3

:íi

100 1000 10,000 100,000

Endurance Time (hrs)

Fig.l Research Efforts for Longer Lifetime

100 1000 10,000 100,000

Endurance Time (hrs)

Fig.l Research Efforts for Longer Lifetime

3. Component Degradation

Alkali carbonates form a highly conductive molten salt with carbonate ions at the high operating temperatures. Cell performance of MCFCs. has been improved steadily in recent years. An MCFC stack will still suffer from component degradation including corrosion of each component, Ni precipitation and gas crossover as well as creepage of electrolyte. Figure 2 shows operating principles and degradation phenomena observed as follows;

Fig.2 Operating Principle and Component Degradation 4. Performance Decay

A 5 kW external reforming type stack with 1 m2 active area, for example, has provided performance decay rate of 3 mV/lOOOhrs with 16,000 hrs under a little lower operating temperature of 617 "C, whose decay rate is estimated as about 5 mV/lOOOhrs under standard operating temperature of 650 'C.

A 20 kW short stack of our state-of-the-art has been also under operation. The gas flow distribution has been well uniformed with internal manifold type. Matrix of porous LiA102 has about I mm thickness. Anode of Ni-Cr-Al powdered alloy metal has also 1 mm thickness. Cathode is made of in-situ oxidized porous NiO with Mg additives. Performance decay rate Qf Kawagoe 1 MW pilot plant, scheduled to be operated in FY 1999, has been estimated as 6 mV/lOOOhrs with initial output of 782 mV from the results.

Generally speaking, overall performance decay rate in present is around 0.5 to 1.0 %/1000hrs and stack life is around 6000 to 7000 hrs from the limitation of Ni precipitation. Several corrosive reactions of each component are induced in molten carbonate during operation.

Figures 3 and 4 show the data published from the world as well as corresponding target of ours as follows;

Fig.3 Ni Precipitation Amount during Operation Fig. 4 Decay Rate in Recent Years

Performance decay rate in FY 1999 is targeted as 0.25 %/1000hrs and lifetime is as 40,000 hrs. Table 1 shows target of Ni short-circuit time and performance decay rate in FY 1999 as well as state-of-the-art of them as follows;

Table 1 Performance Decay Rate of State-of-the-art and Our Target
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