Enhancing the thermal efficiency of a salinity gradient solar pond. Implementation of the study in the design, construction, salinity gradient establishment, operation and energy transfer at industrial scale

Tesi amb diferents seccions retallades per drets de l'editorThe energy model in the last decades has been dominated by the consumption of fossil fuels assuming a high environmental cost. Global warming and the destruction of the ozone layer are two examples of the deterioration that is being suffered due to the use of these energy sources. Increasingly, the use of renewable energy one of the alternatives in building a sustainable economic model. Among renewables, solar energy is presented as an inexhaustible and accessible source of energy. The solar pond is a technology that meets all requirements to be considered an energy storage device. It can store solar energy, charging during the months of high solar incidence (Spring-Summer), storing the energy through the time and making possible its use when it is requested. A salt gradient solar pond is a body of saline water with long term thermal storage capacity. The aim and scope of this PhD thesis is divided in two parts. First, the improvement of the efficiency of the solar pond technology through experimental evaluation the heat extraction and heat supply processes under different weather conditions. These experiments were carried out in a 50 m2 solar pond pilot plant located in Martorell (Catalonia). Heat extraction experiments were performed using both heat exchangers installed (lateral and bottom) individually or both at the same time. The results demonstrated that the efficiency of the pond increases when the heat is removed from the lateral heat exchanger compared to either using the bottom heat exchanger or using both heat exchangers simultaneously. On the other hand, the use of solar collectors as an external source of heat were conducted together with heat extraction process under two different seasonal temperature conditions: winter and summer. The results indicated that the use of solar collectors allowed a 50% increase in daily efficiency during the cold season tests. The second part was focused on the design, construction and operation of a 500 m2 solar pond in Solvay Minerales facilities (Granada). The solar pond was designed to supply the heat required to preheat the water (> 60 °C) and the reagents in the mineral flotation unit at the mineral processing facility. The overall efficiencies obtained after the first and second operation periods are 9.7 and 12.3%, respectively, with maximum values of 28 and 24% obtained during the first months of operation. Regarding the economic savings, reductions of 52 and 68% were obtained in the first and second periods compared with the traditional system without solar pond. Also, the environmental impact is clearly reduced considering the reduction of CO2 emissions. The experience of the Granada solar pond proves that the main advantage of a solar pond is the capacity to store energy in the months with the highest solar radiation to provide a flux of heat to an external system during the whole year even under strong weather conditions, as observed during the January 2015 snowfall.El modelo energético en las últimas décadas ha estado dominado por el consumo de combustibles fósiles, asumiendo un alto coste ambiental. El calentamiento global y la destrucción de la capa de ozono son dos ejemplos del deterioro que se está sufriendo debido al uso de estas fuentes de energía. Cada vez más, el uso de energías renovables es una de las alternativas en la construcción de un modelo económico sostenible. Entre las energías renovables, la energía solar se presenta como una fuente de energía inagotable y accesible. El estanque solar es una tecnología que cumple todos los requisitos para ser considerado un dispositivo de almacenamiento de energía. Puede almacenar energía solar, cargando durante los meses de alta incidencia solar (primavera-verano), almacenando la energía y haciendo posible su uso cuando es necesaria. Un estanque solar con gradiente salino es un cuerpo de agua salina con capacidad de almacenamiento térmico a largo plazo. El objetivo y alcance de esta tesis doctoral se divide en dos partes. Primero, la mejora de la eficiencia del estanque solar a través de la evaluación experimental de los procesos de extracción de calor y aportación de calor en diferentes condiciones climáticas. Estos experimentos se llevaron a cabo en un estanque solar a escala planta piloto de 50 m2 situada en Martorell (Cataluña). Los experimentos de extracción de calor se realizaron mediante el uso de intercambiadores de calor situados en el área lateral y en el área inferior del estanque. El proceso de extracción de calor se llevó a cabo de manera individual (área lateral o inferior) o simultáneamente (área global). Los resultados demostraron que la eficiencia del estanque aumenta cuando el calor es extraído usando el intercambiador de calor lateral en comparación con el uso del intercambiador de calor inferior o con los dos intercambiadores de calor simultáneamente. Por otro lado, el uso de placas solares como fuente externa de energía se llevó a cabo junto con el proceso de extracción de calor en dos condiciones climatológicas diferentes: invierno y verano. Los resultados obtenidos indicaron que el uso de placas solares permitió un aumento del 50% en la eficiencia diaria durante los experimentos llevados a cabo durante la estación fría. La segunda parte se centró en el diseño, construcción y operación de un estanque solar de 500 m2 en las instalaciones de Solvay Minerales (Granada). El estanque solar fue diseñado para suministrar el calor necesario para precalentar el agua (> 60 ° C) y los reactivos en la unidad de flotación de la instalación de procesamiento de minerales. Las eficiencias globales obtenidas después del primer y segundo período de operación son 9.7 y 12.3%, respectivamente, con valores máximos de 28 y 24% obtenidos durante los primeros meses de operación. En cuanto al ahorro económico, se obtuvieron reducciones de 52 y 68% en el primer y segundo período en comparación con el sistema tradicional sin estanque solar. Además, el impacto ambiental se reduce claramente considerando la reducción de las emisiones de CO2. La experiencia del estanque solar de Granada demuestra que la principal ventaja de estos sistemas es la capacidad de almacenar energía en los meses con mayor radiación solar, para poder proporcionar un flujo de calor a un sistema externo durante todo el año, incluso en condiciones climáticas adversas, como se pudo comprobar durante la nevada en enero de 2015.Postprint (published version

