Chemical Looping With Oxygen Uncoupling Research Articles

Screening of different manganese ores for chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU)

Oxygen carriers based on manganese oxides have recently shown great promise for use in chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU). In this work, eleven different manganese ores have been investigated for application in CLC and CLOU. The reactivity towards methane and synthesis gas (50% CO in H2) and the oxygen uncoupling behaviour at 900, 950 and 1000°C have been investigated. The mechanical stability and integrity of the ores were also evaluated in a jet-cup attrition rig. It was found that some of the ores could convert approximately 70–80% of the added methane to carbon dioxide, and most of them provided almost complete conversion of synthesis gas. In these experiments the bed mass was 15g for experiments with methane and 2g for experiments with syngas, corresponding to a specific solids inventory of 57 and 25kg/MW, respectively. All of the oxygen carrier materials released small amounts of gas phase oxygen via CLOU, between 0.01 and 0.03mass% of the oxygen carrier during the inert period. Some of the investigated ores also exhibited low rates of attrition. The combination of high reactivity with different fuel gases, relatively low attrition rates and low cost make some of these manganese ores highly interesting for a CLC process based on interconnected fluidized beds.

Thermodynamic analysis of in situ gasification-chemical looping combustion (iG-CLC) of Indian coal

Chemical looping combustion (CLC) is an inherent CO2 capture technology. It is gaining much interest in recent years mainly because of its potential in addressing climate change problems associated with CO2 emissions from power plants. A typical chemical looping combustion unit consists of two reactors-fuel reactor, where oxidation of fuel occurs with the help of oxygen available in the form of metal oxides and, air reactor, where the reduced metal oxides are regenerated by the inflow of air. These oxides are then sent back to the fuel reactor and the cycle continues. The product gas from the fuel reactor contains a concentrated stream of CO2 which can be readily stored in various forms or used for any other applications. This unique feature of inherent CO2 capture makes the technology more promising to combat the global climate changes. Various types of CLC units have been discussed in literature depending on the type of fuel burnt. For solid fuel combustion three main varieties of CLC units exist namely: syngas CLC, in situ gasification-CLC (iG-CLC) and chemical looping with oxygen uncoupling (CLOU). In this paper, theoretical studies on the iG-CLC unit burning Indian coal are presented. Gibbs free energy minimization technique is employed to determine the composition of flue gas and oxygen carrier of an iG-CLC unit using Fe2O3, CuO, and mixed carrier-Fe2O3 and CuO as oxygen carriers. The effect of temperature, suitability of oxygen carriers, and oxygen carrier circulation rate on the performance of a CLC unit for Indian coal are studied and presented. These results are analyzed in order to foresee the operating conditions at which economic and smooth operation of the unit is expected.

Screening of supported and unsupported Mn–Si oxygen carriers for CLOU (chemical-looping with oxygen uncoupling)

Oxygen carriers based on oxides of Mn and Si in combination with Mg, Al, Ca and Ti (Mn0.63Si0.27X0.1, X = Ca(OH)2, TiO2, MgO, AlOOH) were examined for CLOU (chemical-looping with oxygen uncoupling), in terms of oxygen uncoupling ability and ability to convert both methane and syngas. The focus was on the optimization of the production process to yield mechanically strong oxygen carrier particles with a reasonable activity. For this purpose, 15 types of oxygen carriers were produced by spray-drying and calcined for different time periods and at different temperatures.The oxygen uncoupling behavior and gas conversion of the materials were investigated in a batch fluidized-bed reactor under alternating oxidizing and reducing conditions in the temperature range 850–1050 °C. To determine attrition resistance and mechanical stability, a jet-cup attrition rig was used. Furthermore, physical and chemical properties such as specific surface area and crystal phase composition have been determined.For the oxygen carriers with additives of Mg, Al, Ca, Ti, some material combinations showed a significant increase in reactivity and improved mechanical stability compared to the unsupported Mn–Si particles. Changing the production process (milling process and calcination time) just caused slight difference in attrition resistance, gas conversion as well as oxygen release.

