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[EN] Calcium looping is a post-combustion CO2 capture technology that uses CaO as a regenerable solid sorbent. One potential advantage of this technology is that it allows flue gases to be treated with SO2, avoiding the need for a costly desulfurization step. In this work, we study the desulfurization capacity of a CFB carbonator reactor in a 30 kWth pilot plant that has been used to test CO2 and SO2 co-capture. A simple reactor model is applied to analyze the experimental results obtained and to study the effect of the main variables involved in the process: i.e. the circulation rates of solids and the inventory of active material in the CFB reactor. The results obtained have shown that SO2 capture efficiencies above 0.95 can be achieved in a CFB carbonator even when using a low inventory of active material in the bed. Extreme desulfurization (SO2 emissions below 5-10 ppmv) is thought to be achievable in large scale CFB carbonators designed to capture CO2 with CaO. ; The research presented in this work has received partial funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under the GA 241302-CaOling Project and from the PCTI Asturias Regional Government. J.M. Cordero also acknowledges to FYCIT fellowship for a PhD grant. ; Peer reviewed

Calcium looping technology has a high potential for capturing CO2 in cement plants as the CaO-rich purge from the calciner can be used to replace a sizable fraction of the CaCO3 used as feedstock. Integrating the CaL process into the cement plant requires the carbonator reactor to operate under new conditions (i.e., a higher carbonator CO2 load, a more active sorbent, smaller particle sizes). This work analyzes the impact of some of the new CaL operating conditions on the performance of the carbonator in a retrofitted 30 kWth testing facility as there is little experimental information available nowadays. A wide range of sorbent activities has been tested, including those corresponding to very large makeup flows of limestone that would be characteristic of CaL applications in cement plants. The results have been interpreted using a basic reactor carbonator model that required little modification of previous versions developed for power plants. ; This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 641185 (CEMCAP) and from the Spanish Ministry of Economy and Competitivity ENE2015-68885-C2-1- R. B. Arias also acknowledges the award of a Ramon y Cajal contract from the Spanish MINECO RYC-2012-10147. ; Peer reviewed

13 Figuras.- 2 Tablas ; In this work, the feasibility of an entrained flow reactor for full decarbonisation of gas streams has been proved. Three CaO-based materials (two types of lime and calcined raw meal) with different textural properties and therefore, different CO2 carrying capacities have been fed to the entrained flow reactor in a series of tests in which the Ca/CO2 molar ratio and solid residence time were the operation variables studied. Up to 11 mol CO2 m−2 s−1 has been captured from the gas phase with CaO from calcined lime with a maximum CO2 carrying capacity of 0.57 mol CO2 per mol CaO, reaching CO2 capture efficiencies over 90% for a Ca/CO2 molar ratio of 5 and solid residence times under 5 s. ; This work acknowledges the support from the Spanish Ministry of Economy, Industry and Competitiveness through the funding of the project ENE2015-68885-C2-2-R. The authors are also grateful for support from the Regional Aragon Government (DGA) under the research groups' support program. ; We also acknowledge institutional support from the Unit of Information Resources for Research at the "Consejo Superior de Investigaciones Científicas" (CSIC) for the article-processing charges contribution ; Peer reviewed

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-C2 ; European Union 727348

This paper analyses a CO2 capture system based on calcium looping, designed for power plants that operate with very low capacity factors and large load fluctuations, including shut-down and start-up periods. This can be achieved by decoupling the operation of the carbonator and calciner reactors and connecting them to piles filled with CaO or CaCO3. When the power plant enters into operation, calcined solids are fed into the carbonator to provide the necessary flow of CaO for capturing CO2 and storing the carbonated solids. An oxy-CFB calciner designed to have a modest thermal capacity and operate continuously refills the CaO pile. Mass and energy balances of the entire system, combined with state-of-the-art performance criteria for reactor design, have been solved to identify suitable operating windows. An analysis of the effect of the CaO reactivity of the material stored in the piles indicates that temperatures of around 500–600 °C in the carbonator are compatible with the storage of solids at low temperature (<250 °C). This, together with the low inherent cost of the material, allows large piles of stored material. Electricity costs between 0.13–0.15 $ per kWhe are possible for the system proposed in contrast to standard CaL systems where the cost would increase to above 0.19 $ per kWhe when forced to operate at low capacity. The proposed concept could be integrated into existing power plants operating as back-ups in renewable energy systems in preference to other CO2 capture technologies that are heavily penalized when forced to operate under low capacity factors. ; The authors acknowledge the financial support provided by the European Union under the Research Fund for Coal and Steel (RFCS) Program (FlexiCaL Project, No. 709629). Y. A. Criado thanks the Government of the Principality of Asturias for a PhD fellowship (Severo Ochoa Program). ; Peer reviewed