Enhancing the thermal efficiency of a salinity gradient solar pond. Implementation of the study in the design, construction, salinity gradient establishment, operation and energy transfer at industrial scale

The energy model in the last decades has been dominated by the consumption of fossil fuels assuming a high environmental cost. Global warming and the destruction of the ozone layer are two examples of the deterioration that is being suffered due to the use of these energy sources. Increasingly, the use of renewable energy one of the alternatives in building a sustainable economic model. Among renewables, solar energy is presented as an inexhaustible and accessible source of energy. The solar pond is a technology that meets all requirements to be considered an energy storage device. It can store solar energy, charging during the months of high solar incidence (Spring-Summer), storing the energy through the time and making possible its use when it is requested. A salt gradient solar pond is a body of saline water with long term thermal storage capacity. The aim and scope of this PhD thesis is divided in two parts. First, the improvement of the efficiency of the solar pond technology through experimental evaluation the heat extraction and heat supply processes under different weather conditions. These experiments were carried out in a 50 m2 solar pond pilot plant located in Martorell (Catalonia). Heat extraction experiments were performed using both heat exchangers installed (lateral and bottom) individually or both at the same time. The results demonstrated that the efficiency of the pond increases when the heat is removed from the lateral heat exchanger compared to either using the bottom heat exchanger or using both heat exchangers simultaneously. On the other hand, the use of solar collectors as an external source of heat were conducted together with heat extraction process under two different seasonal temperature conditions: winter and summer. The results indicated that the use of solar collectors allowed a 50% increase in daily efficiency during the cold season tests. The second part was focused on the design, construction and operation of a 500 m2 solar pond in Solvay Minerales facilities (Granada). The solar pond was designed to supply the heat required to preheat the water (> 60 °C) and the reagents in the mineral flotation unit at the mineral processing facility. The overall efficiencies obtained after the first and second operation periods are 9.7 and 12.3%, respectively, with maximum values of 28 and 24% obtained during the first months of operation. Regarding the economic savings, reductions of 52 and 68% were obtained in the first and second periods compared with the traditional system without solar pond. Also, the environmental impact is clearly reduced considering the reduction of CO2 emissions. The experience of the Granada solar pond proves that the main advantage of a solar pond is the capacity to store energy in the months with the highest solar radiation to provide a flux of heat to an external system during the whole year even under strong weather conditions, as observed during the January 2015 snowfall.El modelo energético en las últimas décadas ha estado dominado por el consumo de combustibles fósiles, asumiendo un alto coste ambiental. El calentamiento global y la destrucción de la capa de ozono son dos ejemplos del deterioro que se está sufriendo debido al uso de estas fuentes de energía. Cada vez más, el uso de energías renovables es una de las alternativas en la construcción de un modelo económico sostenible. Entre las energías renovables, la energía solar se presenta como una fuente de energía inagotable y accesible. El estanque solar es una tecnología que cumple todos los requisitos para ser considerado un dispositivo de almacenamiento de energía. Puede almacenar energía solar, cargando durante los meses de alta incidencia solar (primavera-verano), almacenando la energía y haciendo posible su uso cuando es necesaria. Un estanque solar con gradiente salino es un cuerpo de agua salina con capacidad de almacenamiento térmico a largo plazo. El objetivo y alcance de esta tesis doctoral se divide en dos partes. Primero, la mejora de la eficiencia del estanque solar a través de la evaluación experimental de los procesos de extracción de calor y aportación de calor en diferentes condiciones climáticas. Estos experimentos se llevaron a cabo en un estanque solar a escala planta piloto de 50 m2 situada en Martorell (Cataluña). Los experimentos de extracción de calor se realizaron mediante el uso de intercambiadores de calor situados en el área lateral y en el área inferior del estanque. El proceso de extracción de calor se llevó a cabo de manera individual (área lateral o inferior) o simultáneamente (área global). Los resultados demostraron que la eficiencia del estanque aumenta cuando el calor es extraído usando el intercambiador de calor lateral en comparación con el uso del intercambiador de calor inferior o con los dos intercambiadores de calor simultáneamente. Por otro lado, el uso de placas solares como fuente externa de energía se llevó a cabo junto con el proceso de extracción de calor en dos condiciones climatológicas diferentes: invierno y verano. Los resultados obtenidos indicaron que el uso de placas solares permitió un aumento del 50% en la eficiencia diaria durante los experimentos llevados a cabo durante la estación fría. La segunda parte se centró en el diseño, construcción y operación de un estanque solar de 500 m2 en las instalaciones de Solvay Minerales (Granada). El estanque solar fue diseñado para suministrar el calor necesario para precalentar el agua (> 60 ° C) y los reactivos en la unidad de flotación de la instalación de procesamiento de minerales. Las eficiencias globales obtenidas después del primer y segundo período de operación son 9.7 y 12.3%, respectivamente, con valores máximos de 28 y 24% obtenidos durante los primeros meses de operación. En cuanto al ahorro económico, se obtuvieron reducciones de 52 y 68% en el primer y segundo período en comparación con el sistema tradicional sin estanque solar. Además, el impacto ambiental se reduce claramente considerando la reducción de las emisiones de CO2. La experiencia del estanque solar de Granada demuestra que la principal ventaja de estos sistemas es la capacidad de almacenar energía en los meses con mayor radiación solar, para poder proporcionar un flujo de calor a un sistema externo durante todo el año, incluso en condiciones climáticas adversas, como se pudo comprobar durante la nevada en enero de 2015

