Use of alternative fuels obtained from renewable sources in brayton cycles

Analysis and simulation of the behaviour of gas turbines for power generation using different nonconventional fuels obtained from different renewable sources are presented. Three biomass-tobiofuel processes are considered: anaerobic digestion of biomass (biogas), biomass gasification (synthesis gas) and alcoholic fermentation of biomass and dehydration (bioethanol), each of them with two different biomass substrates (energy crops and municipal solid waste) as input. The gas turbine behaviour in a Brayton cycle is simulated both in an isolated operation and in combined cycle. The differences in gas turbine performance when fired with the considered biofuels compared to natural gas are studied from different points of view related with the current complex energetic context: energetic and exergetic efficiency of the simple/combined cycle and CO2 emissions. Two different tools have been used for the simulations, each one with a different approach: while PATITUG (own software) analyses the behaviour of a generic gas turbine allowing a total variability of parameters, GT-PRO (commercial software) is more rigid, albeit more precise in the prediction of real gas turbine behaviour. Different potentially interesting configurations and its thermodynamic parameters have been simulated in order to obtain the optimal range for all of them and its variation for each fuel.

Use of alternative fuels obtained from renowable sources in Brayton cycles

Analysis and simulation of the behaviour of gas turbines for power generation using different nonconventional fuels obtained from different renewable sources are presented. Three biomass-tobiofuel processes are considered: anaerobic digestion of biomass (biogas), biomass gasification (synthesis gas) and alcoholic fermentation of biomass and dehydration (bioethanol), each of them with two different biomass substrates (energy crops and municipal solid waste) as input. The gas turbine behaviour in a Brayton cycle is simulated both in an isolated operation and in combined cycle. The differences in gas turbine performance when fired with the considered biofuels compared to natural gas are studied from different points of view related with the current complex energetic context: energetic and exergetic efficiency of the simple/combined cycle and CO2 emissions. Two different tools have been used for the simulations, each one with a different approach: while PATITUG (own software) analyses the behaviour of a generic gas turbine allowing a total variability of parameters, GT-PRO (commercial software) is more rigid, albeit more precise in the prediction of real gas turbine behaviour. Different potentially interesting configurations and its thermodynamic parameters have been simulated in order to obtain the optimal range for all of them and its variation for each fuel.

Determinación de la higroscopicidad y comportamiento termodinámico de la madera juvenil y madura a través de sus isotermas de sorción

La respuesta higroscópica de la madera varía a lo largo de la dirección radial del árbol. El aumento de corta de ejemplares jóvenes y el uso de troncos de pequeños diámetros en la industria de los productos forestales, hacen preciso estudiar el comportamiento higroscópico tanto de la madera juvenil como de la madura. Su determinación proporciona información para comprender los mecanismos de sorción. Asimismo, la obtención de las propiedades termodinámicas de ambos tipos de madera facilita la modelización de procesos industriales como el secado o el encolado. En el presente trabajo, se ha comparado el comportamiento higroscópico y las propiedades termodinámicas de la madera juvenil y madura de Abies pinsapo Boissier, Abies alba Mill., Pinus canariensis C. Sm. ex DC., Pinus nigra Arnold, Pinus uncinata Mill. ex Mirb. y Pinus pinea L. Para este propósito se han utilizado las isotermas de sorción obtenidas mediante el método tradicional de sales saturadas descrito por COST Action E8 a 15, 35 y 50ºC en Abies pinsapo, Abies alba, Pinus nigra, Pinus uncinata y Pinus pinea, y a 35 y 50ºC en Pinus canariensis. Igualmente, se ha empleado el equipo dynamic vapor sorption (DVS) en la obtención de las isotermas de Pinus pinea a 35 y 50ºC. El ajuste de las curvas se ha realizado mediante el modelo Guggenheim, Anderson y de Boer-Dent (GAB), cumpliendo todas las muestras los criterios de aceptación establecidos. En el estudio de las isotermas se ha calculado el coeficiente y área de histéresis entre el proceso de adsorción y desorción para cada una de las muestras. Con el fin de comprender el comportamiento higroscópico experimentado por cada madera se ha determinado la composición química, espectros de infrarrojos (FTIR) y difractogramas de rayos X de cada una. Los parámetros termodinámicos - calor isostérico neto y total heat of wetting - se han obtenido a partir de las isotermas de sorción mediante el método de integración de la ecuación de Clausius-Clapeyron. Finalmente, se han comparado los datos obtenidos con el método tradicional de sales saturadas y con dynamic vapor sorption con el propósito de conocer la existencia de similitudes entre ambas metodologías. Los resultados mostraron que los puntos de equilibrio son, en la mayor parte de los casos, superiores en la madera madura frente a la juvenil, y por tanto las isotermas de la madera madura se encuentran siempre por encima de las de la juvenil, debido principalmente a la composición química. Respecto a las propiedades termodinámicas, se ha determinado que la energía involucrada en los procesos de sorción es superior en la madera madura que en la madera juvenil, siendo mayor en el proceso de desorción frente al de adsorción. En la comparación de las metodologías de sales saturadas y dynamic vapor sorption no se han detectado casi diferencias significativas en el proceso de adsorción, mientras que sí se han obtenido en el de desorción. ABSTRACT The hygroscopic response of wood varies throughout the radial direction of the tree. The longer cut of young trees and the use of small-diameter trunks in the forest product industry make it necessary to study the hygroscopic behaviour of both juvenile and mature wood. Determining this behaviour in both types of wood provides information for understanding the sorption mechanisms. Similarly, obtaining the thermodynamic properties of juvenile and mature wood facilitates modelling of industrial processes such as drying and bonding. In this study a comparison was made of the hygroscopic behaviour and thermodynamic properties of juvenile and mature wood of Abies pinsapo Boissier, Abies alba Mill., Pinus canariensis C. Sm. ex DC., Pinus nigra Arnold, Pinus uncinata Mill. ex Mirb. and Pinus pinea L. This was done by obtaining the sorption isotherms using the traditional saturated salt method described by COST Action E8 at 15, 35 and 50ºC in Abies pinsapo, Abies alba, Pinus nigra, Pinus uncinata and Pinus pinea, and at 35 and 50ºC in Pinus canariensis. In addition, dynamic vapour sorption (DVS) was used to obtain the isotherms of Pinus pinea at 35 and 50ºC. The curves were fitted using the Guggenheim, Anderson and de Boer- Dent (GAB) model and all samples met the established acceptance criteria. In the study of the isotherms, the hysteresis coefficient and area of the hysteresis loop between adsorption and desorption were calculated for each sample. To understand the hygroscopic behaviour of juvenile and mature wood, the chemical composition, infrared spectra (FTIR) and X-ray diffractograms of each type of wood were determined. The thermodynamic parameters - net isosteric heat and total heat of wetting - were obtained from the sorption isotherms by applying the integration method of the Clausius-Clapeyron equation. The data obtained using the traditional saturated salt method and with dynamic vapour sorption were compared to determine the similarities between the two methods. The results showed that the equilibrium points are greater in the mature wood than in the juvenile wood in most cases, and therefore the mature wood isotherms are always above the juvenile wood isotherms, mainly because of the chemical composition. As regards the thermodynamic properties, it was determined that the energy involved in the sorption processes is greater in the mature wood than in the juvenile wood, and is greater in the desorption process than in the adsorption process. On comparing the saturated salt and dynamic vapour sorption methods, almost no significant differences were detected in the adsorption process, but significant differences were obtained in the desorption process.

