To effect effective heat treatment of a substance to be treated by situating a fire grate in a rotary furnace.
The rotary furnace 43 consists of an outer cylinder 43a made of a steel material and a fire grate 59 in a given shape formed of a fire resisting heat resisting layer 43b inside the outer cylinder 43a, and the fire grate 59 is situated with specified gaps held by a plurality of supporting and spacing bodies 60. A charge jacket 48 is situated on the carbide introduction side on the side situated upper stream of the rotary furnace 43, and a conveying means 42 for carbide, a combustion burner 49 to ignite and burn carbide by supplying fuel and air and an air feed nozzle 50 for promoting combustion are mounted on the charge jacket 48. A box-form discharge jacket 52 having a fire resisting and heat resisting layer 51 is situated on the discharge side for carbide downstream of the rotary furnace 43.