Ammoniun removal from wastewater by liquid-liquid membrane contactors

Removal of ammonia from wastewater generated in a waste treatment plant by a membrane contactor was studied at lab scale. The treated wastewater will be applied in the Hydrogen and Oxygen production by electrolysis via renewable energies. The aim of this study relies on fulfill the process requirements in the electrolysis, since the water used in the electrolysis process must be almost pure water due to efficiency process of Hydrogen and Oxygen production decreases with the ions in the dissolution. The residual ammonium concentration of the aqueous stream feeding the membrane distillation step ranging between 1 to 5 ppm is not removed and arrives to the electrolysis step generating an increase in the conductivity. So the use of a liquid-liquid membrane contactor is proposed to reduce ammonium (NH+4) concentration before membranes distillation step. The experimental set-up was performed by a contactor (Liqui-cel X30 HF (Celgard, USA)) which works in close and open loop mode configuration. In close circuit, it was used a tank of 10 liters to storage ammonium solution and in open circuit it was used 25 liters as initial ammonium volume. A pump (Cole Parmer instrument) was used to feed the contactor from the tank. An aqueous ammonium solution with a low concentration is in the inner side of the membrane contactor (Lumen) and sulphuric acid solution goes in the outside of the membrane contactor (Shell). The pH plays a very important role in the chemical equilibrium; for that reason is motorized during the experiments. On the other hand, it has been carried out the simulation of a mathematical model used by various authors to validate the experimental results by COMSOL Multiphysics progra

Design, construction, and operation of the first industrial salinity-gradient solar pond in Europe: An efficiency analysis perspective

