Optimization of the long-term planning of supply chains with decaying performance

This master's thesis addresses the optimization of supply and distribution chains considering the effect that equipment aging may cause over the performance of facilities involved in the process. The decaying performance of the facilities is modeled as an exponential equation and can be either physical or economic, thus giving rise to a novel mixed integer non-linear programming (MINLP) formulation. The optimization model has been developed based on a typical chemical supply chain. Thus, the best long-term investment plan has to be determined given production nodes, their production capacity and expected evolution; aggregated consumption nodes (urban or industrial districts) and their lumped demand (and expected evolution); actual and potential distribution nodes; distances between the nodes of the network; and a time horizon. The model includes the balances in each node, a general decaying performance function, and a cost function, as well as constraints to be satisfied. Hence, the investment plan (decision variables) consists not only on the start-up and shutdown of alternative distribution facilities, but also on the sizing of the lines satisfying the flows. The model has been implemented using GAMS optimization software. Results considering a variety of scenarios have been discussed. In addition, different approaches to the starting point for the model have been compared, showing the importance of initializing the optimization algorithm. The capabilities of the proposed approach have been tested through its application to two case studies: a natural gas network with physical decaying performance and an electricity distribution network with economic decaying performance. Each case study is solved with a different procedure to obtain results. Results demonstrate that overlooking the effect of equipment aging can lead to infeasible (for physical decaying performance) or unrealistic (for economic decaying performance) solutions in practice and show how the proposed model allows overcoming such limitations thus becoming a practical tool to support the decision-making process in the distribution secto

Decision support strategies for the efficient implementation of circular economy principles in process systems

