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The reversible use of a commercially available molten carbonate fuel cell (MCFC) as a molten carbonate electrolysis cell (MCEC) is an appealing prospect for both storing surplus renewable energy and converting CO 2 into valuable syngas (H 2 and CO). This work aims to explore the dynamic aspects of this type of electrolyzer. The study investigates the dynamic behavior of the MCEC, involving dynamic model development, degradation analysis, and cold start-up evaluation. The findings revealed that cell degradation results in a 0.8 % decrease in H 2 and a 1.5 % decrease in CO at a 1 % degradation rate, rising to 7.9 % H 2 and 14.3 % CO decrease at a 10 % degradation rate, necessitating an increase in the current to maintain the same production. Additionally, the study identifies the most energy-efficient cold start-up heating process for the MCEC. These insights emphasize the importance of addressing degradation issues and optimizing start-up procedures for real-world applications. • MCFC can be used reversibly as MCEC for renewable energy storage and CO2 conversion. • The study explores MCEC's dynamic behavior, degradation, and cold start-up process. • Cell degradation leads to H 2 and CO production decrease: 0.8 %–7.9 % for H 2 , 1.5 %–14.3 % for CO. • Current increase is required to maintain consistent production levels. [ABSTRACT FROM AUTHOR]

The reversible operation of a commercialized molten carbonate fuel cell as an electrolyzer is attractive to store the surplus of renewable energy and convert CO 2 into valuable fuel, like syngas (H 2 and CO). This work aims to assess this capability by developing a model for the co-electrolysis of CO 2 and H 2 O in the molten carbonate electrolysis cell (MCEC). Furthermore, a 1 MW power-to-gas system is simulated and optimized to maximize the process efficiency via a profound sensitivity analysis and a pinch heat integration analysis. The study's results reveal that when CO 2 electrolysis occurs, there is a risk of reaching the limiting current density at lower values, thus affecting the cell's performance. As for the simulation, the process yields an efficiency of 68.87% with an electrolyzer's power density of 0.082 W/cm2 per cell, producing 1.3 tons/day of methane gas ready for injection into the natural gas network. • Co-electrolysis of H 2 O and CO 2 in a molten carbonate electrolyzer was modelled. • 1 MW power-to-gas system is simulated and optimized via a sensitivity analysis. • Process yields an efficiency of 68.87% with 1.3 tons/day methane gas production. • The electrolyzer operates at a power density of 0.082 W/cm2 per cell. [ABSTRACT FROM AUTHOR]

The intermittent nature of renewable energy sources is a key challenge to their integration into the electricity grid. The aim of this paper is to introduce an advanced concept of Power-to-Gas (PtG) plant, which is designed to bring a closed-loop solution able to absorb electricity surplus and to restore it later, via the transient storage of energy carriers. After a brief conceptual overview of the studied unit and its individual components, the paper introduces the key results of the steady state model used to assess process flowsheets as well as operating conditions of the industrial scale unit. These results indicate that during the storage phase, a 200 MW power supply to the electrolysis process leads to a corresponding 155 MW of Synthetic Natural Gas (SNG) produced in a thermally integrated methanation process with an efficiency of 83.1%. By producing and storing enough amount of SNG and oxygen, an Oxy-combustion power plant can be subsequently used to recover up to 480 MW electric power as well as to produce CO 2 rich gas with an overall efficiency of 51.8%. Lastly, a thorough sensitivity analysis was conducted to show that the Electrolysis-Methanation-Oxy-combustion (EMO) unit performance can be further improved by adjusting key design parameters accordingly. [ABSTRACT FROM AUTHOR]

Aqueous ammonia is well known to be a substitute of MEA solvent for absorbing CO 2 in post-combustion process. However, aqueous ammonia is highly volatile it can become gaseous and leaves the absorption column with the treated gas. Several processes that use ammonia solution as solvent deal with this problem. The use of membrane contactor could limit ammonia loss and could widen the operative ranges of temperature, pressure and ammonia concentration. This paper aims at evaluating and comparing different methods to capture CO 2 by ammoniac. The evaluation of all process has demonstrated a high CO 2 removal efficiency. [ABSTRACT FROM AUTHOR]

