Oxygen Carrier Particles Research Articles

Reaction kinetics of Ni-Fe oxygen carriers with high performance for chemical looping hydrogen production

The chemical looping hydrogen production (CLHP) process utilizing iron-based oxygen carriers holds promise for practical hydrogen generation applications. However, challenges persist in developing iron-based carriers that are easy to prepare and demonstrate effective reactivity. Our research focuses on evaluating the CLHP reaction performance using bimetallic Ni-Fe oxygen carrier particles, synthesized by a scalable mechanical mixing method. This study unravels the role of Ni in bimetallic Ni-Fe oxygen carriers and investigates the influence of varying nickel-doping ratios on enhancing the reduction reactivity of iron-based oxygen carriers. Compared to the undoped sample, the 20 wt% nickel-doped Fe2O3/Al2O3 (20NiFe) particles enabled a reduction in the reaction temperature by at least 50 K. With the dopant, the methane conversion rate at 923 K is 500% higher than that of carriers without the dopant. Heterogeneous kinetic analysis demonstrates that the global reduction reaction data for the Ni-Fe oxygen carriers fit with the nucleation-nuclei growth model. Through redox reactivity tests and reduction kinetic analysis, 20NiFe shows the lowest apparent activation energy at 53.93 kJ/mol. Furthermore, the kinetic study and quasi in-situ XRD analysis aid in proposing the evolution process of methane reduction reaction for nickel-doped iron-based oxygen carriers, clarifying the role of doping in improving chemical looping reactivity from a kinetic perspective. This work provides valuable guidance for the design and optimization of oxygen carriers, thus accelerating the readiness for industrial deployment of hydrogen production via chemical looping process.

Mechanism study on quantification of sulfurization effect on methane decomposition with CuO oxygen carrier

The sulfur-containing impurity in natural gas, coal, and organic solid wastes generally exerts significant impacts on the dynamic evolution of sulfur oxides emission in atmosphere, and results in the degraded reaction performance of chemical looping process. Methane is the main component of natural gas and a typical pyrolysis and gasification product of solid waste, so it is of great significance to quantify the toxicological effects on the conversion of methane. this work realizes the accurate prediction of methane heterogeneous conversion in a multiscale kinetic model, and innovatively establishes a framework for quantifying the toxicological effect on the oxygen carrier particles. The kinetic parameters of methane oxidation over fresh and sulfurized oxygen carriers are calculated using density functional theory, and the sensitivity analysis of rate constant is conducted to forecast the priority of different reactions. Results indicate that the effect of residual sulfur in oxygen carrier is complex and not monotonically inhibited, and the sulfurization significantly limits the methane oxidation reactivity by reducing the reaction rate of the rate-limited dissociation step under the high-temperature condition. The multi-scale kinetic simulations reveal that the maximum instantaneous rate of sulfurized oxygen carrier is decreased by 7.45 %, which is deemed as the attenuation factor of 0.9255 derived from the toxicological effects of sulfurization.

CFD modelling of a chemical looping combustion system − Exploring the potential of natural oxygen carriers

Research advancements in Carbon Capture technology has allowed for Chemical Looping Combustion (CLC) to emerge as a promising technique which can be feasibly implemented into existing power plant infrastructures. In this study, a 120 kWth interconnected Dual Circulating Fluidized Bed (DCFB) reactor has been studied, which uses methane fuel and NiO/Al2O3 particles as oxygen carrier. Two-dimensional transient CFD simulations have been conducted for the DCFB – CLC system using an Eulerian – Eulerian model coupled with heterogeneous reactions and the results have been compared to existing literature. Using the same methodology, two natural ore potential oxygen carriers in Pakistan: Hematite (Fe-based) and Hausmannite (Mn-based) have been evaluated for the same pilot scale apparatus. The fuel conversion and combustion efficiencies have been evaluated for the oxygen carrier particles and have been compared with the original system. The results show that Fe ore provides lesser combustion efficiency as compared to NiO, whereas Mn ore exhibits extremely high reactivity. In retrospect, the use of a mixed (Fe-Mn) oxide oxygen carrier can be considered as a viable option.

