Search

The innovative Biomass Chemical Looping Gasification (BCLG) process uses two reactors (fuel and air reactors) to generate nitrogen-free syngas with low tar content under autothermal conditions. A solid oxygen carrier supplies the oxygen for partial oxidation of the fuel. This study investigated the BCLG process, conducted over 25 h of continuous operation at 20 kWth scale, using ilmenite as the oxygen carrier and wheat straw pellets as fuel (WSP). The effect of using torrefied wheat straw pellets (T-WSP) on the syngas quality was assessed. In addition, the impact of several operational variables on the overall process performance and syngas yield was analyzed. The primary factors influencing the syngas yield were the char conversion through gasification and the oxygen-to-fuel ratio. Higher temperatures, extended residence times of solids in the fuel reactor, and using a secondary gasifier led to increased char conversion, enhancing H2 and CO production. Optimizing the air reactor design could enhance the CO2 capture potential by inhibiting the combustion of bypassed char. While char conversion and syngas yield with T-WSP were lower than those with WSP at temperatures below 900 °C, T-WSP achieved a higher syngas yield under conditions favoring high char conversion. The presence of CH4 and light hydrocarbons showed minimal sensitivity to operating conditions variation, limiting the theoretical syngas yield. Overall, the CLG unit operated smoothly without any agglomeration issues.

Table S1: Numerical values of the EIIs for the processes of Case I. Table S2: Numerical values of the EIIs for the processes of Case II. Table S3: Numerical values of the EIIs for the processes of Case III.

Among the approaches to facilitating negative CO2 emissions is biochar production. Biochar is generated in the pyrolysis of certain biomasses. In the pyrolysis process, carbon in the biomass is turned into a solid, porous, carbon-rich, and stable material that can be captured from the soil after a period of from a few decades to several centuries. In addition to this long-term carbon sequestration role, biochar is also beneficial for soil performance as it helps to restore soil fertility and improves the retention and diffusion of water and nutrients. This work presents a Life Cycle Assessment of different pyrolysis approaches for biochar production. Biomass pyrolysis is performed in a fixed-bed reactor, which operates at a mild temperature (550 °C). Biochar is obtained as solid product of the pyrolysis, but there are also liquid (bio-oil) and gaseous products (syngas). The pyrolysis gas is partly used to fulfil the energy demand of the pyrolysis process, which is highly endothermic. In the conventional approach, CO2 is produced during the combustion of syngas and emitted to the atmosphere. Another approach to facilitate CO2 capture and thus obtain more negative CO2 emissions in the pyrolysis process is burning syngas and bio-oil in a Chemical Looping Combustion unit. Life Cycle Assessment was performed of these approaches toward biomass pyrolysis to evaluate their environmental impact. The Chemical Looping Combustion approach significantly reduced the values of 7 of the 16 environmental impact indicators studied, along with the Global Warming Potential among them, it slightly increased the value of one indicator related to the use of fossil resources, and it maintained the values of the remaining 8 indicators. Environmental impact reduction occurs due to the avoidance of CO2 and NOx emissions with Chemical Looping Combustion. The CO2 balances of the different pyrolysis approaches with Chemical Looping Combustion configurations were compared with a base case, which

Chemical Looping Gasification (CLG) has emerged recently as a promising technology for producing non N2-diluted syngas without the need for an external power supply or the expensive use of pure O2. Many studies have focused on development of oxygen carriers since they are considered a crucial factor in CLG processes. Fe2O3/Al2O3 (FeAl) oxygen carriers have been proposed due to previous experience in Chemical Looping Combustion (CLC). However, the aggressive conditions of gasification cause a decrease in the mechanical stability of the particles, which can be a challenge for their use in CLG. In this work, the operating conditions and Fe-content required to maintain the particle integrity of oxygen carrier particles during redox cycles in both CLC and CLG operations were determined. Long-term tests, consisting of 300 redox cycles, were conducted in a TGA to simulate the operation in a continuous unit and the results were compared with attrition data obtained from a 1.5 kWth CLG unit. Three oxygen carriers with varying Fe2O3-content (10, 20 and 25 wt%) were used, and three different solid conversions (0–25 %, 75–100 % and 0–100 %) were performed to emulate CLC or CLG atmospheres at three temperatures (850 °C, 900 °C and 950 °C). The evolution of the microstructure of particles was analyzed using a scanning electron microscope (SEM) and it was found that the lower the Fe2O3 content in the particles, the greater their stability in redox cycles, an increase in the reaction temperature led to a more rapid degradation of the oxygen carrier particles, and the solid conversion variation and degree of reduction/oxidation during redox cycles strongly influenced the evolution of the mechanical stability of the oxygen carrier particles.

