Performance Of Molten Carbonate Fuel Cell Research Articles

Integrated numerical and experimental study of a MCFC-plasma gasifier energy system

In the present work an investigation of the potential use of waste derived fuel gas in molten carbonate fuel cell (MCFC) systems is performed. A simple numerical model of a MCFC is developed following a “system-level” approach that allows to investigate the impact of MCFC performance with respect to efficiency and energy production in complex power systems. An extensive set of experimental tests have been performed on single MCFCs and the experimental data are used to update and validate the numerical model. The fuel cell model is then implemented into a thermo-chemical model of a novel waste treatment system based on plasma torch gasification, previously developed by the authors. The predicted performances of this waste-to-energy system based on the integration of a low pollutant waste treatment technology and a high efficiency power unit are particularly promising.

Fabrication and performance evaluation of electrolyte-combined α-LiAlO 2 matrices for molten carbonate fuel cells

To improve the unit cell performance and stability, molten carbonate fuel cell (MCFC) matrices were fabricated using synthetic α-LiAlO 2 powder and they showed mechanical and microstructural stability under thermal cycle tests. The pure α-LiAlO 2 matrix demonstrated stability with high open-circuit voltage (OCV) and maximum power density during many thermal cycle tests (more than 15 repetitions). Furthermore, to minimize the change in stack height during stack start-up and to improve mechanical and microstructural stabilities of the matrix, the electrolyte-combined α-LiAlO 2 matrix was optimized by controlling the mixing ratio of synthetic α-LiAlO 2 and Li/K carbonate powders. The suitable electrolyte content was fixed at approximately 50 vol.% for the homogeneously filled pores of the pure α-LiAlO 2 matrix. These matrices showed good microstructural stability during five thermal cycle tests in an air atmosphere at 923 K and with improved unit cell performance (0.127 W cm −2) under MCFC operating conditions. In unit cell and thermal cycling tests, the optimized matrices were stable through more than 20 repetitions.

Thermodynamic performance analysis of a molten carbonate fuel cell at very high current densities

This study is basically composed of two sections. In the first section, a CFD analysis is used to provide a better insight to molten carbonate fuel cell operation and performance characteristics at very high current densities. Therefore, a mathematical model is developed by employing mass and momentum conservation, electrochemical reaction mechanisms and electric charges. The model results are then compared with the available data for an MCFC unit, and a good agreement is observed. In addition, the model is applied to predict the unit cell behaviour at various operating pressures, temperatures, and cathode gas stoichiometric ratios. In the second section, a thermodynamic model is utilized to examine energy efficiency, exergy efficiency and entropy generation of the MCFC. At low current densities, no considerable difference in output voltage and power is observed; however, for greater values of current densities, the difference is not negligible. If the molten carbonate fuel cell is to operate at current densities smaller than 2500Am−2, there is no point to pressurize the system. If the fuel cell operates at pressures greater than atmospheric pressure, the unit cell cost could be minimized. In addition, various partial pressure ratios at the cathode side demonstrated nearly the same effect on the performance of the fuel cell. With a 60K change in operating temperature, almost 10% improvement in energy and exergy efficiencies is obtained. Both efficiencies initially increase at lower current densities and then reach their maximum values and ultimately decrease with the increase of current density. By elevating the pressure, both energy and exergy efficiencies of the cell enhance. In addition, higher operating pressure and temperature decrease the unit cell entropy generation.

An Ag-Coated NiO Cathode for MCFCs Operating at Low Temperatures

To increase the lifetime of molten carbonate fuel cell (MCFC) stacks, a reduction of the operating temperature is needed without decreasing the cell performance. In this study, a Ag coating on a conventional NiO cathode material of MCFC was carried out to enhance the cathode performance at the relatively low operating temperature of 600°C. Ag is a material applicable to cathodes for MCFCs because Ag has good catalytic activity for oxygen adsorption and dissociation and high electrical conductivity. The modified cathode was prepared by a vacuum suction method using a nanosized Ag sol suspension, and Ag particles were dispersed homogenously on the surface of a porous Ni plate. After the Ag coating, the cell performance was enhanced significantly from 0.76 to 0.80 V at a 150 mA/cm2 current density at 600°C. The electrochemical impedance spectra show that the reduction of the charge transfer resistance is the main reason for the improvement of the cell performance after the Ag coating.