Kinetics of oxygen uncoupling of a copper based oxygen carrier

Here, an oxygen carrier consisting of 60wt% CuO supported on a mixture of Al2O3 and CaO (23wt% and 17wt% respectively) was synthesised by wet-mixing powdered CuO, Al(OH)3 and Ca(OH)2, followed by calcination at 1000°C. Its suitability for chemical looping with oxygen uncoupling (CLOU) was investigated. After 25 repeated redox cycles in either a thermogravimetric analyser (TGA) or a laboratory-scale fluidised bed, (with 5vol% H2 in N2 as the fuel, and air as the oxidant) no significant change in either the oxygen uncoupling capacity or the overall oxygen availability of the carrier was found. In the TGA, it was found that the rate of oxygen release from the material was controlled by intrinsic chemical kinetics and external transfer of mass from the surface of the particles to the bulk gas. By modelling the various resistances, values of the rate constant for the decomposition were obtained. The activation energy of the reaction was found to be 59.7kJ/mol (with a standard error of 5.6kJ/mol) and the corresponding pre-exponential factor was 632m3/mol/s. The local rate of conversion within a particle was assumed to occur either (i) by homogeneous chemical reaction, or (ii) in uniform, non-porous grains, each reacting as a kinetically-controlled shrinking core. Upon cross validation against a batch fluidised bed experiment, the homogeneous reaction model was found to be more plausible. By accurately accounting for the various artefacts (e.g. mass transfer resistances) present in both TGA and fluidised bed experiments, it was possible to extract a consistent set of kinetic parameters which reproduced the rates of oxygen release in both experiments.

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.

Chemical-Looping Combustion and Gasification of Coals and Oxygen Carrier Development: A Brief Review

Chemical-looping technology is one of the promising CO2 capture technologies. It generates a CO2 enriched flue gas, which will greatly benefit CO2 capture, utilization or sequestration. Both chemical-looping combustion (CLC) and chemical-looping gasification (CLG) have the potential to be used to generate power, chemicals, and liquid fuels. Chemical-looping is an oxygen transporting process using oxygen carriers. Recently, attention has focused on solid fuels such as coal. Coal chemical-looping reactions are more complicated than gaseous fuels due to coal properties (like mineral matter) and the complex reaction pathways involving solid fuels. The mineral matter/ash and sulfur in coal may affect the activity of oxygen carriers. Oxygen carriers are the key issue in chemical-looping processes. Thermogravimetric analysis (TGA) has been widely used for the development of oxygen carriers (e.g., oxide reactivity). Two proposed processes for the CLC of solid fuels are in-situ Gasification Chemical-Looping Combustion (iG-CLC) and Chemical-Looping with Oxygen Uncoupling (CLOU). The objectives of this review are to discuss various chemical-looping processes with coal, summarize TGA applications in oxygen carrier development, and outline the major challenges associated with coal chemical-looping in iG-CLC and CLOU.

Chemical-Looping with Oxygen Uncoupling of Different Coals Using Copper Ore as an Oxygen Carrier

Chemical-looping with oxygen uncoupling (CLOU) has been considered as a revolutionary technology for low-energy consumption CO2 capture. In this work, the performance of copper ore in the CLOU processes for diverse ranks of coal was examined in a batch-scale fluidized-bed at various temperatures. Typical Chinese coals (GaoPing anthracite, FuGu bituminous coal, and ShengLi lignite) were used as fuel. The effects of temperature and coal rank on the redox behavior, carbon conversion rate, and instantaneous rates of char conversion and oxygen generation were first investigated. It was found that both increasing the reactor temperature and decreasing the coal rank had beneficial effects on the carbon conversion rate, instantaneous rates of char conversion, and oxygen generation. In the CLOU processes of coal, the rate-limiting step was the burning of coal char with oxygen of low concentration if the oxygen carrier (OC) was excess to coal. And for higher-rank coals like anthracite, the rate-limitation effect wa...

Evaluation of Manganese Minerals for Chemical Looping Combustion

The use of mineral materials as oxygen carriers for Chemical Looping Combustion (CLC) is an attractive option due to their low cost. This paper reports an experimental study of four manganese minerals as potential oxygen carriers focusing on the behavior in CLC as well as in Chemical Looping with Oxygen Uncoupling (CLOU). Experiments were carried out in a thermogravimetric apparatus (TGA) and a fluidized-bed reactor. Repeated tests with all the minerals showed no sufficient CLOU properties. Then, they can only be used in CLC applications involving the redox pairs Mn3O4/MnO and Fe2O3/Fe3O4. Oxygen transport capacity and reactivity to the main fuel gases (H2, CO, and CH4) were determined in a TGA. Manganese minerals were also tested during 35–54 h in a fluidized-bed reactor to evaluate the evolution of reactivity to H2, CO, and CH4 as well as their attrition rate and mechanical strength. The reactivity of the materials decreased in the first 10 cycles with CH4 and then became quite stable for the rest of th...

