WO2000036157A1

WO2000036157A1 - Device and method for the direct reduction of iron oxides

Info

Publication number: WO2000036157A1
Application number: PCT/IB1999/001941
Authority: WO
Inventors: Alfredo Poloni; Gianpietro Benedetti
Original assignee: Danieli & C. Officine Meccaniche Spa
Priority date: 1998-12-11
Filing date: 1999-12-06
Publication date: 2000-06-22
Also published as: ITUD980214A1; IT1302813B1; AU1292000A

Abstract

Device and method for the direct reduction of iron oxides, comprising a reactor defining in its middle-upper part a reduction zone (110) inside which the reaction takes place, means (15) to introduce the load from above the reactor, means to introduce the gassy current into at least a section of the reactor in correspondence with the reduction zone (110), means to remove the reduced material, and means (20) to discharge the exhaust fumes, the reactor including an upper mouth (12) communicating with said reduction zone (110) for the introduction of the mineral iron and a lower aperture (13) through which the reduced iron exits, wherein said reduction zone (110) has a truncated cone conformation tapering downwards.

Description

DEVICE AND METHOD FOR THE DIRECT REDUCTION OF IRON OX IDES

* * ** * *

FIELD OF THE INVENTION This invention concerns a device to produce metallic iron starting from mineral iron, wherein the iron is present in the form of oxides, and the relative method, wherein the device comprises a reactor defining a reduction zone shaped like a truncated cone wherein the process of direct reduction of the iron is carried out.

The reduced iron may exit from the reactor either hot or cold and may be subsequently sent to a melting furnace to produce liquid steel, or converted into hot briquette steel (HBI) , or transported to a cooling and storage zone. BACKGROUND OF THE INVENTION

In the steel-producing industry, it is becoming more and more common to use reduced iron (D.R.I.) as a loading material for subsequent melting or conversion processes.

The process of obtaining the reduced iron provides to make the mineral iron react with a current of reducing gas inside a suitable device or furnace comprising a reaction container, known as reactor, defining at least a reduction zone.

The reactor is associated at the upper part with means to introduce the material to be reduced and at the lower part with means to remove the reduced material .

The state of the art includes various means to carry out these reaction processes, which have found efficacious operational applications. Among these applications, the state of the art includes those which use the injection of hydrocarbons into the current of reducing gas to allow the reaction of reforming the methane in the reactor with the H₂O and CO₂ in the gas . There are also known processes of direct reduction which use the injection of hydrocarbons with C>5 directly into the reactor in the zone between the injection of the reducing gas and the outlet from above of the burnt gas. From the following patent documents other processes are known for the direct reduction of mineral iron: US-A-2,189,260, US-A-3 , 601 , 381, US-A-3 , 748 , 120, US-A-3,749,386, US-A-3 , 764 , 123 , US-A-3 , 770 , 421 , US-A-4,173,465, US-A-4 , 188 , 022 , US-A-4 , 234 , 169 , US-A-4, 201, 571, US-A-4 , 528 , 030 , US-A-4 , 556 , 417 , US-A-4, 720, 299, US-A-4 , 900 , 356, US-A-5 , 064 , 467 , US-A-5,078,788, US-A-5 , 387 , 274 , and US-A-5 , 407 , 460.

The state of the art also includes processes wherein the hot metallic iron is produced in a reduction furnace of the shaft type, with a vertical and gravitational flow of the material, which is subsequently sent to the melting furnace by means of a closed pneumatic transport system in an inert atmosphere .

The state of the art generally teaches to use reactors defining, in their upper part, cylindrical reaction zones, inside which the gassy current is introduced, normally in a single introduction zone, to achieve the reduction reaction.

This solution is shown, for example, in US-A-4 , 253 , 867 , wherein a vertical reactor is used comprising an upper, cylindrical reduction zone, an intermediate, cylindrical reforming zone including deflectors facing towards the inside and suitable to define annular spaces inside which the mixture of gas flows, and a lower zone, shaped like a truncated cone, wherein the reduced metal is cooled and then discharged.

