ITUD980214A1 - DEVICE FOR THE DIRECT REDUCTION OF IRON OXIDES AND RELATED PROCEDURE - Google Patents

Description

FIELD OF APPLICATION

The present invention refers to a device for the production of metallic iron starting from iron ore, in which iron is present in the form of oxides, and to the related process, in which the device comprises a reactor defining a reduction zone of at least partially truncated cone shape in which the process of direct iron reduction takes place.

The reduced iron can exit the reactor both cold and hot and be subsequently sent to a smelting furnace to produce liquid steel, or converted into hot briquetted iron (HBI), or transported to a cooling and storage area.

STATE OF THE TECHNIQUE

In the steel industry, the use of reduced iron (D.R.I.) as filler material for subsequent smelting or conversion processes is increasingly accentuated.

The process of obtaining the reduced iron involves making the iron ore react with a stream of reducing gas inside a suitable device or furnace comprising a reaction container, called a reactor, defining at least one reduction zone.

The reactor is associated at the top with means for introducing the material to be reduced and at the bottom with means for extracting the reduced material.

Various ways of carrying out such reaction processes are known, which have also found effective operational applications.

Among these applications are known those which use the injection of hydrocarbons in the reducing gas stream to allow the methane reforming or "reforming" reaction in the reactor with the 3⁄40 and CO2 present in the gas.

Direct reduction processes are also known in which the injection of hydrocarbons having O directly into the reactor is used in the zone between the injection of the reducing gas and the exhaust gas outlet from the top.

Other processes for the direct reduction of iron ore are known from the following patent documents:

Processes are also known in which the hot metallic iron is produced in a "shaft" type reduction furnace, having a vertical and gravitational flow of the material, subsequently sent, with a closed pneumatic transport system in an inert atmosphere, to the furnace. merger.

The known art generally teaches to use reactors defining cylindrical reaction zones, inside which the gaseous stream which carries out the reduction reaction is introduced, normally in a single introduction zone.

These known solutions have the drawback of not guaranteeing a good injection efficiency of the gaseous stream if the reaction zone of the reactor has a too large diameter.

Furthermore, if the gas velocity becomes too high, near the top of the reactor there is a large removal of the charge particles of smaller particle size which are evacuated together with the exhaust fumes, with consequent problems to the filtering system and risk of pollution.

Another drawback of the known solutions derives from the fact that the gas temperature progressively decreases as it rises towards the top of the reactor, this entailing a reduction in the speed with which the iron ore reduction reaction takes place.

Furthermore, the shape of the known reactors does not guarantee a homogeneous distribution of the material, with a higher concentration of the finer particles in the central zone of the reactor; this leads to a non-uniformity in the reduction reaction.

In order to solve all these drawbacks, to improve the efficiency of the process and the quality of the product obtained, the present applicant has devised and tested the present invention.

EXPOSURE OF THE FOUND

The device for producing metallic iron from the direct reduction of iron oxides and the related process, according to the present invention, are expressed and characterized in the respective main claims.

Other innovative aspects of the present invention are expressed in the secondary claims.

The present invention provides for the contact, inside a suitably shaped reactor, of the iron ore of variable grain size with a gaseous stream.

The iron ore is fed from the top of the device, and advantageously continuously so that a substantially continuous vertical and gravitational flow of the material itself is created from top to bottom which favors the direct reduction of the mineral.

According to an embodiment of the invention, the reactor has a reduction zone having an at least partially conical or frusto-conical conformation, which narrows progressively downwards.

Along the height of this reduction zone there are, according to the invention, at least two independent sections for introducing a respective gaseous stream suitable for causing the reduction reaction.

The gases introduced at the various heights of the reduction zone can also be different from each other, depending on the result to be obtained, the starting material used and the diameter of the reactor in the introduction section.

The combination of the conical conformation converging downwards of the reduction zone of the reactor with the multiple introduction of the gas carried out at various heights of the same entails a plurality of advantages in the reduction process.

First of all, the gas injection efficiency is increased thanks to the reduction in diameter of the reactor section where said gas is introduced, in particular in the lower part of the reduction area.

Furthermore, there is a lowering of the gas velocity in the upper part of the reactor due to the progressive increase in diameter, this reducing the risk of removal of the particles of smaller particle size and of their evacuation together with the exhaust gases.

The conical shape of the reaction zone also favors the natural distribution within it of the iron ore particles having different granulometry.

