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1.
《Fuel》2004,83(13):1749-1757
In a chemical-looping combustion (CLC) process, gas (natural gas, syngas, etc.) is burnt in two reactors. In the first one, a metallic oxide that is used as oxygen source is reduced by the feeding gas to a lower oxidation state, being CO2 and steam the reaction products. In the second reactor, the reduced solid is regenerated with air to the fresh oxide, and the process can be repeated for many successive cycles. CO2 can be easily recovered from the outlet gas coming from the first reactor by simple steam condensation. Consequently, CLC is a clean process for the combustion of carbon containing fuels preventing the CO2 emissions to the atmosphere. The main drawback of the overall process is that the carriers are subjected to strong chemical and thermal stresses in every cycle and the performance and mechanical strength can decay down to unacceptable levels after enough number of cycles in use.In this paper the behaviour of CuO as an oxygen carrier for a CLC process has been analysed in a thermogravimetric analyser. The effects of carrier composition and preparation method used have been investigated to develop Cu-based carriers exhibiting high reduction and oxidation rates without substantial changes in the chemical, structural and mechanical properties for a high number of oxidation-reduction cycles. It has been observed that the carriers prepared by mechanical mixing or by coprecipitation showed an excellent chemical stability in multicycle tests in thermobalance, however, the mechanical properties of these carriers were highly degraded to unacceptable levels. On the other hand, the carriers prepared by impregnation exhibited excellent chemical stability without substantial decay of the mechanical strength in multicycle testing. These results suggest that copper based carriers prepared by impregnation are good candidates for CLC process. 相似文献
2.
准确测试固固反应,如铁矿炭还原反应的动力学在科学研究和实际应用中均具有重要意义。利用热重程序升温的方法研究了氧化铁石墨还原的固固反应特性,在惰性气氛下分别考察了研磨与浸渍混合后焙烧制得的Fe2O3/C样品的失重曲线,采用Flynn-Wall-Ozawa公式和Coats-Redfern公式相结合的方法分别求算了两种混合样品的固固反应动力学参数,研究发现氧化铁在炭表面的聚集形态与其活化能变化规律直接相关,且浸渍焙烧法所得样品的活化能符合强吸热反应活化能变化规律。结合固体原位XRD表征与气体产物在线分析手段,发现在初始阶段Fe2O3即可与C直接反应生成Fe3O4和CO2。该反应的活化能约为530 kJ·mol-1,反应机理为二级化学反应模型。 相似文献
3.
Gyoung Tae Jin Ho-Jung Ryu Sung-Ho Jo Seung-Yong Lee Sung Real Son Sang Done Kim 《Korean Journal of Chemical Engineering》2007,24(3):542-546
To investigate the feasibility of a chemical-looping hydrogen generation system, we investigated the reduction and water splitting
reaction characteristics for three mediators and two reducing gas in a bubbling fluidized bed reactor (0.02 m I.D.). For three
oxygen carrier particles (NiO/bentonite, Fe2O3/bentonite, (NiO:Fe2O3)/bentonite), hydrogen was used as a reduction gas and water was used as an oxidation gas. For (NiO: Fe2O3)/bentonite particle, carbon monoxide, which is the main component in the syngas from coal or heavy residue, was used as a
reducing gas to check reactivity for the carbon containing fuels and carbon deposition characteristics. Based on the reactivity
tests, (NiO: Fe2O3)/bentonite particle was selected as the best mediator for the chemical-looping hydrogen generation system to achieve stable
continuous operation.
This work was presented at the 6
th
Korea-China Workshop on Clean Energy Technology held at Busan, Korea, July 4–7, 2006. 相似文献
4.
Chemical-looping combustion (CLC) is a novel combustion technology with inherent separation of the greenhouse gas CO2 and low NOx (NO, NO2, N2O) emissions. In CLC, the solid oxygen carrier supplies the stoichiometric oxygen needed for CO2 and water formation, resulting in a free nitrogen mixture. The performance of oxygen carrier is the key to CLC's application. A good oxygen carrier for CLC should readily react with the fuel (fuel reactor) and should be re-oxidized upon being contacted with oxygen (air reactor). In this case, the behavior of CaSO4 as an oxygen carrier for a CLC process, reacting with gas fuels (e.g., CO, H2, and CH4) and solid fuels (e.g., coal and biomass), has been analyzed. The performance of the oxygen carrier can be improved by changing the preparation method or by making mixed oxides. Generally, Al2O3, SiO2, etc., which act a porous support providing a higher surface area for reaction, are used as the inert binder to increase the reactivity, durability, and fluidizability of the oxygen carrier particles. Further, simulation analysis of a CLC process based on CaSO4 oxygen carrier was also analyzed. Finally, some important tendencies related to CaSO4 oxygen carrier in CLC technology are put forward. 相似文献
5.
