Molten carbonate fuel cell (MCFC)-based hybrid propulsion systems for a liquefied hydrogen tanker

This study proposes a molten carbonate fuel cell (MCFC)-based hybrid propulsion system for a liquefied hydrogen tanker. This system consists of a molten carbonate fuel cell and a bottoming cycle. Gas turbine and steam turbine systems are considered for recovering heat from fuel cell exhaust gases. The MCFC generates a considerable propulsion power, and the turbomachinery generates the remainder of the power. The hybrid systems are evaluated regarding system efficiency, economic feasibility, and exhaust emissions. The MCFC with a gas turbine has higher system efficiency than that with a steam turbine. The air compressor consumes substantial power and should be mechanically connected to the gas turbine. Although fuel cell-based systems are less economical than other propulsion systems, they may satisfy the environmental regulations. When the ship is at berth, the MCFC systems can be utilized as distributed generation that is connected to the onshore-power grid.     

Electrochemical performances of NANOCOFC in MCFC environments

The electrochemical performances of fuel cells using nano-ceria-salt composites electrolyte (NANOCOFC) have been investigated at different temperatures in molten carbonate fuel cell (MCFC) environment. The maximum output power density increased with the temperature, and reached 140 mW/cm² at 650 °C. After operating for 200 h, the open circuit voltage (OCV) can keep the same value and the output power density only deceased 0.08%. It demonstrated that the NANOCOFC possessed the perfect stability of electrochemical performance in the MCFC environment. However, it was found that the output power density of the fuel cell in MCFC environment was much lower than that of fuel cell in SOFC environment. It was implied that the carbonate transfer would hinder the conduction of both proton and oxygen ion, which result in the poor output power density of fuel cells.     

Modeling the performance of MCFC for various fuel and oxidant compositions

100 cm² molten carbonate fuel cells (MCFC) was used for testing the fuel and oxidant composition influence on MCFC performance as a temperature function.     

熔融碳酸盐燃料电池的电气特性研究

为了研究熔融碳酸盐燃料电池的电气特性,分析了熔融碳酸盐燃料电池单元的电化学过程机理,建立了基于电化学反应的熔融碳酸盐燃料电池电气模型,推导了熔融碳酸盐燃料电池平均电流密度与燃气利用率的关系,给出了采用电化学方程的熔融碳酸盐燃料电池电气特性的模型结构和算法,并进行了仿真研究和试验.试验结果表明:该模型结构简单、准确度高,可获得千瓦级熔融碳酸盐燃料电池的电气特性曲线.     

Comparison study on different ITM‐integrated MCFC hybrid systems with CO2 recovery using sweep gas

Previous study shows the ITM (oxygen ion transfer membrane)‐integrated MCFC (molten carbonate fuel cell) hybrid system with CO₂ recovery can maintain high efficiency; however, the oxygen partial pressure on the ITM permeate side is usually 1 atm, which requires a very high pressure ratio of the ITM air compressor in order to separate the oxygen; using the sweep gas can solve this problem. In this paper the ITM‐integrated MCFC hybrid systems with CO₂ recovery using different sweep gases are studied. With the Aspen plus software, two systems with different sweep gases are established, and their performances are compared with the benchmark system without sweep gas; the effects of key parameters on the optimum system performance are also investigated. Results show that compared with the benchmark system, the efficiencies of the systems with sweep gases are increased and the pressure ratios of the air compressors are decreased; the system using pure CO₂ as sweep gas can improve the system efficiency by 1.25%, which is superior to the system using the mixture gas of CO₂ and H₂O as sweep gas. Achievements from this paper will provide a valuable reference for CO₂ recovery from the MCFC hybrid power system with lower energy consumption. Copyright © 2016 John Wiley & Sons, Ltd.     

