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This study investigates the enhancement of amine-based chemical absorption for CO 2 capture in the power industry, focusing on reducing energy consumption through the implementation of a Heat Integrated Stripper (HIS) with built-in heat exchangers. Despite its theoretical promise, there is a lack of experimental validation for the HIS modification. The research aims to assess the effectiveness of the modified stripper compared to the standard process, utilizing pilot plant data from Jaworzno and Łaziska Power Plants in Poland. Collaborating with the TAURON Group, a key player in the Polish energy sector, pilot tests employed a mobile plant with a 200 m3/h nominal gas flow rate. MEA 30% solvent was used in the pilot tests, and the results underwent data reconciliation for mass balances, heat losses, and process heat duty. The study reveals that heat integration positively influences the temperature profile in the stripper, leading to increased CO 2 capture without additional heat input. With the escalating prices of CO 2 emission allowances, this research addresses a crucial aspect of the national economy. The findings provide a foundation for the design of a scaled-up CO 2 capture process incorporating HIS, offering potential solutions to mitigate the environmental impact of power generation. • Complex analysis of gas separation by chemical absorption. • Energy efficiency analysis of advanced CO2 capture process based on pilot studies. • Heat-Integrated Stripper reduces amine scrubber energy use by 7%. • The most reliable operating parameters of the carbon dioxide capture process. [ABSTRACT FROM AUTHOR]

Solar-driven biomass gasification is a promising technology to improve the utilization efficiency of solar energy and biomass, which also enhances the thermochemical storage and the subsequent stable utilization. Whereas, the intermittence of solar energy deteriorates the stability and continuity of the thermochemical reaction process, which limits the efficient conversion of the reaction. In this regard, this work proposes a new solar-driven biomass gasification technology based on solid particle heat carrier. Different from the direct solar-driven gasification, solid particles are performed as medium to receive the concentrated solar radiation energy and transfer energy to biomass feedstocks. In addition, the combined power generation scenario is adopted to evaluate the thermodynamics and economics of the technology. The integration of solid particle heat storage, the system dispatch and stable operation will be further enhanced. Results show that under the optimal condition, the system maximum thermal and exergy efficiencies are increased by 12.94% and 12.51%, respectively. Considering the system off-design operation, with the evaluated typical periods of four seasons, the averaged power generation efficiency is increased by 5.16%, with the highest efficiency improvement of 9.41% occurring in the typical winter days. With the change of receiver price and biomass price, the maximum decline of levelized cost of electricity reaches to 17.6%, which presents the favorable economic benefits. As a new solar thermochemical technology, this technology exhibits competitive characteristics, significantly improving the utilization efficiency of solar and biomass energy. • New type of solar driven biomass gasification technology by solid particles is proposed. • The combined power generation scenario is adopted to evaluate the technology. • The optimal operating condition of the system are obtained by genetic algorithm. • The dynamic operating characteristics and economic potential of the system are evaluated. [ABSTRACT FROM AUTHOR]

• Chemical looping combustion is a promising alternative to oxy-fuel combustion. • Chemical looping combustion integrated with supercritical CO 2 (CLC-sCO 2) was considered. • CLC-sCO 2 was shown to achieve the net efficiency of 51.4% at the LCOE of £36.1/MWh. • Techno-economic performance of CLC-sCO 2 is competitive to other power generation cycles. Oxy-fuel combustion is currently gathering attention as one of the promising options for capturing CO 2 efficiently, when applied to power plants, for subsequent carbon sequestration. However, this option requires a large quantity of high-purity oxygen that is usually produced in an energy-intensive air separation unit (ASU). Chemical looping combustion (CLC) is a technology with the potential of reducing the costs and energy penalties associated with current state-of-the-art cryogenic ASUs. In this work, the techno-economic performance of a natural gas-fired oxy-combustion cycle with cryogenic ASU is compared with that based on CLC. Two natural gas-fired cycles are considered: (i) staged oxy-fuel natural gas combined cycle as a reference; and (ii) gas-fired CLC with supercritical CO 2 cycle. The process models were developed in Aspen Plus® in order to evaluate the thermodynamic performance of the proposed system and to benchmark it against the reference cycle. The results show that the net efficiency of the proposed cycle, including CO 2 compression, is more than 51%, which is comparable to that of a conventional natural gas combined cycle with CO 2 capture and 2.7% points higher than that of the reference cycle. Moreover, the economic evaluation indicates that a reduction in levelised cost of electricity from £38.3/MWh to £36.1/MWh can be achieved by replacement of the ASU-based oxy-fuel system with CLC. Hence, gas-fired CLC with a supercritical CO 2 cycle has high potential for commercialisation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Characterization of a manganese-iron mixed oxide to assess oxygen uncoupling. • Optimal sintering to achieve high reactivity, mechanical strength and magnetism. • Regeneration conditions are critical to promote oxygen uncoupling capability. • A maximum in the regeneration rate is found with the reacting temperature. • Further reduction is possible in the presence of a fuel gas. Abstract Bimetallic manganese-iron materials have been identified as suitable oxygen carriers for Chemical Looping Combustion (CLC) and Chemical Looping with Oxygen Uncoupling (CLOU) processes. These materials allow the combustion of a fuel with inherent CO 2 capture according to two parallel mechanisms: reaction with lattice oxygen and oxygen uncoupling. This work is focused on the evaluation of the reactivity and physicochemical characterization of oxygen carrier particles consisting of a manganese-iron mixed oxide with manganese to iron molar ratio of 66:34 and doped with titanium (7 wt% TiO 2) with the objective of determining suitable conditions to be used in CLC and CLOU processes. Particles were prepared by spray drying and the sintering procedure was optimized in order to achieve particles with high reactivity and mechanical strength. In addition, suitable magnetic properties were also sought in order to allow oxygen carrier recover and reuse in a chemical looping unit burning solid fuels. Optimum operating conditions for the fuel combustion and regeneration stages were determined in order to promote the oxygen uncoupling mechanism. Thus, temperature during the fuel combustion must be as high as possible to enhance the oxygen transference; but conditions for oxygen carrier regeneration by air must be carefully selected in order to take advantage of the oxygen uncoupling capability of this material. An oxidizing temperature interval of 1123–1173 K maximized the regeneration, while an air excess higher than 20% would be recommended in order to guarantee oxygen uncoupling capability. [ABSTRACT FROM AUTHOR]

Highlights • Cu-Fe oxygen carriers investigated for syngas and hydrogen coproduction. • Simulated co-current moving bed reactor: 99.5% CH 4 conversion, 97.5% syngas purity. • >99.9% H 2 purity during 5 redox cycles in a fixed bed reactor. • Net H 2 production: 28% higher than autothermal reforming baseline case. • Effective thermal efficiency: 10% higher than autothermal reforming baseline case. Abstract Chemical looping reforming presents an attractive alternative to the conventional processes for chemicals and energy production from carbonaceous fuels with significant reduction in carbon emissions and high exergy efficiency. Production of syngas and hydrogen is important because the former is a critical building block for valuable chemicals and latter is a source of clean energy. The use of copper-iron (Cu-Fe) oxygen carriers for coproducing syngas and hydrogen in a chemical looping reforming process is studied via experiments and process simulations. Three different compositions of Cu and Fe oxides are examined for their properties concerning the reactivity towards fuel and the selectivity towards syngas. The feasibility of using a co-current moving bed reactor configuration for syngas production is probed experimentally in a fixed bed reactor by placing the fully oxidized and reduced oxygen carrier in series. The methane conversion and dry syngas purity as high as 99.5% and 97.5%, respectively, are observed for copper oxide (20 wt%) - iron oxide (60 wt%) - aluminium oxide (20 wt%) oxygen carrier in a simulated co-current moving bed reactor. Key performance parameters including effective thermal efficiency for 5 different configurations of the chemical looping reforming process from ASPEN Plus simulation software are compared against the baseline case of the auto-thermal reforming process. Apart from an improvement in the natural gas conversion and syngas purity in the chemical looping reforming process, the net hydrogen production is increased by 28% and effective thermal efficiency is increased by 10% over that of the auto-thermal reforming process. [ABSTRACT FROM AUTHOR]

Highlights • Techno-economic optimization of a rotary chemical looping power plant is presented. • The optimization model captures and exploits reactor-system feedback effects. • Optimizing an economic objective function identified lower cost solutions. • Scaling and technology maturity projections suggest commercial viability. Abstract The rotary chemical looping combustion reactor design - which utilizes oxygen carriers in a matrix of micro channels for indirect fuel conversion - provides a viable path for fossil-based electric power generation with CO 2 capture. Its thermally integrated matrix of micro channels minimizes irreversibilities associated with heat transfer in the reactor, and establishes multiscale coupling between oxygen carrier kinetics, reactor geometry and plant operating conditions. In this study, we implement an optimization framework that exploits this multiscale coupling for simultaneous reactor design and power plant economic optimization. Results for the methane-fueled power plant reveal optimized thermal efficiencies of 54–56% for a rotary chemical looping recuperative Brayton cycle plant, with compressor pressure ratio in the 3–7 range. By switching from an efficiency to an economic objective, we identified solutions that reduced electricity cost by about 11%; by performing scaling and technology maturity projections, we show competitive economics for the rotary chemical looping plant with CO 2 capture. [ABSTRACT FROM AUTHOR]