Henrik Leion Erik Jerndal Simon Hermansson Erik Jansson Rebecka Thunberg Tobias Mattisson 《Fuel》2009,88(10):1945-4366
Chemical-looping combustion (CLC) is a novel technology that can be used to meet demands on energy production without CO2 emissions. The CLC-process includes two reactors, an air and a fuel reactor. Between these two reactors oxygen is transported by an oxygen carrier, which most often is a metal oxide. This arrangement prevents mixing of N2 from the air with CO2 from the combustion. The combustion gases consist almost entirely of CO2 and H2O. Therefore, the technique reduces the energy penalty that normally arises from the separation of CO2 from other flue gases, hence, CLC may make capture of CO2 cheaper.Iron ore and oxide scale from steel production were tested as oxygen carriers in CLC batch experiments with solid fuels. Petroleum coke, charcoal, lignite and two bituminous coals were used as fuels.The experiments were carried out in a laboratory fluidized-bed reactor that was operating cyclically with alternating oxidation and reduction phases. The exhaust gases were led to an analyzer where the contents of CO2, CO, CH4 and O2 were measured. Gas samples collected in bags were used to analyze the content of hydrogen in a gas chromatograph.The results showed that both the iron ore and the oxide scale worked well as oxygen carrier and both oxygen carriers increased their reactivity with time. 相似文献
6.
High performance of la‐promoted Fe2O3/α‐Al2O3 oxygen carrier for chemical looping combustion
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Ming Tian Chaojie Wang Lin Li Xiaodong Wang 《American Institute of Chemical Engineers》2017,63(7):2827-2838
Iron oxide supported oxygen carrier (OC) is regarded to a promising candidate for chemical looping combustion (CLC). However, phase separation between Fe2O3 and supports often occurs resulted from the severe sintering of supports during calcination, which leads to the sintering and breakage of Fe2O3 thus the decrease of redox reactivity. In this article, La‐promoted Fe2O3/α‐Al2O3 were used as OCs for CLC of CH4 and for the first time found that the OC with the addition of 18 wt % La exhibited outstanding reactivity and redox stability during 50 cycles of CLC of CH4. Such a superior performance originated from the formation of LaAl12O19 hexaaluminate (La‐HA) phase with not only small particle size but also excellent thermal stability at CLC conditions, which worked as a binder to prevent the phase separation thereby the sintering and breakage of active species α‐Fe2O3 were avoided during reaction. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2827–2838, 2017 相似文献
7.
《Fuel》2007,86(10-11):1417-1429
A 200 mm laboratory-scale atmospheric bubbling fluidised bed reactor has been used to obtain experimental data for the air/steam gasification of eucalyptus red gum wood chips and commercial wood pellets. The unique feature of this gasifier is the ability to examine the variations to axial gas composition along the bed height. At present no such data is available in the literature for biomass gasification. Gasification tests were performed using beds of; silica sand, char or clay to determine the effect of bed type on the gas composition. The behaviour of the major gas species (CO, H2, CO2) were observed to be strongly influenced by the water–gas shift reaction within the freeboard of the gasifier resulting in the exit gas being relatively similar in composition as compared to the in-bed variations. These small differences in gas composition for all bed types tested are the result of the achievement of equilibrium in the water–gas shift reaction. The influence of bed type exerted the most impact on the C2–C3 emissions (tar proxy) with the char bed found to best aid in their breakdown and to limit the amount of hydrocarbons surviving into the freeboard. The reduction of iron oxide (Fe2O3) content in the clay to a more reactive form of magnetite Fe3O4 by CO and H2 in the product gas resulted in the clay bed to also exhibit a reduction in C2–C3 emissions compared to silica sand but less then char. The clay bed produced the highest calorific values for the producer gas. However, operation of the clay bed above 800 °C exhibits the potential for over reduction to form iron with subsequent agglomeration of the bed. Changing the fuel type to a biomass pellet resulted in higher emissions of C1–C3 hydrocarbons and in part its contribution is the result of primary particle fragmentation during screw feed conveying to the bed. Feeder location and bed design (conical or cylindrical) also exhibit an influence on hydrocarbon emissions. 相似文献
8.
