Patent Publication Number: US-6342179-B1

Title: Furnace for the direct reduction of iron oxides

Description:
FIELD OF THE INVENTION 
     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. 
     BACKGROUND OF THE INVENTION 
     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 (Fe 2 O 3 , Fe 3 O 4 ). 
     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. 
     SUMMARY OF THE INVENTION 
     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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other characteristics of the invention will become clear from the following description of two preferred forms of embodiment, given as a non-restrictive example, with reference to the attached drawings wherein: 
     FIG. 1 is a sectioned side view of a furnace for the direct reduction of iron oxides according to the invention in a first form of embodiment; 
     FIG. 2 is an enlarged detail of FIG. 1; 
     FIG. 3 is a section along the line A—A of FIG. 1; 
     FIG. 4 is a section along the line B—B of FIG. 1; 
     FIG. 5 is a sectioned side view of a variant of the furnace shown in FIG. 1; 
     FIG. 6 is an enlarged detail of FIG. 5; 
     FIG. 7 is a section along the line C—C of FIG. 5; and 
     FIG. 8 is a section along the line D—D of FIG.  5 . 
    
    
     DETAILED DESCRIPTION OF TWO PREFERRED EMBODIMENTS 
     With reference to FIGS. 1-4, a furnace  10  for the direct reduction of iron oxides according to the invention comprises a container  11 , substantially cylindrical in shape, an upper loading container  12  from which, through distribution tubes  13 , the mineral (iron oxides) is suitable to be introduced, a median reaction zone, or reactor  14 , wherein the reduction reaction of the iron oxides takes place, and a lower zone or discharge zone  15 , shaped like a truncated cone with the taper converging downwards. 
     In correspondence with the reactor  14 , the furnace  10  comprises a pair of circumferential conduits  16 , provided with nozzles  17 , through which a mixture of reducing gas, arriving from corresponding conduits  18 , is suitable to be introduced. 
     The reducing gas and the plant upstream of the conduits  18  can be of any known type, for example of the type described in the patent application n o . UD98A000212, filed by the Applicant on Nov. 12, 1998. 
     According to one characteristic of the invention, in the upper part of the furnace  10 , in Proximity with the roof  19 , an intake device  20  is provided, comprising a chamber  21  with a toroidal grid  22  and a conduit  23  having an inner terminal part  24  which is elbow-shaped and arranged in the center of the chamber  21 , coaxially to the longitudinal axis  25  of the container  11 . 
     An apparatus  27  to regulate the flow of gas taken in is arranged in the terminal part  24  of the conduit  23 . 
     The toroidal grid  22  (FIG. 4) is made with radial elements  28  separated from each other with a variable pitch, so that the pitch has a minimum value in correspondence with the intersection between the chamber  21  and an outlet conduit  29 , and a maximum value in a zone diametrically opposite the chamber  21 . 
     Moreover, to increase the mechanical characteristics of the chamber  21 , it is shaped as a spiral wound on a plane substantially orthogonal to the longitudinal axis  25 . 
     The furnace  10  as described heretofore functions as follows: 
     The mineral iron, for example in pellet form, is introduced into the furnace  10  from the upper container  12  through the distribution tubes  13 , while the reducing gas is introduced from the conduits  18  and distributed in the reactor  14  by the circumferential conduits  16 , through the nozzles  17 . 
     Due to the relatively low pressure with which the reducing gas is injected into the reactor  14 , the flow of the reducing agent in the mass of mineral inside the furnace  10  would have a prevalently peripheral character, if the intake device  20  did not intervene. 
     In fact, by creating a suction effect in the conduit  23 , with any known means which are not shown in the drawings, a depression is created above the mass of material which is in the reactor  14  and the propagation of the reducing gas is increased, from the periphery of the reactor  14  towards the central zone, in correspondence with the longitudinal axis  25 . 
     The particular shape of the toroidal grid  22 , with the elements  28  arranged around the central terminal part  24  of the intake conduit  23  with a variable pitch, ensures that the intake device  20  acts uniformly. 
     The apparatus  27 , arranged in a central position, also increases the efficiency of the upward intake of the reducing gas, in the zone around the longitudinal axis  25 , and consequently also the interaction between the mass of mineral and the reducing gas in that zone. 
     Particular efficacy is obtained by arranging the apparatus  27  at the mouth of the terminal part  24 , at a lower level than the toroidal grid  22 . 
     According to a variant, shown in FIGS. 5-8, the intake device  20  also comprises at least a second outlet conduit  129 , diametrically opposite the First  29 , and a second conduit  123  which puts the latter in communication with the central part  24 . 
     It is therefore obvious that the furnace  10  according to the invention gives the following advantages: 
     the mineral introduced into the furnace  10  is treated with maximum efficiency by the reducing gas, without needing to excessively increase the quantity of reducing gas injected; 
     the toroidal grid  22  also acts as a filter or cleaner element for the particles and impurities which tend to rise from the mass of mineral in the reactor  14  towards the roof  19  of the furnace  10 ; 
     consequently, both the productivity of the furnace  10  and the clarity of the material produced are improved. 
     It is obvious that modifications and additions can be made to the furnace  10  for the direct reduction of mineral iron as described heretofore, but these shall remain within the field and scope of the invention. 
     It is also obvious that, although this invention has been described with reference to specific examples, a person of skill in this field will certainly be able to achieve many other forms of equivalent furnaces, but these shall all come within the field and scope of this invention.