NOVELTY - The system for drying exhaust gases of a fuel cell system, comprises two heat exchangers (4, 6) alternately exposed to exhaust gas, a common exhaust gas inlet (8) and exhaust gas outlet (10), a common coolant inlet (12) and coolant outlet (14), a common air outlet, a valve arrangement with valves, a condensate deflector for discharging the condensate, and a computational unit connected with the valve. The valve arrangement is arranged in order to operate the first heat exchanger or the second heat exchanger in a freezing phase and to operate another heat exchanger in a regeneration phase.    USE - System useful in airplanes for drying an exhaust gas enriched with oxygen of a fuel cell system for tank inertisation (claimed).    ADVANTAGE - The system ensures efficient and safe drying of exhaust gases of a fuel cell system without creating ice crystals and developing bacterial population.    DETAILED DESCRIPTION - The system for drying exhaust gases of a fuel cell system, comprises two heat exchangers (4, 6) alternately exposed to exhaust gas, a common exhaust gas inlet (8) and exhaust gas outlet (10), a common coolant inlet (12) and coolant outlet (14), a common air outlet, a valve arrangement with valves, a condensate deflector for discharging the condensate, and a computational unit connected with the valve. The valve arrangement is arranged in order to operate the first heat exchanger or the second heat exchanger in a freezing phase and to operate another heat exchanger in a regeneration phase. The freezing phase flows a part of exhaust gas flowing into the common exhaust gas inlet and discharging through the common exhaust gas outlet, and a coolant flowing in the common coolant inlet and discharging from the coolant outlet through the heat exchanger for freezing the water steam present in the exhaust gas. In the regeneration phase, a part of the exhaust gas flows from the common exhaust gas inlet through the heat exchanger to the common air outlet, and the formed ion condensate discharges through the condensate outlet. The common coolant inlet and coolant outlet are connected with a tank for liquid hydrogen. The common exhaust gas outlet is connected with a fuel tank for inertising a free tank volume. The computational unit is arranged so that the valve is controlled in such a way that the first heat exchanger and the second heat exchanger are operated in the freezing phase and in the regeneration phase. The computational unit independently determines a favorable time point for actuating the valve based on a freezing line of the first heat exchanger and the second heat exchanger in dependent upon the environmental conditions. The first heat exchanger and the second heat exchanger comprise sensors for determining its respective freezing grades and/or for detecting its temperature. The sensors are connected with the computational unit for determining the time point for actuating the valve. The system further comprises a third and fourth heat exchanger with a third and fourth coolant inlet, a third and fourth coolant outlet, a third and fourth exhaust gas inlet and a third and fourth exhaust gas outlet. The third and fourth coolant inlet is connected with the common coolant outlet of the first heat exchanger and the second heat exchanger, and the exhaust gas outlet is connected with the common exhaust gas outlet of the first heat exchanger and the second heat exchanger. The third coolant outlet is connected with a fuel inlet of a fuel cell system. The fourth exhaust gas outlet is connected with the third exhaust has inlet. INDEPENDENT CLAIMS are included for:    (1) a method for drying exhaust gases of a fuel cell system; and    (2) an airplane.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic representation of a system for drying exhaust gases of a fuel cell system.    Heat exchanger (4, 6)    Exhaust gas inlet (8)    Exhaust gas outlet (10)    Coolant inlet (12)    Coolant outlet. (14)