Mitigating ash-related alkali and heavy metals emissions in rotary kiln through oxygen-carrier-aided combustion of waste

Rotary kiln (RK) incineration technology gains prominence in waste management, aiming to reduce pollution, recover energy, and minimize waste. Oxygen-carrier (OC)-aided incineration of waste in the RK demonstrates notable benefits by enhancing oxygen distribution uniformity and facilitating fuel conversion. However, the effects of OC on ash-related alkali and heavy metals during waste incineration in the RK remain unknown. In this study, manganese ore and ilmenite as OCs are introduced into RK during waste combustion, focusing on their effects on the bottom ashes and the behavior of alkali and heavy metals. Results show that manganese ore exhibits a decreasing reactivity due to oxygen depletion during the conversion from Mn2O3 to Mn3O4, while ilmenite maintains good reactivity due to sustained enrichment of Fe2O3 on the particles even after multiple cycles in RK. The porous structure on the surface of OCs particles verifies the cyclic reaction involving oxidation by air and reduction by fuel as OCs move between the active and passive layers of the bed. The porous OCs particles offer abundant adsorption sites for K from the gaseous phase, with surface-deposited K migrating into the particles and enhancing the OCs' capacity for K adsorption. Adding OCs promotes the formation of stable, less volatile compounds of heavy metals (As, Cr, Pb, and Zn) and enhances their retention in bottom ash while ensuring the leaching toxicity remains below Chinese national standard limits. This study enhances the understanding of OCs in incineration, guiding vital references for waste management practices and environmental sustainability.

Evaluation of Fe-Ni Composite Oxygen Carrier in Coal Chemical Looping Gasification

Although coal chemical looping gasification (CCLG) is a promising technology for the efficient utilization of coal, limited studies concerned about the industrial application of oxygen carrier in CCLG system owing to its performance requirements including high reactivity with solid fuel, high carbon conversion, and good mechanical property. To meet the requirements of oxygen carriers in CCLG system, novel Fe-Ni composite oxygen carrier (OC) samples were successfully prepared. The performances of these OCs were evaluated in a fixed bed reactor, where they were reduced by solid fuel and then fully oxidized by air. Both fixed bed tests and thermodynamic analysis showed that the prepare OCs exhibited high reactivity with coal and syngas selectivity, making them suitable for the CCLG process. Specifically, when the loading amount of NiO was 20 wt%, the Fe-Ni composite OCs achieved the highest carbon conversion (93.03%) and synthesis gas selectivity (73.29%). Additionally, the thermogravimetric data revealed that the Curie temperature of the OCs was higher than 550°C, making them suitable for magnetic separation of the OC particles and carbon residue in the CCLG system.

Chemical looping with oxygen uncoupling of swine manure for energy production with reduction of greenhouse gas emissions

The thermochemical conversion of swine manure using chemical looping processes is an alternative for obtaining bioenergy with CO2 capture and solving environmental problems related to excess nutrients and greenhouse gas emissions. In this study, the combustion of swine manure was performed in a chemical looping with oxygen uncoupling (CLOU) unit at the 0.5 kWth scale with copper-based oxygen carrier particles supported on magnetic MnFe spinel. The effects of the fluidisation agent (CO2 or steam), air excess (7%–23%), and temperature (800–950 °C) on different parameters, namely the CO2 capture rate, combustion efficiency, and nitrogenous compound emissions, were analysed. High combustion efficiencies (95%–98%) were achieved, and tar compounds were not detected in the flue gases. Similarly, elevated CO2 capture efficiency values (82%–99%) were also achieved, which increased by increasing the temperature. Most nitrogen (ca. 93%–96%) is converted into innocuous N2. The NO concentration increased with temperature, whereas N2O and NH3 concentrations decreased.

Mid-temperature chemical looping methane reforming for hydrogen production via iron-based oxygen carrier particles

Chemical looping steam methane reforming (CL-SMR) via iron-based oxygen carriers is a promising method for efficient hydrogen production. To overcome challenges such as high reaction temperatures (>850 °C) and scarcity of low-cost, durable oxygen carriers (OCs), we have developed iron-based particles mixed with various ratios of nickel-based particles to achieve remarkable performance in CL-SMR at 600 °C. The mixed particles showed 85.23% methane conversion and 3.47 and 1.01 mL/min/gOC hydrogen production rates in the reduction and steam oxidation steps, respectively, in the two-step CL-SMR reaction. In the three-step CL-SMR reaction, air oxidation led to full recovery of oxygen carriers, enhancing methane conversion to 93.30% and elevating hydrogen production rate to 1.41 mL/min/gOC during steam oxidation. Precise control over methane conversion and hydrogen production in the three-step CL-SMR system is achievable by manipulating the mixing ratios of iron-based to nickel-based OC particles. Comprehensive experimental tests were conducted, covering practical aspects like support materials, gas velocity, and steam-to-carbon ratios. The outstanding cyclic stability of OC particles was confirmed over 200 consecutive redox cycles at 600 °C. The mid-temperature iron-based oxygen carrier particles, integrated with chemical looping demonstration project, might provide a powerful approach toward more efficient and scalable hydrogen production.

