Molten Carbonate Fuel Cell Plant Research Articles

Plant-Wide Control of an Integrated Molten Carbonate Fuel Cell Plant

This paper presents the design and part-load operation of a molten carbonate-micro gas turbine (MCFC/MGT) hybrid system (HS), and proposes a multiloop control strategy for the HS. A mathematical model of the system is introduced. Then, the structure of process is changed and the performance of HSs at part-load operation is studied. The novelty includes utilizing some part of the main fuel instead of auxiliary fuel in the combustion stage. The results show that the new configuration has more efficiency (about 63%). In order to keep the operating system within safe limits, variables of the control system are determined. Those controlled variables are as follows: stack temperature, fuel utilization (FU), turbine inlet temperature (TIT), and output power of HS. Based on relative gain array (RGA) analysis, control structures are suggested for two HS. Investigations on results of RGA analysis indicate that the new configuration has more interactions between inputs and outputs and so has different control structure. The dynamic simulation results show that the proposed control structure is achievable for MCFC/MGT HSs.

Techno-economic assessment of a repowering scheme for a coal fired power plant through upstream integration of SOFC and downstream integration of MCFC

A thermodynamic and economic assessment of an innovative scheme to repower a thermal power plant is presented here. A solid oxide fuel cell (SOFC) plant is incorporated at upstream of the present boiler and a molten carbonate fuel cell (MCFC) plant is incorporated at downstream of present boiler. Coal feeds are reduced (reduction varied from 10% to 40%) by partially off-loading the mills. Energy, equivalent to that replaced coal, is provided by the exhaust of the direct internal reforming (DIR) SOFC which runs on natural gas. The MCFC plant also consumes some fresh natural gas and separates CO2 from the boiler exhaust. The proposed model, developed and analyzed using Cycle Tempo software, yields better performance while substantially increasing the plant capacity (more than 50%) and reducing the CO2 emission (90%). The findings suggest that at 20% coal replacement the plant becomes most economical, offering electricity at an estimated unit cost of USD 84/MWh, as against USD 111/MWh for MEA retrofitted plant.

A comparative study of models for molten carbonate fuel cell (MCFC) processes

The necessity of this work arose from the need for identification of a comprehensive plant model that can be used in the model-based control of the MCFC plant. Various models for molten carbonate fuel cell (MCFC) processes are presented and evaluated in this paper. Both a rigorous model based on mass and energy balances and implicit models based on operation data were investigated and analyzed. In particular, auto-regressive moving average (ARMA) model, least-squares support vector machine (LSSVM) model, artificial neural network (ANN) model and partial least squares (PLS) model for a MCFC system were developed based on input-output operating data. Among these models, the ARMA model showed the best agreement with plant operation data.

Off-design operation of coal power plant integrated with natural gas fueled molten carbonate fuel cell as CO2 reducer

The paper presents an experimental investigation of a Molten Carbonate Fuel Cell (MCFC) fueled by methane in order to predict how to reduce CO2 emissions from the flue gas of a real power plant. MCFCs can be placed in the flue gas stream of a fossil fired power plant to separate CO2 by transferring it from the cathode side to the anode side. As a result, a mixture of CO2 and H2O is separated from which pure CO2 can be obtained through condensation of water. The main advantages of this solution are: additional power generation, reduced CO2 emissions and higher system efficiency. Furthermore, coal plants seem to be the ideal candidate to retrofit with MCFC plant due to their high exhaust CO2 content and to the low cost of the fuel that encourages its application despite the narrower emission requirement. The experimental results show that use of an MCFC could reduce CO2 emissions by 90% with over 30% efficiency in additional power generation and by demonstrating a broad range of different operative conditions.

Parameter Identification of a Dynamic MCFC Model Using a Full-Scale Fuel Cell Plant

The parameter estimation of a molten carbonate fuel cell (MCFC) model is presented. The model is dynamic, spatially distributed, and describes a cross-flow configuration of the gas channels. It includes direct and indirect internal reforming, a catalytic combustor, and a reversal chamber between the anode and the cathode. The parameter estimation is based on measurements at a full-scale industrial MCFC plant. Because of the complexity of the model, the high number of parameters, and limited measurements, a specific strategy for the parameter adjustment has been developed. It includes a system balancing, sensitivity analysis and stepwise optimization of single parameters and parameter groups.

