Oxygen Carrier For Chemical Looping Combustion Research Articles

Crossing-link of experimental reducibility tests, XPS characterizations and DFT estimates on ferrite oxygen carriers in CLC

Chemical looping combustion (CLC) is an efficient technology of thermal conversion of carbonaceous fuels with CO2 being concentrated. Oxygen carriers, which are generally metal oxides or their composites, are critical in the development of different CL processes, addressing combustion, gasification and H2 production. Iron-based oxide, rich in natural resource and inexpensive, is one of ideal candidates as oxygen carriers in the CL process. Understandings toward the general principles of the selection on iron-based oxygen carriers are highly demanded. A unique approach was applied in the present study to investigate the relationship between the reducibility and the electronic structure of selected three typical ferrites as oxygen carriers, via combining experimental reducibility tests using H2-TPR and CO-TGA, the material characterizations using XRD (X-ray Diffraction) and XPS (X-ray Photoelectron Spectroscopy), and electronic structures using DFT (Density Functional Theory) calculations. Proportions of the lattice oxygen and Fe2+ in ferrites positively and negatively influence their reduction reactivity, respectively. Varieties of oxygen components in ferrites determine their reduction temperatures and reactivity. Both the approaching degrees of the O-2p and M-3d valance bands to Fermi level of ferrites positively influence the initial reducing temperature and the reduction rate, respectively. Using these deeper prediction insights into structure-property relations will greatly increase the success of our subsequent synthetic effort.

Studies on steel slag as an oxygen carrier for chemical looping combustion

Chemical looping combustion (CLC) has been suggested as an energy-efficient method for clean combustion with inherent capture of carbon dioxide. The development of commercially available, less-costly, thermally-stable and good kinetics oxygen carriers is the first propriety in the CLC process. This study is the first to explore the use of steel slag, a typical metallurgical waste, as an oxygen carrier in CLC. The primary advantage of steel slag is its low cost because of its nature of the solid waste. Steel slag mainly contains two interested substances for oxygen transfer in CLC, iron oxides and calcium sulfate (after sulfation). The thermochemical analysis on pre-sulfating steel slag was conducted by the Aspen Plus software, and the experiments of the reduction of pre-sulfating steel slag were carried out using a thermogravimetric analyzer (TGA). Characterizations of used steel slag were carried out by X-ray diffraction (XRD). Results indicated that the pre-sulfating steel slag can be a proper and excellent oxygen carrier, whose reduction kinetics using model fuel gas (CO, carbon monoxide) was rapid at medium temperatures. Further investigations revealed that it is Ca-containing components (CaSO4) in pre-sulfating steel slag that was mainly involved in the redox process using CO. Moreover, the reaction rate has increased by nearly 15 times as compared to that of the pure CaSO4 at the same temperature. The conversion of CaSO4 to CaS can be nearly complete. Higher temperatures were adverse to the stability of CaSO4, leading the decomposition of CaSO4, the degradation of its oxygen transfer capability and the increase of sulfur emissions. However, the use of steel slag rationally control the optimized reduction temperature to be 750 °C, when its kinetics can be maintained rationally at 100% conversion within 30 min and a stable oxygen transfer capability at 10.63 wt% with the minimized sulfur emissions. This finally validated steel slag as a promising oxygen carrier candidate.

Chemical-looping combustion of synthetic biomass-volatiles with manganese-ore oxygen carriers

Carbon capture and storage of CO2 from combustion of biomass, i.e., bio-energy carbon capture and storage (BECCS), makes it possible to obtain so-called negative emissions – the atmosphere is cleansed from carbon dioxide. The purpose of the present study was to investigate the suitability of different manganese ores as oxygen carriers in chemical-looping combustion of biomass fuels. For this screening study, a laboratory-scale, circulating fluidized-bed CLC system with a nominal fuel input of 300 Wth was used. The primary focus was to investigate the reactivity of these oxygen carriers towards biomass fuels, and find a reactive oxygen carrier with sufficient mechanical stability that could be suitable for large-scale chemical-looping combustion of biomass. A synthetic “biomass volatiles” gas was used to study how the different gas components react with the oxygen-carrier particles. Additional experiments were conducted with methane and a syngas. Parameter studies concerning temperature and specific fuel-reactor bed mass (bed mass per fuel thermal power in kg/MWth) were carried out. With the synthetic biomass volatiles, conversion of fuel carbon to CO2 as high as 97.6% was achieved. For a majority of the investigated ores, essentially all C2 and C3 hydrocarbons were converted, as well as a very high fraction of the CO. Reactivity towards CH4 was generally lower, but improved at higher temperatures. The resistance of the oxygen carriers towards mechanical degradation was measured in a jet-cup attrition test rig. The measured attrition was estimated as “intermediate” for four of the five tested materials, while one of the ores displayed high attrition.