Estimation of the solubility parameters of model plant surfaces and agrochemicals: a valuable tool for understanding plant surface interactions

Background Most aerial plant parts are covered with a hydrophobic lipid-rich cuticle, which is the interface between the plant organs and the surrounding environment. Plant surfaces may have a high degree of hydrophobicity because of the combined effects of surface chemistry and roughness. The physical and chemical complexity of the plant cuticle limits the development of models that explain its internal structure and interactions with surface-applied agrochemicals. In this article we introduce a thermodynamic method for estimating the solubilities of model plant surface constituents and relating them to the effects of agrochemicals. Results Following the van Krevelen and Hoftyzer method, we calculated the solubility parameters of three model plant species and eight compounds that differ in hydrophobicity and polarity. In addition, intact tissues were examined by scanning electron microscopy and the surface free energy, polarity, solubility parameter and work of adhesion of each were calculated from contact angle measurements of three liquids with different polarities. By comparing the affinities between plant surface constituents and agrochemicals derived from (a) theoretical calculations and (b) contact angle measurements we were able to distinguish the physical effect of surface roughness from the effect of the chemical nature of the epicuticular waxes. A solubility parameter model for plant surfaces is proposed on the basis of an increasing gradient from the cuticular surface towards the underlying cell wall. Conclusions The procedure enabled us to predict the interactions among agrochemicals, plant surfaces, and cuticular and cell wall components, and promises to be a useful tool for improving our understanding of biological surface interactions.

Estimation of the solubility parameters of model plant surfaces and agrochemicals: a valuable tool for understanding plant surface interactions

Background Most aerial plant parts are covered with a hydrophobic lipid-rich cuticle, which is the interface between the plant organs and the surrounding environment. Plant surfaces may have a high degree of hydrophobicity because of the combined effects of surface chemistry and roughness. The physical and chemical complexity of the plant cuticle limits the development of models that explain its internal structure and interactions with surface-applied agrochemicals. In this article we introduce a thermodynamic method for estimating the solubilities of model plant surface constituents and relating them to the effects of agrochemicals. Results Following the van Krevelen and Hoftyzer method, we calculated the solubility parameters of three model plant species and eight compounds that differ in hydrophobicity and polarity. In addition, intact tissues were examined by scanning electron microscopy and the surface free energy, polarity, solubility parameter and work of adhesion of each were calculated from contact angle measurements of three liquids with different polarities. By comparing the affinities between plant surface constituents and agrochemicals derived from (a) theoretical calculations and (b) contact angle measurements we were able to distinguish the physical effect of surface roughness from the effect of the chemical nature of the epicuticular waxes. A solubility parameter model for plant surfaces is proposed on the basis of an increasing gradient from the cuticular surface towards the underlying cell wall. Conclusions The procedure enabled us to predict the interactions among agrochemicals, plant surfaces, and cuticular and cell wall components, and promises to be a useful tool for improving our understanding of biological surface interactions.