Mechanism of phase segregation in ilmenite oxygen carriers for chemical-looping combustion

The solid particle of oxygen carrier (OC) plays a vital role in chemical looping combustion (CLC) for fossil fuel combustion and inherent carbon capture. Phase segregation or active metal surface layer formation upon redox cycle had been recently noticed to be a predominant factor causing complete failure of OCs. To explored and identified the mechanism behind rapid phase segregation and external iron-rich shell formation of ilmenite OCs during CLC process, this study investigated into OCs’ phase and element distributions, and surface layer morphologies at various redox cycles, and the cross-sectional microstructures of oxidizing OC particles with different exposure times. The detailed information on the exterior Fe-rich shell formation and the progression of phase segregation were visualized, which provided vital information for the new mechanism of rapid Fe phase migration. The new finding ruled out Kirkendall effects or the ionic diffusion mechanism. The immediate formation of surface layer was found to initiate the segregation of Fe2O3 form TiO2 phase. The rapid Fe phase migration was attributed to the driving force arising from the increased local pressure of particles and the violent exothermic oxidation on reaction front. The strong driving force could directly eject iron-containing phases from the reaction front to surface layer. In the new mechanism, different phases separated inside the reduced OC particles provided the vital intermediates for the starting points of deep phase segregation or rapid surface layer formation; O2 dissociation of on the metallic Fe outmost layer and the oxygen ion conduction in TiO2 phase seemed to provide a short-circuit diffusion pathway for particle oxidation. Finally, this study also explored the strategies that might succeed in improving the integrity of ilmenite OC particles.

Alkali desorption from ilmenite oxygen carrier particles used in biomass combustion

Oxygen-carrying fluidized bed materials are increasingly used in novel technologies for carbon capture and storage, and to improve the efficiency of fuel conversion processes. Potassium- and sodium-containing compounds are released during biomass combustion and may have both negative and positive effects on conversion processes. Ilmenite is an important oxygen carrier material with the ability to capture alkali in the form of titanates. This is a desirable property since it may reduce detrimental alkali effects including fouling, corrosion, and fluidized bed agglomeration. This study investigates the interactions of alkali-containing compounds with ilmenite particles previously used in an industrial scale (115 MWth) oxygen carrier aided combustion system. The ilmenite samples were exposed to temperatures up to 1000 °C under inert and oxidizing conditions while the alkali release kinetics were characterized using online alkali monitoring. Alkali desorption occurs between 630 and 800 °C, which is attributed to loosely bound alkali at or near the surface of the particles. Extensive alkali release is observed above 900 °C and proceeds during extended time periods at 1000 °C. The release above 900 °C is more pronounced under oxidizing conditions and approximately 9.1 and 3.2 wt% of the alkali content is emitted from the ilmenite samples in high and low oxygen activity, respectively. Detailed material analyses using scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were conducted before and after temperature treatment, which revealed that the concentrations of potassium, sodium and chlorine decrease at the outermost surface of the ilmenite particles during temperature treatment, and Cl is depleted to a deeper level in oxidizing conditions compared to inert. The implications for ilmenite-ash interactions, oxygen carrier aided combustion and chemical looping systems are discussed.

