Fluidized Bed Reactor Research Articles

A Review: Membrane Reactor for Hydrogen Production: Modeling and Simulation

A membrane reactor is a multifactional vessel used for H2 production. Hydrogen's three spectrum colors are dependent on carbon present. Two types of membrane with high permeability to hydrogen (polymeric and metallic) Hydrogen is produced in two systems: conventional reactors and membrane reactors (which separate and purify hydrogen in a single vessel). There are many types of membrane reactors according to design (catalytic membrane reactor (CMR), fixed bed reactor (FBMR), fluidized bed reactor (FBMR), etc. The transport mechanism of H2 through the membrane by a "sorption-diffusion mechanism" and the government equations that are used for membrane reactor modeling and simulation, such as continuity, momentum, mass, and heat transfer equations of the CMR, and the thickness of the membrane. These equations are solved by MATLAB, COMSOL, and the Finite Element Method to simulate the MR at different parameters: rate of conversion, rate of sweep gas, temperature, pressure, rate of H2 permeation through a membrane, and activity of the catalyst. We summarized theoretical studies for membrane reactors, including the operation conditions, type of hydrocarbon feed, type of production method, kind of catalyst, and heat effect.

Photo-Fenton remediation of textile wastewater in fluidized-bed reactor using modified laterite: Hydrodynamic study and effect of operating parameters

There has been an increased interest for the use of naturally available catalysts in Fenton oxidation procedures. Nevertheless, the potential of laterite soil for the removal of aqueous pollutants via Fenton based technique has not been exhaustively explored. The fluidized bed photo Fenton approach was used in this study to treat textile wastewater with the goal of reducing total organic carbon (TOC) in the wastewater. Thermally modified laterite soil was used as a catalyst in the photo-Fenton process. Severalcharacterizationtechniques including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray powder diffraction (XRD) and X-ray photo-electron spectroscopy (XPS), were used to gain insight into the characteristics of a modified laterite catalyst. The application of this catalyst resulted in a significant reduction of total organic carbon (TOC) present in the textile wastewater. Specifically, a TOC reduction of 83% was observed after a reaction period of 100 min, at pH 3, 10 mm of bed height, 30 mM of H2O2 concentration, and a recirculating feed flow rate of 170 ml/min. Kinetic and hydrodynamic investigations were also carried out to have a better understanding of the catalytic processes occurring inside the fluidized-bed reactor. A first-order kinetics could potentially be used to explain the photo-degradation of textile effluent. Up to three successive oxidation cycles, laterite exhibited notable catalytic stability attributed to lesser surface site deactivation. A cost-benefit analysis of the fluidized bed photo-Fenton technique for treating textile effluent was also performed. The fluidized-bed Fenton approach may be a feasible option for treating wastewater containing different colours because of its low operating costs and low environmental effect.

Solar-driven biomass steam gasification by new concept of solar particles heat carrier with CPFD simulation

Solar-driven biomass gasification is a promising solar thermochemical technology to produce green H2-enriched syngas, and contribute to solar energy upgrade and efficient conversion. Whereas, the continuous and stable operation of solar-driven biomass gasification is challenging due to the non-uniform concentration of solar flux and its fluctuating nature. In this regard, a novel concept of solar-driven gasification is proposed, using solar-heated particles as the heat carrier, and biomass steam gasification in a fluidized bed reactor is numerically investigated based on the computational particle fluid dynamics (CPFD) model. The complex distributions of gas and particle phases, as well as the effects of operation parameters on syngas species are comprehensively analyzed. Results indicate that the biomass material and solar-heated particles can be well-mixed through continuous feeding, and the internal heat transfer and gasification kinetics are enhanced. The mole fraction of H2 and CO in the produced syngas reach to 50.86% and 18.97% under the benchmark operating condition. By using the high-temperature quartz sand as the solar particles heat carrier, the long-term and continuous operation of the endothermic gasification process can be achieved. The newly developed solar-driven biomass gasification method provides a promising approach to mitigate the impact of the fluctuating solar irradiation and enhance the operational flexibility of gasification process.

