Exergy analysis by means of cycle calculation for steam electrolysis systems using Solid Oxide Electrolysis Cells

Solid Oxide Electrolysis Cells (SOECs) can be used for hydrogen generator systems. In this study, two types of SOECs which have different operating temperatures, 850°C and 650°C, were treated. For 850°C-type cell, measurements of current density-voltage characteristic and current efficiency were carried out and the data of 650°C-type cell were obtained from the previous report. For 850°C-type cell, the voltage at 0.4 A/cm2 was 1.20V and the current efficiency was approximately 100%. With the experimental values, cycle calculations for SOEC system models with production capacity of 300Nm3/h were carried out. At a rated operating point of 0.4A/cm2, the exergy efficiencies depending on each source of supplied energy were discussed. When all energy was supplied by electricity, the exergy efficiencies were 80.2% for 850°C-type system and 80.5% for 650°C-type one. When heat of 110°C was supplied, efficiencies were 89.2% for 850°C-type system and 90.5% for 650°C-type one. When heats of 110°C and 850°C or 650°C were supplied, they were 91.4% for both systems. The efficiencies were also discussed at various electric supply loads. At the load area< 950kW, 650°C-type system had higher efficiency than that of 850°C-type one. On the other hand, at the load area> 950kW, the efficiency of 850°C system was higher. © 2013 The Japan Society of Mechanical Engineers.