Economic growth at any expense is no longer an option. Awareness of the growing human footprint is crucial to face the problems that the impoverishment of ecosystems is causing and will cause in the future. One of the key challenges to address it is moving toward approaches to manage resources in a more sustainable way. In this light, circular economy stands as a promising strategy to improve the lifetime of resources by closing material and energy loops. The Process Systems Engineering (PSE) community has been developing methods and tools for increasing efficiency in process systems since the late 1980s. These methods and tools allow the development of more sustainable products, processes, and supply chains. However, applying these tools to circular economy requires special considerations when evaluating the introduction of waste-to-resource technologies. This Thesis aims at providing a set of models and tools to support in the decision-making process of closing material cycles in process systems through the implementation of waste-to-resource technologies from the circular economy perspective. The first part provides an overview of approaches to sustainability, presents the optimization challenges that circular economy and industrial symbiosis pose to PSE, and introduces the methodological and industrial scope of the Thesis. Part two aims at assessing the environmental and economic reward that may be attained through the application of circular economy principles in the chemical industry. With this purpose, a systematic procedure based on Life Cycle Assessment (LCA), economic performance and Technology Readiness Level (TRL) is proposed to characterize technologies and facilitate the comparison of traditional and novel technologies. The third part describes groundwork tasks for optimization models. A methodology is presented for the systematic generation of a list of potential waste-to-resource technologies based on an ontological framework to structure the information. In addition, this part also presents a targeting approach developed to include waste transformation and resource outsourcing, so a new dimension of potential destinations for waste are explored for the extension of material recovery. Finally, part four includes the development of decision-making models at the strategic and tactical hierarchical levels. At the network level, a framework is presented for the screening of waste-to-resource technologies in the design of process networks. The most promising processing network for waste recovery is identified by selecting the most favorable waste transformation processes among a list of potential alternatives. After the network selection, an optimization model is built for the detailed synthesis of individual processes selected in the resulting network. The developed methodologies have been validated and illustrated through their application to a case study under different viewpoints in the process industry, in particular to the chemical recycling of plastic waste. Despite the low Technology Readiness Level of some chemical recycling technologies, the results of this Thesis reveal pyrolysis as a promising technology to close the loop in the polymer sector. Overall, all these positive outcomes prove the advantages of developing tools to systematically integrate waste-to-resource processes into the life cycle of materials. The adaptation to this change of perspective of the well-established methods developed by the PSE community offers a wide range of opportunities to foster circular economy and industrial symbiosis. This Thesis aims to be a step forward towards a future with more economically efficient and environmentally friendly life cycles of materials.El crecimiento económico a cualquier precio ha dejado de ser una opción viable. Tener conciencia sobre nuestra creciente huella ambiental es clave para afrontar los problemas que el empobrecimiento de los ecosistemas está causando y causará en el futuro. Uno de los desafíos clave para abordarlo es avanzar hacia técnicas que permitan una gestión de recursos más sostenible. En esta línea, la economía circular es una estrategia con gran potencial para mejorar la vida útil de los recursos mediante el cierre de ciclos de materiales y energía. Desde finales de los años ochenta, la investigación en Ingeniería de Procesos y Sistemas (PSE) ha permitido generar métodos y herramientas para el desarrollo sostenible de productos, procesos y cadenas de suministro. Sin embargo, su aplicación en economía circular requiere consideraciones especiales al evaluar la introducción de nuevas tecnologías para el reciclaje de materiales. Esta Tesis tiene como objetivo proporcionar un conjunto de modelos y herramientas para apoyar el proceso de toma de decisiones sobre el aprovechamiento de materiales a través de la lente de la economía circular mediante la implementación de tecnologías de conversión de residuos en recursos. La primera parte presenta una visión general de los enfoques de sostenibilidad, lista los desafíos que la economía circular y la simbiosis industrial plantean en PSE, e introduce el alcance metodológico e industrial de la Tesis. La segunda parte tiene como objetivo evaluar los beneficios ambientales y económicos que se pueden obtener mediante la aplicación de los principios de la economía circular en la industria química. Con este propósito, se desarrolla un método sistemático basado en el análisis del ciclo de vida, el rendimiento económico y el nivel de madurez tecnológica para caracterizar las tecnologías de recuperación y facilitar la comparación entre técnicas tradicionales y en desarrollo. La tercera parte describe las tareas previas al desarrollo de los modelos de optimización. Se presenta una metodología para la generación sistemática de una lista de posibles tecnologías de conversión de residuos en recursos utilizando en un marco ontológico para estructurar la información. Además, se expone un método para acotar la transformación de residuos y la externalización de recursos, que permite explorar una nueva dimensión de destinos potenciales para los residuos, extendiendo así el grado de recuperación de materiales. Por último, la cuarta parte incluye el desarrollo de modelos de toma de decisiones a nivel estratégico y táctico. A nivel estratégico, se presenta un marco para la detección de tecnologías de reciclaje de residuos en el diseño de redes de procesos. Tras sintetizar la red, a nivel táctico se construye un modelo de optimización para el diseño detallado de los procesos individuales seleccionados en el mismo. Las metodologías desarrolladas han sido ilustradas y validadas a través de su aplicación en un caso de estudio con diferentes perspectivas sobre el reciclaje químico de residuos plásticos. A pesar del bajo nivel de madurez tecnológica de los procesos de reciclaje químico, los resultados de esta Tesis permiten identificar el gran potencial económico y ambiental de la pirolisis de residuos plásticos para cerrar su ciclo de materiales. En conjunto, los resultados demuestran las ventajas de desarrollar herramientas para integrar sistemáticamente los procesos de reciclaje de residuos en el ciclo de vida de los materiales. La adaptación a las necesidades de este cambio de perspectiva de métodos bien establecidos en la comunidad PSE ofrece grandes oportunidades para fomentar la economía circular y la simbiosis industrial. Esta tesis pretende ser un paso adelante hacia un futuro con ciclos de vida de materiales económica y ambientalmente más eficientes

Targeting economic and environmental benefits associated with the integration of regeneration units in water systems

Water treatment is traditionally seen as an "end-of-pipe" solution to deal with contaminated water satisfying discharge regulations at a minimum expense. However, the reuse of treated water as regenerated water is a promising strategy to counteract water scarcity. This approach to transform waste into resources is motivated by the circular economy paradigm. This study presents a mathematical programming approach to target both the environmental and economic benefits of water systems by introducing additional regeneration units to close the loop. In addition to water users and authorities, the approach also considers operators and dealers, which are revealed as key stakeholders. Hence, the feasible region of the regeneration units design specifications is determined and visualized through a multi-objective optimization approach targeting the systems operating cost and freshwater consumption. Its application is demonstrated on a benchmark case study from the literature, revealing a potential economic benefit of 37.5% and a freshwater reduction of 80.9% over the case without regeneration units. Furthermore, we show that a cooperative exchange strategy leads to higher benefits compared to the solutions presented in the literature. Finally, we demonstrate how the barrier plots introduced in this work can be used by different stakeholders in the water market to support their decision-making.Peer ReviewedPostprint (published version

A circular economy approach to the design of a water network targeting the use of regenerated water