Mature versus emerging technologies for CO2 capture in power plants: Key open issues in post-combustion amine scrubbing and in chemical looping combustion

Carbon capture and storage (CCS) have acquired an increasing importance in the debate on global warming as a mean to decrease the environmental impact of energy conversion technologies, by capturing the CO2 produced from the use of fossil fuels in electricity generation and industrial processes. In this respect, post-combustion systems have received great attention as a possible near-term CO2 capture technology that can be retrofitted to existing power plants. This capture technology is, however, energy-intensive and results in large equipment sizes because of the large volumes of the flue gas to be treated. To cope with the demerits of other CCS technologies, the chemical looping combustion (CLC) process has been recently considered as a solution for CO2 separation. It is typically referred to as a technology without energy penalty. Indeed, in CLC the fuel and the combustion air are never mixed and the gases from the oxidation of the fuel (i.e., CO2 and H2O) leave the system as a separate stream and can be separated by condensation of H2O without any loss of energy. The key issue for the CLC process is to find a suitable oxygen carrier, which provides the fuel with the activated oxygen needed for combustion. The aim of this work is to explore the feasibility of using perovskites as oxygen carriers in CLC and to consider the possible advantages with respect to the scrubbing process with amines, a mature post-combustion technology for CO2 separation.

A Multi-scale model for CO2 capture: A Nickel-based oxygen carrier in Chemical-looping Combustion

In this work, we present a multi-scale modelling framework for the Ni-based oxygen carrier (OC) particle that can explicitly account for the complex reaction mechanism taking place on the contacting surface between gas and solid reactants in Chemical Looping Combustion (CLC). This multi-scale framework consists of a gas diffusion model and a surface reaction model. Continuum equations are used to describe the gas diffusion inside OC particles, whereas Mean-field approximation method is adopted to simulate the micro-scale events, such as molecule adsorption and elementary reaction, occurring on the contacting surface. A pure CO stream is employed as the fuel gas whereas the NiO is used as the metal oxide because it is one of the mostly used material in laboratory and pilot-scale plants. Rate constants for the micro-scale events considered in the present work were obtained from a systematic Density Functional Theory (DFT) analysis, which provides a reasonable elementary reaction kinetics and lays a solid foundation for multi-scale calculations. A sensitivity analysis on the size of intra-particle pore and the adsoprtion rate constant was conducted to assess the mass transport effects on the porous particle. The proposed multi-scale model shows reasonable tendencies and responses to changes in key modelling parameters.

Reduction and oxidation performance evaluation of manganese-based iron, cobalt, nickel, and copper bimetallic oxide oxygen carriers for chemical-looping combustion

Transition metal oxides like Fe2O3, Co3O4, NiO, and CuO have mainly been used in the chemical-looping combustion (CLC) reaction as oxygen carrier particles because of their outstanding performances due to high reduction potential. However, monometal oxides have a serious problem of rapid deactivation due to agglomeration between each particle after several redox cycles. In order to solve this problem, bimetal oxides based on Mn, which undergoes no deactivation, were synthesized. Mn-based bimetal oxygen carrier particles Fea-Mnb-Ox, Coa-Mnb-Ox, Nia-Mnb-Ox, and Cua-Mnb-Ox were synthesized by using a sol–gel method. The range of a and b in the particle label obtained in this study is 0.5–2.5, depending on the metal content added. The chemical and physical properties of the prepared particles were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM), CH4-/CO-temperature programmed desorption, and thermogravimetric analysis (TGA). The XRD results showed that the prepared particles comprised two- or three-phase mixed metal oxides. The Fe2.0-Mn1.0-Ox particle was in the phases of Fe2Mn1O4 and Fe20.16Mn11.84O48, respectively, and the Co2.0-Mn1.0-Ox particle had the phase of Co2Mn1O4. In addition, Ni2.0-Mn1.0-Ox particle has NiO and Ni1Mn2O4 phases, and Cu2.0-Mn1.0-Ox particle exist in the phases of CuO, Cu2O and Cu1Mn1O2, respectively. The distributions of added elements on the particles were observed from the SEM mapping results. The oxygen carrier capacities of the particles were tested by isothermal H2/air and CH4/air redox cycle experiments using TGA at 850°C. The improved results obtained in this study revealed that the Cu2.0-Mn1.0-Ox particle was an enhanced bimetal oxide oxygen carrier for CLC under CH4/air conditions. In particular, among the synthesized particles, the Cu2.0-Mn1.0-Ox particle stably showed 16.7wt% oxygen transfer capacity over 10 redox cycle under CH4/air at 850°C.

