1,720,961 research outputs found
An efficient composite membrane to improve the performance of PEM reversible fuel cells
Full text linkIn this study innovative composite Nafion/GO membranes are tested at different GO loading (0.5% wt., 1% wt. and 1.5% wt.) in electrolyser and fuel cell mode (Unitized reversible fuel cell). Baseline Nafion membranes were used for comparison.Water uptake (WU), ion exchange capacity (IEC), tensile strength, TGA (thermogravimetric analysis) and SEM (scanning electron microscope) analysis are discussed. The SEM revealed the inclusion of GO into the Nafion matrix while the TGA showed an increased thermal stability of the membrane attributed to the inclusion of the carbon material. Moreover, the addition of GO improves the membrane tensile strength, obtaining a maximum enhancement of nearly 90%, while reducing the elongation ratio (80% for the Nafion and 45% for the 1.5% wt. GO membrane). Water uptake increased when increasing the content of GO due to its hydrophilic nature recording the highest values for the membrane with 1.5%wt. of GO (23% against 10% for the Nafion). An increase of IEC (almost 14%) is noticed when GO content is increased. The beneficial effect of GO on the IEC can be attributed to a non-uniform distribution of GO into the Nafion matrix but needs further investigation.Both fuel cell and electrolyser polarization curves were carried out using MEAs with an active area of 9 cm2 and a thickness of 50 mu m. The temperature and the pressure were set to 20 degrees C and 1 atm respectively. Regarding fuel cell mode, the optimum loading of GO has been found to be 0.5%, registering the highest performance, 13% higher than Nafion. Regarding the electrolyser mode, the GO 0.5% wt. membrane, showed performance comparable to the Nafion. A comparison between Nafion based membranes at higher thicknesses showed that, adopting GO, it is possible to obtained similar performance with a reduced membrane thickness, keeping almost equal the performance and the average round trip efficiency (26.1% for the GO and 26.6% for the Nafion). In commercial applications such characteristics allows to strongly reduce the cost of materials. Durability and stability of the GO/Nafion membrane should be properly investigated in successive studies as such membranes are subjected to a rapid deterioration of their performance
Decarbonizing power and fuels production by chemical looping processes: Systematic review and future perspectives
No full textThe decarbonization of power and fuels production is a crucial element of the energy transition. Among several available technologies, chemical looping processes promise to be a feasible solution to support the decarbonization of large-scale industrial sectors. They involve a solid material, commonly called an oxygen carrier, that circulates between two or more reactors according to a redox process. In the reduction step, the oxygen carrier loses some its oxygen atoms by reaction with a fuel. In the oxidation step, it is oxidized back to the initial phase by an oxidizing agent such as air, steam and/or CO2. The flexibility of this process enables it to be used in diverse applications, such as: (1) fuel combustion; (2) hydrocarbon reforming; (3) solid fuels gasification, with limited energy penalties for CO2 separation and possibility of autothermal operation within the cycle. Therefore, this technology has a significant potential to contribute to the sustainable transition. This review paper aims at shedding light on a range of chemical looping progresses and to explore open questions in this field. The discussion is divided into three main chemical looping variants: combustion, reforming, and gasification. For each of these, recent progresses and challenges are highlighted by considering two scales of analysis: lab-scale and system scale. At the lab-scale, advances in materials development and process performance are discussed, while at the system scale, technical, environmental and economic analyses are presented in comparison with benchmark alternative technologies. Materials development and testing represents a crucial element hampering chemical looping development. Combination of costly and often toxic synthetic materials with natural ores is considered a promising solution that can reduce cost, increase stability and environmental compatibility. Iron oxides have several decontaminating properties and due to their low cost, large availability and high stability and appear as promising oxygen carriers. The synergistic mixing of metal oxides is also a solution to optimizing oxygen carrier properties. Different reactor configurations have been proposed with circulating fluidized beds being the most mature in terms of operational hours. Nevertheless, pressurized operation has been mainly conducted with fixed bed reactors. Techno-economic analyses indicate that chemical looping reforming can approach competitiveness with the unabated benchmark, while in power production the limit in the maximum reactor temperature is a significant drawback. An interesting application with still limited experimental and modelling research is the application of chemical looping for energy storage applications
Development of a novel carbon capture and utilization approach for syngas production based on a chemical looping cycle