하부 사이클 추가에 의한 MCFC 시스템의 성능향상

Integration of various bottoming cycles such as the gas turbine (GT) cycle, organic Rankine cycle, and oxy-fuel combustion cycle with an molten carbonate fuel cell (MCFC) power-generation system was analyzed, and the performance of the power-generation system in the three cases were compared. Parametric analysis of the three different integrated systems was carried out under conditions corresponding to the practical use and operation of MCFC, and the optimal design condition for each system was derived. The MCFC/oxy-combustion system exhibited the greatest power upgrade from the MCFC-only system, while the MCFC/GT system showed the greatest efficiency enhancement.

Phase and Microstructural Stability of Electrolyte Matrix Materials for Molten Carbonate Fuel Cells

AbstractLiAlO2 powder is used as a material for molten‐carbonate fuel cell (MCFC) matrices. The physical and chemical stabilities of LiAlO2 powder during MCFC operation determine the performance and lifetimes of the cells. Change to the phase and particle size in the allotropic phase of LiAlO2 was examined with long‐term stability tests on pure α‐LiAlO2 matrix, Al‐reinforced α‐LiAlO2 matrix, Al‐reinforced γ‐LiAlO2 matrix, aqueous γ‐LiAlO2 matrix and an α‐/β‐LiAlO2 mixture powder in molten carbonate at 650 °C in air. In the γ‐LiAlO2 and α‐/β‐LiAlO2 mixture, the particle growth was continuous from the early stages of heat‐treatment to 20,000 h. Crystalline phase transformation (γ‐LiAlO2 and β‐LiAlO2 to α‐LiAlO2 and γ‐LiAlO2, respectively) of these powders and matrices also occurred, and γ‐LiAlO2 made the third phase like LiAl5O8. By contrast, the sizes of these particles and the crystalline phase of α‐LiAlO2 did not change during immersion tests. These results show that, among α‐/β‐ and γ‐LiAlO2, α‐LiAlO2 is the most stable phase in molten carbonate.

Modeling of a Direct Carbon Fuel Cell System

Direct carbon fuel cells (DCFCs) have great thermodynamic advantages over other high temperature fuel cells such as molten carbonate fuel cells (MCFCs) and solid oxide fuel cells. They can have 100% fuel utilization, no Nernst loss (at the anode), and the CO2 produced at the anode is not mixed with other gases and is ready for re-use or sequestration. So far, only studies have been reported on cell development. In this paper, we study the performance of a CO2-producing DCFC system model. The theoretically predicted advantages that are confirmed on a bench scale are also confirmed on a system level, except for the production of pure CO2. Net system efficiencies of around 78% were found for the developed system. An exergy analysis of the system shows where the losses in the system occur. If the cathode of the DCFC must be operated as a standard MCFC cathode, the required CO2 at the cathode is the reason why a large part of the pure CO2 from the anode is recycled and mixed with the incoming air and cannot be used directly for sequestration. Bench scale studies should be performed to test the minimum amount of CO2 needed at the cathode. This might be lower than in a standard MCFC operation due to the pure CO2 at the anode side that enhances diffusion toward the cathode.

Thermal management of the molten carbonate fuel cell plane

The operating temperature range of molten carbonate fuel cells (MCFCs) is about 925–955 K. An input gas temperature of at least 855 K is necessary to guarantee good ionic conduction inside the cells. Maximum local temperatures higher than 960 K should be avoided because they can cause problems such as electrolyte loss and corrosion. The first limit can easily be managed, while the second can only be managed through taking many local measurements or, more properly, reliable detailed simulation models. Using a specific code developed by the authors, the temperature distribution on the cell plane can be calculated with an error of the same order of magnitude as the experimental one. The study of different MCFC operating conditions carried out using our simulation tool highlighted the difficulties in respecting the constraint on the maximum local temperature. The temperature maps of an MCFC plane can be very irregular and some parts of the cell can work under critical conditions even if the average temperature is not too high and this aspect is critical for industrial optimisation of MCFC performance. Different techniques have been tried to obtain a uniform temperature distribution on the cell plane. In particular, having observed that fluid-dynamics plays a predominant role in the problem, a solution based on the use of non-uniform inlet gas-flows has been proposed. The encouraging results obtained will be shown and discussed in detail.

