Solid fuels in chemical-looping combustion using a NiO-based oxygen carrier

The feasibility of using three different solid fuels in chemical-looping combustion (CLC) has been investigated using NiO as oxygen carrier. A laboratory fluidized-bed reactor system for solid fuel was used, simulating a chemical-looping combustion system by exposing the sample to alternating reducing and oxidizing conditions. In each reducing phase 0.2 g of fuel was added to the reactor containing 20 g oxygen carrier. The experiments were performed at 970 °C. Compared to previously published results with other oxygen carriers the reactivity of the used Ni-particles was considerably lower for the high-sulphur fuel and higher for the low-sulphur fuel. Much more unconverted CO was released and the fuel conversion was much slower for high-sulphur fuel such as petroleum coke, suggesting that the nickel-based oxygen carrier was deactivated by the presence of sulphur. The NiO particles also showed good reactivity with methane and a syngas mixture of 50% H₂ and 50% CO. For all experiments the oxygen carrier showed good fluidizing properties without any signs of agglomeration.     

Chemical - Looping with oxygen uncoupling using Mn/Mg-based oxygen carriers - Oxygen release and reactivity with methane

Chemical-looping combustion with oxygen uncoupling (CLOU) is a method for combustion of solid and gaseous fossil fuels, which enables easy separation of carbon dioxide from the gaseous product mixture. In contrast to the related chemical-looping combustion (CLC) technology where gaseous or gasified fuels react directly with oxygen carriers, CLOU processes require oxygen carrier materials to be able to release oxygen in the fuel reactor and to regenerate by re-oxidation in oxygen-rich atmosphere in the air reactor at elevated temperature. Oxygen uncoupling properties and reactivities for methane combustion of 12 oxygen carrier particles, produced from mixtures of manganese and magnesium oxides with optional addition of titanium dioxide or calcium hydroxide, are investigated in a quartz batch reactor at 810 °C, 850 °C, 900 °C and 950 °C. All investigated oxygen carriers have oxygen release characteristics. The addition of calcium hydroxide facilitates oxygen release and combustion of methane, whereas addition of titanium dioxide does not have a pronounced effect on either oxygen uncoupling or reactivity of the oxygen carrier. In general, particles with greater extent of oxygen release have superior methane combustion properties.     

Interaction of mineral matter of coal with oxygen carriers in chemical-looping combustion (CLC)

The chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) processes are novel solutions for efficient combustion with direct separation of carbon dioxide. These processes use a metal oxide as an oxygen carrier to transfer oxygen from an air to a fuel reactor, where the fuel reacts with the solid oxygen carrier. When utilizing coal in CLC, the oxygen carrier particles could be affected through interaction with the ash-forming mineral matter found in coal, causing deactivation and/or agglomeration. In this work, possible interactions between minerals commonly encountered in coal and several promising oxygen carriers that are currently under investigation for their use in CLC are studied by both experiment and thermodynamic equilibrium calculations. Possible interaction was studied for both highly reducing and oxidizing conditions at 900 °C. Under highly reducing conditions pyrite was found to have by far the most deteriorating effect on the oxygen carrier particles, as the sulfur in the pyrite reacted with the oxygen carrier to form sulfides. Quartz and clay minerals were found to have a rather low influence on the oxygen carriers. Out of the oxygen carriers investigated, CuO/MgAl₂O₄ and the Mn₃O₄/ZrO₂ oxygen carriers tended to be quite reactive towards mineral matter whereas ilmenite has been shown to be the most robust oxygen carrier. Although sulfur can clearly deactivate Ni, Cu and Mn based oxygen carriers under sub-stoichiometric conditions, when the fuel is converted fully to CO₂ and H₂O, sulfides are only expected for Ni-based oxygen carriers.     

