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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

Bioenergy coupled with carbon capture utilization and storage (BECCUS) is an attractive greenhouse gas mitigation technology that can produce negative CO2 emissions by combining bioenergy resources with the utilization or geological storage of the captured CO2. The main objective of this work was to evaluate the technical and economic feasibility of two BECCUS technologies based on chemical looping concept with two biomass waste as fuels, i.e., swine manure and pine sawdust, for the production of thermal energy and a pure CO2 stream that is subsequently used as raw material in agricultural greenhouses. Direct use of solid biomass resources was considered for the Chemical Looping with Oxygen Uncoupling option, whereas biogas production was the starting point for Chemical Looping Combustion. The profitability of the chemical looping scenarios was assessed through the Levelized Cost of CO2. This parameter was estimated at 218.31 €/t CO2 for the Chemical Looping Combustion scenario, a value much higher than those for the Chemical Looping with Oxygen Uncoupling scenarios (73.04–87.32 €/t CO2) due to the limited conversion degree of the carbon present in the fuel waste to biogas and the need for an additional experimental plant to the Chemical Looping Combustion unit, i.e., the biogas production plant. Comparing the Chemical Looping with Oxygen Uncoupling scenarios, the economic analysis revealed that the profitability of the biomass-fueled chemical looping facility was markedly sensitive to the selling price of the biomass resource. Furthermore, the values of the Levelized Cost of CO2 parameter for the Chemical Looping with Oxygen Uncoupling scenarios were lower than those estimated in other research studies that implemented BECCUS technologies and utilized the captured CO2 for identical purposes. In the particular case of swine manure, this result becomes even more noteworthy since it demonstrates that the energy use of this biomass resource through Chemical Looping wit

The Calcium Assisted Steel-mill Off-gas Hydrogen production process (CASOH) is able to upgrade and decarbonise blast furnace gases (BFG), which is the main source of CO2 emissions in integrated steel making plants. The three main reaction stages of the process (i.e. H2 production via calcium-assisted water-gas-shift of BFG, Cu oxidation and CO2 sorbent regeneration) have been investigated in a lab-scale fixed bed reactor, using readily available functional materials (i.e. a commercial Cu-based catalyst and calcined limestone for the CO2 capture). The reactivity and stability of the materials have been studied after multiple cycles resembling the operating conditions expected in a TRL7 CASOH pilot plant under construction. A one-dimensional reactor model has been developed to simulate in detail the CASOH process and successfully validated with the experimental results obtained in the packed-bed reactor. Synthetic BFG mixed with steam has been converted into a product gas containing up to 40 vol% of H2 in N2 during the CASOH stage at atmospheric pressure and average temperatures in the bed around 650 ºC. During the Cu oxidation stage, the O2 contained in inlet air has been completely converted leading to moderate temperatures in the oxidation front (i.e. around 800 ºC). The oxidation at 4 bar has minimized the CO2 leakage during this stage. Finally, the reduction of CuO with simulated BFG and CH4 has produced in-situ sufficient heat to partially calcine at temperatures around 880ºC the CaCO3 present in the reactor leaving the solids ready for subsequent reaction cycles, while a CO2-rich gas is produced. The experimental and modelling results obtained in this work will be used to firstly design the experimental campaigns at the TRL7 CASOH pilot, and subsequently to interpret and scale up the pilot results using the validated model.

The Ca-Cu looping process is a promising CO2 capture technology designed to produce H2 and power from a fuel gas. The use of inexpensive and widely available limestone would facilitate the scale up of this technology. This work proposes a novel strategy for packed-bed Ca-Cu looping processes consisting of loading the sufficient amount of CuO to calcine only a well-defined fraction of CaCO3 in every cycle during the transient period until the limestone reaches a residual solid conversion of 0.06 (typically after 150–200 cycles). In this way, the excess of CaCO3 in the bed ensures temperatures below 900 °C during operation. The feasibility of this strategy is simulated for the conversion of blast furnace gas (BFG) into a H2-rich product (35 vol%) diluted in N2 via the Ca-Cu looping process at 2 bar and temperatures between 600 and 850 °C, while a separated CO2 rich gas (55 vol% CO2 in N2) is obtained.