Влияние методики синтеза на физико-химические свойства LaLi0.1Со0.1Fe0.8O3 - δ

The phase composition, conductivity and corrosion resistance under the Molten Carbonate Fuel Cell (MCFC) operating conditions of synthesized using common ceramic and cocrystallization techniques samples of LaLi0.1Со0.1Fe0.8O3 – δ have been studied. It was found, that the phase composition of synthesized by ceramic technique sample differed from the nominal composition. This difference arose from the formation of complex oxide (La1-yLiy)(Li0.1-yCoxFe0.9 – x)O3 – δ', y ≤ 0.1, and La2O3. Synthesized by cocrystallization technique sample was found to be of single phase. Its conductivity differed from the conductivity of two phase sample. Under MCFC operating conditions the difference in properties of synthesized by both techniques samples diminished and converged towards the properties of the sample prepared by ceramic technique.

Molten carbonate fuel cell performance under different cathode conditions

Molten carbonate fuel cells (MCFCs) are electrochemical devices directly converting chemical energy of a redox reaction into electricity: compared with energy conversion by combustion, it is significantly more efficient and less polluting. This paper presents a preliminary study exploring the possibilities of improving the overall MCFC performances, by lowering the cathode polarization. Tests were carried out on single cell systems: these are devices able to simulate full-size plant operation in its essential features. Single cells are constituted by an assembly of porous and metallic components (anode, cathode, matrix, anodic and cathodic current collectors) enclosed by two steel shells. A particular numerical method were used in order to discriminate between the different contributions (anodic polarization, cathodic polarization, internal resistance polarisation and Nernst losses) to the cell’s performance reduction during its operation. This method has been applied to specific single cell test, where only cathode working conditions were changed and the cell’s response (in terms of voltage changes) was recorded. In this way the cathode’s contribution has been identified. These tests have confirmed the possibility of performance improvement possibilities by working on the cathode polarization.

The effect of water on direct ethanol molten carbonate fuel cell

Bio-ethanol can be used directly as a fuel in molten carbonate fuel cell (MCFC). Unfortunately, the high water content of bio-ethanol has several negative effects; decrease in performance, electrolyte loss due to evaporation, and corrosion of anode cell frame. This research was conducted to overcome the negative effects without degrading MCFC's performance and stability. A decrease in performance due to low H 2 contents was unavoidable. An electrolyte loss was minimized when the recycling method was used. The optimum recycling ratio was achieved when the flow rate ratio of output to recycle was in the range of 0.7–1. A corrosion of the cell frame was successfully blocked by Ni-electroplated cell frame. This system was successfully tested for over 2000 h without any decrease in performance.

Fluid-dynamic characterisation of MCFC gas distributors

Previous studies at the plant scale have shown that thermal management is a crucial point in molten carbonate fuel cell operation optimisation. At the local scale, the principal mechanisms controlling the temperature map on the cell plane have been analysed and it has been shown that the fluid dynamics of the anodic and cathodic gases on the cell could have a fundamental role in thermal optimisation. So, the authors have analysed the gas flow in planner cells, using a computational fluid dynamics (CFD) technique and identifying the characteristic fluid-dynamic parameters. The studied structure consists of a typical current collector/gas distributor formed by a plurality of arches with suitable height to provide sufficient reactant flow area, proper stiffness to accept compressive load and adequate resiliently to distribute the load and maintain electrical contact. The results of this analysis are presented and discussed in this paper, while the modelling approach is presented as a useful tool for improving the current collector/gas distributor design, identifying new technological solutions and optimising MCFC performance.

