Chemical Looping Air Separation Research Articles

Solar Energy Driven Chemical Looping Air Separation

Chemical looping is emerging as a feasible alternative to carry out reduction and oxidation processes under different process conditions. This technology proves especially useful when reduction and oxidation processes proceed with different time constants. With the possibility of incorporation of solar energy to the endothermic end of the process, chemical looping technology has recently become more popular. Chemical looping air separation (CLAS) is an alternative to cryogenic separation, by utilizing solar thermal energy. In this process a reducible metal oxide is heated to a temperature such that the metal releases its lattice oxygen. In the second step, the metal oxide is exposed to air and oxygen is captured by the oxide while pure nitrogen is released at the outlet and the loop is closed. Mn2O3 is selected as the oxygen carrier to perform chemical looping cycles. Oxygen mobility of the metal oxide and reversibility through redox cycles are tested with thermogravimetric analysis (TGA). The redox cycles are designed such that the air oxidizes, and the steam reduces the material. The reduction behavior of manganese (III) oxide under inert atmosphere is tested in TGA. It is proved that steam acts as an inert gas under the reaction conditions. The use of steam at the reduction stage results in a more convenient separation of the sweep gas (steam) from the oxygen released from the oxide. It is demonstrated that a redox cycle between Mn2O3 and Mn3O4 can be performed isothermally. The capability of the system to be coupled with solar energy makes it more alluring for environmentally friendly option seekers. The use of solar irradiation is tested with parabolic mirrors to observe the power output. Overall, CLAS process works on milder conditions which is crucial in reducing the energy and equipment costs, and its advantages regarding energy efficiency increase even more when solar energy is incorporated into the system.

Pr doped CeO2 for chemical looping air separation at ultra-low temperatures

Chemical looping air separation (CLAS) represents a promising approach to use thermal energy for high-purity oxygen production. CeO2 represents a class of material that uncouples oxygen using thermal energy, but the required temperature is usually very high (>1400 °C). This limits the potential use for CeO2-based materials in CLAS. This study reports a Pr doped CeO2 oxygen sorbents for chemical looping air separation at ultra-low temperatures. The as-formed Ce1-xPrxO2 solid solution can uncouple oxygen effectively, achieving a redox oxygen capacity of 0.88 wt% at isothermal condition as low as 500 °C. The redox oxygen capacity can be further enhanced to 1.63 wt% in temperature-swing cycles between 400 °C and 900 °C. Moreover, oxygen partial pressure-swing cycles show that the Ce1-xPrxO2 solid solution maintains 95% of its redox oxygen capacity at oxygen partial pressure as low as 0.02 atm, indicating its potential applications in oxygen separation from diluted air. DFT calculations and other physio-chemical characterizations indicate that Pr doping can effectively reduce the oxygen vacancy formation energy, and gaseous oxygen is uncoupled when Pr4+ and Ce4+ are reduced in the Ce1-xPrxO2 solid solution. Overall, this study highlights the novel performance of CeO2 with Pr doping and could offer insights into CeO2 modification strategies for thermal chemical applications.

Life cycle assessment of an efficient biomass power plant supported by semi-closed supercritical CO2 cycle and chemical looping air separation

Biomass power plant with carbon capture facility has great carbon emission reduction potential due to biomass's carbon neutrality characteristic, but it has been long-time suffered from undesirable system efficiency. This paper explored the life cycle carbon emission of a high-efficient biomass power generation system, which was comprised by the semi-closed supercritical CO2 cycle and chemical looping air separation sub-units. This system was proved to be environmentally superior with the life cycle warming impact value at 97.69 kg CO2 eq./MWh, the life cycle carbon emission reduction rate was 49.61 % and 45.46 % compared with traditional biomass gasification combined cycle system and biomass chemical looping gasification combined cycle system, respectively. The fuel and materials preparation stage should receive improvement attention due to its largest emission share of 76 %. In addition, the effects of key parameters, such as CO2 to biomass ratio (CO2/C), biomass gasification temperature, oxygen carrier and biomass types on environmental performance were investigated to further reveal this system's carbon emission reduction potential. The biomass/coal co-fired system showed net zero carbon emission was achieved when biomass share exceeded only around 10 %.