Prediction of fluidization behaviors of rough sphere with a TFM-DEM hybrid model

Some industrial processes like biomass combustion and gasification involve multi-component fluidization systems with a clear discrepancy of particle size, which restricts the utilization of some traditional simulation methods. In this work, a TFM-DEM hybrid model is employed to evaluate flow behaviors of binary mixture in a fluidized bed reactor with a great discrepancy of particle size, where the rotational effect of bed material is described by the kinetic theory of rough sphere (KTRS) and the fluctuating energy transfer between discrete particles and continuous solid phase is considered. The model prediction is validated by the experimental result. The results reveal that considering the collisional effect on solid-solid interaction, bed material fluctuating energy is weakened and more energy is transferred to fuel particles. Meanwhile, the ratio of collisional dissipation to total energy consumption with particle roughness is also analyzed.

Influence of bed material on biomass gasification in fluidized beds via a TFM-DEM hybrid model

In the biomass gasification process, mixing and segregation behaviors of fuel particles and bed materials greatly influence the performance. In this work, the Two-Fluid Model-Discrete Element Method (TFM-DEM) hybrid model is employed to evaluate the impact of bed material on biomass gasification in a fluidized bed reactor, where fuel particles and bed material particles are described by the Lagrangian method and Eulerian method respectively. The biomass particle size distribution is taken into consideration. The kinetic theory of rough sphere (KTRS) is employed to consider the rotation impact of bed materials. Flow behaviors of binary mixture and gas composition distribution are analyzed. The results reveal that the bed materials with greater size can hinder the particle mixing behaviors and make the biomass particles concentrate on the bed surface so as to increase the non-uniformity of temperature distribution in the bed. A good fluidization with smaller bed material particles is beneficial to hydrogen production.

Optimization of multiple-chamber fluidized beds using coarse-grained CFD-DEM simulations: Regulation of solids back-mixing

The intense solids back-mixing has been one of the major disadvantages of gas-solid fluidized bed reactors for certain applications. In this study, coarse-grained CFD-DEM simulations are carried out to regulate the solids back-mixing in multiple-chamber fluidized beds by investigating the effect of the orifice size, the orifice location, the gas velocity of each chamber, and then the effect of the pipe length connecting adjacent chambers. The results indicate that optimizing the orifice size, the orifice location, and the gas velocity of each chamber can suppress the solids back-mixing to a certain extent. However, there is still a gap between the optimized design and the ideal situation. Therefore, using a sufficiently long pipe instead of a baffle with orifice is further proposed to completely suppress the solids back-mixing between adjacent chambers, which is validated using coarse-grained CFD-DEM simulations. Present results provide a means to regulate the solids back-mixing in multiple-chamber fluidized beds via proper design of bed geometry.

Numerical Study on the Process of Chemical Looping Hydrogen Production with Multiple Circulating Fluidized Bed Reactors

Numerical Study on the Process of Chemical Looping Hydrogen Production with Multiple Circulating Fluidized Bed Reactors

Heterogeneous Fe-Co dual-atom catalyst outdistances the homogeneous counterpart for peroxymonosulfate-assisted water decontamination: New surface collision oxidation path and diatomic synergy.

Heterogeneous catalysts lag far behind their homogeneous counterparts in activating peroxymonosulfate (PMS) for water decontamination due to the low site intrinsic activity and sluggish mass transfer. The single-atom catalyst can bridge the gap between heterogeneous and homogeneous catalysts, but the difficulty to break scaling relations originating from the site monotony restricts further efficiency upgradation. Herein through modulating the crystallinity of NH2-UIO-66, a porous carbon support with ultrahigh surface area (1721.71 m2 g-1) is obtained to anchor the dual-atom FeCoN6 site, which exhibits superior turnover frequency over single-atom FeN4 and CoN4 sites (13.07 versus 9.97, 9.07 min-1). The as-synthesized composite thus outperforms the homogeneous catalytic system (Fe3++Co2+) for sulfamethoxazole (SMZ) degradation, and the catalyst-dose-normalized kinetic rate constant (99.26L min-1 g-1) exceeds reported values by 1∼2 orders of magnitude. Moreover, only 20mg of the catalyst can run a fluidized-bed reactor to realize continuous zero discharge of SMZ in multiple actual waters for up to 8.33h. Unlike all reported reaction routes, the catalysis on the diatomic site follows a new surface collision oxidation path, i.e. the dispersed catalyst adsorbs PMS to generate surface-activated PMS with high potential, which collides with surrounding SMZ and directly seizes electron from it to induce pollutant oxidation. Theoretical calculation indicates that the enhanced activity of FeCoN6 site stems from the diatomic synergy, leading to stronger PMS adsorption, larger near-Fermi-level density of states and optimal global Gibbs free energy evolution. Overall, this work provides an effective strategy of constructing heterogeneous dual-atom catalyst/PMS process to achieve faster pollution control than homogeneous system, and sheds light on the interatomic synergetic mechanism for PMS activation.

