Uncertainties and sustainability concepts in biofuel supply chain management: A review

Biofuel energy as an alternative and additive form of energy to fossil fuel has gained much attention in recent times. In order to sustain such a vision, a robust supply chain is of extreme importance in helping to deliver competitive biofuel to the end user markets. In this paper, firstly, an introduction of the evolution of biofuels and the general structure of the biofuel supply chain are presented. Secondly, the three types of decision making levels and uncertainties that are inherent within the biofuel supply chain are discussed. Thirdly, important methodologies for modeling uncertainties in the decision making process are provided. Fourthly, sustainability concepts and models that give perspectives to the social, economical and environmental concepts are reviewed. Finally, conclusions and future research based on incorporating uncertainties and sustainability concepts within the biofuel supply chain are drawn and suggested, respectively.     

Modelling of fluid flow and heat transfer to assess the geothermal potential of a flooded coal mine in Lorraine,France

The flooding of the Lorraine coal mines (France), representing a huge reservoir of about 154 × 10⁶ m³, began in June 2006. After attaining thermal equilibrium with the surrounding rocks, the water temperature in the deepest parts is expected to reach 55 °C, giving the opportunity for the extraction of low-enthalpy geothermal waters that may be suitable for district heating purposes. We present some numerical modelling results of the thermally driven convective flow in an open vertical shaft and in the entire mine reservoir. A dual permeability/porosity approach was used in the reservoir model, which includes open galleries and vertical shafts, coal panels backfilled with sand, and intact rock masses. Two scenarios of heat extraction with different flow regimes were investigated. A sensitivity analysis shows that the temperature decline in the production zone is highly dependent on the permeability of the surrounding porous rocks. Larger permeabilities result in higher water temperatures at the production shaft due to greater inflows of warm water from those rock masses.     

Modelling of water–energy systems. The case of desalination

The primary aim of this work is to assess the long-term sustainability of the desalination technology in alleviating the global freshwater crisis. The Canary Islands (Spain) have a well-established experience in desalination and the Island of Lanzarote –whose water supply is entirely dependent upon this technology—is taken as an illustrative case study. Analytical information obtained from the Material and Energy Flow Accounts of Lanzarote's desalination metabolism are fed into a model developed with the Vensim software to allow future trends, prediction and evaluate different scenarios. To conclude, the main environmental impacts of the desalination technology are addressed and some socially induced factors leading to unsustainable water management are briefly discussed.     

Modelling and control of hydrogen and energy flows in a network of green hydrogen refuelling stations powered by mixed renewable energy systems

The planning of a hydrogen infrastructure with production facilities, distribution chains, and refuelling stations is a hard task. Difficulties may rise essentially in the choice of the optimal configurations. An innovative design of hydrogen network has been proposed in this paper. It consists of a network of green hydrogen refuelling stations (GHRSs) and several production nodes. The proposed model has been formulated as a mathematical programming, where the main decisions are the selection of GHRSs that are powered by the production nodes based on distance and population density criteria, as well the energy and hydrogen flows exchanged among the system components from the production nodes to the demand points. The approaches and methodologies developed can be taken as a support to decision makers, stakeholders and local authorities in the implementation of new hydrogen infrastructures. Optimal configurations have been reported taking into account the presence of an additional hydrogen industrial market demand and a connection with the electrical network. The main challenge that has been treated within the paper is the technical feasibility of the hydrogen supply chain, that is mainly driven by uncertain, but clean solar and wind energy resources. Using a Northern Italian case study, the clean hydrogen produced can be technically considered feasible to supply a network of hydrogen refuelling stations. Results show that the demands are satisfied for each time period and for the market penetration scenarios adopted.     

