Heating – Work chamber having heating means – Having means by which work is progressed or moved mechanically
Reexamination Certificate
1999-12-24
2001-04-03
Wilson, Gregory (Department: 3749)
Heating
Work chamber having heating means
Having means by which work is progressed or moved mechanically
C432S061000, C432S138000, C432S139000, C432S195000, C414S588000
Reexamination Certificate
active
06210155
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a charging device for production of layers of fine-grained loose material one above the other on a rotary hearth. It is particularly suitable for the use of a new direct iron ore reduction process in a rotary hearth furnace.
Sponge iron is produced in a direct reduction process by the reduction of iron oxide with solid or gaseous reducing agents. Carbon, for example, which reacts with oxygen at higher temperatures and forms the reducing gas CO, serves as a solid reducing agent. A process of this type can be carried out, for example, in a rotary hearth furnace, i.e. in a furnace with a rotatable annular furnace bottom, which is lined with refractory material on the top side and is enclosed by a housing. Burners, which penetrate the housing and heat its interior to the required reaction temperature of over 1000° C., are mounted on the top side of the housing.
The iron oxide is deposited together with the reducing agent at a first point of the rotary hearth furnace and is fed by rotation of the rotary hearth to the interior of the housing, where it reacts with the reducing agent because of the high temperatures and is present as directly reduced iron after about one revolution of the rotary hearth. The form in which the iron is present depends on the type of process used.
In the traditional process the iron oxide is compacted before charging into the rotary hearth furnace with the reducing agent to form pellets, which are subsequently charged on to the rotary hearth of the furnace. Inside the furnace, the iron oxide in the individual pellets reacts with the carbon monoxide released by the carbon in a controlled atmosphere and is reduced to iron inside the pellets. The sponge iron is thus present in pellet form after the reduction. The pellets additionally containing the residues of the reducing agent (ash) as well as any impurities such as sulphur. After the reduction process a further process step, in which the directly reduced iron is separated from the ash and impurities, is consequently required.
In an alternative process fine-grained iron oxide and fine-grained reducing agent, e.g. coal, are charged in separate layers on to the rotary hearth of the furnace. In this process only one layer of iron oxide and one layer of reducing agent can be charged or several layers of the individual materials can be placed alternately in layers one above the other. On passage through the furnace carbon monoxide, which penetrates through the fine-grained iron oxide layers and reduces them to iron, is released in the coal layer(s). Consequently the reduced iron is present in a pure form in one or more layers above each other after the reduction process, the individual iron layers being separated from each other by layers of reducing agent residues and these ash layers being present in loose form.
As the individual layers of loose material do not mix with each other during the reduction process, this process offers the advantage that the sponge iron and reducing agent residues can easily be separated from each other. The basic prerequisite for economic implementation of this reduction process, however, is that the charging device of the rotary hearth furnace is capable of producing an optimum layered arrangement of the metal oxide and reducing agent on the rotary hearth. Consequently a task of the invention is to create a rotary hearth furnace, the charging device of which largely meets this prerequisite.
SUMMARY OF THE INVENTION
This problem is solved by the charging device according to this invention.
In the reducing furnace described above a charging device according to the invention consequently has a discharge bunker with a discharge slot and a discharge roller in front of the discharge slot for each metal oxide or reducing agent layer. The discharge slot and discharge roller extend essentially transversely to the direction of rotation of the rotary hearth and the discharge rollers have a variable-speed drive. If the speed of rotation of a discharge roller is increased, the discharge of loose material from the corresponding discharge bunker also increases. If, by contrast, the speed of rotation of a discharge roller is reduced, the discharge of loose material from the corresponding discharge bunker is also reduced. With the charging device according to the invention, metal oxide and reducing agent layers one above the other can thus be deposited on the annular furnace bottom. The ratio of metal oxide to reducing agent in the layers is adaptable to an optimum course of the reduction process via the variable-speed discharge rollers. By briefly stopping a discharge roller a layer can also be interrupted, so that heaps arranged behind each other are formed in the direction of rotation. Such a discontinuous layer simplifies, for example, discharge of the metallic sponge produced, because a continuous strand of material is not formed, but individual pieces of sponge separated from each other.
The reduction process can be further optimised by gravimetric control of the layer build-up. For this purpose the device according to the invention need only have continuous weighing devices, which are integrated in the charging device in such a way that the discharge of metal oxides and reducing agents in loose form can be measured gravimetrically. A speed control system for the variable-speed drives of the discharge rollers controls in this case the speed of the discharge rollers as a function of the corresponding gravimetric measured values of the weighing devices.
In a first embodiment of the weighing device, the discharge bunkers for the metal oxide and for the reducing agent are connected to a storage bunker for the metal oxide or reducing agent, although they can be moved in a vertical direction relative to the respective storage bunker and are suspended by weight measuring cells above the rotary hearth. In this embodiment the discharge of loose material from each discharge bunker can be measured separately, so that the build-up of each individual layer can be controlled gravimetrically.
In a second embodiment of the weighing device the discharge bunkers for the metal oxide together with a storage bunker for the metal oxide form a first separate unit, which is suspended by weight measuring cells above the rotary hearth, and the discharge bunkers for the reducing agents together with a storage bunker for the reducing agents form a second unit, which is suspended by weight measuring cells above the rotary hearth. In this embodiment the total loose material discharge from the storage bunker for the metal oxide and the storage bunker for the reducing agent can be measured separately by gravimetry, so that the total build-up of the metal oxide layers and the total build-up of the reducing agent layers can be adapted to each other gravimetrically.
To prevent mixing of the layers at the interfaces as far as possible and thus ensure a clean boundary layer build-up between the individual layers, a guide section is advantageously arranged under each of the discharge rollers in such a way that the loose material falling from the roller falls on to the guide section and is guided by the latter at a reduced speed on to the top layer in each case.
The discharge bunkers advantageously each have a discharge hopper, a slot-type discharge opening being formed between two free edges. The first edge rests against the discharge roller and the second edge is arranged a certain distance from the surface of the discharge roller, so that a discharge slot, which determines the layer thickness of the loose material on the discharge roller by scraping, is formed between the discharge roller and the second edge. In other words the layer thickness of the loose material on the discharge roller is determined by a scraping edge, so that the layer thickness of the loose material on the discharge roller is independent of the angle of slope of the loose material. In addition the scraping produces more uniform distribution of the loose material over the full width of the discharge ro
Bernard Gilbert
Frieden Romain
Hutmacher Patrick
Lonardi Emile
Paul Wurth S.A.
Smith Gambrell & Russell
Wilson Gregory
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