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

Specific adsorption of trivalent cations in biological nanopores determines conductance dynamics and reverses ionic selectivity

Adsorption processes are central to ionic transport in industrial and biological membrane systems. Multivalent cations modulate the conductive properties of nanofluidic devices through interactions with charged surfaces that depend principally on the ion charge number. Considering that ion channels are specialized valves that demand a sharp specificity in ion discrimination, we investigate the adsorption dynamics of trace amounts of different salts of trivalent cations in biological nanopores. We consider here OmpF from Escherichia coli, an archetypical protein nanopore, to probe the specificity of biological nanopores to multivalent cations. We systematically compare the effect of three trivalent electrolytes on OmpF current–voltage relationships and characterize the degree of rectification induced by each ion. We also analyze the open channel current noise to determine the existence of equilibrium/non-equilibrium mechanisms of ion adsorption and evaluate the extent of charge inversion through selectivity measurements. We show that the interaction of trivalent electrolytes with biological nanopores occurs via ion-specific adsorption yielding differential modulation of ion conduction and selectivity inversion. We also demonstrate the existence of non-equilibrium fluctuations likely related to ion-dependent trapping–detrapping processes. Our study provides fundamental information relevant to different biological and electrochemical systems where transport phenomena involve ion adsorption in charged surfaces under nanoscale confinement

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

Increasing the storage capacity of a solar pond by using solar thermal collectors: heat extraction and heat supply processes using in-pond heat exchangers

In this study, an experimental investigation of the performance of a salinity gradient solar pond (SGSP) integrating solar collectors is presented. The SGSP is located in Barcelona (Spain) and has a cylindrical tank 3¿m in height and 8¿m in diameter with a total area of 50¿m2. For this purpose, four solar thermal collectors (10¿m2) are integrated, as an external source of heat, with the solar pond pilot plant in order to increase the storage capacity and its overall efficiency. The aim of this study is to evaluate heat extraction and heat supply processes from and to the SGSP under different seasonal conditions. Two in-pond heat exchangers are used, a conventional one situated on the bottom of the pond and a second one covering the lateral wall area of the pond. Heat extraction and supply experiments are performed using both heat exchangers individually or both at the same time. The experiments are conducted under two different seasonal temperature conditions: winter (February and March) and summer (July). The variations of the temperature inside the pond during the heat extraction/supply tests are monitored and analyzed. The results have indicated that the use of solar collectors as an extra source of heat for the solar pond led to a 50% increase in the daily efficiency during the cold season tests, while heat extraction only appeared as the best option during the warm season tests. Higher daily efficiency and heat supply results can only be obtained if large amounts of heat are extracted, otherwise, the daily efficiency of the solar pond could decrease. Finally, the solar collectors can be considered a good alternative for avoiding a significant decrease in solar pond temperatures (especially during the cold season), which would not only result in a significant energy storage efficiency improvement but also increase the capacity of the solar pond to supply heat to an external application.Peer ReviewedPostprint (author's final draft

Methodological Experiences in Collaborative Ethnography. Communication and Participation as Frameworks for Constructing in Common

In this article, we will analyze how we built the research process of a collaborative ethnography with the Stop Evictions Granada 15M Movement (SEG15M). We will begin with a brief contextualization of the housing issues in Spain and the SEG15M movement to explain why we started the co-research experience with the movement. Next, we will clarify the composition, function, and main purposes of the ‘debate groups’ in our research, as well as their particular differences and dynamics concerning other qualitative techniques. Finally, we will focus on two main aspects, participation and communication, which emerged within the debates and later materialized into a transmedia project and the development of a radio soap opera. The latter is a product, and a process, of collaborative work that bridges communication and participation at the intra- and inter-group levels. It is a fictional story that emerges from the common lived experiences of the groups

Decolonizar la investigación sobre migraciones: apuntes desde una etnografía colaborativa

Este artículo forma parte del proyecto “Procesos emergentes y agencias del común: praxis de la investigación social colaborativa y nuevas formas de subjetivación política” Proyectos de I+D+i (Convocatoria 2014), del Progra - ma estatal de fomento de la investigación científica y técnica de excelencia, Ministerio de Economía y Competitividad del gobierno de España (Referencia: CSO2014-56960-P). Su origen se remonta a una comunicación oral pre - sentada en el simposio “Metodologías de-coloniales para investigar las migraciones”, en el marco del 4to Congre - so Latinoamericano y Caribeño de Ciencias Sociales (FLACSO), celebrado en Salamanca del 17 al 19 de julio de 2017. Agradecemos a María Fernanda Moscoso y Gennaro Avallone, quienes coordinaron el panel.En este artículo analizamos los significados asumidos por la idea de “(in)migración(es)” y la categoría de “(in)migrante(s)” en los contextos sociales, políticos y académicos contemporáneos. Resaltando su estrecha relación con el pensamiento de Estado y la colonialidad del poder/saber, nos preguntamos por otros posibles acercamientos a la movilidad humana. Discutimos la etnografía colaborativa, entendida como una metodología decolonial que rechaza las representaciones pasivizantes hegemónicas y aspira a visibilizar los procesos de subjetivación política de las personas junto a las que se investiga. Aportando ejemplos de nuestra propia investigación colaborativa junto a Stop Desahucios-Granada 15M, ilustramos cómo la idea de (in)migración(es) y la categoría “(in)migrante(s)” se han materializado en nuestro contexto, que se encuentra definido por el activismo político y no había sido previamente alterizado como “migratorio”. Concluimos resaltando la ambivalencia implícita en estas dos expresiones y reflexionamos sobre los pros y los contras implícitos en su uso.In this paper we analyze the meaning of “immigration” and “immigrant” within contemporary social, political and academic contexts. We emphasize their narrow relation with State thought and the coloniality of power/knowledge and search for alternative approaches to human mobility. With this aim, we discuss collaborative ethnography as a decolonial methodology addressed to visibilize the political subjectivation processes of the people we research with. Drawing on examples from our own collaborative research with Stop Evictions-Granada 15M, we show how the idea of “immigration” and the category “immigrants” have come into being within our field, a space of political activism which had not been previously constructed as a “migratory context”. We conclude underlining the ambivalence implicit in the two aforementioned concepts and discuss the pros and cons of using them

Biphasic concentration patterns in ionic transport under nanoconfinement revealed in steady-state and time-dependent properties

Ion permeation across nanoscopic structures differs considerably from microfluidics because of strong steric constraints, transformed solvent properties, and charge-regulation effects revealed mostly in diluted solutions. However, little is known about nanofluidics in moderately concentrated solutions, which are critically important for industrial applications and living systems. Here, we show that nanoconfinement triggers general biphasic concentration patterns in a myriad of ion transport properties by using two contrasting systems: a biological ion channel and a much larger synthetic nanopore. Our findings show a low-concentration regime ruled by classical Debye screening and another one where ion–ion correlations and enhanced ion–surface interactions contribute differently to each electrophysiological property. Thus, different quantities (e.g., conductance vs noise) measured under the same conditions may appear contradictory because they belong to different concentration regimes. In addition, non-linear effects that are barely visible in bulk conductivity only in extremely concentrated solutions become apparent in nanochannels around physiological conditions