BE491194A

BE491194A -

Info

Publication number: BE491194A
Authority: BE

Description

       

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  "Perfectionnement au traitement des minerais, minéraux et/ou résidus afin d'améliorer leurs propriétés pour l'usage   industriel"   
La présente invention se rapporte à des perfectionnements à la méthode et à l'appareil destinés à chauffer et fondre ensemble des particules de matière finement divisée pour former des agglo- mérats, nodules ou corps de particules fondues, relativement gros, et à éliminer de la matière finement divisée, simultanément et en un seul passage à travers l'appareil, tout   'ou   pratiquement tout le plomb, zinc, soufre ou autres(s)   élément(s)   que la matière contient 

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 et qui peuvent être éliminés par volatilisation et/ou oxydation. 



   La présente invention sera décrite en ce qui concerne l'agglo- mération de particules relativement fines d'oxyde de fer supportant des matières telles que du poussier de charbon déposé dans les boî- yes à fumée ou de la poussière de gueulard, du minerai de fer fi- nement divisé, des battitures de laminoirs et analogues. La présente invention n'est pas limitée à des matières contenant un tel métal et ses principes peuvent être appliqués lorsque le chauffage et la fu- sion de matières contenant un autre métal ou d'autres matières sont effectués comme décrit et revendiqué. 



   Une matière supportant du fer finement divisé telle que du poussier de charbon provenant de fours métallurgiques, du minerai de fer finement divisé, des battitures de laminoirs et analogues, ne peut pas être utilisée facilement dans la plupart des fours mé- tallurgiques tels que le haut fourneau ou le four Siemens-Martin. 



  Spécialement lorsqu'on désire utiliser une telle matière dans le four Siemens-Martin pour remplacer une partie ou la totalité de la charge de ferraille, la matière finement divisée doit se présenter sous forme de corps denses ou agglomérats relativement gros, ayant de préférence un pourcentage relativement plus élevé de fer que d'oxyde de fer. On a proposé de produire de tels agglomérats dans un four rotatif. Suivant le processus proposé, la matière à laquelle une proportion convenable de combustible à l'état également finement divisé a été ajouté , est amenée de façon continue à l'extrémité supérieure d'un four rotatif incliné, qui est maintenu en rotation continue autour de son axe longitudinal incliné.

   La rotation du four détermine la charge à descendre à travers le four, en une couche,et, du moins théoriquement, elle effectue une agitation et un mélange des ingrédients pendant le mouvement à travers le four. Comme la charge descend à travers le four, elle est préalablement chauffée progressivement et, lorsque la matière préalablement chauffée at- teint la zone de fusion à l'extrémité inférieure ou d'évacuation du 

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 four, des parties au moins de la matière sont amenées à la tempéra- ture de fusion ou légèrement au-dessus de celle-ci ; Le chauffage de la charge peut être effectué en dirigeant un courant d'air chaud sur la charge dans la zone de fusion pour brûler les particules de combustible.

   Les particules de matière   contenant   du fer qui se trouvent à la température de fusion sont quelque peu pâteuses et collantes et ont tendance à adhérer l'une à l'autre et à former des agglomérats ou nodules relativement denses. Bien que de nombreux essais aient été faits pour fondre et agglomérer de la matière con- tenant' du fer, finement divisé dans le four du type rotatif, on s'est heurté, au cours de ces essais, à de multiples difficultés, qui ont empêché l'acceptation générale du procédé. 



   Un inconvénient important et gênant rencontré réside en ce qu'il est difficile, en pratique, d'obtenir la valeur et le degré convenables de chauffage préalable associés à la valeur exacte de chauffage de la charge dans la zone de fusion. Ceci est aggravé par le fait que différentes matières contenant du fer nécessitent des degrés différents de chauffage préalable. Il est absolument essen- tiel au bon fonctionnement du four que les matières devant être ag- glomérées soient correctement chauffées préalablement. Ce réglage peut être effectué en réglant la vitesse de rotation du four ou en faisant varier la quantité amenée et/ou la proportion de matière combustible ajoutée au minéral dans la charge.

   Dans la zone de fu- sion, une soufflerie est souvent utilisée pour brûler les particules de matière combustible afin de chauffer et fondre les particules de façon à produire l'agglomération. On laisse passer suffisamment de gaz dans le four pour chauffer préalablement la charge descendante. 



  Lorsqu'un vent de soufflerie est utilisé, sa pression doit être tel- le qu'il pénètre la couche de matière dans la zone de fusion mais pas plus qu'il n'est nécessaire à cet effet, et le volume du vent doit être approximativement de 100 pieds cubes par livre de carbone 

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 dans la matière combustible. Par conséquent, tout réglage du chauf- fage préalable par modification de la vitesse du four rotatif rompt la relation dans la zone de fusion. Il est donc absolument difficile, en pratique, 'd'obtenir les conditions adéquates dans les deux parties ou sections du four rotatif. 



   Lorsque la charge descend à travers le four rotatif, la cou- che de la matière dans le four prend une pente naturelle de repos. 



  La charge a tendance à aller sur le côté montant du four et ensui- te descend en roulant de façon à mélanger complètement et remuer la matière qui est nécessaire pour effectuer le chauffage préalable convenable et la fusion des particules. Les particules ont tendan- ce à se séparer selon leur dimension et leur poids spécifique de telle sorte que de petites masses s'orientent vers la paroi de re- vêtement et se posent au fond de la couche, tout près de la paroi de revêtement. Les matières les plus lourdes tendent également à atteindre le fond de sorte que la partie supérieure de la couche comprend les matières les plus légères et les particules les plus grandes.

   Lorsque de très fines particules sont présentes, en par- ticulier, comme c'est souvent le cas avec des minerais de fer fin, -ces particules fines se rassemblent au fond de la couche et déter- minent la charge à glisser plutôt qu'à rouler et effectuer le mé- lange. Ceci empêche le chauffage uniforme de la charge. De plus, les particules les plus grandes de la matière combustible relati- vement légère, telle que le coke, se rassemblent sur la surface su- périeure de la couche de façon que dans la zone de fusion, la cou- che supérieure seulement de matière est amenée à la température de fusion. Il résulte de ceci que le produit est de pauvre qualité et ne peut pas être utilisé dans les fours Siemens-Martin.

   En outre, lorsque la charge glisse, les particules qui se trouvent à la tem- pérature de fusion ne roulent pas et recueillent des particules ad- ditionnelles pour former des corps plus gros obtenus par l'action "boule de neige" lorsque la charge descend, en roulant, le côté montant du four. 

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   Les gaz chauds résultant de la combustion du combustible par la soufflerie doivent traverser le four à contre-courant par rapport à la direction du trajet de la charge de façon à effectuer le chauf- fage préalable de la charge descendante. Les fines particules pré- sentes ont tendance à traverser le four avec les gaz. A certains moments, de fines particules incandescentes de combustible sont transportées dans le four et sont déposées sur la charge qui est soumise au chauffage préalable. La quantité de particules de carbone incandescentes est, à certains moments, suffisante pour rendre col- lante une partie au moins de la charge dans la zone de chauffage préalable. Cela provoque la formation d'accumulations sur la surface du four, ce qui, à son tour, empêche la descente de la charge dans le four. 



   Une autre difficulté rencontrée dans la production d'agglomé- rats dans un four rotatif est occasionnée par la variation de la quantité de combustible présente de temps en temps dans la charge. 



  En pratique, il est difficile, sinon impossible, de maintenir cons- tant le pourcentage de combustible dans la charge. A certains mo- ments, la charge dans la zone de fusion sera insuffisamment chauf- fée pour former des agglomérats et à d'autres moments, elle peut être surchauffée, avec pour conséquence que le four ne fonctionnera pas de façon convenable. Des essais ont été faits pour ajouter du combustible à la charge lorsque la quantité de combustible dans la charge originale est insuffisante. Le combustible ajouté tend à rester isolé de sorte que la charge n'est pas uniformément ni con- venablement chauffée pour produire des agglomérats ou sinters. 



   En raison de ce qui précède, un objet de la présente inven- tion est de prévoir une méthode et un appareil perfectionnés pour la fusion et l'agglomération de particules de matières finement divisées de façon à améliorer l'agglomération des particules. 



   Un autre objet de la présente invention est de prévoir une méthode et un appareil perfectionnés pour fondre et agglomérer des particules de matières finement divisées, qui apporteront de l'ai- sance dans le fonctionnement,de telle façon qu'il puisse y avoir 

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 compensation pour les différences dans la charge. 



   Un autre objet encore de la présente invention est de pré- voir à la fois une méthode et un appareil pour fondre et agglomé- rer des particules de matière finement divisée, qui empêcheront ou réduiront la ségrégation dans la charge. 



   Un autre objet de la présente invention est de prévoir une méthode et un appareil pour fondre et agglomérer des particules de matière finement divisée, qui permettront que du combustible sup- plémentaire soit ajouté et complètement mélangé avec la charge. 



   Un autre objet de la présente invention est de prévoir une méthode et un appareil pour fondre et agglomérer des particules de matière finement divisée, qui permettront d'ajouter du gaz ou de l'air additionnel de combustion en un point intermédiaire du pro- cessus. 



   Un autre objet de la présente invention est de prévoir une méthode et un appareil pour maintenir simultanément, dans les zones de chauffage préalable et de fusion de l'appareil, respectivement une atmosphère d'oxydation et une atmosphère de réduction, comme il peut être requis par les conditions d'usage, et pour les faire varier à volonté. 