Kemcyklisk förbränning (CLC) involverar en icke komplex separation av den bildade koldioxiden (CO2) efter förbränningen eftersom syret (O2) överförs till bränslet via en syrebärare som cirkulerar mellan luft- och bränslereaktorn. Eftersom O2 separeras effektivt från kvävgasen (N2) i luftreaktorn, erhålls en produkt gas som till majoriteten består av CO2 och vatten (H2O). Detta resulterar således i mindre komplexa och energi-krävande rökgasreningssystem. Vid förbränning av biomassa inom kemcyklisk förbränning kan negativa CO2 utsläpp erhållas om den producerade CO2 gasen infångas och slutförvaras exempelvis i geologiska formationer. Den infångade CO2 gasen måste för att uppfylla stringenta reningskrav för att undvika diverse konsekvenser relaterade till transportkedjan och slutförvaringen. Förutom CO2 och H2O, kommer den genererade rökgasen från CLC innehålla mindre mängder av biprodukter som kväveoxider (NOx), svaveloxider (SOx) och övriga kontaminanter som behöver att reduceras ned till ppm nivåer för att möta reningskravet på CO2 gasen. På grund av en ofullständig förbränning i CLC erfordras en efterförbränningskammare med en extern tillsats av O2 för att uppnå en fullständig förbränning. Det kan därför förväntas att överskotts-O2 kommer att finnas i den utgående gasen efter post oxidationskammaren, som också behöver att renas ned till ppm koncentrationer. De föreslagna rökgasreningssystemen efter CLC involverar de mest konventionella rökgasreningssystem använda inom industrin idag. Till dessa tillhör bland annat elektrofilter (ESP), våt rökgasavsvavling (WFGD), selektiv katalytisk reduktion (SCR) och selektiv icke-katalytisk reduktion (SNCR) för kväveoxireducering. Två kylnings och CO2 förvätskningstekniker diskuteras i detta arbete: den förkylda Linde Hampson systemet och det kryogena destillationssystemet. Ett rökgasreningssystem har föreslagits för varje förvätskningsteknik. Bland de två föreslagna reningssystemen, enbart scenario 2 uppfyllde Northern Lights k, Chemical looping combustion (CLC) involves an inherent separation of carbon dioxide (CO2), since oxygen (O2) is transferred to the fuel via an oxygen carrier, circulating between the air and fuel reactor. With O2 being removed from nitrogen (N2) in the air reactor, a separate stream containing mostly CO2 and water (H2O) is produced in the fuel reactor, eliminating the need of expensive and energy-demanding gas separation technologies. The use of biomass as fuel in CLC may result in negative CO2 emissions if CO2 is captured and stored. The CO2 product gas must comply to certain purity levels depending on ways of CO2 transportation and where it will be stored. Besides H2O and CO2, the generated flue gas stream in CLC will also contain trace amounts of nitrogen oxides (NOx), sulfur oxides (SOx) and other contaminants, thus requiring a deep removal to ppm levels to comply with the stringent CO2 purity criteria for storage in saline aquifers in this work. Due to an incomplete combustion of fuel gases in CLC, an oxy-polishing step is required for a full conversion to gas products CO2 and H2O. Therefore, pure O2 is required for the oxy-polishing step. Some residual O2 will also be expected in the flue gas stream and needs to be reduced to ppm levels. The downstream treatment in CLC involves the best available gas processing technologies practiced commercially today, such as electrostatic precipitators (ESPs), wet flue gas desulfurization (WFGD), selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). Two CO2 processing systems are discussed in this work; the precooled Linde Hampson unit and the Distillation Separation unit. For each CO2 processing unit (CPU), a flue gas treatment is proposed. Amongst the two proposed scenarios, scenario 2, could with highest certainty, produce a liquid CO2 stream with a purity of 99.998%, complying to the CO2 criteria set by the Northern Lights Project in Norway. At the time of writing this thesis, no other litera

Carbon Capture and Storage is a technology of paramount importance for Sustainable Development Goal 7 (Affordable and Clean Energy) and Sustainable Development Goal 13 (Climate Action). The European Union is moving rapidly towards low carbon technologies, see the Energy Union Strategy. Coupling biofuels and carbon capture and storage to decarbonize the power and the industrial sector can be done through the development of BECCS (Bioenergy with Carbon Capture and Storage). However there are some technical barriers to the development of this technology. If a Chemical Looping Combustion (CLC) plant has to be coupled with a gas turbine, it has to work in pressurized conditions. The effect of pressure on chemical reactions and fluidized bed hydrodynamics, at the moment, is not clear. The aim of this paper is to present a model for the dimensioning of an air reactor to be coupled to a gas turbine of the power of about 14 MW. Based on the air mass flow requirements to produce such a power. The fluidized bed is designed choosing geometry parameters and making a sensitivity analysis of the influence of the turbine inlet temperature on final plant efficiency. It can be seen from the analysis presented in this paper that the diameter of the fluidized bed is mainly influenced by the mass flow of the air in the reactor, while the height of the reactor is mainly influenced by elutriation and transport disengaging height calculations.

S.1. Brief description of the CLC model: Figure S1. Fluidization regime for the fuel reactor and air reactor in the flow regime map.