• Low-cost oxygen carriers are a key to facilitating chemical looping technology. • Large-scale chemical looping oxygen carrier production can be very enabling. • Mechanical mixing is more cost-effective than co-precipitation methods. • On-site production is believed to be advantageous over centralized production. The objective of this study was to estimate the cost of commercial production of oxygen carriers (OCs) for large-scale application in a mature, chemical looping combustion (CLC) power generation industry. Estimates of cost were made for two production facility scenarios: (1) build and operate an on-site, OC production facility located at a 550 MW CLC power plant site; and (2) build and operate a central production facility to produce and distribute OCs to the U.S. CLC power generation industry. Two OC production techniques were addressed: mechanical mixing and co-precipitation. Representative OCs that have production raw materials with sufficient commercial availability to support a CLC industry are ilmenite, a natural OC, and four engineered OC types, Fe 2 O 3 -based, CuO-based, NiO-based, and CuFeAlO 4 -based, with candidate OC support materials Al 2 O 3 and TiO 2. The costs of the OC production raw materials represent the major portion of the OC product cost; the OC production cost, in dollars per kg, has been found to be nearly a linear function of the OC raw materials cost, in dollars per kg. The estimated OC product costs can be used to estimate the maximum OC loss rate yielding a designated CLC power plant cost-of-electricity (COE) target as a development guide, and it has been found that the maximum OC makeup rate, in kg per hour, achieving a designated COE reduction goal relative to a conventional pulverized coal (PC) power plant, will be nearly inversely proportional to the OC production raw materials cost, in dollars per kg. [ABSTRACT FROM AUTHOR]

Highlights • World's first chemical looping pilot plant utilizing moving bed reactors. • Achieved near-full conversion of coal-derived syngas in the moving bed reducer. • Achieved 99% purity hydrogen production with in-situ carbon capture. • Validated operational results by ASPEN process simulation. Abstract Chemical looping combustion (CLC) is an advanced technology for converting fossil fuel while achieving in-situ CO 2 capture. The high purity CO generated in the combustion product stream is sequestration/utilization ready, which makes chemical looping one of the most attractive carbon emission control technology. In this paper, the authors present the design, simulation and experimental operation results of the 250 kW th high pressure syngas chemical looping (SCL) pilot plant. The pilot plant's unique countercurrent moving bed design allows near-full conversion of coal-derived syngas with simultaneous production of high purity, carbon-free H 2. Critical aspects of the design efforts, including heat and material balances, reactor sizing approach and solid flow control and measurement devices are presented. An ASPEN Plus® model is constructed to predict the gas and solid conversions of the SCL process the gas and solid conversions of the SCL process under different experimental conditions. The highest syngas conversion achieved was 97.95% with 16.03% oxygen carrier conversion, which were close to the thermodynamic limits for both the gas and solid phases in the reducer. Differences between the experimental results and predicted conversion values were more significant under conditions with lower oxygen carrier to fuel ratio. Greater than 99% purity H 2 was produced from the moving bed oxidizer, and the scalability and feasibility of SCL process were successfully demonstrated. [ABSTRACT FROM AUTHOR]

Graphical abstract In the present work, we propose a strategy for the first time to optimize the overall performance of the CLC system by combining different types of OC sticks in particular sequences. The synergy among different OCs can maximize the advantages and circumvent the weakness of the selected OCs. The combined OCs with CuNiFeMn or FeCuNiMn stacking sequence show both greatly enhanced activity for methane complete oxidation and superior resistance to carbon deposition. The average CH 4 conversion and CO 2 selectivity 97.3% and 98.3% for the CuNiFeMn sequence and 96.9% and 95.7% for FeCuNiMn sequence, respectively. Highlights • CuO/SiO 2 , Fe 2 O 3 /Al 2 O 3 , Mn 2 O 3 /ZrO 2 and NiO/ZrO 2 OCs show complementarity for CLC of methane. • CuO/SiO 2 OC in the combinations can effectively improve the CO 2 selectivity. • NiO/ZrO 2 OC in the combinations is beneficial to the CH 4 conversion. • Combined OCs with a stacking sequence of CuNiFeMn or FeCuNiMn effectively enhance the CLC performance. Abstract Combination of different types of oxides is a general strategy to prepare high performance oxygen carriers (OCs) for chemical looping combustion (CLC) technology. However, the possible chemical interactions among different components during the long-term redox cycling may reduce the stability of OCs. In the present work, we physically combine different types of OC sticks (i.e., CuO/SiO 2 , Fe 2 O 3 /Al 2 O 3 , Mn 2 O 3 /ZrO 2 and NiO/ZrO 2) in particular stacking sequences in a fixed bed reactor to improve the CLC performance. The reaction between methane and CuO is exothermic and the CuO/SiO 2 OC exhibits very high activity for methane oxidation and superior resistance to carbon deposition. It is suitable to place the CuO/SiO 2 in the front of the sequence which can sufficiently convert methane, and the heat releasing from this reaction will promote the following endothermic reactions. NiO/ZrO 2 OC also represents very high activity for CH 4 oxidation but results in serious carbon deposition. Since the reduced metallic Ni is an active catalyst for methane activation, it is suggested to place NiO/ZrO 2 in the middle of the sequence to enhance the further conversion of methane and to provide enough space to remove the carbon deposition via the gasification by CO 2 or H 2 O generated from the front reaction. Mn 2 O 3 /ZrO 2 OC possesses poor activity for methane conversion but high resistance to carbon deposition, which can be used to convert unreacted methane in the end of the sequence. Fe 2 O 3 /Al 2 O 3 OC is not an important issue due to the low activity and reaction rate. As a result, the combined OCs with a stacking sequence of CuNiFeMn or FeCuNiMn show high performance in CH 4 conversion (>97%), CO 2 selectivity (>96%), redox stability and resistance to carbon deposition. These results make a certain reference for using the combined OCs in the large-scale CLC system. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • FA is better than the Al 2 O 3 as a support of OC in anti-carbon deposition and durability. • Iron oxide contained in FA support could provide active oxygen for fuel combustion. • Partially irreversible CuO decomposition is the main reason for the deactivation of OC. • The distribution of Cu on the support became more uniform after reaction. Abstract Developing highly reactive, durable and low-cost oxygen carrier (OC) is the key to the advancement of the chemical looping combustion (CLC) technology that is regarded as the most energy-efficient way for the capture of CO 2 emitted from fossil fuel combustion. In this study, the byproduct from coal power plant, coal fly ash (FA) was utilized as the support for Cu-based OC in methane CLC. Its performance was investigated with a thermogravimetric analyzer and a lab-scale fixed bed reactor. The results showed the FA is better as a support of OC than the most commonly used Al 2 O 3 in anti-carbon deposition and thus beneficial to the importance of the stability of FA supported OCs. Among all the tested OCs, the Cu-based OC synthesized with FA support and impregnation method demonstrated the best performance, with CH 4 conversion of 94–100% and CO 2 selectivity of 91–94% in ten cycles at 800–850 °C, and minor deactivation. The characterization of the fresh and spent OCs revealed that the FA support itself could provide 1.0–2.9 wt% active oxygen for fuel combustion, which is enabled by the iron oxide in FA. In addition, the distribution of Cu on the FA support became more uniform on spent OC than on the fresh one. Also, the partially irreversible CuO decomposition into Cu 2 O during cyclic tests was the main reason for the deactivation of OC. Thus, Use of FA as an OC support is conducive to both development of cost-effective CLC and an environmental-friendly utilization of waste FA. [ABSTRACT FROM AUTHOR]

Highlights • A solar-heat driven perovskite chemical-looping combustion is proposed. • Substituted LaCu x Ni 1−x O 3 as the storage medium are prepared and characterized. • Performance of LaCu x Ni 1−x O 3 in redox cycles is experimentally tested. • The synthesized perovskites show great reactivity and regenerability. • The optimal copper substitution is x = 0.1 (LaCu 0.1 Ni 0.9 O 3). Abstract Solar-heat driven chemical-looping combustion (S-CLC) is an efficient method for storing solar energy. In the S-CLC process, solar heat is used to drive the endothermic reduction reaction between a hydrocarbon fuel and an oxygen carrier. The solar heat is converted into chemical energy and stored in the reduced oxygen carrier. Owing to their high reactivity at low reaction temperatures, perovskites are treated as promising oxygen carriers in S-CLC. Herein, the reactivity and regenerability of LaCu x Ni 1−x O 3 (x = 0.025, 0.050, 0.075, 0.1, 0.2, 0.3, 0.5) perovskites are studied using methane as the fuel gas. The experimental results show that LaCu 0.1 Ni 0.9 O 3 has the highest reactivity and regenerability among the synthesized materials. At a reduction temperature of 350 °C, more than 46% of the LaCu 0.1 Ni 0.9 O 3 is reduced in 5 min, much higher than the amount of other LaCu x Ni 1−x O 3 perovskites reduced under the same conditions. After 30 redox cycles, the reactivity and micrographs of LaCu x Ni 1−x O 3 are similar to those of fresh material, indicating that LaCu 0.1 Ni 0.9 O 3 has a desirable regenerability. Furthermore, no carbon deposition is observed during the reduction reaction between CH 4 and LaCu x Ni 1−x O 3. Our study is expected to provide a new method for storing mid-and-low temperature solar heat using this solid perovskite. [ABSTRACT FROM AUTHOR]