Electricity supply industry modelling for multiple objectives under demand growth uncertainty

Appropriate energy–environment–economic (E3) modelling provides key information for policy makers in the electricity supply industry (ESI) faced with navigating a sustainable development path. Key challenges include engaging with stakeholder values and preferences, and exploring trade-offs between competing objectives in the face of underlying uncertainty. As a case study we represent the South African ESI using a partial equilibrium E3 modelling approach, and extend the approach to include multiple objectives under selected future uncertainties. This extension is achieved by assigning cost penalties to non-cost attributes to force the model's least-cost objective function to better satisfy non-cost criteria. This paper incorporates aspects of flexibility to demand growth uncertainty into each future expansion alternative by introducing stochastic programming with recourse into the model. Technology lead times are taken into account by the inclusion of a decision node along the time horizon where aspects of real options theory are considered within the planning process. Hedging in the recourse programming is automatically translated from being purely financial, to include the other attributes that the cost penalties represent. From a retrospective analysis of the cost penalties, the correct market signals, can be derived to meet policy goal, with due regard to demand uncertainty.     

An evaluation of the competitiveness of the US coal market

This paper examines the competitiveness of the US coal industry. The methodological approach is based on a comparison of what actually occurred in 1979, 1980 and 1981 with what a cost-minimizing (transportation type) model for the same years would have predicted. The level of disaggregation in the model is consistent with that of the National Coal Model [4] which has 31 supply regions, 44 demand regions and 40 different coal types. The clear conclusion which emerges is that modelling the US coal industry in a cost-minimizing framework is valid.     

Coal mining industry restructuring in Poland: implications for the domestic and international coal markets

The paper describes the efforts to improve the profitability of the Polish hard-coal industry. The experience of seven years of restructuring programmes shows that the industry has to reduce the number of existing coal mines. Coal production in Poland will decrease and coal will no longer be the cheap source of energy. The final shape of hard-coal industry will force the change in energy balance of Poland and will change the position of Polish coal in the international coal market.     

Conditions for the sustainability of biomass based fuel use

Sustainability of biomass based fuel use requires that in biomass production erosion and water usage do not exceed addition to stocks of soil and water and that levels of nutrients and organic matter in soils do not decrease. Levels of volatile carbon compounds and N₂O in the atmosphere should remain unaffected. To maintain ecosystems services of nature useful to mankind, restriction of biomass production to degraded and currently fallow land is to be preferred. Also sustainability of biomass-for-energy use requires a high efficiency recycling of nutrients present in ashes and low emissions of persistent organics, acidifying compounds and heavy metals due to biomass combustion. Meeting such conditions requires major efforts.     

Residual coal exploitation and its impact on sustainable development of the coal industry in China

Although China owns large coal reserves, it now faces the problem of depletion of its coal resources in advance. The coal-based energy mix in China will not change in the short term, and a means of delaying the coal resources depletion is therefore urgently required. The residual coal was exploited first with a lower recovery percentage and was evaluated as commercially valuable damaged coal. This approach is in comparison to past evaluations when the residual coal was allocated as exploitation losses. Coal recovery rates, the calculation method of residual coal reserves and statistics of its mines in China were given. On this basis, a discussion concerning the impacts on the delay of China's coal depletion, development of coal exploitation and sustainable developments, as well as technologies and relevant policies, were presented. It is considered that the exploitation of residual coal can effectively delay China's coal depletion, inhibit the construction of new mines, redress the imbalance between supply and demand of coal in eastern China, improve the mining area environment and guarantee social stability. The Chinese government supports the exploitation technologies of residual coal. Hence, exploiting residual coal is of considerable importance in sustainable development of the coal industry in China.     

A simple theoretical analysis of the pyrolysis of an isothermal particle of coal

The pyrolysis of particles of coal (or biomass), small enough for internal conduction of heat not to be a controlling factor, is considered. Altogether five dimensionless groups are identified as characterising both the rates of pyrolysis and the change in temperature of these small isothermal particles. A sensitivity analysis demonstrates that three dimensionless groups easily have most influence on the kinetics of pyrolysis. This enables a simple mathematical model to be formulated, but assuming that only one reaction for thermal decomposition occurs at a time. The heat of devolatilisation is not ignored. It is found that, if the temperature around such a pyrolysing particle exceeds a threshold value, external heat transfer controls the rate of pyrolysis. In fact, whether there is kinetic or external heat transfer control is mainly determined by the two dimensionless groups 3Nuk_l,_∞ /2Aρ_c,o (a modification of the ratio of the characteristic times for chemical reaction and a coal particle to heat up) and RT_∞/E_v. Thus, for kinetic control RT_∞/E_v must be smaller than a critical value, i.e.E_v has to exceed a threshold value. The third important group, RΔH_v/ has less influence. Under kinetic control, a particle’s temperature is close to the ambient temperature and consequently does not change during thermal decomposition, whereas, when external heat transfer controls, the particle’s temperature can rise during pyrolysis by up to 100 K. The mean value of the activation energy for the devolatilisation of many coals is deduced to be ≈240 kJ/mol, i.e. higher than many measured values, which appear to have been obtained, when heat transfer controlled the rate. The temperature during pyrolysis of these “thermally thin particles” is not altered significantly by fragmentation, swelling or a change of shape.     

