Looping System Research Articles

Towards cleaner energy: An innovative model to minimize NOx emissions in chemical looping and CO2 capture technologies

The urgent global challenges of climate change and environmental issues have catalyzed the development of CO2-capture-ready technologies incorporating fluidization, such as fluidized bed (FB) and circulating fluidized bed (CFB) combustion under oxy-fuel conditions, chemical looping combustion (CLC), chemical looping with oxygen uncoupling (CLOU), in-situ gasification chemical looping combustion (iG-CLC), and calcium (or carbonate) looping (CaL) systems. While these technologies have the potential to reduce CO2 emissions significantly, the persistent presence of nitrogen oxides (NOx = NO + NO2) as pollutants remains a critical environmental concern.This paper introduces a comprehensive fuzzy logic-based model for predicting NOx emissions (FuzzyNOx model) from solid fuel combustion in fluidized beds of chemical looping systems. This innovative model takes into account a wide range of operating parameters, including fuel type, fuel particle size, fuel moisture content, air/fuel ratio, and temperature. It also explores advanced coal and biomass combustion modes, including air-firing, oxyfuel, iG-CLC, and CLOU. Furthermore, it delves into the intricacies of two distinct facilities: the 5 kWth dual-fluidized bed Chemical-Looping-Combustion of Solid-Fuels (DFB-CLC-SF) facility at Czestochowa University of Technology, Poland, and the calcium looping dual-fluidized bed (CaL DFB) facility at Niigata University, Japan.Bituminous coal, semi-anthracite, and wood chips are utilized as fuels. Moreover, three various oxygen carriers (OCs) for chemical looping combustion were employed, namely ilmenite, copper oxide (60 % wt.) supported by carbonate waste from ore flotation, and copper oxide (60 % wt.) supported by ilmenite (20 % wt.) and fly ash. Bituminous coal, semi-anthracite, and wood chips are utilized as fuels.The developed knowledge-based fuzzyNOx model allows the optimization of operating parameters to reduce NOx emissions from CO2 capture technologies.

Improving Heat Efficiency of Aniline Production Process by Modifying Heat Transfer Fluid Looping System in Heating and Cooling Process

The nitrobenzene hydrogenation process is a highly exothermic reaction which causes the product temperature will increase and then needs to be cooled down with a heat exchanger. The modification process is needed to improve the heat efficiency of the nitrobenzene hydrogenation process by utilizing the heat from reactor product. Heat transfer fluid is used as a medium of heat transfer for both heating and cooling, so that will create a looping heat transfer process. The looping system of heat transfer fluid receives heat from reactor product and then reuses the heat to reheat the recycled hydrogen and for other utilities, so additional energy for these processes is not required. The process modification was simulated using Aspen HYSYS and the comparison of heat efficiency between the basic and the modified process is calculated using the net-energy formula. The results obtained that the net-energy (NE) value for both basic and modified process is 96,714,359.832 kJ/h and 9.869 kJ/h. This shows that the modified process has better energy efficiency compared to the basic process as the net-energy value is closer to zero. Therefore, this modification increases the heat efficiency of the aniline production through nitrobenzene hydrogenation process. Copyright © 2024 by Authors, Published by Universitas Diponegoro and BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Mechanistic study of chemical looping partial oxidation of methane over Ce2(SO4)3/MgO with CoO modification

