Bed Thermogravimetric Analysis Research Articles

Mechanistic study of integrated CO2 capture and utilization over Cu and Al-modified calcined limestone with high stability using MFB-TGA-MS

This study explores the performance of dual-functional materials (DFMs) in cyclic integrated CO2 capture and reverse water–gas shift (ICCU-RWGS) reactions under fluidized, isothermal conditions. DFMs with a copper catalyst and alumina support on calcined natural limestone were analyzed using micro-fluidized bed thermogravimetric analysis coupled with mass spectrometry (MFB-TGA-MS). The results indicate that the 10 %Cu5%Al-CaO-IMP surpasses others, demonstrating a CO2 capture capacity of 10.67 mmol⋅g−1, 71.5 % in-situ CO2 conversion at 700 °C, and remarkable cyclic stability over 30 cycles. Cu and Al additions curtail CaO agglomeration during extended ICCU-RWGS and enhance CO2 and H2 activation by removing surface formate species, promoting CO production. Furthermore, non-catalytic gas–solid reactions coexist with catalytic gas–solid reactions, leading to gradual Cu particle coating by CaCO3 during carbonation. This phenomenon prevents Cu sintering but slightly reduces catalytic activity. These findings, combined with cost-effective materials (CaO, Cu, Al), hold significant promise for efficient and economically viable ICCU processes.

An experimental and kinetic modeling study of CO2 hydrogenation to CO over Cu-Al catalyst utilizing MFB-TGA-MS

Carbon capture, utilization, and storage (CCUS) are essential technologies for realizing carbon neutrality in the context of fossil fuel decarbonization. Integrated carbon capture and utilization, in conjunction with the reverse water gas shift reaction (ICCU-RWGS), presents a promising strategy for the in-situ conversion of CO2. This approach mitigates the energy penalties associated with CO2 capture and eliminates the additional costs associated with storage and transportation. In this study, we employed a Cu-Al composite catalyst, prepared using the impregnation method, for ICCU-RWGS, with a specific focus on CO2 hydrogenation. The kinetics of hydrogenation for the Cu-Al catalyst were comprehensively investigated using micro-fluidized bed thermogravimetric analysis coupled with mass spectrometry (MFB-TGA-MS). The results indicate that, when subjected to experimental conditions involving 800 °C, 20 vol.% CO2, 30 vol.% H2, and a sample mass of 1 g, the comprehensive evaluation reveals a CO2 conversion rate of 43.67 %. This conversion is accompanied by 100 % CO selectivity and a reaction rate of 0.10 mmol·g−1·s−1, respectively. Furthermore, we calculated the kinetic parameters for the CO2 hydrogenation by analyzing the MFB-TGA-MS data, utilizing the simplified K-L model for fluidized beds. The results indicated an activation energy of 55.8 kJ∙mol−1. These findings highlight the effectiveness of ICCU-RWGS methodologies, especially concerning CO2 hydrogenation, and present a compelling case for their further commercialization.

Metal oxide and nitrate-modified calcium gluconate-based sorbent with high stability for integrated carbon capture and utilization process

In this study, metal oxides (MgO, CeO2, and Al2O3) and metal nitrates (Mn(NO3)2, Al(NO3)3, Mg(NO3)2, and Fe(NO3)3) were used to modify calcium gluconate-based sorbents for the integrated CO2 capture and utilization (ICCU) process. We employed conventional thermogravimetric analysis (TGA) and microfluidized bed thermogravimetric analysis coupled with mass spectrometry (MFB-TGA-MS) to explore the cyclic CO2 capture behavior, physical and chemical properties, and morphology in detail. Our findings reveal that calcium gluconate modified with aluminum nitrate (CG-Al-N) exhibited superior CO2 capture capacity (9.81 mmol∙g−1 over 20 cycles), along with a high surface area (35.67 m2∙g−1) and pore volume (0.16 cm3∙g−1). In comparison, pure calcium gluconate displayed a capacity of 7.09 mmol∙g−1, a surface area of 27.66 m2∙g−1, and a pore volume of 0.06 cm3∙g−1, while commercial calcium oxide demonstrated 1.96 mmol∙g−1, 4.62 m2∙g−1, and 0.01 cm3∙g−1, respectively. Notably, after 100 cycles, CG-Al-N retained a CO2 capture capacity of 11.75 mmol∙g−1, achieving 66% of the capacity of the pure CaO sorbent. This observation strongly suggests that CG-Al-N has excellent anti-sintering properties. Furthermore, data was acquired under fluidized and isothermal conditions by utilizing MFB-TGA-MS. CG-Al-N consistently exhibited an average CO2 capture capacity (9.57 mmol∙g−1), CO yield (5.00 mmol∙g−1), and CO selectivity (∼100%) over 20 ICCU cycles, with the dominant route being the reverse water–gas shift (RWGS) reaction, highlighting the self-catalytic activity of gluconate-based sorbents. Morphological evolution also revealed finer pores and a skeleton structure of cycled CG-Al-N, which affirms the unobstructed gas entry and ensures a continuous gas–solid reaction.

