Integration of high temperature phase change materials in thermal storage systems for advanced energy recovery in industrial furnaces

The energy considered as waste heat in industrial furnaces owing to inefficiencies represents a substantial opportunity for recovery and storage. Nevertheless, the application of thermal energy storage (TES) systems based on phase change materials (PCM) in energy-intensive industries (EII) at very high temperatures is scarce and restricted by technological and economic barriers. The topic of this PhD thesis is framed on the study and analysis of PCM-TES to be used as a waste heat recovery and storage unit for high temperature applications (up to 1000ºC). The main objective of PCM-TES integration is recovering and storing waste heat from combustion gases or other surplus sources, currently unused, to preheat the air temperature entering the furnace, or other heat demanding processes. In this vein, implementing PCM-TES is a sustainable and innovative option to increase energy efficiency (5-10%) and to reduce the environmental impact associated. The combustion air preheated with the recovered thermal energy reached an increase up to 200-300ºC in the cases analysed in the dissertation.Design of latent heat TES requires knowledge of the heat transfer process, as well as the phase change behaviour of the PCM used. On the one hand, the configuration design is specifically adapted to the plant operational requirements, by a methodology combining the search of the best conceptual design and a proper PCMs selection. To that end, key technical, energy and economic factors are weighted by an in-house multiple criteria decision analysis (MCDA) to define the most promising design configuration. The final chosen conceptual design consists of a shell-and-tube system, where the exhaust gases flow inside the tubes, the air combustion is placed in the shell side and the PCM is contained in doubled concentric tubes. On the other hand, thermal characterisation and stability cycle tests were performed on the candidate storage materials for two representative application cases in the ceramic and steel industries. Both metal alloys and inorganic salts were analysed to select the most suitable alternative of PCMs working at high temperature. To investigate the operation of PCM systems, computational simulations can assess the thermal behaviour and expected operational performance. In this sense, temperature profiles of the PCM and the heat transfer fluids are defined by means of 3D numerical model implemented in MATLAB® and COMSOL Multiphysics®. In both models, the energy equation considers both heat conduction and natural convection to predict its effect on the behaviour of the PCM. The first approach is the MATLAB® in-house-developed modelling of the melting and solidification processes. This tool sets the basis for an appropriate system design and sizing, thermal stress resistance and material selection ensuring the technical feasibility of these systems working at critical temperature ranges. The results are reliable and less time consuming; thus, it is a useful tool during the early design stages and for practical application in the engineering and industry. Specifically, for the ceramic sector, the design resulted in a shell-and-tube system with 1188 kg of a PCM melting at 885ºC involving a latent storage capacity of 227 MJ. In this case, it was demonstrated the achievability of very high temperature levels in the combustion air for preheating (over 700ºC, higher than conventional sensible heat exchangers). Similarly, 1606 kg of PCM, whose phase-change temperature is 509ºC, is considered for the steel sector providing a latent capacity of 420 MJ. The combustion air was preheated from 300 to 480°C, matching the intermittent heat treatment and batch processes of the steel plant.In the second model approach, the obtained results from the COMSOL Multiphysics® modelling aims at simulating multiphysics problems and allows predicting the thermal performance with high precision; conversely, it presents a higher computational time cost. This model is used to simulate the industrial prototype and to perform a prospective validation of the MATLAB® model. This thesis aims at promoting and facilitating the integration of PCM-TES systems at industrial scale. In this line, technical documentation and process specifications for the PCM-TES prototype were established to achieve the level of reliability, efficiency and safety required. As a result, the configuration of the system was adapted to the plant requirements and the procedures for working operation and the instrumentation of the monitoring and control system were developed. Regarding simulated PCM-TES prototype performance, the combustion air received 338 kWh of heat from the PCM within 3 hours. During the charging, the PCM absorbed 351 kWh from the flue gas stream for 6 hours. In total, the annual energy savings are 230 MWh. The predicted thermal behaviour provides the PCM-TES design validation and reduces the uncertainty risks in the operational performance and its on-site implementation at large scale.With the aim of proofing the feasibility of a cross-sectorial approach by enlarging its replicability in many industrial sectors, a simplified tool based on the MATLAB® model was developed based on correlations among the most relevant system parameters. Along this line, the thesis conducted a parametric and sensitivity analysis to assess the techno-economic performance of the PCM-TES solution under different working conditions and sectors. This assessment highlighted that a suitable design, material selection and sizing are crucial parameters to obtain energy and economic benefits. Additionally, a multicriteria assessment was conducted with the tool outputs comparing metal alloys and inorganic hydrated PCM salts. Overall, the inorganic PCMs presented NG savings up to 2.6%, which means a higher net economic and energy savings (26,400 €; 480 MWh/year); while metal alloys involved shorter charge/discharge cycles and competitive economic ratios, its commercial development is, conversely, still limited. Finally, acceptable payback periods are observed when operating under 800ºC (between 5-8 years in the steel sector). This fact highlighted the technical and economic barriers existing in working at high temperature levels.All things considered, this thesis aims at demonstrating the feasibility of implementing, at industrial scale, a PCM-TES system of recover wasted energy from EIIs and overcoming the current lack of information, especially at high temperatures. The results obtained are a starting point for consolidating and promoting novel technological solutions and materials towards a more sustainable and efficient industry.<br /

