Thermodynamic assessment of non-catalytic Ceria for syngas production by methane reduction and CO2 + H2O oxidation

Chemical looping syngas production is a two-step redox cycle with oxygen carriers (metal oxides) circulating between two interconnected reactors. In this paper, the performance of pure CeO2/Ce2O3 redox pair was investigated for low-temperature syngas production via methane reduction together with identification of optimal ideal operating conditions. Comprehensive thermodynamic analysis for methane reduction and water and CO2 splitting was performed through process simulation by Gibbs free energy minimization in ASPEN Plus®. The reduction reactor was studied by varying the CH4/CeO2 molar ratio between 0.4 and 4 along with the temperature from 500 to 1000 °C. In the oxidation reactor, steam and carbon dioxide mixture oxidized the reduced metal back to CeO2, while producing simultaneous streams of CO and H2 respectively. Within the oxidation reactor, the flow and composition of the mixture gas were varied, together with reactor temperature between 500 and 1000 °C. The results indicate that the maximum CH4 conversion in the reduction reactor is achieved between 900 and 950 °C with CH4/CeO2 ratio of 0.7–0.8, while, for the oxidation reactor, the optimal condition can vary between 600 and 900 °C based on the requirement of the final product output (H2/CO). The system efficiency was around 62% for isothermal operations at 900 °C and complete redox reaction of the metal oxide.Postprint (published version

System efficiency analysis of dual interconnected bubbling fluidized bed reactors for solar fuel production

Chemical looping syngas production is a two-step syngas fuel production process that produces CO and H 2 . The process is composed of two fluidized bed reactors (oxidation reaction and reduction reactor), oxygen carriers (metal oxides) circulating between the two reactors. A comprehensive model is developed to simulate the chemical looping water and carbon dioxide splitting in a dual fluidized bed reactors interconnected with redox cycling between these two reactors through metal oxides (non-stoichiometric ceria). An extensive FORTRAN subroutine is developed and hooked into Aspen plus V8.8 to appropriately model the complexities of the bubbling fluidized bed reactor including the reaction kinetics. The model developed has been validated for its hydrodynamics and kinetics level and individual correlation was quantified for its validity. The reduction reactor is maintained between the temperatures 1300-1500°C. The heat to attain this high temperature can be achieved with solar beam down tower. The oxidation reactor is supplied with a mixture of CO 2 and H 2 O with different mixture composition combining 60% and remaining N 2 . The oxidation reactor temperature is varied between 700-1000°C to identify the maximum efficiency achieved. It is found that the maximum efficiency achieved is 67.4% corresponding to highest temperature difference between the reactors.Preprin

Simulation of two-step redox recycling of non-stoichiometric ceria with thermochemical dissociation of CO 2 /H 2 O in moving bed reactors – Part I: Model development with redox kinetics and sensitivity analysis

Chemical looping syngas production is a two-step process that produces CO and H2 from water and CO2 splitting. This is performed by exploiting a metal oxide as oxygen carrier material, which is thermally reduced and releases oxygen in a subsequent step. The core-process layout is composed of two reactors (oxidation reaction and reduction reactor) and oxygen carriers (metal oxides) circulating between the two reactors. A comprehensive moving-bed reactor model is developed and applied to simulate both the syngas production from water and carbon dioxide by ceria oxidation as well as the thermal reduction of metal oxide. An extensive FORTRAN model is developed to appropriately simulate the complexities of ceria reaction kinetics and implemented as subroutine into an ASPEN Plus® reactor model. The kinetics has been validated with the model developed by comparing experimental and simulated data on the reduction reactor. The sensitivity of both the reduction and oxidation reactors have been performed. The reduction reactor temperature and pressure were varied between 1200–1600¿°C and 10-3–10-7¿bar, respectively. The oxidation reactor was evaluated by varying the inlet temperatures of the reactants as well as the relative gas composition between CO2 and H2O. Results indicate a non-stoichiometry achievable from the reduction of ceria of 0.198 at 1600¿°C and 10-7¿bar vacuum pressure. In the oxidation reactor, water splitting yields significantly better solid conversion (metal oxide conversion) of 97%, as compared to 91% by CO2 splitting with 5% excess gas flow than the stoichiometric requirements. The metal oxide inlet temperature significantly improves the yield of the oxidation reactor, in contrast to the minimal impact of variation of gas inlet temperature. A selectivity of over 90% can be achieved irrespective of gas composition with over 90% metal oxide conversion in the oxidation reactorPostprint (author's final draft