Performance of cement decorated copper ore as oxygen carrier in chemical-looping with oxygen uncoupling

Chemical-looping with oxygen uncoupling (CLOU) provides a revolutionary route for CO2 capture with low energy consumption. To address the CLOU process, the appropriate oxygen carrier should have the ability of releasing gaseous oxygen in the fuel reactor and regenerating itself in the air reactor at temperatures of interest for combustion. Copper ore, known for its low cost and abundant reserves, has been identified as an applicable oxygen carrier material for CLOU. However, Cu-based oxygen carriers share the common disadvantages of sintering and agglomeration at high temperatures. To enhance the sintering-resistant property of copper ore particles, four types of cement decorated copper ore oxygen carrier were prepared by mechanical mixing. Successive cyclic redox experiments at different temperatures in a thermogravimetric analyzer (TGA) were first conducted to investigate the oxidation and reduction properties of the newly prepared oxygen carriers. The TGA results showed that within 20 cycles, cement modified copper ore (CuC) particles performed better redox reactivity than single copper ore oxygen carrier, especially at elevated temperatures. Among the CuC oxygen carriers, CuC-20 (copper ore modified with 20wt.% of cement) was the best in redox reactivity. Cyclic redox reactivity of Cu-ore and CuC-20 were further tested in a batch-scale fluidized bed reactor with both synthesis gas and coal as fuel at 950°C. The results both indicated that CuC-20 showed little tendency toward agglomeration and no chemical interaction between the active phase of copper ore and cement, which maintained stable and good reactivity after the activation process.

Reduction kinetics analysis of sol–gel-derived CuO/CuAl2O4 oxygen carrier for chemical looping with oxygen uncoupling

Chemical looping with oxygen uncoupling (CLOU) is a promising technology due to its potential to reduce energy efficiency penalty and cost associated with CO2 capture. In this work, a CuO/CuAl2O4 oxygen carrier (OC) prepared by sol–gel was investigated in its oxygen release kinetics (4CuO → 2Cu2O + O2). Based on several well-organized temperature-programmed reduction experiments which were conducted in a thermogravimetric analyzer, the activation energy E (343.7 kJ mol−1) and pre-exponential factor A (3.78 × 1012 s−1) were determined and the Avrami–Erofeev random nucleation and subsequence growth model fitted well with the reduction experimental data. The enhancement of OC reduction rate in real fluidized bed CLOU reactor using different types of solid fuels (petroleum coke, anthracite, bituminous, and lignite) was identified in terms of the chemical kinetics and thermodynamics for the first time. It was found that the CuO reduction rate is more sensitive to the local temperature change than the oxygen concentration driving force. The results could contribute to the design, operation, and performance prediction of real CLOU reactors.

Fuel Nitrogen Conversion in Chemical Looping with Oxygen Uncoupling of Coal with a CuO-Based Oxygen Carrier

The interest in chemical looping with oxygen uncoupling (CLOU) of coal as a method for CO2 enrichment has increased drastically during recent years. The objective of this work was to experimentally investigate fuel nitrogen conversion in the CLOU process of coal with a CuO-based oxygen carrier in a batch fluidized-bed unit. Three coals of different rank (anthracite, sub-bituminous, and bituminous) and their corresponding chars were used as fuels. Furthermore, experiments of coal combustion under air-fired conditions were performed to recognize the unique pathway of fuel nitrogen conversion in CLOU. Experimental results indicated that NO was formed in the largest amount of total NOx. For the Shenhua bituminous coal that was used, most of the NO, NO2, and N2O from fuel nitrogen was formed during the devolatilization stage of the coal. However, with Xuzhou sub-bituminous coal or Huaibei anthracite as fuels, a certain portion of NO was derived from char-N. Under the current experimental conditions (temperatur...