Investigation of barium iron oxides for CO2 capture and chemical looping oxygen uncoupling

The performance of two underexploited ternary oxides – Ba3Fe2O6 and Ba5Fe2O8 are investigated for carbon dioxide capture and chemical looping oxygen uncoupling. The ternary compound Ba3Fe2O6 was found to have a structure characterised by space group Pa3¯. Experimental results have shown that both Ba3Fe2O6 and Ba5Fe2O8 are capable of cyclically capturing CO2 at temperatures above 800 °C. Ba5Fe2O8 demonstrated superior CO2 capture performance compared to Ba3Fe2O6, with consistent gravimetric CO2 uptake capacities of 4.35 wt% and 13.39 wt% at 900 °C and 1000 °C, respectively, over 20 cycles. In comparison, Ba3Fe2O6 demonstrated high initial CO2 uptake capacities which deteriorated cyclically, with 20 cycle average capacities of 7.73 wt% and 11.99 wt% at 900 °C and 1000 °C, respectively. Ba3Fe2O6 also exhibits excellent recyclability and satisfactory chemical looping oxygen uncoupling (CLOU) activity over temperature swing cycles between 550 °C and 950 °C. In contrast, the strong affinity with CO2 makes Ba5Fe2O8 unsuitable for application in chemical looping oxygen uncoupling or chemical looping air separation, especially in the presence of substantial partial pressures of CO2.

Copper-based chemical looping air separation process: Thermodynamics, kinetic modeling, and simulation of the fluidized beds

Chemical looping air separation is one of the potential processes for oxygen separation from air constituents using oxygen carriers with chemical looping oxygen uncoupling properties that are circulated between reduction and oxidation reactors. Copper-based oxygen carriers have been recognized as a suitable class of materials for the process due to their promising properties and low cost. In this study, copper-based material has been investigated for chemical looping air separation to identify the process parameters that affect the performance and oxygen generation. Firstly, thermodynamic analysis was performed to predict the suitable conditions for oxygen generation and oxygen carrier oxidation, and to model oxygen equilibrium partial pressure. Then, CuO (40 wt%)/ZrO2 was prepared by impregnation synthesis technique to examine the oxygen carrier kinetics using a thermogravimetric analyzer. Results showed that 1.5-dimensional Avrami-Erofeev model best fitted the reduction data with an activation energy of 230 ± 25.2 kJ/mol, whereas the oxidation data were fitted by 1.5 reaction order model with an activation energy of 211 ± 8.0 kJ/mol. The process was simulated using Aspen Plus software package, and the reactors were represented using Fluidbed units to account for both the kinetics and hydrodynamics, to identify the suitable fluidization regimes for specific operating conditions. Simulation results showed that the highest oxygen generation occurred while operating both reactors at bubbling fluidization regimes. Moreover, the temperature effects on the process performance and output were examined, and findings indicated that operating the reducer at 1000 °C and the oxidizer at 800 °C would give out the highest solids conversion and oxygen generation flowrate (23.26 ton/day) with specific energy consumption of 132.26 kWh/tonne of oxygen. However, operating the process at high temperatures would increase the energy penalty and the operating costs, and a more comprehensive technoeconomic study will be required to decide whether lower temperatures operation would be feasible.

Oxidation Kinetics of Nanocrystalline Hexagonal RMn1-xTixO3 (R = Ho, Dy).

Hexagonal manganites, RMnO3 (R = Sc, Y, Ho-Lu), are potential oxygen storage materials for air separation due to their reversible oxygen storage and release properties. Their outstanding ability to absorb and release oxygen at relatively low temperatures of 250-400 °C holds promise of saving energy compared to current industrial methods. Unfortunately, the low temperature of operation also implies slow kinetics of oxygen exchange in these materials, which would make them inefficient in applications such as chemical looping air separation. Here, we show that the oxidation kinetics of RMnO3 can be improved through Ti4+-doping as well as by increasing the rare earth cation size. The rate of oxygen absorption of nanocrystalline RMn1-xTixO3 (R = Ho, Dy; x = 0, 0.15) was investigated by thermogravimetric analysis, X-ray absorption near-edge structure, and high-temperature X-ray diffraction (HT-XRD) with in situ switching of atmosphere from N2 to O2. The kinetics of oxidation increases for larger R and even more with Ti4+ donor doping, as both induce expansion of the ab-plane, which reduces the electrostatic repulsion between oxygen in the lattice upon oxygen ion migration. Surface exchange rates and activation energies of oxidation were determined from changes in lattice parameters observed through HT-XRD upon in situ switching of atmosphere.

