The design of the PAFC investigated only allows the electrical output to be preselected, thus permitting power-controlled operation. In CHP in Europe, however, heat-controlled operation is also of considerable significance. In this case, the requirements of the consumer (e.g. a group heating system) in respect of the thermal output to be made available serve as control parameter for the plant.

The amount of heat that can be made available to the group heating system depends, on the one hand, on the preset electrical output and, on the other, on the flow rate of water passing through the fuel cell as well as its supply temperature.

During the trial measurements, thermal output as a function of electrical output based on volumetric water flow rate and return temperature (Trelum) was determined in extensive series of experiments. This resulted in the curves shown in Fig. I.

For the purpose of heat-controlled operation, the thermal output made available to the group heating system was measured and served as actual value for a digital controller based on a PI control algorithm. With the aid of this actual value and the set point for thermal output entered manually, the controller determines the corresponding electrical output as the manipulated variable.

In Europe, natural gas comes from various sources. As a result, the gas available to a consumer may have varying properties. Furthermore, LPG/air may be ad-

40 60 80 100 120 140 160 180 200 220 240 electrical output [kW|


mixed for peak-shaving purposes, primarily in winter.

Thus a further priority of the trial operation at Bochum municipal utility were experiments to investigate plant behaviour in the case of LPG/air admixture. For this purpose, a mixing unit was installed which allowed predefined admixture rates. Propane/air with the heating value of natural gas was used.

In another work package, pollutant emissions were measured under various operating conditions.

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