Moreover, thanks to the multiple introduction of the gas carried out at various heights of the reactor reduction zone, the temperature of the gaseous stream remains substantially constant over the entire height of the same, and the heat exchange between gas and iron ore is, thanks to this, , optimized. The possibility of introducing different gases, in different quantities and with different concentrations at the various heights of the reactor, allows to optimize the reduction process according to the final result to be obtained and the type of iron ore introduced.

Furthermore, the number and the mutual distance between the gas introduction zones can be varied in order to ensure maximum efficiency and maximum flexibility of the reduction reaction.

According to a variant, the reactor has a first substantially cylindrical upper section, which serves to avoid the danger of the filler material getting stuck on the walls of the same when said material has a characteristic of high adhesion, and the lower conical section where the areas of introduction of gas.

According to a variant, the reactor has a lower discharge terminal area having a taper converging towards the bottom which is more pronounced than the reduction area above.

According to a variant of the invention, in the lower part of the reactor there is a system suitable for cooling the material before its evacuation from the reactor itself.

According to a further variant, the lower outlet of the reaction device is of the multiple type to allow simultaneous discharge of several types of product at the same time.

The multi-outlet favors the distribution of the reduction gas inside the kiln and a better distribution of the material inside the kiln itself, avoiding preferential channels that occur in kilns with a single outlet.

The flexibility of use of the extractors, by varying the output flow rates, prevents the formation of bridges in the furnace.

The reduced metallic iron is preferably discharged hot through the multi-outlet, preferably with 3 or 4 cones, which are enabled to discharge the material simultaneously or individually.

This also allows you to adjust the material output by varying the extraction speed of the individual unloading systems.

Furthermore, this movement helps to make the material descend from the upper area in a uniform way, with perfect mixing of the larger particles with the fine ones, always creating a continuous movement of the material and reducing the possibility of gluing of the material itself.

The use of a multi-outlet system also allows the simultaneous unloading of hot material to be destined for different uses: a part can be introduced directly into a melting furnace, for the final melting; some can be briquetted; and a part can be cooled externally in a silo and sent to storage. A further advantage is that of being able to discharge all the hot material exiting the melting furnace to produce steel, reducing energy consumption to the maximum.

The reduction device according to the invention is equipped, in its upper part, with means for feeding the iron ore and, in its lower part, with means for evacuating the reduced metallic iron.

The iron ore undergoes, inside the reactor, the reduction at temperatures generally between 550 ° C and 1100 ° C.

The reduction follows the following steps, proceeding from the top to the bottom of the reactor:

from and finally from

ILLUSTRATION OF DRAWINGS

These and other characteristics of the present invention will become clear from the following description of a preferred embodiment, made by way of non-limiting example with the aid of the attached drawings, in which:

- fig. 1 is a longitudinal section of the device for the direct reduction of iron oxides according to the present invention;

- figs. 2a, 2b and 2c show, respectively, the sections according to A-A, B-B and C-C of fig.

1;

- figs. 3a, 3b and 3c schematically illustrate three embodiments of the reactor of the device of fig. 1;

- fig. 4 shows the section according to D-D of fig.

3b; '- fig. 5 shows a first variant of fig. 1; - fig. 6 shows another variant of fig. 1; - fig. 7 shows the section E-E of fig. 5 in a further variant of the invention;

- fig. 8 shows, in enlarged cross section, a further variant of the reactor according to the invention; and - fig. 9 shows an enlarged cross section along the line F-F fig. 8.

DESCRIPTION OF SOME FAVORITE FORMS OF

REALIZATION

With reference to fig. 1, a device 11 for the direct reduction of iron oxides according to the present invention comprises a reactor 10 defining at least one reduction zone 110 arranged in its middle-upper part.

Said reactor 10 comprises an upper mouth 12 for feeding from above, from which the mineral (iron oxides) is introduced, and a lower opening 13 for the exit of the iron. The internal walls of the reactor 10 are totally or partially lined with refractory material 14.

The reactor 10, in its upper part, is provided with a circumferential opening 20 through which the exhausted gas escapes.

The upper mouth 12 of the reactor 10 cooperates with an iron ore introduction device 15 suitable for uniformly and homogeneously distributing the loaded material.

In particular, said device 15 comprises a funnel system 16 in which the material is discharged by means of bridge cranes, cranes or the like, and a multi-outlet distribution system 17 through which the material is uniformly discharged into the inlet section of the reactor. 10.