Chemical looping partial oxidation of methane (CLPOM) to syngas provides an exceptional opportunity for methane utilization. However, it is still urgent to obtain efficient oxygen carrier (OC) and clarify its microscopic mechanism. In this work, CoO and MgO modified Ce2(SO4)3 OC are optimized based on various preparation methods and different CoO and Ce2(SO4)3 doping amount. Considering the conversion rate (XCH4), selectivities of CO (SCO) and H2 (SH2), H2/CO molar ratio, when the doping amount of CoO, Ce2(SO4)3 and MgO is 20 wt%, 30 wt% and 50 wt% respectively, the OC prepared by mechanical ball milling method has a better thermodynamic and kinetic properties in chemical looping reaction. Compared with literature, this OC has a larger XCH4. In multiple cycles, XCH4 is still higher than 90%, SCO and SH2 remain above 95%. Density functional theory calculation reveal that the Co doping reduces the energy barrier (Eb) of rate-limiting step by 24.3% and lowers the migration Eb of lattice oxygen by 78.2%. The OC with oxygen vacancy can further reduce the Eb of rate-limiting step, but the Eb basically remains unchanged when the oxygen vacancy (Ov) concentration is greater than 1.96%. Because of the high Eb of CO2 formation and low Eb of syngas formation, the syngas demonstrates high selectivity and does not produce CO2 in experiment. Meanwhile, the doping of CoO and MgO reduces carbon deposition, refines the nano-particles of OC, increases the specific surface area (SSA), and enhances resistance to sintering and aggregation. The unique pore structure also provides a favorable microenvironment for the reaction. These findings demonstrate that CoO and MgO modified Ce2(SO4)3 OC have the potential for application in CLPOM, and these basic insights can also be applied to other chemical looping systems.

A nickel-modified perovskite-supported iron oxide oxygen carrier for chemical looping dry reforming of methane for syngas production

The chemical looping dry reforming of methane (CLDRM) process, which converts methane and carbon dioxide into syngas, is an environmentally friendly greenhouse gas utilization strategy. In this work, it is demonstrated that a nickel-modified perovskite-supported iron-based oxygen carrier (Ni-Fe2O3/La0.8Sr0.2FeO3) significantly enhances the reactivity of CLDRM in the temperature range of 770–800 °C while maintaining high CO selectivity and oxygen capacity, as well as good carbon deposition resistance. With the addition of nickel, the methane conversion is 52 % higher than that without nickel at 800 °C. Rational coupling of the oxygen carrier components achieves over 99 % CO selectivity. 160 consecutive isothermal cycles confirm the outstanding stability of Ni-Fe2O3/La0.8Sr0.2FeO3. Based on the experimental results and characterizations, the evolution scheme and synergistic effects between the components of the Ni-Fe2O3/La0.8Sr0.2FeO3 oxygen carrier for CLDRM reaction are proposed. The results provide a pathway for oxygen carrier design to decrease the reforming temperature while maintaining excellent reaction performance in iron-based chemical looping systems.

Carbonation kinetics of calcium-based solids at the centimeter scale for moving bed applications

Countercurrent moving bed reactors were recently proposed to capture CO2 from dispersed sources using calcium materials. Due to disparities with Calcium Looping systems in particle size and solids residence times, additional investigations are required to identify reaction controlling steps and kinetic parameters. This study examines the carbonation reaction of centimeter-scale CaO and Ca(OH)2-derived-CaO pebbles under conditions relevant to moving bed applications. To this end, the impact of carbonation temperature (450–650 °C) and CO2 concentration in the inlet gas (2.5–7.5 %v) was evaluated in TGA, employing particle sizes from 0.26 to 1.65 cm. The obtained results were fitted to a shrinking core model where the rate-determining step is CO2 diffusion through the gas volume that occupies the pores of the solid CaCO3-rich layer formed during carbonation. The experimental findings can be predicted using the effective porosity of the materials as the sole fitting parameter.

Design, optimization, and technical evaluation of coking dry gas chemical looping hydrogen generation systems coupled with solid oxide fuel cell

Coking dry gas from delayed coking processes is rich in light hydrocarbons, making it a comparative ideal feedstock for hydrogen production. Current steam reforming processes have the disadvantages of high energy consumption and carbon emissions, whereas chemical looping hydrogen generation produces high-purity hydrogen with inherent carbon capture and a low energy penalty. Therefore, this study proposes a coking dry gas chemical looping process for hydrogen production, considering two schemes (external-heating and self-heating) and optimizes key parameters of the systems in detail. The optimal molar ratios of the oxygen carrier, steam, and air to coking dry gas for the externally heated and self-heated schemes were 8.62, 4.90, 2.27 and 8.62, 3.78, 4.07, respectively. The energy efficiencies of the two systems can reach 76.55% and 77.93% with carbon capture rates of 76.29% and 100%, 3.26% and 5.13% higher than efficiency of the steam reforming system. The self-heated system had the highest hydrogen production of 2.67 kmol/kmol coking dry gas. Based on a self-heated hydrogen system, a chemical looping hydrogen generation system was coupled with a solid oxide fuel cell. This integrated system achieved the better power generation performance with an anode recycling ratio of about 0.7. The net electrical efficiency of the system was 58.79%, which is 3.34% higher than that of a steam reforming system coupled with a solid oxide fuel cell. The results reveal that the chemical looping systems are suitable for the clean utilization of dry gas and provide a strategy for efficient hydrogen production and power generation.

