Contribución al estudio de la ganadería ecológica en Extremadura: situación actual y perspectivas

La dehesa, es un sistema agroforestal considerado como uno de los ecosistemas más singulares de la Unión Europea, se sitúa en el suroeste de la Península Ibérica y se extiende sobre una superficie aproximada de 6,7 millones de hectáreas. Estos sistemas, aparte de sus producciones ganaderas, aportan valores ambientales, culturales y estéticos y son necesarios para el desarrollo y fijación de la población rural. La principal actividad que se desarrolla en este ecosistema es la ganadería extensiva de ganado vacuno, ovino y porcino ibérico con baja carga ganadera y pocos insumos. La gestión sostenible de estas explotaciones es esencial para asegurar su continuidad, la conservación de los ecosistemas y la mejora de su rentabilidad. Los sistemas de producción ganadera extensiva a pesar de ser un elemento clave en la sostenibilidad de los ecosistemas en España y en la Unión Europea, de forma errónea se engloba con la ganadería de manera genérica y se les considera como una de las principales causas de problemas medioambientales. En este sentido, es necesario diferenciar los sistemas de producción ganadera y promocionar aquellos más sostenible en consonancia con el medio natural. Teniendo en cuenta la necesidad de sistemas ganaderos sostenibles, la implantación de la producción animal ecológica en la dehesa puede reportar beneficios interesantes. Este proceso es aparentemente sencillo desde el punto de vista del cumplimento de la normativa. Sin embargo, esta conversión no debe limitarse al estricto cumplimiento de la legislación en materia de producción ecológica, sino también debe fomentar el desarrollo de otras prácticas y estrategias empresariales que garanticen el éxito. En este contexto, se plantea esta tesis doctoral que profundiza en el análisis de la situación actual de la ganadería ecológica en el suroeste de España y las posibilidades de conversión de la ganadería en zonas de dehesa hacia modelos de producción ecológica. Para ello, se han utilizado marcos metodológicos de investigación participativa como el método Delphi y los Focus Group, y el estudio de casos de explotaciones ecológicas en base al análisis económico y ambiental, centrándose en la rentabilidad económica, la huella de carbono, secuestro de carbono y el balance económico-ambiental.The Dehesa is classified as one of the most singular agroforestry systems in the European Union. In the southwest of the Iberian Peninsula it spreads over an area of approximately 6.7 million hectares. In addition to livestock farming production, these systems also contribute environmental, cultural and aesthetical value to the region and they are necessary for the development and settlement of the rural population. The main business activity that is developed in this ecosystem is extensive livestock farming of cattle, sheep and Iberian pigs with low stocking density and few inputs. The sustainable management of these farms is essential in order to ensure the continuity and preservation of their ecosystems, as well as the improvement of their profitability. In spite of extensive livestock farming production systems being a key element in the sustainability of the Spanish and European Union ecosystems, they are inadequately classified under the same umbrella as generic livestock farming and are described as one of the main reasons for the existing environmental issues. In this regard, it is necessary to clearly differentiate the various livestock farming production systems and promote those that are most sustainable for the natural medium. Given the need of sustainable livestock farming systems, the implementation of organic livestock production in dehesas can provide interesting benefits. This may seem an apparently easy process from the point of view of compliance to the standards. However, such conversion cannot be limited to the strict compliance of the laws regulating organic production, but it also must promote the development of other business practices and strategies to ensure success. This doctoral thesis has been developed within the above context by engaging into a deep analysis of the organic livestock farming sector’s current situation in the southwest of Spain and the potential conversion of dehesa livestock farming towards organic production models. For this purpose, participative research methodological frameworks, such as the Delphi method and the focus groups, have been used. But also the case study of several organic farms has been developed by means of their economic and environmental analysis with a focus on financial profitability, carbon footprint, carbon sequestration and economic-environmental balance.• Junta de Extremadura. Ayuda IB1605

Gasificación de biomasa en un reactor de lecho fijo en equicorriente: un modelo de diagnóstico en tiempo real a partir de la composición del gas pobre