Storing renewable electricity in a natural gas grid is a new approach for seasonal storage. Using the existing natural gas infrastructure, a chemical energy source (methane) is stored efficiently, distributed and made available for use as required. Thus, the main step in the storage process is CO methanation. Modelling of an isothermal methanation catalytic reactor based on a kinetic scheme was carried out with Aspen plus™ software in a temperature range between 520 and 600 K and a H2/CO molar ratio of 3, in the presence of CO2 and steam. The model was validated by comparing simulation results with experimental ones. The maximum relative error is 10.87%. The effects of temperature, pressure and CO2 addition in feed gas (syngas) on CO conversion and the outlet gas composition were carefully investigated. [ABSTRACT FROM AUTHOR]

Abstract: There has been a large increase in anthropogenic emissions of CO2 over the past century. The use of captured CO2 can become a profitable business, in addition to controlling CO2 concentration in the atmosphere. A process for producing fuel grade methanol from captured CO2 is proposed in this paper. The process is designed and simulated with Aspen Plus. The CO2 is captured by chemical absorption from the flue gases of a thermal power plant. The hydrogen is produced by water electrolysis using carbon-free electricity. The methanol plant provides 36% of the thermal energy required for CO2 capture, reducing considerably the costs of the capture. The CO2 balance of the process showed that it is possible to abate 1.6 t of CO2 per tonne of methanol produced if oxygen by-product is sold, or 1.2 t if it is not. [Copyright &y& Elsevier]

Abstract: In this work we present the experimental results of absorption rates and absorption capacity for the CO2 absorption by ammonia (NH3) aqueous solutions. Experiments are carried out in a thermoregulated Lewis-type cell reactor and are achieved in temperature and concentration ranges of 278–303K and 2–5wt.% NH3 respectively. The obtained values for absorption kinetic rates and absorption capacity are compared with those available for alkanolamine solvents, commonly used to absorb CO2. In order to achieve this comparison, data available in studies about alkanolamine solvents at 303–333K and 5–50wt.% for alkanolamines solutions were considered. Results show that CO2 absorption by NH3 is faster than the one carried out by MDEA, except for 2wt.% NH3 at 288K. At 278K and using aqueous solutions of 3wt.% NH3, the absorption rate is almost identical to the one reached with MDEA solvent. The highest absorption capacity, also compared with alkanolamine solution, is reached with aqueous solutions of 5wt.% NH3 at 278K and 303K. [Copyright &y& Elsevier]

The greenhouse gas emissions from the transportation sector are the primary cause of climate change. As a result, many studies have developed new powertrains with reduced CO2 emissions for the automotive industry. The gas turbine cycle coupled to an alternator is an autonomy booster for series hybrid electric vehicles. Many gas turbine configurations are proposed in the literature to obtain the highest cycle efficiency. This paper suggests a new architecture offering higher efficiency than all the previous cycles. The two-step methodology consists at first of a sensibility analysis using VBA and Refprop to determine the optimal operating conditions in terms of higher efficiency. The selected cycle consists of two compression stages with an intercooler, a combustion chamber, a cooled hot pressure turbine, an uncooled low-pressure turbine, and a recuperator. The efficiency of this design reaches 51.39%, which approximately matches the designs compared in the literature, but is more compact because it does not require a second combustion chamber. [ABSTRACT FROM AUTHOR]

• The coolprop thermodynamic equations of state and the implicit fitting method have been investigated for calculating the refrigerants' thermodynamic properties. • A dynamic cascade refrigeration cycle has been developed and simulated with both methods for comparison. • The simulation was 30 times faster with the implicit fitting method than coolprop equations of state. • The implicit fitting method showed high accuracy. Modeling and simulating dynamic and complex energy systems that are composed of a large number of components where every component model is described by mathematical equations can take high computational time. The calculation of the refrigerant thermodynamic properties has a big impact on the computational speed of the model. In an attempt to speed up simulations, two implementation methods for the calculation of refrigerants' thermodynamic properties were investigated, the Coolprop thermodynamic equations of state and the Implicit fitting method. A complex dynamic cascade refrigeration cycle was developed and simulated using the two fluids implementation methods. The advantages and disadvantages of each method were discussed. The results show that using the implicit fitting method instead of Coolprop for the simulations of complex dynamic systems in Dymola will accelerate the simulation by about 30 times. In addition, the implicit method is accurate and offers more flexibility for modeling complex realistic energy systems. [ABSTRACT FROM AUTHOR]

