Emergy analysis of cassava-based fuel ethanol in China

Emergy analysis considers both energy quality and energy used in the past, and compensates for the inability of money to value non-market inputs in an objective manner. Its common unit allows all resources to be compared on a fair basis. As feedstock for fuel ethanol, cassava has some advantages over other feedstocks. The production system of cassava-based fuel ethanol (CFE) was evaluated by emergy analysis. The emergy indices for the system of cassava-based fuel ethanol (CFE) are as follows: transformity is 1.10 E + 5 sej/J, EYR is 1.07, ELR is 2.55, RER is 0.28, and ESI is 0.42. Compared with the emergy indices of wheat ethanol and corn ethanol, CFE is the most sustainable. CFE is a good alternative to substitute for oil in China. Non-renewable purchased emergy accounts for 71.15% of the whole input emergy. The dependence on non-renewable energy increases environmental degradation, making the system less sustainable relative to systems more dependent on renewable energies. For sustainable development, it is vital to reduce the consumption of non-renewable energy in the production of CFE.     

Emergy account for biomass resource exploitation by agriculture in China

On the basis of Odum's ecological economic measure of emergy as embodied solar energy, a system account of biomass resource exploitation by agriculture in China 2004 is developed in this paper, which supplements a former study on corresponding long-term historical trends during 1978 to 2000 (Chen et al., 2006. Emergy-based analysis of the Chinese agriculture. Agriculture, Ecosystems and Environment 115, 161–173). The aggregate fluxes and indicators for biomass resource exploitation in China 2004 are calculated and illustrated when compared with those for 2000 to elucidate the latest status of the Chinese agriculture as the exploitation sector for biomass resource. Data sources and algorithm are presented in detail as basic references for related analysis involving the ecological economy of biomass exploitation in agriculture.     

On the Second-Law inconsistency of Emergy Analysis

The paper argues against the claim made by Emergy Analysts that emergy is an exergy-based procedure. Both Emergy- and Exergy Analysis employ space- and time integrated energy input/output models to quantitatively assess the resource consumption of physical systems: the issue at stake is whether Emergy is embodied energy or embodied exergy. Although the compatibility of Exergy- and Emergy accounting procedures, the significance of the peculiar Emergy Algebra, and some cost-allocation issues have been studied in detail, a final agreement could not be reached, so that some doubt exists about the degree of compatibility of the two methods. The present paper shows that the definitions and the procedures employed in Emergy Analysis are in fact First Law-based, and that they neglect or misrepresent Second Law issues. This conclusion is reached by carefully reviewing and critically analyzing a series of general and specific procedures contained in the original Odum books and in some of the most representative publications by Emergy analysts.     

Emergy as a function of exergy

This paper aims to clarify some aspects of the discussion between “emergists” and “exergists”. First, we address the problem of the differences between energy-based emergy and exergy-based emergy: we show that the two are proportional, having the exergetic equivalent of solar energy as scale factor. In the second part, we show that emergy and transformity can be written as a function of exergy alone, in particular of “partial” efficiencies of the processes involved in a production system, from solar energy to the final product.     

Emergy evaluation of agricultural sustainability of Northwest China before and after the grain-for-green policy

China’s grain-for-green policy (GFGP) was implemented with the goal of improving ecological security. Consequently, agricultural energy and agrochemical inputs have been significantly increased to improve food security and to increase the income of farmers in the regions where the GFGP was implemented. In analysis of the sustainability of the agricultural system affected by the GFGP, it is essential to consider both economic profitability and environmental sustainability. Using Yanchi County as a case study area, this study used an emergy synthesis to examine the sustainability of the agricultural system before and after the GFGP in Northwest China. We found that the total emergy input and energy output of the agricultural system in the study area increased from 1991 to 2008; however, the sustainability of the system declined, and this decline was especially evident after the GFGP was launched in 2001. Increasing inputs of non-renewable purchased resources will not only reduce the effectiveness of the GFGP in Northwest China, but also hinder the implementation of the energy-saving and emission-reduction policy that China launched in 2005. We suggest that sustainable agricultural development in Northwest China should be based on effective use of renewable resources and development of a low-carbon agricultural economy.     