Petroleum coke conversion behavior in catalyst-assisted chemical looping combustion

Efficiently using petroleum coke as fuel and reducing carbon emission meanwhile have become attractive in oil processing industry. The paper is focused on the application of Chemical Looping Combustion (CLC) with petroleum coke, with the purpose of investigating its combustion performance and effects of potassium. Some experiments were performed in a laboratory scale fluidized bed facility with a natural manganese-based oxygen carrier. Experimental results indicated that the coke conversion is very sensitive to reaction temperature. The present natural manganese-based oxygen carrier decorated by K has little effect on the improvement of coke conversion. XRD, SEM-EDX, and H₂-TPR were adopted to characterize the reacted oxygen carrier samples. After being decorated by K, the oxygen carrier's capacity of transferring oxygen was decreased. A calcination temperature above the melting point of K₂CO₃ (891 °C) shows better oxygen transfer reactivity in comparison to the one calcined at a lower temperature. The natural oxygen carrier used in the work has a high content of Si, which can easily react with K to form K(FeSi₂O₆). Further, irrespective of reaction temperature, the coke conversion can be significantly enhanced by decorating the coke with K, with a demonstration of remarkably shorter reaction time, faster average coke gasification rate and higher average carbon conversion rate.     

The use of petroleum coke as fuel in chemical-looping combustion

Chemical-looping combustion is a novel technique used for CO₂ separation that previously has been demonstrated for gaseous fuel. This work demonstrates the feasibility of using solid fuel (petroleum coke) in chemical-looping combustion (CLC). Here, the reaction between the oxygen carrier and solid fuel occurs via the gasification intermediates, primarily CO and H₂. A laboratory fluidized-bed reactor system for solid fuel, simulating a CLC-system by exposing oxygen-carrying particles to alternating reducing and oxidizing conditions, has been developed. In each reducing period, 0.2 g of petroleum coke was added to 20 g of oxygen carrier composed of 60% active material of Fe₂O₃ and 40% inert MgAl₂O₄. The effect of steam and SO₂ concentration in the fluidizing gas was investigated as well as effect of temperature. The rate of reaction was found to be highly dependent on the steam and SO₂ concentration as well as the temperature. Also shown was that the presence of a metal oxide enhances the gasification of petroleum coke. A preliminary estimation of the oxygen carrier inventory needed in a real CLC system showed that it would be below 2000 kg/MW_th.     

Petroleum coke conversion behavior in catalyst-assisted chemical looping combustion

Efficiently using petroleum coke as fuel and reducing carbon emission meanwhile have become attractive in oil processing industry. The paper is focused on the application of Chemical Looping Combustion (CLC) with petroleum coke, with the purpose of investigating its combustion performance and effects of potassium. Some experiments were performed in a laboratory scale fluidized bed facility with a natural manganese-based oxygen carrier. Experimental results indicated that the coke conversion is very sensitive to reaction temperature. The present natural manganese-based oxygen carrier decorated by K has little effect on the improvement of coke conversion. XRD, SEM–EDX, and H₂-TPR were adopted to characterize the reacted oxygen carrier samples. After being decorated by K, the oxygen carrier's capacity of transferring oxygen was decreased. A calcination temperature above the melting point of K₂CO₃ (891 °C) shows better oxygen transfer reactivity in comparison to the one calcined at a lower temperature. The natural oxygen carrier used in the work has a high content of Si, which can easily react with K to form K(FeSi₂O₆). Further, irrespective of reaction temperature, the coke conversion can be significantly enhanced by decorating the coke with K, with a demonstration of remarkably shorter reaction time, faster average coke gasification rate and higher average carbon conversion rate.     

Carbon deposition characteristics and regenerative ability of oxygen carrier particles for chemical-looping combustion

For gaseous fuel combustion with inherent CO₂ capture and low NO_x emission, chemical-looping combustion (CLC) may yield great advantages for the savings of energy to CO₂ separation and suppressing the effect on the environment. In a chemical-looping combustor, fuel is oxidized by metal oxide medium (oxygen carrier particle) in a reduction reactor. Reduced particles are transported to the oxidation reactor and oxidized by air and recycled to the reduction reactor. The fuel and the air are never mixed, and the gases from the reduction reactor, CO₂ and H₂O, leave the system as separate streams. The H₂O can be easily separated by condensation and pure CO₂ is obtained without any loss of energy for separation. In this study, NiO based particles are examined from the viewpoints of reaction kinetics, carbon deposition, and cyclic use (regenerative ability). The purpose of this study is to find appropriate reaction conditions to avoid carbon deposition and achieve high reaction rate (e.g., temperature and maximum carbon deposition-free conversion) and to certify regenerative ability of NiO/bentonite particles. In this study, 5.04% methane was used as fuel and air was used as oxidation gas. The carbon deposition characteristics, reduction kinetics and regenerative ability of oxygen carrier particles were examined by TGA (Thermal Gravimetrical Analyzer).     