Characteristics of aluminum-reinforced γ-LiAlO2 matrices for molten carbonate fuel cells

A key component in molten carbonate fuel cells (MCFCs) is the electrolyte matrix, which provides both ionic conduction and gas sealing. During initial MCFC stack start-up and operation (650°C), the matrix experiences both mechanical and thermal stresses as a result of the difference in thermal expansion coefficients between the LiAlO2 ceramic particles and the carbonate electrolyte that causes cracking of the matrix. A pure γ-LiAlO2 matrix, however, has poor mechanical strength and low thermal expansion coefficients. In this study, fine γ-LiAlO2 powders and pure Al (3/20/50μm)/Li2CO3 particles are used as a matrix and as reinforcing materials, respectively. The Al phase transforms completely into γ-LiAlO2 at 650°C within 10h. The mechanical strength of these matrices (283.48gfmm−2) increases nearly threefold relative to that of a pure γ-LiAlO2 matrix (104.01gfmm−2). The mismatch of the thermal expansion coefficient between the matrix and electrolyte phases can be controlled by adding Al particles, which results in improved thermal stability in the initial heating-up step. In unit-cell and thermal-cycling tests, the optimized matrix demonstrates superior performance over pure γ-LiAlO2 matrices.

Molten carbonate fuel cell operation with dual fuel flexibility

The ability to operate highly efficient, pollution-free, distributed-generation power plants on either natural gas or HD-5 grade propane is of interest to the U.S. Army and the U.S. Department of Homeland Security as secure power for critical power operations. To address this interest, Concurrent Technologies Corporation (CTC) teamed with FuelCell Energy (FCE) to test an internally reforming 250 kW carbonate fuel cell using HD-5 propane. This fuel cell power plant, originally designed to operate on pipeline natural gas or digester gas, was modified for dual fuel operation (natural gas and propane). Fuel cell operation using HD-5 propane was demonstrated for over 3900 h and achieved high-electrical efficiency (45.7–47.1% lower heating value (LHV)) over a broad range of power outputs. In addition, instantaneous and on-load fuel switching from natural gas to propane and back was demonstrated without loss of power. This dual fuel power plant operates efficiently on either fuel and provides the U.S. Army and other power users with a viable technology solution for critical power operations.

MCFC performance diagnosis by using the current-pulse method

Several problems prevent molten carbonate fuel cells (MCFC) operation for an extended period. However, if the degradation factors can be identified and resolved in a timely manner, MCFC could become a valuable technology. Therefore, a performance diagnosis should be developed which enables the simple and instantaneous determination of MCFC degradation factors. A suitable six parameter equation obtained by a current-pulse method, obtainable from MCFC's transient response in 100 ms, is expressible in an equivalent circuit composed of three sub-circuits. The relationship between these parameters and each degradation factor is evaluated by a single MCFC cell, the electrode area of which is 16 cm 2. Degradation factors include cross-leakage, electrolytic loss, cell temperature distribution and gas composition/flow rate. As a result, each of six parameters in the MCFC transient response corresponds to an ohmic potential drop, anode/cathode gas diffusion resistance, reactive resistance, three-phase interfacial resistance and electrolyte properties, respectively. The proposed performance diagnosis specifies the degradation factors by combining the six parameters. Performance diagnosis was applied to a single MCFC cell of an electrode area of 81 cm in extended operations, and the degradation factor diagnosed. As a result, the diagnosis was able to specify the cell degradation factors from the degradation factor ratio, corresponding to cell voltage, cell resistance and the N 2 concentration of MCFC single cell performance. Therefore, the proposed performance diagnosis is able to easily specify the driven MCFC degradation factors in a timely manner.

Experimental comparison of MCFC performance using three different biogas types and methane

Biogas recovery is an environmentally friendly and cost-effective practice that is getting consensus in both the scientific and industrial community, as the growing number of projects demonstrate. The use of fuel cells as energy conversion systems increases the conversion efficiency, as well as the environmental benefits. Molten carbonate fuel cells (MCFC) operate at a temperature of about 650 °C, thus presenting a high fuel flexibility, compared to low temperature fuel cells. Aim of the present study is to compare the performance of an MCFC single cell, fuelled with different biogas types as well as methane. The biogases considered are derived from the following processes: (1) steam gasification in an entrained flow gasifier; (2) steam gasification in a duel interconnect fluidized bed gasifier; (3) biogas from an anaerobic digestion process. The performances are evaluated for different fuel utilization and current densities. The results are an essential starting point for a complete system design and demonstration.

