Chemical Looping Combustion Technology Research Articles

Thermodynamic and optimization analysis of a fuel cell-based combined cooling, heating, and power system integrated with LNG-fueled chemical looping hydrogen generation

Chemical looping combustion technology is essential to achieve efficient decarbonized electricity generation for fossil-fueled power plants. However, the existing chemical looping hydrogen generation (CLHG)-driven cogeneration systems have complex refrigeration units and energy-consuming carbon capture. This study proposes a novel solid oxide fuel cell (SOFC)-based combined cooling, heating, and power (CCHP) system, which is integrated with the CLHG and fueled by a liquid natural gas (LNG) regasification process. The system is designed to enhance the overall performance by directly recovering LNG cold energy for cooling and liquefying the resulting CO2. The energy and exergy performance of the system under the baseline design case are evaluated. Subsequently, we discuss the impact of key design parameters on system performance and weigh between cooling/heating power and net power generation for the system dominated by the combined heat and power (CHP)/combined cooling and power (CCP) mode. Our findings reveal that the proposed system exhibits an electrical efficiency of 66.92 % and an exergy efficiency of 53.94 % under the baseline design case. The exergy loss ratio for condenser1 is identified as the highest among all components, accounting for 29.50 %. The constituent unit with the largest exergy loss contribution is the LNG regasification unit, followed by the SOFC unit, CLHG unit, transcritical CO2 cycle unit, and heating unit. More hydrogen needs to be replenished when fuel flow in the CLHG and fuel utilization in the SOFC are used to improve system performance. The optimal electrical and exergy efficiencies of the system predominantly designed in CCP mode surpass those in CHP mode by 4.27 % and 0.57 %, respectively. The results can guide potential applications of CLHG-based cogeneration systems.

CuxMg1-xFe2O4-type spinels as potential oxygen carriers for waste wooden biomass combustion

Waste wood biomass is considered a renewable energy source. Combining biomass combustion with emerging clean combustion technologies such as chemical looping combustion (CLC) can yield effective and affordable carbon capture and, consequently, lead to negative net emissions of greenhouse gases. Oxygen carrier (OC) is a crucial material in CLC technology that must exhibit certain properties, such as high durability, good chemical stability during numerous red-ox cycles and, important for the combustion of solid fuels, the capability of spontaneously releasing oxygen in a process referred to as chemical looping with oxygen uncoupling (CLOU). In this work, a series of nine CuxMg1-xFe2O4 spinel-based materials were synthetized and evaluated for the first time as potential OCs for a waste biomass combustion. Their properties, such as oxygen transport capacity and reactivity with biomass (wood chips) as a fuel, were evaluated in a function of temperature (900–1000 °C). Tested oxygen carriers were characterized with an excellent oxygen transport capacity in CLOU process (up to 2.78 wt%) and good reaction rates with the fuel (up to 1.19 wt. %/min), and regeneration rates (up to 3.8 wt. %/min). High conversion of the waste biomass was also achieved (98.9 %). Moreover, new findings revealed a strong positive effect of magnesium addition on mechanical strength (crushing strength > 4 N for samples with Mg content above 0.5).

Energy, Exergy, Economic and Exergoeconomic Analyses of Chemical Looping Combustion Plant Using Waste Bark for District Heat and Power Generation with Negative Emissions

The greenhouse gas emissions from the boiler of pulp and paper industries can be minimized by adapting chemical looping combustion (CLC) technology. This work aims to analyze the energy, exergy, economic, and exergoeconomic performance of an industrial scale CLC plant for district heat and electricity generation using waste bark from the paper and pulp industry. The CLC plant with one natural ore and one industrial waste oxygen carrier (OC) is modeled using Aspen Plus. The performance of the CLC plant has been compared to Örtofta combined heat and power plant without CO2 capture and with post‐combustion CO2 capture as the reference cases. Results showed that the CLC‐based power plant is energetically, exegetically, and economically efficient compared to the reference cases. The circulating fluidized bed boiler unit contributes the highest exergy destruction (about 50–80%). Among the CO2 capture plants, the CLC plant with ilmenite has the lowest levelized cost of district heat (4.58 € GJ−1), and a payback period (9.69 years) followed by the CLC plant with LD slag (5.91 € GJ−1 and 11.84 years), and the plant with PCC (6.94 € GJ−1 and 13.58 years). The exergoeconomic analysis reveals that the CLC reactors have the highest cost reduction potential, followed by the steam turbine.

