Direct Internal Reforming Molten Carbonate Fuel Cell Research Articles

Relationship between Catalytic and Gas-phase Pollution Fractions in the Catalyst in DIR-MCFC (Reactivation Method of Polluted Catalyst by Vapor-Phase Carbonate).

In Direct Internal Reforming Molten Carbonate Fuel Cells(DIR-MCFC)deterioration of catalytic activity takes place in the anode channel due to both the liquid-phase pollution and vapor-phase pollution. The liquid-phase pollution meant that catalytic activity is deteriorated by the molten salt's(62 Li2CO3/38K2CO3)adhering to the catalyst. It can be solved by installing the protective barrier in the pollutant pathway. On the other hand, the vapor-phase pollution meant that that catalytic activity is deteriorated by KOH adhering to the catalyst. Because the vapor-phase pollution is caused in the entire electrode, an effective defense method has not established yet. Moreover, a reactivation method of vapor-phase polluted catalyst has not been developed yet. In order to study the reactivation method, the adhesion form of potassium compounds in the polluted catalyst under the various gas conditions was evaluated by using a thermogravimertic analyzer in which water vapor can feed. Additionally, the activity of catalyst treated demonstratively was also tested by a differential reactor. As a result, KOH changes to K2CO3 under the condition which CO2 concentration is larger than 25%. The catalyst with K2CO3 cannot reactive. However, the activity of polluted catalyst is revived until 80% of initial activity by controlling the gas species concentration, especially for CO2. Based on the results obtained by these fundamental experiments, the reactivation methods of polluted catalyst are proposed as follows; i)Catalyst should load more in the upstream in the anode. ii)In order to reactive the polluted catalyst, the ratio of H2O to CH4 in the fuel should increase, when DIR-MCFC is under operation. iii)Gas compositions under cell maintenance mode should be applied in the case that power generation quits.

Alkali resistance of tape-cast SiC porous ceramic membranes

The possibility to limit the alkali poisoning of the internal reforming catalyst in a direct internal reforming-molten carbonate fuel cell (DIR-MCFC) has been investigated by testing porous ceramic membranes in a reactor which simulated DIR-MCFC operative conditions. Silicon carbide (SiC) has been chosen as starting material for the membranes; they have been prepared by adopting the tape-casting procedure, and the reproducibility of this preparative has been verified through several morphological characterizations. Some tests at different lifetimes (150, 700 and 1500 h) have been carried out and it has been found that the membranes are able to retain 50–65% of the potassium after 150 h and this capability decreases at 32% after 1500 h. Because of no variations on the porous ceramic membranes characteristics, before and after the tests, have been evidenced from porosimetric and SEM analyses, we have supposed that the adsorbed K gradually covers the SiC grains surface by forming a thin film without modification of the structure of the samples.

Stack networking for system optimisation: an engineering approach

Direct internal reforming molten carbonate fuel cell (MCFC) systems are generally more efficient and more simple than equivalent external reforming systems. It is demonstrated that even better performance and system simplicity can be achieved by connecting the stacks in networks with the cathode flows and/or anode flows in series. The advantages and disadvantages of such networks are presented. Within the EC's Joule III programme, stack networking has been explored for direct internal reforming molten carbonate fuel cell (DIR-MCFC) systems. This study resulted in the selection of a system which employed anode recycle with the anodes connected in parallel and the cathodes connected in series. It achieved high performance, yet required few system components. In the project `Advanced DIR-MCFC development', led by BCN (P. Kortbeek and R. Ottervanger, J. Power Sources, 71 (1–2) (1998) 223), this system is being assessed with regard to cost, operating window, and controllability. The approach is to design the system to conform to the requirements of ECN's stacks. At the same time the MCFC stack development at ECN (G. Kraaij et al., J. Power Sources, 71 (1–2) (1998)) is geared towards fulfilment of the requirements in such a system with respect to performance, pressure management and lifetime, so the development of the system and the stack have an iterative character. A novel, patented, stack design with two anode outlet streams has been proposed by BG. It can be used in the chosen system and gives increased power output.

A novel configuration for direct internal reforming stacks

This paper presents a stack concept that can be applied to both molten carbonate fuel cell (MCFC) and solid oxide fuel cell (SOFC) internal reforming stacks. It employs anode recycle and allows the design of very simple system configurations, while giving enhanced efficiencies and high specific power densities. The recycle of anode exit gas to the anode inlet has previously been proposed as a means of preventing carbon deposition in direct internal reforming (DIR) stacks. When applied to a normal stack this reduces the Nernst voltages because the recycle stream is relatively depleted in hydrogen. In the concept proposed here, known as the `Smarter' stack, there are two anode exit streams, one of which is depleted, while the other is relatively undepleted. The depleted stream passes directly to the burner, and the undepleted stream is recycled to the stack inlet. By this means high Nernst voltages are achieved in the stack. The concept has been simulated and assessed for parallel-flow and cross-flow MCFC and SOFC stacks and graphs are presented showing temperature distributions. The `Smarter' stacks employ a high recycle rate resulting in a reduced natural gas concentration at the stack inlet, and this reduces or eliminates the unfavourable temperature dip. Catalyst grading can further improve the temperature distribution. The concept allows simple system configurations in which the need for fuel pre-heat is eliminated. Efficiencies are up to 10 percentage points higher than for conventional stacks with the same cell area and maximum stack temperature. The concept presented here was devised in a project part-funded by the EU, and has been adopted by the European Advanced DIR–MCFC development programme led by BCN.

Heat Transfer Characteristics of Molten Carbonate Fuel Cells.

The characteristics of Molten Carbonate Fuel Cells (MCFC) installing offset-type plate fins operated in low-Reynolds-number region are studied. A fuel cell model consisting of electrodes, perforated plate and corrugated current collector was used to elucidate heat transfer characteristics of MCFC. Heat transfer characteristics of MCFC could be obtained from gas temperature, components, surface temperature and horizontal heat flux by changing the condition of reacting gas. The results obtained are as follows. (1) Wieting equation of heat exchanger's heat transfer characteristics could not be applied to MCFC, because the Reynolds-number (1∼10) of MCFC was far less than the applicable range of the equation. (2) Horizontal heat flux depended on thermal conductivity of cell component and gas composition. (3) Temperature control at anode side was better than cathode side. (4) As overall heat flow of direction was from cathode side to anode side. The optimum system could be established by using Direct Internal Reforming Molten Carbonate Fuel Cells (DIR-MCFC) that it had the reforming catalysts at anode channel.

Mass and energy balances in a molten-carbonate fuel cell with internal reforming

The direct internal reforming molten-carbonate fuel cell (DIR-MCFC) can be proposed as a cogeneration system (heat+electricity). The influence of several operating parameters on the mass and energy balances of a 10 kW power plant has been investigated by using a mathematical model. The temperature, the steam/carbon ratio, the electrical power and the useful heat fraction have been found to be relevant parameters for optimizing both the energy and the exergy efficiencies. The results indicate that the performance of the system is improved at higher temperatures (973 K) and at fuel utilization ( U f) in the range of 45 to 70%. At lower U f values the system works endothermically, because the steam reforming reaction prevails and for U f > 70%, a decrease of the efficiencies is produced by the electrode overpotentials and the ohmic losses.