The dynamic operation of thermal power plants becomes more and more important due to more diverse and volatile power sources. Load changes of biomass, bituminous coal and methane were conducted during six experimental runs in a chemical looping combustion pilot plant which combines power generation and CO2 capture. The resulting step responses of the hydrodynamics and gas concentrations were compared to each other to understand the transient behavior of the interconnected fluidized bed system. The influence of the fuel rate and solid circulation on the response time and intensity was assessed.

In the present work, a lab-scale packed bed reactor has been used to decarbonize mixtures of inlet gases simulating the typical composition of blast furnace gases (BFG) and convert them to H2-rich streams by means of the Ca[sbnd]Cu chemical looping concept. The reactor was packed with 355 g of Cu-based oxygen carrier (OC) supported on Al2O3 and natural Ca-based sorbent. The three main reaction stages; namely (i) Calcium Assisted Steel-mill Off-gas Hydrogen (CASOH), (ii) Cu oxidation and (iii) Regeneration of carbonated Ca-based sorbent were examined. In CASOH stage, BFG is converted into H2-rich stream (17% by vol.) under the experimental conditions of 600 °C, 5.0 bar and S/CO molar ratio of 2.0. A controlled oxidation causes a mere 3.5% of CaCO3 to decompose during the Cu-oxidation stage. This resulted in a nearly pure N2 stream at 600 °C and 5.0 bar operating conditions. During the regeneration stage, BFG and mixture of BFG and CH4 is used as a reducing fuel. To ensure the amount of heat needed for the decomposition of CaCO3 during the reduction of CuO, a 1.4 CuO/CaCO3 molar ratio has been used. It resulted in 46% CO2 in N2 at the end of the reduction/calcination stage.

Bioenergy combustion with Carbon Capture and Storage (BECCS) is a key technology to achieve carbon negative emissions power generation. This can be achieved by coupling the biofuels combustion with CO2 capture and storage (CCS). The lowest cost for CCS corresponds at the moment to the Chemical Looping Combustion (CLC) process. This can use biofuels which can be gaseous (biomethane, biogas or syngas etc.), liquid (biodiesel, bioethanol, biobutanol and pyrolysis oils etc.) or solids (wood dust, charcoal dust, wood chips, wood pellets etc.) While plant design with gaseous and liquid biofuels would be simpler, plants using solid biofuels and based on two couple fluidisd beds would need the use of a third reactor named carbon stripper. In the specific case if we plan to couple a CLC plant with a turbo expander (to achieve the high efficiencies of a combined cycle power plant) we have to work with pressurized reactors. However, there are some technical barriers to the coupling of a chemical looping combustor with a turbo expander, such as: the operation of the combustor in pressurised conditions; the inventory balance among reactors; elutriated particles reaching the turbo expander. This explaind why there is no commercial plant at the moment capable to do this. The aim of this paper is to present a model for the dimensioning of an air reactor to be coupled to a turbo expander of the power of about 12 MWe. Based on this, the air mass flow can be obtained and the geometric parameters can be calculated, to have an air velocity which is needed to achieve the fast fluidization regime and to ensure a high conversion rate as well as particles and heat exchage among air and fuel reactor.

Limestone Chemical Looping Combustion (L-CLCTM) is a novel process to burn sulfurous fuels with intrinsic desulfurization and CO2 capture. L-CLCTM is based on using calcium-based sorbents as precursors for CaSO4 formation, which is used as an oxygen carrier. Its principle lies in the in-situ sulfur retention process performed in fluidized bed combustors burning solid fuels with high sulfur content. The target redox pair for the oxygen transference to the fuel is CaSO4/CaS. In this research work, experimental tests burning CH4, syngas and H2 with a moderate H2S concentration were conducted in a continuous CLC unit. This experimental campaign is first in a kind as there is hardly information about the CaSO4/CaS pair for the L-CLCTM process. High combustion efficiencies were achieved at moderate temperatures (800–850 °C) when burning H2 and syngas (∼96–99 %). Likewise, low CH4 combustion efficiency (∼59 %) was found even operating at a temperature as high as 945 °C. Additionally, experimental tests at different Ca/S molar ratios were performed. They revealed that it was possible to reach suitable sulfur retention values (∼82 %) by using a Ca/S molar ratio of 2.25. This value resulted in a very feasible ratio since it is commonly used in fluidized bed combustors.