   Un autre objet de la présente invention est de prévoir à la fois une méthode et un appareil pour fondre et agglomérer des par- ticules de matière finement divisée, qui assureront un chauffage plus efficient de la charge, à la fois dans la zone de chauffage préalable et dans la zone de fusion. 



   Un autre objet de la présente invention est de prévoir une méthode et un appareil pour éliminer des éléments gênants, tels que le plomb, le zinc, l'arsenic, le soufre et analogues, avant de fondre et agglomérer la matière finement divisée, mais néanmoins au cours d'une seule opération composée et continue dans l'appareil 
La présente invention a également pour objet de prévoir un appareil pour fondre et agglomérer de façon continue une charge de 

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 matière finement divisée, contenant du fer, appareil qui fonction- nera de façon continue pendant un laps de temps relativement long pour produire des corps denses et relativement gros d'agglomérats, avec un minimum d'entretien et de réparation. 



   Ces objets et avantages de la présente invention, ainsi que d'autres, apparaîtront plus clairement à l'examen de la description suivante, faite avec référence au dessin ci-annexé, dans lequel : la figure 1 est une vue latérale d'un appareil réalisant les principes de la présente invention, des parties de l'appareil étant montrées en coupe pour illustrer plus clairement les détails ; la figure 2 est une vue en section transversale suivant la ligne 2-2 de la figure 1, et la figure 3 est une vue en section transversale suivant la ligne 3-3 de la figure 1. 



   Si l'on se réfère au dessin, l'appareil d'agglomération com- prend un four rotatif de chauffage préalable 10, incliné vers le bas, et un four rotatif de fusion 11, incliné vers le bas. Le four de chauffage préalable est situé au-dessus du four de fusion de fa- çon que la matière traverse d'abord le four de chauffage préalbble 10 et, ensuite, le four de fusion 11, tout comme il sera décrit plus complètement ci-après. Le four de chauffage préalable 10 com- prend une enveloppe métallique extérieure 12, revêtue d'une couche 13 de matière résistant aux effets de la chaleur, et est monté dans une paire de bagues 14. Les bagues 14 oscillent sur des cylindres 15 montés à rotation dans des paliers 17 portés par des piliers de support 18. Une large transmission annulaire 19 encercle le four 10 et engrène le pignon 20 d'un moteur de commande 21.

   Un dispositif de commande adéquat, non représenté, est prévu pour faire varier la vitesse du moteur de façon à faire tourner le four 10 autour de son axe longitudinal 22, à la vitesse désirée. Le four 10 est in- cliné vers le bas à partir de son extrémité supérieure d'entrée 24, 

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 vers son extrémité inférieure de sortie 25. A l'extrémité supérieu- re du four 10, il y a un carneau 26 qui communique, par le passage 27, avec un corps de cheminée 28 pour éliminer les gaz chauffés s'écoulant en direction ascendante à travers le four 10.

   Un tuyau d'alimentation 30, incliné vers le bas, se prolonge jusque dans l'extrémité supérieure 24, pour amener la matière dans le four.Tout dispositif approprié, non représenté, peut être prévu pour amener la matière à l'extrémité supérieure   du tuyau   d'alimentation 30. La matière est amenée dans le tuyau d'alimentation à un débit d'écoule- ment uniforme et ce débit d'écoulement dépendra d'un certain nombre de facteurs, comprenant les caractéristiques de la matière qui est agglomérée et la vitesse et la capacité du four de chauffage préa- lable. 



   Le four de fusion inférieur 11 comporte une enveloppe externe 32 présentant une couche interne 33 de matière résistant aux effets de la chaleur, pour supporter la matière qui est chauffée. Ce four est monté dans une paire de bagues 34, montées à rotation sur des éléments 36. Une transmission annulaire 38 entoure le four 11 et engrène un pignon de commande 39 relié au moteur 40. Un appareil approprié de réglage, non représenté, est prévu pour commander le moteur et faire tourner le four à la vitesse désirée. 



   Un couvercle 42 entoure les extrémités adjacentes des fours 10 et 11 et couvre l'extrémité ouverte du four 11 qui n'est pas en alignement avec le four 10, de façon à empêcher l'échappement des gaz. Le couvercle 42 comprend une partie 43 qui agit comme un plan incliné pour guider la matière déchargée du four de chauffage préa- lable 10 dans le four de fusion 11. Un second couvercle 44 est pla- cé à l'extrémité inférieure du four de fusion et présente une ou- verture 45 prévue au-dessus d'un plan incliné 46, par laquelle la matière agglomérée est déchargée du four de fusion. 



   Une trémie d'alimentation 48 traverse une partie latérale du couvercle 42, dans une position telle que son extrémité infé- rieure 49 se prolonge dans une zone située approximativement entre 

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 les extrémités adjacentes des fours 10 et 11 et est disposée pour décharger le combustible additionnel dans le four 11. L'extrémité de décharge 49 de la trémie 48 est placée de telle façon que si du combustible est ajouté à la matière, il l'est comme elle tombe du four de chauffage préalable 10 dans le four de fusion 11 ou qu'elle est sur le point de tomber.

   En ajoutant le combustible additionnel en ce point, un meilleur mélange du combustible avec la charge est obtenu lorsque le mélange tombe dans le four inférieur 11, de sorte que la charge est chauffée'plus uniformément dans le four de fusion, Une seconde trémie similaire à la trémie 48 peut être prévue pour ajouter d'autres ingrédients - par exemple, de la chaux, si on le dé- sire. Bien que ceci ne constitue pas une partie essentielle de cette invention, il est souhaitable que les extrémités de décharge de ces trémies soient aussi proches que possible de la surface du mélange tombant, de façon à réduire le risque qu'une partie de ces additions à la charge soient entraînées dans le four de chauffage préalable 10 par les gaz de combustion quittant le four de fusion 11. 



   Dans certains cas,une amenée d'air traverse une partie latérale du couvercle 42, dans une telle position que l'air soufflé de son ex- trémité intérieure vienne frapper la surface de la charge qui appro- che, dans le four de chauffage préalable 10, et se mélange avec les gaz y passant vers le haut, en direction du   carnesude   cheminée 27. Par addition d'air en ce point, l'atmosphère du four 10 peut être réglée de façon plus précise et rendue oxydante quand bien même une atmos- phère fortement réductrice peut être nécessaire, et, pour cette rai- son, être maintenue dans le four 11 pour produire l'agglomérat dési- ré. 



   Pendant le fonctionnement, qui, normalement, est continu, les fours 10 et 11 sont mis chacun en rotation continue, à des vitesses prédéterminées autour de leurs axes longitudinaux respectifs 22 et   41-   Les fours 10 et 11 peuvent être mis en rotation à des vitesses identi ques ou différentes. La matière à agglomérer est amenée de façon con- tinue, à un débit pratiquement uniforme, dans et à travers le tuyau 

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 d'alimentation 30, dans l'extrémité supérieure du four 10. La rota- tion du four fait descendre la matière à travers le four vers l'ex- trémité inférieure, en une couche 51 pratiquement uniforme.

   Ainsi qu'il est représenté plus clairement à la figure 2, la couche 51 prend une pente naturelle de repos, comme indiqué en 52.   La   grandeur de cet angle dépend   d'un   certain nombre de facteurs, comprenant la vitesse de rotation du four,   la   dimension et la forme des particules et le poids spécifique de la matière s'écoulant à travers le four. 



   Comme la matière atteint l'extrémité inférieure du four, elle des- par cend,en cascadant, /la pente 43, dans le four 11. La rotation du four 
11 détermine la matière à descendre à travers ce four, en une couche 
53 qui prend également une pente naturelle de repos, comme il est plus clairement indiqué à la figure 3. La grandeur de l'angle de la pente de repos dépend d'un certain nombre de facteurs, comprenant la vitesse à laquelle le four tourne, la dimension et la forme des particules et le poids spécifique de la matière s'écoulant à travers le four. La pente naturelle de repos de la matière dans le four de fusion peut être sensiblement identique à la pente naturelle de re- pos de la couche de matière passant par le four de chauffage préala- ble 10, ou différente de cette pente. 



   La matière amenée dans l'extrémité supérieure du four de chauf- fage préalable peut ou non contenir de la matière combustible, telle que du coke finement divisé. Le poussier de charbon par exemple com- prend des particules d'oxyde de fer finement divisé et de coke. S'il y a suffisamment de matière combustible présente dans la charge, du combustible additionnel ne doit pas être ajouté par la trémie 48. 



   S'il n'y a pas suffisamment de combustible présent dans la charge, ou qu'il n'y en a pas du tout, du combustible peut être ajouté par la trémie 48 de façon à réaliser le chauffage de la matière. 



   Dans le cas de matières ayant une teneur élevée en certains éléments délétères mais volatilisables et/ou oxydables, il est sou-   haitable   que pendant la phase de chauffage préalable du processus, la charge ne contienne pas le combustible en une quantité supérieure 

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 à la quantité exacte qui est nécessaire pour chauffer préalablement la charge à la température la plus favorable à l'élimination des éléments délétères, et également, que l'atmosphère dans le four de chauffage préalable 10 soit fortement oxydante. Dans le cas de soufr   par/exemple,   par l'introduction d'air à travers un conduit, dans le four 10, comme indiqué ci-dessus, la combustion de cet élément peut elle-même fournir une forte proportion de la chaleur requise pour cette partie du processus, si pas le tout.

