El pasado 21 de diciembre de 2020 Minerva Díaz Heras defendió su tesis doctoral en la Escuela Internacional de Doctorado con el título “Fluidized beds with concentrated solar radiation”, realizada en el Programa de Doctorado en Ciencias y Tecnologías Aplicadas a la Ingeniería Industrial de la Universidad de Castilla-La Mancha bajo la dirección del Dr. José A. Almendros y el Dr. Juan Fco. Belmonte.

The need for a new enduring sustainable energy model is undeniable. Renewable energies are the key factor in this transition but their intermittent nature over time is their greatest disadvantage. Within solar thermal energy CSPs, apart from said intermittency in production, present limitations in their efficiency due to the limit of the operating temperature of conventional heat transfer fluids.

This work aims to address both problems, studying thermal energy storage based on fluidized beds with direct irradiation on the particles. Sensible energy storage is considered a simple and inexpensive way to store thermal energy. There are a multitude of sensible energy storage materials, and for this reason the starting point of this work was to analyze the most suitable materials, with three standing out above the rest: sand, SiC and carbo (CARBOACCUCAST ID50). This doctoral thesis thus focuses on material characterization and experimental and numerical studies to optimize a fluidized bed with concentrated solar energy for CSP applications. In this way, four stages can be distinguished.

Firstly, the properties of the materials were characterized and compared, highlighting the suitability of SiC and carbo. This stage yielded enriching conclusions as a result of the collaboration with the University of Barcelona. Subsequently, these materials were experimentally tested and compared in terms of thermal efficiency under different fluidization technologies (bubbling and spouted beds), varying the airflow rate and irradiation level. From this second stage, SiC was chosen as the material providing the highest efficiency compared to the rest. The comparison of both technologies highlights the lower pumping costs of the spouted bed in achieving similar results, in terms of efficiency and temperature, compared to those obtained in a bubbling fluidized bed.

The third stage involved carrying out different tests on a larger bed using SiC in different airflow configurations in a bubbling fluidized bed: even and un-even fluidization. Uneven fluidization consists of introducing different airflows through the center and periphery of the bed. The experimental results indicate that uneven fluidization reduces the maximum temperatures on the top of the bed, especially for shallow beds. As the bed height is increased (up to 15 cm in this work) the influence of the uneven flow is mitigated.

Finally, in the fourth stage, numerical simulations of the SiC fluidized bed were conducted using Barracuda, aiming to reproduce the experimental conditions as closely as possible. To the best of the author’s knowledge, there are no previous numerical works using a directly irradiated fluidized bed. The numerical results permits a more detailed analysis of the influence of the irradiation on the fluidized bed’s behavior and the heating rate of the particles. Increasing the airflow rate, the maximum temperatures on the top are reduced and the energy stored in the particles increases.

La tesis obtuvo la calificación de Sobresaliente Cum Laude.