This invention concerns a furnace for the production of metal iron by means of the direct reduction of mineral iron, where the iron is present in the form of oxides The furnace is of the gravitational type and is provided with an upper container from which the mineral iron, coarse or in the form of pellets, is introduced, and a lower outlet from which the directly reduced iron (DRI) is removed. In a median reduction zone, the furnace is provided with a circumferential conduit, provided with nozzles, through which reducing gas is injected.
The state of the art includes furnaces of the gravitational type, or shaft furnaces, for direct reduction processes comprising a central part, substantially cylindrical or in the shape of a truncated cone, an upper loading zone, a lower discharge zone, a device to inject reducing gas into the central zone, and a device to suck up the gases in the upper zone.
To achieve acceptable working conditions in the direct reduction of iron oxides, it is necessary, in the loading column, to create conditions of uniform distribution of the reducing gas, both in the peripheral zones and also in the central zones of the load volume.
In conventional direct reduction furnaces, filler with mineral iron, the current of reducing gas is not efficiently distributed among the various zones in the sections of the furnace. The peripheral zone of the load column, especially for large size furnaces, is more affected by the current of gas. In every transverse section of the furnace, therefore, there is a different reducing potential which diminishes the iron reduction process in the whole load volume. The maximum gradient of reducing potential is in the upper part of the furnace, where the highest iron oxides dominate (Fe2O3, Fe3O4).
Conventional gas-intake systems, arranged in the upper zone of the furnace, increase this negative effect due to their localized action, prevalently in the zone of the intake conduit.
A uniform distribution of the gas in the different transverse sections of the furnace, at different heights, depends on the hydraulic resistance of the layer of material loaded, the method used to inject the reducing gas and the upper intake of the gas.
Irregularities in the reduction process in the whole volume of the furnace lead to a worsening in the quality of the final product of the directly reduced iron (DRI) and to a reduction in production.
In conventional devices, the upper intake of the gas tends to occur preferentially through peripheral areas of the working space of the furnace, which excludes a stable process of the reducing gas in the central zone of the furnace.
The problems described above limit the diameters of conventional furnaces and consequently their productivity.
The furnace to produce metal iron by the direct reduction of iron oxides according to the invention is set forth and characterized in the main claim, while the dependent claims describe other innovative characteristics of the invention.
The furnace according to the invention is of the gravitational or shaft type, wherein both the material and the gas are fed continuously, so as to create a vertical and gravitational flow of the material and so that the direct reduction of the mineral occurs.
The reduction furnace is equipped with means to feed the mineral iron and means to discharge the reduced metal iron, and is equipped with at least an inlet collector, arranged laterally, to inject the reducing gas in correspondence with one or more reduction zones inside the furnace.
One purpose of the invention is to achieve a reduction furnace in which here is a uniform flow of reducing gas over the whole section of the shaft through the material.
One effect of this type in the upper part of the shaft leads to a uniform pre-heating of the material and a uniform production.
This invention also has the purpose of retaining the solid particles which are removed from the gas to be later distributed in the outer part of the section of the shaft.
In this way the removal of the fumes is reduced, and they are distributed in an optimum manner with the rest of the material.
In accordance with this purpose, the reduction furnace according to the invention comprises a gas intake device, with a toroidal grid of the cyclone type arranged in proximity with the upper roof of the furnace and associated with the intake conduit.
According to another characteristic feature of the invention, there is a system to partly channel the gas through the central zone of the grid. This system is equipped with a device to regulate the intake flow between the toroidal grid and the central zone of the grid.
In accordance with another characteristic feature, the grid of the upper chamber has a viable pitch from a minimum value, in correspondence with the intersection between the chamber and the intake conduit, and a maximum value, in a diametrically opposite zone of the chamber.
Other characteristic features of the invention are as follows: the toroidal grid is made with spirals wound on a vertical plane; the toroidal grid is provided with radially arranged legs; the lower part of the system to partly channel the gases is arranged lower than the toroidal grid.