Limestone hydrogenation combined with reverse water–gas shift reaction under fluidized and iso-thermal conditions using MFB-TGA-MS

The integrated CO2 capture and utilization (ICCU) in conjunction with the reverse water–gas shift (RWGS) reaction has emerged as a promising approach to achieve carbon neutrality. However, the scalability of CaCO3 hydrogenation in the context of large volumes of industrial flue gas is impeded by the limited understanding of its performance under fluidized and iso-thermal conditions. This study utilized micro-fluidized bed thermogravimetric analysis coupled with mass spectrometry (MFB-TGA-MS) and in-situ measurements to investigate limestone decomposition under H2 and Ar atmospheres. Results showed that H2 atmosphere increased the limestone decomposition rate by 5-fold (79.1% CO2 conversion and ∼100% CO selectivity at 710 °C) compared to Ar, with RWGS as the dominant route and self-catalytic activity of calcined CaO. Morphology evolution revealed finer pores and textures under H2 conditions. Meanwhile, apparent kinetic models analyzed experimental data and showed a reduction in activation energy from 178.5 kJ/mol (Ar) to 161.3 kJ/mol (H2). These findings support the effectiveness of ICCU-RWGS approaches for further commercialization.

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.

Biomass pellet fueled chemical looping gasification: Reaction kinetics study with a fluidized bed - thermogravimetric analysis

Biomass pellets show the advantages of higher energy density, lower transportation and storage costs compared to powder biomass, making them attractive for future industrial applications. In this work, a fluidized bed-thermogravimetric analysis (FB-TGA) is developed. The gas-solid process for gram-scale biomass pellets under fluidization state at high temperature is characterized. The effects of gasification agents, bed material components and operating conditions on devolatilization and char gasification are investigated. The devolatilization is revealed to be a rapid phase transition process of volatiles, of which the rate is mainly affected by the intense heat and mass transfer with increasing temperature. While the char gasification is significantly slower, taking more than 600 s for all conditions, therefore be considered as the rate-control step. The hematite oxygen carrier can effectively promote the char gasification by breaking the concentration balance of gas components near the char surface. The char reaction kinetics is fitted based on the isothermal differential method. Results show that the cylindrical geometrical contraction model exhibits an excellent linear correlation. With a mass ratio of oxygen carrier/quartz sand of 1:9, the average activation energies of 130.58 kJ/mol and 104.17 kJ/mol are obtained when CO2 and steam as gasifying agents.

Limestone Calcination Kinetics in Microfluidized Bed Thermogravimetric Analysis (MFB-TGA) for Calcium Looping

Limestone calcination is an important part of calcium looping (CaL) technology and is critical to the design and operation optimization of fluidized bed reactors. However, obtaining a method of measuring the fast calcination kinetics in a fluidizing environment with isothermal conditions is still a challenge in the field of calcium looping. We address this challenge in this work and develop a new method of obtaining limestone calcination kinetics by injecting limestone particles into the hot fluidizing sands in a microfluidized bed thermogravimetric analysis (MFB-TGA) with a mass measurement resolution of 1 mg. The calcination characteristics of limestone are investigated at different particle sizes (150–1250 μm), temperatures (750–920 °C), and CO2 concentrations (0–30 vol.%). The experimental data measured from MFB-TGA were analyzed using a detailed model including surface reaction and intraparticle and external diffusion. The results show that the kinetics of limestone calcination measured by MFB-TGA are faster than those measured via regular TGA. This particle-injecting method of MFB-TGA provides a new experimental idea for measuring fast calcination kinetics occurring inside fluidized bed reactors and provides guidance on the application of CaL technology.

