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Reduction furnace

Reduction furnace description/claims

The present invention relates to a reduction furnace, in particular a reduction furnace for the production of metallic iron by means of the direct reduction of iron ore, extracted from mines, at a temperature that is less than the melting point of the components.

The product obtained as a result of a direct reduction process is known as DRI or “Direct Reduced Iron”. The direct reduction process converts iron ore into highly metallized iron, in the form of lump ore, pellets or a mixture of these components. The process produces reduced iron containing variable quantities of carbon in the form of Fe3C. This material is the ideal foodstock for electric arc furnaces used in the production of high-quality steel. Direct reduction systems can thus be made to integrate with systems upstream of electric steelmaking plants.

In existing systems, the hot DRI from the furnace or reactor, also known as a shaft furnace, is usually briquetted or cooled in specific vessels, as it is extremely reactive in air at the temperature at which it leaves the reduction furnace.

Transporting the DRI directly to the electric arc furnace is clearly advantageous but involves a number of requirements, namely: the connection between the two furnaces must be rendered inert, as the metal will re-oxidize when exposed to atmospheric air and humidity with a significant loss of metallization; the reduction and steelmaking plants must be separated by means of a temperature buffer to keep the DRI at a suitable temperature for being fed into the electric arc furnace; the flow of hot material from the furnace must be metered; heat loss must be kept to a minimum.

The separation of the reduction and steelmaking plants, by means of a buffer, is necessary because the electric arc furnace operates on a batch cycle basis, whereas direct reduction plants operate continuously and it is neither possible nor advantageous to stop the flow in the reduction furnace according to the amount of DRI that is used. Moreover, reduction plants run for long periods of time, usually without any short scheduled stops during the year, generally being shut down once for approximately 20 days.

Since electric arc furnaces must usually be shut down once a week and, for a variety of reasons, are subject to sudden stoppages, it has been necessary to develop devices so that the production of DRI can continue even in such conditions. This has been achieved by adding a cooling vessel in which the material is cooled to ambient temperature, or at least to temperatures at which rapid re-oxidation is prevented, before being discharged and stored ready for later use.

Note that the cooling system is not necessarily always associated with an arc furnace. Indeed, the cooling vessel can also be used to cool the DRI and render the plant independent of the end use.

For cases in which the material from the reduction furnace is fed into an EAF at the same works, reduction systems providing for the direct connection between the reduction furnace and melting furnace for discharging both hot and cold DRI simultaneously are known in the prior art. For instance, document WO 01/14598 describes a system with a dynamic gas seal or seal leg between the reduction furnace and the buffer. In this way the buffer is rendered inert thanks to the seal leg.

Once the point of delivery to the EAF has been defined in the melting furnace design, the presence of any vertical elements in the high temperature connecting means/system will inevitably and disadvantageously raise the height of installation of the reduction furnace. For this reason systems comprising the lowest number of vertical elements are preferable.

Disadvantageously, the presence of a seal leg means the reduction furnace must be placed even higher up if the electric arc furnace (EAF) is gravity-fed. The reduction shaft, which is already high, is thus made even higher, increasing the costs of construction and installation at the works.

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