Fate of ilmenite as oxygen carrier during 1 MWth chemical looping gasification of biogenic residues

Chemical looping gasification (CLG) is a novel gasification technology, allowing for the efficient conversion of different solid feedstocks (e.g. biogenic residues) into a high-calorific syngas. As in any chemical looping technology, the oxygen carrier (OC), transporting heat and oxygen from the air to the fuel reactor, is crucial in attaining high process efficiencies. To investigate the fate of the OC during CLG in an industrial environment, ilmenite samples, collected during >400 hours of chemical operation in 1 MWth scale using three different biomass feedstocks, were analyzed using different lab techniques. In doing so, changes in OC particle morphology and composition induced by CLG operation were determined. Moreover, the most important physical and chemical characteristics of the utilized OC were measured. The ensuing dataset allowed for an in-depth evaluation of the CLG technology in semi-industrial scale in terms of OC lifetime and durability. It was found that in the absence of agglomeration, the cycled OC exhibits an oxygen transport capacity of 2.6 wt.-%, a particle density of 3400 kg/m3 and particle diameters between 60 and 250 µm in steady-state conditions. Moreover, it was found that OC loss via particle attrition determines the lifetime of the OC inside the 1 MWth CLG system. On the other hand, feedstock-related agglomeration, observed during CLG operation with wheat straw, was shown to impede OC circulation between AR and FR and thus prevent efficient CLG operation. In summary, the present study thus not only highlights that generally long-term CLG operation in industry-like conditions is feasible, but also provides important insights into measures to improve OC lifetime and durability inside an industrial chemical looping system, such as an optimization of cyclone efficiency or tailored pre-treatment of the utilized feedstock.

Multiscale CFD modelling of syngas-based chemical looping combustion in a packed bed reactor with dynamic gas switching technology

Chemical looping combustion (CLC) is a highly efficient energy conversion technology designed for burning fossil fuel with inherent carbon capture potential. The main advantage of running the CLC process in a packed bed configuration over the conventional circulating fluidized bed setup is the ability to operate at high pressure. In this work, a dynamic multiscale model was developed to simulate packed bed syngas CLC with ilmenite oxygen carrier (OC) particles, subsequently validating simulation results in terms of fuel and OC conversion, and temperature distribution using literature data for both oxidation and reduction steps. The model was used for investigation of multiple cycle operation, intraparticle fuel and OC concentration distributions, as well as effects of particle sizes and flow rates during OC reduction. Results revealed pressure drop reductions by 45% for 50% larger particle sizes and 66% for 50% lower flow rates, as well as better bed utilization for lower particle sizes and flow rates based on fuel breakthrough curves. In addition, a CFD multilayer particle model was developed to strengthen multiscale model results on pressure drops and mass transfer efficiency, and study temperature distribution with respect to particle dimensions during OC oxidation. Results indicated a positive effect on energy efficiency for smaller particles due to higher packing density and particle surface area, reaching intraparticle temperatures of 1110 ℃ and exit gas temperatures of 980 ℃ (i.e., 13% higher than base case size) during OC oxidation.

CFD simulation of syngas chemical looping combustion with randomly packed ilmenite oxygen carrier particles

CFD simulation of syngas chemical looping combustion with randomly packed ilmenite oxygen carrier particles

Agglomeration mechanism of Fe2O3/Al2O3 oxygen carrier in chemical looping gasification

In chemical looping gasification (CLG), as one of the most commonly used oxygen carrier (OC), agglomeration is one of the most crucial triggers of Fe2O3/Al2O3 OC deactivation. However, the formation mechanism of agglomeration is not clear due to the complexity of the interaction between biomass and OC. In this study, we investigated agglomeration process of Fe2O3/Al2O3 OC in CLG from two dimensions of time and space. The results showed that in the time dimension, after ten cycles, the DT (deformation temperature) of the spent OC decreased by 5.39%, showing melting point was lower after cycles. Meanwhile, it caused the significant increase of the average particle size (59.73%) and the agglomeration degree (120.13%), indicating more severe agglomeration. Further, it led an obvious decrease in the CLG performance of efficiencies and gas yield. In the space dimension, when agglomeration occurred, low melting point K and Na compounds would first melt on the OC surface to form the K–Na inner layer (KAlSi2O6 and NaAlSiO4). As the reaction continued, high melting point Ca and Mg compounds would also be adhered to the surface of inner layer to form the Ca–Mg outer layer (CaAl2Si2O8 and Mg4Al10Si2O23), resulting in the continuous increase of OC particle size. In addition, more molten substances of KAlSi2O6 and NaAlSiO4 would lead to more adhesion between the OC particles.

