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12 figures, 6 tables.-- Supplementary information available., Chemical looping combustion (CLC) is a novel technology for the combustion of fuels with inherent CO2 capture. CLC is based on the transference of oxygen from air to fuel by means of an oxygen carrier which is based on a metal oxide. CuO/Al2O3 (14 wt.% CuO) and Fe2O3/Al2O3 (20 wt.% Fe2O3) particles have been used in several CLC units with different results when methane combustion was evaluated. In order to shed light on the main processes affecting methane conversion in CLC, a mathematical model for a dual circulating fluidized bed (DCFB) system was developed to simulate the behavior of CuO/Al2O3 and Fe2O3/Al2O3 in a CLC unit. The model consists of the coupling of individual fuel and air reactor models to simulate steady state of the CLC unit. Individual models consider both the fluid dynamics of the fluidized beds at the high velocity regime and the corresponding kinetics of oxygen carrier reactions, that is, reduction in the fuel reactor and oxidation in the air reactor. The model was validated using results obtained in a 120 kWth CLC unit with CuO/Al2O3 and Fe2O3/Al2O3 particles. The validated model was used to simulate the performance of these materials in the 10 MWth CLC unit. Desing parameters of the fuel and air reactors as well as the suitable particle size of the oxygen carriers were determined in order to achieve the complete combustion of natural gas in the CLC unit as a function of the oxygen carrier properties., This work was supported by Grant funded by MCIN/AEI/10.13039/501100011033 and by the European Union NextGenerationEU/PRTR.

16 figures, 5 tables.-- Supplementary information available., Chemical looping combustion (CLC) is a technology allowing CO2 capture at low cost. The development of durable oxygen carrier materials is a key factor for the scale-up of CLC. Once a promising oxygen carrier has been identified dedicated studies into the effects of reaction conditions on the durability of these kinds of materials are required in order to improve their reliability before use at industrial scale. This method requires several long-term tests in CLC units each one of them to fixed conditions, which is time consuming and expensive. In this work, a low-effort method using thermogravimetric analysis was developed and validated against a high-effort method requiring the use of an oxygen carrier material for hundreds of hours in a CLC unit. The reaction pathways and variation in physico-chemical properties of a material with 14 wt% CuO impregnated on γ-Al2O3 during the course of 300 redox cycles were evaluated as a function of reaction temperature, variation in oxygen carrier conversion (ΔXs) and degree of oxidation/reduction in every redox cycle. As a result, preferred conditions to be used in a CLC unit were identified. In general, reactivity and mechanical integrity were not affected when the reaction temperature was 800 °C. However, a temperature of 900 °C was found to be potentially suitable when the material was highly reduced in each redox cycle and ΔXs was low. The use of this method for promising oxygen carriers can boost the identification of long lasting materials for the scale-up of chemical looping processes., This work was funded by the State Research Agency of Spain (projects PID2019-106441RB-I00/AEI/10.13039/501100011033 and ENE2017-89473-R, AEI/FEDER, EU)

7 Figures, 5 Tables.-- © 2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Chemical Looping Combustion (CLC) with solid fuels has been widely developed by using two interconnected fluidized beds, the fuel reactor and the air reactor, with an oxygen carrier continuously circulating between them. Experience gained in this process shows that high CO2 capture values can be reached. However, complete combustion of the fuel is not achieved, with some H2, CO and CH4 as the main unconverted compounds in the combustion products from the fuel reactor. It is believed that the combustion efficiency can be increased by improving the gas-solid contact in the fuel reactor. In this work, the solids distribution in the fuel reactor was modified by using ring-type internals with the objective of enhancing the gas-solid contact. Two experimental campaigns were carried out in a 50 kWth CLC unit burning a bituminous coal with ilmenite particles in the temperature interval of 900–1000 °C. The first campaign was conducted with the original riser of the fuel reactor, which was characterized by a smooth section from bottom to top. For the second campaign, three ring-type internals were implemented in the riser in order to modify the solids distribution in the fuel reactor. The presence of the internals had a beneficial effect on the coal combustion. The major benefit was an improved oxidation of volatile matter in the form of CH4 and the full conversion of H2. As a result, the total oxygen demand decreased by 20%, from 12.2% to 9.8%, with the implementation of the internals., This work was supported by the Ministerio de Economía, Industria y Competitividad (projects ENE2014-56857-R and ENE2016-77982-R), the Spanish National Research Council (CSIC project: 2017-80E035), the Research Fund for Coal and Steel (RFCS project ACCLAIM: RFCP-CT-2012-00006) and the European Regional Development Fund (ERDF).

11 Figures, 4 Tables.-- © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, The in-situ Gasification Chemical Looping Combustion (iG-CLC) process allows combustion with inherent CO2 capture. In this process, the oxygen for combustion is commonly supplied by a solid oxygen carrier based on a metal oxide thus avoiding direct contact between fuel and air. The oxygen carrier circulates between two reactors. In the fuel reactor, the fuel is oxidized to CO2 and H2O while the oxygen carrier is reduced. In the air reactor, the reduced oxygen carrier is regenerated in air. Ilmenite has been widely used as a low-cost oxygen carrier for the iG-CLC process, and it can be taken as a reference material. Recently, the Tierga iron ore has been identified as a promising candidate for further scale-up of the process due to the higher combustion efficiency achieved compared to the results using ilmenite. Modelling of the iG-CLC process with Tierga iron ore as oxygen carrier is a key step to determine the potential of this material. In order to model the iG-CLC process it is necessary to know the reactivity of both oxygen carrier and fuel used. In this paper, the kinetic determination for the reduction and oxidation reactions of the Tierga ore is presented. Reaction orders close to unity were obtained for the main reducing gases, i.e. H2, CO and CH4, as well as O2. The activation energy values obtained were 81.1 ± 7, 76.1 ± 6 and 257 ± 14 kJ/mol for H2, CO and CH4, respectively. The activation energy for oxidation was determined as 18.4 ± 0.5 kJ/mol. In addition, a simple method is used for a comparison of the performance of different oxygen carriers based on their kinetics., This work was supported by the Spanish Ministry of Economy and Competitiveness (projects ENE2014-56857-R, ENE2016-77982-R), by the European Regional Development Fund (ERDF), the EU project ACCLAIM (RFCP-CT-2012-00006). T. Mendiara thanks for the ‘‘Ramón y Cajal’’ post-doctoral contract awarded by the Spanish Ministry of Economy and Competitiveness. The authors also thank PROMINDSA for providing the iron ore used in this work.

6 figures, 3 tables.-- Supplementary information available., Different chemical looping processes allow burning or gasify solid fuels with inherent CO2 capture because the oxygen is transferred from air to the fuel through a metal oxide based material, which is named oxygen carrier. To improve process efficiency and CO2 capture, highly reactive synthetic materials could be used. One of the challenges of using solid fuels is the oxygen carrier separation from the ash, because loss of oxygen carrier particles is expected during ash drainage. So, their costs would have necessary the recovery of the synthetic oxygen carrier. Mn-Fe based materials show magnetic properties in the spinel phase, which could be used for a magnetic separation. When these Mn-Fe materials are used at high temperature under oxidizing or reducing atmospheres, stability of the spinel phase should be guaranteed in order to take advantage of the magnetic properties. The design of low reactive Mn-Fe based materials with magnetic properties, which can be used as a support material for other highly reactive and active phases, was the main objective of this work. In this sense, the support must have high crushing strength, low reactivity under oxidation and reduction atmospheres at high temperatures and permanent magnetism at low temperature for solids separation. Materials prepared with different Mn/(Mn + Fe) molar ratios and calcination conditions were evaluated regarding mechanical strength, inerticity and magnetic properties. A Cu-based oxygen carrier prepared on the optimal support was prepared and evaluated along 240 oxidation-reduction cycles in thermobalance (25 h experiment), exhibiting suitable mechanical and magnetic characteristics as well as high reactivity., This work has been supported by the AEI/FEDER, UE ENE2016-77982-R, ENE2017-89473-R and ID2019-106441RB-I00 projects, and by the Regional Aragon Government via the T05_17R research group funding.

7 figures, 5 tables.-- © 2021. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Chemical Looping Combustion (CLC) is a promising carbon capture technology to contribute to the development of BioEnergy with Carbon Capture and Storage (BECCS) technologies. In CLC, the oxygen needed for combustion is supplied by a solid oxygen carrier. During the last years, intensive research has been conducted to identify potential oxygen carriers. Iron and manganese-based minerals allowed obtaining high CO2 capture efficiencies, but lower values for the combustion efficiency, that is, high oxygen demand values, due to the high content of volatiles in biomass. Manganese-iron mixed oxides doped with titanium possess the capability of releasing molecular oxygen under specific conditions which would enhance volatile conversion. The objective of the present work was to evaluate the potential of one of these materials ((Mn66Fe)-Ti7) to improve the combustion efficiency of CLC with biomass in a 0.5 kWth continuous CLC unit. Almost 100% of CO2 capture efficiency was obtained in all the experiments. Once the operational conditions for the synthetic material (Mn66Fe)-Ti7 were optimized, it was possible to reach oxygen demand values about 10% with the advantage that the (Mn66Fe)-Ti7 oxygen carrier presented magnetic properties that would facilitate its separation from biomass ashes in the fuel reactor., This work was supported by ENE2017-89473-R AEI/FEDER, UE. A. Pérez-Astray thanks the Spanish Ministry of Economy and Competitiveness (MINECO) for the BES-2015-074651 pre-doctoral fellowship co-financed by the European Social Fund. T. Mendiara thanks for the “Ramón y Cajal” post-doctoral contract awarded by MINECO.