The upper mouth 12 is covered by a special lid 18.

The iron-based metal oxides are introduced into the reactor 10 in the form of pellets or raw mineral of suitable size; the iron contained in them is normally between 63% and 68% by weight.

At the end of the process according to the invention, the iron contained in the reduced material leaving the reactor 10 is normally comprised between 80% and 90% by weight.

The reactor 10 illustrated in FIG. 1 has at least the reduction area 110 with a substantially frusto-conical conformation converging downwards, in which the diameter is progressively reduced going towards the outlet 13

The total opening angle a of the reduction zone 110 of the reactor 10 is generally comprised between 8 ° and 30 °, advantageously between 10 ° and 20 °.

In correspondence with three distinct sections of the reduction zone 110, along its height, there are, in this case, three systems for introducing a gaseous stream into the reactor 10 itself.

Said gaseous introduction systems, 19a, 19b and 19c respectively, are independent of each other and are suitable for injecting into the reactor 10 a respective gas of a type and composition different from the gases injected by the other systems, depending on the type of process in progress and the ferrous material to be reduced. Said gaseous introduction systems 19a and 19b and 19c are also suitable to cooperate each with a section arranged at a different height of the reduction zone 110, and therefore having a different diameter from the other sections due to the downward converging conformation of the reduction zone. reduction 110 itself.

This entails a different behavior of the gas, once injected, in terms of speed, turbulence and temperature, which must be taken into account when preparing the gas to be introduced.

The introduction systems 19a, 19b and 19c each comprise a delivery manifold 21 connected to a circumferential duct 25 which feeds respective tubes 22, inserted in the refractory wall 14 of the reactor 10 and having an inclination, in this case, facing the low in order to favor the upward tendency of the gas itself.

The gas introduced by the respective tubes 22, rising upwards, comes into contact in the reduction zone 110 of the reactor 10 with the continuous descending flow of the iron ore, giving rise to the reduction reactions until, at the outlet of the reactor 10 itself, the Fe that is sent to subsequent uses.

From figs. 2a and 2b and 2c it can be seen how at the various heights of the reactor 10 the reducing gas, indicated with 23, cooperates, as it descends towards the end of the reduction zone 110, with sections of smaller diameter, going more and more to wrap and enclose the material that descends. The position of the systems 19a, 19b and 19c on the height of the reduction zone 110 and the distance between them are optimized according to the process parameters, also taking into account the intensity of the heat exchange between ferrous material and gas, as well as the yield reactions in the various sections of the reduction zone 110.

The feed gas to the reactor 10 can consist of a mixture of hydrocarbons, for example natural gas, recirculation gas from the reactor itself and reformed gas.

The presence of natural gas in the reduction gas mixture allows to carry out "reforming" reactions inside the reactor 10 itself.

According to the invention, the quantity of hydrocarbons added to the reducing gas mixture can be dosed in a different way according to the section for introducing the gas into the reactor 10.

The recirculated gas is preheated to a temperature between 650 ° C and 850 ° C.

The gas leaving the preheater is in turn mixed with fresh reformed gas and subsequently with air, or with air enriched with oxygen, or with pure oxygen (O2), to carry out a partial combustion of the H2 and CO present in the reducing gas in order to to raise the temperature to values between 850 ° C and 1150 ° C, preferably between 1050 ° C and 1150 ° C; and the degree of oxidation of the resulting gas feeding the furnace is comprised between 0.10 and 0.15.

After said preheating, the gas is advantageously mixed with the hydrocarbons.

Fig. 3a schematically illustrates the flow of ferrous material, indicated with 24, from top to bottom of the reactor 10.

Figs. 3b and 4 schematically illustrate the system for introducing the gas into a circumferential duct 25 obtained in the reactor 10 from which, through the tubes 22, it penetrates inside the reactor 10 and therefore in contact with the iron ore to be reduced.

This solution determines a more homogeneous distribution of the gas over the entire affected section of the reactor 10 and therefore a better reaction efficiency.

Fig. 7 illustrates a variant in which at least one gas introduction system 19 comprises first tubes 22a arranged in a radial pattern on a horizontal plane along the circumference of the reactor 10, second tubes 22b arranged in a radial pattern which extend up to a peripheral zone of the reactor 10, penetrating for about 2/3 of their length inside the reactor 10 itself, and third tubes 22c arranged in a radial pattern which extend, substantially for their entire extension, up to the central zone of the reactor 10, or in the heart of the material 23.