Biogas is a renewable fuel generated in the anaerobic digestion of organic material. The expansion of biogas as a bioenergy source in the next decades leads to find new ways for its energy exploitation such as the Chemical Looping technologies. In this work, a low-cost Fe-based residue was used as oxygen carrier in two processes with biogas, namely Chemical Looping Combustion (CLC) and Chemical Looping Reforming (CLR). CLC process is focused on the energy production with CO2 capture. CLC experiments showed higher methane combustion efficiency (∼86%) than those referred in literature with other low-cost Fe-based materials. CLR process is dedicated to the production of syngas or hydrogen without CO2 emissions. Ni- or Cu-based oxygen carrier had been successfully used in order to catalyse the methane reforming. Here, the Fe-based material was also used for CLR. The biogas composition facilitated dry reforming of biogas to obtain syngas. In the dry-CLR of biogas, it was possible to reach about 55% methane conversion with a yield to syngas of 1.3 mol (CO + H2)/mol CH4. A suitable management of the effluent gas is proposed to maximize CH4 conversion and syngas yield, which includes CO2 separation, H2 purification and CH4 recirculation. Both results confirm the potential of the energy use of biogas under these technologies and the promising results with the new oxygen carrier developed.

The use of bio-ethanol in chemical looping combustion (CLC) and reforming (CLR) has the potential to produce energy and/or hydrogen and, as a negative-emissions technology (NET), to remove CO2 from the atmosphere at low cost following the principles of bio-energy with CO2 capture and storage (BECCS). The determination of the rate of the chemical processes involving the fuel conversion with the oxygen carrier is required for the modelling and design of a chemical looping unit. In this work, a kinetic study of ethanol conversion is performed considering a NiO-based material as the oxygen carrier. Combined experiments in TGA and fixed bed were conducted. TGA tests confirmed that the oxygen carrier was reduced by a ethanol-containing gaseous stream at temperatures higher than 773 K. An apparent reaction kinetics for the NiO reduction with ethanol was determined, which might be used in simplified fuel reactor models. However, tests performed in a fixed bed revealed that products derived of the ethanol decomposition, such as CH4, CO, H2 were responsible for NiO reduction, instead of the direct reduction with ethanol. High temperature kinetics of processes involved in ethanol conversion, namely dehydration, dehydrogenation and decomposition, were determined. Both, non-catalytic and Ni-catalytic reactions were of relevance under chemical looping conditions. A reaction pathway was described to be used in detailed fuel reactor models of chemical looping units.

La gasificación de biomasa mediante procesos de Chemical Looping (BCLG) permite la producción de gas de síntesis renovable que puede ser utilizado para la obtención de numerosos productos como diésel, gasolina, metanol o amoniaco. La tecnología BCLG se basa en el uso de un transportador sólido de oxígeno que circula entre dos lechos fluidizados interconectados, donde se produce de manera separada la gasificación de biomasa y la generación de energía requerida por la propia gasificación, obteniendo un gas de síntesis de alta pureza sin dilución en N2 y sin el uso de O2 puro. En este trabajo se estudió el efecto de cuatro transportadores de oxígeno sintéticos sobre la composición del gas de síntesis y la formación de alquitranes en una unidad BCLG de 1.5 kWt operando en continuo. Las partículas de transportador frescas y usadas se caracterizaron para determinar su vida útil.

El Pacto Verde de la UE prevé alcanzar la neutralidad climática en 2050. Esto significa una transición de los combustibles fósiles a las fuentes de energía renovables y de una economía basada en el carbono a una basada en el hidrógeno. Esto es muy importante para sectores que dependen de combustibles con alta densidad energética, como la aviación. La mejor solución a corto plazo es el uso de bio-queroseno, porque así la aviación continúa haciendo uso de la infraestructura actualmente existente, reduciéndose los costes de la transición [1]. Sin embargo, hoy en día, la producción de queroseno sintético adolece de una baja eficiencia de proceso y unos costes elevados. Para abordar este problema se propone la implementación de un nuevo proceso de Chemical Looping, CO2 Splitting (CO2SPLIT), para obtención de CO a partir de CO2 e H2 verde como ruta para la producción de biocombustibles a través del proceso de síntesis Fischer-Tropsch (F-T) [2]. El principio del proceso CO2SPLIT es similar al del proceso conocido como Chemical Looping Combustion (CLC) [3], pero el proceso CO2SPLIT utiliza tres reactores en lugar de dos. En el Reactor de Reducción (RR), el transportador de oxígeno (TO) se reduce con H2 verde. El TO reducido pasa al Reactor de CO2 (RC) donde es parcialmente oxidado con CO2, generándose CO que se utilizará en la relación H2/CO adecuada para el proceso F-T. Finalmente, en el Reactor de Oxidación (RO) el TO se oxida completamente con aire, quedando preparado para un nuevo ciclo. El reto dentro del proceso de CO2SPLIT es encontrar un transportador de oxígeno, que además de poseer buenas características físicas, como alta dureza mecánica, ha de poseer una elevada reactividad en las diferentes reacciones, dar una alta conversión y evitar la tendencia a la aglomeración. En este trabajo se han estudiado TOs basados en Fe.