Batch testing of solid fuels with ilmenite in a 10 kWth chemical-looping combustor

Batch experiments were conducted in a 10 kW_th chemical-looping combustor for solid fuels using ilmenite, an iron titanium oxide, as the oxygen carrier with two solid fuels: a petroleum coke from Mexico and a bituminous coal from South Africa. The purpose of these batch tests was to attain detailed information on fuel conversion, complementary to previous continuous operation of the unit. At steady-state, a fuel batch of typically 25 g was introduced in the fuel reactor and gas concentrations were measured at the outlet of both air and fuel reactors. The fuel reactor was fluidized with steam and the amount of bed material was typically 5 kg. The fuel introduced devolatilizes rapidly while the remaining char is gasified and the resulting syngases H₂ and CO react with the oxygen carrier. Operation involved testing at different fuel reactor temperatures from 950 to 1030 °C, and investigation of the influence of particle circulation between air and fuel reactors.The fuel conversion rate was increased at higher temperature: at 950 °C the instantaneous rate of conversion for petroleum coke averaged at 17.4%/min while at 1030 °C, the value was 40%/min. For the much more reactive South African coal, the averaged rate at 970 °C was 47%/min and increased to 101%/min at 1000 °C. For petroleum coke testing with particle circulation, the oxygen demand - defined as oxygen lacking to fully convert the gases leaving the fuel reactor - was typically 12-14% for the gasified char including H₂S, in line with previous experiments with the same unit and fuel. If only syngases are considered, the oxygen demand for char conversion was 8.4-11%. Similar or even lower values were seen for the char of South African coal. This is in line with expectations, i.e. that it is possible to reach fairly high conversion, although difficult to reach complete gas conversion with solid fuel. It was also seen that the volatiles pass through the system essentially unconverted, an effect of feeding the fuel from above. Moreover, the oxygen demand for char conversion decreased with increasing temperature. Finally, the CO₂ capture - defined as the proportion of gaseous carbon leaving the fuel reactor to total gaseous carbon leaving the system - decreased at higher particle circulation and a correlation between capture and circulation index was obtained.     

Ilmenite with addition of NiO as oxygen carrier for chemical-looping combustion

The naturally occurring mineral ilmenite, FeTiO₃, has been examined as oxygen carrier for chemical-looping combustion. NiO-based particles have been used as an additive, in order to examine if it is possible to utilize the catalytic properties of metallic Ni to facilitate decomposition of hydrocarbons into more reactive combustion intermediates such as CO and H₂. Firstly, ilmenite was examined by oxidation and reduction experiments in a batch fluidized-bed reactor. These experiments indicated moderate reactivity between ilmenite and CH₄, which was used as reducing gas. However, adding 5 wt.% of NiO-based particles to the ilmenite improved the conversion of CH₄ greatly, resulting in an increase in combustion efficiency with a factor of 3. Secondly, 83 h of chemical-looping combustion experiments were conducted in a small circulating fluidized-bed reactor, using ilmenite as oxygen carrier and natural gas as fuel. A wide range of process parameters and different levels of NiO addition were examined. Occasionally, there were problems with the circulation of solids between the air reactor and fuel reactor, but most of the time the experiments worked well. The products were mostly CO₂, H₂O and unconverted CH₄. Adding small amounts of NiO-based particles to the reactor increased the conversion of the fuel considerably. For the base case conducted at 900°, the combustion efficiency was 76% for pure ilmenite and 90% for the corresponding experiments with 1 wt.% NiO-based particles added to the reactor. The properties of ilmenite were found to change considerably during operation. Used particles had lower density, were more reactive and more porous than fresh particles. These changes appear to have been physical, and no unexpected chemical phases could be identified.     