Another solution is shown in US-A-4 , 032 , 123 , which provides a cylindrical reduction zone in the lower part of which there is a separating baffle suitable to create, on the sides of the reactor and only in a limited zone thereof, cylindrical passages of a reduced diameter for the material.

The cylindrical passages substantially affect an annular band arranged below the reduction zone, which constitutes a zone where the cooling of the reduced metal is already started by injecting cooling gas. Below the cooling zone there is the tapering zone converging downwards through which the material is discharged.

These solutions have the disadvantage that they do not guarantee an efficient injection of the gassy current since the upper reaction zone of the reactor, which is always substantially cylindrical, has too large a diameter.

Moreover, if the speed of the gas becomes too high, near the top of the reactor a great quantity of the load particles of a smaller granulometry are removed, discharged together with the exhaust fumes, consequently causing problems to the filtering system and a risk of pollution.

Another disadvantage of known solutions is that the temperature of the gas is progressively reduced as it goes up towards the top of the reactor, which entails a reduction in the speed at which the reduction reaction of the mineral iron takes place.

Furthermore, the shape of state of the art reactors, with a substantially cylindrical reduction zone, does not guarantee a homogeneous distribution of the material, with the finer particles being more concentrated in the central zone of the reactor; this entails a lack of uniformity in the reduction reaction.

The present Applicant has devised and tested this invention to overcome all these shortcomings and to improve the efficiency of the process and the quality of the product obtained.

SUMMARY OF THE INVENTION The device to produce metallic iron by the direct reduction of iron oxides and the relative method according to the invention are set forth and characterised in the respective main claims, while the dependent claims describe other innovative features of the invention.

The invention provides to bring the variable granulometry mineral iron into contact with a gassy current, inside a suiζably conformed reactor.

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

According to one characteristic of the invention, the reduction zone of the reactor, that is to say, its upper zone substantially adjacent to the zone where the mineral iron is fed, is conical in shape or shaped like a truncated cone, which progressively tapers downwards.

According to another characteristic of the invention, the reduction zone has a continuous taper for the whole of its extension in height, that is, without any elements to modify the flow of the currents of gas and the shape of the walls.

Along the height of the reduction zone, according to the invention, there are at least two independent sections for the introduction of a respective gassy current suitable to cause the reduction reaction.

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

The combination of the cone conformation tapering downwards of the reactor reduction zone and the multiple introduction of the gas at various heights thereof entails a plurality of advantages in the reduction process.

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

Moreover, the speed of the gas in the upper part of the reactor is lowered because of the progressive increase in diameter, which reduces the risk of smaller granulometry particles being removed and discharged together with the exhaust gases .

The conical shape converging downwards of the reaction zone also encourages the natural distribution inside the reactor of the particles of mineral iron with a different granulometry.

Moreover, thanks to the multiple introduction of the gas at various heights of the reduction zone of the reactor, the temperature of the gassy current remains substantially constant over the whole height thereof, and consequently the heat exchange between the gas and the mineral iron is optimised.

Another advantage of the tapering shape is that, by introducing gassy currents into the lower part of the reduction zone, the currents also affect the central column of the reactor, which the gassy currents usually pass through less, since they are introduced from the side walls of the reactor.

The fact that it is possible to introduce different gases, in different quantities and with different concentrations at different heights of the reactor, allows to optimise the reduction process according to the final result which it is desired to obtain and the type of mineral iron introduced.

Moreover, the number and the reciprocal distance between the gas introduction zones can be varied in order to guarantee maximum performance and maximum flexibility of the reduction reaction.

According to another form of embodiment, the reactor has a short, substantially cylindrical first upper segment, connected to the mouth, which serves to prevent the load material from sticking on the walls of the reactor when the material has highly adherent characteristics, and a subsequent tapered lower segment, where there are the gas introduction zones and where the reduction of the material introduced occurs .

