Carbonate Fuel Cell System Research Articles

Exergy analysis and optimisation of a marine molten carbonate fuel cell system in simple and combined cycle configuration

In this paper we present the exergy analysis and design optimisation of an integrated molten carbonate fuel cell (MCFC) system for marine applications, considering waste heat recovery options for additional power production. High temperature fuel cells are attractive solutions for marine energy systems, as they can significantly reduce gaseous emissions, increase efficiency and facilitate the introduction of more environmentally-friendly fuels, like LNG and biofuels. We consider an already installed MCFC system onboard a sea-going vessel, which has many tightly integrated sub-systems and components: fuel delivery and pre-reforming, internal reforming sections, electrochemical conversion, catalytic burner, air supply and high temperature exhaust gas. The high temperature exhaust gasses offer significant potential for heat recovery that can be directed into both covering the system’s auxiliary heat requirements and power production. Therefore, an integrated systems approach is employed to accurately identify the true sources of losses in the various components and to optimise the overall system with respect to its energy efficiency, taking into account the various trade-offs and subject to several constraints. Here, we present a four-step approach: a. dynamic process models development of simple and combined-cycle MCFC system; b. MCFC components and system models calibration via onboard MCFC measurements; c. exergy analysis, and d. optimisation of the simple and combined-cycle systems with respect to their exergetic performance. Our methodology is based on the thermofluid and chemical reactions modelling of each component, via our in-house ship machinery systems modelling framework, DNVGL COSSMOS. For the major system components spatially distributed exergy balances are considered in order to capture the coupling of the local process phenomena and exergy destruction with component design characteristics. Exhaust heat recovery is considered using a steam turbine combined-cycle module integrated with the rest of the MCFC system. Both the simple and combined cycle MCFC systems are optimised with respect to their overall exergetic efficiency subject to design, technical, operational and space constraints. The exergy analysis identified and ranked the sources of exergy destruction and the subsequent optimisation yielded significant improvement potential for both systems. The simple MCFC system optimisation yielded an exergy efficiency improvement of 7% with 5% more power produced. Heat recovery in the combined cycle MCFC resulted in 40% more power produced, with a 60% overall exergy efficiency (relative increase of 45%). Both MCFC systems outperform conventional dual-fuel engines with respect to efficiency, having also a positive impact on CO2 emissions with a relative reduction of about 30%.

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.

Carbon dioxide emission reduction using molten carbonate fuel cell systems

Abstract The contribution of the molten carbonate fuel cell system (MCFCs) to carbon dioxide (CO2) emission reduction in power application is analyzed. MCFCs can separate and concentrate CO2 emitted from traditional thermal power plants (PPs) without reducing the plant's overall energy efficiency. MCFCs can also be used by itself as an effective CO2 separator or concentrator by managing the anode gas stream to increase the heat utilization of the system. The CO2 separated and concentrated by MCFCs is most effectively captured by condensation. MCFCs is currently used as a CO2 separator only to a limited extent due to its high cost and relatively small scale operation. However, MCFCs will substantially contribute to reduce CO2 emissions in power generation applications in the near future.

Control of a direct internal reforming molten carbonate fuel cell system using wavelet network-based Hammerstein models

Inspired by a direct internal reforming molten carbonate fuel cell (DIR-MCFC) coupled with complicated nonlinear dynamics, the identification and control design of the Hammerstein model is presented. Through the sequential identification procedure, the static nonlinearity block is considered as the wavelet network which is trained and validated by the on-line learning algorithm, and the linear dynamic block is described by the state-space model in which parameters are estimated by the recursive least square algorithm. Using the numerical interpolation technique to approximate the implicit nonlinear function, we present a composite control framework consists of a nonlinear inversion and linear control. Through the closed-loop simulation tests, the nonlinear inversion design for the nonlinearity cancellation of a class of nonlinear systems is validated.

The operation results of a 125 kW molten carbonate fuel cell system

The KEPCO Research Institute has developed the Molten Carbonate Fuel Cell (MCFC) since 1993. Recently, a 125-kW MCFC system has been operated at the Boryeong thermal power plant in Korea from December 2009 to March 2010. This system is made up of a 125-kW stack, mechanical balance-of-plant (MBOP), and an electrical balance-of-plant (EBOP). The stack has 200 unit cells of which the effective area is about 10,000 cm 2. Especially, MBOP is mainly composed of an ejector and a catalytic combustor which help this system to be supplied with cathode inlet gas using anode tail gas and fresh air. After the pretreatment of this system was performed for about 20 days, an initial load operation was carried out in January 2010. At first, the stack showed an open circuit voltage of 214 V. It produced a maximum power of 120 kW DC. Moreover, this system operated for 3270 h.