BaCoO3-δ perovskite-type oxygen carrier for chemical looping air Separation, part Ⅱ: Design of the monolithic oxygen carriers

This work is the second part of the application of BaCoO3-δ perovskite as an oxygen carrier for chemical looping air separation (CLAS). In this paper, monolithic oxygen carriers were prepared by loading BaCoO3-δ powder perovskite onto cordierite ceramics. The oxygen release performance of the monolithic oxygen carriers was evaluated through experimentation on a fixed-bed reactor and simulated using computational fluid dynamics (CFD) numerical methods. The surface temperature variation, oxygen release efficiency, and the effect of the cross-section shape of the loading material were investigated. The results showed that the monolithic oxygen carrier primarily released O2 via the lattice oxygen of BaCoO3-δ perovskite during the reaction process, and the kinetic model for oxygen release and the reaction mechanism of the monolithic oxygen carrier were essentially identical to those of powder BaCoO3-δ perovskite. CFD simulation showed that the surface temperature of the monolithic oxygen carrier decreased and then increased as the oxygen release reaction proceeded. And the temperature on the centerline of the inner surface of the monolithic oxygen carrier was the lowest. The hexagonal monolithic oxygen carrier demonstrated the highest maximum temperature difference along the centerline of its inner surface, reaching 7.26 °C, whereas both square and triangular monolithic oxygen carriers exhibited a maximum temperature difference of 6.73 °C. The monolithic oxygen carriers exhibited the highest conversion rate at the inlet and the lowest at an axial length of 19 mm. Among them, the square-shaped oxygen carrier showed higher surface temperatures and conversion rates, achieving values of 0.830 and 0.814 at the inlet and axial length of 19 mm after a duration of 600 s. These findings suggest that a square cross-section shape is more suitable for loading materials.

Coupling chemical looping air separation with the Allam cycle – A thermodynamic analysis

The Allam cycle is a class of oxy-fuel combustion power cycles using supercritical CO2 (s-CO2) as the thermal fluid to achieve power generation with inherent capture of CO2. Compared to other conventional CO2 capture techniques, the Allam cycle stands out owing to its high fuel-to-electricity conversion efficiency (55–59%), the elimination of the Rankine cycle and reduced physical footprint. A key source of energy penalty of Allam cycle comes from the air separation unit (ASU), which supplies pure oxygen via an energy intensive cryogenic process. This paper presents a thermodynamic analysis of a novel supercritical CO2-based power generation scheme, in which a natural gas fuelled Allam cycle is integrated with a chemical looping air separation (CLAS) system, which supplies oxygen to the combustor. The modelling results show that the Allam-chemical looping air separation (Allam-CLAS) process can achieve 56.04% net electrical efficiency with a 100% CO2 capture rate, when a Co3O4-based oxygen carrier is used. This is 6% higher than the Allam cycle coupled to a cryogenic ASU. The exergetic efficiency of the Allam-CLAS system driven by the Co3O4-CoO redox cycle is 57.13%, also more favourable than a conventional Allam-ASU system (with reported exergetic efficiency of 53.4%). This newly proposed Allam-CLAS power cycle presents a highly efficient, and simple solution to generate zero-carbon electricity from natural gas.

Kinetic and Thermodynamic Enhancement of Low-Temperature Oxygen Release from Strontium Ferrite Perovskites Modified with Ag and CeO2.

