PURPOSE: To utilize sensible heat of flue gas considerably by burning smoke gas at a specified temperature or above and heating outer air, guiding hot gas through a basket filled with scrap and mixing high temperature air flowing out from a heat exchanger with the hot gas.

CONSTITUTION: Air/gas mixture flowing out from a scrap preheating station is fed to a combustion chamber and burnt completely at a temperature of 1200°C or above. A heat exchanger 24 disposed in the way of a flue gas duct 21 is coupled with a high temperature air unit 30. Heated air is guided, on one hand, to a branch 33 and, on the other hand, to a scrap basket 41 or through a coupling pipe 37 to a scrap basket 44. Flue gas in the baskets 41, 44 is fed to a combustion chamber 52, exhausted by means of a suction blower 55 to flow through a flue gas duct 51 and a heat exchanger 54 before being discharged into the atmosphere. An unused air duct 62 is coupled with a bypass duct 65 and low temperature gas can be mixed into the high temperature flue gas in front of a filter 59.