Aspen DynamicsTM와 ACM을 이용한 용융탄산염 연료전지 시스템의 모사 및 제어

최근 대체에너지에 대한 관심이 높아짐에 따라 수소에너지를 기반으로 하는 차세대 발전 장치인 연료전지 관련 기술 개발이 활발하게 이루어지고 있다. 특히, 고온 연료전지의 대표적인 형태인 용융 탄산염 연료전지(MCFC: Molten Carbonate Fuel Cell, 이하 MCFC)는 전력사업용으로의 높은 가능성을 인정받아 화석연료를 대체할 발전방식으로 평가 받고 있다. 본 연구에서는 Aspen Custom Modeler(<TEX>$ACM^{TM}$</TEX>)에서 평형반응식을 이용하여 스택 모델을 구성한 후, Aspen <TEX>$Plus^{TM}$</TEX>에서 BOP(Balance of Plant) 시스템과 스택을 연결하여 전체 MCFC 발전 시스템의 정상상태를 모사하였다. 모델의 유효성을 입증하기 위해서 전류밀도, 연료이용률, S/C ratio, 재순환 흐름 비와 같은 주요 조업변수에 따른 셀 전압, 전력, 효율 등 시스템의 성능을 분석하였다. 그리고 Aspen <TEX>$Dynamics^{TM}$</TEX>에서 PID제어 방식을 적용하여 제어루프를 구성하였고 부하변화, 설정점 변화, 재순환 흐름비 변화에 따른 각각의 사례연구를 통하여 전체 시스템의 성능변화를 예측하였다. 그 결과 연료이용률과 전류밀도의 변화에 따른 전체 시스템의 최대 발전 효율 및 출력전압을 위한 운전조건을 제안하였다. Recentincreasing awareness of the environmental damage caused by the <TEX>$CO_2$</TEX> emission of fossil fuelsstimulated the interest in alternative and renewable sources of energy. Fuel cell is a representative example of hydrogen energy utilization. In this study, Molten Carbonate Fuel Cell system is simulated by using <TEX>$Aspen^{TM}$</TEX>. Stack model is consisted of equilibrium reaction equations using <TEX>$ACM^{TM}$</TEX>(Aspen Custom Modeler). Balance of process of fuel cell system is developed in Aspen <TEX>$Plus^{TM}$</TEX> and simulated at steady-state. Analysis of performance of the system is carried out by using sensitivity analysis tool with main operating parameters such as current density, S/C ratio, and fuel utilization and recycle ratio.In Aspen <TEX>$Dynamics^{TM}$</TEX>, dynamics of MCFC system is simulated with PID control loops. From the simulation, we proposed operation range which generated maximum power and efficiency in MCFC power plant.

용융탄산염형 연료전지 스택의 균질 물성치 추정에 관한 연구

용융탄산염형 연료전지 시스템의 성능 향상을 위해 핵심 부분인 스택을 수치적으로 모사할 필요성이 대두되고 있다. 스택은 다양한 재질, 즉 금속, 세라믹, 폴리머 등으로 이루어져 있고 또한 단위전지 수백 장이 적층되어 제작되기 때문에 이를 전부 세세히 모델링하여 고려하는 것은 거의 불가능하다. 이에 따라 스택 전체를 하나의 균질한 물질로 대체할 수 있는 균질 물성치 도출이 요구되고 있다. 본 논문에서는 단위전지 압축률을 도입하고 모든 압축 변형이 분리판과 매트릭스에서만 일어난다는 등의 몇 가지 기본 가정 하에서 스택의 두 가지 영역, 즉 활성 영역과 매니폴드 영역에서 각각 균질 물성치를 추정하였다. 추정된 물성치를 실제 문제에 적용하여 성공적인 결과를 얻을 수 있었다. The performance and efficiency of a Molten Carbonate Fuel Cell system will improve with the aids of numerical simulations such as finite element analysis. For best simulation results, the virtual model must accurately reflect the actual model including the material properties. It is very difficult, however, to make a detailed numerical model of the stack that consists of hundreds of layers of unit cells composed of various materials like metal, ceramics, polymer, etc. Instead, a practical approach is to find a homogenized material property of the stack as a whole as an approximate replacement. In this paper, the compression ratio of a unit cell is introduced, and a new method is proposed to estimate the homogeneous material properties for both the active and the manifold regions of the stack under the assumption that the compressive deformation occurs only at the separators and matrices in the unit cells. The estimated properties are applied successfully to simulating an actual stack.