The redox behavior of the nonstoichiometric perovskite oxide SrFeO3-δ modified with Ag, CeO2, and Ce was assessed for chemical looping air separation (CLAS) via thermogravimetric analysis and by cyclic release and uptake of O2 in a packed bed reactor. The results demonstrated that the addition of ∼15 wt % Ag at the surface of SrFeO3-δ lowers the temperature of oxygen release in N2 by ∼60 °C (i.e., from 370 °C for bare SrFeO3-δ to 310 °C) and more than triples the amount of oxygen released per CLAS cycle at 500 °C. Impregnation of SrFeO3-δ with Ag increased the concentration of oxygen vacancies at equilibrium, lowering (3 - δ) under all investigated oxygen partial pressures. The addition of CeO2 at the surface or into the bulk of SrFeO3-δ resulted in more modest changes, with a decrease in temperature for O2 release of 20-25 °C as compared to SrFeO3-δ and a moderate increase in oxygen yield per reduction cycle. The apparent kinetic parameters for reduction of SrFeO3-δ, with Ag and CeO2 additives, were determined from the CLAS experiments in a packed bed reactor, giving activation energies and pre-exponential factors of Ea,reduction = 66.3 kJ mol-1 and Areduction = 152 mol s-1 m-3 Pa-1 for SrFeO3-δ impregnated with 10.7 wt % CeO2, 75.7 kJ mol-1 and 623 molO2 s-1 m -3 Pa-1 for SrFeO3-δ mixed with 2.5 wt % CeO2 in the bulk, 29.9 kJ mol-1 and 0.88 molO2 s-1 m-3 Pa-1 for Sr0.95Ce0.05FeO3-δ, and 69.0 kJ mol-1 and 278 molO2 s-1 m-3 Pa-1 for SrFeO3-δ impregnated with 12.7 wt % Ag, respectively. Kinetics for reoxidation were much faster and were assessed for two materials with the slowest oxygen uptake, SrFeO3-δ, giving the activation energy Ea,oxidation = 177.1 kJ mol-1 and pre-exponential factor Aoxidation = 3.40 × 1010 molO2 s-1 m-3 Pa-1, and Sr0.95Ce0.05FeO3-δ, giving the activation energy Ea,oxidation = 64.0 kJ mol-1, and pre-exponential factor Aoxidation = 584 molO2 s-1 m-3 Pa-1.

Highly Efficient CO2 Capture and Utilization of Coal and Coke-Oven Gas Coupling for Urea Synthesis Process Integrated with Chemical Looping Technology: Modeling, Parameter Optimization, and Performance Analysis

The resource endowment structure of being coal-rich and oil-poor makes China’s production of coal-based ammonia and urea, with a low production cost and a good market, a competitive advantage. However, the process suffers from high CO2 emissions and low energy efficiency and carbon utilization efficiency due to the mismatch of hydrogen-to-carbon ratio between raw coal and chemicals. Based on the coal-to-urea (CTU) process and coal-based chemical looping technology for urea production processes (CTUCLAS&H), a novel urea synthesis process from a coal and coke-oven gas-based co-feed chemical looping system (COG-CTUCLAS&H) is proposed in this paper. By integrating chemical looping air separation and chemical looping hydrogen production technologies and the synergies between coal gasification, low-energy consumption CO2 capture and CO2 utilization are realized; the excess carbon emissions of the CTU process are avoided through coupling the pressure swing adsorption of COG, and the low carbon emissions of the proposed system are obtained. In this work, the novel process is studied from three aspects: key unit modeling, parameter optimization, and technical-economic evaluation. The results show that COG-CTUCLAS&H achieves the highest system energy efficiency (77.10%), which is much higher than that of the CTU and CTUCLAS&H processes by 40.03% and 32.80%, respectively, when the optimized ratio of COG to coal gasified gas is 1.2. The carbon utilization efficiency increases from 35.67% to 78.94%. The product cost of COG-CTUCLAS&H is increased compared to CTU and CTUCLAS&H, mainly because of the introduction of COG, but the technical performance advantages of COG-CTUCLAS&H make its economic benefits obvious, and the internal rate of return of COG-CTUCLAS&H is 26%, which is larger than the 14% and 16% of CTU and CTUCLAS&H, respectively. This analysis will enable a newly promising direction of coal and COG-based co-feed integrated chemical looping technology for urea production.

Energy, exergy, economic, environmental (4E) and dynamic analysis based global optimization of chemical looping air separation for oxygen and power co-production

Chemical looping air separation (CLAS) is a promising oxygen generation technology due to its energy conservation nature. It can be integrated with power generation system (PGS) to improve energy efficiency by utilizing high waste heat of CLAS system. This work presents a global optimization strategy for revamping the CLAS-PGS system, in which the comprehensive performance of the system is evaluated by a novel energy, exergy, economic, environmental, and dynamic (4E-1D) analysis method. First, two original after-burner reheating (ABR) and mixed heating (MH) technologies are proposed to optimize the CLAS-HI-PGS scheme. Second, all the schemes are simulated to provide steady-state simulation results for global 4E analysis, and optimized by genetic algorithm (GA) with minimum capital investment cost (CIC) as target to further improve energy efficiency of CLAS-PGS. Finally, the dynamic behaviors of the schemes are investigated with effective control schemes designed to ensure safe and stable operation of CLAS-PGS. In order to measure additional losses caused by disturbance, the 4E analysis is also combined with dynamic analysis. The results show that the scheme combing MH with CLAS-PGS (CLAS-MH-PGS) displays best, proving the effectiveness of this proposal and providing a new way for CLAS-PGS industrial application.