Alkali desorption from ilmenite oxygen carrier particles used in biomass combustion

Oxygen-carrying fluidized bed materials are increasingly used in novel technologies for carbon capture and storage, and to improve the efficiency of fuel conversion processes. Potassium- and sodium-containing compounds are released during biomass combustion and may have both negative and positive effects on conversion processes. Ilmenite is an important oxygen carrier material with the ability to capture alkali in the form of titanates. This is a desirable property since it may reduce detrimental alkali effects including fouling, corrosion, and fluidized bed agglomeration. This study investigates the interactions of alkali-containing compounds with ilmenite particles previously used in an industrial scale (115 MWth) oxygen carrier aided combustion system. The ilmenite samples were exposed to temperatures up to 1000 °C under inert and oxidizing conditions while the alkali release kinetics were characterized using online alkali monitoring. Alkali desorption occurs between 630 and 800 °C, which is attributed to loosely bound alkali at or near the surface of the particles. Extensive alkali release is observed above 900 °C and proceeds during extended time periods at 1000 °C. The release above 900 °C is more pronounced under oxidizing conditions and approximately 9.1 and 3.2 wt% of the alkali content is emitted from the ilmenite samples in high and low oxygen activity, respectively. Detailed material analyses using scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy were conducted before and after temperature treatment, which revealed that the concentrations of potassium, sodium and chlorine decrease at the outermost surface of the ilmenite particles during temperature treatment, and Cl is depleted to a deeper level in oxidizing conditions compared to inert. The implications for ilmenite-ash interactions, oxygen carrier aided combustion and chemical looping systems are discussed.

Fate of ilmenite as oxygen carrier during 1 MWth chemical looping gasification of biogenic residues

Chemical looping gasification (CLG) is a novel gasification technology, allowing for the efficient conversion of different solid feedstocks (e.g. biogenic residues) into a high-calorific syngas. As in any chemical looping technology, the oxygen carrier (OC), transporting heat and oxygen from the air to the fuel reactor, is crucial in attaining high process efficiencies. To investigate the fate of the OC during CLG in an industrial environment, ilmenite samples, collected during >400 hours of chemical operation in 1 MWth scale using three different biomass feedstocks, were analyzed using different lab techniques. In doing so, changes in OC particle morphology and composition induced by CLG operation were determined. Moreover, the most important physical and chemical characteristics of the utilized OC were measured. The ensuing dataset allowed for an in-depth evaluation of the CLG technology in semi-industrial scale in terms of OC lifetime and durability. It was found that in the absence of agglomeration, the cycled OC exhibits an oxygen transport capacity of 2.6 wt.-%, a particle density of 3400 kg/m3 and particle diameters between 60 and 250 µm in steady-state conditions. Moreover, it was found that OC loss via particle attrition determines the lifetime of the OC inside the 1 MWth CLG system. On the other hand, feedstock-related agglomeration, observed during CLG operation with wheat straw, was shown to impede OC circulation between AR and FR and thus prevent efficient CLG operation. In summary, the present study thus not only highlights that generally long-term CLG operation in industry-like conditions is feasible, but also provides important insights into measures to improve OC lifetime and durability inside an industrial chemical looping system, such as an optimization of cyclone efficiency or tailored pre-treatment of the utilized feedstock.

