A system for controlling a flow rate ratio includes a fuel cell comprising an anode for generating a tail gas and having an inlet and an outlet; a fuel reformer for mixing a fuel with the tail gas from the outlet of the anode to generate a reformed stream which is split into first and second branch streams at a splitting position, the first branch stream returned to the inlet of the anode; a cooler for removing heat from the second branch stream; a bottoming cycle including an external or internal combustion engine driven in response to the cooled second branch stream; a measuring device for measuring differential pressures of two of the main stream, the first branch stream and the second branch stream; and a controlling device for controlling a flow rate ratio of the first branch stream to the main stream in response to the measured differential pressures.