10 figures, 3 tables.-- Supplementary material available.-- © 2021. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, The objective of this study was to evaluate the effect of the chemical and thermal stress on the physical and chemical stability of a CuO/Al2O3 impregnated oxygen carrier during methane chemical looping combustion at high oxygen carrier to fuel ratios to ensure low solid conversion variations. The Cu-based particles were subjected to 130 h of operation in a 0.5 kWth chemical looping combustion unit burning CH4 at steady state and unchanged conditions. Two batches of particles were used to operate the fuel and air reactor either at 800 °C or 900 °C. A full solid characterization regarding crystalline compounds, oxidation state, ASTM attrition index, crushing strength and morphology analysis was carried out in order to investigate the physical and chemical stability of the oxygen carrier. Main conclusion derived from this research work is that the low oxygen carrier conversion variation allowed reducing the chemical stress and as consequence the copper loss from particles. However, the oxygen carrier was difficult to reoxidize at 900 °C due to the formation of CuAlO2. Operating at temperatures about 800 °C and at low solid conversion variation is proposed since copper loss was limited maintaining an adequate physical stability., This work has been supported by the projects AEI/FEDER, UE (ENE2017-89473-R) and PID2019-106441RB-I00/AEI/10.13039/501100011033), and by the Regional Aragon Government (T05_17R and LMP180–18).

13 figures, 6 tables., The interest of using bio-oil produced by biomass fast pyrolysis to generate H2 and high value chemicals is growing up in order to reduce CO2 emissions by the use of biomass. In the present work, bio-oil Chemical Looping Reforming was demonstrated in a 1 kWth continuous unit during 60 h of operation using a Ni-based oxygen carrier to produce syngas/H2. No agglomeration of the oxygen carrier was detected. Complete conversion of the bio-oil was obtained in all cases, obtaining as main products H2, CO, CO2 and in much lower concentration CH4. Carbon deposition in the bed appeared in almost all the experiments carried out during the bio-oil reforming, and CO2 was found in the air reactor outlet, although did not affect to the process performance when oxygen carriers were used. This fact only let to a reduction of the CO2 capture efficiency. Fuel reactor temperature was a key factor for the H2 production, the H2/CO ratio and the carbon accumulated in the CLR unit. The maximum H2 production together with the maximum H2/CO ratio of 6 were found at the lowest temperature used, 650 °C. In addition, the carbon formed in the fuel reactor was reactive enough so that it could be burnt in the air reactor with minimum accumulation in the continuous unit. The autothermal H2 production was 13.6 g/100 g of bio-oil without water at 650 °C with a H2O/bio-oil = 6, which corresponds to 68 mol H2/kg of bio-oil without water. Therefore, the CLR process of bio-oil allows obtaining high H2 production with low carbon deposition at 650 °C using less amount of water than in conventional bio-oil reforming., The work presented in this article is partially funded by the Spanish National Research Council (CSIC) through the Project No. 201980E043. I. Adánez-Rubio acknowledges for the grant IJC2019-038987-I funded by MCIN/AEI/10.13039/501100011033.

9 figures, 3 tables.-- © 2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Glycerol availabity, a waste generated in the production of biodiesel, has increased during last years. In this work, Chemical Looping Reforming (CLR) of glycerol has been demonstrated in a 1 kW continuous unit during 35 h using a Ni-based oxygen carrier to obtain a high purity syngas without CO emissions. Complete conversion of the glycerol and syngas composition close to thermodynamic equilibrium was obtained in the fuel reactor. Moreover, pure N was obtained as product in the air reactor. The influence of the main operating variables on the composition and flow rates of synthesis gas was evaluated. The oxygen-to-glycerol molar ratio was the main parameter since the amount of lattice oxygen transferred by the oxygen carrier in the fuel reactor controlled the syngas composition. The increase of the water-to-glycerol ratio produced an increase in the production of H and CO with a decrease in the CO content, increasing both the syngas yield and the H/CO molar ratio in the gas. Fuel reactor temperature affected mainly to the CH content, being lower as higher was the temperature. Close to autothermal conditions, it is possible to obtain a syngas composed by H ≈ 48–50 vol%; CO ≈ 30–35 vol%; CO ≈ 14–18 vol%; and CH ≈ 1.6–3 vol%. In addition, different H/CO ratios can be obtained by modifying the HO/glycerol ratio and temperature. A H/CO ratio of 2 could be reached using either a HO/glycerol ratio of 1.5 at 750 °C or a HO/glycerol ratio of 2 at 800 °C., This work is partially supported by CSIC (project no. 201980E043) and. Petrobras (project No. 5900.0109823.18.9).

6 Figures, 3 Tables.-- © 2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Minerals or industrial waste materials are considered promising oxygen carriers for coal combustion through in-situ Gasification Chemical Looping Combustion (iG-CLC) process in order to maintain CO2 capture at low cost. Nevertheless, complete coal combustion to CO2 and H2O is usually not achieved and different solutions have been outlined to improve it. The aim of this work is to analyze the potential of two of these strategies: (1) using a more reactive oxygen carrier; and (2) to have two fuel reactors by feeding the coal into the carbon stripper. Coal combustion in a 50 kWth CLC unit was carried out using two oxygen carrier materials, namely Norwegian ilmenite and Tierga iron-ore. Also, an additional test was carried out feeding the coal directly into the carbon stripper of the CLC unit, in contrast with the conventional coal feeding to the fuel reactor. CO2 capture efficiency was barely affected by the type of oxygen carrier material, but slightly lower values were obtained when coal was fed to the carbon stripper. In contrast, coal combustion efficiency was enhanced by using the iron-ore material, with a potential decrease of the total oxygen demand of 40%, achieving a minimum value of total oxygen demand of 4.1%. Also, the total oxygen demand was decreased by 24% when coal was fed to the carbon stripper due to the improvement in the combustion of the volatiles in the fuel reactor. The combination of both strategies has high potential to maximize the coal combustion via iG-CLC process., This work was partially supported by the Ministerio de Economía y Competitividad (project ENE2014-56857-R), and by the projects ENE2016-77982 (AEI/FEDER, UE), and ENE2017-89473-R (AEI/FEDER, UE), by the Regional Aragon Government via the T05_17R research group funding and by the Consejo Superior de Investigaciones Científicas (CSIC project: 2017-80E035). T. Mendiara thanks for the “Ramón y Cajal” post-doctoral contract awarded by MINECO.

7 figures, 6 tables.-- © 2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Manganese oxides are capable of releasing molecular oxygen and regenerate in air under determined conditions. This fact makes these materials interesting for applications in different areas, such as thermochemical energy storage processes, oxygen production by chemical looping air separation (CLAS) or CO2 capture-oriented processes, namely chemical looping combustion (CLC) or chemical looping with oxygen uncoupling (CLOU). In this work, the potential to release molecular oxygen and regenerate in air of different manganese‑titanium mixed oxides with mass fractions of titanium from 0 to 50%, were evaluated in a TGA apparatus. Besides, the reactivity of the mixed oxide samples to the main fuel gases (CO, H2 and CH4) has been also evaluated. Consecutive redox cycles have been performed at different temperatures (850 and 940 °C) using nitrogen during reduction and air in oxidation. The oxygen transport capacity as well as the rate index for oxygen uncoupling and gas-solid reactions have been determined and compared to that found for other materials reported in literature. Moreover, solid phase identification in the different mixed oxide samples by XRD has been addressed in order to determine the oxygen release/regeneration mechanism. Results show a great potential of these materials as low-cost and environmentally friendly oxygen carriers., This work was partially supported by the projects ENE2017-89473-R (AEI/FEDER, UE) and PID2019-106441RB-I00. T. Mendiara thanks for the “Ramón y Cajal” post-doctoral contract awarded by the Spanish Ministry of Economy and Competitiveness.

9 Figures, 6 Tables.-- © 2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, A previously developed manganese-iron mixed oxide doped with TiO2 shows promising properties for the combustion of solid fuels with intrinsic CO2 capture by Chemical Lopping assisted by Oxygen Uncoupling (CLaOU) owing to its oxygen uncoupling capability, i.e. ability to generate gaseous oxygen at high temperature, and to oxidize gaseous fuels such as H2, CO or CH4 by reacting with lattice oxygen. In this work, a window of suitable operating conditions was determined to facilitate the use of this material in a CLaOU unit. For this purpose, mass and enthalpy balances were performed for the whole CLaOU unit considering theoretical values of thermochemical parameters, such as the equilibrium constant of relevant reactions in CLaOU and the formation enthalpies of reacting solids. An air reactor temperature of 1148 K and a high air excess ratio are suggested in order to promote the transfer of oxygen via the oxygen uncoupling mechanism, which would be preferable for the combustion of solid fuels. Auto-thermal operation of the CLaOU unit is guaranteed for air excess ratio values λ, This work was partially supported by the Ministerio de Economía, Industria y Competitividad (Projects: ENE2016-77982-R and ENE2017-89473R), by the Fondo Europeo de Desarrollo Regional (FEDER), and by the Consejo Superior de Investigaciones Científicas (CSIC project: 2017-80E035).

12 figures, 3 tables.-- © 2021. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, CaMnO3-based perovskites are attractive for use as oxygen carriers in chemical looping combustion (CLC) because they are made from cheap materials (manganese, calcium). However, these materials show low reactivity with methane, and high oxygen carrier-to-fuel ratios (ϕ) are required to achieve complete fuel combustion. It is believed that energy efficiency in the chemical looping process would be improved if the reactivity of these materials were higher. In this work, the increase in reactivity of a perovskite (CaMn0.775Mg0.1Ti0.125O2.9-δ) material is evaluated during its in-situ activation under determined operating conditions in a 0.5 kWth CLC pilot plant. The combustion efficiency of methane over 60 h of continuous operation was analysed taking into consideration the effect of operating conditions on the activation process for increasing the reactivity of the perovskite. The material increased in reactivity as the ϕ ratio decreased to below 6, improving combustion efficiency. Moreover, the material was pre-activated by being fully reduced in the CLC plant. The conversion of methane with the pre-activated material was subsequently higher than the conversion achieved before the activation process, and almost complete combustion was achieved at a lower ϕ ratio. Characterization of the particles after the combustion tests showed good stability of the material with the operating time, although a negative effect on the crushing strength was observed when the particles were highly reduced. The impact of the perovskite material activation on the energy efficiency of the process is discussed., This work was partially supported by the SWINELOOP project (PID2019-106441RB-I00/AEI/10.13039/501100011033) and the SUCCESS Project, funded by the European Commission under the Seventh Framework Programme (Grant agreement No. 608571). J. Adánez thanks CSIC for the financial support given to the project 201980E043.