Gasification characteristics of organic waste by molten salt

Recently, along with the growth in economic development, there has been a dramatic accompanying increase in the amount of sludge and organic waste. The disposal of such is a significant problem. Moreover, there is also an increased in the consumption of electricity along with economic growth. Although new energy development, such as fuel cells, has been promoted to solve the problem of power consumption, there has been little corresponding promotion relating to the disposal of sludge and organic waste. Generally, methane fermentation comprises the primary organic waste fuel used in gasification systems. However, the methane fermentation method takes a long time to obtain the fuel gas, and the quality of the obtained gas is unstable. On the other hand, gasification by molten salt is undesirable because the molten salt in the gasification gas corrodes the piping and turbine blades. Therefore, a gasification system is proposed by which the sludge and organic waste are gasified by molten salt. Moreover, molten carbonate fuel cells (MCFC) are needed to refill the MCFC electrolyte volatilized in the operation. Since the gasification gas is used as an MCFC fuel, MCFC electrolyte can be provided with the fuel gas. This paper elucidates the fundamental characteristics of sludge and organic waste gasification. A crucible filled with the molten salt comprising 62 Li₂CO₃/38 K₂CO₃, is installed in the reaction vessel, and can be set to an arbitrary temperature in a gas atmosphere. In this instance, the gasifying agent gas is CO₂. Sludge or the rice is supplied as organic waste into the molten salt, and is gasified. The chemical composition of the gasification gas is analyzed by a CO/CO₂ meter, a HC meter, and a SO_x meter gas chromatography. As a result, although sludge can generate CO and H₂ near the chemical equilibrium value, all of the sulfur in the sludge is not fixed in the molten salt, because the sludge floats on the surface of the carbonate by the specific gravity of sludge lighter than the carbonate, and is not completely converted into CO and H₂. Moreover, the rice also shows good characteristics as a gasifying agent. Consequently, there is high expectation to using the organic waste as a molten salt gasifying agent. However, this requires lengthening the contact time between the organic waste and the molten salt.     

Performance analysis and multi-objective optimization of a new molten carbonate fuel cell system

The model of a new molten carbonate fuel cell (MCFC) system is established, in which multi-irreversibilities resulting from the anode, cathode, and ohm overpotentials are taken into account. Based on thermodynamic-electrochemical analysis and the semi-empirical equations available in literature, expressions of some main parameters such as the cell voltage, power output, efficiency and entropy production rate are derived. The influence of the gas inlet compositions on the electrode overpotentials is discussed in detail. It is found that there exist the optimal anode CO₂ concentrations for different anode H₂ concentrations. The performance characteristic curves of the MCFC system are represented through numerical calculation and the optimal operation regions of the main parameters are determined. Moreover, a new multi-objective function is used to further optimize the characteristics of the MCFC system, and consequently, the important problem of how to give consideration to both the efficiency and power output in the optimal operation region of the system is expounded.     

Performance investigation of a combined MCFC system

This study investigates the performance of a combined industrial molten carbonate fuel cell (MCFC) system, including a turbo expander, which was recently installed by Enbridge Inc. in Toronto, Canada. It entails a comprehensive thermodynamic analysis regarding energy and exergy calculations, subject to varying operating conditions. Furthermore, a simplified and novel method is used for a cost analysis to assess the amortization of the system. The results from the base case study suggest that an overall energy efficiency as high as 60% is achievable while fuel cell stack energy and exergy efficiencies of 50.6% and 49.3%, respectively, are reached. The cost analysis indicates that the amortization of the system may take up to 15 years of operational time, depending on the price of electricity and natural gas. However, carbon offsets may make a paramount contribution to the overall savings and economic viability of future combined MCFC systems.     

Industrial experience on the development of the molten carbonate fuel cell technology

The development of the molten carbonate fuel cell (MCFC) technology at Ansaldo Ricerche (ARI) is reported, starting from small scale single cells up to stacks of several kW capacity. The evolution of material and fabrication strategies as well as the progress in terms of electrical performance are described and discussed. The data reported show that the MCFC technology has been successfully tested on stacks in the kW power class, however some problems still need to be solved to improve the stack performance. In particular, better control of the start-up phase, of electrolyte migration through the manifolds and of the gas feed distribution are required, based on the latest experimental data on a 50 cell stack with cell area 0.1 m² (cell active area 0.0702 m²), which operated for 780 h with a maximum performance of 4 kW at 206 mA/cm² at 50% fuel utilisation. Future development steps, which will lead to the realisation and operation of systems of several hundred kW, are presented.     