   Une fois que les tempéra- tures requises ont été établies par l'addition d'autre combustible à la charge, la charge initiale peut contenir une très faible pro- portion de combustible ou même aucun combustible, et l'élimination de l'élément ou des éléments délétères oxydables sera fortement ac- crue. 



   Par conséquent, il peut être remédié à tout manque de combus- tible se produisant par l'introduction de combustible par la trémie 48, directement dans le four 11, et l'atmosphère environnante peut être immédiatement remplacée par l'atmosphère hautement réductrice nécessaire pour la bonne marche de l'agglomération finale dans le four 11. La souplesse du réglage de ces conditions contradictoires et le moyen de le mettre en oeuvre constituent une caractéristique remarquable de cette invention. Un tuyau de soufflerie 55 se pro- longe à travers le couvercle 44, dans le four de fusion 11, et est relié à une source de gaz maintenant la combustion, tel que de l'air chaud. Le tuyau de soufflerie 55 a un orifice de sortie 56, disposé pour diriger le vent en direction descendante, sur la couche de matière 53, pour effectuer la combustion de la matière combustible.

   Le volume du vent, la quantité de matière combustible dans la charge et la vitesse d'écoulement sont coordonnés de tel- le façon que les gaz chauds montant du four de fusion 11 à tra- vers le four de chauffage préalable 10 portent, en montant, la charge à une température voisine de la température de fusion de la matière qui est agglomérée, ou mieux en voie d'agglomération. 

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  Dans le four de fusion 11, la charge est additionnellement chauffée de telle sorte qu'une partie au moins des particules sont portées à la température de fusion. Lorsque ces particules sont portées à la température de fusion, elles deviennent pâteuses et collantes. 



  Comme le four tourne, les particules pâteuses tendent à monter sur le côté du four et ensuite, descendent en roulant de telle sorte que des particules additionnelles sont rassemblées et que des corps re- lativement gros sont formés par cet effet "boule de neige". 



   De nombreux avantages sont obtenus en faisant passer la charge à travers les deux fours 10 et 11, comme décrit, et en prévoyant le four de fusion 11 plus grand que le four de chauffage préalable 10. 



  De bons résultats peuvent être obtenus lorsque le four de fusion a un diamètre environ deux fois aussi grand que le diamètre du four de chauffage préalable. Comme les fours de chauffage préalable et de fusion sont séparés, les fours peuvent tourner indépendamment, chacun à la vitesse optimum. Le four de chauffage préalable par exem- ple peut tourner de telle façon que la charge soit chauffée préala- blement à un degré uniforme, par quoi la température de la charge est accrue d'une valeur sensiblement égale pour chaque pied de tra- jet. Pour certains types de matière , il est souhaitable de faire varier le degré de chauffage de la matière de telle façon que la quantité de chaleur ajoutée à la matière par pied de trajet ne soit pas uniforme sur toute la longueur du four.

   Ces résultats peuvent être obtenus en faisant varier la vitesse de rotation du four de chauffage préalable. 



   La vitesse de rotation du four de fusion peut également être modifiée pour obtenir le chauffage optimum et l'agglomération de la matière. De préférence,le four de fusion tourne à une vitesse rela- tivement faible car, en général, plus faible est la vitesse de rota- tion, plus grands sont les corps des agglomérats produits dans la zone de fusion. 



   Le four de fusion est placé de telle façon que son axe longitu- dinal 41 est parallèle à l'axe longitudinal 22 du four 10 et en 

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 dessous de lui. Le diamètre plus grand du four 11 permet au four de tourner de façon à déplacer la charge à travers ce four plus lente- ment qu'à travers le four 10. Plus le four 11 tourne lentement, plus gros seront les agglomérats produits et plus il y aura de ma- tière disposée par pied linéaire du four. Un autre avantage impor- tant du four de fusion à grand diamètre réside dans le fait que la couche de la charge dans le four est plus grande.

   Les particules de matière contenant du fer, qui sont chauffées à la température de fusion, descendront, pendant le mélange effectué par rotation du four, en roulant à travers cette large couche et viendront en con- tact avec plus d'autres particules qu'elles ne l'auraient fait si le four avait eu un petit diamètre et une couche étroite. Ceci, à son tour,   augmente 1 ' effet   "boule de neige" de sorte que des ag- glomérats plus gros sont produits. 



   Un autre avantage du diamètre relativement grand du four de fusion 11 est que la vitesse de passage des gaz de combustion le long de ce four est moindre qu'elle ne serait autrement et, pour cette raison, toutes les particules de matière fortement chauffées et collantes, recueillies par ces gaz, ont tendance à tomber de la suspension et à rester dans ce four au lieu d'être entraînées dans le four de chauffage préalable 10. 



   De même, un avantage du diamètre relativement plus petit du four de chauffage préalable 10 est que la vitesse de déplacement des gaz de combustion le long de ce four, en direction du carneau de cheminée 27, sera plus élevée, de façon correspondante ; toutes les particules de matière fortement chauffée et collante entraînées du four de fusion 11 dans le four de chauffage préalable 10 subi- ront immédiatement, dès l'entrée dans ce four, un accroissement considérable de vitesse de déplacement et tendront à rester en suspension dans le courant gazeux et à être transportées en avant dans une zone de température dans laquelle la "formation d'anneaux" ("ringing")ne se produit pas. 

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   Le diamètre relativement plus large du four de fusion pro- cure également d'autres avantages. Le fait de modifier la vitesse de rotation du four ou de modifier d'autres conditions provoque un changement dans la masse de charge par pied de longueur. Plus large est le diamètre, plus grande peut être la variation dans la masse par pied de longueur, sans augmenter ou diminuer indûment la profondeur d'épaisseur de la couche. Ceci permet un réglage plus important et une plus grande souplesse du fonctionnement car il est possible d'avoir une plus grande variété de la matière pré- sente dans le four de fusion.

   Avec un four de fusion de diamètre moindre, le même changement dans la masse provoquerait une plus grande variation d'épaisseur de la couche et un accroissement re- lativement petit dans la masse augmenterait l'épaisseur de la cou- che au point que le vent ne pourrait pas pénétrer la charge et brûler le combustible. 



   Lorsque la charge est d'un caractère tel que les matières relativement fines se séparent de telle sorte que la charge tend à glisser le long de la surface du four, la descente en cascade de la matière du four de chauffage préalable dans le four da fu- sion plus grand, permet un mélange complet de la matière. Par conséquent, avant que la matière ait été chauffée à la   températu-   de fusion, la charge est mélangée complètement et est plus uni- forme de telle sorte qu'une meilleure agglomération est obtenue. 



  De plus, ce mélange plus complet de la charge en ce point permet que du combustible soit ajouté et complètement mélangé avec la charge. De préférence, le combustible est ajouté avant que la charge descende en cascadant ou tombe dans le four de fusion, ou au moment où ceci se passe, de telle sorte qu'un chauffage plus uniforme et meilleur est obtenu lorsque le combustible est brûlé. 



   Dans le cas de matières contenant des constituants délé- tères volatilisables et/ou oxydables, il est souhaitable que l'atmosphère dans le four de chauffage préalable 10 soit forte- ment oxydante et, pour cette raison, que la charge initiale 

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 ne contienne que la quantité minimum de combustible (compte tenu de la chaleur fournie par l'oxydation des dits constituants délétè- res, comme, par exemple, le soufre) pour ne chauffer préalablement la charge qu'à la température qui favorise l'élimination du cons- tituant délétère, la déficience de combustible pour l'agglomération subséquente étant compensée dans le four de fusion 11 à l'inter- vention de la trémie 48. 



   Pour obtenir les agglomérats les meilleurs, il est nécessai- re de maintenir une atmosphère fortement réductrice dans le four de fusion 11, condition qui est contradictoire avec les nécessités de la phase de chauffage préalable du processus qui s'effectue en même temps dans le four de chauffage préalable 10. 



   Pour pallier cette difficulté, un tuyau de soufflerie relié à une source d'alimentation en gaz ou air de combustion, se pro- longe à travers la paroi du couvercle 42. 



   Il est situé entre l'extrémité inférieure du four de chauf- fage préalable 10 et l'extrémité de décharge de la trémie 48, et est agencé de telle façon que l'air projeté par lui heurte la sur- face de la matière, à l'extrémité inférieure du four de chauffage préalable 10. L'air fourni par ce tuyau de soufflerie est, de pré- férence, fortement chauffé de façon à augmenter et accélérer l'oxy- dation de la charge dans le four 10. 



   Par cette combinaison des dispositifs d'alimentation pour le combustible et le gaz ou l'air de combustion, les difficultés rencontrées jusqu'ici dans le maintien d'une atmosphère fortement oxydante dans la première partie du processus d'agglomération et d'une atmosphère fortement réductrice dans la dernière partie,et dans le réglage du degré d'une telle oxydation et d'une telle ré- duction, sont tout à fait écartées. 



   Un autre avantage de l'introduction du combustible et de l'air pour sa combustion en deux points séparés, est que, tandis que la quantité totale d'air eu de gaz reste identique, celle qui est requise pour être amenée par le tuyau de soufflerie 55 est ré- duite de la quantité fournie par le tuyau de soufflerie et, de ce 

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 fait, la tendance à entraîner dans le four de chauffage préalable 10, des particules fortement chauffées de minéral se trouvant dans les gaz de combustion du four de fusion 11, est réduite de façon correspondante et la "formation d'anneaux" conséquente, qui carac- térise l'usage du four rotatif usuel et bien connu, est de ce fait réduite.