Industrial-scaled Cu-Fe composite oxygen carrier for chemical looping combustion through extrusion-spheronization

It is crucial for the preparation of the high-performance and low-cost oxygen carrier (OC) in an industrial-scaled application to lay the foundation for the commercialization of chemical looping combustion (CLC) technology. In this work, a bimetallic OC (RCu-10 M) is prepared in an industrial-scaled extruder coupling with roller, composited by the red mud (aluminum industrial waste), copper ore and montmorillonite as raw materials. First, a thermogravimetric analyzer (TGA) is used to carry out 100 redox cycles using H2 as the reducing agent. RCu-10 M OC demonstrate remarkable redox stability and sintering-resistance across multiple cycles, and the oxygen donating capacity do not diminish as the number of cycles increases. The effects of temperatures and excess oxygen coefficients on the reactivities of RCu-10 M OC with Shenhua bituminous coal are then investigated by using a batch fluidized bed reactor. RCu-10 M OC maintains high combustion efficiency, exceeding 94.7 % at 950 °C, with an excess oxygen coefficient of 2.0. Finally, a lab-scaled interconnected fluidized bed reactor is applied to examine the realistic performance of RCu-10 M OC using CH4 fuel. The results demonstrate that the RCu-10 M OC successfully operates for ca. 100 min of continuous time, and there is no de-fluidization occurrence, and the bed pressure decrease is stable during operation, indicating that the RCu-10 M OC exhibits good fluidization properties and had the potential to be used in large-scale fluidized bed reactors. Further characterization data reveal that the chemical composition of RCu-10 M OC is stable throughout multiple cycles, as indicated by the almost uniform distribution of elements.

Spatial migration of lattice oxygen for copper-iron based oxygen carriers in chemical looping combustion

Oxygen carrier (OC) is of great importance in chemical looping combustion (CLC) technology. The migration rate of bulk lattice oxygen during reduction process is detrimental in reaction rate. However, the migration path of lattice oxygen is still not clear. In this study, a thermogravimetric analyzer (TGA) was used to investigate the reaction characteristics and kinetic parameters of the OC. The oxygen migration paths of CuO and CuFe2O4 bulk lattices were studied by density functional theory (DFT) in a five-layer (2 × 1) CuO (1 1 1) and nine-layer (1 × 1) CuFe2O4 (1 0 0) plane model. The kinetic parameters, activation energy changes and relative kinetic model of the OC reduction were explored. According to the DFT results, the deeper bulk phase oxygen requires greater more energy toovercome energy barrier for migration. CuO has a lower oxygen release capacity than CuFe2O4 in the early stages, but higher in the later stage. The reaction kinetics study revealed that the reaction mechanism of the reduction of the copper-iron composite OC is a tertiary chemical reaction control mechanism. During the reaction, the activation energy of the OC changes continuously. The macroscopic reaction kinetics agree with the microscopic simulation, proving the simulation model's validity.

Comparative economic, environmental and exergy analysis of power generation technologies from the waste sludge treatment

As a growing amount of sewage sludge is being produced from wastewater treatment plants, there is an urgency to develop innovative processes to dispose of such municipal waste well. One popular and widely acceptable way of utilizing waste sludge is for power generation. Although there is a good implementation of power generation plants from sewage sludge in Hong Kong, only a few published works have compared the conventional incineration-based process with chemical looping combustion (CLC) technology and the new supercritical water gasification (SCWG) process in detail. In this work, we performed a comprehensive energy, environmental and economic assessment of three power generation processes from the three thermochemical conversions of sewage sludge: i) conventional direct incineration + carbon capture (DI-CC), ii) steam gasification + CLC (G-CLC), and iii) SCWG + gas turbines (SCWG-GT). The final comparative results showed that the G-CLC scheme performed the best from the perspective of economic cost and benefits as well as the environmental global-warming potential (GWP) indicator, although the net energy and exergy efficiencies were not the largest among the three schemes. Notably, the SCWG-GT process for power generation showed its energy superiority with energy and exergy efficiencies of 20.70% and 16.69% consequently. Overall, CLC-based technology can be a promising process for power plant development in the future.