Highlights • Technoeconomic analysis of solar-assisted chemical looping plants is performed. • Exhaust heat utilization can significantly improve the CLC system efficiency. • Cooling by absorption chilling process results in better system performance. • Cost of electricity is very sensitive to the fuel cost. • Solar-assisted CLC plants are economically more feasible at high fuel cost. Abstract Chemical looping combustion (CLC) is a promising technique for CO 2 capture with low energy penalty and low cost. In addition to capturing CO 2 , the solar-assisted CLC process results in the production of significant amount of exhaust waste heat which could be utilized for a variety of purposes. This paper outlines a detailed techno-economic analysis of a solar-assisted natural gas fired CLC power plant with waste heat utilization for absorption chilling purpose. This is particularly important for hot regions such as the United Arab Emirates (UAE) where a significant amount of energy is used for cooling purposes. The power plant studied is about 550 MWe net output power. The study was conducted by developing an Aspen Plus system model. The model was used to calculate the heat recovery efficiency, the absorption chilling system coefficient of performance and the plant efficiency. The economic performance of the plant was analyzed by calculating the cost of electricity, the return on investment and the cost of CO 2 capture. The analysis shows that the poly-generation solar-assisted CLC system had a plant efficiency of 63.4%, waste heat utilization of 49%, electricity cost of 4.9 cents/kWh and the return on investment of 3.98 years at prevalent prices of the plant input materials and a capacity factor of 85 percent. [ABSTRACT FROM AUTHOR]

This work reports a detailed chemical looping investigation of strontium ferrite (SrFeO 3−δ ), a material with the perovskite structure type able to donate oxygen and stay in a nonstoichiometric form over a broad range of oxygen partial pressures, starting at temperatures as low as 250°C (reduction in CO, measured in TGA). SrFeO 3−δ is an economically attractive, simple, but remarkably stable material that can withstand repeated phase transitions during redox cycling. Mechanical mixing and calcination of iron oxide and strontium carbonate was evaluated as an effective way to obtain pure SrFeO 3−δ . In–situ XRD was performed to analyse structure transformations during reduction and reoxidation. Our work reports that much deeper reduction, from SrFeO 3−δ to SrO and Fe, is reversible and results in oxygen release at a chemical potential suitable for hydrogen production. Thermogravimetric experiments with different gas compositions were applied to characterize the material and evaluate its available oxygen capacity. In both TGA and in-situ XRD experiments the material was reduced below δ = 0.5 followed by reoxidation either with CO 2 or air, to study phase segregation and reversibility of crystal structure transitions. As revealed by in-situ XRD, even deeply reduced material regenerates at 900°C to SrFeO 3–δ with a cubic structure. To investigate the catalytic behaviour of SrFeO 3−δ in methane combustion, experiments were performed in a fluidized bed rig. These showed SrFeO 3−δ donates O 2 into the gas phase but also assists with CH 4 combustion by supplying lattice oxygen. To test the material for combustion and hydrogen production, long cycling experiments in a fluidized bed rig were also performed. SrFeO 3−δ showed stability over 30 redox cycles, both in experiments with a 2-step oxidation performed in CO 2 followed by air, as well as a single step oxidation in CO 2 alone. Finally, the influence of CO/CO 2 mixtures on material performance was tested; a fast and deep reduction in elevated p CO2 makes the material susceptible to carbonation, but the process can be reversed by increasing the temperature or lowering p CO2 . [ABSTRACT FROM AUTHOR]

This study focused on Cu x Mg 1-x Fe y Al 2-y O 4 oxygen carriers for application in the chemical looping combustion of methane. Cu x Mg 1-x Fe y Al 2-y O 4 was fabricated by simultaneously substituting Mg 2+ and Al 3+ with Cu 2+ and Fe 3+ in the spinel structure of MgAl 2 O 4 . As a result, a great synergistic effect was observed: Cu 0.75 Mg 0.25 Fe 1.5 Al 0.5 O 4 exhibited 7.85% oxygen transfer capacity in the CH 4 -CO 2 /air redox system. Methane and carbon monoxide were significantly adsorbed on the surface of the Cu x Mg 1-x Fe y Al 2-y O 4 particles. Cyclic voltammetry studies predicted the active lifetime of the oxygen carrier, which had not been reported until now. Cu 0.75 Mg 0.25 Fe 1.5 Al 0.5 O 4 was expected to exhibit the greatest oxygen transfer capacity after 300 redox cycles and maintain an oxygen transfer efficiency of 92% until the 1000th redox cycle in the H 2 -N 2 /air redox system. This study concluded that the active metal species, containing Cu 2+ and Fe 3+ ions, were stably anchored in the spinel structure; this led to the reversible formation of oxygen vacancies in the spinel structure, resulting in an excellent oxygen transfer capacity that could be maintained for a long time. [ABSTRACT FROM AUTHOR]

A model for chemical looping combustion has been developed to allow the effect of different residence time distributions of oxygen carrier particles in the air and fuel reactors to be investigated. The model envisages two, coupled fluidised bed reactors with steady circulation of particles between them. The results show that the process is sensitive to the residence time distributions, particularly when the mean residence time of particles in the reactors is similar to the time required for them to react completely. Under certain operating conditions, decreasing the variance of the residence time distribution, leads to a greater mean conversion of the particles by the time they leave the reactors and higher mean rates of reaction in the beds. In this way the required inventory and circulation rate of solids could be reduced, which would lower the capital and operating costs of a CLC process. Since the residence time distribution of solids is important, it should be taken into account when modelling or designing a chemical looping combustion process, e.g. by using a tanks-in-series model. This work indicates that if the number of tanks, N   ≤  5, knowing N to the nearest integer is generally sufficient, unless a high degree of accuracy is needed. As N increases, the sensitivity of the coupled system decreases, so for N   > 5, knowing the value to the nearest 5 or 10 tanks is sufficient. This is valid whether N is the same or different in the two reactors. Chemical looping combustion is one example of a reactor-regenerator system, so the results are also relevant for other processes of this type, such as fluidised catalytic cracking. [ABSTRACT FROM AUTHOR]

The chemical looping strategy for hydrogen production (CLH 2 ) offers a potentially viable option for efficient fuel conversion to hydrogen with the simultaneous capture of CO 2 . Typically, this process uses an iron-based composite as an oxygen carrier and syngas or methane as a fuel. The environmental and economic concerns motivate the use of abundant by-product iron oxide and the industrial off-gas for CLH 2 . Here we showed that H 2 could be simply recovered from the industrial off-gas in a circulating fluidized bed with a mixture of the inexpensive raw material of by-product iron oxide and sand particle. The fluidization of the by-product iron oxide powder, which showed poor fluidization behavior, is improved by adding 60 vol% of sand particle. The industrial off-gas was completely converted to CO 2 and H 2 O in a two-stage fluidized mode with a solid reactant of Fe 2 O 3 of the binary particles , and then H 2 was produced by oxidizing the reduced by-product iron oxide powder with steam. The binary particles showed consistent catalytic activity under multiple redox cycles by providing macropores with a size of ∼5 μm which facilitated gas diffusion. These findings provided valuable information for the future development of CLH 2 based on by-products. [ABSTRACT FROM AUTHOR]

In this work a novel reactor concept referred to as Membrane-Assisted Chemical Looping Reforming (MA-CLR) has been demonstrated at lab scale under different operating conditions for a total working time of about 100 h. This reactor combines the advantages of Chemical Looping, such as CO 2 capture and good thermal integration, with membrane technology for a better process integration and direct product separation in a single unit, which in its turn leads to increased efficiencies and important benefits compared to conventional technologies for H 2 production. The effect of different operating conditions (i.e. temperature, steam-to-carbon ratio or oxygen feed in the reactor) has been evaluated in a continuous chemical looping reactor, and methane conversions above 90% have been measured with (ultra-pure) hydrogen recovery from the membranes. For all the cases a maximum recovery factor of around 30% has been measured, which could be increased by operating the concept at higher pressures and with more membranes. The optimum conditions have been found at temperatures around 600 °C for a steam-to-carbon ratio of 3 and diluted air in the air reactor (5% O 2 ). The complete demonstration has been carried out feeding up to 1 L/min of CH 4 (corresponding to 0.6 kW of thermal input) while up to 1.15 L/min of H 2 was recovered. Simultaneously, a phenomenological model has been developed and validated with the experimental results. In general, good agreement is observed, with overall deviations below 10% in terms of methane conversion, H 2 recovery and separation factor. The model allows better understanding of the behavior of the MA-CLR concept and the optimization and design of scaled-up versions of the concept. [ABSTRACT FROM AUTHOR]