   L'amenée, du tuyau de soufflerie, du reste de l'air de combustion nécessaire pour la bonne marche de la phase d'oxydation du processus dans le four de chauffage préalable, n'entraîne aucun risque semblable, puisque la température dans le four de chauffage préalable 10 doit et peut être facilement maintenue en dessous de celle à laquelle cette "formation d'anneaux" se produit. 



   Des défauts de puissance ou d'autres défauts peuvent pro- voquer un retard dans le déplacement de la charge à travers le four de chauffage préalable et une perte de chaleur. Ceci également peut être compensé en ajoutant du combustible par la trémie 48. 



   Un autre avantage du présent agencement est que les fines particules de combustible incandescent qui tendent à passer, en mon- tant, dans la zone de chauffage préalable, avec les gaz chauds, sont éliminées ou fortement réduites. Les gaz chauds tendant à entraîner des particules incandescentes de combustible frappent contre le cou- vercle 42 reliant les deux parties, de   telle,sorte   que les particules incandescentes ont tendance à tomber dans la zone de fusion et ne provoquent aucun dommage dans la zone de chauffage préalable. 



   Le diamètre relativement petit du four de chauffage préala- ble met la charge relativement froide dans ce four, en contact plus intime avec les gaz s'écoulant dans le sens inverse, de sorte qu'un meilleur chauffage préalable est obtenu. Comme le four de chauffage préalable 10 est relativement long, on obtient plus de chaleur des gaz, ce qui a pour résultat.un fonctionnement plus efficient et ce qui réduit la quantité de combustible requise. Si le four de fu- sion était approximativement du même diamètre et, par suite, rela- tivement plus long, une perturbation se produirait avec les parties 

 <Desc/Clms Page number 17> 

 de la charge qui est chauffée à la température de fusion, à une distance relativement grande du point de décharge.

   Ceci augmente- rait la tendance de la charge à coller au four, et la zone de fusion aurait tendance à monter et descendre dans le four. Selon ce qui précède, il est important que le diamètre du four de chauffage préa- lable soit relativement plus petit et que le diamètre du four de fusion soit relativement plus grand, le fond du four de fusion étant situé en dessous du fond du four de chauffage préalable. De préfé- rence, l'axe de rotation du four 11 est situé en parallèle avec l'axe de rotation du four 10 mais en dessous de cet axe, ce qui a- baisse en outre le fond du four 11 par rapport au fond du four 10. 



  Les fours 10 et 11 peuvent être concentriques, spécialement si le diamètre du four de fusion est augmenté par rapport au diamètre du four de chauffage préalable. 
 EMI17.1 




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  "Improvement in the treatment of ores, minerals and / or residues in order to improve their properties for industrial use"
The present invention relates to improvements in the method and apparatus for heating and melting together particles of finely divided material to form relatively large agglomerates, nodules, or molten bodies of particles, and removing some of the material. finely divided material, simultaneously and in a single pass through the apparatus, all or substantially all of the lead, zinc, sulfur or other element (s) which the material contains

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 and which can be removed by volatilization and / or oxidation.



   The present invention will be described with respect to the agglomeration of relatively fine particles of iron oxide bearing materials such as coal dust deposited in smoke boxes or throat dust, iron ore. finely divided iron, rolling mill scale and the like. The present invention is not limited to materials containing such a metal and its principles can be applied when the heating and melting of materials containing another metal or other materials is carried out as described and claimed.



   A finely divided iron bearing material such as coal dust from metallurgical furnaces, finely divided iron ore, mill scale and the like, cannot be readily used in most metallurgical furnaces such as the high Siemens-Martin stove or oven.



  Especially when it is desired to use such material in the Siemens-Martin furnace to replace part or all of the scrap charge, the finely divided material should be in the form of dense bodies or relatively large agglomerates, preferably having a percentage. relatively higher iron than iron oxide. It has been proposed to produce such agglomerates in a rotary kiln. According to the proposed process, the material to which a suitable proportion of fuel in an equally finely divided state has been added is continuously fed to the upper end of an inclined rotary kiln, which is kept in continuous rotation around its inclined longitudinal axis.

   The rotation of the oven determines the load to descend through the oven, in one layer, and, at least theoretically, it effects agitation and mixing of the ingredients during movement through the oven. As the charge descends through the furnace, it is gradually preheated and, when the preheated material reaches the melting zone at the lower or discharge end of the

 <Desc / Clms Page number 3>

 furnace, at least parts of the material are brought to or slightly above the melting temperature; Heating of the charge can be accomplished by directing a stream of hot air over the charge in the melting zone to burn off the fuel particles.

   Particles of iron-containing material which are at melting temperature are somewhat pasty and sticky and tend to adhere to each other and form relatively dense agglomerates or nodules. Although many attempts have been made to melt and agglomerate finely divided iron-containing material in the rotary type furnace, many difficulties have been encountered in these trials, which have resulted in numerous difficulties. prevented general acceptance of the process.



   A significant and troublesome drawback encountered is that it is difficult, in practice, to obtain the proper amount and degree of preheating associated with the exact amount of heating of the feed in the melting zone. This is made worse by the fact that different iron-containing materials require different degrees of preheating. It is absolutely essential for the correct functioning of the furnace that the materials to be agglomerated are properly heated beforehand. This adjustment can be carried out by adjusting the speed of rotation of the furnace or by varying the quantity supplied and / or the proportion of combustible material added to the mineral in the charge.

   In the fusion zone, a blower is often used to burn the particles of combustible material in order to heat and melt the particles to produce agglomeration. Sufficient gas is allowed to pass through the oven to preheat the descending charge.



  When a blowing wind is used, its pressure should be such that it penetrates the layer of material in the melting zone but not more than necessary for this purpose, and the volume of the wind should be. approximately 100 cubic feet per pound of carbon

 <Desc / Clms Page number 4>

 in the combustible material. Therefore, any pre-heating adjustment by changing the speed of the rotary kiln breaks the relationship in the melting zone. It is therefore absolutely difficult in practice to achieve the correct conditions in both parts or sections of the rotary kiln.



   As the load descends through the rotary kiln, the layer of material in the kiln assumes a natural slope of rest.



  The charge tends to go to the upright side of the furnace and then rolls down so as to thoroughly mix and stir the material which is necessary to effect the proper preheating and melting of the particles. The particles tend to separate according to their size and specific weight such that small masses orient towards the coating wall and settle at the bottom of the diaper, very close to the coating wall. Heavier materials also tend to sink to the bottom so that the top of the layer includes the lighter materials and larger particles.

   When very fine particles are present, espe- cially, as is often the case with fine iron ores, - these fine particles collect at the bottom of the bed and determine the charge to slide rather than roll up and mix. This prevents uniform heating of the load. In addition, the larger particles of the relatively light combustible material, such as coke, collect on the upper surface of the layer so that in the melting zone only the upper layer of material. is brought to the melting temperature. As a result, the product is of poor quality and cannot be used in Siemens-Martin ovens.

   Furthermore, when the charge slides, the particles which are at the melting temperature do not roll and collect additional particles to form larger bodies obtained by the "snowball" action when the charge goes down. , while rolling, the upright side of the oven.

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   The hot gases resulting from the combustion of the fuel by the blower must pass through the furnace in counter-current with respect to the direction of the load path so as to effect the preliminary heating of the descending load. The fine particles present tend to pass through the oven with the gases. At times, fine glowing particles of fuel are carried through the furnace and deposited on the load which is subjected to preheating. The quantity of glowing carbon particles is, at times, sufficient to make at least part of the charge in the preheating zone sticky. This causes build-up to form on the surface of the furnace, which in turn prevents the load from descending into the furnace.



   Another difficulty encountered in producing agglomerates in a rotary kiln is caused by varying the amount of fuel present from time to time in the charge.



  In practice, it is difficult, if not impossible, to keep the percentage of fuel in the charge constant. At some times the charge in the melting zone will be insufficiently heated to form agglomerates and at other times it may be overheated with the consequence that the furnace will not operate properly. Attempts have been made to add fuel to the charge when the amount of fuel in the original charge is insufficient. The added fuel tends to remain isolated so that the charge is not uniformly or adequately heated to produce agglomerates or sinters.



   In view of the foregoing, it is an object of the present invention to provide an improved method and apparatus for the melting and agglomeration of particles of finely divided materials so as to improve the agglomeration of the particles.



   Another object of the present invention is to provide an improved method and apparatus for melting and agglomerating particles of finely divided materials, which will aid in operation, so that there may be

 <Desc / Clms Page number 6>

 compensation for differences in load.



   Still another object of the present invention is to provide both a method and an apparatus for melting and agglomerating particles of finely divided material which will prevent or reduce segregation in the feed.



   Another object of the present invention is to provide a method and apparatus for melting and agglomerating particles of finely divided material which will allow additional fuel to be added and completely mixed with the charge.



   Another object of the present invention is to provide a method and apparatus for melting and agglomerating particles of finely divided material which will allow additional combustion gas or air to be added at an intermediate point in the process.



   Another object of the present invention is to provide a method and apparatus for simultaneously maintaining, in the preheating and melting zones of the apparatus, respectively an oxidizing atmosphere and a reducing atmosphere, as may be required. by the conditions of use, and to vary them at will.



