PURPOSE: To maintain a sand temperature at a favourable temperature always by a method wherein an air blow quantity from an air dispersing unit located at the center of a furnace is controlled and the air blow quantity from the air dispersing unit provided in this neighborhood is controlled as well.
CONSTITUTION: A deflector 2 giving horizontal momentum to sand which is flowing is provided in the inside of a furnace 1, underneath of which an air dispersing system 3 is provided. This air dispersing unit 3 is provided with plural air supply openings, and is divided into a central air chamber 3' and its outskirts air chamber 3" so that an air blow quantity from the center part and its outskirts of a furnace can be controlled independently. Compressed air sent from a blower not illustrated in a sketch is led to the air chamber 3' and 3" through the deflector 2 which is used as an air preheater also, and is blown into a sand layer depending on openings of valves 12, 13 and 14 controlled automatically or manually and fluidizes the sand layer. A material to be burnt is thrown into through a throw-in hole 9 and incombustibles are taken out from a takeout hole 10.