Coal fly ash-bound limestone-derived sorbent pellets for high-temperature CO2 capture

Poor CO2 capture stability and serious elutriation are the issues commonly occur when limestone circulating in the fluidized bed-based Calcium Looping (CaL) system. Hence, three types of coal fly ash-bound (CFA-bound) limestone-derived sorbents were synthesized via mixing the limestone, calcined lime and hydrated lime with coal fly ash, respectively. The generated ternary Ca-Al-O and Ca-Si-O phases offer structural stability for CFA-bound limestone-derived sorbents and improve their cyclic CO2 capture performance. Moreover, extrusion-spheronization method was adopted to produce CFA-bound limestone and hydrated lime sorbent pellets to synergistically enhance cyclic CO2 capture capability and mechanical properties. It is found that hydrated lime is superior to limestone as the calcium precursor to prepare CaO-based sorbent pellets due to its desirable pore structure and high binding force. Therefore, the CFA-bound hydrated lime pellets containing 15 wt % of fly ash (HL/CFA15-P) exhibits a high carbonation conversion of 40 % after 17 cycles, which is nearly 1.4 times that of limestone pellets. The discrepancy on carbonation conversion between the two sorbent pellets is enlarged to ∼1.6 times after 100 cycles, which is calculated using a semi-empirical equation. Moreover, HL/CFA15-P exhibits outstanding mechanical property, whose compressive strength reaches 6±1.7 MPa, which is comparable to the cement-bound CaO-based sorbent pellets.

Chemical looping process for hydrogen and electricity co-production: Design and operational consideration for moving-bed-reducer-based circulating fluidized bed systems

Chemical looping is an economically advantageous technology for reducing carbon emission from energy, fuels, and chemicals conversion systems utilizing a variety of feedstocks including fossil fuels, renewable materials, and industrial and municipal wastes. Its development relies on two key areas of core competency, i.e., metal oxide reaction engineering, and particle science and technology. The reaction kinetics and the transport phenomena in chemical looping reactors are intrinsically twined with the specific system operational conditions, configuration, and their integration. The optimal design and successful operation of chemical looping systems necessitate a comprehensive consideration of both the reaction rates and multiphase flow characteristics within each reactor. In this article, we analyze the impact of particle hydrodynamic characteristics on optimizing the operational conditions of a syngas-fueled chemical looping (SCL) process, which aims to co-produce hydrogen and electricity. Using this SCL process as an illustrative example, we examine how the particle hydrodynamics influence the system performance and efficiency. The outcome of these effects on the system performance is discussed.

Biomass gasification: Sub-pilot operation of >600 h with extensive tar cracking property and high purity syngas production at H2:CO ratio ∼2 using moving bed redox looping technology

Commercializing biomass-based technologies as an alternative to fossil fuels is necessary for a sustainable future. This study proposes a robust Biomass to Syngas (BTS) chemical looping system to gasify biomass into syngas for a range of downstream applications, with focus on liquid fuel production. The system has been demonstrated on a sub-pilot scale cumulatively for over 600 h, proving the technology's commercial viability. Pelletized corn cob, woody pellets, and unpelletized loose corn cob, were successfully tested, proving the robusticity of the process to handle untreated biomass with batch variation. Tar analysis shows that moving bed reducer can reduce the tar concentration to 0.5 g/m3, owing to uniform residence time, high temperature, and catalytic activity of oxygen carrier, while injection of steam as an enhancer gas increases carbon conversion by char gasification. A variable syngas quality with an H2/CO ratio of ∼2 and a syngas purity greater >70% was achieved, making this syngas suitable for the generation of liquid fuels via Fischer-Tropsch synthesis. The biomass requirement for a chemical looping system decreases by 13.9% over the conventional biomass gasifier for generating the same amount of liquid fuels. Heat integration suggests integrating biomass drying with the combustor exhaust air for process authothermicity.