• A novel technology using a superacid solvent is proposed to purify biogas streams. • Superacid solvent eliminates COVNMs, siloxanes, H 2 S and partially CO 2 from biogas. • Process simulations and hydrodynamic analyses confirm the technology feasibility. • Superacid process shows lower energy demands than other solvents (methanol and MEA). A novel purification technology for raw biogas streams is proposed and it is based on the use of a superacid solution within a bubble column reactor. The solvent is a mixture of sulfuric acid (H 2 SO 4(aq) , 95.0 -->wt.%) and acetic acid glacial (CH 3 COOH (l) , ≥ 99.8 -->vol.%), both commercial grades. A mixture with a molar ratio of 9/1 for H 2 SO 4(aq) , / CH 3 COOH (l) respectively, leads to the interesting physical and chemical absorption properties for biogas treatment. Process simulations of the technology within a frequently used biomethane production process showed simultaneous capabilities for H 2 S elimination, CO 2 absorption and, siloxanes and volatile organic compounds (NMVOCs) complete degradation. A single bubble column reactor was designed for treating 500 N m 3 / h of raw biogas with H 2 S content between 400 and 1500 -->ppmv (dry basis) and for handling a solvent volume flow between 10.23 and 23.39 -->L/min, depending on the H 2 S gas content. Proper functioning and hydrodynamic stability of this unit were evaluated in order to avoid possible issues related to bubbles coalescences or break-up, liquid backmixing and mass transfer limitations. Comparison of the proposed technology with methanol-based and monoethanolamine (MEA (aq))-based absorption processes allowed proving the low energy demands of the proposed unit and the feasible implementation of the technology. [ABSTRACT FROM AUTHOR]

Slurry pipelines are extensively employed in most mining operations to transport raw materials and tailings. The aim of the paper is twofold: on the one hand, to develop a generalized slurry flow model using computational fluid dynamics (CFD) to develop a better insight into the complexity of slurry pipe flows, and on the other hand, to develop a surrogate model for pressure drop predictions, which can be used in operations simulation and monitoring tools. A two-fluid model based on the Eulerian-Eulerian approach along with the SST k-ω turbulence model was used. The motion of the solid phase was modeled by the kinetic theory of granular flow (KTGF) to account for both particle-particle and particle-wall interactions. The model was validated by comparison with experimental data available in literature. A new two-phase pressure drop correlation is proposed based on the numerical computations of horizontal pipes featuring 525 data points. [ABSTRACT FROM AUTHOR]

Methyl mercaptan (CH3SH) absorption kinetics was studied for a hybrid solvent mixture consisting of diethanolamine/water/methanol for concentrations of 40/40/20 wt % and 40/20/40 wt % and for temperatures between 313.9 and 353.0 K. CH3SH is usually found in sour gases and is removed along with other acid gases. Physicochemical characterization is performed for the treatment of CH3SH with the hybrid solvent which is to date lacking chemical absorption data. A systematic methodology is proposed to assess the effect of each mass transfer, thermophysical properties, and the chemical reactions in the system. An empirical novel equation is proposed for the Henry's law constant solubility of CH3SH with respect to the methanol in solution. A chemical kinetic mechanism based on the formation of a zwitterion complex is proposed for the chemical species in the liquid phase. Results validated with experimental data enabled all the reaction constants to be parametrized in terms of the Arrhenius law. [ABSTRACT FROM AUTHOR]