MgO对镍基氧载体化学链燃烧性能的影响

采用等体积浸渍法制备了不同MgO含量的NiO/MgO/SiO₂氧载体,利用XRD和TPR对其物化性能进行表征,并以甲烷为燃料在固定床微型反应器中对氧载体进行化学链燃烧性能考察。结果表明,MgO的加入可以提高NiO的分散度,从而提高反应性能;MgO使NiO在低温下较难被还原,显著降低了低温还原过程中的积炭量,提高了CO2选择性;800 ℃下,经过10次氧化还原循环反应,NiO/MgO/SiO₂氧载体颗粒反应性稳定,甲烷转化率维持在99%,CO₂选择性也达到98%。     

Long-term integrity testing of spray-dried particles in a 10-kW chemical-looping combustor using natural gas as fuel

Chemical-looping combustion, CLC, is a combustion concept with inherent separation of CO₂. The fuel and combustion air are kept apart by using an oxygen carrier consisting of metal oxide. The oxygen carriers used in this study were prepared from commercially available raw materials by spray-drying. The aim of the study was to subject the particles to long-term operation (>1000 h) with fuel and study changes in particles, with respect to reactivity and physical characteristics. The experiments were carried out in a 10-kW chemical-looping combustor operating with natural gas as fuel. 1016 h of fuel operation were achieved. The first 405 h were accomplished using a single batch of NiO/NiAl₂O₄-particles. The last 611 h were achieved using a 50/50_mass-mixture of (i) particles used for 405 h, and (ii) a second batch of particles similar in composition to the first batch, but with an MgO additive. Thus, at the conclusion of the test series, approximately half of the particles in the reactor system had been subjected to >1000 h of chemical-looping combustion. The reason for mixing the two batches was to improve the fuel conversion. Fuel conversion was better with the mixture of the two oxygen carriers than it was using only the batch of NiO/NiAl₂O₄-particles. The CO fraction was slightly above the equilibrium fraction at all temperatures. Using the oxygen carrier mixture, the methane fraction was typically 0.4-1% and the combustion efficiency was around 98%. The loss of fines decreased slowly throughout the test period, although the largest decrease was seen during the first 100 h. An estimated particle lifetime of 33 000 h was calculated from the loss of fines. No decrease in reactivity was seen during the test period.     

反应压力对Ni基与Cu-Fe基混合装填载氧体还原性能的影响

提出将CH4重整融入载氧体还原反应过程的固定床化学链燃烧新工艺,将Ni基载氧体与Cu?Fe基载氧体混合作为装填载氧体,考察了反应压力对其低温反应活性的影响. 结果表明,固相载氧体转化率和气相CH4转化率均随压力升高而增大,工作温度下限从0.1 MPa下的600℃降至0.9 MPa下的525℃, 900℃下20次循环的压力损失在0.9 MPa下较0.1 MPa下增加快,但载氧体性能未劣化,也未出现明显的积碳和烧结.     

A 300 W laboratory reactor system for chemical-looping combustion with particle circulation

Chemical-looping combustion (CLC) is a method to burn gaseous fuels with inherent separation of carbon dioxide. A continuously operated laboratory reactor system for chemical-looping combustion with two interconnected fluidized beds was designed and built. This chemical-looping combustor was designed to operate with a fuel flow corresponding to 100–300 W. The CLC system was operated successfully using a highly reactive nickel-based oxygen-carrier. Furthermore, tests were carried out to determine the degree of gas leakage between the reactors. Although there was some leakage between the fuel and air reactors, it is low enough to enable evaluation of the combustion results. The combustion tests showed a high conversion of the natural gas to carbon dioxide, indicating that the particles are suitable for chemical-looping combustion. No methane was detected in the gas from the fuel reactor, and the fraction of carbon monoxide was in the range 0.5–3%.     

Design and operation of a 10 kWth chemical-looping combustor for solid fuels - Testing with South African coal

This paper presents the results obtained for the operation of a 10 kW_th chemical-looping combustor using a South African coal as the solid fuel and an oxygen carrier of ilmenite, a natural iron titanium oxide. A chemical-looping combustor for solid fuels was designed and built. It consists of two interconnected fluidized beds, an air reactor where the oxygen carrier is oxidized and a fuel reactor where the coal is gasified by steam and the syn-gases react with the oxygen carrier. A constant coal flow corresponding to a thermal power of 3.3 kW was introduced into the fuel reactor. The tests were conducted at temperatures above 850 °C and for a total test duration of 22 h. The particle integrity of ilmenite and the particle circulation between the two reactors were investigated and verified. The effects of particle circulation on coal conversion, gas conversion of the fuel reactor and carbon separation or CO₂ capture between the air and fuel reactors were investigated. The actual CO₂ capture ranged between 82.5% and 96% while the gas conversion from the fuel reactor was in the range 78-81%, based on measurements of unconverted CO and CH₄.     