Combined Electric Power and Carbon-Dioxide Separation (CEPACS) Technology

FuelCell Energy, Inc. has developed novel system concepts for separation of carbon dioxide from greenhouse gas emission sources, using its patented Direct FuelCell® (DFC®) technology. DFC is based on carbonate fuel cells featuring internal reforming. The unique chemistry of carbonate fuel cells offers an innovative approach for separation of CO2 from fossil-fuel power plant exhaust streams (flue gases). DFC-based CO2 separation systems are suitable for many types of coal-based power plants, from existing pulverized coal-fired boiler steam cycle plants to future integrated gasification combined cycle plants. The carbonate fuel cell system also produces electric power at high efficiency. Cost of electricity analysis of the DFC system indicates that the simultaneous generation of power and CO2 capture is an attractive scenario for re-powering the existing coal-fueled power plants.

Optimization of Gasifying Agent Composition in Molten Salts Gasification of Soy Sauce Cake for Molten Carbonate Fuel Cell System

Global warming has been a problem not only for advanced country, but also for developing country since COP15 was held. There-fore, R&D of clean energy like fuel cells is accelerated drastically. Meanwhile, the disposal of soy sauce cake is also important issue in Japan because it has rich sulfur and chlorine. There¬fore, we propose the gasification system of the soy sauce cake using molten salt. Moreover, this gasification gas is used as a fuel gas for MCFC which use same molten salts as an electrolyte. This paper elucidates about the fundamental gasification characteristics of soy sauce cake by optimizing the gasifying agent gas composition, and examines the influence of the gasification gas on the MCFC characteristic. As a result, the gasification is promoted when air is mixed with the gasifying agent, because molten salts temperature and the reactivity between soy sauce cake, gasifying agent and molten salts elevate.

Development of Direct Carbonate Fuel Cell Systems for Achieving Ultrahigh Efficiency

FuelCell Energy, Inc. (FCE) has developed products based on its Direct FuelCell® (DFC®) technology with efficiencies near 50% based on lower heating values of natural gas. DFC is an internally reformed molten carbonate fuel cell, which operates in the 550–700°C range. The combination of the internal reforming of methane and atmospheric pressure and moderately high temperature of operation has resulted in very simple power plant system configurations. Recently, FCE has developed system concepts to further increase the net electric efficiency to beyond 60% efficiency in sub-MW and MW class power plants. One of these system concepts is the arrangement of the fuel cell stacks in series for very high utilization of fuel in the stacks. Although, in principle, the concept of fuel cell stacks in series is very simple, the implementation of the concept in the actual hardware poses challenges requiring innovative solutions. These challenges include concerns with thermomechanical issues, flow and utilization patterns within the fuel cell stacks, and management of the pressure balance between the anode and the cathode. To address these issues, various analytical tools, including system-level modeling and simulation and computational fluid dynamics (CFD), were utilized. FCE has developed a comprehensive fuel cell stack operation simulation model including hydrodynamics, kinetics, electrochemical, and heat transfer mechanisms to investigate and optimize the design for performance as well as endurance. Various system configurations were developed, which included methods for fueling the second tier stacks in the series. System simulation studies using first principle mass and energy conversation laws were performed. Parametric studies were completed. Subsequent to the system modeling results, the fuel cell stack operations were analyzed using the comprehensive stack simulation model. The CFD modeling of the fuel cell stacks was performed in support of the system simulation parametric studies. The results of the CFD modeling provided insight to the thermal and flow profiles of both first and second tier stacks in series. The net outcome of the investigation was the design of the system, which met the goals of ultrahigh efficiency and yet complied with the thermomechanical requirements of the fuel cell stack components. In this paper, FCE will describe various system options for the very high efficiency systems, the issues related to the design, and the practical solutions to overcome the issues.