No full textThe present work assesses the potential of reducing CO2 emissions associated with steel production through the introduction of a decarbonization process downstream of a steel mill eventually producing an alternative fuel/syngas. The analysed system is composed of a calcium looping process for CO2 separation followed by a chemical looping section for syngas production from CO2 and H2Os. The main units in the chemical looping cycle are: the oxidizer, where a flux of CO2 and H2Os reacts with an oxygen carrier to produce CO and H2; the air reactor, where the oxidation of the oxygen carrier is completed by the interaction with air; the reducer, where the reduced oxygen carrier is regenerated to the initial state (Fe2O3 or NiFe2O4 in the present case) through an endothermic reaction occurring at high temperatures. A MATLAB model was created to determine the molar flow rate of the components flowing through the thermochemical cycle and the thermal power associated with each unit at the operating conditions. The analysis is carried out focusing on the treatment of 1 t/h of CO2, resulting in 7.1 t/h of NiFe2O4 or 12.1 t/h of Fe2O3. The syngas at the outlet from the oxidizer reactor is composed of equimolar H2 and CO with a mass flow rate of 0.05 t/h and 0.64 t/h, respectively. A separate MATLAB model was developed to identify the experimental conditions necessary to reach fluidization of FeO particles in a lab-scale oxidizer reactor (u_mf = 0.162 m/s). Companion CFD simulations were carried out to evaluate the hydrodynamics of the lab-scale oxidizer reactor and the associated reaction kinetics (Langmuir-Hishelwood) above minimum fluidization conditions with the aim of assessing the assumptions performed in the MATLAB in terms of conversion rates. For the imposed inlet velocity conditions of the gas mixture (2.6 times above the minimum fluidization velocity) large bubbles with low frequency are observed, while full consumption of the reactant gases is achieved during the first 15 s of simulation, due to the significant reaction rate (2.6 kmol/sm^3). The results of the CFD simulation and the comparison with existing literature allow to validate the assumptions on the oxidizer conversion and the overall accuracy of the model
Municipal solid waste thermochemical conversion to substitute natural gas: comparative techno-economic analysis between updraft gasification and chemical looping
No full textA comparative techno-economic analysis has been performed on two innovative pathways for municipal solid waste (100 t/h) thermochemical processing to substitute natural gas. The first pathway is based on updraft gasification with bottom hydrogen oxy-combustion and ashes melting, the second on autothermal chemical looping hydrogen production with Fe2O3/SiC oxygen carrier. Catalytic methanation in a series of adiabatic fixed bed reactors has been implemented and substitute natural gas quality has been evaluated based on the Italian legislation. Although the updraft gasification process shows higher substitute natural gas productivity (16.3 t/h vs 13.7 t/h), better system energy efficiency (42 % vs 35 %) and energy intensity (125 vs 141 GJ/t), the levelized cost of substitute natural gas is more competitive in the chemical looping configuration due to the lower capital expenditure. Product prices of 2.26 /kg and 1.76 /kg have been calculated for updraft gasification and chemical looping, respectively, assuming 8 % discount rate, 80 % capacity factor, and 90 /MWh electricity cost. Sensitivity analyses indicate that, among other parameters, the plant capacity factor and the electric power cost have a relevant impact on the final product cost. Additionally, both pathways are shown to be economically competitive with substitute natural gas production from H2O electrolysis and CO2 capture/purchase. Finally, actions to reach competitivity with fossil natural gas for industrial uses are qualitatively discussed
On the reduction of NiFe/Al2O3 oxygen carrier in high-pressure chemical looping applications
Full text linkChemical looping represents a promising technology with various applications ranging from clean power production to alternative syngas production. In this work, two oxygen carriers with different Ni loadings (4.3% wt. and 12% wt.) and similar Fe loadings (9.9% wt. and 8.5% wt.) are synthesized through a co-precipitation/impregnation route and tested in two thermogravimetric analyzers. Firstly, the effect of temperature (700-900 degrees C) on the oxygen transport capacity and reduction conversion of both materials is assessed at ambient pressure (0.5 nl/min with 20% H2/N2). The influence of material loading is also studied, and it is shown that higher Ni loadings provide a significant improvement in material activity. A complete reduction conversion is achieved at 900 degrees C and ambient pressure. At high pressure (10-20 bar), tests are carried out in a temperature range of 700-850 degrees C. The effect of flow rate (2 nl/min to 6 nl/min with 50% H2/N2) is first assessed to prevent external mass transfer limitations. Higher total pressures have a negative effect on reduction kinetics, while higher Ni loadings demonstrate increased final reduction con-version also at high pressure, reaching about 75% conversion after 20 min. The long-term cyclability of the material is also investigated both at low (100 cycles) and high pressure (80 cycles) conditions and a conversion gain is observed throughout the cycles in both cases. No changes in the material microstructure are observed after 80 high-pressure cycles.(c) 2023 The Author(s). Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY license (http://creativecommons.org/ licenses/by/4.0/)
Experimental investigation of thermochemical syngas production in a scrap iron-based oxidizer reactor for industrial decarbonisation