A new basis for assessing the sustainability of natural resources

Natural resources are generally referred to as “depleteable” and “renewable.” The term “renewable” typically refers to “biological” resources, such as fish and forests. Other renewable resources, including hydro, solar, tidal, wave and wind power are not explicitly addressed by existing economic theories. Identification of the physical and economic characteristics of natural resources enables the real cost of natural resource use to be identified, providing the basis of a single unifying theory of all resources based on a user cost function. Two key considerations emerge: firstly, in relation to resource depletion, it is necessary to explore the role of rate of consumption relative to rate of supply as a quantitative aspect of resources; secondly, in relation to pollution, it is necessary to investigate the role of rate of change of entropy as a resource is utilised as a qualitative aspect of resources. Once the true costs of resource use have been established, natural resources can be classified in a systematic way. Clear differences between different types of natural resources emerge, leading to new terms being proposed to describe different resource types.     

Comparative study on efficiency performance of listed coal mining companies in China and the US

Continually rising energy prices in global markets highlights a serious concern about the need to improve energy efficiency and the efficiency in energy sector in many countries. China, as one of the fastest growing countries in the world and the largest coal producer, has high coal consumption but a low recovery rate of coal utilization. Coal efficiency and the efficiency in coal industry have therefore attracted a great deal of attention from Chinese policy makers, coal firms and academics. This study attempts to compare the relative technical efficiency performance of listed coal mining companies in China and the US using CCR and BCC models in the advanced DEA linear programming. The results show that the level of relative efficiency in Chinese coal mining enterprises, regardless of total technical efficiency or decomposed pure technical and scale efficiency, is much lower than in American coal firms. The study also highlights the input resources that cause the inefficiency of Chinese coal mining companies. Furthermore, in-depth discussion and analysis of how the institutional environments of the two countries could cause the differences are provided.     

Distinctive features of coal reconversion in the European Union

The phenomenon of industrial rationalization is part of our economic reality. The several rhythms of economic growth, besides the changes in the dynamic of the markets, the endowment of productive factors and the technological change, have made their study a complex task, in which there are elements to keep in mind and numerous points of view that could be adopted. Coal in Europe is in a particularly delicate situation. After more than three decades of restructuring and modernisation, the coal industry is still not competitive, when compared with world market prices, and the social situation of coal workers and coal communities is hard. The importance of these processes and their effects on the economic and social development in areas or regions in which the coal industry affects their whole activity, in our opinion, justifies our interest in deepening the knowledge of the complex reality of coal rationalization. Our objective is to offer an overall impression of the coal sector in the European Union as well as the main instruments for economic and social regeneration in the coal regions.     

Developing a sustainability framework for the assessment of bioenergy systems

The potential for biomass to contribute to energy supply in a low-carbon economy is well recognised. However, for the sector to contribute fully to sustainable development in the UK, specific exploitation routes must meet the three sets of criteria usually recognised as representing the tests for sustainability: economic viability in the market and fiscal framework within which the supply chain operates; environmental performance, including, but not limited to, low carbon dioxide emissions over the complete fuel cycle; and social acceptability, with the benefits of using biomass recognised as outweighing any negative social impacts. This paper describes an approach to developing a methodology to establish a sustainability framework for the assessment of bioenergy systems to provide practical advice for policy makers, planners and the bioenergy industry, and thus to support policy development and bioenergy deployment at different scales. The approach uses multi-criteria decision analysis (MCDA) and decision-conferencing, to explore how such a process is able to integrate and reconcile the interests and concerns of diverse stakeholder groups.     

