Offshore hydrogen production using wave energy

The aim of this thesis is to present and evaluate a proposal for designing an off-grid offshore electrolysis plant powered by wave energy. This plant includes PEM electrolyzers, a Reverse Osmosis system to produce water with adequate conductivity, a compression unit to store the hydrogen for transport, and batteries for temporary storage of electricity for short-time balances. Firstly, a description of the H2OCEAN Project is given. Then, an introduction with previous works and a presentation of the two proposals that will be depicted is presented. After that, the components that comprise the proposed plants are justified and described and simple mathematical models of the different sections of the plant will be calculated. Finally the performance of the plant in a specific location is tested in detailed by using measured data, studying the influence of sizing on the expected performance in the two different proposals.Departamento de Ingeniería de Sistemas y AutomáticaMáster en Investigación en Ingeniería de Procesos y Sistemas Industriale

Control systems of offshore hydrogen production by renewable energies

Esta tesis trata sobre un proyecto de diseño de un Sistema de Gestión de Energía (SGE) que utiliza Modelo de Control Predictivo (MPC) para equilibrar el consumo de energía renovable con electrolizadores productores de hidrógeno. La energía generada se equilibra regulando el punto de operación y las conexiones de los electrolizadores usando un MPC basado en un algoritmo de Programación Mixta-Entera Cuadrática. Este algoritmo MPC permite tener en cuenta previsiones de energía, mejorando así el equilibrio y reduciendo el número de encendidos de los equipos. Se han realizado diferentes casos de estudio en instalaciones compuestas por unidades de generación de energía eléctrica a partir de energía renovable. Se considera la técnica de ósmosis inversa como paso intermedio para la producción de agua que alimenta a los electrolizadores. La validación se realiza utilizando datos meteorológicos medidos en un lugar propuesto para el sistema, mostrando el funcionamiento adecuado del SGE desarrollado.Departamento de Ingeniería de Sistemas y AutomáticaDoctorado en Ingeniería Industria

Offshore hydrogen production from wave energy

The aim of this paper is to present and evaluate a proposal for designing an off-grid offshore electrolysis plant powered by wave energy. This plant includes PEM electrolyzers, a Reverse Osmosis system to produce water with adequate conductivity, a compression unit to store the hydrogen for transport, and batteries for temporary storage of electricity for short-time balances. First, the systems that compose the proposed plant are justified and described. Then a proposal for sizing these subsystems is given, based on using buoy-measured data at the expected location and simple mathematical models of the different sections of the plant. Finally the performance of the plant in a specific location is tested in detailed by using measured data, studying the influence of sizing on the expected performance

Offshore desalination using wave energy

This paper evaluates the design of an offshore desalination plant currently under preliminary development.The purpose is to test the feasibility of producing drinkable water using wave energy in out-of-sight installations, as an alternative for those locations where land use, civil engineering works, and/or environmental impact make a coast-based solution inadequate. After describing the components, a proposal for sizing them is studied, based on using buoy-measured data at the expected location and their mathematical models of the different sections of the plant. Finally, by using measured buoy data, the influence of sizing on the expected performance is studied for a specific location, and one of the designs is developed in detail

Sensitivity analysis for photovoltaic water pumping systems: Energetic and economic studies

In agricultural remote areas where electrical energy is required to supply water pumping plants, photovoltaic modules are considered a good option to generate electricity. The reliability of autonomous Photovoltaic water pumping plants depends essentially on the system components size, which should meet the criteria related to the plant autonomy and the water volume required for irrigation. In this context, this research paper proposes an approach to size the elements of an autonomous photovoltaic system equipped with an energy storage device (a battery bank), and which is used to supply a waterpumping plant with electricity. The proposed approach determines the optimal surface of the photovoltaic modules, the optimal capacity of the battery bank and the volume of the water storage tank. The optimization approach takes into account the monthly average solar radiation, the fulfillment of the water needed for the crops’ irrigation and the number of the days of autonomy. Measured climatic data of 10 ha situated in Northern Tunisia and planted with tomato are used in the optimization process, which is conducted during the tomato vegetative cycle (from March to July). The optimal results achieved for this farm are 101.5 m2 of photovoltaic modules’ surface, 1680 A h/12 V of the battery bank and 1800 m3 of the volume of the water storage tank. Then, to verify the reliability of the proposed optimization approach, the results of the proposed sizing algorithm are compared with those of a commercial optimization tool named HOMER, which shows better results using the proposed approach. Finally, the economic reliability of the obtained size is studied and compared with systems that include a diesel generator, and a diesel generator- photovoltaic panels, respectively, using climatic and economic parameters in three countries: Tunisia, Spain and Jordan. The economic analysis for these water pumping systems showed that photovoltaic- batteries/Pump system is the optimum solution in the three countries. However, the initial cost of the system can be recuperated faster in Spain than in Tunisia and Jordan due to high prices of the diesel these two countries.Ministerio de Economía, Industria y Competitividad (project DPI2014-54530-R