Chemical-looping combustion (CLC) is already treated as a promising way to capture CO 2 in the utilization of fossil fuels. The most used reactors for the CLC are fluidized-beds, in which the fuel conversion and the conversion of fuel to CO 2 is determined by the bed height. Here in this study, the CLC in an advanced 10 kW honeycomb reactor is studied by using natural gas as the fuel and Fe 2 O 3 as the oxygen carrier. In the honeycomb reactor, a honeycomb chamber consisted by the oxygen carrier is employed to enhance the contact area and the disturbance between the fuel gas and the oxygen carrier. Both of these two enhancement are benefit for achieving a high CH 4 conversion and a high conversion of CH 4 to CO 2 . The experiment results show that three stages of Fe 2 O 3 to Fe 3 O 4 , Fe 3 O 4 to FeO and FeO to Fe are occurred in sequence during the reduction reaction of Fe 2 O 3 and CH 4 in the honeycomb reactor. The behaviors and the relationships for these complicated reactions, the oxygen transfer rate, the CH 4 conversion and the conversion of CH 4 to CO 2 at different stages are further experimentally studied. Additionally, to increasing the conversion of CH 4 to CO 2 in the continuous operation, the characteristics for the honeycomb reactor in redox cycles are also experimentally investigated. Our study here would be expected to provide a new method for developing the energy and environment compatible systems. [ABSTRACT FROM AUTHOR]

CuO-Fe 2 O 3 /alumina oxygen carriers were manufactured using two different techniques (i.e., spray drying and wet granulation). The spray drying method produced porous, spherical particles in the range of 100–200 µm. The wet granulation, or tumbling method, produced particles in the range of 200–600 µm. Both batches of material showed good gas conversion and particle durability during tests in NETL’s 50-kWth chemical looping circulating fluidized bed combustor unit at 700–900 °C. No agglomeration was observed, even though the oxygen carrier had a high CuO concentration (30%). The particle losses with 200–600 µm batch were significantly lower than that with the 100–200 µm batch. The oxygen carrier materials in the 200–600 µm range were circulated for approximately 3.1 days in the target temperature range (700–850 °C) and a total of approximately 40 h of chemical looping combustion testing was conducted during that time. The average fuel reactor temperatures ranged from 760 to 815 °C for the chemical looping combustion test periods, and the average air reactor temperature ranged from 840 to 915 °C. The fuel conversion from natural gas to CO 2 ranged from 50 to 80%. Approximately 1.6 h of continuous operation was achieved with no gas preheat and no natural gas augmented heating. During this test period, the average fuel reactor temperature ranged from 780 to 825 °C, the air reactor temperature ranged from 930 to 960 °C, and the natural gas to CO 2 conversion ranged from 50 to 65%. Analysis of the oxygen carrier after the test indicated that there were no significant changes in the particle size or the surface morphology. [ABSTRACT FROM AUTHOR]

Microalgae gasification in the presence of Fe 2 O 3 oxygen carrier and CaO additive was investigated in a fixed bed reactor to simulate the reactions in direct chemical looping gasification, focusing on the thermal behavior of CaO in synthesis gas production and multiple redox cycles. The results showed that Fe 2 O 3 as oxygen carrier improved the synthesis gas but brought much more CO 2 generation, lowering the gas LHV . Introducing CaO efficiently inhibited CO 2 release and improved CO and H 2 production, and gasification efficiency and gas LHV elevated from 55.2% and 13.27 MJ/N m 3 to 66.2% and 14.85 MJ/N m 3 at 850 °C. CaO mainly played as CO 2 absorbent and hardly had catalytic effects on tar crack for synthesis gas production at 650 °C. At 850 °C, CaO mainly played as catalyst and still had a great selectivity for synthesis gas production. The CaO/C molar ratio of 0.5 was sufficient for achieving its function. The multiple redox experiments showed that the gas efficiency and carbon conversion declined in the second reduction and kept at 60.1 ± 1.2% and 77.4 ± 1.5% respectively in 2–10 cycles. XRD and SEM-EDX results showed the coverage of CaO, the formation of calcium ferrites and CaO deactivation accounted for the variation of oxygen carrier reactivity in multiple cycles. [ABSTRACT FROM AUTHOR]

Natural gas is regarded as a high heating-value and low carbon-footprint fuel, but its supply is deficient and global imbalanced. A technical routine toward synthetic natural gas (SNG), sound in both energy efficiency and environmental impact, is therefore highly demanded. Both coke-oven gas (COG) and pulverized coke (PC) are two major by-products of metallurgical industries. There is the conventional SNG process fed by only COG (CGtSNG), which suffers from less hydrogen utilization and energy efficiency, as well as limited SNG capacity. The driving force on the environmentally-responsible and energy-efficient use of the PC calls for the involvement of state-of-the-art chemical looping combustion (CLC) technology. A new process co-fed by both PC and COG for SNG production via a CLC unit (PC CLC -CGtSNG) is therefore proposed in this study. The PC CLC -derived CO 2 can be an effective carbon source to optimize the composition of syngas for high efficient SNG production. The involvement of the CLC in the conventional CGtSNG can achieve intensive material and energy couplings, improve energy and hydrogen utilization efficiencies, and increase SNG productivity. Process modelling results showed that the proposed process possessed about 20% improvement in the hydrogen utilization efficiency and SNG productivity, as well as 6.8% increase of the exergy efficiency, comparing to those of the conventional CGtSNG. [ABSTRACT FROM AUTHOR]

Oxy-fuel combustion is one route to large scale carbon capture and storage. Fuel is combusted in oxygen rather than air, allowing pure CO 2 to be captured and sequestered. Currently, the required oxygen is produced via cryogenic air separation, which imposes a significant energy penalty. Chemical looping air separation (CLAS) is an alternative process for the production of oxygen, and relies on the repeated oxidation and reduction of solid oxygen carriers (typically metal oxides). The energy efficiency is governed by the thermodynamic properties of the oxygen carrier material, and how well the CLAS process can be heat-integrated with the process consuming oxygen. In this study, key thermodynamic properties have been identified and assessed using a steady state model of a CLAS-oxy-fuel power plant. It is demonstrated that energy penalties as low as 1.5 percentage points can be obtained for a narrow range of material properties. Based on density functional theory calculations, 14 oxygen carrier systems, which are novel or have received little attention, have been identified that could potentially achieve this minimal energy penalty. [ABSTRACT FROM AUTHOR]

Chemical-looping combustion (CLC) is already suggested as a promising approach for CO 2 capture with a lower energy penalty. The appropriate reactor plays a paramount role in the application of CLC. Here, a fixed-bed honeycomb CLC reactor is proposed and its design methodology and procedure are given. The honeycomb chamber is a cylindrical monolithic block with a series of axial micro-channels. In this way, a sufficiently contact area and disturbance among reactants are provided for enhancing the reaction kinetics. The oxygen carrier not only consists of the supporting material of the honeycomb CLC reactor but also acts as reactants. A 10 kW prototype is manufactured by using NiO/NiAl 2 O 4 as the oxygen carrier. The reactivity and redox stability of the honeycomb CLC reactor are experimentally examined by using the natural gas as the fuel gas. In the experiment, a CH 4 conversion higher than 99% is obtained. By shortening the reduction time of the NiO/NiAl 2 O 4 , almost all the CH 4 is converted into CO 2 and CO emission is avoided. Additionally, the redox stability in the honeycomb CLC reactor is carried out for 150 h continuous operation. The test results show that the prototype reactor obtains a better reactivity and redox stability in contrast to the fixed-bed reactor without honeycomb chamber. Our results here would be expected to offer a new pathway for facilitating the progress of the CLC reactor. [ABSTRACT FROM AUTHOR]

One of the most important issues for chemical looping technology is to find low-cost oxygen carriers. This work presents the investigation on using a Panzhihua (China) magnetite as oxygen carrier for chemical looping reforming of methane (CLRM). The reactivity for coproduction of syngas and hydrogen was tested by an isothermal redox experiment using methane as a reducing fuel and steam as an oxidizing gas. The kinetics study was performed on both the fresh and recycled magnetite oxygen carriers. In the redox experiments, the produced hydrogen and syngas in a H 2 /CO molar ratio of 2.0 can be stably obtained with high selectivity (ca. 95.1% for syngas and ca. 96.2% for H 2 ). The yields of hydrogen from the original and calcinated magnetite after successive cycling are 4.94 and 5.25 mmol/g, respectively. From the kinetic study via a thermogravimetric analyzer (TGA) method, it is found that the reduction of original magnetite to wüstite is well represented by the phase boundary-controlled (contracting cylinder) mechanism, and the 1-D nuclei nucleation and growth integrated with diffusion mechanism can be successfully applied to describe the reduction of calcined magnetite. The activation energy for the reduction of original magnetite is 93.02 kJ/mol, which slightly decreases to 86.90 kJ/mol after successive cycling due to the formation of pores inside the oxygen carriers. This work gives full evidence to the feasibility of using magnetite concentrates as low-cost oxygen carrier for the CLRM system. [ABSTRACT FROM AUTHOR]