Self-assembly template combustion synthesis of a core–shell CuO@TiO2–Al2O3 hierarchical structure as an oxygen carrier for the chemical-looping processes

Chemical looping combustion (CLC) and chemical looping with oxygen uncoupling (CLOU) are the most promising technologies for capture of CO2 at a low cost. CLC and CLOU involve cyclic reduction and oxidation of a solid oxygen carrier (OC) to transfer active oxygen from air to carbon-based fuels for combustion with the inherent feature of isolating CO2. One key issue with these technologies is to manufacture a high-performance, economical and practical OC material. In this paper, we propose a self-assembly template combustion synthesis (SATCS) method for preparing a hierarchical structure copper-based OC, Cu-rich, Al2O3-supported and TiO2-stabilized in a core–shell microarchitecture. The selection of raw materials and the rational design of OCs are based on the density functional theory (DFT) calculations and the classical Derjaguin–Landau–Verwey-Overbeek (DLVO) theory, respectively. The spontaneous aggregation between α-Al2O3 microparticles (μm-Al2O3) and rutile TiO2 nanoparticles (nm-TiO2) is driven by the van der Waals attractive and electrostatic attractive forces to form core(Al2O3)–shell(TiO2) hard templates in the wet precursor containing copper nitrate and urea. Upon calcination of the dried precursor in air, fewer nitrogen oxides (NOx) are released, demonstrating an environment-friendly fabrication process, whereby a highly dispersed and high-loading Cu-based crystalline layer is deposited on the nanostructured shell. A representative CuO@TiO2–Al2O3 OC (17.5wt% Al2O3, 5wt% TiO2) possesses hierarchical porosity and an interconnected framework and exhibits excellent performance of the reactivity, stability, oxygen release/uptake capacity and mechanical strength in the high-temperature redox cycles. The proper addition of TiO2 nanoparticles is effective in preventing the formation of copper aluminates (CuAl2O4 and CuAlO2) and inhibiting the sintering of active component grain. In addition, the rational design method and novel synthesis technique allow a mass production of various metal oxide composites used for chemical looping processes with CO2 capture and clean utilization of energy.

Highly Efficient Oxygen-Storage Material with Intrinsic Coke Resistance for Chemical Looping Combustion-Based CO2 Capture.

Chemical looping combustion (CLC) and chemical looping with oxygen uncoupling (CLOU) are emerging thermochemical CO2 capture cycles that allow the capture of CO2 with a small energy penalty. Here, the development of suitable oxygen carrier materials is a key aspect to transfer these promising concepts to practical installations. CuO is an attractive material for CLC and CLOU because of its high oxygen-storage capacity (20 wt %), fast reaction kinetics, and high equilibrium partial pressure of oxygen at typical operating temperatures (850-1000 °C). However, despite its promising characteristics, its low Tammann temperature requires the development of new strategies to phase-stabilize CuO-based oxygen carriers. In this work, we report a strategy based on stabilization by co-precipitated ceria (CeO2-x ), which allowed us to increase the oxygen capacity, coke resistance, and redox stability of CuO-based oxygen carriers substantially. The performance of the new oxygen carriers was evaluated in detail and compared to the current state-of-the-art materials, that is, Al2 O3 -stabilized CuO with similar CuO loadings. We also demonstrate that the higher intrinsic oxygen uptake, release, and mobility in CeO2-x -stabilized CuO leads to a three times higher carbon deposition resistance compared to that of Al2 O3 -stabilized CuO. Moreover, we report a high cyclic stability without phase intermixing for CeO2-x -supported CuO. This was accompanied by a lower reduction temperature compared to state-of-the-art Al2 O3 -supported CuO. As a result of its high resistance towards carbon deposition and fast oxygen uncoupling kinetics, CeO2-x -stabilized CuO is identified as a very promising material for CLC- and CLOU-based CO2 capture architectures.