Studies on the modeling calculations of the unit molten carbonate fuel cell

One parameter should be fixed in the process of simulating the performance of a unit MCFC (molten carbonate fuel cell). Distributions of temperature, conversions of hydrogen, and cell performance have been obtained in two different methods: one with a fixed value of cell voltage and the other with a fixed value of current density. Results by both methods have been compared with experimental data. The method with the fixed value of cell voltage resulted in a more reasonable fitting to experimental data.

Cycle Analysis of Micro Gas Turbine-Molten Carbonate Fuel Cell Hybrid System

A hybrid system based on a micro gas turbine (µGT) and a high-temperature fuel cell, i.e., molten carbonate fuel cell (MCFC) or solid oxide fuel cell (SOFC), is expected to achieve a much higher efficiency than conventional distributed power generation systems. In this study, a cycle analysis method and the performance evaluation of a µGT-MCFC hybrid system, of which the power output is 30kW, are investigated to clarify its feasibility. We developed a general design strategy in which a low fuel input to a combustor and higher MCFC operating temperature result in a high power generation efficiency. A high recuperator temperature effectiveness and a moderate steam-carbon ratio are the requirements for obtaining a high material strength in a turbine. In addition, by employing a combustor for complete oxidation of MCFC effluents without additional fuel input, i.e., a catalytic combustor, the power generation efficiency of a µGT-MCFC is achieved at over 60%(LHV).

Evaluation of Ni–Ni 3Al(5 wt.%)–Al(3 wt.%) as an anode electrode for molten carbonate fuel cell : Part I: Creep and sintering resistance

To develop an anode electrode of molten carbonate fuel cell (MCFC) that has higher creep and sintering resistance and more stable reactivity than the traditional anode electrode, the five kinds of nickel anode electrodes such as Ni–Al(5), Ni–Cr(10), Ni–Ni 3Al(7), Ni–Ni 3Al(5)–Cr(5) and Ni–Ni 3Al(5)–Al(3) (number in parenthesis means the weight percent of its component) were prepared and their performance were investigated under the same conditions of MCFC operation. In part I of our study, their relative creep and sintering resistance were compared. The Ni–Ni 3Al(5)–Al(3) anode electrode was the most resistant against the sintering and its porosity was kept over 60% even at 1000 °C. And its porosity decrease and thickness shrinkage by creep were the least among the five kinds of anode electrodes. Thus, the effects of the aluminum and nickel–aluminum intermetallic compound (Ni 3Al) addition to nickel as the dispersant strengthening and the solid solution strengthening agents were confirmed by comparative tests for sintering and creep resistance of five kinds of anode electrodes. Besides these results, we could also know that the creep of anode electrode for MCFC mostly proceeded within 60 h from the start of operation irrespective of the kinds of anode electrodes. And in part II of paper, for more information about the wetting ability and cell performances of these five kinds of anode electrodes, the measurement of wetting ability and unit cell operations were carried out.

A Stochastic Structure Model for Liquid-Electrolyte Fuel Cell Electrodes, with Special Application to MCFCs: I. Electrode Structure Generation and Characterization

Electrolyte distribution plays a crucial role in the performance of the molten carbonate fuel cells (MCFCs), and especially affects their dynamic performance because the electrolyte is redistributed as a function of load. Transients due to load changes depend strongly on the dynamics of this redistribution, which has not been investigated for lack of a realistic model. For future use in studying dynamic MCFC performance due to electrolyte redistribution, a stochastic electrolyte distribution model is developed. It offers the possibility to visualize the electrolyte distribution within the porous electrode and to generate the structural parameters for the performance model as a function of electrolyte filling level. © 2004 The Electrochemical Society. All rights reserved.