The Ammonia Looping System for Mid-Temperature Thermochemical Energy Storage

Thermochemical reactions have a great potential for energy storage and transport. Their application to solar energy is of utmost interest because the possibility of reaching high energy densities and seasonal storage capacity. In this work, thermochemical energy storage of Concentrated Solar Power (CSP) based on an ammonia looping (AL) system is analysed. The AL process for energy storage is based on the reversible reaction of ammonia to produce hydrogen and nitrogen. Concentrating solar energy is used to carry out the decomposition endothermic reaction at temperatures around 650 ºC, which fits in the range of currently commercial CSP plants with tower technology. The stored energy is released through the reverse exothermic reaction. Our work is focused on energy integration in the system modelled by pinch analysis to optimize the process performance and competitiveness. As result a novel configuration is derived which is able to recover high-temperature heat for electricity production with a thermal-to-electric efficiency up to 27 %. The current study shows a clear interest of the system from an energy integration perspective. Further research should be conducted to access the potential for commercial applications

The Calcium-Looping (CaCO3/CaO) Process for Thermochemical Energy Storage in Concentrating Solar Power Plants

Articulo aceptado por la revista. * No publicado aún [28-06-2019]Energy storage based on thermochemical systems is gaining momentum as potential alternative to molten salts in Concentrating Solar Power (CSP) plants. This work is a detailed review about the promising integration of a CaCO3/CaO based system, the so-called Calcium-Looping (CaL) process, in CSP plants with tower technology. The CaL process relies on low cost, widely available and non-toxic natural materials (such as limestone or dolomite), which are necessary conditions for the commercial expansion of any energy storage technology at large scale. A comprehensive analysis of the advantages and challenges to be faced for the process to reach a commercial scale is carried out. The review includes a deep overview of reaction mechanisms and process integration schemes proposed in the recent literature. Enhancing the multicycle CaO conversion is a major challenge of the CaL process. Many lab-scale analyses carried out show that residual effective CaO conversion is highly dependent on the process conditions and CaO precursors used, reaching values as different as 0.07-0.82. The selection of the optimal operating conditions must be based on materials, process integration, technology and economics aspects. Global plant efficiencies over 45% (without considering solar-side losses) show the interest of the technology. Furthermore, the technological maturity and potential of the process is assessed. The direction towards which future works should be headed is discussed.Ministerio de Economia y Competitividad CTQ2014-52763-C2, CTQ2017- 83602-C2 (-1-R and -2-R)Unión Europea Horizon 2020 Grant agreement No 727348, project SOCRATCES

The mOxy-CaL Process: Integration of Membrane Separation, Partial Oxy-combustion and Calcium Looping for CO2 Capture

CO2 capture and storage (CCS) is considered as a key strategy in the short to medium term to mitigate global warming. The Calcium-Looping process, based on the reversible carbonation/calcination of CaO particles, is a promising technology for post-combustion CO2 capture because of the low cost and non-toxicity of natural CaO precursors and the minor energy penalty on the power plant in comparison with amines capture based technologies (4-9 % compared to 8-12 %). Another interesting process to reduce CO2 emissions in power plants is oxy-combustion, which is based on replacing the air used for combustion by a highly concentrated (~95 % v/v) O2 stream. This work proposes a novel process (mOxy-CaL) for post-combustion CO2 capture based on the integration of membrane separation, partial oxy-combustion and the Calcium-Looping process. An oxygenenriched air stream, which is obtained from air separation by using highly permeable polymeric membranes, is used to carry out partial oxy-combustion. The flue gas exiting partial oxy-combustion shows a CO2 concentration of ~30 % v/v (higher than 15 % v/v typical in coal power plants). After that, the flue gas is passed to the CaL process where the CO2 reacts with CaO solids according to the carbonation reaction. Thermogravimetric analysis show that the multicycle CaO conversion is enhanced as the CO2 concentration in the flue gas stream is increased. Process simulations show that the mOxy-CaL process has a high CO2 capture efficiency (~95%) with lower energy consumption per kg of CO2 avoided than previously proposed post-combustion CO2 capture technologies. Moreover, the overall system size is significantly lower that state-of-the-art CaL systems, which allows for an important reduction in the capital cost of the technology

Identification of best available thermal energy storage compounds for low-to-moderate temperature storage applications in buildings

