The present invention relates to a preheating arrangement in a fuel cell apparatus, the fuel cell apparatus comprising at least a fuel cell unit having an anode side and a cathode side with an electrolyte therebetween, the fuel cell apparatus having at least a fuel inlet to the anode side and an oxygen-containing air inlet to the cathode side as well as a sulphur removal unit and a fuel modifying unit and an afterburner for combustion the exhaust gases from the anode and/or cathode side. According to the invention, the afterburner is provided with a separate fuel inlet channel for introducing fuel to the afterburner during the start-up phase of the fuel cell apparatus and that at least a part of the exhaust gases formed in the combustion of the separately fed fuel is arranged to be directed from the afterburner for heating at least the sulphur removal unit and/or the fuel modifying unit during the start-up phase. The outlet channels are provided with heat exchangers and adjustment means for adjusting the exhaust gas flow rate.