Chemical looping combustion (CLC) allows the combustion of a fuel with inherent CO2 capture by using an oxygen carrier to transfer the oxygen from the air to the fuel. Previously to the CLC scale-up, tests should be done in lab-scale CLC units to determine the combustion performance of promising oxygen carriers and, at the same time, to evaluate the durability of these materials. For that, the effect of operating conditions on the oxygen carrier ageing should be considered, which is often disregarded. In this work, tests were done burning a simulated biogas stream in a continuous 500 Wth CLC unit with a promising Cu-based oxygen carrier (Cu14Al_ICB). Operating conditions were carefully selected to maximize the durability of this oxygen carrier while complete CH4 combustion was achieved. These operating conditions were based on limiting both the variation of solids conversion by choosing suitable solids circulation rates and the oxidation degree of the particles in the air reactor by minimizing the air excess. Thus, the Cu14Al_ICB material exhibited an excellent mechanical resistance, estimating a particle lifetime of 20,000 h at 900 °C. In addition, copper migration to the surface of the particles and loss of copper were not relevant. This is the first time that under certain operating conditions, a Cu-based oxygen carrier can exhibit outstanding mechanical properties during continuous CLC operation at 900 °C.

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

Biogas is a renewable fuel that is generated from the decomposition of organic matter through the process of anaerobic digestion. The compound that provides biogas with its energy value is CH4, which accounts for between 40% and 75% of the gas, with CO2 being the other main component of this fuel. Although the biogas valorization process is carbon neutral, the overall process can become carbon negative with the application of CO2 capture technologies, such as chemical looping combustion (CLC). This work presents a techno-economic analysis of a 5 MWth plant for the generation of biogas from livestock farming and agro-industrial waste to produce electricity + heat or heat only (base cases), or for further treatment in a CLC unit (CLC cases), where the captured CO2 is converted into a raw material, e.g. for the production of greenhouse crops. Results from the comparative study of five different oxygen carriers used in CLC are also presented. The profitability of the base cases was evaluated by means of the Levelized Cost of Electricity (LCOE) and Levelized Cost of Thermal Energy (LCOTE) metrics, whereas the economic performance of the CLC cases was measured by the Levelized Cost of CO2 (LCOCO2). LCOE gave a value of €139.90/MWh for the base case, and LCOTE was €56.50/MWh for the modified base case, where biogas was combusted in a boiler to produce only heat. With regard to the CLC cases, LCOCO2 values ranged between €148.60 per tonne for a highly reactive, synthetic Cu-based oxygen carrier and €177.10 per tonne for ilmenite. Finally, by comparing the economic results obtained in this work with those found in the literature for conventional biogas production plants and greenhouse crop production processes, it can be concluded that the implementation of CLC technology in biogas plants has the potential to become a profitable and environmentally sustainable option for the valorization of organic waste because the CO2 generated in the fuel reactor of the CLC unit can be co

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.

El estiércol porcino o purín es un residuo compuesto por una mezcla de excrementos sólidos y líquidos, restos de alimentos y agua de limpieza de camas porcinas cuya fracción sólida se caracteriza por presentar un alto contenido en carbono (51.5% daf), nitrógeno (4.0% daf), azufre (1.1% daf) y cenizas (29%). La conversión termoquímica de este residuo carbonoso se considera una opción interesante para obtener bioenergía. Su uso en tecnologías de captura de CO2 como Chemical Looping Combustion (CLC) puede resolver algunos problemas ambientales relacionados con el exceso de nutrientes en zonas agrícolas y emisiones de gases de efecto invernadero. El objetivo de este trabajo es analizar el efectos de las principales variables de operación (temperatura, agente de fluidización y exceso de oxígeno) sobre la eficacia de combustión en una unidad CLC, la captura de CO2 y la presencia de compuestos nitrogenados (N2, NH3, NOx).

Coupling a Chemical Looping Combustor fed with biofuels with a turbo expander is a promising Negative Emissions Technology (NET) to realize climate neutral targets in China and Europe. This is also an example of Bioenergy with Carbon Capture and Storage (BECCS) technology. To realize it, we need a Pressurized Chemical Looping Combustion process (PCLC). In this work, a Eulerian-Lagrangian hybrid model is developed in Barracuda-VRTM software, incorporating chemical reactions to predict the performance of a Fuel Reactor using Fe2O3 as oxygen carrier and syngas as fuel, under different pressures, ranging from 1 bar to 20 bars. The model predicted the conversion efficiency of syngas reduction using an iron-based oxygen carrier (Fe2O3/Al2O3). The results show, that the increase in pressure promotes the conversion of CO and inhibits the conversion of H2. When the two gases are considered together, the increase in pressure promotes the reaction between syngas and Fe2O3 and reduces the demand for Fe2O3 oxygen carrier per unit of syngas Lower Heating Value and so also the inventory of the reactor. Increasing temperatures promotes both the reaction of H2 and CO with Fe2O3. Dealing with CO conversion, this is more affected by pressure changes and temperature changes than H2. This represents important information for Fuel Reactor design, scale up and optimization. Further validation is neded in batch and continuous pressurised plants.