Control‐oriented nonlinear modelling of molten carbonate fuel cells

Performance and availability of molten carbonate fuel cells (MCFC) stack are greatly dependent on its operating temperature. Control of the operating temperature within a specified range and reduction of its temperature fluctuation are highly desirable. The models of MCFC stack existing are too complicated to be suitable for design of a controller because of its lack of clear input–output relations. In this paper, according to the demands of control design, a quantitative relations model of control‐oriented MCFC between the temperatures of the stack and flowrates of the input gases is developed, based on conservation laws. It is an affine nonlinear model with multi‐input and multi‐output, the flowrates of fuel and oxidant gases as the manipulated vector and the temperatures of MCFC electrode–electrolyte plates, separator plates as the controlled vector. The modelling and simulation procedures are given in detail. The simulation tests reveal that the model developed is accurate and it is suitable to be used as a model in designing a controller of MCFC stack. Copyright © 2004 John Wiley & Sons, Ltd.     

Energy and exergy analyses of a combined molten carbonate fuel cell - Gas turbine system

This study deals with the thermodynamic analysis of molten carbonate fuel cell combined with a gas turbine, based on the first- and second-law of thermodynamics. The mass, energy, entropy and exergy balance equations are written and applied to the system and its components. Some parametric studies are performed to investigate the change of system performance through energy and exergy efficiencies with the change of operating conditions. The irreversibilities occuring in different devices of the integrated system are also investigated through the exergy destruction analysis in these devices. The maximum output work of the MCFC is estimated to be 314.3 kW for an operating temperature of 650 °C. The overall energy and exergy efficiencies achieved for this system are 42.89% and 37.75%, respectively.     

Performance analysis of new cathode materials for molten carbonate fuel cells

The slow dissolution of the lithiated nickel oxide cathode represents one of the main causes of performance degradation in molten carbonate fuel cells (MCFC). Two main approaches were studied in ENEA laboratories to overcome this problem: protecting the nickel cathode covering it by a thin layer of a material with a low solubility in molten carbonate and stabilizing the nickel cathode doping it with iron and magnesium.Among several materials, due to its low solubility and good conductivity, lithium cobaltite was chosen to cover the nickel cathode and slow down its dissolution. A nickel electrode covered with a thin layer of lithium cobaltite doped with magnesium, was fabricated by complex sol-gel process. To simplify electrode preparation, no thermal treatments were made after covering to produce lithium cobaltite, and during the cell start-up LiMg_0.05Co_0.95O₂ was obtained in situ.To stabilize the nickel cathode, metal oxides Fe₂O₃ and MgO were chosen as dopant additives to be mixed with NiO powder in a tape-casting process (Mg_0.05Fe_0.01Ni_0.94O).On the prepared materials TGA analysis, morphological analysis by scanning electron microscopy (SEM-EDS) and electrical conductivity measurements were carried out.A conventional nickel cathode, the nickel cathode covered by lithium cobaltite precursors and the nickel cathode stabilized by iron and magnesium oxides were each tested in a 100 cm² fuel cell.Polarization curves and internal resistance (iR) measurements were acquired during the cell lifetime (1000 h) and the effect of gas composition variation on the cell performance was studied.From a comparison with the conventional nickel cathode it can be observed that the new materials have similar performance and show a good potential stability during the cell operating time. From the post-test analysis both the nickel cathode covered by lithium cobaltite and the nickel cathode doped with iron and magnesium seem to succeed in reducing nickel dissolution.     

