Ca-looping for postcombustion CO2 capture: A comparative analysis on the performances of dolomite and limestone

The low cost and wide availability of natural limestone (CaCO3) is at the basis of the industrial competitiveness of the Ca-looping (CaL) technology for postcombustion CO2 capture as already demonstrated by ~1Mwt scale pilot projects. A major focus of studies oriented towards further improving the efficiency of the CaL technology is how to prevent the gradual loss of capture capacity of limestone derived CaO as the number of carbonation/calcination cycles is increased. Natural dolomite (MgCa(CO3)2) has been proposed as an alternative sorbent precursor to limestone. Yet, carbonation of MgO is not thermodynamically favorable at CaL conditions, which may hinder the capture performance of dolomite. In the work described in this paper we carried out a thermogravimetric analysis on the multicyclic capture performance of natural dolomite under realistic regeneration conditions necessarily implying high calcination temperature, high CO2 concentration and fast transitions between the carbonation and calcination stages. Our study demonstrates that the sorbent derived from dolomite has a greater capture capacity as compared to limestone. SEM analysis shows that MgO grains in the decomposed dolomite are resistant to sintering under severe calcination conditions and segregate from CaO acting as a thermally stable support which mitigates the multicyclic loss of CaO conversion. Moreover, full decomposition of dolomite is achieved at significantly lower calcination temperatures as compared to limestone, which would help improving further the industrial competitiveness of the technology.Junta de Andalucía FQM-5735, TEP-7858, TEP-1900Ministerio de Economía y Competitividad FIS2011-25161, CTQ2011- 2762

CO2 multicyclic capture of pretreated/doped CaO in the Ca-looping process. Theory and experiments

We study in this paper the conversion of CaO-based CO2 sorbents when subjected to repeated carbonation/calcination cycles with a focus on thermally pretreated/doped sorbents. Analytical equations are derived to describe the evolution of conversion with the cycle number from a unifying model based on the balance between surface area loss due to sintering in the loopingcalcination stage and surface area regeneration as a consequence of solid-state diffusion during the looping-carbonation stage. Multicyclic CaO conversion is governed by the evolution of surface area loss/regeneration that strongly depends on the initial state of the pore skeleton. In the case of thermally pretreated sorbents, the initial pore skeleton is highly sintered and regeneration is relevant whereas, for nonpretreated sorbents, the initial pore skeleton is soft and regeneration is negligible. Experimental results are obtained for sorbents subjected to a preheating controlled rate thermal analysis (CRTA) program. By applying this preheating program in a CO2 enriched atmosphere, CaO can be subjected to a rapid carbonation followed by a slow rate controlled decarbonation, which yields a highly sintered skeleton displaying a small conversion in the first cycle and self-reactivation in the next ones. Conversely, carbonation of the sorbent at a slow controlled rate enhances CO2 solid-state diffusion, which gives rise, after a quick decarbonation, to a highly porous skeleton. In this case, CaO conversion in the first cycle is very large but it decays abruptly in subsequent cycles. Data on CaO conversion retrieved from the literature and from further experimental measurements performed in our work are analyzed as influenced by a variety of experimental variables such as preheating temperature program, preheating exposition time, atmosphere composition, presence of additives, and carbonation/calcination conditions. Conversion data are well fitted by the proposed model equations, which are of help for a quantitative interpretation on the effect of experimental conditions on the multicyclic sorbent performance as a function of sintering/ regeneration parameters inferred from the fittings and allow foreseeing the critical conditions to promote reactivation. The peculiar behavior of some pretreated sorbents, showing a maximum of conversion at a small number of cycles, is explained in the light of the mode

Constant rate thermal analysis for thermal stability studies of polymers

This paper explores the relationship between the shapes of temperature-time curves obtained from experimental data recorded by means of constant rate thermal analysis (CRTA) and the kinetic model followed by the thermal degradation reaction. A detailed shape analysis of CRTA curves has been performed as a function of the most common kinetic models. The analysis has been validated with simulated data, and with experimental data recorded from the thermal degradation of polytetrafluoroethylene (PTFE), poly(1,4-butylene terephthalate) (PBT), polyethylene (PE) and poly(vinyl chloride) (PVC). The resulting temperature-time profiles indicate that the studied polymers decompose through phase boundary, random scission, diffusion and nucleation mechanisms respectively. The results here presented demonstrate that the strong dependence of the temperature-time profile on the reaction mechanism would allow the real kinetic model obeyed by a reaction to be discerned from a single CRTA curve.Junta de Andalucía TEP-03002Ministerio de Ciencia e Innovación MAT 2008-06619/MA

Corrugated velocity patterns in the spiral galaxies: NGC 278, NGC 1058, NGC 2500 & UGC 3574