钠修饰铁矿石载氧体的串行流化床煤化学链燃烧试验

利用1 kW_th串行流化床反应器对钠修饰铁矿石载氧体进行试验研究,考察燃料反应器温度对煤化学链催化燃烧特性的影响。结果表明,钠在820～920℃温度下显著促进了煤气化反应的进行,随着燃料反应器温度的提高,使用Na-铁矿石时燃料反应器出口CO₂浓度明显增大,CO浓度明显降低,在920℃时CO₂捕集效率和碳捕集效率分别达到78.60%和80.54%,而使用纯铁矿石时CO₂捕集效率和碳捕集效率仅为40.27%和45.65%。在高温950℃时Na-铁矿石活性下降,出现烧结和团聚现象,燃料反应器出现滞流态化现象,这可能是钠的化合物熔点较低和载氧体过度还原所导致的。XRD和SEM分析结果显示钠修饰铁矿石促使更多的Fe₂O₃被还原为Fe₃O₄。     

Reactivity study and kinetic evaluation of CuO-based oxygen carriers modified by three different ores in chemical looping with oxygen uncoupling (CLOU) process

In the chemical looping with oxygen uncoupling (CLOU) process,CuO is a promising material due to the high oxygen carrier capacity and exothermic reaction in fuel reactor but limited by the low melting point.The combustion rate of carbon is faster than the decoupling rate of oxygen carrier (OC).Hence,high tem-perature tolerance and rapid oxygen release rate of CuO modified by three different ores were investi-gated in this study.The kinetics analysis of oxygen decoupling with Cu-based oxygen carriers was also evaluated.Results showed that CuO modified by chrysolite had faster oxygen release rate than that of CuO.Limestone showed obvious positive effect on the oxidization process.The selected OCs could keep stable in at least 20 cycles,for about 1200 min.Shrinking core model (SCM) fitted well for the decoupling process in the temperature range of 1123-1223 K.Reduction rate kinetic information may aid in the development of chemical looping with oxygen uncoupling (CLOU) technologies during reactor design and process modeling.Ternary doped copper oxide with chrysolite and limestone could improve the reactivity of CuO in decoupling and coupling process and also improve the high temperature tolerance.     

Effect of temperature on reduction reactivity of oxygen carrier particles in a fixed bed chemical-looping combustor

In a chemical-looping combustor (CLC), gaseous fuel is oxidized by metal oxide particle, e.g. oxygen carrier, in a reduction reactor (combustor), and the greenhouse gas CO₂ is separated from the exhaust gases during the combustion. In this study, NiO/bentonite particle was examined on the basis of reduction reactivity, carbon deposition during reduction, and NO_x formation during oxidation. Reactivity data for NiO/bentonite particle with methane and air were presented and discussed. During the reduction period, most of the CH₄ are converted to CO₂ with small formation of CO. Reduction reactivity (duration of reduction) of the NiO/bentonite particle increased with temperature, but at higher temperature, it is somewhat decreased. The NiO/bentonite particle tested showed no agglomeration or breakage up to 900 ‡C, but at 1,000 ‡C, sintering took place and lumps of particles were formed. Solid carbon was deposited on the oxygen carrier during high conversion region of reduction, i.e., during the end of reduction. It was found that the appropriate temperature for the NiO/bentonite particle is 900 ‡C for carbon deposition, reaction rate, and duration of reduction. We observed experimentally that NO, NO₂, and N₂O gases are not generated during oxidation.     

CFD simulation of a chemical-looping fuel reactor utilizing solid fuel

A computational fluid dynamic (CFD) study has been carried out for the fuel reactor for a new type of combustion technology called chemical-looping combustion (CLC). CLC involves combustion of fuels by heterogeneous chemical reactions with an oxygen carrier, usually a granular metal oxide, exchanged between two reactors. There have been extensive experimental studies on CLC, however CFD simulations of this concept are quite limited. In the present paper we have developed a CFD model for the fuel reactor of a chemical-looping combustor described in the literature, which utilized a Fe-based carrier (ilmenite) and coal. An Eulerian multiphase continuum model was used to describe both the gas and solid phases, with detailed sub-models to account for fluid–particle and particle–particle interaction forces. Global reaction models of fuel and carrier chemistry were utilized. The transient results obtained from the simulations were compared with detailed experimental time-varying outlet species concentrations (Leion et al., 2008) and provided a reasonable match with the reported experimental data.     