MCFC versus other fuel cells—Characteristics, technologies and prospects

Characteristics of molten carbonate fuel cell (MCFC) were critically compared to these of polymer electrolyte membrane fuel cell (PEMFC), alkaline fuel cell (AFC), phosphoric acid fuel cell (PAFC) and solid oxide fuel cell (SOFC). In comparison to the other fuel cells, the MCFC operates with the lowest current densities due to limited zones of effective electrode reactions and low solubilities of oxygen and hydrogen in molten carbonates; also it has a thickest electrodes–electrolyte assembly. In consequence, the applications of MCFC are almost limited to stationary power generators. Although the MCFC stationary power generators have now approached high technological level of precommercialization, in the future they may face a serious contest from SOFC and PEMFC, for which improvement of operational parameters is believed to be achieved easier.     

Distributed generation—Molten carbonate fuel cells

High efficiency and ultra-clean molten carbonate fuel cell (MCFC) technology development by FuelCell Energy, with support from the U.S. Department of Energy (DOE), has progressed to commercial power plants for stationary applications such as distributed generation. Lessons learned from this development will also be valuable to DOE for the ongoing Solid State Energy Conversion Alliance (SECA) solid oxide fuel cell (SOFC) development and cost reduction, for fuel cell turbine hybrids, and for hydrogen economy development with FutureGen.     

Design analysis and tri-objective optimization of a novel integrated energy system based on two methods for hydrogen production: By using power or waste heat

Hydrogen is rapidly turning into one of the essential energy carriers for future sustainable energy systems. The main reason for this is the possibility of off-peak excess power production and storage of renewable stations such as wind farms, photovoltaic plants, etc. For hydrogen (itself) or its sub-productions methanol, ammonia, etc. Such energy systems are so-called power2X technologies. For hydrogen and other biogases, using a fuel cell is a promising method for returning the fuel to the power grid or electric cars in the form of electricity. In this paper, a novel hybrid energy system consisting of a molten carbonate fuel cell (MCFC) and different options to generate hydrogen from the waste heat of the MCFC is investigated. The system consists of two scenarios of weather using proton exchange membrane electrolyzer (PEME) of vanadium chloride (VCL) cycle. The article presents a comprehensive thermodynamic, economic, and environmental analysis of the system optimized by tri-objective optimization (as an innovative optimization) methods. The aim of the optimization task here is to minimize the costs and emissions while maximizing efficiency. A parametric study is conducted to see the effect of different design parameters on the system's performance. Results demonstrate that fuel utilization factor, stack temperature, and current density have the most critical effect on the system performance. In addition, the system coupled with the VCL cycle exhibits better performance than the system with PEME. In addition, at the optimized point, the efficiency, cost rate, and emission become 69.28%, 3.73 ($/GJ), and 1.16 kg/kWh, respectively. In addition, the produced hydrogen in VCL and PEME are 585 kg/day and 293 kg/day respectively.     

Performance evaluation of a novel CCHP system integrated with MCFC,ISCC and LiBr refrigeration system

This paper proposes a novel combined cooling, heating, and power (CCHP) system integrated with molten carbonate fuel cell (MCFC), integrated solar gas-steam combined cycle (ISCC), and double-effect absorption lithium bromide refrigeration (DEALBR) system. According to the principle of energy cascade utilization, part of the high-temperature waste gas discharged by MCFC is led to the heat recovery steam generator (HRSG) for further waste heat utilization, and the other part of the high-temperature waste gas is led to the MCFC cathode to produce CO₃^2?, and solar energy is used to replace part of the heating load of a high-pressure economizer in HRSG. Aspen Plus software is used for modeling, and the effects of key factors on the system performances are analyzed and evaluated by using the exergy analysis method. The results show that the new CCHP system can produce 494.1 MW of electric power, 7557.09 kW of cooling load and 57,956.25 kW of heating load. Both the exergy efficiency and the energy efficiency of the new system are 61.69% and 61.64%, respectively. Comparing the research results of new system with similar systems, it is found that the new CCHP system has better ability to do work, lower CO₂ emission, and can meet the cooling load, heating load and electric power requirements of the user side at the same time.     

