Modelos de explotación a corto plazo de centrales hidroeléctricas : Aplicación a la generación hidroeléctrica con velocidad variable

En esta tesis, se estudia con detalle el problema de planificación de la operación o la explotación a corto plazo de una central hidroeléctrica tomadora de precios que vende su energía en un mercado eléctrico liberalizado y organizado sobre la base de un sistema de ofertas de compra y venta de energía, poniendo un énfasis especial en el caso de las centrales con una capacidad de regulación semanal, diaria o menor, en las que es muy importante tener en cuenta, en el corto plazo, el efecto de la variación del salto, o del volumen. Analizando los modelos de explotación a corto plazo descritos en la bibliografía, se detectan en éstos ciertas limitaciones que pueden resumirse en los siguientes puntos: a) Es frecuente ignorar en los estudios a corto plazo la influencia de la variación del volumen del embalse a lo largo del periodo de explotación. b) Se recurre generalmente a dividir el problema en dos partes o problemas distintos: la asignación óptima de grupos y el despacho económico o de carga de los grupos asignados. En esta tesis, se desarrollan tres modelos de explotación a corto plazo originales, que se basan respectivamente en programación lineal entera mixta, programación no lineal y programación dinámica. Los tres modelos resuelven simultáneamente la asignación y el despacho económico de los grupos de la central y los dos últimos tienen en cuenta el efecto de la variación del salto durante el proceso de optimización, superando así las principales limitaciones de la mayoría de los modelos existentes. Los tres modelos se apoyan en la metodología que se propone en la tesis para obtener la característica de generación de la central, quedando implícitos en la solución de los tres modelos el estado óptimo (arranque/parada) y la potencia que producen todos los grupos de la central. Los tres modelos se apoyan además en una serie de procedimientos iterativos, de modelado y de discretización, algunos de los cuales son originales, y otros se basan parcialmente en procedimientos conocidos. Para comprobar la validez de los modelos, se estudia con éstos la explotación a corto plazo de una central de referencia formada por dos grupos generadores, bajo distintas condiciones de operación Además del desarrollo de nuevos modelos de explotación a corto plazo, se encuentran entre los objetivos de esta tesis la aplicación de los modelos desarrollados a una central de generación hidroeléctrica con velocidad variable y su utilización como herramienta de apoyo en estudios de rentabilidad de centrales hidroeléctricas. De acuerdo con los objetivos previstos, se describe en la tesis la metodología a seguir para aplicar los modelos desarrollados a una central de velocidad variable y se estudia la explotación a corto plazo de la central de referencia con dos grupos de velocidad variable bajo distintas condiciones de operación, demostrándose que, al permitir que los grupos de la central giren siempre a su velocidad óptima, aumentan considerablemente: a) El rango de caudales turbinables para cada nivel o volumen de embalse. b) La carrera de embalse aprovechable para producir energía. c) La potencia que produce la central en las mismas condiciones de caudal y salto. d) Los ingresos que recibe la central por vender su energía en el mercado. Cabe destacar que la aplicación de estos modelos a una central de velocidad variable constituye una de las principales aportaciones de esta tesis, ya que no se ha encontrado en la bibliografía ningún modelo de explotación a corto plazo aplicado a una central de este tipo. Por último, se presenta en esta tesis una metodología para estimar, a partir de unas previsiones de aportaciones y de precios horarios, los ingresos anuales que produce una central hidroeléctrica, utilizando los modelos desarrollados. Aplicando esta metodología se obtienen unos resultados más precisos que los que se obtienen en la mayoría de los estudios de rentabilidad consultados, ya que se tienen en cuenta los siguientes aspectos: a) La variación del rendimiento global de la planta en función de las condiciones de operación y del número de grupos que están en funcionamiento. b) La variación horaria de los precios de venta de la energía. c) La capacidad de gestión de la central para maximizar sus ingresos, distribuyendo el agua de la mejor forma posible entre todas las etapas del periodo de estudio, y para maximizar la energía generada en cada etapa, repartiendo de forma óptima el agua asignada entre todos los grupos disponibles. Cabe señalar que toda la tesis se desarrolla bajo un enfoque determinista en lo que se refiere al tratamiento de las aportaciones, los precios y la disponibilidad de los grupos. In this thesis, the short-term scheduling of a price-taker hydropower plant that sells its energy in pool-based electricity market is studied in detail, with special emphasis in the case of plants associated to a reservoir the regulating capability of which is weekly, daily or even smaller, where it is specially important to consider, in the short-term, the influence of the head, or volume, variation. When analyzing the short-term scheduling models found in the technical literature, it is noticeable that there are some limitations that can be summarized as follows: a) In short-term studies, it is usual to neglect the influence of the head, or volume, variation throughout the time horizon. b) The short-term scheduling problem is generally decomposed into two different problems: the unit commitment and the economic dispatch of the committed units. In this thesis, three novel short-term scheduling models, based respectively on mixed integer linear programming, nonlinear programming and dynamic programming are developed. The three models solve simultaneously the commitment and load dispatch of all the plant generating units, and the last two models consider also the influence of the head, or volume, variation during the optimization process, thus overcoming the main limitations found in the existing models. The three models are based on the methodology proposed in this thesis to obtain the plant generation characteristic, which implicitly includes the optimal status (on/off) and the power produced by all the plant generating units. Furthermore, these models use some iterative, modelling and discretization procedures, some of which are original, whereas others are partially based on known procedures. In order to check the validity of these models, they are applied to solve the short-term scheduling of a hydropower plant with two generating units, under different operating conditions. Besides the development of new short-term scheduling models, two more objectives are pursued in this work: the application of the developed models to an adjustable speed hydropower plant and the use of these models as a supporting tool to estimate the economic feasibility of a hydropower plant project. According to the proposed objectives, the application of the developed models to an adjustable speed hydropower plant is discussed in this thesis. The results of the short-term scheduling of a hydropower plant with two adjustable speed generating units are presented. It is demonstrated that, by allowing all the plant generating units to run at their optimal speed, an increase in the following magnitudes results: a) The range of operating flows for each reservoir level or volume. b) The range of operating volumes to produce energy. c) The power produced by the plant under the same operating conditions. d) The income that the plant receives from selling energy in the electricity market. It is worthy to mention that the application of the developed models to an adjustable speed hydropower plant is one of the main contributions of this thesis, provided that, so far, no short-term scheduling model applied to such type of hydropower plants has been found in the technical literature. Finally, it is presented a methodology based on the developed models to estimate the annual income of a hydropower plant, given a series of forecasted water inflows and energy prices. Compared with usual procedures, the approach proposed in this thesis leads to more accurate results, since the following aspects are considered in detail: a) The variation of the plant efficiency with the operating conditions and the number of generating units in operation. b) The hourly variation of the energy prices. c) The management capability of the plant to optimally distribute the water among the available generating units and throughout the time, thus maximizing the energy generated stage and the income that the plant receives from selling energy. It is important to note that the entire thesis is developed in a deterministic framework in that respect to the water inflows, the energy prices and the units’ availability