A 500 m2 industrial salinity-gradient solar pond (SGSP) was constructed in a mineral processing plant (Solvay Minerales) in Granada (Spain). This renewable energy technology was designed to supply a low-temperature heat (up to 60 °C) to achieve the temperature requirements of the flotation mineral purification stage. The low-temperature source was integrated to partially replace the fuel oil boiler used to heat the water used in the flotation stage. Theoretical calculations based on solar radiation indicated that the use of the SGSP would reduce the annual fuel consumption by more than 50%, thus providing a significant improvement at both economic and environmental levels. Two months after the SGSP was established, in August 2014, the temperature in the storage zone of the SGSP reached approximately 90 °C. The overall performance was evaluated in two periods (2014 and 2015) in terms of the retrofitting of mining facility with a solar pond and a new method to assess the thermal efficiency of the solar pond in a long-term perspective has been proposed. The overall efficiencies obtained after the first and second operation periods were 10 and 12%, respectively, with maximum values of 28 and 24% obtained during the first operation months. Regarding the economic savings, the fuel oil cost of the flotation unit was reduced by a higher percentage than the fuel oil consumption, due to the decreasing tendency of fuel oil prices during 2014 and 2015. Reductions of 52 and 68% were obtained in the first and second periods of operation, respectively, when compared to 2013. In addition, not only does the SGSP have considerably reduced operating costs but also the environmental costs are clearly reduced when considering the reduction of CO2 emissions.Peer ReviewedPostprint (author's final draft

Enhancing the efficiency of solar pond heat extraction by using both lateral and bottom heat exchangers

In this study, heat extraction from both the gradient and heat storage zones of a salinity-gradient solar pond (SGSP) has been evaluated. For this purpose, an experimental solar pond pilot plant was constructed in 2009 in Barcelona (Spain). The structure of the pond is a cylindrical tank of 3-m height and 8 m diameter with a total area of 50 m(2). The main objective was to evaluate a heat-extraction system from the SGSP designed to enhance the system efficiency under different conditions. Thus, an in-pond heat exchanger covering all of the lateral wall area of the pond was installed, and its performance was compared with the traditional in-pond heat exchanger situated on the bottom of the pond. Heat extraction experiments were performed using both heat exchangers individually or both at the same time. The study covers the experiments performed at three different seasonal temperature conditions: winter (December), summer (July) and autumn (October and November). The variations of the temperature inside the pond during the heat extraction were measured and analyzed. The results demonstrated that the efficiency of the pond increases when the heat is removed from the lateral heat exchanger alone compared to either using the bottom heat exchanger or using both heat exchangers simultaneouslyPostprint (author's final draft

El sistema de gestión de la calidad en la Facultad de Química de la Universitat de Barcelona

El Real Decreto 1393/2007 obliga a que todos los estudios de grado tengan un sistema de garantía de la calidad. En esta línea, la Facultad de Química de la Universitat de Barcelona ha creado su Sistema de Gestión de la Calidad (SGC). Este SGC empieza con la definición de la Política de Calidad, Medio Ambiente y Seguridad, continúa con el mapa de procesos de la docencia, sigue con la redacción de todos los procedimientos necesarios para documentar cómo llevar a cabo cada uno de los procesos y finaliza con la preparación de las herramientas de análisis y mejora como indicadores, auditorías, etc. Está previsto que su implementación se lleve a cabo a lo largo del año 2012

Ammoniun removal from wastewater by liquid-liquid membrane contactors

Removal of ammonia from wastewater generated in a waste treatment plant by a membrane contactor was studied at lab scale. The treated wastewater will be applied in the Hydrogen and Oxygen production by electrolysis via renewable energies. The aim of this study relies on fulfill the process requirements in the electrolysis, since the water used in the electrolysis process must be almost pure water due to efficiency process of Hydrogen and Oxygen production decreases with the ions in the dissolution. The residual ammonium concentration of the aqueous stream feeding the membrane distillation step ranging between 1 to 5 ppm is not removed and arrives to the electrolysis step generating an increase in the conductivity. So the use of a liquid-liquid membrane contactor is proposed to reduce ammonium (NH+4) concentration before membranes distillation step. The experimental set-up was performed by a contactor (Liqui-cel X30 HF (Celgard, USA)) which works in close and open loop mode configuration. In close circuit, it was used a tank of 10 liters to storage ammonium solution and in open circuit it was used 25 liters as initial ammonium volume. A pump (Cole Parmer instrument) was used to feed the contactor from the tank. An aqueous ammonium solution with a low concentration is in the inner side of the membrane contactor (Lumen) and sulphuric acid solution goes in the outside of the membrane contactor (Shell). The pH plays a very important role in the chemical equilibrium; for that reason is motorized during the experiments. On the other hand, it has been carried out the simulation of a mathematical model used by various authors to validate the experimental results by COMSOL Multiphysics progra