Award-winning paper at III International Congress and V National on Sustainable Construction and Eco-Efficient Solutions (CICSE) March 2017Over the last 40 years different thermal energy storage materials have been investigated with the aim of enhancing energy efficiency in buildings, improving systems performance, and increasing the share of renewable energies. However, the main requirements for their efficient implementation are not fully met by most of them. This paper develops a comparative review of thermophysical properties of materials reported in the literature. The results show that the highest volumetric storage capacities for the best available sensible, latent and thermochemical storage materials are 250 MJ/m3, 514 MJ/m3 and 2000 MJ/m3, respectively, corresponding to water, barium hydroxide octahydrate, and magnesium chloride hexahydrate. A group of salt hydrates and inorganic eutectics have been identified as the most promising for the development of competitive thermal storage materials for cooling, heating and comfort applications in the short-term. In the long-term, thermochemical storage materials seem promising. However, additional research efforts are required.Identificación de los mejores compuestos disponibles de almacenamiento de energía térmica para aplicaciones de baja a moderada temperatura en edificación. En los últimos 40 años se han investigado diferentes materiales de almacenamiento térmico con el objetivo de mejorar la eficiencia energética en los edificios, mejorar el rendimiento de sistemas y aumentar el uso de renovables. Sin embargo, la mayoría no cumple los principales requisitos para su eficiente implementación. Este artículo desarrolla una revisión de las propiedades termofísicas de los materiales existentes en la literatura. Los resultados muestran que las mayores capacidades de almacenamiento volumétrico para los mejores materiales de almacenamiento sensible, latente y termoquímico son 250 MJ/m3, 514 MJ/m3 y 2000 MJ/m3, respectivamente, correspondientes a agua, hidróxido de bario octahidratado y cloruro de magnesio hexahidratado. Un conjunto de sales hidratadas y eutécticos han sido identificados como los más prometedores para el desarrollo de materiales competitivos para aplicaciones de enfriamiento, calefacción y confort a corto plazo. A largo plazo, el almacenamiento termoquímico parece prometedor. Sin embargo, investigación adicional es requerida.Fondo Europeo de Desarrollo Regional SOE1/P3/P0429EUMinisterio de Educación, Cultura y Deportes FPU14/06583Ministerio de Economía y Competitividad BES-2015-0703149Ministerio de Economía y Competitividad CTQ2014-52763-C2-2-RMinisterio de Economía y Competitividad CTQ2017- 83602-C2-2

Carbonation of Limestone Derived CaO for Thermochemical Energy Storage: From Kinetics to Process Integration in Concentrating Solar Plants

Thermochemical energy storage (TCES) is considered as a promising technology to accomplish high energy storage efficiency in concentrating solar power (CSP) plants. Among the various possibilities, the calcium-looping (CaL) process, based on the reversible calcination-carbonation of CaCO stands as a main candidate due to the high energy density achievable and the extremely low price, nontoxicity, and wide availability of natural CaO precursors such as limestone. The CaL process is already widely studied for CO capture in fossil fuel power plants or to enhance H production from methane reforming. Either one of these applications requires particular reaction conditions to which the sorbent performance (reaction kinetics and multicycle conversion) is extremely sensitive. Therefore, specific models based on the conditions of any particular application are needed. To get a grip on the optimum conditions for the carbonation of limestone derived CaO in the CaL-CSP integration, in the present work is pursued a multidisciplinary approach that combines theoretical modeling on reaction kinetics, lab-scale experimental tests at relevant CaL conditions for TCES, process modeling, and simulations. A new analytic equation to estimate the carbonation reaction rate as a function of CO partial pressure and temperature is proposed and validated with experimental data. Using the kinetics analysis, a carbonator model is proposed to assess the average carbonation degree of the solids. After that, the carbonator model is incorporated into an overall process integration scheme to address the optimum operation conditions from thermodynamic and kinetics considerations. Results from process simulations show that the highest efficiencies for the CaL-CSP integration are achieved at carbonator absolute pressures of ∼3.5-4 bar, which leads to an overall plant efficiency (net electric power to net solar thermal power) around 41% when carbonation is carried out at 950 °C under pure CO.Ministerio de Economía y Competitividad CTQ2014-52763-C2, CTQ2017- 83602-C2European Union 72734

Optimizing the CSP-Calcium Looping integration for Thermochemical Energy Storage

Thermochemical energy storage (TCES) is considered a promising technology to overcome the issues of intermittent energy generation in Concentrated Solar Power (CSP) plants and couple them with yearly electricity demand. The development of this technology could favor the commercial deployment of CSP, which is considered as a key factor for new challenges in reducing GHG emissions. Among other possibilities, using the Calcium Looping (CaL) process for TCES is an interesting choice mainly due to the low cost of natural CaO precursors such as limestone (below $10/ton) and the high energy density that can be achieved (around 3.2 GJ/m3). This manuscript explores several configurations in order to maximize the performance of the CSP-CaL integration with the focus on power cycle integration in the carbonator zone. For this purpose, firstly, a discussion about the possibility of using open and closed power cycles is carried out, which leads to the conclusion that a CO2closed cycle is more appropriate. Then, a closed regenerative CO2Brayton cycle is analyzed in further detail and optimized by means of the pinch-analysis methodology. A main output is that high plant efficiencies (of about 45%) can be achieved using a simple closed CO2Brayton power cycle. The optimized integration layout shows good performances at carbonator to turbine outlet pressure ratios around 3, thus allowing for a feasible integration of the power cycle in the CSP-CaL system.Ministerio de Economía y Competitividad CTQ2014-52763-C2-2-

