Influence of stack arrangement on performance of multiple-stack solid oxide fuel cells with non-uniform potential operation

The performance of multiple-stack solid oxide fuel cells (SOFCs) with different stack arrangements is compared with respect to the presence of an in-stack pressure drop. It was demonstrated in our previous work that when a multiple-stack SOFC is arranged in series and the operating voltages are allowed to vary among the different stacks, an improved performance over a conventional SOFC (stacks arranged in parallel and operated under the same operating voltage) can be realized. Nevertheless, the differences in pressure drop and the required power for compression among the different operations were not taken into account. In the study reported here, it is demonstrated that the pressure drop in the stack depends not only on the feed rate and operating voltage, but also on the stack arrangement. The pressure drop in the anode channels is about half that in the cathode channels. The configuration of stacks in series with compressors installed only at the inlets of the first stack is the best option as it shows the highest electrical power generation. The pressure drops in the anode and cathode channels are about 4.7 and 3.75 times those in the corresponding channels of the conventional case with the stacks arranged in parallel. In addition, when considering the net obtained electrical power, it appears that multiple-stack SOFCs with stacks arranged in series are not as attractive as the conventional SOFC because they require much higher compression power. Therefore, it is suggested that a new stack design with a low pressure drop is required for the concept of multiple-stack SOFC with non-uniform potential operation to become practical.