Carbon coating optimization on porous silicon as high-performance anode material via fluidized bed chemical vapor deposition

The carbon layer coating is a promising solution to volume expansion and low electron conductivity in silicon-based anodes during lithiation. While numerous methods exist to generate these carbon coatings, Fluidized Bed Chemical Vapor Deposition (FBCVD) has proven superior due to its capacity for producing remarkably uniform and consistent carbon layers, primarily as a result of efficient mass and heat transfer characteristics. However, its application in the context of lithium-ion battery anodes has been sparsely explored and has been principally limited to silicon oxide as the base material. In this paper, porous silicon (PSi) obtained through acid etching of AlSi alloy with an average particle size of 300 mesh was taken as raw materials, and a fluidized bed reactor was employed to realize a uniform and tightly packed carbon layer. Relatively speaking, the PSi@C30 in this work offers a simpler process and promising electrochemical performance, opening a new door for the preparation of high-performance silicon-carbon anodes by FBCVD. Besides, PSi and high-quality carbon layers with structural advantages enabled the authors to obtain high-performance silicon-carbon anode materials. The resulting PSi@C30 composite demonstrated excellent initial coulomb efficiency (88.8 %) and cycling stability (with 83 % capacity retention after 100 cycles at 0.5 A g-1 and a reversible capacity of 1408 mAh g-1). Such a cost-effective and user-friendly technique facilitates the application of FBCVD in silicon-based anode materials for Li-ion batteries, thus accelerating the industrialization of silicon-carbon anodes for high-performance Li-ion batteries in the future.

In-situ gas flow separation between biochar and the heat carrier in a circulating fluidized bed reactor for biomass pyrolysis

The circulating fluidized bed (CFB) reactor is extensively utilized in biomass fast pyrolysis, which typically employs a heat carrier as a heat transfer medium. The regeneration of the heat carrier relies on carbon combustion. However, direct combustion of carbon for heating purposes results in ash accumulation, leading to decreased yields of bio-oil and biochar. To overcome the limitations of conventional techniques and address the challenges associated with separating biochar from the heat carrier, a novel in-situ gas flow bed separator was designed. This separator enables continuous, rapid, and highly efficient separation of biochar and the heat carrier. The impact of various operational conditions on separation efficiency was investigated, and the operational range that yields effective and efficient separation was obtained. The entrainment effect of bubble wakes on particles and the mechanism of binary particles distribution in the bubble hole in the gas flow bed were investigated by numerical simulation and a high-speed digital camera. The results show that bubble activity, as well as the density and size disparities of binary particles, significantly influence the separation process. When the mass ratio of binary particles and U/Umf (the ratio of fluidization velocity to the minimum fluidization velocity) were 30/1 and 1.67, the separation efficiency of carbon and the heat carrier could reach 99%. This innovative technology holds tremendous potential for substantially enhancing product yields in CFB systems, thereby significantly increasing their competitiveness in fast pyrolysis applications.

System Hydrodynamics of a 1 MWth Dual Circulating Fluidized Bed Chemical Looping Gasifier

Chemical looping gasification (CLG) is a novel dual-fluidized bed gasification technology that allows for the production of high-calorific syngas from various solid feedstocks (e.g., biomass). Solid circulation between the two coupled fluidized bed reactors, serving the purpose of heat and oxygen transport, is a key parameter for the CLG technology, making system hydrodynamics the backbone of the gasification process. This study serves the purpose to provide holistic insights into the hydrodynamic behavior of the dual-fluidized bed reactor system. Here, special focus is placed on the operational principles of the setup as well as the entrainment from the circulating fluidized bed (CFB) reactors, the latter being the driving force for the solid circulation inside the entire reactor system. Using an elaborate dataset of over 130 operating periods from a cold flow model and 70 operating periods from a 1 MWth CLG pilot plant, a holistic set of ground rules for the operation of the reactor setup is presented. Moreover, a novel easily-applicable approach, solely relying on readily-available live data, is presented and validated using data from the 1 MWth chemical looping gasifier. Thereby, a straightforward estimation of solid entrainment from any CFB setup is facilitated, thus closing a crucial research gap.