Study of multistage oxidation by flowsheet calculations on a combined heat and power molten carbonate fuel cell plant

The multistage oxidation configuration consists of a set of serially connected fuel cell stacks. By connecting the stacks serially, more homogenous current distribution over the cell surface can be achieved resulting in lower irreversible losses. This article presents a detailed assessment of multistage oxidation by flowsheet calculations in which the influence of operating temperature and gas composition on the fuel cell performance is incorporated. A 250 kW molten carbonate fuel cell (MCFC) combined heat and power (CHP) plant is used as reference and the fuel cell stack unit is substituted by two serially connected units ( N=2). Two multistage configurations are examined: (A) both anode and cathode flows are serially connected; (B) only the anode flow is serially connected while the cathode flow is parallel connected. For all systems, the total cell active area, cell current density, overall fuel utilization and gas temperature at the inlet and outlet of the fuel cell array are kept constant. Fuel cell performance at the operating conditions is calculated using a numerical model of the flowsheeting program. Influences of operating temperature and gas composition on the cell performance are incorporated using empirical relations that describe irreversible losses of the cell as function of these parameters. System performances are compared in order to assess the benefits of the multistage oxidation configurations. Differences in performance between the two multistage oxidation configurations are studied by analyzing the difference in exergy loss of stacks, stack power output, cooling requirement and cathode gas massflow and composition. Detailed flowsheet calculations show that the improvement in efficiency is about 0.6% for configuration A, and 0.8% for configuration B. Improvements are obtained by the enhanced fuel cell power output while the expander power output is slightly reduced. Heat output is slightly reduced due to the improved fuel cell conversion. Analysis of stack output revealed a intricate interaction between stack and the rest of the fuel cell system. Their mutual influences are examined and the results explain differences in results between configuration A and B.

Efficiency Upgrading of an Ambient Pressure Molten Carbonate Fuel Cell Plant Through the Introduction of an Indirect Heated Gas Turbine

The efficient end environmentally friendly production of electricity is undoubtedly one of the 21st century priorities. Since renewable sources will be able to guarantee only a share of the future demand, the present research activity must focus on innovative energy devices and improved conversion systems and cycles. Great expectations are reserved to fuel cell systems. The direct conversion from chemical to electrical energy eliminates environmental problems connected with combustion and bypass the stringent efficiency limit due to Carnot’s principle. Still in infancy, high-temperature fuel cells present the further advantage of feasible cycle integration with steam or gas turbines. In this paper, a molten carbonate fuel cell plant is simulated in a cycle for power generation. The introduction of an external combustion gas turbine is evaluated with the aim of efficiency and net power output increase. The results show that the proposed cycle can be conveniently used as a source of power generation. As compared to internal combustion gas turbine hybrid cycles found in the literature the plant is characterized by fuel cell greater simplicity, due to the absence of pressurization, and gas turbine increased complexity, due to the presence of the heat exchange system.

The Behavior of MCFCs Using Li/K and Li/Na Carbonates as the Electrolyte at High Pressure

High operating pressure, about 12–25 atm, is required to develop a highly efficient molten carbonate fuel cell (MCFC) plant system combined with a gas turbine or coal gasifier system. Operation at high pressure, over 10 atm, will accelerate dissolution of the NiO cathode and shorten cell life. Therefore, economical applicability as a high‐pressure and high‐efficiency MCFC plant system and the economical requirement of cell life time must be totally investigated. It is very important to clarify the performance of the MCFC under such high pressures as the first step for such an investigation. We have examined the performance of several MCFC cells using Li/K and Li/Na electrolyte at pressures of up to 44.5 atm, avoiding possible carbon formation in the fuel stream. The analysis method for cell performance developed below 7 atm pressure conditions has proved applicable for analyzing cell performance over 10 atm. The smaller cathode polarization concerned with concentration and the higher conductivity of the Li/Na electrolyte enabled a higher performance than that of a Li/K cell. Application of the Li/Na electrolyte to MCFCs seems to be an effective way of prolonging cell life with measurements of the small amount of deposited nickel. Furthermore, the Li/Na cell attained power density, and a high cell voltage (0.82 V) was obtained at in 16 atm. This result shows the possibility of developing a high‐efficiency MCFC plant system. © 1999 The Electrochemical Society. All rights reserved.

Fuel cell power system applications in Japan

Many types of fuel cells such as the PAFC (phosphoric acid fuel cell), MCFC (molten carbonate fuel cell), SOFC (solid oxide fuel cell) and PEFC (polymer electrolyte fuel cell) have been developed for utility use in Japan. Among them, the PAFC is now in the ‘plant’ stage. Several MW class large-capacity demonstration plant and many smaller-capacity units have been constructed and tested for the purpose of evaluation on their efficiency, operability and durability. Those MW class plants are expected to be used as an urban energy cenlre or a cogeneration system. Smaller units arc installed for many kinds of applications such as in hospitals, hotels, restaurants, etc. Efficient performance of fuel cell power plant has been demonstrated by those PAFC plants and units. In addition, the possibility of higher efficiency is indicated by other fuel cells in their stack level, and MCFC plant is under construction to demonstrate its performance. In the next stages, it will be required to demonstrate superior durability and cost perspective in comparison with a conventional power generation system.

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.