Synthesis of dark Li4−3xFexSiO4 for simultaneous direct solar thermal conversion and durable thermochemical energy storage

Thermochemical energy storage (TCES) technique based on Li4SiO4 looping system probably offers a mid-term if not near-term solution to the next generation concentrated solar power (CSP) plants featured with excellent stability and low regeneration temperature. However, traditional Li4SiO4 material commonly possesses dense microstructure with white superficial color, thus resulting in the unsatisfactory energy storage density and considerable radiant heat loss. This study involved doping Fe into Li4SiO4 to synthesize dark Li4−3xFexSiO4 heat carriers for thermochemical energy storage (TCES). By replacing Li+ with Fe3+, vacancies were created in the crystal lattice structure, resulting in the high energy storage density (456.14 kJ/kg) as well as the excellent cyclic long-term stability of I-Li3.7Fe0.1SiO4. Furthermore, Fe-doped dark Li4SiO4 showed obviously enhanced direct solar absorptance with the average solar absorptance of I-Li3.7Fe0.1SiO4 being 10 times higher than that of the undoped Li4SiO4. Such obvious enhancement in solar absorptance was attributed to the darkening superficial color through Fe doping. In summary, the synthesized Fe-doped Li4SiO4 heat carrier solved the encountered problems of traditional energy storage materials and exhibited as a promising heat carrier for practical thermochemical energy storage.

Waste2Watts: Techno-Economic Feasibility of Biogas-Fed SOFC Power System Integrated with Biogas Cleaning Unit and Carbon Capture Technologies

As a promising power generation technology, the solid oxide fuel cell (SOFC) system demonstrates high electrical efficiency and overall efficiency in cogeneration mode. Operating at high temperatures (> 680 ˚C), SOFCs cogenerate high-quality heat and can be integrated with different industry facilities. Furthermore, SOFC technology demonstrates high fuel tolerance, including hydrogen, natural gas, ammonia, LPG, etc. Unlike other fuel cell technologies, SOFC systems can also tolerate impurities in the fuel, e.g., CO2, N2 or even a small amount of O2. Besides, the compact system configuration makes SOFC system of great potential in the decentralized application.In the context of the Paris Agreement, more and more solutions to replace fossil fuels have been proposed, where biogas is considered as one promising alternative. Biogas generally contains several impurities, making its application limited in the fuel cell technology field. Removing all the impurities and making it compatible for all the fuel cell technologies would be expensive. Whereas, since SOFC has high tolerance in fuel impurities, keeping certain harmful impurities under safe thresholds with a biogas cleaning unit and injecting the purified biogas into the SOFC system will be less costly. In this case, a biogas-fed SOFC system integrated with a biogas cleaning unit can be considered as a promising renewable technology by avoiding fossil fuel use and converting biowaste into electricity and heat.Although biogas is produced from a renewable source, its use in SOFCs still generates CO2 emissions when it is fed with biogas. To realize carbon neutrality or even being carbon negative in a biogas-fed SOFC system, carbon capture (CC) technology is introduced to meet the net-zero carbon emission target in 2050. One conventional carbon capture storage (CCS) technology is the calcium looping system, which uses CaO/CaCO3 in a carbonation-calcination loop to separate and capture the CO2 from the exhaust gas. This type of technology is quite mature for large-scale applications and has been widely used in thermal power plants for the desulfurization and denitrification of exhaust. Novel technology based on sodium carbonate solution is capable of not only carbon capture, but also biogas cleaning. For the carbon capture utilization (CCU) technology, the Fischer-Tropsch (FT) synthesis can convert CO2 with hydrogen into syngas via electrochemical or thermochemical catalytically driven processes.Focusing on the decentralized power system, small-scale biogas-fed SOFC system integrated with a biogas cleaning unit and CC system should be considered with capacity ranging from 20 kW to 200 kW. As a cogeneration system, the integration should not be limited to mass exchange. The electricity consumed by the biogas cleaning unit and CC system can be fulfilled via the SOFC system. Based on the system temperature pattern, a bigger heat exchange network can be formulated between three parts, which can avoid extra heat input. In this case, the optimality of overall system efficiency and revenue can be achieved.In this study, one biogas-fed SOFC power system is proposed with capacity ranging from 20 kW to 200 kW. The techno-economic evaluation is carried out in two cases, with or without heat and electrical integration. Meanwhile, in different cases, the techno-economic analysis of different biogas cleaning technologies and CC technologies will be performed as well. Two operation modes of the SOFC system are considered: (1) hot recirculation mixed before the reformer, (2) cold recirculation mixed before the reformer. Without the biogas cleaning unit and the CC technology, the biogas-fed SOFC system's electrical efficiency can exceed 65% as is demonstrated in Figure 1. Furthermore, Detailed techno-economic analysis has been carried out by three indicators: capital expenditure (CAPEX), operating expenditure (OPEX) and levelized cost of electricity (LCOE). Integrated with biogas cleaning unit via only mass exchange, the LCOE of the biogas-fed system without CC technology ranges from around 0.11 EUR/kWh (20 kW) to 0.085 EUR/kWh (200 kW). The cost breakdown is shown in Figure 2(a). Based on the SOFC system techno-economic analysis, different CC technologies are added and compared. When the conventional CC technologies like Calcium looping (CaL) and Fischer-Tropsch (FT) synthesis are scaled down to 20-200 kW and applied, unaffordable LCOE prices (0.65 EUR/kWh for CaL and 5 EUR/kWh for FT) indicate that these large-scale conventional technologies are not feasible for our cases. However, a novel technology based on Sodium carbonate looping with 97% CC efficiency is rather promising and shows much lower cost. As is indicated in Figure 2(b), the LCOE cost of the whole system is only around 0.151 EUR/kWh at 200 kW system capacity, indicating that it is a techno-economically feasible solution for a carbon-neutral biogas-fed SOFC system. Figure 1