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.

Nonlinear feedback control of a preheater-integrated molten carbonate fuel cell system

A kW-class molten carbonate fuel cell with direct internal reforming is presented. Within an additional preheating framework, the estimation and control technique is implemented to this kind of nonlinear systems. By the proposed algorithm, the steady-state optimization algorithm subject to prescribed physical constraints is used to determine the desired operating condition, an open-loop observer design provides effective state estimation, and the nonlinear feedback control ensures the bounded stack temperature regulation in spite of unknown inlet perturbations. Finally, the proposed control methodology is successfully verified by numerical simulations.

Carbonate Fuel Cell Application for Synergistic Power Generation and Carbon Dioxide Capture

FuelCell Energy, Inc. (FCE) has developed novel system concepts for separation of carbon dioxide from greenhouse gas emission sources, using Direct FuelCell® (DFC®) technology. DFC is based on carbonate fuel cells featuring internal reforming. The unique chemistry of carbonate fuel cells offers an innovative approach for separation of CO2 from fossil-fuel power plant exhaust streams (flue gases). DFC-based CO2 separation systems are suitable for many types of coal-based power plants, from existing pulverized coal (PC) plants to future integrated gasification combined cycle (IGCC) plants. The carbonate fuel cell system also produces electric power at high efficiency. Cost of electricity (COE) analysis of the DFC system suggests that the simultaneous generation of power and CO2 capture is an attractive scenario for re-powering the existing coal-fueled power plants.

Optimum start-up strategies for direct internal reforming molten carbonate fuel cell systems

The study of start-up performance for a direct internal reforming molten carbonate fuel cell (DIR-MCFC) system is presented. Since a kW-class stack is assembled with an additional preheating design, the improvement of start-up behavior is conducted to find the proper operating strategy. For a cold start-up fuel cell system, both start-up delay and inverse response are strictly detected. When the optimum operating strategy is determined by solving the steady-state optimization algorithm subject to stack temperature constraint, the rapid system start-up as well as the maximum power output can be achieved simultaneously.

Technical Analysis of an Eco‐Friendly Hybrid Plant With a Microgas Turbine and an MCFC System

AbstractThis article refers to a Molten Carbonate Fuel Cell (MCFC) system coupled to a plant with a microgas turbine and a heat recovery system for obtaining a small sized hybrid system in co‐generative arrangement.MCFC are devices capable of concentrating carbon dioxide (CO2) produced in anode exhaust gases. If they are handled conveniently, it is possible to separate and store the surplus CO2 produced by the plant instead of emitting it into the atmosphere.From the simulation model of the MCFC system, previously developed by the authors, a zero‐dimensional and stationary simulation model for the whole hybrid system was formulated and implemented in the same language.By the simulation model of the MCFC system it has been possible to make a parametric analysis of the hybrid plant to find some optimal operating conditions of the fuel cell(s) that maximise the performance of the entire hybrid plant. In addition, the separation of the CO2 surplus produced by the hybrid plant was simulated by the model and then the emissions of carbon monoxide (CO) and nitrogen oxides (NOx) from the same plant were evaluated.

Syngas from sugarcane pyrolysis: An experimental study for fuel cell applications

The use of biomass for the production of electrical energy is a promising technological solution for those countries where there are problems with the disposal of agricultural waste and/or the production of low-cost energy. The gasification and/or pyrolysis of the biomass produces a gas rich in hydrogen that can be used in a fuel cell system to produce electrical energy with reduced environmental impact and significant energy recovery. In this work, a study of the pyrolysis of Brazilian sugarcane bagasse was carried out. The experimental process consisted of the pyrolysis of the biomass material in a batch pyrolysis reactor. In some runs the biomass was dry, while in others it was pre-treated by the addition of water. It was noted that the water added to the biomass before the pyrolysis process resulted in a decrease in the quantity of steam added to the fuel cell feeding gas, necessary to avoid carbon deposition, and in an increase in cell power, but, at the same time, caused a decrease in the quantity of syngas produced. Then, the composition of the gas obtained from the experimental pyrolysis of the sugarcane was inserted in a simulation tool of a molten carbonate fuel cell system in order to estimate the feasibility of the entire process in terms of operating conditions and electrical performance. The present study indicates that the syngas obtained from the sugarcane biomass (about 40%) can be converted into electricity using a fuel cell system with a high efficiency.