Almacenamiento termoquímico en plantas CSP basado en calcium-looping: retos y oportunidades

Libro de Actas del XVI Congreso Ibérico y XII Congreso Iberoamericano de Energía Solar, 20 – 22 de junio de 2018 Madrid, EspañaLa integración de sistemas termoquímicos de energía en plantas CSP está ganando interés en los últimos años. De entre los posibles sistemas termoquímicos, el proceso de Calcium-looping (CaL), basado en la calcinación/carbonatación multicíclica de CaCO3, está considerado como uno de los más prometedores. Tras la aparente sencillez del proceso se encuentran una serie de retos que deben ser resueltos para que la tecnología pueda alcanzar una escala comercial. En el presente trabajo se muestra un análisis crítico del estado actual de la tecnología con el objetivo de evaluar los retos y oportunidades que presenta la integración del CaL como sistema de almacenamiento termoquímico en plantas CSP. El proyecto SOCRATCES, financiado dentro del programa H2020, tiene como principal objetivo desarrollar un prototipo a escala piloto de la integración CSP-CaL en Sevilla (España).Thermochemical energy storage is gaining attention in last years to be integrated in CSP plants. Among the various possibilities, the Calcium-looping (CaL) process, based on the multicyclic calcination/carbonation of CaCO3, is considered as one of the most promising systems. However, for a commercial deployment of CSP, several challenges must be solved. This work presents a critical analysis on the status of the technology with the aim of evaluating the main challenges and opportunities of the CSP-CaL integration. The SOCRATCES project, founded from the European Union’s Horizon 2020 research and innovation programme, aims to develop a CSP-CaL prototype at pilot scale in Seville (Spain)

Programa online de apoyo en matemáticas básicas en la Escuela Politécnica Superior de Zamora

Memoria ID-202. Ayudas de la Universidad de Salamanca para la innovación docente, curso 2018-2019

Power cycles integration in concentrated solar power plants with energy storage based on calcium looping

Efficient, low-cost and environmentally friendly storage of thermal energy stands as a main challenge for large scale deployment of solar energy. This work explores the integration into concentrated solar power plants of the calcium looping process based upon the reversible carbonation/calcination of calcium oxide for thermochemical energy storage. An efficient concentrated solar power-calcium looping integration would allow storing energy in the long term by calcination of calcium carbonate thus overcoming the hurdle of variable power generation from solar. After calcination, the stored products of the reaction (calcium oxide and carbon dioxide) are brought together in a carbonator reactor whereby the high temperature exothermic reaction releases the stored energy for efficient power production when needed. This work analyses several power cycle configurations with the main goal of optimizing the performance of the overall system integration. Possible integration schemes are proposed in which power production is carried out directly (using a closed carbon dioxide Brayton power cycle) or indirectly (by means of a steam reheat Rankine cycle or a supercritical carbon dioxide Brayton cycle). The results obtained show that the highest plant efficiencies (up to 45–46%) are achievable using a closed carbon dioxide Brayton power cycle.Ministerio de Economia y Competitividad CTQ2014-52763-C2-1-R, CTQ2014- 52763-C2-2-R, MAT2013-41233-

A new model of the carbonator reactor in the Calcium Looping technology for post-combustion CO2 capture

The Ca-Looping (CaL) process is considered as a promising technology for CO2 post-combustion capture in power generation plants yielding a minor penalty on plant performance as compared with other capture technologies such as conventional amine-based capture systems. This manuscript presents a new carbonator reactor model based on lab-scale multicyclic CaO conversion results, which take into account realistic CaO regeneration conditions that necessarily involve calcination under high CO2 partial pressure and high temperature. Under these conditions, CaO conversion in the diffusion controlled stage is a relevant contribution to the carbonation degree in the typical residence times. The main novelty of the model proposed in the present work is the consideration of the capture efficiency in the diffusion controlled phase of carbonation. It is demonstrated that increasing the residence time by a few minutes in the carbonator yields a significant improvement of the capture efficiency. Model predictions are shown to agree with experimental results retrieved from pilot-scale tests. The new model allows a more accurate evaluation and prediction of carbonator’s performance over a wider range of residence times. The results obtained may be relevant for the optimization of CaL operation parameters to be integrated in real power plants