| Industrial societies are increasingly recognizing the need for shifting to more environmentally conscious activities. Consequently, there is a need for modifying existing processes and developing new technologies that minimize environmental impact while providing stimulating economic value to businesses. However, this task poses formidable challenges to the chemical engineering community because traditional tools are inadequate due to their primary emphasis on economic objectives and narrow view that ignores the life cycle, economy and environment. Methods like Life Cycle Assessment have broader views and focus more on ecological aspects---impact of emissions and resource consumption---but they lack a rigorous thermodynamic framework, and may even violate thermodynamic laws. In addition, like traditional engineering methods, they ignore the crucial role that ecosystems play in sustaining all industrial activity. Decisions based on approaches that take nature for granted continue to cause significant deterioration in the ability of ecosystems to provide goods and services that are essential for every human activity. In contrast, emergy analysis, a thermodynamic method from systems ecology, does account for ecosystems, but has encountered a lot of resistance and criticism, particularly from economists, physicists and engineers.; This dissertation develops a thermodynamic framework for evaluating ecological objectives in traditional process engineering. It expands the engineering concept of Cumulative Exergy Consumption (CEC) analysis to include the contribution of ecosystems, which leads to the concept of Ecological CEC (ECEC). Practical challenges in computing ECEC are identified and a formal algorithm based on network algebra is proposed. ECEC is shown to be closely related to emergy, and both concepts become equivalent for certain conditions. This insight permits combination of the best features of emergy and exergy analysis, and shows that most of the controversial aspects of emergy analysis need not hinder its use for including the exergetic contribution of ecosystems. Adopting a broader view requires expanding the analysis boundaries. Defining the system boundaries by including only the relevant processes may result in large truncation errors, while expanding it to include all interactions is computationally intractable. In practice, data and models are available at multiple spatial scales ranging from individual equipment and processes, to the supply and demand chains, to the economy and ecosystem. This work introduces a hierarchical approach that utilizes available information at all these scales and determines the trade-off between economic and ecological objectives of the process life cycle at multiple scales. A hierarchical approach was also developed for handling and representing ecological metrics at multiple spatial scales and degrees of aggregation. Examples illustrate the approaches presented in this dissertation and highlight the potential benefits of using thermodynamic principles to account for ecological aspects. An approach for enhancing the quality of life cycle inventories by reconciling it with the laws of thermodynamics was also developed. |
