Molten Carbonate Research Articles

Direct, efficient and selective capture of low concentration of CO2 from natural gas flue gas using a high temperature tubular carbon capture membrane

Natural gas (NG) fired power plants emit low concentration (4–5%) of CO2, which presents additional technical and economic challenges to the current benchmark amine absorption technology. The newly emerged high-temperature multiphase membranes operated on molten carbonate (MC) chemistry for CO2 capture/separation/conversion have been demonstrated with great potential to meet this challenge. In this study, we report on the CO2 capture performance of such a membrane in tubular geometry from a mockup NG flue gas. The membrane is comprised of a mixture of Gd0.20Ce0.80O1.95 (GDC) and MC, in which GDC forms a porous skeleton to contain MC. We show that the membrane with a dimension of 6.1 mm in outer diameter, 5.1 mm in inner diameter and 5 cm in effective length (resulting in 4 cm2 effective surface area) can achieve a CO2 flux density of 0.46–0.55 mL/min·cm2 at 650 °C, capturing 97% pure CO2 at a rate of 37–42% from 5%CO2–N2 using moistened Ar as the sweep gas. The level of performance demonstrated by this study suites the membrane well for stationary CO2 capture from NG power plants.

Conceptual design and technical analysis of a hybrid natural gas/molten carbonate fuel cell system for combined cooling, heating, and power applications

Hydrogen can be extracted by various processes such as coal gasification, natural gas modification, and electrolysis. it can be used in fuel cell systems that have been used for energy generation. Fuel cell systems are several types including polymer membranes, sulfuric acid, solid oxide, methanol, alkali, and molten carbonate, which are mainly used in combination with other energy systems. In this research, methods of hydrogen production and types of fuel cells are reviewed. Then, an attempt was made by using a hybrid system connected to the molten carbonate fuel cell (MCFC) system which is capable of generating electricity and heating synchronously, to meet the welfare needs of a family in Bandar-e Deyr, such as heating, cooling, drinking water, hot water, and electricity. The MCFC produces 117 kW of required power in total. The cell can generate 12 kW power to supply the electricity required. Furthermore, this hybrid system can supply cooling and heating loads, which are 96 kW and 36 kW, respectively. the investment in the hybrid system is up to $1257,780, which can be reduced by economic analysis. Also, this system has the lowest amount of carbon dioxide emission, i.e. 4 %, and has the least amount of pollution.

Design and tri-criteria optimization of an MCFC based energy system with hydrogen production and injection: An effort to minimize the carbon emission

The threat of rapid depletion of fossil fuel reserves and the discharge of pollutants due to the depletion of these resources has had catastrophic consequences for the ecosystem. Using efficient energy systems, waste heat recovery from these systems, and decreased carbon dioxide emission cycles is one approach to averting this looming threat in this context. It is proposed in this paper to utilize the electricity generated by the bottoming absorption power cycle to create hydrogen for use in a molten carbonate fuel cell-based energy system. The system is called near-zero carbon since the efficient waste heat utilization allows maximum hydrogen and minimum hydrocarbon fuel use. The concept of the near-zero carbon cycle is being explored from the viewpoints of technology, economics, and the environment. It is necessary to do multi-criteria optimization to establish the optimum operating point of the system under consideration to reduce costs and CO2 emissions while simultaneously increasing efficiency. A parametric analysis is performed to discover the important design parameters that impact the system's performance under consideration. Included among the factors under investigation are the fuel utilization factor (Uf), current density (J), stack temperature (Tstack), and the steam to carbon ratio (rsc). Upon investigation, it was discovered that the suggested system had an energy and exergy efficiency of around 66.21% and 59.5%, respectively. According to the findings of the exergy analysis, the MCFC and afterburner ranked highest in terms of exergy destruction (93.12 MW and 22.4 MW, respectively). The tri-objective optimization findings also reveal that the most optimal solution point has an exergy efficiency of 59.5%, a total cost rate of 11.7 ($/GJ), and CO2 emission of 0.58 ton/MWh.

Regulating electrolyte basicity via CaCO3 additives for enhanced corrosion resistance of Ni anodes in low-temperature molten carbonate

Electrochemical reduction of CO2 in molten carbonate at low temperatures (< 500 °C) is restricted by the instability of Ni anodes. Herein, we revealed that the corrosion of Ni anodes in low-temperature molten carbonates was induced by the decrease in local basicity of anode/electrolyte interface during electrolysis. Thus, CaCO3 was used as an additive to increase electrolyte basicity and modulate the anode/electrolyte interface. The addition of CaCO3 significantly reduced the solubility of NiO scale in molten carbonate and enhanced the corrosion resistance of Ni at 475 °C, thereby making Ni as a suitable inert anode for low-temperature molten carbonate electrolysis.