According to a variant, at the lower part the reactor has a terminal discharge zone which tapers downwards with a more accentuated taper than the taper of the reduction zone above.

According to one embodiment of the invention, in the lower part of the reactor there is a system suitable to cool the material before it is discharged from the reactor.

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

The multiple outlet encourages the distribution of the reduction gas inside the reactor and a better distribution of the material inside the reactor, preventing preferential channels which occur in reactors with a single outlet.

The flexible use of the extractors, to vary the outlet delivery, prevents the formation of bridges in the reactor.

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

This also allows to regulate the outlet delivery of material by varying the speed of removal of the individual discharge systems.

Moreover, this movement helps to make the material descend from the upper zone in a uniform manner, with a perfect mixing of the larger particles with the finer particles, creating a continuous movement of the material and reducing the possibility of blockages of the material.

Using a multiple outlet system also allows to simultaneously discharge hot material which will then be used in various ways: one part may be introduced directly into a melting furnace, for final melting; a part may be made into briquettes; and a part may be cooled outside in a silo and sent for storage.

A further advantage is that it is possible in any case to discharge all the output hot material into the melting furnace to produce steel, greatly reducing energy consumption.

The reduction device according to the invention is equipped, at its upper part, with means to feed the mineral iron and, at its lower part, with means to discharge the reduced metallic iron.

Inside the reactor the mineral iron is reduced to temperatures of generally between 550° and 1100°C.

The reduction occurs in the following stages, starting from the top of the reactor and going down: from Fe₂θ₃ to Fe₃θ₄, then from Fe₃U₄ to FeO, and finally from FeO to Fe.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other characteristics of the invention will become clear from the following description of some preferred forms of embodiment, given as a non-restrictive example with the aid of the attached Figures wherein:

Fig. 1 is a longitudinal section of the device for the direct reduction of iron oxides according to the invention; Figs. 2a, 2b and 2c show, respectively, sections from A to

A, from B to B and from C to C of Fig. 1; Figs. 3a, 3b and 3c show in diagram form three forms of embodiment of the reactor of the device shown in Fig.

1; Fig. 4 shows a section from D to 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 from E to E of Fig. 5 in a further variant of the invention; Fig. 8 shows an enlarged cross section of a further variant of the reactor according to the invention; and Fig. 9 shows an enlarged cross section along a line from F to F of Fig. 8.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS With reference to Fig. 1, a device 11 for the direct reduction of iron oxides according to the invention comprises a reactor 10 defining a reduction zone 110 arranged in the middle-upper part thereof.

The reactor 10 comprises an upper mouth 12 for feeding from above, through which the mineral (iron oxides) is able to be introduced, and a lower aperture 13 through which the iron is discharged. The inner walls of the reactor 10 are totally or partly lined with refractory material 14.

The reactor 10 is provided in its upper part with a circumferential aperture 20 through which the exhaust gas exits .

The upper mouth 12 of the reactor 10 cooperates with a device 15 to introduce the mineral iron, suitable to distribute the loaded material uniformly and homogeneously.

To be more exact, the device 15 comprises a funnel system 16 into which the material is unloaded by means of crane bridges, cranes or similar, and a multiple outlet distribution system 17 through which the material is unloaded uniformly into the inlet section of the reactor 10.

The upper mouth 12 is covered by a suitable cover 18. The iron-based metal oxides are introduced into the reactor 10 in the form of pellets or crude mineral in the appropriate sizes; the iron contained therein is usually between 63% and 68% in weight.

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

At least the reduction zone 110 of the reactor 10 shown in Fig. 1 is shaped substantially like a truncated cone tapering downwards, wherein the diameter is progressively reduced as it goes towards the outlet mouth 13.

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

The taper is substantially continuous, without any protrusions or deflector elements on the walls which would alter a correct flow of the material.

In the embodiment shown in Fig. 1, the taper is continuous for the entire height of the reactor 10, from the mouth 12 where the material is introduced, to the outlet mouth 13. In correspondence with three distinct sections of the reduction zone 110, along its height, there are in this case three systems to introduce a gassy current inside the said reactor 10.