Preliminary investigation on the use of waste cork dust as filler in hot-mix asphalt

Este póster foi presentado no congreso "Cork in Science and Applications 2019. New Trends in Cork Innovation: From the Wine Industry to the New Applications" que foi organizado polo Institut Catalá del Suro e que tivo lugar en Palafrugell (Girona) o 22 e 23 de maio de 2019.[Abstract:] The cork contains significant amounts of a biopolymer called suberin (45%). Polymers have been frequently used in the manufacture of hot-mix asphalt (HMA) to improve their properties. At the Universidade da Coruña (UDC), a preliminary investigation was carried out in which the feasibility of using waste cork dust from the manufacture of plugs, as filler in the manufacture of HMA was analyzed. Firstly, the aggregate-binder adhesion was analyzed by means of two types of tests: the boiling water test and the rolling bottle method. The performance of the cork filler was compared with the performance of conventional natural filler. In both tests it was obtained that with the cork filler, the aggregate-binder adhesion was better than with the natural filler. Secondly, a HMA type AC 22 bin S was manufactured, with a bitumen content of 3.8%. Indirect tensile test after immersion in water were conducted, in order to compare the moisture damage resistance of mixtures made with filler cork and natural filler. It was concluded that the filler cork helped to slightly improve the water resistance of the mixture. Although further investigation is needed, it can be stated that the filler cork could replace the conventional natural filler in the production of HMA