Nanoparticle surface charge-enhanced heat capacity in molten salt phase change materials for thermal energy storage

Nanoparticle-enhanced molten salt phase change materials have been used extensively for thermal energy storage. However, the role of nanoparticles in enhancing the specific heat capacity remains elusive with contradicting reports. In this work, to clarify the mechanism behind the specific heat enhancement in nanoparticle (SiO2) embedded nitrate (NaNO3–KNO3) and carbonate (Li2CO3–K2CO3) molten salts. Due to the surface charges on nanoparticles, an orderly layered distribution of molten salt ions near the surface is observed in molecular dynamics simulations, which lead to higher electrostatic potential energies near the nanoparticle surface. This makes the ionic layers with the same charge type easier to expand when temperature rises, leading to a larger local thermal expansion coefficient. Since the thermal expansion coefficient is positively correlated with the specific heat based on the phonon interpolation, the increased local thermal expansion coefficient is the main reason for the enhancement in the specific heat. The enhancement in the specific heat and the enrichment of charged functional groups on the nanoparticle surface are also confirmed experimentally. The specific heat can be significantly enhanced, by up to 19% here with 1 wt% nanoparticle, after we tailor the surface chemistry of nanoparticles, in particular, by coating active functional groups such as hydroxyl groups on the surface. This study clarifies the fundamental role of surface changes on nanoparticles in enhancing the specific heat of molten salts, and suggests that nanoparticles can have higher surface charge densities, if protonated in an acidic environment, can lead to larger specific heat enhancement in molten salts.

Influence of Growth Parameters on the Electrochemical Performance of Electrodeposited Carbons

Generating useful chemicals from CO2 is driving research into carbon capture and utilization. In this work, hard carbons are electrodeposited on various substrates from molten carbonate melts in CO2 atmospheres. These electrodeposited carbons are subsequently used as anodes in sodium-ion batteries, with preliminary investigations into their performance in potassium-ion batteries. The hard carbons were characterized using X-ray diffraction (XRD) and Raman spectroscopy. Hard carbons grown on graphite substrates produced initial reversible capacities of 405 ± 29 mAh/g and capacity retention of 85.2 ± 1.1% after 50 cycles when cycled at 10 mA/g which are amongst the highest capacities reported for hard carbons to date. This work clearly illustrates that the carbons generated via CO2 mediated electrodeposition are suitable for application in next generation batteries.

Catalytic effect of cesium on the oxidation behavior of cation exchange resins in Li2CO3-Na2CO3-K2CO3 melt.

After the treatment of liquid radioactive waste, there is a certain amount of Cs in the waste resin, and these Cs-doped resins are prone to volatilize during the thermal treatment process and cause radionuclide leakage. The molten salt oxidation (MSO) can effectively prevent the volatilization of toxic metal, especially the volatilization of Cs. Under nitrogen and air conditions, it is found that the oxidation behavior between Cs-doped and clean cation exchange resins (CERs) is quite different. In the presence of oxygen and molten carbonate salt, Cs2CO3 is generated by the destruction of functional groups in Cs-doped CERs. The Cs2CO3 in Na2CO3-K2CO3-Li2CO3 reacts with oxygen to form Li2O2, which reduces the content of S in residue from 26.33 to 13.38% in air conditions at 400 °C and promotes the generation of sulfate in the molten carbonate salt. The elements Cs and S in the Cs doped CERs spontaneously form thermally stable Cs2SO4 in the molten carbonate salt.

Molecular dynamic investigation on the thermophysical properties of binary molten carbonate mixtures

Because of massive advantages such as large latent heat, wide temperature range, large density and small corrosion, carbonate has been considered as a great potential material in the heat storage system of solar energy. This work, the thermophysical properties of binary molten carbonate Na2CO3-K2CO3 mixtures such as density, thermal conductivity, viscosity have been investigated via molecular dynamic simulations, and the influences of temperature and components have been explored from a microscopic perspective. The results show that the molecular dynamics model of the statistical thermal conductivity and viscosity can be used to study the molten carbonate at high temperature with satisfactory precision. Temperature has an obvious effect on the thermophysical properties of the alkali co-anion carbonate system. With the increase of temperature, the density, the thermal conductivity and shear viscosity all decreases. In addition, as the mole fraction of component Na+ increases in the co-anion carbonate system, the density and the thermal conductivity has an obvious increase. While the shear viscosity shows a slightly decrease with the increase of component K+.

