory and solar thermal utilization.     

Local entropy generation for saturated two-phase flow

This paper addresses the estimation of local entropy generation rate for diabatic saturated two-phase flow of a pure fluid. Two different approaches have been adopted for this thermodynamic characterization: the separated flow model using the classical vapor flow quality, and the mixture model, using the thermodynamic vapor quality. Based on these two models, two distinct expressions for the local entropy generation have been proposed. The analysis explicitly shows the contribution of heat transfer and pressure drop respectively to the local entropy generation. The contribution due to phase-change process is also determined using the mixture model. The developed formulation is applied to analyze the thermodynamic performance of enhanced heat transfer tubes under different conditions. It is shown that enhanced tubes may be a relevant solution for reducing entropy generation at low mass velocities whereas smooth tubes remain the best solution at higher ones.     

Sustainability assessment of wood-based bioenergy – A methodological framework and a case-study

The sustainability of the utilization of wood biomass for energy and other purposes has been widely assessed in different studies. Especially discrete methods from the family of Multi-Criteria Decision Analysis (MCDA), such as Outranking methods, Multi-Attribute Utility Theory, and Analytic Hierarchy Process (AHP) are often applied. AHP is considered one of the most promising options to be used in sustainability assessments, because it is comprehensible to apply and it incorporates the preferences of decision-makers in an advanced manner. In this study, we present a theoretical multi-dimensional framework based on a modified version of AHP for assessing sustainability and apply it in a case of wood-based bioenergy production in eastern Finland. The framework includes four dimensions of sustainability and life cycle phases from the acquisition of raw material to manufacturing the final product. The production systems used in the empirical sustainability assessments are a local heat production plant, a combined heat and power production plant, and a wood pellet processing plant. Local sustainability experts identified indicators relevant at the regional scale. The impact assessment data were obtained from literature, by interviewing the managers of the bioenergy plants, and from a postal survey administered to local people. The local heat provider received the highest sustainability index; however, there were no considerable differences between the sustainability indexes. None of the bioenergy production systems can be considered the most sustainable regardless of the assumptions employed in the framework. The framework provided the basis for a quantitative, interdisciplinary approach to assess sustainability.     

无缝钢管制造许可鉴定评审质量控制

本文概述了压力管道元件制造许可鉴定评审程序、型式试验及鉴定评审的基本要求，并从取证单位的资源条件、质量保证体系以及产品安全性能等5个方面介绍了压力管道元件（无缝钢管）制造许可鉴定评审的质量控制及其评审中常见的主要问题。提出了通过提高制造单位的质量意识完善鉴定评审机构严格执行生产准入制度以及加大监察机关加强证后监管力度，确保压力管道元件（无缝钢管）产品的安全。     

The energy demand in the manufacturing sector of Pakistan: some further results

The purpose of this study was to re-examine the role of energy in the manufacturing sector of Pakistan using a Partial Equilibrium Approach. GL restricted cost function along with the factor demand equations were estimated using Zellner’s iterative procedure. Higher energy prices do not seem to adversely affect investment in capital. Substitution possibilities between energy and non-energy inputs are very limited and therefore energy price hikes may directly affect the cost of production. Inter-fuel cross price elasticities indicate that there are substitution possibilities between electricity and gas.     

The threshold effects of energy efficiency on the elasticity of substitution between energy and non-energy factors

Considerable efforts have been made to estimate the relationship between energy and non-energy inputs in the production process. However, it remains controversial whether energy and non-energy inputs are complements or substitutes. Empirical analysis is conflicting on this issue. This study seeks to explore an alternative way to explain these conflicting results by examining the issue from the perspective of energy efficiency. This study is based on time series data for capital, labor, and energy from 28 Chinese provinces, covering 1985 to 2012. The results show that capital and energy are substitutes in all of the provinces, whereas labor and energy are complements in most of the provinces. Using the threshold effect model, we discover evidence of a threshold point based on the amount of energy efficiency activity in a province. This point separates the substitution behavior of provinces between energy and non-energy inputs. Low-energy efficiency provinces do not substitute as readily as high-energy efficiency provinces. The findings imply that the energy-saving technologies should be applied in provinces with comparatively higher energy intensity because they have more energy conservation potential.     

Industrial energy analysis,thermodynamics and sustainability

Thermodynamic methods of (energy and exergy) analysis are employed to illustrate energy use in industry. The scope for increasing energy efficiency, and the extent of exergetic ‘improvement potential’ are examined. Poor thermodynamic performance is principally the result of exergy losses in combustion and heat-transfer processes. The late Professor Willem van Gool (a distinguished Dutch physical chemist) was at the forefront of the development and application of energy and exergy methods. He also explored the link between energy and economics. The work of van Gool and others researchers who laid down the foundations of industrial energy analysis are reviewed. These contributions are placed in the broader context of the modern paradigm of sustainable development, and their implications for the future direction of European Union energy and environmental strategies are discussed. Thermodynamic concepts have been utilised by practitioners in a variety of disciplines with interests in environmental sustainability, including ecology, economics and engineering. Widespread concern about resource depletion and environmental degradation are common to them all. Van Gool was instrumental in stimulating a dialogue across the economic and physical sciences. Some researchers view thermodynamic parameters as mirroring energy transformations within society. However, it is argued (after Hammond GP. Engineering sustainability: thermodynamics, energy systems, and the environment. Int J Energy Res 2004;28:613–639.) that they may simply reflect a weak analogy or metaphor, rather than representing thermodynamic limits in a physical sense.