Alberto Abad Juan Adánez Ana Cuadrat Francisco García-Labiano Pilar Gayán Luis F. de Diego 《Chemical engineering science》2011,(4):689
The objective of this study was to establish the kinetic of both reduction and oxidation reactions taking place in the chemical-looping combustion (CLC) process using ilmenite as an oxygen carrier. Because of the benefits of using of pre-oxidized ilmenite and the activation of the ilmenite during the redox cycles, the reactivity of both the pre-oxidized and activated ilmenite was analyzed. The experimental tests were carried out in a thermogravimetric analyzer (TGA), using H2, CO or CH4 as reducing gases, and O2 for the oxidation step. Thus, the reactivity with the main reacting gases was analyzed when natural gas, syngas or coal are used as fuels in a CLC system. The changing grain size model (CGSM) was used to predict the evolution with time of the solid conversion and to determine the kinetic parameters. In most cases, the reaction was controlled by chemical reaction in the grain boundary. In addition, to predict the behaviour of the oxidation during the first redox cycle of pre-oxidized ilmenite, a mixed resistance between chemical reaction and diffusion in the solid product was needed. The kinetic parameters of both reduction and oxidation reactions of the pre-oxidized and activated ilmenite were established. The reaction order for the main part of the reduction reactions of pre-oxidized and activated ilmenite with H2, CO, CH4 and O2 was n=1, being different (n=0.8) for the reaction of activated ilmenite with CO. Activation energies from 109 to 165 kJ mol−1 for pre-oxidized ilmenite and from 65 to 135 kJ mol−1 for activated ilmenite were found for the different reactions with H2, CO and CH4. For the oxidation reaction activation energies found were lower, 11 kJ mol−1 for pre-oxidized and 25 kJ mol−1 for activated ilmenite.Finally, simplified models of the fuel and air reactors were used to do an assessment of the use of ilmenite as an oxygen carrier in a CLC system. The reactor models use the reaction model in the particle and the kinetic parameters obtained in this work. Taking into account for its oxygen transport capacity, the moderated solids inventory and the low cost of the material, ilmenite presents a competitive performance against synthetic oxygen carriers when coal or syngas are used as fuel. 相似文献
9.
C.R. Forero P. Gayán L.F. de Diego A. Abad F. García-Labiano J. Adánez 《Fuel Processing Technology》2009
Chemical-Looping Combustion (CLC) is an emerging technology for CO2 capture because separation of this gas from the other flue gas components is inherent to the process and thus no energy is expended for the separation. For its use with coal as fuel in power plants, a process integrated by coal gasification and CLC would have important advantages for CO2 capture. This paper presents the combustion results obtained with a Cu-based oxygen carrier in a continuous operation CLC plant (500 Wth) using syngas as fuel. For comparison purposes pure H2 and CO were also used. Tests were performed at two temperatures (1073 and 1153 K), different solid circulation rates and power inputs. Full syngas combustion was reached at 1073 K working at f higher than 1.5. The syngas composition had small effect on the combustion efficiency. This result seems to indicate that the water gas shift reaction acts as an intermediate step in the global combustion reaction of the syngas. The results obtained after 40 h of operation showed that the copper-based oxygen carrier prepared by impregnation could be used in a CLC plant for syngas combustion without operational problems such as carbon deposition, attrition, or agglomeration. 相似文献
10.
Chemical looping combustion (CLC) is the process in which metal oxides, rather than air or pure oxygen, supply the oxygen required for combustion. In this process, different gaseous fuels can be burnt with the inherent separation of CO2. The feasibility of the CLC system depends greatly on the selection of appropriate metal oxides as oxygen carriers (OC). In this study, NiO-NiAl2O4, Cu0.95Fe1.05AlO4, and CuO-Cu0.95Fe1.05AlO4 were tested experimentally in a fluidized bed reactor as a function of oxidation-reduction cycles, temperature, bed inventory and superficial gas velocity. The results showed that flue gases with a CO2 concentration as high as 97% can be obtained. The flue gases should be suitable for transport and storage after clean-up and purification. With an increase in the bed inventory or a decrease in superficial gas velocity, the flue gas characteristics improved i.e. more CO2 and fewer secondary components or less unreacted fuel were obtained. Carbon formation could occur during the reduction phase but it decreased with an increase in temperature and inventory and could be completely avoided by mixing steam with the fuel. The reactivity of NiO/NiAl2O4 was higher than the Cu- and Fe-based oxygen carriers. Increasing the CuO fraction in the oxygen carrier led to defluidization of the bed during the reduction and oxidation phases. 相似文献
11.