Improving attrition resistance of oxygen carriers by biomass ash in chemical looping process

Chemical looping combustion (CLC) relies on cyclic circulation of oxygen carriers (OCs) between fuel reactor and air reactor to transfer lattice oxygen and heat. OCs’ attrition is an important issue hindering large scale application of CLC technology. Attrition is caused by cracks and abrasion, and method to stop crack propagation is an effective way to mitigate attrition. Biomass ash contains inert and alkali metal components, and it may have the potential to increase the reactivity and reinforce the skeleton structure of OCs. The effects of rape straw ash, corn straw ash and bagasse ash on the reactivity, cumulative attrition rate of red mud OCs were evaluated, and their effects on skeleton structure were analyzed, and finally, the strengthening mechanism of OCs skeleton structure was proposed. The results showed that the rape straw ash rich in K and Ca components promoted the reactivity of OCs. Although the Si-rich bagasse ash decreased the reactivity of OCs, it improved the attrition resistance of OCs. Corn straw ash rich in K and Si components was an effective skeleton strengthening material, which improved both the reactivity and the attrition resistance. The cumulative attrition rate of red mud was 2.74%, and the cumulative attrition rate of CSA sample was 0.35%, which was 87.32% lower than that of OC sample, indicating fine attrition resistance. The fiber structure could strengthen the skeleton of OC, therefore, decreasing attrition rate.

Degradation and phosphorus immobilization treatment of organophosphate esters hazardous waste by Fe-Mn bimetallic oxide

Organophosphate esters (OPEs) waste is difficult to dispose effectively because of its stability and the potential risk of P element. In this study, taking one typical organic extractant of tributyl phosphate (TBP) as an example, we proposed a strategy to treat OPEs inspired by chemical looping combustion (CLC) technology—oxygen carrier immobilization process (OCIP), aiming at efficient TBP degradation and simultaneous P immobilization. Adopting Fe-Mn bimetallic oxide (FMBO) as oxygen carrier, an almost 100% P immobilization efficiency was achieved under recommended conditions which were obtained by response surface methodology. Meanwhile, gaseous products released from TBP degradation, e.g., non-methane hydrocarbon, was lower than the maximum allowable emission concentration limit. Further characterizations implied that P-species released from reaction process were mainly immobilized as stable inorganic forms of metaphosphate, phosphate and pyrophosphate. On the basis of identifying degradation intermediates, we proposed a possible degradation pathways. FMBO as an oxygen carrier provided sufficient oxygen molecules for flameless combustion of OCIP process. Electron paramagnetic resonance measurement confirmed the existence of oxygen vacancies on FMBO surface, which contributed to the formation of •O2−. Oxidation by oxygen molecules and •O2− attack resulted in the degradation and mineralization of TBP, with simultaneously achieving P stabilization.

Macroscopic analysis of chemical looping combustion with ilmenite versus conventional oxides as oxygen carriers