Utilization of Menteş iron ore as oxygen carrier in Chemical-Looping Combustion

The performance of a natural iron ore originated from Menteş mine (Kayseri-Turkey) as an oxygen carrier in the CLC process was assessed in this study. A laboratory scale, alternating atmosphere fluidized bed set-up was used in order to simulate the CLC conditions. The oxygen carrier material was stable until the end of tests, and it exhibited more than 90% gas yield during the tests when fueled with pure CO (flow rates between 130 and 200 Wth) at 800 °C (1073 K). On the other hand, the syngas yield was approximately 83% at almost the same test conditions (flow rates between 120 and 180 Wth). It was determined that test temperature had almost no effect on fuel gas yield.

Manganese ores as oxygen carriers for chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU)

Manganese-based oxygen carriers can be used in chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU). This paper expands on a previous investigation into manganese ores as oxygen carriers for CLC. The paper presents reactivity data for eight ores with widely different compositions. Most importantly, the ores contained significant quantities of Fe, Si, and Ca, with Fe/Mn and Si/Mn molar ratios that varied between 0.1–4.5 and 0.07–0.48, respectively. Pre-treatment of the ores consisted of heat treatment in air at 950°C for 24h followed by sieving to obtain a particle size fraction of 125–180μm. Reactivity towards methane and synthesis gas (50 vol% CO in H2) and the oxygen uncoupling behaviour at 900, 950, and 1000°C was investigated in a fluidized batch reactor. Material characterization of the ores included an attrition test, crushing strength, and BET surface area measurement. The oxygen carriers had a CO2 yield of 31–80% for syngas with 2g of oxygen carriers using 450ml/min of syngas. The performance for all ores as a function of number of cycles was stable. By using a pseudo-first-order rate constant, apparent activation energies were calculated at ω=0.999 and 0.99 for methane and syngas, respectively, and the apparent activation energies varied in a wide range, from 110 to 328kJ/mol for CH4 and 10 to 168kJ/mol for CO. The attrition resistance of the particles was measured using a jet cup attrition rig. The findings indicate that a higher reactivity is associated with higher attrition, however, there is no direct correlation between the two.

The redox reaction kinetics of Sinai ore for chemical looping combustion applications

The objective of this work was to study the use of Sinai ore, a Fe–Mn-based ore from Egypt, as a low-cost oxygen carrier (OC) in Chemical Looping Combustion (CLC). The Sinai ore was selected because it possesses relatively high amounts of iron and manganese oxides. Furthermore, those oxides have low cost, very favorable environmental and thermodynamic properties for the CLC process. The performance of the Sinai ore as an OC in CLC was compared to that of ilmenite (Norway Tellnes mine), the most extensively studied naturally occurring Fe-based mineral.The kinetics of the reduction and oxidation reactions with the two minerals were studied using a thermogravimetric analyzer (TGA). Experiments were conducted under isothermal conditions, with multiple redox cycles, at temperatures between 750 and 950°C. For the reduction and oxidation reactions, different concentrations of CH4 (10–25vol.%) and O2 (5–20vol.%) were applied, respectively. The kinetic parameters, such as the activation energy (Ea), pre-exponential factor (A0), and reaction order (n), were determined for the redox reactions. Furthermore, models of the redox reactions were selected by means of a model-fitting method. For the Sinai ore, the D3 model (3-dimensional diffusion) was suitable for modeling reduction reaction kinetics. The calculated Ea was 35.3kJ/mole, and the reaction order was determined to be approximately 0.76. The best fit for the oxidation reaction was obtained for the R3 model (shrinking core). The oxidation (regeneration) reaction Ea was equal to 16.7kJ/mole, and the determined reaction order was approximately 0.72.The crystalline phases present, as well as the morphology and inhomogeneities in elemental composition were studied for both materials, fresh as well as after multiple redox cycles, by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) combined with X-ray Microanalysis - Energy Dispersive Spectroscopy (EDS). Structural and morphological changes were detected and correlated to the reaction temperature as well as the reactant compositions and thus the stability of the ores in repetitive CLC cycles was determined.

