Publication: Análisis térmico y mecánico de un tubo receptor de un colector solar
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2014-09
Defense date
2014-10-09
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Abstract
Las plantas de termosolares de torre de potencia son una de las alternativas de energías
renovables más eficientes hoy en día. Dentro de estas instalaciones, el receptor solar es una de
las piezas clave de las instalaciones ya que éste transforma la radiación incidente del sol en
energía térmica. Dado el alto coste de estas instalaciones es importante que se obtenga el
máximo rendimiento de ellas y que la vida útil sea lo más larga posible para rentabilizar la
inversión inicial.
El receptor está sometido a una radiación incidente muy concentrada y trabaja en rangos de
temperaturas altos y extremos. Por ello, un estudio en profundidad de este componente es de
gran utilidad para poder controlar su buen funcionamiento. En este estudio se ha analizado
térmica y mecánicamente un receptor muy similar al de la planta Gemasolar. Se ha estudiado
la evolución de la temperatura de las sales térmicas que circulan por el receptor y de los tubos
que lo componen. Para el buen funcionamiento de la instalación es necesario que no se
sobrepasen los límites de las temperaturas del tubo y de las sales. El análisis muestra que las
temperaturas más altas se encuentran en los heliostatos situados en las caras oeste y este por
lo que deben ser controlados con más cautela.
Con el objetivo de tener el mayor rendimiento y vida útil posible se estudian diferentes
diseños del receptor variando el diámetro de tubos y el número de paneles en el receptor. La
variación de la geometría del receptor muestra que el rendimiento térmico es muy similar de
un diseño a otro puesto que la energía absorbida es muy parecida independientemente del
modelo. Sin embargo, entre los diferentes modelos las condiciones de trabajo varían
enormemente. Para los diseños con diámetros de tubos grandes y menor número de paneles,
las temperaturas alcanzadas se acercan a las temperaturas límite reduciendo la vida útil del
receptor. Por el contrario, con la reducción del diámetro de los tubos, los rangos de
temperatura son más favorables para la larga duración del receptor. Por otra parte, con la
reducción del diámetro de tubos y del número de paneles se obtienen flujos másicos menores
en la instalación. Gracias a esta reducción es desgaste de los tubos disminuye
considerablemente. Sin embargo las mejores condiciones para el incremento de la vida útil del
receptor suponen costes muy elevados. Por esa razón es importante encontrar un balance
entre el coste del diseño manteniendo las mejores condiciones posibles del receptor.
Nowadays, solar power-tower plants are one of the most efficient renewable energies. The receiver from these plants has a key function since due to the receiver the solar radiation is converted into thermal energy. Due to the high cost of these plants, obtaining a high efficiency and a long life time is one of the main objectives of the current plants. High values of efficiency and lifetime make the initial investment of the plant be worth. The receiver works under very high and extreme temperature conditions, also it receives highly concentrated radiation. Therefore, a deep knowledge of the receiver is needed in order to ensure the correct operation of this device. In this paper, a thermal analysis has been performed of a receiver very similar to the one used in Gemasolar. The analysis of the temperature progress along the receiver was made to understand salt and tubes temperature variations. To ensure the good performance of the receiver, the temperature of the thermal fluid and the receiver’s tube should never go over the temperatures limits. The analysis shows that highest temperatures exist in the east and west sides of the receivers, therefore special caution should be taken while controlling these sides of the receiver. In order to have the highest efficiency and largest lifetime of the receiver, different designs have been studied by making variations in the number of panels and in the diameter of the tubes. After the analysis, it is shown that the geometric variations of the receivers have little impact in the thermal efficiency. This is due to the fact that overall absorbed energy is very similar from one design to another. However, by comparing all the designs, big differences in the work conditions exists between all of them. For little number of panels and high tube diameters, temperatures reach the limit values. This implies an important reduction in the lifetime of the receiver. On the opposite side, by reducing tubes diameter and increasing the number of panels working temperatures are reduced. Also, mass flux changes with the geometry of the receiver, by reducing number of panels and the diameter of the tubes smaller mass fluxes are obtained. With reduced mass fluxes, the tubes wear slowly, increasing receiver’s lifetime. However, the best conditions for the receiver are achieved with the most expensive designs. As a consequence a balance between cost and optimum design should be found in order to have the best possible receiver’s conditions.
Nowadays, solar power-tower plants are one of the most efficient renewable energies. The receiver from these plants has a key function since due to the receiver the solar radiation is converted into thermal energy. Due to the high cost of these plants, obtaining a high efficiency and a long life time is one of the main objectives of the current plants. High values of efficiency and lifetime make the initial investment of the plant be worth. The receiver works under very high and extreme temperature conditions, also it receives highly concentrated radiation. Therefore, a deep knowledge of the receiver is needed in order to ensure the correct operation of this device. In this paper, a thermal analysis has been performed of a receiver very similar to the one used in Gemasolar. The analysis of the temperature progress along the receiver was made to understand salt and tubes temperature variations. To ensure the good performance of the receiver, the temperature of the thermal fluid and the receiver’s tube should never go over the temperatures limits. The analysis shows that highest temperatures exist in the east and west sides of the receivers, therefore special caution should be taken while controlling these sides of the receiver. In order to have the highest efficiency and largest lifetime of the receiver, different designs have been studied by making variations in the number of panels and in the diameter of the tubes. After the analysis, it is shown that the geometric variations of the receivers have little impact in the thermal efficiency. This is due to the fact that overall absorbed energy is very similar from one design to another. However, by comparing all the designs, big differences in the work conditions exists between all of them. For little number of panels and high tube diameters, temperatures reach the limit values. This implies an important reduction in the lifetime of the receiver. On the opposite side, by reducing tubes diameter and increasing the number of panels working temperatures are reduced. Also, mass flux changes with the geometry of the receiver, by reducing number of panels and the diameter of the tubes smaller mass fluxes are obtained. With reduced mass fluxes, the tubes wear slowly, increasing receiver’s lifetime. However, the best conditions for the receiver are achieved with the most expensive designs. As a consequence a balance between cost and optimum design should be found in order to have the best possible receiver’s conditions.
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Keywords
Energías renovables, Plantas termosolares, Receptores solares, Instalaciones eléctricas