《Fuel》2007,86(12-13):1947-1958
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/MWth. 相似文献
12.
The reduction and oxidation behaviour of oxygen carrier particles of NiO and NiAl2O4 has been investigated in a fluidized bed reactor as well as a thermogravimetric analyzer (TGA). The particles showed high reactivity and gas yield to CO2 with methane in the temperature interval 750–950°C. In the fluidized bed the yield to CO2 was between 90 and 99% using bed masses corresponding to 16–57 kg/MWfuel. Complementary experiments in a TGA at 750 and 950°C showed a clear reaction of the NiAl2O4 with CH4 at the higher temperature. There was methane released from the reactor at high degrees of solid oxidation, which is likely associated with the lack of Ni‐sites on the particles which can reform the methane. There was some carbon formation during the reduction, although the amount was minor when the gas yield to carbon dioxide and degree of oxidation of the solid was high. A simple reactor model using kinetic data from a previous study predicted the gas yield during the reduction in the fluidized bed experiments with reasonable accuracy. The oxygen carrier system investigated in this work shows high promise for use in a real CLC system, provided that the particle manufacturing process can be scaled up with reasonable cost. 相似文献
13.
Peng Gao Yue Shen Min Zheng Guirong Bao Hua Wang Haitao Xie Lulu Wang 《加拿大化工杂志》2023,101(5):2444-2456
Chemical looping is a novel fuel conversion and material separation technology. It can be applied to obtain sulphur through selective oxidation of H2S. Further, chemical looping combustion (CLC) of sulphur can generate SO2 with a high concentration without NOx formation. The high SO2 concentration is adjustable and facilitates large-scale H2SO4 production. In this study, we examined the thermodynamics of the CLC of sulphur for H2SO4 production, which has not been reported previously. We analyzed the effects of reactor temperature and sulphur to Fe2O3 oxygen carrier (OC) ratios on sulphur allotrope transformations and on the distributions of reaction products. Moreover, the reactors were operated auto-thermally. Based on this design, we examined the effects of fuel reactor (FR) and air reactor temperatures on the minimum recirculation of the OC, as well as the gas and solid products and heat released from the air reactor. Our results showed that the CLC of sulphur with Fe2O3 OC could occur through an auto-thermal process. The FR in a sulphur CLC system should be operated over a temperature range of 800–950°C, with an Fe2O3 OC recirculation between 45 and 143 kg/kgS(s). Furthermore, when the FR was operated in the auto-thermal mode, we achieved 100% SO2 conversion. The findings of this study may be applied to reactor design for large-scale H2SO4 production through CLC of sulphur. 相似文献
14.
《Journal of the European Ceramic Society》2019,39(9):2960-2972
The formation of sp2 carbon by the Boudouard reaction significantly damages the refractory ceramics. Sulphur is an efficient way to prevent the carbon deposition catalysed by Fe3C, in the presence of H2. Thermogravimetric analysis was carried out on Fe2O3 samples exposed to a CO/H2 gas mixture at 600 °C. Solid sulphur was mixed with Fe2O3 powder or continually added in the form of gas into the CO/H2 reducing gas. The samples were characterised by X-ray diffraction, Raman spectroscopy, SEM and TEM. The addition of 100 ppm of sulphur species in the gas prevents the formation of carbon. The mechanism that governs the inhibition of the reaction is proposed, in which the formation of a thin protective FeS layer (0.5–1 nm) is involved. This study paves the way to an effective solution to inhibit the sp2 carbon deposition in the refractories by poisoning the Fe3C catalyst with sulphur. 相似文献
15.
