Suchergebnisse

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

The application of hydration/dehydration reactions of CaO/Ca(OH)2 to thermochemical energy storage systems can be facilitated by the development of Ca-based materials with improved mechanical properties when compared to the natural Ca-precursor, while maintaining good chemical activity. For this purpose, we are developing composite materials for fluidized bed or fixed bed applications synthesized using sodium silicate to bind fine CaO/Ca(OH)2 particles. In this work, the mechanism of decay in the mechanical properties of the resulting CaO/Ca-silicates composites over hundreds of hydration/dehydration cycles has been investigated. Based on the observed mechanism, improvements to the method of synthesis of the materials have been introduced, in order to retain the original carbonate grain volumes, which are larger than those of the equimolar quantity of the expanding Ca(OH)2 during hydration. A noticeable improvement in the mechanical stability of the resulting pellets was observed when the material was exposed to temperatures of around 880 °C in pure CO2 before calcination in order to avoid the decomposition of CaCO3 during the formation of the hard Ca-silicates that provide mechanical strength to the composite. Further gains in mechanical stability were achieved by avoiding the complete hydration of the CaO grains in the composites. These results confirm the primary role of Ca(OH)2 anisotropic expansion as the main cause of the reduction in crushing strength of the pellets. It can be concluded that the formation of calcium silicates as binders of CaO rich grains is a promising route for the development Ca-based composite materials. However, more effort is still needed to overcome the decay in performance observed after several hundreds of cycles. ; 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). Help from Dr. A. Borrego in the microscopic analysis of the samples is also acknowledged. ; Peer reviewed

This work describes a material that has improved mechanical and reactivity properties for use in thermochemical energy storage systems based on CaO/Ca(OH)2 reversible reactions. The composite material uses sodium silicate as a binder of active CaO particles. The observed mechanical stability of the material is due to the formation of hard Ca silicates resulting from the reaction of the binder with the exterior of the CaO particles. A screening of the main synthesis variables affecting the composite was carried out, including Ca precursors of different particle size, a range of molar Ca/Si ratios, as well as the curing and calcination conditions. The most suitable material (containing CaCO3 with a particle size of 36–63 μm as calcium precursor and a molar Ca/Si ratio of 4.8–6.2, calcined in air at 850 °C) was tested over many hydration/dehydration cycles (up to 500) in a thermogravimetric apparatus. The material sustained high molar hydration conversions (between 0.6 and 0.7) and crushing strength values of >2 N after 200 cycles, when dehydrated in pure steam. ; 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 reviewed

The calcium oxide hydration/dehydration reaction is proposed as a suitable reaction couple for thermochemical energy storage systems. However, limited work has been reported on the reaction kinetics of CaO/Ca(OH)2 under appropriate operation conditions for storage applications involving fluidized beds. This study focuses on the effect of temperature, partial steam pressure, and particle size upon the intrinsic hydration and dehydration reaction kinetics when natural materials are used. The experimental data have been fitted satisfactorily to a shrinking core model for both hydration and dehydration reactions, at reaction temperatures between 400 and 560 °C and partial steam pressures between 0 and 100 kPa. The reaction rates measured are higher than those previously reported in the literature. In the case of large particle sizes of natural material, particle attrition has been detected indicating the need to develop more suitable materials for thermochemical energy storage applications. ; The authors acknowledge the financial support provided by the European Commission under the 7th Framework Program (StoRRe Project GA 282677). Y.A. Criado thanks the Government of the Principality of Asturias for a Ph.D. fellowship (Severo Ochoa Program). ; Peer reviewed