Increasing water demand by the process and allied industries coupled with global water stress and scarcity have underlined the importance of water as a crucial resource and increased the need for widespread adoption of water reuse and recycle. Early research based on water-pinch analysis addressed the use of systematic methods to identify the most promising opportunities for water reuse within a process plant. More recent work has addressed similar concepts in the framework of industrial symbiosis and Eco-Industrial Parks (EIP) under the assumption of the leadership of an EIP authority. However, many wastewater plants continue processing wastewater to condition water for disposal, which means meeting the limits given by regulations at a minimum cost. These wastewater treatment plants may play a role in a growing market of regenerated water in which an increasing number of businesses and public services would be demanding water with different quality specifications. Hence, this work is presenting an MINLP model aimed at exploiting the flexibility of a wastewater treatment plant and maximizing its profit within this market. Results and discussion are provided in regard of a case study based on a wastewater treatment plant nearby Barcelona.Peer ReviewedPostprint (published version

Towards automated information retrieval of process data and knowledge from academic databases

Process modeling requires both data (chemical reaction yields, kinetic constants, cost estimates, environmental indicators, etc.) and knowledge (operation models and formulations, alternative processes and technologies, etc.). Searching in databases and published research may provide such information, but there is a lack of systematic methods and tools guiding this procedure. The present work describes and assesses an information retrieval methodology that is part of a proposed retrieval and extraction cycle addressing this problem. Two query construction methods for sampling academic databases are proposed, assessed and compared. Departing from a seed corpus of a limited number of papers, Scopus® is used as an academic database to retrieve literature containing information associated with pyrolysis processes of waste plastic. It is found that, with minimal human intervention, the methodology is able to return a ranked list of candidate documents that have a considerable (linguistic) relevance.Postprint (published version

Information retrieval from scientific abstract and citation databases: A query-by-documents approach based on Monte-Carlo sampling

The rapidly increasing amount of information and entries in abstract and citation databases steadily complicates the information retrieval task. In this study, a novel query-by-document approach using Monte-Carlo sampling of relevant keywords is presented. From a set of input documents (seed) keywords are extracted using TF-IDF and subsequently sampled to repeatedly construct queries to the database. The occurrence of returned documents is counted and serves as a proxy relevance metric. Two case studies based on the Scopus® database are used to demonstrate the method and its key advantages. No expert knowledge and human intervention is needed to construct the final search strings which reduces the human bias. The methods practicality is supported by the high re-retrieval of seed documents of 7/8 and 26/31 in high ranks in the two presented case studies.Peer ReviewedPostprint (author's final draft

Optimization of the long-term planning of supply chains with decaying performance

This master's thesis addresses the optimization of supply and distribution chains considering the effect that equipment aging may cause over the performance of facilities involved in the process. The decaying performance of the facilities is modeled as an exponential equation and can be either physical or economic, thus giving rise to a novel mixed integer non-linear programming (MINLP) formulation. The optimization model has been developed based on a typical chemical supply chain. Thus, the best long-term investment plan has to be determined given production nodes, their production capacity and expected evolution; aggregated consumption nodes (urban or industrial districts) and their lumped demand (and expected evolution); actual and potential distribution nodes; distances between the nodes of the network; and a time horizon. The model includes the balances in each node, a general decaying performance function, and a cost function, as well as constraints to be satisfied. Hence, the investment plan (decision variables) consists not only on the start-up and shutdown of alternative distribution facilities, but also on the sizing of the lines satisfying the flows. The model has been implemented using GAMS optimization software. Results considering a variety of scenarios have been discussed. In addition, different approaches to the starting point for the model have been compared, showing the importance of initializing the optimization algorithm. The capabilities of the proposed approach have been tested through its application to two case studies: a natural gas network with physical decaying performance and an electricity distribution network with economic decaying performance. Each case study is solved with a different procedure to obtain results. Results demonstrate that overlooking the effect of equipment aging can lead to infeasible (for physical decaying performance) or unrealistic (for economic decaying performance) solutions in practice and show how the proposed model allows overcoming such limitations thus becoming a practical tool to support the decision-making process in the distribution secto

Decision support strategies for the efficient implementation of circular economy principles in process systems