Carbon Capture and Storage is a technology of paramount importance for the fulfillment of the Sustainable Development Goal 7 (Affordable and Clean Energy) and the Sustainable Development Goal 5 (Climate Action). The European Union is moving rapidly towards low carbon technologies, for instance via the Energy Union Strategy. Coupling biofuels and carbon capture and storage to decarbonize the power and the industrial sector can be done through the development of BECCS (Bioenergy with Carbon Capture and Storage). Chemical Looping combustion is one of the cheapest way to capture CO2. A Chemical Looping Combustion (CLC) plant can be coupled with a turbo expander to convert energy to power, but it has to work in pressurised conditions. The effect of pressure on the chemical reactions and on fluidised bed hydrodynamics, at the moment, is not completely clear. The aim of this review is to summarize the most important highlights in this field and also provide an original method to optimize power plant efficiency. The main objective of our research is that to design a pressurised Chemical Looping Combustion plant which can be coupled to a turbo expander. To achieve this we need to start from the characteristics of the turbo expander itself (eg. the Turbine Inlet Temperature and the compression ratio) and then design the chemical looping combustor with a top down approach. Once the air and the fuel reactor have been dimensioned and the oxygen carrier inventory and circulation rate have been identified, the paper proposes a final optimization procedure based on two energy balances applied to the two reactors. The results of this work propose an optimization methodology and guidelines to be used for the design of pressurised chemical looping reactors to be coupled with turbo expanders for the production of power with carbon negative emissions.

Chemical looping combustion (CLC) is one of the most efficient and advantageous CO2 capture technologies from an economic and energy point of view. An important key factor in this process is the oxygen carriers (OCs) used to transfer oxygen from the air to the fuel. In this work, three natural iron ores from Brazil were selected as interesting oxygen carriers for the CLC process due to their low cost and abundance in nature. Their chemical composition, redox properties, and structural evolution when submitted to a reactivity test in a thermobalance with 15% CH4 and H2 were investigated. The OCs (ItaHP-MG, ItaHP-RN, and ItaLP-RN) revealed good resistance to fracture, and their reactivity increased after the first reaction cycle due to the occurrence of an activation process, leading to a gain in reactivity in the following cycles. The reactivity tests showed that for all OCs, the reactivity with hydrogen was higher when compared to methane, highlighting ItaHP-MG oxygen carrier with relevant rate index values for both fuels (9.60%/min and 3.55%/min for H2 and CH4, respectively). However, OCs performed differently depending on the degree of use of the Fe2O3 phase. Interestingly, ItaHP-MG, with a high Fe2O3 content (96.5%), showed a regeneration of only 60%, while ItaLP-RN, whose Fe2O3 content is 41.5%, presented a degree of use above 85%. This effect is the result of preferential gas–solid interaction on the surface of the OC.

The study presents a new modelling approach applied to hematite to magnetite reduction, which is the dominant reaction in atmospheres with a high CO2/CO ratio, expected in chemical looping combustion. The structure of the Fe2O3 particle was simulated using the percolation theory, while the reduction was modelled using the stochastic approach to simulate nucleation, gaseous diffusion, solid-state diffusion, and chemical reaction. To account for differences between 3-D and 2-D pores, the model allowed for pore-hopping. The obtained results agreed with experimental results for Fe2O3 derived from natural ore (pyrite), and, to a lesser extent, with results for lab-synthesised Fe2O3 particles. The model provides useful insight into the complexity of the investigated process. For materials with undeveloped porosity, a simple shrinking-core approximation will be sufficient. In contrast, for materials with well-developed porosity, the models should incorporate information about the particle structure. © 2020 Elsevier B.V.

Bed material particle layer formation plays a significant role in thermo-chemical conversion of biomass. The interaction between biomass ash and bed material in fluidized bed conversion processes has been described for a variety of different applications and spans from fundamental research of formation mechanisms to effects of this layer formation on long-term operation in industrial-scale. This review describes the current state of the research regarding the mechanisms underlying layer formation and the positive influence of bed material particle layer formation on the operation of thermo-chemical conversion processes. Thus, the main focus lies on its effect on the catalytic activity towards gasification reactions and the impact on oxygen transport in chemical looping combustion. The review focuses on the most commonly investigated bed materials, such as quartz, feldspar or olivine. While the most relevant results for both the underlying mechanisms and the subsequently observed effects on the operation are presented and discussed, knowledge gaps where further research is necessary are identified and described.