Towards sustainability of energy systems: A primer on how to apply the concept of energy services to identify necessary trends and policies

Virtually all goods and services that characterize modern societies’ welfare depend on the provision of commercial energy. The core objective of this paper is to identify necessary changes in trends for achieving a transition towards more sustainable energy systems and development paths. The major conclusions of this analysis are (i) a rigorous rethinking process has to take place to identify which level of energy services per capita lead to enhancing human welfare and quality of life; (ii) a significant increase in energy conversion efficiency has to be triggered to finally provide energy services with far less input of energy than today; (iii) a continuous increase in the share of renewable energy sources and other low-emission options has to be brought about; (iv) however, as history has shown this process of technological learning has to be accompanied by proper energy price and regulatory policies. Otherwise, it is very likely that energy conservation gains due to technical efficiency improvements will be outweighed again by increases in energy service demand and, straightforward, energy consumption and CO₂ emissions.     

Steps to discern sustainability criteria for a certification scheme of bioethanol in Brazil: Approach and difficulties

Taking Brazilian bioethanol as an example, this paper presents possible sustainability criteria for a certification scheme aimed to minimize negative socio-ecological impacts and to increase the sustainable production of biomass. We describe the methods that have led us to the identification of a first set of feasible sustainability criteria for Brazilian bioethanol and discuss issues to be considered when developing certification schemes for sustainability. General problems of a certification scheme lie in the inherent danger of introducing new non-tariff trade barriers and in the problems of including important higher scale issues like land conversion and food security. A certification system cannot replace a thorough analysis of policy impacts on sustainability issues.     

Lessons from first generation biofuels and implications for the sustainability appraisal of second generation biofuels

AimsThe emergence of second generation (2G) biofuels is widely seen as a sustainable response to the increasing controversy surrounding the first generation (1G). Yet, sustainability credentials of 2G biofuels are also being questioned. Drawing on work in Science and Technology Studies, we argue that controversies help focus attention on key, often value-related questions that need to be posed to address broader societal concerns. This paper examines lessons drawn from the 1G controversy to assess implications for the sustainability appraisal of 2G biofuels.ScopeWe present an overview of key 1G sustainability challenges, assess their relevance for 2G, and highlight the challenges for policy in managing the transition. We address limitations of existing sustainability assessments by exploring where challenges might emerge across the whole system of bioenergy and the wider context of the social system in which bioenergy research and policy are done.ConclusionsKey lessons arising from 1G are potentially relevant to the sustainability appraisal of 2G biofuels depending on the particular circumstances or conditions under which 2G is introduced. We conclude that sustainability challenges commonly categorised as either economic, environmental or social are, in reality, more complexly interconnected (so that an artificial separation of these categories is problematic).     

Assessing the sustainability of biofuels: A logic-based model

Over the last decade, the production and consumption of biofuels increased rapidly worldwide, in an attempt to reduce GHG (greenhouse gas) emissions, diversify transportation fuels, promote renewable energy, and create or maintain employment, especially in rural areas and developing countries. Although policy instruments being currently implemented in industrialized regions focus on sustainable biofuels, the definition and assessment of sustainability remains a highly debated issue. Several countries have adopted compulsory targets or financial incentives for promoting biofuels, and only a few countries have accounted for sustainability certification schemes for those biofuels within their policy framework. In this paper, a logic-based model for assessing the sustainability of biofuels is presented. The model uses a hierarchical structure to link multiple factors from the more specific variables to the most general one, sustainability performance. The strengths and limitations of the model are discussed and the anticipated improvements are provided.     

Application of the computer code TOUGH2 to the simulation of supercritical conditions in geothermal systems

At the high pressures and temperatures found in deep geothermal systems, supercritical conditions can occur. Current numerical geothermal simulators are either not capable of modelling these conditions, or can do so only at significantly reduced computation speed. This paper describes modifications to the TOUGH2 simulator to extend its applicability. It employs the updated IAPWS-97 thermodynamic formulation, and uses density and temperature as primary thermodynamic variables under supercritical conditions. Results from test problems are in agreement with results produced by other simulators, giving confidence that the simulator can be used for modelling deep geothermal reservoirs.