A novel moving bed chemical looping process with integration of combustor heat exchangers for hydrogen production: Process simulation and techno-economic analysis

In this study, using natural gas as the feedstock, a new scheme – a chemical looping combustion system with a moving bed reducer, coupled with the steam methane reforming (MCLC-SMR), is proposed and simulated for hydrogen production. This suggested process configuration is compared with other hydrogen production systems including the fluidized bed chemical looping combustion system coupled with the steam methane reforming (FCLC-SMR), the chemical looping partial oxidation system combined with the water-gas-shift reaction (CLPO-WGS), the 3-reactor chemical looping system for hydrogen generation (CLHG-3R), the conventional steam methane reforming (SMR) and auto-thermal reforming (ATR) systems with CO2 capture. The simulation results indicate that the particle circulation rate in MCLC-SMR is 64% less than in FCLC-SMR. MCLC-SMR also shows the best system performance regarding cold gas efficiency (79%) and effective thermal efficiency (75%). The economic assessment indicates that MCLC-SMR can achieve the lowest levelized cost of hydrogen (LCOH) of $1.34/kg at 30 ton/hr H2 production capacity, and CLHG-3R can achieve the lowest LCOH of $2.06/kg at 1 ton/hr H2 production capacity among the six hydrogen production methods. At 30 ton/hr H2 production capacity, the chemical looping reactors in MCLC-SMR are 37% cheaper than in FCLC-SMR. The sensitivity analysis also indicates that MCLC-SMR remains the most economical hydrogen production method over a wide range of price parameters (the prices of particles, chemical looping reactors, natural gas, and electricity).

Particles attrition of binary mixtures in the coal-fueled chemical looping system based on fluidized bed

In this work, a reactive air jet attrition device with auto-recording and collection of elutriated fines was developed. Results established insights into the physiochemical interaction and further correlated attrition behaviors between char and oxygen carriers under various operation modes. The attrition rate increased by over 110% upon the introduced CO2, which brought in the significant effect of thermochemical stress, similarly in effects of the increased char addition ratio and the decreased sizes of char or hematite in different extents. For the char-hematite co-attrition process, the elutriated carbon loss of char with poor mechanical strength was found to be over 10%, while the reactive iron loss of hematite was found to be 6.3%, and was enriched in elutriated fines. The reaction-derived thermochemical stress and the collision-derived mechanical stress jointly controls the particle attrition during the cyclic transformation of oxygen carrier particles in coal-fueled chemical looping fluidization, especially significant in its reduction stage.