Embodied greenhouse gas emission by Macao

Comprehensive inventory of cities' greenhouse gas emissions (GHG) is the basis for cities to make appropriate mitigation plans. However, previous studies on cities' GHG emissions consider emissions occurring within the city boundary (Scope 1) and out of boundary electricity emissions (Scope 2), but neglect indirect emissions associated with commodities consumed by cities (Scope 3), resulting in emission leakage. To cope with this problem, a systematic accounting covering all 3 scopes is presented in a case study of Macao for the years 2005–2009, based on the latest embodied emission intensity databases for China and for the world. The results show that total emissions are dominated by indirect emissions mainly embodied in imports, which is 3–4 times direct emissions during the period concerned. It is verified that accounting under Scopes 1 and 2 cannot capture the full picture of cities' emissions, especially cities like Macao which are dominated by service industry and inevitably sustained by massive materials and services from other regions. Our study suggests that Macao should adjust its current GHG mitigation policies which consider only its emissions occurring within its border, as Macao is a net GHG emissions importer. This work is the first assessment of Macao's embodied GHG emissions.     

Emergy analysis of cropping–grazing system in Inner Mongolia Autonomous Region,China

An ecological energetic evaluation is presented in this paper as a complement to economic account for the cropping–grazing system in the Inner Mongolia Autonomous Region in China in the year 2000. Based on Odum's well-known concept of emergy in terms of embodied solar energy as a unified measure for environmental resources, human or animal labors and industrial products, a systems diagram is developed for the crop and livestock productions with arms and sub-arms for free renewable natural resource input, purchased economic investment, yields of and interactive fluxes between the cropping and grazing sub-industries. In addition to conventional systems indices of the emergy yield ratio (EYR), emergy investment ratio (EIR), environmental load ratio (ELR) and environmental sustainability index (ESI) introduced for congregated systems ecological assessment with essential implication for sustainability, new indicators of soil emergy cost (SEC), self-support intensity (SSI) and self-support orientation (SSO) are defined to characterize the desertification and internal recycling associated with the special agricultural system. Extensive emergy accounting is made for the cropping-grazing system as a whole as well as for the cropping and grazing subsystems. The overall cropping–grazing system is shown with outstanding production competence compared with agricultural systems in some other provinces and the national average in China, though confronted with severe desertification associated with soil loss. The production of crops has higher emergy density and yield rate per unit area as well as higher rate of soil loss than grazing system. The soil emergy cost defined as the soil loss emergy divided by the yield emergy is estimated to be of the same value for both of the subsystems, but the grazing activity is with less extraction intensity, leaving rangeland to rest and rehabilitate. Suggestions with regard to the local sustainability and national ecological security in northern China are explored for land-use policy making.     

Ecosystem health pattern analysis of urban clusters based on emergy synthesis: Results and implication for management

The evaluation of ecosystem health in urban clusters will help establish effective management that promotes sustainable regional development. To standardize the application of emergy synthesis and set pair analysis (EM–SPA) in ecosystem health assessment, a procedure for using EM–SPA models was established in this paper by combining the ability of emergy synthesis to reflect health status from a biophysical perspective with the ability of set pair analysis to describe extensive relationships among different variables. Based on the EM–SPA model, the relative health levels of selected urban clusters and their related ecosystem health patterns were characterized. The health states of three typical Chinese urban clusters – Jing-Jin-Tang, Yangtze River Delta, and Pearl River Delta – were investigated using the model. The results showed that the health status of the Pearl River Delta was relatively good; the health for the Yangtze River Delta was poor. As for the specific health characteristics, the Pearl River Delta and Yangtze River Delta urban clusters were relatively strong in Vigor, Resilience, and Urban ecosystem service function maintenance, while the Jing-Jin-Tang was relatively strong in organizational structure and environmental impact. Guidelines for managing these different urban clusters were put forward based on the analysis of the results of this study.     

A multi-criteria assessment of six energy conversion processes for H2 production

The study of Very Large Complex systems (“VLCS”), of which modern energy conversion systems are an important subset, requires a holistic approach to analyze the system itself and all of its “external” and “internal” interactions. The view taken in this paper is that the VLCS should be considered as an “extended” (in a sense specified below) thermodynamic system. The evaluation of the flows of matter and energy sustaining a VLCS and the knowledge of the transformations therein can be used to describe the rate of exploitation of the available natural resources, to assess the efficiency of the conversion process, and to provide a quantitative estimate of the impact of the system on the environment. This kind of information is an important part of the essential database of any Decision Support System for both the internal and global policy planning and for resources management. Several assessment methods are in use at present, and each one of them provides a different insight in the “performance” of the conversion chain under examination.     

