Abstract:
An industrial furnace, for instance a heating and/or reducing furnace, arranged to treat material in powder or in small pieces and having a chamber with refractory walls to which energy is supplied by electric means and/or by combustion and into which the material to be treated is charged. The material is moved forward from an inlet orifice to a discharge orifice by a member provided with teeth which are preferably hollow and are cooled by water, air or vapor circulation.

Description:
FIELD AND BACKGROUND OF THE INVENTION 
     The present invention relates to an industrial furnace, and more particularly to a heating and/or reducing furnace for treating materials in powder form and/or in small pieces. 
     The furnaces intended for such operations have a small thermal efficiency as the material becomes strongly heated at the surface exposed to the heat source but badly transmits the heat to the interior of the bulk. Moreover these furnaces are complex and therefore expensive; in particular they use complex means to move the material from the charge to the discharge orifices and often the reducing furnaces cannot use the combustible gases, in particular the carbon monoxide, developing during the reduction process. 
     SUMMARY OF THE INVENTION 
     The invention aims to obviate to the above mentioned drawbacks and to provide a furnace which is simple to construct and easy to operate, and which has a long life and allows a continuous operation. 
     In its more general aspect, the furnace comprises a chamber which has refractory walls and is arranged to receive thermal energy from electric means and/or from a fuel. The chamber has inlet and discharge orifices and is equipped with means which stir the material inside the chamber and push it from the inlet zone to the discharge zone. 
     These stirring and pushing means comprise a movable rod ending in a cross-bar having downwardly projecting teeth. 
     In case the furnace is to operate at a relatively high temperature, above 1000° C., the movable rod, the cross-bar and the teeth are hollow elements in which a cooling fluid can flow. 
     The furnace according to the invention may have several different shapes. To achieve the above mentioned requirements of simplicity, the chamber can suitably have either a circular or a rectilinear plan. 
     The stirring and pushing means, consisting of said moving rod, cross-bar and teeth, may have cavities of relatively large sections, through which the whole furnace charge or a part thereof can also pass. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be better understood with reference to the accompanying drawings, in which: 
     FIG. 1 is a horizontal cross sectional view of a furnace according to the invention, of the annular type; 
     FIG. 2 is a vertical cross section through the annular furnace of FIG. 1 and taken on line II--II of FIG. 1; 
     FIG. 3 is a horizontal cross-section on enlarged scale of a tooth for pushing the material, taken on line III--III of FIG. 4; 
     FIG. 4 is a vertical cross section of the tooth shown in FIG. 3; 
     FIG. 5 is a vertical cross section of a furnace with rectilinear axis, taken on line V--V of FIG. 6; and 
     FIG. 6 is a vertical longitudinal section on a reduced scale of the furnace shown in FIG. 5. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     According to the invention, if the particulate material to be heated is also to be reduced, for instance with coal, so that carbon monoxide develops during the reaction phase, by introducing into the furnace air, which is possibly pre-heated, the combustion of CO to CO 2  can be exploited within the furnace. The furnace can have burning nozzles or even air supplying nozzles. 
     If coal in powder form or in small pieces is introduced into the furnace, it can be gasified with air or even water, producing CO and H 2 . 
     According to a first embodiment (FIGS. 1 and 2) the furnace, when viewed in plan, has the shape of an annulus delimited by outer and inner refractory walls 2, 3, connected by a sole 4 having a discharge orifice 5 and by a crown 6 through which a charge duct 7 is realized. Wall 2 is pierced by burners 29. 
     Internally to wall 3 a metal gear or ring 8 is supported by a set of rollers 9 and is kept in its position by a second set of upper rollers 10. The gear or ring is rigidly linked to another gear 11 internal to the first one and fastened thereto by spokes 12 and arms 13 which pass through inner wall 3. To permit the passage (and motion) of arms 13, wall 3 has an opening 14 (FIG. 2) with a gas-tight labyrinth seal 15. Gear 11 is an internal gear and meshes with pinion 16 driven by reduction gear 17 in turn driven by motor 18. 