Calcium looping technology could be one of the most efficient ways to drastically reduce the carbon footprint of cement manufacture since CaCO3 is a major component of the raw meal used to produce clinker. However, calcined raw meal can be a poor CO2 sorbent due to the fact that the formation of Ca2SiO4 (belite) causes a reduction in the amount of free CaO. Effective reaction rates for the formation of belite from both CaCO3 and CaO (i.e., after calcination) were obtained in this work for different raw meals with similar compositions but very different levels of Ca–Si aggregation. Tests carried out in thermogravimetric analyzers revealed that belite can be formed quickly, even with calcination periods of about 1 min. The 3D-diffusion model proposed by Jander and Hoffmann [Jander, W.; Hoffmann, E. Reaktionen im festen Zustande bei höheren Temperaturen. XI. Mitteilung. Die Reaktion zwischen Calciumoxyd und Siliciumdioxyd. Z. Anorg. Allg. Chem. 1934, 218, 211−223] represents reasonably well the conversion of the solids to belite in marl-type raw meals at temperatures between 800 and 900 °C. The activation energy calculated in this temperature range (i.e., 325 kJ/mol) is consistent with the data reported in the literature on belite formation in CaO/SiO2 materials at higher temperatures. The differences in the reaction rates between the materials are due to the pre-exponential factors, related to the level of aggregation of Ca and Si in the materials. The information on this topic will help to predict the decrease in the CO2 sorption capacity of the calcined raw meals used in calcium looping systems integrated in cement plants. ; This study has been funded by the European Union's Horizon 2020 Research and Innovation Programme under Grant Agreement 764816 (CLEANKER Project) and by the Spanish Ministry of Economy, Industry and Competitivity (Grant ENE2015-68885-C2-1-R). We also acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI). ; Peer reviewed

The use of cement raw meals as sorbent precursors for CO2 capture can reinforce the synergies between the cement production process and calcium looping CO2 capture technology. In this work, we measure the CO2-carrying capacity of different calcined samples of a particular marl, which were obtained under very different calcination conditions and setups (a thermogravimetric analyzer, a drop tube furnace, and an industrial calciner). We find that the reactivity toward CO2 of these calcined materials displays a strong sensitivity to the calcination conditions, in particular to calcination time. A pronounced competition between the belite (Ca2SiO4) formation reaction and the formation of free CaO needed for CO2 capture is detected. As the calcination of the raw meal approaches flash conditions (i.e., >90% calcination conversion in less than 10 s), the belite formation is shown to be minimized, leading to sorbents with CO2-carrying capacities of approximately 0.4 mol CO2/mol CaO. ; This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreements Nos 641185 and 764816 (CEMCAP and CLEANKER) and from the Spanish Ministry of Economy and Competitivity ENE2015-68885-C2-1-R. ; Peer reviewed

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. ; The authors acknowledge the financial support provided by the European Commission under the 7th Framework Program (StoRRe Project GA 282677). Y.A. Criado thanks the Government of the Principality of Asturias for a Ph.D. fellowship (Severo Ochoa Program). ; Peer reviewed

Calcium looping, CaL, is an emerging CO2 capture technology that is of special interest for use in cement plants, as it offers the possibility of exploiting several energy and material synergies. In this work, the CO2 carrying capacity of calcined raw meal materials for cement plants has been investigated with thermogravimetric equipment in a wide range of testing conditions. When calcination was carried out at high temperatures and over long times, some raw meals display a sharp decrease in their subsequent CO2 capture capacity compared to their limestone counterparts, while others perform as expected from their CaO content. XRD observations of calcined samples confirmed the formation of Ca2SiO4, i.e., belite, as the main deactivation agent, since belite formation removes active CaO for CO2 capture during the carbonation stage. The extent of belite formation was found to be greatly influenced by the nature of the raw meal (in particular by the level of aggregation of Ca and Si atoms in the material), by the calcination temperature, by reaction atmosphere, and by the duration of the calcination stage. The screening of conditions to minimize belite formation indicates that calcination time should be below 1 min, at the typically high calcination temperatures required in CaL systems (i.e., slightly over 900 °C), thus ensuring that the CO2 carrying capacity of these raw meals is kept at a level as close as possible to the value in equivalent materials with the same CaCO3 content. ; 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 Competitiveness ENE2015-68885-C2-1-R. ; Peer reviewed

13th International Conference on Greenhouse Gas Control Technologies, GHGT-13, 14-18 November 2016, Lausanne, Switzerland ; This poster presents the first experimental results obtained from a 30 kWth Calcium Looping test facility upgraded to work at conditions closer to those expected in a calcium looping system retrofitted to a cement plant. The main modification in the facility is the use of a second recycle of fine solids (<40 micron) collected in the secondary cylones located after the main calcium loop for CO2 capture. This allowed the operation of the main calcium loop using finer particle size distributions (dp50 around 60-75 micron), which should generate solid purges more suitable to be processed in clinker ovens. High CO2 capture efficiencies have been achieved in preliminary experiments with high make-up flow of limestone and high CO2 concentrations. Further experimental work and modeling activities for an adequate interpretation of results are ongoing within the CEMCAP H2020 project. ; This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no 641185 (CEMCAP). ; Peer reviewed

[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