An advantage of this solution is given by the fact that it is possible to introduce reduction gas at the same time from several points with the possibility of regulating the reducing gas flow rate.

A further and considerable advantage is that of being able to have a uniform reduction of oxides over the entire cross section of the reactor 10, creating the best flow-dynamic conditions for the distribution of the reducing gas.

This results in a uniform temperature distribution over the entire section, unlike traditional reactors in which the hot gas better touches the material placed towards the peripheral part and enters with difficulty into the core from the reactor 10. Another advantage is that the direct reduction becomes uniform and therefore you can have both a higher productivity and lower gas and energy consumption, as the gas itself is used in the best way.

According to the further variant of fig. 3c, the reactor 10 has a first short upper portion 10a substantially cylindrical and a second lower truncated-conical portion 10b in order to avoid that, in the upper part, the interlocking of the charge occurs due to the formation of bridges when the raw material it has characteristics of high adhesion to the walls of the reactor 10.

According to the variant illustrated in figs. 8 and 9, the reducing gas is distributed by means of one or more, preferably three, horizontal pipes 28, made of a material resistant to heat and oxidizing and fueling agents.

The tubes 28 are arranged transversely to the reactor 10 and are each provided with a plurality of peripheral openings or radial tubes 29, from which the gas itself can flow inside the reaction zone 14.

Each tube 28 consists of a central tube 30 made of refractory material and is internally cooled with cooling water circulating in a circumferential cavity 26.

Furthermore, each tube 28 can be passing through and provided with a rotary movement, so that the peripheral openings 29 can describe a rounded angle and distribute the reducing gas in the best possible way and uniformly inside the reduction zone 14.

The variant of fig. 5 illustrates a reactor 10 which has a conical course with a first angle a for a substantial portion of its length, and a terminal section having a conical course with a second angle β smaller than the angle a.

This solution allows to facilitate and speed up the discharge of the material through the outlet mouth 13.

In cooperation with the lower part of the reactor 10 there is a cooling system for the ferrous material to be evacuated, comprising an inlet manifold 27a and a respective outlet manifold 27b for a flow of cold gas or gas suitable for activating endothermic reactions.

According to the further variant of fig. 6, the reactor 10 has, in correspondence with its outlet mouth 13, three lower ends of conical or truncated cone shape 13a, 13b and 13c, with taper facing downwards.

Said lower ends are each provided with respective lower openings through which, in a selective manner, the directly reduced metal iron (DRI) can be discharged individually or simultaneously.

The great advantage of being able to unload the material from several points at the same time is given by the fact that it is possible to regulate the flow rate of the outgoing material by varying the extraction speed of the individual unloading systems.

Another advantage lies in the fact that this movement helps to make the material descend from the upper area in a uniform way, with perfect mixing of the larger particles with the fine ones, always creating a continuous movement of the material and reducing the possibility of gluing of the material. same .

A further and notable advantage is also that of being able to discharge hot material at the same time to be destined for different uses: a part can be introduced directly into a melting furnace, for the final melting; some can be briquetted; and a part can be cooled externally in a silo and sent to storage.

Another advantage is that of being able to discharge all the hot material exiting the melting furnace to produce steel, reducing energy consumption to the maximum.

All the material can also be hot briquetted or cooled and stored.

It is obvious that modifications or additions of parts can be made to the present invention, without thereby departing from the scope of the present invention.

Claims (1)

