Improvement of electricity generating performance and life expectancy of MCFC stack by applying Li/Na carbonate electrolyte Test results and analysis of 0.44 m~2/10 kW- and 1.03 m~2/10 kW-class stack

摘要

Following the development of a 10 kW-class MCFC stack with a reactive area of 0.44 and 1.03 m~2, which applies a Li/Na carbonate electrolyte and a press stamping separator, many tests have now been carried out. In the installation tests, the observed cell voltages of the 0.44 m~2/10 kW-class stack agreed with the voltage predicted from the test results of the 100 cm~2 bench scale cell. This agreement proves that the installing procedure of the bench scale cell can be applied to the 0.44 m~2/10 kW-class stacks. The temperature distribution analysis model applied to the 100 kW-class stack was modified to calculate the temperature distribution of the 0.44 m~2/10 kW-class stack. Taking the heat loss and the heat transfer effect of the stack holder into account, the calculated temperature was close to the measured temperature; this result proves that the modification was adequate for the temperature analysis model. In the high current density operating tests on the 0.44 m~2/10kW-class stack, an electrical power density of 2.46 kW/m~2 was recorded at an operating current density of 3000 A/m~2. In the endurance test on the 0.44 m~2/10 kW-class stack, however, unexpected Ni shortening occurred during the operating period 2500-4500 h, which had been caused by a defective formation of the electrolyte matrix. The shortening seems to have been caused by the crack, which appeared in the electrolyte matrix. The voltage degradation rate of the 0.44 m~2/10 kW-class stack was 0.52% over 1000 h, which proves that the matrix was inadequate for a long life expectancy of the MCFC stack. A final endurance test was carried out on the 1.03 m~2/10 kW-class stack, of which the matrix had been revised. The fuel utilisation and the leakage of anode gas never changed during the 10,000 h operating test. This result suggests that no shortening occurred during the 10,000 h endurance test. The cell voltage degradation rate was around 0.2-0.3% over 1000 h in the 1.03 m~2/10 kW-class stack. According to a comparison of the stack electricity generating performance of the 0.44 m~2 and the 1.03 m~2/10kW-class stack under the same operating conditions, the performance of the 1.03 m~2 stack was lower at the beginning of the endurance test, however, its performance exceeded the performance of the 0.44 m~2/10kW-class stack during the 10,000 h operating test. By carrying out the high current density operating test and the 10,000-hour endurance test using commercial sized 10 kW-class stacks, the stability of the MCFC stack with a Li/Na carbonate electrolyte and a press stamping separator has been proven.