Improvement of coal and Petroleum coke combustion in a fluidized bed by using ilmenite ore as bed material

Oxygen carrier-aided combustion (OCAC) is an innovative technology that adopts the reactive oxygen carrier (OC) particles as bed materials instead of inert ones, which improves the uniformity of temporal and spatial oxygen distribution in the fluidized bed combustor. However, the existing research of OCAC mainly focuses on high-volatile fuels, less attention has been paid to high-ash and low-volatile fuels (such as coal), which are widely used in the world. In this work, three kinds of solid fuels have been comprehensively evaluated in a lab-scale fluidized bed reactor. Results show that compared to quartz sands as bed material, the OC as bed material shows an apparent “oxygen buffering capacity”, improving combustion stability and reducing the unburnt gas. The promotion effect of OCAC increases with the increase of volatile content in fuel, which indicates that OCAC mainly improves combustion through the redox reaction between volatile and OC particles. The solid-solid reaction between OC and char was negligible. The OCAC experiment was carried out for more than 20 h and found that due to the abrasion of the OC surface, the generated fly ash has a significantly higher Fe content than that using quartz sand as bed material at the initial stage of the experiment, and the abrasion of OC decreases with the increase of experimental time. Interestingly, during a 20-h continuous operation, the reactivity of ilmenite ore increased gradually, which was attributed to the development of pore structure and Fe diffusion of ilmenite ore. In addition, the content of unburnt carbon in the fly ash is similar regardless of the bed materials.

Biomass ash chemistry in oxygen carrier aided combustion: Interaction between potassium and red mud

Oxygen Carrier Aided Combustion (OCAC) is a process that uses oxygen carrier particles to improve oxygen distribution in circulating fluidized bed reactors. Its application using biomass as fuel can increase fuel conversion, thus enhancing combustion efficiency. However, ash generated during combustion is a major challenge, with potassium-based ash being particularly problematic. Red mud is considered a potential low-cost oxygen carrier. In this study, the interaction mechanism of organic potassium (CH3COOK), as well as inorganic potassium (K2CO3, KCl, K2SO4, K3PO4) and red mud oxygen carriers, was investigated under an oxidizing atmosphere at 950 °C. Experiments were carried out on a TGA test bench and a fixed bed reactor. XRD and SEM-EDS were used to characterize the reaction products of the mixtures. Thermodynamic equilibrium calculations to support the experimental data. The results show that K enters the red mud oxygen carrier and forms mainly KAlSiO4 and KAlSi3O8. Some of the potassium salts lead to the formation of K-Fe-O material. The agglomeration of the bed material depends on the proportion of elements in the oxygen carrier and ash mixture. CH3COOK and K2CO3 are more likely to cause the reacting particles to stick together. KCl, K2SO4, and K3PO4 react with the red mud particles but have no obvious effect on the particles’ agglomeration.

Sulfur Interaction and Regeneration of CaMn0.775Ti0.125Mg0.1O2.9-δ Perovskite as Oxygen Carrier during Combustion of Sour Gas in a 500 Wth Chemical Looping Combustion Unit.

In the present study, the performance of a CaMn0.775Ti0.125Mg0.1O2.9-δ perovskite used as an oxygen carrier to burn sour gas with different H2S concentrations (up to 3000 vppm) in a continuous 500 Wth chemical looping combustion (CLC) prototype was investigated. After 29 h of sour gas combustion, the combustion efficiency had dropped by 18% in comparison with the reference test without sulfur addition. The characterization of the used particles of the perovskite confirmed that the presence of sulfur in the fuel gas had a poisonous effect through the formation of undesired compounds, such as CaSO4. The reactivity with CH4 and oxygen uncoupling capacity decreased, which could explain the decrease in the combustion efficiency. Two regeneration processes, one at high temperature (1273 K) and another one at low temperature (773-873 K), were carried out in a batch fluidized bed reactor to remove the amount of sulfur accumulated in the oxygen carrier particles. The detection of appreciable amounts of gaseous sulfur-based compounds (SO2 and H2S) during the experimentation and the postcharacterization results obtained through different techniques such as X-ray diffraction, ultimate analysis, and thermogravimetric analysis confirmed the effectiveness of both processes. Finally, the feasibility of implementation of the regeneration processes in a commercial CLC unit was thoroughly analyzed.

Understanding the structural changes on Fe2O3/Al2O3 oxygen carriers under chemical looping gasification conditions

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.