17 figures, 6 tables.-- © 2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, The reaction kinetics of CaMn0.775Ti0.125Mg0.1O2.9-δ perovskite, prepared at ton-scale to be used as an oxygen carrier in a CLC process with methane, was determined. The variation of the reaction rates, oxygen transport capacity, and oxygen uncoupling behaviour of the selected material with the number of cycles was evaluated in a thermogravimetric analyser. The perovskite was activated for the reduction reaction with all the combustible gases, i.e., H2, CO and CH4. On the contrary, the oxidation rate barely changed throughout the cycles. The oxygen transport capacity underwent a slight decrease during the activation period. Kinetics of reduction, oxidation and oxygen uncoupling reactions were determined for the fresh and activated material assuming a grain model controlled by chemical reaction at low values of solids conversion and diffusion through the product layer at high values of solids conversion. This model predicted correctly the solids conversion vs. time curves as a function of temperature and gas concentration for the oxygen carrier reactions evaluated in this kinetics study. The kinetics data were introduced in a validated mathematical model of a fuel reactor to analyse the amount of solids required to fully combust CH4. A solids inventory of 350 kg/MWth was estimated in the fuel reactor at a temperature of 1243 K. However, this value could be reduced to 160 kg/MWth if the material operates under activation conditions within the CLC unit., This work was partially supported by the project ENE2016-77982-R (AEI/FEDER, UE), ENE2017-89473-R (AEI/FEDER, UE) and the SUCCESS Project, funded by the European Commission under the Seventh Framework Programme (Grant agreement No. 608571 ).

10 Figures, 4 Tables.-- © 2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Chemical looping combustion allows the carbon dioxide capture by using an oxygen carrier, which transports the oxygen required for combustion from the air to the fuel. But complete combustion of a solid fuel is not achieved when low cost materials were used as oxygen carriers. Manganese‑iron mixed oxide doped with titanium has been identified as a promising oxygen carrier to improve combustion efficiency due to its oxygen uncoupling capability. The objective of this work was to assess the potential of this oxygen carrier when burning coal in a chemical looping unit. The coal combustion efficiency and carbon dioxide capture were evaluated as a function of the operating conditions both in the fuel and air reactor. Carbon dioxide capture was affected by the solids residence time in the fuel reactor. Coal combustion efficiency increased as the oxygen uncoupling capability was enhanced by using suitable operating conditions in the air reactor. Almost full coal combustion (99.4%) was achieved by setting an air reactor temperature of 880 °C, an air excess of 1.8, a fuel reactor temperature of 925 °C, and an oxygen carrier to fuel ratio >3. The oxygen carrier showed magnetic properties, allowing its re-use after being separated from ash., This work was partially supported by the project ENE2016-77982-R (AEI/FEDER, UE) and project ENE2017-89473R (AEI/FEDER, UE), and by the Consejo Superior de Investigaciones Científicas (CSIC project: 2017-80E035).

5 Tables, 8 Figures.-- © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, A simple model based on oxygen carrier kinetics has been developed for the in situ Gasification Chemical Looping Combustion (iG-CLC) process. Once the kinetic parameters for different oxygen carriers and solid fuels are known, the model allows easy and fast comparison of different oxygen carrier-solid fuel pairs, which is the main purpose of the model here presented. The comparison is based on the estimation of the CO2 capture efficiency value (ηCC) and the total oxygen demand (ΩT) as evaluating parameters. To show the proposed procedure for the comparison, two Fe-based oxygen carriers (ilmenite and Tierga ore), and five different types of solid fuels: anthracite (Yangquan), sub-bituminous (Tremedal), two bituminous coals (Cerrejón and Taldinsky) and one biomass (olive tree pruning) have been considered. The comparison of the calculated CO2 capture efficiency and total oxygen demand must be done including the effect of operating conditions such as temperature and solids circulation rate. A set of optimized operating conditions are given as a reference for future evaluations of different oxygen carrier-solid fuel pairs. This method is thought as a useful tool for a preliminary evaluation of new oxygen carriers for iG-CLC with different solid fuels., This work was supported by the Spanish Ministry of Economy and Competitiveness (projects ENE2014-56857-R, ENE2016-77982-R), by the European Regional Development Fund (ERDF), the EU project ACCLAIM (RFCP-CT-2012-00006). T. Mendiara thanks for the “Ramón y Cajal” post-doctoral contract awarded by the Spanish Ministry of Economy and Competitiveness. The authors also thank PROMINDSA for providing the iron ore used in this work.

10 Figuras, 7 Tablas.-- Información complementaria disponible en línea en la página web del editor, Two different oxygen-carrier materials with similar molar ratios of Mn:Fe:Al were tested in continuous chemical-looping combustion operation with different fuels, i.e., syngas (H2/CO), methane, and kerosene. One oxygen carrier was manufactured by spray drying, and the other one was a naturally occurring ore that was crushed. Experiments were conducted in a bench-scale, chemical-looping combustion reactor with continuous fuel addition and continuous circulation of oxygen-carrier particles. In fresh state, i.e., before fuel operation, both materials showed clear CLOU properties. In used state, i.e., after fuel operation, the CLOU properties of the manufactured oxygen carrier were slightly higher than before, whereas those of the natural material decreased significantly. Operation with fuel was conducted for a total of about 47 h between 850 and 950 °C, and clear differences in fuel conversion were observed. At similar oxygen-carrier-to-fuel ratios and temperatures, the manganese ore achieved a clearly higher methane conversion, whereas the manufactured material achieved a higher conversion of H2 and CO. Near-complete conversion of syngas, i.e., >99%, was reached with both materials tested. Particle circulation was indirectly measured and used to estimate solids conversion during continuous operation. The materials were characterized with ICP-SFMS, XRD, and SEM/EDX, and rate indices were calculated based on data obtained in TGA tests with different reactants. Thermodynamic equilibrium calculations were made and used to interpret results from oxygen release and TGA tests. Attrition indices and material porosity were determined for fresh and used samples of the materials used. The manganese ore exhibited a clearly lower structural integrity during redox operation compared to the manufactured material. However, the cost of producing an oxygen carrier from an ore is significantly lower than manufacturing an oxygen carrier by spray drying., This work was partially supported by the Spanish Ministry of Science and Innovation (MICINN Project ENE2011-26354) and the European Regional Development Fund (ERDF). A.S. also thanks the Spanish Ministry of Economy and Competitiveness for the F.P.I. fellowship. Additional funding was received from the European Research Council (ERC) under the European Union’s Seventh Framework Programme (FP7/2007-2013) (grant agreement no. 291235).

7 Figures, 2 Tables.-- Supplementary material available.-- © 2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Chemical-Looping Combustion (CLC) is a promising technology for performing CO2 capture in combustion processes at low cost and with lower energy consumption. Fuel conversion modelling assists in optimizing and predicting the performance of the CLC process under different operating conditions. For this work, the combustion of natural gas was modelled using a CaMnO3-type perovskite as oxygen-carrier and taking into consideration the processes of fluid dynamics and reaction kinetics involved in fuel conversion. The CLC model was validated against experimental results obtained from the 120 kWth CLC unit at the Vienna University of Technology (TUV). Good agreement between experimental and model predictions of fuel conversion was found when the temperature, pressure drop, solids circulation rate and fuel flow were varied. Model predictions showed that oxygen transfer by means of the gas–solid reaction of the fuel with the oxygen-carrier was relevant throughout the entire fuel-reactor. However, complete combustion could be only achieved under operating conditions where the process of Chemical-Looping assisted by Oxygen Uncoupling (CLaOU) became dominant, i.e. a relevant fraction of the fuel was burnt with molecular oxygen (O2) released by the oxygen-carrier. This phenomenon was improved by the design configuration of the 120 kWth CLC unit at TUV, in which oxidized particles are recirculated to the upper part of the fuel-reactor. Thus, the validated model identified the conditions at which complete combustion can be achieved, demonstrating that it is a powerful tool for the simulation and optimization of the CLC process with the CaMnO3-type material., This work was supported by the seventh Framework Programme of the European Commission (INNOCUOUS Contract 241401), by the Spanish Ministry of Economy, Industry and Competitiveness (project ENE2016-77982-R), by the European Regional Development Fund (ERDF) and by the CSIC (project 2017-80E035). Authors thanks to K. Mayer and S. Penthor (TUV) for providing experimental data.

2 figures.-- Work presented at the 7th International Congress on Biofuels and Bioenergy, October 02-04, 2017 Toronto, Canada, Bioenergy and Carbon Capture and Storage (BECCS), is an interesting option to remove CO2 from the atmosphere, thus mitigating the CO2 emissions from the use of non-renewable sources, i.e., fossil fuels. BECCS has been identified as a relevant measure to achieve the target enforced by the United Nations Framework Convention on Climate Change (UNFCCC) in the Paris Agreement: To limit the increase in the average world temperature to 2ºC above pre-industrial levels. However, implementing CO2 capture in bioenergy through common technologies has the drawback of high economic and energetic costs. In this sense, the Chemical Looping Combustion (CLC) technology allows inherent CO2 capture at low cost during combustion. The benefits of CLC are based on avoiding the costly separation steps required in commercial CO2 capture processes, e.g., CO2 separation in flue gases or O2 production for oxy-fuel combustion, by the use of an oxygen carrier. The purpose of the oxygen carrier, usually a particulate metal oxide, is to transfer oxygen from air to fuel in order to avoid the direct contact between them. Thus, the oxygen carrier provides the oxygen required for combustion in the so-called fuel reactor. The oxygen carrier is later regenerated by air in the air reactor. The most common design of a CLC unit includes two fluidized bed reactors, being those mentioned fuel and air reactors with the oxygen carrier continuously circulating among them. CLC has been widely investigated for the use of gaseous fuels and coal but the interest of using biomass has recently increased considering that negative CO2 emissions would be possible. The objective of this work is to contribute to the development of biomass combustion by CLC evaluating the use of new and highly reactive Mn-based materials as oxygen carriers. Experiments were performed in a continuous 500 Wth CLC unit at Instituto de Carboquimica (ICB-CSIC), consisting of two interconnected fluidized-bed reactors. After determination of both gas streams composition, the performance of the CLC process was assessed by calculating the CO2 capture rate and the combustion efficiency as a function of the operating conditions. During the experimental campaign, the temperature in fuel reactor and the circulation rate of the oxygen carrier were varied. In general, CO2 capture rates close to 100% were obtained, which increased with temperature. In addition, high values of combustion efficiency were obtained. When the combustion was incomplete, the major unburnt compounds from the fuel reactor were H2, CO and CH4. Likely, these unburnt gases could proceed from the volatile matter as a high conversion of char would be expected. Interestingly, the amount of tar detected was low and they do not contribute significantly to the combustion efficiency., This work presents an overview of the recent advances in bio-CLC technology within the key strategies arising nowadays to mitigate climate change. The Paris Agreement, the new treaty of the United Nations Framework Convention on Climate Change (UNFCCC), urges to decarbonize the world energy systems in the near future in order to limit the increase in the average world temperature to 2ºC above pre-industrial levels. To reach this goal, CO2 emissions should start to decrease by 2020 and become negative by the end of the century. Among the different options, most of the low-carbon scenarios rely on the use of BECCS (Bioenergy and Carbon Capture and Storage) as mandatory technologies to reach negative emissions. In this sense, Chemical Looping Combustion (CLC) is considered one of the most promising CCS technologies for power plants and industries because its inherent CO2 capture avoids the energetic penalty present in other competing technologies. CLC process is based on the use of a solid oxygen carrier to transfer the oxygen from air to the fuel avoiding direct contact between them. The technology has undergone a great development during last 15 years including operational experience in continuous units and oxygen carrier’s manufacture. In addition, the new Chemical Looping with Oxygen Uncoupling (CLOU) process represents a qualitative step forward in solid fuel combustion due to the use of materials with capability to release oxygen. There are several renewable energy sources that can be used in chemical looping processes, including both solid and liquid fuels. The use of biomass in CLC represents important advantages compared to conventional biomass combustion. Besides CO2 negative balance, higher thermal efficiency, NOx formation reduction and lower corrosion in heat exchangers have been reported. In addition, several renewable liquid fuels, such as bioethanol can be also used both in combustion (CLC) and reforming (CLR) processes for heat/electricity and syngas/H2 production, respectively. In summary, the use of renewable fuels in chemical looping processes represents at this moment a very promising opportunity for future green energy development.