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 co

One of the main advantages of chemical looping gasification (CLG) in comparison to conventional gasification technologies is its potential to enhance in situ tar removal. This is due to the catalytic properties of the oxygen carrier used in the CLG process, which can facilitate tar oxidation, cracking, and reforming reactions under specific operating conditions. Furthermore, this catalytic effect can be harnessed to convert hydrocarbons (C1–C3), thereby increasing syngas production during the process. In this study, the catalytic activity of eight different oxygen carriers (two ores, two wastes, and four synthetic materials) was examined in a batch fluidized bed reactor. The reactions were mainly conducted at three temperatures (850, 900, and 950 °C), utilizing benzene and ethylene as model compounds. The results revealed that the ores and wastes exhibited a low catalytic effect over benzene and ethylene conversion at low temperatures, although this effect was increased with a rising temperature. Conversely, the synthetic materials demonstrated higher catalytic activity in the benzene and ethylene conversion reactions, which also increased with higher temperatures. It should be noted that the Cu/Al oxygen carrier achieved nearly complete conversion of benzene and ethylene at temperatures exceeding 900 °C. Methane production was observed in most of the experiments, indicating its role as an intermediate in the conversion of tar byproducts. Additionally, the Cu/Al oxygen carrier exhibited a promising catalytic performance in methane conversion. These findings highlight the potential of certain synthetic oxygen carriers, such as the Cu/Al oxygen carrier, to serve as effective catalysts for the removal of tar byproducts and light hydrocarbons during CLG processes.

Other related processes such as chemical looping gasification (CLG) and reforming (CLR) were aimed to obtain high-quality syngas as a first step for biofuels production. The climate change on the planet because of the emission of greenhouse gases makes decision making urgent. To maintain the limit of 1.5°C of temperature increase as proposed in the Paris agreement, it is urgent to reduce greenhouse gas emissions. In all IPPC projections, carbon capture, use and storage (CCUS) is considered one of the essential technologies to achieve this objective. Within the range of possibilities of CO2 capture processes, chemical looping combustion (CLC) is considered one of the most promising technologies in the production of clean energy due to the low cost related to the process and its flexibility in terms of fuels. In addition, the use of renewable fuels opens the possibility of achieving negative CO2 emissions, one of the key points to get the decarbonization required by 2050.

Biomass Chemical Looping Gasification (BCLG) is an innovative process that uses lattice oxygen from a solid oxygen carrier to produce high-quality synthesis gas without CO2 emissions. It is well known that one of the main targets for the reduction of greenhouse gas emissions (GHG) is to replace the use of fossil fuels in the transport sector with renewable sources. In this work, the BCLG technology is used to obtain clean synthesis gas from biomass for the production of liquid biofuels through Fischer Tropsch (FT) synthesis. The BCLG process is based on the circulation of a solid oxygen carrier between two interconnected fluidized bed reactors, the fuel and air reactors, providing the oxygen needed for the partial oxidation of the biomass to generate a non-nitrogen diluted syngas with low tar content. Also, the oxygen carrier is responsible for transporting the heat required for the endothermic reactions occurring in the fuel reactor from the heat generated in the exothermic reactions occurring in the air reactor, thus reaching autothermal conditions. In addition, negative emissions could be achieved by combining this technology with CO2 storage since biomass is a carbon-neutral fuel. The experimental campaign of this work was carried out in a BCLG unit at 18 kWth power during 60 hours of continuous operation with ilmenite as oxygen carrier and wheat straw pellets as fuel. The main factors affecting the syngas production was the oxygen-to-biomass ratio and char conversion. Increasing temperature showed a considerable effect on the char conversion in the fuel reactor since caused an increase in the gasification rate; also, the char conversion was affected by the mean residence time in the fuel reactor. The existing carbon stripper in the CLG unit did not show the ability to separate the unconverted char entrained from the fuel reactor since char still retained its initial pellet form. However, carbon stripper behaves as a secondary gasifier when using steam as fluidi