The fate of sulfur in the coal-direct chemical looping system was investigated in the sub-pilot reactor system. The sulfur balance was successfully closed during the injection of high sulfur coal. More than 69% of the total amount of atomic sulfur in coal was released as SO 2 and H 2 S from the reducer flue gas stream while less than 5% was emitted as SO 2 from the combustor spent air. The remaining atomic sulfur was retained in coal ash as inorganic sulfur compounds. The finding suggests an acid gas removal system targeting both H 2 S and SO 2 is required to meet the recommended quality of CO 2 stream for sequestration and transportation. Using the determined ratio of SO 2 and H 2 S, a properly designed Claus plant can enable the recovery of elemental sulfur as a value-added byproduct. The combustor spent air was found to comply with the US EPA sulfur emission regulation and can be released to the atmosphere without a costly acid removal system. The relationship between the sulfur and carbon capture efficiencies was established experimentally and was found to be proportional to each other throughout the experiment at a slope of 0.8 below 93% of carbon capture efficiency and near 1 above 93%. This was attributed to the delayed release of organic sulfur during incomplete char gasification in the reducer. The finding affirms the effectiveness of the counter-current moving bed design for minimizing the amount of carbon and sulfur emission in the combustor spent air with an average carbon and sulfur capture efficiency of 96.5 and 95%, respectively. Sulfur deposition on the iron based oxygen carriers did not affect the system performance, and complete removal of deposited sulfur was observed during oxidation in a thermogravimetric analyzer. Compared with chemical looping systems using circulating fluidized bed configuration, the use of a moving bed reducer has the additional benefit of minimizing slippage of char into the combustor due to the use of large oxygen carrier; resulting in lower sulfur emission in the combustor spent air. The findings demonstrate the robustness of the coal-direct chemical looping system to handle high sulfur coal without a complicated acid gas cleaning scheme or severe performance penalties. [ABSTRACT FROM AUTHOR]

The Chemical Looping with Oxygen Uncoupling (CLOU) process is a form of Chemical Looping Combustion (CLC) technology that enables the combustion of solid fuels by means of oxygen carriers that release gaseous oxygen in the fuel reactor, i.e. with oxygen uncoupling capability. In recent years, tests have found several Cu-based, Mn-based and mixed oxide oxygen carriers with suitable properties for the CLOU process. Among them, Cu-Mn mixed oxides show high reactivity and high O 2 equilibrium concentration at temperatures of interest for coal combustion. In this work, proof of concept was demonstrated by burning coal with Cu-Mn mixed oxides in a 1.5 kW th CLOU unit for the first time. The effect of fuel reactor temperature, solids circulation flow, fluidization agent in the fuel reactor (inert N 2 or steam as gasifying agent), and excess air in the air reactor on combustion efficiency and CO 2 capture rate was analysed. The results showed that high combustion efficiency and CO 2 capture are feasible using this material at relatively low fuel reactor operating temperatures. Therefore, the developed Cu-Mn mixed oxide was a suitable material for use as an oxygen carrier for the CLOU combustion of solid fuels. Optimum operating conditions were determined for this oxygen carrier with regard to the oxygen circulation rate and air reactor conditions for the regeneration of the oxygen carrier. [ABSTRACT FROM AUTHOR]

Due to the severity of the worldwide climate change problem and the ocean acidification problem, chemical looping combustion (CLC) technology is studied worldwide by researchers in order to meet the urgency of carbon emission reduction after its concept has been put forward. An experimentally validated computer model has been implemented in Ansys-Fluent code with the most appropriate kinetic model implemented in User Define Functions. The validated model has been used to carry out a numerical study on a model fuel reactor using CaSO 4 as oxygen carrier and H 2 as fuel; is conducted in the present work. Effects of mole fraction of CaS, operating temperature, superficial feeding velocity magnitude of fuel and the diameter of oxygen carrier particles were discussed. The results indicate that the superficial feeding velocity of gaseous fuel has significant effects on the flow condition with fuel reactor and conversion performance, while operating temperature mainly affects the fuel conversion. The effects of particle diameter on flow condition within FR are obvious but insignificant on conversion performance of fuel. The mole fraction of CaS has the least effect among these three parameters. Several velocity distributions are also studied. The rectangle-trianble distributor results in better bubbles distributions, but the gain of higher fuel conversion rate is insignificant due to the low chemical activity of OC used in this study. [ABSTRACT FROM AUTHOR]

In this work, calcination under high-concentration steam that can be implemented by O 2 /H 2 O combustion was proposed to replace high-concentration CO 2 that usually was implemented by O 2 /CO 2 combustion in calcium looping. CO 2 capture performance of the carbide slag, an industrial solid waste from chlor-alkali plants, was investigated in a dual fixed-bed reactor under high-concentration steam calcination condition during the calcium looping cycles. Calcined under high-concentration steam (95%) atmosphere, the carbide slag can be completely and quickly decomposed at 800 °C, which is 150 °C lower than the calcination temperature under high-concentration CO 2 (100%) atmosphere. The carbonation conversions of the carbide slag calcined under high-concentration steam condition after 1 and 10 cycles are about 42% and 36% higher than those calcined under high-concentration CO 2 condition, respectively. This is because when the carbide slag is calcined under high-concentration steam, the relatively smaller CaO grains and more porous structure are generated, which are beneficial for CO 2 capture by carbide slag. Due to the low calcination temperature and the high CO 2 capture capacity of the carbide slag, the energy requirement in the calciner to capture per mole CO 2 under high-concentration steam condition is lower than that under high-concentration CO 2 condition. High-concentration steam calcination in place of high-concentration CO 2 calcination improves the CO 2 capture efficiency from 0.68 to 0.88 and saves a quarter of the energy consumption in the calciner for capturing per mole CO 2 in the calcium looping system, when the ratio of recycled carbide slag flow rate to CO 2 flow rate is 2 and the sorbent make-up ratio is 0.09. Thus, it is reasonable to consider O 2 /H 2 O combustion as an alternative energy-supply way of O 2 /CO 2 combustion for the calcium looping of carbide slag. [ABSTRACT FROM AUTHOR]

High purity H 2 could be produced through modified chemical looping steam methane reforming (CL-SMR) process using calcium as an essential component in the structure of bifunctional catalyst-sorbents. Herein, we present an effective approach to the production of high purity hydrogen in chemical looping reforming of methane via modification of a bifunctional Ca-Co-Zr catalyst-sorbent. The synthesis of the samples including pure Ca, Ca-Co and zirconium modified Ca-Co with different molar ratios was performed using co-precipitation method. The influence of reaction variables such as steam to carbon molar ratio (S/C = 1–5), reaction temperature (500–750 °C) and lifetime of the samples are investigated on methane conversion and hydrogen yield. Moreover, Ca/Co mass ratio (0.11–9) is optimized and subsequently, different amounts of zirconium promoter (mass ratio = 2.25–18) are added to improve the bifunctional catalyst-sorbent structure. The characterization of samples was performed using XRD, FESEM, BET and EDX techniques. It is found that the addition of zirconium to the sample could improve the textural features and stability of bifunctional catalyst-sorbent. The results reveal that Ca-Co-Zr (via mass ratios of Ca Co = 9 and Ca Zr = 4.5 ) exhibits the highest catalytic activity among all tested samples and shows 98.3% methane conversion and 84.5% hydrogen yield at 700 °C. The cyclic life time results at 700 °C indicated that the Ca-Co-Zr (9,4.5) bifunctional catalyst-sorbent remained stable up to 16 cycles, while non-promoted samples showed fast deactivation after about 10 redox cycles. The coke formation is inhibited, while the reaction pathway changes to a combined reaction. In summary, the obtained results show the suitable efficiency of the synthesized catalyst in the modified CL-SMR process. [ABSTRACT FROM AUTHOR]

In this work, bimetallic oxygen carriers (OCs) were prepared from waste fine particles (<0.1 mm) of natural copper ore and hematite for possible application in chemical looping combustion (CLC) processes. The mixtures with different mass ratios of copper ore to hematite were physically bonded by 20 wt% of calcium aluminate cement to obtain OC particles with relatively high disperse structure and good mechanical strength. Cyclic isothermal redox tests were first conducted in a thermogravimetric analyzer (TGA) to optimize the copper ore to hematite mixing ratio in the bimetallic OC. Synergistic effect between copper ore and hematite was observed, and the copper ore to hematite mixing ratio was optimized at 20:80 (namely Cu20Fe80@C) based on a comprehensive consideration of OC reactivity, economic cost and auto-thermal balance in fuel reactor. Subsequently, performance of Cu20Fe80@C and Fe100@C (cement bonded pure hematite) were further evaluated in a batch fluidized bed reactor, using coal as fuel. The Cu20Fe80@C was found to be more reactive towards coal gasification products than that of Fe100@C, which is mainly attributed to the synergistic effect attained by the coexistence of copper ore and hematite in the Cu20Fe80@C OC. Moreover, the effects of steam concentration, oxygen to fuel ratio and coal type on the performance of Cu20Fe80@C were investigated. It was found that both the increase of steam concentration and oxygen to fuel ratio can facilitate the coal conversion, but they are not the higher the better and should be balanced between coal conversion and operational cost when turning to industrial application. Lignite was more suitable to be converted by Cu20Fe80@C OC in i G-CLC process due to its better gasification reactivity than anthracite. 30 cyclic redox tests with lignite showed that Cu20Fe80@C exhibited superior redox reactivity, nice fluidization behavior and good anti-sintering property in fluidized bed tests. This work demonstrated that cement bonded fine particles of hematite and copper ore could be a promising and competitive OC candidate for industrial application in i G-CLC processes. [ABSTRACT FROM AUTHOR]