Power-to-Substitute-Natural-Gas (SNG) processes are studied since they can offer solutions for renewable energy storage and transportation. In the present study, an original Power-to-SNG process combining high-temperature steam electrolysis and CO 2 methanation is economically assessed. This evaluation is based on experimental data describing the electrolyser performance and its degradation during long-term operation. These data are obtained on a commercial single cell. Tests are originally conducted by imposing voltage and steam conversion rate. The main conclusions of this experimental work are that two fields of current density evolution are evidenced in the tested conditions: a first transient one where the current density absolute value decreases very quickly, followed by a second field where the evolution of current density achieves a steady state. The influence of the operating point seems not significant once this state is achieved. The process assessed here has been developed in a previous work where a precise framework matching with a wide range of applications was defined. The design of the process main units and the calculation of matter and energy fluxes are based on this work. To go further, the economic assessment of this process is proposed. In this study, various scenarios of initial performance of the electrolyser are considered and integrate the performance degradation associated. The SNG production cost is estimated between 211 and 570 €/MWh HHV according to the scenario and the hypotheses considered. The two major items accounting for this high cost are the purchase cost of the electrolyser and its performance degradation. It also evidenced that none of the other items can be neglected. Through a sensitivity analysis, it is shown that an increase of plant annual availability and capacity makes the SNG production cost decrease. [ABSTRACT FROM AUTHOR]

Power-to-Substitute Natural Gas processes are investigated to offer solutions for renewable energy storing or transportation. In the present study, an original Power-to-SNG process combining high-temperature steam electrolysis and CO 2 methanation is implemented and simulated. A reference process is firstly defined, including a specific modelling approach of the electrolysis and a methanation modelling including a kinetic law. The process also integrates a unit to clean the gas from residual CO 2 , H 2 and H 2 O for gas network injection. Having set all the units, simulations are performed with ProsimPlus 3™ software for a reference case where the electrolyser and the methanation reactors are designed. The reference case allows to produce 67.5 Nm 3 /h of SNG with an electrical energy consumption of 14.4 kW h/Nm 3 . The produced SNG satisfies specifications required for network injection. From this reference process, two sensitivity analyses on electrolysis and methanation working points and on external parameters and constraints are considered. As a main result, we observe that the reference case maximises both process efficiency and SNG production when compared with other studied cases. [ABSTRACT FROM AUTHOR]

Abstract: High Temperature ELectrolysers (HTEL) operate around 1073 K with steam at 1073 K. Water is previously heated up in the Balance of Plant by the hot outlet gases and optionally by electrical heaters. If liquid water is fed to the system, vaporisation needs are covered by electrical heating, which leads to a low system efficiency of 89% vs. HHV. Using steam instead of liquid water would suppress vaporisation needs, thus increase the efficiency. This work aims to analyse the potential benefits of a steam supply. Calculation is performed without considering the energy required to preheat water. Results show that feeding the system with low-temperature steam instead of liquid water enables a system efficiency jump of 18%. Further increasing the steam temperature to 933 K negligibly impacts the system efficiency and is therefore unnecessary. It is concluded that a low-temperature steam source is sufficient to increase significantly the HTEL system efficiency. [Copyright &y& Elsevier]

Abstract: The objective of this study is to describe the steady-state behaviour of a Solid Oxide Electrolysis Cell (SOEC) system operated at different power loads without an external heat source and producing compressed hydrogen (3MPa). A zero-dimensional model is proposed to describe the system, which is composed of an SOEC unit and a Balance of Plant. Results found that the system efficiency equals 91% vs. HHV and is slightly impacted by the operating load. However, due to the SOEC sensitivity to thermal gradients, the SOEC unit has to be operated close to the thermoneutral mode, which restricts the SOEC system power load to the range 60–100%. Control strategies, such as additional heating and independently operated SOEC units, should be employed below 60% load to enable the electrolyser operation across a wider load range. [Copyright &y& Elsevier]

Abstract: This paper presents a hybrid algorithm to be used for kinetics modelling and based on the Adaptive Random Search Method (ARSM) enhanced by the Genetic Algorithms (GA) theory. This algorithm is validated comparing modelled pressure values to experimental pressure data from Carbonyl sulfide (COS) absorption by aqueous solvents. An excellent fit is shown when COS absorption by N-methyldiethanolamine (MDEA) aqueous solutions is modelled. Preliminary results for the modelling of CO2 absorption by NH3 aqueous solutions show an accurate fit and open the door to further studies on more complex reaction mechanisms suggested for the ammonia-carbon dioxide reaction. Besides, the proposed method leads to lower computational time and slightly more accurate calculated pressure values than classic methods such as Downhill simplex. [Copyright &y& Elsevier]