AEM-electrolyzer based hydrogen integrated renewable energy system optimisation model for distributed communities

18 figures, 8 tables.-- © 2023. This manuscript version is made available under the CC-BY-NC-ND 4.0 license https://creativecommons.org/licenses/by-nc-nd/4.0/The development of sustainable and renewable energy technologies has received significant attention to realize Net-Zero CO2 equivalent emission goals and meet the growing energy demand. Hydrogen is a promising energy carrier that can facilitate the large-scale deployment of renewable energy sources and assist in the replacement of fossil fuels and to reduce the impact of global warming. The objective of this research is to present an advanced hydrogen-integrated renewable energy system model to meet the energy demand of a distributed community and produce green hydrogen from excess/curtailed renewable energy. The study employs an anion exchange membrane water electrolyzer (AEM) for producing hydrogen. An optimization model of the renewable energy system and a mathematical model of the electrolyzer are developed to achieve this objective. The model uses an energy maximisation approach and optimally combines wind system, biogas plant, and solar PV system to meet the residential and commercial load demands. To increase the system stability, the model is interconnected with the local grid station for energy exchange. Moreover, an uncertainty analysis is also performed to analyse the system response under random variation in load demand. The study results show that a significant amount of clean energy (15,025 MWh/year) is produced by the system at the lowest levelized cost of 0.084 €/kWh and a reduction of 6,078 tons of CO2 emission during the first year of operation is obtained. The electrolyzer produces 63 kg/hr of hydrogen, while the cell performance remains stable at 60 °C and the cell voltage reaches 2.019 V at 2.415 A/cm2 current density.Sincere gratitude and special thanks to the Department of Mechanical Engineering at Northern Illinois University, and the Biomass Research Center, CIRIAF and the University of Perugia for providing the facilities and support to conduct this research work.Peer reviewe

Techno-economic and exergetic assessment of an oxy-fuel power plant fueled by syngas produced by chemical looping CO2 and H2O dissociation

Natural Gas Combined Cycle (NGCC) is presently the most efficient fossil fuel power plant but with no carbon capture. The efficiency penalty resulting from the integration of carbon capture and storage (CCS) is, however, a major challenge. The present study proposes an oxyfuel NGCC integrated with Chemical looping (CL) syngas production (OXY-CC-CL), for power generation with CCS. The chemical looping CO2/H2O dissociation would produce syngas (CO and H2 with methane reduction step in redox cycle) from recycled exhaust gas for additional power generation within the power plant. This integration of CL unit with the existing conventional oxy fuel power plant would be expected to decrease the efficiency penalty. Therefore, the thermodynamic (both energetic and exergetic), economic and environmental performance of the integrated chemical looping unit oxyfuel NGCC power plant with carbon capture were assessed. A 500¿MW scale plant was modelled and compared with a conventional NGCC and oxyfuel NGCC plant with carbon capture (OXY-CC). The net efficiency penalty of the proposed OXY-CC-CL unit was 4.2% compared to an efficiency penalty of 11.8% of the OXY-CC unit with a 100% carbon capture. The energetic efficiency obtained hence was 50.7%, together with an exergetic efficiency of 47.1%. Heat integration via pinch analysis revealed the possibility to increase the system energetic efficiency up to 61%. Sensitivity analyses were performed to identify relative impacts of system operational parameters. The specific capital cost of the proposed OXY-CC-CL was obtained as 2455 $/kW, with a corresponding LCOE of 128$/MWh without carbon credits.Peer ReviewedPostprint (author's final draft

Techno-economic and exergetic assessment of an oxy-fuel power plant fueled by syngas produced by chemical looping CO2 and H2O dissociation

