The invention relates to a device for preheating dry materials according to the preamble of claim 1.
Masses for manufacture of electrodes (anodes, cathodes) for aluminium production by molten electrolyte electrolysis are composed of dry materials--dry materials are mixtures of petrol coke and granulated electrode scrap -, to which pitch is added as a binder directly before shaping. Masses with this composition are also called green masses, the electrodes are formed from them and subsequently baked. In order to admix the binder, the dry material has to be heated, in relation to which the term preheating is used, which takes place in so-called preheaters, into one end of which dry material is conveyed by means of weigh-feeders, the conveyed material is heated in the preheater and from the other end of which the heated dry material is removed in the direction of mixers. As preheaters, heating screws, heating silos and heating drums are known. The invention has a heating silo as subject-matter.
A heating silo--they are termed batch preheaters in the technical terminology--is known, in which the dry material is preheated by electrical resistance heating. In the interior of the preheater several electrodes are provided, arranged one below the other--penetrating the walls of the preheater in an insulated manner--for the initiation and discharge of the current (direct or alternating current) flowing through the dry material and thereby heating it. The known device is polygonal in plan view and is characterised by an inhomogeneous mass flow and irregular heating, which leads to graphitisation of the unremoved mass on the electrodes and burning through of the insulation. These disadvantages are increased by the arrangement of preheaters in installations for manufacturing green masses, so that the arrangements are affected to the extent that the repair of a preheater brings entire manufacturing installations to a standstill.