Multiple-Criteria Decision Analysis and characterisation of phase change materials for waste heat recovery at high temperature for sustainable energy-intensive industry

A latent heat storage system based on Phase Change Materials (PCMs) is proposed to increase the energy and environmental efficiency by recovering and storing waste heat from combustion gases or other surplus sources at in the energy-intensive industries (EII), currently unused. The final configuration design is specifically adapted to the plant operational requirements, by means of a methodology combining the search of the best conceptual design and a proper selection of core PCMs. To that end, a selection of suitable PCM is carried out by using characterisation techniques and thermal stability testing. Furthermore, relevant key factors are weighted by an in-house Multiple-Criteria Decision Analysis (MCDA) to define the most promising design options to be implemented in two plants belonging to the EII sector. For the ceramic sector, the design resulted in a shell-and-tube system with 1188 kg of a PCM melting at 885 °C and encapsulated in double concentric tubes, involving a storage capacity of 227 MJ. Similarly, 1606 kg of PCM, whose phase-change temperature is 509 °C, is selected for the steel sector providing a PCM-TES system capable to store 420 MJ

Environmental assessment of electrochemical energy storage device manufacturing to identify drivers for attaining goals of sustainable materials 4.0

Electricity from the combination of photovoltaic panels and wind turbines exhibits potential benefits towards the sustainable cities transition. Nevertheless, the highly fluctuating and intermittent character limits an extended applicability in the energy market. Particularly, batteries represent a challenging approach to overcome the existing constraints and to achieve sustainable urban energy development. On the basis of the market roll-out and level of technological maturity, five commercially available battery technologies are assessed in this work, namely, lead-acid, lithium manganese oxide, nickel-cadmium, nickel-metal hydride, and vanadium redox flow. When considering sustainable development, environmental assessments provide valuable information. In this vein, an environmental analysis of the technologies is conducted using a life cycle assessment methodology from a cradle-to-gate perspective. A comparison of the environmental burden of battery components identified vanadium redox flow battery as the lowest environmental damage battery. In terms of components, electrodes; the electrolyte; and the set of pumps, motors, racks, and bolts exhibited the greatest environmental impact related to manufacturing. In terms of materials, copper, steel, sulphuric acid, and vanadium were identified as the main contributors to the midpoint impact categories. The results have highlighted that challenging materials 4.0 are still needed in battery manufacturing to provide sustainable technology designs required to the future urban planning based on circular economy demands

Accumulation of De-Icing Salt and Leaching in Spanish soils surrounding roadwayss

The environmental implications of soil salinity caused by accumulation of de-icing salt and leaching in soils of northeastern Spain were examined. For this purpose, the concentrations of ions associated with diagnosing and managing this problem were evaluated from several measurements performed over one year along a road. This analysis demonstrated a higher concentration of soluble Na+ in the soil 3 m from a road in the northernmost part of the study area in February, which made the soil saline-sodic. Data from the rest of the study period (during the spring and summer) demonstrated that the de-icing salt moved to areas farther south by runoff water, which caused environmental impacts by modifying soil characteristics. These results suggest that leaching of Ca2+ and Mg2+ cations occurred faster in the studied systems in sodic soils. Leaching of these cations may affect plant yield, and results in environmental impacts within 3–30 m from the road. Awareness of this impact will be useful for developing future strategies for evaluating and reporting these complex relationships within Spain’s transport system and environment

Evaluación de impacto ambiental mediante análisis de ciclo de vida (ACV) de la incorporación de materiales de cambio de fase (PCM) en edificación

Análisis de los Materiales de Cambio de Fase (PCM) en la edificación, teniendo en cuenta la degradación de éstos. Evaluación de impacto ambiental mediante Análisis de Ciclo de Vida en términos de categorías de impacto ambiental midpoint, de la incorporación de 4 PCM distintos en 3 soluciones constructivas. Se analiza si el ahorro energético alcanzado al incorporar el PCM compensa el impacto ambiental asociado a la fabricación y montaje del PCM en la solución constructiva y se verifica la existencia de un beneficio en términos ambientales gracias a la utilización de esta tecnología

Technical and environmental evaluation of a new high performance material based on magnesium alloy reinforced with submicrometre-sized TiC particles to develop automotive lightweight components and make transport sector more sustainable