RESUMEN: Este artículo se centra en la técnica de diagnóstico utilizada en el Laboratorio de Máquinas y Motores Térmicos de la Universidad de Valladolid (España) en una planta piloto de gasificación de biomasa, con el fin de monitorear y almacenar las variables calculadas en tiempo real y de esta manera caracterizar el proceso. Esta técnica se desarrolla mediante el análisis de la composición del gas pobre y otras mediciones, tales como temperaturas locales y el flujo másico del gas pobre. Asumiendo algunas hipótesis simplificadas es posible calcular los principales parámetros que caracterizan la gasificación, tales como tasa de consumo de biomasa, dosado relativo de gasificación, eficiencia térmica, potencia térmica generada, etc. El objetivo de este trabajo es describir la técnica implementada y presentar su gran potencial de aplicabilidad, destacando su sencillez, fiabilidad y el bajo costo de la instrumentación utilizada.ABSTRACT: This article is focused on the diagnostic technique used in the Thermal Engines Laboratory of the University of Valladolid (Spain), to perform real time calculation, monitoring and recording of gasification physical variables, only from gas composition analysis and some other measurements such as local temperatures and gas flow rate. By assuming some simplifying hypothesis it is possible to calculate the main gasification parameters such as biomass consumption, air/fuel ratio, thermal efficiency, and generated thermal power. The aim of this work is to explain the technique implemented and to give an idea of the wide range of applications that it can have, underlining its simplicity, its reliability and the low costs of the equipment needed

A correlation for turbulent combustion speed accounting for instabilities and expansion speed in a hydrogen-natural gas spark ignition engine

[EN] An analysis of the turbulent premixed combustion speed in an internal combustion engine using natural gas, hydrogen and intermediate mixtures as fuels is carried out, with different air-fuel ratios and engine speeds. The combustion speed has been calculated by means of a two-zone diagnosis thermodynamic model combined with a geometric model using a spherical flame front hypothesis. 48 operating condi- tions have been analyzed. At each test point, the pressure record of 200 cycles has been processed to calculate the cycle averaged turbulent combustion speed for each flame front radius. An expression of turbulent combustion speed has been established as a function of two parameters: the ratio between turbulence intensity and laminar combustion speed and the second parameter, the ratio between the in- tegral spatial scale and the thickness of the laminar flame front increased by instabilities. The conclusion of this initial study is that the position of the flame front has a great influence on the expression to calculate the combustion speed. A unified correlation for all positions of the flame front has been ob- tained by adding one correction term based on the expansion speed as a turbulence source. This unified correlation is thus valid for all experimental conditions of fuel types, air¿fuel ratios, engine speeds, and flame front positions. The correlation can be used in quasi-dimensional predictive models to determine the heat released in an ICE.The authors of this work would like to thank the Spanish Ministry of Science and Innovation for the financial support of this research through the ENE 2012-34830 (with FEDER funds) and the Regional Government of Castile and Leon for funding the Excellence Research Group GR203Gimenez, B.; Melgar, A.; Horrillo, A.; Tinaut-Fluixá, FV. (2021). A correlation for turbulent combustion speed accounting for instabilities and expansion speed in a hydrogen-natural gas spark ignition engine. Combustion and Flame. 223:15-27. https://doi.org/10.1016/j.combustflame.2020.09.026S152722

Prediction of the flame kernel growth rate in spark ignition engine fueled with natural gas, hydrogen and mixtures

Producción CientíficaThe knowledge of combustion duration is a key tool in the development of engines, specially nowadays for engines adapted to new fuels with low C/H ratio such as natural gas and hydrogen. This work is aimed to develop a correlation that predicts the duration of the first phase of combustion until the process becomes turbulent in a SI engine. The flame kernel radius when this transition occurs, , is the study variable. To determine this variable from the experimental pressure records, a flame kernel growth predictive model is used. The predictive model is adjusted to the experimental data, determining the most appropriate value. The pressure records of 500 consecutive cycles of 48 test points have been processed. The averaged values of of each test point have been correlated with the characteristic parameters of the process: turbulence and properties of the fuel–air mixtures. Finally, and integral length scale ratio is correlated with Damköhler number. A wide range of operating conditions have been studied, reaching the novel conclusion that it is possible to analyze the kernel growth phenomenon from a spatial point of view rather than from a temporal point of view, as had been studied in many previous works. The developed correlation can be used in combustion predictive modeling to support SI engine design. Other practical conclusion from the work, that can be used in SI engine development, is that decreasing the integral length scale reduces the time of the first phase of combustion.Ministerio de Ciencia e Innovación (PID2019-106957RB-C22). “Analysis and characterization of dual fuel combustion for the reduction of CO2 emissions in the transport sector