The introduction systems, respectively 19a, 19b and 19c, are independent from each other and are suitable to inject inside the reactor 10 a respective gas of a different type and composition from the gases injected by the other systems, according to the type of process taking place and the ferrous material to be reduced.

The introduction systems 19a, 19b and 19c are also suitable to cooperate with a section arranged at a different height of the reduction zone 110, and therefore with a different diameter from the other sections due to the downward tapering shape of the reduction zone 110.

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

Moreover, the injection of gas in correspondence with the lower section 19c allows to send the gases in correspondence with the central column of the reactor 10 too, which in conventional reactors is less affected by the gassy currents introduced from the sides.

The introduction systems 19a, 19b and 19c each comprise a delivery collector 21 connected to a circumferential pipe 25 which feeds respective tuyeres 22, inserted into the refractory wall 14 of the reactor 10 and with an inclination, in this case, sloping downwards in order to encourage the tendency of the gas to ascend upwards.

The gas introduced by the respective tuyeres 22 rises upwards and comes into contact, in the reduction zone 110 of the reactor 10, with the continuous descending flow of the mineral iron, generating reduction reactions until, at the outlet of the reactor 10, Fe is obtained and sent to subsequent uses .

Figs. 2a , 2b and 2c show how, at the various heights of the reactor 10, as the reducing gas indicated by the reference number 23 gradually descends towards the end of the reduction zone 110, it cooperates with sections of a lesser diameter, surrounding and enveloping the descending material more and more . The position of the systems 19a, 19b and 19c on the height of the reduction zone 110 and the distance between them are optimised according to the processing parameters; the intensity of the heat exchange between the ferrous material and the gas is also taken into account, and also the efficiency of the reactions in the various sections of the reduction zone 110.

The gas feeding the reactor 10 may consist of a mixture of hydrocarbons, for example natural gas, gas recircled from the reactor itself and reformed gas.

The presence of natural gas in the reduction gas mixture allows to achieve reforming reactions inside the reactor 10.

The quantity of hydrocarbons added to the reduction gas mixture, according to the invention, may be proportioned in a different manner according to the section in which the gas is introduced inside the reactor 10.

The recircled gas is pre-heated to a temperature of between 650°C and 850°C.

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

After this pre-heating, the gas is advantageously mixed with the hydrocarbons .

Fig. 3a shows in diagram form the flow of ferrous material, indicated by the reference number 24, from the top of the reactor 10 downwards.

Figs . 3b and 4 show in diagram form the system to introduce the gas into a circumferential pipe 25 made in the reactor 10 from which it penetrates, through the tuyeres 22, inside the reactor 10 and thence into contact with the mineral iron which is to be reduced.

This solution causes the gas to be distributed more homogeneously over the whole section of the reactor 10 affected, and therefore a more efficient reaction.

Fig. 7 shows a variant wherein at least one system 19 to introduce the gas comprises first tuyeres 22a arranged radially on a horizontal plane along the circumference of the reactor 10, second tuyeres 22b arranged radially which extend to a peripheral zone of the reactor 10, penetrating by about 2/3 of their length inside the reactor 10, and third tuyeres 22c arranged radially which extend, substantially for their whole length, to the central zone of the reactor 10, that is to say, into the core of the material 23.

One advantage of this embodiment is that it is possible to introduce reduction gas simultaneously from several points, and to regulate the rate of delivery of the reducing gas. Another, considerable advantage is that it is possible to have a uniform reduction in the oxides over the whole transverse section of the reactor 10, thus creating the best fluido-dynamic conditions for the distribution of the reducing gas. Thus we have a uniform distribution of temperature over the whole section, unlike in traditional reactors where the hot gas best laps the material located near the peripheral part and enters the core of the reactor 10 only with difficulty. Another advantage is that the direct reduction becomes uniform and therefore it is possible to have a higher productivity and lower consumption of gas and energy, since the gas itself is used in the best possible way. According to the further variant shown in Fig. 3c, the reactor 10 has a first, brief, substantially cylindrical upper segment 10a and a second, lower segment 10b shaped like a truncated cone in order to prevent blockages of the load material in the upper part, due to the formation of bridges when the raw material has characteristics of great adherence to the walls of the reactor 10.