Estudios termodinámicos de los procesos de vitrificación en la crioconservación de germoplasma vegetal=Thermodynamic studies of vitrification processes in plant germplasm cryopreservation

En la actualidad, las técnicas de crioconservación poseen una importancia creciente para el almacenamiento a largo plazo de germoplasma vegetal. En las dos últimas décadas, estos métodos experimentaron un gran desarrollo y se han elaborado protocolos adecuados a diferentes sistemas vegetales, utilizando diversas estrategias como la vitrificación, la encapsulación-desecación con cuentas de alginato y el método de “droplet”-vitrificación. La presente tesis doctoral tiene como objetivo aumentar el conocimiento sobre los procesos implicados en los distintos pasos de un protocolo de crioconservación, en relación con el estado del agua presente en los tejidos y sus cambios, abordado mediante diversas técnicas biofísicas, principalmente calorimetría diferencial de barrido (DSC) y microscopía electrónica de barrido a baja temperatura (crio-SEM). En un primer estudio sobre estos métodos de crioconservación, se describen las fases de enfriamiento hasta la temperatura del nitrógeno líquido y de calentamiento hasta temperatura ambiente, al final del periodo de almacenamiento, que son críticas para la supervivencia del material crioconservado. Tanto enfriamiento como calentamiento deben ser realizados lo más rápidamente posible pues, aunque los bajos contenidos en agua logrados en etapas previas de los protocolos reducen significativamente las probabilidades de formación de hielo, éstas no son del todo nulas. En ese contexto, se analiza también la influencia de las velocidades de enfriamiento y calentamiento de las soluciones de crioconservación de plantas en sus parámetros termofísicos referente a la vitrificación, en relación su composición y concentración de compuestos. Estas soluciones son empleadas en la mayor parte de los protocolos actualmente utilizados para la crioconservación de material vegetal. Además, se estudia la influencia de otros factores que pueden determinar la estabilidad del material vitrificado, tales como en envejecimiento del vidrio. Se ha llevado a cabo una investigación experimental en el empleo del crio-SEM como una herramienta para visualizar el estado vítreo de las células y tejidos sometidos a los procesos de crioconservación. Se ha comparado con la más conocida técnica de calorimetría diferencial de barrido, obteniéndose resultados muy concordantes y complementarios. Se exploró también por estas técnicas el efecto sobre tejidos vegetales de la adaptación a bajas temperaturas y de la deshidratación inducida por los diferentes tratamientos utilizados en los protocolos. Este estudio permite observar la evolución biofísica de los sistemas en el proceso de crioconservación. Por último, se estudió la aplicación de películas de quitosano en las cuentas de alginato utilizadas en el protocolo de encapsulación. No se observaron cambios significativos en su comportamiento frente a la deshidratación, en sus parámetros calorimétricos y en la superficie de las cuentas. Su aplicación puede conferir propiedades adicionales prometedoras. ABSTRACT Currently, cryopreservation techniques have a growing importance for long term plant germplasm storage. These methods have undergone great progress during the last two decades, and adequate protocols for different plant systems have been developed, making use of diverse strategies, such as vitrification, encapsulation-dehydration with alginate beads and the dropletvitrification method. This PhD thesis has the goal of increasing the knowledge on the processes underlying the different steps of cryopreservation protocols, in relation with the state of water on tissues and its changes, approached through diverse biophysical techniques, especially differential scanning calorimetry (DSC) and low-temperature scanning electron microscopy (cryo-SEM). The processes of cooling to liquid nitrogen temperature and warming to room temperature, at the end of the storage period, critical for the survival of the cryopreserved material, are described in a first study on these cryopreservation methods. Both cooling and warming must be carried out as quickly as possible because, although the low water content achieved during previous protocol steps significantly reduces ice formation probability, it does not completely disappear. Within this context, the influence of plant vitrification solutions cooling and warming rate on their vitrification related thermophysical parameters is also analyzed, in relation to its composition and component concentration. These solutions are used in most of the currently employed plant material cryopreservation protocols. Additionally, the influence of other factors determining the stability of vitrified material is studied, such as glass aging. An experimental research work has been carried out on the use of cryo-SEM as a tool for visualizing the glassy state in cells and tissues, submitted to cryopreservation processes. It has been compared with the better known differential scanning calorimetry technique, and results in good agreement and complementary have been obtained. The effect on plant tissues of adaptation to low temperature and of the dehydration induced by the different treatments used in the protocols was explored also by these techniques. This study allows observation of the system biophysical evolution in the cryopreservation process. Lastly, the potential use of an additional chitosan film over the alginate beads used in encapsulation protocols was examined. No significant changes could be observed in its dehydration and calorimetric behavior, as well as in its surface aspect; its application for conferring additional properties to gel beads is promising.