BaCoO3−δ perovskite-type oxygen carrier for chemical looping air separation, part Ⅰ: Determination of oxygen non-stoichiometry and cyclic stability of oxygen carrier

Chemical looping air separation (CLAS) is a cost-effective high-temperature air separation technology, and finding suitable oxygen carriers with high oxygen selectivity and capacity is of vital importance to it. Perovskite-type oxides have been extensively studied as oxygen carriers due to their high oxygen selectivity. In this work, BaCoO3-δ perovskite oxide with large oxygen capacity was proposed as an excellent oxygen carrier for CLAS. BaCoO3-δ perovskite powder was synthesized through a sol–gel method, and the determination of oxygen non-stoichiometry and cyclic stability of BaCoO3-δ was investigated via thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). Results indicated that the oxygen non-stoichiometry of BaCoO3-δ was a function of temperature and oxygen partial pressure, and the empirical formula was determined by linear fitting in the range of δ less than 0.5. The standard enthalpy change and standard entropy change of the oxygen desorption reaction were 169.43 kJ/mol and 156.19 kJ/(mol·K) at δ of 0.38, which increased to 292.58 kJ/mol and 298.81 kJ/(mol·K) at δ of 0.47, respectively. The oxygen desorption amount and desorption rate of BaCoO3-δ remained extremely stable during 50 cycles at 875℃, with an oxygen capacity of approximately 0.018 g O2/g BaCoO3 of each cycle. The kinetics of the oxygen desorption process of BaCoO3-δ perovskite was described using the 3-D diffusion Jander model, and the obtained values of apparent activation energy (Ea) and pre-exponential factor (A) were 209.79 kJ/mol and 1.93E06, respectively. Further results indicated that BaCoO3-δ demonstrated a hexagonal perovskite phase, the desorbed oxygen was provided by lattice oxygen in perovskite, the crystal structure remained stable during cycles, and the micro-morphology slightly changed after 50 cycles.

High-efficient and carbon-free biomass power generation hybrid system consisting of chemical looping air separation and semi-closed supercritical CO2 cycle with a bottoming organic Rankine cycle

Herein, a novel biomass power generation system, comprising of CO2-assisted gasification unit, chemical looping air separation (CLAS) unit, semi-closed supercritical CO2 (sCO2) cycle with the bottoming ORC unit, was proposed to overcome the problems of low-efficiency and high-pollution rendered by traditional biomass utilization method. And the heat integration between those subunits was well designed based on the principle of energy cascade utilization. The sensitive analysis was carried out to clarify the reasons behind thermodynamic performance variation, and the optimized net power efficiency reached 38.76% when the CO2/C ratio was 0.25, gasification temperature was 830 °C, sCO2 turbine inlet temperature and pressure were 1200 °C and 300 bar respectively, which was superior to 28.01% of biomass integrated gasification combined cycle system. In addition, the exergy analysis found that modification efforts should be exerted on CLAS and sCO2 compression pump, whose exergy destruction were 7.58 MW and 5.15 MW, respectively. Besides, its environmental and economic merits were obvious with the CO2 specific emission at 0.31 kg/MWh, and the levelized cost of electricity at 57.38 $/MWh. Furthermore, three typical biomasses were examined for the proposed system, the results showed that the dryer and carbon-richer biomass could benefit system thermodynamic and economic performance.