   Another object of the present invention is to provide both a method and an apparatus for melting and agglomerating particles of finely divided material, which will provide more efficient heating of the charge, both in the pre-heating zone. and in the fusion zone.



   Another object of the present invention is to provide a method and apparatus for removing troublesome elements, such as lead, zinc, arsenic, sulfur and the like, before melting and agglomerating the finely divided material, but nevertheless in a single compound and continuous operation in the device
Another object of the present invention is to provide an apparatus for continuously melting and agglomerating a charge of

 <Desc / Clms Page number 7>

 A finely divided material containing iron, an apparatus which will operate continuously for a relatively long period of time to produce dense and relatively large bodies of agglomerates, with minimal maintenance and repair.



   These objects and advantages of the present invention, as well as others, will emerge more clearly on examination of the following description, made with reference to the accompanying drawing, in which: FIG. 1 is a side view of an apparatus Embodying the principles of the present invention, parts of the apparatus being shown in section to more clearly illustrate the details; Figure 2 is a cross-sectional view taken along line 2-2 of Figure 1, and Figure 3 is a cross-sectional view taken along line 3-3 of Figure 1.



   Referring to the drawing, the agglomeration apparatus comprises a preheating rotary kiln 10, inclined downwards, and a rotary melting kiln 11, inclined downwards. The preheating furnace is located above the melting furnace so that the material passes first through the preheating furnace 10 and then through the melting furnace 11, as will be described more fully below. after. The preheating furnace 10 comprises an outer metal casing 12, coated with a layer 13 of material resistant to the effects of heat, and is mounted in a pair of rings 14. The rings 14 oscillate on cylinders 15 mounted at rotation in bearings 17 carried by support pillars 18. A large annular transmission 19 encircles the furnace 10 and meshes the pinion 20 of a control motor 21.

   A suitable control device, not shown, is provided to vary the speed of the motor so as to make the oven 10 rotate about its longitudinal axis 22, at the desired speed. The oven 10 is inclined downwards from its upper inlet end 24,

 <Desc / Clms Page number 8>

 towards its lower outlet end 25. At the upper end of the furnace 10, there is a flue 26 which communicates, through the passage 27, with a chimney body 28 to eliminate the heated gases flowing in an upward direction. through the oven 10.

   A feed pipe 30, inclined downwards, extends into the upper end 24, to bring the material into the furnace. Any suitable device, not shown, may be provided to bring the material to the upper end of the furnace. feed pipe 30. The material is fed into the feed pipe at a uniform flow rate and this flow rate will depend on a number of factors, including the characteristics of the material being agglomerated and the speed and capacity of the preheating oven.



   The lower melting furnace 11 has an outer shell 32 having an inner layer 33 of material resistant to the effects of heat, to support the material which is heated. This furnace is mounted in a pair of rings 34, rotatably mounted on elements 36. An annular transmission 38 surrounds the furnace 11 and meshes with a control pinion 39 connected to the motor 40. A suitable adjustment device, not shown, is provided. to control the motor and run the oven at the desired speed.



   A cover 42 surrounds the adjacent ends of the ovens 10 and 11 and covers the open end of the oven 11 which is not in alignment with the oven 10, so as to prevent the escape of gases. The cover 42 includes a portion 43 which acts as an inclined plane to guide material discharged from the pre-heating furnace 10 into the melting furnace 11. A second cover 44 is placed at the lower end of the melting furnace. and has an opening 45 provided above an inclined plane 46, through which the agglomerated material is discharged from the melting furnace.



   A feed hopper 48 passes through a side portion of cover 42, in a position such that its lower end 49 extends into an area approximately between.

 <Desc / Clms Page number 9>

 the adjacent ends of the furnaces 10 and 11 and is arranged to discharge additional fuel into the furnace 11. The discharge end 49 of the hopper 48 is positioned such that if fuel is added to the material it is added. as it falls from the preheating furnace 10 into the melting furnace 11 or is about to fall.

   By adding the additional fuel at this point, a better mixing of the fuel with the charge is obtained when the mixture falls into the lower furnace 11, so that the charge is heated more evenly in the melting furnace. A second hopper similar to hopper 48 may be provided to add other ingredients - eg, lime, if desired. Although this is not an essential part of this invention, it is desirable that the discharge ends of these hoppers be as close as possible to the surface of the falling mixture, so as to reduce the risk that a part of these additions to the charge are entrained in the preheating furnace 10 by the combustion gases leaving the melting furnace 11.



   In some cases an air supply passes through a side portion of the cover 42, in such a position that the air blown from its inner end strikes the surface of the approaching charge in the preheating furnace. 10, and mixes with the gases passing upwards therein, in the direction of the chimney flue 27. By adding air at this point, the atmosphere of the furnace 10 can be regulated more precisely and made oxidizing even when A strongly reducing atmosphere may be necessary, and for this reason, maintained in furnace 11 to produce the desired agglomerate.



   During operation, which normally is continuous, the furnaces 10 and 11 are each rotated continuously, at predetermined speeds about their respective longitudinal axes 22 and 41. The furnaces 10 and 11 can be rotated at high speeds identical or different. The material to be agglomerated is fed continuously, at a substantially uniform rate, into and through the pipe.

 <Desc / Clms Page number 10>

 feed 30 into the upper end of oven 10. Rotation of the oven lowers material through the oven to the lower end in a substantially uniform layer 51.

   As shown more clearly in FIG. 2, the layer 51 assumes a natural slope of rest, as indicated at 52. The magnitude of this angle depends on a number of factors, including the speed of rotation of the furnace, the size and shape of the particles and the specific gravity of the material flowing through the furnace.



   As the material reaches the lower end of the furnace, it cascading down / slope 43 into furnace 11. Rotation of the furnace
11 determines the material to be lowered through this furnace, in one layer
53 which also assumes a natural slope of rest, as more clearly shown in Figure 3. The magnitude of the angle of the slope of rest depends on a number of factors, including the speed at which the furnace is rotating, the size and shape of the particles and the specific gravity of the material flowing through the furnace. The natural slope at which the material rests in the melting furnace may be substantially the same as, or different from, the natural slope of the layer of material passing through the preheating furnace 10.



   The material supplied to the upper end of the preheating furnace may or may not contain combustible material, such as finely divided coke. Coal dust, for example, comprises particles of finely divided iron oxide and coke. If there is sufficient combustible material present in the charge, additional fuel should not be added through hopper 48.



   If there is not enough fuel present in the charge, or there is none at all, fuel can be added through the hopper 48 so as to heat the material.



   In the case of materials having a high content of certain deleterious but volatilizable and / or oxidizable elements, it is desirable that during the pre-heating phase of the process, the feed does not contain the fuel in a greater quantity.

 <Desc / Clms Page number 11>

 to the exact amount which is necessary to preheat the load to the temperature most favorable to the elimination of deleterious elements, and also, that the atmosphere in the preheating furnace 10 is strongly oxidizing. In the case of sulfur for example, by the introduction of air through a duct, in the furnace 10, as indicated above, the combustion of this element can itself provide a high proportion of the heat required for this part of the process, if not all.

   Once the required temperatures have been established by adding other fuel to the charge, the initial charge may contain a very small proportion of fuel or even no fuel, and the removal of the element or deleterious oxidizable elements will be greatly increased.



   Therefore, any fuel shortage occurring can be remedied by introducing fuel through hopper 48, directly into furnace 11, and the surrounding atmosphere can be immediately replaced by the highly reducing atmosphere necessary for the good functioning of the final agglomeration in the furnace 11. The flexibility of the adjustment of these contradictory conditions and the means of implementing it constitute a remarkable characteristic of this invention. A blower pipe 55 extends through cover 44 into melting furnace 11 and is connected to a source of gas maintaining combustion, such as hot air. The blower pipe 55 has an outlet 56, disposed to direct the wind in a downward direction, over the material layer 53, to effect combustion of the combustible material.

   The volume of the wind, the amount of combustible material in the feed and the flow velocity are coordinated such that the hot gases rising from the melting furnace 11 through the preheating furnace 10 carry, ascending. , the charge at a temperature close to the melting point of the material which is agglomerated, or better still in the process of agglomeration.

 <Desc / Clms Page number 12>

 



  In the melting furnace 11, the charge is additionally heated so that at least part of the particles are brought to the melting temperature. When these particles are brought to melting temperature, they become pasty and sticky.



  As the oven rotates, the pasty particles tend to rise up the side of the oven and then roll down so that additional particles are gathered and relatively large bodies are formed by this "snowball" effect.



   Many advantages are obtained by passing the charge through the two furnaces 10 and 11, as described, and by making the melting furnace 11 larger than the preheating furnace 10.



  Good results can be obtained when the melting furnace has a diameter about twice as large as the diameter of the preheating furnace. As the preheating and melting furnaces are separate, the furnaces can run independently, each at the optimum speed. The preheating furnace, for example, may rotate such that the load is preheated to a uniform degree, whereby the temperature of the load is increased by a substantially equal amount for each foot of travel. For some types of material, it is desirable to vary the degree of heating of the material such that the amount of heat added to the material per foot of path is not uniform throughout the length of the furnace.

   These results can be obtained by varying the rotational speed of the preheating furnace.



   The speed of rotation of the melting furnace can also be varied to achieve optimum heating and agglomeration of the material. Preferably, the melting furnace rotates at a relatively low speed because, in general, the lower the speed of rotation, the larger the bodies of agglomerates produced in the melting zone.



