Search

Abstract: The authors have been engaged in numerical simulations of the planar type solid oxide fuel cell (SOFC) to make clear the dependence of the cell performance on its operating conditions. Up to now, the authors have already developed the simulation codes for the one channel region and the single cell plate in its cell stack. To calculate accurately the effect of radiation heat transfer from the cell stack surfaces, however, a code that can treat the whole cell stack is necessary. In the present study, therefore, the authors newly develop a three dimensional simulation code of the planar SOFC stack, and the detailed effect of the radiation heat transfer is investigated. It is made clear that the conventional codes are sufficiently accurate, and the newly developed whole cell stack code is not inevitable to predict the maximum cell temperature. This is because the thermal conductivity of the cell materials made of ceramics is very small, and the central part of the cell stack is almost free from the influence of radiation heat transfer. On the other hand, the stack simulation is needed to calculate accurately the cell voltage because the radiation heat transfer reduces it when the ambient temperature is low. The bad influence of low ambient temperature on the voltage is, however, small and relatively high voltage is obtained even when the ambient temperature is very low. [Copyright &y& Elsevier]

Abstract: The solid oxide fuel cell (SOFC) has a problem in durability of the ceramics used as its cell materials because its operating temperature is very high and the cell temperature fluctuation induces thermal stress in the ceramics. The cell temperature distribution in the SOFC, therefore, should be kept as constant as possible during variable load operation through control of the average current density in the cell. Considering this fact, the authors numerically optimize the operating parameters of air utilization and the inlet gas temperature of the planar SOFC by minimizing the cell temperature shift from its nominal value and propose a new cell temperature control method that adopts these optimum operating parameters for each average current density. The effectiveness of the proposed method is very high and the temperature variation is suppressed to a very low level without lowering the single cell voltage for both the co-flow and counter-flow type cells, indicating that the proposed cell temperature control method makes variable load operation of the planar SOFC possible. [Copyright &y& Elsevier]

A new fossil fuel utilized high performance combined power generation system with liquefaction recovery of carbon dioxide is proposed. In the system, pure oxygen is used as the oxidant gas to prevent the mixture of nitrogen in the exhaust gas and to make the liquefaction recovery of carbon dioxide possible. A solid oxide fuel cell (SOFC) is selected as the topping cycle. The exhaust fuel gas of the SOFC is afterburned with its exhaust oxidant gas of pure oxygen, and the heat of the combustion gas is utilized in the bottoming cycle. A closed cycle MHD/noble gas turbine cycle is selected as the bottoming cycle because the temperature of the combustion gas reaches about 2300 K. It is made clear through detailed examination of the energy balance that the total thermal efficiency of the system using natural gas (methane) as the fuel reaches 63.66% (HHV) or 70.64% (LHV). This efficiency is very high for the system with carbon dioxide recovery. The proposed system, therefore, has excellent performance and is worth further research and development. [ABSTRACT FROM AUTHOR]

The authors developed a simulation program for a single cell of industrial-sized planar solid oxide fuel cell (SOFC) with a scandia-ceria-stabilized-zirconia (10Sc1CeSZ) electrolyte fed with hydrogen fuel gas, to investigate its operating characteristics under fuel gas leakage conditions. Firstly, the numerical and corresponding experimental results were compared under conditions with no fuel gas leakage. The results confirmed the sufficient validity of the developed simulation program. Next, using the program, simulations involving fuel gas leakage on both sides of the SOFC were carried out. It was found that fuel gas leakage alters the stream of the fuel gas and induces a serious shortage of fuel gas in the downstream area of both side channels. This leads to a significant reduction in the local electromotive force and the appearance of regions where local electrolysis of water vapor occurs, in the downstream area on both sides. The effect of fuel gas leakage on the single cell voltage and the differential resistance was also investigated. It was revealed that the fuel gas leakage cannot be detected by only measuring the single cell voltage. On the other hand, the fuel gas leakage can be detected at an early stage, when only several percent of its inlet flow rate leaks, by measuring the differential resistance under a high fuel utilization rate condition of about 90 % and above. Based on this result, the authors proposed to employ the differential resistance, instead of the single cell voltage, as an evaluation index to detect the fuel gas leakage. [ABSTRACT FROM AUTHOR]

Energetic feasibility analyses were conducted when an SOFC CGS with EV charging equipment is installed in a facility with a high hot-water demand and a high thermo-electric demand ratio. The university cafeteria located on the Hitachi Campus of Ibaraki University in Japan was selected as an installation target because its electric and hot-water demands fulfilled the intended criterion of a high thermo-electric demand ratio. It was made clear that the merits of a co-generation system are not optimal in the case a gas water heater is selected as the backup hot-water supply. To solve the problems contributing to this bad result and to improve the performance, the authors next selected a heat pump water heater as the backup hot-water supply. It was made clear that this system possesses sufficiently high energy savings performance. It was also shown that the coexistence and co-prosperity of the cafeteria and EV charging equipment are successfully achieved. These results reveal that an SOFC CGS with EV charging equipment can be a feasible candidate for a future energy supply system installed in Japanese cafeteria, which is a facility with a large hot-water demand and a high thermo-electric demand ratio, by adopting a heat pump water heater, instead of the usual gas water heater, as the backup hot-water supply. [ABSTRACT FROM AUTHOR]

Abstract: The authors propose a solid oxide fuel cell (SOFC) co-generation system integrated with an electric vehicle (EV) charging station. To examine the feasibility of the proposed system, the authors numerically simulated the operation pattern of the proposed system, using the electric and thermal demands measured at a multifamily apartment from May 2003 to April 2004. Based on the simulation results, the authors calculated the overall efficiency of the system as well as the primary energy saving rate. The available electric energy for EV charging was also evaluated for the case of the proposed system installed in the multifamily apartment. As a result, it is made clear that the annually averaged overall efficiency reaches about 77% (LHV) and the expected primary energy saving rate exceeds 30% throughout the year. In addition, it is also found that sufficient amount of electric energy for EV charging can be obtained from the proposed system. Therefore, it can be concluded that the proposed SOFC system can successfully combine electrical/thermal energy co-generation and electric vehicle charging while maintaining high energy efficiency and good matching to energy consumption patterns. [Copyright &y& Elsevier]