Enhancing the thermal efficiency of a salinity gradient solar pond. Implementation of the study in the design, construction, salinity gradient establishment, operation and energy transfer at industrial scale

The energy model in the last decades has been dominated by the consumption of fossil fuels assuming a high environmental cost. Global warming and the destruction of the ozone layer are two examples of the deterioration that is being suffered due to the use of these energy sources. Increasingly, the use of renewable energy one of the alternatives in building a sustainable economic model. Among renewables, solar energy is presented as an inexhaustible and accessible source of energy. The solar pond is a technology that meets all requirements to be considered an energy storage device. It can store solar energy, charging during the months of high solar incidence (Spring-Summer), storing the energy through the time and making possible its use when it is requested. A salt gradient solar pond is a body of saline water with long term thermal storage capacity. The aim and scope of this PhD thesis is divided in two parts. First, the improvement of the efficiency of the solar pond technology through experimental evaluation the heat extraction and heat supply processes under different weather conditions. These experiments were carried out in a 50 m2 solar pond pilot plant located in Martorell (Catalonia). Heat extraction experiments were performed using both heat exchangers installed (lateral and bottom) individually or both at the same time. The results demonstrated that the efficiency of the pond increases when the heat is removed from the lateral heat exchanger compared to either using the bottom heat exchanger or using both heat exchangers simultaneously. On the other hand, the use of solar collectors as an external source of heat were conducted together with heat extraction process under two different seasonal temperature conditions: winter and summer. The results indicated that the use of solar collectors allowed a 50% increase in daily efficiency during the cold season tests. The second part was focused on the design, construction and operation of a 500 m2 solar pond in Solvay Minerales facilities (Granada). The solar pond was designed to supply the heat required to preheat the water (> 60 °C) and the reagents in the mineral flotation unit at the mineral processing facility. The overall efficiencies obtained after the first and second operation periods are 9.7 and 12.3%, respectively, with maximum values of 28 and 24% obtained during the first months of operation. Regarding the economic savings, reductions of 52 and 68% were obtained in the first and second periods compared with the traditional system without solar pond. Also, the environmental impact is clearly reduced considering the reduction of CO2 emissions. The experience of the Granada solar pond proves that the main advantage of a solar pond is the capacity to store energy in the months with the highest solar radiation to provide a flux of heat to an external system during the whole year even under strong weather conditions, as observed during the January 2015 snowfall.El modelo energético en las últimas décadas ha estado dominado por el consumo de combustibles fósiles, asumiendo un alto coste ambiental. El calentamiento global y la destrucción de la capa de ozono son dos ejemplos del deterioro que se está sufriendo debido al uso de estas fuentes de energía. Cada vez más, el uso de energías renovables es una de las alternativas en la construcción de un modelo económico sostenible. Entre las energías renovables, la energía solar se presenta como una fuente de energía inagotable y accesible. El estanque solar es una tecnología que cumple todos los requisitos para ser considerado un dispositivo de almacenamiento de energía. Puede almacenar energía solar, cargando durante los meses de alta incidencia solar (primavera-verano), almacenando la energía y haciendo posible su uso cuando es necesaria. Un estanque solar con gradiente salino es un cuerpo de agua salina con capacidad de almacenamiento térmico a largo plazo. El objetivo y alcance de esta tesis doctoral se divide en dos partes. Primero, la mejora de la eficiencia del estanque solar a través de la evaluación experimental de los procesos de extracción de calor y aportación de calor en diferentes condiciones climáticas. Estos experimentos se llevaron a cabo en un estanque solar a escala planta piloto de 50 m2 situada en Martorell (Cataluña). Los experimentos de extracción de calor se realizaron mediante el uso de intercambiadores de calor situados en el área lateral y en el área inferior del estanque. El proceso de extracción de calor se llevó a cabo de manera individual (área lateral o inferior) o simultáneamente (área global). Los resultados demostraron que la eficiencia del estanque aumenta cuando el calor es extraído usando el intercambiador de calor lateral en comparación con el uso del intercambiador de calor inferior o con los dos intercambiadores de calor simultáneamente. Por otro lado, el uso de placas solares como fuente externa de energía se llevó a cabo junto con el proceso de extracción de calor en dos condiciones climatológicas diferentes: invierno y verano. Los resultados obtenidos indicaron que el uso de placas solares permitió un aumento del 50% en la eficiencia diaria durante los experimentos llevados a cabo durante la estación fría. La segunda parte se centró en el diseño, construcción y operación de un estanque solar de 500 m2 en las instalaciones de Solvay Minerales (Granada). El estanque solar fue diseñado para suministrar el calor necesario para precalentar el agua (> 60 ° C) y los reactivos en la unidad de flotación de la instalación de procesamiento de minerales. Las eficiencias globales obtenidas después del primer y segundo período de operación son 9.7 y 12.3%, respectivamente, con valores máximos de 28 y 24% obtenidos durante los primeros meses de operación. En cuanto al ahorro económico, se obtuvieron reducciones de 52 y 68% en el primer y segundo período en comparación con el sistema tradicional sin estanque solar. Además, el impacto ambiental se reduce claramente considerando la reducción de las emisiones de CO2. La experiencia del estanque solar de Granada demuestra que la principal ventaja de estos sistemas es la capacidad de almacenar energía en los meses con mayor radiación solar, para poder proporcionar un flujo de calor a un sistema externo durante todo el año, incluso en condiciones climáticas adversas, como se pudo comprobar durante la nevada en enero de 2015