   The melting furnace is placed so that its longitudinal axis 41 is parallel to the longitudinal axis 22 of the furnace 10 and in

 <Desc / Clms Page number 13>

 below him. The larger diameter of furnace 11 allows the furnace to rotate so as to move the load through this furnace more slowly than through furnace 10. The slower the furnace 11 rotates, the larger the agglomerates produced and the more likely it is. there will be material arranged per linear foot of the oven. Another important advantage of the large diameter melting furnace is that the layer of charge in the furnace is larger.

   The particles of iron-containing material, which are heated to the melting temperature, will, during mixing by rotating the furnace, roll down through this large layer and come into contact with more other particles than they are. would not have done if the furnace had had a small diameter and a narrow layer. This, in turn, increases the "snowball" effect so that larger agglomerates are produced.



   Another advantage of the relatively large diameter of the melting furnace 11 is that the rate of passage of the combustion gases along this furnace is less than it would otherwise be and, for this reason, all the strongly heated and sticky material particles , collected by these gases, tend to fall from the slurry and remain in this furnace instead of being drawn into the pre-heating furnace 10.



   Likewise, an advantage of the relatively smaller diameter of the preheating furnace 10 is that the speed of movement of the combustion gases along this furnace towards the chimney flue 27 will be correspondingly higher; all particles of strongly heated and sticky material entrained from the melting furnace 11 into the preheating furnace 10 will immediately undergo, upon entry into this furnace, a considerable increase in travel speed and will tend to remain suspended in the furnace. gas stream and to be carried forward into a temperature zone in which "ringing" does not occur.

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   The relatively larger diameter of the melting furnace also provides other advantages. Changing the rotational speed of the furnace or changing other conditions causes a change in the mass of charge per foot of length. The larger the diameter, the greater can be the variation in mass per foot of length, without unduly increasing or decreasing the depth of layer thickness. This allows for greater control and flexibility in operation as it is possible to have a greater variety of the material present in the melting furnace.

   With a smaller diameter melting furnace, the same change in mass would cause a greater variation in layer thickness and a relatively small increase in mass would increase layer thickness to the point that the wind could not penetrate the load and burn the fuel.



   When the charge is of such a character that the relatively fine materials separate such that the charge tends to slide along the surface of the furnace, the cascade descent of the material from the preheating furnace into the furnace da fu - larger dimension, allows complete mixing of the material. Therefore, before the material has been heated to the melting temperature, the feed is mixed thoroughly and is more uniform so that better agglomeration is obtained.



  In addition, this more thorough mixing of the charge at this point allows fuel to be added and completely mixed with the charge. Preferably, the fuel is added before the charge cascades down or falls into the melting furnace, or at the time of this happening, so that more uniform and better heating is obtained when the fuel is burned.



   In the case of materials containing volatilizable and / or oxidizable deleterious constituents, it is desirable that the atmosphere in the preheating furnace 10 be strongly oxidizing and, therefore, that the initial charge

 <Desc / Clms Page number 15>

 contains only the minimum quantity of fuel (taking into account the heat supplied by the oxidation of the said deleterious constituents, such as, for example, sulfur) in order to first heat the load only to the temperature which favors elimination of the deleterious component, the fuel deficiency for subsequent agglomeration being compensated for in the melting furnace 11 through the intervention of the hopper 48.



   In order to obtain the best agglomerates, it is necessary to maintain a strongly reducing atmosphere in the melting furnace 11, a condition which is contradictory to the requirements of the preliminary heating phase of the process which is carried out at the same time in the furnace. pre-heating 10.



   To overcome this difficulty, a blower pipe connected to a supply source of gas or combustion air, extends through the wall of cover 42.



   It is located between the lower end of the preheating furnace 10 and the discharge end of the hopper 48, and is arranged so that the air projected by it strikes the surface of the material, at the lower end of the preheating furnace 10. The air supplied by this blower pipe is preferably strongly heated so as to increase and accelerate the oxidation of the charge in the furnace 10.



   By this combination of the feed devices for fuel and gas or combustion air, the difficulties encountered heretofore in maintaining a strongly oxidizing atmosphere in the first part of the agglomeration process and an atmosphere strongly reducing in the last part, and in the adjustment of the degree of such oxidation and reduction, are quite excluded.



   Another advantage of introducing the fuel and the air for its combustion at two separate points is that, while the total quantity of air and gas remains the same, that which is required to be supplied through the gas pipe. blower 55 is reduced by the quantity supplied by the blower pipe and, therefore

 <Desc / Clms Page number 16>

 In fact, the tendency to entrain in the preheating furnace 10 strongly heated particles of mineral present in the combustion gases of the melting furnace 11 is correspondingly reduced and the consequent "ring formation", which causes - Terise the use of the conventional and well-known rotary kiln, is thereby reduced.

   The supply, from the blower pipe, of the rest of the combustion air necessary for the proper functioning of the oxidation phase of the process in the pre-heating furnace, does not entail any similar risk, since the temperature in the furnace preheating 10 should and can be easily kept below that at which this "ring formation" occurs.



   Power faults or other faults can cause delay in moving the load through the preheating furnace and loss of heat. This too can be compensated for by adding fuel through hopper 48.



   Another advantage of the present arrangement is that the fine particles of glowing fuel which tend to pass up through the preheating zone with the hot gases are eliminated or greatly reduced. The hot gases tending to entrain glowing particles of fuel strike against the cover 42 connecting the two parts, so that the glowing particles tend to fall into the melting zone and do not cause any damage in the heating zone. prior.



   The relatively small diameter of the preheating furnace brings the relatively cool charge in that furnace into more intimate contact with the gases flowing in the reverse direction, so that better preheating is obtained. Since the preheating furnace 10 is relatively long, more heat is obtained from the gases, resulting in more efficient operation and reducing the amount of fuel required. If the smelting furnace were of approximately the same diameter and, therefore, relatively longer, a disturbance would occur with the parts

 <Desc / Clms Page number 17>

 of the charge which is heated to the melting temperature at a relatively large distance from the point of discharge.

   This would increase the tendency of the charge to stick to the furnace, and the melting zone would tend to move up and down in the furnace. According to the above, it is important that the diameter of the pre-heating furnace is relatively smaller and that the diameter of the melting furnace is relatively larger, the bottom of the melting furnace being located below the bottom of the melting furnace. pre-heating. Preferably, the axis of rotation of the furnace 11 is located in parallel with the axis of rotation of the furnace 10 but below this axis, which further lowers the bottom of the furnace 11 relative to the bottom of the furnace. oven 10.



  Furnaces 10 and 11 may be concentric, especially if the diameter of the melting furnace is increased relative to the diameter of the preheating furnace.
 EMI17.1

Claims

CLAIMS.

1. Operations, in the method of continuous fusion and agglomeration of particles of material, comprising passing a charge of this material, in a downward direction, through a pre-heating zone, in an inclined path. - born at a predetermined angle with the horizontal; preheating the feed, as it passes through said zone, to a temperature below the melting temperature; subsequently passing the previously heated material down through a melting zone, in a path parallel to the first-mentioned path, and heating at least part of the particles to the melting temperature;

agglomeration of the particles to form relatively larger bodies, the passageway through the melting zone being shifted downward from the passageway through the pre-heating zone; and cascading down the preheated charge from the preheating zone to the melting zone, where the material is completely mixed before it passes through the melting zone.

2. Operations, in the method of continuous melting and agglomeration of particles of material, comprising the passage of a charge of this material, in a downward direction, through a pre-heating zone, of a length relatively larger and of a smaller diameter, in a track at a predetermined angle to the horizontal; heating / of the load to a temperature below the melting temperature;

the subsequent passage of the previously heated charge, in a downward direction, through a melting zone of relatively shorter length and larger diameter, in a path parallel to the passageway through the pre-heating zone, the passageway through the melting zone being offset downwardly from the passageway through the pre-heating zone; cascading descent of the previously heated load, of the pre-heating zone into the melting zone, and the addition of ma- particles. <Desc / Clms Page number 19> -tare fuel to the load, before it reaches the passageway through the melting zone, from where the added fuel is mixed with the load, during the cascade fall.

3. Operations, in the method of continuous melting and agglomeration of particles of material, comprising passing a charge of this material in a downward direction through a pre-heating zone at a relatively high rate. elevated, in a track inclined at a predetermined angle to the horizontal; preheating the charge, as it moves through said zone, to a temperature below the melting temperature; the subsequent passage of the previously heated material, in a downward direction, through a melting zone, at a relatively slower speed, in a path parallel to the first mentioned path; heating at least part of the particles to the melting temperature;

agglomeration of the particles to form relatively larger bodies, the passageway through the melting zone being shifted downward from the passageway through the pre-heating zone; the cascading descent of the preheated charge from the preheating zone into the melting zone, where the material is completely mixed before it passes through the melting zone.

4. In the method of fusion and continuous agglomerations of particles of material, by passing a charge of this material, in a downward direction, through a first rotary kiln inclined downwards and then in a downward direction. descending, through a second rotary kiln inclined downwards, the diameter of said second kiln being greater than the diameter of said first kiln and the axes of rotation of said kilns being parallel to the axis of said second kiln, which is arranged in below the axis of said first furnace, operations comprising passing the load, in a downward direction, through the first furnace; preheating: of the load to a temperature below its melting point;

<Desc / Clms Page number 20> the cascade descent of the load from the first furnace into the second furnace; the subsequent passage of the load in a downward direction through the second furnace; heating at least a portion of the particles to the melting temperature to agglomerate the particles.