The principle of chemical looping has by now mainly been used for the combustion of fuels, i.e. chemical looping combustion (CLC). However, limited work has been done with respect to chemical looping gasification (CLG) of biomass in continuous operation, especially at a large scale. The main advantage of CLG compared to the most common oxygen-driven gasification technologies is the avoidance of an expensive and energy-consuming Air Separation Unit (ASU), which significantly reduces the total investment and the electricity consumption of converting biomass to syngas. In CLG, the produced CO2 is obtained in the concentrated form together with the syngas leaving the fuel reactor, meaning that CO2 can be removed with low energy penalty and subsequently stored in geological formations. When using biomass, storage of CO2 could result in the removal of CO2 from the atmosphere, thus leading to net negative CO2 emissions of the entire process chain for biofuel production. In addition, in comparison to normal indirect gasification, no fuel is used in the air/combustion reactor, meaning that high-temperature corrosion should be avoided to a large extent. Finally, oxygen carrier particles may provide catalytic sites for hydrocarbons, thus enhancing syngas production and suppressing tar formation. The objectives of the EU-financed H2020 project “CLARA” are to develop and test a concept for the gasification of biomass residues with the production of FT-diesel. CLG is the gasification technology which is utilized for syngas production. The main research with respect to CLG development is carried out at Chalmers University of Technology (CTH), Sweden and Consejo Superior de Investigaciones Científicas (CSIC), Spain. The work combines studies in small fixed and fluidized bed units where important results can be reached, with moderate efforts and larger units providing additional key results of industrial relevance. As the final aim is to use CLG at a commercial scale for the product

Chemical Looping Combustion (CLC) is a low-cost CO2 capture technology highly competitive for industrial and energy applications. Up to date, CLC has been mostly developed at atmospheric pressure. Pressurized CLC may bring additional advantages due to the intensification of the process. The main objective of this work was to determine whether an increase in the operating pressure could improve the fuel conversion in CLC systems of gaseous fuels when ilmenite was used as oxygen carrier. Fluid dynamics considerations were evaluated to determine a window of suitable design parameters at pressurized conditions. A theoretical model previously validated at atmospheric pressure was modified to consider fluid dynamics and reaction kinetics at pressurized conditions, both in the bubbling and turbulent regimes, using ilmenite as oxygen carrier. The conversion of natural gas was estimated as a function of several design and operating parameters, such as the gas velocity, particle size and reacting temperature. Uncompleted combustion of natural gas was predicted at atmospheric conditions, and a limited improvement was estimated at pressurized conditions. A discussion about the required reactivity of the oxygen carrier to achieve complete combustion was performed. Furthermore, an energy analysis of a CLC system operating at atmospheric or pressurized (0.5 MPa) conditions with fuel reactor designed under the bubbling or turbulent regimes was carried out using the Aspen HYSYS process simulation software for two different applications of heat generation: production of domestic hot water and process steam. From this energy balance, it could be concluded that the energy efficiency achieved at pressurized conditions was slightly higher than that obtained at atmospheric pressure, essentially because at pressurized conditions it was possible to use the latent heat of condensation of the water generated in the fuel reactor. In addition to the results obtained in this work, a thorough ass

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.

A major challenge in biomass chemical looping gasification (BCLG) is the conversion of CH4 and light hydrocarbons to syngas (CO + H2) when the goal is the use for bioliquid fuel production. In this work, tests were performed in a batch fluidized bed reactor to determine the catalytic effect on the CH4 reforming reaction of oxygen carriers used in the BCLG process. Three ores (ilmenite, MnGB, and Tierga), one waste (LD slag), and five synthetic materials (Fe10Al, Fe20Al, Fe25Al, Cu14Al, and Ni18Al) were analyzed. These results were compared to those obtained during ∼300 h of continuous biomass gasification operation in a 1.5 kWth BCLG unit. The low-cost materials (ores and waste) did not show any catalytic effect in the CH4 reforming reaction, and as a consequence, the CH4 concentration values measured in the syngas produced in the continuous prototype were high. The synthetic oxygen carriers showed a catalytic effect in the CH4 reforming reaction, increasing this effect with increasing temperature. With the exception of the Ni-based oxygen carrier (used as a reference), the Cu-based oxygen carrier, working at 940 °C, showed the best catalytic properties, in good agreement with the low CH4 concentration values measured in the syngas generated in the continuous unit. The tests performed in a batch fluidized bed reactor were demonstrated to be very useful in determining the catalytic capacity of oxygen carriers in the CH4 reforming reaction. This fact is highly relevant when a syngas with a low CH4 content is desired as a final product.

Una de las opciones más relevantes para la reducción de emisiones de gases de efecto invernadero (GEI) en el sector del transporte es la producción de bio-combustibles sintéticos a partir de gas de síntesis. El proceso Biomass Chemical Looping Gasification (BCLG) es una prometedora opción para producir gas de síntesis de alta calidad mediante la gasificación de biomasa sin emisiones de CO2. En el proceso BCLG un transportador sólido de oxígeno (TO) circula entre dos reactores de lecho fluidizado interconectados, reactor de combustible (RC) y reactor de aire (RA), proporcionanado el oxígeno y el calor necesario para llevar a cabo la oxidación parcial de la biomasa obteniendo un gas de síntesis libre de nitrógeno bajo condiciones autotérmicas. En el RC se produce la gasificación de la biomasa y la combustión parcial de los gases producto con los sólidos, mientras que en el RA se regenera el TO en atmósfera de aire. El objetivo de este trabajo es investigar el efecto de las principales variables operacionales sobre el comportamiento y el rendimiento a gas de síntesis del proceso BCLG en una unidad en continuo de 50 kWt, utilizando ilmenita como TO.