Aplicat embargament entre la data de defensa i l'1 de març de 2021Economic growth at any expense is no longer an option. Awareness of the growing human footprint is crucial to face the problems that the impoverishment of ecosystems is causing and will cause in the future. One of the key challenges to address it is moving toward approaches to manage resources in a more sustainable way. In this light, circular economy stands as a promising strategy to improve the lifetime of resources by closing material and energy loops. The Process Systems Engineering (PSE) community has been developing methods and tools for increasing efficiency in process systems since the late 1980s. These methods and tools allow the development of more sustainable products, processes, and supply chains. However, applying these tools to circular economy requires special considerations when evaluating the introduction of waste-to-resource technologies. This Thesis aims at providing a set of models and tools to support in the decision-making process of closing material cycles in process systems through the implementation of waste-to-resource technologies from the circular economy perspective. The first part provides an overview of approaches to sustainability, presents the optimization challenges that circular economy and industrial symbiosis pose to PSE, and introduces the methodological and industrial scope of the Thesis. Part two aims at assessing the environmental and economic reward that may be attained through the application of circular economy principles in the chemical industry. With this purpose, a systematic procedure based on Life Cycle Assessment (LCA), economic performance and Technology Readiness Level (TRL) is proposed to characterize technologies and facilitate the comparison of traditional and novel technologies. The third part describes groundwork tasks for optimization models. A methodology is presented for the systematic generation of a list of potential waste-to-resource technologies based on an ontological framework to structure the information. In addition, this part also presents a targeting approach developed to include waste transformation and resource outsourcing, so a new dimension of potential destinations for waste are explored for the extension of material recovery. Finally, part four includes the development of decision-making models at the strategic and tactical hierarchical levels. At the network level, a framework is presented for the screening of waste-to-resource technologies in the design of process networks. The most promising processing network for waste recovery is identified by selecting the most favorable waste transformation processes among a list of potential alternatives. After the network selection, an optimization model is built for the detailed synthesis of individual processes selected in the resulting network. The developed methodologies have been validated and illustrated through their application to a case study under different viewpoints in the process industry, in particular to the chemical recycling of plastic waste. Despite the low Technology Readiness Level of some chemical recycling technologies, the results of this Thesis reveal pyrolysis as a promising technology to close the loop in the polymer sector. Overall, all these positive outcomes prove the advantages of developing tools to systematically integrate waste-to-resource processes into the life cycle of materials. The adaptation to this change of perspective of the well-established methods developed by the PSE community offers a wide range of opportunities to foster circular economy and industrial symbiosis. This Thesis aims to be a step forward towards a future with more economically efficient and environmentally friendly life cycles of materials.El crecimiento económico a cualquier precio ha dejado de ser una opción viable. Tener conciencia sobre nuestra creciente huella ambiental es clave para afrontar los problemas que el empobrecimiento de los ecosistemas está causando y causará en el futuro. Uno de los desafíos clave para abordarlo es avanzar hacia técnicas que permitan una gestión de recursos más sostenible. En esta línea, la economía circular es una estrategia con gran potencial para mejorar la vida útil de los recursos mediante el cierre de ciclos de materiales y energía. Desde finales de los años ochenta, la investigación en Ingeniería de Procesos y Sistemas (PSE) ha permitido generar métodos y herramientas para el desarrollo sostenible de productos, procesos y cadenas de suministro. Sin embargo, su aplicación en economía circular requiere consideraciones especiales al evaluar la introducción de nuevas tecnologías para el reciclaje de materiales. Esta Tesis tiene como objetivo proporcionar un conjunto de modelos y herramientas para apoyar el proceso de toma de decisiones sobre el aprovechamiento de materiales a través de la lente de la economía circular mediante la implementación de tecnologías de conversión de residuos en recursos. La primera parte presenta una visión general de los enfoques de sostenibilidad, lista los desafíos que la economía circular y la simbiosis industrial plantean en PSE, e introduce el alcance metodológico e industrial de la Tesis. La segunda parte tiene como objetivo evaluar los beneficios ambientales y económicos que se pueden obtener mediante la aplicación de los principios de la economía circular en la industria química. Con este propósito, se desarrolla un método sistemático basado en el análisis del ciclo de vida, el rendimiento económico y el nivel de madurez tecnológica para caracterizar las tecnologías de recuperación y facilitar la comparación entre técnicas tradicionales y en desarrollo. La tercera parte describe las tareas previas al desarrollo de los modelos de optimización. Se presenta una metodología para la generación sistemática de una lista de posibles tecnologías de conversión de residuos en recursos utilizando en un marco ontológico para estructurar la información. Además, se expone un método para acotar la transformación de residuos y la externalización de recursos, que permite explorar una nueva dimensión de destinos potenciales para los residuos, extendiendo así el grado de recuperación de materiales. Por último, la cuarta parte incluye el desarrollo de modelos de toma de decisiones a nivel estratégico y táctico. A nivel estratégico, se presenta un marco para la detección de tecnologías de reciclaje de residuos en el diseño de redes de procesos. Tras sintetizar la red, a nivel táctico se construye un modelo de optimización para el diseño detallado de los procesos individuales seleccionados en el mismo. Las metodologías desarrolladas han sido ilustradas y validadas a través de su aplicación en un caso de estudio con diferentes perspectivas sobre el reciclaje químico de residuos plásticos. A pesar del bajo nivel de madurez tecnológica de los procesos de reciclaje químico, los resultados de esta Tesis permiten identificar el gran potencial económico y ambiental de la pirolisis de residuos plásticos para cerrar su ciclo de materiales. En conjunto, los resultados demuestran las ventajas de desarrollar herramientas para integrar sistemáticamente los procesos de reciclaje de residuos en el ciclo de vida de los materiales. La adaptación a las necesidades de este cambio de perspectiva de métodos bien establecidos en la comunidad PSE ofrece grandes oportunidades para fomentar la economía circular y la simbiosis industrial. Esta tesis pretende ser un paso adelante hacia un futuro con ciclos de vida de materiales económica y ambientalmente más eficientes.Postprint (published version