化学链燃烧反应器具有广泛的燃料适应性,可同时兼顾气、液、固多类型燃料的运行。本文依托耦合内构件的3kW塔式串行流化床反应器,分别开展异丙醇、污泥以及煤炭的化学链燃烧实验,探究燃料物化属性对化学链燃烧过程与反应器运行的影响,揭示面向目标燃料的反应器针对性设计、载氧体性能选择与流化操作策略,助力形成指向性强、碳捕集效率高与操作灵活的化学链燃烧技术。面对碳化程度低、有机质含量高的固体燃料,焦炭气化速率已非强化重点,如污泥在3kW塔式反应器910℃与150s停留时间内,可实现大于99%的CO2捕集效率,化学链燃烧反应器应侧重改善可燃气体转化与旋风分离器对轻质焦炭颗粒的捕捉。当采用异丙醇等高CH4含量的燃料时,Fe基矿石载氧体的反应性能不足,3kW反应器的额外耗氧率高达10%~19%,其中未燃尽CH4对额外耗氧率的贡献占比超80%。化学链燃烧反应器需依据热解反应气的物化特性,选择或掺混功能性载氧体,以针对性改善气固转化。在煤等高碳化燃料的化学链燃烧过程中,焦炭气化是反应的限制性步骤,简化循环结构的3kW塔式反应器停留时间不足,仅可... 相似文献
16.
Some biomass fuels produce more NOx than coal on the basis of heating value, giving rise to the necessity and importance of controlling NOx emission in biomass combustion. The present study investigated the NO reduction over biomass char in a fixed bed quartz reactor in the temperature range of 973–1173 K. The reaction rates of three biomass chars (sawdust, rice husk and corn straw) with NO were compared with Datong bituminous coal char. The results show that the reaction orders of biomass chars for NO are of fractional order and independent of temperature. Biomass chars are more active in reducing NO than coal char. The characteristics of biomass char affect NO conversion. Biomass char formed at high pyrolysis temperature, especially large in particle size, is less active in reducing NO. To some extent, increase of reaction temperature and char loading enhance NO conversion. There exists an optimum bed height for the highest NO conversion. Moreover, NO reduction over biomass char is also enhanced in the presence of CO, O2 and SO2. 相似文献
17.
Kongzhai Li Hua Wang Yonggang Wei Dongxia Yan 《Chemical engineering journal (Lausanne, Switzerland : 1996)》2010,156(3):512-518
Three kinds of complex oxides oxygen carriers (CeO2–Fe2O3, CeO2–ZrO2 and ZrO2–Fe2O3) were prepared and tested for the gas–solid reaction with methane in the absence of gaseous oxidant. These oxides were prepared by co-precipitation method and characterized by means of XRD, H2-TPR and Raman. The XRD measurement shows that Fe2O3 particles well disperse on ZrO2 surface and Ce–Zr solid solution forms in CeO2–ZrO2 sample. For CeO2–Fe2O3 sample, only a small part of Fe3+ has been incorporated into the ceria lattice to form solid solutions and the rest left on the surface of the oxides. Low reduction temperature and low lattice oxygen content are observed over ZrO2–Fe2O3 and CeO2–ZrO2 samples, respectively by H2-TPR experiments. On the other hand, CeO2–Fe2O3 shows a rather high reduction peak ascribed to the consuming of H2 by bulk CeO2, indicating high lattice oxygen content in CeO2–Fe2O3 complex oxides. The gas–solid reaction between methane and oxygen carriers are strongly affected by the reaction temperature and higher temperature is benefit to the methane oxidation. ZrO2–Fe2O3 sample shows evident methane combustion during the reducing of Fe2O3, and then the methane conversion is strongly enhanced by the reduced Fe species through catalytic cracking of methane. CeO2–ZrO2 complex oxides present a high activity for methane oxidation due to the formation of Ce–Zr solid solution, however, the low synthesis gas selectivity due to the high density of surface defects on Ce–Zr–O surface could also be observed. The highly selective synthesis gas (with H2/CO ratio of 2) can be obtained over CeO2–Fe2O3 oxygen carrier through gas–solid reaction at 800 °C. It is proposed that the dispersed Fe2O3 and Ce–Fe solid solution interact to contribute to the generation of synthesis gas. The reduced oxygen carrier could be re-oxidized by air and restored its initial state. The CeO2–Fe2O3 complex oxides maintained very high catalytic activity and structural stability in successive redox cycles. After a long period of successive redox cycles, there could be more solid solutions in the CeO2–Fe2O3 oxygen carrier, and that may be responsible for its favorable successive redox cycles performance. 相似文献
18.