The objective of this work was to assess the suitability of a synthetic Cu-based oxygen carrier in a continuous pilot plant for the production of blue and green hydrogen through the autothermal Chemical Looping Reforming (CLRa). In CLRa, methane is converted to a H2 + CO mixture through partial oxidation and reforming reactions in the fuel reactor. The degree of the partial oxidation of methane was defined by controlling the oxygen flow in the air reactor. Steam was used as reforming gas in natural gas to produce blue H2, but the existing CO2 in biogas was the reforming gas to produce green H2. Operating at 950 °C in the fuel and air reactors, CH4 conversion and H2 yield parameters were 96 % and 2.60 mol of H2 per mole of CH4, respectively. These experimental results were close to the theoretical values that could be achieved in the CLRa process. Furthermore, the physicochemical characterization of the samples extracted from the pilot plant throughout the experimental campaign revealed that the Cu-based oxygen carrier maintained its mechanical integrity and chemical stability under harsh operating conditions. Therefore, it can be concluded that Cu-based oxygen carriers can be considered a promising alternative to Ni-based materials for the production of blue and green hydrogen through the CLRa process.

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.

In this work, the Biomass Chemical Looping Gasification (BCLG) process was evaluated for syngas production at the 20 kWth scale using wheat straw pellets as the fuel feedstock and ilmenite as the oxygen carrier. The effect of different operational variables –namely the fuel reactor temperature, the mean residence time of solids in the fuel reactor, the oxygen-to-biomass ratio (controlled by the oxygen fed into the air reactor) and the gas velocity in the carbon stripper– on the process performance and the syngas yield was analyzed. Interestingly, smooth operation of the CLG unit was observed and no agglomeration issues detected. In addition, char produced during devolatilization still retained its initial pellet shape and unconverted char pellets were elutriated from the fuel reactor mixed with the finer oxygen carrier particles. Both steady-state and transition periods were evaluated to have a complete overview of the process. Transition periods were characterized by a different oxygen transfer rate in the air and fuel reactors. Steady state was reached when the oxygen transference rate was the same in both reactors. In this sense, the oxygen transference rate in the fuel reactor was the main factor affecting the syngas yield and the cold gas efficiency. Also, the temperature and mean residence time of solids in the fuel reactor showed a considerable effect on the char conversion and, consequently, on the syngas yield. However, operating conditions hardly affected the production of light hydrocarbons (CH4 and C2-C3) and tar, which were maintained roughly constant throughout the experimental campaign.

Six iron and manganese ores and one by-product from the steel industry was preselected as oxygen carriers for chemical looping gasification (CLG). The selected oxygen carriers have been evaluated at different scales at CTH and CSIC to develop a comprehensive understanding and establish a portfolio of suitable oxygen carriers for CLG. After pre evaluation step in Task 3.1, five oxygen carrier selected for continuous operation in Task 3.3. The selected oxygen carriers from prescreening were Ilmenite, Tierga, LD slag, Elwaleed B, and Moanda. In Task 3.3 a total of 600 hours of continuous CLG operation has been done in 10 kWth reactor at CTH and 1.5 kWth reactor at CSIC. After a vast experimental evaluation at CTH and CSIC, it has been confirmed that using oxygen carrier in CLG has a positive effect on gasification of biomass by reducing tar formation, increasing syngas yield, biomass conversion and H2/CO ratio compare to conventional steam gasification using sand as a bed material. Among the tested oxygen carriers, Ilmenite and LD slag show better biomass gasification performance compared to Mn ores (Elwaleed B and Moanda) and Tierga ore. LD slag has a lower lifetime than ilmenite and needs heat pretreatment, but a slightly higher syngas yield and H2/CO. Therefore, ilmenite has been selected for Task 3.5 and the final demonstration at TUDA (WP5), considering the operational performance, availability of the material at multi-ton scale, lifetime and pretreatments required for the material prior to CLG operation.