Oxygen production routes assessment for oxy-fuel combustion

Oxyfuel combustion is a promising alternative to decarbonize the power sector. However, the main barrier to commercial deployment of the technology is the high energy consumption associated with oxygen production (∼200–300 kWh per ton of O2), which penalizes the thermal-to-electric efficiency of 8.5–12% compared to traditional air combustion plants. Typically, oxygen is obtained from a cryogenic air separation process. However, other technologies have been gaining momentum in recent years, such as membrane technologies, chemical looping air separation, and renewable-driven electrolysis. The present work evaluates all these options for O2 production to retrofit a 550 MWe coal-fired power plant with oxyfuel combustion. A techno-economic assessment is carried out to estimate the energy penalty, the O2 production cost (€/ton) and the Levelized Cost of Electricity. The best results are obtained by combining oxygen transport membranes and electrolysis since the energy consumption has been reduced to 98.56 kWh/ton of O2, decreasing by 59.31% the cryogenic distillation energy consumption (242.24 kWh/ton O2), reducing the overall energy penalty compared to cryogenic air separation from 8.88% points to 7.56%points. The oxygen transport membrane presents the lowest cost of electricity in retrofitting cases, 51.48 $/MWh, while cryogenic distillation estimated cost is 52.7 $/MWh. Their costs of avoided CO2 are 31.79 $/ton CO2 and 34.15 $/ton CO2 respectively.

Integration of molten carbonate fuel cell and chemical looping air separation for high-efficient power generation and CO2 capture

Molten carbonate fuel cell (MCFC) allows concentrating the CO2 from the cathode side to the anode side, generating electricity concurrently. Chemical looping air separation (CLAS) can produce an O2 and CO2 mixture stream as cathode feeding gas of MCFC. In this paper, a natural gas-fueled MCFC with internal reforming is integrated with CLAS as O2 and CO2 source for high-efficient power generation with CO2 capture. An O2 and CO2 mixture stream is produced from CLAS by recirculating a portion of CO2-rich flue gas after the afterburner to CLAS. The system is analyzed through thermodynamic and economic performance. At the baseline case, the plant net power efficiency is 59.5%, with 99.9% CO2 capture rate. Based on sensitivity analysis, the higher fuel cell temperature and fuel utilization factor can increase the plant net power efficiency, while the steam carbon ratio and the CLAS reduction reactor temperature are preferable to be at lower levels for higher plant net power efficiency. Finally, economic analysis is conducted. With a MCFC specific cost of $1327/kW and a natural gas price of $2.79/million Btu, the cost of electricity (COE) is $0.094/kWh. The results show the proposed system is attractive for natural gas-fueled power generation with CO2 capture.

Limits of performance of chemical looping air separation in packed bed coupled with electricity production

Oxyfuel combustion, as a carbon capture method, requires oxygen to be separated from nitrogen. Currently, cryogenic air separation is used for this purpose. An alternative is to use chemical looping, where an oxygen carrier is cycled between reducing and oxidising conditions. In this paper, the feasibility of using packed bed reactors in chemical looping air separation is studied. By introducing a compressor and turbine, oxidisers can be operated at an elevated pressure and the proposed scheme can be viewed as a power-station in its own right, in addition to its more recognised application of producing oxygen for a downstream oxy-fuel combustion. For typical oxygen carriers, a single packed bed reactor is not able to meet the 0.30–0.35 oxygen molar fraction needed for an oxyfuel combustor. Therefore, multiple beds must be used in series or heat must be added radially along the bed length to increase the oxygen molar fraction in the bed.

The effect of alkali and alkaline earth metals oxides addition on oxygen uncoupling rate of copper-based oxygen carrier: A kinetic and experimental investigations

• Oxygen uncouples ability of CuO at low temperatures tested by adding AAEMs oxides. • 5% wt of Na 2 O, K 2 O, MgO, and CaO added to CuO. • An isothermal test was done; MgO, CaO enhanced the process and Na 2 O, K 2 O declined. • Kinetic analysis has been conducted for a more in-depth investigation. • Kinetic results was matched with the experimental, in both MgO was the best. Oxygen uncoupling is one of the most valued properties of oxygen carriers in chemical looping field. It allows to combust the fuel without gasification step and significantly enhances reactivity in all chemical looping fuel oxidation technologies (combustion, gasification, and reforming). Furthermore, it progressed recently to produce pure oxygen (Chemical looping air separation). However, few materials have this merit, among which CuO has the highest reactivity and oxygen transport (uncoupling) capacity. However, it needs a high temperature (about 950 °C) for a high effective reaction rate; in contrast, it suffers high attrition rate and sintering about this temperature. This work aimed to test the ability to enhance the uncoupling at lower temperatures by adding a small amount of common alkali and alkaline earth metals (AAEMs) oxides. CuO was prepared with 5%wt of Na 2 O, K 2 O, MgO, and CaO. An isothermal test was conducted in TGA at (850, 890, and 930 °C) to investigate the effect of additions. For deeper investigation, kinetic analysis has been conducted based on isothermal results. The model of reaction inferred was A 2 α of Avrami-Erofeev ( g α = - l n 1 - α 1 / 2 ) for pure CuO and with all additions, and then the activation energies and pre-exponential factors were calculated. Accordingly, CaO addition showed little increase in the reaction rates while the effect of MgO was significant. In contrast, Na 2 O and K 2 O addition declined the uncoupling rate.