Investigation of Cu–Fe and Mn–Ni oxides as oxygen carriers for chemical-looping combustion

Combined Cu–Fe and Mn–Ni oxygen carriers were investigated as bed materials for chemical-looping combustion. The aim was to identify material combinations which yield oxygen carriers with a high reactivity towards gaseous fuels, such as CO, H2 and CH4, as well as sufficient mechanical durability. For this purpose, 18 different oxygen carriers were spray-dried and calcined at defined temperatures.Gas conversion as well as release of gaseous oxygen was investigated in a batch fluidized bed reactor setup at temperatures between 850 and 1050°C. For testing the mechanical durability, a jet-cup attrition rig was used. Moreover, properties like specific surface area, oxygen transfer capacity and crystalline phase composition were examined to physically and chemically characterize the oxygen carrier particles.For both the Cu–Fe and Mn–Ni-based materials, oxygen carriers could be produced which showed a high reactivity with gaseous fuels like CO or CH4 while having a sufficiently high mechanical strength. These properties make them interesting candidates for application in chemical-looping combustion.

Influence mechanism of H2S on the reactivity of Ni-based oxygen carriers for chemical-looping combustion

First-principle calculations based on the density functional theory (DFT) were used to clarify the influence mechanism of H2S on the reactivity of Ni-based oxygen carriers. A systematic investigation about the adsorption behaviors of H2S on NiO(001) perfect and defect surface was firstly performed. H2S molecule is very likely to produce the sequential dehydrogenation reaction on NiO(001) defect surface, while this phenomenon was not observed on NiO(001) perfect surface. Then the mechanism of CO adsorption on the H2S pre-adsorption NiO(001) perfect and defect surface was clarified. It was revealed that the existence of H2S could notably restrain the CO adsorption process on NiO(001) surface. The H2S influence on the diffusion of the O anion in the NiO slab was also studied in detail. Results showed that the presence of H2S would lead to the higher thermodynamic driving force required for the O anion diffusion, limiting the rate of the diffusion.

Nickel Oxides Supported on Alumina as Oxygen Carriers for Chemical-Looping Combustion and Reforming of Methane

Chemical-Looping Combustion (CLC) and Chemical-Looping Reforming (CLR) processes are technologies in development, considered as economically viable alternatives for CO2 mitigation. Both processes employ two interconnected reactors (air reactor and fuel reactor), by which oxides particles (called oxygen carriers) circulate. CLC process produces heat with inherent separation of CO2 from gaseous hydrocarbons combustion. CLR process performs the fuel partial oxidation, generating synthesis gas (H2 and CO), which is the major industrial intermediate for hydrogen (H2) and other hydrocarbons production, thru Fischer-Tropsch reactions. The employment of OCs enables the total or partial oxidation of fuel, in the absence of atmospheric air, which allows great reduction of the separation costs. Nickel-based OCs are the most investigated, showing high performance and reactivity. This work presents the synthesis of OCs composed by different contents of nickel oxides supported on alumina, textural, physical and chemical characterizations by several techniques, and experimental results obtained when these materials were applied to CLC and CLR processes, using CH4 as fuel, mixed or not, with H2O or CO2. The results showed the potential industrial applications of these materials, which are preferentially selective to the CLR process, and the addiction of H2O or CO2 greatly reduces the carbon deposition.

Performance of Combined Manganese–Silicon Oxygen Carriers and Effects of Including Titanium

Combined oxides of manganese and silicon were previously identified as suitable oxygen carriers for chemical-looping combustion. In this study, one pure manganese–silicon oxide and one similar material with titanium included in the formulation were examined as oxygen carriers. Experiments studying the oxygen release and the reactivity with syngas, methane, and wood char were carried out in a bench-scale circulating chemical-looping combustor and in a batch fluidized-bed reactor in the temperature range of 800–1050 °C. Both oxygen carriers released oxygen in inert atmosphere, and the concentration of oxygen released increased with temperature. The conversion of syngas and methane also increased with temperature for both materials and in both experimental setups. The reactivity with devolatilized wood char showed that the rate of oxygen uncoupling increased with temperature. However, it was concluded that the main fuel conversion mechanism was CLC and not CLOU for these materials. The inclusion of titanium ...

