Yoshinori Sakaki

Performance analysis of planar-type unit SOFC considering current and temperature distributions

The solid oxide fuel cell (SOFC) is expected to be a candidate for distributed power sources in the next generation, due to its high efficiency, high-temperature waste heat utilization and low emission of pollutants to the environment. In this study, a quasi-two- (co- and counter-flow) and three- (cross-flow) dimensional simulation program for planar-type SOFC was made considering mass, charge and heat balances along the flow directions and perpendicular to the electrolyte membrane, in order to obtain temperature and current density distributions along the flow direction. Numerical results from this simulation with adiabatic boundary conditions show that the temperature increases along the flow direction in the co-flow case and the temperature profile has a maximum near the fuel inlet in the counter-flow case. The effects of the gas re-circulation ratio, operating pressure and physical properties on current and temperature distributions were also studied. The temperature distribution is uniform irrespective of flow type under the boundary condition of radiative exchange between the outer interconnector and the electric furnace surface with a realistic view factor. Temperature and current density profiles are discussed considering the Nernst potential and overvoltage changes along the flow direction.

Cycle Analysis of Combined Power Generation by Planar SOFC and Gas Turbine Considering Cell Temperature and Current Density Distributions

The planar solid oxide fuel cell (SOFC) with a Y 2 O 3 -stabilized ZrO 2 electrolyte is expected to be a candidate for distributed power sources in the next generation due to its high efficiency of power generation. In this study, we analyzed the system performance of a SOFC/gas turbine combined cycle of about 500 kW electrical output, using our two-dimensional simulation code for the planar SOFC with internal reformer. The effects of cell temperature, cell pressure, recirculation rations of fuel and air, utilization ratios of fuel and air, and average current density of SOFC on both the system efficiency and the cell temperature and current density distributions, were calculated under typical operating conditions taking account of realistic efficiencies and heat losses for auxiliary equipment. The addition of a Cheng cycle to the SOFC/gas turbine combined cycle improved system efficiency by 1-3%. The combined SOFC/gas turbine/Cheng cycle gave a high efficiency of 61.2% (based on a higher heating value) even under a small power generation scale of 500 kW class at 2.0 MPa SOFC pressure. We also discussed the possibility of carbon deposition at both external and internal reformers by calculating the chemical equilibrium carbon activities for estimated carbon deposition reactions.