Biomass Chemical Looping Gasification (BCLG) is a promising route to obtain N2 free high purity syngas. In this work, heat and mass balances were solved to determine the auto-thermal operation conditions that maximize the syngas yield in a BCLG system. A Fe-based oxygen carrier and pine wood as fuel were considered for the simulation. Two methods to control the transference of oxygen between the air reactor (AR) and fuel reactor (FR) were analysed. Syngas yield was higher controlling the oxygen fed to the AR by the air flow (OCM-1) than controlling the oxygen supplied to the FR by the oxygen carrier circulation flow (OCM-2). The influence of different operating parameters, such as oxygen carrier transport capacity, preheating of gases fed to the system, steam/biomass ratio, fuel reactor temperature, was also analysed. It is noteworthy that working with OCM-2 it is necessary to optimize the amount of active phase in synthetic oxygen carriers or to dilute the natural oxygen carriers (ores, wastes) with an inert material to maintain realistic temperature difference values between reactors. Therefore, it is recommended to operate with the OCM-1 as it has the advantages of a more flexible operation and the possibility of obtaining pure N2.

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.

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.

Limestone Chemical Looping Combustion process (LCL-C™) patented by Alstom Power Inc. proposes the formation of a CaSO4 oxygen carrier via sulfur retention process when supplying a Ca-based sorbent together with sulfurous fuels in the fuel reactor. In the present research work, four Ca-based sorbents, three limestones and one dolomite with different physico-chemical characteristics, have been evaluated as oxygen carrier precursors during consecutive redox cycles by thermogravimetric analysis. 5% H2 and 3000 vppm H2S (N2 to balance) and 10% O2 (N2 to balance) were selected as reducing and oxidizing gases, respectively. Additionally, an anhydrite ore has also been studied for comparison purpose. Results from SEM-EDX characterization of the sorbent particles revealed the existence of three different sulfation patterns: (1) uniform distribution, (2) core–shell structure and (3) high sulfur content with high limitation to be converted into CaSO4. All sorbents exhibited high oxygen transport capacity (Roc = 13.3–20.8%), except for the material showing pattern (3) (Roc = 2.6%). Likewise, the materials presented high reactivity with rate index values ranged between 11.0 and 18.8%/min. Therefore, the Ca-based sorbents herein assessed can be considered suitable precursors for the formation of CaSO4 based oxygen carriers to be used in CLC systems burning sulfurous fuels.

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 attrition behaviour of several promising oxygen carriers tested in Chemical Looping Combustion (CLC) units has been evaluated using an air-jet apparatus based on ASTM D5757 at 20 and 800 °C. Results were evaluated to determine a general testing procedure that allows estimating the adequacy at working temperature of a potential oxygen carrier. For both fresh and used oxygen carriers, attrition was lower when the temperature of the Air Jet attrition Index (AJI) test was increased. Thus, tests with potential oxygen carriers must be performed close to the temperature they are planned to be used to obtain reliable information. Results indicated that used oxygen carriers with AJI value at hot conditions between 1 and 2% showed long lifetimes under continuous CLC operation.

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.

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.

Negative Emission Technologies (NETs) should be implemented to reach the objectives set by the Paris Agreement to limit the average temperature increment to 2 °C. One of the options is the development of bioenergy with Carbon Capture and Storage (BECCS) technologies. In this sense, Chemical Looping Combustion (CLC) is one of the most efficient CO2 Capture technologies both from economical and energy points of view. In CLC, a solid oxygen carrier is used to transfer the oxygen from air to the fuel. In this work two manganese-based ores were used as oxygen carriers to burn three different types of biomass (pine sawdust and two Spanish agricultural residues) in a 0.5 kWth CLC continuous unit. Operational conditions were varied to evaluate their effect on the CO2 capture efficiency and the total oxygen demand of the process. Almost 100% of CO2 capture efficiency was reached working with pine sawdust as well as with almond shells. However, high values of total oxygen demand (10–20%) were found, which led to consider further technological solutions to increase the combustion efficiency. In this respect, fuel reactor outlet recycling was evaluated as an operational solution to reduce the oxygen demand with good results (about 30% reduction in the total oxygen demand value). NOx and tar formation from the CLC system were also evaluated. There were no NOx emissions during the experimental campaign and low tar content in the fuel reactor outlet gas was reached (0.3–3.2 g/Nm3), being naphthalene the major tar compound.

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.

La presente invención se refiere a un soporte magnéticamente estable, estructural y químicamente a altas temperaturas en atmósferas oxidantes y reductoras, y que muestra y mantiene propiedades magnéticas a temperatura ambiente, de fórmula general (MnxFe1-x)3O4, que tiene estructura cristalina tipo espinela, y al sistema de fórmula general (MnxFe1-xMy)3O4+5/FA formado por dicho soporte y una fase activa. La presente invención además se refiere a los procedimientos de obtención de dicho soporte y de dicho sistema magnético, así como a sus usos en procesos en que dicho sistema necesita ser separado de otros materiales tras su uso en procesos industriales con atmósferas oxidantes y/o reductoras. La presente invención se engloba dentro del sector industrial y de la energía en procesos dirigidos a la mitigación del cambio climático