     As shown in FIG. 2, arms 13 extend over almost the whole radial width of the furnace chamber and have downwardly projecting teeth 19. 
     In correspondence with the furnace centre, at a certain height above gear 11, connecting members, for instance bars 20 and 21 linking arms 13, are provided. 
     According to a first embodiment such arms, as well as arms 13 and teeth 19, may be solid. In this case bars 20, 21 and the rotatable joint with seals 22, shown in FIG. 2, can be dispensed with. This solution is convenient when the furnace is intended for operation at relatively limited temperature, for instance up to 1000° C. 
     According to a second embodiment arms 20, 21, arms 13 and teeth 19 are hollow, and the respective cavities communicate with one another thereby allowing the circulation of a cooling fluid (for instance water, air, water vapour, gas, etc.) so that the furnace can operate at high temperature. In this case, as shown in FIG. 2, hollow bars 20, 21 are fed from the outside through a rotatable joint whose tightness is achieved through seals 22. 
     According to a third embodiment, besides said communicating cavities, other cavities are provided which communicate with the furnace interior, for instance through the tooth bottom. In this case the rotating seal joint comprises three coaxial tubular elements two of which serve for the inlet and outlet of the cooling fluid and the third is intended for the introduction of a material in powder form or in small pieces, such as ore and/or fuel, which forms a part or the whole of the furnace charge. 
     A solution of this kind is shown in FIGS. 3 and 4, which are cross sectional views of a tooth 19 with a first, outer pipe 23, a central pipe 24 and an inner pipe 24. Pipes 23 and 24 are connected at their lower end by a square ring or bottom 26. 
     FIG. 4 shows material 27 outgoing from the tooth and material 28 lying on furnace sole 4. 
     The operation of the described furnace is as follows: through orifice 7 a first part of the material to be heated and/or treated is introduced; arms 13, driven by motor 18, rotate and through teeth 19 stir and push the material to be treated. After a run somewhat shorter than a complete turn, the material has been sufficiently heated for instance by burners 29 and has arrived at orifice 5 through which it falls into an underlying container. 
     In the case of the high-temperature furnace the coolant fluid arriving through the rotating joint with seals 22 cools arms 13 and teeth 19 and is upwardly discharged through the same rotating joint. 
     In the case of the third embodiment, the material is introduced through the cooled teeth (FIGS. 3, 4). 
     FIGS. 5 and 6 show an embodiment of the invention including a furnace with rectilinear cross-section. In this case means are provided which allow reciprocation of the toothed arms, with means for lifting the arms and teeth to avoid, during the return stroke, the teeth coming into contact with the material thereby hindering the forward movement thereof. A chamber 30 of refractory material, preferably of parallelepipedal shape, with burners 29 in the crown and/or in the walls, has a charge opening 31 and a discharge opening 32. Vertical wall 33 has an opening 34 for passage of an arm 35 supported by rollers 36 driven by a motor, not shown. These rollers are in turn supported by jacks 37. Arm 35 ends within the furnace in a cross-bar 38 having teeth 39. At the opposite end arm 35, which is assumed to be hollow, is connected to at least a pipe 40 supplying the cooling fluid and/or the charge material. 
     The operation of the furnace is the same as that of the circular furnace, the only difference being that jacks 37, when arm 35 has ended its stroke to the left, allow it to be lifted to such an extent that the teeth are no longer in contact with the material, to move the arm back to the starting position. The crucible shown at output 32 can be heated by an electric arc or by a combustion torch thereby melting the material contained therein. The same arrangement may be provided for the container receiving the material from orifice 5 (FIG. 1). 
     The furnace according to the invention is very well suited to treat small material which in the conventional furnaces creates several difficulties. 
     It is self evident that in the practice of the invention, variants and modifications are possible without departing from the scope of the invention.