Adhesion Analysis of Waste Cork Dust as Filler for Bituminous Mixtures

No libro: Wastes: Solutions, Treatments and Opportunities III: Selected Papers from the 5th International Conference Wastes 2019, September 4-6, Lisbon, Portugal (pp.1-6). CRC Press, 2020. ISBN 978-0-367-25777-4[Abstract] Suberin is a biopolymer that can be found in high amounts in natural cork. As is well known, polymers can be used as bitumen modifiers to improve the properties of bituminous mixtures. This paper describes laboratory adhesion analysis that was conducted to analyse the use of waste cork dust as a filler in hot-mix asphalt (HMA). The performance of the waste cork dust as a filler was compared with that of a typically used natural filler and with Portland cement. These three fillers were characterized by their grain size distributions, morphological studies, and X-ray fluorescence spectroscopy experiments. The adhesion between the aggregates and the binder was analysed using two adhesion tests: a “boiling water test” and using the “roll-ing bottle method”. Both tests led to the same result: the waste cork dust was a better filler than the natural filler.https://doi.org/10.1201/978042928979

Neural Networks for optimal operation of a run-of-river adjustable speed hydro power plant with axial-flow propeller turbine

This paper analyzes the regulating capabilities of both turbine speed and guide vanes position in an axial-flow propeller turbine. Two neural networks are implemented in order to simulate the turbine behavior and the turbine efficiency. A maximum-efficiency-tracking algorithm is developed to set the guide vanes position. An experimental power plant built in the Hydraulics Laboratory is described. In order to validate the proposed operation control, the dynamics of this run-of- river pilot plant has been simulated. Substantial increases in the turbine efficiency have been found

Optimización de los movimientos de tierras en proyectos de obras lineales mediante técnicas de programación lineal: modelo basado en rendimientos de construcción

Las operaciones de movimiento de tierras representan una de las partidas más importantes en el presupuesto de cualquier obra lineal, e influyen de forma relevante tanto en el proceso de planificación como en el plazo de la obra. El estudio detallado y la optimización de estas operaciones son aspectos importantes a considerar durante la redacción de un proyecto de obra lineal. La asignación de los volúmenes de materiales que deben transportase desde los centros de producción (desmontes y préstamos) a los centros de consumo (terraplenes y vertederos) es un problema relativamente complejo, para cuya resolución se han propuesto en la literatura científica básicamente dos grupos de metodologías: una más tradicional, basada en el denominado diagrama de masas; y otras más novedosas, que se apoyan en técnicas de optimización. Mediante el diagrama de masas se establece una compensación longitudinal de los materiales, y se limita a informar sobre distancias medias de transporte. En relación al segundo grupo de metodologías, en las últimas décadas se han desarrollado diferentes procedimientos basados en programación lineal, en su forma particular del problema del transporte. Estas técnicas permiten optimizar de forma más precisa las operaciones de movimiento de tierras si bien no se ha estudiado con detalle la manera de generar o definir los centros de producción y consumo considerando aspectos relacionados con la planificación. En este artículo se desarrolla un procedimiento para la optimización de los movimientos de tierras en obras lineales mediante técnicas de programación lineal, en el cual los centros de producción y consumo son obtenidos a partir de los rendimientos de construcción de los equipos disponibles por el contratista. El procedimiento permite obtener tanto el coste mínimo de las operaciones de movimiento de tierras como el plazo de ejecución de las obras. Finalmente, se presentan los resultados de la aplicación a un caso real de una carretera

Study of the effect of four warm mix asphalt additives on bitumen modified with 15% crumb rubber

Due to a growing concern over global warming, the bituminous mixture industry is making a constant effort to diminish its emissions by reducing manufacturing and installation temperatures without compromising the mechanical properties of the bituminous mixtures. The use of mixtures with tyre rubber has demonstrated that these mixtures can be economical and ecological and that they improve the behaviour of the pavements. However, bituminous mixtures with a high rubber content present one major drawback: they require higher mixing and installation temperatures due to the elevated viscosity caused by the high rubber content and thus they produce larger amounts of greenhouse gas emissions than conventional bituminous mixtures. This article presents a study of the effect of four viscosity-reducing additives (Sasobit®, Asphaltan A®, Asphaltan B® and Licomont BS 100®) on a bitumen modified with 15% rubber. The results of this study indicate that these additives successfully reduce viscosity, increase the softening temperature and reduce penetration. However, they do not have a clear effect on the test for elastic recovery and ductility at 25 °C