We address the study of the H α vertical velocity field in a sample of four nearly face-on galaxies using long-slit spectroscopy taken with the Intermediate dispersion Spectrograph and Imaging System (ISIS), attached to the William Herschel Telescope (WHT) at the Roque de los Muchachos Observatory (Spain). The spatial structure of the velocity vertical component shows a radial corrugated pattern with spatial scales higher or within the order of 1 kpc. The gas is mainly ionized by high-energy photons: only in some locations of NGC 278 and NGC 1058 is there some evidence of ionization by low-velocity shocks, which, in the case of NGC 278, could be due to minor mergers. The behaviour of the gas in the neighbourhood of the spiral arms fits, in the majority of the observed cases, with that predicted by the so-called hydraulic bore mechanism, where a thick magnetized disc encounters a spiral density perturbation. The results obtained show that it is difficult to explain the H α large-scale velocity field without the presence of a magnetized, thick galactic disc. Larger samples and spatial covering of the galaxy discs are needed to provide further insight into this problem.We acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through grants AYA2010-17631 and AYA2013-40611-P, and from the Consejeria de Educacion y Ciencia (Junta de Andalucia) through TIC-101, TIC-4075 and TIC-114Peer Reviewe

Approximation of integration maps of vector measures and limit representations of Banach function spaces

[EN] We study whether or not the integration maps of vector measures can be computed as pointwise limits of their finite rank Radon¿Nikodým derivatives. The positive cases are obtained by using the circle of ideas related to the approximation property for Banach spaces. The negative ones are given by means of an appropriate use of the Daugavet property. As an application, we analyse when the norm in a space L 1 (m) of integrable functions can be computed as a limit of the norms of the spaces of integrable functions with respect to the Radon¿Nikodým derivatives of m.E. Jiménez Fernández was supported by Junta de Andalucía and FEDER (grant no. P09-FQM-4911 (Spain)) and by Ministerio de Economía, Industria y Competitividad (grant no. MTM2012-36740-C02- 02 (Spain)). E. A. Sánchez Pérez was supported by Ministerio de Economía, Industria y Competitividad (grant no. MTM2016-77054-C2-1-P (Spain)).Jiménez Fernández, E.; Sánchez Pérez, EA.; Werner, D. (2017). Approximation of integration maps of vector measures and limit representations of Banach function spaces. Annales Polonici Mathematici. 120(1):63-81. https://doi.org/10.4064/ap170407-21-9S6381120

Unsupervised machine learning approach for building composite indicators with fuzzy metrics

[EN] This study aims at developing a new methodological approach for building composite indicators, focusingon the weight schemes through an unsupervised machine learning technique. The composite indicatorproposed is based on fuzzy metrics to capture multidimensional concepts that do not have boundaries, suchas competitiveness, development, corruption or vulnerability. This methodology is designed for formativemeasurement models using a set of indicators measured on different scales (quantitative, ordinal and binary)and it is partially compensatory. Under a benchmarking approach, the single indicators are synthesized.The optimization method applied manages to remove the overlapping information provided for the singleindicators, so that the composite indicator provides a more realistic and faithful approximation to the conceptwhich would be studied. It has been quantitatively and qualitatively validated with a set of randomizeddatabases covering extreme and usual cases.This work was supported by the project FEDER-University of Granada (B-SEJ-242.UGR20), 2021-2023: An innovative methodological approach for measuring multidimensional poverty in Andalusia (COMPOSITE). Eduardo Jimenez-Fernandez would also like to thank the support received from Universitat Jaume I under the grant E-2018-03.Jiménez Fernández, E.; Sánchez, A.; Sánchez Pérez, EA. (2022). Unsupervised machine learning approach for building composite indicators with fuzzy metrics. Expert Systems with Applications. 200:1-11. https://doi.org/10.1016/j.eswa.2022.11692711120

Multicyclic conversion of limestone at Ca-looping conditions: The role of solid-sate diffusion controlled carbonation

Limestone derived CaO conversion when subjected to multiple carbonation/calcination cycles is a subject of interest currently fueled by several industrial applications of the so-called Ca-looping (CaL) technology. The multicyclic CaO conversion at Ca-looping conditions exhibits two main features as demonstrated by thermogravimetric analysis (TGA). On one hand, carbonation occurs by two well differentiated phases: a first kinetically-driven fast phase and a subsequent much slower solid-state diffusion controlled phase. On the other, carbonation in the fast phase usually shows a drastic decay with the cycle number along the first carbonation/calcination cycles. This trend can be reversed by means of heat pretreatment, which induces a marked loss of fast conversion in the first carbonation but enhances diffusion of CO2 in the solid. Upon decarbonation the regenerated CaO skeleton displays an increased conversion in the fast carbonation phase of the next cycle, a phenomenon which has been referred to as reactivation. Nonetheless, sorbent reactivation is hampered by looping carbonation/calcination conditions as those to be likely found in practice such as carbonation stages characterized by low CO2 concentrations and short duration and calcination stages at high temperatures in a CO2 enriched atmosphere, which causes a sintering and loss of activity of the regenerated CaO skeleton. We analyze in this work sorbent reactivation as affected by heat pretreatment and carbonation/calcination conditions. Aimed at shedding light on the role played by these conditions on reactivation we look separately at the multicyclic evolution of conversion in the kinetic and diffusive phases. Generally, the evolution of multicyclic conversion after the first cycle can be described by a balance between the surface area gain due to diffusive carbonation and the surface area loss as caused by sintering in the calcination stage. A significant gain of relative surface area after the first cycle, which is favored by harshening the heat pretreatment conditions, leads however to a marked decay of it during subsequent cycles, which precludes reactivation for an extended interval of cycles. On the other hand, sorbent grinding, if performed before heat pretreatment, leads to a less marked but more sustainable reactivation along the cycles. A novel observation reported in our work is that pretreatment of limestone in a CO 2 atmosphere leads upon a subsequent quick decarbonation to a CaO skeleton with extraordinarily enhanced reactivity in the kinetically-driven carbonation phase and with a high resistance to solid-state diffusion, which can be attributed to annealing of the crystal structure as reported by independent studies