Numerical investigation of sewage sludge combustion in a fluidized bed reactor: A comparison of 2D and 3D simulations

Combustion of sewage sludge is a technology with high relevance both, regarding energy efficiency and recovery of valuable substances like phosphor. The combustion is usually performed in a fluidized bed. CFD modelling is a central element of the optimization of this process. However, there are a number of modelling approaches available, with different advantages and disadvantages concerning accuracy and computational power. In this study, a new simplified reactor design for sewage sludge fluidized bed combustion was analyzed by CFD simulations based on the Eulerian multiphase approach and a formulated model for thermal conversion. The CFD simulations were carried out in 2D as well as 3D and the numerical results were utilized for a methodological comparison. This enables a scientifically sound recommendation on a suitable numerical approach based on the evaluation parameters of interest. As a conclusion of the investigations, the computationally more expensive 3D approach regarding simulation time should be used if the quantitative flow evaluation of the entire reactor is in focus. The 2D approach is well suitable to resolve fluidization and sludge mixing behavior within the sand bed, if the general combustion behavior is of interest. In the light of the significantly faster simulation, it can be recommended as a suitable method for preliminary analyses. The numerical results for typical evaluation parameters like gas temperature or the residual oxygen content at the gas outlet are presented. Local flow differences within the freeboard are deduced between the 2D and 3D approaches so that expectable differences are better assessable during the reactor design phase.

Investigation of hydrogen production via waste plastic gasification in a fluidized bed reactor using Aspen Plus

Plastic waste-to-energy conversion via gasification is a promising method for hydrogen production. In this study, the effects of waste plastic type, equivalence ratio, operating temperature and pressure on the hydrogen production from waste plastics in a fluidized bed reactor were investigated. A precise model of the air gasification process of five different types of waste plastics was developed using modules available in Aspen Plus. Following the model validation, a parametric study was conducted by varying the temperature in the range of 600 °C–1200 °C, the equivalence ratio between 0.05 and 0.50, and the pressure between 1 bar and 50 bar. This study provides valuable information on the impact of different process parameters on the air gasification of various waste plastics which has not been reported extensively. The conversion behaviours of air gasification process for waste plastics were characterized based on syngas composition, syngas lower heating value, hydrogen yield and cold gas efficiency. The simulation results for hydrogen production, which ranged from 15.33 Nm3/ton feed to 284.40 Nm3/ton feed for all plastics, were found to be consistent with experimental results. As a result, the optimal conditions for achieving maximum hydrogen yield in the waste plastic gasification process have been determined and reported.

Enhancing the pyrolytic conversion of biosolids to value-added products via mild acid pre-treatment

High concentrations of inorganic matter such as silicates, alkali and alkaline earth metals (AAEMs), and heavy metals (HMs) in biosolids limit their pyrolysis conversion to high-value products. Therefore, the reduction or passivation of the deleterious pyrolytic activities of these native inorganics in biosolids can enhance the yield and quality of products obtained during pyrolysis. The pyrolysis of raw and 3% sulfuric acid pre-treated biosolids was carried out in a fluidised bed reactor at 300–700 ℃, and the influence of pre-treatment was examined on biochar properties, gas production, and bio-oil composition. At all temperatures, the selective removal of ash-forming elements (demineralisation) in biosolids by pre-treatment improved organic matter devolatilisation yielding higher bio-oil and lower biochar than untreated biosolids. Demineralisation weakened gas production, particularly at higher pyrolysis temperatures. At 700 ℃, the in-situ formation of acidic metal sulfate salts in sulfuric acid-infused biosolids facilitated H+ release, thereby increasing H2 yield to a maximum of 15 mol% compared to 8 mol% from untreated biosolids and 4 mol% from demineralised biosolids. Biochar produced from treated biosolids had considerably lower HMs concentration and higher organic matter retention compared to raw biosolids biochar. The effect of pre-treatment on biochar properties was profound at 700 ℃ pyrolysis temperature. Pre-treatment increased biochar fixed carbon by 57%, calorific value by 37%, fuel ratio by 44%, doubled the specific surface area from 55 to 107 m2/g, and enhanced porous structure formation. At 300 ℃, the major chemical compounds in the bio-oil were amides (20%), N-heterocyclics (25%), and ketones (30%), and higher temperatures favoured phenols and aromatic hydrocarbon production. Pre-treatment enhanced the selectivity of furans by 10-fold, anhydrosugars by 2-fold, and aromatic hydrocarbons by 1.5-fold relative to the raw biosolids bio-oil. Acid pre-treatment is a promising strategy for improving biosolids quality as feedstock for pyrolysis to generate high-value products.