Environmental protection and specifically Climate Change, has been become a global problem not only of social responsibility but also an obstacle for economic growth and development. The 5th Assessment Report of the International Panel on Climate Change (IPCC) and the 2015 Paris Agreement conclude it is needed to reduce the Greenhouse Gasses (GHG) emissions and even to develop carbon Negative Emission Technologies (NETs) to limit the global average temperature increase to 2 ºC during the present century. The energy sector is considered as one of the major contributors to anthropogenic CO2 emissions. Capture and Storage (CCS) technologies are an interesting technological option to reduce CO2 emissions from these punctual large emitters. The combination of CCS technologies with thefact that CO2 emissions from biomass combustion are considered neutral opens the possibility to Bio-Energy with Carbon Capture and Storage (BECCS), a recently proposed alternative among NETs. BECCS development wouldcontribute to achieve Paris Agreement objectives on atmospheric GHG concentrations. Chemical Looping Combustion (CLC) has been studied during the last decades as a promising capture technology due to the low cost of CO2 capture and its low energy penaltyassociated [1]. This technology allows the combustion in a N2-free atmosphere. The oxygen is transferred to the fuel by a solid Oxygen Carrier (OC) circulating between two fluidized bed reactors. In the fuel reactor the fuel is oxidized and an almost pure CO2 stream generated. In the air reactor, the oxygen carrier is regenerated in air. The objective of this work is to analyze the feasibility of the CLC with biomass as a BECCS technology. For that purpose, three biomass residues (pine sawdust, olive stone and almond shell) were evaluated between 900-1000ºC in a continuous 500 Wth unit operating under In situ Gasification-Chemical Looping Combustion (iG-CLC) mode at Instituto de Carboquímica (ICB-CSIC, Spain) withlow-cost oxygen carriers.

47 Figuras,11 Tablas.-- Título del postprint: Review and assessment of experimental results from Chemical Looping Combustion units burning solid fuels.-- © 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Chemical Looping Combustion (CLC) has arisen during last years as a very promising combustion technology for power plants and industrial applications, with inherent CO2 capture which reduces the energy penalty imposed on other competing technologies. The use of solid fuels in CLC has been highly developed in the last decade and currently stands at a technical readiness level (TRL) of 6. In this paper, experience gained during CLC operation in continuous units is reviewed and appraised, focusing mainly on technical and environmental issues relating to the use of solid fuels. Up to now, more than 2700 h of operational experience has been reported in 19 pilot plants ranging from 0.5 kWth to 4 MWth. When designing a CLC unit of solid fuels, the preferred configuration for the scale-up is a two circulating fluidized beds (CFB) system. Coal has been the most commonly used solid fuel in CLC, but biomass has recently emerged as a very promising option to achieve negative emissions using bioenergy with carbon dioxide capture and storage (BECCS). Mostly low cost iron and manganese materials have been used as oxygen carriers in the so called in-situ gasification CLC (iG-CLC). The development of Chemical Looping with Oxygen Uncoupling (CLOU) makes a qualitative step forward in the solid fuel combustion, due to the use of materials able to release oxygen. The performance and environmental issues of CLC of solid fuels is evaluated here. Regarding environmental aspects, the pollutant emissions (SO2, NOx, etc.) released into the atmosphere from the air reactor are no cause of concern for the environment. However, the presence of SO2, NOx and Hg at the exit of the fuel reactor affects CO2 quality, which must be taken into account during the later compression and purification stages. The effect of the main variables affecting CLC performance is evaluated for fuel conversion, CO2 capture rate, and combustion efficiency obtained in different CLC units. Solid fuel conversion is normally not complete during operation, due to the undesired loss of char. A methodology is presented to extrapolate the current information to what could be expected in a larger CLC system. CO2 capture near 100% has been reported using a highly efficient carbon stripper, highly reactive fuels (such as lignites and biomass, etc.) or by the CLOU process. Operational experience in iG-CLC has showed that it is not possible to reach complete fuel combustion, making an additional oxygen polishing step necessary. For the further scale-up, it is essential to reduce the unburnt compounds at the fuel reactor outlet. Proposals to achieve this reduction already exist and include both improvement to the gas-oxygen carrier contact, or new design concepts based on the current scheme for iG-CLC. In addition, CLOU based on copper materials has shown that complete fuel combustion could be achieved. Main challenges for the future development and scale-up of CLC technology have been also identified. A breakthrough in the future development of CLC technology for solid fuels will come from developing long-life materials for CLOU that are easy to recover from the ash purge stream., This work was supported by the Spanish Ministry of Economy and Competitiveness (projects ENE 2013-45454-R, ENE2014-56857-R and ENE2016-77982-R), by the European Regional Development Fund (ERDF), by the CSIC (projects 2014-80E101 and 201780E035) and by the Government of Aragón (Spain, Ref. T06). T. Mendiara gives thanks for the Ramón y Cajal post-doctoral contract awarded by the Spanish Ministry of Economy and Competitiveness.

11 Figuras, 2 Tablas.-- Material suplementario disponible en línea en la página web del editor.-- © 2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Among the different Carbon Capture and Storage (CCS) technologies being developed in the last decades, Chemical Looping Combustion (CLC) stands out since it allows inherent CO2 capture. In the CLC process, there is a solid oxygen carrier circulating between two reactors in a cycle that allows providing the oxygen needed for combustion. In one of the reactors, named as fuel reactor, the fuel is introduced and combusted while the oxygen carrier reduction takes place. In the second reactor, named air reactor, the oxygen carrier is reoxidized in air. Different materials based on copper, nickel and iron oxides have been proposed as oxygen carriers for the CLC process. This work presents an environmental evaluation of the CLC process for natural gas based on Life Cycle Assessment (LCA). Five different oxygen carrier materials already tested in pilot plants were considered and the results compared to the conventional natural gas combustion in a gas turbine in a combined cycle without and with CO2 capture using postcombustion capture with amines. In view of the results, lower impact of the CLC process compared to the base case is expected without and with CO2 capture. The influence of several variables on the results was considered, such as temperature in the air reactor, lifetime of the oxygen carrier and possibility of recuperation of the depleted oxygen carrier. The nickel-based oxygen carriers were identified as the most adequate to be used in natural gas combustion. However, due to their toxicity, several analyses were also performed in order to identify improvements in the known oxygen carriers that can qualify them to replace nickel-based materials., This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) [grant numbers ENE2017-89473-R, ENE2016-77982-R] and the European Regional Development Fund (ERDF) under the program “Programa Operativo FEDER Aragón 2014-2020 - Construyendo Europa desde Aragón. Proyecto BiosinCO2 (LMP180_18)”. T. Mendiara thanks for the ‘‘Ramón y Cajal’’ post-doctoral contract awarded by MINECO.

15 Figures, 11 Tables.-- © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, In order to limit the increase in the global average temperature to 2 °C or below, the Paris Agreement proposed the reduction of CO2 emissions throughout this century. Bioenergy with CO2 capture and storage (BECCS) technologies represent an interesting option in order to allow this goal to be metgoal, because they are able to achieve negative CO2 emissions. Chemical looping (CL) is recognized as one of the most innovative CO2 capture technologies owing to its low energy penalty. CL processes permit the utilization of renewable fuels in a nitrogen-free atmosphere, given that the required oxygen is supplied by solid oxygen carriers. The present work presents an overview of the status of development of the use of biofuels in chemical looping technologies, including chemical looping combustion (CLC) and chemical looping with oxygen uncoupling (CLOU) for the production of heat/electricity, as well as chemical looping reforming (CLR), chemical looping gasification (CLG) and chemical looping coupled with water splitting (CLWS) for syngas/H2 generation. The main milestones in the development of such processes are shown, and the future trends and opportunities for CL technology with biofuels are discussed., This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness (projects ENE2014-56857-R, ENE2016-77982-R, and ENE2017-89473-R), the European Regional Development Fund (ERDF), the Spanish National Research Council -CSIC- (201780E035) and the Regional Government of Aragón (T05_17R). T. Mendiara is grateful for the “Ramón y Cajal” post-doctoral contract awarded by MINEICO.