Natural Gas Combined Cycle (NGCC) is presently the most efficient fossil fuel power plant but with no carbon capture. The efficiency penalty resulting from the integration of carbon capture and storage (CCS) is, however, a major challenge. The present study proposes an oxyfuel NGCC integrated with Chemical looping (CL) syngas production (OXY-CC-CL), for power generation with CCS. The chemical looping CO2/H2O dissociation would produce syngas (CO and H2 with methane reduction step in redox cycle) from recycled exhaust gas for additional power generation within the power plant. This integration of CL unit with the existing conventional oxy fuel power plant would be expected to decrease the efficiency penalty. Therefore, the thermodynamic (both energetic and exergetic), economic and environmental performance of the integrated chemical looping unit oxyfuel NGCC power plant with carbon capture were assessed. A 500¿MW scale plant was modelled and compared with a conventional NGCC and oxyfuel NGCC plant with carbon capture (OXY-CC). The net efficiency penalty of the proposed OXY-CC-CL unit was 4.2% compared to an efficiency penalty of 11.8% of the OXY-CC unit with a 100% carbon capture. The energetic efficiency obtained hence was 50.7%, together with an exergetic efficiency of 47.1%. Heat integration via pinch analysis revealed the possibility to increase the system energetic efficiency up to 61%. Sensitivity analyses were performed to identify relative impacts of system operational parameters. The specific capital cost of the proposed OXY-CC-CL was obtained as 2455 $/kW, with a corresponding LCOE of 128$/MWh without carbon credits.Peer Reviewe

System efficiency analysis of dual interconnected bubbling fluidized bed reactors for solar fuel production

Chemical looping syngas production is a two-step syngas fuel production process that produces CO and H 2 . The process is composed of two fluidized bed reactors (oxidation reaction and reduction reactor), oxygen carriers (metal oxides) circulating between the two reactors. A comprehensive model is developed to simulate the chemical looping water and carbon dioxide splitting in a dual fluidized bed reactors interconnected with redox cycling between these two reactors through metal oxides (non-stoichiometric ceria). An extensive FORTRAN subroutine is developed and hooked into Aspen plus V8.8 to appropriately model the complexities of the bubbling fluidized bed reactor including the reaction kinetics. The model developed has been validated for its hydrodynamics and kinetics level and individual correlation was quantified for its validity. The reduction reactor is maintained between the temperatures 1300-1500°C. The heat to attain this high temperature can be achieved with solar beam down tower. The oxidation reactor is supplied with a mixture of CO 2 and H 2 O with different mixture composition combining 60% and remaining N 2 . The oxidation reactor temperature is varied between 700-1000°C to identify the maximum efficiency achieved. It is found that the maximum efficiency achieved is 67.4% corresponding to highest temperature difference between the reactors

Simulation of two-step redox recycling of non-stoichiometric ceria with thermochemical dissociation of CO 2 /H 2 O in moving bed reactors – Part I: Model development with redox kinetics and sensitivity analysis

Chemical looping syngas production is a two-step process that produces CO and H2 from water and CO2 splitting. This is performed by exploiting a metal oxide as oxygen carrier material, which is thermally reduced and releases oxygen in a subsequent step. The core-process layout is composed of two reactors (oxidation reaction and reduction reactor) and oxygen carriers (metal oxides) circulating between the two reactors. A comprehensive moving-bed reactor model is developed and applied to simulate both the syngas production from water and carbon dioxide by ceria oxidation as well as the thermal reduction of metal oxide. An extensive FORTRAN model is developed to appropriately simulate the complexities of ceria reaction kinetics and implemented as subroutine into an ASPEN Plus® reactor model. The kinetics has been validated with the model developed by comparing experimental and simulated data on the reduction reactor. The sensitivity of both the reduction and oxidation reactors have been performed. The reduction reactor temperature and pressure were varied between 1200–1600¿°C and 10-3–10-7¿bar, respectively. The oxidation reactor was evaluated by varying the inlet temperatures of the reactants as well as the relative gas composition between CO2 and H2O. Results indicate a non-stoichiometry achievable from the reduction of ceria of 0.198 at 1600¿°C and 10-7¿bar vacuum pressure. In the oxidation reactor, water splitting yields significantly better solid conversion (metal oxide conversion) of 97%, as compared to 91% by CO2 splitting with 5% excess gas flow than the stoichiometric requirements. The metal oxide inlet temperature significantly improves the yield of the oxidation reactor, in contrast to the minimal impact of variation of gas inlet temperature. A selectivity of over 90% can be achieved irrespective of gas composition with over 90% metal oxide conversion in the oxidation reacto