Extraction of lithium from the simulated pyrometallurgical slag of spent lithium-ion batteries by binary eutectic molten carbonates

Extraction of lithium from the simulated pyrometallurgical slag of spent lithium-ion batteries by binary eutectic molten carbonates

Fabrication and Characterization of a Composite Ni-SDC Fuel Cell Cathode Reinforced by Ni Foam.

High-temperature fuel cells (namely, molten carbonate and solid oxide; MCFCs and SOFCs) require the cathode to be designed to maximize oxygen catalytic reduction, oxygen ion transport, electrical conductivity, and gas transport. This then leads to the optimization of the volume fraction and morphology of phases, as they are a pathway for electrons, ions, and gases to be continuous and self-interpenetrating. Apart from the functional properties, the cathode must be mechanically stable to prevent cracking during fuel cell assembly and operation. The manufacturing process of the composite cathode was optimized to meet such requirements in this research work. The tape casting technique and further firing process were used to fabricate the cathodes. The slurry for the green tape was composed of nickel (Ni), cerium oxide doped with samarium oxide (SDC), water (solvent), and an organic binder (which becomes pore space after firing). Each of these elements is necessary for the effective transport of specific species: electrons, oxygen, ions, and gas particles, respectively. Moreover, the nickel foam was embedded into the powder-based structure to improve mechanical strength. The study involved many technological issues, such as the effect of the SDC fraction on the cathode microstructure, mechanical strength, and chemical stability at high temperatures, and also involved environmental issues.

Numerical assessment of a hybrid energy system based on solid oxide electrolyzer, solar energy and molten carbonate fuel cell for the generation of electrical energy and hydrogen fuel with electricity storage option

In recent years, due to increasing energy requirements and special attention to the issue of carbon, hydrogen fuel has become an efficient alternative to energy carriers. The aim of this article is to present and investigate of a novel solar-driven hydrogen generation process. The introduced hybrid energy system (HES) is comprised of a solid oxide electrolyzer (SOE), solar photovoltaic (SPV) modules, and solar dish collectors (SDCs). Further, since one of the most attractive utilizations of hydrogen fuel is as a fuel cell's fuel, the present HES suggests that hydrogen fuel be injected into molten carbonate fuel cell (MCFC) to convert it into useful electrical and thermal energies. Finally, the electrical energy obtained from HES is stored via a relatively new hybrid storage system (i.e., pumped hydro and compressed air (PHCA) storage system) for peak and night hours. Therefore, the considered HES in the present study can generate electrical and thermal power, hydrogen fuel and oxygen gas, and store electricity. Although some publications on solar-driven hydrogen generation process are available, there is no study on proposed HES of the present article that considers both energy production and storage. In other words, the components embedded in the proposed HES are developed in such a way that the relationships between them are novel. According to the numerical simulation, it was found that the electrical energy production rate and electrical efficiency of HES are almost 183.1 kWh/day and 33.6 %, respectively. HES can also produce approximately 3.9 kg of hydrogen fuel per day. Moreover, the storage system size for storing the electricity yielded from the considered HES should be nearly 29.9 m3 (at n = 1.2). Also, the storage efficiency of the energy cycle is 59.1 %. The considered process is investigated under different effective parameters in order to identify their effectiveness.

Advanced design of a x-ray absorption spectroscopy setup for measuring transition metals speciation in molten carbonates, hydroxides and hydrogenosulfates

Battery recycling is currently becoming a crucial issue. One possible treatment path involves the use of molten salts. A mechanistic understanding of the underlying processes requires being able to analyze in situ speciation in molten salts at various temperatures. This can be advantageously achieved using x-ray absorption spectroscopy, the use of Quick-EXAFS facilities being particularly appropriate. Consequently, this paper presents the design and development of a new setup allowing carrying out Quick-EXAFS experiments in oxidizing molten salts at high temperatures. We describe the different components of a cell and the performance of the heating device. We illustrate the capabilities of the setup by analyzing the temperature evolution of Co speciation upon dissolution of LiCoO2, a typical battery electrode material, in molten carbonates, hydroxides, and hydrogenosulphates.

Electrolysis Assisted Biomass Gasification for Liquid Fuels Production

Gasification is a promising pathway for converting biomass residues into renewable transportation fuels and chemicals needed to comply with the ambitious Swedish environmental targets. The paper investigates the integration of a molten carbonate electrolysis cell (MCEC) in biofuel production pathway from sawmill byproducts, to improve the performance of gas cleaning and conditioning steps prior to the final conversion of syngas into liquid biofuels. The energy, material, and economic performance of process configurations with different gasification technologies are simulated and compared. The results provide relevant information to develop the engineering of gas-to-liquid transportation fuels utilizing renewable electricity. The MCEC replaces the water-gas shift step of a conventional syngas conditioning process and enables increased product throughput by as much as 15%–31%. Depending on the process configuration and steam-methane reforming technology, biofuels can be produced to the cost range 140–155 €/MWh in the short-term.