Optimal short-term operation and sizing of pumped-storage power plants in systems with high penetration of wind energy

In this paper the short-term optimal operation of an electric system comprising several thermal power plants and one pumped storage plant is studied in several scenarios of power demand and wind penetration in order to draw conclusions about the contribution of the pumped storage plant to system operation costs. A mixed integer linear programming model is used to obtain the optimal hourly thermal, hydro and pumping powers so that the production cost of the entire system is minimized. An aggregated piecewise linear hourly production cost curve is used to represent the thermal generation; the marginal production cost varying as a function of the power generated according to the slope of each piecewise linear segment. Main design parameters of the pumped storage plant are not considered fixed in the model but rather they are obtained in the solution with the purpose of drawing conclusions about the plant optimal sizin

Adaptive Vectorial Filter for Grid Synchronization of Power Converters Under Unbalanced and/or Distorted Grid Conditions

This paper presents a new synchronization scheme for detecting multiple positive-/negative-sequence frequency harmonics in three-phase systems for grid-connected power converters. The proposed technique is called MAVF-FLL because it is based on the use of multiple adaptive vectorial filters (AVFs) working together inside a harmonic decoupling network, resting on a frequency-locked loop (FLL) which makes the system frequency adaptive. The method uses the vectorial properties of the three-phase input signal in the αβ reference frame in order to obtain the different harmonic components. The MAVF-FLL is fully designed and analyzed, addressing the tuning procedure in order to obtain the desired and predefined performance. The proposed algorithm is evaluated by both simulation and experimental results, demonstrating its ability to perform as required for detecting different harmonic components under a highly unbalanced and distorted input grid voltage

Mechanical behavior of hot-mix asphalt made with recycled concrete aggregates from construction and demolition waste: a design of experiments approach

[Abstract:] The present work is a re-evaluation of previous research on the durability of hot-mix asphalt made with recycled concrete aggregates from construction and demolition waste (CDW) with a different approach. Response surface methodology (RSM) was used to conduct this study. The kind of natural aggregates (schist and calcite-dolomite), the recycled concrete aggregates percentage (0%, 20%, 40% and 60%) and the water saturation (0% and 100%) were the pertinent factors for this methodology. Indirect tensile stress (ITS) was determined in mixtures fabricated with 0%, 20%, 40% and 60% recycled concrete aggregates. According to the results, the ITS of the bituminous mixtures increases as the percentage of recycled concrete aggregate increases. This behavior is more significant when calcite-dolomite is used as a natural aggregate. Water saturation has the same influence in both natural aggregates. The indirect tensile strength ratio (ITSR) was calculated to evaluate the stripping potential. According to the Spanish specifications, the results suggest that the percentage of CDW that can be used for hot mixes is 17% when schist is used as natural aggregate and 14% for calcite-dolomite

Contribution of re-regulation reservoirs considering pumping capability to environmentally friendly hydropower operation

Environmental constraints imposed on hydropoweroperation are usually given in the form of minimum environmental flows and maximum and minimum rates of change of flows, or ramp rates. One solution proposed to mitigate the environmental impact caused by the flows discharged by a hydropower plant while reducing the economic impact of the above-mentioned constraints consists in building a re-regulationreservoir, or afterbay, downstream of the power plant. Adding pumpingcapability between the re-regulationreservoir and the main one could contribute both to reducing the size of the re-regulationreservoir, with the consequent environmental improvement, and to improving the economic feasibility of the project, always fulfilling the environmental constraints imposed to hydropoweroperation. The objective of this paper is studying the contribution of a re-regulationreservoir to fulfilling the environmental constraints while reducing the economic impact of said constraints. For that purpose, a revenue-driven optimization model based on mixed integer linear programming is used. Additionally, the advantages of adding pumpingcapability are analysed. In order to illustrate the applicability of the methodology, a case study based on a real hydropower plant is presente