According to the variant shown in Figs. 8 and 9, the reducing gas is distributed by means of one or more, preferably three, horizontal tubes 28 made of material resistant to heat and to oxidising and carburising agents.

The tubes 28 are arranged transverse to the reactor 10 and are each provided with a plurality of peripheral apertures or radial tuyeres 29, through which the gas can flow into the reaction zone 14.

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

Each tube 28 may also be through and equipped with rotary movement, so that the peripheral apertures 29 can describe a round angle and distribute uniformly, in the best possible manner, the reducing gas inside the reduction zone 14.

The variant shown in Fig. 5 shows a reactor 10 which has a continuous conical development with a first angle for a substantial segment of its length, and a terminal segment with a continuous conical development with a second angle β which is smaller than α.

This solution encourages and accelerates the discharge of material through the outlet mouth 13. In cooperation with the lower part of the reactor 10 there is a system to cool the ferrous material to be discharged; this comprises an inlet collector 27a and a respective outlet collector 27b to collect a flow of cold gas or gas suitable to activate reactions of an endothermic type.

According to a further variant shown in Fig. 6, in correspondence with its outlet mouth 13, the reactor 10 has three lower ends 13a, 13b and 13c, shaped like a cone or a truncated cone tapering downwards.

The lower ends are each equipped with respective lower apertures through which, selectively, the directly reduced metallic iron (DRI) can be discharged individually or simultaneously . The great advantage of being able to discharge the material simultaneously from several points is that it is possible to regulate the delivery of material at outlet by varying the speed of extraction of the individual discharge systems . Another advantage is that this movement helps to make the material descend from the upper zone in a uniform manner, with a perfect mixing of the larger particles with the finer particles, creating a continuous movement of the material and reducing the possibility of the material sticking. A further, considerable advantage is that it is possible to simultaneously discharge hot material for various uses: one part may be introduced directly into a melting furnace, for final melting; a part may be made into briquettes; and a part may be cooled outside in a silo and sent for storage. A further advantage is that it is possible in any case to discharge all the output hot material into the melting furnace to produce steel, greatly reducing energy consumption.

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

Obviously, it is possible to make modifications and additions to the invention, but these will remain within the field and scope of the invention.

Claims

1 - Device for the direct reduction of iron oxides of the type with a gravitational load, comprising a reactor defining in its middle-upper part at least a reduction zone (110) inside which the reaction takes place, means (15) to introduce the load from above the reactor, means to introduce the gassy current into at least a section of the reactor in correspondence with said reduction zone (110), means to remove the reduced material from the bottom of the reactor, and means (20) to discharge the exhaust fumes, said reactor including an upper mouth (12) communicating with said reduction zone (110) for the introduction of the mineral iron and a lower aperture (13) through which the reduced iron exits, the device being characterised in that said reduction zone (110) has a truncated cone conformation tapering downwards .

2 - Device as in Claim 1, characterised in that said reduction zone (110) has a substantially continuous taper for the whole of its extension. 3 - Device as in Claim 1 or 2 , characterised in that the total angle of aperture of the reduction zone (110) of the reactor (10) is between 8° and 30°, advantageously between 10° and 20°.

4 - Device as in Claim 1, characterised in that said reactor (10) has a first, brief, substantially cylindrical upper segment through which the material is introduced, and a second lower segment shaped like a truncated cone tapering downwards comprising said reduction zone (110) .

5 - Device as in Claim 1, characterised in that said reactor (10) has a first upper segment shaped like a cone tapering continuously downwards with a first angle ("α") comprising said reduction zone (110) and a second lower segment shaped like a cone tapering continuously downwards with a second angle ("β") which is less than the first angle ("oc") and cooperating with said outlet mouth (13).