Water-gas shift reaction in ceramic-carbonate dual-phase membrane reactor at high temperatures and pressures

Water-gas-shift (WGS) reaction is a critical step in integrated gasification combined cycles (IGCC) power plants with CO2 capture. Membrane reactors made with a CO2-permselective ceramic-carbonate dual-phase (CCDP) membrane offers the potential to enhance hydrogen yield with simultaneous CO2 capture for WGS reaction. The present work studies operation of WGS reaction in a tubular membrane reactor made of samarium-doped ceria infiltrated with lithium/sodium molten carbonate mixture. The WGS reaction was performed in the membrane reactor with and without a high-temperature WGS catalyst at 800–850 °C, feed pressure of 7 bar, the space velocity of 150–3000 h−1, and a feed gas mixture of 45.7/13.1/41.3 mol% CO/CO2/N2 with steam to carbon ratio of 4. The results show that the catalyst-free membrane reactor can convert 92% of carbon monoxide into CO2 and H2 and recover 29% CO2 at 850 °C and a space velocity of 150 h−1. However, in the catalyst-free membrane reactor, a significant amount of unwanted carbon deposition is observed. The side reactions can be minimized by reducing the operating pressure and increasing the operating temperature and space velocity, and completely avoided using a high-temperature catalyst at space velocity>500 h−1. The membrane reactor with a WGS catalyst achieves CO conversion of about 85%, above the equilibrium conversion, and 40% CO2 recovery without carbon deposition at high temperature and pressure. The membrane remains in the same structure and gas-tightness after the WGS reaction tests.

Performance of membranes based on novel Ce0.8Sm0.2O2-δ /Ag cermet and molten carbonates for CO2 and O2 separation

• SDC-Ag cermets exhibit outstanding wettability against molten carbonates. • Cermet shows metallic-like electrical conductivity; therefore, σ cermet ≫σ MC. • The cermet phase shows no degradation induced by molten carbonates. • Simultaneous CO 2 and O 2 separation are achieved for the long-term test. This work proposes a cermet infiltrated with a mixture of Li 2 CO 3 /Na 2 CO 3 /K 2 CO 3 as a dense membrane to selectively separate CO 2 and O 2 at high temperatures. The cermet consisted of a mixture of the Ce 0.8 Sm 0.2 O 2-δ (SDC) ceramic and silver as the metallic phase. This type of membrane is a novel design of the ceramic/carbonates type and represents an improvement of state-of-art designs by avoiding microstructural changes in the metallic phase and improving chemical inertness and wettability with the carbonate phase. First, an SDC nanostructured powder was chemically synthesized by direct combustion of urea: lanthanide nitrates-based deep eutectic solvent; then, SDC and silver powders were mixed in a 50:50 vol% ratio by using high energy ball milling. The mixture was uniaxially pressed and sintered to form a support. This cermet exhibited excellent wettability properties against the ternary molten carbonate phase; therefore, it readily allowed infiltration of the molten salts to form a dense membrane. Hence, the cermet showed excellent electronic conductivity as well as corrosion resistance in contact with carbonates for 200 h of continuous immersion. The cermet-carbonate membrane showed permselectivity by separating CO 2 and O 2 at high temperatures. It reaches simultaneous permeation values of 0.49 and 0.26 ml·min −1 ·cm −2 , for CO 2 and O 2, respectively, at 850 °C. Finally, continuous permeation tests at 825 °C for 85 h proved the excellent chemical stability of the cermet-carbonate membrane. Any chemical reactivity was not observed between the cermet and the carbonates.

Hydrogen produced at low temperatures by electrochemically assisted pyrolysis of cellulose in molten carbonate

Cellulose was used as feedstock to investigate the effect of electrolysis on the molten salt pyrolysis process. The mechanism of cellulose transformation in the electrochemically assisted molten carbonate pyrolysis (EMCP) system was evaluated by comparison with the molten carbonate pyrolysis (MCP) system. The gas product yield from the EMCP system reached 70.5 wt%, at the expense of the liquid product and tar. The maximum H2 yields up to 8.31 mol/kg of cellulose at low temperatures without the catalyst in the EMCP system. Cellulose decomposition was catalyzed by the molten salt to produce a large number of volatiles, where the aldehyde groups in the volatiles were electrochemically oxidized to carboxyl groups. Subsequently, the carboxyl compounds combined with alkali metal cations to release hydrogen radicals and then underwent secondary cracking, along with the volatiles having low chemical bond energies. The EMCP system follows the Shrink Cylinder model, which is dominated by the two-dimensional reaction on the surface of the graphite electrode, where the electrolysis process is the determining step.