15 Figures, 11 Tables.-- © 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ In order to limit the increase in the global average temperature to 2 °C or below, the Paris Agreement proposed the reduction of CO2 emissions throughout this century. Bioenergy with CO2 capture and storage (BECCS) technologies represent an interesting option in order to allow this goal to be metgoal, because they are able to achieve negative CO2 emissions. Chemical looping (CL) is recognized as one of the most innovative CO2 capture technologies owing to its low energy penalty. CL processes permit the utilization of renewable fuels in a nitrogen-free atmosphere, given that the required oxygen is supplied by solid oxygen carriers. The present work presents an overview of the status of development of the use of biofuels in chemical looping technologies, including chemical looping combustion (CLC) and chemical looping with oxygen uncoupling (CLOU) for the production of heat/electricity, as well as chemical looping reforming (CLR), chemical looping gasification (CLG) and chemical looping coupled with water splitting (CLWS) for syngas/H2 generation. The main milestones in the development of such processes are shown, and the future trends and opportunities for CL technology with biofuels are discussed. This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness (projects ENE2014-56857-R, ENE2016-77982-R, and ENE2017-89473-R), the European Regional Development Fund (ERDF), the Spanish National Research Council -CSIC- (201780E035) and the Regional Government of Aragón (T05_17R). T. Mendiara is grateful for the “Ramón y Cajal” post-doctoral contract awarded by MINEICO.

© 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Chemical looping combustion (CLC) involves the use of a solid oxygen carrier to transport the oxygen from the air to a fuel. Attention has recently been focused on oxygen carriers based on Mn-Fe mixed oxides because they are cheap materials that are able to release oxygen at high temperature, the so-called oxygen uncoupling step. The aim of this work was to assess the use of (Mn0.77Fe0.23)2O3 material as an oxygen carrier with the ability to transport oxygen both by reduction with gaseous fuels and by oxygen uncoupling, i.e. typical mechanisms in CLC and in Chemical Looping with Oxygen Uncoupling (CLOU), respectively. The particles prepared by mechanical mixing were screened to obtain particles of sufficient reactivity and mechanical strength for use in a fluidized bed reactor. The preparation methodology and calcining temperature were varied. The reactivity of one selected material was evaluated by performing redox cycles both in a TGA and a batch fluidized-bed reactor. Thus, its behaviour was assessed during both decomposition-regeneration of bixbyite phase [(Mn0.77Fe0.23)2O3] in CLOU and the reduction-oxidation of spinel phase [(Mn0.77Fe0.23)3O4] with gaseous fuels, i.e. H2, CO and CH4. Its oxygen uncoupling and re-oxidation capability was highly influenced by the reaction temperature and oxygen concentration. On the other hand, CLC redox cycles with gaseous fuels showed high reactivity with H2 and CO and high oxygen transport capacity by reduction to mangano-wüstite phase [(Mn0.77Fe0.23)O]. Good fluid-dynamic behaviour was observed for the oxygen carrier particles along the redox cycles without agglomeration problems, regardless of the operating conditions used in the batch fluidized-bed reactor. Thus, the selected material was considered a promising candidate for use in both in CLC with syngas and CLC with coal., This work was partially supported by the Spanish Ministry for Economy and Competitiveness via the ENE2013-45454-R, ENE2014-56857-R and ENE2016-77982-R projects, by the European Regional Development Fund (ERDF), and by the Spanish National Research Council (CSIC) via the 2014-80E101 project. R. Pérez-Vega is grateful to MICINN for the FPI Fellowship.

4 Figuras.- 1 Tabla, [EN] Today’s society is increasingly aware of the reality of climate change and the need to reduce greenhouse gas emissions into the atmosphere. The recent Paris Agreement aims to prevent the average temperature of the earth from rising by more than 2 °C by the end of the century. The CO2 capture and storage (CCS) is according to all forecasts one of the technologies needed to achieve this goal. In this sense, Chemical Looping is considered as one of the most promising CO2 capture technology from the economic point of view. Its great versatility allows the realization of a large number of combinations that includes both Chemical Looping Combustion (CLC) processes for heat or electricity production, and Chemical Looping Reforming, for H2 production with CO2capture or syngas production to be used in chemical applications. It also allows the use of different types of fuel including gaseous (natural gas, syngas, etc.), liquids (diesel, oils, bioethanol, etc.) or solids (coal, biomass, etc.). This paper shows the current state and main future research lines regarding Chemical Looping technology., [ES] La sociedad actual está cada vez más concienciada sobre la realidad del cambio climático y sobre la necesidad de reducir las emisiones de gases de efecto invernadero a la atmósfera. El reciente Acuerdo de París trata de impedir que la temperatura media de la tierra aumente más de 2 ºC a finales de siglo. La captura y almacenamiento de CO2 es según todas la previsiones una de las tecnologías para alcanzar dicho objetivo. En este sentido, la tecnología de Chemical Looping aplicada a la captura de CO2 se plantea como una de las más ventajosas desde el punto de vista económico. Su gran versatilidad permite la realización de un gran número de combinaciones que abarcan tanto procesos de combustión (Chemical Looping Combustion) para la producción de calor o electricidad, como de reformado (Chemical Looping Reforming), para la producción de H2 con captura de CO2 o de gas de síntesis para diferentes aplicaciones. Asimismo permite la utilización de diferentes tipos de combustibles tanto en forma de gas (gas natural, gas de síntesis, etc.), líquidos (gasóleo, aceites, bioetanol, etc.) o en forma sólida (carbón, biomasa, etc.). En este trabajo se muestra el estado actual y las principales líneas de evolución de la tecnología de Chemical Looping en los diferentes ámbitos., Este trabajo ha sido financiado por el Ministerio de Economía y Competitividad (proyecto ENE2014-56857-R), por el Fondo Europeo de Desarrollo Regional, por el CSIC (proyecto 201780E035) y por el Gobierno de Aragón (Ref. T06).

4 Figuras.- 1 Tabla [EN] Today’s society is increasingly aware of the reality of climate change and the need to reduce greenhouse gas emissions into the atmosphere. The recent Paris Agreement aims to prevent the average temperature of the earth from rising by more than 2 °C by the end of the century. The CO2 capture and storage (CCS) is according to all forecasts one of the technologies needed to achieve this goal. In this sense, Chemical Looping is considered as one of the most promising CO2 capture technology from the economic point of view. Its great versatility allows the realization of a large number of combinations that includes both Chemical Looping Combustion (CLC) processes for heat or electricity production, and Chemical Looping Reforming, for H2 production with CO2capture or syngas production to be used in chemical applications. It also allows the use of different types of fuel including gaseous (natural gas, syngas, etc.), liquids (diesel, oils, bioethanol, etc.) or solids (coal, biomass, etc.). This paper shows the current state and main future research lines regarding Chemical Looping technology. [ES] La sociedad actual está cada vez más concienciada sobre la realidad del cambio climático y sobre la necesidad de reducir las emisiones de gases de efecto invernadero a la atmósfera. El reciente Acuerdo de París trata de impedir que la temperatura media de la tierra aumente más de 2 ºC a finales de siglo. La captura y almacenamiento de CO2 es según todas la previsiones una de las tecnologías para alcanzar dicho objetivo. En este sentido, la tecnología de Chemical Looping aplicada a la captura de CO2 se plantea como una de las más ventajosas desde el punto de vista económico. Su gran versatilidad permite la realización de un gran número de combinaciones que abarcan tanto procesos de combustión (Chemical Looping Combustion) para la producción de calor o electricidad, como de reformado (Chemical Looping Reforming), para la producción de H2 con captura de CO2 o de gas de síntesis para diferentes aplicaciones. Asimismo permite la utilización de diferentes tipos de combustibles tanto en forma de gas (gas natural, gas de síntesis, etc.), líquidos (gasóleo, aceites, bioetanol, etc.) o en forma sólida (carbón, biomasa, etc.). En este trabajo se muestra el estado actual y las principales líneas de evolución de la tecnología de Chemical Looping en los diferentes ámbitos. Este trabajo ha sido financiado por el Ministerio de Economía y Competitividad (proyecto ENE2014-56857-R), por el Fondo Europeo de Desarrollo Regional, por el CSIC (proyecto 201780E035) y por el Gobierno de Aragón (Ref. T06).

© 2016. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, One of the most important current objectives of the Chemical Looping Combustion (CLC) technology for gaseous fuels lies in scaling-up the aforementioned technology in the short term from 100 kWth to 10 MWth scale. In order to meet this challenge, the commercial availability of suitable multi ton-scale oxygen carrier materials at competitive price is needed. In this work, a Cu-based oxygen carrier prepared by the impregnation method using a commercial alumina as support, referred as Cu14γAl_Commercial, has been developed and evaluated in a 500 Wth CLC pilot plant during the combustion of CH4 at two different temperatures, i.e., 800 °C and 900 °C. The outstanding results obtained in terms of both combustion efficiency and mechanical stability have shown that the Cu14γAl_Commercial impregnated oxygen carrier can be selected to upscale CLC technology for gaseous fuels., The work presented in this article is partially funded by the Spanish Ministry of Economy and Competitiveness (ENE 2014-56857-R), by the European Regional Development Fund (ERDF), and by the European Commission Seventh Framework Programme under the grant agreement No. 608571 (Project acronym SUCCESS). A. Abad and A. Cabello thank CSIC for the financial support given to the project 201480E101.

Autothermal Chemical-Looping Reforming (a-CLR) is a process which allows hydrogen production avoiding the environmental penalty of CO2 emission typically produced in other processes. The major advantage of this technology is that the heat needed for syngas production is generated by the process itself. This heat necessary for the endothermic reactions is supplied by a Ni-based oxygen-carrier (OC) circulating between two reactors: the air reactor (AR), where the OC is oxidized by air, and the fuel reactor (FR), where the fuel is converted to syngas. Other important advantage is that this process also allows the production of pure N2 in the AR outlet stream. A renewable fuel such as bioethanol was chosen in this work due to their increasing worldwide production and the current excess of this fuel presented by different countries. In this work, mass and heat balances were done to determine the auto-thermal conditions that maximize H2 production, assuming that the product gas was in thermodynamic equilibrium. Three different types of bioethanol has been considered according to their ethanol purity; Dehydrated ethanol (≈100 vol.%), hydrated ethanol (≈96 vol.%), and diluted ethanol (≈52 vol.%). It has been observed that the higher H2 production (4.62 mol of H2 per mol of EtOH) has been obtained with the use of diluted ethanol and the surplus energy needed could be compensated by the energy save achieved during the purification of ethanol in the production process., This work is partially supported by the Spanish Ministry for Science and Innovation (MICINN project ENE2011-26354), by European Regional Development Fund (ERDF), by the Government of Aragón (Spain, DGA ref. T06) and by CTGAS-ER (project OTT20130989).