Transforming cities towards sustainable low-carbon energy systems using emergy synthesis for support in decision making

Recognized as implementation actors of operative measures for transition towards a low carbon economy, cities must establish a development roadmap integrating local resources with local energy development plans. A systematic approach does not exist yet and cities develop their plans individually, which is difficult for small and medium sized cities due to limited development capacities. Conventional city planning approaches do not integrate considerations on energy, economy and environment in transition plans in an easily comparable way, yet making decisions with regards to these parameters is vital to determine outcomes of planned developments on future sustainability of the city.The paper presents a framework model based on emergy synthesis which integrates energy, economic and environmental city systems in the decision making process, examining associated theoretical challenges and application limitations. The method is applied on the city of Sisak in Croatia which has developed plans to implement several initiatives geared towards creating a smart energy city. The model enables simulation and assessment of impacts of individual projects targeting the development of a smart energy city on city sustainability expressed through emergy performance, used as a tool for evaluating local development alternatives within the boundary of local resources.     

A key review on emergy analysis and assessment of biomass resources for a sustainable future

The present study comprehensively reviews emergy analysis and performance evaluation of biomass energy. Biomass resources utilization technologies include (a) bioethanol production, (b) biomass for bio-oil, (c) biodiesel production, (d) straw as fuel in district heating plants, (e) electricity from Municipal Solid Waste (MSW) incineration power plant, (f) electricity from waste landfill gas. Systems diagrams of biomass, which are to conduct a critical inventory of processes, storage, and flows that are important to the system under consideration and are therefore necessary to evaluate, for biomasses are given. Emergy indicators, such as percent renewable (PR), emergy yield ratio (EYR), environmental load ratio (ELR) and environmental sustainability index (ESI) are shown to evaluate the environmental load and local sustainability of the biomass energy. The emergy indicators show that bio-fuels from crop are not sustainable and waste management for fuels provides an emergy recovery even lower than mining fossil fuel.     

Performance simulation for an anode-supported SOFC using Star-CD code

Experimental activities and computational fluid dynamics (CFD) simulation are presented in this paper for investigating the performance of an anode-supported solid oxide fuel cell (SOFC). The goal of this work is to assess a commercial CFD code, Star-CD with es-sofc module, to simulate the current–voltage (I–V) characteristics with respect to the experimental data. Compiled with the geometry of cell test housing, a 3D numerical model and test conditions were established to analyze the anode-supported cell (ASC) performance including current density and temperature distributions, fuel concentration, and fuel utilization. After adjusting parameters in the electrochemical model, the simulation results showed good agreements with the experimental data. The results also revealed that the power density increased while the fuel utilization decreased as the fuel flow rate increased.     

能值与传统方法的能源足迹比较分析

采用能值理论与生态足迹理论相结合的方法以及传统的能源足迹计方法,计算了中国1978年至2007年的能源足迹,从运算结果和方法上对两种计算方法进行了比较,指出,30a来,传统的能源足迹增长了3.38倍,能值的能源足迹增长3.46倍,总量上能值能源足迹是传统方法的1.77倍;原理上能值生态足迹在比传统生态足迹更能够反映出区域可持续发展的现状。提出,由于能值生态足迹还处于起步阶段,仍需进一步完善;二者均面临能源足迹指标单一化、政策意义不十分明确的问题。     

生物质电厂节能降耗改造能值分析

以某生物质电厂为研究对象,应用能值理论,借助能值转换率η_(Tr)、能值产出率η_(EYR)、环境负载率η_(ELR)、能值可持续指数η_(ESI)等指标,对企业主要耗能设备降耗改造进行能值分析。研究结果表明:烟气余热回收技术改造后的能值转换率最低,但是环境负载率也最高,所有的改造技术都能提高能值产出率,除了烟气余热回收技术,其余节能技术在能源可持续指标上都有良好的表现。综合考虑经济效益和污染等问题,烟气余热回收虽然有很好的节能效果,但是会对环境造成一定的污染,而光伏水泵发电和变频改造技术则具有较为平衡的效果。     

Conventional chiller performances simulation and field data

In most commercial buildings and industrial plants HVAC systems consume large amounts of energy, and usually offer the most significant potential for savings. Liquid conventional chillers play a very important role in providing these savings. Proper design, installation, and maintenance of these systems are therefore the key steps leading to improved efficiency which benefit both the customers and the utilities. To effectively materialize this concept two steps have been followed here. In the first section of this paper conventional chillers of different types have been modelled and simulated using a software (DOE2). The chillers are rated for a generic building and meteorological weather of San Diego. Performance parameters such as the part/full-load efficiencies, the number of occurrences during peak hours and load frequencies are then calculated. These results gave typical performance values (curves) which can be used to compare screw, centrifugal, and reciprocating chillers among each other within a predefined scope. In the following section the field data of 39 conventional chillers and the manufacturers specifications of some of them are collected and analysed. This gave an overall view of their actual field performance and their deviation from the manufacturers' specifications. Comparison of the simulated and collected data also provided better vision of the expected performances versus the actual performances, and pinpointed some major drawbacks in the design and sizing methodology. The results also led to important conclusions regarding the status quo and the possibilities in the immediate future. Preferred chiller types and methods of providing the required cooling energy recommended by the simulation results are compared with the existing ways of providing energy in order to conform the eventual promises and quantify the room for efficiency.     