A theoretical study of molten carbonate fuel cell combined with a solar power plant and Cu–Cl thermochemical cycle based on techno-economic analysis

A novel power and hydrogen coproduction system is designed and analyzed from energetic and economic point of view. Power is simultaneously produced from parabolic trough collector power plant and molten carbonate fuel cell whereas hydrogen is generated in a three-steps Cu–Cl thermochemical cycle. The key component of the system is the molten carbonate fuel cell that provides heat to others (Cu–Cl thermochemical cycle and steam accumulator). A mathematic model is developed for energetic and economic analyses. A parametric study is performed to assess the impact of some parameters on the system performance. From calculations, it is deduced that electric energy from fuel cell, solar plant and output hydrogen mass are respectively 578 GWh, 25 GWh and 306 tons. The overall energy efficiency of the proposed plants is 46.80 % and its LCOE is 7.64 c€/kWh. The use of MCFC waste heat allows increasing the solar power plant efficiency by 2.15 % and reducing the annual hydrogen consumption by 3 %. Parametric analysis shows that the amount of heat recovery impacts the energy efficiency of fuel cell and Cu–Cl cycle. Also, current density is a key parameter that influences the system efficiency.

Effect of dynamic conditions on high-temperature corrosion of ternary carbonate salt for thermal energy storage applications

Li2CO3–Na2CO3–K2CO3 salt is one of the candidates for 3rd generation concentrated solar power (CSP) plants, aiming to increase the operational temperature. This rise of temperature significantly increases the corrosion issue of molten salts. However, there is a lack of studies focused on the effect of salt flow on the corrosion kinetic for this ternary carbonate salt. In this work, corrosion experiments under static and dynamic conditions are compared for SS310 subjected to ternary carbonate salt at 600 °C. A complete characterization of the corrosion layer, surface and cross-section, was carried out by means of SEM-EDX and XRD, while the molten salts after the corrosion tests were analysed by ICP-OES and XPS. The dynamic experiment exhibited an enlarged spallation of the corrosion layer, leading to a thinner and less homogeneous scale. This feature exposed the chromium containing phase and considerably increased the extent of its dissolution into the salt. The obtained results remark that the detrimental effect of dynamic conditions on the corrosivity of molten carbonate salt cannot be neglected and must be taken into account in the design of 3rd generation CSP plants.

Performance analysis of a molten carbonate fuel cell

Performance analysis of a molten carbonate fuel cell

Thermo-economic optimization of a hydrogen storage structure using liquid natural gas regasification and molten carbonate fuel cell

Liquid natural gas (LNG) regasification and fuel cells can be employed to supply the required precooling and electrical power for hydrogen liquefaction, respectively. Such an approach helps reduce the process complexity and the number of equipment, total costs, and carbon footprints, and enhance the controllability of the process. This paper proposes an integrated structure for hydrogen liquefaction and storage by employing the LNG regasification process for precooling and four multi-component refrigerant cycles for liquefaction. Molten carbonate fuel cells, gas turbines power cycles, the two-stage organic Rankine cycle, and the carbon dioxide power cycle are used for supplying the electrical power. A liquid hydrogen production capacity of 1766 kmol/h and 1576.7 MW electrical power generation are attained in this integrated process. The coefficient of performance, specific energy consumption, and specific power consumption of the integrated structure are calculated to be 0.175, 4.772 kWh/kgLH2, and 3.872 kWh/kgLH2, respectively. The exergy efficiency of 83.03% and the exergy destruction of 47.87 MW are obtained based on the exergy analysis. The maximum shares of exergy destruction are attributed to the heat exchangers, gas turbines, and fuel cells with the magnitudes of 45.43%, 24.75%, and 10.93%, respectively. The prime cost of product and rate of return are calculated to be 0.0840 US$/kWh and 24.02%, respectively. According to the sensitivity analysis, it is found that increasing the molar fraction of helium in the multi-component refrigerant cycle from 81.31% to 93.61% leads to a reduction in the net power production (151.2 MW) and total exergy efficiency (81.39%) of the proposed process. Using the multi-objective genetic algorithm method, the total exergy efficiency and the rate of return are optimized to be 86.32% and 29.66%, respectively.