Chemical looping combustion (CLC) is a promising combustion technology that generates heat and sequestration-ready carbon dioxide that is undiluted by nitrogen from the combustion of carbonaceous fuels with an oxygen carrier, or metal oxide. This process is highly dependent on the reactivity and stability of the oxygen carrier. Thus, the development of oxygen carriers remains one of the major barriers for commercialization of CLC. Synthetic oxygen carriers, consisting of multiple metal components, have demonstrated enhanced performance and improved CLC operation compared to single metal oxides. However, identification of the complex mixed metal oxide phases that form after calcination or during CLC reactions has been challenging. Without an understanding of the dominant metal oxide phase, it is difficult to determine reaction parameters and the oxygen carrier reduction pathway, which are necessary for CLC reactor design. This is particularly challenging for complex multi-component oxygen carriers such as copper iron manganese oxide (CuFeMnO 4 ). This study aims to differentiate the unique phase formation of a highly reactive, complex trimetallic oxygen carrier, CuFeMnO 4 , from its single and bimetallic counterparts using thermochemical and reaction data obtained from simultaneous differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) during temperature programmed reductions (TPR) with methane. DSC/TGA experiments during TPR with methane provides heat flow data and corresponding reaction rate data that can be used to determine reaction routes and mechanisms during methane reduction. Furthermore, non-isothermal TPR data provides the advantage of distinguishing reactions that may not be observable in isothermal analysis. The detailed thermochemical and reaction data, obtained during TPR with methane, distinguished a unique reduction pathway for CuFeMnO 4 that differed from its single and bimetallic counterparts. This is remarkable since X-ray diffraction (XRD) data alone could not be used to distinguish the reactive trimetallic oxide phase due to overlapping peaks from various single and mixed metal oxides. The unique reduction pathway of CuFeMnO 4 was further characterized in this study using in-situ XRD TPR with methane to determine changes in the dominant trimetallic phase that influenced the thermochemical and reaction rate data. [ABSTRACT FROM AUTHOR]

Calcium looping (CaL), the cyclic carbonation and calcination of limestone, is a prominent carbon capture option considering reduced parasitic energy consumption compared to amine scrubbing. The main issue preventing application is sorbent performance decay during cycling. Therefore hydration and extended carbonation reactivation strategies, as well as synthetic approaches to enhance or sustain reactivity, are of interest. Results of an investigation are presented on the impact of reactivation strategies on carbonate formation through detailed study using in-situ infrared spectroscopy. Surface and bulk carbonate formation regimes were readily distinguished allowing the influence of temporal, hydration and thermodynamic conditions within each regime to be studied. Surface chemistry of CaO during two initial cycles was shown to change. Significantly, it was shown that the CaO surface produced from the calcination of Ca(OH) 2 possessed more highly reactive sites compared to the surface produced from CaCO 3 . The presence of water enhanced bulk carbonate formation at 300 °C and influenced the complexation of surface carbonates during looping. The results are of interest in the CaL community, offering molecular scale explanations for macroscale observations, whilst also informing on the role of humidity in direct air capture and sorption enhanced reaction processes. [ABSTRACT FROM AUTHOR]

Chemical looping process is a novel energy conversion scheme, in which the in-situ carbon capture and high energy conversion efficiency could be realized without energy penalty. Ferrite (Fe 3 O 4 ) is one of many good oxygen carrier candidates, due to its unique lattice structure containing a number of empty tetrahedral and octahedral interstitial sites. We calculated electronic properties of the original Fe 3 O 4 primary cell and its lattice substituted by Ca or Ba, focusing on the correlation of their electronic structures and redox activities. Differences in their electronic densities and atomic charges in Mulliken Populations reveal more negative oxygen ions appearing in the substituted cells. Electronic structure analysis demonstrates that the substitution of Ba makes Fe 3 O 4 more electric conductive and its electron is prone to be exited, that is in consistent to the experimental fact that BaFe 2 O 4 performed better in chemical looping reactions compared to ferrites substituted by other alkali earth elements. [ABSTRACT FROM AUTHOR]

Chemical Looping Gasification (CLG) is an emerging technology that shows promise for efficient coal gasification by eliminating the need for energy intensive gas separations to achieve a non-nitrogen diluted syngas stream. Oxygen from oxygen carriers, such as CaFe 2 O 4 , are used for coal gasification in place of conventionally produced gaseous oxygen from cryogenic separation of air. These oxygen carriers are unique for their ability to selectively oxidize coal to form syngas and show limited reactivity with syngas components (H 2 , CO). This study was carried out to determine the kinetic model representation and parameters associated with the selective oxidation of coal derived char (Wyodak and Illinois #6) with a metal ferrite (CaFe 2 O 4 ) of which are needed for advancement of the process concept. Using thermogravimetric analysis (TGA) coupled with mass spectrometry, the selective oxygen release from metal ferrite in the presence of char by proximal contact was examined. The application of model fitting approaches was used to describe controlling resistances during oxygen release. A combination of the modified shrinking core model (SCM) with planar oxygen ion diffusion control and reaction order based models were applied for kinetic parameter determination. CaFe 2 O 4 particle size plays a major role in the prevailing mode of oxygen release. Particle sizes on the range of 40–50 µm tend to favor first order kinetically controlled regimes independent of geometric and diffusion controls. The probability for oxygen ion diffusion controlling regimes increased when the particle size range of the oxygen carrier was increased up to 350 µm. Char type also impacted the prevalence of the controlling regime. Higher ranked chars react in a slower manner, limiting the gradient for oxygen ion release from the oxygen carrier. Activation energies determined for this process range from 120 to 200 kJ/mol and oxygen ion diffusion coefficients are on the order of 10 −8 cm 2 /s. It is suggested that oxygen ion movement is regulated by lattice diffusion out of partially reduced phases (Ca 2 Fe 2 O 5 ) and through reduced outer layers composed of CaO and Fe. The controlled movement of oxygen ions influences the rate of carbon oxidation in the char and therefore the selectivity towards partial oxidation products, which are desirable in CLG applications. [ABSTRACT FROM AUTHOR]

Ilmenite ore is one of the promising oxygen carriers (OCs) used for coal-fueled Chemical-Looping Combustion (CLC) for electricity generation and CO 2 capture. However, the low reactivity and natural activation of ilmenite OC are two major constrains impeding its application. This effort is to improve ilmenite OC’s performance by introducing a small amount of foreign elements, including alkali or alkaline earth metals (K and Ca) and transition metals (Cu, Mn, and Ni). Coating and re-granulation methods were used to prepare OCs where ilmenite ore was the primary constituent. The reactivity, transport capacity, and selectivity of these ilmenite-based OCs with wet syngas, as well as their performances in coal char-fueled CLC were investigated using a TGA, fixed- and fluidized-bed reactors. The addition of K-element significantly improved the OC’s reactivity with wet syngas and coal char. The strong catalytic function for WGSR from K-added OCs was found to play a vital role. Cu-coating hindered effectively Fe-element segregation on the surface of ilmenite OC during cyclic reaction, and the OC structural integrity was well maintained. Ca-, Ni- and Mn-added ilmenite OCs did not show promising prospects. The gasification rate and combustion efficiency could be respectively correlated to the reactivity and selectivity of different OCs except for the K-added samples. [ABSTRACT FROM AUTHOR]

A new concept for syngas production is proposed in which a liquid metal oxide (here copper oxide) is implemented as an oxygen carrier for chemical looping gasification. The proposed system consists of two interconnected bubble reactors as the fuel and air reactors, through which a liquid metal oxide is circulated to be successively reduced and oxidised providing the required heat and oxygen for the gasification reaction. The proposed system offers a potential process to avoid challenges such as agglomeration and sintering that are typically associated with the solid metal oxides that have previously been proposed for chemical looping gasification. Thermochemical equilibrium models are presented that show acceptable agreement with the available data. The model is then used to estimate that the carbon conversion of feedstock is up to 84.6% for gasification and 100% for combustion with the proposed concept. In addition, the mole fraction of gaseous copper oxide in the outlet stream from the air reactor is estimated to be 10 −11 , which implies that no further process is required to separate the evaporated copper oxide from the syngas. [ABSTRACT FROM AUTHOR]