Among the different pollutant gases released from oxy-coal combustion, mercury is the responsible for important operational issues in the CO2 processing unit, being able to cause material corrosion. Some studies concerning the fate of mercury during oxy-coal combustion are referred to pulverized coal (PC) boilers. However, the fate of mercury emissions in fluidized bed (FB) combustors has yet to be elucidated. In this work, mercury emissions from a 3 kWth bubbling FB combustor operating under oxy-fuel combustion conditions have been evaluated. For this purpose, two Spanish Ca-based sorbents and two Spanish coals were used. The effects of type of Ca-based sorbent, the Ca/S molar ratio, temperature and recycled gases (NO, SO2 and H2O) typical in oxy-fuel combustion process on the distribution of mercury species have been analyzed. It was observed that the presence of Ca-based sorbents in the combustor favored mercury fixation as particle-bound mercury which exhibited a maximum at a temperature about 925 °C corresponding to the highest degree of limestone sulfation. SO2 recirculation inhibited the Hg0 oxidation and thus the mercury fixation as particle-bound mercury decreased. However, neither NO nor steam recirculation affected mercury speciation., This work has been supported by The Spanish Ministry of Science and Innovation (MICINN, Projects: CTQ2008-05399/PPQ, ENE2011-23412) and the European Regional Development Fund (ERDF). M. de las Obras-Loscertales thanks to MICINN for the F.P.I. fellowship.

The use of a renewable liquid fuel, such as ethanol, in a Chemical Looping Combustion (CLC) process, in the context of carbon capture and sequestration (CCS) technologies can lead to carbon negative power system. This work presents experimental results obtained in a continuously operating CLC unit (1 kWth) using ethanol as fuel during more than 100 h. Complete ethanol conversion was reached under all operating conditions. The combustion efficiency as a function of the oxygen carrier to ethanol ratio was determined for four oxygen carriers: Cu14–γAl, Ni21–γAl, Ni18–αAl and Fe20–γAl. The oxygen carriers were prepared by impregnation on γ- and α-Al2O3. The performance of these materials was evaluated on the basis of their reactivity with ethanol and its intermediate gaseous products. The suitability of the use of the oxygen carriers was finally decided by taking into account oxygen transport capacity and hydrodynamic criteria. Cu14–γAl and Ni18–αAl fulfill all the requirements to successfully conduct a CLC process and almost 100% CO2 capture efficiency was obtained. On the contrary, the Ni21–γAl oxygen carrier was discarded due to the low reactivity of the spinel NiAl2O4 at normal operating conditions. Iron-based materials are suitable for the CLC process, although higher Fe-content or higher operating temperatures (≈950 °C) would be necessary to make use of the Fe20–γAl material feasible., This work partially supported by the Spanish Ministry for Science and Innovation (MICINN project ENE2011-26354) and the European Regional Development Fund (ERDF). A. Serrano also thanks the Spanish Ministry of Economy and Competitiveness for the F.P.I fellowship.

The use of Ca-based sorbents in circulating fluidized beds (CFB) allows the in-situ desulfurization in oxy-fuel combustion processes. The sulfation process involves important changes in the sorbent morphology, which could vary depending on the operating conditions and be different to those observed in conventional air combustion. This work analyzes the morphological variations observed during limestone and dolomite sulfation at typical oxy-fuel combustion conditions (high CO2 concentration, higher temperatures than in air combustion) in CFB combustors (long reaction times). Sulfated samples prepared in a thermogravimetric analyzer were analyzed by Scanning Electron Microscope (SEM). The space limitations due to the higher molar volume of CaSO4 compared to CaO in the external surface of the particles make that the CaSO4 product layer trend to grow outwards to form a honeycomb-shaped structure. This structure appeared for limestone at both calcining and non-calcining conditions. A strong effect of the CaSO4 sintering phenomenon was observed at temperatures above 950 °C. Moreover, the honeycomb structure was never observed working with dolomite in spite of the high sulfation conversions reached with this sorbent., This work has been supported by The Spanish Ministry of Science and Innovation (MICINN, Project: CTQ2008-05399/PPQ) and by the European Regional Development Fund (ERDF). M. de las Obras-Loscertales thanks to MICINN for the F.P.I. fellowship and A. Rufas to CSIC for the JAE fellowship.

21st World Hydrogen Energy Conference (WHEC), Zaragoza, SPAIN, JUN 13-16, 2016, The autothermal Chemical-Looping Reforming (a-CLR) is a process where syngas is produced with two main advantages; there are captured CO2 emissions and the heat required for the syngas production is generated by the process itself. A Ni-based material is used as oxygen carrier circulating between two fluidized bed reactors: the fuel and air reactors. In this work, the auto-thermal conditions in a global H2 production process, integrated by the a-CLR process and a Water Gas Shift reactor, using different liquid fossil fuels were theoretically determined. The hydrogen production per mol of carbon in the fuel was similar for all fossil fuels, taking a value of 2.2 at the optimal operating temperature (700 °C). In addition, the possibility of working at low temperature for a maximum H2 production was experimentally demonstrated in a continuous 1 kWth a-CLR unit., This work is partially supported by the Spanish Ministry for Science and Innovation (MICINN project ENE2011-26354), by European Regional Development Fund (ERDF) and by the Government of Aragón (Spain, DGA ref. T06).

© 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Finding suitable low-cost materials to be used as oxygen carrier in Chemical Looping Combustion (CLC) of coal is a key issue to achieve the CO2 capture at low economic cost. Recently, a Mn-ore from Gabon has been identified as an alternative to the state of the art of oxygen carriers based on minerals or wastes with high iron content. This Mn-ore showed a high reactivity and a long particle lifetime during batch characterization to be considered as a suitable oxygen carrier. To evaluate the potential of this material in CLC, this work analyses the behaviour of the Mn-ore during continuous combustion of a bituminous coal in a 0.5 kWth CLC unit. The CLC process was evaluated and the effect of the main operating variables - such as fluidizing medium, oxygen carrier circulation rate, temperature, and solids inventory in the fuel reactor - on the combustion efficiency and CO2 capture was investigated. A direct relation between the char conversion rate and the CO2 capture is given, being mainly affected by the mean residence time of solids and temperature in the fuel reactor. The use of a carbon separation system with separation efficiency above 90% would be required to achieve CO2 capture rates higher than 95%. Total oxygen demand values as low as 4.5% were found when optimal operating conditions were selected, mainly being related to oxygen carrier to fuel ration higher than ϕ > 3. At these conditions, the Mn-ore material showed similar combustion efficiencies than other Fe-based low-cost materials previously tested, but with higher CO2 capture rates., This work was partially supported by the Ministry of Economy, Industry and Competitiveness via ENE2014-56857-R, ENE2016-77982-R and CSIC-2017-80E035 projects, and the European Regional Development Fund (ERDF). J.A. Bueno thanks for the FPI Fellowship. T. Mendiara thanks for the ‘‘Ramón y Cajal’’ post-doctoral contract.

© 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Chemical looping combustion (CLC) is a low-cost CO2 capture technology with a low energy penalty. Bio-energy with CO2 capture and storage (BECCS) opens up the possibility for negative CO2 emissions involving the removal of CO2 already emitted into the atmosphere. The oxygen needed for combustion in CLC processes is supplied by a solid oxygen carrier circulating between the fuel reactor and the air reactor. In this work, the combustion of different types of biomass, such as pine sawdust, olive stones and almond shells, was studied in a continuous 1.5 kWth CLC unit. A mixed Cu-Mn oxide was used as the oxygen carrier. This material releases gaseous oxygen when reduced, resulting in Chemical looping combustion with oxygen uncoupling (CLOU). The released oxygen reacts with both the volatiles and char generated inside the fuel reactor when biomass is fed into it. The oxygen carrier is reoxidized in air inside the air reactor. High CO2 capture and 100% combustion efficiencies were achieved with this Cu-Mn oxygen carrier. The oxygen concentration inside the air reactor did not affect CO2 capture efficiency under the studied conditions., This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO Project: ENE2014-56857-R) and European Regional Development Fund (ERDF) funds. T. Mendiara is grateful for the ‘‘Ramón y Cajal’’ post-doctoral contract awarded by MINECO. I. Adánez-Rubio acknowledges the MINECO and University of Zaragoza (UZ) for the post-doctoral grant awarded (FJCI-2015-23862). A. Pérez-Astray thanks MINECO for the BES-2015-074651 pre-doctoral fellowship co-financed by the European Social Fund.

1 figure.-- Work presented at the Carbon 2018 ´"The World Conference of Carbon", Madrid (Spain), 01st-6th July, According to the IPCC, warming of the climate system is unequivocal and this is mainly consequence of the increase in the CO2 concentration in the atmosphere. In addition, “Human influence on the climate system is clear, and recent anthropogenic emissions of greenhouse gases are the highest in history”. These emissions are mainly consequence of the burning of C-fuels, mostly fossil fuels, which result in a net increase in carbon concentration in the atmosphere, soil and oceans. In fact, the natural carbon cycle in the earth is being affected. Limiting climate change would require substantial and sustained reductions in greenhouse gas emissions. The measures considered for the reduction of CO2 emissions to the atmosphere include the improvement in the use and generation of energy, the use of nuclear energy, the boost of energy generation from renewable sources and the CO2 capture and storage (CCS)., This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness (projects ENE2014-56857-R, ENE2016-77982-R, and ENE2017-89473-R), by the European Regional Development Fund (ERDF), by the CSIC (201780E035), and by the Government of Aragón. T. Mendiara thanks for the “Ramón y Cajal” post-doctoral contract awarded by MINEICO.

