• Energy Research

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. Peer reviewed

The conceptual design of a 100 MWth unit for coal combustion with CO2 capture by in-situ Gasification Chemical Looping Combustion (iG-CLC) was done. Ilmenite was considered the oxygen carrier and a highly reactive sub-bituminous coal was the fuel. The main components of the iG-CLC unit were a fuel reactor, a carbon stripper and an air reactor. Mass and enthalpy balances were performed to determine the solids circulation flow rate, temperature of the reactors, steam and air requirements, and heat duty of heat exchangers. Fluid dynamics considerations and cyclones sizes were taken into account for the conceptual design and the dimensioning of these devices. In addition, optimized operating conditions obtained with a mathematical model were considered in the design procedure. Then, the performance of the iG-CLC unit was estimated with the model. Some benefits were identified when recirculated CO2 was used to fluidize the carbon stripper and fuel reactor, regarding both fuel reactor performance and energy integration of the iG-CLC system. Thus, a CO2 capture value of 95% with a carbon stripper with 98% efficiency and an oxygen demand in exit gases from the fuel reactor of 7% was predicted with a solids inventory in the fuel reactor of 750 kg/MWth. Moreover, the energy penalty related to steam generation was minimized when H2O was replaced by CO2. Results presented in this work can be used to estimate the net efficiency of the plant in future works. This work was partially supported by the Spanish Ministry for Science and Innovation (MICINN project ENE2011-26354 and ENE2013-45454-R), the European Regional Development Fund (ERDF), and by Shell Global Solutions International BV (Contract PT26961). Peer reviewed

13 pages, 13 figures, 3 tables. Chemical looping combustion (CLC) is considered a promising technology for CO2 capture and sequestration (CCS), since the CO2 generated during the combustion process of a gaseous fuel is inherently separated. Recently, perovskite-type particles based on Mn have been investigated for use as oxygen carrier materials in CLC processes. These materials present some advantageous characteristics, in comparison with metal oxides, such as reduced cost, environmentally friendly behavior, and the oxygen uncoupling effect. In this sense, the objective of this study was to assess the performance of the CaMn0.9Mg0.1O3-δ perovskite as an oxygen carrier.. The influence of different parameters such as the solids inventory, oxygen carrier-to-fuel ratio (φ), operational time, and sulfur content of fuel on CH4 combustion efficiency, was studied in a continuous 500-Wth CLC unit. In addition, the evolution of oxygen carrier reactivity, mechanical integrity, and agglomeration behavior, relative to operating time, was analyzed. When combustion tests were carried out without sulfur addition, it was observed that a very high excess of oxygen over the stoichiometric conditions (φ > 11) was needed to reach full CH 4 conversion. Under these conditions, the oxygen uncoupling effect was relevant to fully convert the fuel, and some O2 appeared at the outlet of the fuel reactor with concentrations close to 1 vol %. The presence of H2S in the fuel gas produced the deactivation of the oxygen carrier in terms of an important decrease in the reactivity and oxygen uncoupling capacity, resulting in a relevant drop in the combustion efficiency, decreasing from full combustion to 72% after 17 h of operation with H2S addition. Moreover, the presence of H2S caused an unstable circulation of solids, because of agglomeration problems. Therefore, in order to use this reactive oxygen carrier with H2S-containing fuels in future CLC industrial plants, it would be necessary to fully desulfurize them due to the high sensitivity to sulfur poisoning of this material. © 2014 American Chemical Society. 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 No. 241401). Peer Reviewed

7 Figures, 3 Tables Greenhouse gas emissions, especially CO2, formed by combustion of fossil fuels, highly contribute to the global warming problem. Chemical-Looping Combustion (CLC) has emerged as a promising option for CO2 capture because this gas is inherently separated from the other flue gas components and thus no energy is expended for the separation. This technology would have some advantages if it could be adapted for its use with coal as fuel. In this sense, a process integrated by coal gasification and CLC could be used in power plants with low energy penalty for CO2 capture. This work presents the combustion results obtained with a Ni-based oxygen carrier prepared by impregnation in a CLC plant under continuous operation using syngas as fuel. The effect on the Manuscript Click here to view linked References oxygen carrier behaviour and the combustion efficiency of several operating conditions was determined in a continuous CLC plant. High combustion efficiencies (~99%), close to the values limited by thermodynamic, were reached at oxygen carrier-to-fuel ratios higher than 5. The temperature in the FR has a significant influence, although high efficiencies were obtained even at 1073 K. The syngas composition has small effect on combustion, obtaining high and similar efficiencies with syngas fuels of different composition, even in presence of high CO concentrations. The low reactivity of the oxygen carrier with CO seems to indicate that the water gas shift reaction acts an intermediate step in the global reaction of the syngas in a continuous CLC plant. No agglomeration or carbon deposition problems were detected during 50 hours of continuous operation in the prototype. The obtained results showed that the impregnated Ni-based oxygen carrier could be used in a CLC plant for syngas combustion produced in an Integrated Gasification Combined Cycle (IGCC). This research was conducted with financial support from the Spanish Ministry of Education and Science (Projects No. CTQ2004-04034 and CTQ2007-64400). C. Dueso thanks MEC for a F.P.I. fellowship. Peer reviewed