Coal-based Pressurized Chemical Looping Combustion Combined Cycle (PCLC-CC) is the second generation of coal-fueled CLC plant, which possesses much higher plant efficiency and lower-CO 2 capture cost compared to the first generation - Coal-based CLC combined solely with steam cycle. PCLC-CC has a similar plant configuration to the Pressurized Fluidized Bed Combined Cycle (PFBC), and is composed of a PCLC Island, gas turbine, Heat Recovery Steam Generator (HRSG) and steam cycle. In the fuel reactor of PCLC Island, the metal-based oxygen carrier (OC) supplies oxygen for coal combustion and in-situ CO 2 capture. The air reactor of PCLC Island, where the OC is re-oxidized by air, serves as a combustion reactor to produce oxygen-depleted air of high temperature and high pressure to drive the gas turbine and the following steam cycle for large-scale power generation. This research provides an initial understanding of the complex reactions in the fuel reactor of the solid-fueled PCLC Island in the pressures range of 1–6 bars. Experiments conducted in the TGA apparatus and the fixed- and fluidized-bed reactors demonstrated the effects of operational pressure, coal char reactivity and different iron-based OCs behavior on the performance of PCLC. [ABSTRACT FROM AUTHOR]

This work presents a detailed investigation of biomass and coal co-fuelled gasification chemical looping combustion for combined cooling, heating and power (BCCLC-CCHP) generation system from both thermodynamic and environmental aspects. Addition of biomass (corn stover) as blending fuel not only provides possibility of utilizing renewable energy, but also greatly reduces greenhouse gas emissions. The application of chemical looping combustion for oxidation of syngas is aimed at inherent separation of CO 2 without extra energy penalty. At based design conditions, the energy efficiency and exergy efficiency can reach 60.16% and 22.16% in summer, respectively. Three key parameters, namely oxygen to carbon ratio (O/C), operating temperature of air reactor in the chemical looping combustion and share of corn, are considered to analyze their influences on system performances. O/C ratio is not sensitive to energy output, however an optimum value of O/C = 0.42 is found to obtain maximum system efficiency and primary energy saving ratio (PESR). Increasing AR operating temperature benefits power generation but lowers down cooling and heating production. Increasing corn mass share from absence to 50 wt.% to replace part of coal results in energy efficiency losses by approximately 6 point percentages but the PESR is increased by up to 5 point percentages. Capture of photosynthetically-derived CO 2 (from corn) by CLC offers negatively cradle-to-grave greenhouse gas emissions in the BCCLC-CCHP process when corn mass share is higher than 15%. [ABSTRACT FROM AUTHOR]

In this paper, Canadian ilmenite ore-based oxygen carriers (OCs) were, for the first time, prepared by coating the ilmenite ore particles with metal oxides of CeO 2 , ZrO 2 , NiO, or Mn 2 O 3 by using precursors of Ce(NO 3 ) 3 , Zr(O-t-Bu) 4 , Ni(NO 3 ) 2 or Mn(NO 3 ) 2 , respectively. The reduction reactivity of OCs with methane was examined by temperature-programmed methane reduction (CH 4 -TPR), and their cyclic performance during the chemical looping methane combustion was investigated isothermally in a thermogravimetric analyzer (TGA). It was demonstrated that the addition of all types of these metal oxides had a positive effect, such as an accelerated reactivity towards methane reduction and enhanced resistance to agglomeration. Specifically, the modification using CeO 2 and ZrO 2 improved the reactivity of ilmenites towards CH 4 reduction at a lower temperature of 750 °C. However, the promotion effect decreased when the temperature was elevated to 800 °C. NiO modification not only enabled the ilmenite to improve reaction with CH 4 due to the generation of a more active compound NiFe 2 O 4 , but also to result in higher oxygen transport capacity. Similarly, Mn 2 O 3 modification showed a higher reactivity and a fast reaction rate towards the oxidation of CH 4 attributed to the generation of ferrimanganic oxides. Furthermore, the overall oxygen transport capacity of Mn 2 O 3 composed OCs was increased caused by the variable valence of Mn. The addition of CeO 2 , ZrO 2 , and NiO always retarded the activation process of ilmenite ore, by contrast, Mn 2 O 3 modified samples accelerated the activation due to the irreversible phase transformation from Mn 2 O 3 to Mn 3 O 4 accompanied by a volume shrinking that led to a flawed particle surface reducing the diffusion resistance. [ABSTRACT FROM AUTHOR]

The present article reports on the first application of geopolymers for the production of oxygen carriers for chemical looping combustion. Granules with different properties and in typical sizes for fluidized bed applications were produced starting from geopolymer/iron oxide slurries. These slurries were prepared according to a previously-developed formulation, modified by adding iron oxides and pore-forming agents to obtain oxygen carriers with different micro- and macrostructures. The performance of these novel oxygen carriers was tested in thermogravimetric equipment, measuring a capacity very close to the theoretical value 1.3 after repeated cycles. Tests conducted in a laboratory-scale differential reactor gave rise to a lower O-carrying capacity (<1.0%), but rather high kinetics (i.e. rate index) by comparison with other materials and published data. The analysis on the sample (ESEM, XRD and MIP) provided a reasonable interpretation of the phenomena observed, attributable mainly to the influence of internal porosity. Fluidization tests, elutriation/attrition results and the lack of any sign of particle agglomeration proved the suitability of the synthesized granules for use in fluidized beds. [ABSTRACT FROM AUTHOR]

The objective of this research is to investigate the effect of steam on reducing carbon deposition during CH 4 chemical looping combustion (CLC) on a fixed bed reactor. Steam proved to be significantly effective not only for the fuel utilization efficiency of CLC but also for the stability of the oxygen carrier (OC). The evaluation tests were performed with CuO/γ-Al 2 O 3 OCs prepared with three different methods. The results showed that OC prepared using co-precipitation method performed the best with the highest reactivity for CH 4 combustion at low temperature (700 °C) compared to that prepared using mechanical mixture and impregnation methods. It was also found that the carbon deposition was the main reason for the low combustion efficiency and the deactivation of OCs in redox cycles. For OCs at 800 °C, after 10 cycles without steam, 25–44% CO 2 selectivity reductions were observed, accompanied by Barrett-Joyner-Halenda (BJH) pore volume decreases of 31–47%. With the steam introduction, the CO 2 selectivity consistently achieved ∼100% in 10-cycle CLC, and the pore volumes of OCs decreased by only 11–22%, which was mostly attributed to the carbon-steam gasification reaction. The OCs for CH 4 CLC with and without steam were characterized by using different methods, including surface area and pore analysis, thermal gravimetric analysis (TGA), X-ray diffraction (XRD), H 2 temperature programming reduction (TPR), and scanning electron microscope (SEM). The results demonstrated that steam could easily gasify the carbon deposition, greatly intensify the redox degree of OCs at 800 °C, and strengthen the redistribution of Cu on the surface of Al 2 O 3 , contributing to the fine and uniform distribution of CuO. Therefore, steam can be successfully used for considerable enhancement of the overall performance of CH 4 CLC. [ABSTRACT FROM AUTHOR]

Owing to the unclear temporal and spatial variations of axial solid conversion in a packed bed using iron (III) oxide as an oxygen carrier, we directly observe these variations by means of a sub-layer approach. The results indicate that the behaviour of the multiple reaction fronts during iron (III) oxide reduction by CO or H 2 within a packed bed for chemical looping water splitting (CLWS) is strongly dependent on the reaction temperature. When the reaction temperature is lower than the merging temperature, three reaction fronts, i.e., Fe 2 O 3 -Fe 3 O 4 , Fe 3 O 4 -Fe 0.947 O and Fe 0.947 O-Fe, and three product zones, i.e., Fe 3 O 4 , Fe 0.947 O and Fe, will appear in the packed bed. In contrast, when the reaction temperature is higher than the merging temperature, the Fe 2 O 3 -Fe 3 O 4 and Fe 3 O 4 -Fe 0.947 O fronts merge, leading to the disappearance of the Fe 3 O 4 zone. As a result, only the Fe 2 O 3 -Fe 0.947 O and Fe 0.947 O-Fe fronts, as well as Fe 0.947 O and Fe zones will appear in the packed bed. These reduction behaviours are verified by two breakthrough curves, one for T < T m and one for T > T m , from the thermodynamically controlled reduction of iron (III) oxide in the packed bed. The reaction front movement model, which is proposed based on the reduction behaviour, can be used to determine the maximum solid conversion of the reduction step, i.e., the thermodynamic limitation of the reduction step, in the packed bed CLWS. The maximum solid conversion can reach 0.409 for the CO case and 0.554 for the H 2 case. The first discovery of both the behaviours of the reaction fronts movement and the thermodynamic limitations of the reduction step standardizes the criteria for both the oxygen carrier evaluation and the optimization of the operating conditions and provides theoretical support for scaling up the packed bed and developing new technology for packed bed CLWS. [ABSTRACT FROM AUTHOR]

The rotary chemical looping combustion reactor has great potential for efficient integration with CO 2 capture-enabled energy conversion systems. In earlier studies, we described a one-dimensional rotary reactor model, and used it to demonstrate the feasibility of continuous reactor operation. Though this detailed model provides a high resolution representation of the rotary reactor performance, it is too computationally expensive for studies that require multiple model evaluations. Specifically, it is not ideal for system-level studies where the reactor is a single component in an energy conversion system. In this study, we present a reduced fidelity model (RFM) of the rotary reactor that reduces computational cost and determines an optimal combination of variables that satisfy reactor design requirements. Simulation results for copper, nickel and iron-based oxygen carriers show a four-order of magnitude reduction in simulation time, and reasonable prediction accuracy. Deviations from the detailed reference model predictions range from 3% to 20%, depending on oxygen carrier type and operating conditions. This study also demonstrates how the reduced model can be modified to deal with both optimization and design oriented problems. A parametric study using the reduced model is then applied to analyze the sensitivity of the optimal reactor design to changes in selected operating and kinetic parameters. These studies show that temperature and activation energy have a greater impact on optimal geometry than parameters like pressure or feed fuel fraction for the selected oxygen carrier materials. [ABSTRACT FROM AUTHOR]