Carbon Sequestration Systems Using Direct FuelCell for Combined Carbon Dioxide Separation and Power Generation

FuelCell Energy (FCE) has developed novel system concepts for separation of carbon dioxide from greenhouse gas emission sources, using Direct FuelCell® (DFC®) technology. DFC is based on carbonate fuel cells featuring internal reforming. The unique chemistry of carbonate fuel cells offers an innovative approach for separation of CO2 from fossil-fuel power plant exhaust streams (flue gasses). DFC-based CO2 separation systems are suitable for many types of coal-based power plants, from existing pulverized coal (PC) plants to future integrated gasification combined cycle (IGCC) plants. The carbonate fuel cell system also produces electric power at high efficiency. Cost of electricity (COE) analysis of the DFC system suggests that the simultaneous generation of power and CO2 capture is an attractive scenario for re-powering the existing coal-fueled power plants.

Optimal Control of Load Changes for Molten Carbonate Fuel Cell Systems: A Challenge in PDE Constrained Optimization

Molten carbonate fuel cells provide a promising technology for the operation of future stationary power plants. In order to enhance service life, a detailed understanding of the dynamical behavior of such fuel cell systems is necessary. In particular, fast load changes shall be simulated, (resp., optimized) without risking material stress due to the extreme temperature differences usually accompanying fast load changes. Fast load changes are important for daily operations in order to react on varying demands. Material stress may lead to irreparable damage of the fuel cell stack. For these contradicting goals, a family of hierarchically ordered mathematical models has been developed with the aim of simulating and optimizing the temporal and spatial dynamical behavior of the gas streams, chemical reactions, and potential fields within the fuel cells. Altogether, the most complicated system, which is investigated in the present paper, results in a Pareto-optimal control problem with constraints in form of a huge system of 28 partial differential algebraic equations and ordinary integro-differential algebraic equations and boundary conditions which are themselves partly given by an ordinary differential algebraic system of dimension 9. The PDEs are of parabolic and hyperbolic type; some are degenerate. Moreover, the variables involved in the different submodels of this fully coupled multiphysical system live on considerably different time scales. Optimal control results are presented for a compromise between sufficiently fast load changes and sufficiently small temperature differences within the cell's solid part by means of a specially tailored formulation of a chain of optimal control problems. This procedure benefits from the different time scales of the state variables and keeps the problem manageable and computable despite its tremendous complexity and scale, although standard numerical methods are employed.

Energy and exergy analyses of a hybrid molten carbonate fuel cell system

This study deals with the energy and exergy analysis of a molten carbonate fuel cell hybrid system to determine the efficiencies, irreversibilities and performance of the system. The analysis includes the operation of each component of the system by mass, energy and exergy balance equations. A parametric study is performed to examine the effect of varying operating pressure, temperature and current density on the performance of the system. Furthermore, thermodynamic irreversibilities in each component of the system are determined. An overall energy efficiency of 57.4%, exergy efficiency of 56.2%, bottoming cycle energy efficiency of 24.7% and stack energy efficiency of 43.4% are achieved. The results demonstrate that increasing the stack pressure decreases the overpotential losses and, therefore, increases the stack efficiency. However, this increase is limited by the remaining operating conditions and the material selection of the stack. The fuel cell and the other components in which chemical reactions occur, show the highest exergy destruction in this system. The compressor and turbine on the other hand, have the lowest entropy generation and, thus, the lowest exergy destruction.

Economic analysis of a combined heat and power molten carbonate fuel cell system

Fuel cells can be attractive for use as stationary combined heat and power (CHP) systems. Molten carbonate fuel cell (MCFC) power plants are prime candidates for the utilization of fossil based fuels to generate high efficiency ultra clean power. However, fuel cells are considerably more expensive than comparable conventional technologies and therefore a careful analysis of the economics must be taken. This work presents analysis on the feasibility of installing both a FuelCell Energy DFC ® 1500MA and 300MA system for use at Adams Thermal Systems, a manufacturing facility in the U.S. Midwest. The paper examined thoroughly the economics driving the appropriateness of this measure. In addition, a parametric study was conducted to determine scenarios including variation in electric and natural gas rates along with reduced installation costs.