Results

The time profile of thermal output shown in Fig. 2 demonstrated that heat-controlled operation of a PAFC is possible without any difficulties by using the controller developed by Ruhrgas. The actual value (-2-) excellently follows the set point for thermal output (-3-).

FIG 2: HEAT-CONTROLLED OPERATION: CHANGE OF SET POINT

The experiments on LPG/air admixture were carried out with admixture rates between 5 % and 25 %. It became clear that, with the existing fuel cell design, trouble-free operation using peak-shaving gas over the entire performance range is only possible up to a maximum admixture rate of 15 %.

This is due to the peripheral components of gas treatment, which are not adequately dimensioned for reliable peak-shaving gas operation. This is evident in Fig. 3. It shows the position of the ejector as a function of the electrical output. The ejector controls the admixture of steam for the reforming reaction to produce hydrogen-rich process gas from natural gas. Its dimensions are evidently too small.

This means that, during operation with peak-shaving gas, the maximum ejector position is reached at high outputs and thus leads to plant shutdown.

The results of emission measurements revealed that, in the case of large increases in electrical output, emission peaks may occur in respect of CO and hydrocarbons. However, they drop after a short time and are thus negligible for the overall emissions.

ELECTRICAL OUTPUT [kW] FIG 3: EJECTOR POSITION VS. ELECTRICAL OUTPUT

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