Cycling performance of composite hematite and copper ore oxygen carrier in chemical looping combustion

A single natural ore oxygen carrier (OC) has a limited industrial application due to its weak reactivity and cyclic stability. For the composite hematite and copper ore OC prepared by spray drying granulation, long-term chemical looping combustion (CLC) cycle tests were performed on a fluidized bed thermogravimetric analyzer (FB-TGA). The results showed that a substantial mechanical stress and the presence of partially enriched fine particles on the surface of new OC particles caused a high attrition rate of OC at the early stage of fluidization. After 6 min, the attrition rate of the particle was stabilized at 0.28 %/h. The OC was subjected to chemical and thermal stresses during the redox cycle reaction, which decreased the mechanical strength and increased particle attrition and sintering. The particle sintering also hindered the oxidation stage, which led to a deep reduction of OC to a lower valence state, which drove particle agglomeration and eventual defluidization. Therefore, lowering the oxygen transfer capacity and residence time in the fuel reactor is beneficial for the safe operation of OC in industry.

Redox Reaction Kinetics of a Fe–Cu-Based Oxygen Carrier Measured with Microfluidized Bed Thermogravimetric Analysis

Redox Reaction Kinetics of a Fe–Cu-Based Oxygen Carrier Measured with Microfluidized Bed Thermogravimetric Analysis

First-principles-based multiscale modelling of heterogeneous CoO oxidation kinetics in high-temperature thermochemical energy storage

Metal oxides experiencing reversible oxygen release and uptake reactions involve the scale-span (surface→grain→particle→reactor) problem in a thermochemical energy storage reactor. This study developed a first-principles-based multiscale modelling to calculate the heterogeneous CoO oxidation kinetics. At the surface scale, density function theory (DFT) is used to compute the reaction mechanism, and the data from DFT calculation are integrated into the transition state theory (TST) to calculate the reaction rate constants. At the grain scale, a rate equation theory is proposed to couple the surface reaction with the lattice oxygen in bulk phase. At the particle scale, intraparticle diffusion and external diffusion of gas molecules are calculated by the effective factor and mass transfer coefficient. At the reactor scale, a two-phase fluidization model is adopted to describe the mass transfer of oxygen from bubble phase to emulsion phase. The model was used to simulate the oxidation kinetic characteristics of a newly prepared kaolin-supported Co-based oxide. The reaction mechanism and kinetic rates constants obtained from DFT and TST are directly used to predict the CoO oxidation kinetics instead of by fitting the experimental data. The oxidation kinetics were validated by comparing with the experimental data obtained using a micro-fluidized bed thermogravimetric analysis technology. Results show the oxidation will be fully finished within ~10 s in the temperature of 700–750 °C, and the reaction is first-order when the O2 partial pressure is within 21 vol%. The effect of particle size shows three-zone characteristics of chemical reaction and gas diffusion combined controlling mechanism. It is demonstrated the first-principle-based multiscale modelling can provide an accurate prediction of the CoO oxidation kinetics in thermochemical energy storage.

Evaluation of Different Red Muds as Oxygen Carriers in a Fluidized Bed Thermogravimetric Analyzer

Evaluation of Different Red Muds as Oxygen Carriers in a Fluidized Bed Thermogravimetric Analyzer

Oxidization and reduction kinetics of a manganese oxygen carrier granulated with the spray drying method at a tonnage scale for chemical looping combustion

Upscaling the preparation of oxygen carrier particles is a challenge in the demonstration of chemical looping combustion (CLC) technology. In this work, tonnage-scale preparation of a manganese oxygen carrier is reported. Fines of original manganese ore and kaolin are manufactured as oxygen carrier particles by using industrial spray drying granulation. The oxidization and reduction kinetics were measured using microfluidized bed thermogravimetric analysis (MFB-TGA). Morphological characterization of the fresh and tested particles was performed by scanning electron microscope coupled with an energy dispersive spectrometer (SEM-EDS). The effects of the reaction temperature and gas concentrations of O2, H2 and CH4 on the redox kinetics were investigated. The oxidization and reduction processes were composed of an initially fast reaction stage dominated by a chemical reaction mechanism and a second slow reaction stage controlled by gas diffusion through the solid product layer. The influence of temperature on the fast stage of the oxidization reaction is not obvious. Reduction by H2 is ~6 times faster than reduction by CH4. The conversion vs. time curves were described by a reactor model coupled to a two-stage kinetics model to obtain the kinetic parameters.