AbstractOver 40% of global energy-related CO2emissions are due to the combustion of fossil fuels for electric energy generation. Albeit CO2capture and storage have been identified as promissory actions to mitigate its emissions, the problem separating N2and CO2remains. A very effective solution for the former problem is to obtain the combustion CO2as a pure molecule, which is possible using the Chemical Looping Combustion (CLC) technology, which uses a solid oxygen carrier to transport the oxygen from an oxidating media (regeneration reactor) to a reducing media (combustion reactor). One of the key issues to apply CLC is to find or develop some material, suitable from the kinetic and thermodynamic points of view, for the reduction-oxidation cycles taking place inside combustion and regenerator reactors. The evaluation of “oxygen carrier” candidates for CLC is based on reactivity (rates and conversions), resistance to carbon accumulation, and “regenerability”, which means the ability of the material for cyclic reduction and oxidation. Another challenging issue to use CLC processes is the loss of oxygen carrier; this problem involves the use of supported metals on materials, such as zirconia, Al2O3, etc. Preparation of this kind of supported carriers requires time, money, and equipment. Meanwhile, the natural mineral ore named ilmenite, which consists of a mixture of iron and titanium oxides, and do not need to be supported, has been seen as promising to increase CLC efficiency as oxygen carrier. In this work, the performance of ilmenite is compared with some other oxygen carriers used in CLC.

Migration and emissions of selenium during chemical looping combustion of coal

AbstractSelenium is one of the most volatile toxic elements in coal, and its emissions must be strictly controlled. Chemical looping combustion (CLC) is a clean and efficient technology for coal. Herein, the iron‐based oxygen carrier (OC) was used as an adsorbent to study the migration and emissions of selenium during the CLC of coal. Due to the oxidation and adsorption of selenium by iron‐based OC, most of the selenium was retained in OC or distributed in the CO2 stream. The proportion of gaseous selenium released into the atmosphere was less than 10%—significantly lower than that from the traditional combustion process of coal, which had a value of 91.79%. The presence of OC increased the distribution phase of selenium, promoted the conversion of gaseous selenium to solid selenium, and reduced selenium emissions in flue gas. During CLC of coal, the fuel reactor (FR) temperature and the number of OC re‐oxidation cycles played an important role in the emissions and retention of selenium. The increasing FR temperature increased the gaseous selenium in the CO2 stream, reduced the particulate selenium absorbed by OC, and reduced the selenium emissions in the atmosphere. After 10 continuous CLC cycles, the selenium concentration in OC increased from 0.889 to 8.20 mg kg−1. The continuous cycling of CLC could realize the enrichment of selenium from coal to OC. Furthermore, the migration and transformation mechanism of selenium during CLC was deduced by experiments and thermodynamic simulation. This research provides a suitable reference for reducing selenium emissions and developing CLC technology.

Enhancement in oxygen transfer rate of CuMn2O4 oxygen carrier via selective dopants: Role of dopant effects on O migration for chemical looping combustion

Chemical looping combustion technology has been widely studied because this platform can convert fossil fuels efficiently into sustainable energy with an in situ carbon capture capability. The redox property of the oxygen carrier (usually a transition metal oxide) plays a critical role in determining the kinetics of the combustion process. This study investigated computationally and experimentally methane oxidation on spinel structure of Mn–Cu bimetallic oxygen carriers due to its facile oxygen uncoupling (Mn and Cu) with high durability in the reduction cycle. Our simulation predicted that the mechanism of complete methane oxidation on CuMn2O4 involved two competitive rate-limiting steps: 1) thermodynamic controlled step of CH2O* formation (CH3O* + O → CH2O* + OH) and 2) kinetic controlled step of CO formation (CHO* + O → CO* + OH). Multiple dopants (Co, Cr, Fe, Ni, Ti, V, and Zn) to the activation barriers of the rate-limiting steps were tested to enhance the performance of oxygen carriers by improving the oxygen transfer rate. Ni-doped CuMn2O4 and V-doped CuMn2O4 showed promising results computationally (significant decrease in ∆E of rate limiting steps). The enhanced oxygen transfer rate of Ni-doped CuMn2O4 was confirmed experimentally. On the other hand, experimentally, V-doped CuMn2O4 provided a lower oxygen transfer rate than the other CuMn2O4 materials, which is inconsistent with the computational predictions. Computation studies showed that the lower oxygen transfer rate stems from the hindrance of O migration by surface V dopants; surface V atom energetically hampers O migration from the subsurface to the top surface. This behavior adversely affects the oxygen transfer rate, resulting in a lower net oxygen transfer rate. These results suggest that the effects of dopants on O migration should be carefully considered when designing enhanced oxygen carriers using a dopant strategy.