6 - Device as in Claim 1, characterised in that said means to introduce the gassy current inside the reactor (10) comprise at least two independent injection systems arranged at different heights, each of which cooperates with a section of the reactor (10) with a different diameter.

7 - Device as in Claim 6, characterised in that each of said injection systems (19a, 19b, 19c) comprises at least a circumferential pipe (25) connected to at least a tuyere (22) arranged radially.

8 - Device as in Claim 6, characterised in that at least an injection system (19a, 19b, 19c) comprises injection tuyeres (22b, 22c) which extend, for at least part of their extension, inside the volume of the reactor (10) .

9 - Device as in Claim 6, characterised in that at least an injection system (19) comprises at least a tubular element (28) arranged transverse to and inside the reactor (10), provided with radial apertures or tuyeres (29) to deliver the gas into the reduction zone (110) .

10 - Device as in Claim 1, characterised in that it comprises a cooling system (27a, 27b) cooperating with the terminal part of the reactor (10) .

11 - Device as in Claim 1, characterised in that the reactor (10) cooperates at the end with a multiple outlet system with at least two independent outlets shaped like a cone or a truncated cone (13a, 13b, 13c) .

12 - Device as in Claim 1, characterised in that the means (15) to introduce the load into the reactor (10) comprise funnel means (16) for loading and means (17) to distribute the material uniformly and homogeneously in the upper part of the reactor (10) .

13 - Method for the direct reduction of iron oxides inside a reactor defining in its middle-upper part at least a reduction zone, wherein it is provided to bring the ferrous material which is to be reduced into contact with at least a reducing gas introduced inside the reactor in at least a section thereof, wherein the ferrous material is fed through the upper mouth (12) of the reactor so as to determine a substantially continuous gravitational flow which meets the injected gassy flow in counter-flow, the method being characterised in that it provides to use a reactor (10) defining in its upper and median part a reduction zone (110) shaped like a truncated cone tapering continuously downwards and at least two systems (19a, 19b, 19c) to introduce the gas, independent of each other and arranged at different heights of said reduction zone (110), each of the introduction systems (19a, 19b, 19c) cooperating with a section of said reduction zone (110) of a different diameter, each of said introduction systems (19a, 19b, 19c) being fed with its own gas, of a different type, composition and delivery rate, according to the processing parameters, the result to be obtained, the starting material used and the section of the reduction zone (110) where the gas is introduced.

14 - Method as in Claim 13, characterised in that it provides to reduce the mineral iron at a temperature of between about 550°C and 1100°C.

15 - Method as in Claim 13, characterised in that the reducing gas is mixed with hydrocarbons, preferably natural gas, before being injected into the reactor (10), in order to achieve reforming reactions inside the reactor (10) . 16 - Method as in Claim 15, characterised in that the hydrocarbons mixed with the reducing gas are proportioned and controlled independently in the different injection zones on the height of the reactor (10) . 17 - Method as in Claim 15 or 16, characterised in that, before being mixed with the hydrocarbons, the reducing gas is heated to a temperature of between 850°C and 1150°C, the heating being achieved by making the reducing gas partly interact with O₂.

18 - Method as in Claim 13, characterised in that it provides to inject the gas by means of introduction systems

(19a, 19b, 19c) creating a ring around the wall of the reactor (10) in correspondence with the specific introduction section and injecting it into contact with the ferrous material through peripheral apertures (26) provided for the purpose.

19 - Method as in Claim 13, characterised in that it provides to inject the mixture of reducing gas at least partly inside the volume of the reactor (10) by means of tuyeres (22b, 22c) which extend for a substantial part of their length inside the reactor (10) itself.

20 - Method as in Claim 13, characterised in that it provides to cool the reduced ferrous material before it is removed from the reactor (10) .

21 - Method as in Claim 20, characterised in that the cooling is achieved by injecting a cold gas or one suitable to start reactions of an endothermic type.