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 Chemical Looping with Oxygen Uncoupling (CLOU) process is a derivative technology of the Chemical Looping Combustion (CLC) process for the combustion of both renewable and non-renewable solid fuels. The present work studies the combustion and CO2 capture efficiency of burning coal or biomass using a single Cu-based oxygen carrier with magnetic properties as an oxygen carrier. The combustion of two different coals and three different biomasses was performed in a 1.5 kWth CLOU continuously operated unit for 36 h. The magnetic properties of the oxygen carrier were also studied after combustion and its separation from the ashes. Complete combustion of the fuel to CO2 and H2O was achieved in all cases. For both coals, CO2 capture efficiency increased with fuel reactor temperature, with both reaching values of 97% at 900 °C. The same increase was obtained with the biomasses. The highest CO2 capture efficiency for a biomass was obtained with pine sawdust, which achieved a value of 93%, followed by almond shell (86%) and olive stone (80%) at 900 °C. Oxygen carrier reactivity remained constant after use in the continuous unit with one small increase in the attrition jet index (AJI) value. The used particles were found to still be as magnetic as the fresh particles, and the fines were also highly magnetic. Values higher than 99% were achieved with separation from the fines reached. It was therefore proven that the elutriated oxygen carrier from the plant was still magnetic and could be easily separated from the elutriated ash.

Based on CFD modeling and detailed kinetics models a batch reactor is simulated in the framework of the Marie Curie project GTCLC-NEG.

The Power Sector is undergoing a rapid technological change with respect to implementation of low carbon technologies. The IEA Energy Outlook 2017 shows that the investments in Renewables for the first time are equal to those on the fossil sources. It is likely that the conventional gas turbines and internal combustion engines will need to be integrated in systems employing biofuels and/or CCUS (Carbon Capture Usage and Storage). Also, the European Union is moving rapidly towards low carbon technologies (i.e. Energy Efficiency, Smart Grids, Renewables and CCUS), see the Energy Union Strategy. Currently 28% of the installed power capacity in Europe is based on natural gas plants. Gas-based power capacity has reached 418 GW in 2016 and is likely to continue to grow in the future. To efficiently capture the carbon dioxide emissions generated by the combustion of natural gas in the combustion chamber a possible solution could be to adopt new combustion processes, like Chemical Looping Combustion. The combination of CLC and GTs can decrease the efficiency of a combined cycle power plant from 60% to about 40.34%. These performances influence costs and environmental burdens and this is also the same for oxyfuel combustion, which is a competing technology to realize CCS. This paper, starting from literature mass and energy balances of a conventional combined cycle, a combined cycle coupled with chemical looping combustor and a combined cycle coupled with oxyfuel combustion, calculates the reduction of CO2 emissions which can be achieved during the whole life cycle of the power plant and then identifies the value of the carbon credit which is needed to have an interesting payback period for such kind of investment.

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.

We analyse the viability of a novel reactor concept for chemical looping combustion applications with CO2 capture. The reactor consists of a packed bed of reduced oxygen carrier particles traversed by a series of empty conducts oriented in the axial direction. These conducts are made of permeable but non-selective porous walls, through which air diffuses towards the region of reacting solids. The diffusion flux of air through the orifices, which is perpendicular to the main bulk flow of gas along the conducts, imposes very long oxidation times for all the reacting particles and a quasi-steady heating up of the air flow. The conducts designed to have a very high length/diameter ratio (i.e. above 50) allow a large bypass of pressurized air through the reactor without coming into direct contact with the solids, resulting in a modest pressure drop of the gas (i.e. below 5% at the reactor exit). A preliminary reactor design example is described for a case using Fe/Fe2O3 pellets as oxygen carrier, which are packed into a reactor (L = 100 m, I.D. = 2 m) traversed by air conducts (I.D. = 0.05 m) with a wall 2 mm thick and orifices occupying an area fraction of 0.12. The reactor can initially generate 100 MWth, with a gas flow at the exit at close to 1050 °C and 19 atm, and it could be used intermittently for more than 9 h as the main heater in a highly efficient Brayton cycle.

В работе рассмотрены основные методы улавливания диоксида углерода с целью повышения экологичности энергетических установок. Рассмотрены основные технологии: pre-combustion, post-combustion, oxy-fuel, chemical looping combustion. Выполнен анализ перспектив применения рассмотренных технологий секвестрования СО2., The main methods of carbon dioxide capture are discussed in order to improve the environmental friendliness of power plants. The main technologies are considered: pre-combination, post-combination, oxy-fuel, chemical looping combination. Analysis of prospects of application of the considered technologies of СО2 sequestration was performed.

