Experimental investigation and model validation of a CaO/Ca(OH)2 fluidized bed reactor for thermochemical energy storage applications

The CaO/Ca(OH)2 hydration/dehydration chemical loop has long been recognized as a potential candidate for application in energy storage systems for concentrated solar plants. However, the technology still remains at a conceptual level because little information has been published on the performance of the key reactors in the system. In this work, we experimentally investigate the hydration and dehydration reactors in a 5.5 kWth batch fluidized bed reactor, in conditions relevant to larger systems (superficial gas velocities of up to 0.53 m/s, temperatures of up to 500°C for dehydration, input H2O(v) fractions between 0 and 0.8 etc.). Furthermore, to assist in the interpretation of the experimental results, a standard 1D bubbling reactor model has been formulated and fitted to the experimental results by including kinetic information at particle level independently measured in a thermogravimetric apparatus. The results indicate that the hydration reaction is mainly controlled by the slow kinetics of the CaO material tested while significant emulsion-bubble mass-transfer resistances were identified during dehydration due to the much faster dehydration kinetics.The financial support provided by the European Commission under the 7th Framework Program (StoRRe Project GA 282677) is acknowledged. Y.A. Criado thanks the Government of the Principality of Asturias for a Ph.D. fellowship (Severo Ochoa Program).Peer reviewe

Continuous CaO/Ca(OH)2 Fluidized Bed Reactor for Energy Storage: First Experimental Results and Reactor Model Validation

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Industrial and Engineering Chemistry Research, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/acs.iecr.6b04105Novel thermochemical energy storage systems that employ fluidized beds of CaO/Ca(OH)2 for hydration/dehydration reactions are under development because of the inherent advantages of the low cost of the materials and their relatively high temperature operation windows (450 °C–550 °C). We report in this work the results of the first steady state experiments conducted in a new pilot plant designed to test the concept under realistic reactor conditions. The pilot has a fluidized bed reactor with an internal diameter of 0.108 m and a height of 780 mm fed continuously with gas and solids as well as heat exchangers to supply/extract the required reaction heat. The experimental results during dynamic and steady state periods were fitted to a KL reactor bubbling bed model, using kinetic parameters from thermogravimetric studies and a single crossflow factor. The resulting continuous reactor model will serve as useful tool for the continued scaling up of this technology.Financial support provided by the European Commission under the 7th Framework Program (StoRRe Project GA 282677) is acknowledged.Peer reviewe

Conceptual process design of a CaO/Ca(OH)2 thermochemical energy storage system using fluidized bed reactors

This paper analyses a thermochemical energy storage process using a CaO/Ca(OH)2 chemical loop. A single circulating fluidized bed reactor is proposed to carry out the hydration-dehydration alternating reactions. During the energy discharge step, steam is fed to the reactor and used as a fluidizing gas and as a reactant with the CaO coming from a silo, enabling heat to be recovered at a sufficiently high temperature (around 743 K) from the hydration reaction taking place in the fluidized bed. During the dehydration of Ca(OH)2 (energy charging step), heat (i.e. from a concentrated solar field) is stored in thermochemical form as CaO by using steam as a fluidizing gas. A basic process integration scheme for a reference case with a power output of 100 MWt is analysed in this work, by solving the mass and energy balances during charging and discharging steps and by calculating the volume of the silos and characteristic dimensions of the fluidized bed reactor. The effective energy storage densities of the CaO silo is shown to be over 260 kWh/m3 with reasonable activities of the solids when storing CaO solids in the silo at around 813 K

Oxy-fired fluidized bed combustors with a flexible power output using circulating solids for thermal energy storage

This paper presents a power plant concept based on an oxy-fired circulating fluidized bed combustor (oxy-CFBC) combined with thermal energy storage on a large scale. The concept exploits to full advantage the large circulation flows of high temperature solids that are characteristic of these systems. Two solid storage silos (one for high temperature and the other for low temperature solids) connected to the oxy-fired CFBC allow variability in power output without the need to modify the fuel firing rate and/or the mass flow of O2 to the combustor. During the periods of high power demand the system can deliver additional thermal power by extracting heat from a series of fluidized bed heat exchangers fed with solids from the high temperature silo. Likewise, during period of low power demand, the thermal power output can be reduced by using the energy released in the combustor to heat up the low temperature solids on their way from the low temperature silo to the oxy-CFBC and storing them in the high temperature silo located below the cyclone. A preliminary economic analysis of two designs indicates that this highly flexible system could make this type of power plant more competitive in the electricity markets where fossil fuels with CCS will be required to respond to a large variability in power output.Y.A. Criado thanks the Government of the Principality of Asturias for a Ph.D. fellowship (Severo Ochoa Program). B. Arias thanks the Spanish MINECO for the award of a Ramon y Cajal contract.Peer reviewe

Arqueología en la ACEGA 2: el área arqueológica de O Peto (Vedra, A Coruña)