Evaluation of a Mixed Fe–Mn Oxide System for Chemical Looping Combustion

In coal-based chemical looping combustion (CLC) technology, relatively cheap metal oxides, referred to as oxygen carrier materials (OCMs), are required because some of the OCMs will be removed together with the residual ashes after combustion. CLC technology will have an estimated loss in efficiency of around 2% compared to standard combustion technology without capture if a proper OCM is found that can give full combustion, removing the need of an air separation unit (ASU). Materials with a chemical looping oxygen uncoupling (CLOU) effect will even give further benefits in faster gasification and combustion of the fuel. One can already find produced materials that can give such a desirable effect, but fabrication and material cost are still an issue in these cases. If such a material can be delivered by the mining industry, cost savings and plant efficiency will be high. Before selection of the natural minerals with strong inert inherent support that contain Fe and Mn, the need for a better understanding...

Ca1−xAxMnO3 (A = Sr and Ba) perovskite based oxygen carriers for chemical looping with oxygen uncoupling (CLOU)

Operated under a cyclic redox mode with an oxygen carrier, the chemical looping with oxygen uncoupling (CLOU) process offers the potential to effectively combust solid fuels while capturing CO2. Development of oxygen carriers capable of reversibly exchanging their active lattice oxygen (O2−) with gaseous oxygen (O2) under varying external oxygen partial pressure (PO2) is of key importance to CLOU process performance. This article investigates the effect of A-site dopants on CaMnO3 based oxygen carriers for CLOU. Both Sr and Ba are explored as potential dopants at various concentrations. Phase segregations are observed with the addition of Ba dopant even at relatively low concentrations (5% A-site doping). In contrast, stable solid solutions are formed with Sr dopant at a wide range of doping level. While CaMnO3 perovskite suffers from irreversible change into Ruddlesden–Popper (Ca2MnO4) and spinel (CaMn2O4) phases under cyclic redox conditions, Sr doping is found to effectively stabilize the perovskite structure. In-situ XRD studies indicate that the Sr doped CaMnO3 maintains a stable orthorhombic perovskite structure under an inert environment (tested up to 1200°C). The same oxygen carrier sample exhibited high recyclability over 100 redox cycles at 850°C. Besides being highly recyclable, Sr doped CaMnO3 is found to be capable of releasing its lattice oxygen at a temperature significantly lower than that for CaMnO3, rendering it a potentially effective oxygen carrier for solid fuel combustion and carbon dioxide capture.

Design and operation of a 50 kWth Chemical Looping Combustion (CLC) unit for solid fuels

A Chemical Looping Combustion (CLC) unit for solid fuels has been designed, erected and operated. The design was based on a thermal power of 20kWth for in-situ Gasification Chemical Looping Combustion (iG-CLC) or 50kWth for Chemical Looping with Oxygen Uncoupling (CLOU). Fuel and air reactors are two interconnected circulating fluidized beds reactors, with the coal being fed at the bottom of the fuel reactor to maximize the contact between the volatile matter and the oxygen carrier particles. A carbon stripper has been included between fuel and air reactors to increase the CO2 capture rates. In this unit, the char particles are separated from the oxygen carrier particles and recirculated to the fuel reactor. The solids flow exiting from the fuel reactor is split into two different streams by using a double loop seal down the fuel reactor cyclone. One goes to the carbon stripper and the other is recirculated to the fuel reactor. In this way it is possible to have an independent control of solids inventory in the fuel reactor and the global solids circulation flow rate between fuel and air reactors. First operational results at steady state have been obtained with stable operation in iG-CLC mode during combustion of a bituminous coal with ilmenite being the oxygen carrier. A CO2 capture value of 88% at 991°C and a total oxygen demand value of 8.5% were obtained with a solids inventory in the fuel reactor of 470kg/MWth.

Screening of Combined Mn-Fe-Si Oxygen Carriers for Chemical Looping with Oxygen Uncoupling (CLOU)

Combined oxygen carriers of Mn, Fe, and Si were screened for the chemical looping with oxygen uncoupling process with the objective of identifying materials with high reactivity and sufficient attrition resistance. Eleven oxygen carrier materials were produced by spray-drying and then calcined for 4 h at 1100 and 1200 °C. The ability of the oxygen carriers to release oxygen and to convert gaseous fuels was investigated in a batch fluidized-bed reactor under alternating reducing and oxidizing conditions for temperatures ranging from 850 °C to 1050 °C. The attrition behavior of the different materials was evaluated in a jet-cup attrition rig. All investigated oxygen carriers proved to release oxygen and showed high reactivity toward synthesis gas (50% CO in H2). Oxygen carrier materials with comparably lower mechanical stability were found to have a higher reactivity toward methane. One of the investigated formulations showed to have both high mechanical stability and resistance toward attrition, as well as good methane conversion and oxygen release.

