Indirect heating system with upgrading of ultra-fine fuel particles

The invention relates to an indirect heating system in which a solid fuel circulates in the form of particles. The inventive system comprises a grinding station, a furnace, at least one intermediate silo, a separator, at least one cyclone and, optionally, a gas recirculation fan. The invention is characterized in that a dust extractor captures the finest particles which are subsequently introduced into the furnace by means of at least one specific conduit and burnt by at least one specific burner. The aforementioned ultra-fine particles are then stored in a specific silo, dosed into a feeding device, mixed in well defined proportions with hot air and conveyed to the specific burner through the specific conduit.