Multi-objective optimization of molten carbonate fuel cell system for reducing CO2 emission from exhaust gases

The aim of this paper is to investigate the implementation of a molten carbonate fuel cell (MCFC) as a CO₂ separator. By applying multi-objective optimization (MOO) using the genetic algorithm, the optimal values of operating load and the corresponding values of objective functions are obtained. Objective functions are minimization of the cost of electricity (COE) and minimization of CO₂ emission rate. CO₂ tax that is accounted as the pollution-related cost, transforming the environmental objective to the cost function. The results show that the MCFC stack which is fed by the syngas and gas turbine exhaust, not only reduces CO₂ emission rate, but also produces electricity and reduces environmental cost of the system.     

MCFC and microturbine power plant simulation

The consistent problem of the CO₂ emissions and the necessity to find new energy sources, are motivating the scientific research to use high efficiency electric energy production's technologies that could exploit renewable energy sources too. The molten carbonate fuel cell (MCFC) due to its high efficiencies and low emissions seems a valid alternative to the traditional plant. Moreover, the high operating temperature and pressure give the possibility to use a turbine at the bottom of the cells to produce further energy, increasing therefore the plant's efficiencies. The basic idea using this two kind of technologies (MCFC and microturbine), is to recover, via the microturbine, the necessary power for the compressor, that otherwise would remove a consistent part of the MCFC power generated. The purpose of this work is to develop the necessary models to analyze different plant configurations. In particular, it was studied a plant composed of a MCFC 500 kW Ansaldo at the top of a microturbine 100 kW Turbec. To study this plant it was necessary to develop: (i) MCFC mathematical model, that starting from the geometrical and thermofluidodynamic parameter of the cell, analyze the electrochemical reaction and shift reaction that take part in it; (ii) plate reformer model, a particular compact reformer that exploit the heat obtained by a catalytic combustion of the anode and part of cathode exhausts to reform methane and steam; and (iii) microturbine-compressor model that describe the efficiency and pressure ratio of the two machines as a function of the mass flow and rotational regime. The models developed was developed in Fortran language and interfaced in Chemcad^© to analyze the power plant thermodynamic behavior. The results show a possible plant configuration with high electrical and global efficiency (over 50 and 74%).     

A methodology for improving the performance of molten carbonate fuel cell/gas turbine hybrid systems

In the present article a molten carbonate fuel cell (MCFC) system has been developed, modeled and implemented in Matlab language. It enables definition of the optimal operating conditions of the fuel cell, in terms of electrical and thermal performance, when it is a part of a hybrid plant composed of an MCFC system, a gas turbine and a possible heat recovery system. The thermal energy, which is recoverable from the adequately treated anodic exhaust gases, is utilized in a gas turbine plant to reduce its fuel consumption. Therefore, in the present article a methodology is illustrated to calculate the optimal values of some parameters characterizing the MCFC/gas turbine integrated system in terms of the electrical, first law and equivalent efficiencies. A choice is made among the sets of values of parameters investigated to improve the performance of the same integrated system according to its use (for the production of electric energy only or for the contemporary production of electric and thermal energy). Copyright © 2010 John Wiley & Sons, Ltd.     

The economics of a fuel cell cogeneration system using a by-product hydrogen stream

A site-specific fuel cell cogeneration study was conducted. A molten carbonate fuel cell (MCFC) system, sized at a nominal 25 MW (d.c.) to use an available by-product hydrogen stream, was compared with the alternative of purchased electricity and the use of natural gas to produce steam. The economic analysis objectives were to determine; the savings due to the reduced amount of purchased energy; the cost/benefit ratio; and the payback period for the MCFC cogeneration system. Another objective was to determine if the high capital cost of the first prototype MCFC plant would require a commercialization subsidy to make it attractive to an industrial owner. It was found that a commercialization subsidy would be required for the initial high cost prototype plant, but this technology promises an energy utilization of 84% of the input fuel heating value which represents a strong incentive for commercialization.