Perovskite oxygen carrier with chemical memory under reversible chemical looping conditions with and without SO2 during reduction

Oxygen carrier materials (OCM) are usually exposed to sulfur-contained gases in the fuel reactor for chemical looping combustion. This work provides both experimental and model work to understand the SO2 effect on the heterogeneous redox kinetics of a CaMn0.375Ti0.5Fe0.125O3-δ-based perovskite oxygen carrier. The cycle reactivity and redox kinetics under reducing conditions were conducted with and without SO2 in a micro-fluidized bed thermogravimetric analysis technology (MFB-TGA). The redox kinetic behaviors were simulated by a bubbling fluidized bed reactor model coupled with a two-stage kinetic model. The SO2 can react with the perovskite to increase the oxygen transfer capacity from 4 wt% to 5 wt%. When the temperature is higher than 1173 K, SO2 has almost no effect on the H2 reduction reactivity, while the oxidation reactivity decreases by 50%, but the oxidation is still fast enough to achieve 4 wt% capacity within 8 s. When the temperature is lower than 1173 K, there is a significant sulfur-poisoning effect during oxidation and reduction. The analyses of XRD, SEM-EDS, and in-situ DRIFTS indicated that most of the absorbed sulfur mainly existed in the sulfate/sulfide shell on the particle surface. The chemical kinetics and physical structure of CaMn0.375Ti0.5Fe0.125O3-δ perovskite can be completely recovered in the absence of SO2, and this perovskite oxygen carrier is chemically memorable and reversible in its solid structure. The fundamental understanding of the sulfur effect on the redox kinetics and solid structure of the perovskite oxygen carrier provides a new insight to the material development and corresponding reaction mechanisms.

Catalytic combustion behaviors of petroleum coke with hematite catalyst in a micro fluidized bed thermogravimetric analysis

Both conventional TGA and fluidized bed have some inherent limitations in the accurate measurement of gas–solid reaction. To characterize the gas–solid process under the fluidization state, a micro fluidized bed thermogravimetric analysis (MFB-TGA) was developed based on the real-time measurement with precision of 0.1 mg mass, 0.1°C temperature, and 0.01 kPa pressure. In this study, we preliminarily applied the MFB-TGA in evaluating catalytic combustion of petroleum coke with respect to deducing Fe2O3 catalytic mechanism, lattice oxygen migration pathway, and apparent combustion kinetics. The measurement stability of MFB-TGA was impacted by various factors, such as inhomogeneous temperature distribution and slight gas disturbance. Even char combustion heat could destabilize the weight signal by inducing vigorous particle collisions. The lightweight design and several structural optimizations were implemented to improve the MFB-TGA performance with the result of realizing smooth weight loss curves with 0.1 mg errors during the entire experiment. The experimental analysis revealed that the catalytic mechanism of hematite was identified as CO homogeneous catalysis. Hematite accelerated the char combustion rate by intensifying the driving force of bulk oxygen diffusion to the carbon surface. It served as an oxygen carrier, transferring lattice oxygen to oxidize carbon monoxide surrounding char particles. The apparent intrinsic kinetics of 33.73 kJ/mol was determined by the isothermal differential approach, which was lower than the published results measured in regular TGA. The zero-order model exhibited an excellent linear correlation in describing combustion behaviors based on a function fitting process. The MFB-TGA had the potential for extensive application by providing a reliable and straightforward method in characterizing gas–solid reactions under a fluidization state.

Redox performance of manganese ore in a fluidized bed thermogravimetric analyzer for chemical looping combustion

A key issue for commercial application of chemical looping combustion (CLC) technology is the selection of oxygen carriers (OCs) with good fluidization and high reactivity during the long-term redox operation. Conventional fluidized bed reactors and thermogravimetric analyzer (TGA) are fail to simultaneously satisfy the fluidization and real-time mass measurement of bed materials. A fluidized bed thermogravimetric analyzer (FB-TGA) combining the advantages of fluidized bed and TGA is believed to be a novel powerful tool for screening OCs for industrial CLC units. In this work, an innovative FB-TGA with a high weight measurement accuracy is designed to reflect the lifetime, redox reactivity, particle sintering and agglomeration characteristics of OCs during the CLC. Manganese ore was selected as a representative OC and redox cyclic tests with hydrogen as the reduction gas were conducted. Results indicate that the Mn3O4-MnO system acts as the main redox pair. The redox chemical reactions may intensify the attrition of manganese ore particles. This may be due to the pore-opening effect of H2 during the reduction of manganese ore, reducing mechanical strength and accelerating attrition of particles. In the reducing atmosphere, it is speculated that the generation of manganese silicates with a low melting point results in particle sintering and agglomeration at the bottom of the bed. The particle agglomeration gradually spreads inward and upward, and eventually leads to total collapse of the fluidized bed. Therefore, a high-grade manganese ore with less silicon element is more suitable for industrial CLC pilots.

