• CH4 at the reformer outlet A CO at the CO shift outlet r«»' V» * •

0 5000 10000 15000 20000 25000 Time (h)

Figure 1. Performance of a demonstration plant process.

Elapsed time changes in sintering level

In general, it is known that the activity of the CO shift corresponds to the surface area of Cu metal (4). Therefore the surface area of Cu is used as an index of sintering level.

Figure 2 shows the analysis results of surface area of Cu on the CO shift catalyst extracted from 50 kW PAFC demonstration plants. The surface area of active metal on the catalyst generally decreases largely in the initial phase, and then decreases gradually. If this tendency could be analyzed precisely, a sintering level after a target operation period can be estimated by extrapolating this tendency to extended operation hours.

The decrease in the surface area of the active metal on a catalyst can be expressed in the form of an equation dt kb

(S ; active metal surface area, k ; rate constant)

This equation is transformed into In S=-kt+in So

Applying this equation to the analysis results of the used catalysts, this equation is best fitted to the results in case of n=l. This regressed linear line (n=l) is shown in figure 2. By extrapolating this line to extended operation hours based on the analysis results of the catalysts used in demonstration plants, the sintering level in operation time can be estimated.

By the catalytic activity test of the CO shift catalyst in the estimated sintering level, the life evaluation is possible. However, it is necessary to consider the following points when the whole performance of the CO shift process is evaluated.

■ inlet (demo.) A midd[e(demo.) ♦ outlet (demo.) -inlet (n=l)

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