Optimization of the long-term planning of supply chains with decaying performance

This master's thesis addresses the optimization of supply and distribution chains considering the effect that equipment aging may cause over the performance of facilities involved in the process. The decaying performance of the facilities is modeled as an exponential equation and can be either physical or economic, thus giving rise to a novel mixed integer non-linear programming (MINLP) formulation. The optimization model has been developed based on a typical chemical supply chain. Thus, the best long-term investment plan has to be determined given production nodes, their production capacity and expected evolution; aggregated consumption nodes (urban or industrial districts) and their lumped demand (and expected evolution); actual and potential distribution nodes; distances between the nodes of the network; and a time horizon. The model includes the balances in each node, a general decaying performance function, and a cost function, as well as constraints to be satisfied. Hence, the investment plan (decision variables) consists not only on the start-up and shutdown of alternative distribution facilities, but also on the sizing of the lines satisfying the flows. The model has been implemented using GAMS optimization software. Results considering a variety of scenarios have been discussed. In addition, different approaches to the starting point for the model have been compared, showing the importance of initializing the optimization algorithm. The capabilities of the proposed approach have been tested through its application to two case studies: a natural gas network with physical decaying performance and an electricity distribution network with economic decaying performance. Each case study is solved with a different procedure to obtain results. Results demonstrate that overlooking the effect of equipment aging can lead to infeasible (for physical decaying performance) or unrealistic (for economic decaying performance) solutions in practice and show how the proposed model allows overcoming such limitations thus becoming a practical tool to support the decision-making process in the distribution secto

Economic and environmental assessment of plastic waste pyrolysis products and biofuels as substitutes for fossil-based fuels

The global economy is shifting toward more sustainable sources of energy. The transportation sector is a remarkable example of this fact, where biofuels have emerged as promising alternatives to traditional fossil fuels. This work presents a techno-economic and environmental assessment of existing liquid fuels in hard-to-decarbonize sectors and their emerging renewable substitutes. The comparison focuses on fossil-based, biomass-derived, and plastic waste-sourced fuel alternatives that can be used in spark-ignition (gasoline) and compression-ignition (diesel) engines. Results for diesel substitutes prove the superior performance of plastic waste pyrolysis oil in terms of production cost reduction (-25% compared to diesel) and “well-to-tank” life cycle impact reduction (-54% human health, -40% ecosystems, -98% resources). Consequently, research and development toward the conversion of plastic waste into fuels should be extended to make the technology more accessible and robust in terms of fuel quality. On the contrary, the results for gasoline alternatives are not as conclusive: bioethanol and ethanol from plastic pyrolysis have a considerably lower impact on resource scarcity than gasoline (-80% and -35% respectively) and higher on the other two life cycle endpoint categories, but they have higher production costs compared to gasoline (+57% and +130% respectively). While blends of gasoline with pyrolysis-sourced ethanol can reduce the impact on human health and ecosystems, blends with bioethanol have a lower impact on resource scarcity and increase economic profitability. This allows fuel providers to offer tradeoff solutions in the form of blends based on their priorities.Peer ReviewedPostprint (published version