Syngas Production from Protective Face Masks through Pyrolysis/Steam Gasification

The COVID-19 pandemic has caused a heavy expansion of plastic pollution due to the extensive use of personal protective equipment (PPE) worldwide. To avoid problems related to the entrance of these wastes into the environment, proper management of the disposal is required. Here, the steam gasification/pyrolysis technique offers a reliable solution for the utilization of such wastes via chemical recycling into value-added products. The aim was to estimate the effect of thermo-chemical conversion temperature and steam-to-carbon ratio on the distribution of gaseous products obtained during non-catalytic steam gasification of 3-ply face masks and KN95 respirators in a fluidized bed reactor. Experimental results have revealed that the process temperature has a major influence on the composition of gases evolved. The production of syngas was significantly induced by temperature elevation from 700 °C to 800 °C. The highest molar concentration of H2 gases synthesized from both types of face masks was estimated at 800 °C with the steam-to-carbon ratio varying from 0 to 2. A similar trend of production was also determined for CO gases. Therefore, investigated thermochemical conversion process is a feasible route for the conversion of used face masks to valuable a product such as syngas.

Predictive control of reactor network model using machine learning for hydrogen-rich gas and biochar poly-generation by biomass waste gasification in supercritical water

Supercritical water gasification (SCWG) technology can convert biomass into hydrogen rich gas and biochar. Fluidized bed reactor is promising for the industrialization of this technology, and the reactor dynamic performance study is of great significance for its scaling up. However, current simulation studies mainly focus on steady-state analysis using Computational Fluid Dynamics (CFD) software, it is difficult to conduct dynamic study due to its high computational costs. To this end, a reactor network model (RNM) that accounts for the flow, heat transfer, and kinetic dynamics for fluidized bed reactor is firstly developed based on the partitioning theory, which can reduce the computation time of dynamic simulation from several days to seconds. Additionally, extensive open-loop simulations of the RNM are carried out to generate the dataset for the development of a recurrent neural network (RNN) model. Additionally, current studies mainly focus on open-loop simulation, closed loop optimization is absent. To this end, a framework for building a machine learning (ML) model and a ML-based nonlinear predictive control scheme is developed. Model predictive control (MPC) schemes based on the RNN model is used to optimize the SCWG process to achieve multiple objectives, such as maximizing hydrogen yield and carbon yield. The open loop simulation results demonstrate that H2 yield decreases from 0.00022 to 0.0002 kg s−1 with temperature reducing from 700 to 600 °C. To increase H2 yield to the setpoint, MPC increases temperature and mass flowrate to 708 °C and 417.57 kg h−1. Additionally, MPC increases carbon yield and minimizing CO2 yield by decreasing temperature to 475 °C and increasing mass flowrate to 407.38 kg h−1.

Carbon dioxide gasification characteristics of disposable COVID-19 masks using bubbling fluidized bed reactor

The global demand for masks has increased significantly owing to COVID-19 and mutated viruses, resulting in a massive amount of mask waste of approximately 490,000 tons per month. Mask waste recycling is challenging because of the composition of multicomponent polymers and iron, which puts them at risk of viral infection. Conventional treatment methods also cause environmental pollution. Gasification is an effective method for processing multicomponent plastics and obtaining syngas for various applications. This study investigated the carbon dioxide gasification and tar removal characteristics of an activated carbon bed using a 1-kg/h laboratory-scale bubble fluidized bed gasifier. The syngas composition was analyzed as 10.52 vol% of hydrogen, 6.18 vol% of carbon monoxide, 12.05 vol% of methane, and 14.44 vol% of hydrocarbons (C2–C3). The results of carbon dioxide gasification with activated carbon showed a tar-reduction efficiency of 49%, carbon conversion efficiency of 45.16%, and cold gas efficiency of 88.92%. This study provides basic data on mask waste carbon dioxide gasification using greenhouse gases as useful product gases.

Solvent-Free Enzymatic Synthesis of Dietary Triacylglycerols from Cottonseed Oil in a Fluidized Bed Reactor.