Intensification Insights from Chemical Looping Combustion Using Coal–Biomass Mixtures with Fe-Based Oxygen Carrier

Chemical looping combustion (CLC) is a modern technology that enables the mitigation of the CO2 concentration without any expense of energy. Experimental evidence shows that combustion of coal/biomass in CLC technology leads to negative carbon emission by replacing the portion of coal with biomass. In the present work, CLC was simulated using a mixture of coal/biomass in CLC; using their different proportions resulted in enhanced CO and CO2 fractions in the fuel reactor. The carbon capture and oxide oxygen fraction were also found to increase with the enhancement of the fuel reactor’s temperature with different proportions of coal/biomass. Increases in the carbon capture efficiency and oxide oxygen fraction of up to 98.86% and ~98%, respectively, were observed within the experimental temperature range. The simulated results of various parameters were predicted and validated with the published experimental results. The stated parameters were also predicted as a function of the different rates of solid circulation and gasification agents. Higher coal char conversion was confirmed in the fuel reactor with the presence of higher biomass concentrations.

Techno-economic analysis of a chemical looping combustion process for biogas generated from livestock farming and agro-industrial waste

Biogas is a renewable fuel that is generated from the decomposition of organic matter through the process of anaerobic digestion. The compound that provides biogas with its energy value is CH4, which accounts for between 40% and 75% of the gas, with CO2 being the other main component of this fuel. Although the biogas valorization process is carbon neutral, the overall process can become carbon negative with the application of CO2 capture technologies, such as chemical looping combustion (CLC). This work presents a techno-economic analysis of a 5 MWth plant for the generation of biogas from livestock farming and agro-industrial waste to produce electricity + heat or heat only (base cases), or for further treatment in a CLC unit (CLC cases), where the captured CO2 is converted into a raw material, e.g. for the production of greenhouse crops. Results from the comparative study of five different oxygen carriers used in CLC are also presented.The profitability of the base cases was evaluated by means of the Levelized Cost of Electricity (LCOE) and Levelized Cost of Thermal Energy (LCOTE) metrics, whereas the economic performance of the CLC cases was measured by the Levelized Cost of CO2 (LCOCO2). LCOE gave a value of €139.90/MWh for the base case, and LCOTE was €56.50/MWh for the modified base case, where biogas was combusted in a boiler to produce only heat. With regard to the CLC cases, LCOCO2 values ranged between €148.60 per tonne for a highly reactive, synthetic Cu-based oxygen carrier and €177.10 per tonne for ilmenite.Finally, by comparing the economic results obtained in this work with those found in the literature for conventional biogas production plants and greenhouse crop production processes, it can be concluded that the implementation of CLC technology in biogas plants has the potential to become a profitable and environmentally sustainable option for the valorization of organic waste because the CO2 generated in the fuel reactor of the CLC unit can be considered a marketable, high value-added product for the niche market of the greenhouse farming of horticultural crops.

Application of Aspen Plus fluidized bed reactor model for chemical Looping of synthesis gas

Chemical Looping Combustion technologies are a recent innovation with a natural ability to capture carbon dioxide. In these processes, two interconnected fluidized bed reactors are employed to achieve oxidation and reduction reactions separately. In the current study, an Aspen Plus simulation uses the specialized Fluidized Bed Reactor block to model a Fuel Reactor in which carbon monoxide and hydrogen react with hematite. This reactor block includes a hydrodynamic model that describes the solid volume fraction, particle size distribution and solids entrainment effects, and a reactor model that employs reaction kinetics for the gas–solid reactions. A comparison is performed with an established Stoichiometric Reactor approach for validation purposes, and results agree closely. Several sensitivity studies are carried out to explore the impacts of process variables on carbon dioxide generation and selected hydrodynamic parameters. For the range of conditions simulated, these studies revealed that solid volume fraction decreases with the height of the bed and with increasing superficial velocity. It is also observed that the height to diameter ratio of the fluidized bed is a key variable in sizing the reactor. Based on an analysis performed on two distributor configurations, a bubble cap is the best option to provide a smaller pressure drop. The results presented in the current work also suggest that the application of the Fluidized Bed Reactor model in Aspen Plus provides additional design insights and is a valuable alternative to the commonly used Stoichiometric Reactor approach.

