New Techniques for Assessing Critical Raw Material Aspects in Energy and Other Technologies.

Transitioning to more sustainable energy technologies is a vital step in the move toward reducing global greenhouse gas emissions. However, several physical constraints could hinder the implementation of these technologies, and many of the raw materials required to produce new infrastructure are scarce, nonrenewable, and nonsubstitutable. Various factors relating to material extraction and processing activities may also affect the security and sociopolitical aspects of future supply lines. Here, we introduce methods for quantifying three key indicators relating to raw material supplies for specific production processes: (1) overall supply risk, (2) environmental impacts from sourcing raw materials, and (3) environmental justice threats at sourcing locations. The use of the proposed methods is demonstrated via an exploratory case study examining projected electricity production scenarios within the European Union. Results suggest that renewable sources of electricity─particularly wind, solar, and geothermal technologies─are more likely to exacerbate supply risks and environmental issues than other technologies. Furthermore, projected expansions of wind and solar technologies mean that all three indicators appear likely to rise significantly systemwide by 2050. Ultimately, the methods represent a much-needed first attempt at providing practitioners with simple and robust approaches for integrating factors relating specifically to raw material supply into energy modeling and other applications.

Exergy efficiency in industry: where do we stand?

Efficiency is a term generally used to determine how well a system performs. However, efficiency can have different meanings and, unaccompanied by a formal definition or taken out of context, can lead to serious misconceptions. In many official publications, efficiency is calculated as the ratio of useful output to energy input. This measure reflects the first law of thermodynamics (conservation of energy) but does not reflect the potential for improvement. A better measure, that also reflects the second law of thermodynamics, is the ratio of the potential useful (exergy) output to the potential useful (exergy) input. We estimate second law efficiencies for the inorganic and organic chemical industries to be 29% and 35% respectively. We also estimate the efficiency of the U.S. industry sector as a whole to be 37.6%, as compared to only 7.7% for the overall U.S. economy. These figures are far lower than the "first law" figures published by the U.S. Department of Energy (80% for industry and 42.5% overall) and they imply a significant potential for improvement.

Greenhouse gas emissions from global cities.

The world's population is now over 50% urban, and cities make an important contribution to national greenhouse gas (GHG) emissions. Many cities are developing strategies to reduce their emissions. Here we ask how and why emissions differ between cities. Our study often global cities shows how a balance of geophysical factors (climate, access to resources, and gateway status) and technical factors (power generation, urban design, and waste processing) determine the GHGs attributable to cities. Within the overall trends, however, there are differences between cities with more or less public transit while personal income also impacts heating and industrial fuel use. By including upstream emissions from fuels, GHG emissions attributable to cities exceed those from direct end use by upto 25%. Our findings should help foster intercity learning on reducing GHG emissions.

Exergy analysis of integrated waste management in the recovery and recycling of used cooking oils.

Used cooking oil (UCO) is a domestic waste generated daily by food industries, restaurants, and households. It is estimated that in Europe 5 kg of UCO are generated per inhabitant, totalling 2.5 million metric tons per year. Recovering UCO for the production of biodiesel offers a way of minimizing and avoiding this waste and related pollution. An exergy analysis of the integrated waste management (IWM) scheme for UCO is used to evaluate such a possibility by accounting for inputs and outputs in each stage, calculating the exergy loss and the resource input and quantifying the possible improvements. The IWM includes the collection, pretreatment, and delivery of UCO and the production of biodiesel. The results show that the greatest exergy loss occurs during the transport stages (57%). Such exergy loss can be minimized to 20% by exploiting the full capacity of collecting vans and using biodiesel in the transport stages. Further, the cumulative exergy consumption helps study how the exergy consumption of biodiesel can be further reduced by using methanol obtained from biogas in the transesterification stage. Finally, the paper discusses how increasing the collection of UCO helps minimize uncontrolled used oil disposal and consequently provides a sustainable process for biodiesel production.