Rule-based control of off-grid desalination powered by renewable energies

A rule-based control is presented for desalination plants operating under variable, renewable power availability. This control algorithm is based on two sets of rules: first, a list that prioritizes the reverse osmosis (RO) units of the plant, based on the current state and the expected water demand; secondly, the available energy is then dispatched to these units following this prioritized list. The selected strategy is tested on a specific case study: a reverse osmosis plant designed for the production of desalinated water powered by wind and wave energy. Simulation results illustrate the correct performance of the plant under this control strategy

Predictive control for hydrogen production by electrolysis in an offshore platform using renewable energies

An Energy Management System (EMS), based on Model Predictive Control (MPC) ideas, is proposed here to balance the consumption of power by a set of electrolysis units in an offshore platform. In order to produce renewable hydrogen, the power is locally generated by wind turbines and wave energy converters and fully used by the electrolyzers. The energy generated at the platform by wind and wave is balanced by regulating the operating point of each electrolysis unit and its connections or disconnections, using an MPC based on a Mixed-Integer-Quadratic-Programming algorithm. This Predictive Control algorithm makes it possible to take into account predictions of available power and power consumption, to improve the balance and reduce the number of connections and disconnections of the devices. Two case studies are carried out on different installations composed of wave and wind energies feeding a set of alkaline electrolyzers. Validation using measured data at the target location of the platforms shows the adequate operation of the proposed EMS

Online integrated fractionation-hydrolysis of lignocellulosic biomass using sub- and supercritical water

Producción CientíficaA novel process coupling the fractionation and hydrolysis reactors is presented. Holm oak was used as real lignocellulosic biomass to be treated. In the fractionation reactor, hemicellulose and cellulose were solubilized and partially hydrolyzed in different stages with the aim of feeding the hydrolysis reactor with high C5 or C6 concentrations respectively. The fractionation was performed in two stages: at 180 °C optimizing the hemicellulose extraction and at 260 °C extracting cellulose and hard hemicellulose remaining in the biomass structure. Three water flows were tested: 11, 17 and 26 cm3/min. Sugar yields from 71 to 75% were reached, mainly composed of xylose and glucose oligomers and lower amounts of other chemicals, like retro-aldol products, acetic acid or 5-HMF. The outlet stream from the fractionation reactor was directly mixed with sub or supercritical water at the inlet mixer of a supercritical hydrolysis reactor where the reaction time was precisely controlled. The temperature, pressure and reaction time were modified to get an insight of their effect on the yield of retro-aldol condensation products. Yields of 24% for glycolaldehyde, and pyruvaldehyde were found at 8.3 s, 350 °C and 162 bar (hydrolysis reactor conditions). On other hand, 25% of lactic acid was found at 0.23 s, 396 °C and 245 bar. A discussion based on a known reaction pathway is proposed. Moreover, a kinetic model for the hydrolysis reactor was put forward, being able to reproduce the experimental data with deviations below 10% for sugars and other products extracted. This combined process performs a selective valorization of real lignocellulosic biomass, avoiding the costly process of extreme grinding needed for the fluidization in a continuous hydrothermal process.Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA330U13

XXXVI Jornadas de Automática

El artículo trata sobre el diseño de una estrategia de control en una plataforma que produce hidrógeno a partir de la energía del viento y de las olas de mar en alta mar localizada en el Océano Atlántico. Se considera la generación de la energía mediante energías renovables como la fuente energética que alimenta a un conjunto de electrolizadores, teniendo en cuenta la energía disponible y optimizando la operación de la planta. Se presentan los resultados de las simulaciones, mostrando la correcta operación de la plataforma bajo el control propuesto