TECHNOLOGY FOCUS - ELECTRICAL POWER AND ENERGY - Preferred Arrangement: An indirect heat exchange between exhaust gas and oxygen carrier takes place in the heat exchanger system. The exhaust gas and the oxygen carrier are conducted in counterflow through two ring-gap-shaped sub-chambers (41, 42) which are largely arranged in prolongation of the stack periphery. Co-axial supply tubes (33, 46) in a central region of the reaction device form the in feed point for fuel and preheated oxygen carrier. The supply tubes are designed, so that sufficient amount of heat for the vaporization of fuel during current delivering operation is transferred from the preheated oxygen to the fuel. The reaction device is equipped with in-built elements (5) for forming loop flow and has a large volume so that dwell time for carrying out the partial oxidation results where the predominant proportion of the carbon in the fuel reacts to form carbon mono- or di-oxide. The in-built elements are co-axial cylinders which are arranged about the in-feed point. The first cylinder has a jacket surface and closed end surfaces which cause a deflection of the gas flows emerging from the in-feed point. The second cylinder is arranged inside the first cylinder and comprises jacket surface having apertures which cause a loop-like circulation flow in the first cylinder. The in-built elements are designed in their order of magnitude so that the second cylinder has a diameter of 5 cm and the first cylinder has a diameter of 10 cm. A ring gap having a gap width of 2 cm is provided around the first cylinder where the reformed gas can flow to an input point of the distributor passage. An electrical heating element is provided at a supply line to start up the current delivering operation, and ignition electrodes are arranged at the in-feed point so that a combustion in the auxiliary burner and the partial oxidation can be ignited. A ring-shaped sub-chamber is provided at the periphery of the heat exchanger system where air or another oxygen carrier can flow. The reaction device can be used as an auxiliary burner. Preferred Parameters: The ratio for the proportions of oxygen carrier and fuel is chosen so that at least 50% (preferably 80-90%) of carbon in the fuel is oxidized to carbon monoxide and the rest to carbon dioxide. The battery is provided for an electrical power of more than 1 kW and less than 5 kW.