Particles attrition of binary mixtures in the coal-fueled chemical looping system based on fluidized bed

In this work, a reactive air jet attrition device with auto-recording and collection of elutriated fines was developed. Results established insights into the physiochemical interaction and further correlated attrition behaviors between char and oxygen carriers under various operation modes. The attrition rate increased by over 110% upon the introduced CO2, which brought in the significant effect of thermochemical stress, similarly in effects of the increased char addition ratio and the decreased sizes of char or hematite in different extents. For the char-hematite co-attrition process, the elutriated carbon loss of char with poor mechanical strength was found to be over 10%, while the reactive iron loss of hematite was found to be 6.3%, and was enriched in elutriated fines. The reaction-derived thermochemical stress and the collision-derived mechanical stress jointly controls the particle attrition during the cyclic transformation of oxygen carrier particles in coal-fueled chemical looping fluidization, especially significant in its reduction stage.

Integration of a novel Chemical Looping Combustion reactor into a thermochemical energy storage system

This study analyses the performance of a back-up power process that uses a novel chemical looping packed bed air reactor to oxidize a batch of reduced solids while heating high pressure flowing air. In this arrangement, the solids are slowly oxidized by a diffusionally-controlled flow of oxygen perpendicular to the main air flow, thus imposing very long oxidation times for all reacting particles. A decay in the thermal power output of the reactor can be expected with time due to the increasing resistance to O2 diffusion towards the unreacted oxygen carrier particles as the reaction progresses. In this work, integration of the dynamic system formed by the reactor and the power plant used to produce power from the exploitation of the variable thermal output of the reactor is investigated. Different case studies are assessed for decarbonization of energy production and storage of renewable energy. The reactor is rated at a maximum 50 MWth power output in all cases, employing iron- or nickel-based particles as oxygen carrier. A simplified model for mass and heat transfer in the proximity of the wall orifices allows the definition of operating windows and reactor dimensions. In the chosen case examples, each single reactor operates in discharge mode for around 4–5 h (depending on plant configuration) as a back-up power generator, heating up a compressed air stream up to ∼ 1000 °C and achieving an energy density between 816 and 2214 kWhth/m3. Gas turbines in recuperative, steam injected and combined cycle power plant architectures integrated in the novel chemical looping combustion (CLC) reactor are investigated. Cycle efficiencies up to 49% are calculated for systems that make use of a single reactor configuration and exploit the residual heat for power production through a organic Rankine cycle (ORC) bottomed system. A more flexible multi-reactor configuration is also investigated to address the unavoidable decay in power output during discharge and provide power output controllability. The levelized cost of electricity (LCOE) is estimated be comparable to system elements from the literature when H2 is used as reducing gas. The use of biogas to reduce the solids during the energy charge stage is found to be particularly advantageous, leading to LCOE values between ∼ 120 and 175 €/MWh for the reference reactor system using iron-based solids. This also allows achieving negative CO2 emissions if the captured CO2 generated during the reduction stage is stored.

Sintering and agglomeration characteristics of industrially prepared CaMn0.5Ti0.375Fe0.125O3-δ perovskite oxygen carrier in chemical looping combustion

The development of oxygen carrier particles that can be prepared on an industrial scale with good cycling stability remains a challenge in the field of chemical looping. In this work, a perovskite oxygen carrier (CaMn0.5Ti0.375Fe0.125O3-δ) was prepared by an industrial-scale spray drying granulation and tested on a fluidized bed thermogravimetric analyzer for long-term chemical looping combustion. The results showed that the attrition of oxygen carrier particles originated from irregular parts of the fresh particle surface early in the cycle, and the chemical stress on particles gradually increased with the number of redox cycles, increasing the attrition and sintering of the particles. In addition, as the cycle proceeds, the perovskite structure was destroyed and the oxygen carrier reacted chemically with the quartz tube wall and the air distribution plate leading to bonding. The deep redox cycling reactions indicated that agglomeration of particles occurred mainly in the reduction stage, with the bed entering repeated periods of defluidization during the 37th-43rd and 47th-55th cycles due to the changes in particle bonding and bed pressure. Fixed bed experiment showed that particle activation came from an increase in the active area of the particles during the cycle, independent of whether they were fluidized or not. In addition, agglomeration started at the contact surface between the air distribution plate and the particles, resulting in blocked oxidation of the particles and deepening agglomeration due to excessive reduction of the particles.