5. In the method of continuous fusion and agglomeration of particles of matter, by passing a charge of this downward; material in a downward direction through a first ro- and then in a downward direction through a second rotary kiln, inclined downwardly inclined, the diameter of said second kiln being greater than the diameter of said first kiln and the axes of rotation of said furnaces being parallel to the axis of said second furnace, which is arranged below the axis of said first furnace, operations comprising the passage of the load, in a downward direction, through the first furnace, at a relatively higher speed; preheating the feed to a temperature below its melting point; cascade descent of the load from the first furnace into the bottom of the second furnace;

subsequent passage of the charge in a downward direction through the second furnace at a relatively slower speed; adding fuel particles to the feed before it is at the bottom of the second furnace; burning the fuel in the combustion zone to bring the charge to the melting temperature; and passing the gaseous products of combustion in an upward direction through the first furnace to heat the downward charge.

6. In the method of continuous melting and agglomeration of particles of material, operations comprising passing a charge of this material in one layer, in a downward direction, through a pre-heating zone of a. relatively greater length and of lesser diameter, in a track at a predetermined angle to the horizontal; preheating the feed to a temperature below the melting temperature;

subsequent passage of the previously heated charge, in one layer, in a downward direction, through <Desc / Clms Page number 21> a melting zone of relatively less length and greater diameter, in a path parallel to the passageway through the pre-heating zone, the passageway through the fusion zone being parallel to the passageway passage through the pre-heating zone and shifted down from the latter; maintaining the layer in the melting zone at a thickness greater than that of the layer of the pre-heating zone; and the cascade descent of the preheated load from the preheating zone into the melting zone.

7. In the method of continuously melting and agglomerating a charge of material containing at least one undesirable constituent such as sulfur, lead and zinc, and containing particles of metal-containing material, operations as follows. passing such a load, in a downward direction, through a pre-heating zone, in a path inclined at a predetermined angle with respect to the horizontal; preheating the charge, as it moves through said zone, to a temperature below the melting temperature of the metal-containing material; the subsequent passage of the previously heated load, in a downward direction, through a melting zone, in a lane parallel to the lane mentioned first; heating at least part of the particles to the melting temperature;

agglomeration of the particles to form relatively larger bodies, the passageway through the melting zone being shifted downward from the passageway through the pre-heating zone; the cascade descent of the preheated charge from the preheating zone into the melting zone, whereby the material is completely mixed before it passes through the melting zone; adding carbonaceous fuel particles to the preheated feed, as it passes from the preheating zone to the melting zone, whereby the added fuel is mixed with the feed, during the fall <Desc / Clms Page number 22> Cascade;

directing a combustion-supporting gas stream against the layer in the fusion zone to burn the fuel in the charge and form gaseous products of combustion containing usable oxygen; passage of the combustion products, against the current, through the pre-heating zone; preheating the feed, and oxidizing and volatilizing the unwanted component.

8. In the method of continuously melting and agglomerating a charge of material containing at least one undesirable constituent such as sulfur, lead and zind, and containing particles of material containing metal, operations comprising passing such a load, in a downward direction, through a pre-heating zone, in a track inclined at a predetermined angle with respect to the horizontal; preheating the charge, as it moves through said zone, to a temperature below the melting temperature of the metal-containing material; maintaining an oxidizing atmosphere in the pre-heating zone by adding the necessary volume of air, at the required temperature and pressure, to the gaseous product of combustion entering the pre-heating zone;

subsequent passage of the previously heated charge, in a downward direction, through a melting zone, in a path parallel to the path mentioned first; heating at least part of the particles to the melting temperature; agglomeration of the particles to form relatively large bodies, the passageway through the melting zone being shifted downward from the passageway through the pre-heating zone; the cascade descent of the preheated charge from the preheating zone into the melting zone, the material thus being completely mixed before it passes through the melting zone;

the addition of carbonaceous fuel particles to the previously heated feed, as it passes from the preheating zone to the melting zone, the added fuel thus being mixed with the feed during the fall in <Desc / Clms Page number 23> waterfall; sending a combustion-supporting gas stream against the layer in the melting zone, to burn the fuel in the feed but still so as to maintain a reducing atmosphere in the melting zone; passage of the combustion products, countercurrently, through the pre-heating zone; preheating the feed, and oxidizing and volatilizing the unwanted component.

9. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a rotary kiln, inclined downwardly, having a relatively smaller diameter for pre-heating the charge; a downwardly inclined rotary kiln having a relatively larger diameter, for heating the charge to the melting temperature; means supporting, in a rotary manner, said furnaces, the upper end of the melting furnace being adjacent to the lower end of the pre-heating furnace and an upper part of the melting furnace opening into the pre-heating oven.

10. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a rotary kiln, inclined downwards, for preheating the charge, having a cylindrical surface. relatively smaller internal diameter; rotary furnace, inclined downwards, for heating the charge to the melting temperature, having an internal cylindrical surface of relatively larger diameter; and means rotatingly supporting said furnaces, the upper end of the melting furnace being adjacent to the lower end of the preheating furnace and an upper part of the melting furnace opening into the furnace. pre-heating.

11. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a downwardly inclined rotary furnace having a relatively smaller diameter, for pre-heating the charge; rotary kiln, inclined downwards, having a diameter <Desc / Clms Page number 24> relatively higher, for heating the charge to the melting temperature, the melting furnace having a diameter equivalent to at least about twice the diameter of the pre-heating furnace; and means rotatingly supporting said furnaces, the upper end of the melting furnace being adjacent to the lower end of the preheating furnace and an upper part of the melting furnace opening into the heating furnace. prior.

12. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a downwardly inclined rotary furnace having a relatively smaller diameter, for pre-heating the charge; a downwardly inclined rotary kiln having a relatively larger diameter for heating the charge to the melting temperature; means rotatingly supporting said furnaces, the upper end of the melting furnace being adjacent to the lower end of the preheating furnace and an upper part of the melting furnace being in the same alignment as and opening in the pre-heating furnace, and the lower part of the melting furnace being placed below the pre-heating furnace;

a cover surrounding adjacent ends of the furnaces and including a wall portion extending over and covering the portion of the open top end of the melting furnace which is not in alignment with the preheating furnace.

13. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a downwardly inclined rotary kiln having a relatively smaller diameter for preheating the material. charge ; a downwardly inclined rotary kiln having a relatively larger diameter, for heating the charge to the melting temperature;

means rotatingly supporting said furnaces, the upper end of the melting furnace being adjacent to the lower end of the preheating furnace and an upper part of the melting furnace being in the same alignment as <Desc / Clms Page number 25> and opening into the preheating furnace, and the lower part of the melting furnace / placed below the preheating furnace; a cover surrounding adjacent ends of the furnaces and comprising a wall portion extending over and covering the portion of the open top end of the melting furnace which is not in alignment with the pre-heating furnace;

and a feed pipe passing through the cover and having an interior discharge end located above the lower portions of adjacent ends of the ovens.

14. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a downwardly inclined rotary furnace having a relatively smaller diameter for pre-heating the charge; rotary kiln, inclined downwards, having a relatively larger diameter, for heating the charge to the melting temperature; means rotatably supporting said furnaces, the upper end of the melting furnace being adjacent to the lower end of the preheating furnace and an upper part of the melting furnace being aligned with and opening into the pre-heating furnace, and the lower part of the melting furnace being placed below the pre-heating furnace;

a cover surrounding the adjacent ends of the furnaces and comprising a wall portion extending over and closing the part of the open upper end of the melting furnace which is not in alignment with the pre-diaufing furnace; a toyao. feeder passing through the cover and having an interior discharge end located above the lower portions of adjacent furnace ends;

an air supply pipe extending through the cover and having an internal discharge end disposed between the aforesaid supply pipe and the preheating zone, and arranged so that the air coming from this discharge end hits the <Desc / Clms Page number 26> lower inner surface of the pre-heating zone at its lower end.

15. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a rotary kiln, inclined downwardly, having a relatively smaller diameter for the preliminary heating of the material. charge ; rotary kiln, inclined downward, having a relatively larger diameter, for heating the charge to the melting temperature; means rotatably supporting said furnaces, the upper end of the melting furnace being adjacent to the lower end of the pre-heating furnace, an upper part of the melting furnace being aligned with and opening in the pre-heating furnace and the lower part of the melting furnace being located below the pre-heating furnace;

cover surrounding the adjacent ends of the furnaces and including a wall portion extending over and closing the part of the open upper end of the melting furnace which is not in alignment with the pre-heating furnace ; an inclined plane extending from the lower end of the preheating furnace in a downward direction, substantially vertically, towards the bottom of the melting furnace.

16. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a rotary kiln, inclined downward, having a relatively smaller diameter, for pre-heating the charge. ; rotary kiln, inclined downward, having a relatively larger diameter, for heating the charge to the melting temperature; means rotatably supporting said furnaces, the upper end of the melting furnace being adjacent to the lower end of the pre-heating furnace, an upper portion of the melting furnace being in alignment with and opening into the preheating furnace and a lower part of the melting furnace being located below the preheating furnace;

cover surrounding the ends <Desc / Clms Page number 27> adjacent furnaces and comprising a wall portion extending over and closing off the portion of the upper open end of the melting furnace which is not in alignment with the preheating furnace; the feed pipe extending through the cover and having an interior discharge end disposed above the lower portions of adjacent ends of the ovens; an inclined plane extending from the lower end of the preheating furnace substantially vertically in a downward direction toward the bottom of the melting furnace.

17. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a downwardly inclined rotary kiln having a relatively smaller diameter, for pre-heating the charge; rotary kiln, inclined downwards, having a relatively larger diameter, for heating the charge to the melting temperature; means rotatably supporting said furnaces, the upper end of the melting furnace being adjacent to the lower end of the preheating furnace, a top portion of the melting furnace being aligned with and opening into the pre-heating furnace and the lower part of the melting furnace being placed below the pre-heating furnace;

cover surrounding the adjacent ends of the furnaces and comprising a wall portion extending over and closing the part of the open upper end of the melting furnace which is not in alignment with the preheating furnace; a feed pipe extending through the cover and having an inner discharge end disposed above the lower portions of adjacent ends of the ovens; inclined plane extending from the lower end of the preheating furnace, substantially vertically, in a downward direction, towards the bottom of the melting furnace;

and an air supply pipe extending through the cover and having an inner discharge end located between the aforesaid supply pipe and the pre-heating zone, and <Desc / Clms Page number 28> @ arranged in such a way that the air coming from this discharge end strikes the lower internal surface of the pre-heating zone, at its lower end.

18. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a preheating rotary kiln, inclined downwards, having a relatively smaller diameter and having one end. lower open, through which the load is discharged; a downwardly inclined rotary smelting furnace having a relatively larger diameter and having an open upper end, a portion of which is aligned with the open lower end of the preheating furnace;

and means supporting said furnaces, the upper end of the melting furnace being adjacent to the lower end of the pre-heating furnace, said furnaces being supported with a view to their rotation about their respective longitudinal axes, the longitudinal axis of the furnace melting furnace extending in a direction parallel to the longitudinal axis of the preheating furnace and below that axis, whereby the preheating furnace extends only over a part of the upper open end of the melting furnace.

19. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a preheating rotary kiln, inclined downwards, having a relatively smaller diameter and having an open lower end. through which the load is discharged; a downwardly inclined rotary melting furnace having a relatively larger diameter and having an open upper end part of which is aligned with the open lower end of the preheating furnace;

means supporting said furnaces, the upper end of the melting furnace being adjacent to the lower end of the preheating furnace, said furnaces being supported for their rotation about their respective longitudinal axes, the longitudinal axis of the furnace fusion extending in a parallel direction <Desc / Clms Page number 29> to the longitudinal axis of the pre-heating furnace and below this axis, whereby the pre-heating furnace extends only over a part of the upper open end of the melting furnace; and a cover surrounding the adjacent ends of the furnaces and comprising a wall portion extending over and closing the part of the open end of the melting furnace over which the preheating furnace does not extend.

20. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a preheating rotary kiln, inclined downwards, having a relatively smaller diameter and having one end. lower open through which the load is discharged; a downwardly inclined rotary smelting furnace having a relatively larger diameter and having an open upper end part of which is aligned with the open lower end of the preheating furnace; means supporting said furnaces, the upper end of the melting furnace being adjacent to the lower end of the pre-heating furnace;

said furnaces being supported for their rotation about their respective longitudinal axes and the longitudinal axis of the melting furnace extending in a direction parallel to the longitudinal axis of the pre-heating furnace and below this axis, whereby the furnace preheating extends only over part of the upper open end of the melting furnace; a cover surrounding the adjacent ends of the furnaces and comprising a wall portion extending over and closing the part of the open end of the melting furnace over which the pre-heating furnace does not extend; and a feed pipe extending through the cover and having an interior discharge end located above the lower portions of adjacent ends of the ovens.

21. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a preheating rotary kiln, inclined downwards, having a relatively smaller diameter and <Desc / Clms Page number 30> having an open lower end through which the load is discharged; downwardly inclined rotary melting furnace having a relatively larger diameter and having an open upper end part of which is aligned with the open lower end of the preheating furnace;

means supporting said furnaces, the upper end of the smelting furnace being adjacent to the lower end of the preheating furnace, said burrows being supported for their rotation about their respective longitudinal axes, and the axis longitudinal axis of the melting furnace extending in a direction parallel to the longitudinal axis of the pre-heating furnace and below this axis, whereby the pre-heating furnace extends only over a part of the end open top of the melting furnace; a cover surrounding the adjacent ends of the furnaces and comprising a wall portion extending over and closing the part of the open end of the melting furnace over which the pre-heating furnace does not extend;

a feed spout extending through the cover and having an inner discharge end located above the lower portions of adjacent ends of the ovens; an air blowing pipe extending through the cover and having an internal discharge end situated between the aforesaid supply pipe and the pre-heating zone and arranged so that the air coming from of the discharge end in question strikes the lower inner wall of the pre-heating zone at its lower end.

22. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a preheating rotary kiln, inclined downwards, having a relatively smaller diameter and having an open lower end. through which the load is discharged; a downwardly inclined rotary melting furnace having a relatively smaller diameter and having an open upper end part of which is aligned with the lower end <Desc / Clms Page number 31> - open front of the pre-heating oven;

means supporting said furnaces, the upper end of the melting furnace being adjacent to the lower end of the preheating furnace, said furnaces being supported for their rotation about their respective longitudinal axes and the longitudinal axis of the heating furnace - sion extending in a direction parallel to the longitudinal axis of the preheating furnace and below this axis, whereby the preheating furnace extends only over a part of the upper open end of the preheating furnace. fusion; a cover surrounding the adjacent ends of the furnaces and comprising a wall portion extending over and closing the part of the open end of the melting furnace over which the pre-heating furnace does not extend;

and an inclined plane, in said wall portion, extending from the bottom of the preheating furnace, substantially vertically, in a downward direction, towards the bottom of the melting furnace.

23. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a preheating rotary kiln, inclined downwards, having a relatively smaller diameter and having one end. lower open through which the load is discharged; a downwardly inclined rotary melting furnace having a relatively larger diameter and having an open upper end part of which is aligned with the open lower end of the preheating furnace;

means supporting said furnaces, the upper end of the melting furnace being adjacent to the lower end of the pre-heating furnace. said furnaces being supported for their rotation about their respective longitudinal axes and the longitudinal axis of the smelting furnace extending in a direction parallel to the longitudinal axis of the preheating furnace and below this axis, whereby the preheating furnace extends only over part of the open upper end of the melting furnace; a cover surrounding the adjacent ends of the furnaces and including a wall portion extending over and closing off the part of the open end of the melting furnace on which the heating furnace prepares. <Desc / Clms Page number 32> -lable does not extend;

an inclined plane, in said portion of wall, extending from the bottom of the preheating furnace, substantially vertically, in a downward direction, towards the bottom of the melting furnace; an air blowing pipe extending through the cover and having an interior discharge end located between the aforesaid supply pipe and the preheating zone, and arranged so that the air coming from this discharge end strikes the lower internal surface of the pre-heating zone, at its lower end.

24. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a preheating rotary kiln, inclined downwards, having a relatively smaller diameter and having an open lower end through which the load is discharged; a downwardly inclined rotary melting furnace having a relatively larger diameter and having an open upper end part of which is aligned with the open lower end of the preheating furnace;

means supporting said furnaces, the upper end of the melting furnace being adjacent to the lower end of the pre-heating furnace, said furnaces being supported for their rotation about their respective longitudinal axes and the longitudinal axis of the furnace. melting furnace extending in a direction parallel to and below the longitudinal axis of the pre-heating furnace, whereby the pre-heating furnace extends only over a part of the open upper end of the furnace fusion; a cover surrounding the adjacent ends of the furnaces and comprising a wall portion extending over and closing the part of the open end of the melting furnace over which the preheating furnace does not extend;

a feed pipe extending through the cover and having an interior discharge end located above the lower portions of adjacent furnace ends and an inclined plane, in said <Desc / Clms Page number 33> wall portion, extending from the bottom of the preheating furnace, substantially vertically, in a downward direction, towards the bottom of the melting furnace.

25. In the apparatus for the continuous melting and agglomeration of a charge of particles of finely divided material, an arrangement comprising a preheating rotary kiln, downwardly inclined, having a relatively smaller diameter and having one end. lower open through which the load is discharged; a downwardly inclined rotary melting furnace having a relatively larger diameter and having an open upper end part of which is aligned with the open lower end of the preheating furnace;

means supporting said furnaces, the upper end of the melting furnace being adjacent to the lower end of the preheating furnace, said furnaces being supported for their rotation around their respective longitudinal axes, and the longitudinal axis of the furnace being fusion extending in a direction parallel to the longitudi- and below this nal axis of the pre-heating furnace /, whereby the pre-heating furnace extends only over a part, of the open upper end the melting furnace; a cover surrounding the adjacent ends of the furnaces and comprising a wall portion extending over and closing the part of the open end of the melting furnace over which the pre-heating furnace does not extend;

a feed pipe extending through the cover and having an interior discharge end located above the lower portions of adjacent ends of the ovens; inclined plane in said wall portion, extending from the bottom of the preheating furnace, substantially vertically, in a downward direction, towards the bottom of the melting furnace; an air blowing pipe extending through the cover and having an internal discharge end situated between the aforesaid supply pipe and the preheating zone, and arranged so that the air coming from this discharge end hits the lower inner surface of the heating zone <Desc / Clms Page number 34> prior, at its lower end.