The CO2 capture from back-up power plants by making use of calcium looping systems combined with large piles of Ca-solids has been studied in this work. A flexible CO2 capture system based on a concept described in a previous work has been integrated into an existing power plant by including a small oxy-fired calciner (that represents just 8% of the total thermal capacity) to steadily regenerate the sorbent and a carbonator reactor following the back-up power plant operation periods to capture 90% of the CO2 as CaCO3 and two large piles of rich CaO and CaCO3 solids stored at modest temperatures. When the back-up plant enters into operation, the calcined solids are brought into contact with the flue gases in the carbonator reactor; meanwhile, the oxy-calciner operates continuously at a steady state. In order to improve the flexibility of the CO2 capture system and to minimize the increase of CO2 capture costs associated with the additional new equipment used only during the brief back-up periods, we propose using the steam cycle of the existing power plant to recover a large fraction of the heat available from the streams leaving the carbonator. This makes it possible to maintain the electrical power output but reducing the thermal input to the power plant by 12% and thus the size of the associated CO2 capture equipment. To generate the auxiliary power required for the oxy-calciner block, a small steam cycle is designed by integrating the waste heat from the streams leaving this reactor. By solving the mass and heat balances and proposing a feasible thermal integration scheme by using Aspen Hysys, it has been calculated that the CO2 emitted by long-amortized power plants operated as back-up can be captured with a net efficiency of 28%. ; The authors acknowledge the financial support provided by the European Union under the Research Fund for Coal and Steel (RFCS) Program (FlexiCaL project, no. 709629), the Spanish Ministry of Science, Innovation and Universities (RTI2018-097224-B-I00) and the FEDER Funds of the Principality of Asturias (IDI/2018/000138). ; Peer reviewed

[EN]Calcium looping, CaL, is rapidly developing as a postcombustion CO2 capture technology because its similarity to existing power plants using circulating fluidized bed combustors, CFBC. In this work we present experimental results from a pilot built to demonstrate the concept at the MWth scale. The pilot plant treats 1/150 of the flue gases of an existing CFBC power plant ("la Pereda") and it has been operated in steady state for hundreds of hours of accumulated experimental time. The pilot includes two 15 m height interconnected circulating fluidized bed reactors: a CO2 absorber (or carbonator of CaO) and a continuous CaCO3 calciner operated as an oxy-fuel CFBC. Operating conditions in the reactors are resembling those expected in large CaL CO2 capture systems in terms of reactor temperatures, gas velocities, solid compositions and circulation rates and reaction atmospheres. The evolution of CO2 capture efficiencies and solid properties (CO2 carrying capacity and CaO conversion to CaCO3 and CaSO4) have been studied as a function of key operating conditions. It is demonstrated that CO2 capture efficiencies over 90% are feasible with a supply of active CaO slightly over the molar flow of CO2 entering the carbonator. Closure of carbon and sulphur balances has been satisfactory during steady state periods. A basic reactor model developed from smaller test facilities seems to provide a reasonable interpretation of the observed trends. This should facilitate the further scale up of this new technology. ; The research presented in this work has received partial funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under the GA 241302-CaOling Project and from the PCTI Asturias Regional Government. M.E. Diego acknowledges a fellowship grant under the CSIC JAE Programme, co-funded by the European Social Fund. M. Fernández, M. Pereiro and A. Méndez have been excellent operators of the rig during the experimental runs of the pilot. ; Peer reviewed

The calcium looping technology using entrained flow reactors seems particularly suited for integration in cement plants due to the fine particle diameters and high gas velocities that are characteristic of these plants. However, there is little experimental information available in the literature on the carbonation performance of fine CaO-based particles with a few seconds of gas/solid contact times. In this work, the carbonation of calcium oxide has been experimentally investigated in a 6 m long and 0.1 m internal diameter drop tube reactor. Carbonation tests between 600 and 700 °C using sorbents with different CO2 sorption capacities have been carried out. The effect of the carbon dioxide and steam on the extent of the carbonation reaction has been evaluated. The experimental results can be described by means of a simple plug flow reactor model with a modest axial dispersion, and they enable the determination of the kinetics parameters for the carbonation of CaO particles in these emerging carbonator reactors. ; This project has received funding from the European Union's Horizon 2020 Research and Innovation Programme under Grants 641185 and 764816 (CEMCAP and CLEANKER) and from the Spanish Ministry of Economy and Competitiveness Grant ENE2015-68885-C2-1-R. ; Peer reviewed

The calcium looping process based on the CaO/CaCO3 carbonation/calcination cycle has been proven to be an efficient CO2 capture technology. Most of the experimental work describing the behavior of the CaO particles has been performed under carbonation reference conditions of 650 °C and 10–15% vol CO2. Although, process schemes recently proposed have pointed out the practical benefits of operating the carbonator reactor at lower temperatures, on the assumption that these would lead to higher CO2 capture efficiencies. However, there is a lack of correlations for estimating the evolution of the carrying capacity along cycling at temperatures below 650 °C. Therefore, in this work the carrying capacity of a high purity natural Ca-material used as reference has been studied in a selected range of representative carbonation temperatures (450–725 °C). The parameters on the CaO deactivation curve that is widely employed have been readjusted to accord with a more general decay model that takes into account the effect of the carbonation temperature on the thickness of the CaCO3 product layer that marks the end of the fast kinetically controlled regime. ; The authors acknowledge the financial support provided by the European Union under the Research Fund for Coal and Steel (RFCS) Program (Development of flexible coal power plants with CO2 capture by Calcium Looping, FlexiCaL Project, No. 709629) and by the Spanish Ministry of Economy and Competitiveness ENE2015-68885-C2-1-R. The support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI) is also acknowledged. ; Peer reviewed