Chemical Looping Combustion of Petcoke Using Two Natural Ores in a 10 kWth Continuous Pilot Plant: A Performance Comparison

Chemical looping combustion (CLC) technology has emerged as one of the most important clean fossil fuel combustion technologies, because it allows for sequestration of CO2 with a minimal increase in energy requirements and fuel demand in comparison to traditional plants. In the framework of the Chinese–European Emission-Reducing Solutions project, the core technology of the CLC process is being developed in a 3 MWth system prototype for demonstration in an operational environment using petcoke as fuel. One of the main objectives is the selection of the oxygen carrier because it will impact the design and sizing of the demonstration unit as well as the nominal power of the unit. Two minerals, ilmenite T1 and LY Mn ore, with high potential for a well-performing oxygen carrier were tested in a 10 kWth continuous pilot unit. The collected fines were analyzed by scanning electron microscopy and X-ray fluorescence analysis to characterize the compositional and morphological evolution of the particles during operation. The performance of both oxygen carriers was compared with respect to solid fuel conversion, capacity for oxygen transfer, and particle lifetime in continuous circulation. A higher methane conversion can be obtained using ilmenite, while LY Mn is better at converting petcoke. Where the reduction potential of oxygen carriers is concerned, it was observed that LY Mn ore has a high initial R0ΔX value (R0ΔX = 0.8), which leads to a shorter activation period in comparison to ilmenite T1, which requires a longer activation period to reach its full potential. LY Mn ore is however more sensitive to attrition than ilmenite, under similar operating conditions, which is a critical characteristic for large-scale deployment. Finally, key operating parameters were identified for large-scale unit operation, including fuel reactor temperature, oxygen carrier flow rate, and fuel flow rate.

Tributyl phosphate degradation and phosphorus immobilization by MnO2: Reaction condition optimization and mechanism exploration

The treatment of tributyl phosphate (TBP) extractant waste from specific industry, eg., nuclear industry, is a great challenge due to its stability and high environmental risk of phosphorus-containing species releasing. Inspired by chemical looping combustion (CLC) technology, a MnO2-assisted thermal oxidation strategy is proposed for TBP degradation and simultaneously P immobilization. Under recommended reaction conditions of 220 °C, 10 g MnO2 mL−1 TBP and 3 h reaction duration, a high P immobilization efficiency of 93.99% is achieved. Material characterization results indicate that P is mainly immobilized in the form of Mn2P2O7, which greatly reduces the environmental risk of P-containing species. TBP degradation intermediates are further identified by thermogravimetric-gas chromatography-mass spectrometry (TG-GC-MS), liquid chromatography-mass spectrometry (LC-MS) and gas chromatography-mass spectrometry (GC-MS), which facilitates understanding of reaction mechanisms as well as proposing possible pathways of TBP degradation. It is suggested that MnO2 provides essential oxygen as oxygen carrier for flameless combustion. Meantime, MnO2 reduction leads to the generation of Mn(III) species. The existence of oxygen vacancy in MnO2 also facilitates •O2- radical generation. Under flameless combustion and attacks of Mn(III) and •O2-, TBP is firstly degraded into intermediates and finally mineralized into CO2 and H2O, while P is mainly immobilized as pyrophosphate.