Chemical looping air separation with Sr0.8Ca0.2Fe0.9Co0.1O3-δ perovskite sorbent: Packed bed modeling, verification, and optimization

Chemical looping air separation (CLAS) represents a promising approach for efficient O2 production from the air. The present study aims at optimizing the absorber/desorber operations and the separation process with extensive experimental validation. Specifically, a one-dimensional packed bed model was developed to investigate the CLAS operation with a Sr0.8Ca0.2Fe0.9Co0.1O3-δ perovskite sorbent. The redox thermodynamics of perovskite sorbent was measured by TGA and then incorporated into a linear driving force model to describe the O2 absorption and desorption rates. Both 4-step and 5-step air separation cycle configurations, with various cyclic structures, were performed in a subpilot-scale packed bed. The model predicted O2 purity and productivity were consistent with experimental results, supporting its accuracy and applicability. Parametric analysis and multi-objective optimization were further carried out to assess the performance of CLAS. Both O2 purity and recovery increased monotonically with the cycle time, airflow rate, steam flow rate, and absorption pressure. Meanwhile, optimal O2 productivity and power consumption can only be achieved by specific combinations of these parameters. The optimized results showed that CLAS can be highly competitive when compared to conventional pressure swing adsorption (PSA) or cryogenic distillation. The 5-step cycle configuration achieved a minimum power consumption of 118 kW·h for producing 1 ton O2 with ≥ 95% purity. The maximum O2 productivity reached 0.0932 gO2/(gsorbent·h) with 390 kW·h/ton O2 of energy consumption (95% pure). The optimization results also indicate that CLAS can potentially be more efficient than cryogenic distillation even when the required O2 purity is above 99%.

Effects of introducing foreign ion K on the reduction kinetics of oxygen carriers in chemical looping air separation process

AbstractIn the previous work, YBaCo4O7 + δ and Y0.2Ti0.05Dy0.75BaCo4O7 + δ monolithic oxygen carriers worked at low temperature, were reported with good reactivity in oxygen absorption and desorption. Oxygen carriers reacted at low temperature can save amount of energy for the chemical looping air separation process. The objective of this work is to explore the detailed effect of new foreign ion K+ on reaction process of oxygen releasing and the reduction kinetics for YBaCo4O7 + δ and Y0.2Ti0.05Dy0.75BaCo4O7 + δ monolithic oxygen carriers in fixed‐bed reactor. The results showed that introducing K+ can improve the reaction rate of oxygen releasing. The process of oxygen releasing can be described by A model with different model exponentials of 2, 3, and 4. Adding K+ promotes reaction of oxygen releasing. The apparent activation energies and pre‐exponential factor of oxygen releasing process range from 23.11 to 29.72 kJ/mol and 12.46 to 29.73 min−1, respectively. The kinetic model of oxygen releasing process of monolithic oxygen carriers is established based on obtained kinetics parameters. The got kinetics parameters could be used for designing of a chemical looping air separation reactor.

Thermodynamic evaluation and modelling of an auto-thermal hybrid system of chemical looping combustion and air separation for power generation coupling with CO2 cycles

Chemical looping technologies have been demonstrated to have favorable economy for CO2 separation and high exergy efficiency. In order to realize the energy cascade utilization, a hybrid system combing autothermal coal-fueled chemical looping combustion (CLC), chemical looping air separation (CLAS), supercritical CO2 Brayton cycle and transcritical CO2 cycle is constructed for high-efficiency power production and CO2 separation. The proposed hybrid system is first modeled and simulated under fundamental condition to investigate the basic performance and exergy efficiency of each component. Then the thermodynamic evaluations of the system performance are conducted under different conditions with five variables. Finally, using these simulation results as training samples, a neural network model (NNM) of the system is constructed to predict the power output under variable working parameters. As the energy is used in different subsystems according to its grade, the net power efficiency of this hybrid system can reach to a high value of 64.59%. The established NNM is accurate for power prediction under random conditions with correlation coefficient of 0.9931.