© 2018. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Synthetic manganese-iron mixed oxides are considered promising materials to be used as oxygen carriers for Chemical Looping Combustion of coal with carbon dioxide capture at low cost. The aim of this work was to evaluate a manganese-iron mixed oxide material with a manganese to iron molar ratio of 0.77:0.23 as oxygen carrier for coal combustion by means of chemical looping processes, including both ex-situ and in-situ gasification of coal. The preparation method -spray drying followed by calcination- was optimized in order to produce particles with high reactivity and mechanical strength. The material was studied in two continuously operated facilities designed to burn either gaseous or solid fuels. While full combustion was achieved burning syngas, showing the feasibility of the use of this material considering the ex-situ gasification process. Coal combustion efficiency by in-situ gasification process was improved in comparison with other previously tested low-cost materials such as ilmenite and iron ore. Moreover, the oxygen carrier particles showed an interesting magnetic behavior that was able to facilitate oxygen carrier recovery from the purge ash stream. In view of these results, the manganese-iron mixed oxide as oxygen carrier is proposed as a promising candidate for use coal combustion by the chemical looping process., This work was partially supported by the Spanish Ministry for Economy, Industry and Competitiveness (MINECO Projects: ENE2014-56857-R and ENE2016-77982-R projects), by the European Regional Development Fund (ERDF) and by the Spanish National Research Council (CSIC) via the 2015-80E100 and 2017-80E035 projects. The authors also thank Ing. Konrad Holscher from “Mina Invierno” (Chile) for providing the subbituminous coal used in this work.

© 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, The Chemical Looping with Oxygen Uncoupling (CLOU) process is a form of Chemical Looping Combustion (CLC) technology that enables the combustion of solid fuels by means of oxygen carriers that release gaseous oxygen in the fuel reactor, i.e. with oxygen uncoupling capability. In recent years, tests have found several Cu-based, Mn-based and mixed oxide oxygen carriers with suitable properties for the CLOU process. Among them, Cu-Mn mixed oxides show high reactivity and high O2 equilibrium concentration at temperatures of interest for coal combustion. In this work, proof of concept was demonstrated by burning coal with Cu-Mn mixed oxides in a 1.5 kWth CLOU unit for the first time. The effect of fuel reactor temperature, solids circulation flow, fluidization agent in the fuel reactor (inert N2 or steam as gasifying agent), and excess air in the air reactor on combustion efficiency and CO2 capture rate was analysed. The results showed that high combustion efficiency and CO2 capture are feasible using this material at relatively low fuel reactor operating temperatures. Therefore, the developed Cu-Mn mixed oxide was a suitable material for use as an oxygen carrier for the CLOU combustion of solid fuels. Optimum operating conditions were determined for this oxygen carrier with regard to the oxygen circulation rate and air reactor conditions for the regeneration of the oxygen carrier., This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO Project: ENE2013-45454-R, ENE2014-56857-R and ENE2016-77982-R) and the European Union FEDER funds. Our thanks to Ing. Konrad Holscher from Mina Invierno Chile, for supplying the subbituminous coal.

A Chemical Looping Combustion (CLC) unit for solid fuels has been designed, erected and operated. The design was based on a thermal power of 20 kWth for in-situ Gasification Chemical Looping Combustion (iG-CLC) or 50 kWth for Chemical Looping with Oxygen Uncoupling (CLOU). Fuel and air reactors are two interconnected circulating fluidized beds reactors, with the coal being fed at the bottom of the fuel reactor to maximize the contact between the volatile matter and the oxygen carrier particles. A carbon stripper has been included between fuel and air reactors to increase the CO2 capture rates. In this unit, the char particles are separated from the oxygen carrier particles and recirculated to the fuel reactor. The solids flow exiting from the fuel reactor is split into two different streams by using a double loop seal down the fuel reactor cyclone. One goes to the carbon stripper and the other is recirculated to the fuel reactor. In this way it is possible to have an independent control of solids inventory in the fuel reactor and the global solid circulation flow rate between fuel and air reactors. First operational results at steady state have been obtained with stable operation in iG-CLC mode during combustion of a bituminous coal with ilmenite being the oxygen carrier. A CO2 capture value of 88% at 991 ºC and a total oxygen demand value of 8.5% were obtained with a solids inventory in the fuel reactor of 470 kg/MWth., This work was supported by the Spanish Ministry for Science and Innovation (Project ENE2013-45454-R). R. Pérez-Vega thanks for the FPI Fellowship.

Emissions from coal oxy-fuel combustion are receiving significant attention during the last years. This paper is focused on the analysis of fuel-N emissions in fluidized bed combustion systems. Experiments were carried out in a bubbling fluidized bed unit in the temperature interval 850-950ºC. Different coals (anthracite, bituminous and lignite) were used as fuels and different sorbents were employed for in-bed sulphur retention. In the experiments, NO, N2O and NO2 were measured. NO2 was not detected in any of the operating conditions. The influence of temperature on NO and N2O emissions was the same as in conventional combustion: NO emission increased as temperature increased while N2O emission decreased. Nevertheless, the total fuel-N conversion to nitrogenous species seemed to be lower than in combustion with air. As in air-firing combustion, the highest levels of NO and N2O were registered with the highest rank coals. The Ca-sorbent was found to have a key role on NO reduction via catalytic reaction and this catalytic effect seemed not to be affected by the high CO2 levels present in oxy-fuel combustion. Also, the moisture content in the coal affected the NO formation, which decreased 2 with an increase in the coal moisture content. A similar effect was observed by increasing the oxygen concentration fed to the combustor., The authors thank the Spanish Ministry for Science and Innovation, MICCIN, (CTQ2008- 05399/PPQ) and the Government of Aragón, DGA, (PI023/08) for the financial support. This work was also partially supported by FEDER funds. M. de las Obras-Loscertales thanks 16 MICCIN for the FPI grant awarded and T. Mendiara for the “Ramón y Cajal” post-doctoral contract awarded by the Ministry of Economy and Competitiveness, MINECO.

Work presented at the 13th International Conference on Greenhouse Gas Control Technologies, GHGT-13, 14-18 November 2016, Lausanne, Switzerland., The present work accomplishes a screening of the performance of Mn-Fe-Ti based oxygen carriers, prepared with different Mn/(Mn+Fe) molar ratios in the general formula (MnyFe1-y)Ti0.15Ox. The oxygen carriers were prepared by physical mixing followed by pelletizing under pressure, calcining, crushing and sieving in the 100-300 μm particle size interval. The characterization of the carriers is based on the evaluation of their crushing strength, magnetic properties and reduction and oxidation behavior through TGA experiments at temperatures suitable for the CLC process (i.e. 850-950 °C). In addition, the main chemical structures of the Mn-Fe-Ti system were identified as a function of the Mn/(Mn+Fe) molar ratio. Oxygen uncoupling property was analyzed by reduction under a N2 atmosphere and the capability to interact with fuel gases was analyzed by using CH4, H2 and CO. Results indicate that the (MnyFe1-y)Ti0.15Ox oxygen carriers with Mn/(Mn+Fe) molar ratios of 0.55-0.87 have very promising properties for the CLC process with solid fuels., This work was partially supported by the Spanish Ministry for Economy and competitiveness via the ENE-2013-45454-R project, by the European Regional Development Fund (ERDF) and by the CSIC via the 2014-80E101 project. M. Abian acknowledges the MINECO and Instituto de Carboquimica (ICB-CSIC) for the post-doctoral grant awarded (FPDI-2013-16172)

© 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, The integrated use of low-value hydrocarbons from the refining of crude oil under Chemical Looping Combustion (CLC) conditions can satisfy the demands of heat and steam of the refining process itself while at the same time reducing CO2 emissions up to 50% in oil refineries. This work evaluated the use of three different fossil liquid fuels, i.e., diesel, mineral lubricant oil and synthetic lubricant oil in a 1 kWth CLC continuous unit working with a Fe-based oxygen carrier prepared by impregnation method. The effect of key parameters of the CLC process behavior was studied with the same batch of oxygen carrier particles for a total of 150 operation hours. With regard to the results obtained, every fuel tested was able to achieve 90% combustion efficiency being synthetic lubricant oil the most reactive fuel studied. Hydrocarbon reactivity seems to depend on the nature of the chemical bonds, being higher for alkenes (synthetic lubricant oil) than for alkanes (diesel and mineral lubricant oil). CH4 was revealed as a relatively stable intermediate combustion product for these liquid fuels. Therefore, oxygen carrier’s reactivity towards this gas becomes crucial for the overall conversion. The characterization carried out to the oxygen carrier after operation revealed no evidence of changes derived from the sulphur or impurities present in the fuel. Therefore, the Fe-based material herein used seems to be suitable for conversion of fossil liquid fuels., This work is partially supported by the Spanish Ministry for Science and Innovation (MICINN project ENE2011-26354), by European Regional Development (ERDF), and by the Government of Aragón (Spain, DGA ref. T06). A Serrano thanks the Spanish Ministry of Economy and Competitiveness for the F.P.I fellowship.

© 2017. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/, Mixed oxides of Mn-Fe have been identified as suitable materials for Chemical Looping Combustion (CLC) with solid fuels both via in-situ Gasification Chemical Looping Combustion (iG-CLC) and Chemical Looping with Oxygen Uncoupling (CLOU) processes. These materials show the property of react with gaseous fuels as well as release oxygen under given conditions, while cheap metals are used. In addition, these materials can show magnetic properties that can be used for an easy separation from ash in CLC with solid fuels. Thus, losses of oxygen carrier material in the ash drain stream would be reduced. Different cations have been proposed for improving the magnetic properties of manganese ferrites, including Ti4+. In this context, the present work accomplishes a screening of (MnxFe1−x)2O3 doped with 7 wt.% TiO2, with x ranging from 0 to 1. The influence of Mn:Fe ratio on their physical and chemical properties was evaluated. In general, particles with high crushing strength values (>4 N) were obtained, and magnetic characteristics were highlighted when x ⩽ 0.66. The oxygen uncoupling capability depended on the Mn:Fe ratio and the oxidation conditions, i.e. temperature and oxygen partial pressure. Broader oxidation conditions to take advantage of the oxygen uncoupling capability were found for materials with low Mn content. On contrary, the reactivity with fuel gases (CH4, H2 and CO) increased with the Mn content. Thus, oxygen carriers with Mn/(Mn + Fe) molar ratio in the 0.5–0.9 interval showed interesting properties at suitable temperatures for the iG-CLC and CLOU processes (i.e. 850–980 °C). The material with Mn/(Mn + Fe) = 0.55 was preferred considering a trade-off between reactivity and magnetic properties., This work was partially supported by the Spanish Ministry for Economy and Competitiveness via the ENE2013-45454-R and ENE2014-56857-R projects, by the European Regional Development Fund (ERDF), and by the CSIC via the 2014-80E101 project. M. Abián acknowledges the MINECO and Instituto de Carboquímica (ICB-CSIC) for the post-doctoral grant awarded (FPDI-2013-16172).