Evaluation of oxygen uncoupling characteristics of oxygen carrier using micro-fluidized bed thermogravimetric analysis

• MFB-TGA was used to evaluate the CLOU characteristics of oxygen carriers. • Oxygen release rate measured by MFB-TGA are ~2 faster than that tested in Q500. • Oxygen uptake rate measured by MFB-TGA are ~4 faster than that tested in Q500. Oxygen uncoupling characteristics of a natural manganese ore and a perovskite-type oxide CaMn 0.5 Ti 0.37 5Fe 0.125 O 3 were studied by using a microfluidized bed thermogravimetric analysis (MFB-TGA) technology which is based on a real-time mass measurement of fluidizing particles inside a bubbling bed reactor. The chemical stability, kinetics of the oxygen release and uptake reactions and fluidization property were investigated and the experimental data measured by MFB-TGA were compared with the results in a regular TGA instrument (TGA Q500). The regular TGA Q500 results show the reactivity of both the manganese ore and perovskite oxide are stable for multi cycles, and the oxygen uncoupling capacity of the manganese ore is ~1.2% (mass) which is ~2 times higher than that of the perovskite oxide. However, the experimental results from the MFB-TGA indicated that there is a serious agglomeration for the manganese ore. A very important finding is that the reaction rate of oxygen release and oxygen uptake of the perovskite oxide measured by the MFB-TGA are ~2 and ~4 times faster than that of testedby the TGA Q500. We can conclude that MFB-TGA is a very useful tool to measure the reactivity stability and kinetics of oxygen carriers in high-throughput analysis instead of the regular TGA.

Conversion characteristics of lignite and petroleum coke in chemical looping combustion coupled with an annular carbon stripper

Chemical looping combustion (CLC) of solid fuels was studied in a 30 kW dual fluidized-bed system coupled with an annular carbon stripper for char separation by using a kaolin-promoted manganese ore oxygen carrier. Two solid fuels, a lignite and a petroleum coke, were tested in the CLC unit. The CLC unit was operated continuously for more than 160 h. The effects of the fuel size and residence time in the fuel reactor on the carbon capture efficiency and oxygen demand were investigated. The char separation efficiency of the annular carbon stripper reached 90%, and a maximum carbon capture efficiency of 97% was achieved for the 106–212 μm lignite. The carbon capture efficiency was affected by the fuel particle size and residence time. When >212 μm lignite particles were used, there was a ~ 12% oxygen demand. The carbon capture efficiency in the experiment with petroleum coke was only 45% due to the slow gasification rate. A model was applied to analyze the influence of key factors on the carbon capture efficiency. The redox kinetics of the tested oxygen carrier were studied by a micro-fluidized bed thermogravimetric analysis method.

Heterogeneous reaction kinetics of a perovskite oxygen carrier for chemical looping combustion coupled with oxygen uncoupling

• A new perovskite oxide, CaMn 0.5 Ti 0.375 Fe 0.125 O 3-δ , was developed as oxygen carrier. • Micro-fluidized bed thermogravimetric analysis (MFB-TGA) was used for kinetic study. • Oxygen uncoupling kinetics was accurately measured by MFB-TGA. • Full oxidation can be achieved within 5 s. The determination of more exact heterogeneous kinetics of oxygen carriers is a crucial task for modelling, used to predict performance and design of demonstrating pilot units. Thermogravimetric analysis (TGA) is the most widely used method to measure the kinetics. However, the mass and heat transfer limitations observed inside the TGA specially for oxygen uncoupling effect will lead to underestimation of the kinetics. Micro-fluidized bed thermogravimetric analysis method (MFB-TGA) solve this challenge to measure the fast heterogeneous kinetics precisely, based on real-time mass measurement of oxygen carrier in a fluidizing state with similar mass and heat transfer characteristics as in a CLC reactor. In this study the oxygen uncoupling kinetics and redox reactions kinetics of a newly developed perovskite oxygen carrier material (CaMn 0.5 Ti 0.375 Fe 0.125 O 3-δ ) is established using a MFB-TGA method. The oxygen uncoupling kinetics measured by MFB-TGA is ~4 times faster than that measured by regular TGA. The oxidization reaction of CaMn 0.5 Ti 0.375 Fe 0.125 O 3-δ occurs only in the initial stage controlled by chemical reaction, and the time required for full oxidation is ~5 s, while the reduction kinetics consists of a fast reaction stage and a slow reaction stage, controlled by chemical reaction and diffusion through the product layer, respectively. Both the oxygen uncoupling kinetic parameters and redox kinetic parameters are obtained by analyzing the MFB-TGA data based on the simplified K-L model for the fluidized bed. The morphology characterizations of the fresh and tested CaMn 0.5 Ti 0.375 Fe 0.125 O 3-δ particles were investigated by SEM-EDS. The comparison of heterogeneous reaction kinetics with the mainstream OCMs were done.