Uno de los grandes retos a los que se enfrenta la sociedad actual y la futura es la lucha contra el cambio climático. El término captura y almacenamiento de CO2 (CAC) alude al conjunto de tecnologías que consiguen la separación y la captura del CO2 generado en procesos industriales y de generación eléctrica, y su posterior transporte hasta un lugar adecuado y seguro para su almacenamiento permanente. De esta manera se logra aislar el CO2 de la atmósfera durante un periodo largo de tiempo. La tecnología CLC es la opción más adecuada desde un punto de vista termodinámico para capturar el CO2 ya que se hace de forma inherente al propio proceso, lo que minimiza la pérdida de eficiencia energética respecto de una instalación sin sistema de captura. Este proceso se basa en transferir oxígeno del aire al combustible usando un transportador sólido de oxígeno, basado en un óxido metálico, que se encuentra circulando continuamente entre dos reactores de lecho fluidizado interconectados, denominados reactor de reducción y reactor de oxidación. Ello evita el contacto entre el combustible y el aire durante todo el proceso de combustión.

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.

Bimetallic manganese-iron materials have been identified as suitable oxygen carriers for Chemical Looping Combustion (CLC) and Chemical Looping with Oxygen Uncoupling (CLOU) processes. These materials allow the combustion of a fuel with inherent CO2 capture according to two parallel mechanisms: reaction with lattice oxygen and oxygen uncoupling. This work is focused on the evaluation of the reactivity and physicochemical characterization of oxygen carrier particles consisting of a manganese-iron mixed oxide with manganese to iron molar ratio of 66:34 and doped with titanium (7 wt% TiO2) with the objective of determining suitable conditions to be used in CLC and CLOU processes. Particles were prepared by spray drying and the sintering procedure was optimized in order to achieve particles with high reactivity and mechanical strength. In addition, suitable magnetic properties were also sought in order to allow oxygen carrier recover and reuse in a chemical looping unit burning solid fuels. Optimum operating conditions for the fuel combustion and regeneration stages were determined in order to promote the oxygen uncoupling mechanism. Thus, temperature during the fuel combustion must be as high as possible to enhance the oxygen transference; but conditions for oxygen carrier regeneration by air must be carefully selected in order to take advantage of the oxygen uncoupling capability of this material. An oxidizing temperature interval of 1123–1173 K maximized the regeneration, while an air excess higher than 20% would be recommended in order to guarantee oxygen uncoupling capability.

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.

We have studied the reversible uptake and release of oxygen in the layered metal oxide system AB2O4 to understand their suitability as oxygen storage materials. We examined their structures at their most reduced, oxidized, and intermediate phases of AFe2O4 for A= Lu, Yb, Y, and In, and studied their structures with high-resolution synchrotron X-ray diraction. Under simulated chemical looping conditions, we monitored their structures and reactivity towards H2 and O2 utilizing in-situ X-ray diraction, neutron diraction, and thermogravimetric analysis measurements. The nature of the trivalent A cation aects the oxidation kinetics, thermal cycling stability, and oxygen storage capacity (OSC). With the exception of the A = In analogue, these layered oxides underwent various phase transitions above 200 °C that included the creation of a superstructure as oxygen incorporates until a high temperature phase is established above 400 °C. To understand trends in the oxygen incorporation kinetics, we employed bond valence sum analysis of the Fe-O bonding across the series. The more underbonded the Fe cation, the more facile the oxygen insertion. During the cycling experiments all samples exhibited reversible oxygen insertion at 600 °C for this series, and displayed OSC values between 0.2-0.27 O2 mol/mol. The Y analogue displayed the fastest kinetics for oxidation, which may make it the most suitable for oxygen sensing applications. The structure of the oxidized phase was solved from with simulated annealing and Fourier dierence maps. Structural parameters were reported with combine neutron and X-ray Rietveld renement. PDF and XAS were used to conrm the nal structural model. As the nal steps experiments were carried out to explore the chemical looping reactivity of AB2O4 layered oxides, with A= Lu, Yb, Y and B=Mn, Fe. We reported the reactivity with methane of AB2O4 layered oxides for the rst time. The RT pristine structure was regenerated at 600 °C under methane. Mn substituted

Chemical looping combustion is especially competitive for electrical power generation with integrated CO2 capture when it is operated at high temperatures (1000–1200 °C) and high pressures (15 bar or higher). For these demanding conditions, dynamically operated packed bed reactors have been proposed, providing a good alternative to fluidized bed technology. This work addresses the importance of including the formation and reduction kinetics of spinel compounds to proper predict the packed bed reactor performance by validating a pseudo-homogeneous packed-bed reactor model to describe the redox kinetics of a CuO/Al2O3 oxygen carrier with experiments in a lab-scale packed bed reactor setup. A grain model describing the reaction kinetics of all solid species, including both spinel compounds (CuAl2O4 and CuAlO2), was included in a particle model and used to develop correlations for the effectiveness factor as a function of the particle conversion in order to account for internal solids concentration profiles and mass transfer limitations. The particle effectiveness factors were subsequently included in the source terms of the component mass balances of the reactor model accounting for all the reactions of the spinel compounds. Cyclic experiments (oxidation with air and reduction with a H2-N2 mixture) have been carried out in a lab-scale packed bed reactor with a 12.5 wt% CuO/Al2O3 oxygen carrier at different temperatures ranging from 600 to 1000 °C. The experimental results are well described by the packed bed reactor model, only when including the developed particle effectiveness factors to fully account for the kinetics of the formation and reduction of the spinel compounds. The results confirm that it is neccesary to include a detailed description of the redox kinetics at the particle level to be able to accurately estimate the breakthrough time, cycle time