9 figures, 5 tables. In the framework of the EU H2020 CLARA project, jet biofuel production via Fischer-Tropsch synthesis is intended from syngas generated by Biomass Chemical Looping Gasification (BCLG). BCLG is based on the lattice oxygen transference between a solid oxygen carrier and the biofuel to energetically support the biomass gasification. This process produces low tar and nitrogen-free syngas under autothermal conditions, and at the same time includes an intrinsic separation of carbon compounds from nitrogen in air, avoiding future carbon capture costs. This work evaluates the syngas production from pine forest residue (PFR) through the BCLG process with ilmenite as the oxygen carrier. The effects of several key operating variables, including temperature, oxygen-to-biomass ratio and mean residence time of solids, on the performance of the BCLG process were analyzed at 20 kWth scale. The syngas yield depended on the oxygen-to-biomass ratio and improved with the char conversion in the fuel reactor. Temperature and mean residence time of solids in the fuel reactor were identified as the primary factors affecting char conversion. A dedicated study was performed to assess the impact of the biomass size on char conversion, as well as the relevance of a carbon stripper unit on the improvement on char gasification due to its role either as a secondary gasifier or as a char-oxygen carrier separator. Higher char conversion values were achieved with the lowest biomass particle size (1–2 mm vs. pellets 6 mm Ø) due to lower restrictions to gas diffusion inside the particles. The carbon stripper may act as a secondary gasifier, thus improving the char conversion, but it was not able to take away the unconverted char particles from ilmenite in any case due to it was designed for powdered fuels. Besides, the generation of light hydrocarbons was hardly affected by any operating variables. The tar content remained below 4.5 g/kg dry biomass. The ilmenite showed a good performance during the continuous operation without signs of defluidization. This work was conducted in the CLARA project (Chemical Looping gAsification foR sustainAble production of biofuels), which is funded by the European Union's Horizon 2020 - Research and Innovation Framework Programme under grant agreement No 817841. Peer reviewed

15 páginas, 20 figuras, 4 tablas. Chemical-Looping Combustion (CLC) is a combustion technology with inherent separation of the greenhouse gas CO2. CLC is considered to be an option with low energy penalty and low cost for CO2 capture. An option for use CLC with solid fuels is the in-situ Gasification-CLC (iG-CLC), where the solid fuel gasification and the oxidation of gaseous products, i.e. volatile matter and gasification products, simultaneously take place in the fuel reactor of the CLC system. The objective of this work was to optimize the operating conditions for direct CLC with solid fuels using ilmenite as oxygen carrier. A simplified model for the fuel reactor has been developed, which describes the complex processes happening in the fuel reactor. Thus, the effect of the main operating variables in the iG-CLC process can be analyzed in a simpler way than using a detailed model. The model includes the possibility of using a carbon separation system to recirculate unreacted char particles exiting from the fuel reactor, reducing the by-pass of carbon to the air reactor. Also, the gasification kinetics of a bituminous coal for both H2O and CO2 as gasification agents and the kinetics of the reduction reaction of ilmenite with H2, CO and CH4 are incorporated to the model. First, the simulated results have been compared to experimental results from tests performed in a continuous 500Wth CLC plant. Later, model simulations were performed to evaluate the effect of the main operating variables of the fuel reactor (e.g. temperature, solids inventory, efficiency of the carbon separation system, oxygen carrier to fuel ratio, or flow and type of gasification agent) on the combustion and carbon capture efficiencies. The carbon capture was directly related to the extent of gasification, which is promoted by increasing the temperature or the residence time of char particles in the fuel reactor. It is highly beneficial to increase the solids inventory up to 1000 kg/MWth, but further increase does not give a relevant improvement in the carbon capture and it is better to increase the carbon separation efficiency than the solids inventory. With an inventory of 1000 kg/MWth, at 1000ºC and a carbon separation efficiency of 90% the carbon capture predicted was 86.0%. This work was partially supported by the Spanish Ministry of Science and Innovation (Project ENE2010-19550). A. Cuadrat thanks CSIC for the JAE Pre. fellowship. Alberto Abad thanks to the Ministerio de Ciencia e Innovación for the financial support in the course of the I3 Program. Peer reviewed

Chemical-Looping Combustion of coal (CLCC) is a promising process to carry out coal combustion with carbon capture. The process should be optimized in order to maximize the carbon capture and the combustion efficiency in the fuel reactor, which will depend on the reactor design and the operational conditions. In this work, a mathematical model of the fuel reactor is used to make predictions about the performance of the CLCC process and simulate the behaviour of the system over different operating conditions. The mathematical model considers the fluid dynamic characteristics of the fuel reactor, being a high-velocity fluidized bed reactor. It also considers the chemical processes happening inside the reactor, and the effect of a carbon separation system on the char conversion in the process. A sensitivity analysis of the effect of the efficiency of the carbon separation system, the solids inventory in the fuel reactor, the temperature in the fuel reactor, ratios of oxygen carrier to fuel, oxygen carrier reactivity, coal reactivity and coal particle on the carbon capture and combustion efficiency is carried out. Also the relevance o 1 f the water–gas shift reaction (WGS) is evaluated. The most relevant parameters affecting the carbon capture are the fuel reactor temperature and the efficiency of the carbon separation system, CSS. A value for CSS as high as 98% should be necessary to reach a carbon capture efficiency of 98.6%. Regarding the combustion efficiency, to use highly reactive oxygen carrier materials are desirable. In any case, additional actions or a modified design for the fuel reactor should be implemented to reach complete combustion of coal. This work was partially supported by the European Commission, under the RFCS Program (ECLAIR Project, Contract RFCP-CT-2008-0008), and from Alstom Power Boilers. Peer reviewed

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. Peer reviewed