Characterization of a sol–gel derived CuO/CuAl2O4 oxygen carrier for chemical looping combustion (CLC) of gaseous fuels: Relevance of gas–solid and oxygen uncoupling reactions

A new sol–gel CuO/CuAl2O4 material was characterized in a thermogravimetric analyzer (TGA) for chemical looping combustion (CLC) with gaseous fuels, including the relevance of the oxygen uncoupling mechanism in oxygen transference was considered. This material possesses high reactivity and oxygen transport capacity, which combines the best features of the previously reported impregnated and spray-dried materials. During the cycles with N2 and air, CuO was fully decomposed into Cu2O in N2 and then regenerated to CuO in air, similarly to chemical looping with oxygen uncoupling (CLOU) for solid fuels. Decomposition of CuAl2O4 to CuAlO2 was quite slow, and the followed regeneration cannot be accomplished. Subsequently, the adequate and stable reaction rates of this material were examined in high numbers of cycles (>50 cycles) with gaseous fuels. The material undergone such cycles with gaseous fuels was then subjected to cycles with N2 and air. Segregation of CuO from Al2O3 in the CuAl2O4 was observed during gaseous fuels combustion, which produced more available oxygen for CLOU than the initial material. Finally, the relative importance of gas–solid reactions in CLC against oxygen uncoupling in CLOU was examined with the appearance of gaseous fuel.

Fuel reactor modelling in chemical looping with oxygen uncoupling process

Solid fuel combustion via chemical looping with oxygen uncoupling (CLOU) represents a novel route for CO2 capture with minimal energy penalty. An essential part of the viability of a CLOU system is based on the behaviour of the fuel reactor. This paper presents a one-dimensional fluidized bed model capable of describing the operation of the fuel reactor involved in CLOU. The model considers physical phenomena relevant to CLOU, such as oxygen carrier decomposition, combustion of coal with molecular oxygen, fluidized bed hydrodynamics, and transfer of heat within the reactor. The performance of a CLOU fuel reactor fed with bituminous coal and a TiO2-supported CuO oxygen carrier was evaluated by means of modelling. A reference case was first defined and simulated, after which the effect of various process parameters on the results was assessed by parameter variation. For the reference case conditions with a temperature of 960°C and solids inventory of 400kg/MWf in the reactor and without utilization of a carbon separation system, a CO2 capture efficiency of approximately 90% was predicted. A CO2 capture efficiency of 95% could be reached by optimizing the operating conditions. It was found that when using low-reactive coals, a carbon stripper is required to obtain a feasible CO2 capture rate. Overall, the model predictions appeared to be in agreement with results presented in the literature.

Redox kinetics of CaMg0.1Ti0.125Mn0.775O2.9−δ for Chemical Looping Combustion (CLC) and Chemical Looping with Oxygen Uncoupling (CLOU)

The objective of this study was to establish the kinetic of reactions involved in redox cycles of an oxygen carrier material based on a perovskite type structure with the formula CaMg0.1Ti0.125Mn0.775O2.9−δ. The oxygen transport capacity and reactivity of this material during reduction with gaseous fuels (CH4, H2 and CO) and the subsequent oxidation with oxygen are studied in a TGA apparatus. Besides, the oxygen uncoupling properties of this material are analysed. Thus, kinetics for relevant reactions involved in Chemical Looping Combustion (CLC) and Chemical Looping with Oxygen Uncoupling (CLOU) were determined.CaMg0.1Ti0.125Mn0.775O2.9−δ reactivity increased with the number of redox cycles, whereas the total oxygen transport capacity decreased from 8.5 to 8.0wt.%. Particles that reached the maximum reactivity were denoted as “activated” material. Kinetics for both fresh and “activated” particles was determined. Conversion vs. time curves at different temperatures (973–1273K), and reacting gas concentration (5–60vol.% for CH4, H2 or CO; 5–21vol.% for O2) were obtained for both fresh and “activated” material. For kinetics determination, the shrinking core model with control by chemical reaction and diffusion through the product layer was used to obtain the kinetic parameters.