Experimental Evaluation of a Chinese Sulfur-Containing Lean Iron Ore as the Oxygen Carrier for Chemical-Looping Combustion

A series of chemical-looping combustion (CLC) tests were conducted in a thermogravimetric analysis (TGA) reactor to investigate the potential of a Chinese sulfur-containing lean iron ore as the oxygen carrier. Two main products of solid-fuel pyrolysis and gasification, namely, CH4 and CO, were selected as the reducing gases. Consecutive reduction–oxidation cycles were first carried out in the TGA reactor to evaluate the cyclic stability and agglomeration tendency of the oxygen carrier. The effects of the temperature, fuel gas concentration, and reaction gas composition on the reduction reaction were further investigated. Increasing the reaction temperature or fuel gas concentration enhanced the reduction rate and reaction degree of the oxygen carrier. Meanwhile, CO showed much higher reduction reactivity than CH4. A comparison of the rate index of the iron ore used with those of high-grade minerals indicated that the iron ore had adequate reactivity for its application in solid-fuel CLC technology. The si...

Experimental investigation of binary and ternary combined manganese oxides for chemical-looping with oxygen uncoupling (CLOU)

Some binary and ternary combined manganese oxides of Mn with one or two additional metals or metalloids of Fe, Si, Ca and Mg were investigated as oxygen carriers for chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU). More specifically the following systems were investigated: (1) MnyMgOx, (2) CaMnO3–(Fe0.25Mn0.75)2O3, (3) CaMnO3–(Fe0.67Mn0.33)2O3, (4) CaMnO3–MnMgOx, (5) MnMgOx–(Fe0.25Mn0.75)2O3 and (6) Mn2SiOx–Fe2SiOx. The general trend was that the binary systems, where two metals are used in the formulation showed the most promising results in terms of oxygen uncoupling and reactivity. However, there are several ternary combinations which show a combination of high oxygen uncoupling, reactivity with methane and reasonable strength. A pseudo first-order effective rate constant was evaluated for the investigated particles. The measured rates are lower than for benchmark nickel oxide and calcium manganites, but higher than for ilmenite. The ternary System 6, Mn2SiOx–Fe2SiOx was investigated in more depth, including solid fuel experiments to determine the rate of oxygen release. At 850 and 900°C (Mn0.5Fe0.5)2SiOx had the highest average reactivity, with a maximum average yield of 91.5% at 850°C. On the other hand, at higher temperatures, the particles with the highest Mn content showed best behavior, i.e. (Mn0.67Fe0.33)2SiOx. Reactivity experiments with char in the FB reactor with this OC showed that the oxygen capacity for CLOU was high, 3.5wt% at 950°C, with a maximum release rate of 0.2gO2/kgOC,s. The low rate of uncoupling means that the experiments with gaseous fuel were likely dominated by the direct gas–solid reaction, and not CLOU. X-ray powder diffraction suggests that the main reaction path is via (MnxFe1−x)2O3 to (MnxFe1−x)3O4, although the reaction between Mn7SiO12 to MnSiO3 cannot be ruled out as a possible route of oxygen transfer. This was supported by thermodynamic calculations of this multi-component system.

Fluidizable NiO/Ce-γAl2O3 Oxygen Carrier for Chemical Looping Combustion

This communication presents the effects of Ce modification on NiO/Ce-γAl2O3 oxygen carrier for chemical-looping combustion (CLC). The NiO/Ce-γAl2O3 samples are prepared by an incipient wetness technique using successive metal loading. The reduction characteristics of the prepared oxygen carriers are evaluated in repeated temperature-programmed reduction/oxidation cycles. The results show that the presence of Ce minimizes metal/support interaction and improves the reducibility and oxygen carrying capacity of the oxygen carriers. As a result, almost 94 wt % nickel oxides on Ce-γAl2O3 is reduced as opposed to only 77 wt % of nickel oxides on bare γAl2O3. The presence of Ce also provides stable reduction performance over repeated oxidation/reduction cycles, which is essential for a CLC process. The sustained reducibility of the samples is mainly due to the absence of agglomeration and the formation of easily reducible nickel oxide species instead of nickel aluminate. The EDX mapping of the oxygen carrier show...