Enhancing the thermal efficiency of a salinity gradient solar pond. Implementation of the study in the design, construction, salinity gradient establishment, operation and energy transfer at industrial scale

Tesi amb diferents seccions retallades per drets de l'editorThe energy model in the last decades has been dominated by the consumption of fossil fuels assuming a high environmental cost. Global warming and the destruction of the ozone layer are two examples of the deterioration that is being suffered due to the use of these energy sources. Increasingly, the use of renewable energy one of the alternatives in building a sustainable economic model. Among renewables, solar energy is presented as an inexhaustible and accessible source of energy. The solar pond is a technology that meets all requirements to be considered an energy storage device. It can store solar energy, charging during the months of high solar incidence (Spring-Summer), storing the energy through the time and making possible its use when it is requested. A salt gradient solar pond is a body of saline water with long term thermal storage capacity. The aim and scope of this PhD thesis is divided in two parts. First, the improvement of the efficiency of the solar pond technology through experimental evaluation the heat extraction and heat supply processes under different weather conditions. These experiments were carried out in a 50 m2 solar pond pilot plant located in Martorell (Catalonia). Heat extraction experiments were performed using both heat exchangers installed (lateral and bottom) individually or both at the same time. The results demonstrated that the efficiency of the pond increases when the heat is removed from the lateral heat exchanger compared to either using the bottom heat exchanger or using both heat exchangers simultaneously. On the other hand, the use of solar collectors as an external source of heat were conducted together with heat extraction process under two different seasonal temperature conditions: winter and summer. The results indicated that the use of solar collectors allowed a 50% increase in daily efficiency during the cold season tests. The second part was focused on the design, construction and operation of a 500 m2 solar pond in Solvay Minerales facilities (Granada). The solar pond was designed to supply the heat required to preheat the water (> 60 °C) and the reagents in the mineral flotation unit at the mineral processing facility. The overall efficiencies obtained after the first and second operation periods are 9.7 and 12.3%, respectively, with maximum values of 28 and 24% obtained during the first months of operation. Regarding the economic savings, reductions of 52 and 68% were obtained in the first and second periods compared with the traditional system without solar pond. Also, the environmental impact is clearly reduced considering the reduction of CO2 emissions. The experience of the Granada solar pond proves that the main advantage of a solar pond is the capacity to store energy in the months with the highest solar radiation to provide a flux of heat to an external system during the whole year even under strong weather conditions, as observed during the January 2015 snowfall.El modelo energético en las últimas décadas ha estado dominado por el consumo de combustibles fósiles, asumiendo un alto coste ambiental. El calentamiento global y la destrucción de la capa de ozono son dos ejemplos del deterioro que se está sufriendo debido al uso de estas fuentes de energía. Cada vez más, el uso de energías renovables es una de las alternativas en la construcción de un modelo económico sostenible. Entre las energías renovables, la energía solar se presenta como una fuente de energía inagotable y accesible. El estanque solar es una tecnología que cumple todos los requisitos para ser considerado un dispositivo de almacenamiento de energía. Puede almacenar energía solar, cargando durante los meses de alta incidencia solar (primavera-verano), almacenando la energía y haciendo