No full textThe syngas production performance of scrap iron reacting with carbon dioxide and water steam was assessed under different operating conditions in a fixed bed oxidizer reactor. The syngas generation step is part of a novel process scheme encompassing the reutilization of iron scrap from steelmaking and the combined splitting of industrially captured carbon dioxide and steam into a syngas. At 1050 degrees C, a maximum volume percentage of 37 % carbon monoxide was detected in the product gas with the injection of 1 NL/min carbon dioxide. The carbon dioxide conversion was confirmed to be promoted by temperature. Subsequently, combined tests with carbon dioxide and water steam were carried out to assess the production and quality of the syngas (H2 and CO) by varying the reactants total flow rate, the iron bed mass and the reactants molar ratio. By decreasing the total reactants flow rate, the reactants splitting process was promoted and below a certain flow rate carbon dioxide splitting prevailed on that of water steam. By increasing the H2Ov/CO2 molar ratio, the splitting was enhanced for both species. In particular, for the tested flow rate the water splitting increased by 10% compared to 3.5% of the CO2 splitting. This indicated that a high H2Ov/CO2 ratio optimizes syngas production in the designed system. Finally, with H2Ov/CO2 = 6 and the optimal thermochemical syngas composition was achieved, including 41 % H2 and 12.1 % CO, being the remaining part constituted by CO2 when computed on a dry basis
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
METHANOL PRODUCTION BY A CHEMICAL LOOPING CYCLE USING BLAST FURNACE GASES
No full textSteel mills are responsible for high direct CO2 emissions. To mitigate climate changes, carbon capture and utilization strategies (CCU) aiming at neutralizing such emissions should be employed. Currently, the most widespread technologies for carbon capture (CC) are represented by chemical/physical absorption, adsorption, membrane separation, calcium looping cycles (CaL). One promising pathway for carbon capture and utilization (CCU) is represented by the coupling of chemical looping cycles with liquid fuel synthesis processes, such as methanol synthesis. Methanol is an interesting low-cost fuel for gas turbines engines, due to its potential reduction of NOX and particulate emissions along with the absence of SO2 emissions. Furthermore, being one promising solution to store excess power production from renewables, its availability is expected to increase significantly with the years. In this work, methanol production from the syngas generated by a three-reactors chemical looping process (TRCL) is investigated by mass and energy balances. The TRCL cycle is composed by a reducer reactor, where Fe2O3 is reduced to FeO by an endothermic reaction occurring at high temperatures and promoted by biogenic carbon; an oxidizer reactor, where FeO reacts exothermically with a gas stream composed of CO2 and H2O in order to produce a syngas (CO + H2); a fuel reactor, where the non-reacted FeO is oxidized to Fe3O4 and subsequently the whole amount of Fe3O4 is regenerated to Fe2O3 by the interaction with ambient air. The produced syngas is then sent to a methanol synthesis plant modelled with the Aspen Plus software. Several syngas compositions, deriving from different oxidizer’s inlet CO2/H2O molar fractions, are investigated and the resulting methanol production rates are compared. A WGS unit is located at the plant inlet in order to increase the H2 molar fraction in the feed stream. Results indicate that methanol production is almost equal in all investigated configuration and amounts to about 0.35 ton/h. From an energy standpoint, global heating/cooling duty is almost equal in all cases, while the electric power required is greater for higher hydrogen contents in the syngas. However, the case with high H2 content (0.75 in molar fraction) is characterized by the greatest methanol yield (12.6%), carbon efficiency (23%) and a limited feed over recirculation ratio, thus representing the most indicated configuration among the investigated one
Assessment of a multistep revamping methodology for cleaner steel production
No full textA novel revamping methodology is proposed to achieve the decarbonization of currently operating integrated steel mills (step 0) without reducing steel production levels. Such a method encompasses four successive steps involving cleaner and more energy efficient technological pathways for steel production.
The decarbonization strategy is reported: step 1, partial replacement of coke with recycled plastic in a conventional Blast Furnace – Basic Oxygen Furnace (BF-BOF) plant; step 2, implementation of a Direct Reduction-Electric Arc Furnace (DR-EAF) line combined with the BF-BOF plant; step 3, complete shut-down of the BF-BOF line and full operation of two DR-EAF lines fed by CH4; step 4, installation of an alkaline electrolyzer and use of 100% green H2 as a reducing agent in the DR plants.
The gradual replacement of the integrated steel mill with DR-EAF lines causes a progressive drop in CO2 emissions, ranging from 8.5 Mt/y at step 0 to a minimum of 0.68 Mt/y at step 4 (92% decrease).
Coke replacement with recycled plastic in the blast furnace in step 1 leads to a slight decrease in CO2 emissions without altering the structural layout of the plant. In step 2, the combined operation of BF-BOF and DR-EAF lines determines a 39% decrease in CO2 emission compared to the initial configuration, while keeping total steel production constant. Step 3 involves two DR-EAF lines fed by CH4 and reduces the CO2 emissions by 75% compared to the initial configuration. The operation of two DR-EAF lines increases the electricity consumption, especially when 100% green H2 is involved as a reducing agent in step 4. By increasing the scrap mass fraction in the EAFs of step 4, both electricity and H2 demands of the DR plant are expected to decrease, while the CO2 emission levels remain almost unchanged, leading to about 92% total CO2 emissions reduction compared to the initial configuration (provided that green electricity is used). By assuming an initial 10% scrap mass fraction at the EAFs inlet of step 4, the demand of green hydrogen is significant, thus requiring the installation of a 1.42 GW electrolyzer. The capital expenditure (CAPEX) estimated upon completion of the revamping methodology amounts to approximately 2.97 B€. The transition towards a full decarbonization of steel production technologies is demonstrated to be technically feasible, though strictly dependent upon the large availability of low emissions electric power and scrap material
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