Power to Gas (PtG) has appeared in the last years as a potential long-term energy storage solution, which converts hydrogen produced by renewable electricity surplus into synthetic methane. However, significant economic barriers slow down its massive deployment (e.g. operating hours, expensive investments). Within this framework, the PtG-Oxycombustion hybridization can palliate these issues by improving the use of resources and increasing the overall efficiency. In this study we assess the requirements for electrolysis, depending on the size of the oxycombustion plant, the fuel physical and chemical properties and the final application of the hybrid system. Most suitable heat demanding options to implement this PtG-Oxycombustion hybridization are district heating, industrial processes and small combined cycled power plants. The latter case is modelled and simulated in detail and thermally integrated. The global efficiency of this hybrid system increases from 56% to 68%, thanks to avoiding the requirement of an air separation unit and integrating up to 88% of the available heat from methanation in a LP steam cycle. [ABSTRACT FROM AUTHOR]

Abstract: In this study, an exergy-based system level methodology is conducted to assess the energy penalty reduction potential of different configurations of first generation oxy-fired pulverized coal power plants. Once the process improvement potential is identified by exergy analysis on an oxy-fired plant with minimal integration, a heat integration methodology minimizing the exergy losses is carried out. Exergy analysis is employed as a guideline weighted by technological and operational constraints. This methodology has been applied to study the conventional cold flue gas recycle scheme and three alternative flue gas recirculation options including the widely studied warm recycle scheme. The integration potential of advanced cryogenic ASUs (air separation units) has also been assessed. Finally, the energy penalty associated to the capture when a high-purity CO2 flow is required has been determined. Among the different cases considered in this study, recirculation of the flue gas before the regenerative heater with an advanced ASU and a double-column CPU (compression and purification unit) leads to the highest NPE (net plant efficiency). For this case, the NPE is 39.1 % based on the lower heating value (7 %-pts energy penalty), which corresponds to a 6.5% improvement compared to the base-case plant. When high-purity CO2 is desired, the energy penalty is increased by 0.2 %-pts for the same configuration. [Copyright &y& Elsevier]

Abstract: In order to investigate the transient behaviour of a solid oxide electrolysis cell, tests were carried out on a single SOEC both under steady-state and transient conditions for 600 h. Steady-state operation was performed at the reference current of −20 A, corresponding to the thermoneutral voltage (1.28 V), whereas transient tests consisted in 1800 square waves applied over 140 cumulated hours, with a current of −1 A and −20 A as well as 0 A and −20 A. Independently from the operating conditions, the measured voltage degradation rate of 5% (70 mV)/1000 h was stable for the entire experiment. Consequently, it was concluded that an SOEC can be operated under on–off conditions with no increase of the degradation rate. This result paves the way for modular operation of a high temperature electrolyser fed with intermittent electrical energy. [Copyright &y& Elsevier]

Biomass conversion into biofuels and biogas is a promising way for power and heat generation. Lately, research has focused on the production of biomethane based on biomass gasification followed by methanation as an alternative to fossil natural gas. The challenge of this process remains in the intensive gas cleaning and required tar removal. In order to study tar removal from the producer gas downstream biomass gasification, solid–vapor and liquid–vapor equilibrium must be known for different tar concentrations, ranging between 0.001 and 100 g.Nm−3. To assess tar removal by condensation at low temperatures, psychrometric charts are developed. Since the composition of tar is complex, toluene, phenol, indene, naphthalene and fluoranthene are selected as tar representatives. Each component is studied separately in four different producer gas compositions formed mainly of hydrogen, carbon monoxide, carbon dioxide and methane in addition to water and nitrogen. Methods for calculating saturation, isenthalpic and constant relative concentration lines are presented. Psychrometric charts of the different tar components are finally plotted at atmospheric pressure. Results show that temperature of 196.15 K is required to reduce the tar content to 0.001 g.Nm−3. Image 1 • Tar removal via a secondary physical method at low temperature by condensation. • Fluoranthene, naphthalene, indene, phenol and toluene represent tar components. • Indicate the temperature required to start removal process per tar category. • Liquid-Vapor, Solid-Vapor equilibrium and enthalpy function of temperature. [ABSTRACT FROM AUTHOR]