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).
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 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
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
The joint performance of a CaO-based sorbent and a Ni-based commercial catalyst has been assessed under relevant conditions for the SER stage in the Ca/Cu H 2 production process. These conditions comprise processing CH 4 space velocities suitable for the scaling up of the process, operation of the sys- tem at pressure, and testing materials that had experienced up to 200 oxidation/reduction cycles. The system, catalyst and CaO-based sorbent, was able to fulfil the SER equilibrium composition up to 2.5 kg CH 4 h 1 kg cat 1 ,CH 4 space velocity that would allow the scaling up of the process. In this way, a gas stream containing up to 95% vol. H 2 was obtained at 923 K, steam to carbon ratios of 3.2 and 4, sor- bent to catalyst weight ratios from 4 to 15 and for operation pressures between 1 and 9 bar. The effect of oxidation/reduction cycles on catalyst performance was assessed, and the mixture sorbent and aged cat- alyst was able to process up to 2.5 kg CH 4 h 1 kg cat 1 , corroborating the operational limit determined for the fresh materials. The total operation pressure (from 1 to 9 bar) did not have an important influence on H 2 yield, and/or materials performance. Sorbent carbonation reaction rates up to 4.42 * 10 2 kmol h 1 kg sorb 1 were determined in the experiments, being this parameter responsible of the limit in CH 4 space velocity that can be successfully converted through this sorbent/catalyst system. The experimental results have been successfully described by a pseudo-homogeneous reactor model that incorporates the main kinetic expressions of the reactions involved in the SER stage. ; This work acknowledges the support by European Union Seventh Frame Programme FP7 under grant agreement n° 608512 (ASCENT Project). Laura Díez acknowledges the FPI fellowship (ENE 2012-37936-CO2-01, BES-2013-064616 financed by MICINN). The authors want also to thank the support from the Regional Aragon Government (DGA) under the research groups support program ; Peer reviewed
This paper introduces a new mathematical model that is used to compute either the interfacial tension of quiescent axisymmetric pendant/sessile drops and pendant/captive bubbles. This model consists of the Young–Laplace equation, that describes interface shape, together with suitable boundary conditions that guarantee a prescribed volume of drops/bubbles and a fixed position in the capillary. In order to solve the problem numerically, the Young–Laplace equation is discretized by using numerical differentiation and the numerical solutions are obtained applying the well-know Newton method. The paper contains a validation of the new methodology presented for what theoretical bubble/drops are used. Finally, some numerical results are presented for both drops and bubbles of water as well as several surfactant solutions to demonstrate the applicability, versatility and reproducibility of the proposed methodology ; This work has been supported by Ministerio de Economía y Competitividad under the Projects MTM2015-66640-P, CTQ2014-55208-P, CTQ2017-84354-P and PGC2018-096696-B-I00, Xunta de Galicia (GR 2007/085; IN607C 2016/03 and Centro singular de investigación de Galicia accreditation 2016-2019, ED431G/09) and the European Union (European Regional Development Fund-ERDF), is gratefully acknowledged ; SI