Copper oxide supported on silica and supported on alumina are often used as oxygen carriers for chemical looping combustion owing to their very high reduction rates at lower temperatures and their very good mechanical and chemical stability at temperatures below 1000 °C compared to other oxygen carriers. In this work, a comprehensive experimental study has been carried out to better understand the reaction mechanism and quantitatively describe the reaction kinetics of the oxygen uncoupling reaction and the reduction and oxidation reactions under different reaction conditions. First, the oxygen uncoupling and reduction reaction kinetics of the CuO/SiO2 oxygen carrier was studied. A shrinking core type model (SCM) was developed that can well describe the oxygen uncoupling reaction rate and final conversion. Subsequently, a SCM and a simplified pseudo-homogeneous model was developed to describe the reduction kinetics of CuO/SiO2. Subsequently, the study was extended to investigate the reduction kinetics of CuO/Al2O3, where it was observed that the formation of tenorite spinel (CuAl2O4) and cuprite spinel (CuAlO2) strongly affects the overall reduction kinetics. Assuming that the reduction of CuO to Cu is independent of the support, the pseudo-homogeneous model was extended to include the reduction and oxidation kinetics of the spinel compounds, with which the experimentally determined redox kinetics could be well described. Regarding the CuO on Al2O3, The maximum temperature reached was 1000 °C in thermogravimetric analysis (TGA) without observing any sintering or melting effects. It can be due to the good stability with the Al2O3 support and the relatively small amount of CuO (13%). However, for CuO/SiO2 (70% CuO), the maximum temperature tested in the TGA was 900 °C, since at higher temperatures the sample was melting, due to the lower melting point of Cu. The main results of the study can be summarized as: i) the oxygen uncoupling and reduction/oxid

The objective of this work was to determine suitable design parameters NORWAY and operating conditions for the complete combustion of CH4 with the impregnated Cu-based oxygen carrier developed by ICB-CSIC.

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.

Chemical Looping Combustion (CLC) has been extensively investigated up to pilot scale. Despite promising results, this CO2 capture technology has to be further developed towards a potential industrial application. In order to accelerate the scale up of the process, it is essential to simulate the CLC using a process simulation software. In this study, a process simulation model of the CLC pilot plant at Technische Universität Darmstadt is developed employing Aspen Plus®. The air reactor and the fuel reactor are integrated in the process model to calculate the conversion of the oxygen carrier and gases. The solids distribution and also the chemical conversion of gases and solids are implemented by user-defined functions programmed with FORTRAN. These codes are based on mathematical equations for fluidized beds and kinetic data of the chemical reactions taken into consideration. For this reason, dedicated thermal gravimetric analysis (TGA) experiments were carried out to determine both kinetics of redox reactions of oxygen carrier and gasification kinetics of the coal used in the 1 MWth CLC unit. The one-dimensional solids distributions and gas/solid mixing are calculated from empirical correlations according to Kunii and Levenspiel. The models are validated by means of experimental data obtained from the 1 MWth CLC pilot plant with ilmenite as oxygen carrier and Russian hard coal (“Taldinsky”) as fuel. Among others, pressure profiles and gas concentrations at reactor exits are calculated for various operational points with autothermal operation. The results show good agreement with the experimental data. The process model was applied to optimize the operational conditions of the pilot plant.

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) has emerged in recent years as a very promising combustion technology for power plants and industrial applications with inherent CO2 capture, which circumvent the energy penalty imposed on other competing technologies. The process is based on the use of a metal oxide to transport the oxygen needed for combustion in order to prevent direct contact between the fuel and air. CLC is performed in two interconnected reactors, and the CO2 separation inherent to the process practically eliminates the energy penalty associated with gas separation. The CLC process was initially developed for gaseous fuels, and its application was subsequently extended to solid fuels. The process has been demonstrated in units of different size, from bench scale to MW-scale pilot plants, burning natural gas, syngas, coal and biomass, and using ores and synthetic materials as oxygen-carriers. An overview of the status of the process, starting with the fundamentals and considering the main experimental results and characteristics of process performance, is made both for gaseous and solid fuels. Process modelling of the system for solid and gaseous fuels is also analysed. The main research needs and challenges both for gaseous and solid fuel are highlighted.