Chemical-looping combustion using combined iron/manganese/silicon oxygen carriers

Combined oxides of iron, manganese and silicon have been used as oxygen carriers for chemical-looping combustion. Three materials with varying composition of iron, manganese and silicon have been evaluated in oxygen release experiments and during continuous operation with syngas and natural gas as fuels. The concentration of oxygen released increased as a function of temperature and the highest concentrations of oxygen were measured with the material with the highest fraction of manganese. It was also this material which gave the best conversion of both syngas and natural gas; essentially full conversion of syngas and above 95% conversion of natural gas above 900°C. The other two materials showed similar performance, albeit with higher syngas conversion for the material with the lowest manganese fraction and the lowest conversion of natural gas for the same material. The materials lasted for 10–14h of operation with fuel addition before circulation disruption occurred, which was likely caused by particle attrition in all three cases. A phase diagram of the iron–manganese–silicon–oxide system was constructed and the possible relevant phase transitions were identified. This analysis showed that more phase transitions could be expected for the materials with higher manganese content which could explain the superior performance during fuel operation of the material with the highest manganese content. It should however be noted that this material was operated with the highest fuel reactor inventory per thermal power which could also be a contributing factor to the better performance of this material.The study shows that it is possible to achieve very high fuel conversion with combined oxides of iron, manganese and silicon as oxygen carrier. The mechanical stability of the particles was rather poor though and would need to be improved. On the other hand the findings relating to material stability is not necessary valid for natural materials containing a number of additional elements. The results are also of interest as an indication of how natural materials with similar composition, i.e. manganese ores, would perform as oxygen carriers.

Reactivity of Oxygen Carriers for Chemical-Looping Combustion in Packed Bed Reactors under Pressurized Conditions

For the design, scale-up, and optimization of pressurized packed bed reactors for chemical-looping combustion (CLC), understanding of the effect of the pressure on the reactivity of the oxygen carriers is very important. In this work, the redox reactivity of CuO/Al2O3 and NiO/CaAl2O4 particles at elevated pressures have been measured in a pressurized high-temperature magnetic suspension balance. The experiments have demonstrated that the pressure has a negative influence on the reactivity and that this effect is kinetically controlled. The negative effect of the pressure might be caused by the decrease in the number of oxygen vacancies at higher pressures. Moreover, the reactant gas fraction has been demonstrated as an important parameter, probably related to competition between different species for adsorption on the oxygen carrier surface. These effects have been included in the kinetic model leading to a good description of the experimental results. The impact of these findings on packed bed CLC applications with larger oxygen carrier particles has been investigated with a particle model that considers diffusion limitations and kinetics. It has been shown that the impact of diffusion limitations decreases with increasing pressure, due to the decrease in reaction rates and the increase in diffusion fluxes caused by Knudsen diffusion. The results have been validated by experiments with 1.7 mm NiO/CaAl2O4 particles. These results corroborate that the selection of larger particles because of pressure drop considerations does not lead to a large decrease in effective reaction rates, which is beneficial for packed bed CLC applications.

Possibility of Morphological Control To Improve the Activity of Oxygen Carriers for Chemical Looping Combustion

Morphological control of transition-metal oxides has received great attention for the preferential exposure of catalytically active sites. However, in contrast to catalytic processes, structural damage and relaxation of metal-oxide-based oxygen carriers (OCs) occur during the chemical looping combustion (CLC) processes. To answer the doubt whether surface-controlled preparation to obtain active and efficient OCs for CLC is practical, we supported Fe2O3 with the high-index [104] surface on Al2O3 (denoted as Fe2O3[104]/Al2O3) as an OC via surface-controlled preparation and experimentally detected the reaction behavior between the probe model fuel gas CO and Fe2O3[104]/Al2O3 during CLC processes. The results showed that Fe2O3[104]/Al2O3 is more efficient than the reference Fe2O3/Al2O3 prepared via the traditional method of precipitation, as less carbon was deposited on the reduced Fe2O3[104]/Al2O3 than on the reduced Fe2O3/Al2O3. Then we theoretically revealed the detailed mechanisms of reactions between CO and different surfaces of Fe2O3 to further confirm the high activity and behavior of Fe2O3[104] as an oxygen carrier for CLC. Finally, the results of structural characterizations and reuse experiments verified the regeneration ability of Fe2O3[104]. These findings indicate that morphological control of oxygen carriers is very rewarding for CLC.

Characteristics of a CaSO4 oxygen carrier for chemical-looping combustion: reaction with polyvinylchloride pyrolysis gases in a two-stage reactor

Chemical-looping combustion (CLC), which is a promising technique that includes an inherent separation of CO2 may reduce the generation of dioxins in municipal solid waste (MSW) disposal because in a CLC system, no free oxygen is available for incineration process.