The synthesis of structured lipids with nutraceutical applications, such as medium-long-medium (MLM) triacylglycerols, via modification of oils and fats represents a challenge for the food industry. This study aimed to synthesize MLM-type dietary triacylglycerols by enzymatic acidolysis of cottonseed oil and capric acid (C10) catalyzed by Lipozyme RM IM (lipase from Rhizomucor miehei) in a fluidized bed reactor (FBR). After chemical characterization of the feedstock and hydrodynamic characterization of the reactor, a 22 central composite rotatable design was used to optimize capric acid incorporation. The independent variables were cycle number (20-70) and cottonseed oil/capric acid molar ratio (1:2-1:4). The temperature was set at 45 °C. The best conditions, namely a 1:4 oil/acid molar ratio and 80 cycles (17.34 h), provided a degree of incorporation of about 40 mol%, as shown by compositional analysis of the modified oil. Lipozyme RM IM showed good operational stability (kd = 2.72 × 10-4 h-1, t1/2 = 2545.78 h), confirming the good reuse capacity of the enzyme in the acidolysis of cottonseed oil with capric acid. It is concluded that an FBR configuration is a promising alternative for the enzymatic synthesis of MLM triacylglycerols.

Synthesis and application of alginate-nanocellulose composite beads for defluoridation process in a batch and fluidized bed reactor

Electronegative Fluorine has great reactivity and it exists as organic or inorganic fluoride compounds. Biosorption feasibility of fluoride onto alginate-cellulose composites was investigated in this study. Extracted cellulose has been utilized to synthesize calcium alginate impregnated composite beads for fluoride remediation process in batch and fluidized-bed reactors. Physiochemical characteristics were analyzed by FTIR, SEM, TGA and BET. From the BET properties analysis, the surface area of prepared composite beads was 87.13 m2/g. The point zero charge (PZC) value of composite beads was attained at pH 7.32. The relationship between biosorption efficiency and independent variables have been observed to evaluate the effects on the fluoride biosorption efficiency of composites and its components. The hypothetical development of the removal technique has been explained using various nonlinear model-fitting methods to evaluate Isotherm study, bio-sorption Kinetics, Thermodynamic parameters and Mass transfer study. Maximum monolayer adsorption capacity (qm) obtained by following Langmuir model for fluoride removal was found to be 23.809 mg/g at 30 °C using adsorbent dosage of 2 g/L for an initial fluoride concentration of 6 mg/L. The optimized condition for fluoride adsorption experiment was observed by evaluating response surface methodology (RSM) was pH-5.67, dose 1.89 g/L and time 85.71 min and removal was found as 82.79%. Experimental data of fluidized-bed study were evaluated by designing mathematical modeling. Fluidization velocities was adjusted in between Umf and 2Umf for optimizing external mass transfer and adsorbent loss. Regeneration study of fluoride loaded biosorbent and cost analysis of composite production have been estimated.

Effect of time-dependent layer formation on the oxygen transport capacity of ilmenite during combustion of ash-rich woody biomass

Oxygen carrier aided combustion (OCAC) is a novel technology that aims to enhance combustion of heterogenous fuels by replacing the inert bed material with an active oxygen carrier. One of the promising oxygen carriers is natural ilmenite which shows decent oxygen transport capacity and mechanical stability under OCAC operating conditions. However, interactions between ilmenite and woody biomass ash lead to the formation of a calcium-rich ash layer, which affects the ability of the oxygen carrier (OC) to transfer oxygen throughout the boiler and subsequently decreases the combustion efficiency. This paper focuses on the time-dependent morphological and compositional changes in ilmenite bed particles and the consequence effects on the oxygen transport capacity and reactivity of ilmenite. Ilmenite utilized in this study was investigated in a 5 kW bubbling fluidized bed combustion unit, utilizing ash-rich bark pellets as fuel. A negative effect of iron migration on the oxygen transport capacity was observed in ilmenite bed particles after 6 h of operation in the bubbling fluidized bed reactor. The decrease in the oxygen transport capacity of ilmenite was found to correlate with the increased exposure time in the fluidized bed reactor and was caused by the migration and subsequent erosion of Fe from the ilmenite particles. On the other hand, the older bed particles show an increase in reaction rate, presumably due to the catalytic activity of the calcium-enriched outer layer on the bed particle surface.