El Acuerdo de París fijó el objetivo de limitar en 2 ºC el incremento de temperatura media global sobre los valores preindustriales. Para tal efecto, el IPCC señala a la bioenergía con captura y almacenamiento de CO2 (BECCS en inglés) como una de las tecnologías clave para reducir el impacto del cambio climático pudiendo alcanzarse emisiones negativas de CO2. La implementación de biocombustibles en las tecnologías tradicionales de captura de CO2 implica un alto coste energético del combustible obteniendo una corriente de CO2 prácticamente puro con uno de los menores costes energéticos asociados. El proceso se basa en la utilización de un transportador de oxígeno (TO), normalmente un óxido metálico, que al transportar el oxígeno del reactor de oxidación al de reducción, evita la mezcla del oxígeno del aire y los gases de combustión, evitando de este modo la aplicación de un proceso de separación de gases. En este trabajo se evaluó en una planta piloto de 20 kW de potencia, el efecto de las principales variables de operación bajo condiciones de In situ Gasification-CLC como son la circulación de sólidos, el tipo de agente gasificante y el inventario específico de sólidos en el reactor de reducción sobre los principales parámetros de rendimiento del proceso como son la eficacia de captura de CO2 y la demanda total de oxígeno.

Bioenergy with Carbon Capture and Storage (BECCS) represents an interesting option to achieve the negative CO2 emissions needed to comply with the climate challenges set in the Paris Agreement (COP21-2015). Chemical Looping Combustion (CLC) technology has revealed as one of the CO2 capture technologies with less energy penalty and lower cost. CLC combined with biomass could become a promising BECCS technology. The objective of this work was to asses the feasibility of the CLC technology using biomass as fuel as a future BECCS technology.

Para cumplir con el principal objetivo del Acuerdo de Paris en 2015 de mantener el aumento de la temperatura global por debajo de 2oC, en la Unión Europea se quiere conseguir un 20 % de penetración de energías renovables en la energía final para 2020. En un reciente modelo se espera que en 2030 en España un 29.7 % de la energía final generada sea de origen renovable, y se predice que los vertidos de renovables, definidos como la energía generada que no ha podido ser vertida a la red eléctrica crezcan hasta un 2.7 % de la energía generada (4400 GWh)1. Estos vertidos se generan al no existir sistemas de almacenamiento de energía que acumulen la energía excedente en los momentos en los que la demanda es baja y la producción de renovables es alta. Existen varias ideas para el almacenamiento de esta energía, siendo la generación de hidrógeno por electrólisis de agua (Power-to-Gas), la que mejores expectativas tiene de implantación gracias a que puede almacenar con flexibilidad distintas cantidades de energía dependiendo del excedente generado, además de no depender de la topografía del entorno. El hidrógeno generado con los vertidos de renovables puede tener varios usos, entre ellos el de ser transformado en gas natural sintético (Power-to-Methane). La fuente de carbono es el CO2, que puede provenir de centrales eléctricas u otras industrias que emitan este gas a gran escala y dispongan de la tecnología necesaria para capturarlo. De esta manera se conseguiría aprovechar los vertidos de renovables, reutilizar CO2 y producir un combustible. La captura de CO2 en centrales térmicas puede llevarse a cabo en los gases de postcombustión mediante un sistema de absorción con aminas. Sin embargo, durante los últimos años la tecnología de captura basada en transportadores de oxígeno (TO) se ha convertido en una de las opciones con mayor potencial dentro de las tecnologías de captura ya que permite la captura inherente de CO2 durante la combustión. En esta tecnología el oxígeno nece

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.

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.

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.

La presente invención se refiere a un procedimiento para producir un material transportador de oxígeno mediante la mezcla de CuO y Mn3O4, preparado por granulación en lecho fluidizado. El material así obtenido presenta una elevada reactividad, alta resistencia mecánica, bajo índice de atrición y baja velocidad de atrición. Dicho material se aplica en un proceso CLOU de combustión de sólidos con captura inherente de CO2

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.

La creciente necesidad de reducir las emisiones de CO2 a la atmósfera hace necesario el desarrollo de nuevas tecnologías que puedan aplicarse en todos los grandes focos emisores. La Captura y Almacenamiento de CO2 (CAC) se postula como una de las tecnologías necesarias y que puede contribuir de forma importante en la reducción de dichas emisiones, tanto para su aplicación en grandes centrales térmicas como en el sector industrial. Este trabajo muestra el estado actual de la tecnología CAC tanto a nivel mundial como a nivel nacional, para posteriormente centrarse en aquellas tecnologías más adecuadas para la industria del cemento. En este sentido, la oxicombustión y especialmente la realizada para la calcinación de la caliza (oxicalcinación) parece ser la más adecuada en instalaciones de nueva construcción, mientras que en instalaciones existentes es preferible la utilización de procesos post-combustión. Finalmente se muestran las diferentes iniciativas que se están desarrollando a nivel mundial para la captura de CO2 en la industria del cemento.