Osami Nakayama Na-oki Ikenaga Takanori Miyake Eriko Yagasaki Toshimitsu Suzuki 《Catalysis Today》2008,138(3-4):141
The gas–solid reaction between methane and the lattice oxygen of Ni, Co, and Fe-oxides loaded on various support materials produced a synthesis gas (hydrogen and carbon monoxide) at 600–800 °C. Metal oxides were reduced to metals or lower valence oxides, and they were re-oxidized to oxides by introducing air after the reaction. Thus, production of hydrogen or synthesis gas free from nitrogen can be achieved alternatively without using pure oxygen. As a metal oxide, Fe2O3 and Rh2O3-loaded on Y2O3 exhibited the highest H2 selectivity of 60.1% with a moderate CH4 conversion of 54% and a high lattice oxygen utilization of 84% at 800 °C. 相似文献
19.
C. D. Bohn J. P. Cleeton C. R. Müller J. F. Davidson A. N. Hayhurst S. A. Scott J. S. Dennis 《American Institute of Chemical Engineers》2010,56(4):1016-1029
Results are reported for the repeated reduction of iron oxide particles, 300–425 μm diameter, by a mixture of CO, CO2, and N2 in a fluidized bed of 20 mm internal diameter. The conclusions were as follows: (1) Reduction of either Fe2O3 to Fe3O4 or of Fe3O4 to Fe0.947O is first‐order in CO. (2) With the particle sizes used, the rates of the reduction reactions are controlled by intrinsic chemical kinetics. Activation energies and pre‐exponential factors are reported. (3) The first cycle gave anomalous results, but (a) the rate of reduction of Fe2O3 to Fe3O4 remained constant over cycles 2–10; (b) the rate of reduction of Fe3O4 to Fe0.947O declined by 60–85% over cycles 2–10. (4) The rates of reduction declined with solids conversion down to zero at 80% conversion. The rates were incorporated into a conventional model of a fixed bed, which was used to predict, satisfactorily, the reduction behavior of iron oxide. © 2009 American Institute of Chemical Engineers AIChE J, 2010 相似文献
20.
Chemical looping combustion (CLC) has the inherent property of separating CO2 from flue gases. This paper is concerned with the application of chemical looping to the combustion of a solid fossil fuel (a lignite and its char) in a technique whereby the fuel is gasified in situ using CO2 in the presence of a batch of supported copper oxide (the “oxygen carrier”) in a single reactor. As the metal oxide becomes depleted, the feed of fuel is discontinued, the inventory of fuel is reduced by further gasification and then the contents are re-oxidised by the admission of air to the reactor, to begin the cycle again. The choice of oxides is restricted because it requires an oxide which is exothermic during reduction to balance the endothermic gasification reactions. Copper has such oxides, but a key question is whether or not it can withstand temperatures at which gasification rates are significant (∼1173 K), particularly from the point of view of avoiding sintering and deactivation of the carrier in its reduced form. It was found that an impregnated carrier, made by impregnating a θ-alumina catalyst support (BET area 157 m2/g) with a saturated solution of copper and aluminium nitrates, acted as a durable carrier over 20 cycles of reduction and oxidation, using both Hambach lignite coal, and its char, and with air as the oxidising agent. During the course of the experiments, the BET surface area of the support fell from ∼60 m2/g, just after preparation, to around 6 m2/g after 20 cycles. However, this fall did not appear to affect the overall capacity of the oxygen carrier to react with fuels and its effect on the kinetics of the reaction with CO did not influence the outcome of the experiments, since the overall performance of the looping scheme is dominated by the much slower kinetics of the gasification reaction. The apparent kinetics of the gasification are faster in the presence of the looping agent: this is because the bulk concentration of CO in the presence of the looping agent is lower, and partly because the destruction of CO in the vicinity of a gasifying particle enhances the rate of removal of CO by mass transfer (and increases the local concentration of CO2). There was little evidence to suggest a direct reaction between carbonaceous and carrier solids, other than via a gaseous intermediate. However, the observation of finite rates of conversion in a bed of active carrier, fluidised by nitrogen, is a scientific curiosity, which we have not been able to explain satisfactorily. At 1173 K, as used here, rates of gasification of Hambach lignite, and its char, are significant. The CuO in the carrier decomposes at 1173 K to produce gas-phase O2 and Cu2O: both can react with CO produced by gasification, whilst the O2 can react directly with the char. 相似文献