Chemical looping partial oxidation process has more advantages over conventional chemical looping process, which can not only completely avoid the problem of greenhouse gas emissions, but also supply syngas products for chemical industry. The aim of the present work is to perform fundamental investigation on chemical looping partial oxidation of solid fuels. Production of CO through chemical looping partial oxidation of carbon was investigated in order to find proper oxygen carrier with good reactivity and high selectivity. A simple and easy to use method based on the zone division of Ellingham diagram was offered to distinguish the oxidation ability of various metal oxides, and three zones including complete oxidation, partial oxidation and inert zones were divided. CaFe 2 O 4 , Ca 2 Fe 2 O 5 and FeAl 2 O 4 in partial oxidation zone together with Fe 2 O 3 in complete oxidation zone were chosen as target oxygen carriers (OCs) for chemical looping partial oxidation of carbon in this work. Of the target metal oxides, CaFe 2 O 4 and Ca 2 Fe 2 O 5 were found to have fast reaction rate, large oxygen-carrying capacity, high CO selectivity, and good regeneration performance, which made them very attractive for the purpose of chemical looping partial oxidation of solid fuels in real applications. [ABSTRACT FROM AUTHOR]

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 CH 4 (10–25 vol.%) and O 2 (5–20 vol.%) were applied, respectively. The kinetic parameters, such as the activation energy ( E a ), pre-exponential factor ( A 0 ), 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 E a was 35.3 kJ/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 E a was equal to 16.7 kJ/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. [ABSTRACT FROM AUTHOR]

Gas Switching Combustion (GSC) is a promising new process concept for energy efficient power production with integrated CO 2 capture. In comparison to conventional Chemical Looping Combustion (CLC) carried out in interconnected fluidized beds, the GSC concept will be substantially easier to design and scale up, especially for pressurized conditions. One potential drawback of the GSC concept is the gradual temperature variation over the transient process cycle, which leads to a drop in electric efficiency of the plant. This article investigates heat management strategies to mitigate this issue both through simulations and experiments. Simulation studies of the GSC concept integrated into an IGCC power plant show that heat management using a nitrogen recycle stream can increase plant efficiency by 3 percentage points to 41.6% while maintaining CO 2 capture ratios close to 90%. Reactive multiphase flow simulations of the GSC reactor also showed that heat management can eliminate fuel slip problems. In addition, the GSC concept offers the potential to remove the need for a nitrogen recycle stream by implementing a concentrated air injection that extracts heat while only a small percentage of oxygen reacts. Experiments have shown that, similar to nitrogen recycle, this strategy reduces transient temperature variations across the cycle and therefore merits further investigation. [ABSTRACT FROM AUTHOR]

Abstracts Chemical looping combustion (CLC) is an advanced technology developed to achieve highly efficient fuel combustion with in-situ CO 2 capture. In this process, metal oxide particles are used as an oxygen carrier (OC) to transport lattice oxygen for fuel combustion. In this process, a stream of CO 2 and steam is produced by successful separation of atmospheric N 2 and the gaseous product of combustion. In CLC of solid fuel, metal oxide particles are physically mixed and react with solid fuel at high temperature using gasification enhancer, such as steam, or CO 2 . A full understanding of the reaction mechanism between the OC and solid fuel is vital for OC development and the fuel reactor design. Several reactions may be involved in solid-fueled CLC when an iron-based OC is used, including (1) solid fuel devolatilization/gasification, (2) OC reduction with intermediate syngas, (3) the solid-solid reaction between OC and solid fuel via direct contact, and (4) the homogeneous water-gas shift reaction. The former two reactions have been extensively studied in recent years. This study focuses on the third reaction, the solid-solid reaction, which occurs thermodynamically at typical operational temperatures of CLC. The direct solid-solid reaction between coal char and two iron-based OCs via random particle collision in a fluidization bed regime was investigated and focuses on the reaction kinetics and the carbon conversion at different temperature. The contribution of the solid-solid reaction to the global carbon conversion was estimated for steam-gasified CLC at different temperature. The solid-solid reaction via static contact in a thermal-gravimetric analyzer (TGA) was also tested to evaluate the role of different OCs and to better understand the reaction mechanism between the two solid particles. [ABSTRACT FROM AUTHOR]

Ilmenite ore has shown promise as an oxygen-carrier in chemical looping combustion operation. Since operating at higher pressures has been proven to hold important benefits for chemical looping combustion, this study aims to investigate the performance of ilmenite ore under pressurized conditions. The reduction reactivity and oxygen-transport capacity of Canadian ilmenite ore in pressurized chemical looping combustion during redox cycles were investigated in a pressurized thermogravimetric analyzer, using carbon monoxide and air as reductant and oxidant respectively. While increasing the CO partial pressure from 0.32 to 0.80 MPa (at a constant total pressure) led to higher rates of reaction and higher oxygen-transport capacity, increasing the total pressure up to 2.4 MPa (at a constant CO partial pressure while varying the p CO 2 ) had the reverse effect. Furthermore, increasing the temperature from 1123 to 1323 K resulted in a pronounced increase in the reduction rate. Although increasing the particle size from 75–125 μm to 300–425 μm resulted in a slower rate of reduction, the effect was minor. A kinetic grain model with a changing grain size was fitted to reduction rate data obtained at 1.6 MPa. The order of reaction with respect to the CO partial pressure was calculated as 0.67, while the activation energy was determined to be 115 kJ/mol. [ABSTRACT FROM AUTHOR]

This paper presents data on conversion of two different coals with a chemical looping oxygen carrier, CuO-Fe 2 O 3 -alumina, and over a range of conditions including steam and various levels of reduction of the oxygen carrier. Reactions of coal/steam/CuO-Fe 2 O 3 -alumina oxygen carrier and coal/steam/partially reduced CuO-Fe 2 O 3 -alumina oxygen carrier were investigated with Wyodak coal and Illinois #6 coal in a fluidized bed reactor. Temperature programmed reaction studies indicated that the oxygen carrier enhanced the steam gasification/combustion rates of both coals. Rates of gasification/combustion were higher with Wyodak coal (sub bituminous) than that with Illinois #6 coal (bituminous). In addition to the increase in reaction rates, the total moles of carbon that were gasified and combusted from coal/steam increased in the presence of the oxygen carrier. The reduced oxygen carrier promoted the water-gas shift reaction when reacted with synthesis gas in the presence of steam, but the reverse water gas shift reaction was observed when steam was not present. The partially reduced oxygen carrier enhanced the production of H 2 from coal/steam, which was different from the observations with un-reduced oxygen carrier. Water splitting reaction to produce H 2 was also observed with the reduced oxygen carrier. CuO-Fe 2 O 3 -alumina reacted with coal during the temperature ramp to 850 °C even in the absence of steam due to the chemical-looping oxygen uncoupling (CLOU) reaction. Fourier transform infra-red (FTIR) analysis indicated the presence of volatile aromatics during the temperature ramp and these may have also contributed to the reactions with the oxygen carrier in the absence of steam. Increasing steam concentration had a negative effect on the CLOU reaction. [ABSTRACT FROM AUTHOR]

High purity H 2 was produced by a novel low-energy sorption enhanced steam methane reforming process by introducing a second loop in order to provide part of the required heat for the endothermic sorbent calcination in the regeneration stage. The feasibility of the intensified reforming process was demonstrated experimentally over a mixture of a bifunctional NiO-based oxygen transfer material/reforming catalyst supported on ZrO 2 , and a ZrO 2 -promoted CaO-based CO 2 sorbent. The experiments were performed in a bench-scale fixed bed reactor unit. The influence of operating parameters, such as reformer’s temperature, steam/methane and NiO/CaO molar ratios and space velocity of the feed stream, was investigated in order to determine the optimum operating conditions and assess the full potential of the combined process over the two solids. The presence of the CO 2 sorbent in the reactor facilitated H 2 production of high purity. Equilibrium concentrations were obtained over all studied conditions, even at very high space velocities. The process was further demonstrated with a continuous cyclic test of 20 reforming/regeneration cycles at a temperature of 650 °C. The CO 2 sorbent and the oxygen transfer material exhibited excellent stability without deterioration in performance for 20 consecutive cycles, corresponding to more than 60 h of testing. H 2 concentration over 95% was achieved throughout the sorbent’s prebreakthrough region during the reduction/reforming/carbonation stage. During the reoxidation/calcination step, the highly exothermic Ni oxidation provided adequate heat to raise the temperature of the solids and decompose up to 45% of the saturated sorbent without external heating. [ABSTRACT FROM AUTHOR]