Model predictive control of a microgrid with energy-stored quasi-Z-source cascaded H-bridge multilevel inverter and PV systems

This paper presents a new energy management system (EMS) based on model predictive control (MPC) for a microgrid with solar photovoltaic (PV) power plants and a quasi-Z-source cascaded H-bridge multilevel inverter that integrates an energy storage system (ES-qZS-CHBMLI). The system comprises three modules, each with a PV power plant, quasi-impedance network, battery energy storage system (BESS), and voltage source inverter (VSI). Traditional EMS methods focus on distributing the power among the BESSs to balance their state of charge (SOC), operating in charging or discharging mode. The proposed MPC-EMS carries out a multi-objective control for an ES-qZS-CHBMLI topology, which allows an optimized BESS power distribution while meeting the system operator requirements. It prioritizes the charge of the BESS with the lowest SOC and the discharge of the BESS with the highest SOC. Thus, both modes can coexist simultaneously, while ensuring decoupled power control. The MPC-EMS proposed herein is compared with a proportional sharing algorithm based on SOC (SOC-EMS) that pursues the same objectives. The simulation results show an improvement in the control of the power delivered to the grid. The Integral Time Absolute Error, ITAE, achieved with the MPC-EMS for the active and reactive power is 20 % and 4 %, respectively, lower than that obtained with the SOC-EMS. A 1,3 % higher charge for the BESS with the lowest SOC is also registered. Furthermore, an experimental setup based on an OPAL RT-4510 unit and a dSPACE MicroLabBox prototyping unit is implemented to validate the simulation result

Desarrollo de productos cárnicos innovadores para el consumidor: percepciones hacia las hamburguesas de cordero enriquecidas con aditivos naturales

El consumo de carne de cordero ha disminuido considerablemente en los últimos años (Rabadán et al., 2020), lo que ha provocado importantes pérdidas para el sector. Esto unido a los cambios en el tipo de alimentación de la población (comida rápida, comida preparada…) ha influido para la posible apertura de nuevos nichos de mercado para la carne de cordero. En el presente trabajo se ha llevado a cabo un estudio a través de la metodología de focus group para valorar las percepciones de los consumidores con respecto a la introducción en el mercado de una hamburguesa de cordero con aditivos naturales (cereza y nuez pecana). Los resultados muestran una elevada frecuencia en el consumo de hamburguesas entre los participantes, el lugar de consumo en los hogares y como principal factor de compra el precio. En cuanto a las hamburguesas propuestas (cordero enriquecidas), los participantes expusieron una reticencia a la carne de ovino, prefiriendo las de vacuno. La mayoría de los participantes mostraron indiferencia hacia los aditivos, aunque, si son naturales como la cereza y la nuez pecana y en la etiqueta se especifica con mayor claridad podrían ser beneficiosos para su venta

Hall effect measurements to calculate the conduction control in semiconductor films of SnO2

Hall effect measurement is one of the most powerful methods for obtaining information about transport mechanisms in polycrystalline semiconductor compounds that constitute the basis for understanding the sensing function of semiconductor gas sensors. The presence of grain boundaries represents the essential difference between single-crystal and polycrystalline semiconductors. The boundaries are important because they generally contain fairly high densities of interface states which trap free carriers from the bulk of the grains. In this paper the grain size of the semiconductor (calculated by the XRGA technique) and Hall effect measurements are used in order to obtain conduction-band profiles. Depending on the preparation method (reactive sputtering, electron beam, serigraphy), three types of conduction control can be distinguished. Similar results are obtained from analysis of the material microstructure

Convergencia entre la identidad docente y la de alumno como medio de atención a la diversidad. Una propuesta de análisis e intervención