Solar emergy evaluation for Chinese economy

A unified evaluation integrating various forms of energy sources and natural resources, products and services, and imports and exports is carried out systematically at the national scale for the booming Chinese economy 1978–2005, based on the ecological measure of solar emergy. The development of the economy is shown heavily dependent on the consumption of nonrenewable natural resources. Of the total resources use, the indigenous resources contribute the most, along with the increasing imports of nonrenewable resources. The development of the Chinese economy is characterized with the recovery stage during 1978–1981, transformation stage during 1981–1991, steady growth stage during 1991–2000, and accelerated increase stage after 2000, with specific distinctive systems indications.     

Fuel ejector design and simulation model for anodic recirculation SOFC system

In this paper, a new modeling technique for fuel ejectors with high entrainment ratio, low pressure increment and over heated working gases in an anodic recirculation solid oxide fuel cell (SOFC) system is presented. By utilizing the thermodynamic, fluid dynamic principles and chemical constraints inside ejectors and employing a two-dimensional function to compute fluid velocity, the developed model involves no more than nine algebraic equations and this is very simple compared to all existing models. The detailed procedures for fuel ejector design and simulation are provided and its effectiveness is verified through simulation and compared with testing results. It shows that the proposed model is more accurate than presently available models, and therefore can be better used for ejector design and performance simulations. The ejector performances for both situations of stand-alone and integrated into the SOFC system are also studied.     

Numerical simulation for rib and channel position effect on PEMFC performances

Simulation is an important method for engineers to probe the detailed transportation and reaction information inside fuel cells and guide their designs without large amount of experiments. Although many papers discussing fuel cell flow fields design could be found in documents, relative positions of the ribs and channels in the anode and cathode flow field plates haven't been paid attention to surprisingly. In this paper, simulation results were given to explain the influences of relative positions of the ribs and channels in the anode and cathode flow field plates on the proton exchange membrane fuel cell (PEMFC) performances. It is interesting that the influence differs with several factors and the information will be helpful for fuel cell design.     

Integration of genetic algorithm,computer simulation and design of experiments for forecasting electrical energy consumption

This study presents an integrated algorithm for forecasting monthly electrical energy consumption based on genetic algorithm (GA), computer simulation and design of experiments using stochastic procedures. First, time-series model is developed as a benchmark for GA and simulation. Computer simulation is developed to generate random variables for monthly electricity consumption. This is achieved to foresee the effects of probabilistic distribution on monthly electricity consumption. The GA and simulated-based GA models are then developed by the selected time-series model. Therefore, there are four treatments to be considered in analysis of variance (ANOVA) which are actual data, time series, GA and simulated-based GA. Furthermore, ANOVA is used to test the null hypothesis of the above four alternatives being equal. If the null hypothesis is accepted, then the lowest mean absolute percentage error (MAPE) value is used to select the best model, otherwise the Duncan Multiple Range Test (DMRT) method of paired comparison is used to select the optimum model, which could be time series, GA or simulated-based GA. In case of ties the lowest MAPE value is considered as the benchmark. The integrated algorithm has several unique features. First, it is flexible and identifies the best model based on the results of ANOVA and MAPE, whereas previous studies consider the best-fit GA model based on MAPE or relative error results. Second, the proposed algorithm may identify conventional time series as the best model for future electricity consumption forecasting because of its dynamic structure, whereas previous studies assume that GA always provide the best solutions and estimation. To show the applicability and superiority of the proposed algorithm, the monthly electricity consumption in Iran from March 1994 to February 2005 (131 months) is used and applied to the proposed algorithm.     

A critical comparison between thermoeconomic and emergy analyses algebra

Both thermoeconomic accounting and emergy analysis methodologies deal with energy systems and are aimed at allocating costs of input resources among system products. They have, however, different goals and fields of application. The former focuses on energy systems converting the energy of fuel/s into the desired product/s. The latter amplifies the perspective by extending it to the wider level of biosphere, by including all the processes that are involved in the formation of system inputs, either devices or material and energy flows.