The concentration of CO2 in the atmosphere has greatly increased over the last decades, very recently exceeding 400 ppm as a consequence of the anthropogenic CO2 emissions. The use of new alternatives to reduce these emissions is therefore highly encouraged. BioEnergy and Carbon Capture and Storage (BECCS) is emerging as an interesting option for the removal of CO2 from the atmosphere, and is seen as one of the best alternatives for meeting the target set out by the United Nations Framework Convention on Climate Change (UNFCCC) in the Paris Agreement: to limit the increase in the average world temperature to 2°C above pre-industrial levels. In this context, Chemical Looping (CL) is considered to be one of the most promising CO2 capture technology due to its low economic and energy costs. The process is based on the use of an oxygen carrier to transfer the oxygen from air to the fuel, preventing the contact between them. The large-scale deployment of CL technologies could present an important advantage for future bioethanol uses. This chapter describes the current status of bioethanol use in two processes: Chemical Looping Combustion (CLC) for energy production (heat & electricity), and Chemical Looping Reforming (CLR) for syngas/H2 generation. The chapter includes the basic concepts of the technology with a focus on the use of bioethanol and potential oxygen carriers, and operational experience in continuous units. Special interest is given to the use of bioethanol in autothermal-CLR processes, where H2 can be obtained as a final product without the need for external heat input, and with high CO2 capture efficiencies and producing a pure N2 stream. In addition, the possibility of using low-grade bioethanol in the process implies important savings in energy and economic costs during the bioethanol production process.

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.

Chemical looping combustion (CLC) processes combined with CO2 sequestration and sustainable management of biomass represent a promising BioEnergy with Carbon Capture and Storage (BECCS) technology. One of the aspects to be considered in the combustion of biomass is the formation of NOx and the possible existence of tar in the gaseous product stream. The advantage of the CLC technology compared to other CO2 capture technologies is that only fuel-N contributes to nitrogen oxides formation. Moreover, scarce information is available about tar formation in CLC. Thus, this work focuses on these two aspects and compares the results obtained when two different chemical looping combustion modes are used, namely In Situ Gasification Chemical Looping Combustion (iG-CLC) and Chemical Looping with Oxygen Uncoupling (CLOU). Important differences were observed depending on the combustion mode. In both cases most of the fuel-N appeared as N2 in the fuel reactor. However, in iG-CLC more than 94% of the nitrogen measured in the fuel reactor was N2 independently of the biomass used. These percentages under the CLOU mode were lower. In this case, low amounts of N2O were also detected, although it decreased to almost zero at 850 °C. In the air reactor, NO was found and its concentration remained below the legal limit for NOx emissions in power installations with all the types of biomass tested and operating modes. Tar species and concentrations found at the fuel reactor outlet stream were different under the two combustion modes. About 2.5–3.7 g/Nm3 total tar could be found at 980 °C burning under iG-CLC mode, mostly naphthalene. On the contrary, insignificant tar amounts were found in CLOU.

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.

Chemical Looping Combustion (CLC) is considered one of the low cost alternatives for CO2 capture for fossil fuels combustion and to reach negative emissions through biomass CLC. The cornerstone of the CLC process is the oxygen carrier performance that represents the main additional cost with respect to the conventional combustion. Manganese-based oxygen carriers are subjected to a growing interest because they are low cost, not toxic and environmentally friendly. In this work five impregnated oxygen carriers, with manganese oxide Mn3O4 or Mg6MnO8 as their active phase and three commercial supports based on zirconia and synthetic calcium aluminate, were prepared. Their behaviour for CLC was examined by TGA, batch fluidized bed reactor, TPR, SEM-EDX and XRD. After a preliminary screening two carriers (Mn-ZrM and Mn-ZrSG) were subjected to multiple redox cycles by TGA and batch fluidized bed reactor. Both showed high solids conversion by TGA under the tested conditions, appropriated resistance to fracture, rate indexes relatively high, although Mn-ZrM showed agglomeration and deactivation during batch fluidized bed tests. Reactivity in batch fluidized bed reactor of the Mn-ZrSG oxygen carrier with methane increases with temperature although suffered from significant deactivation. This was different to the results found during multiple redox cycles by TGA. There was not a clear reason for this decrease in the reactivity that likely could be due to the uncomplete oxidation in the batch fluidized bed reactor, although further investigations are needed. On the other hand, it presented high and constant reactivity with CO and H2 in all the range of temperatures tested, being suitable for iG-CLC processes of coal or biomass and syngas combustion. Agglomeration problems were not found and the attrition losses were small. Calculated lifetime was around 11,000 h, much higher than any other Mn-based material developed or tested for CLC.

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.

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 ca