CLAIMS 1 - Device for the direct reduction of iron oxides of the gravitationally charged type, comprising a reactor defining, in its middle-upper part, at least one reduction zone within which the reaction takes place, means (15) for the introduction of the charge from the top of the reactor, means for introducing the gaseous stream into at least one section of the reactor in correspondence with the reduction zone (110), means for extracting the reduced material from the bottom of the reactor, and means (20 ) for the evacuation of exhausted fumes, said reactor having an upper mouth (12) for introducing iron ore and a lower opening (13) for leaving the reduced iron, characterized in that said reduction zone (110) has , at least partially, a truncated conical conformation converging downwards. 2 - Device as in claim 1, characterized in that the total opening angle of the reduction area (110) of the reactor (10) is between 8 ° and 30 °, advantageously between 10 ° and 20 °. 3 - Device as per Claim 1, characterized in that the reactor (10) is constituted by a first short upper section of substantially cylindrical conformation for introducing the material and by a second lower section of truncated conical configuration comprising the reduction zone (110). 4 - Device as in Claim 1, characterized in that the reactor has a first upper section of conical conformation converging downwards with a first angle ("a") comprising the reduction zone (110) and a second lower section of conformation conic converging downwards with a second angle ("β") smaller than the first angle ("a"). 5 - Device as in Claim 1, characterized in that the means for introducing the gaseous stream into the reactor (10) comprise at least two independent injection systems arranged at different heights, each cooperating with a section of different diameter of the reactor (10) itself. 6 - Device as claimed in Claim 5, characterized in that each injection system (19a, 19b, 19c) comprises at least one circumferential duct (25) connected to at least one tubing (22) arranged radially. 7 - Device as claimed in Claim 5, characterized in that at least one injection system (19a, 19b, 19c) comprises injection tubes (22b, 22c) which extend, for at least part of their extension, inside the volume of the reactor (10). 8 - Device as in Claim 5, characterized in that at least one injection system (19) comprises at least one tubular element (28) arranged transversely to the reactor (10) and inside it, provided with radial openings or tubing (29 ) for the supply of gas inside the reduction zone (110). 9 - Device as claimed in Claim 1, characterized in that it comprises a cooling system (27a, 27b) cooperating with the terminal part of the reactor (10). 10 - Device as claimed in Claim 1, characterized in that the reactor (10) cooperates at the end with a multi-outlet system with at least two independent conical or frusto-conical outlets (13a, 13b, 13c). 11 - Device as claimed in Claim 1, characterized in that the means (15) for introducing the charge into the reactor (10) comprise funnel means (16) for loading and means (17) for uniforming and distribution homogeneous material in the upper part of the reactor (10). 12 - Process for the direct reduction of iron oxides inside a reactor defining, in its middle-upper part, at least one reduction zone, in which it is foreseen to bring the ferrous material to be reduced into contact with at least one reducing gas introduced inside the reactor in at least one section of the same, in which the feeding of the ferrous material takes place through the upper mouth (12) of the reactor to determine a substantially continuous gravitational flow which encounters the injected gaseous flow in countercurrent, characterized by the fact which envisages the use of a reactor (10) having a reduction zone (110) with a truncated conical conformation converging downwards and at least two gas introduction systems (19a, 19b, 19b) independent of each other and arranged at different heights of the reduction (110) itself, each of said gas introduction systems (19a, 19b, 19b) cooperating with a section of different diameter of the zone reduction unit (110), each of said introduction systems (19a, 19b, 19b) being fed with its own gas of different type, composition and flow rate depending on the process parameters, the result to be obtained, the starting material used and of the section for introducing the reduction zone (110). 13 - Process as claimed in Claim 12, characterized in that it provides for carrying out the reduction of the iron ore at a temperature of between about 550 ° C and 1100 ° C. 14 - Process as in claim 12, characterized in that the reducing gas is mixed with hydrocarbons, preferably natural gas, before being injected into the reactor (10), in order to carry out reforming reactions inside the reactor (10) itself . 15 - Process as claimed in Claim 14, characterized in that the hydrocarbons mixed with the reducing gas are dosed and controlled independently in the different injection zones on the height of the reactor (10). 16 - Process as claimed in Claim 14 or 15, characterized in that the reducing gas, before being mixed with the hydrocarbons, is heated to a temperature between 850 ° C and 1150 ° C, this heating being obtained by partially reacting this reducing gas with O2. 17 - Process as per Claim 12, characterized in that it provides for injecting the gas by means of the introduction systems (19a, 19b, 19c) creating a ring around the reactor wall (10) in correspondence with the specific introduction section and injecting it at contact with the ferrous material through suitable peripheral openings (26). 18 - Process as in Claim 12, characterized in that it provides for injecting the reducing gas mixture at least partially into the reactor volume (10) by means of tubing (22b, 22c) which extend for a substantial part of their extension within the reactor (10) itself. 19 - Process as claimed in Claim 12, characterized in that it provides for cooling the reduced ferrous material before its extraction from the reactor (10). 20 - Process as claimed in Claim 19, characterized in that the cooling is carried out by injection of a cold gas or adapted to initiate reactions of the endothermic type. 21 - Device for the direct reduction of iron oxides and relative process substantially as described and illustrated in the attached drawings.