posible su uso cuando es necesaria. Un estanque solar con gradiente salino es un cuerpo de agua salina con capacidad de almacenamiento térmico a largo plazo. El objetivo y alcance de esta tesis doctoral se divide en dos partes. Primero, la mejora de la eficiencia del estanque solar a través de la evaluación experimental de los procesos de extracción de calor y aportación de calor en diferentes condiciones climáticas. Estos experimentos se llevaron a cabo en un estanque solar a escala planta piloto de 50 m2 situada en Martorell (Cataluña). Los experimentos de extracción de calor se realizaron mediante el uso de intercambiadores de calor situados en el área lateral y en el área inferior del estanque. El proceso de extracción de calor se llevó a cabo de manera individual (área lateral o inferior) o simultáneamente (área global). Los resultados demostraron que la eficiencia del estanque aumenta cuando el calor es extraído usando el intercambiador de calor lateral en comparación con el uso del intercambiador de calor inferior o con los dos intercambiadores de calor simultáneamente. Por otro lado, el uso de placas solares como fuente externa de energía se llevó a cabo junto con el proceso de extracción de calor en dos condiciones climatológicas diferentes: invierno y verano. Los resultados obtenidos indicaron que el uso de placas solares permitió un aumento del 50% en la eficiencia diaria durante los experimentos llevados a cabo durante la estación fría. La segunda parte se centró en el diseño, construcción y operación de un estanque solar de 500 m2 en las instalaciones de Solvay Minerales (Granada). El estanque solar fue diseñado para suministrar el calor necesario para precalentar el agua (> 60 ° C) y los reactivos en la unidad de flotación de la instalación de procesamiento de minerales. Las eficiencias globales obtenidas después del primer y segundo período de operación son 9.7 y 12.3%, respectivamente, con valores máximos de 28 y 24% obtenidos durante los primeros meses de operación. En cuanto al ahorro económico, se obtuvieron reducciones de 52 y 68% en el primer y segundo período en comparación con el sistema tradicional sin estanque solar. Además, el impacto ambiental se reduce claramente considerando la reducción de las emisiones de CO2. La experiencia del estanque solar de Granada demuestra que la principal ventaja de estos sistemas es la capacidad de almacenar energía en los meses con mayor radiación solar, para poder proporcionar un flujo de calor a un sistema externo durante todo el año, incluso en condiciones climáticas adversas, como se pudo comprobar durante la nevada en enero de 2015

Enhancing the efficiency of solar pond heat extraction by using both lateral and bottom heat exchangers

In this study, heat extraction from both the gradient and heat storage zones of a salinity-gradient solar pond (SGSP) has been evaluated. For this purpose, an experimental solar pond pilot plant was constructed in 2009 in Barcelona (Spain). The structure of the pond is a cylindrical tank of 3-m height and 8 m diameter with a total area of 50 m(2). The main objective was to evaluate a heat-extraction system from the SGSP designed to enhance the system efficiency under different conditions. Thus, an in-pond heat exchanger covering all of the lateral wall area of the pond was installed, and its performance was compared with the traditional in-pond heat exchanger situated on the bottom of the pond. Heat extraction experiments were performed using both heat exchangers individually or both at the same time. The study covers the experiments performed at three different seasonal temperature conditions: winter (December), summer (July) and autumn (October and November). The variations of the temperature inside the pond during the heat extraction were measured and analyzed. The results demonstrated that the efficiency of the pond increases when the heat is removed from the lateral heat exchanger alone compared to either using the bottom heat exchanger or using both heat exchangers simultaneousl