Cada estudiante afronta el proceso de aprendizaje de manera diferente en función de su identidad de alumno, entendida como el conjunto de voces o posiciones que el alumno pone en marcha en el contexto escolar, y que determinan cómo uno aprende. La atención a la diversidad en el aula pasa por la convergencia entre la identidad de alumno y la identidad docente, de manera que entre ambos se establezca una relación de entendimiento y de ajuste mutuo; por ello, es necesario que el docente conozca cómo aprende su alumnado. En esta tesis se han realizado dos estudios y se han elaborado dos productos. El primer estudio analiza la identidad de alumno a partir de una muestra de 3003 estudiantes de educación secundaria obligatoria (ESO) de Cataluña. Entre los resultados cabe destacar que el género del alumno, el curso o la materia no son factores diferenciales, mientras que el centro educativo o el docente sí tienen un impacto más acentuado. El segundo estudio analiza la relación intersubjetiva entre docentes y alumnado alrededor de la identidad de alumno de 23 grupos-clase de ESO de diferentes institutos españoles y concluye que la perspectiva del profesorado no coincide con la de sus alumnos en ninguno de los casos. En relación a los productos, el primero es un cuestionario para el análisis de la identidad de alumno y el segundo es un programa para el aprendizaje universal. Este último, dirigido al profesorado, propone basar la atención a la diversidad en dos pilares: la personalización del aprendizaje y la construcción de relaciones positivas en el aula, estableciendo la negociación como el eje principal del proceso de enseñanza-aprendizaje. El programa propone cuatro acciones principales: potenciar la competencia de aprender a aprender, utilizar un diseño universal del aprendizaje, implementar metodologías de aprendizaje cooperativo y mejorar la interacción y la comunicación entre docentes y alumnado.Each student faces learning in a different way depending on his or her learner identity, understood as the set of voices or positions that the student activates in the school context, and which determine how each of them learns. The attention to diversity in the classroom needs the convergence between the learner identity and the teacher identity, to establish a relationship of understanding and mutual adjustment. Therefore, it is necessary that the teacher knows how his or her students learn. In this thesis, two studies have been carried out and two products have been developed. The first study analyzes learner identity based on a sample of 3003 students from Catalonia. The results suggest that the student's gender, course or subject are not differential factors, while the school or the teacher does have more impact. The second study analyzes the intersubjective relationship between teachers and students around the learner identity of 23 class groups from different Spanish secondary schools and concludes that the teachers' perspective does not coincide with their students' perspective in any case. Regarding products, the first one is a questionnaire to analyze learner identity and the second one is a universal learning program. This program, addressed to teachers, proposes to focus the attention to diversity on two points: the personalization of learning and the construction of positive relationships in the classroom, placing negotiation as the main axis of the teaching-learning process. The program proposes four main actions: to enhance the learning to learn competence, to establish a universal design for learning, to use cooperative learning methodologies and to improve interaction and communication between teachers and students

Thermodynamic methodology to support the selection of feedstocks for decentralised downdraft gasification power plants

Thermodynamic criteria as a feedstock selection tool for decentralised downdraft gasifiers coupled to spark-ignition engines are presented in this work. The methodology consists of an energy and exergy analysis of gasification process. The analysis is carried out by computational modelling of the gasification process as a function of biomass type (ultimate analysis, moisture content and heating value) and fuel/air ratio. Considering a system operating with different wood species, analysed parameters are gas heating value, energy and exergy efficiencies and engine fuel quality (EFQ). With a fixed fuel/air ratio (2.6) and moisture content (20%wt), it is highlighted that as the carbon-oxygen molar ratio of wood decreases from 2.0 to 1.78 as model input, reaction temperature increases by 9%, energy and exergy efficiencies diminish by 1.8% and 4.2%, respectively, while EFQ increases by 3.2%. Therefore, for decentralised power plants, biomass should be selected to produce higher EFQ

A qualitative study on the development of short supply channels in the Spanish agri-food sector: Producers’ perspectives and expectations

This study focuses on gaining insight on the current state of implementation and development of short food supply channels (SFSC), as an alternative or complement to long food supply channels. Therefore, the aim of this study is to identify the various challenges, barriers and advantages that Spanish agri-food producers face regarding the use of SFSC. To this aim, 22 in-depth interviews were conducted with Spanish agri-food producers who used SFSC in their businesses. Each interview lasted approximately 30 min and covered all aspects associated with the implementation of SFSC, mainly including the drivers and the barriers they had met. The results show that the implementation of SFSC is mainly driven by consumers’ willingness to pay a premium for their products, which means a higher margin for the businesses, whereas the main barrier refers to transport and logistics, due to the potential impact on costs, quality, and consumer satisfaction. Therefore, the implementation of SFSC in the businesses has had a positive impact on their sales, although effective solutions for more sustainable and efficient distribution systems in the SFSC and more marketing activities are needed to boost this type of supply channel