煤化学链燃烧载氧体研究进展

煤的化学链燃烧是清洁煤燃烧的重要技术之一。化学链中载氧体的使用可以避免煤和空气直接接触,从而避免氮氧化物等污染物的产生并提高能量转化效率。一般来说,煤的化学链燃烧有2种反应途径:煤气化化学链燃烧和氧解耦化学链燃烧;不同反应途径将极大影响载氧体组分以及结构设计。详细论述了2015-2020年煤化学链燃烧中固态金属载氧体的研究进展,包括铁基、锰基、铜基、镍基、硫酸钙以及其他复合金属载氧体。总结了不同金属载氧体的优缺点、反应路径、气-固和固-固反应机理、金属与载体的相互作用以及载氧体失活原理。铁基载氧体被广泛应用于气化化学链燃烧中,但单一铁基载氧体的反应速率较低。适量添加碱金属或碱土金属可以提升载氧体的反应活性。锰基载氧体在化学链燃烧中具有两面性:一方面可以在高温缺氧气氛中释放气态氧,另一方面也可以与还原性气体发生气-固反应。通过使用惰性载体以及碱金属添加剂可以提高锰基载氧体的机械强度和氧解耦能力。含铜载氧体具有出色的氧解耦能力和反应活性而被广泛关注,然而铜及其氧化物低熔点所带来的金属聚集导致载氧体的失活问题亟需克服。研究发现使用铁、锰和铜矿石制得的载氧体具有良好的反应性能。硫酸钙载氧体具有较好的反应活性,但煤的化学链燃烧时潜在的二氧化硫和硫化氢副产物需要引起重视。镍基载氧体虽然在煤的化学链燃烧中反应性能较好,但硫毒化、成本较高和环保性能不佳等缺点导致近年来镍基载氧体的研究较少。新型双金属或多金属载氧体可以同时结合2种金属的反应特性,从而显著提高载氧体的整体反应活性。基于载氧体的研究现状,对未来的发展方向提出了4点建议:结合2种煤的化学链燃烧机理设计新型氧解耦辅助化学链燃烧载氧体;发展新型材料和金属组分的载氧体;利用冶金工业废料制得载氧体;开发新型结构的载氧体。     

Reactivity of a CaSO<Subscript>4</Subscript>-oxygen carrier in chemical-looping combustion of methane in a fixed bed reactor

Chemical-looping combustion (CLC) is a promising technology for the combustion of gas or solid fuel with efficient use of energy and inherent separation of CO₂. A reactivity study of CaSO₄ oxygen carrier in CLC of methane was conducted in a laboratory scale fixed bed reactor. The oxygen carrier particles were exposed in six cycles of alternating reduction methane and oxidation air. A majority of CH₄ reacted with CaSO₄ to form CO₂ and H₂O. The oxidation was incomplete, possibly due to the CaSO₄ product layer. The reactivity of CaSO₄ oxygen carrier increased for the initial cycles but slightly decreased after four cycles. The product gas yields of CO₂, CH₄, and CO with cycles were analyzed. Carbon deposition during the reduction period was confirmed with the combustible gas (CO+H₂) in the product gas and slight CO₂ formed during the early stage of oxidation. The mechanism of carbon deposition and effect was also discussed. SO₂ release behavior during reduction and oxidation was investigated, and the possible formation mechanism and mitigation method was discussed. The oxygen carrier conversion after the reduction decreased gradually in the cyclic test while it could not restore its oxygen capacity after the oxidation. The mass-based reaction rates during the reduction and oxidation also demonstrated the variation of reactivity of CaSO₄ oxygen carrier. XRD analysis illustrated the phase change of CaSO₄ oxygen carrier. CaS was the main reduction product, while a slight amount of CaO also formed in the cyclic test. ESEM analysis demonstrated the surface change of particles during the cyclic test. The reacted particles tested in the fixed bed reactor were not uniform in porosity. EDS analysis demonstrated the transfer of oxygen from CaSO₄ to fuel gas while leaving CaS as the dominant reduced product. The results show that CaSO₄ oxygen carrier may be an interesting candidate for oxygen carrier in CLC. This work was presented at the 7 ^th China-Korea Workshop on Clean Energy Technology held at Taiyuan, China, June 26–28, 2008.