Reduced-order model for CaO carbonation kinetics measured using micro-fluidized bed thermogravimetric analysis

A reduced-order model was developed to describe the CaO carbonation kinetics by simplifying the detailed one-dimensional rate-equation-based grain model. The reduced-order model was derived using the Thiele modulus method and is an analytical model, which can be easily used in the reactor scale model or computational fluid dynamics (CFD) simulation. In the reduced-order model, physical/chemical steps occurring during the carbonation process were considered, including external diffusion of gas around the particle, intraparticle diffusion, surface reaction, product islands growth and product layer diffusion. This model can be used to investigate the complex kinetic behaviors such as reaction controlled steps, kinetics transition from chemical reaction to product layer diffusion, and the effect of particle structure change on intraparticle diffusion, such as pore plugging phenomenon. The prediction accuracy of reduced-order model was verified by the detailed one-dimensional model. In order to demonstrate the application of the reduced-order model for reactor scale analysis, the CaO carbonation kinetics under different temperatures (600–750 °C), CO2 concentrations (25–75 vol%) and particle sizes (0.2–3 mm) were measured using a novel micro-fluidized bed thermogravimetric analysis (MFB-TGA) method, which is based on real-time mass measurement of CaO sample in a fluidizing state. The reduced-order model was implemented into a K-L two-phase bubbling bed reactor model to analyze the experimental data of a micro-fluidized bed reactor. Results indicated that the two-stage behavior of carbonation kinetics can be described successfully using the model, and the effect of particle structure change on pore plugging and intraparticle diffusion can be well predicted and explained. The carbonation is first-order reaction when the CO2 partial pressure is within 75% (1 bar). The effect of particle size on carbonation kinetics shows three-zone characteristics of reaction/diffusion combined controlling mechanism, and was discussed in detail. The reduced-order model provides a promising application for describing multiscale mechanisms (surface, particle and reactor) of carbonation kinetics.

Fast redox kinetics of a perovskite oxygen carrier measured using micro-fluidized bed thermogravimetric analysis

Redox kinetics of oxygen carrier in chemical looping combustion (CLC) is important for reactor design and its oxidation enthalpy is important in order to establish auto thermal demonstration. Most published redox kinetics of oxygen carrier has been measured by thermogravimetric analysis (TGA) which can include additional diffusion limitations and thus underestimate the overall kinetics. In this study, the redox kinetics of a new perovskite oxygen carrier (CaMn0.375Ti0.5Fe0.125O3-δ) was measured by a novel micro-fluidized bed thermogravimetric analysis (MFB-TGA) method which can achieve real-time weight measurement of oxygen carrier in a fluidizing state with similar mass and heat transfer characteristics as in a CLC reactor. The experimental data from MFB-TGA were analyzed with a reactor model. The redox kinetics was described by a two-stage model of gas-solid reaction. The effect of temperature, O2 concentrations and reducing gas type (H2 and CH4) on the redox kinetics in MFB-TGA was investigated and compared with other oxygen carriers such as natural manganese ore and ilmenite. It is observed that the oxidation of both manganese ore and ilmenite can be divided into two stages, a fast initial stage followed by a second slower stage, resulting in slower total oxidation rates. A very interesting finding is that there is only the fast initial stage for the oxygen carrier of CaMn0.375Ti0.5Fe0.125O3-δ, and the full oxidation of CaMn0.375Ti0.5Fe0.125O3-δ can be finished within ∼4 s which is ∼7.5 and ∼30 times faster than that of manganese ore and ilmenite. The reduction kinetics of CaMn0.375Ti0.5Fe0.125O3-δ by H2 is also ∼5 and ∼2.2 times faster than that of manganese ore and ilmenite, respectively. The kinetic parameters of three oxygen carriers were compared and the redox mechanism of CaMn0.375Ti0.5Fe0.125O3-δ was discussed.