Cadernos de Arqueoloxía e Patrimonio (CAPA)[EN] The archaeological area of O Peto was discovered during the construction of the highway Santiago-Alto de Santo de Domingo. This site shows the existence of archaeological structures near of the galician Iron Age hillforts. In fact O Peto is an artificialized space (where a set of several structures was exhumed) that belongs to a prerroman iron mining complex that suffered several changes in the beginning of Romanization.[ES] El área arqueológica de O Peto se descubrió durante el control arqueológico de la construcción de la Autopista Santiago-Alto de Santo Domingo. Se trata de un ejemplo significativo de la existencia de estructuras anejas en el entorno inmediato del recinto habitacional de los castros de la Edad del Hierro. Constituye un espacio claramente artificializado en el que se superponen estructuras excavadas en la roca, de naturaleza y finalidad diferentes. A este respecto se configura un espacio construido –aparentemente multifuncional- que experimentó sucesivos procesos de ampliación, redefinición, sellado intencionado y abandono entre la Edad del Hierro y Época Romana. La información aportada por la excavación indica que este yacimiento albergó un complejo minerometalúrgico caracterizado tecnológicamente por la utilización de hornos bajos prerromanos sin sangrado de escoria que procesarían el mineral extraído en el propio yacimiento.Proyecto financiado por la Dirección Xeral de Investigación e Desenvolvemento da Consellería de Innovación, Industria e Comercio (Xunta de Galicia) con cargo a la convocatoria Programa de Tecnoloxías para a Innovación- Tecnoloxías da Construcción e da Conservación do Patrimonio do ano 2004. Código de Proxecto: PGIDIT04CCP606003PRPeer reviewe

Arqueología en la ACEGA 2: el área arqueológica de O Peto (Vedra, A Coruña)

Cadernos de Arqueoloxía e Patrimonio (CAPA)[EN] The archaeological area of O Peto was discovered during the construction of the highway Santiago-Alto de Santo de Domingo. This site shows the existence of archaeological structures near of the galician Iron Age hillforts. In fact O Peto is an artificialized space (where a set of several structures was exhumed) that belongs to a prerroman iron mining complex that suffered several changes in the beginning of Romanization.[ES] El área arqueológica de O Peto se descubrió durante el control arqueológico de la construcción de la Autopista Santiago-Alto de Santo Domingo. Se trata de un ejemplo significativo de la existencia de estructuras anejas en el entorno inmediato del recinto habitacional de los castros de la Edad del Hierro. Constituye un espacio claramente artificializado en el que se superponen estructuras excavadas en la roca, de naturaleza y finalidad diferentes. A este respecto se configura un espacio construido –aparentemente multifuncional- que experimentó sucesivos procesos de ampliación, redefinición, sellado intencionado y abandono entre la Edad del Hierro y Época Romana. La información aportada por la excavación indica que este yacimiento albergó un complejo minerometalúrgico caracterizado tecnológicamente por la utilización de hornos bajos prerromanos sin sangrado de escoria que procesarían el mineral extraído en el propio yacimiento.Proyecto financiado por la Dirección Xeral de Investigación e Desenvolvemento da Consellería de Innovación, Industria e Comercio (Xunta de Galicia) con cargo a la convocatoria Programa de Tecnoloxías para a Innovación- Tecnoloxías da Construcción e da Conservación do Patrimonio do ano 2004. Código de Proxecto: PGIDIT04CCP606003PRPeer reviewe

Termochemical energy storage by CaO cycles

Tesis doctoral presentada en el Departamento de Energía de la Universidad de Oviedo, diciembre de 2016[EN] During the last century, the sharp increase in greenhouse gases emissions due to the use of fossil fuels as main energy source in most of the global economies was the main factor responsible for climate change. Therefore, the progressive adoption of new energetic mixes with reduced greenhouse gas emissions and a more effective use of available energy resources are considered essential for tackling climate change. The use of high-temperature (>400ºC) thermal or thermochemical energy storage technologies has been presented as a suitable solution since it would contribute to increasing the energy efficiency, favour the flexibility of conventional energy production systems and facilitate the development of intermittent renewable energies by establishing a temporal bridge between energy demand and supply. Despite the significant advantages of the high temperature energy storage systems, they have not been developed to a state-of-the-art level on a large scale. Therefore, the main objective of this Thesis has been to contribute to the study and development of newly energy storage systems based on the use of reversible reactions at high temperature using CaO. The work developed within the framework of this Thesis is focused on the use of the carbonation/calcination of CaO/CaCO3, and hydration/dehydration of CaO/Ca(OH)2 as energy storage systems in conventional combustion systems and in concentrated solar power plants respectively. Conceptual design studies of the new energy storage systems as well as reactor modelling (validated against experimental results from pilot plants) and the evaluation of CaO materials for their practical use have been conducted. Two main research paths, that share certain similarities, are followed in this Thesis. Firstly, the use of energy storage systems for conventional combustion processes using fluidized bed combustors (with or without integrated CO2 capture systems) is studied at a conceptual level. These energy storage systems are presented as an economic and competitive alternative in highly flexible energy markets. Basic designs have been proposed and the related mass and heat balances solved. Secondly, the hydration and dehydration reactions of CaO and Ca(OH)2 have been studied in-depth for use in concentrated solar power systems to allow a more stable energy production of this inherent intermittent renewable energy. Studies at a conceptual level as well as reactor models have been developed using fluidized bed reactors for the hydration/dehydration reactions as the key element of the energy storage system. The reactor models have been compared and validated against experimental results obtained from pilot plant tests performed under operation conditions relevant to the large scale application of this energy storage system. The final section of this Thesis investigates CaO/Ca(OH)2-based materials (both natural and synthesized) for their use over hundreds of charge and discharge cycles. The chemical and mechanical properties of different CaO/Ca(OH)2-based materials have been studied in-depth to test for reactivity/reversibility and crushing strength/attrition resistance, respectively.Peer reviewe