Enhanced performance of red mud for chemical-looping combustion of coal by the modification of transition metal oxides

Red mud has been considered a promising candidate of low-cost oxygen carriers (OCs) for chemical looping combustion (CLC) technology due to its relatively high Fe2O3 content, but it shows poor stability during long-term redox cycling. In the present work, NiO, MnO2 and CuO are used as additives to tune the components of red mud used for the CLC of coal. The results show that the addition of NiO (e.g. 15 wt%) can significantly improve the reactivity of red mud for coal combustion, but it suffers a sharp decline after a chemical looping. In the case of MnO2, it significantly improves the selectivity for coal oxidation to CO2, which yields relatively high-purity CO2 in the combustion step. The presence of CuO in the red mud oxygen carriers obviously enhances the reactivity, selectivity and redox stability. The sample with 20 wt% CuO (20Cu-RM) shows a stable carbon capture rate with a CO2 purity higher than 90% during the long-term chemical looping process. The XRD and H2-TPR characterization results for the cycled 20Cu-RM sample shows that part of Cu element was separated from CuFe2O4 spinel structure and may act as active phase for improving redox performance.

Chemical Looping Combustion: A Brief Overview

The current development of chemical looping combustion (CLC) technology is presented in this paper. This technique of energy conversion enables burning of hydrocarbon fuels with dramatically reduced CO2 emission into the atmosphere, since the inherent separation of carbon dioxide takes place directly in a combustion unit. In the beginning, the general idea of the CLC process is described, which takes advantage of solids (so-called oxygen carriers) being able to transport oxygen between combustion air and burning fuel. The main groups of oxygen carriers (OC) are characterized and compared, which are Fe-, Mn-, Cu-, Ni-, and Co-based materials. Moreover, different constructions of reactors tailored to perform the CLC process are described, including fluidized-bed reactors, swing reactors, and rotary reactors. The whole systems are based on the chemical looping concept, such as syngas CLC (SG-CLC), in situ Gasification CLC (iG-CLC), chemical looping with oxygen uncoupling (CLOU), and chemical looping reforming (CLR), are discussed as well. Finally, a comparison with other pro-CCS (carbon capture and storage) technologies is provided.

Simulation study on modification of reaction performance for ferrite oxygen carrier based on doping with K3FeO4

Developing the oxygen carriers with large oxygen carrying capacity, high reactivity, and strong cycle stability is one of the research focuses in the chemical looping combustion technology. In this study, the effect of spinel-structured K3FeO4 on the reactivity of Fe-based oxygen carrier was investigated based on the density functional theory involving the electronic structural properties such as the density of states, adsorption energy, and activation energy. The results show that when the K3FeO4 is loaded on the α-Fe2O3(001) surface, the microscopic electronic structure of α-Fe2O3(001) surface is changed, the Fe–O bond on the surface is elongated, the O-p orbital electrons transition to a higher energy level, and the electron activity of oxygen atom is improved. The energy barriers of CO reaction with the surface lattice oxygen show a decreasing trend at the three lattice oxygen sites after the loading of K3FeO4 which can improve the activity of surface oxygen atoms and make the breakage of Fe–O bond via elongation easier with less energy required. In addition, CO can bond with the more active oxygen atom in K3FeO4, and also can combine with the O2 atom to form a new C–O bond, by which CO is adsorbed on the surface in the form of bidentate carbonate that would be decomposed and released as CO2.

Numerical investigation of hydrodynamics and cluster characteristics in a chemical looping combustion system

Chemical looping combustion (CLC) technology is promising for high-efficient carbon dioxide capture with low energy penalty. Most existing CLC systems were constructed based on two fluidized bed reactors. In this work, a full-loop numerical model was established for a novel CLC system integrated with a circulating fluidized bed riser fuel reactor and a moving bed air reactor. For the fuel reactor, the radial and axial distributions of gas-solid concentration and velocities are fully investigated. It is found single-sided particle return affects radial distribution symmetry of gas-solid flows, but the influence gradually decreases with increasing reactor height. The cluster characteristics including time fraction, frequency, duration time and concentration are also investigated, and results demonstrate the particle clusters are more difficult to form and last long in the center of fuel reactor. For the air reactor, the operation performance of a tower-type reactor is compared with a common cylindrical reactor, and the cavity is not formed in the top of the tower-type reactor. For the whole system, effects of the particle diameter on pressure profiles, solid circulation stability and other flow dynamics are evaluated. Overall, the inner flow characteristics will provide fundamental guidance for the design, optimization and scale-up of the system.