Integration of calcium looping and calcium hydroxide thermochemical systems for energy storage and power production in concentrating solar power plants

Energy storage is a key factor in the development of renewables-based electrical power systems. In recent years, the thermochemical energy storage system based on calcium-looping has emerged as an alternative to molten salts for energy storage in high-temperature concentrated solar power plants. This technology still presents some challenges that could be solved by integrating the thermochemical energy storage system based on calcium hydroxide. This work studies a novel concentrated solar power system integrating calcium-looping and calcium hydroxide thermochemical energy storage systems. The results show that the combined use of hydration-dehydration cycles in the calcination-carbonation processes of the calcium looping for energy storage could partially solve the issue related to the multicyclic deactivation of calcium oxide. The improvement in the conversion of calcium oxide during carbonation is demonstrated experimentally when hydration-dehydration cycles are combined. Numerical simulations demonstrate the technical feasibility of the integrated process, with efficiencies ranging between 38-46%, improved with the increase in calcium oxide conversion in the carbonator, showing the potential of the proposed integration.

Conversion of Catalytic Coke Into Synthetic Gas From A Fluid Catalytic Cracking (FCC) Process Using A Chemical Looping System And Methods Related Thereto

Conversion of Catalytic Coke Into Synthetic Gas From A Fluid Catalytic Cracking (FCC) Process Using A Chemical Looping System And Methods Related Thereto

Co3O4-CeO2 for enhanced syngas by low-temperature methane conversion with CO2 utilization via a catalytic chemical looping process

Fabricating effective transition metal-based oxygen carriers (OCs) in a low-temperature methane chemical looping conversion is of considerable importance but remains challenging. Herein, a series of Co3O4-CeO2 metal oxides were synthesized and used as OCs in a low-temperature methane conversion with CO2 utilization via chemical looping systems. Co3O4/CeO2–3 (Co/Ce ratios =7/3) showed the better performance with CH4 conversion above 70%, the highest hydrogen yield and CH4 conversion up to 55.73 mmol/g and 94.09% at 700 °C. The enhancement on the performance of Co3O4/CeO2–3 for hydrogen production is attributed to the interaction between Co3O4 and CeO2 particles at the interfaces, which could cause charge redistribution. Compared to pristine Co3O4, this structure endows Co3O4-CeO2 with higher CH4 conversion performance. Moreover, the resulting Co0 in the reduced OCs is beneficial for catalytic methane decomposition toward C and H2, followed by C gasification into CO during CO2 atmosphere with CO2 conversion as high as 81%. In the proposed chemical looping processes, catalytic methane decomposition step is active for hydrogen production, coupling with CO2 conversion toward CO to adjust the H2/CO ratio of syngas.

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.

Interactions between potassium ashes and oxygen carriers based on natural and waste materials at different initial oxidation states

AbstractOne of the most essential features of an oxygen carrier is its ability to be oxidized and reduced in order to transfer oxygen in a chemical looping system. A highly reduced oxygen carrier can experience multiple performance issues, such as decreased reactivity, agglomeration, and defluidization. This is crucial for processes that require limited oxygen transfer from the air reactor to the fuel reactor. Meanwhile, biomasses as environmentally friendly fuel options contain ashes, which would inevitably react with oxygen carriers and exacerbate the performance issues. To mimic the interactions between a highly reduced oxygen carrier and biomass ash compounds, four iron‐based oxygen carriers, based on natural ores and waste materials, and three potassium salts, K2CO3, KH2PO4, and K2SO4, were investigated in a tubular reactor under an atmosphere consisting of 2.5% H2 and 10% steam in Ar and N2 at 900°C for 3 h. The results from the X‐ray diffraction (XRD) material analysis showed that both initially fully oxidized and highly reduced materials reach the same oxidation state after the experiment. Based on the scanning electron microscopy coupled with energy dispersive X‐ray spectroscopy results, K from K2CO3 and K2SO4 diffuses in the oxygen carrier particles, while K from KH2PO4 always forms a distinct layer around the particles. The initial oxidation state of an oxygen carrier surface affects the interactions with the potassium salt only to minor extents. Thus, the final state of the material and its performance in a large‐scale process are only occasionally and mildly affected by its initial oxidation state. © 2023 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.