Sour gas represents about 43% of the world's natural gas reserves. The sustainable use of this fossil fuel energy entails the application of CO2 Capture and Storage (CCS) technologies. The Chemical Looping Combustion (CLC) technology can join the exploitation of the energy potential of the sour gas and the CO2 capture process in a single step without the need of a sweetening pre-treatment unit. In this work, a total of 60 h of continuous operation with sour gas and H2S concentrations up to 15 vol% has been carried out in a 500 Wth CLC unit, from which 40 corresponded to a Cu-based oxygen carrier (Cu14γAl) and 20 to a Fe-based material (Fe20γAl). This is the first time that so high H2S concentrations are present in a fuel to be burnt in a CLC process. The Cu14γAl oxygen carrier seems to be not recommendable for the combustion of sour gas because, although all the H2S is burnt to SO2, copper sulfides were formed at all combustion conditions. In contrast, the Fe20γAl oxygen carrier presented an excellent behavior with no agglomeration problems and maintaining the reactivity of the fresh material. The sour gas (CH4, H2 and H2S) was completely burnt, and neither SO2 was released in the AR nor iron sulfides were formed at usual CLC operating conditions. These tests demonstrated the possibility to use sour gas in a CLC process with 100% CO2 capture without any SO2 emissions to the atmosphere., This work has been financed by Shell Global Solutions International B.V. within the frame of the agreement PT22648 signed between Shell Global Solutions International B.V. and Instituto de Carboquímica—Consejo Superior de Investigaciones Científicas (ICB—CSIC).

3 figures.-- Talk delivered in the IEA GHG, 3rd Oxyfuel Combustion Conference, Ponferrada (Spain), 6th -13th september 2013., The success of a Chemical-Looping Combustion (CLC) system for coal combustion is greatly affected by the performance of the fuel reactor. When coal is gasified in-situ in the fuel reactor, several parameters affect to the coal conversion, and hence to capture and combustion efficiencies. In this work a mathematical model for the fuel reactor is validated against experimental results obtained in a 100 kWth CLC unit when reactor temperature, solids circulation flow rate or solids inventory are varied. The validated model can be used to evaluate the relevance of operating conditions on process efficiency., This work was partialy supported by the European Commission, under the RFCS program (ECLAIR Project, Contract RFC-PP-07011), Alstom Power Boilers, and the Spanish Ministry for Science and Innovation via the ENE2010-19550 project.

10 pages, 5 figures, 4 tables., The behavior of a Ni-based oxygen carrier with low NiO content (11.8wt.% NiO) prepared by impregnation on CaAl2O4 has been studied in a continuous CLC unit (500Wth) using different gases as fuels (methane, H2, CO, syngas, ethane and propane). More than 90h of successfully operation at high temperature (1173K) have been carried out analyzing the effect of the oxygen carrier-to-fuel ratio and fuel gas composition regarding combustion efficiency and product gas distribution. Using syngas, pure CO or H2 as fuels, full combustion can be achieved working at oxygen carrier-to-fuel ratios, φ, higher than 1.2. Regarding methane, the maximum fuel combustion efficiency is reached in a narrow range of φ values close to 1 (1.0-1.2). An increase in the value of this parameter produces a decrease in the combustion efficiency. This behavior is different to that found using most of the Ni-based oxygen carriers present in literature, and can be attributed to the low global catalytic activity of the reduced oxygen carrier for reforming reactions. When light hydrocarbons are used as fuels, the oxygen carrier presents a similar behavior than in the case of methane combustion tests, reaching to the maximum fuel combustion efficiency at the same φ values. This fact also indicates that light hydrocarbons combustion mechanism is carried out through cracking reaction. The solids inventory needed to obtain a methane combustion efficiency of 99% is lower than 180kg/MWth, which corresponds to a metallic Ni inventory around 17kg/MWth. This value is the lowest referred in the literature for any kind of Ni-based oxygen carrier. This remarkable result is due to the low NiO content (11.8wt.%) and the very high reactivity of this oxygen carrier because all nickel in the particle is present as free NiO, since the formation of less reactive nickel compounds is avoided using CaAl2O4 as inert support., This paper is based on the work performed in the frame of the INNOCUOUS (Innovative Oxygen Carriers Uplifting Chemical- Looping Combustion) Project, funded by the European Commission under the seventh Framework Programme (Contract 241401). P. Gayán thanks to CSIC for the financial support of the project 201180E102.

The interest in the use of solid fuels such as coal in Chemical Looping Combustion is growing because of the benefits of the direct use of coal in this technology on the reduction of the costs linked to carbon dioxide capture. In CLC, the oxygen needed for the combustion is supplied by a solid oxygen carrier therefore avoiding the direct contact between fuel and air. Focusing on the use of solid fuels in the In-Situ Gasification Chemical Looping Combustion (iG-CLC), the oxygen carrier is mixed with the coal in the fuel reactor, where gasification of the coal and reaction of the gasification products with the oxygen carrier particles takes place. In this process, the possible loss of oxygen carrier together with the ashes makes it interesting to find inexpensive materials to be used as carriers, such as natural minerals or industrial residues. In this work, an Fe-based bauxite waste is used as oxygen carrier in the combustion of different types of coal. Experiments were performed in a TGA and a batch fluidized bed (FB) using both coal and char from the corresponding coal. The influence of temperature as well as the gasifying agent composition on the performance of coal conversion in an iG-CLC process was evaluated. Tests in a thermogravimetric analyzer (TGA) revealed direct char combustion by oxygen in the bauxite waste material, but no evidences of such direct combustion were found in the experiments in the batch fluidized bed. In this case, gasification of char by H2O or CO2 was found as a necessary step in char conversion. Using steam as gasifying agent, higher char gasification rates were observed than using CO2 and in all conditions lignite presented the highest char gasification rate. At 980ºC, the lignite char gasification rate in CO2 doubled the value obtained with anthracite using steam, indicating that recirculated CO2 can be fed to the fuel reactor of a CLC system if lignite is used as fuel. For the rest of the fuels, it was possible to use a mixture of H2O and CO2 as gasifying agent without decreasing the feasibility of the iG-CLC process. The bauxite 3 waste was able to burn the gaseous products generated during the gasification of the different types of coal with high combustion efficiencies., The authors thank the Spanish Ministry for Science and Innovation for the financial support via the ENE2010-19550 project. T. Mendiara thanks for the “Juan de la Cierva” post-doctoral contract awarded by this Ministry.

5 figures, 3 tables.-- Work presented at the GHGT-11, 11th International Conference on Greenhouse Gas Control Technologies, 18-22 November 2012, Kyoto, Japan., Chemical-Looping Combustion, CLC, is one of the most promising processes to capture CO2 at a low cost. It is based on the transfer of the oxygen from air to the fuel by using a solid oxygen carrier that circulates between two interconnected fluidized-bed reactors: fuel and air reactors. The CO2 capture is inherent to this process, as the air does not get mixed with the fuel. In this work two options are evaluated in a 1 kWth continuously operated unit for coal fueled Chemical-Looping. The first one is the gasification of coal in the fuel reactor –in-situ Gasification Chemical- Looping Combustion (iG-CLC)–. Ilmenite or a bauxite waste material is used as oxygen carrier. The second one is the combustion of coal in the fuel reactor by using oxygen carriers which release gaseous oxygen –Chemical-Looping with Oxygen Uncoupling (CLOU)–. A Cu-based material is used in this mode. Coals ranging from anthracite to lignite were used. Complete combustion was always reached in CLOU mode, whereas unburnt compounds were present in iG-CLC. Both in iG-CLC and CLOU processes the CO2 capture increased with temperature and decreased with the coal rank. The highest CO2 capture rate was obtained for lignite, being 93% for iG-CLC and 99% for CLOU, even without a carbon separation system. The key aspects for the good performance of iG-CLC and CLOU processes are analyzed through the performance results obtained with different coals, This work was partially supported by the European Commission, under the RFCS program ECLAIR Project, Contract RFCP-CT-2008-0008), ALSTOM Power Boilers (France) and the Spanish Ministry of Science and Innovation (PN,ENE2010-19550)

11 pages, 8 figures, 4 tables, In order to compare potential oxygen carriers for the iG-CLC with coal a methodology was developed from results obtained in a batch fluidized reactor. The methodology is based on the solids inventory in the fuel reactor. The solids inventory values will be used for comparison purposes among different materials rather than for design purposes. In a companion paper, experiments with different types of Fe-based oxygen carriers were presented. Based on these experimental results, the present paper proposes two theoretical approaches for a fast evaluation of different materials as potential oxygen carriers for the iG-CLC process with different fuels. The methodology is focused on the study of the gasification of the char generated in the process after the devolatilization of the corresponding solid fuel and the subsequent combustion of the gasification products. Considering the results of carbon capture and combustion efficiency, the adequacy of the material can be evaluated. Four different Fe-based materials are tested in this work: ilmenite, bauxite waste, a mineral based on hematite, and a synthetic material. Based on the results obtained, the bauxite waste and the hematite mineral present the best performance for iG-CLC. As a rough estimation, an inventory around 1600 kg/MWth will be needed using any of the above materials to achieve carbon captures above 0.93 and combustion efficiencies of 0.99 at 1000 °C., This work was supported by the Spanish Ministry of Science and Innovation (Project ENE2010-19550) and DGA and La Caixa (Project 2012 GALC 076). T. Mendiara thanks for the “Juan de la Cierva” postdoctoral contract awarded by this Ministry. A. Cuadrat thanks CSIC for the JAE Pre. Fellowship. The authors also thank Alcoa Europe-Alúmina Española S.A. for providing the bauxite waste used in this work and PROMINDSA for providing the mineral based on hematite.