Kissinger kinetic analysis of data obtained under different heating schedules

The dynamic heating rate method developed by TA Instruments ( Hi-Res ™ ) is a kind of sample controlled thermal analysis in which a linear relati onship between the logarith m of the heating rate and the rate of weight change is imposed. It is s hown in this paper that the reacted fraction at the maximum reaction rate strongly depends on the parameters selected for the Hi-Res heating algorithm, what invalidates the use of the Kissinger method for analysing Hi-Res data unless that the reaction fits a first order kinetic law. Only in this latter case, it has been demonstrated that it is not required that a constant value of the reacted fr action at the maximum reaction rate is fulfilled for determining the activation energy from the Kissi nger method. In such a case the Kissinger plot gives the real activation energy, independently of both the heating schedule used and the value of the reacted fraction, α m , at the maximum

Calcium-looping for post-combustion CO2 capture. On the adverse effect of sorbent regeneration under CO2

The multicyclic carbonation/calcination (c/c) of CaO solid particles at high temperature is at the basis of the recently emerged Calcium-looping (CaL) technology, which has been shown to be potentially suitable for achieving high and sustainable post-combustion CO2 capture efficiency. Despite the success of pilot plant projects at the MWth scale, a matter of concern for scaling-up the CaL technology to a commercial level (to the GWth scale) is that the CaO carbonation reactivity can be recovered only partially when the sorbent is regenerated by calcination at high temperatures (around 950 °C) as required by the CO2 high concentration in the calciner. In order to reactivate the sorbent, a novel CaL concept has been proposed wherein a recarbonator reactor operated at high temperature/high CO2 concentration leads to further carbonation of the solids before entering into the calciner for regeneration. Multicyclic thermogravimetric analysis (TGA) tests demonstrate the feasibility of recarbonation to reactivate the sorbent regenerated at high calcination temperatures yet at unrealistically low CO2 partial pressure mainly because of technical limitations concerning low heating/cooling rates. We report results from multicyclic c/c and carbonation/recarbonation/calcination (c/r/c) TGA tests at high heating/coling rates and in which the sorbent is regenerated in a dry atmosphere at high CO2 partial pressure. It is shown that at these conditions there is a drastic drop of CaO conversion to a very small residual value in just a few cycles. Moreover, the introduction of a recarbonation stage has actually an adverse effect. Arguably, CaCO3 decomposition in a CO2 rich atmosphere is ruled by CO2 dynamic adsorption/desorption in reactive CaO (1 1 1) surfaces as suggested by theoretical studies, which would preclude the growth of the regenerated CaO crystal structure along these reactive surfaces, and this effect would be intensified by recarbonation. Nevertheless, the presence of H2O in the calciner, which is also adsorbed/desorbed dynamically in CaO reactive planes, would shield CO2 adsorption/desorption thus mitigating the deeply detrimental effect of CO2 on the carbonation reactivity of the regenerated CaO structure. Oxy-combustion, which produces a significant amount of H2O, is currently used in pilot-scale plants to raise the temperature in the calciner. Auxiliary techniques are being explored to help heating the partially carbonated solids since oxyxombustion represents an important penalty to the CaL technology. Our study suggests that steam injection would be necessary in a dry calciner environment to avoid a sharp loss of CaO conversion if the sorbent is regenerated at high CO2 partial pressure.Junta de Andalucía FQM-5735 TEP-7858España Mineco Feder FIS2011-25161 CTQ2011-2762

Critical study of the isoconversional methods of kinetic analysis

A critical study of the use of isoconversional methods for the kinetic analysis of non-isothermal data corresponding to processes with either a real or an apparent variation of the activation energy, E, with the reacted fraction, α, has been carried out using for the first time simulated curves. It has been shown that the activation energies obtained from model-free methods are independent of the heating rate. However, the activation energy shows a very strong dependence of the range of heating rates used for simulating the curves if the apparent change of E with α is caused by overlapping processes with different individual activation energies. This criterion perhaps could be used for determining if a real dependence between E and α is really occurringEspaña Ministerio de Educación y Ciencia No. MAT2004-0264