Development of a Quantitative Exergy-Based Measure of Sustainability

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Sustainable development has rapidly grown to become a key concern and driver for change, but what does it truly mean to be sustainable? Principles like "reduce, reuse, recycle" help to guide our thinking, but they do not provide a quantitative, generally applicable measure that can be used to rationally make difficult decisions. Similarly, current methods of quantifying sustainability, including carbon footprints and emissions, tend to only focus on one particular aspect of sustainability, such as climate change, and neglect the multitude of problematic issues with environmental degradation. For example, when comparing the carbon footprints of coal-generated power to nuclear power, nuclear power easily wins; however, this assessment neglects the obvious environmental issues surrounding nuclear waste. Unlike these narrowly focused measures, economic cost can provide a universal basis to quantify sustainability; however, it is influenced by other factors that can be artificially manipulated (e.g., through speculation or government subsidies) and does not always accurately reflect the true value of resources and environmental impact of their use. Exergy, the usable energy within a resource, provides a general, rigorous thermodynamic measure of sustainability. Exergy has been used extensively to characterize sustainability in industrial processes (e.g., power generation and chemical manufacture) environmental engineering, city planning, and ecosystems. Crucially, exergy can be used to quantify inefficiency within processes, compare technological pathways, quantify the damage inflicted on an ecosystem and estimate the costs of ecosystem restoration. Despite its merits, it does not consider many important practical factors, such the value of time, and the availability, efficiency and cost of the technology required to utilize a given resource. This project will develop a novel quantitative measure of sustainability, based on extending the concept of exergy to include these practical factors. The initial work will compare the modified exergy analysis to standard methods, such as thermoeconomic analysis and pinch technology, for well-established engineering processes. It will then move to more current problems, such as feedstock and product selection in biomass valorisation. The project will provide an effective tool to guide policy makers, companies, and individuals to make decisions to make better use of our very limited resources.