This study evaluated the use of submicrometre-sized particles based on titanium carbide from both technical and environmental points of view. The objective was to improve the mechanical properties of the magnesium alloy intended for use in the automotive component industry. To this end, an Al/TiC master compound containing 60 wt.% of TiC was produced through a self-propagating, high-temperature synthesis process and embedded in a magnesium alloy by a mechanical stirring method. The life cycle assessment methodology was then used to evaluate the environmental impact of the manufacturing of the magnesium alloy reinforced with submicrometre-sized particles. X-ray diffraction and scanning electron microscopy techniques revealed the nature and purity of the TiC present in the material and revealed particle sizes below submicrometre range (300–500 nm). The incorporation of TiC particles into the magnesium alloy resulted in improvements in yield stress and ultimate tensile strength of more than 10% and 18%, respectively, and increases in ductility values by 30%. Finally, the results indicated that the submicrometre particle production had a low environmental impact compared with the total impact associated with manufacturing the magnesium alloy reinforced with submicrometre-sized particles; the greatest environmental burden was attributed to the magnesium production stage. However, this impact is offset in the use phase of the vehicle, providing approximately 28,000 km of mileage for a car.The research leading to these results has been received funding form the European Union Seventh Framework Programme( FP7/20072013) under grant agreement n 314582 EFEVE project. The authors thank the project partners for providing support to this research

Caracterización energética y ambiental de materiales de almacenamiento de calor latente

El uso de materiales de cambio de fase representa una de las alternativas más prometedoras en cuanto a sistemas pasivos utilizados en edificación. No obstante, la correcta selección de estos materiales es fundamental, ya que su funcionamiento depende de varios aspectos como la climatología, la ubicación, el tipo de material seleccionado y sus características termofísicas. Por tanto, el objetivo de este trabajo es realizar la caracterización energética y ambiental de la aplicación de estos materiales en edificación. Por un lado, mediante simulación se determina la demanda energética de climatización existente en un edificio modelo, con y sin la aplicación de estos materiales, y posteriormente, se realiza la caracterización ambiental considerando el enfoque del Análisis de Ciclo de Vida, obteniendo resultados para diferentes escenarios de aplicación sobre una base cerámica donde se ha estudiado el efecto de diversas variables como las Severidades Climáticas existentes en España o la naturaleza de los materiales de cambio de fase. Esta investigación evidencia como la utilización de una solución constructiva formada por una baldosa cerámica y una capa de materiales de cambio de fase seleccionados adecuadamente, no solo aporta descensos en la demanda energética en todas las condiciones climáticas, siendo en algunas de ellas superiores al 15%, sino que también se obtienen beneficios ambientales en cortos espacios temporales en comparación con la vida útil de la solución constructiva.Consejo General de la Arquitectura Técnica de Españ

Virtualización de la tutoría académica en alumnos de nuevo ingreso de magisterio

Se presenta un estudio evaluativo que trata de optimizar la tutoría académica centrada en la evaluación auténtica que se orienta hacia la construcción transversal de un proyecto profesional del estudiante de nuevo ingreso en el grado en magisterio. Se aborda un proceso hacia la virtualización de las tutorías académicas analizando las necesidades del estudiante, los requisitos competenciales de estudiantes y docentes universitarios y las buenas prácticas. An evaluative study is presented that tries to optimize the academic tutoring focused on the authentic evaluation that is oriented towards the transversal construction of a professional project of the new student of degree in primary education teaching. A process towards the virtualization of the academic tutorials is approached, analyzing the needs of the student, the competence requirements of students and university professors and the good practices

Gestión térmica y del agua en una pila de combustible tipo PEM: Diseño y fabricación de pilas

Las pilas de combustible de membrana polimérica de intercambio protónico (PEM) son una prometedora alternativa para sustituir los motores de combustión interna en el sector del automóvil. Pese a los avances obtenidos en los últimos años, aún es posible optimizar los materiales de los diferentes elementos que forman estas pilas y los procesos que tienen lugar en su interior. Esta tesis doctoral se centra en estudios de gestión térmica y del agua en pilas tipo PEM, en la evaluación de diferentes materiales como recubrimientos para placas bipolares de aluminio en condiciones reales de operación, así como el desarrollo y optimización de pilas de pequeña y mediana potencia. Para ello ha sido también necesario desarrollar una instalación experimental que permite caracterizar desde pequeñas pilas hasta dispositivos de 3 kW. Los resultados obtenidos han permitido el diseño y fabricación de una pila de 2 kW de cátodo abierto

Experimental validation of a hybrid power-to-heat storage based on high temperature phase change materials to enhance sector coupling and flexibility

An innovative power-to-heat storage (electric charging, thermal discharging) is proposed to increase the flexibility, sector coupling and manageability of renewable generation systems. The hybrid thermal energy storage (TES) system integrating phase change materials (PCM) is designed based on flat pillow plates in combination with heating rods. The prototype is validated by means of experimental testing to characterize its electrical and thermal. In this sense, a parametric analysis is proposed involving different charging and discharging control strategies. The proposed hybrid-TES provides a total storage capacity of 4.87 kWh integrating nitrate salts as PCM (eutectic mixture of KNO3 and NaNO3). Depending on the charging/discharging strategy, the charging efficiency is 65-90% and the discharging period could be reduced by more than 1h. Active control of the heating rod temperature reduces the charging period by half, enabling a high flexibility of the storage system. This reveals the PCM-TES potential to contribute in decision-making for an optimal energy management in the renewable energy and industry context